The pin numbers for 4 and 6 are in the wrong place; exchange them. The emitter side (on the left) has a Vf of around 1.2v @10mA. Calculate your current limiting resistor R1 as: Rlimit = (Vsupply - 1.2v)/10mA So, if your V1 is either 5v or 0v, then: Rlimit = (5v-1.2v)/10mA = 3.8/0.01 = 380 Ohms. Optocoupler, Phototransistor Output, with Base Connection DESCRIPTION This datasheet presents five families of Vishay industry standard single channel phototransistor couplers. These families include the 4N35, 4N36, 4N37, 4N38 couplers. Each optocoupler consists of gallium arsenide infrared LED and a silicon NPN phototransistor.
optoisolator (optical coupler or optocoupler): An optoisolator (also known as optical coupler , optocoupler and opto-isolator ) is a semiconductor device that uses a short optical transmission path to transfer an electrical signal between circuits or elements of a circuit, while keeping them electrically isolated from each other. These.
A 220V mains voltage is stepped down to 9V using a step-down transformer and then it is sent to a 4N25 Optocoupler. This optocoupler has a built-in LED and an output transistor that de-actives when the AC wave goes close to the zero-crossing point and they both are activated when the signal increases to the peak point.