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Triac Dimmer not turning off during negative going half cycle of AC main

Question asked by Nazmul Hasan on Feb 5, 2018
Latest reply on Feb 19, 2018 by Benoit RENARD

Hello,

I got a problem with my light dimmer pet project using ST's snubberless triac, T435-800T. It's working fine (turning on and off based on the control input) with the positive going half cycle of AC main. But during negative going half cycle, I found a strange behavior. Traic failed to turn off  during the negative going half cycle of AC main. I tried two separate rated incandescent lamp as a load. One rated at 25 W and another 60 W. What I found are, for 25 W lamp, turning off of Triac during negative half cycle not working at random intervals (please find the attachment) and for 60 W lamp, there is no turning off of Triac during negative going pulse. Please be noted that I checked control signal for both cased, and controller producing exact signal as the positive going half cycle.

 

Can you please share your experience if I got same problem earlier? Do I need a Triac with higher Irms (on-state) value to overcome the issue? T435-800T has a Irms (on-state) of 4A.

 

Thanking you.Benoit RENARD 

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