4N35 Optocoupler Phototransistor IC DIP-6

4N35 Optocoupler with Phototransistor Output is a foundational component in electronics, providing crucial electrical isolation between two circuits. Engineers frequently employ this device to protect sensitive low-voltage digital circuits, like microcontrollers, from high-voltage or noisy power circuits. Inside the standard DIP-6 package, the 4N35 couples an infrared light-emitting diode (LED) with a silicon NPN phototransistor. When a small current activates the internal LED, the light generated turns on the phototransistor, allowing a current to flow in the isolated output circuit. This mechanism ensures perfect galvanic isolation, which is critical in industrial controls, power supply feedback loops, and noise reduction applications, making the 4N35 an invaluable tool for safely interfacing disparate voltage levels.

Key Features:

• High Isolation Voltage: The device safely separates the input and output stages, offering a typical isolation voltage of 5300 Vrms, ideal for bridging safety barriers.
• Phototransistor Output: The output side uses a transistor, allowing you to switch moderate DC currents and voltages in the isolated circuit.
• Current Transfer Ratio (CTR): Provides a predictable gain mechanism, ensuring that a small input current effectively drives the output transistor.
• Low Input Drive Current: The input LED requires a low current, making it easy for microcontrollers (like Arduino) or standard logic gates to drive it directly.
• Versatile Use: You can operate the output phototransistor in either saturated switching mode or linear amplifier mode, depending on the application.
• Standard DIP-6 Package: The widely available, through-hole format simplifies prototyping and assembly on perforated boards or custom PCBs.

Technical Specifications:

• Output Device: Phototransistor
• Maximum Collector-Emitter Voltage (V_CEO): 30 V
• Maximum Collector Current (I_C): 100 mA
• Input LED Forward Voltage (V_F): Typically 1.3 V
• Input LED Forward Current (I_F): Maximum 60 mA
• Current Transfer Ratio (CTR): Minimum 100% (I_C/I_F at specified conditions)
• Isolation Voltage: 5300 Vrms (Minimum)
• Package Type: DIP-6

Mechanical Specifications:

• Pin Count: 6 Pins
• Mounting: Through-Hole (DIP)
• Material: Plastic molded package.

Dimensions:

• Length (Body): ~7.1 mm
• Width (Body): ~6.5 mm
• Pin Pitch (Spacing between pins): 2.54 mm (0.1 in)
• Row Spacing: ~7.62 mm (0.3 in)

Pinout and Wiring:

• Pin 1 (Anode): Connect the positive side of the control signal (from microcontroller/logic).
• Pin 2 (Cathode): Connect the negative side of the control signal and ground.
• Pin 3 (Base – N/C): Often left unconnected; you can connect it to bias the transistor or improve switching speed.
• Pin 4 (Emitter): Connect to the ground or the negative return of the isolated output circuit.
• Pin 5 (Collector): Connect to the positive supply or the load (the switching point of the output circuit).
• Pin 6 (No Connection): Leave this pin floating for mechanical stability and isolation.
• Wiring Note: Always include a current-limiting resistor in series with the LED input (Pin 1) to protect the LED. Connect a pull-up resistor between Pin 5 (Collector) and the output supply voltage to use the transistor as a switch.

Datasheet Reference:

• Download Datasheet

Commonly Used in:

• Digital Signal Isolation: Safely transmitting on/off signals between different ground references.
• Switching Power Supplies: Providing an isolated feedback path for voltage regulation.
• Noise Reduction: Breaking ground loops and preventing electrical noise from coupled power circuits.

Applications:

• Microprocessor Interfacing: Protecting MCU I/O pins when switching high-voltage DC loads or reading signals from noisy environments.
• Telecom Equipment: Isolating telephone line circuits and modems.
• Relay Driving: Safely driving the coil of a mechanical relay from a logic circuit.

Equivalent Models:

• PC817: A smaller, single-channel optocoupler often found in the cheaper, four-pin SIP package, commonly used for non-critical isolation.
• 4N25: A direct equivalent with similar specifications but often a slightly lower minimum CTR.
• TIL111: Another common phototransistor-output optocoupler with similar pinout and ratings.

Package Includes:

• 1 x 4N35 Optocoupler Phototransistor IC – DIP-6