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Reverse current protection not needed in synchronous rectifiers?

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cupoftea

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Hi,
We are doing synchronous pushpull 300w, 24vin, 32vout, 153khz txformer frequency.
We use the LTC3901 synch rect driver. It has reverse current protection. But is there any point in using it? The attached LTspice simulation shows its not needed. When you go into no_load….the output inductor current just oscillates harmlessly back and forth. (LTspice sim and jpeg attached)

LTC3901

LTC3723
 

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  • pupull300w_syncrects_fm.zip
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  • Synch rects.pdf
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The circulating current results in higher losses when the load is very small. Also tends to increase EMI as well. I believe that's the main motivation for synchronous converters sometimes having a "forced DCM" behavior.

Also preventing reverse current is sometimes desirable when the load can actually source significant power, for example in battery chargers.
 
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