The circuit is totally simple but the resistance will give it protection at the input in HIGH voltages. Whenever the IR signal will be generated at then the logic state will be changed from 1 to 0, due to change in the flow of current. The optocoupler at input requires current limiting one resistance but at the output, we will need to connect the logic output pin with the power pin. The working of PC817 is very simple but to use it with different devices comes with specifications. These are the alternative options: 4N25, 6N136, MOC3021, MOC3041, 6N137 PC817 IC Equivalent It will be used to make the common ground with Power supply and the circuit. It will give the logical output by receiving the IR signal. Pin 3 is an output pin of the internal IR receiver of the optocoupler. It will give the IR to make the common ground with the circuit and Power supply. Pin 2 is the cathode pin of the IR within the optocoupler. It will give the logical input signal to the internal IR. So we can change 9V in one micro second.Pin 1 is an anode pin of IR input within the Optocoupler. The graph below will give you a good understanding of the time take.įor example at 30 degree Celsius of ambient temperature the rate of change of voltage with respect to time will be 9V per unit time, where unit time is uS. This switching speed depends in the amplitude of voltage that is being controlled by the TRIAC and the operating ambient temperature. When trying to switch AC loads it is important to understand the switching speed of the Opto-coupler. When we switch the TRIAC using PWM signals then the output voltage across the load can be controlled thus controlling the speed/brightness of the load. The MOC3021 can be used to switch loads by just turning the LED on or off, or we can also use PWM signals to switch the LED and thus the TRIAC. A simple circuit diagram in which an AC bulb is controlled using a microcontroller is shown below. They are normally connected to another power switch like a Triac in our case, this TRIAC will be able to provide enough current to drive the loads and will be controlled using the opto-coupler. Either way, an opto-coupler will not be allowed to drive loads directly due to its limited current rating. The MOC3021 is normally used to control AC appliance, like brightness of a Bulb, speed of a motor etc. So if you are looking for a opto-isolator to control a AC application through DC then this IC might be the right choice for you. Since the output is controlled we can control the intensity of the light or the speed of a AC motor. This features of MOC3021 makes it an ideal choice for controlling high voltage AC loads through digital controllers like MPU/MCU. It also has a decent rise and fall time and hence can be used to control the output voltage. Also since it has zero-crossing ability, when the AC load is switched on for the first time the TRIAC will start conductiong only after the AC wave reaches 0V this way we can avoid direct peak voltages to the Load and thus preventing it from getting damaged. Since the output is driven by a TRIAC we can drive loads upto 400V and the triac can conduct in both directions hence controlling AC loads will not be a problem. The speciality of MOC3021 is that it has Zero-Crossing ability and is driven by a Triac. As we know the term Optocoupler/optoisolater means the same that is we use light to indirectly couple to sets of circuits. The MOC3021 is a Zero-Crossing TRIAC driven Optocoupler or Optoisolator. Where to use MOC3021 Phototransistor Optocoupler MCT2E (non-Zero transistor), MOC3041 (Non-Zero Cross TRIAC), FOD3180 (High-Speed MOSFET), Note: More details can be found at the MOC3021 datasheet which is available for download at the end of this page. Available as 6-pin PDIP with and without M-suffix.TRIAC output terminal voltage: 400V (max). Opto-isolator with Zero-Crossing Triac Driver.Other end of the Triac which is present inside the IC One end of the Triac which is present inside the IC
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