LM311 IC : Pin Configuration, Circuit Diagram and Applications

LM311 IC is one kind of integrated circuit, and it can be built with one comparator. This IC is mainly used to compare the input voltages and decides the superior value. Based on this concept only the electronic choices can be made. Therefore, a comparator can be used to build various electronic circuits, so this IC plays an essential role in many circuits. Before going to design an LM311 based circuit, we must know about the IC LM311 pinout, so that we can know the main function of every pin in the IC. Does this article discuss what is LM311IC? Pin configuration, circuit diagram, and applications.

About LM311 IC?

Basically, the LM 311 IC is one kind of voltage comparator with high speed. The operating voltage of this IC ranges from -15Volts to15Volts. This IC can also function with 5Volts for the logic systems. The output levels of the IC have the MOS logic or TTL, RTL, DTL compatibility level circuits. This IC can be used to drive Solenoids, Lamps, Relays, etc. However, when contrasted to other operational amplifiers, the LM311 IC pin connections are dissimilar.

LM311 Integrated Circuit
LM311 Integrated Circuit

LM311 IC Pin Configuration

The LM311 IC pin configuration is discussed below.

LM311 Pin Configuration
LM311 Pin Configuration
  • Pin1 (Emit Out): This pin is the output transistor’s emitter pin
  • Pin2 (IN+: Non-Inverting Input): The IN+ Pin of the comparator can be given to a variable voltage for comparing voltages.
  • Pin3 (IN-Inverting Input): The IN-pin can be given to a set voltage which is contrasted with the Non-inverting input
  • Pin 4 (VCC-) Ground Pin: This GND pin can be connected to the GND terminal of the system
  • Pin5 (Balance): Balance pin can be used to switch off the DC offset voltage
  • Pin6 (Strobe/Balance): This pin is mainly used for turning off the o/p phase
  • Pin7 (Collector Out): This pin is the collector terminal o/p of the transistor
  • Pin8 (VCC+): This pin provides the operating voltage to the operational amplifier. For IC LM311, the operating voltage is up to +15V.

LM311 IC Specifications and Features

The features and specifications of the LM311 IC include single supply as well as dual supply.

  • Singe supply of LM311 IC ranges from 5V to 30V
  • Dual supply of this IC ranges from – ±2.5V to ±15V
  • The maximum current of this IC is 7.5mA
  • A single supply of two operational amplifiers allow consistent operation
  • The driving load capability ranges up to 50V & 50 mA
  • This IC can drive most of the TTL & MOS loads
  • The o/p can be isolated from System Ground

LM311 Packages with Dimensions

The package can be defined as the different device models, and these are used to separate the most recent products as contrasted to the previous. Each package can be allocated by different sizes to distinguish them simply. The LM311 packages with dimensions are shown below.


Part No Dimensions (Units)

SO (8)


6.2X5.3 mm

SOIC (8)


4.9 X 3.91 mm

PDIP (8)


9.8 X 6.35 mm


3 X 4.4 mm

LM311 IC Circuit Diagram

The LM311 IC circuit namely night light circuit diagram with working is discussed below. This circuit can be built with several electronic components which include LM311 IC, Photoresistor, Resistors 33KΩ, and 220Ω, Potentiometer, LED, and DC power supply. So by using these components, this basic circuit can be designed.


The main function of this night light circuit is, the LED will ON in the night time and LED will OFF in the morning time. The circuit can be operated by a potentiometer in two situations.

LM311 IC Circuit Diagram
LM311 IC Circuit Diagram

This night light circuit next compares the reference voltage through the generated voltage from the voltage divider among the 33KΩ resistor as well as a photoresistor. This concept is very simple. Whenever the photoresistor detects the bright light, then its resistance will drop under 30KΩ. So, most of the voltage will be allocated to the 33KΩ resistor & remaining voltage will supply to the photoresistor.

Therefore, the voltage which is generated from the voltage divider can be low than the reference voltage. So, the output can be drawn to the ground, that means the light emitting diode will not get the power. But, during night time, the resistance of the photoresistor is very high, thus most of the voltage gets assigned across it. Hence, the generated voltage from the voltage divider circuit will be over the reference voltage. So, the output can be drawn far above the ground to Vcc, as well as the LED will turn ON.

Applications of LM311 IC

The LM311 IC applications mainly include the following.

Thus, this is all about IC LM311 data sheet. This IC has two inputs like another single operational amplifier namely inverting input as well as noninverting input. In typical operational amplifiers, the pin-2 is the inverting input & pin3 is the non-inverting input. However, in IC LM311, the inputs are reversed like pin-2 is the non-inverting input & pin-3 is the inverting input. Here is a question for you, what are the key features of the LM311 IC?

Image Source: LM311 IC & pin Configuration