Thyristors Lec 2.pptx - Thyristors The Basic Four Layer Device \u2022 The basic thyristor is a 4-layer device with two terminals the anode and the cathode

Thyristors Lec 2.pptx - Thyristors The Basic Four Layer...

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Thyristors
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The Basic Four Layer Device The basic thyristor is a 4-layer device with two terminals, the anode and the cathode. It is constructed of four semiconductor layers that form a pnpn structure. The device acts as a switch and remains off until the forward voltage reaches a certain value; then it turns on and conducts. Conduction continues until the current is reduced below a specified value. This basic thyristor is also known as a silicon unilateral switch (SUS), Shockley diode, or 4-layer diode.
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Two Transistor Model of 4-Layer Diode The 4-layer diode (also known as Shockley diode and SUS) is a type of thyristor, which is a class of devices constructed of four semiconductor layers. The pnpn structure can be represented by an equivalent circuit consisting of a pnp transistor and an npn transistor.
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Holding Current Once the 4-layer diode is conducting (in the on state), it will continue to conduct until the anode current is reduced below a specified level, called the holding current, I H . When I A falls below I H the device rapidly switches back to the off state and enters the forward-blocking region. Switching Current The value of the anode current at the point where the device switches
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