How to Use LM393: Examples, Pinouts, and Specs

The LM393 is a dual comparator integrated circuit (IC) designed to compare two input voltages and output a digital signal based on the comparison. It features two independent voltage comparators in a single package, making it versatile and efficient for a wide range of applications. The LM393 operates with a wide supply voltage range and is known for its low power consumption.

• Voltage level detection
• Signal conditioning
• Zero-crossing detection
• Pulse-width modulation (PWM) circuits
• Analog-to-digital signal conversion
• Overvoltage or undervoltage protection systems
• Control systems in industrial and consumer electronics

The LM393 is a robust and reliable component with the following key technical details:

The LM393 is typically available in an 8-pin package. Below is the pinout and description:

The LM393 is straightforward to use in a circuit. Below are the steps and considerations for its proper usage:

1. Power Supply: Connect the Vcc pin (Pin 8) to a positive voltage source (2V to 36V) and the GND pin (Pin 4) to ground.
2. Input Connections:
   • Connect the voltage to be compared to the non-inverting input (Pin 3 or Pin 5).
   • Connect the reference voltage to the inverting input (Pin 2 or Pin 6).
3. Output: The output (Pin 1 or Pin 7) will be low (close to GND) if the inverting input voltage is higher than the non-inverting input voltage. Otherwise, the output will be high (close to Vcc).
4. Pull-Up Resistor: The LM393 has an open-collector output, so a pull-up resistor is required on the output pin to ensure proper operation. Typical values range from 1kΩ to 10kΩ, depending on the application.

• Input Voltage Range: Ensure that the input voltages do not exceed the supply voltage range to avoid damage to the IC.
• Bypass Capacitor: Place a decoupling capacitor (e.g., 0.1µF) close to the Vcc pin to reduce noise and improve stability.
• Output Loading: Avoid excessive loading on the output pin to maintain proper operation and response time.
• Hysteresis: To prevent output oscillations in noisy environments, consider adding hysteresis by using a feedback resistor between the output and the non-inverting input.

The LM393 can be used with an Arduino UNO for voltage level detection. Below is an example circuit and code:

• Connect the LM393's Vcc to the Arduino's 5V pin and GND to the Arduino's GND.
• Connect the non-inverting input (Pin 3) to the voltage to be monitored.
• Connect a reference voltage (e.g., from a potentiometer) to the inverting input (Pin 2).
• Use a 10kΩ pull-up resistor on the output (Pin 1) and connect it to an Arduino digital input pin.

// LM393 Comparator Example with Arduino UNO
// This code reads the output of the LM393 and turns on an LED if the monitored
// voltage exceeds the reference voltage.

const int lm393OutputPin = 2; // LM393 output connected to digital pin 2
const int ledPin = 13;        // Onboard LED pin

void setup() {
  pinMode(lm393OutputPin, INPUT); // Set LM393 output pin as input
  pinMode(ledPin, OUTPUT);        // Set LED pin as output
}

void loop() {
  int comparatorState = digitalRead(lm393OutputPin); // Read LM393 output

  if (comparatorState == HIGH) {
    digitalWrite(ledPin, HIGH); // Turn on LED if output is HIGH
  } else {
    digitalWrite(ledPin, LOW);  // Turn off LED if output is LOW
  }
}

1. No Output Signal:

   • Ensure the pull-up resistor is connected to the output pin.
   • Verify that the input voltages are within the specified range.
   • Check the power supply connections.

2. Output Oscillations:

   • Add hysteresis by connecting a feedback resistor between the output and the non-inverting input.
   • Use a decoupling capacitor near the Vcc pin to reduce noise.

3. Slow Response Time:

   • Minimize capacitive loading on the output pin.
   • Use a smaller pull-up resistor value to improve response speed.

4. Overheating:

   • Ensure the supply voltage does not exceed the maximum rating (36V).
   • Avoid excessive current draw from the output pin.

Q: Can the LM393 be used for AC signal comparison?
A: Yes, the LM393 can compare AC signals, but you may need to bias the inputs appropriately to keep the signals within the input voltage range.

Q: What is the purpose of the pull-up resistor on the output?
A: The LM393 has an open-collector output, which requires a pull-up resistor to define the output voltage level when the output transistor is off.

Q: Can I use the LM393 with a single power supply?
A: Yes, the LM393 is designed to operate with a single supply voltage. Ensure the input signals are within the common-mode voltage range.

This concludes the LM393 documentation.