GTO (Gate Turn-off Thyristor) and IGBT (Insulated Gate Bipolar Transistor) are two types of semiconductor devices with three terminals. Both of them are used to control currents and for switching purposes. Both devices have a controlling terminal called ‘gate’, but have different principals of operation.
GTO (Gate Turn-off Thyristor)
GTO is made of four P type and N type semiconductor layers, and the device structure is little different compared to a normal thyristor. In analysis, GTO is also considered as coupled pair of transistors (one PNP and other in NPN configuration), same as for normal thyristors. Three terminals of GTO are called ‘anode’, ‘cathode’ and ‘gate’.
In operation, thyristor acts conducting when a pulse is provided to the gate. It has three modes of operation known as ‘reverse blocking mode’, ‘forward blocking mode’ and ‘forward conducting mode’. Once the gate is triggered with the pulse, thyristor goes to the ‘forward conducting mode’ and keep conducting until the forward current become less than the threshold ‘holding current’.
In addition to the features of normal thyristors, ‘off’ state of the GTO is also controllable through negative pulses. In normal thyristors, ‘off’ function happens automatically.
GTOs are power devices, and are mostly used in alternating current applications.
Insulated Gate Bipolar Transistor (IGBT)
IGBT is a semiconductor device with three terminals known as ‘Emitter’, ‘Collector’ and ‘Gate’. It is a type of transistor which can handle a higher amount of power and has a higher switching speed making it high efficient. IGBT has been introduced to the market in 1980s.
IGBT is has the combined features of both MOSFET and bipolar junction transistor (BJT). It is gate driven like MOSFET and has current voltage characteristics like BJTs. Therefore it has the advantages of both high current handling capability and ease of control. IGBT modules (consists of a number of devices) handle kilowatts of power.
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What’s the difference between IGBT and GTO? 1. Three terminals of IGBT are known as emitter, collector and gate, whereas GTO has terminals known as anode, cathode and gate. 2. Gate of the GTO only needs a pulse for switching, whereas IGBT needs a continuous supply of gate voltage. 3. IGBT is a type of transistor and GTO is a type of thyristor, which can be considered as a tightly coupled pair of transistors in analysis. 4. IGBT has only one PN junction, and GTO has three of them 5. Both devices are used in high power applications. 6. GTO needs external devices to control turn-off and on pulses, whereas IGBT doesn’t need.
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