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LED Flasher/Oscillator. LM3909 Datasheet |
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February 1995
LM3909 LED Flasher Oscillator
General Description
The LM3909 is a monolithic oscillator specifically designed
to flash Light Emitting Diodes By using the timing capacitor
for voltage boost it delivers pulses of 2 or more volts to the
LED while operating on a supply of 1 5V or less The circuit
is inherently self-starting and requires addition of only a bat-
tery and capacitor to function as an LED flasher
Packaged in an 8-lead plastic mini-DIP the LM3909 will op-
erate over the extended consumer temperature range of
b25 C to a70 C It has been optimized for low power drain
and operation from weak batteries so that continuous oper-
ation life exceeds that expected from battery rating
Application is made simple by inclusion of internal timing
resistors and an internal LED current limit resistor As
shown in the first two application circuits the timing resis-
tors supplied are optimized for nominal flashing rates and
minimum power drain at 1 5V and 3V
Timing capacitors will generally be of the electrolytic type
and a small 3V rated part will be suitable for any LED flasher
using a supply up to 6V However when picking flash rates
it should be remembered that some electrolytics have very
broad capacitance tolerances for example b20% to
a100%
Features
Y Operation over one year from one C size flashlight cell
Y Bright high current LED pulse
Y Minimum external parts
Y Low cost
Y Low voltage operation from just over 1V to 5V
Y Low current drain averages under 0 5 mA during
battery life
Y Powerful as an oscillator directly drives an 8X speaker
Y Wide temperature range
Applications
Y Finding flashlights in the dark or locating boat mooring
floats
Y Sales and advertising gimmicks
Y Emergency locators for instance on fire extinguishers
Y Toys and novelties
Y Electronic applications such as trigger and sawtooth
generators
Y Siren for toy fire engine (combined oscillator speaker
driver)
Y Warning indicators powered by 1 4V to 200V
Schematic Diagram
Typical 1 5V Flasher
Connection Diagram
Dual-In-Line Package
C1995 National Semiconductor Corporation TL H 7969
Top View
TL H 7969 – 2
Order Number LM3909N
See NS Package Number N08E
TL H 7969 – 1
RRD-B30M115 Printed in U S A
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Absolute Maximum Ratings
If Military Aerospace specified devices are required
please contact the National Semiconductor Sales
Office Distributors for availability and specifications
Power Dissipation
500 mW
Va Voltage
6 4V
Operating Temperature Range
Lead Temperature (Soldering 10 sec )
b25 C to a70 C
260 C
Electrical Characteristics
Parameter
Supply Voltage
Operating Current
Flash Frequency
High Flash Frequency
Compatible LED Forward Drop
Peak LED Current
Pulse Width
Conditions
(Applications Note 3)
(In Oscillation)
300 mF 5% Capacitor
0 30 mF 5% Capacitor
1 mA Forward Current
350 mF Capacitor
350 mF Capacitors at Amplitude
Min
1 15
0 65
1 35
Typ
0 55
10
11
45
60
Max
60
0 75
13
21
Units
V
mA
Hz
kHz
V
mA
ms
Typical Applications (See applications notes on following page)
Triac Trigger
Provides 40 mA 10 ms pulses at about 8 kHz
Triac gate may be pulse transformer isolated if
desired
TL H 7969 – 3
2
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Typical Applications (Continued)(See applications notes below)
Warning Flasher High Voltage Powered
Typical Operating Conditions
Nominal
Va
Flash Hz
CT
RS RFB VaRANGE
6V 2 400 mF 1k 1 5k 5V – 25V
15V 2 180 mF 3 9k 1k 13V – 50V
100V 1 7 180 mF 43k 1k 85V – 200V
1W
TL H 7969 – 4
1 5V Flasher
TL H 7969 – 6
Estimated Battery Life
(Continuous 1 5V Flasher Operation)
Note Nominal flash rate 1 Hz
TL H 7969 – 5
Size Cell
AA
C
D
Type
Standard
Alkaline
3 months
7 months
1 3 years
6 months
15 months
2 6 years
Note Estimates are made from our tests and manufacturers
data Conditions are fresh batteries and room temperature Clad
or ‘‘leak-proof’’ batteries are recommended for any application
of five months or more Nickel Cadmium cells are not recom-
mended
APPLICATIONS NOTES
Note 1 All capacitors shown are electrolytic unless marked otherwise
Note 2 Flash rates and frequencies assume a g5% capacitor tolerance Electrolytics may vary b20% to a100% of their stated value
Note 3 Unless noted measurements above are made with a 1 4V supply a 25 C ambient temperature and an LED with a forward drop of 1 5V to 1 7V at 1 mA
forward current
Note 4 Occasionally a flasher circuit will fail to oscillate due to an LED defect that may be missed because it only reduces light output 10% or so Such LEDs can
be identified by a large increase in conduction between 0 9V and 1 2V
3
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