We are using below circuit for home automation. We are facing problem when 5v battery is not passing to the circuit,but even 1 volt is being passed trough load, even triac is OFF condition.. Please help us to fix this issue.enter image description here

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  • \$\begingroup\$ Where exactly are you seeing 1V? What do you expect to see? What kind of bulb are you using? \$\endgroup\$ – Elliot Alderson Feb 6 '19 at 17:48
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    \$\begingroup\$ And what is the supply voltage? And why are you concerned about 1 V? Note that you have a snubber, C1, R2, bypassing your triac so this will pass a small current. \$\endgroup\$ – Transistor Feb 6 '19 at 17:54
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    \$\begingroup\$ For a CFL/LED bulb with a bridge rectified input, the input resistance below 2 diode drops is extremely high. Leakage across the snubber network can easily develop that potential. \$\endgroup\$ – sstobbe Feb 6 '19 at 18:38
  • \$\begingroup\$ Based on the OP's comments to my answer I suspect the OP is using LED lights. They will have a dim glow at 500uA, leaking through C1 and R2. \$\endgroup\$ – Sparky256 Feb 7 '19 at 19:56

As long as you are plugged into an AC supply the snubber circuit (C1, R2) to protect the triac from inductive loads is going to allow a trickle of current to flow. Yes, without a load to drag the voltage down the triac output would be a shock hazard.

At 120VAC the leakage is only about 500uA, so at 240VAC it becomes ~1mA, enough to hurt but not burn.

SCR's and Triac's often have snubber circuits to protect them from inductive loads such as motors. There is usually a warning label stating that with AC power plugged in to an active AC outlet there is a potential shock hazard, mostly if there is no load to drag the voltage down. That is a small load to even have 1 volt across it.

NOTE: If you use LED lights they may glow some even if the Triac is OFF. The fix for that is to always have a small load, even if it is hidden, to keep the voltage too low to turn ON LED lamps and too low to ever be a shock hazard.

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  • \$\begingroup\$ Thanks Sparky256, Could you please share us any useful circuit to fix snubber voltage leakage. \$\endgroup\$ – venkat y Feb 7 '19 at 13:47
  • \$\begingroup\$ The 'fix' is to keep a minimum load on it at all times. It is working like it's supposed to. You cannot change the design to make the leakage current go away. \$\endgroup\$ – Sparky256 Feb 7 '19 at 14:41
  • \$\begingroup\$ 1 volt across the load is NOT a shock hazard. \$\endgroup\$ – Sparky256 Feb 7 '19 at 14:43
  • \$\begingroup\$ but we are getting issue with celling dimming with this triac snubber voltage leak \$\endgroup\$ – venkat y Feb 7 '19 at 15:07
  • \$\begingroup\$ Then buy a different type of dimmer. \$\endgroup\$ – Sparky256 Feb 7 '19 at 15:23

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