0-30 Vdc Stabilized Power Supply

[audioguru2]

Hi Chapz,
An N-channel power Mosfet needs to have its gate at a much higher voltage than its source to turn on. Then this modified project would have a max voltage output of only about 26V instead of 30V.

 

[chapz]

Thanks so much, you've been a GREAT help!

 

[LanDoctor]

Hi All,
I have been following this thread and am confused as to the latest revision of the circuit. I have most of the parts to build it, but want to make sure I am building the "best" version of it. Can someone please give me a link to the latest parts list and layout? I would really appreciate it. It has been frustrating trying to go through the 100+ pages to find this info.
Thanks for your time,
Donovan

 

[audioguru2]

The improved circuit is basically the same. The transformer has a higher voltage and current rating, the opamps have a higher voltage rating , One additional output transistor is added and they each have an emitter resistor, a couple of transistors are bigger and some resistors and capacitors are bigger.

The improved version will fit on the original pcb if some of the bigger resistors are stood up and the main filter capacitor and rectifier bridge module are strapped to the chassis.

Here is the improved parts list:

View attachment 40483

 

[LanDoctor]

Thank you for the reply.
Is there another designation for the opa445 components. I can only get NTE components locally and it doesn't look like they have a cross referenced part available.
Thanks again,
Donovan

 

[audioguru2]

The OPA445 opamp is the only one I found with a high enough max supply voltage rating.
It is made by the Burr-Brown division of Texas Instruments and is available through Farnell world-wide.

NTE buys ICs and sells them as replacements.

 

[Pawel_K]

Hi
It's my first post on this forum.

I built this power supply, but it doesn't ot work.
I changed TL081 with uA741.
I also changed 2N2219 with BD139-16.
I can regulate voltage from 0,1 to 1V. :-[

Sorry for my english.

 

[audioguru2]

Hi Pawel,
Welcome to our forum. ;D
The BD139 is a good substitute for the little 2N2219. It should have a heatsink.

The project will be easy to fix if you measure and post some of its voltages without a load. Put the negative lead from your voltmeter on the 0V output of the project:
1) Pin 7 of all the opamps should be about +34VDC.
2) Pin 4 of U2 and U3 should be -5.6VDC.
3) Pin 6 of U1 should be +11.2VDC.
4) Pin 6 of U3 should be about +32VDC.

Then U2 amplifies the 0V to 11.2V from the voltage adjust pot by slightly more than 3 times and the voltage output of the project should go from 0V to about +28V.

 

[Pawel_K]

I checked voltages.

Pin 7 of all the opamps is +32,2V
Pin 4 of U2 and U3 is -7,1V
Pin 6 of U1 is +10,5VDC
Pin 6 of U3 is -4,7V
current limit diode is lighting all the time.

When the 2N3055 wasn't solder I could regulate output voltage from 0,1V to 1V.
Now after solder 2N3055 I can't regulate output voltage. It's -0,6V. :-\

 

[AN920]

What is the voltage on U3 (pin 2,3)?

 

[Pawel_K]

Voltage on U3 PIN2,3 is 2,5V

 

[AN920]

Sorry, I meant voltage between GND-pin2 and GND-pin3

 

[Pawel_K]

GND-PIN2 0V
GND-PIN3 2,5V

GND is "-" on the PCB ??

 

[AN920]

Yes "-"
U3 seems faulty. pin 6 should be positive as the non inverting input dominates.

 

[AN920]

Can you adjust the output voltage with U3 removed?

 

[Pawel_K]

Voltages with removed U3:
between 3pin and GND  minus 29V
between 3pin and + also minus 29V
between 2pin and + 0V
between 2pin and - 0V


Here is the opamp tester.
When I put U3 into the tester the diode flash.

 

[AN920]

Something strange in your circuit. Make sure you don't have any stupid mistakes, solder bridges, wiring errors etc.

 

[Pawel_K]

I checked PCB and it looks ok.
Diode D10 is very hot.
I checked also rest of elements and they are ok.

 

[AN920]

This should help you, and others to find faults in this PSU.

Voltages to expect with three different conditions.

1) PSU with almost no load (2.2k) set to 12V
2) PSU with 1A load (22 Ohm) set to 23V
3) PSU with current limit turned down to about 500mA, from condition (2). Current limit LED is on.

Measurements taken with input GND as reference and not out "-" !

View attachment 40485

View attachment 40486

View attachment 40487

 

[audioguru2]

D10 is supposed to be reversed biased with about 1.4V across it and no current flowing. Therefore it should not be hot. Check its wiring in the circuit.