Skip to content
LearnTronics menu

LearnTronics

Electronic Parts

Integrated Circuits

Analog ICs

LM393 and Related Comparators

The LM393 contains two independent voltage comparators. A comparator looks superficially like an op-amp, but its normal job is not linear amplification. It answers the question: which input voltage is higher?

PartChannelsWhy it is familiar
LM3932Classic dual comparator.
LM3394Closely related quad comparator.
LM3111Classic single comparator with a flexible output stage.
Open-collector output

A very important LM393 detail is its open-collector output. The output transistor can pull the output LOW, but an external pull-up resistor normally provides the HIGH state.

sensor voltage→LM393
COMPARE→ON / OFF decision
+ input− inputopen-collector output
Threshold circuits

One input can be connected to a fixed reference voltage and the other to a sensor. When the sensor voltage crosses the reference, the output changes state. That makes comparators useful for thermostats, battery monitors, light detectors, zero-crossing detectors, alarms, and level sensing.

Hysteresis

If a noisy signal sits close to the switching threshold, the output can chatter rapidly between states. A small amount of positive feedback can create two slightly different thresholds—one for switching ON and another for switching OFF. This is called hysteresis.

Do not automatically substitute an ordinary op-amp for a comparator. Input range, output structure, speed, saturation recovery, and supply requirements are different design concerns.

Manufacturer reference: TI LM393.