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0-30V Stabilized Power Supply


redwire
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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.
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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.
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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.

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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.
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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?

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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.
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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)
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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

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what will happen we use tl081 instead of mc34071 or tle2141 with a low AC input such as 15Vac?

When rectified and filtered, 15VAC makes about 19VDC. The entire circuit will be starved for current unless the values of many resistors are reduced. The maximum output voltage from the project will be about 12V to 14V.

The old TL081 has a problem called "Opamp Phase Inversion" which was stopped with transistor Q1 in the original circuit. Without the transistor then the output of opamp U2 and the output of the entire circuit goes as high as it can for a few seconds when the power is turned off.

Another problem with the TL081 is that it needs a negative supply of about -5.6V. The MC34071 and TLE2141 do not need a negative supply.

post-1706-14279144564766_thumb.png

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hi, I'm modifying mi original circuit to adapt it to the last revision, now when i connect the board i get 37,5 V at the output and the pots don't modify this value, i have observed that the U2 circuit is getting to hot very fast then i have checked all the conections and it seems to be ok, i have also measured the tension on U2 and between V- and V+ there is 31 V on the input there is 12V (between IN- and IN+) and i don't know is that values are correct.

Thanks

Edit: I'm using TLE2141

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hi, I'm modifying mi original circuit to adapt it to the last revision, now when i connect the board i get 37,5 V at the output and the pots don't modify this value, i have observed that the U2 circuit is getting to hot very fast then i have checked all the conections and it seems to be ok, i have also measured the tension on U2 and between V- and V+ there is 31 V on the input there is 12V (between IN- and IN+) and i don't know is that values are correct.

If you connected the pins on the driver or output transistors backwards or if they are shorted then you will have your problems.
The driver and output transistors are emitter-followers. Their emitter voltage should be 0.6V to 1V less than their base voltage.

The (-) input and (+) input of a linear opamp amplifier (U2) should always have the same voltage because its open-loop voltage gain is 200,000 times or more.

When the (+) input of U2 is 0V from the voltage-setting pot then negative feedback through R11 and R12 causes the (-) input to also be 0V. Then the opamp turns off the driver and output transistors so that the output voltage of the project is 0V.

When the (+) input of U2 is +5V then the negative feedback causes the (-) input to also be +5V and the voltage gain of 2.68 causes the output voltage of the project to be +13.4V.

Your U2 might be destroyed by the excessive heat. 
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Hi,
I've checked the circuit again after your advice and I realized that the BD139 wasn't connected right because in this device the Base pin is in the middle.... , now i have fix this but i still having the same problem, the circuit had been turned on for lees than 30 sec then i don't think the tle2141 could be burned, i just turn it on take a measure and turn it off again, i have also realized that the BD139 have only a 1,2 Ohm between Emitter and Colector i don't know is this is normal in this device or because of the bad connection it may be broken.

Thanks.

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