LM393 dual comparator explained, pinout, uses, hysteresis tricks, thresholds and practical circuits examples Simple projects, level detection, oscillator mods, sensor interfaces

 

LM393 Dual Comparator  Practical Guide 🔎⚡

LM393 dual comparator explained, pinout, uses, hysteresis tricks, thresholds and practical circuits examples Simple projects, level detection, oscillator mods, sensor interfaces, troubleshooting tips and design notes

Overview 🔍

The LM393 is a widely used, low power, dual voltage comparator. It accepts a wide supply range and can operate from a single supply as low as Vcc = 2.0 V in many designs, though common practical designs use Vcc = 5 V or Vcc = 12 V. Each comparator compares two input voltages and outputs a switched low or high open-collector output that needs a pull-up resistor to produce a logic level. The device is ideal for threshold detection, zero crossing detection, simple oscillators and many sensor interfacings.

Hint Box ➤ 📌 Note

Always use a pull-up resistor on the output. Typical pull-up values are 4.7k ohm to 100k ohm depending on speed and current needs.

Pinout and Electrical Specs ⚡

The package contains two independent comparators. Typical pin functions to remember are Vcc, ground, two inverting inputs, two non-inverting inputs, and two open-collector outputs. Important plain text parameters you may use in calculations are supply current, input common mode range, output saturation characteristics, and propagation delay. Input protection diodes are not guaranteed so avoid driving inputs beyond the supply rails.

Supply , Vcc typical 5 V in many projects

Input range , includes ground when powered from single supply in many uses

Output , open-collector, needs pull-up resistor

How it Works ⚙️

The comparator measures the difference between the non inverting input and the inverting input. When V+ > V minus, the output transistor is turned off and the pull-up resistor brings the output to high level. When V+ < V minus, the output transistor sinks current and the output is pulled low. For stable switching around thresholds, add hysteresis by positive feedback to avoid chatter when the input slowly crosses the threshold.

Design trick, hysteresis example

Add a resistor from output back to non-inverting input to create a small positive feedback. Choose resistances so that threshold shifts are appropriate for your sensor noise level. Example plain text values may use R1 = 100k, R2 = 10k and a pull-up of 10k.

Hint Box ➤ 📎 Quick

When using single supply, never let inputs go below ground or above Vcc. Use clamping resistors or divider networks to protect inputs.

Practical Circuits and Examples 🛠️

Comparator as a level detector

Use a resistive divider to make a Vref and feed sensor signal to the other input. When sensor voltage exceeds Vref, the output changes state. Use a pull-up resistor of about 10k to the logic supply. If you need open drain logic, the LM393 output suits directly.

LED flasher, square wave oscillator

Combine one comparator as a relaxation oscillator with a capacitor and resistor to generate pulses. Easily control duty cycle by changing resistor ratios. Use plain text values like C = 100 nF, R = 100k for a slow blink.

Applications and Use Cases 🔌

The LM393 finds uses in battery voltge monitoring, zero crossing detection, level comparators, motor driver interlocks, and simple sensor thresholds. Hobbyists use it for light sensors, touch sensors, and overcurrent alarms. The compartor is robust and cheap, but mind input common mode limits. For refernce creation use stable voltage, and for fast switching choose low pull up resitance. Designers also tune sensivity with small hysteresis to avoid false tripping in noisy enviroments.

Hint Box ➤ 📍 Pro Tip

If switching speed is critical, reduce pull-up resistor value and check propagation delay in datasheet. Lower pull-up increases current draw.

Troubleshooting and Design Notes 🩺

If output stays low, check pull-up resistor and ensure Vcc is present. If switching is noisy, add hysteresis. For inputs near rails consider level shifting or rail to rail comparators. Use decoupling capacitor 0.1 uF near Vcc and ground to reduce supply noise. When interfacing to microcontrollers, pull the output up to the MCU supply to match logic levels.

Quick checklist

• Check pull-up resistor value
• Confirm inputs within allowed common mode range
• Use hint box tips above for hysteresis and decoupling

Quick reference, ASCII schematic

      Vcc -----+-----------------------
               |                       |
              10k                     LM393 output (open-collector)
               |                       |
    Sensor -->+--||---> non-inverting  |----/\/\/\----> To MCU input (pull-up)
               |        input          |
    Vref -----+-----------------------+
  

If you need a printable wiring table, copy the ASCII schematic into a text file. For production designs, always consult the LM393 datasheet for absolute maximum ratings and timing figures.

 

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