Kapanadze Cousin - DALLY FREE ENERGY

[verpies]

The flaw is already present in Verpies proposed circuit especially if the BEMF is way to high.

What flaw exactly is present if the "BEMF is too high" ?

[Hoppy]

A switching device, such as a MOSFET, can be destroyed by a Drain-Source overvoltage as well as Gate-Source overvoltage.
Apparently Magpwr had in mind only the protection of the Gate-Source junction.

Protection of which did you have in mind?

Primarily Drain-Source overvoltage.

[verpies]

The simple thing to think about - what cause MOSFETs to heat up in first place?

R_DS-ON*I_MEAN² + Integral(I_INST*V_INST)  ...the latter term is related to the rise/fall time of the current/voltage across MOSFETs Drain-Source junction. When the MOSFET is fully ON, then only the firs term matters.

It is not their normal operating amperage by the way...

"Not only" is very different form "not at all"

Also the circuit I shared is already on PCB and is part of PLL circuit in my place. Way too far from debating about it.

And how much heat are you wasting as heat in your snubbers ?

So I will just skip non-constructive part of the posts here.

Don't want to finish what you started?

[magpwr]

Primarily Drain-Source overvoltage.

hi Hoppy,

Exactly what i wanted to say.

Solution-
The number of winding for the additional winding needs to be factored in as well for the active recovery circuit if the BEMF is high.

Alot of complication arises just because the gate capacitance of the mosfet is high before and after implementing active recovery circuit.
That was the root cause of the problem.

It's one of the reason why i stick with 600volts Silicon mosfet with gate capacitance around 2nf in the past.

[verpies]

Primarily Drain-Source overvoltage.

OK that is a valid concern and in my opinion, a greater one that the Gate-Source overvoltage, which can only happen due to bad driver design or the C_D-G Miller capacitance.

I think it is fine for Magpwr to use a TVS diode to protect the Gate-Source junction as long as the TVS diode does not add a lot of C_G-S capacitance and really clamps well below 20V.

The Drain-Source overvoltage can be dealt with TVS Diodes, Zener diodes, RC & RCD snubbers and even with Varistors, but all of these methods are dissipative and don't recycle the clamped-off energy back into the power supply circuit.