0-30V Stabilized Power Supply

[Guest liquibyte]

I just finished building the power supply.  Liquibyte did a nice job on his board!

One weird issue... has anyone experienced this: When turning the voltage down (like from say 25 volts to 5 volts) the voltage descends rather SLOWLY. Raising the the voltage is just about instantaneous, but lowering it makes me wonder.

Any ideas??

Neither of mine do that.  It's instantaneous, or nearly so, so it can't be C7.  I tested loaded and unloaded.  Can you upload a pic of the board in good resolution?

[Guest philtherepairman]

Redwire... using a 10k with a 1k in series (1 turn),  the slow descent happens if it's loaded or unloaded, using a 10 uf electrolytic for C7.

Otherwise, everything works. I'm not getting a full 3AMPS @30 volts, but I believe that's do to my transformer.

liquibyte...  thanks again!

[Guest liquibyte]

I'm glad they're working for you.  I wouldn't think that an electrolytic cap would cause asymmetrical response from the voltage adjustment, especially at 10uF but my experience is limited to voltage regulators.  I'd still like to see pics though, these were my first boards and I'm rightly or un-rightly proud of them.

I did order two LT1074HVCT7's to see if I can come up with something along the lines of what tcjeep wants.  The L296 is being deprecated so I thought I'd give it a go with something more modern.  I'll probably just end up releasing the magic smoke but I'd like to give it a try any way.

[Guest tcjeep]

Redwire... using a 10k with a 1k in series (1 turn),  the slow descent happens if it's loaded or unloaded, using a 10 uf electrolytic for C7.

Otherwise, everything works. I'm not getting a full 3AMPS @30 volts, but I believe that's do to my transformer.

liquibyte...  thanks again!

Philtherepairman, You could look at C4, I think it should be  0.1uF or 100nF polyester. I larger value might cause the input of of U2 to hang high for too long. Just a thought, a shot in the dark.

[Guest tcjeep]

I'm glad they're working for you.  I wouldn't think that an electrolytic cap would cause asymmetrical response from the voltage adjustment, especially at 10uF but my experience is limited to voltage regulators.  I'd still like to see pics though, these were my first boards and I'm rightly or un-rightly proud of them.

I did order two LT1074HVCT7's to see if I can come up with something along the lines of what tcjeep wants.  The L296 is being deprecated so I thought I'd give it a go with something more modern.  I'll probably just end up releasing the magic smoke but I'd like to give it a try any way.

Had a look at the LT1074HVCT7 datasheet and app notes. Its a nice looking chip with some good protection (should help to keep that dreaded magic smoke inside where it belongs). I'm looking for a similar device but 300V input. I want to get rid of that huge capacitor and the transformer. The problem really begins when one tries to make this type of power supply variable. Changing the mark/space ratio messes up the inductance and the characteristics of the waveform. I have spent far to long with discrete components, a mosfet chopper at 40Khz followed by the typical buck down converter. I can get it to work with fixed outputs, but to change the output voltage requires a lot of component changes. Someone must have done this somewhere.

[redwire]

I was checking the output of the power supply when the power is quickly disconnected and discovered some large spikes.  I set the PS at about 12V hooked up the scope to the output with a trigger at 13V and got the following picture.  I did the same thing with the output at max with the same result.  I also checked the output with a load and had similar spikes.  I'm wondering the Q1 protection needs to be added back.  Has anyone else check the output at shutdown?

[audioguru]

Hi Redwire. When the power is turned off, I do not see how the output can swing to +61V then to -65V.
It is ringing at about 4MHz.

[redwire]

The first photo is when it is set at 12V and the transformer is unplugged. 

The second photo is at when output is at max (approx. 30v)  and the transformer is unplugged.  It  looks like it is swinging approx. 30 volts negative then  30V positive resulting in approx. 64 Vpp. 

[audioguru]

Oh. Do you have a very inductive shunt on a current meter in series with the output of this power supply?
Or maybe R7 is inductive?

[Guest liquibyte]

I've been reading about this because I can't test it due to not having a decent scope.  It's sounding like inductive ringing to me.  Snubber maybe?

[redwire]

Oh. Do you have a very inductive shunt on a current meter in series with the output of this power supply?
Or maybe R7 is inductive?

I have a IC and LCD display attached and powered from a separate small transformer.  I tested it with the display on and off.  Perhaps I need to disconnect it then retest.

