The Insulated-Gate Bipolar Transistor (IGBT) merges the high-impedance, voltage-driven gate of a MOSFET with the low-saturation, high-current output of a BJT. On a schematic, the IGBT transistor symbol visually reflects this hybrid nature: it features a MOSFET-style insulated gate line paired with a BJT-style collector and emitter, distinguished by an arrow on the emitter leg. The arrow points outward for an N-channel device (the vast majority of power applications) and inward for a P-channel device. Pin names follow BJT conventions—Gate (G), Collector (C), and Emitter (E)—rather than the Drain/Source terminology used for MOSFETs.
The IGBT Transistor Symbol & Pinout Reference Table
Below is the primary reference matrix for the most common IGBT symbols you will encounter in power electronics schematics, motor drives, and inverter designs. This table maps the schematic symbol to physical pinouts and real-world silicon.
| Symbol Variant | Schematic Features | Pin Mapping (Physical) | Governing Standard | Example Part Number & Package |
|---|---|---|---|---|
| Standard N-Channel | Gate isolated from channel; Emitter arrow points OUT. | 1: Gate (G) 2: Collector (C) 3: Emitter (E) |
IEC 60617-11 / IEEE 315 | Infineon IRG4PC50U (TO-247, 3-pin) |
| N-Channel with Co-Packaged Diode | Standard N-IGBT symbol with an anti-parallel freewheeling diode drawn across C and E. | 1: Gate (G) 2: Collector (C) 3: Emitter (E) |
IEC 60617-11 | Infineon IKW40N120 (TO-247, 3-pin) |
| P-Channel IGBT | Gate isolated; Emitter arrow points IN toward the channel. | 1: Gate (G) 2: Collector (C) 3: Emitter (E) |
IEEE 315 | Rare in high power; mostly specialty/low-voltage ASICs |
| Half-Bridge Module | Block diagram or dual-symbol showing two IGBTs and two diodes in series. Often includes a thermistor symbol. | Multiple: G1, E1, G2, E2, C1/E2 (Phase Out), C2, Temp+ | IEC 60617 (Block level) | Mitsubishi CM300DY-24A (Module, 11-pin) |
Standard Variants: IEEE 315 vs. IEC 60617 & Schematic Conventions
Depending on where your schematic was drafted, the exact rendering of the IGBT transistor symbol will shift slightly based on regional and organizational standards. Understanding these differences prevents misinterpretation when reading legacy US drawings versus modern international motor drive schematics.
- IEC 60617 (International / Modern Standard): The IEC standard draws the gate as a distinct line parallel to the main channel, with a clear gap indicating the insulated gate (the oxide layer). The emitter arrow is placed on the main vertical channel line. This is the dominant standard in modern Infineon and STMicroelectronics datasheets.
- IEEE 315 (US Standard): Older US schematics sometimes draw the gate line touching the channel but intersected by a perpendicular hash mark to denote insulation. The arrow placement remains the same, but the visual weight of the gate connection can occasionally be confused with a standard BJT if the hash mark is poorly printed.
- The Co-Packaged Diode Omission: Under strict IEC rules, if a discrete IGBT includes an internal freewheeling diode (like the popular IKW series), the diode must be drawn in the symbol. However, many US-based schematic capture libraries default to the 3-pin standard N-channel symbol even when the specified BOM part includes a diode. Always cross-reference the BOM part number against the manufacturer datasheet rather than trusting the schematic symbol alone.
Rows People Get Wrong: Faded Markings, Co-Packaged Diodes, and Module Pins
When moving from schematic capture to the physical workbench, engineers and technicians frequently misinterpret IGBT pinouts and symbols. Here are the most common failure points and how to resolve them.
1. The Faded TO-247 Pinout Dilemma
High-power IGBTs in TO-247 and TO-220 packages are often subjected to extreme thermal cycling, flux residue, and physical abrasion. If the laser-etched pinout marking on the plastic body is faded or missing, never guess the pinout based on the schematic symbol alone. Different manufacturers occasionally swap the physical pin 1 and pin 3 assignments for specific thermal pad optimizations.
The DMM Verification Fix: Set your multimeter to diode test mode. Assuming a standard N-channel IGBT with a co-packaged diode (the most common topology):
- Place the Red probe on the middle pin (usually Collector) and Black probe on the right pin (usually Emitter). It should read 'OL' (Open Loop).
- Swap the probes: Black on the middle pin, Red on the right pin. You should read a forward voltage drop between 0.4V and 0.7V. This confirms the internal freewheeling diode and verifies the C and E pins.
- Test the left pin (Gate) against both C and E in both polarities. It must read 'OL' in all four combinations. If it reads a short or a diode drop, the gate oxide is punctured and the IGBT is dead.
2. Misinterpreting the Emitter Arrow Direction
Beginners often confuse the IGBT emitter arrow with the standard diode triangle arrow. Remember that the arrow on the IGBT symbol indicates conventional current flow direction when the device is turned on. For an N-channel IGBT, current flows from Collector to Emitter, so the arrow points out (away from the channel). If you see an arrow pointing in, you are looking at a P-channel device, which requires a negative gate drive relative to the emitter and is exceptionally rare in modern >600V power switching.
3. Half-Bridge Module 'Phase Out' Confusion
In module symbols, the connection point between the top IGBT's Emitter and the bottom IGBT's Collector is the AC output (Phase Out). Schematics often label this simply as 'OUT' or 'Phase U/V/W'. On the physical module (like a Mitsubishi CM series), this pin is typically a massive, isolated copper lug located in the center of the terminal row. Torque these lugs to the exact datasheet specification (usually 2.5 to 3.5 Nm); under-torquing causes thermal runaway, while over-torquing cracks the internal ceramic substrate.
Practical Bench Identification and Safe Interpretation
When interpreting an IEC 60617 compliant schematic featuring IGBTs, pay close attention to the gate drive circuitry drawn alongside the symbol. The symbol itself only tells you the switch topology; the surrounding components dictate survival.
- Gate Threshold vs. Drive Voltage: The IGBT symbol does not indicate the required gate voltage. While the threshold voltage ($V_{GE(th)}$) might be 5V, you must drive the gate to +15V to fully enhance the channel and minimize conduction losses ($V_{CE(sat)}$).
- Miller Clamp and Negative Bias: In high-speed switching schematics, you will often see a negative voltage rail (e.g., -5V to -8V) connected to the gate driver. This is not shown in the basic IGBT symbol but is critical. It prevents 'Miller turn-on', where a fast voltage spike on the Collector couples through the gate-collector capacitance ($C_{gc}$) and inadvertently turns the IGBT back on, causing a catastrophic shoot-through short circuit.
- Short Circuit Ruggedness: Unlike MOSFETs, IGBTs do not have a parasitic body diode inherent to their silicon structure; the diode shown in the 'co-packaged' symbol is a separate silicon die wired in parallel inside the plastic housing. This makes the IGBT symbol's diode representation a literal physical map of the package interior, not just a semiconductor junction artifact.
By anchoring your schematic reading to the exact IEC/IEEE standard variant and verifying physical pinouts with a multimeter diode test, you eliminate the guesswork that leads to blown gate drivers and shattered TO-247 packages.
