IGBT Symbol
Definition: The IGBT (Insulated Gate Bipolar Transistor) symbol represents a three-terminal voltage-controlled power switching device that combines the high-input-impedance gate drive of a MOSFET with the low on-state saturation voltage of a bipolar transistor, shown in power electronics schematics as a Gate (G), Collector (C), and Emitter (E) device per IEC 60617-05 and ANSI/IEEE 315-1975, designated Q in circuit diagrams.
Also known as: insulated gate bipolar transistor, IGBT transistor, power IGBT, N-channel IGBT, punch-through IGBT, non-punch-through IGBT.
What the IGBT symbol means
The IGBT symbol denotes a four-layer semiconductor device (P-N-P-N structure) that is controlled by applying a voltage to its Gate terminal. When the Gate-Emitter voltage (V_GE) exceeds the threshold voltage (V_GE(th), typically 4–8 V), the IGBT turns on and conducts current from Collector to Emitter with a low saturation voltage (V_CE(sat) ≈ 1–3 V). When V_GE drops below the threshold, the IGBT turns off and blocks the full collector-emitter voltage rating (V_CES), which can be 600 V to 6.5 kV for high-voltage devices.
IGBTs are the dominant switching device in medium- and high-power applications where MOSFETs' on-resistance becomes prohibitively high at high voltages. The IGBT symbol in a power electronics schematic identifies a switch capable of handling kilowatts to megawatts of power while being driven by a low-power gate signal, making it ideal for motor drives, inverters, and power converters.
How to identify the IGBT symbol
The IGBT symbol resembles the N-channel MOSFET symbol but with an additional arrow on the Emitter terminal indicating bipolar current flow. The symbol shows a vertical channel line, a Gate terminal (horizontal line on the left connected to the channel via a gap representing the insulated gate oxide), a Collector terminal at the top, and an Emitter terminal at the bottom with an inward-pointing arrow (for N-channel IGBT). A diode is often shown in antiparallel between Emitter (anode) and Collector (cathode), representing the integral body/freewheeling diode.
Function in a circuit
The IGBT functions as a voltage-controlled switch in high-power circuits: the Gate-Emitter voltage controls the conductivity of a P-N channel that modulates current flow from Collector to Emitter. Unlike a bipolar transistor that requires base current drive, the IGBT's insulated gate draws negligible steady-state gate current, allowing simple gate driver ICs (e.g., IR2110, HCPL-314J) to drive it with a logic-level signal. The IGBT's antiparallel body diode allows reverse current flow during inductive load commutation, essential in H-bridge and three-phase inverter topologies.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-05 covers semiconductor symbols; the IGBT is represented as an insulated-gate transistor with a bipolar output symbol — a gate line separated from the channel by a gap (insulated gate), with the channel extending to Collector (top) and Emitter (bottom) terminals, and an arrow on the Emitter indicating N-type (arrow pointing in, into the gate channel) for the common N-channel device. |
|---|---|
| ANSI/IEEE 315 | ANSI/IEEE 315-1975 (section 5.4.3) defines the insulated-gate bipolar transistor symbol identically to IEC 60617: Gate on the left with an insulating gap, Collector at top, Emitter at bottom with directional arrow. The reference designator is Q for all transistor types including IGBTs. |
| Key difference | IEC 60617 and ANSI/IEEE 315 use effectively identical IGBT symbols — both show the insulated gate (gap between Gate line and channel), bipolar-style Collector and Emitter terminals, and an arrow on the Emitter. The integral antiparallel diode is sometimes explicitly drawn in ANSI schematics but omitted in simplified IEC representations where it is understood to be present in power IGBT packages. |
Terminals / pins
| Pin | Name |
|---|---|
| gate | Gate |
| collector | Collector |
| emitter | Emitter |
Typical values
Collector-emitter voltage V_CES: 600 V, 1200 V, 1700 V, 3300 V, 6500 V. Collector current I_C: 10 A to 1000 A (single device), larger in modules. Gate-emitter threshold voltage V_GE(th): 4–8 V. Gate drive voltage: +15 V (on), −5 V to −15 V (off). Saturation voltage V_CE(sat): 1–3 V at rated current. Switching frequency: 1 kHz–100 kHz (trench-gate IGBTs to 150 kHz). Package types: TO-247, TO-3P, IPAK, half-bridge modules (e.g., Infineon EconoPACK, Semikron SKIIP).
