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0-30V Stabilized Power Supply


redwire
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Liquibyte,  That is a beast!

Looks well organized with no expense spared.    I have a couple of questions:
What size transformer is in the middle (to power the display I assume?)?  Is the rectifier for that mounted on the bottom?
What is the VA of the large transformers?
It looks like you have 2 output transistors per half mounted to the rear.  What kind of heat sink is on the back?
How many turns are your 4 Potentiometers and where did you get them.
You have 2 heat sinks near with transistors, attached near the bridge rectifiers are those the BD139's?
I see you have headers with the green and black wires so you will have no need to additional pinouts on the board for the microcontroller connections for R7.

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Guest liquibyte

Liquibyte,   That is a beast!

Looks well organized with no expense spared.    I have a couple of questions:

It is rather large but once I get done with it, I'm hoping it looks like I bought it.


What size transformer is in the middle (to power the display I assume?)?  Is the rectifier for that mounted on the bottom?

That one is a Radio Shack (#273-1512) 12.6-0-12.6 @ 2A.  It's going to be for the displays and cooling fans and associated circuitry.  The aluminum bar that the BD139 heat sinks are attached to is one of two that I'm mounting another circuit board on top of and in between with the stuff to control all that.


What is the VA of the large transformers?

Those transformers are Triad Magnetics VPS28-4600's @ 130VA.


It looks like you have 2 output transistors per half mounted to the rear.  What kind of heat sink is on the back?

I got the heatsink on Ebay and is exactly like this one.  I've also got two 80mm fans mounted to it as well for active cooling once I get the temp sensors and associated circuitry worked out.


How many turns are your 4 Potentiometers and where did you get them.

Those are 10-turn pots from Digikey (987-1523-ND).


You have 2 heat sinks near with transistors, attached near the bridge rectifiers are those the BD139's?

Yeah, those are the BD139's.  they're actually mounted upside down on really beefy heatsinks I salvaged out of another power supply and cut in half to get two.


I see you have headers with the green and black wires so you will have no need to additional pinouts on the board for the microcontroller connections for R7.

That was the plan I had in mind.
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Guest liquibyte

I haven't worked out the low voltage stuff yet but may just have boards made and then redo the whole thing from scratch.  Most of the components on the board are cheap enough.

Here's a few pics of the back and how I mounted the fans.  It's kind of hackish but worked out fairly well.

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Guest liquibyte

This is what I've come up with for a dual board that can be cut down the middle so that the boards can be separatec into two single supplies.  Sorry for the largish nature of the image but i wanted people to be able to see the text.  I didn't use the part numbers, just the values because I think that would be the most useful.  The board is 10cm square so it can be fabricated relatively inexpensively.  If I don't catch any glaring errors, this is what I'm going to have made to put in my box.

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Do you intend to have the board professionally made?  Some board houses require a minimum of 3 boards (OSH Park)and you pay by the area.  If you only need 2 boards,  than you may want to make single boards and have one spare. 

All of the traces are the same size.  My preference would be to use small traces for the millivolt powered parts which are 90% of the parts and use double the size shown for the power traces.  For example, you have conveniently located IN+ and 2N3055 Collector very close.  I would have doubled the size of that trace.    Between IN- and R7 I would have done the same and then from R7 to the output.  The only other item that has some power is the CE pins of the BD139 but your traces look adequate for that.



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Guest liquibyte

Do you intend to have the board professionally made?  Some board houses require a minimum of 3 boards (OSH Park)and you pay by the area.  If you only need 2 boards,  than you may want to make single boards and have one spare. 

All of the traces are the same size.  My preference would be to use small traces for the millivolt powered parts which are 90% of the parts and use double the size shown for the power traces.  For example, you have conveniently located IN+ and 2N3055 Collector very close.  I would have doubled the size of that trace.    Between IN- and R7 I would have done the same and then from R7 to the output.  The only other item that has some power is the CE pins of the BD139 but your traces look adequate for that.


Itead has a deal of 10 two layer 10cm square boards for $20, can't beat that.

