National Semiconductor LM3900N Vintage Quad Norton Operational Amplifier DIP-14

Vintage National Semiconductor LM3900N quadruple Norton operational amplifier in a 14-pin DIP through-hole package.

The LM3900N contains four independent high-gain, internally frequency-compensated Norton amplifiers. Unlike a conventional voltage-differencing operational amplifier, the LM3900 operates by comparing input currents, giving circuit designers useful capabilities for single-supply analog circuits.

The device was designed for operation over a wide range of supply voltages and became useful in amplifiers, waveform generators, oscillators, filters, comparators, level detectors, control circuits, timers, voltage-controlled circuits, and numerous general-purpose analog applications.

This original National Semiconductor example carries the three-digit marking 412. That code is consistent with production during week 12 of a year ending in 4. Because the abbreviated marking does not independently establish the decade, an exact manufacturing year is not assigned.

LIFECYCLE STATUS: ACTIVE

The LM3900 design remains available in current semiconductor production, although this original National Semiconductor-branded version represents historical production from before National Semiconductor became part of Texas Instruments.

HISTORICAL BACKGROUND:
The LM3900 occupies an interesting place in analog integrated-circuit history because it is not simply another conventional operational amplifier.

National Semiconductor documented the LM3900 by 1972 and described it as a new current-differencing or Norton amplifier. The device was developed during a period when engineers were looking for inexpensive analog circuits that could operate conveniently from a single positive power supply rather than requiring the positive and negative supply rails commonly associated with traditional op-amp designs.

A Norton amplifier responds primarily to the difference between currents at its inputs rather than directly comparing input voltages in the manner of a conventional operational amplifier. External resistors are therefore used to convert circuit voltages into input currents.

National Semiconductor promoted the LM3900 heavily for single-supply applications. Its four independent amplifier sections could be configured for a surprisingly wide variety of functions, including amplifiers, active filters, oscillators, pulse generators, triangle-wave generators, voltage-controlled oscillators, comparators, current sources, timers, and control circuitry.

The four-amplifier architecture was also economical. Designers could obtain several analog functions from one 14-pin package at a time when reducing component count, circuit-board space, and manufacturing cost was increasingly important.

The LM3900 became familiar to engineers and experimenters throughout the 1970s and later decades. It appeared in industrial electronics, instrumentation, control systems, consumer products, hobby projects, waveform generators, music and audio-related circuits, and general analog electronics.

National Semiconductor published an extensive application note for the LM3900 in September 1972, illustrating the unusual operating principle and numerous practical circuits that could be constructed around the device. That surviving documentation provides a useful snapshot of early-1970s analog design practices and demonstrates how versatile the LM3900 was considered at the time.

National Semiconductor remained a major American analog semiconductor manufacturer for decades. Texas Instruments acquired National Semiconductor in 2011, bringing many National-origin analog product families into the TI portfolio. The LM3900 family survives today, giving the design a production history extending more than half a century from its early-1970s origins.

This original National Semiconductor-marked LM3900N therefore represents an earlier generation of the same long-lived analog IC family still recognized today.