LM3914

The LM3914 is an integrated circuit (IC), designed by National Semiconductor in the late 1970s, used to operate displays that visually show the magnitude of an analog signal.[1] It can drive up to 10 LEDs, LCDs, or vacuum fluorescent displays on its outputs. The linear scaling of the output thresholds makes the device usable, for example, as a voltmeter. In the basic configuration it provides a ten step scale which is expandable to over 100 segments with other LM3914 ICs in series.[1]

LM3914 driving an LED bargraph display
LM3915 IC in DIP-18 package

Features

The LM3914 / LM3915 / LM3916 are identical except for the ten resistor divider inside each part.

  • LM3914 - linear steps, scaled by a resistor divider consisting of ten 1000 ohm resistors.[1]
  • LM3915 - 3dB logarithmic steps, scaled by a resistor divider consisting of 6630, 4690, 3310, 2340, 1660, 1170, 830, 590, 410, 1000 ohm resistors.[2]
  • LM3916 - VU-meter steps, scaled by a resistor divider consisting of 1087, 970, 864, 769, 1298, 1031, 819, 923, 1531, 708 ohm resistors.[3]

All the devices in this group operate with a range of voltages from 3-25 V, can drive LED and VFD displays.[4] They can provide a regulated output current between 2-30 mA to directly drive displays.

Internally, each device contains ten comparators and a resistor scaling network, as well as a 1.25 volt reference source. As the input voltage increases, each comparator turns on. The device can be configured for either a bar-graph mode, where all lower-output terminals switch on, or "dot" mode in which only one output goes on. [5] The device is packaged in an 18 pin dual in-line package or in a surface mount leadless chip carrier.

See also

References
  1. LM3914 Datasheet; National Semiconductors; 1988.
  2. LM3915 Datasheet; National Semiconductors; 1988.
  3. LM3916 Datasheet; National Semiconductors; 1988.
  4. Note that the voltage measured has to be no closer than about 1.5-2.0V to supply voltage rail.
  5. R. M. Marston Audio IC Users Handbook Newnes, 1997 ISBN 0080572634, pp. 177-192
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