817B Optocoupler
This component is an 817B Optocoupler (also known as an Optoisolator) in a 4-pin package (common equivalents include PC817B, EL817B, or LTV-817B).
Description
This component is an 817B Optocoupler (also known as an Optoisolator) in a 4-pin package (common equivalents include PC817B, EL817B, or LTV-817B).
Marking Breakdown
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817B: Core part family (817 series) with a Rank B Current Transfer Ratio (CTR), which typically ranges from 130% to 260%.
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L2045: Manufacturer batch / date code.
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Small Dimple/Dot: Indicates Pin 1.
Pinout Configuration
| Pin | Name | Description |
| Pin 1 (Dot mark) | Anode (+) | Input Infrared LED Positive terminal |
| Pin 2 | Cathode (-) | Input Infrared LED Negative terminal |
| Pin 3 | Emitter | Output Phototransistor Emitter |
| Pin 4 | Collector | Output Phototransistor Collector |
Function & Typical Applications
An optocoupler transmits electrical signals using light rather than a direct wire, providing galvanic isolation between two parts of a circuit.
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High-Voltage Protection: Protects sensitive microcontrollers (like Arduino, Raspberry Pi, or ESP32) from high voltages or voltage spikes on the load side.
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Power Supplies: Commonly used in the feedback loop of Switched-Mode Power Supplies (SMPS) to regulate voltage safely.
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Noise Reduction: Eliminates ground loops and isolates electrical noise in industrial control systems and relay driver circuits.