I've been thinking about the layout and figured I could get two boards into the case stacked on top of each other because it's so tall.  Taking things into consideration that folks have been suggesting, I redid the board again but with just one PS per board.  I've tried to keep the power traces wide and fairly far away from the other traces.  To facilitate easier routing, I also changed most of the terminal blocks to be two wire except for the positive in/collectors which is three wire.  The only thing I don't understand is whether or not I'd need power/ground planes and what sizes to actually use for the traces.  I think I'm getting close with this one though.

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Liquibyte,  Are you using EAGLE?  I would suggest shrinking the outline because most fabricators charge by the outer dimension. 

Itead has a deal of 10 two layer 10cm square boards for $20, can't beat that.
  The price is likely for a minimum of 10 boards at $20 each.  $200 total.  Better verify.

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Guest liquibyte

Liquibyte,  Are you using EAGLE?  I would suggest shrinking the outline because most fabricators charge by the outer dimension.

The price is likely for a minimum of 10 boards at $20 each.   $200 total.  Better verify.

Yes, using Eagle.  I've been shrinking things a bit as I get the parts exactly where I want them and spaced out a bit more.  I wanted to have a hole in the center for a fifth standoff because I'll be stacking two boards and want really good rigidity.

According to everything I've read in reviews they are decent enough and that's the price for 10 boards even according to their site.

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Guest jeffrey13

hey liquibite i would sure like to get a look at that code for the microchip display. ive built this same board and mine is a duel also. and man has it been a ride. i fried it numerouse times but mainly from assembly. after two years off and on ive finally got her and works great but no display. ive worked with the microchip and have all i need to program but just didnt want to go thru the programing hassle. ive been out of it a while and it will take a little to get going again but i really want to get the display going for now.

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Guest liquibyte

hey liquibite i would sure like to get a look at that code for the microchip display. ive built this same board and mine is a duel also. and man has it been a ride. i fried it numerouse times but mainly from assembly. after two years off and on ive finally got her and works great but no display. ive worked with the microchip and have all i need to program but just didnt want to go thru the programing hassle. ive been out of it a while and it will take a little to get going again but i really want to get the display going for now.

I haven't even started on that part yet.  I was just going to use what amounts to an arduino and a couple of max3219's to output the values on 7 segment displays.  There's numerous examples around the web doing it this way and if you look on the arduino website, you'll find several examples of the code as well.  If you're willing to wait, I'll eventually get this thing done and post the code and schematics here as well.
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Guest liquibyte

I ordered my boards today.  Doing these has been a learning experience.  Here's a view from GerbV and I'm attaching the board files Itead required to get the boards made plus the Eagle .brd and .sch files in the hopes that these might be useful to someone.  Total cost for 10 boards was $28.80 including shipping.  One of the cool things about Itead is that if you "open source" your board design, they'll send you two boards for free of two other open sourced designs that other people have done and released as such.  I don't think you can find out what until you receive them but either way it's a cool idea.  I did this just to see what I get.

The off board parts are the two 2N3055's, the BD139, the 12,000uF smoothing cap, the bridge rectifier, the 10W current sense resistor (in my case 16W so you'll have to change that on the silk screen layer), the two 10K pots and the LED.  Connectors are marked for all of these except where the bridge rectifier goes across the smoothing cap, in that case it's just marked In+ and In- respectively.  The center connector for the pots is the wiper and I haven't marked this on the board to indicate it but it should be obvious as it's the center.  The parts are pretty bog standard except for the 10uF cap at the output on the schematic (C7).  I changed that to be a film cap instead of an electrolytic and is rather large on the board due to this fact.  They aren't exactly cheap either.

Quick edit to remove the zip file because the board and schematic aren't correct due to the BC557 being reversed.  I'll put up the corrected version at the end of this thread tomorrow along with the gerbers.

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Liquibyte,  your board looks good.  The only thing that stands out it your  OUT+ and OUT - header is very close to the mounting hole.  I think there if enough room to miss the mounting bolt but if you are stacking board is may be more difficult to make connections once installed.  I probably would have either moved the terminal block between the first 2 headers on the upper right side of the board, or just soldered an additional wire  to the emitter on the 2N3055 (after the 0.33 ohm resistors) and solder an additional  wire to the  0.47 ohm Sense Resistor and those 2 wires would serve as the main power carrying wires for the PS front panel, whereas the OUT+- pins can be used for  testing/Misc but you wouldn't need to carry 3-5 amps through your board.  I guess stacking the boards back to back is a possibility.

