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albal59

0 30V power supply

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Hello

I am french, and i thry to explain my problem.
I realise a 0 30V power supply and this one work correctly.
But there is a problem now because it work at 35V and the adjsutement is locked.
Have you got an idea for find the breakdown?
Have you got a detail for a point of test with the voltage?

Beforehand thank you for your reponses

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Did you make the original 0V to 30V/3A power supply that has errors or did you make the corrected version discussed in the forums that works fine?

The regulated 11.2V reference voltage is made from U1 and D8 that is fed to the voltage control pot P1.

P1 feeds U2, Q2, and Q4 that form a power amplifier with a voltage gain of about 3 times.

The original version uses a tiny old 2N2219 transistor for Q2 that is overloaded and when it fails it shorts and causes the output voltage to go almost as high as possible.
The corrected version uses a BD139 power transistor for Q2 and uses two output transistors in parallel (each with a 0.33 ohm emitter resistor).

The original version uses TL081 opamps that have a total supply voltage too high for them. If U2 fails it could cause the output voltage to go almost as high as possible.

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Thank you for reply of this subject.
I realise the first (original)version of the power supply.
If i test the pin 6 of u1 i mesure 10.5v.
Have you got a link who explain the detail of the corrected version?

Thanks

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If i test the pin 6 of u1 i mesure 10.5v.

The negative feedback for U1 uses a 5.6V zener diode. R5 and R6 have equal values so the voltage gain of U1 is 2 which makes the zener current (also the current in R4) 5.6mA and makes the voltage at the output 2 x 5.6V= 11.2V.
Yours has a voltage too low probably because you used a different zener diode that is rated at a much higher current than 5.6mA.

Have you got a link who explain the detail of the corrected version?

No because it is an extremely simple circuit that works almost the same as the original circuit except it uses parts that are not overloaded.
Learn about howsimple transistors and opamps work then you will understand this circuit.

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If Q2 with original component(2N2219) is fail.
Is it possible, to lower voltage at pin 6(10,5V) because at this moment my power supply deliver max voltage, 35V.
I try to change my original circuit with the BD139 and have you got a detail for "two output transistors in parallel (each with a 0.33 ohm emitter resistor)"?
Have you got a link or a reference of this transistors?

Best regards

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Q2 with original component (2N2219) failed.

Yes because it is an old transistor that is difficult to cool and it is overloaded in the original circuit. Use a BD139 REAL power transistor instead with a medium size REAL heatsink.

Is it possible, to lower voltage at pin 6(10,5V) because at this moment my power supply deliver max voltage, 35V.

The voltage at the output pin 6 of U1 is supposed to be 11.2V if you use a 5mA zener diode.
The maximum output voltage of this project is determined by the voltage gain of the output amplifier which is controlled by the ratio of R11 ands R12. The fixed version of this project has a 20k ohms trimpot in series with R11 so that it can set the maximum output voltage at 30.0V.

I try to change my original circuit with the BD139 and have you got a detail for "two output transistors in parallel (each with a 0.33 ohm emitter resistor)"?
Have you got a link or a reference of this transistors?

Many datasheet sites have the datasheet for the BD139 here is its datasheet.

The latest schematic of the fixed version of this project shows the two output transistors with a 0.33 ohm resistor in series with the emitter pin.

Best regards

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