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0-30V Stabilized Power Supply


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Guest liquibyte

I've been rearranging things based on a few lessons I learned and have come up with a semi-final version.  The only thing I'll add later is whatever components needed to take care of the voltage transients.  This is what's going to go into my case X2.  The reason it has the center hole is because I'm going to be stacking these on top of the display circuitry and want a really solid board with minimal flex.

Oh, and sorry audioguru, I like to work with the schematics in a dark format, makes things easier on my eyes in the middle of the night.

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Guest liquibyte

Yeah, I missed some of that.  I was more worried about the board than anything.  I redid things in white because I know there are some that prefer it that way.  The ratsnested image doesn't look right with a white background, you can hardly see the text.  I can upload the Eagle files if anyone wants but I haven't made any gerbers yet.

I caught a few other mistakes on the schematic and fixed both the light and dark versions.

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I gave your white schematic as much contrast as is possible which caused its background to be a little grey.
I noticed that you changed most of the parts designation numbers so that when most of the other schematics used R11 and R12 to set the gain of the voltage amplifier now you have R18 and R24 doing it. Therefore do you have a new parts list that matches your new schematic?

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Guest liquibyte

I noticed that you changed most of the parts designation numbers so that when most of the other schematics used R11 and R12 to set the gain of the voltage amplifier now you have R18 and R24 doing it. Therefore do you have a new parts list that matches your new schematic?

Point taken, I modified the schematic to have the parts list on the image.  Attached is a zip file of the .sch and .brd for Eagle as well.  Just in case anyone wants to play around with it or have boards made.

What do you use for your schematics and boards?  I'm just curious.

Edit: added the parts list as a text file and a pdf.  These have the Digikey part numbers on them.

0-30V-0-3A.zip

parts.txt

parts.pdf

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I gave your white schematic as much contrast as is possible which caused its background to be a little grey.
I noticed that you changed most of the parts designation numbers so that when most of the other schematics used R11 and R12 to set the gain of the voltage amplifier now you have R18 and R24 doing it. Therefore do you have a new parts list that matches your new schematic?
Try converting it to monochrome (1-bit per pixel).  Not only is it more clear but the file size has shrunk too.

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What do you use for your schematics and boards?  I'm just curious.

I have not made this project. I make many circuits on stripboard instead of on a pcb then half the wiring are the parts and a few jumper wires.
In my electronics career I made custom one-of-a-kind circuits (some were very complicated) and the prototype made on stripboard worked perfectly and looked good enough to be sold and installed.

I use Microsoft Paint program to copy and paste things and make schematics.
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Guest liquibyte


I have not made this project. I make many circuits on stripboard instead of on a pcb then half the wiring are the parts and a few jumper wires.
In my electronics career I made custom one-of-a-kind circuits (some were very complicated) and the prototype made on stripboard worked perfectly and looked good enough to be sold and installed.

I use Microsoft Paint program to copy and paste things and make schematics.

I thought you might have been using Altium or something.  I tend to rearrange simple circuits to my liking using GIMP but will create more complicated things in Eagle and either export the image or just upload the files zipped up.


Try converting it to monochrome (1-bit per pixel).  Not only is it more clear but the file size has shrunk too.

Monochrome with the parts added in.  Sometimes I think I should do the schematic and boards in Eagle, Diptrace, and Kicad just for completeness.  I haven't tried exporting and importing yet, but I'll try that soon to see if it can be done and not cause issues.

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I populated a new board and set up the clamp down transistor as shown on the original project but  using the new resistor values.  I tested and when I remove the negative voltage to the base it will turn off.    I then setup the scope on the output set at 12V connected to a tail light bulb and pulled the plug on the transformer and the first picture is the result.      I added a second channel to the scope and connected it to the emitter of the clamp down transistor.  That result is shown in blue on the second photo.  Note that the second photo is at a greater scale but it is nearly identical to the first.

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Guest liquibyte

See what the output does unloaded and set at a strict 3.3 volts with current set both at min and max and maybe with a load and without.  I'm curious what you get on power on as well as power off at 500mV/div or so I guess.  From the discussions I've had it seems like this shouldn't be happening.  Now that I've got a better scope, things seem to have tamed down with the better equipment but I'm still learning how to use it too so I may be getting better readings because I'm not using it right.

