kathmandu
Full Member level 5
Hello,
I've just build a two-switch flyback converter (Vin=48VDC, Vout=12VDC, Pout=50W) but the boostrap circuit for the high-side driver doesn't work quite well. That's it, during the Mosfet switches OFF period, the low-side freewheeling diode is only forward biased for a (too) small period of time (I suppose) hence the bootstrap capacitor doesn't get enough charge.
I've seen a workaround for this issue, by adding an extra switch across the low-side freewheeling diode and make it close (ON state) during main switches OFF periods. Anyway, I want to avoid this kind of circuit thus I was thinking of a way to make use of the freewheeling current.
This is the purposed circuit:
As you can see, I moved the low-side freewheeling diode as to include the bootstrap capacitor on the freewheeling path. The downside of this circuit could be the increased current through the zener diode (but I could use an overrated one) and the increased voltage across the high-side Mosfet in OFF state (48V+12V instead of 48V) but, than again, the Mosfet I am using is already overrated (Vds=150V).
Is there any (other) problem with the circuit above? Btw, giving the rated output (50W), what could be the amplitude (max/average values) of the freewheling curent?
Thank you very much for your time.
I've just build a two-switch flyback converter (Vin=48VDC, Vout=12VDC, Pout=50W) but the boostrap circuit for the high-side driver doesn't work quite well. That's it, during the Mosfet switches OFF period, the low-side freewheeling diode is only forward biased for a (too) small period of time (I suppose) hence the bootstrap capacitor doesn't get enough charge.
I've seen a workaround for this issue, by adding an extra switch across the low-side freewheeling diode and make it close (ON state) during main switches OFF periods. Anyway, I want to avoid this kind of circuit thus I was thinking of a way to make use of the freewheeling current.
This is the purposed circuit:
As you can see, I moved the low-side freewheeling diode as to include the bootstrap capacitor on the freewheeling path. The downside of this circuit could be the increased current through the zener diode (but I could use an overrated one) and the increased voltage across the high-side Mosfet in OFF state (48V+12V instead of 48V) but, than again, the Mosfet I am using is already overrated (Vds=150V).
Is there any (other) problem with the circuit above? Btw, giving the rated output (50W), what could be the amplitude (max/average values) of the freewheling curent?
Thank you very much for your time.