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I'm attempting to switch a resistive DC load (50VDC @ 10 amps) using an N-channel MOSFET.

This is the particular MOSFET I'm considering. https://www.ti.com/lit/ds/symlink/csd18536kcs.pdf

On page 1 there is a plot for Vgs vs Rds(on). I will be powering the gate using a microcontroller GPIO pin at 3.3VDC.

Rds(on) appears to be very large at 3.3V, meaning a lot of heat will need to be dissipated, correct?

In my circuit, I have 7VDC available (regulated down to 3.3VDC for the microcontroller). I was thinking of driving the power MOSFET gate with another MOSFET at 7VDC.

Is this commonplace? Is this there a name for this pairing? Using this pairing, under a watt of power will need to be dissipated as heat, correct?

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  • \$\begingroup\$ I would recommend driving the MOSFET 5V. If you have a 7V supply, use it to drive the MOSFET. Look for a logic level shifter circuit. \$\endgroup\$ Apr 23, 2021 at 15:00
  • \$\begingroup\$ Yes this is commonplace, and it's called a "gate driver". The driver transistor can also be a BJT. If you do some basic research, make a first try at the driver circuit, and update the question with some more information about your circuit (e.g. switching frequency, which matters) you might get better answers here on how to improve it. \$\endgroup\$
    – Theodore
    Apr 23, 2021 at 15:20
  • \$\begingroup\$ That's a rather big MOSFET for driving only 10A \$\endgroup\$
    – user28910
    Apr 23, 2021 at 15:42

1 Answer 1

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You should not use less than 5V to drive the gate.

If you use a commercial gate driver chip such as the MCP1415 you can turn that MOSFET on and off relatively quickly which will reduce the dissipation during switching. 140nC is a fair bit of charge to deal with- some gate drivers can supply 5 or 6A peak current. They also level-shift.

It's also possible to make a simple gate driver with a few BJTs that will also level shift to 7V, and would be perfectly suitable for lower switching frequencies.

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  • \$\begingroup\$ Thank you. Accepted answer. Gate driver is what I need. As someone else mentioned, that MOSFET is rather big for my requirements so I'll be using this MOSFET which seems to be closer to the size I need. ti.com/lit/ds/symlink/csd18534kcs.pdf \$\endgroup\$
    – cbake
    Apr 23, 2021 at 17:46
  • \$\begingroup\$ The advantage of the first one is that you won't need a heatsink (based on 10A continuous). The second one you definitely will, more than 2W dissipation worst-case. \$\endgroup\$ Apr 23, 2021 at 17:55

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