Snubber leakage current problem

[efendi]

Hi

I use triac, with RC snubber, as AC switch. Snubber to cancel the inductive loads effect. I get snubber leakage current problem, when the triac is off the leakage current through the snubber make the bulbs (connect with triac) flickering. How can I solve this problem ?

 

[crutschow]

Use a smaller capacitor and/or a larger resistor in the snubber circuit.

 

[efendi]

Ok, I can use this but still there is XL value of the capacitor !!

 

[crutschow]

Ok, I can use this but still there is XL value of the capacitor !!

What does that mean?

 

[betwixt]

I think they mean XC not XL.

There isn't much you can do about that, the leakage is the normal operation of the capacitor, making it's value smaller or increasing the resistor value will reduce the leakage but also reduce the effectiveness as a snubber network.

What you might be able to do is provide an alternative path for the leakage current to flow through. Possibly you bulbs have electronic ballasts in them which tend to charge from the leakage until the bulb 'ignition' point is reached then discharge again, making the cyclical flashing you see. If you wire a resistor across the bulb to sink some of the current you migh be able to keep the voltage low enough that it gets ignored by the bulb.

Brian.

 

[schmitt trigger]

What Brian is describing is exactly what is going on. This is very common.

If your loads only consists of compact fluorescent lamps, then completely remove the snubber, the load doesn't need it!

 

[DanyR]

You can also do the following:
- move the snubber circuit such that it is over the load, AND
- add an extra capacitor (large value much more than the snubber capacitor, e.g. 220nF, 230Vac) across the mains connection of your circuit (close to the triac). Due to the large capacitor the load snubber will be virtually present over the triac and should still do its job.