LM324 Working Principle, Pinout and Specifications

The LM324 remains a popular quad operational amplifier because it combines four independent op-amps in one low-cost package. This guide explains the LM324 pin functions, electrical ratings, internal operation, circuit examples, common limitations, applications, alternatives, package dimensions, and manufacturing information.

Catalog

LM324 Quad Op-Amp IC

The LM324 is a general-purpose integrated circuit containing four independent operational amplifiers in one package. Each amplifier can increase the difference between two input voltages and can operate separately while sharing the same power-supply connections.

The IC supports single- or dual-supply operation. Depending on the manufacturer and version, its supply range is typically 3 V to 30 V, while newer LM324B versions may support up to 36 V. Its input common-mode range includes the negative supply or ground, which simplifies many single-supply circuit designs.The LM324 offers low power consumption, internal frequency compensation, and unity-gain stability. However, it is not a rail-to-rail op-amp, so its input and output cannot normally reach the positive supply voltage.

LM324 Pinout & Functions

Pin	Pin Name	Function
1	1OUT	Output of operational amplifier 1
2	1IN−	Inverting input of operational amplifier 1
3	1IN+	Non-inverting input of operational amplifier 1
4	VCC+	Positive power-supply connection
5	2IN+	Non-inverting input of operational amplifier 2
6	2IN−	Inverting input of operational amplifier 2
7	2OUT	Output of operational amplifier 2
8	3OUT	Output of operational amplifier 3
9	3IN−	Inverting input of operational amplifier 3
10	3IN+	Non-inverting input of operational amplifier 3
11	VCC−	Negative power supply or ground in a single-supply circuit
12	4IN+	Non-inverting input of operational amplifier 4
13	4IN−	Inverting input of operational amplifier 4
14	4OUT	Output of operational amplifier 4

LM324 Specifications and Electrical Ratings

Specification	Rating
Number of amplifiers	4 independent op-amps
Recommended supply voltage	3 V to 30 V or ±1.5 V to ±15 V
Absolute maximum supply voltage	32 V total
Maximum differential input voltage	32 V
Input voltage limit	−0.3 V to 32 V
Input common-mode range	0 V to VCC − 1.5 V at 25°C; upper limit reduces to VCC − 2 V across the full temperature range
Input offset voltage	3 mV typical, 7 mV maximum at 25°C
Input bias current	20 nA typical, 250 nA maximum at 25°C
Open-loop voltage gain	100 V/mV typical; 25 V/mV minimum at 25°C
Gain-bandwidth product	1.2 MHz typical
Slew rate	0.5 V/µs typical
Common-mode rejection ratio	80 dB typical, 65 dB minimum
Supply current	0.7 mA typical and 1.2 mA maximum for all four amplifiers at 5 V with no load
High-level output voltage	At least VCC − 1.5 V at 25°C with a 2 kΩ load
Low-level output voltage	5 mV typical, 20 mV maximum with a load connected to ground
Output source current	30 mA typical at a 15 V supply
Output sink current	20 mA typical
Short-circuit output current	±40 mA typical
Operating temperature	0°C to +70°C
Storage temperature	−65°C to +150°C

How Does the LM324 Work?

The diagram shows the internal circuit of one LM324 operational amplifier. The other three amplifiers use the same basic structure and share the VCC and ground connections. The current regulators provide stable internal bias currents, helping the amplifier operate consistently when the supply voltage changes.

The IN+ and IN− pins connect to the differential input stage. This stage compares the two input voltages. When IN+ is higher than IN−, the circuit drives the output upward. When IN− is higher, it drives the output downward.

The middle transistor stage provides most of the voltage gain. The internal capacitor controls the frequency response and helps prevent oscillation, allowing stable unity-gain operation.

The output stage delivers the amplified signal through the OUT pin. It can operate close to ground, but it cannot normally reach the positive supply rail. In a practical circuit, external negative feedback controls the final voltage gain and keeps the LM324 operating in its linear region.

LM324 Input and Output Limitations

The LM324 can sense input voltages at or near the negative supply rail. In a single-supply circuit, this means its input common-mode range includes ground. However, the input voltage should not approach the positive supply rail. At 25°C, the normal input range extends from ground to approximately 1.5 V below the positive supply. For reliable operation across the full temperature range, allow about 2 V of headroom.

The LM324 output is also not rail-to-rail. It can move close to ground when sinking only a small current, but it cannot reach the positive supply voltage. The highest output level depends on the load and is commonly about 1.5 V below the positive rail. Heavier loads reduce the available output range further.

Its limited 1.2 MHz gain-bandwidth product and typical 0.5 V/µs slew rate make it unsuitable for fast or high-frequency signals. The LM324 also supplies and sinks only modest output current, so it should not directly drive motors, relays, speakers, or other high-current loads. Exceeding these limits can cause clipping, distortion, inaccurate output, overheating, or unstable circuit operation.

LM324 Typical Circuit Configurations

LM324 Dual-Oscillator Buzzer Circuit

This circuit uses two amplifiers inside the LM324 to produce a changing buzzer signal from a 12 V supply. U1:A works as a low-frequency oscillator. R1–R4 and capacitor C1 control its charging and discharging cycle, creating a slowly changing output signal.

