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Calculate switching loss in Mosfet

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I asked a broader question before and it must have been too much.

Here is a simpler version and more to the point of what I'm after.

Using the above MOSFET in a switching application with the following specifications.

Configuration: half bridge Bus Voltage: 500V peak flat top current 1.5A (start of ramp on step is 1A, Anti-parallel diode freewheels the inductaive load) May place an external diode if the internal diode causes too much dissipation.

switching freq = 10kHz 90% duty cycle

I can figure out the losses due to the Rds_on but I'd like to get an estimate of the switching losses.

The FETs will be driven with a TC4427 1.5A fet driver with a small ~5 ohm resistor to damp the resonant tank between the pin an trace inductance and the gate capacitance.

Can someone help me with this please?

Reply to
Mook Johnson
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As an approximation, take the switching times (on/off) and assume that the FET resistance goes linearly from 0 to infinity (or vice versa) in that time. Integrate over the power; that'll give you the energy that each switching process leaves in the FET. Multiply by the number of switches per second, and you get the average switching power loss in the FET.

Gerhard

Reply to
Gerhard Fiedler

Please help me understand, why is this information important ??

donald

Reply to
Donald

Reply to
J.A. Legris

I thought I wrote down the formula...but can't find it...anyways.. I had to Google for it. It's out there..in the wild...somewhere.. D from BC

Reply to
D from BC

worst case with inductive load, assume the current doesnt change untill the top freewheel diode starts conducting, vds rises linearly limited by the gate current charging cdg, the power at switch off will then be 1/2 V * I * tfall * freq power at switch on depends on the initial current.

dont forget the gate energy required too, although it should be much less.

Colin =^.^=

Reply to
colin

Sometimes, when you're switching fast enough, the switching losses are the ones that determine the necessary heat dissipation. Or the available dissipation determines the maximum switching frequency.

Gerhard

Reply to
Gerhard Fiedler

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