Skip to main content
Electrical Engineering

Return to Answer

added 159 characters in body
Source Link
Oli Glaser
Oli Glaser
  • 55.5k
  • 3
  • 77
  • 148

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.

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.

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.

Source Link
Oli Glaser
Oli Glaser
  • 55.5k
  • 3
  • 77
  • 148

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.