Types of optocouplers and alternative methods

Optocouplers are widely used in switching power supply circuits to provide electrical isolation between different parts of a system. These devices can be categorized into two main types: nonlinear and linear optocouplers. Common nonlinear optocouplers include the 4N series, such as 4N25, 4N35, 4N26, and 4N36. On the other hand, linear optocouplers like the PC817A–C series, PC111, and TPL521-1 are often used in applications requiring more precise signal transmission. There are numerous types of optocouplers available, but only four are commonly found in home appliance circuits. Let’s take a closer look at each type: 1. **First Type – LED and Phototransistor Package**: This optocoupler comes in a dual-inline 4-pin plastic package. The internal circuit is typically shown in a table, and it is primarily used in switching power supply circuits for signal isolation. 2. **Second Type – LED and Phototransistor with Different Pin Configuration**: Similar in function to the first type, this optocoupler uses a 6-pin dual-inline plastic package. Its internal structure is also illustrated in a table, and it serves the same purpose in power supply circuits. 3. **Third Type – LED, Phototransistor with Terminal Attachment**: This version also has a 6-pin dual-inline package and includes an additional terminal for external connections. It is mainly used in audio circuits for AV (Audio-Video) conversion. 4. **Fourth Type – LED, Photodiode, and Transistor with Terminal Attachment**: This type features a 6-pin dual-inline package and combines a photodiode with a transistor. It is specifically used in video circuits for AV signal transmission. Here are some common examples of each type: **First Category:** PC817, PC818, PC810, PC812, LTV817, TLP521-1, TLP621-1, ON3111, OC617, PS2401-1, GIC5102 **Second Category:** TLP632, TLP532, TLP519, TLP509, PC504, PC614, PC714, PS208B, PS2009B, PS2018, PS2019 **Third Category:** TLP503, TLP508, TLP531, PC613, 4N25, 4N26, 4N27, 4N28, 4N35, 4N36, 4N37, TIL111, TIL112, TIL114, TIL115, TIL116, TIL117, TLP631, TLP535 **Fourth Category:** TLP551, TLP651, TLP751, PC618, PS2006B, 6N135, 6N136 In terms of substitution, optocouplers from the first and second categories are generally interchangeable, provided the pin configuration matches. However, optocouplers from the third category can sometimes replace those from the first or second, but the reverse is not always true due to differences in functionality and design. Always check the datasheet before making any substitutions to ensure compatibility and proper performance.

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