How to Use LM393: Examples, Pinouts, and Specs

The LM393 is a dual independent precision voltage comparator, capable of comparing two input voltages and determining which is higher. It is designed to operate from a single power supply over a wide range of voltages or from dual supplies. The LM393 is widely used in electronic circuits for sensor interfacing, voltage level detection, and for driving loads when a specific voltage threshold is crossed.

• Sensing and detection circuits
• Simple analog to digital converters
• Battery chargers
• Voltage monitors
• Relay drivers
• Motor control circuits

• Supply Voltage Range: 2.0V to 36V (or ±1.0V to ±18V)
• Input Offset Voltage: 5mV max (at 25°C)
• Input Bias Current: 25nA (typical)
• Output Current: 20mA (typical)
• Response Time: 1.3μs (typical)
• Operating Temperature Range: 0°C to 70°C

1. Power Supply: Connect the Vcc pin to a positive supply voltage and the GND pin to the ground of the circuit.
2. Input Signals: Apply the voltages to be compared to the IN+ and IN- pins of the respective comparator.
3. Output Connection: Connect the OUT pin to the load or next stage in your circuit. Note that the LM393 has an open-collector output, which requires a pull-up resistor to the supply voltage.

• Always use a pull-up resistor on the output to ensure proper logic levels.
• Bypass the power supply with a 0.1μF capacitor close to the LM393 to minimize power supply noise.
• Avoid placing noisy digital signals close to the analog inputs to prevent false triggering.
• Ensure that the input voltages do not exceed the supply voltage range to prevent damage.

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

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

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

• No Output Signal: Ensure that the pull-up resistor is connected and that the input voltages are within the specified range.
• False Triggering: Check for noise in the input signals or power supply, and ensure proper decoupling.

• If the output remains low regardless of input, check the connections and the pull-up resistor.
• For erratic outputs, add a small capacitor (e.g., 10nF) between the input pin and ground to filter noise.
• Verify that the supply voltage is within the specified range and stable.

Q: Can the LM393 be used with a single supply? A: Yes, the LM393 can operate with a single supply voltage.

Q: What is the purpose of the open-collector output? A: The open-collector output allows for voltage level shifting and the ability to connect multiple outputs together for a wired-AND configuration.

Q: How can I interface the LM393 with a microcontroller? A: Connect the output of the LM393 to a digital input pin of the microcontroller with a suitable pull-up resistor. Use digitalRead() to detect the output state.

Q: Can the LM393 outputs drive a relay directly? A: Yes, but ensure that the relay coil current is within the output current limits of the LM393 and use a flyback diode across the relay coil to protect the comparator from voltage spikes.