0-30 Vdc Stabilized Power Supply

[audioguru2]

It is [b ]NOT[/b ] an MC4071 which might be a Cmos quad 2-input OR logic gate with 14 legs.
Instead it is an MC34071 single opamp with 8 legs.

 

[mroy559]

Somewhere with this topic, somebody said, that some capacitor should be changed through electrolytic in order to tantal as well as something. Attempt to browse somewhat.

 

[audioguru2]

Somewhere with this topic, somebody said, that some capacitor should be changed through electrolytic in order to tantal as well as something. Attempt to browse somewhat.

We talked about the 10uF electrolytic output capacitor having dielectric absorption which might cause the output voltage to rise when it is turned down and there is no load. We recommended using a poly type of capacitor to eliminate this problem.

I do not remember anybody talking about using a tantalum capacitor in this project.

 

[audioguru2]

I have made this supply but I am suffering with the problem of loading effect as am using it with very low ohms coil the output voltages get decrease with connection of load. My load resistance is not more than 12 ohms.

Please tell me what should I do to remove loading effect and get steady, constant output.

The improved circuit is designed to supply a maximum output current of 3.0A. It can be modified to supply 5.0A.
Ohm's Law calculates that 3A will flow in a resistance of only 12 ohms when the DC voltage is 36V. When the DC voltage is 30V then only 2.5A will flow so your project does not work properly.

The original project cannot supply 3A at 30V.

 

[audioguru2]

Can you tell me from where I can get improved circuit with 5A?

We talked about modifying this circuit for an output up to 30VDC at up to 5A DC a few years ago. It is the same circuit as the latest 3A circuit except the transformer produces more current (7.1A AC), there are three 2N3055 output transistors and R7 is 0.27 ohms at 10W.

 

[audioguru2]

This project uses AN OPAMP for its voltage regulation. Its typical DC voltage gain is 100,000 so if the output voltage drops only a tiny amount then it corrects it.
Its output voltage should not drop more than 0.03V when its load is increased from zero to 3A.

Maybe your project has wrong values in the current regulation section. The LED should not light when the voltage is being regulated but it should light to warn you that the current regulation is reducing the output voltage.

 

[audioguru2]

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.

 

[audioguru2]

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.

 

[redwire]

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.

 

[redwire]

Sorry, not familiar with PIC

 

[mjvision]

Hi!

In this modified version (http://diyfan.blogspot.com.br/2012/02/adjustable-lab-power-supply.html) he seems to have some good points. But why has he stripped audioguys two 3055 to only one 3055 and no emitter resistor?

 

[mjvision]

Buggy forum... When I posted my first post, 24 new pages appeared.
I placed an order on components today, can you please say if there is any changes in this projects design in the last 24 pages?

 

[audioguru2]

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. 

 

[mjvision]

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?

 

[audioguru2]

...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.

 

[mjvision]

Only oner diode is needed.
When a diode is added in series with a regulated supply then the voltage is not regulated well anymore.

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.

 

[audioguru2]

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.

 

[josko]

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?

 

[audioguru2]

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.

 

[nannasin281]

Also that the LF411 can be used as a substitute for the TL081.