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UC3843A Buck Problem

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R_Maverick

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Attached buck design works fine with UC3845B operating at Freq of100KHz and Input voltage of 56V. Since my input varies from 36 to 56V, UC3843A may have to be used... With UC3843A plugged in, I don't see any output at all. At pin 6, a 96% Duty cycle square waveform appears. Should it not be close to 70% while operating at 36V? The pulse transformer is unable to handle the 96% duty cycle and is not firing the mosfet. Do I have to only look at high side mosfet driver ?
 

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Yes, you need a proper high side driver (for either P or N channel FETs). A gate drive transformer isn't feasible for duty cycles far from 50%.

Your current sense transformer is also going to be problematic, especially with a primary inductance of 1.5uH. If you absolutely must use a transformer for current sense, consider putting it on the other side of the FET.
 

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