LM3915
Dot/Bar Display Driver
General Description
The LM3915 is a monolithic integrated circuit that senses
analog voltage levels and drives ten LEDs, LCDs or vacuum
fluorescent displays, providing a logarithmic 3 dB/step analog display. One pin changes the display from a bar graph toa moving dot display. LED current drive is regulated andprogrammable, eliminating the need for current limiting resistors. The whole display system can operate from a single
supply as low as 3V or as high as 25V.
The IC contains an adjustable voltage reference and an
accurate ten-step voltage divider. The high-impedance input
buffer accepts signals down to ground and up to within 1.5Vof the positive supply. Further, it needs no protection against
inputs of ± 35V. The input buffer drives 10 individual comparators referenced to the precision divider. Accuracy is
typically better than 1 dB.
The LM3915’s 3 dB/step display is suited for signals withwide dynamic range, such as audio level, power, light intensity or vibration. Audio applications include average or peaklevel indicators, power meters and RF signal strength
meters. Replacing conventional meters with an LED bargraph results in a faster responding, more rugged display
with high visibility that retains the ease of interpretation of ananalog display.
The LM3915 is extremely easy to apply. A 1.2V full-scale
meter requires only one resistor in addition to the ten LEDs.
One more resistor programs the full-scale anywhere from
1.2V to 12V independent of supply voltage. LED brightness
is easily controlled with a single pot.

© 2004 National Semiconductor Corporation

DS005104

The LM3915 is very versatile. The outputs can drive LCDs,
vacuum fluorescents and incandescent bulbs as well as
LEDs of any color. Multiple devices can be cascaded for adot or bar mode display with a range of 60 or 90 dB.
LM3915s can also be cascaded with LM3914s for a linear/log display or with LM3916s for an extended-range VU
meter.

Featuresn 3 dB/step, 30 dB rangen Drives LEDs, LCDs, or vacuum fluorescentsn Bar or dot display mode externally selectable by usern Expandable to displays of 90 dB
n Internal voltage reference from 1.2V to 12V
n Operates with single supply of 3V to 25V
n Inputs operate down to groundn Output current programmable from 1 mA to 30 mA
n Input withstands ± 35V without damage or false outputs
n Outputs are current regulated, open collectors
n Directly drives TTL or CMOS
n The internal 10-step divider is floating and can bereferenced to a wide range of voltages
The LM3915 is rated for operation from 0˚C to +70˚C. The
LM3915N-1 is available in an 18-lead molded DIP package.

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LM3915 Dot/Bar Display Driver

February 2001

LM3915

Typical Applications
0V to 10V Log Display

00510401

Notes: Capacitor C1 is required if leads to the LED supply are 6" or longer.
Circuit as shown is wired for dot mode. For bar mode, connect pin 9 to pin 3. VLED must be kept below 7V or dropping resistor should be used to limit IC power
dissipation.

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2Input Signal Overvoltage (Note 4)

If Military/Aerospace specified devices are required,please contact the National Semiconductor Sales Office/Distributors for availability and specifications.

Divider Voltage

Power Dissipation (Note 6)
Molded DIP(N)

Lead Temperature(Soldering, 10 sec.)

25V

Voltage on Output Drivers

25V−100 mV to V+

Reference Load Current

10 mA

Storage Temperature Range

1365 mW

Supply Voltage± 35V−55˚C to +150˚C
260˚C

Electrical Characteristics (Notes 2, 4)Parameter

Conditions (Note 2)

Min

Typ

Max

Units

COMPARATOR
Offset Voltage, Buffer and First
Comparator

0V ≤ VRLO = VRHI ≤ 12V,
ILED = 1 mA

3

10

mV

Offset Voltage, Buffer and Any Other
Comparator

0V ≤ VRLO = VRHI ≤ 12V,
ILED = 1 mA

3

15

mV

Gain (∆ILED/∆VIN)

