Do not use pwm for heated bed. I would certainly avoid doing that. When mosfet opens and closes, before reaching its end state (fully open), it goes through a state where its partially open and the difference that cant flow through has to be burned out in heat. At high currents of a power mosfet and a bed, that is going to be big. So better avoid having the mosfet through the transition zone as much as possible. So pwm-ing means you just abuse the mosfet making it go through transition zone a lot, repetitively. Even as that is just a relatively fast transition, a tiny fraction of time, because the current is high, the dissipation during that is again high, so overall becomes relevant. On a modern switched mode power supply the biggest losses are switching losses. Simple solution for us, just avoid pwm switching the bed because its not necessary. Bang-bang at full on and full off works fine.
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