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LM311 IC Introduction

Lm311 is a voltage comparator operational amplifier IC, which has many excellent functions. In this paper, we will discuss lm311 pin, application, equivalent product, description, function and other details about the IC.

What is LM311 IC

The LM111, LM211, and LM311 devices are single high-speed voltage comparators. These devices are designed to operate from a wide range of powersupply voltages, including ±15-V supplies for operational amplifiers and 5-V supplies for logic systems. The output levels are compatible with most TTL and MOS circuits. These comparators are capable of driving lamps or relays and switching voltages up to 50 V at 50 mA. All inputs and outputs can be isolated from system ground. The outputs can drive loads referenced to ground, VCC+ or VCC−. Offset balancing and strobe capabilities are available, and the outputs can be wire-OR connected. If the strobe is low, the output is in the off state, regardless of the differential input.

LM311 datasheet

LM311 Pinout &Configuration

LM311 has eight terminals, as shown in the table.

Pin NumberPin NameDescription
1EMIT OUTEmitter Output – This is the Emitter pin of the output transistor
2Non-Inverting Input (IN+)The Non-Inverting Pin of the comparator is give a variable  voltage to compare
3Inverting Input (IN-)The Inverting pin is also given a fixed voltage which is compared with the (IN+)
4Ground (VCC-)This pin is connected to the ground of the system (Negative voltage can also be used)
5BalanceThis pin can be used to turn off  the DC-offset voltage
6Balance/StrobeThis pin can be used to turn off the output stage
7COL OUTCollector Out – This is the Collector output of the transistor
8VCC+Provide the operating voltage for the Op-Amp. For LM311 it is upto +15V
LM311 Pinout &Configuration
lm311 pinout
lm311 pinout

LM311 Features

  • Lm311 needs very low input current in bias and offset state.
  • Dual power supply and single power supply are available
  • It can operate under wide power supply voltage.
  • It can drive loads up to 50 V with a current of 50 ma.
  • The input and output of the IC can be isolated from the circuit ground.
  • The IC can be easily used in TTL and MOS circuits.
  • Low power design.
  • The output is short-circuit protected for up to 10 seconds.
  • The IC can drive loads up to 50 ma.
  • Ability to offset balance
  • Stroboscopic function

LM311 Equivalent IC

  • The LM311 Equivalent IC are: LT111A, NTE922
  • The LM311 ICs are: LM393,LM741LM358

How does a LM311 IC work?

Like all voltage comparators, lm311 has a reverse pin and a non reverse pin. If the voltage on the in-phase terminal (pin 2) is higher than the reverse phase terminal (pin 2), the output (pin 7) will also be high, otherwise the output will be low.

Lm311 can operate in single power supply voltage or dual power supply mode. Now, let’s focus on + 5V supply voltage circuit, because this is the most commonly used design of digital circuit. In this type, VCC + (pin 8) is connected to the + 5V supply voltage and VCC (pin 4) is grounded to maintain it at 0V. An example circuit is shown below, in which the reverse terminal is set to 2.5V and the in-phase terminal voltage is changed using a potentiometer. You can note that when the voltage at pin 2 is higher than that at pin 7, the output voltage remains high and vice versa.

If the DC bias voltage is to be adjusted manually, use pins 5 and 6 on the op amp to set the balance voltage. These pins are usually not used because input misalignment itself can be better controlled. Pins 5 and 6 should be shorted as described above when not in use. You can also note that the collector pin (pin 7) of the transistor is for output and the emitter pin (pin 1) is grounded. This design is called a collector output circuit, but it is not always the case. You can refer to other possible circuits in the lm311 data sheet (shown at the bottom). An emitter output circuit is shown below.

NOTE: In order to obtain long-term performance from the IC, it is important not to operate the IC at a voltage greater than 30 v. Always connect the power supply and IC with the correct polarity. The load shall not exceed 50mA, so the load shall not exceed 50mA. Always operate the IC below + 70 ° C and store the IC above – 65 ° C and below + 150 ° C.

LM311 Circuit

heat sensor using lm311 IC

Where to use the LM311 Comparator Op-Amp

The lm311 differential comparison operational amplifier is a very old Ti comparison IC which has been used in voltage comparison with electronic design for a long time. Any operational amplifier can be used as a voltage comparator, but lm311 proves its advantage by placing an output transistor in its package. The collector and emitter pins of the transistor can also be controlled by hardware, which makes it suitable for many applications.

The transistor can drive loads up to 50V and 50mA, and is suitable for driving most TTL, MOS and RTL loads. Transistors also insulate the load from the system ground, so if you are looking for a voltage comparator to drive these specifications of the load, the IC may be the right choice for you.

LM311 Applications

  • Desktop PCs
  • Body Control Modules
  • White Goods
  • Building Automation
  • Oscillators
  • Peak Detectors

That’s all for today. Hope you enjoyed this article. However, if you have doubts or have any questions about this, you can contact me in the comments section below. I’ll be happy to help you as best I can. Let us know your feedback and suggestions at any time, they allow us to provide you with high-quality work that responds to your needs and expectations, and helps you continue to give back to our products. Thank you for reading this article.


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