Analysis of the role and principle of thyristor

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A thyristor is a kind of switching element. As its name suggests, his name has a gate, which is the meaning of a switch. He is widely used in various circuits and electronic equipment. Here we introduce the role and principle of the thyristor. A thyristor is a typical device for controlling large currents with a small current. It triggers the thyristor to be in a conducting state by a pulse with a small current. At this time, his resistance becomes very small equivalent to a wire.

The role and principle of thyristors

When we analyze the function and principle of the thyristor, we can think of it as consisting of a PNP tube and an NPN tube. The equivalent diagram is as shown in the figure above. When the anode A plus the forward voltage, the BG1 and BG2 tubes are in the amplified state. . At this time, if a forward trigger signal is input from the gate G, the BG2 has a base stream ib2 flowing through it, and is amplified by BG2, and its collector current IC2 = β2ib2. Since the collector of BG2 is directly connected to the base of BG1, ib1 = ic2. At this time, the current ic2 is amplified by BG1, so that the collector current ic1 of BG1 = β1ib1 = β1β2ib2. This current flows back to the base of BG2, which is positive feedback, which increases the ib2. As a result of the forward feed loop, the current of the two tubes increases sharply, and the thyristor turns the saturation on. Due to the positive feedback effect of BG1 and BG2, once the thyristor is turned on, even if the current of the gate G disappears, the thyristor can maintain the conduction state, since the trigger signal only acts as a trigger, and does not turn off. Function, so this thyristor is not switchable.

Since he has only two states of conduction and shutdown, the thyristor has a switching characteristic, which is also the function of the thyristor. His switch requires certain conditions to be converted.

Thyristor turn-on and turn-off conditions