PC817 Optocoupler: Pinout, Features, and Applications

The PC817 is a widely used optocoupler IC designed to isolate different sections of a circuit. It allows signal transmission without a direct electrical connection. Inside, it combines an infrared LED and a phototransistor, enabling signals to pass through light. This setup provides safety and protects sensitive components from high voltages or electrical noise.

Features of PC817 Optocoupler

• Electrical Isolation: Offers galvanic isolation between input and output up to 5,000V. It’s ideal for separating high- and low-voltage circuits.
• High Sensitivity: Provides efficient signal transfer, thanks to the infrared LED and phototransistor combination.
• Compact 4-Pin Package: Has a small footprint in a 4-pin DIP package, making it suitable for compact designs.
• Fast Switching: Capable of high-speed switching, which is useful in many digital applications.
• Low Input Current: Operates with low input current, making it suitable for interfacing with low-power microcontrollers and devices.
• Wide Operating Temperature Range: Operates reliably between -30°C to +100°C, making it adaptable to various environments.

PC817 Pinout Diagram

The PC817 comes in a 4-pin DIP package, with the following pin configuration:

Figure 1 depicts the PC817 pinout diagram.

• Input Side (Pins 1 and 2): The infrared LED is connected between these pins. When a current flows through this LED, it emits light, activating the phototransistor.
• Output Side (Pins 3 and 4): The phototransistor is controlled by the LED’s light and is electrically isolated from the LED side. The transistor conducts when the LED is on, creating a coupling through light instead of direct electrical contact.

Working Principle

The PC817 operates by transmitting a signal through an isolated light path. When current flows through the LED (Pins 1 and 2), it emits infrared light. This light activates the phototransistor on the output side (Pins 3 and 4), allowing current to flow through the collector-emitter path based on the LED’s intensity. This creates an optically isolated signal transfer from input to output, isolating both circuits.

Application Example: Microcontroller to Relay Interface

The PC817 is commonly used to control high-power loads through a relay from a microcontroller. This isolates the microcontroller from the high-voltage relay circuit.

• Circuit Setup:
  • Connect the anode (Pin 1) to a digital output pin of a microcontroller and the cathode (Pin 2) to the ground through a current-limiting resistor.
  • On the output side, connect the collector (Pin 4) to the positive side of a relay control circuit, and the emitter (Pin 3) to ground.
  • When the microcontroller outputs a high signal, it activates the LED, which in turn activates the phototransistor, allowing current to flow and energizing the relay.
• Benefits:
  • Isolation: The optocoupler separates the high-voltage relay circuit from the low-voltage microcontroller, protecting the microcontroller from potential high-voltage spikes or noise.
  • Noise Reduction: Reduces interference between control and output circuits.
  • Compact and Reliable: The PC817 is small, reliable, and easily integrated into various relay-driving applications.

Other Applications

• Switch-Mode Power Supplies (SMPS): Used to provide feedback across high-voltage isolation barriers.
• Signal Isolation in Microcontroller Projects: Prevents noise from high-power devices from affecting sensitive microcontroller circuits.
• Triac or Thyristor Triggering: For isolating and triggering AC loads in home automation or industrial control systems.
• Data Communication: Provides isolated data transfer in noisy industrial environments.

Conclusion

The PC817 optocoupler is an essential component in applications that require isolation between circuits, offering both protection and signal integrity. Its versatility and ease of use make it popular in automation, industrial control, and home electronics.