If you end up doing a lot of assembly and disassembly/testing  I would suggest  using a push on type connector (such as molex KK  with a ramp) for the voltage and current adjustment potentiometers) These carry very little current .  Assembly, testing and disassembly is quick and  easy because  you don't need to figure out which wire goes where - the ramp only goes one way.  Also if you have stacked boards you can use a right angle connector and won't need a tool to remove. 

Again these are really incidental  comments .

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Guest liquibyte

My intention is to do all of the testing etc. out of the case first and make sure things are working right then install the bottom board then do the same for the top board.  As far as the mounting hole goes, the standoffs I'm using are 4-40 so the screw heads are tiny for the most part and the screws that tighten the terminal blocks are on the top so I'm not concerned about clearances there.

I've also done a mockup of the front panel with the measurements being fairly precise so this is basically what it's going to look like on the front.  I did order the big 1.25 inch knobs because it's common that people have stated they wished they had bought bigger knobs.  So, that's what I did.

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  • 3 weeks later...
Guest liquibyte

OK, my boards came in today.  I populated one of them and almost everything is working right.  The only issue I have is that the current limit LED stays on.  I think there was someone else here with the same issue but I haven't looked back through the thread yet to see if it solves the problem.

Redwire, just an FYI, I did receive 10 boards for the price they quoted and I think they came out nice enough.  I'm attaching a few pics for everyone to see.  The total for the board order was:

Subtotal $19.90
Shipping & Handling $8.98
Grand Total $28.88

All in all, I think that's not too bad a price for what you get but I have no idea what I'm going to do with the other eight.  I'll probably end up making a few of these just to have around I guess.

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The only issue I have is that the current limit LED stays on.

You did not say if the current regulation LED is on all the time or only if the current-setting pot is at zero and there is no load.

Opamp U3 is simply a comparator. Resistor R7 is simply a current to voltage converter of the load current.
When the voltage produced by the current-setting pot exceeds the voltage produced by the current sensing resistor R7 then the output is high and there is no current regulation and the LED does not light.

Resistor R17 sets the lowest voltage produced by the current-setting pot and was 33 ohms. If the LED lights when the pot is at zero and there is no load then increase R17 to 68 ohms.
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Guest liquibyte

LED is on all the time and R17 is 68 ohms already.  One of the problems I did have with R17 is that they sent me 1/2 watt resistors instead of 1/4 watt for some reason.  I figured that wouldn't matter much in the grand scheme of things.  I used your parts list with these but I did make sure that I got 10 turn trimmers this go around as I wanted finer control over things..

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OK, my boards came in today.  I populated one of them and almost everything is working right.  The only issue I have is that the current limit LED stays on.  I think there was someone else here with the same issue but I haven't looked back through the thread yet to see if it solves the problem.

Redwire, just an FYI, I did receive 10 boards for the price they quoted and I think they came out nice enough.  I'm attaching a few pics for everyone to see.  The total for the board order was:


All in all, I think that's not too bad a price for what you get but I have no idea what I'm going to do with the other eight.  I'll probably end up making a few of these just to have around I guess.


Yes, the price seems out of line with other board manufactures.  Your boards looks good enough and it is hard to make them yourself for that price!      I actually made an order from them for a simple rectifier board, similar to what you would use for your Radio Shack transformer.  I'm waiting for them to arrive.

As for your LED always being on, check your transistor Q3 to make sure it is connected properly. You could have leads crossed.  Post the voltage reading of all of the pins on U3.  Check to make sure you didn't swap R19 and R20. 
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Guest liquibyte

You nailed it man.  I had Q3 collector and emitter reversed.  I don't know if the package comes that way in Eagle or if I mirrored it somehow.  Everything is now right with my world, thanks.  I wish I had caught that before I sent out for the boards.  I'll just have to remember to reverse the transistor when I build further versions.

