What is a GaN Transistor?

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Editorial Team - everything PE

Sep 12, 2021

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Gallium nitride (GaN) transistor is high electron mobility (HEMT) semiconductor device that consists of three terminals – gate, source, and drain. High electron mobility means that the GaN transistor has higher electric-field strength compared to silicon-based transistors. The GaN transistor offers benefits such as low on-state resistance, lower conduction losses, lower switching losses, high-frequency switching, high efficiency, small form factor, higher power density, and can withstand high temperature.

GaN transistors are ideal for use in consumer power supplies, multi-level converters, solar inverters, industrial motor drives, UPS, high voltage battery chargers, telecom, SMPS, totem pole PFC, high-frequency LLC, and enterprise and networking power applications.

Types of GaN Transistors

The GaN transistors are classified into two types - Enhancement mode GaN power transistor (e-GaN) and Depletion mode GaN power transistor (d-GaN).

Enhancement mode GaN Transistor: In enhancement mode, the GaN transistor is equivalent to the “Normally Open” switch (normally OFF). This means that when there is no voltage applied across the gate terminal, the GaN transistor does not conduct. It is turned on by applying positive gate-source voltage.

Depletion mode GaN Transistor: In this mode, the GaN transistor is equivalent to the “Normally closed” switch (normally ON). The mode indicates that the transistor is at an ON state at zero gate-source voltage. It is turned off by applying a negative voltage relative to the drain and source electrodes.

Key Specifications of GaN Transistors

Configuration of GaN transistor: The GaN transistors are available with different configurations – single, dual, and half-bridge.

Gate Threshold Voltage: It represents the minimum voltage that is applied between the gate and source terminal to make the GaN transistor turn ON. It is expressed in volts (V).

Drain source voltage: It denotes the maximum voltage that can be applied across drain and source terminals, after which the GaN enters an off state. It is expressed in volts (V).

Drain source resistance: It represents the drain to source on-state resistance and is usually measured in the milli-ohm range.

Continuous drain current: It is the maximum continuous drain current that the GaN transistor can handle and is expressed in Ampere (A).

Pulsed Drain Current: It is the maximum pulsed drain current that the GaN transistor can handle and is expressed in Ampere (A).

Total charge: It represents the total charge that is accumulated at the gate terminal. The gate charge value is used to find how fast a GaN Transistor switches from ON to OFF state, and vice-versa.

Turn-on Delay Time: It is the time required to charge the input capacitance of the GaN Transistor before the drain current conduction starts.

Turn-off Delay Time: It is the time interval at which the voltage across the gate and source terminal drops below 90 % when the drain current falls below load current.

Rise time: The time taken for the drain current to reach from 10% of its initial value to 90% of its final value.

Fall time: The time taken for the drain current to reach from 90% of its maximum value to 10% of its initial value.