N-channel MOSFET
An N-channel MOSFET conducts current from drain to source whenever the gate sits sufficiently above the source. It's the workhorse switch and amplifier of modern electronics — efficient, fast, and easy to drive.
In an enhancement-mode N-channel MOSFET, suitable positive gate-to-source voltage forms a conducting channel. The insulated gate draws little steady current but must be charged and discharged when switching. Real leakage, gate-voltage limits, body-diode behaviour and the specified on-resistance conditions still matter.
In plain terms
Think of a valve controlled by an electric field. Threshold is when it just starts to open, not when the flow path is wide open. The gate needs very little steady current, but changing its voltage quickly still means moving charge.
Why designers use it
- Switch a high-side or low-side load from a microcontroller pin (with a driver if needed).
- Form the high-frequency switching elements of buck, boost, and synchronous regulators.
- Drive motors, solenoids, and LEDs at currents well beyond what a logic pin can handle.
- Build low-noise analog amplifiers with extremely high input impedance.
Best for
- Low-side switching
- Buck/boost
- Motor drive
Key specifications
- VDS rating: Allow for supply and switching transients
- RDS(on): Specified at a particular VGS and temperature
- Continuous current: Depends on thermal and package limits
- VGS(th): Beginning of conduction, not fully-on voltage
- Gate charge: Determines charge the driver must move
- Switching loss: Depends on the device, driver and circuit
When not to use it
- When you need to switch the high side of a rail above the gate's pin — use a P-MOSFET or a high-side driver.
- When the datasheet does not specify an acceptable on-resistance at your available gate-source voltage.
Common mistakes
- Using threshold voltage as the fully-on gate-drive requirement.
- Assuming a 3.3 V output can drive any MOSFET at the required current and speed.
- Leaving the gate floating or selecting gate resistors without considering the driver and switching requirements.
- Exceeding gate-to-source, drain, current or thermal limits.
Where you will find it
- A low-side load switch places the MOSFET between the load and ground. Its gate driver must provide enough gate-source voltage for the required on-resistance.
- A high-side N-channel switch sits between the supply and load. Its driver must raise the gate above the moving source voltage, not just above ground.
- In a switching DC-DC converter, lower on-resistance can reduce conduction loss, but gate charge and switching loss also affect the best device choice.
A short history
The Computer History Museum describes early MOS transistor development at Bell Labs, RCA and Fairchild. Its 1964 commercialization account distinguishes General Microelectronics and Fairchild's p-channel devices from RCA's n-channel 3N98. That distinction matters: the history of MOS devices as a whole must not be presented as the history of n-channel products alone.
Good to know
- A MOSFET can be above its threshold voltage and still be a poor power switch. Check the on-resistance specified at the gate voltage you can actually provide.
- The lowest on-resistance is not always the lowest-loss choice. A larger device can require more charge to switch.
- A floating gate can hold enough charge to turn a MOSFET on unintentionally. A suitable gate-to-source resistor helps define its off state.