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Diode junction capacitance and inter-winding capacitance in xformer are in parallel, putting an extra cap across diode in a bad idea unless, as stated by others, it's a low Q type, i.e. low Q at the ringing frequency, which is generally in the 10MHz region. You use a single, low cost part...
You are right, my mistake:oops: I was probably thinkin about turn-on
You are right again, oh gosh what the hell I was think to?:oops: :oops:
I agree completely, but this way we are almost certainly increasing CM noise. I still don't get the point of null turn-off losses, but it's probably a...
Hello Orson, first of all thank you for clarifying things with me.
Second, we are perhaps going off topic.
I think that what you say is true at turn-on. Turning-on in ZVS, like in LLC resonant, or BCM flyback with Vreflected>Vrect, clearly cancels out switching losses associated to overlap in...
not completely. It depends on many things: you may increase aux winding turns' number, reduce series resistance, use a schottky diode, reduce consumption of whatever is connected to it: resistive dividers, PWM IC and associated gate charge, etc.
Increasing the elcap is a viable approach, but not...
Well, in my opinion, and focusing on the flyback,
switching losses are higher in turn-off for DCM, for their higher primary peak currents, while at turn-on are higher in CCM due to the non-zero initial primary current.
Turn-on switching losses are almost entirely capacitive for DCM and BCM.
In...
Well, I don't think you are right. I made some preliminary calculations, leading to almost 6W switching turn-off losses, with an expected 96nsec current-fall-time and a gfs of 8S (@265Vac, starting from a peak drain current of 3.5Amps)
How can turn-off losses be so small for you?
You must walk...
You got the point. The remaining 7W of power losses must be shared between transformer core&copper losses, shunt resistors on primary and secodary side, MOSFET conduction&switching losses, EMI filter&diode bridge drop, and biasing&startup circuitry.
At 230Vac, the worst seems to be MOSFET...
I guess you mean bifilar or trifilar winding on secondary, with diodes in parallel, do you? What efficiency were you able to reach? Our design should have a 88% min at 230Vac, full load.
Hi all, I'm in the very same situation when choosing between 1-mos forward and CCM flyback for wide-input 90W, 14.6Vout battery charger.
Forward has 3 diodes in power-plant, output inductor and demag winding, while flyback just has 1 diode, 1 xformer, and probably the same voltage rating for...
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