What Is the LM393? Dual Comparator: Pinout, Open-Collector and Uses
The LM393 is an IC with two independent voltage comparators in one package. It compares two voltages and drives its output to a logic level (high/low). Because its output is open-collector, it always needs a pull-up resistor (typically 4.7–10 kΩ). It is used in threshold-detection and zero-crossing circuits; it is not a linear amplifier.
The LM393 is an IC with two independent voltage comparators in one package. It resembles an op-amp but is different: it compares two input voltages and drives its output to a logic level (high/low). Because its output is open-collector, it always needs a pull-up resistor. For the concept, see what is a comparator.
What is the LM393 used for?
Threshold detection (triggering when a voltage crosses a reference), zero-crossing detection, sensor thresholds (light/temperature modules), voltage-level monitoring and simple oscillators. The open-collector output makes it easy to match a different logic voltage (e.g. 3.3 V) and to do wired-OR connections.
LM393 pinout (DIP-8 / SOIC-8)
| Pin | Function |
|---|---|
| 1 | Output A (open-collector) |
| 2 | Input A − |
| 3 | Input A + |
| 4 | GND |
| 5 | Input B + |
| 6 | Input B − |
| 7 | Output B (open-collector) |
| 8 | VCC |
Key electrical specifications
| Parameter | Typical value |
|---|---|
| Number of comparators | 2 (independent) |
| Supply (single) | 2 V – 36 V |
| Supply (dual) | ±1 V – ±18 V |
| Output type | Open-collector (pull-up required) |
| Response time | ~1.3 µs |
| Input common-mode range | includes ground |
Open-collector output — why a pull-up is mandatory
The LM393 output can only pull to ground (low) or release (high impedance). To create the high level, connect a pull-up resistor (typically 4.7 kΩ–10 kΩ) between the output and VCC (or your desired logic voltage, e.g. 3.3 V). Without a pull-up there is no "high" level at the output.
Comparator, not op-amp: watch out
The LM393 is not a linear amplifier; it is NOT used as an amplifier with negative feedback like an op-amp. It compares its two inputs and switches the output on/off. To avoid unstable triggering (chattering), hysteresis (positive feedback, a Schmitt trigger) is usually added.
Limitations
- Does not work without a pull-up resistor.
- Cannot be used as a linear amplifier (use an op-amp like the LM358 for that).
- On noisy transitions the output can chatter unless hysteresis is added.
LM393 equivalents and alternatives
- LM339: the quad (4 comparator) version.
- LM311: single, more flexible (push-pull/strobe) comparator.
- LM2903: the automotive (AEC-Q100) counterpart.
- TLV3501: for work that needs a much faster comparator.
Find it in our catalog
To compare price and stock for the LM393 and its alternatives, use the LM393 search.