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famousken
famousken is offline
#4
Dec3-09, 06:20 PM
P: 108

Why does a MOSFET heat up with slow rise/fall times at gate?


Quote Quote by saad87 View Post
Thank you!

Does this phenomena occur in BJTs too? If so, why are inverter BJTs circuits used to improve the rise/fall times of the waveform?

In my case, I was recommended that I should insert a BJT inverter between the output of the comparator and the input of the MOSFET. There is a resistor connected between the collector and power supply. This resistor ends up making a RC circuit with the input capacitance of the MOSFET and due to a time constant of 1uS, the rise/fall time is much faster.

Does this make sense?

Also, do slow rise/fall times affect the switch speed of a transistor?
Exactly, an inverter circuit would be able to source/sink more current than the comperator, allowing the mosfet to switch on and off more quickly, meaning that it will be in the linear range for a shorter amount of time, thus reducing switching losses.