P0102DA 1AA3

Thyristors - SCRs

The P0102DA 1AA3 (also commonly known as SCR) is a Silicon Controlled Rectifier semiconductor device. It is a two-terminal device that uses a small amount of external current to switch or rectify a large amount of current in a circuit. Generally, it is used in applications where input power is required to turn on and trigger other devices.

Application Field

SCRs have a wide range of applications. They are frequently used as switches in AC power control systems, including those for controlling igniters, semiconductor dimmers for tungsten lighting, electrostatic precipitators and applications involving motor drives and arc furnaces. In all these cases, power control through soft start and inrush current limiting are required. SCRs are also commonly used as protection devices against short-term overvoltages and overcurrents, such as those during current limiting or the quick reversing of a large current.

SCRs are widely used in the industrial, electronics, instrumentation and lighting sectors. In the electronics area, SCRs are employed in the process of switching saturation, in linear voltage regulators and for amplifiers as well as for power supply rectifiers.

Working Principle

A Silicon Controlled Rectifier is constructed using four alternating layers of n-type and p-type silicon. The four layers form an anode (A), cathode (K), gate (G), and a control terminal (C). The SCR device will switch on when a small voltage is applied between the gate and the cathode. The gate threshold trigger current is typically on the order of micro-Amperes. When the device is triggered and the anode is made more positive than the cathode, a forward current passes through the device.

When triggered, the gate control current is amplified by the junction between the anode and the gated so that a much larger current can flow through the anode-cathode junction. The device is not triggered until the potential difference between the anode and the gated is large enough to respond to the low level gate control current. SCRs are usually triggered by switches, electrical pulse sources, or other SCR devices.

Once the SCR device is triggered, the current through the anode and the cathode cannot be turned off by merely removing the gate current. Unless the voltage between the anode and the cathode is taken down to a certain level, typically below 0.7V, the current continues to flow through the device until it reaches its breakdown or maximum current level. This feature makes SCRs comparable to ideal switches, as their current can be controlled through the use of external voltages or currents.

SCRs are also referred to as thyristors, because of their similarities to triacs and rectifiers. Essentially, they are combinations of transistors, diodes, and resistors. This makes them more complex devices than the standard triac and diode devices.