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Under some user suggestion, I decided to drive my 10-ohm load heater using a low side NFET. I put a 1k resistor (R1) at the NFET gate to reduce ringing. I got, before placing the resistor, a very bad Vpp of around 44V. Now the Vpp is around 26.7V. Is it ok for this kind of circuit? Or I need to add something more?

schematic

simulate this circuit – Schematic created using CircuitLab

Here is the oscilloscope output:

enter image description here

enter image description here

Do I need to add an input filter for my circuit? Is it needed? I would like to use a standard (certified) desktop power supply at 24V.

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    \$\begingroup\$ Your requirements need twisted pair to reduce load inductance and a spec for heat rise. Overshoot will reduce but is normal. The overshoot is not an issue unless you define it. ( do U have a spec?) The risetime appears to be under the SOA curve for the result. \$\endgroup\$
    – Tony Stewart EE75
    Commented Jun 14, 2021 at 17:04
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    \$\begingroup\$ For a 40 V transistor, I would call it ok if this is your worst case scenario. You could perhaps get away with an RC snubber across your MOSFET if you need to damp further. What’s your max switch frequency you are planning on? \$\endgroup\$
    – winny
    Commented Jun 14, 2021 at 19:18
  • \$\begingroup\$ Have you an idea about the heater inductance ? \$\endgroup\$
    – user288518
    Commented Jun 14, 2021 at 19:47
  • \$\begingroup\$ @winny switching frequency should be 60Hz or 30Hz. I need to test them both. \$\endgroup\$
    – Daniele
    Commented Jun 15, 2021 at 7:38
  • \$\begingroup\$ If you go with external RC, calculate your losses in R for 60 Hz and your max input voltage. \$\endgroup\$
    – winny
    Commented Jun 15, 2021 at 8:32

1 Answer 1

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To discharge the Cgs capacitance quicker you may add an RD network in parallel to R1.

R = 47 to 100 Ohm D = 1N4148 or BAS16

The anode of D is connected to the gate of the MOSFET.

The cathode of D is connected to R.

This RD network is not an odd invention of mine but it's quite often used when driving the gate of an N MOSFET.

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