How Much Current Is Required to Drive a MOSFET?

Many engineers hold a misunderstanding: MOSFETs are voltage-controlled devices, so no driving current is needed.

In fact, almost no current flows through the gate under steady-state conditions. However, instantaneous peak current is required to charge and discharge the gate capacitance during switching. The magnitude of driving current directly affects switching speed, heat generation, EMI performance and MOSFET reliability.

1. Basic Principle

The MOSFET gate is equivalent to a capacitor. Turning the device on or off essentially charges and discharges the gate capacitor.

Core formula:

Ipeak = Qg ÷ tsw

Qg: Total gate charge (check datasheet, unit: nC)
tsw: Target rise/fall switching time (unit: ns)

Key concept distinction

Peak current: Pulse current at switching transients, which determines switching speed. This is the primary indicator for driver IC selection.
Average driving current: Ig_avg = Qg × fsw, used to evaluate continuous heat generation of the driver IC.

2. Practical Engineering Reference (For BLDC Motors & Switching Power Supplies)

Small-signal MOSFET (AO3400, 2N7002, low-load switching)

Qg ＜ 5 nC

Recommended peak driving current: 50mA ~ 200mA

Applications: Signal switching, low-current load switches

⚠️ Direct driving via MCU GPIO works in some scenarios, but a push-pull buffer is still recommended for high-frequency operation.

Medium & small-power SMD power MOSFET (Widely used in BLDC fan & water pump controllers)

Qg: 20 ~ 60 nC

Recommended peak driving current: 0.5A ~ 1.5A

Most consumer BLDC pre-driver ICs offer 0.6A ~ 1.2A peak driving capability.

High-power silicon MOSFET (E-bikes, high-power power supplies)

Qg: 80 ~ 150 nC

Recommended peak driving current: 2A ~ 4A

SiC MOSFET

Lower gate charge, yet strict control of switching edges is required

Recommended peak driving current: 2A ~ 5A

3. Calculation Example for BLDC Design

MOSFET Qg = 50 nC, target switching time = 50 ns

Ipeak = 50nC ÷ 50ns = 1A

A safety margin of 1.3~1.5 times should be reserved for engineering design. The driver IC must support at least 1.3A peak current.

4. Two Common Design Pitfalls

Source current and sink current are equally critical

Many driver ICs have asymmetric source and sink parameters. Insufficient sink capacity easily causes Miller-induced false turn-on, leading to shoot-through and permanent damage of upper/lower bridge MOSFETs.
Higher driving current does not equal better performance

Excessive driving current creates ultra-fast switching edges and high dv/dt, resulting in severe gate oscillation, EMI noise and voltage spikes.

Solution: Add a gate resistor (Rg) to limit peak current, balancing power loss and EMC performance.

5. Summary for BLDC Brushless Motor Design

Standard 3-phase BLDC with 10kHz ~ 20kHz PWM frequency

Medium & low-power solutions: Select pre-driver ICs with 0.6A ~ 1.2A peak driving capability
High-speed high-power motors: Adopt drivers with peak current above 2A