4N35 Chip & Pinout | ic circuit diagram Everlight Electronics Co Ltd

4N35 Optocoupler Complete Details | Working Principle and Best 5 Equivalent Optocouplers

4N35 Optocoupler

The 4N35 is a commonly used optocoupler with a six-pin package, widely applied in circuits requiring electrical isolation. It transmits signals through an internal LED and phototransistor. The LED emits light at the input side, and the phototransistor receives the light and converts it into an electrical signal at the output side, effectively isolating high and low voltage signals. This device is primarily used in microcontroller circuits, power supplies, and other systems that require signal isolation.

4N35 Pinout

4N35 Equivalent

4N35 Optocoupler Circuit Design

Circuit Working Principle:

Input Side (Arduino Uno R3):

An Arduino digital output pin connects through a 1kΩ resistor to the input LED anode (pin 1) of the 4N35 optocoupler, with the cathode (pin 2) connected to Arduino GND.

When the Arduino outputs a high signal, current flows through the resistor into the internal LED of the 4N35, causing it to emit infrared light.

Output Side (4N35 Phototransistor):

The emitted infrared light activates the internal phototransistor of the 4N35, causing it to conduct.Once the phototransistor conducts, a closed circuit is created from Arduino’s 5V supply through the external LED and the 220Ω resistor, then through the 4N35 phototransistor to GND, lighting up the external LED.

4N35 Alternative to PC817 Optocoupler

Here is a clear side-by-side comparison table highlighting the key differences between the 4N35 and PC817 optocouplers:

how to use 4n35 optocoupler

Simply put, using a 4N35 optocoupler involves lighting its internal LED to activate the internal phototransistor, providing electrical isolation between input and output circuits.