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
MOSFET Gate Drive: Practical Design Guide
Use this calculator when designing a PWM power stage: motor H-bridge, DC-DC converter, LED dimmer, solenoid driver. The two critical parameters are Qg (total gate charge from the datasheet) and your switching frequency. Example: an IRF540N has Qg=71nC. At 100kHz with a 10V gate drive and 10Ω gate resistor, the gate drive power is 71nC×10V×100kHz=71mW — easily handled by a logic gate driver IC like the TC4420.
The gate resistor Rg controls how fast the gate charges. A larger Rg slows the transition, reducing gate ringing and EMI but increasing switching losses (the MOSFET spends more time in its linear region during each transition). A smaller Rg switches faster but can cause ringing on the drain that damages the MOSFET or radiates EMI. Typical values for low-power applications: 10–47Ω. For high-frequency power converters: 4.7–22Ω.
For N-channel low-side switching (most common), the gate drive is straightforward — the source is at ground. For N-channel high-side switching (better efficiency for buck converters), you need a bootstrap or charge pump circuit to drive the gate above the drain voltage. Logic-level MOSFETs (Vth < 2V) can be driven directly from 3.3V microcontrollers like Arduino or ESP32 without a gate driver IC, but only at low switching frequencies.
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
MOSFET key parameters
Id = (µn × Cox / 2) × (W/L) × (Vgs – Vth)² (saturation)Pd = Id² × Rds(on) (conduction)Psw = ½ × Vds × Id × (tr+tf) × fsw (switching)t_switch = Qg / Ig_driver | FOM = Qg × Rds(on) (lower = better)Popular MOSFET Reference
| Part | Type | Vds | Id | Rds(on) | Qg | Package | Application |
|---|---|---|---|---|---|---|---|
| 2N7000 | N | 60V | 0.2A | 5Ω | 1nC | TO-92 | Logic-level, signal |
| BSS138 | N | 50V | 0.2A | 3.5Ω | 1nC | SOT-23 | Level shifter |
| IRLZ44N | N | 55V | 47A | 22mΩ | 48nC | TO-220 | Motor drive, 5V gate |
| IRF540N | N | 100V | 33A | 44mΩ | 71nC | TO-220 | Power switching |
| IRFZ44N | N | 55V | 49A | 28mΩ | 59nC | TO-220 | H-bridge, DC motor |
| AO3401 | P | 30V | 4A | 90mΩ | 6nC | SOT-23 | High-side switch |
| IRF9540N | P | 100V | 23A | 117mΩ | 95nC | TO-220 | High-side power |
| SiS412DN | N | 30V | 12A | 10mΩ | 8nC | PowerPAK | Sync rectifier |
Practical Examples
Arduino PWM motor control (12V, 2A)
Gate: 5V PWM → IRLZ44N (logic-level, Vth=2V). Rds(on)=22mΩ.
Pd = 2² × 0.022 = 88mW. No heatsink needed.
Add 10Ω gate resistor to suppress ringing.
High-side P-channel switch (12V load, 500mA)
Use AO3401 P-MOSFET. Vgs = 0V (on), –12V (off). Drive with NPN BJT.
Pd = 0.5² × 0.090 = 22.5mW << 1.4W max. SOT-23 sufficient.
Design Tip
For logic-level gates (3.3V/5V MCU), choose MOSFET with Vth < 2V. Always add a gate resistor (10–100Ω) to damp switching oscillations. Add a pull-down (10kΩ) on gate to ensure MOSFET stays off during power-up. Bootstrap gate drivers needed for high-side N-channel switches (e.g., IR2110).
Did you know? The MOSFET (1960, Atalla & Kahng) is the most widely manufactured device in history — with over 13 sextillion (10²²) MOSFETs produced as of 2020. Every smartphone contains several billion of them. Modern process nodes (2–3 nm) make individual gates smaller than a virus.