MOSFET Calculator
Calculate gate resistor, gate power, and switching times for N-channel MOSFET circuits.
Component Values
Results
N-Channel MOSFET — Low-Side Switch
Vgs vs Id — Transfer Curve
How do MOSFET gate drive circuits work?
A MOSFET is a voltage-controlled switch: applying a voltage above Vth to the gate turns it on, allowing current to flow from drain to source. Unlike BJTs, the gate draws essentially no DC current — but it does have capacitance (Qg) that must be charged and discharged at every switching cycle.
The gate resistor Rg limits the peak current during switching transitions, reducing voltage ringing and EMI. Too small an Rg causes ringing; too large an Rg slows switching and increases power loss. The gate drive power Pg = Qg × Vgs × f increases linearly with frequency.
N-channel MOSFETs are preferred for low-side switching because they can be driven directly from a logic-level signal. P-channel MOSFETs are used for high-side switching but require inverted gate drive. Enhancement-mode MOSFETs (normally off) are standard for switching applications.
Gate Power
Pg = Qg × Vgs × fGate Resistor
Rg = Vdrv × t_rise / QgKey Points
- Gate is capacitive: Qg must be charged every switching cycle
- Rg controls switching speed and ringing
- Power loss increases with frequency: Pg = Qg × Vgs × f
- Logic-level MOSFETs have Vth < 2.5V for direct µC drive
Applications
- PWM motor control and H-bridges
- DC-DC converter power stages
- LED dimming circuits
- Power switch and load control