IL(REF) = 2 mA, ILED = 10 mA

Input Bias Current (at Pin 5)

0V ≤ VIN ≤ (V − 1.5V)

Input Signal Overvoltage

No Change in Display−35

Divider Resistance

Total, Pin 6 to 4

16

Relative Accuracy (Input Change Between
Any Two Threshold Points)(Note 3)2.0

Absolute Accuracy at Each Threshold
Point(Note 3)

3

+

8
25

mA/mV
100

nA

35

V

28

36

kΩ

3.0

4.0

dB

dB

VOLTAGE-DIVIDER

VIN = −3, −6 dB

−0.5

+0.5

VIN = −9 dB

−0.5

+0.65

dB

VIN = −12, −15, −18 dB

−0.5

+1.0

dB

VIH = −21, −24, −27 dB

−0.5

+1.5

dB

Output Voltage

0.1 mA ≤ IL(REF) ≤ 4 mA,
V+ = VLED = 5V

1.2

1.28

1.34

V

Line Regulation

3V ≤ V+ ≤ 18V

0.01

0.03

%/V

Load Regulation

0.1 mA ≤ IL(REF) ≤ 4 mA,
V+ = VLED = 5V

0.4

2

%

Output Voltage Change with
Temperature

0˚C ≤ TA ≤ +70˚C, IL(REF) = 1 mA,
V + = VLED = 5V

1

VOLTAGE REFERENCE

Adjust Pin Current

75

%
120

µA
mA

OUTPUT DRIVERS
LED Current

V + = VLED = 5V, IL(REF) = 1 mA

10

13

LED Current Difference (Between
Largest and Smallest LED Currents)

VLED = 5V, ILED = 2 mA
VLED = 5V, ILED 20 mA

0.12

0.4

1.2

3

LED Current Regulation

2V ≤ VLED ≤ 17V, ILED = 2 mA
ILED = 20 mA

0.1

0.25

1

3

Dropout Voltage

ILED(ON) = 20 mA, @ VLED = 5V,∆ILED = 2 mA

Saturation Voltage

ILED = 2.0 mA, IL(REF) = 0.4 mA

Output Leakage, Each Collector(Bar Mode) (Note 5)

Output Leakage
Pins 10–18(Dot Mode) (Note 5)

Pin 1

7

60

3

mA
mA

1.5

V

0.15

0.4

V

0.1

10

µA

0.1

10

µA

150

450

µA

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LM3915Absolute Maximum Ratings (Note 1)

LM3915

Electrical Characteristics (Notes 2, 4) (Continued)
Parameter

Conditions (Note 2)

Min

Typ

Max

Units

2.4

4.2

mA

6.1

9.2

mA

SUPPLY CURRENT
V+ = +5V, IL(REF) = 0.2 mA
V+ = +20V, IL(REF) = 1.0 mA

Standby Supply Current(All Outputs Off)

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device isfunctional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions whichguarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit
is given, however, the typical value is a good indication of device performance.
Note 2: Unless otherwise stated, all specifications apply with the following conditions:
3 VDC ≤ V+ ≤ 20 VDC−0.015V ≤ VRLO ≤ 12 VDC

3 VDC ≤ VLED ≤ V+

VREF, VRHI, VRLO ≤ (V+ − 1.5V)−0.015V ≤ VRHI ≤ 12 VDC

TA = 25˚C, IL(REF) = 0.2 mA, pin 9 connected to pin 3 (bar mode).
For higher power dissipations, pulse testing is used.

0V ≤ VIN ≤ V+ − 1.5V

Note 3: Accuracy is measured referred to 0 dB = + 10.000 VDC at pin 5, with + 10.000 VDC at pin 6, and 0.000 VDC at pin 4. At lower full scale voltages, buffer andcomparator offset voltage may add significant error. See table for threshold voltages.
Note 4: Pin 5 input current must be limited to ± 3 mA. The addition of a 39k resistor in series with pin 5 allows ± 100V signals without damage.
Note 5: Bar mode results when pin 9 is within 20 mV of V+. Dot mode results when pin 9 is pulled at least 200 mV below V+. LED #10 (pin 10 output current) is
disabled if pin 9 is pulled 0.9V or more below VLED.
Note 6: The maximum junction temperature of the LM3915 is 100˚C. Devices must be derated for operation at elevated temperatures. Junction to ambient thermal
resistance is 55˚C/W for the molded DIP (N package).

