4N28 Phototransistor Optocoupler IC: Circuit, Datasheet and Pinout

A 4N28 optocoupler is a single-channel, industry-standard phototransistor coupler. Instead of the 4N28, optocouplers from the 4N25, 26, 27, and other families are available. Electrically isolated Tx and Rx parts, such as GaAs IR LED and a-Si NPN phototransistor, are included in every optocoupler.

The 4N28 is a six-pin integrated circuit that comes in a variety of packaging. In general, we only use four pins in the chip, but we can use up to five. The diode and photo transistor's internal connections are described below.

4N28 Pinout

4N28 Symbol

4N28 Footprint

4N28 3D Model

Vishay Semiconductor Opto Division 4N28 technical specifications, attributes, parameters and parts with similar specifications to Vishay Semiconductor Opto Division 4N28.

• Isolation test voltage 5000 VRMS

• Interfaces with common logic families

• Input-output coupling capacitance < 0.5 pF

• Industry-standard dual-in-line 6 pin package

• Compliant to RoHS directive 2002/95/EC and in accordance to WEEE 2002/96/EC

• IR LED Forward Current during ON (IF): 10mA - 80mA (Typically 10mA, 80mA being absolute maximum forward current)

• IR LED MaximumReverse Voltage: 6V

• IR LED Maximum Reverse Current: 10uA

• The maximum voltage across COLLECTOR and EMITTER of PHOTOTRANSISTOR: 70V

• Maximum current allowed through TRANSISTOR COLLECTOR(IC): 100mA

• Current Transfer Ration (CTR): 10%

• Typical Rise Time: 3us

• Typical Fall Time: 3us

4N25, 4N26, 4N27, 4N33, and MCT2E are equivalent 4N28 optocoupler ICs. However, electrical factors such as current, frequency, and voltage may differ. So, before replacing these ICs with 4N28ICs, these parameters must be checked, else the ICs may be damaged.

• Circuit isolation

• DC motor speed control

• Lighting systems

• PWM applications

• AC mains detection

• Reed relay driving

• Switch-mode power supply feedback

• Telephone ring detection

• Logic ground isolation

• Logic coupling with high-frequency noise rejection

• Interfacing of an optocoupler is simple by logic circuits.

• Small size component

• Lightweight

• Wideband signal transmission

• Because of the unidirectional signal transmission, the noise from output to input doesn’t get integrated

• Ensures the control circuits’ protection due to the electrical isolation

To establish electrical isolation between two circuits, 4N28 and other equivalent optocouplers such as 4N26, 4N27, and 4N25 can be utilized. In other words, photonics signals such as infrared LEDs and phototransistors are employed to build an electrical connection between two electrical circuits. In short, the 4N28 optocoupler is employed in applications where electrical circuits must be isolated from one another. Check out the samples in the next section for further details.

The Photo Transistor and the IR Diode are the two major components of the 4N28 Optocoupler. This diode can be linked between two terminals (1&2), while the phototransistor is attached between the remaining three terminals (4, 5, and 6). To construct an application circuit, this optocoupler IC is coupled to a few simple components.

4N28 Circuit

In the circuit above, the microcontroller sends trigger pulses to the optocoupler IC, which acts as input signals. The collector terminal is connected to an electric motor, which acts as an output.

The IR diode will be engaged when it receives a +3.3V input signal from the controller.

When it receives electricity, it will generate infrared signals that will trigger the phototransistor. When the transistor is turned on, current flows through the load circuit, and a voltage appears across the electric motor. As a result, once the microcontroller generates HIGH logic toward the IC at the input, this motor will turn.

When the microcontroller's trigger pulses are turned off, the infrared diode's input is turned off. As a result, no power is supplied to the IR DIODE, and it ceases to emit emissions. When no emission is present, the phototransistor is turned off, and the transistor switches from low to high resistance.

The entire voltage supply will come out across the transistor due to excessive resistance, and the current flow within the load circuit will be ZERO. As a result, whenever the microcontroller delivers less logic to the IC at the input, the motor stops rotating.

Both the motor and the transistor act as load circuits in the aforementioned circuit, while the controller and the infrared diode act as trigger circuits. The voltage source employed in the circuit can be used to provide power to the motor.

 4N28 Package Dimensions

Vishay, an important partner of Digi-Key, serves as a globally recognized manufacturer famous for its discrete semiconductors and passive electronic components. Their discrete semiconductors include diodes, MOSFETs, optoelectronics, etc and their passive components include resistors, inductors, capacitors, etc. These products are widely used for almost all kinds of electronic devices and equipment in the fields of industrial, computing, automotive, telecommunications, military, aerospace, and medical.