[neonixie-l] Re: Constant current source design

[Nick]

On Friday, 12 May 2017 17:42:58 UTC+4, Luka C wrote:
>
> @Nick - I know that cathode current control per segment might seem a bit 
> of an overkill, but as @greg said, considering the price of the tubes, I 
> think we should do our best to meet all of the datasheet specs if possible. 
> And if you carefully look at the datasheet, consider the case you want to 
> display a character like "*" (asterisk), then add together the currents of 
> each segment from the datasheet and it will exceed the maximum anode 
> current defined in the same datasheet, this is why each cathode current 
> should be adjusted so that if you add them all together, the sum will be 
> lower than the maximum anode current (of course, how much this really 
> impacts the life of the tube will remain a mystery I guess, but we should 
> still be careful)
>

Are you sure you're not looking at the maximum rather than the normal 
current ratings for each element ?

Nick

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/500f0094-d787-4796-90c6-346d6ced8cd3%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[gregebert]

I hope to find that out this weekend.  My hunch is that segments with the 
highest voltage-drop will be impacted the most. I dont have my IV curves 
handy at the moment, so I cant say which particular segments would be 
affected. I recall seeing 3 clusters of IV curves for each tube.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/7733191a-a47b-4bed-a880-4a659a322288%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Tomasz Kowalczyk]

I'm happy to read that.


I'm curious what would happen in a circuit with both anode 22mA limiter and 
cathode limiters after the anode limiter kicks in - will the current of 
each lit cathode get lowered by same percentage or will it equalize to same 
value on each cathode and then lower further with the same value? 
Anode limiter could possibly lead to uneven illumination of segments, if 
first option was the real one. Unfortunately, B7971s are totally out of my 
league and I can't test it myself.

W dniu środa, 10 maja 2017 09:39:03 UTC+2 użytkownik Luka C napisał:
>
> I'm glad you've done the test with BSS139 and it turned out to work fine. 
> I've used the same transistor for the cathode current control on my B7971 
> clock, completed routing the PCB and currently sparing some money to send 
> it to the fab house :)
>
> Dana utorak, 18. travnja 2017. u 11:08:58 UTC+2, korisnik Tomasz Kowalczyk 
> napisao je:
>>
>> I've ran some tests with BSS139 + a potentiometer as a variable resistor.
>> Conclusions:
>>  - this design offers cheap and stable current limiting
>>  - it varies with voltage dropped over the circuit, so it should be 
>> tunable - the difference is about 14% change between 5V dropped and 105V 
>> dropped across it (4,37mA vs 4,91mA).
>>  - it is thermally stable - at 100V dropped and 4,93mA cold current I am 
>> breaking the allowed power dissipation (allowed 0,36W, here - 0,5W), it 
>> heats up to a bit over 50°C (many probe cables connected close to the 
>> transistor act like a radiator), the current has changed by 40µA 
>>  - while testing it I found out that striking voltage of tubes is a max 
>> value - I've tested one Z567M and one LC-631, they both strike with 
>> voltages lower than their normal maintaing voltage! While powered correctly 
>> they sit at 140V across the tube, and I was able to lower power supply 
>> voltage to 135V, disconnect tube, connect it again and it worked. I 
>> suspected that due to large resistors and a cap in the feedback I have high 
>> pulses over 170V in my supply, but it is not true - at 135V the spikes 
>> measured with an oscilloscope were less than 5V. Of course, with voltage 
>> lower than 140V + minimum drop over BSS39 and resistor, the current was 
>> lowered.
>>  - due to that it is possible to create a clock wasting very low power on 
>> anode limiting - classic operation uses 170V, 180V or 200V supply + 
>> resistor, which wastes quite a lot of power on those resistor. here we can 
>> tune the power supply just above striking voltages of all tubes and be sure 
>> that we don't have to recalculate the resistors. This will have a very 
>> positive effect in clocks which run on batteries or USB supplies - with 
>> both lower voltage required and lower power consumption.
>>  - after tuning to desired current it is very stable - drift is max 20µA 
>> I wonder if this low striking voltage is common among different tubes or 
>> does the striking voltage change with temperature.
>>
>> In my opinion the only drawback of this design is that it is changing the 
>> current with voltage drop across the limiter. This change in normal 
>> operation shouldn't be noticable, because normally power supply doesn't 
>> change much - maybe 10V under bad circumstances. With such voltage change 
>> the current will be pretty much the same, but a resistor calculated once 
>> isn't universal for every design. 
>> Everything else (simplicity, price) says that this is it, I'll be using 
>> this instead of resistors.
>>
>> I'm attaching photos of setup - left multimeter measures voltage across 
>> the tube, middle measured power supply voltage, and the right one measures 
>> current (in mA). Voltage across limiter is of course the difference between 
>> middle and left.
>>
>

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/8b4f3f02-97bc-419c-b6f8-59a07bf76641%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[gregebert]

In addition to current-control per-segment, I also have an anode-current 
limiter. It's probably overkill but it does cover the case where I have a 
few characters that exceed to max total current.

I'm trying to fire this up for the first time this weekend. I've never used 
a RasPi before, so I have a bit of software to develop.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/ca961213-c96e-436c-871e-f9fc24742088%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Luka C]

@Nick - I know that cathode current control per segment might seem a bit of 
an overkill, but as @greg said, considering the price of the tubes, I think 
we should do our best to meet all of the datasheet specs if possible. And 
if you carefully look at the datasheet, consider the case you want to 
display a character like "*" (asterisk), then add together the currents of 
each segment from the datasheet and it will exceed the maximum anode 
current defined in the same datasheet, this is why each cathode current 
should be adjusted so that if you add them all together, the sum will be 
lower than the maximum anode current (of course, how much this really 
impacts the life of the tube will remain a mystery I guess, but we should 
still be careful)

This could be achieved by adjusting the resistor value in each of the 
segment lines but this carries a side effect. These tubes will presumably 
run in our clocks for years and during the that time, their characteristics 
will probably change. The voltage drop on the tube will probably change and 
if the supply voltage is fixed this will also result in changes to the 
segment current (Is = (Ua - Um) / Rs). If Um rises over time, this would 
result in lower voltage drop across the resistor and in turn lower the 
segment current (perhaps to the point where brightness might not be what we 
would like it to be) and this is why a constant current sink might come 
handy to make sure current in each segment remains fixed over the years of 
operation.

Dana četvrtak, 11. svibnja 2017. u 17:36:02 UTC+2, korisnik gregebert 
napisao je:
>
> The problem is that if the segment currents stated in the Burroughs 
> datasheet are summed-up for various characters, many characters exceed the 
> max-spec for anode current. However, the average character-current is 
> on-par with the max anode-current spec. Unfortunately, we'll never know 
> what Burroughs intended.
>
> I took a different approach and gathered a lot of data on my 7971's, 
> including a guesstimate of the current that gives good visual illumination 
> for each segment.
> When I scaled-back the spec-value for segment currents to get most 
> characters within the 22mA max anode-current spec, I found that the 
> 'visually good' current was on-par with the scaled current. What I ended up 
> with is segment currents that are visually good, and within the 
> max-anode-current spec limit (slightly over for 2 characters).
>
> Hopefully I will have time this weekend to finish my board and try it out.
>

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/a4d95431-e69e-4e94-98be-d782587d70fd%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[gregebert]

The problem is that if the segment currents stated in the Burroughs 
datasheet are summed-up for various characters, many characters exceed the 
max-spec for anode current. However, the average character-current is 
on-par with the max anode-current spec. Unfortunately, we'll never know 
what Burroughs intended.

