TOP 250YN Bias problem

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Hi, My nane is Simon,

I'm writing this post becouse I stack with my design.

I 'm designing the power supplay 30v 5 Amps output, standart input.It is bild with the PI Expert software symulation and exactly with the sme schematic. the problem is: bias capacitor isbraking down just after switching on the circut, so the power supplayer is not starting. The bias voltage is about 0.04 t0 0.1 volts. please help!"

Regards Simon 

Kindly check your bias output voltage (before the rectifier diode) and confirm that it is not higher than the voltage rating of the bias capacitor used.

Thank you for your quick answer.

I measured the voltage on across bias on the transformer. It jumps up to 8volts and then drops down to 0volts in about 3sec. I change the bias capacitor and the voltage across this is 0.9volts, the power supply still does'nt start...
I will be very grateful for any sugestions or ideas.

Regards, Simon.

Since you referred to a PIExper design to implement your power supply, I would recommend the following:

1. Check all component values and ratings.

2. Check to see if the feedback loop is open i.e the feedback resistors, the RC components around the C-pin, the optocoupler and the TL431/Zener.


Could you please provide me with the drain current + C-pin + Bias voltage waveforms please?