AN303 Datasheet, PDF (1/13 Pages) Silicon Laboratories – Si55X VCXO TEMPERATURE STABILITY DEFINITION

AN303
Application note
Thyristors and TRIACs: latching current
Introduction
The purpose of this note is to familiarize TRIAC or thyristor (SCR) users with the latching
current I_L.
The importance of this parameter is illustrated with some typical examples. Procedures are
given for measurement of I_L. The variation of I_L with operating conditions and device
sensitivity are described.
This application note presents only the TRIAC case. However, the concepts are valid for
SCRs (except for the various conduction modes).
Definition
The latching current (I_L) of a TRIAC is the minimum value of the load current (current flowing
between electrodes A₂ and A₁) that keeps the device conducting when the gate signal is
removed (see Figure 1).
Figure 1 below shows the latching current and the gate current pulse. After the TRIAC
triggering, a current (I_T) flows through the TRIAC. If the gate current (I_G) is removed while
the current I_T is lower than the latching current I_L, the TRIAC switches off.
Figure 1. Blocked TRIAC
IG
I_G > I_GT
RL
I_T
Gate current ^t
IG
A_{2 IT}
IL
A1
G
Main current
t
April 2009
Doc ID 3654 Rev 3
1/13
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