I took a different approach and gathered a lot of data on my 7971's, 
including a guesstimate of the current that gives good visual illumination 
for each segment.
When I scaled-back the spec-value for segment currents to get most 
characters within the 22mA max anode-current spec, I found that the 
'visually good' current was on-par with the scaled current. What I ended up 
with is segment currents that are visually good, and within the 
max-anode-current spec limit (slightly over for 2 characters).

Hopefully I will have time this weekend to finish my board and try it out.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/f007eee7-e872-4610-a9a5-319383d63453%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Nick]

I like the general idea of what your attempting, but it's really not suited 
to segmented tubes like the B7971.

The Burroughs data sheets for the valve clearly state the currents for each 
segment and give examples for the differing cathode resistors to use to 
achieve this on a per-cathode basis.

There is no "right" single anode current for a B7971 - they are also pretty 
bullet-proof - I've never known one fail and have several hundred out 
there. Bearing in mind that all known B7971 are ex-equipment, I would stick 
with the Burroughs recommendations on those.

For single-cathode digits, a current limiter would be fine.

Cheers

Nick

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/b5652fe1-0436-42b1-9607-50b623c3b5a7%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Luka C]

@greg, I have taken a look at 
this: http://tayloredge.com/storefront/1386_B7971SmartSocket/1386.pdf . 
When using 175V as supply voltage and assuming 140V voltage drop on the 
tube, the currents should be: 

S15, S4, S1 = 1.59mA
S14, S10 = 1.06mA
S13, S11, S9, S7 = 1.46mA
S12, S8, S6, S5, S3, S2 = 1.30mA

When you add them all together, you get 20.53mA which is just right under 
the specs of the datasheet so I adjusted the currents according to it. I 
know this will result in less brightness than the maximum possible when all 
segments are not lit up because plenty of margin will be left then, but I 
see no other way, other than implementing the anode current limiter as well 
as you have described in earlier posts.

Dana srijeda, 10. svibnja 2017. u 20:26:24 UTC+2, korisnik gregebert 
napisao je:
>
> Luka - What segment currents are you using for the 7971 ?
>
> If you turn all segments on at the rated datasheet current, there are 
> several characters, such as 8 and Q, that will cause the total current to 
> significantly exceed the max rating of 22mA. I analyzed current-draw for 
> most characters, and even the average (~26mA) exceeds spec.
>
> I scaled-back the current in my design so I never exceed the max 22mA.
>
> 7971's are really expensive & rare, so I'm not taking any chances.
>

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/e39361f0-3003-43c9-8612-78e17df62b11%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[gregebert]

Luka - What segment currents are you using for the 7971 ?

If you turn all segments on at the rated datasheet current, there are 
several characters, such as 8 and Q, that will cause the total current to 
significantly exceed the max rating of 22mA. I analyzed current-draw for 
most characters, and even the average (~26mA) exceeds spec.

I scaled-back the current in my design so I never exceed the max 22mA.

7971's are really expensive & rare, so I'm not taking any chances.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/e110a5b4-de8d-4da4-982b-ce22b6efa0f2%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Luka C]

I'm glad you've done the test with BSS139 and it turned out to work fine. 
I've used the same transistor for the cathode current control on my B7971 
clock, completed routing the PCB and currently sparing some money to send 
it to the fab house :)

Dana utorak, 18. travnja 2017. u 11:08:58 UTC+2, korisnik Tomasz Kowalczyk 
napisao je:
>
> I've ran some tests with BSS139 + a potentiometer as a variable resistor.
> Conclusions:
>  - this design offers cheap and stable current limiting
>  - it varies with voltage dropped over the circuit, so it should be 
> tunable - the difference is about 14% change between 5V dropped and 105V 
> dropped across it (4,37mA vs 4,91mA).
>  - it is thermally stable - at 100V dropped and 4,93mA cold current I am 
> breaking the allowed power dissipation (allowed 0,36W, here - 0,5W), it 
> heats up to a bit over 50°C (many probe cables connected close to the 
> transistor act like a radiator), the current has changed by 40µA 
>  - while testing it I found out that striking voltage of tubes is a max 
> value - I've tested one Z567M and one LC-631, they both strike with 
> voltages lower than their normal maintaing voltage! While powered correctly 
> they sit at 140V across the tube, and I was able to lower power supply 
> voltage to 135V, disconnect tube, connect it again and it worked. I 
> suspected that due to large resistors and a cap in the feedback I have high 
> pulses over 170V in my supply, but it is not true - at 135V the spikes 
> measured with an oscilloscope were less than 5V. Of course, with voltage 
> lower than 140V + minimum drop over BSS39 and resistor, the current was 
> lowered.
>  - due to that it is possible to create a clock wasting very low power on 
> anode limiting - classic operation uses 170V, 180V or 200V supply + 
> resistor, which wastes quite a lot of power on those resistor. here we can 
> tune the power supply just above striking voltages of all tubes and be sure 
> that we don't have to recalculate the resistors. This will have a very 
> positive effect in clocks which run on batteries or USB supplies - with 
> both lower voltage required and lower power consumption.
>  - after tuning to desired current it is very stable - drift is max 20µA 
> I wonder if this low striking voltage is common among different tubes or 
> does the striking voltage change with temperature.
>
> In my opinion the only drawback of this design is that it is changing the 
> current with voltage drop across the limiter. This change in normal 
> operation shouldn't be noticable, because normally power supply doesn't 
> change much - maybe 10V under bad circumstances. With such voltage change 
> the current will be pretty much the same, but a resistor calculated once 
> isn't universal for every design. 
> Everything else (simplicity, price) says that this is it, I'll be using 
> this instead of resistors.
>
> I'm attaching photos of setup - left multimeter measures voltage across 
> the tube, middle measured power supply voltage, and the right one measures 
> current (in mA). Voltage across limiter is of course the difference between 
> middle and left.
>

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/935caee2-bcee-4d8b-ae6d-901e10314c13%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[gregebert]

Assuming you have high-enough HV power-supply headroom for the nixies (180V 
or more), the choice for the resistor begins with the isolated power 
supply; I chose 12V because there are a lot of small, efficient DC-DC 
converters that provide 12V. You can use other values, but be careful to 
stay below the rated Vgs(max). 

Next, you want some adjustment range for the anode current. I set the 
nominal gate voltage at 10V. That gives +/- 2V of range to adjust the anode 
current without changing resistors.

Next, from the datasheet, you need to find Vgs(on) for the MOSFET. It's 
usually plotted on a curve. For the FQD7P20TM that I use, it's about 4V 
(see the transfer characteristics curve).

Next, you need the target anode current. For a Burroughs 5092, it's 2.2mA.

The voltage-drop across the resistor is 10V - Vgs(on); in this case, it's 
6V. Now you can solve for the resistor value:
   R=V/I= 6/0.0022   = 2727 ohms. The nearest standard value = 2.7K.

Sanity-check the power in the resistor: P=I^2R; in this case,  P=13mW, so 
even with tiny surface-mount devices you are fine.

