An
insulated-gate bipolar transistor (
IGBT) is a three-terminal
power semiconductor device primarily used as an electronic switch which, as it was developed, came to combine high efficiency and fast switching. It switches electric power in many modern appliances:
variable-frequency drives (VFDs),
electric cars, trains, variable speed refrigerators, lamp ballasts, air-conditioners and even stereo systems with
switching amplifiers. Since it is designed to turn on and off rapidly,
amplifiers that use it often synthesize complex waveforms with
pulse-width modulation and
low-pass filters. In switching applications modern devices feature
pulse repetition rates well into the ultrasonic range—frequencies which are at least ten times the highest audio frequency handled by the device when used as an analog audio amplifier.