Difference Between SCR And TRIAC

What Is Silicon Controlled Rectifier (SCR)?

A silicon Controlled Rectifier is a 3 terminal and 4 layer semiconductor current controlling device. It is mainly used in the devices for the control of high power. Silicon Controlled Rectifier is also referred to as SCR diode, 4-layer diode, 4-layer device or Thyristor. It is made up of a silicon material which controls high power and converts high AC current into DC current (rectification).

Silicon Controlled Rectifiers are used in power control applications such as power delivered to electric motors, relay controls or induction heating elements where the power delivered has to controlled.

What You Need To Know About SCR

SCR is a three terminal device.
SCR can only conduct current in one direction; it can thus be described as a unidirectional device.
SCR can function by positive gate control voltage only.
SCR can operate in only one mode.
It has 4 layers of semiconductor.
SCR can only control either positive or negative half cycle of AC input.
The SCR control DC power only or it can control forward biased half cycle of AC input in the load.
It is more reliable.
It requires two heat sinks.
SCR has large current capabilities and most SCRs are available in large ratings.
The forward characteristics of SCR are similar to the forward and reverse characteristics of TRIAC.

What Is Triode For Alternating Current (TRIAC)?

A Triac is a high-speed solid-state device that can switch and control AC power in either direction when triggered. Its formal name is bidirectional triode thyristor or bilateral triode thyristor. Most TRIACs can be triggered by applying either a positive or negative voltage to the gate. Once triggered, TRIACs continue to conduct, even if the gate current ceases, until the main current drops below a certain level referred to as the Holding Current.

The bidirectionality of TRIACs makes them convenient switches for alternating current (AC). In addition, applying a trigger at a controlled phase angle of the AC in the main circuit allows control of the average current flowing into a load (phase control).

Low-power TRIACs are used in many applications such as light dimmers, speed controls for electric fans and other electric motors and in the modern computerized control circuits of many household small and major appliances.

What You Need To Know About TRIAC

TRIAC is a three terminal device.
TRIAC can conduct in both directions; it can thus be described as a bidirectional device.
TRIAC function by either positive or negative gate control voltage.
TRIAC can operate in four different modes.
It has 5 layers of semiconductor.
TRIAC can control both positive and negative half cycles of AC signal input.
The TRIAC control DC as well as AC power.
It is less reliable.
It needs only one heat sink.
Typically, most TRIACs are available in ratings less than 40 Amp and at voltages up to 600 Volt.
The forward and reverse characteristics of TRIAC are similar to the forward characteristics of SCR device.