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Simple DIY Linear PSU

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xavier60:

--- Quote from: panoss on March 14, 2020, 05:00:41 pm ---
--- Quote from: xavier60 on March 14, 2020, 04:45:04 pm ---When the Inverting input voltage is less than the Non-inverting input voltage, the output of the op-amp should go to its maximum voltage. About 1.4V less than supply voltage for the LM358.

--- End quote ---

RL=no load, Vpin7=8.52V   Vpin8=9.69V
RL=20 Ohm,  Vpin5=8.13    Vpin8=9.30V
RL=10 Ohm,  Vpin5=7.87    Vpin8=9.04V

--- End quote ---
  Vpin8 going from 9.69V to 9.04V  means that the input voltage is dropping by a lot.

panoss:

--- Quote from: xavier60 on March 14, 2020, 05:05:51 pm ---No problem using a SMPS so long as the voltage is correct and holds up when loaded.
The Collector of Q1 should be close to 18V?


--- End quote ---

RL=no load, Q1 Vc = 17.33V
RL=20 Ohm, Q1 Vc = 15.22V
RL=10 Ohm, Q1 Vc = 14.04V

I also tried with an SMPS (12V):
RL=no load, Vout=11.4V
RL=20 Ohm, Vout=10.3V
RL=10 Ohm, Vout=9.9V

EDIT: I tried with a second SMPS (a PC power supply). The results are the same.

xavier60:

--- Quote from: panoss on March 14, 2020, 05:46:22 pm ---
--- Quote from: xavier60 on March 14, 2020, 05:05:51 pm ---No problem using a SMPS so long as the voltage is correct and holds up when loaded.
The Collector of Q1 should be close to 18V?


--- End quote ---

RL=no load, Q1 Vc = 17.33V
RL=20 Ohm, Q1 Vc = 15.22V
RL=10 Ohm, Q1 Vc = 14.04V

I also tried with an SMPS (12V):
RL=no load, Vout=11.4V
RL=20 Ohm, Vout=10.3V
RL=10 Ohm, Vout=9.9V

--- End quote ---
RL=10 Ohm, Q1 Vc = 14.04V, means that 4.5V is being applied to B-E of Q2 which means that it's damaged. This is assuming that the supply is holding up at 18.5V.
But why was the 9V rail dropping before? Are you using an LM317?

panoss:

--- Quote from: xavier60 on March 14, 2020, 05:55:54 pm ---RL=10 Ohm, Q1 Vc = 14.04V, means that 4.5V is being applied to B-E of Q2 which means that it's damaged. This is assuming that the supply is holding up at 18.5V.
But why was the 9V rail dropping before? Are you using an LM317?

--- End quote ---
Yes, I 'm using an LM317. (I just took one more look to make sure  :D)
I 'll replace it to be sure, maybe it 's damaged.

panoss:
Well, I replaced:
-the S8550 with the BC557
-the LM317 with another LM317

Results are the same.

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