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Choosing Power Mosfet.

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mengghee

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choose mosfet

Hi, I am currently trying to build a boost converter and i am wondering .. what is the main consideration that i need to know in choosing a mosfet. I am designing a 5V to 10V boost converter with 500mA load current and my switching frequency is 50Khz. thank you

regards,
mengghee
 

how to choose mosfet

for choosing MOSFET you must consider:
Vds: minimum 1.5-2 times of maximum voltage you need.
RdsOn: minimum Rds is in the on-state, choose this so that conduction loss as low as possible.
Switching parameter : such as input capacitans and turn-on time turn off time.

For your design i think you can choose MOSFET with following parameter:
Vds (max): greater than 30-40V
Rds(on): smaller than 0.5 ohm
Turn-on & Turn-off time : smaller than 200nS (50KHz> period 20uS)
Cin depend on your drive output impedance.

for your design try with IRF530.

Note: some of these value are experimental values. i hope there are helpfull.
 
how to select power mosfet

It really depends on what kind of process you have. You should choose a device which breakdown to sub is more than the boost voltage. It have a lot of paper in IEEE, you better goto read some.
 

    M

    mengghee

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how to choose a mosfet

davood,

what do you mean by cin ?? thank you

regards,
Jeffrey
 

cin mosfet

Hi mengghee
Sorry for late,
Cin is equivalent input capacitance which seen from input pin.
it is sum of Cgs+Cgb+(Cgd°)
Cgd° is subject to miller effect

I can say Cgd° ≈ Cgd * (Δ Vds) / (Δ Vgs)
 
selecting power mosfet parameters

what is the difference between cgd° and cgd ? thank you

regards,
mengghee
 

how to choose a power mosfet

I use [°] just for notation.
because its value proporation of Cgd and feedback.
becouse we have feedback, actual value of Cgd capacitance is multiplied by voltage gain, and input capacitance is much more.
as i remember, this effect called miller effect

Regards.
 
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