Optical Coupler Parameter Resistor Selection
Subtract the led voltage from the supply voltage, this gives the Voltage across the resistor, and divide it by the led current, that will give you the resistance to use. An optocoupler, also known as photocoupler or opto-isolator, is a device which can transfer an electrical signal across two galvanically-isolated circuits by way of optical coupling. Unlike transformers or capacitors, which can only transfer AC signals across the isolation barrier, optocouplers can. This document outlines the basic characteristics and application design of general-purpose transistor output photocouplers (optical isolators). Since a nano will probably fry instantly if the 12v trigger wire is directly connected to it, i used to use a 5v1 Zener diodes coupled with a few resistors to step down voltage to 5v. An EL817 without suffix letter has minimum CTR (current transfer ratio) of 50% at an LED current of 5 mA. The UCC23513 is a 4-A, 5-kVRMS single channel isolated gate driver in a stretched SO6 package.
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