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MOSFET (Si/SiC) Forum Discussions

NXTY_Fujioka
Level 2
First solution authored 5 replies posted 10 sign-ins
Level 2

Could you let me how to calculate the loss of MOSFET used in PFC?

For example, in the case of MOSFETs used in DC/DC, etc., the IDS and VDS of the MOSFET repeat regular switching.

When calculating losses from real waveforms, it is generally necessary to calculate turn-on loss, conduction loss, and turn-off loss.

For an accurate calculation, the total loss could be calculated by dividing the IDS and VDS into linear sections, integrating at each section, calculating the power loss per section, and adding them together.

On the other hand, I think the basic idea is the same for PFC, but in the case of PFC, the input current is controlled to be sinusoidal, so the IDS flowing in the MOSFET also changes every cycle.

In this case, how should the MOSFET loss generally be calculated?

Thanks.

 

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1 Solution
Pablo_EG
Moderator
Moderator 250 sign-ins 250 replies posted 25 likes received
Moderator

Hello Fujioka-san,

Thank you for posting on Infineon Community.

Calculating the losses of a power MOSFET in a PFC is not simple.
There are several papers that propose different calculation methods.
However, based on your definition of switching losses, I understand that a simplistic approach (trigonometrical) should be enough in this case.
Such that the switching losses are assumed as a triangle:

Pablo_EG_0-1652147869385.png

 

Depending on the PFC type, the equations will vary.
The simplest calculation is for the critical conduction mode PFC, as it only has turn-off losses.
The output voltage is assumed to be constant and the ripple negligible.

Conduction losses:
As the current waveform is a triangle, Id is not constant.
Therefore, the following common expression needs to be integrated for a switching period.

Pablo_EG_1-1652147916008.png

After some substitution and replacing by sinusoidal expressions, we integrate for a half-period AC.
As a result, the conduction losses can be calculated by using the formula below.

Pablo_EG_2-1652147954034.png

Switching losses:
Based on the triangular power loss calculation, we start with

Pablo_EG_3-1652148007630.png

Substituting with the definition of a switching period

Pablo_EG_4-1652148066298.png

Then, we need to integrate for a half-period AC

Pablo_EG_5-1652148187063.png

With the following relations, we can substitute

Pablo_EG_6-1652148255098.png

Pablo_EG_7-1652148271195.png

And as a result, the switching losses can be calculated by using the formula below.

Pablo_EG_8-1652148311058.png

In reality, the "ton" time will vary with the phase of the AC line, which means that we can expect some error from the equation due to this.

 

If accurate losses need to be calculated, I recommend creating a simulation of your specific PFC design.

Infineon provided SPICE models for all power devices, as well as PLECS models for certain products.

Alternatively, you can find a PFC simulation circuit on our online simulator:

TINA CLOUD

Best regards,

Pablo

View solution in original post

1 Reply
Pablo_EG
Moderator
Moderator 250 sign-ins 250 replies posted 25 likes received
Moderator

Hello Fujioka-san,

Thank you for posting on Infineon Community.

Calculating the losses of a power MOSFET in a PFC is not simple.
There are several papers that propose different calculation methods.
However, based on your definition of switching losses, I understand that a simplistic approach (trigonometrical) should be enough in this case.
Such that the switching losses are assumed as a triangle:

Pablo_EG_0-1652147869385.png

 

Depending on the PFC type, the equations will vary.
The simplest calculation is for the critical conduction mode PFC, as it only has turn-off losses.
The output voltage is assumed to be constant and the ripple negligible.

Conduction losses:
As the current waveform is a triangle, Id is not constant.
Therefore, the following common expression needs to be integrated for a switching period.

Pablo_EG_1-1652147916008.png

After some substitution and replacing by sinusoidal expressions, we integrate for a half-period AC.
As a result, the conduction losses can be calculated by using the formula below.

Pablo_EG_2-1652147954034.png

Switching losses:
Based on the triangular power loss calculation, we start with

Pablo_EG_3-1652148007630.png

Substituting with the definition of a switching period

Pablo_EG_4-1652148066298.png

Then, we need to integrate for a half-period AC

Pablo_EG_5-1652148187063.png

With the following relations, we can substitute

Pablo_EG_6-1652148255098.png

Pablo_EG_7-1652148271195.png

And as a result, the switching losses can be calculated by using the formula below.

Pablo_EG_8-1652148311058.png

In reality, the "ton" time will vary with the phase of the AC line, which means that we can expect some error from the equation due to this.

 

If accurate losses need to be calculated, I recommend creating a simulation of your specific PFC design.

Infineon provided SPICE models for all power devices, as well as PLECS models for certain products.

Alternatively, you can find a PFC simulation circuit on our online simulator:

TINA CLOUD

Best regards,

Pablo