why flyback?
I´d tend to push-pull.
Flyback needs a regulation (any feedback). And flyback needs the (big) core to store (all the transformed) energy. Simple electronics.Is there a reason why push-pull would be better in this situation?
This is the "no feedback" regulation. The disadvantage is that it wastes all the power.let the zeners do the regulation.
At 6W typical for a GD situation - the power wastage is almost immaterial - however, if the gate drive itself uses 0.8 W ( fairly typical ) at nominal flat out - then in fact very little is wasted.The disadvantage is that it wastes all the power.
This brings up a point for calculating power, I'm not actually sure how to do the power calculation. I plan on driving 6 pairs of MOSFETs at 18V 6A meaning peak power would be around 110W, but that would last a ~30ns and then for the next ~62000ns no power would be drawn. I'm assuming I still need to size the flyback for the 110W peak, right?The power in the flyback is Freq x 0.5 Lpri Ipk^2 ( less losses ) so if you need 6 outputs at 1W each - make a 6W flyback and let the zeners do the regulation. ( the control can be a buffered TLC555 timer with fixed freq and duty cycle driving the flyback fet ).
shot answer = no, you appear to have overlooked the explanation regarding constant power, most of the power goes into the GD ckt, when the gate drive is constant low - the excess power goes to the Zener.As for the 555 solution, driving the flyback with a fixed frequency and duty cycle seems odd to me, as I'm not expecting a constant power draw. Wouldn't the primary current rise as no power is drawn on the secondary?
This comment makes me fear very greatly as to the success of your endeavour.how to do the power calculation. I plan on driving 6 pairs of MOSFETs at 18V 6A meaning peak power would be around 110W, but that would last a ~30ns and then for the next ~62000ns no power would be drawn. I'm assuming I still need to size the flyback for the 110W peak, right?
You're right, everything after the comment i replied to completely went over my head, makes sense now.shot answer = no, you appear to have overlooked the explanation regarding constant power, most of the power goes into the GD ckt, when the gate drive is constant low - the excess power goes to the Zener.
Learning is a process. I've never worked with magnetics, this is the first time I'm actually going deep into the calculations for a flyback. Peak power is provided by decoupling caps makes perfect sense... once you hear it. If my uni wasn't trash maybe someone would have mentioned that to me.This comment makes me fear very greatly as to the success of your endeavour.
Just want to ask about this, to calculate the average current I'd take the average current during the gate charge period, I_avg, multiply it by the time it takes to charge the gate, t_on, and divide by the whole switching period, T?as a rule of thumb - driving a big mosfet needs about 40mA ave at say 15V - this is 600mW.
Indeed.This comment makes me fear very greatly as to the success of your endeavour.
There is more to it than this as any gate drive cktry is not 100% efficient - build a gate drive, attach a fet or a dummy load and measure.Just want to ask about this, to calculate the average current I'd take the average current during the gate charge period, I_avg, multiply it by the time it takes to charge the gate, t_on, and divide by the whole switching period, T?
so (I_avg * t_on) / T
For I_avg = 6A, t_on = 100ns and f_sw = 16kHz that gives 9.6mA or 0.17W@18V if my understanding is right
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