![]() It never crosses into positiveterritory and never changes sign.This certainly happens and is a real problem with power transformers.It happens because the current through the inductive element is the integral of the applied voltage and this is the main reason why transformer primaries can reach high core saturation levels when voltage is initially applied. What I see here is that flux starts at 0, and reaches some negativepeak, then heads back to zero. It never crosses into positive territory and never changes sign.In typical full bridge SMPS design, how is flux made to be bipolar and actually change polarity?I am assuming it is desirable and possibly required to make it do this in order to prevent flux walking and also because if current is to change polarity in secondary, flux must also change polarity. At that point, flux will increase (positively), and so on.What I see here is that flux starts at 0, and reaches some negative peak, then heads back to zero. Take a full bridge switching circuit connected to the primary of a transformer.Assume:No load on secondary.Voltage into full bridge is DC.Duty cycle of switching is 50%.At t = 0, full bridge connects voltage to primary, lets call it 'positive'.Faraday's law says slope of flux will be opposite in magnitude, and flux will increase (negatively) linearly until half cycle is over and voltage flips.
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