Silicon controlled rectifier (SCR for short) is an important semiconductor device, widely used in the field of power electronics. It has the advantages of small size, light weight, high efficiency and long life, and can achieve precise control of large current and high voltage.

Silicon controlled rectifier, also known as thyristor, is a four-layer semiconductor device with a structure of P-N-P-N alternating semiconductor layers. It consists of a P layer, an N layer, a P layer and an N layer. This structure gives it unique electrical properties and can turn on or off current under appropriate trigger signals.

Working principle of thyristor

The working principle of thyristor is based on its special PN junction structure and the effect of applied voltage. Its working process can be divided into the following stages:

Off state: When there is no forward voltage applied between the anode and cathode of the thyristor, or there is no trigger signal at the control pole, the thyristor is in the off state. At this time, the PN junction is in a reverse biased state, and almost no current passes through.

Trigger conduction: When a positive trigger pulse is applied to the control electrode of the thyristor, the trigger signal changes the reverse bias state of the PN junction, causing the thyristor to enter the conduction state. At this time, the current can flow from the anode to the cathode.

Maintain conduction: Once the thyristor enters the conduction state, it will remain in the conduction state even if the trigger signal is removed until the anode current drops below the holding current or the anode voltage changes to the reverse voltage.

Off state: When the anode current drops below the holding current or the anode voltage changes to the reverse voltage, the thyristor will enter the off state and return to a non-conductive state.

Common applications of thyristors

Due to their unique properties, thyristors play an important role in power electronics, motor drives, automatic control and other fields. Common applications include:

Controlled rectifier: Thyristors can be used to convert AC power into DC power, and adjust the output DC voltage by controlling the timing of the trigger signal.

AC voltage regulation: In an AC circuit, thyristors can adjust the AC voltage by controlling the phase of the trigger signal to achieve power control of the load.

Contactless switch: Thyristor can be used as a contactless electronic switch, with the advantages of fast switching speed, no sparks, and long life, and is widely used in various switch control circuits.

Inversion and frequency conversion: Thyristor can be used in inverters and frequency converters to achieve the conversion of DC to AC and the regulation of AC frequency.

Summary

Thyristor is a powerful semiconductor device, whose structure and working principle allow it to be used as a control element in the circuit. Through reasonable triggering and shutdown control, thyristor is widely used in power electronics and can effectively control and regulate current and voltage.