Overview

The LM3914 is a monolithic integrated circuit manufactured by Texas Instruments that senses analog voltage levels and drives a 10-LED display, providing a linear 10-step analog display. A single pin (MODE) changes the display from a solid moving Bar Graph to a single Moving Dot display.

The IC features an internal 1.25V precision voltage reference and programmable LED current regulators (2 mA…30 mA2\text{ mA} \dots 30\text{ mA}) that eliminate the need for external current-limiting resistors for all 10 LEDs. It operates across a wide supply voltage range of 3.0V to 25.0V DC and can be cascaded to drive 20 to 100+ LED displays.

Quick reference

Supply Voltage (V+)3.0 V to 25.0 V DC
Decoded LED Outputs10 Regulated Current Sink Outputs (LED1 to LED10)
Display ModesBar Graph (Mode Pin tied to V+) / Moving Dot (Mode Pin floating)
Internal Reference Voltage1.25 V nominal (expandable up to 12V via divider)
Programmable LED Current2 mA to 30 mA (set by resistor between Pin 7 & 8/GND)
Package18-pin DIP / PLCC-20

Pinout (DIP-18 Package)

text
             ┌───┴───┐
        LED1 1│ 1   18│ LED2
          V- 2│       │17 LED3
          V+ 3│       │16 LED4
         RLO 4│ LM3914│15 LED5
         SIG 5│       │14 LED6
         RHI 6│       │13 LED7
     REF OUT 7│       │12 LED8
     REF ADJ 8│       │11 LED9
        MODE 9│       │10 LED10
             └───────┘
PinNameTypeDescription
1LED1OutputOpen-collector LED 1 driver output (First threshold step)
2V-PowerSignal and power ground reference (0 V)
3V+PowerPositive supply power pin (+3.0V to +25.0V DC)
4RLOInputLow-end of internal reference divider (Connect to GND or offset voltage)
5SIGInputAnalog voltage signal input pin (0V to V_RHI)
6RHIInputHigh-end of internal reference divider (Connect to REF OUT for 1.25V full scale)
7REF OUTOutputInternal 1.25V reference output / LED current programming pin
8REF ADJOutputVoltage reference adjust pin (Ground for 1.25V output)
9MODEInputDisplay mode select pin (V+ = Bar Graph; Floating = Moving Dot)
10–18LED10–LED2OutputOpen-collector LED driver outputs 10 down to 2

Specifications

ParameterSymbolMinTypMaxUnitConditions
Supply VoltageV+V^+3.0—25.0VDC
Reference VoltageVREFV_{REF}1.201.251.30VPin 7 to Pin 8
LED Driver CurrentILEDI_{LED}2.010.030.0mARL(REF)=1.2kΩR_{L(REF)} = 1.2\text{k}\Omega
Signal Input RangeVINV_{IN}−0.5-0.5—V+−1.5V^+-1.5VSafe input range
Divider Step Linearity——0.52.0%Relative step error
Standby Supply CurrentISI_S—2.49.2mADot mode, all LEDs off

Basic Application Circuit (0V to 1.25V 10-LED Voltmeter)

text
                       +5V to +12V Power
                               │
                       [Pin 3: V+] ────────── [Pin 9: MODE] (Tie to V+ for Bar Mode)
                        LM3914
                       [Pin 2: V-] ────────── GND
                               │
   Analog In (0..1.25V) ──► [Pin 5: SIG]
                               │
                       [Pin 6: RHI] ──┬────── [Pin 7: REF OUT]
                       [Pin 4: RLO] ──┴──┬─── [Pin 8: REF ADJ] ───[1.2kΩ Resistor]─── GND
                                         │
                                        GND
   LED Anodes (+VCC) ──► (10x LEDs) ───► [Pins 1, 18..10: LED1..LED10 Outputs]

LED Current Formula:ILED≈12.5RL(REF)(RL(REF)=1.2 kΩ⇒ILED≈10.4 mA)\text{LED Current Formula:} \quad I_{LED} \approx \frac{12.5}{R_{L(REF)}} \quad \left(R_{L(REF)} = 1.2\text{ k}\Omega \Rightarrow I_{LED} \approx 10.4\text{ mA}\right)

Common mistakes

  • Adding external current-limiting resistors to individual LEDs: The LM3914 contains built-in internal constant-current regulators on all 10 LED outputs. Connecting external resistors is unnecessary and reduces LED brightness uniformity.
  • Power dissipation in Bar Graph mode at high supply voltages: In Bar mode, when all 10 LEDs are lit at 20mA20\text{mA} each (200mA200\text{mA} total), if VLEDV_{LED} is 12V12\text{V} and LED forward drop is 2V2\text{V}, the chip dissipates (12V−2V)×0.2A=2.0W(12\text{V} - 2\text{V}) \times 0.2\text{A} = 2.0\text{W}, triggering thermal shutdown. Power LED anodes from a lower +3.3V⋯+5V+3.3\text{V} \dots +5\text{V} rail.
  • Floating RLO or RHI pins: Leaving reference divider end-points floating causes erratic LED activation threshold levels.

Notes

  • LM3914 vs LM3915 vs LM3916: LM3914 is linear (125mV125\text{mV} per step); LM3915 is logarithmic (3dB3\text{dB} per step); LM3916 is a VU meter scale (logarithmic −20dB-20\text{dB} to +3dB+3\text{dB}).

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