Figure of Merit of power MOSFETs used in driving a PMDC Motor

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I am an engineering student doing a project on power electronics. While looking for some material related to MOSFET gate drive circuits for control of motors I came across
[1] Mößlacher Christian and Guillemant Olivier, Simple Design Techniques for Optimizing Efficiency and Overvoltage Spike of Synchronous Rectification in DC to DC Converters, Application Note AN 2012-03 V 2.1. March 2012, Infineon Technologies Austria AG, 2011. (page 5)

I shall be really grateful if I could have the answers to some queries in regard to topics mentioned in the note. I am working on optimizing a power MOSFET driver circuit for a PMDC motor with a PWM input at the gate for speed control. I wished to know how should I be calculating the FOM for a power MOSFET used for this application and whether this value would be significant for determining the optimum Rds(on) value and gate voltage amplitude and frequency.

Regards,
Surabhi Agarwal
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1 Solution
Dipti_Kiran
Moderator
Moderator
Moderator
250 sign-ins 10 likes received 50 replies posted

Hi,

The FOM for a power MOSFET used for certain application can be calculated using the formula:

Dipti_Kiran_0-1663062584279.png

By knowing the Vout and Iout for a desired application, Vds and Id of a MOSFET is determined. Based on Vds and Id, a list of MOSFET is available for certain application.

FOM is calculated for the list of available MOSFET by finding Qg and Rds(on) from the datasheet. The MOSFET with lowest FOM is chosen for certain application but we cannot say Rds(on) calculated from lowest FOM is the optimum one.

 FOM would not be significant for determining gate voltage amplitude and frequency as gate voltage and frequency is application dependent.

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1 Reply
Dipti_Kiran
Moderator
Moderator
Moderator
250 sign-ins 10 likes received 50 replies posted

Hi,

The FOM for a power MOSFET used for certain application can be calculated using the formula:

Dipti_Kiran_0-1663062584279.png

By knowing the Vout and Iout for a desired application, Vds and Id of a MOSFET is determined. Based on Vds and Id, a list of MOSFET is available for certain application.

FOM is calculated for the list of available MOSFET by finding Qg and Rds(on) from the datasheet. The MOSFET with lowest FOM is chosen for certain application but we cannot say Rds(on) calculated from lowest FOM is the optimum one.

 FOM would not be significant for determining gate voltage amplitude and frequency as gate voltage and frequency is application dependent.