TO264EG Troubleshooting.Not Starting

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Hi,
In a simple 3 terminal setup up on applying even 100v on drain thru transformer primary, The control pin voltage not going above 2.1v. Since it is not reaching 5.8v, switching never happens. Please give ideas to troubleshoot the situation

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Hi Jacob,

Please check the layout, transformer winding polarities. Check polarity of electrolytic capacitors C3 & C8. Check any possibility of short on ceramic capacitors C2 & C9.
The startup bias current is drawn from Drain pin to charge the capacitor on control pin. For debugging purpose disconnect VR2 and slowly vary the input voltage, monitor the control and drain pin voltages with respect to source. Please note that, since feedback is open, you may experience overshoot on output if you apply high voltage at input.