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Simple DIY Linear PSU

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panoss:
By 'input voltages from LM358' you mean voltage on pin 5 (and maybe 6), right?
Here they are:
RL=no load,  Vpin5=4.63V  Vpin6=3.18, Q1's Vb=8.97V 
RL=20 Ohm,  Vpin5=4.67V  Vpin6=2.26, Q1's Vb=8.55V   
RL=10 Ohm,  Vpin5=4.70V  Vpin6=1.72, Q1's Vb=8.30V   

xavier60:

--- Quote from: panoss on March 14, 2020, 04:30:46 pm ---By 'input voltages from LM358' you mean voltage on pin 5 (and maybe 6), right?
Here they are:
RL=no load,  Vpin5=4.63V  Vpin6=3.18, Q1's Vb=8.97V 
RL=20 Ohm,  Vpin5=4.67V  Vpin6=2.26, Q1's Vb=8.55V   
RL=10 Ohm,  Vpin5=4.70V  Vpin6=1.72, Q1's Vb=8.30V

--- End quote ---
So the voltage across R10 is about 4V?
What is the unregulated input voltage?
Try doing the test at a lower output voltage setting.

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.

panoss:

--- Quote from: xavier60 on March 14, 2020, 04:45:04 pm ---So the voltage across R10 is about 4V?

--- End quote ---
It 's 3.26V, no matter the load.


--- Quote from: xavier60 on March 14, 2020, 04:45:04 pm ---What is the unregulated input voltage?

--- End quote ---
18.50V


--- Quote from: xavier60 on March 14, 2020, 04:45:04 pm ---Try doing the test at a lower output voltage setting.

--- End quote ---
A regulated output from an SMPS would not be a good power supply, right?

panoss:

--- 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

xavier60:
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?
It seems that the output stage has too little gain or a fault.

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