Optocoupler

[chaitrali]

hello,
i am using MOC3021 optocoupler for dimming of the bulb.I have done it but if i change the another same MOC3021 i am observing different output

 

[Minder]

That is a random phase control triac driver, not really intended to drive a load directly and meant for control of AC loads.
Are you switching the load with the opto?
More info needed!
Look up Fairchild app note AN-3006. For phase control .
M.

 

[chaitrali]

i am driving the triac gate with the help of moc3021

 

[Minder]

That is a random phase opto couple and has to be synced to the zero cross over, either by logic or RC methods see the app note for both methods.
Show your circuit.
M.

 

[chaitrali]

See the digram

 

[Minder]

You don't have any phase control circuitry?
M.

 

[chaitrali]

no

 

[Minder]

Then you have no control if and where on the incoming phase where it is going to fire!
M.

 

[hevans1944]

Even if the BC547 transistor collector were not wired to a pin that is not connected (NC) on the datasheet, the most this obsolete optocoupler would do is turn the triac on or off. No dimming effect will occur without some sort of phase control of the input pulse with respect to the AC power connected between HOT and NEUTRAL

Collector of BC547 should connect to pin 2.(CATHODE) of the LED, with a current-limiting resistor in series between +3.3 V DC supply and pin 1 (ANODE) of the LED. Or Is that what the thick black vertical "wire" in the drawing is supposed to represent?

See attached page from datasheet for application information.