0-30V Stabilized Power Supply

[audioguru]

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,

[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

[audioguru]

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.

[bugmenot]

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).

[bugmenot]

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.

[bugmenot]

And the voltage and current in the LCD meter are oscilating... :( :-\ ???

[audioguru]

I have problems with my PSU (Redwire 5A version).
The voltage pot works good, but the current pot in the minimum setting, without load, lights the led.

I have a Redwire schematic 5/04/2008 that is missing how the current-setting pot is connected.
In my version, opamp U3 is a TLE2141 that has a max input offset voltage of only 1.4mV. R17 is 33 ohms and is connected at the lowest voltage pin of the current-setting pot to make a voltage of 5.6mV for the non-inverting input pin of U3. Without a load the inverting input of U3 has a voltage of 0V. Therefore the output of U3 is high and the LED is not turned on.

And the zero volt regulation trimpot don't adjust to zero.

Redwire's schematic and parts list have the correct parts and wiring for the input offset voltage null trimpot for the TLE2141 opamp U2.
But the output capacitor C7 is an electrolytic type that has a problem called "dielectric absorption" which causes its output voltage to rise without a load. Try using a film type capacitor or add a load that provides a couple of mA. Then maybe the input offset voltage null trimpot will work when the output voltage is supposed to be 0V.

I don't know why your meters are oscillating.

[bugmenot]

I use the TLE2141 too. I'll measure the voltage in input of U3. The schematics I have is the november/09 version.
I put the parts in the part list.
The meters are oscilating I think is because the input voltage for the LCD meter are above 35V, the limit for the 12V regulator. I put a 22R resistor in series and it don't oscilate more.

I have the previous version of the PSU (3A) and it adjust the zero and the current pot in the minimum don't light the led.

[noworries2004]

Fantastic news got newmc34071 yesterday and the circuit works perfectly,
Found problem in other circuit, pin 4 of U3 was 20V, 187ohms between pin 7 and 4 so chip blown,

Working perfectly now,
Thanks a million for your help everyone especially Audioguru and Redwire.

[bugmenot]

Hi AudioGuru,
R17 is 33 ohms and is connected at the lowest voltage pin of the current-setting pot. But I measure the voltages enter -C1 point (0V) and pin 3 of U3 (wiper connection in current POT): 8,3mV (current pot set to minimum and led on); 12mV (current pot set to led off). When the led is off the output is 21,4mV (zero adjust trimpot set to minimum).
In this test I used only 2 2N3055, to have access to the PCB and make the measurements.

[audioguru]

Hi AudioGuru,
R17 is 33 ohms and is connected at the lowest voltage pin of the current-setting pot. But I measure the voltages enter -C1 point (0V) and pin 3 of U3 (wiper connection in current POT): 8,3mV (current pot set to minimum and led on); 12mV (current pot set to led off).

Then the input offset voltage of your U3 opamp is worse than the maximum spec'd. A TLE2141 opamp has a max input offset voltage of only 1.4mV and an MC34071 opamp has a max input offset voltage of only 5mV. Replace U3.

When the led is off the output is 21,4mV (zero adjust trimpot set to minimum).

Then maybe your U2 opamp also has its input offset voltage higher than the max in its spec. Replace it.
Maybe your output transistors or driver transistor have a leakage current too high. Replace them.

Did you try exchanging the electrolytic capacitor C7 with a film capacitor?
Did you try adding a load on the output of the project of a few mA?

[bugmenot]

For now I only have 6 OPA445 opamps... No more TLE2141  :'(.  (Samples from TI)
The film capacitor you are talking are polyester film type?
If I increase R17 value I will solve the led on problem in the current pot set to minimum?
And the current LCD meter shows less current than the multimeter shows when I power 1 120mm PC Fan 12V 0,33A (The multimeter shows constant 0,23A and the LCD meter shows 0,14A.

The R7 is two 0,47R 10W in paralel (0,235R = 0,24R?).

[audioguru]

For now I only have 6 OPA445 opamps... No more TLE2141

I can't remember which version you are making.
my latest version works only with MC34071 or TLE2141 opamps and will not work with 741 or OPA445 opamps.

The film capacitor you are talking are polyester film type?

Yes.
There are many plastic films. Mylar is another one.

If I increase R17 value I will solve the led on problem in the current pot set to minimum?

Yes.

And the current LCD meter shows less current than the multimeter shows when I power 1 120mm PC Fan 12V 0,33A (The multimeter shows constant 0,23A and the LCD meter shows 0,14A.

I think your current meter is not calibrated correctly.

The R7 is two 0,47R 10W in paralel (0,235R = 0,24R?).

Yes.

[bugmenot]

I can't remember which version you are making.
my latest version works only with MC34071 or TLE2141 opamps and will not work with 741 or OPA445 opamps.

I build the redwire 5A version with TLE2141 opamps.


Yes.
There are many plastic films. Mylar is another one.

I don't change the capacitor because I don't find a 10uF in polyester or mylar type.


Yes.
To the led go off in the current pot set to minimum and the voltage pot set to minimum or maximum I have to increase the R17 to 150R.


I think your current meter is not calibrated correctly.

I calibrate the meter folow the instructions in the autor site. http://www.elfly.pl/multimetr/multimetr_en.htm

[audioguru]

The redwire circuit will not work with OPA445 opamps.

[bugmenot]

Ok, I know. I don't change the opamps. It's the same TLE2141.
What about the R17 increase changes? It's ok?
When I calibrate the LCD meter it's show the correct current load of the same 120mm PC fan (0,23A), but when the calibration finish the meter shows 0,13A only. :'(