0-30 Vdc Stabilized Power Supply

[glockshotz]

I noticed that I can only get the 0-30V when I have a load attached to the output. Is this because of the negative supply rail?

It should work fine without a load. What happens without a load?
I get about 15.4v to 30v and the 2N3055 transistor is connected correctly

 

[audioguru2]

I get about 15.4v to 30v and the 2N3055 transistor is connected correctly

Then Q2 or Q4 leaks. Probably Q2 from being fried.

Measure the output voltage at pin 6 of U2. It is probably negative in its attempt to reduce the output voltage down to normal.

 

[glockshotz]

Then Q2 or Q4 leaks. Probably Q2 from being fried.

Measure the output voltage at pin 6 of U2. It is probably negative in its attempt to reduce the output voltage down to normal.

Come to think of it, it was working fine until I exceeded 3A.  The output on pin 6 is 30v to -0.15v.  I couldn't find a TIP31A but I did find a TIP32C 140V 5A 40W will it work the same? 

 

[glockshotz]

Sorry I see the TIP32C is PNP I'll have to keep looking

 

[glockshotz]

Ok it works!
I replaced Q2 with TIP31C and Q4 with a new 2N3055.

 

[audioguru2]

Ok it works!
I replaced Q2 with TIP31C and Q4 with a new 2N3055.

Great! You made a good fix. ;D

 

[Roelli]

Hello!

I just build the cool power supply and it works great. Many thanks for this nice project!  8)

I can regulate the current with a hot-wired Output from 0,01A to 4,6A. Works great.

But how can I protect the output transistor when there is a short at the output. I fear I will demolish the 3055 when making a short with maximum current.
Using some 3055 parallel? I don't want to use a heatsink which's bigger than my workbench 

Any ideas about a protection circuit or so? Maybe a relais which turns off the voltage when the LED is on or so?

Many Thanks!

Roelli.

 

[audioguru2]

Hi Roelli,
Welcome to our forum. ;D
It is good to hear that your project works great, but it is too bad that you are worried about it dying.

The LED lights whenever the load current exceeds the setting of the current-regulation pot. Maybe you will need its current regulation and don't want it to shut off by your relay idea.

Shorting the output when its current-regulation is set to a high current is nearly the same as setting a low voltage of up to 6V at full current (3A). The Q2 and Q4 transistors will still have a high voltage across them which when multiplied by the current makes a lot of heat. With the recommended 30VAC transformer, Q4 must dissipate 117W with its 3A output shorted. So a pretty big heatsink or fan cooling is needed and Q4 should be two paralleled 2N3055 transistors (with emitter resistors to match them).
Q2 must dissipate a max of about 4.8W which is way too high for a little 2N2219, so a TIP31A real power transistor on a finned heatsink is recommended as its replacement.

We have discussed how its original little 2N2219 for Q2 will die due to overheat, and the same for a single 2N3055 for Q4.

 

[Roelli]

Cool! Many thanks.

What a nice forum - and nice people here  ;D
And I thought I'll be executed because of not reading EVERYTHING of the 69 pages thread.

Which emitter resistors can you advise?  0,1R/2W Resistors each?

Thank you very much audioguru!

 

[audioguru2]

Hi Roelli,
I'm glad to help fix this project.
Some people made a supply with two 0.1 ohm resistors and one 2N3055 was hot and the other was cold. Transistors are all different. One had a high current gain and the other had a low current gain. Changing the resistors to 0.33 ohms allowed the mis-matched transistors to have much better balance.

Here is my recommended modified parts list:

View attachment 39214

 

[Tedy1]

Hi again  ;D
Is that normal that R2 get hot ~60

 

[audioguru2]

Is that normal that R2 get hot ~60

 

[dp492]

Hello!

I want to build this project. I have  2X24V/100VA toroid transformer. Can I use it, or I should decrease the current limit(3A) or the voltage limit(30V).
If I should make some modification, what I have to do?

 

[audioguru2]

I want to build this project. I have

 

[dp492]

Thanks Audioguru,

Could you tell me exactly what I have to do modify in fayour of the max. 25V working? (R11 resistor? or the P2? or what?)

 

[audioguru2]

Could you tell me exactly what I have to do modify in fayour of the max. 25V working? (R11 resistor? or the P2? or what?)

To allow you to calibrate its max output to 25.0VDC, add a 5k trimpot wired as a rheostat between U1 and P1. If the ripple is too high with a 25V/3A load then increase the value of C1 to 10,000uF and decrease the value of R15 to 100 ohms.

 

[faizanbrohi]

i have a question how can we implement negative voltages in this power supply , i mean +-30V , do we have to build another unit for negative voltage ,

 

[audioguru2]

This supply can be "floating" so that its output isn't grounded. Then for a positive output just ground the 0V terminal and for a negative output just ground the positive terminal.
For both polarities then add a completely separate project.

 

[megatech123]

We have tried the 0-30 V circuit and have a differnt problem.

1.At 26 Volts we are able to get 2 Amps constant output...but in between 26 -30 Volts we are able to get a current of 600mA - 100mA max.What is the reason any sugession please.

2. we ahve used a transformer sec., rated at 3 A max.

3. What modifications should we need to do to get a constant current of 3 A at 30 Volts.?

Please suggest its very urgent.

 

[audioguru2]

We have tried the 0-30 V circuit and have a differnt problem.

The original project's circuit or the improved one?