4N25

The 4N25 is a 6-pin optocoupler with an infrared LED and an NPN phototransistor in one package. Light from the LED switches the transistor, so a signal passes from input to output with no electrical connection between the two sides. It is a standard part for protecting microcontrollers from noisy or higher-voltage circuits.

4N25 Specifications

• Type: phototransistor optocoupler (optoisolator)
• Input: infrared LED, forward voltage about 1.2 V typical
• Output: NPN phototransistor with base connection
• Current transfer ratio (CTR): 20% minimum
• LED forward current: 60 mA absolute maximum
• Pinout: 1 anode, 2 cathode, 3 not connected, 4 emitter, 5 collector, 6 base
• Isolation: galvanic isolation between input and output, rated in the kilovolt range (see the datasheet)

4N25 Applications

• Isolating Arduino and ESP32 outputs from relays and motor drivers
• Isolated digital inputs for PLCs and industrial controls
• Sensing higher-voltage signals safely
• Breaking ground loops between circuits

What's in the Box

• 1 × 4N25 optocoupler

Tip: Drive the LED through a resistor: about 330 Ω gives roughly 10 mA from a 5 V pin. On the output side, connect a pull-up resistor (for example 4.7 kΩ to 10 kΩ) from the collector to the output supply and take the signal from the collector.

Orders placed before 14:00 are ready for pickup the same day. Delivery across Lebanon usually takes 1–3 working days.