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TL431 linear power supply

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mike_mike:
Hello, I built the power supply from the attached image but I found that it is oscillating. What should I do to prevent the oscillations that appeared on the scope at the output of the power supply as a sine wave with vpp amplitude of about a few tens of volts ?
While the power supply was oscillating, the voltage drop on the 1N4148 diode was 4V instead of 0.7V and there was a high frequency noise.
Also, the load was about 6-7A at 25Vdc output.

What should I do to eliminate the oscillations ?

*in the tested schematic, R6 was 2 0.1R in parallel resistors.

xavier60:
Try adding some frequency compensation to the TL431. Start with a series 1K and 1uF between K and R.

AngraMelo:
What is the purpose of R4 and R12?

Zero999:

--- Quote from: AngraMelo on December 11, 2018, 11:52:23 pm ---What is the purpose of R4 and R12?

--- End quote ---
They improve the transient response by discharging the base-emitter capacitance, when the base current decreases.

David Hess:
What is the frequency of oscillation?

Get rid of C2.  It belongs either at the load or where the leads enter the chassis.

AC bypass R18 with a low value capacitor.

Swap the positions of R8 and R9.  Then AC bypass the top fixed resistor with a capacitor or series capacitor and resistor.  This adds phase lead and works in combination with xavier60's suggestion.

Lower the value of R4.

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