The symbol of an IGBT (Insulated Gate Bipolar Transistor) merges the insulated gate structure of a MOSFET with the collector and emitter terminals of a Bipolar Junction Transistor (BJT). For standard 3-pin through-hole packages like the TO-247 and TO-220, facing the component with the text toward you and pins pointing down, the pinout from left to right is Gate (1), Collector (2), and Emitter (3). The mounting tab on the back is internally tied to the Collector.
IGBT Schematic Symbols and Physical Pinout Reference
When reading a schematic or replacing a blown power semiconductor, you need to match both the logical symbol and the physical footprint. The table below covers the standard IEC 60617 schematic symbols alongside the physical pinouts for the most common through-hole and surface-mount packages you will encounter on the bench.
| Category | Symbol / Package | Pinout / Description | Practical Application Notes |
|---|---|---|---|
| Schematic | N-Channel IGBT (No Diode) | Gate (left), Collector (top), Emitter (bottom, arrow pointing OUT) | Used in resonant converters where external fast-recovery diodes are specified. |
| Schematic | N-Channel IGBT (Co-packaged Diode) | Same as above, with an anti-parallel diode symbol across Collector-Emitter | Standard for motor drives and VFDs; the diode handles inductive freewheeling current. |
| Schematic | P-Channel IGBT | Gate (left), Emitter (top), Collector (bottom, arrow pointing IN) | Extremely rare in power electronics; mostly limited to specific high-side logic circuits. |
| Physical | TO-247-3 (e.g., Infineon IKW40N120H3) | 1: Gate, 2: Collector, 3: Emitter. Tab = Collector. | The workhorse of 1200V/40A+ welder and solar inverter circuits. |
| Physical | TO-247-4 (Kelvin Emitter) | 1: Gate, 2: Collector, 3: Emitter (Power), 4: Emitter (Kelvin/Sense) | Pin 4 provides a clean ground reference for the gate driver, eliminating di/dt noise. |
| Physical | TO-220AB (e.g., ON Semi FGA25N120ANTD) | 1: Gate, 2: Collector, 3: Emitter. Tab = Collector. | Used in lower-power SMPS and PFC circuits (up to ~25A). Requires isolation pad if heatsink is grounded. |
| Physical | D2PAK / TO-263 (SMD) | 1: Gate, 2: Collector (Tab), 3: Emitter | Surface mount. The large solder tab acts as the Collector and the primary thermal path. |
Schematic Standard Variants: IEC 60617 vs. IEEE/ANSI
While the physical pinouts of an IGBT remain consistent globally, the way the component is drawn on a schematic depends on the regional drafting standard your engineering team follows. Understanding these variants prevents misinterpretation when repairing imported machinery or reading legacy schematics.
IEC 60617 (Global / European Standard)
The IEC standard is the dominant global format. The symbol explicitly draws the MOSFET gate structure (a vertical line separated by a gap from the semiconductor body) connected to a BJT collector/emitter path. The arrow on the emitter leg clearly denotes the conventional current flow direction (outward for N-channel). If a co-packaged anti-parallel diode is present, it is drawn as a distinct diode symbol wired in reverse parallel across the collector and emitter, enclosed within a dashed or solid box indicating a single physical package.
IEEE 315 / ANSI Y32.2 (North American Legacy)
Older North American schematics sometimes use the IEEE/ANSI standard. The core hybrid structure (MOSFET gate + BJT body) is identical, but the enclosure styling and terminal labels may differ. ANSI schematics frequently label the terminals explicitly with "G", "C", and "E" directly adjacent to the symbol, whereas IEC relies on the arrow direction and circuit topology. Furthermore, some legacy ANSI drawings omit the co-packaged diode from the schematic symbol entirely, listing it only in the bill of materials (BOM) notes, which can cause massive confusion during troubleshooting if you assume the physical part lacks a diode.
Rows and Pinouts People Get Wrong on the Bench
When you are elbows-deep in a blown inverter, misinterpreting a symbol or a physical package will result in catastrophic failure the moment you apply power. Here are the most common bench mistakes and how to avoid them.
