Could not turn on triac/ how to test it

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Vindhyachal Takniki

Joined Nov 3, 2014
594
1. I have attached a circuit in which triac is driven using MOC3021. Load is connected as shown in ckt attched . It is pure resistive load of 350mA.
2. Ac voltage is 220Vac,50Hz, +5V to MCU is driven by using capacitive supply.
3. Attached fine picture of zero cross & signal to MOC3021. There is some logic by which I have to drive triac on after 1ms of zero cross pulse detect. Triac pulse is of 85us .


4. Problem is there is no load current flow, even I turn on moc3021 after zero cross detect. What is the problem?
I have checked the circuit connection multiple times all are ok.

Mod edit: removed and archived schematic with tranformerless power supply
 
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AlbertHall

Joined Jun 4, 2014
12,345
To learn more about the location of the problem, you can:
1. Ensure that MOC3021 is switched on and see whether that turns on the triac. Disconnect R8 from the PIC and connect it to +5V instead. If the PIC is in a socket you could remove the PIC and then link pins 1 & 5 on the socket.
2. Ensure that that the triac has gate drive and see if switches on then. Short together MAIN1 and MAIN2 on the MOC3021.
 

#12

Joined Nov 30, 2010
18,224
I wonder if 85 microseconds is enough time to fire the 2 triacs.
also, can't find the spec sheet for your larger triac.
 

Thread Starter

Vindhyachal Takniki

Joined Nov 3, 2014
594
Attached is image of zero cross detect & pulse at MOC3021 anode. Now I give triac pulse 2ms after zero cross is detected & triac pulse is 340us long.
I am not driving another larger triac by T1M5F-A, just connected load in series with it. But current does not flow thorugh load
 

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AlbertHall

Joined Jun 4, 2014
12,345
The larger triac specification says typical turn on time 2uS. I couldn't find an equivalent specification for the MOC device but it shows a graph of pulse width going down to 10uS, so it looks as if 85uS should be OK.
 

benta

Joined Dec 7, 2015
101
The MOC3021 needs at least 8 mA (worst case 15 mA) of LED current to trigger, which it is not getting. Don't forget to subtract the LED forward voltage as well as the output voltage drop on the 12F675 when calculating R8. Either make R8 smaller (if the 12F675 can supply more current), or use MOC3023 instead, then it should work.
BTW, even with MOC3023 you'll probably need to reduce R8.

Benta
 
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DickCappels

Joined Aug 21, 2008
10,152
Hello and welcome to All About Circuits.

Discussion of transformerless power supplies such as the one you are working on is not allowed according to the Terms of Service that we all read carefully before agreeing to abide by it.
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  1. Restricted topics. The following topics are regularly raised however are considered "off-topic" at all times and will result in Your thread being closed without question:
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