I don't see how. They're just the result of the switching node returning to Vout, in a very undamped oscillation. It does not increase dissipation. The only way to "reduce them" would be to short out the inductor after the ringing starts, or to damp the oscillation with resistance (which would obviously decrease efficiency).Dear mtwieg
Hi
At buck converters , those ringings can decrease the efficiency . and it is better to reduce them .
I've never heard of applying a RCD snubber to DCM ringing (and RCD snubbers are by definition dissipative). Can you provide an example?Dear mtwieg
again Hi
Hes can use a simple snubber network to reduce them ( non dissipative RCD snubber ) . and it will not decrease the efficiency .
Best Regards
Goldsmith
Yes, but I'm wondering how you could apply it to DCM ringing. I'm not going to buy a reference book just to see that.if you read some expert books about SMPS design ( like pressman's book ) you will see the Application of the snubber networks and at that season , ( that book has a season about snubber ) , you will see non dissipative RCD snubber networks . ( the dissipation is insignificant ) .
All the best
Goldsmith
Both. I can't see how you could clamp it or dampen it without introducing dissipation. And I don't see how allowing it to ring introduces dissipation.What thing is not clear? probably : how the snubber can reduce the ringings ? or how ringings will increase the dissipation here? which one is not clear ?
Respect
Goldsmith
No, the FET isn't switching at that frequency. Nothing is. It's just an oscillation between the inductance and parasitic capacitance at the drain node.Hello mtwieg
If those spikes has large amplitude ( as you can see at his attachment ) , thus the mosfet have to try to switch with that frequency and that wave form will have effect on the current wave form . ok ?
The changing capacitance of the FET is irrelevant, and has nothing to do with the miller affect.thus with this amplitude changing , the internal capacitors of mosfet will change ( according to the miller effect ) .
Yes.ok , now , do you like to write the dissipation equation ??!!!
I'm pretty sure you're wrong, but I'll give you the opportunity to show otherwise.it will has effect on dissipation .
This looks like an equation for conduction losses (though it's wrong), which has nothing to do with that ringing.because the dissipation at best situation is 1/T integral from 0- ton Rdson^2*ID dt . ok ?
No, the ringing does not change the effective duty cycle. It does not affect the current drawn from the source or delivered to the load (unless you consider exactly when the start of the next switching cycle begins, which may either improve or worsen efficiency, similar to quasiresonant converters. But in general it has no effect overall).thus you can see that ton increased ( and you didn't want it . ) . and the other disadvantage is that you can not control the duty cycle exactly .
What.Dear mtwieg
My mean by that mosftet have to switch ...... was not the voltage . as i told at top the current will be some thing like that . and i know that the didn't provided by mosfet . my mean was it's current.
That's the equation for dissipation caused by conduction through the PFET. But the PFET is off during that ringing. It's not conducting, so it has no conduction losses during the ringing.And about the equation of dissipation : it we have to take it's average because it is a discontinuous wave ( square ) . and the average of that will be : 1/T integral rdson*ID^2 dt ( from zero up to ton ) isn't it ?
The FET clearly turns off properly, and quickly. The ringing only begins after the catch diode is no longer forward biased, and persists until the FET turn on again.and the ton increased by those spikes ( the mosfet should be turn off at that time . and you can not say that the operation of regulator is in discontinuous region ( wave is discontinuous of course ) because for discontinuous behavior the wave will clip from right not left .
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