IGBT
Transistor
A hybrid power switch: MOSFET-style voltage-driven gate with a BJT-style low-loss conduction path. The workhorse for switching hundreds of volts at tens/hundreds of amps — motor drives, welders, induction cooktops.
Schematic symbol
MOSFET (N-channel)
How igbt appears in a circuit diagram.
Types & variants
Key specs
Vces
VCollector-emitter blocking voltage: 600 V and 1200 V are standard.
Ic
AContinuous collector current at case temperature.
Vce(sat)
VOn-state drop (~1.5–2.5 V) — sets conduction loss.
Switching energy (Eon/Eoff)
mJLoss per switching event — limits usable frequency.
Laws that govern it
- Watt's lawP = V × I = I²R = V²/R
An IGBT's loss is a near-constant Vce(sat) × I plus switching loss — which is why it beats a MOSFET at high voltage and loses at high frequency.
- Lenz's lawthe minus sign in EMF = −N × dΦ/dt
It nearly always drives inductive loads (motors, induction heaters), so the freewheel path for the collapsing current is not optional.
- Joule's law of heatingH = I² × R × t
Short-circuit withstand time is an I²t number: an IGBT can survive a fault for about 10 µs before the die overheats.
Each law is stated in full — with its diagram, variables and worked meaning — on the electrical laws page.
Markings
Part number on the tab package or module lid (e.g. FGA25N120, IRG4PC50).
Standard values
600 V/1200 V classes at 15–75 A discrete; modules go far higher.
How to choose
IGBT beats MOSFET above roughly 400 V and below ~20 kHz switching. Pick Vces ≥ 2× bus voltage, check Eon/Eoff at your frequency, and use a proper gate driver (±15 V typical).
Pinout & package
TO-220 — front view, tab at back
Check first: Gate–Collector–Emitter is the usual TO-220 IGBT order (tab = collector), the same physical order as an N-channel MOSFET's G-D-S. Verify with the datasheet.
TO-247: G-C-E left to right (check the datasheet). Collector tied to the metal tab.
Example circuits
- Three-phase inverter bridge in a VFD
- Induction cooktop resonant switch
- Welder chopper stage
Common failures
Shoot-through or desaturation during faults blows them short C–E, often taking the gate driver along. Overheating from switching too fast a frequency.
How to test
Diode mode: the anti-parallel diode reads E→C; C–E should be open both ways otherwise. Charge the gate briefly from a 9 V battery (G–E) — C–E should then conduct; short G–E to turn off.
Substitutes
SiC MOSFET (faster, pricier) or paralleled Si MOSFETs at lower voltages. Match package, Vces and gate-drive requirements.