Threshold Voltage (Note 3)
Output

dB

Min

Typ

Max

Output

dB

Min

Typ

Max

1

−27

0.422

0.447

0.531

6

−12

2.372

2.512

2.819

2

−24

0.596

0.631

0.750

7

−9

3.350

3.548

3.825

3

−21

0.841

0.891

1.059

8

−6

4.732

5.012

5.309

4

−18

1.189

1.259

1.413

9

−3

6.683

7.079

7.498

5

−15

1.679

1.778

1.995

10

0

9.985

10

10.015www.national.com

4Supply Current vs Temperature

Operating Input Bias Current vs Temperature

00510434

00510435

Reference Voltage vs
Temperature

Reference Adjust Pin
Current vs Temperature

00510437

00510436

LED Current-Regulation
Dropout

LED Driver Saturation
Voltage00510438

00510439

5

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LM3915

Typical Performance Characteristics

LM3915

Typical Performance Characteristics (Continued)
Input Current Beyond
Signal Range (Pin 5)

LED Current vsReference Loading

00510440
00510441

LED Driver Current
Regulation

Total Divider Resistancevs Temperature

00510443

00510442

Common-Mode Limits

Output Characteristics

00510445

00510444

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6LM3915

Block Diagram (Showing Simplest Application)

00510404

7

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LM3915

Functional Description

LM3915 Output Circuit

The simplified LM3915 block diagram is included to give thegeneral idea of the circuit’s operation. A high input impedance buffer operates with signals from ground to 12V, and isprotected against reverse and overvoltage signals. The signal is then applied to a series of 10 comparators; each ofwhich is biased to a different comparison level by the resistor
string.
In the example illustrated, the resistor string is connected tothe internal 1.25V reference voltage. In this case, for each
3 dB that the input signal increases, a comparator will switch
on another indicating LED. This resistor divider can be connected between any 2 voltages, providing that they are atleast 1.5V below V+ and no lower than V−.

00510406

Outputs may be run in saturation with no adverse effects,
making it possible to directly drive logic. The effective saturation resistance of the output transistors, equal to RE plus
the transistors’ collector resistance, is about 50Ω. It’s also
possible to drive LEDs from rectified AC with no filtering. To
avoid oscillations, the LED supply should be bypassed with a
2.2 µF tantalum or 10 µF aluminum electrolytic capacitor.

INTERNAL VOLTAGE REFERENCE
The reference is designed to be adjustable and develops anominal 1.25V between the REF OUT (pin 7) and REF ADJ(pin 8) terminals. The reference voltage is impressed acrossprogram resistor R1 and, since the voltage is constant, aconstant current I1 then flows through the output set resistor
R2 giving an output voltage of:

MODE PIN USE
Pin 9, the Mode Select input, permits chaining of multiple
LM3915s, and controls bar or dot mode operation. The
following tabulation shows the basic ways of using this input.
Other more complex uses will be illustrated in the applications.
Bar Graph Display: Wire Mode Select (pin 9) directly to pin
3 (V+ pin).
Dot Display, Single LM3915 Driver: Leave the Mode Selectpin open circuit.
Dot Display, 20 or More LEDs: Connect pin 9 of the first
driver in the series (i.e., the one with the lowest input voltage
comparison points) to pin 1 of the next higher LM3915 driver.
Continue connecting pin 9 of lower input drivers to pin 1 ofhigher input drivers for 30 or more LED displays. The lastLM3915 driver in the chain will have pin 9 left open. All
previous drivers should have a 20k resistor in parallel withLED #9 (pin 11 to VLED).

