Instructables

Small Triac Switch

Picture of Small Triac Switch
ssr-206-circuit.JPG
triacswitch.jpg
ssr-206top2.jpg
In order to switch some floodlights by my Arduino, the small switch circuits I built around a 39mf22 were just not man enough to handle the current needed, so I decided to build a switch with discrete components around a TRIAC.

Now these circuits are very easy and come a dime a dozen on the internet: just google for TIC206 or MOC3041 and you have lots of choice. The reason I make an instructable for such a simple circuit is to also provide a print design for those people to lazy or unable to make a design themselves :-)

But let me start with a disclaimer/warning:
This circuit is connected to a mains voltage that can kill you. If you do not know what you are doing then do not build this circuit.. Do not touch it when it is connected to the mains. The metal plate of the Triac is connected  to it's Terminal 2 and thus to the mains voltage. When in use, do not touch that plate to feel how warm it gets.
Put this circuit in a proper container.


Materials List
Triac TIC206  €1.20
MOC3041 €0.65
DIL 6 IC foot €0.15
LED €0.15
Resistor 220 Ohm 1/4 Watt €0.10
Resistor 470 Ohm 1/4 Watt €0.10
Connector €0.20
Piece of scrap PCB 23x43 mm

That is a total of €2.55
The links are just there to illustrate what I mean and to give a price indication. I have no links to that webshop other than that i use it and am satisfied with it.
It is also possible to use the considerably cheaper BT136-600, that like the TIC206 can deliver 4Amps, but it's gate current is a hefty 35-70mA as compared to the TIC206's 5mA. If a BT136 is used, the 470Ohm resistor may need to be a bit smaller (150 Ohm)

additionally you may need:
capacitor 10-100nF 400V
resistor 39-100 Ohm
resistor 330 Ohm

The PCB is here.
and mirorred here.

The circuit
The main components in this circuit are the MOC3041 optocoupler and the TIC206 TRIAC (M or D version). I have chosen for a MOC3041 because it has a zero crossover circuit in the chip, ensuring smooth switching. The TIC 206  is a triac that has a relatively sensitive gate.

The output from an Arduino or other uP  is led to the MOC3041 via a 22o Ohm resistor and an LED. This way one can see for sure if there is current flowing through the optocoupler. 
The gate of the thyristor is fed  from a 470 Ohm resistor that connects through the MOC3041 optocoupler
On the printed circuit board there is room for a 330 Ohm resistor (labelled with a '*'). If one uses the TIC206 TRiac this resistor is not necessary. Some other thyristors however may need that resistor in order to start.

As I am switching a lamp, I have no use for a snubber circuit (formed by the 100R resistor and C1). However, if you switch inductive loads you will need one. The values of the resistor and capacitor may vary depending on your situation but a proper way to start would be a 100 Ohm resistor and a 100nF capacitor. The PCB offers holes at various distances, suitable for different sizes of capacitors.

The PCB
Download the PCB design(s) above and use your favorite method to etch your PCB. With regard to the design: the pcb picture in this ibble is seen from the component side: The copper traces thus are actually seen as if you are looking through the board. That is why the writing is in reverse. This design is suitable for a direct toner transfer

If you use the mirrorred design, the writing  is in fact not mirrorred. 

I have used the non mirrorred design for a direct toner transfer (printing it on glossy paper and ironing it on a copperplate)  and that works well. Etching in Hydrochloric acid and Hydroyperoxide.

Connecting
There is only a two pole connector on this PCB that can be thought of as a switch, interrupting the 'Live' line of a connection, just like a regular switch. The figure shows the proper way to connect it according to EU codes: Blue is neutral, brown is live black is switched and yellow green is earth. Outside the EU there are different colour codes.


rmatkar2 months ago

Thanks for the post. So I have implemented a similar circuit with 470ohm resistor and BT136 triad The resistors that i have used are of 1 watt. Correct me if I am wrong but, the wattage of the resistor does not matter where the 470 ohm resistor is placed! and how much current can this circuit handle as in ...can I use this circuit to control may be an AC or a refrigerator?

diy_bloke (author)  rmatkar2 months ago

Tnx rmatkar. The wattage of the 470 ohm resistor ofcourse is important, but it doesn't need to be so high. :-) Unless you want to cater for worst case scenario's 1/4 w or 1/2 w is ok.
the BT136 can handle 4 ampere so as long as the current consumption of your ac or refrigerator stays within that it shld be ok. can advise though to add a heatsink to yr bt136 and to add the snubber network as I indicated

diy_bloke (author)  rmatkar2 months ago

Tnx rmatkar. The wattage of the 470 ohm resistor ofcourse is important, but it doesn't need to be so high. :-) Unless you want to cater for worst case scenario's 1/4 w or 1/2 w is ok.
the BT136 can handle 4 ampere so as long as the current consumption of your ac or refrigerator stays within that it shld be ok. can advise though to add a heatsink to yr bt136 and to add the snubber network as I indicated

samueltoast2 months ago

hi people! i have 1 question:

wich pin of the moc 3041 gives the zero-crossing signal to the arduino?

PS: im an italian student so excuse me for my english

diy_bloke (author)  samueltoast2 months ago

Hi Samuel. Nothing wrong with yr english.
It isn't specifically 1 pin that gives the zero crossing signal: the MOC3041's output is between pin 4 and 6. It doesn't give a zerocrossing signal, it connects between pin 4 and 6 if it gets an input signal on pin 1 and 2, but it makes that connection at zerocrossing. The MOC3041 therefore has a zero crossing detector, but doesnt give a zerocrossing signal

Thank you!!

eticzon2 months ago

can i use a stm32 instead of arduino to control the light ..??

diy_bloke (author)  eticzon2 months ago

Yes, ofcourse :-) The circuit is not depending on one specific kind of controller. Any uC that has a pin that can switch HIGH and LOW is useable

AnonCh4rl17 months ago
Great Simple stuff, Thanks for posting this.

But I don't understand one thing.. with the zero crossing MOC - when not being triggered externally by arduino is it totally off or does it still trigger the Triac a little every crossing of the zero line?

Is this the reason some Triacs can only regulate down to like 10-30%

Many thanks
diy_bloke (author)  AnonCh4rl17 months ago
Thanks for your kind words.
The zero crossing opto-coupler needs input to do its work. If no input, no action. The zero cross filter does not do any thing autonomously.

Therefore it also has nothing to do with Triacs only being able to regulate down to 10-30% only. In fact I am not even sure if that in itself is true :-)

Mind you though that this circuit is a switch, it is on or off. I am sure there may be some loss in the Triac, but not 10-30%

If you have any more questions dont hesitate to ask
zant761 year ago
How many watt can be load..
diy_bloke (author)  zant761 year ago
That largely depends on the used Triac. The Tic206 has an RMS load of 4 Ampere so it can load 880 Watt
Nice project, just a small (but serious) correction.Although the image specifies phase, neutral and earth in correct colors, the description in the end states brown as neutral and blue as live (phase). And i live in Europe!
(besides, its not the colors that matter but the essence of the circuit, that it controls the "live" line, not the neutral.
Other than that, great little project!
diy_bloke (author)  tkefalopoylos1 year ago
Thanks I made a mistake as I surely know blue is the 'safe' one. I will correct it. Thanks
chipper351 year ago
Simple, clear....perfect!!
diy_bloke (author)  chipper351 year ago
thanks :-)
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