How to Use LM393: Examples, Pinouts, and Specs

The LM393 is a dual independent precision voltage comparator, designed to operate from a single power supply over a wide range of voltages. It is capable of comparing two voltage inputs and providing a digital output to indicate which input is higher. This component is widely used in various applications such as sensor interfacing, voltage level detection, and threshold monitoring.

• Battery chargers
• Voltage level monitoring
• Automotive sensors
• Motor control
• Logic voltage translation
• Window comparators

• Supply Voltage Range: 2.0V to 36V, or ±1.0V to ±18V (dual supplies)
• Input Bias Current: 25 nA (typical)
• Input Offset Current: ±5 nA (typical)
• Differential Input Voltage Range: Equal to the supply voltage
• Output Voltage Compatible with TTL, DTL, ECL, MOS, and CMOS logic systems

1. Power Supply Connection: Connect the Vcc pin to a positive supply voltage within the specified range and the GND pin to the system ground.

2. Input Signal Connection: Apply the two voltages to be compared to the inverting (IN-) and non-inverting (IN+) inputs of the comparator.

3. Output Connection: The output can be connected to a digital logic input, or used to drive a transistor or relay with the appropriate external components.

4. Pull-up Resistor: The LM393 has an open-collector output, which requires an external pull-up resistor to the positive supply voltage to function correctly.

• Ensure that the power supply voltage does not exceed the maximum rating of the IC.
• Avoid applying voltages to the input pins that exceed the supply voltage range.
• Use bypass capacitors close to the power supply pins to filter out noise.
• When interfacing with microcontrollers, ensure that the output voltage levels are compatible.

The following example demonstrates how to use the LM393 to compare a variable voltage with a fixed reference voltage and provide an output to an Arduino UNO.

// Define the Arduino pin connected to the LM393 output
const int comparatorOutputPin = 2;

void setup() {
  // Set the comparator output pin as an input
  pinMode(comparatorOutputPin, INPUT);
  // Begin serial communication at 9600 baud rate
  Serial.begin(9600);
}

void loop() {
  // Read the digital state of the comparator output
  int comparatorState = digitalRead(comparatorOutputPin);
  
  // Print the comparator state to the Serial Monitor
  Serial.println(comparatorState);
  delay(500); // Wait for half a second
}

• No Output Signal: Ensure that the pull-up resistor is correctly connected and that the input voltages are within the specified range.
• Erratic Output: Place a bypass capacitor near the power supply pins to stabilize the operation.

• Check Power Supply: Verify that the supply voltage is within the specified range and is stable.
• Inspect Connections: Ensure that all pins are properly soldered and connected.
• Pull-up Resistor: Confirm that the pull-up resistor value is appropriate for the supply voltage and load.

Q: Can the LM393 operate with a single supply voltage? A: Yes, the LM393 is designed to operate with a single supply voltage.

Q: What is the purpose of the pull-up resistor on the output? A: The pull-up resistor is required to provide a high level on the output when the open-collector output is in the off state.

Q: Can the LM393 outputs be connected directly to a microcontroller? A: Yes, but ensure that the microcontroller's input voltage levels are compatible with the LM393's output levels.