Using a Thyristor (TRIAC) to Switch 220VAC Line Power

[AlStorm Prime]

Hi there guys!

So am looking at MOC3043M Zero-Cross Triac Driver Output Optocouplers datasheet (link) and it suggests next circuit for Hot-Line Switching applications (Figure 15):



The problem is that this drawing specifies "Neutral" line.
How can I find / determine the 'Neutral" line in my 220V, two wire, wall outlet?
Thank you!

[Towz]

Since your control circuit is isolated from the mains it doesn't really matter. BUT, I guess deppending on your local ac configuration (Y or delta) you could measure the ac voltage across both mains outputs against mains earth, the one with the lower drop will be the neutral (N) and the other one will be line (L). Note that the neutral is not the same as mains earth and should be treated same as the line.
A voltage probe (those pen looking thingys) should also be able to detect the line output.

[Tomorokoshi]

What kind of load?

Perhaps add a fuse to it.

Any PCB layout yet?

[paulhm81]

Hi
I don't want to be the one to say this, but maybe you shouldn't play with 220 if you don't know to determine the neutral. Be very careful and check whatever you are trying to do 10 times before plugging it in!
Wish you all the best!

[AlStorm Prime]

Towz,

This is what actually confused me.
The drawing clearly specifies positioning of 'Load' from the 'Neutral' side. But, is it crucial or I can tweak things around - I don't know.

Tomorokoshi,

The first load will be 220V LED bulb, like this one. And the idea is to use control signal from PIR (like this) to 'automatically' switch light ON/OFF.
The end product might be similar to this. For now I am not sure how I am going power PIR sensor with a DC supply and where I will put photoresistor
(to force lights OFF during daytime) so no PCB layout just yet.

paulhm81,

Thank you for the warnings. What confused me was that this device do care in which way it's connected to the outlet.
I am also open for any safaty advices.

[Cerebus]

That circuit (Fig. 15) will work quite happily with live and neutral either way around. Both components, the opto-triac and the triac proper, are agnostic as to which is phase and which is neutral as long as they are wired the same in relation to each other. The only time you need to worry with as simple a triac switch as this is if you have more than one phase kicking around, when things can get interesting if you're using parts that are rated for phase-to-neutral but not for phase-to-phase.

And yes, a fuse is essential. Also make sure your triac is rated for both the voltage and the current that you're using, noting that triac ratings are normally peak not rms. Also don't assume that the resistors you're using are rated for that voltage, use identifiable manufacturers parts and check the data sheet. And be conservative about ratings, if in doubt plump for the next band up in voltage or current rating.

[Towz]

There will be no difference for the load, the triac or the optotriac; from their point of view the supply will look exactly the same. You can place the load either on the "high" or the "low" side.

[AlStorm Prime]

Thank you guys, it clarifies a lot!

I also was suggested that the load is placed from the Neutral side for a safety reasons in case if this load is stationary, like a chandelier.
So you want to cut off your Hot line to make lamp replacement safe. And in other cases, when load is unpluggable it doesn't matter, since you can unplug a socket before maintanence.

[SeanB]

Just remember that driving a LED lamp with a TRIAC can cause issues of flashing when off, as the slight leakage current through the snubber capacitors can be enough to charge the power supply in the lamp up to startup, which will make the lamp either flicker when off, or flash every few seconds.

In most of the PIR lamp units I have met they tend to use a capacitor power supply to provide the supply, using a 48V relay to drive the load. The relay is driven from a 48V supply so the coil current is very low, and they use this supply as well to make the 5V and 12V ( if needed) rail for the controller using a resistor and zener diode. They use a 51V zener diode and a 100uF capacitor for the power rail, which provides enough power to pull in the relay, even though this supply might drop down to 30V with the relay pulled in, which is enough to keep the relay held in. Relay drive is simple, using a single transistor with a 100ma current rating and 100V Vceo, or a small logic level high voltage MOSFET.

Relay has around 100000 cycles at low load, more than enough for a light, as it will still last 3 years switching a 1A load ( the rating is 10A) 300 times a night.

[getfast_kiran]

Just remember that driving a LED lamp with a TRIAC can cause issues of flashing when off, as the slight leakage current through the snubber capacitors can be enough to charge the power supply in the lamp up to startup, which will make the lamp either flicker when off, or flash every few seconds.

I am facing this exact issue....Do you have any method to rectify this Issue. I am using a snubberless TRIAC and MOC3021 as opto coupler.