LM3909 LED Flasher/Oscillator

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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 the addition of only a battery and capacitor to function as an LED flasher. Packaged in an 8-lead plastic mini-DIP, the LM3909 will operate over the extended consumer temperature range of b25C to a70C. It has been optimized for low power drain and operation from weak batteries so that continuous operation life exceeds that expected from battery rating.

Application is made simple by the inclusion of internal timing resistors and an internal LED current limit resistor. As shown in the first two application circuits, the timing resistors 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 electrolytic have very broad capacitance tolerances, for example, b20% to a100%.

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LM3909 Pinout

LM3909 Pin Configuration

Pin No	Pin Name	Description
1	3k FAST RC	3k Fast RC Pin
2	OUT	Output Pin
3	NC	No Connection
4	V-	-ve Voltage Pin
5	V+	+ve Voltage Pin
6	RL	Load Resistor Pin
7	NC	No Connection
8	9k SLOW RC	9k Slow RC Pin