You should also sanity-check the PMOS transistor worst-case power 
dissipation. Assume a ridiculously low nixie voltage of 125V. The voltage 
across the PMOS is Supply_voltage - Nixie_voltage - Resistor_voltage = 
200-125-6.

PMOS power = Max voltage * typical current = 69*0.0022 = 150mW.

This device has a Theta j-a of 110C/W, so the temp-rise = 110*0.15 = 17 
degrees. Plenty of margin here.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/42998d43-12fe-48f9-8e3f-e3b98a7a7b6a%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Paul Andrews]

Hi (Greg?),

Using the datasheet for the PMOS transistor you use in your circuit, how do 
you calculate the value of R116 (the resistor between +200V and the source 
of your MOSFET)?

On Saturday, March 25, 2017 at 12:30:53 PM UTC-4, gregebert wrote:
>
> That's basically what I use in my designs. I'll highlight the differences:
>
>- I use a PMOS instead of PNP, mainly because it requires no 
>drive-current.
>- R1 & R2 are replaced with a pot to make the current adjustable.
>- The above pot can driven from a small DC-DC converter (my 
>preference), or between the HV supply & GND. There's essentially zero 
>current for PMOS gate-drive, so high resistance values are fine. Not the 
>case with PNP, though, due to finite base-currrent.
>- A zener diode is added to clamp any spikes that may arise at the 
>gate of the PMOS device. It's a paranoia item.
>- A filter cap was added, in case there is unexpected noise from the 
>DC DC converter, and also to suppress any very-short transient that may 
>arise that are too fast for the zener to kick-in. (paranoia item).
>- A large resistor across the PMOS to bleed any potential ESD. Without 
>it, there is a remote possibility of charge-buildup. (paranoia item)
>
> So, this circuit is replicated for each anode. When multiple anodes are 
> driven, they all share the same gate-drive signal, which I call PDRV on the 
> attached schematic.
>
>
>

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/51d0a30b-a31a-4331-8222-babb2654b502%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

Re: [neonixie-l] Re: Constant current source design

[gregebert]

Nobody in this forum is dumb; some of us just havn't been bitten as hard as 
othersI found out the hard way you have to read and understand 
every spec item in the datasheet, or you will get into trouble. I've 
refused to use quite a few parts because a spec value wasn't provided; 
other cases (like the HV5530), I was forced to design-around a missing spec 
item, like min prop delay.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/964ea914-7fb4-4985-883d-20c93deca14e%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

Re: [neonixie-l] Re: Constant current source design

[Paul Andrews]

Well that makes me feel dumb (which is fine, I will learn)! I should have had 
the sense to calculate a suitable load value and I should read the data sheets 
more carefully! Hopefully my trial and error will be instructive to others as 
well as myself. 

I'll do it again with calculated load values, if only to ram the lesson home.

I will also get around to trying out the mosfet version of the pmos current 
source at the start of this discussion.

Thanks for all your input into this. 

> On May 9, 2017, at 12:23 AM, gregebert  wrote:
> 
> A 5K-ohm load with 2mA thru it only drops 10V; with a 200V supply, you would 
> have 190V across the mosfet. At 2mA load current, that translates to 380mW 
> dissipation in the mosfet. From the datasheet, the max Theta ja I saw listed 
> was 170 C/W. That would translate to a 65C rise, which is fine for room-temp 
> even in a hot climate.
> 
> At 4mA, though, you will get into trouble as you noted.
> 
> Typically you wont see anywhere near that much voltage across a nixie 
> current-limiter. Assuming 150V typical nixie voltage, and 10V for the 
> resistor, you will get 40V across the transistor. That translates to 80mW, 
> and a temp-rise of about 15C, which is plenty of margin.
> 
> A current limiter wont reduce the overall power dissipation, but it will 
> reduce the variation in nixie current over supply-voltage variations and 
> nixie aging.
> 
> 
> 
> -- 
> You received this message because you are subscribed to a topic in the Google 
> Groups "neonixie-l" group.
> To unsubscribe from this topic, visit 
> https://groups.google.com/d/topic/neonixie-l/gbJ0Beiu66I/unsubscribe.
> To unsubscribe from this group and all its topics, send an email to 
> neonixie-l+unsubscr...@googlegroups.com.
> To post to this group, send email to neonixie-l@googlegroups.com.
> To view this discussion on the web, visit 
> https://groups.google.com/d/msgid/neonixie-l/820f82b0-8b70-4c70-b589-d224f70db2f3%40googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/45D3CF44-2397-4BF4-A7EE-3F03400982D9%40gmail.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[gregebert]

A 5K-ohm load with 2mA thru it only drops 10V; with a 200V supply, you 
would have 190V across the mosfet. At 2mA load current, that translates to 
380mW dissipation in the mosfet. From the datasheet, the max Theta ja I saw 
listed was 170 C/W. That would translate to a 65C rise, which is fine for 
room-temp even in a hot climate.

At 4mA, though, you will get into trouble as you noted.

Typically you wont see anywhere near that much voltage across a nixie 
current-limiter. Assuming 150V typical nixie voltage, and 10V for the 
resistor, you will get 40V across the transistor. That translates to 80mW, 
and a temp-rise of about 15C, which is plenty of margin.

A current limiter wont reduce the overall power dissipation, but it will 
reduce the variation in nixie current over supply-voltage variations and 
nixie aging.



-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/820f82b0-8b70-4c70-b589-d224f70db2f3%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Paul Andrews]

I finally got around to trying this using a 200V supply and one of these 
. I tried it 
first for a 2mA load current. I had to determine the Vgs experimentally. 
The datasheet looks like it should be about -2.5V. I got about -1.9V. I 
gave it a 5K load. The mosfet heats up quite a lot while operating, so the 
current across the load gradually climbs, though it wasn't too bad - the 
end result was about 2.05mA

I then tried it for a 4mA load current. The mosfet got really hot, and the 
current climbed up to about 4.5mA before I disconnected it.

In short, I won't be using this method to limit current.

BTW I tried two different pieces of the same mosfet - the Vgs was the same 
for both. I ordered them at the same time so they could well be from the 
same batch. So far, if I wanted to use a constant current source, I would 
go with the very first option.

On Friday, April 7, 2017 at 5:34:49 PM UTC-4, Paul Andrews wrote:
>
> Here is a link 
> 
>  
> to a paper about using a depletion mode MOSFET for the same purpose. It 
> gives this equation for calculating the resistor value, which I assume 
> would be the same for all depletion mode MOSFETS (!?):
>
>
> 
>
> VGS(th) is the gate threshold voltage of the MOSFET, IDSS is the on 
> current at VGS = 0 V and ID is the required current.
>
>
> There are plenty of these around with suitable voltage characteristics.
>
>

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/b1fe91c3-2cff-490e-a49c-b7bfec8b4a5d%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Dekatron42]

Have you tried to ask for instance Supertex (nowadays Microchip) about 
their LR8, the IXCP10M45S (10M90S) or the DN2540 regarding CCS designs?

It seems like some audio people use the DN2540/IXCP10M45S in combination 
with either a low dropout voltage regulator like LD1085 or the LM317 to 
either make a high voltage regulated power supply or to make a CCS (see for 
instance the GlassWare PS-1 PSU: 
http://glass-ware.stores.yahoo.net/ps1kit.html and here: 
http://tubecad.com/2008/11/blog0151.htm). The LR8 (or the LR12) can be used 
as a CCS with just one resistor and it works up to 450V with a few 
milliamperes. Using the DN2540 with an LM317 is probably the easiest 
design. A DN2540 & LM317 CCS can be found 
here: https://vwws.wordpress.com/2011/06/21/dn2540-lm317-cascode-ccs/ .

