IGBT
An IGBT controls collector-emitter current using gate-emitter voltage. It is commonly used as a power switch. The insulated gate reduces steady drive current, but a driver must still charge and discharge the gate quickly and respect its voltage limits.
In a typical N-channel IGBT, gate voltage forms a MOS channel. This enables electron flow and hole injection from the collector into the drift region. The extra carriers increase conductivity, helping reduce on-state voltage. When the gate turns off, stored carriers must leave or recombine, producing a tail current that contributes to switching loss.
In plain terms
A small control gate opens a busy transport lane. Opening the gate is easy; clearing the remaining traffic when it closes takes time, much like the IGBT's turn-off tail current.
Why designers use it
- Switching high-voltage power with an insulated control gate.
- Balancing conduction and switching losses in power converters.
- Building motor-drive and inverter stages with an appropriate driver, protection and cooling system.
Best for
- Motor drives
- Welders
- Induction heating
Key specifications
- Gate drive: Use the exact device's recommended VGE and gate-charge data
- VCE(sat): Conduction voltage at stated current, gate voltage and temperature
- Switching energy: Eon and Eoff depend on test conditions and gate resistance
- Safe operating area: Check the relevant voltage, current, time and temperature limits
- Diode: Verify whether one is integrated or must be provided externally
When not to use it
- When the required switching speed or loss budget is better served by another device technology.
- When the design cannot provide the required gate voltage, peak drive current or isolation.
- As a direct GPIO-controlled replacement for a small signal transistor.
Common mistakes
- Connecting an IGBT gate directly to a microcontroller because it has high input impedance.
- Using threshold voltage as the fully-on drive voltage.
- Ignoring turn-off tail current, switching energy or the safe operating area.
- Assuming every IGBT includes a suitable freewheeling diode.
- Treating maximum collector current as available regardless of case temperature, cooling or pulse duration.
Where you will find it
- In a motor inverter, a controller commands a gate-driver stage; the driver supplies the current needed to switch the IGBT gates. The power stage also needs fault protection, dead time and a cooling design.
- A converter designer compares conduction loss with turn-on and turn-off energy rather than assuming the lowest saturation voltage is always the best choice.
A short history
In his IEEE oral history, B. Jayant Baliga recalls pitching the IGBT concept at General Electric in early 1980 and roughly ten months of work from conception through a working product. The important technical idea combines insulated-gate control with bipolar conduction; later structures refine the trade-off between conduction voltage and switching loss.
Good to know
- An insulated gate still needs charging current each time the switch changes state.
- Tail current explains why turning the gate off does not make collector current disappear instantaneously.