The 4N35 is a widely utilized optocoupler that facilitates electrical isolation between input and output circuits. It achieves this by employing an internal light-emitting diode (LED) and a phototransistor, allowing signal transmission without direct electrical connection. This design is particularly advantageous in applications requiring the separation of high-voltage components from low-voltage control systems.

Key Features and Specifications

• Isolation Voltage: The 4N35 offers an isolation test voltage of up to 5000 VRMS, ensuring robust separation between input and output, which is crucial for protecting low-voltage circuits from high-voltage transients.

• Voltage and Current Ratings:

  • Maximum Collector-Emitter Voltage: 30V
  • Forward Current: 50mA
  • Forward Voltage: 1.5V
  • Reverse Voltage: 6V
  • Power Dissipation: 70mW
    

• Package: It comes in an industry-standard 6-pin dual in-line package (DIP), facilitating easy integration into various circuit designs.

Pin Configuration

The 4N35's pinout is as follows:

• Pin 1 (Anode): Connects to the positive terminal of the input signal.
• Pin 2 (Cathode): Connects to the negative terminal (ground) of the input signal.
• Pin 3 (Not Connected): No internal connection.
• Pin 4 (Emitter): Emitter of the phototransistor, typically connected to the ground of the output circuit.
• Pin 5 (Collector): Collector of the phototransistor, connected to the output load or power supply.
• Pin 6 (Base): Base of the phototransistor, often left unconnected or used for biasing purposes.
  

Operation Principle

When a voltage is applied across the input pins (Anode and Cathode), the internal LED emits infrared light. This light activates the phototransistor, allowing current to flow between the Collector and Emitter pins on the output side. This mechanism enables signal transmission while maintaining electrical isolation between the input and output circuits.