0-30V Stabilized Power Supply

[audioguru2]

The driver transistor and the output transistor are simple emitter-followers.
The base voltage is the input and the emitter voltage is the output which is about 0.7V less than the base voltage if the project has a load of about 100mA.
The collectors of the transistors are connected to +41V so if a transistor is shorted from collector to emitter then the output will always be at or near +41V.

If a transistor is shorted from base to collector then it will always be turned on and the output will always be near +41V.

Remove a transistor from the circuit and use an ohm-meter to see if it is shorted.

 

[redwire]

noworries2004,     audioguru
   
          To isolate the problem couldn't noworries simply remove the output transistor then connect a multimeter to the emitter of the driver resistor- BD139 (PIN Eight) and the other lead on PIN 4( ground) and adjust the voltage pot.  Wouldn't the voltage range vary between 0 and 40V?  This would let him know if everything else is working.   I'm guessing the lack of feedback voltage wouldn't be a problem.

noworries could you send a picture of your completed pcb board?   Perhaps I could spot something compared to mine.
               
 

 

[audioguru2]

Without any negative feedback then opamp U2 will have a input voltage but no output feedback so its gain of about 200,000 will force its output as high as it can go.

Remove the output transistors then short their base-emitter terminals for the driver transistor and U2 to work properly and drive a high resistance load.

 

[noworries2004]

Please find the enclosed pics of my project, problem still exists

View attachment 40981

View attachment 40982

View attachment 40983

 

[noworries2004]

some more pics

View attachment 40984

View attachment 40985

 

[noworries2004]

\Audioguru following reststances were taken between collector, base emmitter
collector - base  0L
Base - emmitter  0L
Collector - emitter 2.341 M Ohms

 

[audioguru2]

Hi No Worries,
I cannot see how your transistors are connected.
Is "OL" on your ohm-meter a very high resistance?

The 2N3055 output transistors are emitter-followers. Their emitter voltage is 0.4V to 1.0V less than their base voltage.
The BD139 driver transistor is also an emitter-follower. Its emitter voltage is  0.4V to 0.7V less than its base voltage.
Opamp U2 also has emitter-followers at its output. Its max output is 1.0V to 1.5V less than its power supply voltage.

Therefore with your 41V unregulated supply, the max output voltage will be 37.8V to 39.2V, not 41V.

Measure the voltages of opamp U2 with the voltage setting pot at zero and at max: input pin3, feedback pin2, output pin6. 

 

[Scooter_3D]

Hi all, it looks like the voltage and current pots are connected up wrong,
I could be wrong but isnt the wiper part of the pot the middle terminal ??
in your pic its connected to one of the outside terminals which has
wiper marked on the board

 

[noworries2004]

Just changed the wiper on the 2 pots,
prob still there but U2 not heating up as fast
Quick question, Think R7 (0.47ohm ) is blown, disconnected it from the circuit and it is measuring 26Kohms,
dont have a replacement, is there any other resistor that i could put in.

I am measuring all my voltages with the neg lead of voltmeter at the - sign between r7 and c7 on the schematic is this correct is this ground ?

Cheers

 

[Scooter_3D]

Mate you need to double check all the components on the board
i have found 2 that are the wrong value R1 and R22

 

[noworries2004]

This is my power supply connected to the bridge rectifier D4 is connected to the pin opposite the rest which connects to r1 and c1,

R1 is correct 2.2K, the rest of the parts im possitive are correct,

View attachment 40986

 

[Scooter_3D]

looking at the picture with everything on it, it seems the wiring
to and from the bridge rectifier is all wrong there should only be
4 wires in total on it  2 in and 2 out, you also have 4 wires at the
input part of the board where there should only be 2

 

[noworries2004]

Ok starting again with a fresh PCB.
All components have correct value double checked all resistors with ohm meter.
How ever i am missing 34071 Opamps. The only available opamps are 741 opamps. Is it ok to use these instead?

Also i dont have .47ohm (R7) resistos. Will it be ok to leave this out and forget about the current limiting. Is it ok to put in a piece of wire instead?

Also any more suggestions.
My problem with the last PCB was that i had it on aero board and when i first plugged it in a couple of components smoked. (R7 and U2). Can i test this circuit with a dc power supply first before i plug in the transformer, bridge rectifier.


Thanks for all your help.

Regards

 

[Scooter_3D]

I cant really comment on the op amp substitution or the resistor question
but i would not use a wire in place of the resistor. I think on the new board
you should use some IC sockets

 

[audioguru2]

The latest circuit works only with MC34071 or TLE2141 opamps.
Their max allowed supply is 44V while most 741 opamps have a max allowed supply of only 36V. The latest circuit has a negative supply of only 1.3V and the required opamps work fine but a 741 opamp needs at least -3V to -5V for a negative supply which makes its max allowed voltage even less.

A resistor value of 0.47 ohms is very common. If you don't limit the current then something on your project might smoke and be destroyed.

 

[bugmenot1]

Hehehe, I had the same pot problem... usually I put the wiper in the center in the PCB, but I build the PSU and it don't work, then I change the pots wiper position and it's seemingly looks ok now... I'll test a little bit more... Thanks notedly to AudioGuru and Redwire for the support.
Thanks to all who comment in my previous posts: hero999, erivanst, and others.
I'll post some pictures soon.

 

[noworries2004]

Ok thanks audioguru for your help yet again,
I will try and get the mc34071 opamps,
and i will get the r7 resistor will let ye know how i get on

 

[noworries2004]

Just found the main problem i think,
0.33 ohm resistor were connected to the base, So therefore that would explain the high output all over the circuit.

 

[redwire]

Noworries2004,      Why don't you test your circuit with only one output transistor without a load.  You don't need  the .33ohm resistor or the heat sink.  you should only have 4 wires.  1) point 7 to  the collector on the  transistor  2) point 8 on PCB to base    3) Emitter output from the transistor to your multimeter    4) emitter connected back to pcb point 3  ( wires 3 and 4 are connected).

 

[bugmenot1]

I have problems with my PSU (Redwire 5A version). I used 3 2N3055, two 0,47R 10W (it's the only I got) for R7, two 10.000uF caps for C1.
The voltage pot works good, but the current pot in the minimum setting, without load, lights the led.
And the zero volt regulation trimpot don't adjust to zero.
Can anyone help me?
Regards.