LM393N

The LM393N from Texas Instruments is the dual version of the LM339N, containing two independent comparators in a compact 8-pin PDIP package. It shares all the key characteristics of the LM339 family: open-collector outputs, ground-including input common-mode range, 2mV typical offset voltage, and 1.3µs response time. The smaller 8-pin package makes the LM393 ideal for applications needing only one or two comparators, saving board space compared to the 14-pin LM339. The open-collector outputs can be tied together for wired-AND logic — useful for window comparators where the output should be HIGH only when the input is within a specified range. The N suffix denotes the commercial temperature range (0°C to +70°C) in PDIP-8. For single-comparator applications, the TL331 (same family, one comparator, SOT-23) saves even more space.

Each comparator in the LM393N continuously monitors the voltage difference between its non-inverting (+) and inverting (−) inputs. When V+ > V−, the internal output transistor is OFF, and the open-collector output floats (appears HIGH through the external pull-up resistor). When V+ < V−, the output transistor turns ON, sinking current to ground and pulling the output LOW. The comparator has no internal hysteresis; adding positive feedback (a resistor from output to the non-inverting input) creates hysteresis that prevents output oscillation when the input signal is near the threshold. The input common-mode range includes ground, meaning both inputs can be at 0V without causing phase inversion or latch-up. The open-collector output requires a pull-up resistor to a supply voltage (which can be different from the comparator's VCC), enabling level translation: the comparator can run from 12V while the output pulls up to 5V for TTL logic compatibility.

LM393N uses the PDIP-8 package with standard dual comparator pinout: Pin 1 = Output A (open-collector), Pin 2 = Inverting Input A (-), Pin 3 = Non-inverting Input A (+), Pin 4 = GND, Pin 5 = Non-inverting Input B (+), Pin 6 = Inverting Input B (-), Pin 7 = Output B (open-collector), Pin 8 = VCC. The open-collector outputs require external pull-up resistors to VCC or a separate logic supply. This allows output level shifting — the pull-up voltage can differ from VCC. Maximum output sink current is 16mA. Input common-mode range includes ground. Pinout is identical to LM2903, LM393A, and LM2903V comparators. For surface-mount, LM393DR (SOIC-8) provides the same pinout.

• Window Comparator: Comp1: IN+=signal, IN−=upper limit; Comp2: IN−=signal, IN+=lower limit; outputs wired-AND; HIGH only when within window
• RC Oscillator: Output feeds back to IN+ through resistor divider; RC on IN−; oscillates at ~1/(2×R×C×ln(3))
• Sensor Threshold: IN+ = sensor voltage; IN− = reference (TL431 or divider); output drives relay or LED through transistor
• Overcurrent Detect: IN+ = shunt voltage; IN− = threshold; output trips shutdown circuit when current exceeds limit
• Level Shifter: Comparator at 12V supply; pull-up to 5V; converts 12V logic to 5V TTL-compatible output

LM393 is the industry-standard dual voltage comparator with open-drain output and 2-36V supply range. The 1.3µs response time suits general-purpose threshold detection. LM393AN offers lower offset voltage. LM339 provides 4 comparators in DIP-14. For high-speed applications, TLV3202 offers 40ns response with push-pull output at 2.7-5.5V supply.