LM324 Comparator IC Pin Configuration, Working and Applications

The LM324 is a widely used integrated circuit (IC) that can be used as comparators, making the LM324 a popular choice for comparator applications. It is commonly used in both analog and digital systems, providing a cost-effective and reliable solution for voltage comparison tasks. This article discusses an overview of the LM324 Comparator IC.

What is a Comparator?

A comparator is an electronic circuit that compares two input voltages and produces an output indicating which one is larger. It determines whether one voltage is greater than, less than, or equal to another voltage.

The basic operation of a comparator involves two input terminals: an inverting input (-) and a non-inverting input (+), and one output terminal. When the voltage at the non-inverting input is higher than the voltage at the inverting input, the output of the comparator typically goes to a high voltage level (often the positive supply voltage). Conversely, when the voltage at the inverting input is higher, the output typically goes to a low voltage level (often ground).

LM324 Comparator IC

LM324  IC consists of four independent, high-gain operational amplifiers on a single chip. The op-amps inside the LM324 can compare two input voltages and provide a digital output based on the comparison result. When the voltage at the non-inverting input (+) is higher than the voltage at the inverting input (-), the output of the comparator will be high (logic 1). Conversely, when the voltage at the non-inverting input is lower than the voltage at the inverting input, the output will be low (logic 0).

Pin Configuration of LM324 IC

The following diagram shows the pin configuration of the LM324 comparator circuit. In DIP package it consists of 14 pins and the function of each pin is described below:

Specifications of LM324 IC

Supply Voltage Range (Single Supply): Typically operates from a single power supply voltage ranging from 3V to 32V.
Supply Voltage Range (Dual Supply): Typically operates from dual power supply voltages ranging from ±1.5V to ±16V.
Input Offset Voltage: Typically around 3 mV.
Input Offset Current: Typically around 2 nA.
Input Bias Current: Typically around 20 nA.
Input Common Mode Voltage Range: Typically includes ground.
Gain Bandwidth Product (GBP): Typically ranges from 1 MHz to 1.3 MHz.
Input Impedance: High input impedance.
Output Impedance: Low output impedance.

Basic Configuration of LM324 IC

 As shown in the Images above, you can see when the voltage at pin 3 is greater than voltage at negative input then LED turns ON. In above application, we have used only one op-amp out of 4 op-amp. To produce variable voltages at +ve and -ve input variable resistors are used.

Now when voltage at +ve input is less than voltage at negative input then LED turns OFF as shown in image below:

Applications of LM324 IC

LM324 can be used in variety of applications which uses voltage comparisons as well as normal Op-amp Applications i.e. it can also be used in Applications which uses u741 IC. Some of the applications are mentioned below:

Voltage Comparators: The high gain and low input offset voltage of the LM324 make it suitable for voltage comparator circuits that are used in applications such as overvoltage protection, window detectors, and waveform generators.

Signal Conditioning: The LM324 can be used to condition signals from sensors such as temperature sensors, light sensors, and pressure sensors, by amplifying, filtering, or linearizing the output signal.

Active Filters: Its high gain-bandwidth product and low input offset voltage make the LM324 suitable for designing active filter circuits such as low-pass, high-pass, band-pass, and band-reject filters used in audio, communications, and instrumentation applications.

Voltage Followers: The LM324 can be configured as a voltage follower to provide isolation between the input and output signals, maintaining the same voltage level as the input signal with high input impedance and low output impedance.

Oscillators and Waveform Generators: The LM324 can be used in oscillator circuits to generate square, triangular, or sawtooth waveforms for various applications such as waveform synthesis, clock generation, and frequency modulation.

Power Supply Circuits: The LM324 can be used in voltage regulation circuits, voltage reference circuits, and current sensing circuits in power supply designs to improve stability, efficiency, and protection.

Voltage-Controlled Oscillators (VCOs): Its high gain and low input offset voltage make the LM324 suitable for designing VCOs used in frequency modulation and frequency synthesizers.

Application of LM324 in Over Temperature Sensing Circuit

This uses LM324 IC and is based on the principle of PTC thermistor i.e., positive temperature coefficient thermistor. As temperature increases the the resistance of PTC thermistor also increases.

This circuit is used to run Pump motor when temperature reaches 50 degree Celsius. When temperature is less than 50 degrees then voltage at pin 3 (positive input) is less than voltage at pin 2 (-ve input) hence comparator output is low. 

Voltage at pin 3 becomes larger than voltage at pin 2 hence output of comparator gets high which is provided at base of BC547.

In this application BC547 is used as a switch. BC547 is an NPN transistor when base is high current flows from collector to emitter in transistor hence relay will be activated which in turn , turns the Water Pump motor ON. As soon as temperature decreases, voltage at pin 3 (positive input) goes down and become less than voltage at pin 2 (-ve input) hence comparator output turns low and hence base of transistor goes low.

In this case transistor will act as open switch, no current flows through coil of relay hence it deactivates, and pump motor turns OFF. In above application diodes D1 and D3 are protection diodes and D2 is green LED.

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