0-100V variable DC power supply - Page 1
Forum section: electronics / beginners

author: belzrebuth
author_rank: Frequent Contributor
timestamp: June 13, 2020, 09:13:31 pm
content: I've been messing quite a bit with transformers lately and now I've got a few laying around including a 2x48v 100VA toroidal.I also have a ton of heatsinks and spare cases etc..And I may have some analog voltmeters around.Okay you've guessed it..!I thought I could make a nice adjustable 0-100V power supply since my Rigol DP832 can only reach 60V with its main channels in series.There are times I've needed more than that so I thought why not roll my own since I've got most of the expensive parts at hand anyways.So..Is anybody aware of a solid design?Preferably regulated.I've came across a few dodgy ones on the net but I don't think I've seen anything regulated.Ideally I'd like to have half an amp or so of avalaible current.Maybe an amp tops, just what this 100VA transformer can output more or less.Current limit is not that important but welcome of course.Higher voltage is also fine with me.I mean I can adapt it for less I guess and my transformer is good for around 120V anyways.

author: Wolfgang
author_rank: Super Contributor
timestamp: June 13, 2020, 10:48:41 pm
content: maybe some of this:https://electronicprojectsforfun.wordpress.com/power-supplies/high-voltage-lab-power-supplies/

author: belzrebuth
author_rank: Frequent Contributor
timestamp: June 14, 2020, 10:04:33 am
content: Plenty of info there! Thanks:)

author: Zero999
author_rank: Super Contributor
timestamp: June 14, 2020, 10:07:33 am
content: Of course this is possible, but it's not a beginner friendly project.If you're talking about a linear supply, burning off 100W at a relatively high voltage in semiconductors is a bad idea. The safe operating area of BJTs is tiny, at high voltages. Look at the graphs on the data sheets.https://en.wikipedia.org/wiki/Safe_operating_areaA switched mode power supply makes more sense, but it's still non-trivial, especially over such a wide voltage range. You're better off building two fixed voltage, 60VDC power supplies and connecting them in series with your lab power supply, to get higher voltages. You'll need a reverse diode in parallel with the lab PSU, to protect it against damage from reverse voltage.Needless to say there's a risk of shock, from borderline deadly voltages.

author: belzrebuth
author_rank: Frequent Contributor
timestamp: June 14, 2020, 10:17:11 am
content: Yes I understand.I'm close to last year of my EE studies and I'm only starting getting familiar with higher voltages but one has to start somewhere I guess. Two 60V power supplies in series wouldn't be a bad idea I guess and I could probably have them regulated and current limited far easier too.I already have a Rigol DP832 and a Farnell LT-30 which could be wired in this fashion but I essentially use 4 power supplies for a 120V one and without independent control so it seems like like a hassle already.It's far tidier to have a single source independently controllable.I could use the dual 48V transformer to build two separate 60V supplies (one from each winding pair).I guess it will be easier to find a design for a 0-60 adjustable supply (maybe regulated too?)

author: wizard69
author_rank: Super Contributor
timestamp: June 16, 2020, 11:33:43 pm
content: It might help to say what your intended usage is. A fixed voltage power supply is relatively easy but if you need multiple variable supplies it might not be too useful Given that I find fixed voltage supplies very useful if they come in the commonly used increments. That is a hefty 12 VDC (13.supply for Auto electronics, a 24 VDC supply for industrial circuits & etc.. If you have any desire to do automotive stuff a fixed voltage (battery eliminator as they are sometimes called) power supply is a very good option in my opinion. Your desire for much higher voltages though have me wondering if there is even a standard voltage for you to target.If you do have a good idea of what your usage might be you might want to consider a partially variable supply to avoid the high heat of a full range linear. I'm not sure if the approach would be worthwhile. Again it depends upon how you expect to use them.As others have indicated take care! High voltage DC can be lethal very quickly. At work I have to diagnose and repair servo drive systems from time to time with 500VDC bus voltages. Let me tell you it puts you in a different frame of mind, know your safety procedure for testing such hardware.Quote from: belzrebuth on June 14, 2020, 10:17:11 am

author: Jwillis
author_rank: Super Contributor
timestamp: June 17, 2020, 12:59:37 am
content: Have you considered a Variac DC supply. A small 4 amp Variac with a rectifier and PI filter would work. The Variac would give you the isolation . Current control would be fairly easy if you drive a couple Mosfets with an Op amp powered by a separate small transformer. Your only dealing with at most a couple amps so Linear Mosfet 's like the IXTH30N60L2 would work.

author: bob91343
author_rank: Super Contributor
timestamp: June 17, 2020, 02:49:07 am
content: A variac does not give isolation.

author: xavier60
author_rank: Super Contributor
timestamp: June 17, 2020, 05:08:14 am
content: I would suggest a conventional transformer rectified and filtered to about 130Vdc followed by a MOSFET/diode Buck regulator.A half bridge comes with complications of needing to be able change to diode mode to prevent current flow back in some situations.A high-side driver would be used like the FAN73611.I'm hoping that a high value resistor from the 130Vdc to the Vb pin will keep the bootstrap capacitor charged during inactive periods.This will need to be confirmed at an early stage.A Zener diode would be needed to stop the capacitor from overcharging.With a UC3843, the slope compensation could be set to prevent the duty cycle from reaching 100%.EDIT: The TL494 could be better suited.

author: Jwillis
author_rank: Super Contributor
timestamp: June 17, 2020, 07:12:45 am
content: Quote from: bob91343 on June 17, 2020, 02:49:07 amYour right . I was thinking of the double wound variable transformer but the are very expensive.