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Re: MOSFET specs for RAMPS

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Apart from the parameters you mentioned, the other critical one is Rds(on) measured at Vgs= 4.5V. Multiply this by the square of the maximum current that the mosfet will be required to pass to get the static power dissipation. Try to keep this down to 1W or less, then you won't need a heatsink.

You don't need a voltage divider on the gate. You need a gate series resistor to moderate the load on the Arduino output and slightly slow down the switching time, to avoid ringing, avalanching and excessive EMI. A suitable value is 100 to 180 ohms. A high value resistor to ground is also recommended so that the mosfet is held off when the Arduino output pin has not been initialised.

From memory, I think Farnell sells the IRLU8743, which is the same as the IRLB8743 but in a slightly different package, still suitable for through hole mounting but less suitable for attaching a heatsink.

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