The 4N35 optocoupler is a versatile and fundamental building block in the realm of electronics. It excels at providing isolated signal transmission, making it a go-to component for various applications. This comprehensive guide delves into the key features, specifications, pin configuration, operation principles, and practical uses of the 4N35 optocoupler.

4N35 Features and Specifications 

• Number of Channels: 1 Channel – Handles a single isolated signal path.
• Maximum Collector-Emitter Voltage (Vce): 30V – Defines the maximum voltage that can be applied between the collector and emitter of the phototransistor.
• Forward Current (IF): 100mA – The maximum current that can flow through the LED without damaging it.
• Forward Voltage (VF): 1.5V – The typical voltage drop across the LED when conducting current.
• Reverse Voltage (VR): 6V – The maximum voltage that can be applied in the reverse direction across the LED without causing damage.
• Isolation Voltage: 5300 Vrms – A critical parameter indicating the electrical isolation between the input and output sides, ensuring safety in circuits with varying voltage levels.
• Operating Temperature: -55°C to 100°C – The operational temperature range of the optocoupler.
• Power Dissipation (Pd): 250 mW – The maximum amount of power the optocoupler can dissipate without overheating.
• Available Packages: DIP 6 – The standard package type for the 4N35 optocoupler.
• Alternatives: MCT2E, PC817, 6N137 (if applicable) – These are optocouplers with similar functionalities that can be considered as alternatives depending on specific project requirements.

4N35 Pinout Configuration

The 4N35 comes in a 6-pin dual inline package (DIP). Here’s a breakdown of each pin’s function:

How 4N35 Works

The 4N35 operates on the principle of photoelectric isolation. It integrates two key components:

• Gallium Arsenide Infrared LED: When a current flows through the LED (controlled by the input signal), it emits infrared light.
• Silicon NPN Phototransistor: This light-sensitive transistor is on the output side. When the infrared light strikes the base region of the phototransistor, it allows current to flow between its collector and emitter, mimicking a standard transistor’s behaviour.

By regulating the current flowing through the input LED, you indirectly control the current flow on the output side through the phototransistor. This enables safe and isolated signal transmission between circuits with differing voltage levels or even entirely separate ground references.

Applications of 4N35

The 4N35’s ability to provide isolated signal transmission makes it a valuable component in various electronic projects, including:

• Relay Driving Circuits: Optocouplers are commonly used to drive relays, enabling low-voltage control circuits to activate high-power circuits safely.
• Switch-Mode Power Supply Feedback: It maintains isolation between the primary and secondary sides of a switch-mode power supply while facilitating feedback control.
• AC Mains Detection: Optocouplers can safely detect the presence of AC voltage, isolating low-voltage control circuits from high-voltage AC mains.
• Logic Ground Isolation: Isolates the ground planes of different digital circuits to prevent ground loop currents and enhance signal integrity.
• Logic Coupling with High-Frequency Noise Rejection: Optocouplers offer excellent immunity to electromagnetic interference, making them ideal for interfacing with noisy environments.

Additional Resources

• Datasheet: A more comprehensive technical reference for the 4N35 optocoupler can be found in the datasheet.

By understanding the features, working principle, and applications of the 4N35 optocoupler, you can effectively utilize it in your electronic projects to achieve safe and reliable isolated