0-30V Stabilized Power Supply

[Canyoncruz]

There is a paper on noise and the TLE2141, the recommend two caps, 10u and .1u power supply decouplin. There a reason this has been omitted? ight this help?

 

[tcjeep]

I just received my Rigol 1074z scope.  I'm probing around the circuit and learning how to use this thing at the same time. Here is a screen shot of the output with the voltage set at zero- there is about 35mV output.  I am using a 10uF electrolytic cap, when I get a film cap i'll post the results.    The only unusual thing I noticed was that Pin 3 of U3 had substantial noise, this could be my set up and perhaps having 12" of wire from the pot to the board had an effect.  I had a 1uF cap handy so I hooked it between ground and pin3 and it tamed things down substantially.  I didn't notice any substantial change with the output whether or not this extra cap is utilized.

Congratulations on the Rigol 1074, my '70s vintage philips just started to look uglier. The noise on the input pin on U3 is broad spectrum and may be induced, but from where? Its most likely coming from the output of U1. 1uf on the input might make current control sluggish and delay response. I've not probed this far into mine, but I'll do it today and come back to you.

 

[redwire]

tcjeep,    I agree that a 1uF is a bit large, I  had the same concern.  I have a single turn pot and really didn't have issue with the responsiveness.    How often is there a need to instantly change the current control setting on pin 3?  Usually it is set ahead of time for a particular use.  When I get time I'll try a .1 uf . 

Hey the 1074Z is niccccccccccce!

 

[audioguru2]

I suspect that the noise comes from the 5.6V Zener diode voltage reference. If it has a bypass capacitor then I hope that opamp U1 does not oscillate.

Another reason to use a REAL voltage reference.

 

[philtherepairman]

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??

 

[redwire]

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??

Are you using a single turn or multi turn pot to adjust the voltage?  Is the slow descent only when there is no load?    C7 does need some time to discharge.

 

[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?

 

[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!

 

[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.

 

[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.

 

[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?

View attachment 42100

View attachment 42101

 

[audioguru2]

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. 

 

[audioguru2]

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?

 

[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.

View attachment 42103

 

[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. 

View attachment 42105

 

[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