PC817 Phototransistor Output Optoisolator IC

Prototyping and Engineering Tips from Robogears

• Pin 1 Identification: Look for a small circular dimple on the top of the IC. That corner is Pin 1 (Anode of the internal LED). Wiring the LED backward will not damage the chip but will prevent it from switching.

• The Input Resistor: Never connect the input pins (1 and 2) directly to power. You must use a current-limiting resistor (typically 220Ω to 470Ω for 5V signals) to prevent the internal IR LED from burning out.

• Understanding CTR: The Current Transfer Ratio (CTR) means that if you put 10mA into the LED, the transistor side can only reliably handle a certain percentage of that current (e.g., 5mA at 50% CTR). Do not try to drive a motor or a large solenoid directly with a PC817; instead, use the PC817 to trigger a larger Power Transistor or MOSFET.

• Common Ground Isolation: To get the full benefit of isolation, do not connect the grounds of the two circuits together. If the input ground and output ground are the same, a high-voltage surge can still find a path to your controller, bypassing the optical gap.

Package Includes

• 1 x PC817 DIP-4 Transistor Output Optocoupler

Disclaimer

This component is designed for signal-level isolation. While it can handle high isolation voltages, the output transistor is limited to low-current switching (50mA). Overloading the output side will result in permanent failure of the IC.