Semiconductor Power Switches and Supplementary Components and Systems

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Some sources define silicon controlled rectifiers and thyristors as synonymous Other sources define thyristors as a larger set of devices with at least four layers of alternating N and P-type material. 12

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The thyristor is a four-layered, three terminal semiconductor device, with each layer consisting of alternately N- type or P-type material, for example P-N-P-N. The main terminals, labelled anode and cathode, are across all four layers. The control terminal, called the gate, is attached to p-type material near the cathode. (A variant called an SCS—Silicon Controlled Switch—brings all four layers out to terminals.) The operation of a thyristor can be understood in terms of a pair of tightly coupled bipolar junction transistors, arranged to cause a self-latching action: 20

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SCR - Thyristors can only be turned ON and cannot be turned OFF. Thyristors are switched ON by a gate signal, but even after the gate signal is de-asserted (removed), the thyristor remains in the ON-state until any turn-off condition occurs (which can be the application of a reverse voltage to the terminals, or when the current flowing through (forward current) falls below a certain threshold value known as the "holding current"). Thus, a thyristor behaves like a normal semiconductor diode after it is turned on or "fired". 22

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 TRIAC, from Triode for Alternating Current  Conduct current in either direction when it is triggered (turned on), and is formally called a bidirectional triode thyristor or bilateral triode thyristor.  TRIACs are part of the thyristor  TRIACs are bidirectional and so current can flow in either direction.  TRIAC current flow can be enabled by either a positive or negative current applied to its gate electrode  Continues to conduct until the current drops below a threshold – holding current.  Applying a trigger pulse at a controlled phase angle in an A.C. cycle allows control of the percentage of current that flows through the TRIAC to the load (phase control  Used in controlling the speed of low-power induction motors, in dimming lamps, and in controlling A.C. heating resistors. 28

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31 GTO - Gate Turn-Off Thyristor

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 An IGCT is a special type of thyristor similar to a GTO.  Have lower conduction loss as compared to GTOs, and withstand higher rates of voltage rise (dv/dt), such that no snubber is required for most applications.  The structure of an IGCT is very similar to a GTO thyristor.  In an IGCT, the gate turn off current is greater than the anode current.  This results in a complete elimination of minority carrier injection from the lower PN junction and faster turn off times. The main difference is a reduction in cell size, plus a much 34

 The very high gate currents plus fast dI/dt rise of the gate current means that regular wires can not be used to connect the gate drive to the IGCT.  The drive circuit PCB is integrated into the package of the device.  The IGCT's much faster turn-off times compared to the GTO's allows them to operate at higher frequencies—up to several of kHz for very short periods of time.  Because of high switching losses, typical operating frequency up to 500 Hz. 35

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Bipolar Junction Transistor BJT 38

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44 The upper transistor is functioning as an active pull-up, in linear mode, while the lower transistor works digitally. For this reason they aren't capable of supplying as much current as they can sink (typically 20 times less). With two transistors stacked vertically, normally with a level shifting diode in between, they are called "totem pole" outputs.

A disadvantage of totem-pole outputs is that two or more of them cannot be connected together, because if one tried to pull while another tried to push, the transistors could be damaged. To avoid this restriction, some push–pull outputs have a third state in which both transistors are switched off. In this state, the output is said to be floating (or, to use a proprietary term, tri-stated). 45

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 Reduce the storage time of a switching bipolar junction transistor (BJT) by applying a nonlinear negative feedback through various kinds of diodes.  Slow turn-off times of saturated BJTs is the stored charge in the base.  It must be removed before the transistor will turn off.  The diode-based Baker clamps prevent the transistor from saturating and thereby accumulating a lot of stored charge 51

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Insulated-gate bipolar transistor IGBT 54

55 Used as an electronic switch which, as it was developed, came to combine high efficiency and fast switching. The IGBT combines the simple gate-drive characteristics of MOSFETs with the high- current and low-saturation-voltage capability of bipolar transistors. Used in medium- to high-power applications like switched-mode power supplies, traction motor control, plasma physics and induction heating

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Metal oxide semiconductor field-effect transistor MOSFET 60

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