The principle of thyristor is the sauce purple drop ~~~

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Guide: SCR has controllable rectification, inverter, frequency conversion, voltage regulation, use as a non-contact switch and so on. What is the principle of thyristor ? Let's take a look at it. ~~~

First, the principle of thyristor - - Introduction

SCR is the abbreviation of thyristor rectifier component. It is also called silicon thyristor in the world. It is a four-layer high-Power Semiconductor Device with three PN junctions. It is only turned on and off. It has two characteristics, such as fast response, high efficiency and no noise. It has been widely used.

Second, the principle of thyristor - - structure

The thyristor is a four-layer structure of P1N1P2N2, which includes three PN junctions (J1, J2, J3), and has three ports of anode A, cathode K, and gate G, as shown in the following figure. Among them, the anode A end is taken from the P1 layer, the cathode K end is taken out from the N2 layer, and the control electrode G end is taken out from the P2 layer.

When analyzing the thyristor principle , the thyristor can be decomposed as shown below and decomposed into a PNP tube and an NPN tube.

Third, the principle of thyristor

In the above figure, when the forward voltage is applied to the anode A end, both the BG1 tube and the BG2 tube are in an amplified state. At this time, a positive trigger signal is input from the control electrode G, and the BG2 tube has a base current ib2. Flowing, the current flows through the BG2 tube to the collector, and is amplified to ic2, ic2=β2ib2, and ic2 flows along the circuit to the base of the BG1 tube, so there is ib1=ic2, flowing through the BG1 tube, and reaching the collector, the current changes. For ic1, ic1=β1ib1=β1β2ib2, this current flows back to the base of BG2, so that ib2 increases to ib2=ic1, so that the loop forms positive feedback and the current increases sharply, so the thyristor reaches saturation and conducts.

The thyristor has only two states of conduction and shutdown, and has switching characteristics, and its state transition has certain preconditions. When changing from the off state to the on state, it is necessary to satisfy that the anode potential is always higher than the cathode potential, and the control electrode has sufficient forward voltage and current; when the conduction state is maintained, the anode potential is required to be higher than the cathode potential, and The anode current is greater than the sustain current; when changing from the on state to the off state, the anode potential is required to be lower than the cathode potential, or the anode current is less than the sustain current.

SCR principle