00510405

Since the 120 µA current (max) from the adjust terminal
represents an error term, the reference was designed tominimize changes of this current with V+ and load changes.
For correct operation, reference load current should be between 80 µA and 5 mA. Load capacitance should be lessthan 0.05 µF.

Mode Pin Functional Description
This pin actually performs two functions. Refer to the simplified block diagram below.
Block Diagram of Mode Pin Function

CURRENT PROGRAMMING
A feature not completely illustrated by the block diagram is
the LED brightness control. The current drawn out of thereference voltage pin (pin 7) determines LED current. Approximately 10 times this current will be drawn through eachlighted LED, and this current will be relatively constant despite supply voltage and temperature changes. Current
drawn by the internal 10-resistor divider, as well as by theexternal current and voltage-setting divider should be included in calculating LED drive current. The ability to modulate LED brightness with time, or in proportion to input voltage and other signals can lead to a number of novel displays
or ways of indicating input overvoltages, alarms, etc.
The LM3915 outputs are current-limited NPN transistors asshown below. An internal feedback loop regulates the transistor drive. Output current is held at about 10 times thereference load current, independent of output voltage andprocessing variables, as long as the transistor is not saturated.
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00510407*High for bar

8worst case required to hold off LED #10 yet small enoughthat LED #11 does not conduct significantly.

(Continued)

OTHER DEVICE CHARACTERISTICS
The LM3915 is relatively low-powered itself, and since any
number of LEDs can be powered from about 3V, it is a very
efficient display driver. Typical standby supply current (allLEDs OFF) is 1.6 mA. However, any reference loading adds
4 times that current drain to the V+ (pin 3) supply input. For
example, an LM3916 with a 1 mA reference pin load (1.3k)
would supply almost 10 mA to every LED while drawing only
10 mA from its V+ pin supply. At full-scale, the IC is typicallydrawing less than 10% of the current supplied to the display.

DOT OR BAR MODE SELECTION
The voltage at pin 9 is sensed by comparator C1, nominallyreferenced to (V+ − 100 mV). The chip is in bar mode whenpin 9 is above this level; otherwise it’s in dot mode. The
comparator is designed so that pin 9 can be left open circuit
for dot mode.
Taking into account comparator gain and variation in the
100 mV reference level, pin 9 should be no more than 20 mV
below V+ for bar mode and more than 200 mV below V+ (oropen circuit) for dot mode. In most applications, pin 9 iseither open (dot mode) or tied to V+ (bar mode). In bar mode,
pin 9 should be connected directly to pin 3. Large currents
drawn from the power supply (LED current, for example)
should not share this path so that large IR drops are avoided.

The display driver does not have built-in hysteresis so thatthe display does not jump instantly from one LED to the next.
Under rapidly changing signal conditions, this cuts downhigh frequency noise and often an annoying flicker. An “overlap” is built in so that at no time are all segments completely
off in the dot mode. Generally 1 LED fades in while the otherfades out over a mV or more of range. The change may bemuch more rapid between LED #10 of one device and LED#1 of a second device “chained” to the first.

DOT MODE CARRY
In order for the display to make sense when multiple
LM3915s are cascaded in dot mode, special circuitry has
been included to shut off LED #10 of the first device when
LED #1 of the second device comes on. The connection for
cascading in dot mode has already been described and is
depicted below.
As long as the input signal voltage is below the threshold of
the second LM3915, LED #11 is off. Pin 9 of LM3915 #1 thus
sees effectively an open circuit so the chip is in dot mode. As
soon as the input voltage reaches the threshold of LED #11,
pin 9 of LM3915 #1 is pulled an LED drop (1.5V or more)
below VLED. This condition is sensed by comparator C2,
referenced 600 mV below VLED. This forces the output of C2
low, which shuts off output transistor Q2, extinguishing LED#10.
VLED is sensed via the 20k resistor connected to pin 11. Thevery small current (less than 100 µA) that is diverted fromLED #9 does not noticeably affect its intensity.
An auxiliary current source at pin 1 keeps at least 100 µA
flowing through LED #11 even if the input voltage rises highenough to extinguish the LED. This ensures that pin 9 of
LM3915 #1 is held low enough to force LED #10 off when
any higher LED is illuminated. While 100 µA does not normally produce significant LED illumination, it may be noticeable when using high-efficiency LEDs in a dark environment.
If this is bothersome, the simple cure is to shunt LED #11
with a 10k resistor. The 1V IR drop is more than the 900 mV

