High output voltage feedback problem

Posted by: Victor M.Dzugutov on 04/21/2010

I used PI Expert 7 to designe 75V output voltage power supply based on TOP262
device. PI recommends TL431 in feedback circuit and 4.1K resistor between
TL431 cathode and output voltage circuit.
But the voltage drop across this resistor does not exceed 24V.
So the TL431 suffers overvoltage (Vmax = 36V).
That is why I get output voltage less than 50 V really.
Increasing the resistor is doubtful because the current in this circuit is
not stable.
What is the best solution in this situation?

Thank you in advance!

Victor

Comments

I usually put a zener diode in series with a resistor between cathode and high output voltage.

Thank you for advise.
The only question: does the Phase Margin calculation remains valid
in such situation?

Regards,
Victor

Well,

The effective resistance between output and TL431-K is lowered, and it might be necessary to change the resistor value to have the same phase margin