12/30/2023 0 Comments Opto isolator inpug ic![]() ![]() The led can be controlled using DC, and the TRIAC used to control AC. TRIAC is mainly used where AC based control or switching is needed. PHOTO-TRIAC OPTOCOUPLER In the upper image the internal construction or the TRIAC based opto-coupler is shown. 4N32, 4N33, H21B1, H21B2, H21B3 are few photo-Darlington based opto-coupler example. The 6th pin which is internally connected to the base of the transistor, used to control the sensitivity of the transistor as discussed previously in photo-transistor description. This type of opto-coupler also used in DC circuit related area for the isolation. As usual the LED emits infrared led and controls the base of the pair transistor. In this configuration the Darlington Transistor provide high gain ability. Darlington Transistor is two transistor pair, where one transistor controls other transistor base. PHOTO-DARLINGTON TRANSISTOR OPTOCOUPLER In the upper image there are two types of symbol, internal construction of Photo-Darlington based opto-coupler is shown. ![]() Photo – Transistor based opto-coupler is used in DC circuit related isolation. PC816, PC817, LTV817, K847PH are few widely used photo-transistor based optocoupler. Also, before using Photo-transistor based optocoupler, the user must know the maximum rating of the transistor. In this configuration, false triggering due to noise or electrical transients can be controlled effectively. Often the pin is used to connect with ground or negative using a high value resistor. This pin 6 is used to control the sensitivity of the photo-transistor. On the second image on the left, there is additional pin out which is internally connected with transistor’s base. Photo-Transistor can be further of two types depending on the output pin availability. The Transistor type can be anything whether PNP or NPN. In the upper image the internal construction is shown inside a Photo-transistor Optocoupler. ![]() an optocoupler, electrical isolation up to 10kV is achieved.Since there is no direct electrical connection between the input and output of.Both the input Andthe output lines of a system can be protected in this way. Typicaldevices produce several kilovolts of electrical isolation.The important aspectof the operation of this arrangement is that there is no electrical connectionbetween the input and the output – they are linked only by light. Thus, the opto-isolator acts as a logical inverter.will be illuminated, causing the phototransistorto turn on.If a positive voltage (logical 1) is applied to theinput of the opto-isolator, the LED.resistor R therefore produces an outputvoltage of approximately VCC.The phototransistor receives no lightand is also turned off. When zero volts (logical 0) is applied to the input of theopto-isolator, the LED is.The opto-isolator consists of an LED and a phototransistor within a single package.The photo-transistor and photo-darlington devices are mainly for use in DC circuits while the photo-SCR and photo-triac allow AC powered circuits to be controlled. The four optocouplers are called the: Photo-transistor, Photo-darlington, Photo-SCR and Photo-triac as shown below. Optocouplers are available in four general types, each one having an infra-red LED source but with different photo-sensitive devices.The basic design of an optocoupler, also known as an Opto-isolator, consists of an LED that produces infra-red light and a semiconductor photo-sensitive device that is used to detect the emitted infra-red beam.But we can also provide electrical isolation between an input source and an output load using just light by using a very common and valuable electronic component called an Optocoupler.In other words, transformers isolate the primary input voltage from the secondary output voltage using electromagnetic coupling and this is achieved using the magnetic flux circulating within their laminated iron core. OPTO ISOLATOR We know from our tutorials about Transformers that they can not only provide a step-down (or step-up) voltage, but they also provide “electrical isolation” between the higher voltage on the primary side and the lower voltage on the secondary side. ![]()
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