555 timer drives multiple LEDs from one NiMH cell
This design idea from EDN demonstrates how to use a CMOS 555 timer to drive seven high-brightness LEDs from a single 1.25V cell.
Here is an excerpt from the orginal article at EDN. "Using a CMOS 555 timer and a single NPN transistor, you can drive as many as seven LEDs using a minimal amount of voltage and power from a single NiMH (nickel-metal-hydride) AA cell. The circuit works by creating much higher-voltage pulses than the voltage for powering the circuit by pulsing a high-Q power inductor. The circuit creates voltage pulses of 23V using a 1.25V NiMH cell with seven connected LEDs.
The circuit uses a CMOS timer because it functions on low voltages—in this case, as low as 1V. A single white LED rated at 9300 mcd maintains its brilliance down to this low voltage. The circuit works for 192 hours using a 2000-mAHr-rated NiMH cell. The output of the timer is a 4.5-µsec pulse repeating at a 222-kHz rate. Although you can use the circuit to power any LED, it works best using high-brightness, high-power LEDs rated at 3000 mcd or higher. Obviously, the higher the millicandela rating, the brighter the LED will appear.
Comments