Understanding Zero Cross Triac operation

Thread Starter

Vindhyachal Takniki

Joined Nov 3, 2014
568
1. I have a application in which need to turn on & off a load, resistive in nature.
mains is 220va/50Hz & load is 750ohms approx. MCu is +5V operated.

2. I was looking at MOC3063M ( https://www.fairchildsemi.com/datasheets/MO/MOC3061M.pdf ),

As it only needs 5mA forward current for tun on & off its diode at input.

3. Does zero cross triac works as :
a)If I send +5V input on diode (Pin 1 & 2), with minimum 5mA of current, then the load will be turned on whenever zero cross happens
& load will be on as long as +5V is there on 1 & 2 pin.

b) And If I send zero input on diode (Pin 1 & 2),then the load will be turned off whenever zero cross happens
& load will be on aff long as zero is there on 1 & 2 pin.

c) is this how this triac will work?

d) Will use Figure 12 ckt as datasheet link provided above except the snubber circuit.

4. is there any other zero cross triac to use ?

crutschow

Joined Mar 14, 2008
26,064
3 a) Yes, but you need to add a resistor in series to limit the current, as the input is a diode with a forward voltage of about 1.4V.
Applying 5V directly to the input will likely burn out the diode.

3 c) Yes.

4. I'm sure there are but why would you want to?

MrAl

Joined Jun 17, 2014
7,891
1. I have a application in which need to turn on & off a load, resistive in nature.
mains is 220va/50Hz & load is 750ohms approx. MCu is +5V operated.

2. I was looking at MOC3063M ( https://www.fairchildsemi.com/datasheets/MO/MOC3061M.pdf ),

As it only needs 5mA forward current for tun on & off its diode at input.

3. Does zero cross triac works as :
a)If I send +5V input on diode (Pin 1 & 2), with minimum 5mA of current, then the load will be turned on whenever zero cross happens
& load will be on as long as +5V is there on 1 & 2 pin.

b) And If I send zero input on diode (Pin 1 & 2),then the load will be turned off whenever zero cross happens
& load will be on aff long as zero is there on 1 & 2 pin.

c) is this how this triac will work?

d) Will use Figure 12 ckt as datasheet link provided above except the snubber circuit.

4. is there any other zero cross triac to use ?

Hello there,

Yes a zero cross triac turns on at zero degrees or near that and that helps reduce surges and EMI in some applications, and you do need a resistor in series with the LED.

The more important thing here though is the load and line voltage and size of the package. These little devices are not usually used alone but with a separate triac, even if it is a small one like a 1 amp rated device. This package has a rating around 250mw and with 220vac rms and 750ohm load that could lead to a power dissipation of over 700mw which is almost three times as high as the package rating.
This means the package could easily burn out.

Better is to use it with a small triac (even a 1amp rated unit) and go from there.
Check the data sheet for more info though on both this unit and the triac of choice.

Is there a single device that can handle the power? There might be but probably in a larger package. There are also the solid state relays that have everything in one package even the resistor for the LED.

MaxHeadRoom

Joined Jul 18, 2013
22,049
See Fairchild APP note AN-3006 for explanation of both.
Max.

bertus

Joined Apr 5, 2008
21,055
Hello,

Here are two application notes.
One for random and one for zero crossing switching.
Read them and you will understand the difference.

Bertus

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