Application Hints
The most difficult problem occurs when large LED currents
are being drawn, especially in bar graph mode. These currents flowing out of the ground pin cause voltage drops inexternal wiring, and thus errors and oscillations. Bringing thereturn wires from signal sources, reference ground and bottom of the resistor string to a single point very near pin 2 isthe best solution.
Long wires from VLED to LED anode common can cause
oscillations. Depending on the severity of the problem
0.05 µF to 2.2 µF decoupling capacitors from LED anodecommon to pin 2 will damp the circuit. If LED anode line
wiring is inaccessible, often similar decoupling from pin 1 topin 2 will be sufficient.
If LED turn ON seems slow (bar mode) or several LEDs light(dot mode), oscillation or excessive noise is usually the
problem. In cases where proper wiring and bypassing fail tostop oscillations, V+ voltage at pin 3 is usually below suggested limits. Expanded scale meter applications may haveone or both ends of the internal voltage divider terminated atrelatively high value resistors. These high-impedance ends
should be bypassed to pin 2 with at least a 0.001 µF capacitor, or up to 0.1 µF in noisy environments.

Cascading LM3915s in Dot Mode

00510408

9

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LM3915Mode Pin Functional DescriptionLM3915

gain difference means that the display may have a ± 1 dB
error when the input is a nonsymmetrical transient). The
averaging time constant is R5–C2. A simple modification
results in the precision full-wave detector of Figure 4. Since
the filter capacitor is not buffered, this circuit can drive only
high impedance loads such as the input of an LM3915.

Application Hints (Continued)
Power dissipation, especially in bar mode should be given
consideration. For example, with a 5V supply and all LEDs
programmed to 20 mA the driver will dissipate over 600 mW.
In this case a 7.5Ω resistor in series with the LED supply will
cut device heating in half. The negative end of the resistor
should be bypassed with a 2.2 µF solid tantalum capacitor topin 2.
TIPS ON RECTIFIER CIRCUITSThe simplest way to display an AC signal using the LM3915
is to apply it right to pin 5 unrectified. Since the LED illuminated represents the instantaneous value of the AC waveform, one can readily discern both peak and average valuesof audio signals in this manner. The LM3915 will respond topositive half-cycles only but will not be damaged by signals
up to ± 35V (or up to ± 100V if a 39k resistor is in series with
the input). It’s recommended to use dot mode and to run theLEDs at 30 mA for high enough average intensity.

00510409*DC Couple

True average or peak detection requires rectification. If an
LM3915 is set up with 10V full scale across its voltage
divider, the turn-on point for the first LED is only 450 mV. A
simple silicon diode rectifier won’t work well at the low end
due to the 600 mV diode threshold. The half-wave peakdetector in Figure 1 uses a PNP emitter-follower in front of
the diode. Now, the transistor’s base-emitter voltage cancels
out the diode offset, within about 100 mV. This approach isusually satisfactory when a single LM3915 is used for a 30
dB display.
Display circuits using two or more LM3915s for a dynamic
range of 60 dB or greater require more accurate detection. In
the precision half-wave rectifier of Figure 2 the effective
diode offset is reduced by a factor equal to the open-loop
gain of the op amp. Filter capacitor C2 charges through R3
and discharges through R2 and R3, so that appropriate
selection of these values results in either a peak or an
average detector. The circuit has a gain equal to R2/R1.
It’s best to capacitively couple the input. Audio sources
frequently have a small DC offset that can cause significant
error at the low end of the log display. Op amps that slew
quickly, such as the LF351, LF353, or LF356, are needed tofaithfully respond to sudden transients. It may be necessary
to trim out the op amp DC offset voltage to accurately covera 60 dB range. Best results are obtained if the circuit isadjusted for the correct output when a low-level AC signal(10 mV to 20 mV) is applied, rather than adjusting for zero
output with zero input.
For precision full-wave averaging use the circuit in Figure 3.
Using 1% resistors for R1 through R4, gain for positive andnegative signal differs by only 0.5 dB worst case. Substituting 5% resistors increases this to 2 dB worst case. (A 2 dB