/Martin

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/965c6e09-db29-4a02-8b9b-f17019f39a5a%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Tomasz Kowalczyk]

I ran the temperature test with 120°C hot air aimed directly at the JFET. 
Conclusion - the higher the temperature of JFET, the lower the current - so 
it is self stopping rather than increasing current, which is good for tubes 
(slight undercurrenting shouldn't damage them like overcurrenting would). 
Because of nature of the circuit (10k resistor + JFET limiter + Z567M as 
load), lower current means higher voltage drop on JFET, so power 
dissipation increases a bit, because voltage drop on the resistor 
decreases. I'm looking for a transistor with similar parameters as BF256B, 
but with higher breakdown voltage (at least 50V), so I could run the test 
without additional resistor. If I find one and it will pass the tests, I 
think that it would be it - a small circuit limiting anode current, 
allowing to conserve power by using HV just above striking voltage, while 
still having current under control. Next step would be some kind of a 
constant current step up converter.

If this is too unstable due to differences in Vg curves between 
transistors, then only an active current sensing and driving circuit is 
needed. I have an idea to use an isolated 5V supply, which would allow to 
use some simple circuits near HV voltage - an opamp amplifying voltage on 
current sensing resistor and driving a transistor, all connected somehow to 
HV. I'm afraid it is only a loose idea - I am not willing to test it 
myself, for me the JFET circuit is good enough, if I ever decide to use 
current limiting instead of good old resistors.

W dniu sobota, 8 kwietnia 2017 14:52:13 UTC+2 użytkownik Tomasz Kowalczyk 
napisał:
>
> I'm afraid all active current limiters will change with temperature, just 
> some will be affected more and some less. But small changes (0,1mA or less) 
> won't be critical in a nixie clock, I think. So if a circuit will be stable 
> enough to provide desired current +-0,1mA in temperature range of 0°C to 
> about 70°C, with supply voltage changing 20V max - I'd call it good enough.
> About variations of Vgs curves - within one production batch of 
> transistors differences are usually minimal. So after ordering a batch of 
> transistors you have to check just one of them and you can safely assume 
> that all other will behave almost identically. Vbe differences in current 
> mirrors are much more critical, as the difference gets amplified.
>
> If those two factors are still too big, then you have to use a circuit 
> using a current sensing resistor, an amplifier of Rsense voltage drop and a 
> drive transistor. Multiply that by 15 segments and by number of tubes and 
> you end up with a large and costly circuit. I think that that level of 
> current stability is not needed here.
>
> I'll test J-FET current limitter with a hot air gun - how it behaves in 
> temperature range of 20-150°C, both with 5V and 30V dropping on it.
> If I find some time, I'll do the same with a very similar circuit using 
> LM317 (similar - both use only one resistor and one cheap active component).
>
> W dniu sobota, 8 kwietnia 2017 05:02:25 UTC+2 użytkownik gregebert napisał:
>>
>> My concern with current limiters that rely heavily upon the datasheet 
>> specs (Vgs  for Depletion-mode regulator; Vbe for current-mirror)  is that 
>> variations due to process & temperature will have significant impact on the 
>> actual current. Using a slightly more complex+costly design will mitigate 
>> this; well-worth it in my opinion when you consider the value of the tubes 
>> you are protecting. 
>>
>>
>>

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/88eb74eb-45ca-465c-97f6-e991df2c1238%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[GastonP]

Yes... JFETs are extremely variable on their parameters so circuits using 
them need trimming of the external components if one needs a certain degree 
of precision. That, or negative feedback.


On Saturday, April 8, 2017 at 12:02:25 AM UTC-3, gregebert wrote:
>
> My concern with current limiters that rely heavily upon the datasheet 
> specs (Vgs  for Depletion-mode regulator; Vbe for current-mirror)  is that 
> variations due to process & temperature will have significant impact on the 
> actual current. Using a slightly more complex+costly design will mitigate 
> this; well-worth it in my opinion when you consider the value of the tubes 
> you are protecting. 
>
>
>

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/54ea6325-162e-4425-9302-cab67a67558c%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

Re: [neonixie-l] Re: Constant current source design

[Paul Andrews]

Totally agree. This is one reason I like to actually try these things out.

> On Apr 7, 2017, at 11:02 PM, gregebert  wrote:
> 
> My concern with current limiters that rely heavily upon the datasheet specs 
> (Vgs  for Depletion-mode regulator; Vbe for current-mirror)  is that 
> variations due to process & temperature will have significant impact on the 
> actual current. Using a slightly more complex+costly design will mitigate 
> this; well-worth it in my opinion when you consider the value of the tubes 
> you are protecting. 
> 
> 
> -- 
> You received this message because you are subscribed to a topic in the Google 
> Groups "neonixie-l" group.
> To unsubscribe from this topic, visit 
> https://groups.google.com/d/topic/neonixie-l/gbJ0Beiu66I/unsubscribe.
> To unsubscribe from this group and all its topics, send an email to 
> neonixie-l+unsubscr...@googlegroups.com.
> To post to this group, send email to neonixie-l@googlegroups.com.
> To view this discussion on the web, visit 
> https://groups.google.com/d/msgid/neonixie-l/5c9c7941-efba-4967-acee-24c8701874b4%40googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/EF88509D-B0C1-44B8-88C8-BD448FAC7A88%40gmail.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[gregebert]

My concern with current limiters that rely heavily upon the datasheet specs 
(Vgs  for Depletion-mode regulator; Vbe for current-mirror)  is that 
variations due to process & temperature will have significant impact on the 
actual current. Using a slightly more complex+costly design will mitigate 
this; well-worth it in my opinion when you consider the value of the tubes 
you are protecting. 


-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/5c9c7941-efba-4967-acee-24c8701874b4%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Paul Andrews]

Although a mosfet current mirror would use fewer components as you only 
need one Rset (section three of this 
paper).

I guess I need to place yet another order with digikey to try some of these 
out.

On Friday, April 7, 2017 at 5:34:49 PM UTC-4, Paul Andrews wrote:
>
> Here is a link 
> 
>  
> to a paper about using a depletion mode MOSFET for the same purpose. It 
> gives this equation for calculating the resistor value, which I assume 
> would be the same for all depletion mode MOSFETS (!?):
>
>
> 
>
> VGS(th) is the gate threshold voltage of the MOSFET, IDSS is the on 
> current at VGS = 0 V and ID is the required current.
>
>
> There are plenty of these around with suitable voltage characteristics.
>
>

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/33831f40-c2a4-4cd6-b18b-a49d604165f7%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Paul Andrews]

Here is a link 

 
to a paper about using a depletion mode MOSFET for the same purpose. It 
gives this equation for calculating the resistor value, which I assume 
would be the same for all depletion mode MOSFETS (!?):



VGS(th) is the gate threshold voltage of the MOSFET, IDSS is the on current 
at VGS = 0 V and ID is the required current.


