Power Supply

[ade77]

I am trying to build a power supply that can deliver 55V, and up to 15 A.

The power supply I designed though will deliver 55V, but not sure the components will hold up to 15A.

How can I go about this.

[lacy]

 I know your power supply ciruit that you posted previously and the one component that I researched was the 2N3055A and it is capable of 100V at 15A according to the datasheet. I didn't reasearch the op amp, bridge or tranformer. You could try an internet search for these components. As far as the Filter Caps go that is easy at about 150V or more. I would probably go higher to about 250V just make sure Can never be too cautious with a power supply. I am, of course assuming this is the same circuit as before.

You will have to research the bridge, op-amp and tranformer. You can easily figure your resistor wattage by measuring the current through them and multiplying the voltage drop across them P=E*I. 

You are in the hardest part of design work and that is finding components that meet your specs and sourcing those parts.

There is no magic wand here that you can wave. You just have to dig in and do some searching and datasheet reading at this point.

What I usually do (and this is just me and I am not trying to tell you what to do or that this is even proper design procedure) is to do the research as I am building the circuit with the simulator. I will find my specs like say for a transistor and then pop that into an internet search. This is how I found out about the 2N3055A. I put in something like "15 Amp Transitor" and then I compare what popped up with what is in the Multisim Database and then use that in my circuit. That way I have all the real world component already in the print. Now the only thing I have to do is find a source for these. I usually use my local electronics stores when possible. Anyway, this is what I do so that I am sure the components I am simulating with will match what is available in reality. This may help you or it may not, but that is my piece of advice for the day.

Message Edited by lacy on 10-15-2007 09:45 PM

[ade77]

Thank you Lacy. I have almost found all the components that can withstand that amonut of current.

However, I have one question not related to the components, but just on simulation.

From the schematic, how can I design a neagive voltage. My schematics only have +55V, however, I am trying to also produce -55V, do I have to mirror the whole voltage regulator?

I have attached the circuit.

Thank you. 

[lacy]

O.K. I have a solution. It may not be the best one and there may be an easier way of doing this, but I will tell you anyway. What you could do is recreate your ciruit from the bridge out. You would have to reverse the bridge to where the positive half of the AC signal is at ground and the bridge will pass the Negative cycle to the circuit. Reverse your zener and your op amp connections and then use a PNP Transistor as your series regulator. This should give you your -55V.

This is just off the top of my head. But it seem to me that it may be the qucikest way, since you already have the postive half more or less figured out. You could try this in the simuator to see if it will do what I think it will. Let me know this it works for you if you decide to try it or until maybe an easie/betterr solution presents itself.

Edit: Don't forget to reverse you filter caps if they are electrolytic. Forgot to mention that and it is very important for the real circuit not to reverse polarize these. To answer your question properly, yes you would have tio mirrior everything from the bidge out using what I have described. I can't see a way of doing with what you have, but it may be possible and I just can't see it (which would not ne unusual for me since I tend to see the easiest method for doing something with the least amount of brainwork)

Message Edited by lacy on 10-17-2007 05:23 PM

Message Edited by lacy on 10-17-2007 05:31 PM

[lacy]

Hey, Brain flash here. Don't know how this would affect regulation (or if this is proper) but technically you already have -55 if you just reverse the output connection. Ground is just a reference point and you can have your reference where you want it. Just tie your meter + terminal to ground and the - terminal to the transistor output and there is -55V.

This may not be what you after (I would prefer to have Pos-Gnd-Neg like would be accomplished with the other method) but I thought you might want to experiment with it and see if you could possibly use this (it would save a bunch on components)

[lacy]

The previous technique would only require 2 lines from your positive and ground. But you would have to arrange these so that the positive wire is below the ground wire. I will repost your circuit with this so you can see what it is I am refering to. It is easier to see than explain.

[ade77]

Thank you Lacy. I tried your first method of mirroring the whole circuit right from the bridge rectifier, it showed a promising result but not accurate. Also it was very sensitive to component changes and resistor values. Also, I have decided to add a transistor in parallel with the first, so that the current can be shared.

I have attached the modified circuit. The second method of reversing the polarity, while very simple, will not work in my case, as I have two rails I have to connect one +55V, and the other -55V.

Thank you for your continous support.

[lacy]

Hi there again. I understand aboyt the the configuration you need and I probably woud prefer that also POS>GND>NEG. I thought I would just through that out there in hpes that you could use it and maybe save you some components.

I was just looking at the recent schematic and I believe it would work like you have it, but I need to point out some things that you should look at. I am using Multisim 10 so this may not be happening in yours.

1) When I load you schematic the transformer blows in mine. This may be due only to the fact that Version 10 may be loading a different Virtual Transformer than yours. (Not a real big deal but I thought you may need to check it in your version)

2). I was looking at the voltage output from the transformer and it is way low like it is being loaded down. I am not sure if this reading is just not accurate due to the bridge rectifier or is indication of a loading problem. Just take a peak and see what you think.

3) This isn't a problem but a suggestion. The output transitor combo looks good to me, but would require 2 Transistors on each side. You might want to consider a Darlington Transistor. This would give you the current and voltage and just be 2 transitors instead of 4.

I believe it won't be too much longer until you have a working supply and it looks like a very good design job.