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shaiqbashir

Problem in an H-Bridge

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hai audioguru,
can u recommand what type of mosfet driver ic?
i have try to put the diod across the the drain and source mosfet, but the result is same. if i using the snubber at every mosfet to cut out the over shoot current when turn on and off the mosfet, itz can reduce the over heat?? 

thanks for ur reply..... :)

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I don't know which Mosfet driver ICs you can buy, there are many of them.
Get one that has a bootstrap diode for a boosted voltage to the gates of its high side Mosfets.

Your Mosfets overheat because the 10k resistors charge and discharge their high input capacitance slowly and therefore they are ramping instead of quickly switching.

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Hai audioguru,

if i using the snubber at every mosfet to cut out the over shoot current when turn on and off the mosfet, itz can reduce the over heat?? 

Your Mosfets overheat because the 10k resistors charge and discharge their high input capacitance slowly and therefore they are ramping instead of quickly switching.

u mean the charging and dischagrging slow will cos the mosfet heat?? Can i reduce the resistor 10K? so that the charging and discharging time will more faster and the heat will reduce.

is there any way to modified the circuit so that the mosfet won't over heat?? cos i didn't have much time to change type of mosfet again.

thanks for ur replying.......... :)

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A 10k resistor charges or discharges the 3nF capacitance of a Mosfet in about 30us. A Mosfet would be heating for that 30us.
If your PWM frequency is 50kHz then each half-cycle is only 10us long so the Mosfets are never fully turned on and are not fully turned off. They are heating all the time.

A Mosfet driver iC provides about 1A of current to charge and discharge the capacitance of a Mosfet very quickly so it is linear for a short time so it stays cool.

Reduce the PWM frequency to 500Hz to see the Mosfets become much cooler when they are turned on and off with 10k resistors.

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