Electronics > Beginners

How to drive a low Rdson mosfet for PWM

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sahko123:
Im trying to drive a heater element in a jbc t245 soldering iron and I'm having issues getting an Rdson of less than 2-3ohms which for a 2.5 ohm heater element, means that half of the power gets burned away into heat in the mosfet and the other half gets turned into heat on purpose. The mosfet I am using is a PSMN1R1-40BS mosfet with a quoted Rdson of 1.3mOhms and im trying to get at most 500mOhm. I've not used power mosfets too often so im definetely doing something wrong just not sure what it is.

The circuit below is what im using. There is pwm coming from an arduino nano every.
[attach=1]

My main question is how do I go about driving the mosfet to be able to get as low an Rdson as possible?

rob77:
why on earth are you using a N-channel mosfet as a high side switch ?

sahko123:

--- Quote from: rob77 on May 16, 2022, 11:35:05 am ---why on earth are you using a N-channel mosfet as a high side switch ?

--- End quote ---

Because I am not familiar with mosfets. Why shouldnt i use it as a high side switch?

rob77:

--- Quote from: sahko123 on May 16, 2022, 11:36:31 am ---
--- Quote from: rob77 on May 16, 2022, 11:35:05 am ---why on earth are you using a N-channel mosfet as a high side switch ?

--- End quote ---

Because I am not familiar with mosfets. Why shouldnt i use it as a high side switch?

--- End quote ---

because when you open it, the voltage at it's source will raise to supply voltage as the gate is and it will immediately close itself.. when N-chan is used as high side it has to have it's gate driven with voltage above supply voltage.

furthermore 24V is not safe  for the gate , Vgs max of your mnosfet is 20V, so it will not work (problem above) and most probably just kill your mosfet.

best way is to move your load into the drain - use the mosfet as a low side switch and use a proper gate driver.

RoGeorge:
The schematic in the OP is not the best, here's why and a way to fix it:



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