Hello,
On page 9 of Dr Ray Ridley's book, Dr Ridley states that "transformer flux balancing" is a thing that one should be wary of in a full bridge converter.
What does he mean by this?
I mean, surely, if one has primary current sensing via a current sense transformer, then it isn't going to be a problem?
Also, if one ensures that at the maximum on_time of the fet, the primary magnetising current cant rise to saturation level, then surely there will never be a problem with flux balancing?
...However, I fear that the attached simulation proves Dr Ridley correct.....
S0, I have just found a very good reason why Dr Ridley might be very correct about full bridge transformer imbalance.......when you have a full bridge with a duty cycle of above 0.5, then during start-up, the adjacent primary current pulses can be vastly different in length, (subharmonic oscillation) and this can be so for many many cycles.........ie, going one way through the primary, the current pulse is wide, then going the other way, it is always narrow......BANG!.....the following LTspice simulation, as attached, demonstrates this.......I fear now that the current mode full bridge is indeed not safe for duty cycles above 0.5, due to subharmonic oscillation, because even with slope compensation, during start up, subharmonic oscillation still happens....just take a look yourself, -this could consign the full bridge to the history books for duty cycles above 0.5.....
On page 9 of Dr Ray Ridley's book, Dr Ridley states that "transformer flux balancing" is a thing that one should be wary of in a full bridge converter.
What does he mean by this?
I mean, surely, if one has primary current sensing via a current sense transformer, then it isn't going to be a problem?
Also, if one ensures that at the maximum on_time of the fet, the primary magnetising current cant rise to saturation level, then surely there will never be a problem with flux balancing?
...However, I fear that the attached simulation proves Dr Ridley correct.....
S0, I have just found a very good reason why Dr Ridley might be very correct about full bridge transformer imbalance.......when you have a full bridge with a duty cycle of above 0.5, then during start-up, the adjacent primary current pulses can be vastly different in length, (subharmonic oscillation) and this can be so for many many cycles.........ie, going one way through the primary, the current pulse is wide, then going the other way, it is always narrow......BANG!.....the following LTspice simulation, as attached, demonstrates this.......I fear now that the current mode full bridge is indeed not safe for duty cycles above 0.5, due to subharmonic oscillation, because even with slope compensation, during start up, subharmonic oscillation still happens....just take a look yourself, -this could consign the full bridge to the history books for duty cycles above 0.5.....
