AN440 Datasheet, PDF (1/8 Pages) STMicroelectronics – QII and QIII TRIAC triggering with positive power supply

AN440
Application note
QII and QIII TRIAC triggering with positive power supply
Introduction
New TRIACs with high commutation and dv/dt performances are now available on the
market.
Generally these TRIACs can be triggered only in the first three quadrants (case of
Snubberless™, logic level and Snubberless high temperature TRIACs) as shown in
Figure 1.
This paper describes a trigger circuit supplying a negative gate current for quadrants II and
III implemented in a system using a positive power supply.
Without a new design, just by adding a capacitor and a diode, new series TRIACs can
replace conventional TRIACs.
Figure 1. The quadrants of Snubberless, logic-level, and Snubberless high
temperature TRIACs
IT
+-
++
2 ^nd
1 ^st
IG
3 ^rd
4 ^th
NOT
--
TRIGGERABLE
A1
IT
IG
A2
TM: Snubberless is a trademark of STMicroelectronics
March 2008
Rev 3
1/8
www.st.com