Theoretical Calculation of Losses in MOSFETs

Thread Starter

mohtishamali

Joined Jul 9, 2021
55
Good Day,

I would like to ask if we can calculate the switching losses of an MOSFET using same formulas and methodology with which switching losses of an IGBT is calculated for same application? If yes then how we can do that because there is no RDSon in IGBTs while in MOSFETs RDSon primarily contributes to the losses. If some one can give me some leads to that so that i can take that as starting point.
Thanks
 

MrAl

Joined Jun 17, 2014
11,575
Good Day,

I would like to ask if we can calculate the switching losses of an MOSFET using same formulas and methodology with which switching losses of an IGBT is calculated for same application? If yes then how we can do that because there is no RDSon in IGBTs while in MOSFETs RDSon primarily contributes to the losses. If some one can give me some leads to that so that i can take that as starting point.
Thanks
Motorola has good app notes about this.
You can estimate switching losses by assuming straight lines for current and voltage.
In modern designs though even the gate power is considered part of the losses and is one of the things that is minimized. Doesnt seem like there should be any but there is because a modern design uses a gate driver which quickly charges the gate capacitance and that takes energy.
 

Thread Starter

mohtishamali

Joined Jul 9, 2021
55
The switching losses do not depend on Rdson. The losses due to a Rdson are another term in the total losses.
Thanks for your comment
yes i agree but i need to calculate total losses that includes switching and conduction. In that case what would be the difference in computing the losses using mathematical formulas
thanks
 

Thread Starter

mohtishamali

Joined Jul 9, 2021
55
Motorola has good app notes about this.
You can estimate switching losses by assuming straight lines for current and voltage.
In modern designs though even the gate power is considered part of the losses and is one of the things that is minimized. Doesn't seem like there should be any but there is because a modern design uses a gate driver which quickly charges the gate capacitance and that takes energy.
Thanks for your valuable feedback. Could you please share the link of application notes to which you are referring?
 

MrAl

Joined Jun 17, 2014
11,575
Thanks for your valuable feedback. Could you please share the link of application notes to which you are referring?
Hi,

I think you are going to have to do a search i am not sure where the app notes are anymore, but if you have too much trouble finding them i'll look around for my old data book.
 

ronsimpson

Joined Oct 7, 2019
3,145
Switching losses from the data sheet are for a circuit with a very good layout of the PCB. The Gate resistor is known. The losses you get might be worse because of many factors.

If you have done an IGBT than you know how.
DC losses is from current and RDSon and duty cycle.
AC losses is from the crossover time(s) X frequency. (Turn on energy + Turn off energy) X frequency
 
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