1. Confusing the Co-Packaged Diode for a Separate Component
When reading the "Co-packaged Diode" row in the table above, many hobbyists assume the diode is a separate silicon die wired internally. In modern trench-field-stop IGBTs (like the STMicro STGW40V120DF), the diode is often a monolithically integrated reverse-conducting (RC) structure or a highly optimized co-packaged silicon die. The mistake: Testing the IGBT with a multimeter and assuming a shorted diode means the IGBT is bad. The reality: If you read a 0.35V to 0.65V forward voltage drop from Emitter to Collector (positive lead on Emitter), the diode is healthy. If it reads 0.00V (dead short), the IGBT has suffered a thermal runaway event and is destroyed.
2. Miswiring the TO-247-4 Kelvin Emitter
The transition from 3-pin to 4-pin TO-247 packages is a major trip-up. In a 4-pin package (like Infineon's TO-247-4), Pin 3 is the Power Emitter (carrying the massive load current) and Pin 4 is the Kelvin Emitter (carrying only the milliamp-level gate return signal). The mistake: Wiring the gate driver's ground reference to Pin 3. Because high di/dt switching causes voltage spikes across the parasitic inductance of Pin 3, this spike couples into the gate, causing false turn-offs or destructive oscillation. The fix: Always wire the sensitive gate driver return directly to Pin 4.
3. Interpreting Faded or Sanded Silkscreen Markings
Counterfeiters often sand off the markings on TO-220 and TO-247 packages and reprint them with fake part numbers (e.g., selling a 10A NPN BJT as a 40A IGBT). If the silkscreen is faded, suspiciously smooth, or missing, do not trust the pinout blindly. Safe interpretation protocol: Use a digital multimeter in diode-test mode. The Gate (Pin 1) is insulated; it must read "OL" (Open Loop) in both directions to Pins 2 and 3. If you read any continuity or resistance between the Gate and the other pins, the component is either a BJT, a MOSFET, or a completely shorted, dead IGBT. Furthermore, the thick metal mounting tab on the back of standard TO-220/TO-247 IGBTs is almost universally the Collector. If the tab tests as the Emitter or Drain, you are likely holding a MOSFET or a Darlington BJT, not an IGBT.
Frequently Asked Questions
How to identify the symbol of an IGBT on a schematic versus a MOSFET?
The easiest way to differentiate the symbol of an IGBT from a standard MOSFET is to look at the terminal names and the arrow. A MOSFET symbol features a Gate, Drain, and Source, and the arrow is located on the body diode or the source terminal depending on the drafting style. An IGBT symbol explicitly uses the terms Collector and Emitter (borrowed from BJT terminology), and the arrow is always placed on the Emitter leg, pointing outward for N-channel devices. Additionally, the IGBT symbol lacks the physical body connection to the gate structure that is visible in a standard enhancement-mode MOSFET symbol.
What does the diode inside the IGBT schematic symbol mean?
The diode drawn across the Collector and Emitter in the symbol represents the anti-parallel (or freewheeling) diode. In inductive load applications like motor drives, when the IGBT switches off, the collapsing magnetic field generates a massive reverse voltage spike. This co-packaged diode provides a safe path for that inductive kickback current to circulate back to the DC bus, protecting the fragile silicon of the IGBT from avalanche breakdown. If your schematic shows an IGBT symbol without this diode, you must ensure an external ultra-fast recovery diode is wired across the physical component in the actual circuit.
How to test IGBT pins with a multimeter when the silkscreen markings are faded?
Set your multimeter to the diode-test setting. First, touch the probes across all three pins in both directions to identify the Gate: the Gate will read "OL" (infinite resistance) against both other pins in both directions because of the insulated gate oxide layer. Once the Gate is identified, the remaining two pins are the Collector and Emitter. Place your red (positive) probe on one of the remaining pins and the black (negative) probe on the other. If you read a forward voltage drop between 0.3V and 0.7V, the pin with the red probe is the Emitter and the pin with the black probe is the Collector (forward-biasing the internal anti-parallel diode). Reversing the probes should yield an "OL" reading. If it reads shorted (0.00V) in both directions, the IGBT has failed catastrophically.
