N-Channel MOSFET Symbol
Definition: The N-Channel MOSFET symbol represents an enhancement-mode n-channel metal-oxide-semiconductor field-effect transistor (MOSFET) defined in IEC 60617-05 and ANSI Y32.2 / IEEE 315, depicted as a gate electrode separated from the semiconductor body by an insulating layer, with drain and source terminals, and a body diode arrow pointing from source to drain (i.e., arrow pointing inward toward the channel line).
Also known as: NMOS, N-channel FET, enhancement NMOS, power MOSFET n-channel, n-type MOSFET.
What the N-Channel MOSFET symbol means
The N-Channel MOSFET symbol denotes a voltage-controlled switch or amplifier in which a positive gate-to-source voltage (Vgs) greater than the threshold voltage (Vth) creates a conducting n-type channel between the drain and source terminals. When Vgs < Vth, the device is off and the drain-source channel is non-conducting.
In circuit schematics the N-Channel MOSFET symbol conveys that the device is driven by voltage (not current), has a very high input impedance at the gate, and can switch or amplify signals with minimal gate drive power. The three pins — Gate (G), Drain (D), and Source (S) — are labelled, with drain conventionally at the top and source at the bottom for an N-channel device handling conventional positive load current flowing from drain to source when on.
How to identify the N-Channel MOSFET symbol
The N-Channel MOSFET symbol consists of a vertical channel line at the centre, a gate line to the left separated from the channel by a gap (representing the oxide insulator), and two horizontal lines extending right from the channel to represent the drain (upper) and source (lower) connections. An arrow on the body or source line points inward (toward the channel), indicating N-channel polarity — the opposite direction from the P-channel MOSFET where the arrow points outward. A parasitic body diode is often shown between source and drain.
Function in a circuit
The N-Channel MOSFET acts as a voltage-controlled switch in digital and power circuits, and as a variable resistor or amplifier in analogue circuits. Applying a gate voltage above the threshold (typically 2–4 V for logic-level MOSFETs, 4–10 V for standard power types) inverts the p-type body beneath the gate oxide, forming an n-type conducting channel. Drain current flows from drain to source (conventional current) proportional to Vgs − Vth in the linear region, or is limited by the load in the saturation region. NMOS devices are preferred for low-side switching because the source pin connects to ground, keeping Vgs easily achievable from a logic supply.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-05 defines the MOSFET symbol for insulated-gate field-effect transistors. The N-channel enhancement-mode MOSFET uses an arrow pointing toward the channel line to indicate the N-channel body polarity. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315-1975 defines the IGFET (insulated-gate FET) symbol. The N-channel enhancement-mode type uses the same inward-pointing arrow convention as IEC; the gate is shown as a line separated from the channel by a gap representing the gate oxide. |
| Key difference | IEC 60617 and ANSI/IEEE 315 symbols are functionally identical for the N-channel enhancement MOSFET. Minor drafting differences exist in line weights and whether the body terminal is shown explicitly, but the arrow direction (inward = N-channel) is the same in both standards. |
Terminals / pins
| Pin | Name |
|---|---|
| gate | Gate |
| drain | Drain |
| source | Source |
Typical values
Gate threshold voltage (Vth): 2–4 V (logic-level) or 4–10 V (standard). Drain-source on-resistance (Rds(on)): 1 mΩ–10 Ω depending on voltage rating and die size. Drain-source voltage (Vds): 20 V–1700 V. Continuous drain current (Id): 0.1 A–hundreds of amperes for power devices. Gate-source voltage (Vgs): typically ±20 V maximum. Popular examples: IRF540N (100 V, 33 A), 2N7000 (60 V, 200 mA), AO3400 (30 V, 5.7 A).
Where the N-Channel MOSFET symbol is used
- Low-side power switching of DC loads (motors, solenoids, LEDs) driven directly from microcontroller GPIO pins via a gate resistor
- H-bridge motor driver circuits where lower NMOS devices switch the ground side of each motor winding
- Synchronous buck converter switching stages where NMOS devices replace the freewheeling diode for higher efficiency
- Logic-level gate drivers where a small NMOS (2N7000, BSS138) translates a 3.3 V signal to switch a 12 V load
- RF switch and attenuator circuits where NMOS devices are used in their linear region for variable resistance
- Battery protection circuits in lithium-ion packs where a back-to-back NMOS pair controls charge and discharge paths
Example
In an Arduino motor-control circuit, an IRL520N (logic-level NMOS, 100 V, 10 A) has its Gate connected through a 220-ohm resistor to Arduino pin D9 (PWM), its Source connected to GND, and its Drain connected to the negative terminal of a 12 V DC motor. A flyback diode (1N4007) is connected across the motor. When pin D9 goes HIGH (5 V), Vgs ≈ 5 V > Vth ≈ 2 V, the channel conducts and the motor runs. Duty-cycle PWM on D9 controls motor speed.
