LM3909

The LM3909 is a monolithic oscillator specifically designed o flash Light Emitting Diodes. By using the timing capacitor or voltage boost, it delivers pulses of 2 or more volts to the ED while operating on a supply of 1.5V or less. The circuit isinherently 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 -25 to a70. 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%.