DC dimmer circuit

MOSFET turn on (and off) time is determined by drive current (Ig) and MOSFET gate charge (Qg). Based on datasheet specifications for IRF5210, we can calculate drive current required for a target Ton (50ns) as follows:

Ig = Qg / Ton = 180nC / 50ns = 3.6A

Assuming a nominal voltage of 13.7, this dictates a total gate resistance as low as 3.8 ohm (13.7V / 3.6A). Output resistance for the TC4429 is specified as 2.5 Ohm and so the gate resistor should be 1.4 Ohm (3.8 – 2.5).

To get to 80ns (as quoted in the datasheet) and using TC4429/IRF5210, Rg should be 3.7 Ohm.

Another useful calculation is to check if a heat sink is required. With a load of 8A, the MOSFET will drop about 3.84W (8A * 8A * 0.06 Ohm). Max wattage for a TO-220 package is about 1W and so a heat sink will be required.