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The 4N35 optocoupler (optoislator) chip can be obtained from a number of online retailers for a very inexpensive price. The 4N35 is a 6-pin IC. Its pinout is. These families include the 4N35/ 4N36/ 4N37/ . Collector-base breakdown voltage1). IC = µA, IB = µA. 4N BVCBO. V. 4N Voltage 30V Feature Phototransistor Optocouples Isolation Voltage (RMS) Vrms CTRmin % t (ON) / t (OFF), us 3us/3us. IF max 60mA. IC max mA.

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And this is how an optocoupler circuit works. In 44n35 project, we will show how to connect an optocoupler chip to a circuit. On the output side, being there is electrical isolation, we need to place a power source so that the load, in this case, an LED can turn on.

We aren’t going to use any very high voltages. The chip we will use is the popular 4N35 optocoupler chip.

How to Build an Optocoupler Circuit

This would be the main application and use for optoisolators. It’s going to be very simple. This above circuit built on a breadboard is shown below. Optocoupler Circuit The optocoupler circuit we will build with a 4N35 chip is shown below. And this controls the entire circuit. To separate this noise from being induced into the output, electrical isolation is necessary and solves the problem.

4N35 Optocouplers Phototransistor 30V IC

To see the real-life circuit of it below, see the video below. An optocoupler or optoisolator chip is a chip that allows for electrical isolation between the input of the circuit and the output of the circuit. So if the power to the input is changed, this does not affect the power on the output, and vice versa.


The first 2 pins are the anode and the cathode. When switched on, the phototransistor receives IR light and conducts. And we leave the base terminal of the phototransistor unconnected. Without these being powered, the output side cannot turn on, because the phototransistor needs infrared IR light in order to conduct.

Electrical isolation can be very important, especially in circuits where the input power to the circuit is very high and there are other parts in the circuit that only require a very small amount of power. The power sources are isolated, so they are completely independent.

So these are all the pin connections. By electrical isolation, we mean that the power going into the input has no effect whatsoever on the power on the output.

How to Build an Optocoupler Circuit

Being that there’s no direct conductive pathway, the input and output aren’t linked, so there’s electrical isolation. Once on, it beams infrared light onto the phototransistor. But after, you’ll know how to wire up any type of photocoupler IC. And how it works is we give enough power to the anode and cathode pins, so that the LED is sufficient power to turn on.

Therefore, without the IR LED being on, the phototransistor will be in nonconduction move and no current can flow through the phototransistor, meaning anything connected to output will not be powered. The 4N35 optocoupler optoislator chip can be obtained from a number of online retailers for a very inexpensive price.

Optocouplers can also be used if the input power may bring in a lot of noise, which for many applications can be very undesirable. A rundown of all the pin connections is shown in the table below. Jc connect the output and the voltage necessary to power the output to the collector terminal. A toggle switch was placed on iv input side of the optocoupler circuit in order to switch on and off the circuit. We will show how to wire this chip up to any circuit so that you can obtain electrical isolation as needed.


When off, the phototransistor cannot conduct. And now there is isolation between the input and output of the circuit. How to Build an Optocoupler Circuit In this project, we will show how to connect an optocoupler chip to a circuit. The 4N35 is a 6-pin IC.

A lot of optocoupler chips do not even have a terminal for the base because it’s unnecessary to connect it. We connect the emitter terminal to ground. The third pin is left unconnected. With this setup, there’s no direct conductive path from the input to the output of the circuit. This is a just basic circuit showing how to connect up a photocoupler IC.

Its pinout is shown below. With infrared, the phototransistor can conduct across from collector to emitter and power on any load connected to the output, which in this case is a LED.

So if there is an incident such as a surge of power into the input of the circuit, it doesn’t affect the area that only requires a small amount of power, since it’s isolated from the input. So we connect a 3V power supply source to the collector and this powers on the LED.