0-30V Stabilized Power Supply

[bugmenot1]

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

 

[audioguru2]

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.

 

[bugmenot1]

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.

 

[bugmenot1]

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.

 

[audioguru2]

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?

 

[bugmenot1]

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?).

 

[audioguru2]

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.

 

[bugmenot1]

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

 

[audioguru2]

The redwire circuit will not work with OPA445 opamps.

 

[bugmenot1]

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. :'(

 

[bugmenot1]

And the PSU don't reach zero volts... Can I make any modifications in R10 or in RV1 to make the 0V adjust reach zero?

 

[audioguru2]

And the PSU don't reach zero volts... Can I make any modifications in R10 or in RV1 to make the 0V adjust reach zero?

1) Try shorting R10.
2) The driver transistor and/or output transistors might be leaking current, replace them.
3) C7 is an electrolytic type that has a voltage absorption problem. Use a film capacitor instead that is used in high quality speaker crossover networks.
4) Try adding a permanent load of about a few mA.

 

[bugmenot1]

I'll change the 3 TLE2141, the BD139 and the 3 2N3055 for new ones (and put R17 the original value 33R). I want this PSU to work better than my old (fixed) version (3A).
I don't like the way the PSU (Redwire 5A) is working now... the old (fixed) version I build is working better than this one... :-\
I hope with the changes it will work better than my old PSU... :'(
And after I change the components

 

[panmil92]

Hi. I want to make this psu, but i don't know which of all the designs to follow?? I have to take notice of Sam Carmel's modifications? Plz enlight me.

Thanks.

 

[audioguru2]

Hi. I want to make this psu, but i don't know which of all the designs to follow?? I have to take notice of Sam Carmel's modifications? Plz enlight me.

The latest schematic and parts list has been posted many times. It works well, is reliable and parts for it are available nearly everywhere.

Please post a link to Sam Carmel's modifications.

 

[Holt]

Hi. I want to make this psu, but i don't know which of all the designs to follow??

Have a look at page 30 for links to the newest designs

 

[audioguru2]

I added the values for the calibration trimpots:

View attachment 41072

 

[panmil92]

Thank's. For the mod check at the end of this page http://www.electronics-lab.com/projects/power/001/index.html .

 

[audioguru2]

For the mod check at the end of this page

It looks like Sam Carmel made the original version that has many faults. His mod is not shown.