AN439 Datasheet, PDF (1/16 Pages) STMicroelectronics – The use of TRIACs is limited by their switching behavior

AN439
Application note
Snubberless™ and logic level TRIAC behavior at turn-off
Introduction
The use of TRIACs is limited by their switching behavior. Indeed, there is a risk of spurious
triggering after conduction if the slope of the decreasing current is too high, and/or if the
slope of the reapplied voltage is too high. The designer must then take some precautions:
device over-rating, switching aid network (snubber), and junction temperature margin, and
so on. This generally involves additional costs.
After a brief discussion of commutation when a TRIAC is turned off, this article will describe
the behavior of the logic level and Snubberless TRIACs, which present high commutation
capabilities.
Contents
1
TRIAC turn-off description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 (dI/dt)c versus (dV/dt)c characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Application requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3.1 TRIAC with resistive load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3.2 TRIAC with inductive load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4 TRIAC without snubber network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2
Logic level and Snubberless TRIACs . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1 Operation in Q1-Q2-Q3 quadrants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2 Performances and specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.1 Logic level TRIACs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.2 Snubberless TRIACs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3 Typical applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.1 Logic level TRIACs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.2 Snubberless TRIACs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
March 2008
Rev 3
1/16
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