LM393 Overview

The LM393 integrates two independent Voltage Comparators in a single 8-pin package. It operates over a wide supply voltage range and can perform precision voltage comparison with low input bias current. Its robust design and ease of use make the LM393 a go-to choice for many analog circuit designs.

LM393 Pinout

The LM393 comes in an 8-pin dual inline package (DIP-8). The pin configuration is as follows:

Pin	Function
1	Output of comparator 1
2	Inverting input (-) of comparator 1
3	Non-inverting input (+) of comparator 1
4	Ground (GND)
5	Non-inverting input (+) of comparator 2
6	Inverting input (-) of comparator 2
7	Output of comparator 2
8	Positive supply voltage (VCC)

The two comparators are functionally identical but fully independent of each other. Each comparator has its own inverting (-) and non-inverting (+) inputs and open-collector output.

LM393 Features

Key features of the LM393 comparator include:

• Wide supply voltage range: 2V to 36V
• Low input bias current: 25nA maximum
• Input common-mode voltage range extends to ground
• Low input offset voltage: 2mV maximum
• Open-collector output compatible with various logic levels
• Output voltage compatible with TTL, DTL, ECL, MOS and CMOS logic
• Two independent comparators in a single package

These features provide design flexibility, high performance, and suitability for battery-powered and single-supply applications.

LM393 Applications

The LM393’s versatility lends itself to a wide range of applications, such as:

1. Zero-crossing detector: The LM393 can detect when a signal crosses a reference voltage, making it useful for generating timing pulses or synchronizing circuits.

2. Window comparator: By using both comparators, the LM393 can determine if a signal lies within a specific voltage range, acting as a window comparator. This is handy for voltage monitoring and alarm systems.

3. Pulse Generator: The LM393 can generate pulses when the input signal crosses a certain threshold. This is useful in pulse width modulation (PWM) circuits, switching power supplies, and Motor Controllers.

4. Level shifter: With its open-collector output, the LM393 can interface circuits operating at different voltage levels, acting as a level shifter.

5. Analog-to-digital conversion: The comparator forms the heart of many analog-to-digital converters (ADCs). The LM393 can be used to build simple ADCs like the successive approximation type.

6. Overcurrent protection: By comparing the voltage across a current-sensing resistor with a reference, the LM393 can detect overcurrent conditions and trigger protection circuits.

7. Battery monitoring: The LM393 can monitor battery voltage and provide a low-battery indication when the voltage falls below a preset threshold.

8. Smoke and gas detection: In smoke and gas detectors, the LM393 compares the output of the sensor with a reference to determine the presence of smoke or gas.

These are just a few examples; the LM393’s applications are limited only by the designer’s creativity.

LM393 Working Principle

The LM393 is a voltage comparator that compares two analog input voltages and provides a digital output based on their relative magnitudes.

Comparator Basics

A comparator has two analog inputs: the inverting (-) and non-inverting (+) inputs. It compares these voltages and outputs a digital signal indicating which one is higher.

• If the non-inverting input voltage (V+) is higher than the inverting input voltage (V-), the output is high (near VCC).
• If the inverting input voltage (V-) is higher than the non-inverting input voltage (V+), the output is low (near GND).

The comparator’s output switches rapidly between high and low states as the input voltages cross each other. This rapid switching makes comparators useful for generating precise timing signals and detecting signal edges.

LM393 Comparator Operation

In the LM393, each comparator has an open-collector output. This means the output transistor’s collector is not internally connected to VCC. Instead, it requires an external pull-up resistor to VCC.

When the non-inverting input voltage is higher than the inverting input voltage, the output transistor is off, and the output is pulled high by the external resistor. When the inverting input voltage is higher, the output transistor turns on and sinks current, pulling the output low.

The LM393’s inputs are not internally clamped, so the input voltage can swing to the full supply voltage range, from GND to VCC. However, it’s essential to keep the input voltages within the specified common-mode and differential voltage ranges to ensure proper operation.

Hysteresis

One important aspect of comparator operation is hysteresis. Hysteresis introduces a small voltage difference between the comparator’s switching thresholds for rising and falling input signals. This difference, called the hysteresis voltage, prevents output oscillation when the input signal has noise or slow transitions near the comparison threshold.

To add hysteresis, a small positive feedback is introduced from the output to the non-inverting input. This shifts the effective comparison threshold depending on the output state. Hysteresis is not built into the LM393 but can be easily added externally with a few resistors.

LM393 FAQs

1. What is the difference between the LM393 and LM339 comparators?
   The LM393 contains two independent comparators, while the LM339 contains four. Functionally, the individual comparators are the same.

2. Can the LM393 be used with a single power supply?
   Yes, the LM393 is designed for single-supply operation. Its input common-mode voltage range extends down to GND, making it suitable for single-supply applications.

3. What is the purpose of the pull-up resistor on the LM393’s output?
   The LM393 has open-collector outputs, meaning the output transistor’s collector is not internally connected to VCC. The pull-up resistor is necessary to provide a high output state when the output transistor is off.

4. How do I add hysteresis to the LM393 comparator?
   Hysteresis can be added by introducing a small positive feedback from the output to the non-inverting input. This is typically done by connecting a high-value resistor between the output and non-inverting input and a lower-value resistor from the non-inverting input to GND.

5. What is the maximum supply voltage for the LM393?
   The LM393 can operate with a supply voltage up to 36V, making it suitable for a wide range of applications, including automotive and industrial systems.

By understanding the LM393’s pinout, features, applications, and working principle, designers can effectively use this versatile comparator in their projects. Its simplicity, robustness, and wide operating voltage range make it a popular choice for analog voltage comparison in various domains, from basic electronic projects to industrial control systems.