6N139 Optocoupler : Pin Configuration & Its Applications

Optocoupler is one kind of integrated circuit used to allow efficient DC signal transmission across two circuits and at the same time, it maintains outstanding electrical isolation in between them. Industry-standard type ICs are 4N29, 4N30, 4N31, 4N32 4N33, 6N138, and 6N139 optocoupler.


Optocouplers can block transmitting noise across the ICs for changing logic levels & removing ground loops. Alternate names of an optocoupler are; a photocoupler, an optical coupler & an optocoupler. This article discusses an overview of the 6N139 optocoupler and its working with applications.

What is 6N139 Optocoupler?

6N139 optocoupler is generally required when two circuits need to isolate electrically with a direct control mechanism. The output gain of the circuit is extremely high, so it is capable of driving at extremely less input current. This optocoupler is mainly designed to use in high switching frequency, high gain, low input current-based applications.

6N139 Optocoupler IC
6N139 Optocoupler IC

This optocoupler IC uses a LED & a photodetector for providing an extremely high current transfer ratio in between input & output. This IC is available with high speed, less input, 100kBd, and photodiode Darlington pair output. It includes an IR emitting diode which is connected optically to a high gain-based Darlington photodetector.

Pin Configuration

The pin configuration of the 6N139 Optocoupler is shown below. This IC includes 8-pins where each pin and its functionality are discussed below.

6N139 Optocoupler Pin Configuration
6N139 Optocoupler Pin Configuration
  • Pin1 (NC): No connection
  • Pin2 (Anode): This pin is the internal LED’s positive (+) terminal
  • Pin3 (Cathode): This pin is the internal LED’s negative (-) terminal
  • Pin4 (NC): No connection
  • Pin5 (GND): This is a GND pin, where the internal Darlington transistor’s emitter terminal is connected to this pin
  • Pin6 (VO): Collector terminal of the second transistor in Darlington pair which is normally connected to load to obtain current
  • Pin 7 (VB): Base terminal of the second transistor in Darlington pair
  • Pin 8 (VCC): Collector terminal of the first transistor in Darlington pair, connected to positive (+) power supply.

Features & Specifications

The features and specifications of the 6N139 Optocoupler include the following.

  • It is compatible with LSTTL and CMOS
  • The high current transfer ratio is typically 2000%
  • Gain bandwidth adjustment can be possible with extra-base pin access
  • Required low i/p current is 0.5 mA
  • Output current is high
  • Interfacing can be possible through common logic families
  • Common mode rejection is high like 500 V/μs
  • Temperature ranges from 0°C – 70°C
  • Infrared LED forward voltage (Max) is 1.7V
  • Infrared LED forward current (Max) during ON is 25mA
  • The reverse voltage of infrared LED (Max) is 5V
  • The reverse current of infrared LED (Max) is 10uA
  • Typical rise time is1.5µs
  • The typical fall time is 0.6µs
  • Maximum o/p current is- 60 mA
  • Maximum o/p power dissipation is 100mW
  • CTR or Current transfer ratio is 400%
  • The minimum required input current is 0.5 mA
  • Max supply & output voltage from Pin 8 – pin 5 & pin 6 – pin 5 is 18V
  • Output with TTL compatibility is 0.1 V

Equivalent 6N139 optocouplers are; HCPL-0701, 6N138, HCPL-0700, HCNW-138 & HCNW139.

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How to use the 6N139 Optocoupler?

This 6N139 optocoupler IC mainly includes three essential components like Darlington pair transistor, Photo Diode & infrared LED. The simple example circuit is shown below for understanding the working of the 6N139 optocoupler.

Electrical Isolation using 6N139 Optocoupler
Electrical Isolation using 6N139 Optocoupler

In the above circuit, the optocoupler IC gets the logic signals from the microcontroller which are fed to infrared LED within the IC and it acts as a control circuit. Here, the Darlington pair transistor can be powered through a second power source like a 12V battery. Once this transistor starts conducting, the ‘R3’ resistor restricts the flow of current.

For a given input, the output response can be observed through an LED at the ‘VO’ pin. The ‘R2’ resistor which is connected to an LED is used to restrict the flow of current. In a fixed time, we can get +3.3V logic signals from the microcontroller which acts like INPUT. When these voltage signals arrive at infrared LED, then it will produce IR signals internally & falls on the photodiode.

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Here, the IC will start conducting depending on the photodiode characteristic within reverse bias mode in the occurrence of reverse voltage. Once the optocoupler starts conducting then the transistor’s base terminal gets current, so it turns ON. The flow of current from the primary transistor is used to drive the second transistor into conduction because the emitter terminal of the primary transistor is connected toward the base terminal of the second transistor.

Once this transistor is switched ON, the flow of current will be supplied throughout the collector terminal. So, the voltage will be appeared across the LED to make it ON. Therefore, the LED will be turned ON once the microcontroller gives a HIGH logic signal to the optocoupler at the input.


Once the signal from the microcontroller goes LOW state then the LED will be turned OFF. So by controlling the secondary circuit from the primary circuit through light triggering, we have achieved electrical isolation with a 6N139 optocoupler. In this way, we can utilize 6N139 optocoupler IC in different applications.

Where to use 6N139 Optocoupler/Applications

The applications of the 6N139 Optocoupler include the following.

  • Isolation of digital logic ground
  • The detector of the telephone ring
  • Used in PWM based applications
  • Lighting systems
  • Detection of AC mains
  • For driving off Reed relay
  • Feedback of SMPS or Switch mode power supply
  • Interfacing of a microprocessor system
  • Input/Output isolation of ATE, PLC
  • In EIA RS232 based line receiver
  • Used to transmit multiplexed data
  • Insulation of high voltage
  • Used to eliminate electrical noise
  • Used in most of the logic families COMS/TTL, TTL/TTL, LSTTL/TTL, CMOS/CMOS, & CMOS/LSTTL.
  • Low Input Current Line Receiver
  • EIA RS-232C Line Receiver
  • Telephone Ring Detector
  • 117 V ac Line Voltage Status Indicator – Low Input Power Dissipation
  • Low Power Systems – Ground Isolation

Please refer to this link to download the 6N139 Optocoupler Datasheet

Thus, this optocoupler IC is mainly used for isolating two circuits electrically like primary & secondary but the Darlington pair (LED & photodiode) forms the triggering mechanism. This IC is mainly designed to use in high gain, low input current & High speed based switching applications. Here is a question for you, What is a Darlington pair transistor?

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