There are plenty of these around with suitable voltage characteristics.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/c02f17e0-a13b-4095-b2a0-d17fd8bbb11d%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Tomasz Kowalczyk]

Update 2 - I've found a 130,5V transil at work, so I've been able to 
substitute a nixie tube with a nice dummy load. Results are: 208V supply, 
139V dropped on transil, 49V dropped on 3x33k resistors in parallel, rest 
dropped on my limiter. Current is 4,55mA. Everything seems to work just as 
expected! 

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/eb25fe02-ddda-4e12-adcd-c0f5bd442a67%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Tomasz Kowalczyk]

Update: success! I've found a way to limit current using few components and 
without any voltage dividers.
The key was using a N-JFET. I guess if one used a N-MOSFET which opens with 
negative gate voltage, the result would be simmilar. I wonder if a similar 
circuit with a P-MOSFET would work, but I'm not going to check it soon.
The schematic is ultra simple:
https://i.stack.imgur.com/sKtpJ.png
I used a BF256B (the only N-JFET I have laying around) and changed resistor 
to 1k. The current is limited to 2mA - I've tested it with voltages from 0 
to 30V and as soon as I reach 2V across it, it starts blocking current. It 
changes slightly with voltage, on 3V across circuit it is exactly 2mA and 
with 30V it is 2,1mA, but I think it is close enough. A 270 resistor gives 
about 4,5mA, the difference between 5V and 30V is about 0,15mA - still very 
good,
Drawbacks of this method? JFETs are only low voltage, max 30V difference 
between any two pins, usually. So to use those with Nixies, you'd have to 
use a resistor + this limiter - so if you have 50V to drop on current 
limiter and you want it to work on 2mA, you have to use a 22k resistor + 
this limiter to drop 44V across resistor and 6V on limiter. And, of course, 
it will blow if Nixie gets shorted, so whole circuit will have to drop 200V 
instead of 50v.
I'll probably test this on nixies during next days. 

Idea and schematics taken 
from 
http://electronics.stackexchange.com/questions/105326/is-there-any-physical-device-called-current-source/105394

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/98e3cac4-6a49-4fbf-a15a-c15ca6ec3853%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Tomasz Kowalczyk]

Sorry for late reply, I've destroyed my boost converter somehow and had to 
rebuild it from scratch. I've tried the current limiter, but without 
success - I don't know why, I followed the article and I think that this 
just won't work for such voltage drops or something. Funny thing is that 
I've chosen a small R1 for one try and with intention to blow things up 
I've connected it directly to converter, without any load. Of course, R1 
blew up, but funny thing is that after burning the circuit was passing 
1,2mA - and I was aiming at 1mA :D
Of course this was just a resistor burning from 1,2k to around 250k, not a 
working limiter.

I have another idea. What do you think about using optoisolator in active 
range? It would require testing each batch of components, as they tend to 
have varying current transfer ratio, but you'd be able to control the 
current on low voltage side (even from DAC).
I'm looking for a stable method of controlling it without any resistors 
going from HV to ground, as it would waste alot of power, at least with 
bipolar transistors - with a p-mosfet it could work with resistances in 
voltage divider like 4,7MOhm, but mosfets tend to change their 
characteristics with temperature.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/6ee30a29-8979-4f80-ad23-88531c176788%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[gregebert]

I'm not able to reason-out how the last circuit acts as a regulator. 
Basically, the path from the 200V supply to Rload (output) is 2 diode-drops 
(base-emitter junction) in series with 100K of resistance. Assuming the 
nixie tube takes about 150V to ionize, a current of 0.5mA thru R1 causes a 
50V drop.

Adding-up the voltage drops around the circuit, everything is accounted for:

200V supply = 0.5mA * 100K + Vbe +Vbe + Nixie_tube. Solving, the nixie tube 
will have around 148.6V, assuming Vbe of 0.7V. This is in the ballpark for 
nixie tubes.

If you want 2mA, reduce R1 to around 25K. But I dont think it will act as a 
regulator when you change the supply; the current will also change.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/be8a0173-88ee-45cb-824c-65d07ec376d6%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Paul Andrews]

Next installment. First I tried the current mirror with 2K resistors 
between +300V and the emitters. This works fine, but is also no more stable 
than the first solution. It presumably also wastes more power as R2 has to 
be higher - it is setting the current, so I chose 100K here to get 2mA:



Next I tried the current limiter as described in several places, but in 
particular here 
as
 
suggested by Tomasz. I used an Rsense (R3) of 330 Ohms as I wanted 2mA. 
This was not successful. With test loads it delivers <2mA (or exactly 2mA 
for a short circuit!). So I tried a 6844A nixie (which is what started off 
this whole current source thing). It delivered approx 0.5mA, so the tube 
barely lit.





-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/b89e7779-fc4c-40c7-8c72-091ee33c9b45%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[gregebert]

Dont use the current mirror without emitter resistors; it will likely be 
inaccurate with discrete devices.

The current mirror as shown uses the operating point of Q2 (which is very 
controllable and stable) to set the current through Q1. The problem is that 
in this configuration, Q1's collector current is exponentially sensitive to 
Vbe. Any mismatch in characteristics between Q1 & Q2 will result in 
substantial current mismatch between Q1 and Q2. I believe a 26mV mismatch 
at room temp can produce a 2:1 mismatch in collector current. Circuit 
wiring will also be a factor because it only takes milliohms to contribute 
to mismatch.

In order to match the currents between Q1 and Q2 independently of device 
variations, you need to add equal resistance at their emitters. If you are 
targerting, say 3mA, an emitter resistor of 1K will greatly improve 
matching. The reason why is that variations in Vbe are much smaller than 
the voltage drop across the emitter resistor.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/04490d97-5cf6-4d2b-ba7f-bd27b3253f39%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

Re: [neonixie-l] Re: Constant current source design

[gregebert]

There are lots of inexpensive isolated DC-DC converters. I've been using 
products from Cui and Recom. Here's a 12V unit I use: 
http://www.digikey.com/product-detail/en/VIBLSD1-S5-S12-SIP/102-1432-ND/989887

They are available in all sorts of input and output voltages. Be careful 
that some require a *minimum* load, which can be for driving a power-on LED 
indicator. Also be careful filter caps on the output; they often have 
max-cap limits in the datasheet.

Anyways, they are easy to use. Connect the 2 input pins to your low-voltage 
supply observing correct polairty.
For the DC-DC converter outputs, connect the *positive* terminal to your 
anode supply; the negative output becomes the bias supply for your current 
regulator(s).

To make the anode current adjustable, connect a pot across the DCDC 
converter's output, then use the wiper to supply the bias voltage. I'd 
suggest 10-turn trimmers, rather than standard (cheap) 3/4 turn.

   - If you are using PNPs, be mindful of the base current. It may force 
   you to use lower-value potentiometers (ie,below 1K).
   - If you use PMOS, there is no current so just use any pot you have; 
   anything from 1K to 100K or more is fine. Best to add a zener diode to 
   clamp any potential voltage spikes that could happen (startup/shutdown 
   transients, ESD, etc) to protect the PMOS. The zener voltage needs to be 
   greater than the DC-DC converters output voltage, AND less than the max Vgs 
   specified in the PMOS datasheet.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/f0928756-40c1-4d62-9c32-1ef20b28d743%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

Re: [neonixie-l] Re: Constant current source design

[JohnK]

I think he was talking about a -5supply that you make from a low voltage AND 
that both rails of teh 5V supply are insulated very well from earth/ground. 
ie Floating.
Then you can wire each of its leads to a place that could be a voltage well 
above [or below] earth/gnd. Let's wait for him to pipe up. I was only 
replying early in case it put you on the right track.