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FIGURE 1. Half-Wave Peak Detector

00510410

D1, D2: 1N914 or 1N4148

Average

Peak

R2

1k

100k

R3

100k

1k

R1 = R2 for AV = 1
R1 = R2/R10 for AV = 10
C1 = 10/R1

FIGURE 2. Precision Half-Wave Rectifier

10LM3915

Application Hints (Continued)

00510411

D1, D2: 1N914 or 1N4148

FIGURE 3. Precision Full-Wave Average Detector

00510412

D1, D2, D3, D4: 1N914 or 1N4148

FIGURE 4. Precision Full-Wave Peak Detector
CASCADING THE LM3915
To display signals of 60 dB or 90 dB dynamic range, multiple
LM3915s can be easily cascaded. Alternatively, it is possible
to cascade an LM3915 with LM3914s for a log/linear display
or with an LM3916 to get an extended range VU meter.
A simple, low cost approach to cascading two LM3915s is to
set the reference voltages of the two chips 30 dB apart as in
Figure 5. Potentiometer R1 is used to adjust the full scale
voltage of LM3915 #1 to 316 mV nominally while the second
IC’s reference is set at 10V by R4. The drawback of thismethod is that the threshold of LED #1 is only 14 mV and,since the LM3915 can have an offset voltage as high as
10 mV, large errors can occur. This technique is not recommended for 60 dB displays requiring good accuracy at thefirst few display thresholds.
A better approach shown in Figure 6 is to keep the reference
at 10V for both LM3915s and amplify the input signal to thelower LM3915 by 30 dB. Since two 1% resistors can set theamplifier gain within ± 0.2 dB, a gain trim is unnecessary.
However, an op amp offset voltage of 5 mV will shift the first
LED threshold as much as 4 dB, so that an offset trim may
be required. Note that a single adjustment can null out offset
11

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LM3915

Application Hints (Continued)

Alternatively, instead of amplifying, input signals of sufficient
amplitude can be fed directly to the lower LM3915 andattenuated by 30 dB to drive the second LM3915.

in both the precision rectifier and the 30 dB gain stage.

00510413

FIGURE 5. Low Cost Circuit for 60 dB Display

00510414

FIGURE 6. Improved Circuit for 60 dB Display
To extend this approach to get a 90 dB display, another
30 dB of amplification must be placed in the signal pathahead of the lowest LM3915. Extreme care is required as thelowest LM3915 displays input signals down to 0.5 mV! Several offset nulls may be required. High currents should notshare the same path as the low level signal. Also power line
wiring should be kept away from signal lines.