Where the IGBT symbol is used
- Variable frequency drives (VFDs) / motor drives: three-phase IGBT bridge inverter converts DC bus voltage to variable-frequency AC to control induction motor speed in HVAC, pumps, and conveyors
- Solar inverters and wind turbine converters: IGBT-based DC-AC inverter stage converts photovoltaic or wind-turbine DC power to grid-synchronised AC at efficiencies >98%
- Uninterruptible power supplies (UPS): IGBT inverter provides clean AC output from battery DC bus during mains failure in data centres and critical facilities
- Induction heating and cooking: IGBT resonant inverter (typically 20–100 kHz) drives induction coils for industrial induction heating, hardening, and domestic induction cooktops
- Electric vehicle (EV) traction inverters: high-voltage (400–800 V), high-current IGBTs or SiC MOSFETs drive three-phase permanent-magnet motors in EVs; IGBTs dominate in conventional 400 V designs
- HVDC transmission and FACTS devices: series-connected IGBT stacks in modular multilevel converters (MMC) for high-voltage DC power transmission at hundreds of kV and thousands of amperes
Example
In a single-phase inverter schematic, four IGBTs (Q1–Q4) form an H-bridge. Q1 and Q4 are turned on simultaneously to apply +V_DC across the load, then Q2 and Q3 to apply −V_DC. Each IGBT symbol shows its Gate terminal driven by a gate driver IC, its Collector connected to the DC bus rail or circuit midpoint, and its Emitter connected to the opposite rail or output node. The antiparallel diodes across each IGBT carry the freewheeling current during dead-time between switching transitions.
Key facts
- The IGBT symbol has three terminals: Gate (G, voltage-controlled input), Collector (C, current output), and Emitter (E, current return with directional arrow); the N-channel Emitter arrow points inward toward the gate channel.
- IGBTs turn on when the Gate-Emitter voltage V_GE exceeds the threshold voltage V_GE(th) (typically 4–8 V) and turn off when V_GE drops below threshold; gate current is negligible in steady state.
- The on-state Collector-Emitter saturation voltage V_CE(sat) of a modern trench-gate IGBT is typically 1–2 V at rated current, much lower than an equivalent-rated MOSFET at high voltages.
- Most IGBT power devices include an antiparallel freewheeling diode (body diode or discrete co-packaged diode) between Emitter (anode) and Collector (cathode) to carry inductive load commutation current.
- IGBTs are specified in four primary voltage classes: 600 V (low-voltage drives), 1200 V (standard industrial), 1700 V (medium voltage), and 3300/6500 V (high-voltage traction and HVDC).
- The IGBT was invented by Jayant Baliga at General Electric in 1979 and patented in 1982; commercial devices became widely available in the late 1980s and transformed power electronics.
- In ANSI/IEEE 315 and IEC 60617, the IGBT reference designator is Q — the same letter used for all transistor types including BJTs and MOSFETs.
- Gate drivers for IGBTs typically apply +15 V to turn on and −5 V to −15 V to turn off; the negative off-state voltage prevents spurious turn-on due to Miller capacitance during fast switching transients.
Frequently asked questions
What does the IGBT symbol mean in a schematic?
The IGBT symbol represents an insulated gate bipolar transistor — a voltage-controlled power switch that turns on when the Gate voltage exceeds the threshold and turns off when it drops below it. It combines the easy voltage-drive of a MOSFET with the low saturation voltage of a bipolar transistor, making it ideal for high-power applications such as motor drives and inverters.
What does the IGBT symbol look like?
The IGBT symbol resembles an N-channel MOSFET but with a bipolar-style output. It shows a Gate terminal (G) on the left with a gap (insulated oxide layer) before the channel, a Collector terminal (C) at the top, and an Emitter terminal (E) at the bottom with an arrow pointing inward (for N-channel). An antiparallel diode is often drawn between Emitter (anode) and Collector (cathode) representing the integral freewheeling diode.
What are the three terminals of an IGBT?
An IGBT has three terminals: Gate (G), Collector (C), and Emitter (E). The Gate is the voltage-controlled input; the Collector is the current-carrying terminal connected to the positive supply; and the Emitter is the return terminal, also the reference for the Gate-Emitter voltage V_GE.
What is the difference between an IGBT and a MOSFET?
A MOSFET conducts current through a single-type semiconductor channel (unipolar) and has a higher on-resistance at high voltages; an IGBT uses minority-carrier injection (bipolar conduction) to achieve a lower saturation voltage at high voltages and currents. MOSFETs are preferred at low voltages and high switching frequencies; IGBTs are preferred above ~600 V and for high current applications where their lower V_CE(sat) reduces conduction losses.
What voltage does an IGBT need to turn on?
An IGBT turns on when the Gate-Emitter voltage V_GE exceeds the threshold voltage V_GE(th), typically 4–8 V depending on the device. Gate drivers normally apply +15 V (on) to ensure full enhancement and −5 V to −15 V (off) to prevent spurious turn-on due to the Miller capacitance effect during fast switching transitions.
What standard defines the IGBT symbol?
The IGBT symbol is defined in IEC 60617-05 (semiconductor device symbols) and ANSI/IEEE 315-1975 (section 5.4.3). Both standards use an identical symbol: insulated Gate on the left, Collector at top, Emitter at bottom with arrow indicating current direction. The reference designator is Q in both standards.
What are typical IGBT applications?
IGBTs are used in variable frequency drives (VFDs) for motor control, solar and wind power inverters, UPS systems, induction heating equipment, electric vehicle traction inverters, and HVDC power transmission converters. Any application requiring controlled switching of hundreds to thousands of volts at tens to hundreds of amperes typically uses IGBTs or their modern SiC MOSFET replacements.
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