LED Torch

White light LEDs have been a long time in the making. This design (as part of our Mini Project series) employs a simple circuit to make the best use of the properties of these devices in a neat key-fob torch design.White light LEDs are an attractive alternative to the traditional tungsten lamp. They offer far greater reliability and efficiency but also have a much higher forward conduction voltage compared to red or green LEDs. This means that if you want to build a small key-fob sized torch powered by just one battery cell then it will be necessary to resort to a little electronic wizardry to increase the voltage to a level that will cause the LED to conduct.

Resistors:
R1,R3 = 1kOhm 
R2 = 2kOhm 2
Capacitors:
C1 = 470pF
C2 = 100µ F 3V
Semiconductors:
D1 = LED, white
T1,T2 = BC548C, BC549C or BC550C
Miscellaneous:
L1 = 470µ H miniature choke
S1 = pushbutton with 1 make contact
Battery (see text)
Enclosure (see text)
Battery mounting materials
PCB, order code 010130-1