High voltage supply - Page 1
Forum section: electronics / beginners

author: neo
author_rank: Super Contributor
timestamp: April 24, 2017, 10:48:12 pm
content: I need a high voltage supply and i have the good fortune to have a small transformer for old tube gear. It has 110 out which i then feed into the below circuit to get 220v nominal, since it is a cockroft walton the voltage drops to 170 with an approximation of the nixie current draw. Will this work in practice?The worst case i can think of is one tube were to stop drawing current then the voltage would rise but from my calculations if one tube were to die the voltage would raise and so would the current and thus it would be relatively safe, correct?Perhaps make the resistors have a maximum current draw equal to the maximum of the nixies so as to have a level of safety or maybe a glass fuse?

author: Buriedcode
author_rank: Super Contributor
timestamp: April 24, 2017, 11:47:56 pm
content: I don't see a schematic in your post.So, you're after a nixie tube power supply? I believe there's plenty of examples floating about on the web and in this forum.I am unsure of what your problem is. You say you have a small transformer.. that has 110v out.. from what? mains? or a primary switching circuit? If the transformer is on a board built as a DC-DC converter then a voltage multiplier won't help, but it should taken straight off the transformer. You are correct in assuming the output with 'sag' with current draw, but how much, depends on your setup.Are you worried that you'll 'blow' a nixie tube if one of them fails causing the power supplies voltage to increase? If you limit the power supply voltage, it won't. Adding a permanent load should indeed keep the voltage lower if its coming from a voltage multiplier.I think you would get more answers if you stated the problem more specifically.

author: neo
author_rank: Super Contributor
timestamp: April 25, 2017, 01:43:53 am
content: I have a converter that takes 70 VAC into 175 VDC but only if it has a load of 10k ohms, if one nixie were to die the voltage would jump to approximately 185 VDC. The problem is i know it works but this metaphorical problem of one nixie dying throws a variable in the mix and the question is what do i do about it, if anything? It is a very old transformer the date on it is the 40th week of 1960 so no circuitry just voltage.

author: rdl
author_rank: Super Contributor
timestamp: April 25, 2017, 04:07:39 am
content: Voltage regulator maybe?

author: neo
author_rank: Super Contributor
timestamp: April 25, 2017, 05:21:14 am
content: At 170 volts it seems impractical and/or too hard to get.

author: rdl
author_rank: Super Contributor
timestamp: April 25, 2017, 05:57:22 am
content: Maybe an LM317 could be used. I seem to remember a Sparkfun video (According to Pete) where he regulated a 400+ volt supply with an LM317. I think with an LM317 all you have to worry about is the input/output voltage difference. I've never tried it though.

author: jeroen79
author_rank: Frequent Contributor
timestamp: April 25, 2017, 08:46:16 am
content: Quote from: neo on April 25, 2017, 05:21:14 amWhy? What have you tried so far?It would not be much more dificult than a 17 volt supply.But you'll need to choose the right parts.But first: What are your specifications?What voltage range?What current?

author: Zero999
author_rank: Super Contributor
timestamp: April 25, 2017, 08:48:42 am
content: With the LM317 care is needed to avoid exceeding the maximum differential voltage rating of 40V.Another option is the TL431.A single transistor can be added to enable it to shunt regulate higher voltage. Here's an example showing a 50V shunt regulator.Adding another Darlington pair creates a linear regulator. Here's an example showing a design which regulates 350V down to 250V.Obviously you'll need to change the component values in the above circuits to get the voltage you need.

author: neo
author_rank: Super Contributor
timestamp: April 25, 2017, 02:38:06 pm
content: Here is a thought, a zener diode. It can supply the needed current, 20 MA max at 180 VDC, and can keep it in regulation.

author: vltr
author_rank: Contributor
timestamp: April 25, 2017, 04:39:26 pm
content: I use an pair of 0A2 tubes with a step up transformer(gives 240VAC out, rectified a bit over 370VDC). I use the tubes in series to get a 150V and 300V tap(don't currently use the 300 for anything, it was just to keep from using a huge power resistor). You can check the 0B3 datasheet for a simple example schematic:https://frank.pocnet.net/sheets/137/0/0B3.pdfThese tubes work similar to modern zeners if you want something a little more modern(I like powering tubes with tubes, but that's purely an aesthetic thing). If you want to stay old school you can also get more fancy and use these tubes as a voltage reference for another pass tube to get more current if you need it.

author: Zero999
author_rank: Super Contributor
timestamp: April 25, 2017, 05:05:25 pm
content: Quote from: neo on April 25, 2017, 02:38:06 pmPossibly.If what you've said there is true, te zener would need to be rated for 3.6W.Although, according to the figures provided previously:Vunloaded= 185VVloaded= 175VRL= 10kCalculate the output resistance of your power supply:ROUT= ((Vunloaded-Vloaded)*RL)/VloadedROUT= ((185-175)*10*103)/175 = (10*10*103)/175 = 571.4RSo a 180V zener would not draw 20mA. I = (185-180)/571 = 5/571 = 8.75mA, so 1.6W is more than enough.Perhaps 1N5955B would do:http://www.onsemi.com/pub/Collateral/1N5913B-D.PDFNote the tolerance, the temperature coefficient and that VRonly specified to be 180V with a current of 8mA.