Thyristor Devices designed specifically for high-power switching application. Constructed of 4 semiconductor layer (pnpn layer). pnpn layer can be represented as a pnp transistor and an npn transistor.
Thyristor It is a device that acts as a latch. It use internal feedback to produce switching actions used for over voltage protection, motor controls, heaters, lighting systems, and other heavy-current loads. Other names: Shockley diode; 4-layer diode; PNPN diode; Silicon Unilateral Switch (SUS).
History of Thyristors Early 1900s: vacuum tube ` – Lee DeForest --- triode, 1906 1920-1940: mercury arc tubes to convert 50Hz, 2000V to 3000VDC for railway 1930s: selenium rectifiers 1948 - Silicon Transistor, (BJT) introduced (Bell Labs)
History of Thyristors 1950s - semiconductor power diodes begin replacing vacuum tubes. 1952 - Power semiconductor devices first appeared by the introduction of the power diode by R.N. Hall. It was made of Germanium and had a voltage capability of 200 volts and a current rating of 35 amperes. 1956 - GE introduces Silicon- Controlled Rectifier (SCR)
History of Thyristors 1957 - The thyristor appeared and able to withstand very high reverse breakdown voltage and are also capable of carrying high current. One disadvantage of the thyristor for switching circuits is that once it is 'latched-on' in the conducting state it cannot be turned off by external control. The thyristor turn-off is passive, i.e., the power must be disconnected from the device.
History of Thyristors 1960s - The first bipolar transistors devices with substantial power handling capabilities were introduced. These components overcame some limitations of the thyristors because they can be turned on or off with an applied signal. - switching speed of BJTs allow DC/DC converters possible in 10-20 kHz range. - Metal Oxide Semiconductor Field-Effect Transistor (MOSFET) for integrated circuits.
History of Thyristors 1970s - Improvements of the Metal Oxide Semiconductor technology (initially developed to produce integrated circuits), power MOSFETs became available. 1976 - power MOSFET becomes commercially available, allows > 100 kHz operation.
History of Thyristors 1978 - International Rectifier introduced a 25 A, 400 V power MOSFET.These devices allow operation at higher frequency than bipolar transistors, but are limited to the low voltage applications. 1982 - The Insulated Gate Bipolar Transistor (IGBT) developed and became widely available in the 1990s. This component has the power handling capability of the bipolar transistor, with the advantages of the isolated gate drive of the power MOSFET.
UNIDIRECTIONAL THYRISTORS Devices in which the current can flow in one direction.
Shockley Diode A thyristor with 2 terminals (anode & cathode) Constructed of four pnpn semiconductor layer.
Shockley Diode Anode Cathode Equivalent Circuit Symbol Basic Construction Cathode Cathode Anode Anode Figure 1.
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