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FAQ02153 of Solid-state Relays FAQ

FAQ No. FAQ02153

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What is the difference between triacs and thyristors?


They are essentially the same in terms of resistive loads. For inductive loads, however, back-to-back thyristors are effective.
Thyristors connected back-to-back or a triac can be used for Solid-state Relay switching elements.

Thyristors and the triacs differ in their characteristics to enable the elements to adjust to a rapid rise or fall.

These characteristics are expressed as dv/dt (unit: V/ μs). The dv/dt value for thyristors is greater than the value for triacs.

Triacs help downsize Solid-state Relays because they can sufficiently perform switching for motors of up to the 3.7-kW class with inductive loads, and one triac element provides functionality equivalent to two thyristors connected back-to-back.

Note:dv/dt is the rate of voltage rise.

Resistive loadInductive load
40 A max.Over 40 A3.7 kW max.Over 3.7 kW
TriacOKOKOKNot as good
Two thyristorsOKOKOKOK

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