HI,
I want to use a MOC3023 optocoupler to switch an 20V/100mA current. For my understanding the TRIAC will be in a 'closed' (leading) -state as long as the led is turned on. Right so far? Because the TRIAC is designed as two diodes in reverse direction, I could switch AC and DC currents. Couldn't I?
Thanks
Kai
Not really, a triac, once it's turned on, doesn't turn off unless the voltage goes to 0 (really, the current goes to 0). So your optocoupler couldn't turn off the DC current through the triac once it's turned on. The triac can control AC current this way because the AC voltage automatically goes to zero 120 times a second (100 times a second for 50 Hz systems).
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The Ruggeduino: compatible with Arduino UNO, 24V operation, all I/O's fused and protected
doesn't turn off unless the voltage goes to 0 (really, the current goes to 0).
Actually it is both voltage and current dropping below a certain threshold at the same time.
Sometimes you can't turn off a triac with an inductive load on AC because the phase between the voltage and the current never meets the commutating condition at the same time.
Grumpy_Mike:
Actually it is both voltage and current dropping below a certain threshold at the same time.
Sometimes you can't turn off a triac with an inductive load on AC because the phase between the voltage and the current never meets the commutating condition at the same time.
Not quite, the condition is for the current to drop below the holding value and dV/dt to remain below the commutating value when this happens. The problem with inductive loads is that when the triac switches off, the current in the inductor is no longer changing so the back emf in the inductive load collapses, and this change in voltage can exceed the commutating dV/dt limit for the device.