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[Moved] SMPS Power Supply circuit using UC3845B PWM controller - frequency varies

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ThirunavukkarasuThoondi

ThirunavukkarasuThoondi

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we have followed the standard design of UC3845 to make 15V x 3 Amps Power supply. we have decided to use 120KHz . But we are unable achieve the same frequency of 120KHz. the frequency of the UC3845B is varying from 100KHz to 250KHz while seeing through Digital storage oscilloscope with or without Load condition.But we are able to load up to 2.5 Amps in the output with stabilized DC output.
 

is your supply stable?
The RC circuit connected to pin-8 V.ref (5 V)
if Vi not stable ==>> V.ref not stable ==>> freq. not stable
 

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