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1.5V battery cell LED flasher circuit diagram




Download: 1.3V IC Flasher, Oscillator, Trigger or Alarm LM3909


LED flasher circuit diagram 1.5V battery cell 1.3V IC Flasher, Oscillator, Trigger or Alarm. Most linear integrated circuits are designed to operate with power supplies of 4.5 to 40V. Practically no battery/portable equipment is provided with indicator lights due to unacceptable power drain. Even LEDs (solid state lamps) won't light from a 1.5V battery, and drain the common 9V radio battery in a few hours. The LM3909 changes all this. Obtaining long life from a single 1.5V cell, it opens a whole new area of applications for linear integrated circuits.

Sufficient voltage for flashing a light emitting diode is generated with cell voltage down to 1.1V. In such low duty cycle applications batteries will last for months to years of continuous operation. Such flasher circuits then become practical for marking location of flashlights, emergency equipment, and boat mooring floats in the dark. The LM3909 is simple in design, easy to use, and includes extra resistors to minimize external circuitry and the size of the completed flasher or oscillator.

The LM3909, although designed as a LED flasher, is ideal for other applications such as high current, trigger pulse for SCRs and ``Triacs.'' The frequency of oscillation adjusts from under 1 Hz to hundreds of kHz. Waveshape can be set from pulses a few ms wide to approximately a square wave. Thus the LM3909 can perform as a sound effects generator, an audible alarm, or audible continuity checker. Finally it can be a radio (detector/amplifier), low power one-way intercom, two-way telegraph set, or part of a ``mini-strobe'' light flashing up to 7 times per second. Operating with only a 1.5V battery as a supply gives the LM3909 several rather unique characteristics. First, no known connection can cause immediate destruction of the IC. Its internal feedback loop insures self-starting of properly loaded oscillator circuits. Experimenters can safely explore the possibilities of the LM3909 as an AC amplifier, one-shot, latch circuit, resistance limit detector, multi-tone oscillator, heat detector, or high frequency oscillator. With the accent on the practical, a brief circuit description will be given followed by circuits in the following application areas: Flasher & Indicator Applications Audio & Oscillator Applications Trigger & Other Applications For those who want to modify or design their own circuits using the LM3909, application hints will be covered near the end of this note.

CIRCUIT DESCRIPTION The circuit of Figure 2 again shows the typical 1.5V LED flasher, but with the internal circuitry of the IC illustrated. The flasher achieves minimum power usage in two ways. Operated as above, the LED receives current only about 1% of the time. The rest of the time, all transistors but Q4 are off. The 20k resistor from Q4's emitter to supply-common draws only about 50 mA. The 300 mF capacitor is charged through the two 400X resistors connected to pin 5 and through the 3k resistor connected to pin 1 of the circuit.

Transistors Q1 through Q3 remain off until the capacitor becomes charged to about 1V. This voltage is determined by the junction drop of Q4, its base-emitter voltage divider, and the junction drop of Q1. When voltage at pin 1 becomes a volt more negative than that at pin 5 (supply positive terminal) Q1 begins to conduct. This then turns on Q2 and Q3. The LM3909 then supplies a pulse of high current to the LED. Current amplification of Q2 and Q3 is between 200 and 1000. Q3 can handle over 100 mA and rapidly pulls pin 2 close to supply common (pin 4). Since the capacitor is charged, its other terminal at pin 1 goes below the supply common. The voltage at the LED is then higher than battery voltage, and the 12X resistor between pins 5 and 6 limits the LED current. Many of the other oscillator circuits work in a similar fashion. If voltage boost is not needed (with or without current limiting) loads can be hooked between pins 2 and 6 or pins 2 and 5.


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