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# Mosfet Conduction Loss formula

## Mosfet Conduction Loss formula

Level 1
Level 1

Based on "MOSFET Power Losses Calculation Using the Data-Sheet Parameters" application note, Conduction losses mosfet for a Three-Phase AC motor drive contain a current expression equal to Io^2*(1/8+ma*cos(phi)/3*pi).

My question is: How the terms (1/8+ma*cos(phi)/3*pi) comes from?

Any reference on how to calculate the terms?

Thanks very much

6 Replies
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## Re: Mosfet Conduction Loss formula

Moderator
Moderator

Hi,

Thank you for posting on the Infineon community.

Please refer section 4 of the attached document. Let me know if you have any further doubts.

Regards,
Abhilash P

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## Re: Mosfet Conduction Loss formula

Level 1
Level 1

Thanks for the reply. Very useful doc.

Another question. The expression for the Idc in the next formula is calculated as Idc = Io*(1/pi). This should be the average sine current value in half cycle (0 to pi)

The average value of half-cycle sine (0-pi) based on the application of the average integral formula should be Iavg = Io*(2/pi).

So why it has been considered (1/pi) as average factor and not (2/pi)?

Thanks

## Re: Mosfet Conduction Loss formula

Moderator
Moderator

Hi,

The calculated Idc is based on the assumption that a DC current equivalent to AC is flowing, then it is 1/pi

Regards,
Abhilash P

## Re: Mosfet Conduction Loss formula

Level 1
Level 1

Whic formula applies to get 1/pi?

## Re: Mosfet Conduction Loss formula

Moderator
Moderator

Hi,

As explained in my previous response, the 1/pi is used on the assumption that a DC current equivalent to AC is flowing.

Regards,
Abhilash P

## Re: Mosfet Conduction Loss formula

Level 1
Level 1

I understand that 1/pi is used as assumption that a DC current is flowing, but how to derive the terms 1/pi?

Which formulas have been used to transform a sine current into a 1/pi DC current?

Thanks