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Thread: Mosfet heat dissipation help

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    Default Mosfet heat dissipation help

    Hey folks I am wondering how to get the power loss of the mosfets like buildzoid does here https://www.youtube.com/watch?v=zSqhVlpgw3U&t=825s around the 12:00 mark.. he has a video of explaining it but I can't get mine to match up with his
    Equation is on this reddit https://www.reddit.com/r/AskEngineer...sipation_help/

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    Power loss from the MOSFETs will consist of conduction losses and switching losses. The bulk of power loss will be during switching.

    Power loss while in conduction will be equal to the duty cycle (time on / total time) * saturation voltage (Vsat) * load current across the transistor. Vsat can be further broken down as load current * characteristic saturation resistance (Rds-on). The values will use will depend on whether you're calculating from measurements or a datasheet. Switching loss will result primarily from non instantaneous voltage transition at the junction and is expressed as 1/2 * Vds-off * Id-on * (Trise+Tfall) * switching frequency. You will also have small losses from gate capacitance and leakage, but these will be minor contributions.

    Don't use Vgs. There will be negligible conduction through the gate. The only time it will come into play is if you ever calculate losses due to gate charging, and you're not doing that here. Use Vds-off, the max voltage across the transistor.

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