At the beginning, let's talk about SCR first. SCR can be divided into one-way SCR and two-way SCR. The unidirectional thyristor has three pins: anode A, cathode middle and control pole G. The bidirectional thyristor has three pins: a first anode A1 (T1), a second anode A2 (T2), and a control electrode G.
What is a thyristor?
Since the advent of the 1950s, thyristors have developed into a large family. Its main members include unidirectional thyristors, bidirectional thyristors, light-controlled thyristors, reverse-conducting thyristors, turn-off thyristors, fast thyristors, and so on. Today everyone uses a unidirectional thyristor, which is often referred to as an ordinary thyristor. It is composed of four layers of semiconductor materials, with three PN junctions and three electrodes: the electrode from the first layer of P-type semiconductor is called anode A The electrode from the third layer P-type semiconductor is called the control electrode G, and the electrode from the fourth layer N-type semiconductor is called the cathode K. As can be seen from the circuit symbol of the thyristor, it is a unidirectional conductive device like the diode. The key is the addition of a control pole G, which makes it have completely different operating characteristics from the diode. The thyristor is P1N1P2N2 four-layer three The end structure element has three PN junctions. When analyzing the principle, it can be regarded as composed of a PNP tube and an NPN tube.
When the positive voltage is applied to the anode A, the BG1 and BG2 tubes are in an amplified state. At this time, if a positive trigger signal is input from the control electrode G, the base current ib2 flows through BG2, and after being amplified by BG2, its collector current ic2 = β2ib2. Because 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 the collector current ic1 of BG1 = β1ib1 = β1β2ib2. This current flows back to the base of BG2, which is expressed as positive feedback, so that ib2 continues to increase. As a result of the positive feed cycle, the current of the two tubes increases sharply, and the thyristor turns on saturation.
Due to the positive feedback function formed by BG1 and BG2, once the thyristor is turned on, even if the current of the control electrode G disappears, the thyristor can still maintain the on state. Since the trigger signal only acts as a trigger, there is no shutdown function, so this The seed thyristor is not shut-off.
What is the relationship between SCR and thyristor?
The original international name of Thyristor (SCR) is Thyyistor, which is referred to as thyristor in Chinese. It can work under the conditions of high voltage and large current, and has the characteristics of high withstand voltage, large capacity and small volume. It is a high-Power Semiconductor Device and is widely used in electric power and electronic circuits. As such, although thyristor and thyristor are two terms, they all refer to the same semiconductor device.
How does it work?
In the working process of the thyristor, its anode (A) and cathode (K) are connected to the power supply and the load to form the main circuit of the thyristor, and the gate electrode G and the cathode K of the thyristor are connected to the device controlling the thyristor to form the control circuit of the thyristor.
The thyristor is a semi-controlled power electronic device, and its working conditions are as follows:
1. When the thyristor withstands the reverse anode voltage, no matter what the gate electrode withstands
Voltage, thyristors are in the reverse blocking state.
2. When the thyristor is subjected to a positive anode voltage, the thyristor will only conduct when the gate electrode is subjected to a positive voltage. At this time, the thyristor is in the forward conduction state, which is the thyristor characteristic of the thyristor, that is, the controllable characteristic.
3. When the thyristor is turned on, as long as there is a certain positive anode voltage, regardless of the gate voltage, the thyristor remains turned on, that is, the gate is disabled after the thyristor is turned on. The gate only acts as a trigger.
4. When the thyristor is turned on, when the main circuit voltage (or current) decreases to near zero, the thyristor turns off.
Having said so much, the general sentence is that thyristors are thyristors, and thyristors are also called thyristors. Because it only has two working states of on and off, it has switching characteristics, which require certain conditions to be transformed.
