What is the Difference Between LM339 and LM324 Op-Amps? | Comparator vs Op-Amp

The LM339 is a quad-voltage comparator, which means it contains four separate comparators. The LM324 is a quad operational amplifier (op-amp) with four amplifiers. While it is not explicitly designed as a comparator, it can still be used for basic comparator applications due to its high gain and similar functionality. 

Differences Between LM339 & LM324 Op-Amps

Definition of LM339 and LM324 Op-Amps

LM339 Op-Amp: The LM339 is a versatile and widely-used operational amplifier, belonging to the LMx39 series of quad comparators. Developed initially by Texas Instruments (who are also known for developing  SN74AHCT1G00-Q1 integrated circuits for automotive electronic systems), this component has earned a reputation for its reliability and adaptability in diverse electronic applications.

The LM339 provides four high-speed voltage comparators within a single package, making it an excellent choice for tasks requiring precise voltage comparisons. It boasts a broad voltage supply range, typically ranging from 2 to 36 volts, allowing it to function effectively in both low and high-voltage scenarios. This component’s low input offset voltage and high open-loop gain ensure accurate and dependable signal comparisons, making it indispensable in applications such as limit switches, window detectors, and voltage level sensing.

LM324 Op-Amp: The LM324 operational amplifier, a member of the LMx24 series, is a quad op-amp renowned for its versatility and widespread use in electronics. Developed by Texas Instruments, it has become a fundamental component in various applications.

Notably, the LM324 is characterized by its low input offset voltage and high open-loop gain, ensuring accurate and dependable signal processing. This op-amp is highly effective in audio amplification, voltage followers, active filters, and instrumentation amplifiers, making it a trusted choice for both hobbyists and professionals in the electronics field.

Its low power consumption and reliable performance have solidified its reputation as an indispensable component in electronic circuits and systems, contributing to its enduring popularity in the industry.

Pin Configuration

LM339: The LM339 typically comes in a 14-pin. Each comparator has two input pins (inverting and non-inverting), one output pin, and a ground pin.

LM324: Each op-amp in the LM324 contains two input pins (one inverting and one non-inverting), one output pin, and a ground pin. It also comes in a 14-pin package.

Fig: Pin Diagram of LM339 IC.

Fig: Pin Diagram of LM324 IC.

LM339		LM324
Number of channels	4	Number of channels	4
Iq per channel (typ) (mA)	0.2	4 Iq per channel (typ) (mA)	0.175
Input bias current (±) (nA)	50	Input bias current (pA)	250000
Supply Voltage (max) (V)	30	Supply Voltage max) (V)	32
Supply Voltage (min) (V) 2	2	Supply Voltage (min) (V) 3	3
Rail-to-rail	Out	Rail-to-rail	In to V-
Offset voltage at 25°C (mV)	5	Offset voltage at 25°C (mV)	7
Slew rate (typ) (V/µs)	Not Specified	Slew rate (typ) (V/µs)	0.5
Operating temperature range (°C)	0 to 70	Operating temperature range (°C)	0 to 70

Number of Comparators

LM339: It contains four independent voltage comparators in a single package. 

LM324: It consists of four separate operational amplifiers in a single package.

Input Offset Voltage and Common Mode Rejection Ratio (CMRR)

LM339: Compared to op-amps, voltage comparators like the LM339 have a lower input offset voltage and a higher common mode rejection ratio (CMRR). They are therefore more suited for applications requiring precision voltage comparison, where it is necessary to measure even the smallest voltage variations accurately.

LM324: Compared to specialized comparators, op-amps like the LM324 may have a marginally greater input offset voltage and a lower CMRR. They may not be as accurate as voltage comparators in some high-precision workloads, but they still offer acceptable performance for most op-amp applications.

Schmitt Trigger Action

LM339: The LM339 often includes hysteresis also known as Schmitt trigger action, which prevents output oscillation when the input voltages are near the threshold point. This capability is beneficial when dealing with input signals that slowly change or in noisy situations.

LM324: LM324 typically lacks built-in Schmitt Trigger Action. As a result, they could require extra hardware or circuitry to implement hysteresis for uses where noise immunity is crucial.

Functionalities

LM339: The LM339 is specifically designed as a voltage comparator, optimized for comparing two input voltages and producing a digital output based on their relationship. The LM339 features an open-drain output, which allows direct interfacing with other digital devices for various logic implementations, making it suitable for applications requiring digital switching.

LM324: The LM324 is primarily an operational amplifier (op-amp). Op-amps are designed for amplifying and processing analog signals, providing high gain and linearity, making them suitable for various signal conditioning and mathematical operations, making them a popular choice for a wide range of applications. 

While not a dedicated comparator, the LM324 can be used for basic comparator applications due to its open-loop configuration and high gain.

Cost-Effectiveness

LM339: Cost-Generally more expensive than LM324, as specialized voltage comparators are less common and may have higher unit costs.

LM324: More cost-effective due to its widespread use and larger production volumes, leading to lower unit costs.

Frequently Asked Questions (FAQs)

1. What comparator is equivalent to LM339?

Answer:  The equivalents of LM339 are LM311, LM2901, LM239, LM139, LM397 and LM324.

2. How does the open-drain output of the LM339 differ from the standard op-amp outputs of the LM324?

Answer: The open-drain output of the LM339 can only pull the output voltage to the ground, requiring an external pull-up resistor for high-level voltage. In contrast, the standard op-amp outputs of the LM324 can actively drive the high and low output voltage without additional circuitry.

To Conclude

The LM339 and LM324 are different integrated circuits with distinct functionalities. The LM339 is a dedicated voltage comparator with an open-drain output, ideal for digital switching applications, while the LM324 is a quad operational amplifier primarily used for analog signal processing tasks. Understanding these differences is important as it helps to choose the appropriate IC for specific applications, ensuring optimal performance and efficiency, and cost-effectiveness in electronic designs.