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0-30 Vdc Stabilized Power Supply


Sallala
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The original project used TL081 opamps and their total power supply voltage was higher than allowed. Then I changed the opamps to ones that are allowed the high supply voltage.

The original project used a transformer that was overloaded and its voltage was too low.
I changed it so it works perfectly.
What transformer are you using?

This project has the driver and output transistors inside the negative feedback loop of the voltage regulating opamp so the voltage regulation is excellent.
But you said that you added "a pair of 2N3055 as voltage follower" that are not needed and might ruin the voltage regulation.
Please post your schematic.

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also, may I use 2n3055 as Darlington pair?

The fixed and modified 3A version of this project uses two 2N3055 output transistors in parallel to share the heat. The 5A version uses three paralleled 2N3055 output transistors. Each 2N3055 transistor has a series emitter resistor so the transistors share the current. They are driven by a BD139 little power transistor Q2 making a darlington pair. The first transistor in a darlington pair uses a fairly low current. The original version used an old 2N2219 transistor for Q2 that got too hot and was not designed for a good heatsink.

If you use a 2N3055 transistor for Q2 then the circuit might oscillate because a 2N3055 transistor is very slow.
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hi piyushghumelia,    I wonder if you really hooked this up in real world.    The diagram does not show any connections to sample the voltage of the  power supply and the code provided does not show any computations to  determine voltage or current. The diagram looks like a generic LCD hookup to a PIC.

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  • 3 weeks later...

But why has he stripped audioguys two 3055 to only one 3055 and no emitter resistor?

He must be using liquid nitrogen and a huge fan to cool his single 2N3055 transistor.

can you please say if there is any changes in this projects design in the last 24 pages?

Some people said that the output voltage does not drop to zero volts when there was an voltage then the voltage was reduced. It is because the electrolytic output capacitor C7 has "dielectric absorption".
They changed the capacitor to a film type that fixed the problem. A 10uF film capacitor is frequently used in a speaker crossover network. 
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He must be using liquid nitrogen and a huge fan to cool his single 2N3055 transistor.

Hehe, yes thats probably the case.   ;D
Well, I will go with three of them. Nothing negative with that isnt it?

I thought about protections. If I am  charging an led-acid battery with this PSU, do I need diodes on the outputs to ensure the PSU isnt going to break if switched of with battery connected or something like that?
What about diodes on both positive and negative output for protection against wrong polarity from battery? Will that affect the rest of the circuit?

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...single 2N3055 transistor.
Well, I will go with three of them. Nothing negative with that isnt it?

Each output transistor needs its own 0.33 ohm resistor in series with its emitter so that they share the current.

I thought about protections. If I am  charging an led-acid battery with this PSU, do I need diodes on the outputs to ensure the PSU isnt going to break if switched of with battery connected or something like that?

Yes an output diode is needed.

What about diodes on both positive and negative output for protection against wrong polarity from battery? Will that affect the rest of the circuit?

Only oner diode is needed.
When a diode is added in series with a regulated supply then the voltage is not regulated well anymore.
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Ok. Now I´m lost. If you have time, can you please shortly describe how a diode will be negative for the regulation? More than 0.7V less voltage.

A diode has a forward voltage drop of 0.7V only at one temperature and at one current.
Its forward voltage drops as its current heats it and its forward voltage changes if its current changes.

Simply look at the datasheet of a diode to see how much its forward voltage drop changes.

The output voltage of a half-decent voltage regulator does not change with temperature and with current so a diode in series with this power supply ruins its excellent voltage regulation.
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  • 3 weeks later...

I have built this supply long ago, it sits in old AT case, but today I found problem, that on negative (-) supply I am having -40V DC against wall plug ground. It's not problem in general, but if you want to supply something that is for example connected to computer through USB it'll blow the fuse if not USB port of computer..
What could be causing this problem?

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I have built this supply long ago, it sits in old AT case, but today I found problem, that on negative (-) supply I am having -40V DC against wall plug ground. It's not problem in general, but if you want to supply something that is for example connected to computer through USB it'll blow the fuse if not USB port of computer..
What could be causing this problem?

If the case is connected to the wall plug ground then the negative supply of this project or its 0V output will be around -40VDC if the positive rail is shorted to the case. Probably bad insulation from the driver or output transistor case to its heatsink which is probably bolted to the case.
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  • 3 weeks later...

I have built this supply long ago, it sits in old AT case, but today I found problem, that on negative (-) supply I am having -40V DC against wall plug ground. It's not problem in general, but if you want to supply something that is for example connected to computer through USB it'll blow the fuse if not USB port of computer..
What could be causing this problem?


Serial communications between external devices often have these same sort of grounding problems which are overlooked mainly because the data is transfered reliably. Your better off using an opto-isolator.
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I think it was discussed here how to protect the power supply from destroying when you switch it off and forget to disconnect the load first.

I don't think anybody said that before. How can it be destroyed when it is switched off?


I cannot find the modified schematics; can someone please provide a link?

The modified schematic has been posted on this website a few hundred times.
It uses a transformer with a high enough voltage so the circuit can produce 30VDC at 3A. The original circuit could not. Its new transformer spec is not overloaded like the original one was.

It uses modern opamps that have a high enough maximum supply voltage rating. The original opamps were over-voltaged even with the transformer that had a voltage too low.

The new opamps have input and output voltages that can go to ground so the negative supply voltage is not as high.

post-1706-1427914451289_thumb.gif

post-1706-14279144513118_thumb.png

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OK, maybe I did not understand (or do not remember) the purpose of the change.

Many of the parts in the original project got too hot and/or were over-voltaged. Then it was not reliable.
It could not produce 30VDC at 3A,  instead it produced about 25VDC at 3A with lots of ripple.

someone posted this diagram (attached) with the red diode. Can you please comment if it is of any use?

Maybe somebody used this project to charge a battery and the diode prevents the battery from blowing up the transistors when the power is turned off.

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  • 2 months later...
Guest seb1982

Hi everyone!

Wow, so I actually managed to make it to the end of the thread!  Incredible work by Audioguru, Mixos and others on here!

Just a very quick, simple query if anyone's able to help me - if I only needed a 2A output, would I need to alter any other components than the transformer to achieve it, as long as the circuit still had a 28-30v input?

What VAC rating transformer do you think I should get to achieve a 2A output?

I'm guessing that I wouldn't need such huge heatsinks on the 2N3055s at 2A either.

Thanks ever so much.

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If I only needed a 2A output, would I need to alter any other components than the transformer to achieve it, as long as the circuit still had a 28-30v input?

Use a transformer rated for 2.8A AC output.
Change R7 to 0.68 ohms/5W.

What VAC rating transformer do you think I should get to achieve a 2A output?

2.8A x 28V= 78.4VA.

I'm guessing that I wouldn't need such huge heatsinks on the 2N3055s at 2A either.

The power in each 2N3055 when the output voltage is low or shorted and the current is 2A, is 38W.
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