Thyristor Applications – Possibilities for Utilizing an SCR
Perhaps you have heard the terms “silicon controlled rectifier (SCR)” and “thyristor” used interchangeably, which occurs often with technical and specialized terminology. In fact, an SCR clamp is actually one type of a thyristor, and also may be referred to as a PN device. Other types of thyristors include Uni-Junction transistor (UJT), Triode for Alternating Current (TRIAC), Diode for Alternating Current, Silicon Control Switch (SCS), and more. The term “thyristor” is actually derived from the term “transistor”, and “thyratron” – a gas fluid tube that functions as an SCR. Let’s explore the diverse thyristor applications for power control in engineering.
Thyristor applications proliferate electronics to such a degree because they are highly reliable, able to handle a substantial current, require minimal maintenance, have a low overall cost of production, and produce no sound during operation since they lack moving parts. As a type of thyristor, an SCR clamp also possesses these beneficial characteristics. Because they are made of silicon, they are able to withstand high temperatures as well as high levels of power. Additionally, current leakage is minimized with silicon as compared to devices made of other materials.
Relay and Phase Control
As mentioned, SCR and thyristor applications are numerous. You may find them used to control the speed of AC and DC motors, convert/invert DC into AC, and ultimately for relay control and phase control. They are beneficial in emergency lighting systems, mechanical switches, battery chargers, heater controls, motor controls or fire controls. An SCR clamp is often used in a series of combinations within a single device, to allow for an even greater span of functionality. There are extensive benefits of using an SCR, but we’re going to investigate the two most common thyristor applications.
DC Motor Start/Stop Control Circuit
One of the most practical thyristor applications is as a source of overvoltage protection in a DC circuit. When serving this function in a DC circuit, the SCR is referred to as a “crowbar device”. This “crowbar circuit” places the output of the DC power supply parallel to the SCR clamp. Arranged in this manner, excessive voltage is prevented from reaching the load, where it could cause potential damage.
AC Power Control
Even though SCRs are unidirectional devices – and as a result, inherently used with DC devices – they are still often used for AC power control (which is bidirectional). When a bidirectional current is needed, multiple SCRs are used with one or more SCRs facing each direction. By using an SCR, we can allow for time-proportioned power control to the load.
These examples discussed above comprise just two of many SCR or thyristor applications. Considering their low cost, high degree of reliability, and multitude of uses, the possibilities for utilizing SCRs can seem endless.