Electronic – Back-to-Back N-MOSFET inrush current limiting

mosfetpowermosfet

I try to develop an application where I need to switch 55V at 20A in both directions using MOSFETs.

Because of the high current, I decided to use N-MOSFETs (because they are available with lower rdson) back to back and using a photvoltaic MOSFET driver to switch the gates.

My problem now is that the load I try to switch has a lot of capacitance (about 20 mF) which kills my MOSFETs every time because of the high power dissipation during the switching transition.

I already tried to to use an RC Lowpass to drive the gates more slowly through the threshold but the power dissipation is still too high, peaking at 200W (see simulation)

enter image description here

Is there any way I can limit the inrush current using this back to back topology?

Best Answer

@20 A, I'd have been looking at relays already, but you likely have a reason for Mosfets.

If opening an alternate path to alleviate the load on the mosfets (routing it through a high wattage resistor) is an option, you could try that. Essentially you:

  1. Allow a path through a high wattage resistor (this reduces the current that your mosfets would have to halt)
  2. Halt flow through your mosfets
  3. Halt flow through high wattage resistor

General idea is that by splitting it up over 2) and 3) you need to halt smaller currents at each step. The resistor gives another outlet for the 20mF to discharge while the main path was shut.

That all said, something is bugging me about your mosfet use. I feel like using all N mosfets (or even all P) and "both directions" is setting off a big red flag somewhere, the kind that tells me not to power a circuit up when those words are together.

Related Topic