TLH7969

February 1995

LM3909 LED FlasherOscillator

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 15V 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

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 15V 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

a

100%

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 05 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 14V to 200V

Schematic Diagram

Typical 15V Flasher

TLH7969 – 1

Connection Diagram

Dual-In-Line Package

TLH7969 – 2

Top View

Order Number LM3909N

See NS Package Number N08E

C1995 National Semiconductor Corporation

RRD-B30M115Printed in U S A