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Opto isolators TRIAC output

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su1c1d4l

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Im trying to control the operation of a 16watt, 220vac fluorescent bulb with electronic ballast through the PIC. will MC3021 be fine? I need help on the schematics.
 

See Fig.8:
https://kitsrus.com/pdf/moc3021.pdf
In this example the load is turned on by the triac when the output from a microcontroller is "L" ..
If you want to revers it, connect pin2[MOC3021] to the PIC's GND and drive pin1 through a resistor .. see picture below ..

Rgds,
IanP
 

thanks..can you guide me in calculating the Rin ? Im not familiar with Triacs and opto isolators.. basing on the diagram, do i need another external triac (near the LOAD)?
 

R[in] can be estimated from the following assumptions:

PIC output “H” ≈ 5V (PICs can source of up to 25mA per pin)
Voltage drop across LED inside the optocoupler => VF ≈ 1.5V
I[FT] – current required to latch output ≈ 15mA

(5V – 1.5V) / 15mA => 233Ω

You can choose 220Ω or 240Ω, it’s not critical ..

TRIAC on the diagram is “the TRIAC”, you don’t need anything else ..

Rgds,
IanP
 

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    su1c1d4l

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IanP said:
See Fig.8:
https://kitsrus.com/pdf/moc3021.pdf
In this example the load is turned on by the triac when the output from a microcontroller is "L" ..
If you want to revers it, connect pin2[MOC3021] to the PIC's GND and drive pin1 through a resistor .. see picture below ..

Rgds,
IanP
Click to expand...

i dont seem to understand the figure. if the TRIAC in the diagram is the TRIAC (mc3021) itself, i only need to connect the fluorescent bulb to the output terminals then?
 

su1c1d4l said:
i dont seem to understand the figure. if the TRIAC in the diagram is the TRIAC (mc3021) itself, i only need to connect the fluorescent bulb to the output terminals then?
Click to expand...

Leave the triac inside MOC3021 alone .. don't think about it ..
We are talking about an external power triac (see attached picture), that is triac that will switch the power on and off ..
What's inside MOC3021 - doesn't matter - it just drives the Gate of the power TRIAC ..

Rgds,
IanP
 

    S

    su1c1d4l

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oh i get it now...thanks for your help. maybe its much easier for me to use optocouplers + relays then..
 

Using a relay is just another option ..
However, if you use it you don't need an optocoupler, but a transistor to drive it .. see attached picture ..

Rgds,
IanP
 

actually i have the transistor-relay set-up now. but i have problems deactivating the relays. it affects the display of my LCD or worse, it resets the program! i have a LCD timer that controls the operation of these relays. i have no problems activating the relays, but deactivating them surely affects the LCD. what seems to be the problem?
i have replaced the 100 ohms with 330 ohm resistors
**broken link removed**
 

Hi su1c1d4l,
Sorry, why is it good/neded for you to start in same part/subject a second topic with same problematic pls!?
K.
 

Hi ALL,

I got some question on the method to drive external opto triac.
In order to turn on the external triac, the gate signal shall must be a AC signal. Am I right? As i read from the some triac data sheet, the gate signal is always a dc 5V or less signal.
Please advise me if i am wrong?

Thank you.
 

You apply DC to Gate of Triac. There is no conduction until GATE is triggred (firing angle). There is conduction after gate is triggred (conduction angle).
 

Hi jayanth.devarayanadurga,

After i apply a DC into the opto-triac, the internal triac of opto-triac will start to conduct. There means there will be a 240VAC signal flow through the triac and feed into the gate of external triac. Will it blow the external triac? As i read few datasheet regards the triac, it always mention the gate signal into triac shall be a DC signal and usually 5v or less. I am really confuse regards this portion.
But most of the AC switching circuit with opto-triac are using the same configuration. So i think the configuration shall be correct. But why AC signal can use to control the triac ?
 

In the second post IanP has given the circuit. Also see the datasheet. It shows example circuits for resistive load, inductive load, etc... Post your exact circuit. By controlling the conduction angle of AC you can control the power to the Load.
 

Hi,

If you look on ebay there are some good value triac boards like these 2 or 8 channels ones, they simply connect direct to the micros output pins.
Have used them myself and seems to work well.
**broken link removed**
 

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