March 2008

Rev 3

1/10

AN302

Application note

Thyristors and TRIACs: holding current - an important parameter

Introduction

The purpose of this note is to familiarize the users of TRIACs or thyristors with the

The importance of this parameter is illustrated by some typical examples. Then a description

is given of how to measure it and on its variation with the conditions of use and the

sensitivity of the components.

This application note discusses only the TRIAC; however, the concepts are also valid for

SCRs.

Definition

To keep an electromechanical relay turned on, it is necessary to have a minimum current

circulating in its coil. If the current falls too low the relay would turn off. The same

phenomenon can be observed in a TRIAC. This minimum current which keeps the TRIAC

TRIAC current falls below the holding current the TRIAC is blocked and requires another

gate pulse before it can turn on again.

Figure 1.

Current control

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