Key facts
- The N-Channel MOSFET is an enhancement-mode device: it is normally off (non-conducting) and turns on when the gate-to-source voltage (Vgs) exceeds the threshold voltage (Vth), typically 2–10 V depending on the device.
- The body diode arrow in the NMOS symbol points inward toward the channel line, indicating the N-channel type — this distinguishes it from the P-channel MOSFET (PMOS) where the arrow points outward.
- The NMOS has three primary pins: Gate (G), Drain (D), and Source (S); the Source is typically connected to ground in low-side switching configurations, making Vgs equal to the gate drive voltage.
- NMOS devices are preferred over PMOS for high-current low-side switching because for a given die area they have lower on-resistance (Rds(on)) due to higher electron mobility in the n-type channel.
- The gate input impedance of a MOSFET is very high (>10 MΩ DC) because the gate is insulated by silicon dioxide; however, gate capacitance (Cgs, Cgd) limits switching speed and requires a low-impedance gate driver for fast transitions.
- High-side NMOS switching requires a bootstrap or charge-pump gate driver to raise Vgs above the drain voltage, because the source sits at the high rail voltage rather than ground.
- IEC 60617-05 and ANSI Y32.2 / IEEE 315 both define the N-channel enhancement MOSFET symbol with an inward-pointing body arrow and a gate separated from the channel by an insulating gap.
Frequently asked questions
What does the N-Channel MOSFET symbol mean in a circuit diagram?
The N-Channel MOSFET symbol represents a voltage-controlled semiconductor switch or amplifier. A positive gate-to-source voltage above the threshold (Vth, typically 2–10 V) turns the device on, allowing current to flow from drain to source. It is defined in IEC 60617-05 and ANSI Y32.2 / IEEE 315.
What does the NMOS symbol look like and how do I identify it?
The NMOS symbol has a vertical channel line in the centre, a gate line to the left separated from the channel by a gap (the oxide insulator), drain at the upper right, and source at the lower right. The body diode arrow points inward toward the channel — an inward arrow means N-channel. The P-channel MOSFET has the arrow pointing outward.
What is the difference between NMOS and PMOS symbols?
In the NMOS symbol the body arrow points inward (toward the channel line), while in the PMOS symbol the body arrow points outward (away from the channel line). Functionally, NMOS turns on with a positive Vgs, while PMOS turns on with a negative Vgs (gate lower than source voltage).
What are the pin names on the N-Channel MOSFET symbol?
The N-Channel MOSFET has three pins: Gate (G, the control input), Drain (D, conventionally at the top — the terminal current flows into from the load), and Source (S, at the bottom — connected to ground in low-side switching). A four-pin symbol also shows the Body (B), which is internally connected to Source in most discrete devices.
What standard defines the N-Channel MOSFET symbol?
IEC 60617-05 defines the insulated-gate FET symbols, including the N-channel enhancement MOSFET. ANSI Y32.2 / IEEE 315-1975 defines the equivalent IGFET symbol. Both standards use an inward-pointing body arrow to indicate the N-channel type.
Why is NMOS preferred for low-side switching?
NMOS is preferred for low-side switching because the source is connected to ground, making the gate-to-source voltage (Vgs) equal to the gate drive voltage. This is easily achieved from a logic-level supply. Additionally, electron mobility is about twice that of holes, giving NMOS lower on-resistance (Rds(on)) for the same die area compared to PMOS.
What is the threshold voltage of an N-Channel MOSFET?
The threshold voltage (Vth) of an N-Channel MOSFET is typically 2–4 V for logic-level devices (e.g., AO3400, IRL520N) and 4–10 V for standard power MOSFETs (e.g., IRF540N). Logic-level MOSFETs are designed to be fully on with a 3.3 V or 5 V gate signal from a microcontroller.
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