Nowadays you can buy white LEDs, which emit quite a bit of light. They are so bright that you shouldn’t look directly at them. They are still expensive, but that is bound to change. You can make a very good solid-state pocket torch using a few of these white LEDs. The simplest approach is naturally to use a separate series resistor for each LED, which has an operating voltage of around 3.5 V at 20 mA. Depending on the value of the supply voltage, quite a bit of power will be lost in the resistors. The converter shown here generates a voltage that is high enough to allow ten LEDs to be connected in series.
In addition, this converter supplies a constant current instead of a constant voltage.
Resistors: R1 = 1kΩ2 R2 = 68Ω Capacitors: C1 = 100µF 16V radial C2 = 680nF C3 = 100µF 63V radial Inductors: L1 = 200µH 1A Semiconductors: D1 = Schottky diode type PBYR745 or equivalent D2-D5 = zener diode 10V, 0.4W D6-D15 = white LED IC1 = LM2585T-ADJ (National Semiconductor)
In addition, this converter supplies a constant current instead of a constant voltage.
