[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.

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[neonixie-l] Re: Need IN-14

[Yuriy Ovchinnikov]

I have:

IN-14 – 81 pcs. for $5,

IN-14 used – 8 pcs. for $2.5

I can send by express mail - 2 week for delivery from Russia.

среда, 29 марта 2017 г., 20:00:29 UTC+3 пользователь Terry S написал:
>
> Has anyone in the states got a long leaded IN-14 to "front" me?
>
> I'm fixing another clock for a fellow, and I've ordered tubes, but they 
> may be weeks in coming. If anyone can send me a NOS IN-14 with long leads, 
> I will repay with a NOS tube plus postage & an extra $5.upon their 
> arrival.
>
> What's your experience with ordering tubes from Russia? Do they really 
> take as long as they claim to arrive? This transaction is saying mid May. 
> USPS tracking says they are en-route already.
>
> If it's only a couple weeks I can wait.
>
> Terry
>
>

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[neonixie-l] Re: Need IN-14

[Yuriy Ovchinnikov]

I have:

IN-14 – 81 pcs. for $5,

IN-14 used – 8 pcs. for $2.5

I can send by express mail - 2 week for delivery from Russia.
.

среда, 29 марта 2017 г., 20:00:29 UTC+3 пользователь Terry S написал:
>
> Has anyone in the states got a long leaded IN-14 to "front" me?
>
> I'm fixing another clock for a fellow, and I've ordered tubes, but they 
> may be weeks in coming. If anyone can send me a NOS IN-14 with long leads, 
> I will repay with a NOS tube plus postage & an extra $5.upon their 
> arrival.
>
> What's your experience with ordering tubes from Russia? Do they really 
> take as long as they claim to arrive? This transaction is saying mid May. 
> USPS tracking says they are en-route already.
>
> If it's only a couple weeks I can wait.
>
> Terry
>
>

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RE: [neonixie-l] loose-pin sockets

[Tidak Ada]

It’s not the insertion of the tube that worries me, but the long term stress 
due to slight misalignment of the bushings. That concerns particular hydrogen 
and helium filled tubes. Keep in mind tubes like EZ10A and B have a very dense 
13 pin socket that needs narrow tolerances in alignment. It’s therefore not 
wise to use PCB-sockets, a floating wiring is better.

 

eric

 

 

Van: neonixie-l@googlegroups.com [mailto:neonixie-l@googlegroups.com] Namens 
gregebert
Verzonden: zaterdag 1 april 2017 17:22
Aan: neonixie-l
Onderwerp: Re: [neonixie-l] loose-pin sockets

 

I do mine in 2-steps:

*   Low-insertion socket pins soldered to PC bpard
*   3D-printed collar that sets over the pins. It's mostly for aesthetic 
reasons, because the pins dont fit snugly into the collar. The collar certainly 
helps guide the tube into the socket. However, you should avoid 
plugging/unplugging unless necessary.

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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.

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Re: [neonixie-l] loose-pin sockets

[gregebert]

I do mine in 2-steps:

   - Low-insertion socket pins soldered to PC bpard
   - 3D-printed collar that sets over the pins. It's mostly for aesthetic 
   reasons, because the pins dont fit snugly into the collar. The collar 
   certainly helps guide the tube into the socket. However, you should avoid 
   plugging/unplugging unless necessary.

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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" 

To: 
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  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" 
To: "neonixie-l" 
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.

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[neonixie-l] loose-pin sockets

[JohnK]

What is the latest on low stress sockets?
3D printer ones coming along?

I am keen to hear from you all about the latest successes.

Anyone contemplating a ZIF style  - either rotate or slide locking etc?

John K

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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" 

To: "neonixie-l" 
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.

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[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.

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