Business > Industrial Devices > Automation Controls Top > Components & Devices > Relays / Couplers > Solid State Relays > SSR Principle of Operation

SSR Principle of Operation

Here is PDF of this page.

SSR Switching Characteristics

1.SSR for AC Loads

1.Zero-crossing SSR

The zero-crossing SSR uses a phototriac coupler to isolate the input from the output (see the circuit configuration on the previous page). When the input signal is activated, the internal zero-crossing detector circuit triggers the triac to turn on as the AC load voltage crosses zero.
The load current is maintained by the triac’s latching effect after the input signal is deactivated, until the triac is turned off when the load voltage crosses zero. The following describes voltage and current wave forms for different types of loads:

●Resistive loads

Since resistive loads cause no phase shift between the voltage and current, the triac turns on when the AC load voltage crosses zero after the input signal is activated. The SSR turns off when the AC load voltage crosses zero and the load current is turned off after the input signal is subsequently deactivated.

●Inductive loads

The SSR turns on when the load voltage crosses zero after the input signal is activated. It turns off when the load current subsequently crosses zero after the input signal is deactivated. A phase difference between the voltage and current may supply a transient spike to the SSR when it is turned off. While the snubber circuit absorbs this spike, an excessively large spike may result in a dv/dt error in the SSR’s internal triac.

2.Random type SSR

Random type SSR uses a phototriac coupler to isolate the input from the output. When the input signal is activated, the output immediately turns on, since there is no zero-crossing detector circuit. The load current is maintained by the triac’s latching effect after the input signal is deactivated, until the AC load voltage crosses zero.

●Resistive loads

2.SSR for DC Loads

The SSR for DC loads uses a MOS-FET driver to isolate the input from the output.
The output immediately responds to the input, since the MOS-FET driver directly turns the output MOS-FET ON or OFF.

Return to top

Solid State Relays Related Information

SSR's Cautions for Use

Catalog Download

Title	Language	File size	Update
SSR動作原理の説明ソリッドステートリレー	JP	120.9KB	April 1, 2022
SSR Principle of Operation Solid State Relays	EN	49.3KB	April 1, 2022
SSD工作原理的说明	CN-Simplified	345.6KB	August 22, 2019

Return to top

Please click your area to select country or region

Europe
Africa
Middle East
Asia-Pacific
East Asia
The Americas

BY PHONE

U.S.A.: +1-800-344-2112
Europe: +49-89-45354-1000
China: +86-10-59255988
Singapore: +65-6299-9181

Global Sales Network

RECOMMENDS

Introduction to
Automation
Controls

FEATURES

A Vital Piece
to the EV and
HEV Puzzles

Energy Management Applications

Automotive Applications

Solid State Relays

	Phototriac Coupler
	Phototriac coupler for the industrial machinery and consumer electronics

	AQ1 Solid State Relay
	High capacity up to 3 A/10 A PC board terminal type

	AQ8 Solid State Relay
	SIL type with 9 mm thickness, 3,000 V AC high dielectric voltage, controls up to 2 A/3 A

	AQ-A (AC output type) Solid State Relay
	Load current up to Max. 40 A in the series, Small Screw Terminal SSR

	AQ-A (DC output type) Solid State Relay
	Small Screw Terminal SSR Ideal for DC Control

	AQ-G Solid State Relay
	Slim type SSR for 1 A and 2 A control

	AQ-H Solid State Relay
	Compact DIP type SSR Ideal for AC load control

	AQ-J Solid State Relay
	Small tab terminal SSR, Slim heat sink combined type also available

Related Information

Service & Support