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Guest liquibyte

Yeah, I double checked the part and it has reversed legs, why I don't know.  I mirrored it and corrected the board file and gerbers to reflect the correct part I used.  I deleted the zip file from my previous post so I don't cause confusion and I'm attaching the corrected version here for anyone that wants to use the files.  Included are the schematic and board files plus the gerbers that I used at Itead to get the boards made.  The recommended weight should be 2oz copper for 3A given the trace width, however, that adds $25 to the cost of the boards with them.  I used 1oz and am going to run 22awg jumper wire along the bottom between the components and the outputs to handle the current.  Probably not the best solution but I imagine it will work alright.

Edited to include a parts list of Digikey part numbers.

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30V.zip

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Yeah, I double checked the part and it has reversed legs, why I don't know.  I mirrored it and corrected the board file and gerbers to reflect the correct part I used.  I deleted the zip file from my previous post so I don't cause confusion and I'm attaching the corrected version here for anyone that wants to use the files.  Included are the schematic and board files plus the gerbers that I used at Itead to get the boards made.  The recommended weight should be 2oz copper for 3A given the trace width, however, that adds $25 to the cost of the boards with them.  I used 1oz and am going to run 22awg jumper wire along the bottom between the components and the outputs to handle the current.  Probably not the best solution but I imagine it will work alright.


I had concerns that the traces were on the thin side as noted earlier  but  I still think you can rearrange parts  and small traces, and widen the power traces to use  1oz copper.  The overall placement is pretty good as the power traces are nearly a straight line on the left side of the board. 
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Guest liquibyte

I might end up doing that later on but I think that everything should be ok with solid core wire on the bottom helping handle the current for now.

I did build the second unit and everything is working as expected so I'm happy with that.  Oddly enough for as big a case as I put these in, I'm starting to run out of room.  I managed to get two of these in side by side so the vertical space will be used for the two power supplies for the thermal circuitry, fans and the four displays.  I planned on using linear voltage regulators there to keep things as small and simple as possible and 328's and AS1100's to drive the meter stuff.  I'm working out how to do this on my own so it will probably take awhile.

I've yet to fully calibrate these and was going to ask if there were a specific procedure that you use on yours when you do it.  I know that you set the voltage pot to zero and then adjust RV1 to get an output of zero but past that I'm not sure.  One thing I have noticed is that I can't get to an absolute 0V but bottom out at about 28mV.  I have a feeling that it probably needs to be fine tuned in other places as well to get that true 0V.  Any advice?

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I've yet to fully calibrate these and was going to ask if there were a specific procedure that you use on yours when you do it.  I know that you set the voltage pot to zero and then adjust RV1 to get an output of zero but past that I'm not sure.  One thing I have noticed is that I can't get to an absolute 0V but bottom out at about 28mV.  I have a feeling that it probably needs to be fine tuned in other places as well to get that true 0V.  Any advice?


The two things to adjust are:
1.  Voltage limit.  The 20K trimmer connected to U2 is to limit output to 30V.  You will likely find that the 20K trimmer straight from the factory was set at approximately 10K and is right about where you need it.    Set P1 to the maximum output, then adjust the the 20K on board trimmer to get  30V on the output.

2.  Current limit.  Without a load on the PS, adjust P2 so that you have the maximum voltage on pin 3 of U3.    Now adjust the 100K trimmer on the board to  to limit the max current that the board will output.  Because you are using a 0.47 Ohm Resistor , Using V=IR,  If you want a 3A limit,  the maximum voltage on pin 3  of U3 would be 3A x 0.47 Ohms = 1.41 V.  So adjust the 100K trimmer so that the maximum voltage on pin 3 of U3  is  1.41 volts.  You can fine tune from there.

Neither of the above adjustment will bring the voltage to exactly zero.  You will probably find that if you have small  load on your PS you can bring the Voltage down 0.    If you still want zero with no load, touch a 5k or 10k resistor across the output points on your header blocks and see if that brings the voltage to zero.  If that does the trick you can permantently connect it to your output header block along with your output wires.
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Guest liquibyte

Yep, that did the trick, thanks.  Now I just have to do the circuits for the displays and find out what the libraries offer in terms of resolution.  I think I'll be good at 10mV reading current but I'd like to get 1mV out of the voltage side if it's possible.  If arduino doesn't offer what I need, I may just get into the bare metal and see what I can come up with using C or assembler.

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