0-30V Stabilized Power Supply

[Kevin Weddle]

Are there still problems with this general purpose power supply. Give some better designs or a link to better ones.

 

[audioguru2]

Does someone have any ideas what's wrong with my circuit?

Since your U3 opamp does not perform correctly as a comparator then replace it.

 

[audioguru2]

Hi, is there any place in the circuit of this project, where safely, without any harmful consequencies or bad interference to other parts of the circuit, could be added additional LED diode, which should be on all the time, when the power supply is on?

The rectified and filtered +40V can light an LED if it has a current-limiting resistor.
An LED is 1.8V to 3.8V depending on its colour. If the LED is a 1.8V red one then for 15mA the resistor is (40V - 1.8V)/15mA= 2547 ohms. Use 2.7k. Its power is a little more than 1/2W so use a 1W or 2W resistor.

 

[audioguru2]

Did you mean exactly this place is the best to connect an LED? (modification in red color).

Yes.

 

[sobol]

Since your U3 opamp does not perform correctly as a comparator then replace it.

I replaced it with 3 other opamps, and the effect is still the same.

 

[audioguru2]

Why do you add a switch to force the output to the positive unregulated voltage?
Don't you want a switch to force the output to 0V?
Then add a switch to the input of U2 and ground.

 

[sobol]

I have fixed my ps, P1 was wrongly soldered. I have believed that pin order in pcb is correct... it's not.

Why do you add a switch to force the output to the positive unregulated voltage?
Don't you want a switch to force the output to 0V?
Then add a switch to the input of U2 and ground.

Inverting or non-inverting input?

 

[audioguru2]

Inverting or non-inverting input?

U2 is a non-inverting amplifier. Pin 3 is its input and pin 2 is used for negative feedback.
If you ground pin 3 then the output transistors will turn off and the load will discharge the output capacitor.
If the load current is low and the output voltage is high then it might take a long time for the output voltage to come down.

 

[Kevin Weddle]

Question it doesn't look like a bad place to put a power on/off LED. It should turn off rapidly.

 

[sobol]

Can I increase output voltage with voltage calibration trimpot without any consequences? Or it's not recommended?

 

[audioguru2]

Can I increase output voltage with voltage calibration trimpot without any consequences? Or it's not recommended?

Then at maximum output current you might have ripple instead of voltage regulation.
That was a problem with the original circuit that used a 24VAC transformer.

 

[nitro199]

Hi, i`m gattering all information that i can get i read entire topic and found 3 or 5A versions, but maybe there is any chance to get 7 or 10A with thease shematics?

 

[audioguru2]

Hi, i`m gattering all information that i can get i read entire topic and found 3 or 5A versions, but maybe there is any chance to get 7 or 10A with thease schematics?

When the output is shorted or set to a low voltage then at 10A the heating is 40V x 10A= 400W!
You will need many output transistors on huge heatsinks and a fan.
You must parallel a few driver transistors, each with an emitter resistor and a huge heatsink.
The opamp U2 might not be able to provide enough current to the driver transistors and the opamp might over-heat.

 

[nida]

Hi,I am facing the problem Plz help me out. At the output of U1 I get 11.8V and at the output of U2 I get 34V . But at pin 2 and pin 3 of  U3 i get the 14.2V and 15V  respectively . R3 gets heated up and i replaced three times already.Across the load resistor(20W ,10K) I get 41V and  the same voltage is across the output of bridge and output voltage is not varying by 20K Pot.

I have not tested the current limiting feature yet.

Is there any specific load that I have to use? Should it be variable or fixed or what type of rating?

Waiting for your reply.....

 

[nitro199]

When the output is shorted or set to a low voltage then at 10A the heating is 40V x 10A= 400W!
You will need many output transistors on huge heatsinks and a fan.
You must parallel a few driver transistors, each with an emitter resistor and a huge heatsink.
The opamp U2 might not be able to provide enough current to the driver transistors and the opamp might over-heat.

thanks audioguru i will try first without any modifiation, then it will be easyer to upgrade

 

[audioguru2]

Hi,I am facing the problem Plz help me out.

You have many serious problems, probably caused by wiring errors.

1) The output of U1 should be +11.2V but yours is 11.8V which is only 5% high so it is fine.
2) The output of U2 should go from 0V to +33V when the voltage setting pot is adjusted. It might always be +34V if you have the pins of the driver transistor or the output transistors connected backwards. Look at the datasheets to see the pins.
3) Pin 2 of U3 has an extremely low current and is connected through R21 which is 10k to the output ground so how can it be +14.2V? Maybe your R7 is not 0.47 ohms?
4) Pin 3 of U3 connects to the current setting pot between 0V and about +2V so how can it be +15V?
5) R3 has only the few mA of U3 in it so how can it get hot?
6) Your output is shorted to the output of the bridge rectifier.

 

[nida]

I have checked my circuit again and resolved the wiring errors.The voltage across two 1N4148 diodes connected in series is -11.2V not -1.3V. why?
voltage across R3=14V thats why it gets burn.Why?
Can I connect two 0.8ohm resistors in parrallel to make 0.4ohm(the one connected in series with load)?
I have C1 (10000uF,63V) so can i connect 1000uf,50V in parallel?
Transformer is of 24VAC.

 

[audioguru2]

I have checked my circuit again and resolved the wiring errors.The voltage across two 1N4148 diodes connected in series is -11.2V not -1.3V. why?

The two diodes are supposed to conduct a small current which clamps the voltage to -1.3V.
Maybe your diodes are connected backwards or maybe they are burned out.

voltage across R3=14V thats why it gets burn.Why?

R3 is fed a small current from rectifier D6 which has its current limited by R2. The other end of R3 is fed to the voltage-limiting diodes and the negative power supply pin 4 of U3 that draws only a couple of mA.
The current in R3 is supposed to be low.

Can I connect two 0.8ohm resistors in parrallel to make 0.4ohm(the one connected in series with load)?

R7 is 0.47 ohms for the 3A version and is 0.27 ohms for the 5A version. Why do you want 0.4 ohms?

I have C1 (10000uF,63V) so can i connect 1000uf,50V in parallel?

Transformer is of 24VAC.
A 24V transformer does not have enough voltage for this project to supply 30VDC at 3A. Your maximum output might be 26V at 3A and full of ripple.
12,000uF is recommended with a 28V or 30V transformer.

 

[nida]

I have replaced two 1N4148 diodes still it gives the same voltage.
12000uF capacitor is not available here, so can i connect C1(10,000uF  63V) with a capacitor(1000uF 50V)?
I bought 0.47ohm resistor but ( 10W0ohm47) is written on that and it is giving 0.9ohm resistance so can I connect these two resistors in parallel combination? power rating of both resistors is 10W.
I don't need 30V at output, 26V with 3A is enough for my project so still Do I need to replace my transformer?

Waiting for your reply....

 

[BrokenRandomBit]

Hi,

This design is a linear power supply, right ?

I found 3 toroid transformers, with values
input: 220V 50 Hz 50VA
output: 12V 4,1A
T50/1 - 723/2

Would it be possible to use them for this project ? maybe wire them in series?



I'm new to electronics, sorry for my questions, I'm new here