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Tool/software:
We always use UC3843 in our designs.. In our new SMSP;
We design a 10W 72VDC input 5V output Flyback Converter with UC3843A with 20V VCC aux winding
The problem is when we connect 28K or lower value pull down resistance to increase start up current at VCC startup circuit, the power supply could not start but if I isolate VCC pin and connect external 15V power supply to VCC pin it works well. and I see 20V in aux winding.
There is an issue on start up or UVLO since I always seen 7-8V at this pin
What can be a problem?