Edit  I disconnected everything from the PS and still get the spike.

[redwire]

Audioguru,  The power supply generates this kind of output at both startup and  shutdown.  Here is a shot of the startup with voltage set at approx. 0V.  The frequency is approx 24Mhz.

As a side note if you end up leaving the load connected to the PS and start the unit or if you accidently have the output shorted when you start up,  the current control does not take over.  For some reason I have done both at least once and it will usually let the blue smoke out of some part. Now it works well once the unit has stabilized.

[redwire]

A few weeks ago I changed the board by deleting U1 and associated components and replaced it with a 12V linear voltage regulator (PN  L78L12ACUTR).    I added two cap to keep the voltage regulator smooth.  Today the new PCB boards came in.    The only other board change was C7.  I switched to a film instead of electrolytic.  I ran the same tests on the scope and there was no ringing.  Based on that, I assume the ringing was U1 trying to stabilize when the power supply was removed but C1 still had a charge. 

[Guest Twentysix]

Hi there,

I built this (0- 30 v 5amp version) power supply over 1 year ago and has been a very solid performer, has not failed on me yet.
What my issue is when I switch off the P.S the volt Panel meter (analogue type) shows zero volts as it should, but then after say 1- 2 seconds the volt meter jumps to approx 7 volts and then slowly goes back to zero volts.

By the way the only change I have made to the design is I added an NPN (BC546) transistor between the neg rail and pin 6 of U2 to eliminate any voltage at output after the PS is switched off and a 24v Zener at pin 7 of U1

Any suggestions to point me in the right direction would be much appreciated

[Guest Canyoncruz]

Have you guys seen this variation?

[redwire]

Have you guys seen this variation?

Something similar was discussed several pages back.    IC1A seems to be missing the connections on pins 4 and 7.  It lists older  OpAmps  Tl082 which has a maximum voltage rating of 36 which is where it must operate.  I think the components used for the 9.5 V reference voltage is overkill, but I support the concept.  This design uses a voltage regulator for the negative rail.  I prefer the simplicity of the dual diodes to create the negative reference voltage and the 10V zener to tame down the rail voltage for the op amps that Audioguru has suggested.    It may be a matter of preference.

[Guest Canyoncruz]

Redwire,  here is the link:

http://diyfan.blogspot.com/2013/03/adjustable-lab-power-supply-take-two.html

[redwire]

Redwire,  here is the link:

http://diyfan.blogspot.com/2013/03/adjustable-lab-power-supply-take-two.html

Thanks  I wish I could read Czech to see the designers write-up from the original article.

[redwire]

Hi Twentysix,

By the way the only change I have made to the design is I added an NPN (BC546) transistor between the neg rail and pin 6 of U2 to eliminate any voltage at output after the PS is switched off and a 24v Zener at pin 7 of U1

what design did you use and what values did you use for R13 and R14?  The reason I ask is because if you use the latest design that has a negative rail of -1.2 V instead of -5.6V and you use the original values for R13 and R14 then the voltage to the base of  Q1 may be positive all the time instead of being slightly negative until shutdown.

[Guest Canyoncruz]

I google translated it and I copied to word, too long to past here. Send me an email address and I will forward

[Hero999]

I google translated it and I copied to word, too long to past here. Send me an email address and I will forward

Can you please save it and attach the file in plain text or PDF format, as the forum software doesn't allow Word documents.

[Guest Canyoncruz]

Hero,

I wasn't asking for help. I was pointing out there was another variation of the circuit and it is in Czech. The translated file is large. I guess anyone can go to the link and translate it themselves.

[Guest liquibyte]

This is just basically a bog standard google or bing translation.  Canyoncruz sent me the .docx and I converted it to a pdf.  I had to resize a few of the images but I think it's ok for the most part.

Quick edit:  I did some better formatting and the pdf looks much better now.

czech_power_supply.pdf

[Guest EmbeddedCom]

Hi All,
Ive decided to build this power supply. Where can I find the transformer ?
Thank you.

[Guest liquibyte]

Hi All,
Ive decided to build this power supply. Where can I find the transformer ?
Thank you.

I used this one.  $24.46 each isn't too bad considering the prices on transformers lately.  I know a lot of people tend to use toroids but I had a large case that wasn't doing anything so I went with traditional transformers.