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Mosfet max drain current rating

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OM222O:
Hi
I was wondering if the mosfet max drain current rating is like a limit or rather something to watch out for. I want to build a charge pump and use totem-pole fets for charging / discharging the capacitors and I'm not sure if that can damage the fets, since the current is only limited by RDSon and ESR of the capacitor which is usually way too small to do any sort of "limiting". I know in cases like capacitve discharge welders, multiple fets are used in parallel but I think in those applications the overall capacity and current are much much larger than a charge pump.

If the max drain current does not limit the current, what's the best way of achieving this? adding resistors in series with the capacitors?

Zero999:
Presumably you're talking about the surge current, when the power is first turned on? The maximum drain current is irrelevant. What's more important is whether the MOSFETs can withstand the large power surge or not. Take a look at the surge and safe operating area information on the data sheet.

OM222O:
it's not a surge current, rather a repeated pulse which charges / discharges the capacitors every cycle. I'm not sure which ratings I should consider. in lt spice simulations it seems the mosfet kind of limits the current to 2 or 3 amps peak, but just using a resistor with the same RDSon value yields upwards of 100A so I'm not sure what the limiting factor in the fet is or if the simulation is wrong.

magic:
Safe operating area, transient thermal impedance.

Zero999:

--- Quote from: OM222O on August 16, 2019, 01:26:50 pm ---it's not a surge current, rather a repeated pulse which charges / discharges the capacitors every cycle.
--- End quote ---
But those repeated pulses are small, compared to the turn on transient.


--- Quote --- I'm not sure which ratings I should consider. in lt spice simulations it seems the mosfet kind of limits the current to 2 or 3 amps peak, but just using a resistor with the same RDSon value yields upwards of 100A so I'm not sure what the limiting factor in the fet is or if the simulation is wrong.

--- End quote ---
Resistors just waste power.

What's the load current? It will have to be very high to get 100A pulses. Please post some schematics.

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