Exploring the LM393 Comparator IC: Pinout, Applications, and Circuits

The LM393 is a dual differential comparator IC, a workhorse in analog circuits used to compare two voltages. Featuring two independent comparators with open-drain outputs, it’s incredibly versatile for applications like voltage comparison, zero-crossing detection, and interfacing with sensors.

Features of the LM393 Comparator

• Dual Comparator: Houses two independent comparators within a single package.
• Wide Operating Voltage Range: Operates from 2V to 36V (single supply) or ±1V to ±18V (dual supply), providing flexibility in various setups.
• Low Input Offset Voltage: Guarantees accurate comparisons with minimal error.
• Open-Drain Output: Offers flexibility for interfacing with different voltage levels. This requires a pull-up resistor for proper operation.
• Low Power Consumption: Operates efficiently, making it perfect for battery-operated devices.
• Fast Response Time: Responds typically within a few microseconds, ensuring rapid comparisons.
• Temperature Stability: Functions reliably across a broad temperature range (from -40°C to +85°C).
• Package Types: Available in DIP, SOIC, and other compact packages, simplifying integration into different designs.

LM393 Comparator Pinout

Figure 1 depicts the LM393 Comparator pinout diagram.

Working Principle

The LM393 compares the voltage applied to the non-inverting input (V₊) and the inverting input (V_-). The output state is determined as follows:

• Output Low: When V₊ is less than V_-.
• Output High: When V₊ is greater than V_-.

Since the LM393 has open-drain outputs, a pull-up resistor is usually connected to the output pin. This ensures a clear high or low output signal, as the comparator output can only pull the voltage down to ground. The pull-up resistor provides the path for the output to go high when the internal transistor is off.

Application Example: Light-Activated Switch

The LM393 comparator excels in light-activated switch circuits where the output changes based on the light level. An LDR (Light Dependent Resistor) and a regular resistor create a voltage divider, setting the switching point according to ambient light.

• Circuit Setup:

  • Connect the LDR and a fixed resistor to form a voltage divider. Connect this divider to the non-inverting input.
  • Set a reference voltage using a potentiometer connected to the inverting input.
  • Connect the comparator’s output to an LED with a pull-up resistor.

• Working:

  • Changes in light level alter the LDR’s resistance, adjusting the voltage at the non-inverting input.
  • If the non-inverting input’s voltage exceeds the reference voltage, the comparator output goes low, turning the LED off.
  • When the ambient light drops below the set threshold, the non-inverting input voltage becomes lower than the reference voltage, and the output goes high, turning the LED on.

Other Applications

The LM393 isn’t just for light-activated switches; it’s useful in many other circuits:

• Zero-Crossing Detector: Detects when an AC waveform crosses zero voltage, often used in phase control applications.
• Battery Level Indicator: Compares battery voltage to a reference voltage to indicate low or full charge.
• Oscillator Circuit: The LM393 can be used to create square wave signals for timing applications. The open-collector output lends itself well to this.
• Over-Temperature Protection: Monitors temperature by comparing the voltage from a temperature sensor to a reference voltage, activating a fan or alert if the temperature exceeds a threshold.

Conclusion

The LM393 Comparator is a versatile and cost-effective component for analog comparisons. It enables designers to integrate voltage sensing, control, and threshold detection in diverse applications, from light sensors to sophisticated control systems. Its simple operation and wide availability make it a staple in many electronic designs.