What is gate loss?

Gate charge losses are losses that, in this example, are due to the Qg (total gate charge) of external MOSFETs. Losses are equal to the product of the MOSFET Qg, the driver voltage, and the switching frequency.

What is a gate charge?

The Total Gate Charge (Qg) is the amount of charge that needs to be injected into the gate electrode to turn ON (drive) the MOSFET. The unit of Qg is the Coulomb (C), and if the total gate charge is large, it will take time to charge the capacitor necessary for turning ON the MOSFET, increasing switching loss.

How are switches losses calculated?

The switching losses during the transition from the off to the on state say on transition and vice verse say off transition can be calculated by the formula: Eon= Integral vD iD dt , on the the on time ton, and the same formula for the off period toff as an integration interval.

What causes MOSFET losses?

MOSFET switching losses are a function of load current and the power supply’s switching frequency as shown by Equation 4. Switch-MOSFET gate losses can be caused by the energy required to charge the MOSFET gate. That is, the QG(TOT) at the gate voltage of the circuit. These are both turn-on and turn-off gate losses.

What is meant by switching losses?

Switching losses occur when the power switch or rectifier is transitioning between the ON state to the OFF state and vice versa. These are frequency depend- ent since there are more transitions per second at higher frequencies.

What is gate resistance MOSFET?

MOSFET gate resistance is a very high value (much higher than megohms) and so should be of next to zero concern when working out how to drive the gate. On the other hand the gate of a MOSFET will have a capacitance.

How do I choose a gate resistor?

Select a gate resistor that will give your design a quality factor Q between 0.5 (critically damped) and 1 (under damped). A quality factor greater than 0.5 will give you faster turn-on and turn-off if needed. Start by recording the gate drive ring with no external resistance.