Does heat of MOSFET caused by its conduction losses or switching losses? or by both?
if the heat of MOSET causd by both its conduction losses and switching losses, which is dominating reason?

thank u

Rg.

 

Heat of MOSFET
Does heat of MOSFET caused by its conduction losses or switching losses? or by both?
if the heat of MOSET causd by both its conduction losses and switching losses, which is dominating reason?

thank u

Rg.

 

Heat is caused by current passing through a resistance.

 

This Application Note shows a circuit with two MOSFETs. One has losses dominated by the switching losses and the other by conduction losses.

http://www.fairchildsemi.com/an/AN/AN-6005.pdf

 

Very vague question, but assuming you mention switching losses because the devices is switching...

Typically the switching losses predominate. Conduction losses are minimal, especially with a modern fet with a near zero on resistance.

Switching losses, while only generated during brief intervals, will be the predominant contribution, especially during turn off.

At turn off you have a large current flowing which requires the fet turning off by increasing resistance, so the voltage across is rising as the current thru is falling.

Back when I did switching supplies we could see both current and voltage on our scope, frequently we would see the voltage across the fet go to half the supply as the current had only fallen to half its max.

That be alotta power, you betcha.

 

Remember that power = IV for any device. If your Mosfet works in any region P dissipated = ID * VDS.
The mayor dissipations are in the saturation region. because VDS is big.
The minor dissipations are in the cutt off region, because thereisno current, and triode because VDS is the the minimum compared to the VDS in the saturation region.
However in switching operation, that means the mosfet must go from triode to cut off, for a very small instant the mosfet passes for the saturation region. But remember that there are no rising and falling times, the time that takes in the saturation region, equals to cero. so when switching frequency increases so the losses due the conmutaion does beacuse the time in the saturation region increases compared the high and low states.

greetings

 

Hello,

I merged both threads to keep the information together.

Bertus