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UC3844 based design - help needed

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dipnirvana

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UC3844 based design

Our Input specification of flyback smps is 60VAC to 300VAC and output is 5V at 200mA.

Now to startup the UC3844B, bias current require is 0.5mA, so the startup resistor will be 100K. But at maximum input voltage that’s 300VAC (424VDC) , power dissipated will be 1.5W .


Now this too much of power dissipation for the 2W(output) requirement .

Please help.
 

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