Look into supplies that have "floating" outputs. Get that concept figured 
out firmly. [I noticed that you said you are willing to learn.]


jk




- Original Message - 
From: "Paul Andrews" <judge2...@gmail.com>

To: <neonixie-l@googlegroups.com>
Sent: Sunday, April 02, 2017 12:36 AM
Subject: Re: [neonixie-l] Re: Constant current source design


As I see it, the base voltage needs to be -5V wrt to the emitter, so if the 
emitter voltage is 200, then the base voltage needs to be 195. Am I missing 
something?



On Apr 1, 2017, at 9:42 AM, JohnK <yend...@internode.on.net> wrote:

I suspect that he meant if you wanted the 1ve supply, then the devices he 
mentioned give it easily directly from your low voltage supply - I don't 
think he meant you to use up your precious High Voltage.  Presumably you 
are running the high voltage generator DCDC conv off a low voltage? You 
aren't getting High Volts dangerously from the mains?


John K




- Original Message - From: "Paul Andrews" <p...@nixies.us>
To: "neonixie-l" <neonixie-l@googlegroups.com>
Sent: Saturday, April 01, 2017 11:51 PM
Subject: [neonixie-l] Re: Constant current source design


If I just look at all of the circuit diagrams for various current 
limiters, it begins to seem like any combination of a couple of 
transistors and a bunch of resistors works! Hence my need to do some 
'practicals', it makes me go in to it all in enough depth to actually 
begin to understand.


BTW, how exactly would I drop 5V from 200V using a DCDC converter? I.e. 
which converter (part number?) and how would it be wired up (diagrams 
help, I'm a visual type of person).


Thanks in advance.

Maybe I should just do a masters in electronics.

--
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an 
email to neonixie-l+unsubscr...@googlegroups.com.

To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/c8b42ecf-2ec3-4b13-9bdf-60756b034537%40googlegroups.com.

For more options, visit https://groups.google.com/d/optout.

--
You received this message because you are subscribed to a topic in the 
Google Groups "neonixie-l" group.
To unsubscribe from this topic, visit 
https://groups.google.com/d/topic/neonixie-l/gbJ0Beiu66I/unsubscribe.
To unsubscribe from this group and all its topics, send an email to 
neonixie-l+unsubscr...@googlegroups.com.

To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/B1651375EFEC4E4096A7089BAAA54BC5%40compunet4f9da9.

For more options, visit https://groups.google.com/d/optout.


--
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an 
email to neonixie-l+unsubscr...@googlegroups.com.

To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/6875DA44-C17F-4161-AAE8-AD4B877C89E9%40gmail.com.
For more options, visit https://groups.google.com/d/optout. 


--
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/1F4DAC1F496B49F1973DED44BED398A0%40compunet4f9da9.
For more options, visit https://groups.google.com/d/optout.

Re: [neonixie-l] Re: Constant current source design

[JohnK]

I suspect that he meant if you wanted the 1ve supply, then the devices he 
mentioned give it easily directly from your low voltage supply - I don't 
think he meant you to use up your precious High Voltage.  Presumably you are 
running the high voltage generator DCDC conv off a low voltage? You aren't 
getting High Volts dangerously from the mains?


John K




- Original Message - 
From: "Paul Andrews" <p...@nixies.us>

To: "neonixie-l" <neonixie-l@googlegroups.com>
Sent: Saturday, April 01, 2017 11:51 PM
Subject: [neonixie-l] Re: Constant current source design


If I just look at all of the circuit diagrams for various current limiters, 
it begins to seem like any combination of a couple of transistors and a 
bunch of resistors works! Hence my need to do some 'practicals', it makes me 
go in to it all in enough depth to actually begin to understand.


BTW, how exactly would I drop 5V from 200V using a DCDC converter? I.e. 
which converter (part number?) and how would it be wired up (diagrams help, 
I'm a visual type of person).


Thanks in advance.

Maybe I should just do a masters in electronics.

--
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an 
email to neonixie-l+unsubscr...@googlegroups.com.

To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/c8b42ecf-2ec3-4b13-9bdf-60756b034537%40googlegroups.com.

For more options, visit https://groups.google.com/d/optout.

--
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/B1651375EFEC4E4096A7089BAAA54BC5%40compunet4f9da9.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Paul Andrews]

If I just look at all of the circuit diagrams for various current limiters, it 
begins to seem like any combination of a couple of transistors and a bunch of 
resistors works! Hence my need to do some 'practicals', it makes me go in to it 
all in enough depth to actually begin to understand.

BTW, how exactly would I drop 5V from 200V using a DCDC converter? I.e. which 
converter (part number?) and how would it be wired up (diagrams help, I'm a 
visual type of person). 

Thanks in advance.

Maybe I should just do a masters in electronics.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/c8b42ecf-2ec3-4b13-9bdf-60756b034537%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[gregebert]

A word of caution...the next article in the allaboutcircuits link in Paul's 
posting discusses current mirrors. You *can* use that technique for 
multiple anodes with a few caveats

   1. If you use the R1//R2 voltage divider, you will need to account for 
   base-current of additional regulators. This means smaller R1 & R2 values, 
   hence more power dissipation in those resistors (heat).
   2. You can also use a PMOS device instead of the PNP [base--> gate, 
   emitter --> source, collector --> drain]; the gate current will be zero. 
   Just be careful about ESD handling procedures, and be sure to have plenty 
   of voltage margin (Vds > 200V for Paul's circuit)
   3. You can omit R2, and replace R1 with a negative voltage supply; 
   isolated DCDC converters are perfect for this. -5V for PNP, -12V for PMOS 
   is a god choice. Remember: the gate or base must be* negative* with 
   respect to the emitter.

Don't follow the current-mirror literally in the allaboutcircuits link, 
because there will be device-to-device variations in current for a given 
Vbe. This technique is fine for IC's when the mirrors are in close 
proximity on the same die and other symmetry rules are followed. Entirely 
different story when offchip. Having resistor R3 swamps-out the effect of 
Vbe variations between devices.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/2b5a6280-0266-42f8-8b8a-3cad879afed7%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[ZY]

I just want to add that for the low current scenario, the voltage should be 
consumed by the nixie. The voltage across the LM317 will continue to drop 
with reducing current, down to about 0.75V at 0.2mA under a test I did. 
Only in overcurrent would there be an issue, as the voltage across it will 
increase beyond it's limit. 

