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LED Torch

semiconductor white light

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.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

R1,R3 = 1kOhm
R2 = 2kOhm 2
C1 = 470pF
C2 = 100µ F 3V
D1 = LED, white
T1,T2 = BC548C, BC549C or BC550C
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
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