An Introduction to Field Effect Transistor (FET) AO3401

AO3401 is a field effect transistor (FET), belonging to voltage-controlled semiconductor devices. AO3401 has the advantages of high input resistance, low noise, low power consumption, no secondary breakdown, wide safe working area, as well as low temperature and radiation effects. AO3401 is especially suitable for high sensitivity and low noise circuitry. The AO3401 utilizes advanced trench technology to provide excellent RDS(ON), low gate charge and operation at gate voltages as low as 2.5V. The device is suitable for use as a load switch or is used in pulse width modulation applications. Standard product AO3401 is lead free (RoHS and Sony 259 compliant).

The AO3401 leads out 3 pins in the SOT-23 package and is a low power FET. The pulsed drain current (IDM) of AO3401 is 30A, the zero gate voltage drain current (IDSS) is 1uA. Its temperature resistance range is -55~150 degrees Celsiusn during operation. The gate-source voltage (VGS) of the AO3401 is ±12V. AO3401 SMD package series feature a body length of 1.7mm, plus pin length of 2.95mm, width of 3.1mm, height of 1.3mm, and pin spacing of 1.9mm.

The AO3401 is especially suitable for high sensitivity and low noise circuits and can be used as a load switch or in pulse width modulation applications.


Operating Temperature: -55°C~150°C TJ

Power Dissipation-Max: 1.4W Ta


FET Type: P-Channel

Transistor Application: SWITCHING

Rds On (Max) @ Id, Vgs: 50m Ω @ 4A, 10V

Vgs(th) (Max) @ Id: 1.3V @ 250μA

Input Capacitance (Ciss) (Max) @ Vds: 645pF @ 15V

Current – Continuous Drain (Id) @ 25°C: 4A Ta

Gate Charge (Qg) (Max) @ Vgs: 14nC @ 10V

Drain to Source Voltage (Vdss): 30V

Drive Voltage (Max Rds On,Min Rds On): 2.5V 10V

Vgs (Max): ±12V

Drain Current-Max (Abs) (ID): 4A

Drain-source On Resistance-Max: 0.05Ohm

DS Breakdown Voltage-Min: 30V

Where to Use

AO3401 control 3.3V 5V power supply circuit

AO3401 is cheap and low cost for small voltage circuit control

The working principle of the circuit is:

PWR_CTL is connected to the GPIO port of the microcontroller and needs to be pulled up internally or externally.

When PWR_CTL is high level: the transistor SS8050 is turned on at this time, the gate (G) of Q1 is equivalent to grounding, there is a negative voltage between the gate (G) and the source (S), the MOS tube is turned on, and the drain (D) ) has a 3.3V output.

When PWR_CTL is low level: the transistor SS8050 is not turned on at this time, there is no voltage difference between the gate and the source stage of the MOS tube, the MOS tube is turned off, and there is no voltage output.

The application of field effect transistor AO3401 in the circuit

This is a circuit that controls the power on and off, AO3401 is an enhancement mode PMOS. Simply put, Q7 turns on when Vgs (that is, the voltage between 1-2 of Q7) is negative. For AO3401, the full turn-on voltage is around -10V, but -3.3V can basically be turned on, but the impedance is slightly larger (about 100 milliohms). For the specific on-resistance under different Vgs voltage, please refer to the AO3401 manual. For the circuit in the figure, when CMMB_PWRON is greater than or equal to 3.3V, the AO3401 is off, and the back-end circuit is not powered. When CMMB_PWRON is 0V, AO3401 is turned on and the back-end circuit is powered. When using this switch, L12 should not be soldered, otherwise this circuit is meaningless.

The differences between field effect transistor AO3401 and triode

1. The triode is controlled by current, and the MOS tube AO3401 is voltage controlled.

2. Power consumption problem: The triode loss is large.

3. Driving ability: MOS tubes are often used in power switches and high-current switching circuits.

Triodes are often used for switching control of digital circuits. MOS tube AO3401 is used in high-frequency high-speed circuits, high-current occasions, and places sensitive to base or drain control currents.

Both the FET AO3401 and the triode can control and amplify the signal, but because their structure and working principle are completely different, the difference between the two is very large. In some special applications, the field effect transistor AO3401 is better than the triode and cannot be replaced by the triode.

The role of field effect transistor AO3401 and triode

(1) The FET is a voltage control element, and the transistor is a current control element. FETs should be used when only less current is allowed to be drawn from the signal source; transistors should be used when the signal voltage is low and more current is allowed to be drawn from the signal source.

(2) The FET uses the majority of carriers to conduct electricity, so it is called a unipolar device. The transistor has both majority and minority carriers for conduction, and it is called a bipolar device.

(3) The source and drain of some FETs can be used interchangeably, and the gate voltage can also be positive or negative, which is more flexible than transistors.

(4) The field effect transistor can work under very low current and low voltage conditions, and its manufacturing process can easily integrate many field effect transistors on one silicon wafer. Therefore, field effect transistors have been widely used in large-scale integrated circuits.

(5) FET has the advantages of high input impedance and low noise, so it is also widely used in various electronic equipment. In particular, the use of field effect transistors as the input stage of the entire electronic device can obtain performance that is difficult to achieve with ordinary transistors.


A creator, developer and global provider of a comprehensive range of power semi-conductors including an extensive portfolio of power MOSFET and power IC products, Alpha and Omega Semiconductor, Inc. or AO S.p.. In order to optimize product performance and cost, AOS aims to differentiate by integrating its expertise in device physics, process technology, design and advanced packaging, and its product portfolio is designed to meet the increasing power efficiency requirements in high-volume applications including portable computers, flat panel TVs, battery packs, motive media players, and power supply.
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