LM3909 LED Flasher Oscillator
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
b
25 C to
a
70 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
b
20% to
a
100%
Features
Y
Y
Y
Y
Y
Y
Y
Y
Operation over one year from one C size flashlight cell
Bright high current LED pulse
Minimum external parts
Low cost
Low voltage operation from just over 1V to 5V
Low current drain averages under 0 5 mA during
battery life
Powerful as an oscillator directly drives an 8X speaker
Wide temperature range
Applications
Y
Y
Y
Y
Y
Y
Y
Finding flashlights in the dark or locating boat mooring
floats
Sales and advertising gimmicks
Emergency locators for instance on fire extinguishers
Toys and novelties
Electronic applications such as trigger and sawtooth
generators
Siren for toy fire engine (combined oscillator speaker
driver)
Warning indicators powered by 1 4V to 200V
Schematic Diagram
Typical 1 5V Flasher
Connection Diagram
Dual-In-Line Package
TL H 7969 鈥?2
Top View
Order Number LM3909N
See NS Package Number N08E
TL H 7969 鈥?1
C
1995 National Semiconductor Corporation
TL H 7969
RRD-B30M115 Printed in U S A
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