Electronics > Beginners
TL431 linear power supply
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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