On Monday, 27 March 2017 02:36:01 UTC-4, Tomasz Kowalczyk wrote:
>
> It all depends on R11 and desired current. Most nixies have a minimum 
> voltage drop of around 120V (although they will maintain 130 for most of 
> the time, they will just continue to work with lower voltage), so if 
> voltage drop on R11 is more than (supply voltage - 120V - 
> LM317_max_voltage), then it is safe - the only case where the nixie doesn't 
> have that voltage drop is when it is internally shorted.
> In this schematic, assuming that U15 is fully open, so voltage at R11 left 
> side is just about 180V, everything will be okay - the LM317 is set for 
> 8mA, so voltage drop over R11 would be around 34V and everythin would be 
> safe. The problem is that if current is significantly lower that (nixie is 
> heavily poisoned), then stuff can get bad: as far as I understand, R11 
> voltage drop has to be lower (Ohms law), so the voltage across LM317 will 
> get higher, I think - it has to drop somewhere.
> Long story short, you are right - LM317 can fail in non-standard 
> situation. That's why I would go for a two-transistor design using MMBTA42 
> (or MPSA42), which will withstand almost anything. The only problem is 
> power dissipation - 5mA with 50 volts drop across current limiting circuit 
> is 0,25W. With such constant current design one should lower HV voltage to 
> minimum (just above striking point of all nixies), normally the 
> significantly higher voltage (200V) is used to make choosing limiting 
> resistor easier.
>
> W dniu poniedziałek, 27 marca 2017 04:17:46 UTC+2 użytkownik gregebert 
> napisał:
>>
>> I dont see anything fundamentally wrong; I just have paranoia about 
>> running devices in an environment where this is potential for overvoltage. 
>> The LM317 is rated for ~35V, and the HV supply is around 180V, so you are 
>> relying on the voltage drop across the nixie tube. There are all kinds of 
>> unexpected things that happen during power-up/down; maybe there are 
>> scenarios that could damage the LM317.
>>
>>
>>
>>
>>

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/0d854699-9439-4c03-ad10-376766ebada2%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Paul Andrews]

My parts arrived, so I finally got to try it. It actually works! Now on to 
trying variations - I plan to follow the course here 

.

On Friday, March 24, 2017 at 11:26:32 PM UTC-4, Paul Andrews wrote:
>
> I wanted to start a discussion about constant current sources (as opposed 
> to sinks, because I want to provide a constant current to the anode 
> regardless of which cathode is pulled to ground). I've found many articles 
> on the web. Some for Nixie constant current sinks, some for LED constant 
> current sources, some more theoretical, some very simple, some very 
> complex. But no constant current *sources *for Nixies - i.e. designs for 
> a constant current source that include actual part numbers and component 
> values. I wanted to start simple, to make sure I have at least some grasp 
> of this topic, so here is my first stab. I would be grateful if anyone 
> could let me know if it would work as is or if I have made some fundamental 
> errors - ignoring improvements such as temperature stability for now (BTW 
> R3 is Re in the equations).
>
> Be gentle - this is all new to me!
>
>
> 
>
>

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/9a50fca9-5718-4e7d-8239-997ee6e321bb%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

Re: [neonixie-l] Re: Constant current source design

[gregebert]

To elaborate a bit more about what happens to the b7971 when the anode 
current-limiter kicks-in, I will need to study the I-V plots I generated 
from tube measurements. What will happen is that the anode current-limiter 
will effectively vary the voltage at the anode to maintain the total 
current at the limit.

If all segments had identical I-V characteristics, they would equally share 
the reduction in current imposed by the anode current-regulator.
I think that the segment with the highest voltage-drop will "suffer" the 
most, followed by the segment with the next-highest voltage-drop. This is 
why I tried to keep all displayable characters at/below the max current 
limit. The intent of the anode current-limiter is for protection only.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/373dbbbf-6336-4679-8282-9a23c8a77144%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

Re: [neonixie-l] Re: Constant current source design

[robin bussell]

For
example, http://tayloredge.com/storefront/1386_B7971SmartSocket/1386A.pdf

Segment 11 in the datasheet is defined for a max current of 5.5mA, but
the above schematic would produce (170V - 140V) / 24 kOhm = 1.25mA. This
seems rather low?


I use those boards in this: https://hackaday.io/project/9155-nixiebot 
and it seems plenty bright enough to my eyes. Occasionally when the sun 
is full on the tubes through the window the pictures it produces can be 
a bit less legible but that's likely the camera having to adjust the 
sensitivity down due to bright reflections on the tubes.


Cheers,
 Robin.



--
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/1dad61a3-6373-713d-7db2-04192e519a41%40cqr-ltd.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[gregebert]

Timely subjectmy 7971 PC boards just cleared US customs and are on the 
plane to Oregon

I have independent current-regulators on each cathode. 4 tubes * 15 
cathodes = 60 current regulators. The driver transistor is a dual NPN in a 
surface-mount package to save area. The cathode (segment) currents are not 
adjustable, but there are SO many available resistor values it's easy to 
tweak to fine resolution. I purposely chose 1% tolerance SMT (0805) 
resistors. The NPNs are controlled by a TTL-level shift register (74HC595) 
running at 3.3V.

For the anodes, each tube has an overall current limit (PMOS), set to 22mA 
(datasheet max). Total of 4 per board.

The boards are end-to-end abuttable, so my first (and only) project will 
have 7 tubes to start with.

Of my seven b7971 tubes, I gathered I-V data for each segment. This gave me 
an overall idea how much current it takes to get decent illumination.
Next, I wrote a spreadsheet that calculates the total current for a variety 
of ASCII characters (0-9, A-Z, _ ^ - * ). By setting the individual segment 
currents in the spreadsheet so that most characters are at/below the tubes 
max-rated value, I get an idea where to start. A few characters go over the 
22mA spec value, and that's where the anode regulator kicks-in. Hopefully 
it will result in segments fair-sharing their current. From there, it's 
easy to calculate the cathode resistor and select from available values.



-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/4b2db638-ce71-4aa8-a71d-918168648d24%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Luka C]

@greg

I'd like to ask something related to the B7971 since I'm designing a PCB 
for the clock at the moment. I have implemented the controlled current 
sinks for each cathode and will fine tune the current for each segment 
(already discussed in the HV control chips thread with the schematic). I'm 
wondering if you implement both the cathode sink drivers and the anode 
driver you proposed here:

1) If sum of all lit cathodes currents exceeds the maximum value in the 
datasheet (the current set on the PMOS controlled source) what will happen 
to the currents of the individual segments, will they proportionally go 
down for each activated cathode? If so, will this cause the tube to reduce 
the glow?

2) If the sum of all lit cathodes is less than the maximum defined in the 
datasheet, it's supposed to stay that way because the PMOS source only 
limits the upper maximum current but does not enforce it constantly to flow 
trough the tube when it's activated?

3) How important do you think the maximum current per tube control is? 
Before deciding to go with the sink controller for each cathode, I browsed 
for other solutions to drive the B7971 and most of them use resistors, but 
these resistors have to limit the current to rather low values, are these 
enough to light the tube properly?

For 
example, http://tayloredge.com/storefront/1386_B7971SmartSocket/1386A.pdf

Segment 11 in the datasheet is defined for a max current of 5.5mA, but the 
above schematic would produce (170V - 140V) / 24 kOhm = 1.25mA. This seems 
rather low?

