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Sparkfun's EL Escudo Dos breakout board uses this circuit for an EL wire driver channel, with R2 = R3 = 330.
I was wondering what the function of R2 and R3 is? Are they required? What would happen if they were simply replaced with a short?

EDIT: additional info
The HV lines are 110VAC and the channel will be driving EL tape (I think resistive and capacitive load?)

enter image description here

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    \$\begingroup\$ You're way too fast with accepting. Questions with an accepted answer get less new answers, which otherwise might be interesting too. I suggest to wait for a day or so, so that the question has time to go around the world. (I'm awake, but the rest of Europe isn't.) Or at least until there are a couple of other answers. \$\endgroup\$
    – stevenvh
    Commented Aug 13, 2012 at 0:40
  • \$\begingroup\$ @stevenvh Hmm, good point. Will keep in mind. \$\endgroup\$
    – Shubham
    Commented Jan 9, 2013 at 23:02

2 Answers 2

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Current limiting. The MOC3043 has a photodiode, and just like any diode can fry if not current limited.

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  • \$\begingroup\$ I understand that, but I was asking about R2 and R3. \$\endgroup\$
    – Shubham
    Commented Aug 12, 2012 at 23:19
  • \$\begingroup\$ So was I. R1 is for the LED, R2 and R3 are for the photodiode. \$\endgroup\$
    – mordac
    Commented Aug 12, 2012 at 23:22
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It's there to limit the peak current through the driver triac.
In the datasheet for the MOC3043 this is given as 1A. So for a 115V RMS line with a pk-pk of ~170V, a resistor of around 180 ohms is suitable. The 330 ohms given is more suited to a 240V line, but if it works okay for your application then fine - the resistor value also sets the turnon angle, and too high a value may prevent the power triac getting enough gate current to turn on fully.

This App Note has some good info on (optocoupled) triac driving.

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