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TIPS ON REFERENCE VOLTAGE
AND LED CURRENT PROGRAMMING
Single LM3915
The equations in Figure 7 illustrate how to choose resistor
values to set reference voltage for the simple case where no
LED intensity adjustment is required. A LED current of 10 mA
to 20 mA generally produces adequate illumination. Having
10V full-scale across the internal voltage divider gives best
accuracy by keeping signal level high relative to the offset
voltage of the internal comparators. However, this causes
450 µA to flow from pin 7 into the divider which means that12

separate channels for stereo. This technique can be extended for larger numbers of LM3915s by varying the valuesof R1, R2 and R3 in inverse proportion to the number ofdevices tied in. The ICs’ internal references track within
100 mV so that worst case error from chip to chip is only
0.1 dB for VREF = 10V.

the LED current will be at least 5 mA. R1 will typically be
between 1 kΩ and 2 kΩ. To trim the reference voltage, varyR2.
The circuit in Figure 8 shows how to add a LED intensity
control which can vary LED current from 9 mA to 28 mA. The
reference adjustment has some effect on LED intensity but
the reverse is not true.
Multiple LM3915s
Figure 9 shows how to obtain a common reference trim andintensity control for two LM3915s. The two ICs may beconnected in cascade for a 60 dB display or may be handling

00510415

FIGURE 7. Design Equations for Fixed LED Intensity

13

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LM3915

Application Hints (Continued)

LM3915

Application Hints (Continued)

00510416*9 mA < ILED < 28 mA @ VREF = 10V

FIGURE 8. Varying LED Intensity

00510417

FIGURE 9. Independent Adjustment of Reference Voltage and LED Intensity for Multiple LM3915s
The scheme in Figure 10 is useful when the reference and
LED intensity must be adjusted independently over a wide
range. The RHI voltage can be adjusted from 1.2V to 10V
with no effect on LED current. Since the internal divider here
does not load down the reference, minimum LED current ismuch lower. At the minimum recommended reference loadof 80 µA, LED current is about 0.8 mA. The resistor values
shown give a LED current range from 1.5 mA to 20 mA.
At the low end of the intensity adjustment, the voltage drop
across the 510Ω current-sharing resistors is so small thatchip to chip variation in reference voltage may yield a visible
variation in LED intensity. The optional approach shown ofconnecting the bottom end of the intensity control pot to anegative supply overcomes this problem by allowing a larger
voltage drop across the (larger) current-sharing resistors.

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Other Applications
For increased resolution, it’s possible to obtain a display witha smooth transition between LEDs. This is accomplished byvarying the reference level at pin 6 by 3 dBp-p as shown in
Figure 11. The signal can be a triangle, sawtooth or sine
wave from 60 Hz to 1 kHz. The display can be run in either
dot or bar mode.
When an exponentially decaying RC discharge waveform isapplied to pin 5, the LM3915’s outputs will switch at equalintervals. This makes a simple timer or sequencer. Each timeinterval is equal to RC/3. The output may be used to drive
logic, opto-couplers, relays or PNP transistors, for example.

14

LM3915

Typical Applications

00510418*Optional circuit for improved intensity matching at low currents.
See text.

FIGURE 10. Wide-Range Adjustment of Reference Voltage and LED Intensity for Multiple LM3915s

00510419

FIGURE 11. 0V to 10V Log Display with Smooth Transitions

15

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LM3915

Typical Applications (Continued)
Extended Range VU Meter

00510420

This application shows that the LED supply requires minimal filtering.
*See Application Hints for optional Peak or Average Detector.
†Adjust R3 for 3 dB difference between LED #11 and LED #12.

Vibration Meter

00510421

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LED

ThresholdLED

Threshold

1

60 mV

6

320 mV

2

80 mV

7

440 mV3

110 mV8630 mV4

160 mV

9890 mV5

220 mV

10

1.25V

16

LM3915

Typical Applications (Continued)
Indicator and Alarm, Full-Scale Changes Display from Dot to Bar

00510422*The input to the dot bar switch may be taken from cathodes of other LEDs.
Display will change to bar as soon as the LED so selected begins to light.
**Optional. Shunts 100 µA auxiliary sink current away from LED #1.

60 dB Dot Mode Display

00510423**Optional. Shunts 100 µA auxiliary sink current away from LED #11.

17

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LM3915

Typical Applications (Continued)
Driving Vacuum Fluorescent Display

00510424

R7 thru R15: 10k ± 10%
D1, D2: 1N914 or 1N4148*Half-wave peak detector.
See Application Hints.

