FAQ: Stop LED flickering by use of snubberless triac ?

Document created by Central Support Employee on Jun 25, 2018
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Q:

I have a problem with triac BTA06-600B, when I try to power off some led lamps they start flickering. I use triac to manage the main power (220V 50Hz), if the load is a traditional, alogen or cfl lamp all works fine. I tried to unmount the snubber circuit and the led stops flickering, but I'm worried for the lifetime of triac in case of inductive load. Is snubberles triac a solution? Are there any other components to manage main voltage?

 

 

 

 

 

 

A:

I understand that the triac is spuriously triggered while the control signal is not applied. LED is flickering with snubber and no flicker appears without snubber.

 

I'm fear that the leakage current that charge the snubber capacitor is able to light ON this low wattage lamp. Behavior also known as "ghosting effect". It appears with poor LED electronic designs without bleeder circuit.

 

Use a snubberless Triac without snubber is a good reflex, because it features a better turn-off performance on inductive load (as BTA06-600BW).

You can easily check the suitable device according to your max inductive load power using attached Application Note AN439.

 

But snubber also helps your circuit to withstand high dV/dt coming from the MAINS (as described in the IEC61000-4-4), especially because the opto-Triac has often a poor dV/dt withstanding. Then, if you remove the snubber and use a snubberless Triac, please check the dV/dt withstanding of your circuit (and maybe adapt the opto-Triac reference for a better immunity).

 

If a snubber is still mandatory because of the poor opto-Triac immunity, please take note of below design tip. It allows to reduce resistor in series with opto-Triac (R2) and Triac gate, and then increase snubber efficiency against dV/dt across the opto, keeping the  leakage current low as you can adjust R1 to reduce it.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(extracted from ST Online Support)

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