The Insulated Gate Bipolar Transistor (IGBT) merges the high-impedance gate drive of a MOSFET with the high-current, low-saturation output of a BJT. Because they dominate motor drives, induction heaters, and solar inverters, reading an IGBT symbol correctly is mandatory for troubleshooting and design. Below is the definitive reference for schematic symbols, standard variants, and physical pinouts.
IGBT Symbol and Pinout Reference Chart
The following table maps the schematic symbols you will encounter in datasheets and service manuals to their physical terminal equivalents. This covers both the international IEC standard and the North American IEEE/ANSI standard.
| Symbol Variant | Governing Standard | Terminals (Left/Right/Bottom) | Co-Pack Diode | Common Application |
|---|---|---|---|---|
| N-Channel IGBT (Basic) | IEC 60747 | Gate / Collector / Emitter | No | DC choppers, soft-switching resonant converters |
| N-Channel IGBT with Diode | IEC 60747 | Gate / Collector / Emitter | Yes (Anti-parallel) | VFDs, motor drives, hard-switched inverters |
| P-Channel IGBT | IEC 60747 | Gate / Emitter / Collector | Rarely | High-side switches in specialized legacy circuits |
| N-Channel IGBT (US Style) | IEEE 315 / ANSI Y32.2 | Gate / Collector / Emitter | Varies | North American military and legacy aerospace schematics |
| IGBT Module (4-Terminal) | IEC 60747 | Gate / Collector / Emitter / Kelvin Emitter | Yes (Usually) | High-di/dt industrial motor drives, EV traction inverters |
Decoding the Schematic: Standard Variants and Terminal Functions
When reading a schematic, the first step is identifying which drafting standard the engineer used. The IEEE 315 standard (common in older US documentation) draws the IGBT similarly to a MOSFET but adds a distinct arrow on the emitter terminal to denote the bipolar junction. The modern IEC 60747 standard, which dominates global datasheets from manufacturers like Infineon, Mitsubishi, and ON Semi, uses a hybrid symbol: a MOSFET gate structure combined with a BJT collector/emitter arrow.
The Anti-Parallel Diode (Co-Pack Diode)
In the IEC symbol, you will frequently see a diode drawn in parallel with the Collector and Emitter, with the cathode pointing toward the Collector. This is not a parasitic body diode like you find in a standard power MOSFET. IGBTs do not have an intrinsic body diode. Instead, manufacturers physically wire a separate, fast-recovery silicon or SiC PIN diode inside the same TO-247 or TO-220 package.
If your schematic shows an IGBT symbol without this diode, but you are driving an inductive load (like a motor winding or a transformer), you must add an external freewheeling diode across the Collector and Emitter. Failing to do so will result in inductive kickback destroying the silicon upon turn-off.
Understanding the Kelvin Emitter (E')
High-power modules and advanced discrete parts (like the TO-247-4 package) feature a fourth terminal: the Kelvin Emitter, often labeled as E' or E_sense. While the main Emitter carries the high load current (often 40A to 100A+), the Kelvin Emitter provides a dedicated, low-current sense path directly to the gate driver ground. This prevents the high di/dt voltage spike across the package's internal emitter inductance from falsely biasing the Gate and causing parasitic turn-on.
Pinout Identification and Faded Marking Recovery
On the bench, you will frequently encounter salvaged or heavily used IGBTs where the silkscreen part number and pinout diagram on the TO-247 or TO-220 package have been rubbed off by heat sink friction or thermal cycling. Before you scrap the component or risk blowing up your gate driver, you can map the pins using a standard digital multimeter (DMM).
Standard Discrete Pinout (TO-247 / TO-220)
With the component facing you (text side forward) and the pins pointing down, the universal industry standard for 3-pin discrete IGBTs is:
- Pin 1 (Left): Gate (G)
- Pin 2 (Middle): Collector (C) — usually also bonded to the metal mounting tab.
- Pin 3 (Right): Emitter (E)
The DMM Diode-Test Verification Method
If the pins are bent, cut, or you suspect a non-standard pinout, set your DMM to Diode Test mode and perform these measurements:
- Gate to Emitter / Gate to Collector: Should read "OL" (Open Loop) in both directions. The gate is insulated by a silicon dioxide layer. If you read a short or a low voltage drop, the gate oxide is punctured and the IGBT is dead.
- Collector to Emitter (Red lead on C, Black on E): Should read "OL". The device is normally off.
- Emitter to Collector (Red lead on E, Black on C): If the IGBT has a co-pack diode, you will read a forward voltage drop (typically 0.4V to 1.2V depending on the diode chemistry). If it reads "OL", it is a diode-free IGBT.
For a deeper dive into semiconductor testing and internal structures, All About Circuits provides an excellent primer on IGBT physics that complements this bench-testing approach.
The "Rows People Get Wrong" and Common Bench Mistakes
Even experienced technicians misinterpret IGBT symbols and datasheet parameters. Here are the specific rows and concepts that cause the most failures in the field.
Mistake 1: Confusing the IGBT Symbol with a Power MOSFET
Because the gate structure in the IEC symbol looks identical to a MOSFET, builders often substitute one for the other without checking the drive requirements. A standard logic-level MOSFET might have a Gate-Emittter threshold voltage ($V_{GE(th)}$) of 2V to 4V. An IGBT typically requires a $V_{GE(th)}$ of 5V to 6V just to begin conducting, and needs a full 15V on the gate to achieve its rated low saturation voltage ($V_{CE(sat)}$). Driving an IGBT with a 5V Arduino or ESP32 GPIO pin directly will result in the device operating in its linear (high-resistance) region, leading to immediate thermal runaway and catastrophic failure.
Mistake 2: Ignoring the "Tail Current" in Switching Loss Calculations
When reading the switching characteristics table in a datasheet, hobbyists often look only at the turn-on delay and rise time. However, the IGBT's defining flaw is the tail current during turn-off. Because minority carriers (holes) are trapped in the drift region, the collector current does not snap to zero instantly like a MOSFET; it "tails" off slowly. If your schematic symbol indicates a hard-switched inductive load, you must calculate your dead-time and snubber requirements based on the turn-off tail time ($t_{tail}$), not just the fall time ($t_f$).
Mistake 3: Misinterpreting the Collector-Emitter Voltage Rating
In the reference table, the application column notes that IGBTs are used in VFDs and inverters. A common mistake is selecting an IGBT with a $V_{CES}$ (Collector-Emitter Breakdown Voltage) rating that exactly matches the DC bus voltage. For a 480V AC line, the rectified DC bus is roughly 680V DC. However, inductive ringing can easily push transient spikes to 900V. Always select an IGBT with a $V_{CES}$ rating of at least 1200V for 480V AC systems, and 600V for 230V AC systems. The symbol on the schematic won't warn you about bus transients; your engineering margin must.
