The 4N25 is a single channel photo transistor optocoupler IC. This is most common in many consumer electronics boards and applications. The IC provides proper electrical isolation (no direct contact electrically) from low voltage side and high voltage side. This article describes the 4N25 optocoupler pinout, equivalent and other important information’s helpful while you are working with this IC circuit.
Technical Specifications
- Isolation voltage is 2500 Vrms to 5300Vrms.
- Led forward voltage is 1.2v to 1.5V.
- Maximum LED forward current is 60mA to 80mA.
- Maximum collector to emitter voltage is 30V to 70V ( This value is depends on the manufacturer).
- Maximum collector current is 100mA.
4N25 Single Channel Phototransistor Output Optocoupler Pinout
Pinout Configuration and Each Pin functions
| Pin | Symbol | Function | Description |
|---|---|---|---|
| 1 | Anode | LED Anode connection | This is the Positive terminal of the internal input infrared LED. |
| 2 | Cathode | LED Cathode connection | This is the Negative or ground terminal of the internal input infrared LED. |
| 3 | NC | No Connection | Not internally connected. |
| 4 | Emitter | Phototransistor Emitter pin | Emitter terminal of the output NPN phototransistor. |
| 5 | Collector | Phototransistor Collector pin | Collector terminal of the output NPN phototransistor. |
| 6 | Base | Phototransistor Base | Base connection of the output photo transistor. This connection can be left open or used for external biasing/noise rejection. |
The 4N25 IC Supply Voltage Max is 30-70v then How It Handle 2500vrms?
The isolation voltage of 2500Vrms to 5300Vrms means the maximum voltage range where the optocoupler can safely tolerate between the input side and output side without breaking the internal barrier.
The supply voltage and isolation voltage are two separate terms. The IC works in 30 to 70V supply voltage. When the supply voltage exceeds this voltage the transistor inside the IC damaged. The 2500Vrms is separate terms. If the supply voltage exceed suddenly to 1000v the the LED burn out and the barrier between the LED and photo transistor is protected because it can handle voltage of 2500Vrm to 5300Vrms.
Equivalent Optocoupler IC as Replacement
4N26, 4N27, and 4N28 are the same series of optocoupler IC only one difference is in isolation voltage. The 4N35, 4N36, 4N37 also has same six pin configuration, so you can use these as the direct replacement.
Why the 4N25 Has an External Base Pin
The pin 6 is Base of the internal photo transistor. This pin is provided for external controlling the output photo transistor. In normal condition the infrared LED turns ON the phototransistor, additional pin is used for physical access to the phototransistor base section for engineers to solve noise reduction and faster switching speed.
Working of 4N25 Optocoupler IC
This optocoupler works by converting the electrical signal (input signal or voltage) to light and it will transmitted through the electrical barrier and reaches to the photo transistors base pin. When the IR light receives the photo transistor turns ON and conduct the electricity through the collector-emitter pins. The barrier inside the IC protect it from 2500Vrms voltage.