Low Current Bar Mode Display

00510425

Supply current drain is only 15 mA with ten LEDs illuminated.

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18

LM3915

Typical Applications (Continued)
Driving Liquid Crystal Display

00510426

Bar Display with Alarm Flasher

00510427

Full-scale causes the full bar display to flash. If the junction of R1 and C1 is connected to a different LED cathode, the display will flash when that LED lights,
and at any higher input signal.

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LM3915

Typical Applications (Continued)
Precision Null Meter

00510428

Logarithmic response allows coarse and fine adjustments without changing scale.
Resolution ranges from 10 mV at VIN = 0 mV to 500 mV at VIN = ± 1.25V.

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LM3915

Typical Applications (Continued)
Operating with a High Voltage Supply (Dot Mode Only)

00510429

The LED currents are approximately 10 mA, and the LM3915 outputs operate in saturation for minimum dissipation.
*This point is partially regulated and decreases in voltage with temperature. Voltage requirements of the LM3915 also decrease with temperature.

Light Meter

00510430*Resistor value selects exposure
1/2 f/stop resolution
Ten f/stop range (1000:1)
Typical supply current is 8 mA.

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LM3915

Typical Applications (Continued)
Audio Power Meter

00510431

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Load
Impedance

R1

4Ω

10k

8Ω

18k

16Ω

30k

See Application Hints for optional Peakor Average Detector

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LM3915

Connection Diagram
Dual-in-Line Package

00510432

Top View
Order Number LM3915N-1
See NS Package Number NA18A
Order Number LM3915N *See NS Package Number N18A
*Discontinued, Life Time Buy date 12/20/99

sured at the current source outputs. As the forward voltage
of an LED does not change significantly with a small change
in forward current, this is equivalent to changing the voltage
at the LED anodes by the same amount.
Line Regulation: The average change in reference output
voltage (VREF) over the specified range of supply voltage(V+).
Load Regulation: The change in reference output voltage
over the specified range of load current (IL(REF)).
Offset Voltage: The differential input voltage which must be
applied to each comparator to bias the output in the linear
region. Most significant error when the voltage across theinternal voltage divider is small. Specified and tested with pin
6 voltage (VRHI) equal to pin 4 voltage (VRLO).
Relative Accuracy: The difference between any two adjacent threshold points. Specified and tested with 10V acrossthe internal voltage divider so that resistor ratio matchingerror predominates over comparator offset voltage.

Definition of Terms
Absolute Accuracy: The difference between the observed
threshold voltage and the ideal threshold voltage for eachcomparator. Specified and tested with 10V across the internal voltage divider so that resistor ratio matching error predominates over comparator offset voltage.
Adjust Pin Current: Current flowing out of the reference
adjust pin when the reference amplifier is in the linear region.
Comparator Gain: The ratio of the change in output current(ILED) to the change in input voltage (VIN) required to produce it for a comparator in the linear region.
Dropout Voltage: The voltage measured at the current
source outputs required to make the output current fall by
10%.
Input Bias Current: Current flowing out of the signal input
when the input buffer is in the linear region.
LED Current Regulation: The change in output current overthe specified range of LED supply voltage (VLED) as mea-

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LM3915

Physical Dimensions inches (millimeters) unless otherwise noted

Note: Unless otherwise specified.
1. Standard Lead Finish:
200 microinches /5.08 micrometer minimum
lead/tin 37/63 or 15/85 on alloy 42 or equivalent or copper
2. Reference JEDEC registration MS-001, Variation AC, dated May 1993.

Molded Dual-In-Line Package (N)Order Number LM3915N-1
NS Package Number NA18A

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24LM3915 Dot/Bar Display Driver

Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

Molded Dual-In-Line Package (N)Order Number LM3915N *NS Package Number N18A
*Discontinued, Life Time Buy date 12/20/99

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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