Toff current in full bridge forward converter

[snafflekid]

bridge forward converter

During Ton, the transformer core becomes magnetized and one secondary coil applies a voltage to the filter inductor. What happens during Toff I understand less. I read that half the inductor current flows through each secondary coil. So the input voltage to the inductor must go below ground to forward bias the diodes. Looking at the dot convention of the secondary coils, I think that the Toff current flow would produce two opposing flux in the core and stop the current flow. What happens in the transformer to allow current flow during this period?

 

[FvM]

forward converter 2009

I think that the Toff current flow would produce two opposing flux in the core and stop the current flow. What happens in the transformer to allow current flow during this period?

I don't understand your consideration. Why should opposite fluxes "stop the current flow"? Actually, because the fluxes are compensating each other, high currents can flow without causing a total flux respectively a core magnetization. Generally, a high main inductance would be designed for the transformer, thus the magnetization current can be assumed low related to output current.

 

[snafflekid]

bridgeforward

See, I wasn't thinking. So ideally the secondary coils would produce cancelling flux, or zero flux thus no inductance in the secondary. Then the secondary coils act like wires to ground?