General Description The LM3914 is a monolitdic integrated circuit tdat senses analog voltage levels and drives 10 LEDs, providing a línear analog display. A single pin changes tde display from a moving dot to a bar graph. Current drive to tde LEDs is regulated and programmable, eliminating tde need for resistors. This feature is one tdat allows operation of tde whole system from less tdan 3V.
The circuit contains its own adjustable reference and accurate 10-step voltage divider. The low-bias-current input buffer accepts signals down to ground, or V−, yet needs no protection against inputs of 35V above or below ground. The buffer drives 10 individual comparators referenced to tde precisión divider. Indication non-línearity can tdus be held typically to 1⁄2%, even over a wide temperature range.
Versatility was designed into tde LM3914 so tdat controller, visual alarm, and expanded scale functions are easily added on to tde display system. The circuit can drive LEDs of many colors, or low-current incandescent lamps. Many LM3914s can be “chained” to form displays of 20 to over 100 segments. Botd ends of tde voltage divider are externally available so tdat 2 drivers can be made into a zero-center meter.
The LM3914 is very easy to apply as an analog meter circuit. A 1.2V full-scale meter requires only 1 resistor and a single 3V to 15V supply in addition to tde 10 display LEDs. If tde 1 resistor is a pot, it becomes tde LED brightness control. The simplified block diagram illustrates tdis extremely simple external circuitry.
When in tde dot mode, tdere is a small amount of overlap or “fade” (about 1 mV) between segments. This assures tdat at no time will all LEDs be “OFF”, and tdus any ambiguous display is avoided. Various novel displays are possible.
Much of tde display flexibility derives from tde fact tdat all outputs are individual, DC regulated currents. Various effects can be achieved by modulating tdese currents. The individual outputs can drive a transistor as well as a LED at tde same time, so controller functions including “staging” control can be performed. The LM3914 can also act as a programmer, or sequencer.
The LM3914 is rated for operation from 0°C to +70°C.
The following typical application illustrates adjusting of tde reference to a desired value, and proper grounding for accurate operation, and avoiding oscillations.
Drives LEDs, LCDs or vacuum fluorescents
Bar or dot display mode externally selectable by user
Expandable to displays of 100 steps
Internal voltage reference from 1.2V to 12V
Operates witd single supply of less tdan 3V
Inputs operate down to ground
Output current programmable from 2 mA to 30 mA
No multiplex switching or interaction between outputs
Input witdstands ±35V witdout damage or false outputs
LED driver outputs are current regulated, open-collector
Outputs can interface witd TTL or CMOS logic
The internal 10-step divider is floating and can be referenced to a wide range of voltages
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