I'm also curious about this statement that was made over at eevblog concerning the outputs and inputs of the op amps.

The output U2 showed the same glitch.  That needs to be tracked down by looking at if the same glitch is showing up earlier in the signal chain at the non-inverting input of U2.  If it is *not* there, then maybe the output is being dragged up which can be tested by disconnecting it from Q2 and shorting it to the other end of R12 which removes the pass transistors from the circuit.

I haven't gotten this far yet to be honest.
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I suspect that the inductance of the 0.47 ohm resistor and the 10uF output capacitor cause the darlington connected driver and output transistors to ring at about 10MHz when the power is turned off.
Maybe the emitter of the clamp transistor should connect to the output ground on the other side of the 0.47 ohm resistor.

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I tried at 3V with the current at max and I got a flat line with no load.    I tried with 12V and got a ringing.  I am using a darlington power transistor so tomorrow I want to swap to a non darlington transistor.

I moved the emitter ground to the transformer side of R7 but it did not solve the problem.  I'm using R7 of 0.27ohms.  The ringing seemed to be around 10-12 mhz.  I need to check the inverting and non inverting inputs of U2.

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Guest liquibyte

I suspect that the inductance of the 0.47 ohm resistor and the 10uF output capacitor cause the darlington connected driver and output transistors to ring at about 10MHz when the power is turned off.
Maybe the emitter of the clamp transistor should connect to the output ground on the other side of the 0.47 ohm resistor.

I don't have the issue at power off, the transistor solved that problem for me.  I do have the problem at turn on if the filter caps have been drained.  What would cause that?  I know you said that R15 and D10 were removed for a reason but would they have been there to mitigate some of this?


I tried at 3V with the current at max and I got a flat line with no load.    I tried with 12V and got a ringing.  I am using a darlington power transistor so tomorrow I want to swap to a non darlington transistor.

I find that interesting.


I moved the emitter ground to the transformer side of R7 but it did not solve the problem.  I'm using R7 of 0.27ohms.  The ringing seemed to be around 10-12 mhz.  I need to check the inverting and non inverting inputs of U2.

The board I have it on was tied into the transformer side of R7 as per the original schematic and it eliminated the spike immediately.  I feel like we're missing something simple here.  The amp guys talk a lot about oscillations but to be honest quite a bit of it goes beyond my understanding.  For instance, in this thread they seem to be discussing a similar problem.
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I know you said that R15 and D10 were removed for a reason but would they have been there to mitigate some of this?

I removed R15 from the original circuit because it wasted some important voltage headroom. I removed D10 because I saw no purpose for it.
Try adding D10 back. Can you try a non-inductive resistor for the current sensing 0.47 ohms?

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Guest liquibyte

I removed R15 from the original circuit because it wasted some important voltage headroom. I removed D10 because I saw no purpose for it.
Try adding D10 back. Can you try a non-inductive resistor for the current sensing 0.47 ohms?

I'll do some testing with R15 and D10 to see what effect it has on the circuit.  This should be easy to do with my boards as all of the power transistors are off board.  Unfortunately I don't have any power resistors in a non-inductive package.  The only other thing I can think to do would be to wind one myself bifilar but I don't have any magnet wire either and the last time I was at Radio Shack they were out too.  I found a TO220 package on Digikey and have added a couple to an order I have going but I don't know when I'll be able to place it due to some unforeseen medical expenses with my wife right now and at $7 a pop isn't too high of a priority.  These would probably be a good idea to use anyway as the type I'm using now gets rather hot at full load and I could heatsink these a little better, plus they're 50W.
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I was using a darlington MJ11016 power transistor with long leads (18") so I hooked up a 2n5886 with shorter leads and didn't notice any elimination of spikes.
I ordered a 0.22ohm current sense resistor but in the mean time  I used a jumper across the wirewound sense resistor.  While it kills the overcurrent feature, it did not seem to make a difference in terms of spikes.
I cut off the negative charge pump but didn't notice much difference besides I could not go any lower than 1.8V.
I will insert D10 and R15 and test later. 

