full-bridge transformer-isolated boost converter

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Dingyuan

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Hi all, I’m struggling with understanding a full-bridge transformer-isolated boost converter. The author mentions that during the first subinterval, Q1, Q2, Q3, and Q4 are all on at the same time, leading to transformer saturation. However, I don’t understand why the transformer would saturate if no current is flowing through it.

Please help me. Thank you all in advance and have a nice Sunday
 

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Agreed, if it's supposed to act like a boost converter, then we'd expect Amperes to ramp up in inductor L while Q1 Q2 Q3 Q4 turn on.

I see no benefit to letting either inductive element saturate. In fact the graph labeled 'I' looks like a triangle wave which should be an Ampere waveform and it's not saturated.
 

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The transformer cannot saturate if it is shorted by a pair of mosfets, check your reading of the article.

If you do a simulation - you will see that for slightly asymmetric gate drive - you can get flux walking and saturation in the Tx

this is normally easily avoided by pk current mode control - sensed by a suitable CT in series with the Tx
 

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The author's comment might be due to a wrongly interpreted observation. If saturation occurs, it starts at end of +/- vT phase, extending into vT = 0 phase. Apart from avoiding asymmetrical drive, special measures may be necessary to prevent from saturation during startup. Suggested peak current control is the best way to catch it all.
 

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