U1:B forms another oscillator using R5–R8 and capacitor C2. The signal from U1:A affects the operation of U1:B, causing its output frequency or switching pattern to change. The resulting waveform drives the buzzer and produces a pulsing or alternating alarm sound. The exact sound depends on the resistor values, capacitor tolerances, and buzzer type. Although the diagram labels a 3–24 V buzzer, the applied voltage is limited by the circuit’s 12 V supply.

LM324 Output-Current Booster Circuit

In this circuit, the first amplifier, IC1a, receives the input signal and controls three additional LM324 amplifiers. IC1b, IC1c, and IC1d are connected as voltage followers, so their outputs reproduce the same voltage while sharing the load current.

R2, R3, and R4 are 10 Ω output-balancing resistors. They reduce current differences between the three amplifiers and prevent their outputs from directly competing with one another. R1 returns the combined output signal to the inverting input of IC1a, creating overall negative feedback. C1 provides frequency compensation to improve stability. This arrangement increases the available output current, but it is still unsuitable for high-power loads because the LM324 has limited current capacity and may overheat.

LM324 RF Signal Detector and Alarm Circuit

This circuit is designed to detect a radio-frequency signal picked up by the antenna. The 1 nF capacitor couples the high-frequency signal into the detector while blocking direct current. The 1N34 germanium diodes rectify the received signal and produce a small voltage at the LM324 non-inverting input.

The LM324 compares this detected voltage with the level at its inverting input. When the detected signal is high enough, the LM324 output activates the 2N4401 transistor through the 1 kΩ resistor. The transistor then supplies current to the LED and piezo buzzer, producing a visual and audible warning.

This is a simple experimental detector rather than a precise RF measuring circuit. Its sensitivity depends strongly on the antenna, signal strength, diode characteristics, wiring, and nearby electrical noise. A defined reference voltage, filtering, and hysteresis would be needed for more reliable switching.

LM324 Wide Applications

• Sensor signal conditioning

• Light and sound detectors

• Battery voltage monitors

• Battery chargers

• Voltage and current measurement

• Active filters

• Oscillators and waveform generators

• LED level indicators

• Low-frequency function generators

• Voltage followers and buffers, etc.

LM324 vs. Other Op-Amps

Feature	LM324	LM358	LM741	TL074	MCP6004
Number of amplifiers	4	2	1	4	4
Typical supply range	3–30 V	3–30 V	Usually ±10 to ±15 V	7–36 V	1.8–6 V
Gain-bandwidth product	1.2 MHz	1.2 MHz	1 MHz	3 MHz	1 MHz
Slew rate	0.5 V/µs	0.5 V/µs	0.5 V/µs	13 V/µs	0.6 V/µs
Input includes negative rail	Yes	Yes	No	No	Yes
Rail-to-rail input	No	No	No	No	Yes
Rail-to-rail output	No	No	No	No	Yes
Input technology	Bipolar	Bipolar	Bipolar	JFET	CMOS
Main advantage	Four low-cost op-amps in one package	Compact dual version of LM324	Simple traditional op-amp	Faster response and high input impedance	Low-voltage rail-to-rail operation
Main limitation	Low speed and limited positive output swing	Only two amplifiers	Poor low-voltage and single-supply performance	Not suitable for very low supply voltages	Maximum supply limited to 6 V
Best suited for	General low-frequency circuits	Designs requiring one or two channels	Older dual-supply circuits	Faster signal and audio circuits	Low-voltage battery and microcontroller circuits

LM324 Alternatives and Replacements

• LM324A

• LM324B

• LM324BA

• LM324LV

• LM224

• LM124

• LM2902

• LM2902B

Mechanical Dimensions

Manufacturer

Texas Instruments designs, manufactures, packages, and tests analog ICs such as the LM324 through its global semiconductor operations. Its manufacturing network includes wafer fabrication plants, assembly and testing factories, wafer-bumping and probing facilities, and distribution centres. During production, individual dies are electrically tested at wafer level, packaged, and tested again to confirm that they meet the specified electrical, quality, and reliability requirements.

Frequently Asked Questions [FAQ]

1. Can the LM324 operate correctly from a 3.3 V or 5 V supply?

Yes, but its limited positive input and output ranges must be considered. At low supply voltages, the LM324 cannot process or produce signals close to the positive rail. A rail-to-rail op-amp may provide better signal range.

2. What should be done with unused LM324 amplifier channels?

Do not leave unused inputs floating. Configure each unused amplifier as a voltage follower by connecting its output to the inverting input and connecting the non-inverting input to ground or another valid reference voltage.

3. Why does an LM324 circuit work in simulation but fail on a breadboard?

Simulations may exclude supply noise, component tolerances, wiring resistance, parasitic capacitance, and incorrect grounding. Missing supply decoupling, floating inputs, and exceeding the input common-mode range are also common causes.

4. What decoupling capacitor should be used with the LM324?

A 100 nF ceramic capacitor should normally be placed close to the LM324 supply pins. A larger capacitor, such as 1–10 µF, may also be added near the IC when the power supply is noisy or the load changes quickly.

5. Is the LM324 suitable for high-quality audio circuits?

It can handle basic low-frequency audio signals, but its low slew rate, moderate noise, and crossover distortion limit sound quality. A low-noise audio op-amp is usually better for high-fidelity equipment.

6. Why does the LM324 output oscillate when driving a long cable or capacitor?

Capacitive loads reduce the amplifier’s phase margin and can make the feedback loop unstable. A small resistor placed in series with the output can isolate the capacitance and improve stability.