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Guest liquibyte

Sorry about the quality but here's a shot of 30V @ 3A fully loaded at 2mV/div @ 20mS.  The trace is centered on the graticule.  I can take a better picture tonight on my wife's phone, the camera on mine isn't very good.  I can't really see the spike as a peak, more as a line that shoots off the top of the screen and settles back or if set at a higher V/div, a jump up in the voltage to the peak as a straight trace and then back.  If I do it just right I can momentarily see a spike but there's not much chance of catching this unless I do a movie of it and even then I'm not sure what it'll capture.  This one's mine, not the surface mount you sent.

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liquibyte,  did you have the Q1 clamp transistor installed?  Did you have D10 and R15 installed?

Have you tested at 12V with the current setting at about half way?

On a couple of my tests I have also noticed what appears to be a one point spike both postive and negative early in the the decaying voltage signal.

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Guest liquibyte

liquibyte,  did you have the Q1 clamp transistor installed?  Did you have D10 and R15 installed?

Have you tested at 12V with the current setting at about half way?

On a couple of my tests I have also noticed what appears to be a one point spike both postive and negative early in the the decaying voltage signal.


Yes, I'm testing on the side that has Q1 installed but no, I don't have D10 and R15 in there yet.

I'm not getting the ripple at much lower than 30 volts and definitely not at 12V @ 1.2A with my load.  I get zero ripple unloaded (AC coupled) at any voltage for what it's worth.  The load I'm testing with is a big assed 10 ohm power resistor so I'm not getting the same results at the lower voltages.  I don't have an electronic load yet so that'll have to wait.  I built my load out of a stove burner and it tests the PS at the full 30 volts and 3 amps nicely though.

Being that this is an analog scope what's happening is going by almost too fast to see with the naked eye and I'm not sure a movie of it will capture anything but I'll try rigging up a better camera tonight and doing a movie of it.  I'd like to know how all the screenshots I see of analog scopes online are so clear when showing transients because mine shows it very, very fast, almost to fast to see and I have to switch on at just the right time to see it at a really slow time/div.
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Being that this is an analog scope what's happening is going by almost too fast to see with the naked eye and I'm not sure a movie of it will capture anything but I'll try rigging up a better camera tonight and doing a movie of it.  I'd like to know how all the screenshots I see of analog scopes online are so clear when showing transients because mine shows it very, very fast, almost to fast to see and I have to switch on at just the right time to see it at a really slow time/div.


I don't know how you could see a transient spike without a trigger and screen capture.  It happens so fast.  I often have to change the trigger voltage,  type of edge trigger, and capture rate because the first shot doesn't always  catch it.    If the event happens early, the scope will capture the initial spike but not the actual drop/increase in voltage at the output because it used all of the available memory, so I will do a second shot at a much slower rate.  I am still learning the features on the caputure end.
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Guest liquibyte

I wish I could afford something digital but I have to admit that even with what I managed to get my hands on, things are looking better as far as being able to see what's going on.  As for the trigger, I do have that but I'm not entirely sure if I'm working things right.  I've seen scopes in use for most of my life but have never used one so I'm still learning as well.  I'm starting to wonder if a soft start may be the only real solution here.  The spike happens before the input on the circuit altogether and isn't being controlled by it and I'm not sure it can be, at least how it's designed now.  As far as the rest of the performance goes, things look fairly good from my standpoint.

Want to try out my version?  I still have four unpopulated boards and I will probably have the new version I came up with made regardless if we solve the transients because I'm thinking soft start circuit.  We never heard much back from the two I've send boards to as far as their builds or testing goes.  I've changed the pinouts for the input and output connections in the new design to be grouped by device and to use Molex KK .156 friction lock connectors for ease of getting the boards in and out.  I learned my lesson there but have to admit the performance of the boards is really quite good even if they are a pain to get in and out.

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I installed the diode between the emitter and base of the output transistor. It seems to have helped but I still seem to be getting a spike right (first picture)  before the voltage drops when I pull the plug on the transformer.  The second picture is an expanded view of the first picture.  I wonder if it is from the transformer when the field collapses.

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Guest liquibyte

I installed the diode between the emitter and base of the output transistor. It seems to have helped but I still seem to be getting a spike right (first picture)  before the voltage drops when I pull the plug on the transformer.  The second picture is an expanded view of the first picture.  I wonder if it is from the transformer when the field collapses.

Is that with Q1, R13 and R14 as well as D10?  I don't understand the waveform in the first picture.  Is the trace inverted?
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