[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

@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

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

@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

[neonixie-l] Re: Constant current source design

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,

[neonixie-l] Re: Constant current source design

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,

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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.

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

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

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

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

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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

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

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

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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,

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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,

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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:

[neonixie-l] Re: Constant current source design

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

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

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

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

<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

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

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 curren

[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,

[neonixie-l] Re: Constant current source design

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.

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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

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

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

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

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:

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

@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).

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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"

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

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

[neonixie-l] Re: Constant current source design

> > 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

[neonixie-l] Re: Constant current source design

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