Triac leakage current control

Hi All,

I am working on phase control of electrical appliances using a Triac. I have an RC snubber circuit.The problem is that the snubber has a leakage of around 5-6mA, which causes loads such as CFL bulbs to flicker even at OFF state.

Please suggest me a way, to overcome this issue.Do Triac's which have an in-built snubber, not require an external snubber circuit.

I intend to control both inductive and resistive loads at 230V AC.

Thanks in Advance.

Best Regards,
Syed Aban

First off the simple snubber circuits are a small cap and resistor in series, say 100 nF and 2v to 5 ohms. This is also known as a Boucherot Cell, and well as another name I forget. If this is leaking at all you have a component problem.

In fact Triacs shouldn't need a snubber circuit unless they are exposed to a very high dV/dT.. Once they're turned on they stay on until the current goes to zero as it changes polarity. As such there is no current to snub.

I have used "snubberless" Triacs successfully without external circuitry for decades with highly inductive loads that killed relays. I have never had one fail under normal circumstances. (I did once have one fail - it disappeared and left a hole in the board when a loose neutral wire contacted L1.) I prefer the BTA12-600BW, driven by an MOC3043 or equivalent. If you need more current you can use a BTA24.

The MOC3043 (probably an MOC3063 is now more common) is an opto isolated triac driver circuit that is in fact a triac itself. It can be driven directly with 5v through most microprocessor low true outputs. I believe The MOC3043 turns on at zero crossings as well as turning off at zero crossings, very nice unless you want to control power with a PWM, say for dimming.

Hi Stephen,

Thanks for your prompt reply.

I have attached a pdf of my circuit .Please give your valuable feedback.

Best Regards,
Syed Aban

Dear Mr.Syed Aban,

The leakage you report, is certainly due to a lost of insulation in the snubber's capacitor. Change it by a good one.

Best regards

Dear Mr.Geraldo Lopes Serodio,

Thanks for your reply.

I did not get what you mean by "*lost of insulation in the snubber’s capacitor*".
Also, can I ignore the snubber circuit altogether if i use a *Snubberless Triac*, instead of a standard Triac.

Best Regards,
Syed Aban