how to us moc3020 and 4N25

how to use moc3020 and 4N25 in one circuit

any circuit diagram??????????

Going to need more to go on. What are you trying to do?

i m having project on light control system in which i have triac trigging is used and also have to generate a wave and vary its phase.......so i have to use both of them but how????

This example is a classic dimmer system for lighting

dfullmer said:

This example is a classic dimmer system for lighting

Click to expand...

in the schematic you provided .... what is the purpose of using two opto coupler together.....?

It's exactly as described on the diagram, it's a zero crossing detector.

You have to understand why it's needed to see how it works. The remainder of the circuit (including the missing RC parts) is there to produce a pulse to trigger the triac. When you trigger the triac it starts conducting but will not turn off until the voltage across it is removed (or reduced to a very low voltage). When you are trying to control the power to the load it is necessary to control the time within each voltage cycle you produce the trigger pulse. If you trigger immediately the voltage starts to rise, it will conduct over the whole half cycle, if you trigger it at the end it will only conduct for a short time before the lack of voltage will stop it conducting by itself. So to set the power you require you adjust the trigger point delay from the start of each cycle. To do that you need to discover the zero crossing point which is where the AC passes through the zero as it changes between negative and positive polarities, in other words the start of the cycle.

Looking at the two opto-couplers you will notice the output sides are in parallel so if either LED turns on, the transistors will conduct and output side will go to a low voltage. The low voltage is used to feed the timing circuit. The LED side of the opto-couplers are wired in parallel but with the connections reversed. This means on one half cycle one LED will illuminate and on the other half cycle the other will illuminate, at the point where the voltage is below the LEDs Vf, neither will illuminate. The output of the opto-couplers will therefore be a high pulse starting just before AC zero crossing and ending just after it. This is the reference time or zero crossing point you use as the timing reference.

You can do the same by using a bridge rectifier and single opto-coupler but the extra voltage drop in the bridge rectifier makes detecting the exact zero point less precise.

Brian.

thanx both of fo making me clear

---------- Post added at 17:16 ---------- Previous post was at 17:07 ----------

i have only 1 ic of 4n25....................nowwwwwwww?????????????? can i make this ?????????

alina,
bitwixt (Brian) gave you a great expanation (thanks). Without two of them you will not be able to develop the zero cross timing pulse. Can you get a second in time for your project? They are inexpensive and availible.

dave

yeah m thnkful to brian and understood same thing u told but afta some time

i am working on this cct basically and have to add 4n25 in this circuit.. so thats y was a bit confused

I Think I understand now. This cct uses the full wave dc to produce a zero cross detect. as the dc voltage drops to zero (at the half cycle) it develops a signal to your controller. This is what is used to develop a delay signal to the moc to turn on the triac. This can also work fine.

dave

now how can i add 4n25 in this cct????? because in cct given by you 4n25 is having ac voltage and in this cct i ll give rectified input to 4n25?????and then output of 4n25 to microcontroller is it ok???????? plz comment

You can use the 4N25 in this circuit in place of the transistor circuit to do the same job.

ok thank you sooo much