Dana nedjelja, 26. ožujka 2017. u 09:01:56 UTC+2, korisnik gregebert 
napisao je:
>
> Some other things I forgot to mention...
>
> 1. Generally, you would use a current-regulator on the anode side for 
> non-segmented tubes (0-9), where all cathodes use the same current.
>
> 2. Segmented displays (b7971) have different currents for various 
> segments, so you will need cathode-side current-regulation. I chose to 
> include an anode-side current-limiter as well because the Burroughs 
> datasheet specifies a max total current. This max current is about half the 
> sum of all the spec'd individual segment currents.
>
> 3. If you use MOS devices, be very careful not to exceed the max-voltage 
> specs. Doing so will damage the device (impaired reliability, or outright 
> destruction). I've done some research on MOS device-failures and they often 
> fail-shorted, which is disastrous. Fortunately, those kinds of failures are 
> mostly caused by overstress (voltage or temp).
>

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/bea2bf0a-852e-4d8a-a6f1-57e7ffe79835%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Tomasz Kowalczyk]

It all depends on R11 and desired current. Most nixies have a minimum 
voltage drop of around 120V (although they will maintain 130 for most of 
the time, they will just continue to work with lower voltage), so if 
voltage drop on R11 is more than (supply voltage - 120V - 
LM317_max_voltage), then it is safe - the only case where the nixie doesn't 
have that voltage drop is when it is internally shorted.
In this schematic, assuming that U15 is fully open, so voltage at R11 left 
side is just about 180V, everything will be okay - the LM317 is set for 
8mA, so voltage drop over R11 would be around 34V and everythin would be 
safe. The problem is that if current is significantly lower that (nixie is 
heavily poisoned), then stuff can get bad: as far as I understand, R11 
voltage drop has to be lower (Ohms law), so the voltage across LM317 will 
get higher, I think - it has to drop somewhere.
Long story short, you are right - LM317 can fail in non-standard situation. 
That's why I would go for a two-transistor design using MMBTA42 (or 
MPSA42), which will withstand almost anything. The only problem is power 
dissipation - 5mA with 50 volts drop across current limiting circuit is 
0,25W. With such constant current design one should lower HV voltage to 
minimum (just above striking point of all nixies), normally the 
significantly higher voltage (200V) is used to make choosing limiting 
resistor easier.

W dniu poniedziałek, 27 marca 2017 04:17:46 UTC+2 użytkownik gregebert 
napisał:
>
> I dont see anything fundamentally wrong; I just have paranoia about 
> running devices in an environment where this is potential for overvoltage. 
> The LM317 is rated for ~35V, and the HV supply is around 180V, so you are 
> relying on the voltage drop across the nixie tube. There are all kinds of 
> unexpected things that happen during power-up/down; maybe there are 
> scenarios that could damage the LM317.
>
>
>
>
>

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/b7218ec0-7532-48d0-9220-074fc3febf69%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[gregebert]

I dont see anything fundamentally wrong; I just have paranoia about running 
devices in an environment where this is potential for overvoltage. The 
LM317 is rated for ~35V, and the HV supply is around 180V, so you are 
relying on the voltage drop across the nixie tube. There are all kinds of 
unexpected things that happen during power-up/down; maybe there are 
scenarios that could damage the LM317.




-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/7eb263ef-6d23-4953-b9e1-0590f1906db3%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[ZY]

I'd like some opinions on using something like a LM317 inline on the high 
side, as in the image attached. I've tested it and it seems to work 
although maybe there is a flaw that I'm not seeing somewhere.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/84afc927-598c-4a96-a5c2-4b0d676af07a%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[gregebert]

Some other things I forgot to mention...

1. Generally, you would use a current-regulator on the anode side for 
non-segmented tubes (0-9), where all cathodes use the same current.

2. Segmented displays (b7971) have different currents for various segments, 
so you will need cathode-side current-regulation. I chose to include an 
anode-side current-limiter as well because the Burroughs datasheet 
specifies a max total current. This max current is about half the sum of 
all the spec'd individual segment currents.

3. If you use MOS devices, be very careful not to exceed the max-voltage 
specs. Doing so will damage the device (impaired reliability, or outright 
destruction). I've done some research on MOS device-failures and they often 
fail-shorted, which is disastrous. Fortunately, those kinds of failures are 
mostly caused by overstress (voltage or temp).

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/d1fba42b-580a-4733-8ab2-e81178a4bea9%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[gregebert]

That's basically what I use in my designs. I'll highlight the differences:

   - I use a PMOS instead of PNP, mainly because it requires no 
   drive-current.
   - R1 & R2 are replaced with a pot to make the current adjustable.
   - The above pot can driven from a small DC-DC converter (my preference), 
   or between the HV supply & GND. There's essentially zero current for PMOS 
   gate-drive, so high resistance values are fine. Not the case with PNP, 
   though, due to finite base-currrent.
   - A zener diode is added to clamp any spikes that may arise at the gate 
   of the PMOS device. It's a paranoia item.
   - A filter cap was added, in case there is unexpected noise from the DC 
   DC converter, and also to suppress any very-short transient that may arise 
   that are too fast for the zener to kick-in. (paranoia item).
   - A large resistor across the PMOS to bleed any potential ESD. Without 
   it, there is a remote possibility of charge-buildup. (paranoia item)

So, this circuit is replicated for each anode. When multiple anodes are 
driven, they all share the same gate-drive signal, which I call PDRV on the 
attached schematic.


-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/fdb55e53-78ef-4c09-b908-42e051dd380c%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Laurence Wilkins]

>
> Yes, I agree with Tomasz, the first circuit shown in the article he links 
> to is the way to do it. Advantages: No "wasted" current draw, cheap and 
> easy.  Ignore the comments in that article about the problems of voltage 
> drop - that might be important when you've only got 5V to play with, but 
> with 200V on tap... !!
>

Suggest RSense of 120 Ohms should regulate the current to 5mA, then make R1 
anywhere between 100K and 220K. Not critical.  Use a high voltage MPSA42 
transistor or similar for T1, T2 can be any old jelly bean type. 

While this constant current source will be inherrently short-circuit proof 
(the most current that will ever flow will be 5mA), be aware that under 
those conditions a humble MPSA42 will be dropping 1 Watt and will fry 
pretty quickly! Something a little beefier in the power stakes might then 
be a better choise.

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/a9018ffa-cc32-439e-8a11-5d7a549310c7%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Re: Constant current source design

[Tomasz Kowalczyk]

I would recommend using design like first one from link below: I haven't 
tested it myself, but it looks like it loses less power (doesn't have any 
resistors going from 200V to GND), and the mentioned minimum voltage drop 
on it will be not noticable in nixie application. It is not really a 
current source, but a current limiter, but again - it should do it's job. 
It uses one more transistor, but I think that with MMBTA42 or MPSA42 prices 
it shouldn't matter much.
http://electronicdesign.com/power/current-limiter-offers-circuit-protection-low-voltage-drop

W dniu sobota, 25 marca 2017 04:26:32 UTC+1 użytkownik Paul Andrews napisał:
>
> I wanted to start a discussion about constant current sources (as opposed 
> to sinks, because I want to provide a constant current to the anode 
> regardless of which cathode is pulled to ground). I've found many articles 
> on the web. Some for Nixie constant current sinks, some for LED constant 
> current sources, some more theoretical, some very simple, some very 
> complex. But no constant current *sources *for Nixies - i.e. designs for 
> a constant current source that include actual part numbers and component 
> values. I wanted to start simple, to make sure I have at least some grasp 
> of this topic, so here is my first stab. I would be grateful if anyone 
> could let me know if it would work as is or if I have made some fundamental 
> errors - ignoring improvements such as temperature stability for now (BTW 
> R3 is Re in the equations).
>
> Be gentle - this is all new to me!
>
>
> 
>
>

-- 
You received this message because you are subscribed to the Google Groups 
"neonixie-l" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/b8455dc3-4668-403f-bf86-92ed3c917723%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.