Economical Desk Lamp For Camping

This LED
lamp was originally designed for use on a budget solar-charged 12V
electrical system. It is bright enough for comfortable reading at night
and features constant LED brightness with diminishing battery voltage. The circuit uses six high-brightness white LEDs
mounted in a 90mm diameter reflector. The upper half of a stainless
steel ice cream bowl makes a good reflector but almost any torch
reflector of a similar size will do. As shown, two banks of three
series-connected LEDs are powered from a 12V (nominal) DC supply. The LEDs used are rated at 20mA maximum with a measured voltage drop of 3.2V.

Economical Desk Lamp Circuit For Camping

Economical Desk Lamp Circuit Diagram For Camping

Each bank combines an inexpensive LM334 current source IC with a BC558 transistor to provide a constant 20mA to the LED
string. Basically, the LM334 controls the base current of the BC558
such that 64mV appears between its “R” and “V-” terminals. With the 3.3O
resistor shown, this results in close to the desired 20mA through the LEDs.
The components can be mounted on a small piece of Veroboard. An old
desk lamp makes an ideal body, with a metal disc used to cover the hole
left after the 240V lamp fitting is removed. The metal disc can also be
used to mount the power switch and rubber grommet for the power supply
leads. Three M3 screws and nuts spaced 120° apart keep the reflector in
place.

Author: John Amos – Copyright: Silicon Chip Electronics

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