Pc817 Ic3/18/2021
The device is uni-directional and can only pass a signal in one direction.Most often, they are used in a digital circuit to provide electrical isolation between a uC and a high energy output circuit such as a motor or to provide an additional layer of protection when using something like a relay to control a high energy device.
They work by blocking any electrical spikes that might otherwise find their way back down the line to the uC. Pc817 Ic Full Isolation IsThis is typically over-kill for most hobby applications, but something to consider when full isolation is desired. Driving the LED causes the base of the phototransistor to also be driven, thus turning on the phototransistor. The absolute maximum current through this LED is 50ma, but in practice the current should be limited to no more than 20mA for safe use with a uC. The max current is again 50ma, but it is typically operated at a lower current. Pc817 Ic Series Resistor IsDepending on what the optocoupler is being used to interface to, typically either a pull-up resistor is used that connects between the collector of the optocoupler and the power (Vcc) that is being used on the output side of the circuit or a series resistor is used that is connected between the emitter and the base of a transistor if a transistor is being used on the output. A 470 ohm resistor can usually be used as a starting point for this resistor as well. A logic HIGH on the input should light the LED on the output.
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