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Mosfet paralleling reliability in real life - more smaller ones vs fewer bigger

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splin:

--- Quote from: T3sl4co1l on September 23, 2019, 05:38:27 pm ---Switching loss goes as a fraction of the total 8kVA range -- all the capacitance and inductance and voltage and current swing are available whether you're using them or not.

Tim

--- End quote ---

Not if you have paralled units,  interleaved or not,  powering up only as many as required for the given load. That also allows you to optimize the convertor efficiency as they only need to operate at a fixed output current,  voltage or power (apart from one of them of course). Control could be interesting though - especially for more dynamic loads.

T3sl4co1l:
Dropping cylinders on a lightly loaded engine, nice.

Good for multi-channel (usually phased), in parallel so variable over a range of current; harder to do over a range of voltage (outputs stack in series), but can be arranged that way as well.

You could even make a grid of both, say 4 or 6 or 9 or however many channels wired back and forth like this, and remove channels that are unused due to the constant power curve!

In the large-NxM limit, each stage could be a fixed V/I converter of whatever sort (probably resonant), and it would be a two-dimensional power DAC.  Just turn channels on and off as needed.  Probably a binary series though; well, maybe not strict binary, but a unary coded n-ary may be cheaper due to parts reuse (that is, use say base 3 instead, where each digit is coded as 00, 01, 11).

And you could still, after all that, have a continuous section, which could even be linear, to fill in the remaining gaps while costing very little overall efficiency.

Probably, the all around ideal N and M are very small, due to sheer parts count increasing cost and size, versus possible efficiency savings, or efficiency losses due to repetition.

Tim

Miyuki:
So I put it in Spice and when expecting tight layout to keep inductances low
Simulated results are promising, turn on is very soft and at turn off it is still manageable (I know real diodes will be somewhat worse than LTspice ones), secondary side should also be fine with 200V schottkyes
Transistor models are from Infineons library driven with +-15V
Even calculated snubber losses arent something huge

So I thing it worth try to build prototype

mzzj:
Your sim model doesn't have any shared source inductance?

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