0-30V Stabilized Power Supply

[audioguru2]

The output voltage stays -19mV when P1 and P2 are set to minimum (adjusting RV1 do not change it at all) (at this time LED is glowing).

When I turn P2 a little, so the LED does not glow, I am able to see the change in the output when adjust RV1, and it is from +19mV to +32mV. What is wrong here?

The LED lights to warn you that the current regulation is reducing the output voltage because it senses that the load current is higher than a few mA set by the value (33 ohms) of R21.

I notice now that the idle current and load of U1 is part of the load and the idle current of the TLE2141 is higher than the original TL081.
So increase the value of R17 until the LED does not glow with no output load.

 

[audioguru2]

I tried several values of R21 from 10kOhm to 50kOhm, but changing it does not change anything at all, and the problem still remains..

Sorry, It is R17 that should be increased a little.
Here I show that when R17 is the original value of 33 ohms, the TLE2141 opamp U1 has its maximum supply current of 4.4mA, its load is 5.6mA and its input offset voltage is at its maximum of 1.4mV. Then the output of U3 is low and turns on the LED.

I also show if R17 is increased to 56 ohms then the output of U3 is high and the LED is turned off. Maybe 47 ohms will work fine.
View attachment 41929

 

[WinDTrek]

i have the same problem. when i apply power to my power supply LED will light up. moving the current pot 1/8 clockwise will turn off the LED. increasing the value of R17 to 56 ohms fix this problem.

 

[WinDTrek]

Preview of the PSU that 'I'm working on.. Please visit

 

[WinDTrek]

Actually the problem I have was when I power on my power supply LED lights up. This problem goes a way when you turn P2 1/8 clockwise. After that returning P2 while the power is still on to minimum LED remain off. The problem only occurs upon powering up the power supply. Changing the value of R7 from 33 to 56 ohm fixed the problem.  Before I'm getting 0.6mV at Pin 3 when P2 is minimum. Now I'm getting 4.5mV. In the video noticed that when I power up the power supply LED did not turn on. Maybe the one you saw was when I put load into it.

 

[Kevin Weddle]

Jfet input opamps are a great improvement because they are square law devices. Their input voltage needs to be very close to the supply voltage based on Jfet VGS. Maybe 5V less. Does this opamp need a transistor bias voltage so that the bias impedance is higher than would be a resistor.

 

[audioguru2]

Jfet input opamps are a great improvement because they are square law devices. Their input voltage needs to be very close to the supply voltage based on Jfet VGS. Maybe 5V less. Does this opamp need a transistor bias voltage so that the bias impedance is higher than would be a resistor.

Kevin, the improved and fixed project uses opamps with PNP bipolar transistor inputs, not Jfet inputs so that they work with an input voltage as low as the negative supply voltage.
The input voltage of opamp U2 goes from 0V (its negative supply voltage) to +11.2V and never goes as high as the positive supply where it will have its output saturated as high as it can go.

 

[audioguru2]

See my video

Your circuit board is a mess of long wires all over the place. The capacitance between the wires and their inductance will cause problems. Use a compact stripboard layout or a good pcb.

I do not see what your meter is measuring. mV? mA?

If C7 is electrolytic then it has the "electrolyte absorption problem" where it produces its own voltage when the output is supposed to be zero volts. Use a film capacitor to prevent this problem.

 

[audioguru2]

I forgot to say: meter shows mV on the power supply output without load.

If you have the voltage pot P1 turned down to zero and C7 is a film capacitor then the VR1 trimmer should be able to adjust the output from about -30mV to about +30mV.

 

[WinDTrek]

WinDTrek, what do you use as C7?

i used poly film capacitor... you'll find that in the video yellow in color on top of the pcb.

 

[Kevin Weddle]

A polyester capacitor is very cheap.

 

[audioguru2]

A polyester capacitor is very cheap.

It is not cheap, instead it is inexpensive. It is half-way between inexpensive and expensive but it is very high quality. 

 

[_pike]

Audioguru has attached on the sixth post the bill of materials.The date is a little bit long "but i suppose that it is a stable version" .
WinDTrek i would like to ask you if you could post the pcb layout of the power supply you built.

Regards Panagiotis.

 

[audioguru2]

Audioguru has attached on the sixth post the bill of materials.The date is a little bit long "but i suppose that it is a stable version".

That is the latest bill of materials but recently we found that the red LED indicates current regulation when it shouldn't. Increase the value of R17 to 47 ohms, 56 ohms or 68 ohms to fix it.

 

[WinDTrek]

[No message]

 

[_pike]

audioguru thanks for replying but which value of these 3 is the most appropriate?


windtrek you have done an AMAZING job and my congratulations!!!!.I couldn't believe in my eyes when i saw that you wind your transformer.WELL DONE and thank you for all the files!!!!!


P.s Eagle files have problems. They dont exist in the database that you have upload.
If it doesn't bother you can you tell me the connections of your pcb with transistors.... etc?

P.s2 With the blue trimmers what settings can you make?

 

[audioguru2]

audioguru thanks for replying but which value of these 3 is the most appropriate?

Each opamp has a different supply current and a different input offset voltage. Select a resistor value that works with your opamp.

With the blue trimmers what settings can you make?

One trimmer sets the output to exactly 0V when the voltage pot is zero.
Another trimmer sets the maximum output voltage to exactly 30.0V.
Another trimmer sets the maximum output current to 3.0A.

 

[WinDTrek]

P.s Eagle files have problems. They dont exist in the database that you have upload.
If it doesn't bother you can you tell me the connections of your pcb with transistors.... etc?

P.s2 With the blue trimmers what settings can you make?

Please check my last post, I replaced the files with screenshots as i'm having problem sharing the eagle files. In the screenshot, I think I have all the labels including from to connections. e.g. from board 1 to board 2, from board 2 to transistors... etc.. Should be easy to follow.. : 8)

 

[_pike]

Ok thank you all !!! I am going to begin the construction in about two days.i am waiting from farnell the op amps (mc34071).By the way they are very expensive 2Euros each!!!! I am wondering why's that???
I will post my results here....
Thank you all again for helping me out

Regards Panagiotis

 

[audioguru2]

Newark, Element 14 is Farnell in the US. They sell an MC34071CP for $.484US today which is 0.37 Euros.
You are being ripped off.