Weekend Projects with Bre Pettis: Make a Joule Thief - It's a little wisp of a circuit that allows you to drive a blue or white LED from a low
voltage. Normally, if you want to light up a blue or white LED you need to provide it with 3, 3.5 V, like from a
3 V lithium coin cell. But a 1.5V battery like a AA cell simply will not work. But using the Joule Thief, it
works like a charm. Not only does it work with a brand new battery, but it works until the battery is nearly
dead-- down to 0. 3 V. That's well below the point where your other toys will tell you the battery is dead, so it
can steal every last joule of energy from the battery (hence the name). To learn how to make one, watch the
video, which is available in a variety of formats. . . . [Evil Mad Scientists Laboratories]
White LED Array that is Lined Powered - There has been
a lot of excitement lately in the lighting industry. Some companies are beginning to manufacture general lighting
fixtures, which replace incandescent and fluorescent lamps, using LED lights. When proper heat management is
designed . . . [Hobby Circuit designed by David Johnson P.E., 02/28/10]
White LED Circuits - . . .
White LED Drive Circuit - . . .
White LED Drive Circuit. Part
1 - How do you get 3.5 volts to drive a white LED when you
only have a 1. 5v battery? Be Careful About Peak Current A note of caution: These LEDs are comparatively
expensive, so I suggest putting a small resistor (1 to 10 Ohms) in series. . . [by Richard Cappels]
White LED Drive Circuit. Part
2 - Alternative Types of Cores If you can't find a ferrite
core, or even an old rusty nail, all is not lost. You can still make a pretty good white LED power supply by
using a non-magnetic core. It sounds like an oxymoron, but a. . . [by Richard Cappels]
White LED drive from 1.5V - How do you get 3.5 volts to drive a white LED when you only have a 1. 5v battery?. . .
[From Dick Cappels' project pages]
White LED driver backlights LCD and keypad - 11/13/03 EDN
Design Idea Designers widely use white LEDs to backlight color LCDs and keypads in handheld devices, such as
cell phones, MP3 players, GPS navigators, and PDAs. Their spectrum and brightness represent near-ideal light
sources. One possible con. . . [by Fabien Franc, Catalyst Semiconductor, Sunnyvale, CA]
White LED Driver
powered by a 3v Battery - The circuit below will drive
any LED color, including white LEDs, using a DC power supply ranging from 2v to 3.3v. White and blue LEDs
normally require over 3v, so the circuit below uses a charge pump scheme to deliver a constant LED light
intensity from . . . [Hobby Circuit designed by David Johnson P.E., 08/15/10]
White LED driver provides 64 step logarithmic dimming - 10-Jun-04 EDN Design Idea The circuit of Figure 1 is designed for portable-power
applications that require white LEDs with adjustable, logarithmic dimming levels. The circuit drives as many as
four white LEDs from a 3.3V source and adjusts the total LED cur. . . [by William Hadden, Maxim Integrated
Products, Sunnyvale, CA]
White LED Head Lamp - A white LED head lamp which can operate with only two AA batteries. The LEDs are driven in
constant current, so that the brightness is maintained until end of battery life. . . . [The Electronic Lives
Manufacturing-presented by Chan]
White LED
inductorless drive from 1.5V & 3V - The operating voltage
of white LEDs coupled with my emotional need for low cost for a given function, motivates me to make LED drivers
suitable for battery operated lanterns that can run from a small number of cells. White and Ultraviolet LEDs
available at the time of this writing, require higher voltages than colored LEDs. . . [From Dick Cappels'
project pages]
White LED is Powered By
One Nimh Cell - There are a lot of white LED driver
circuits floating around. A popular circuit called the “Joule Thief” can drive one white LED from a single 1. 2v
or 1. 5v battery cell. Most of these circuits use one or two transistors to form a voltage boost circuit . . .
[Circuit by Dave Johnson P.E., 09/26/09]
White LED Lamp - . . .
White LED
Light Probe for Inspection - This circuit is useful for
inspecting narrow spaces like the inside of the CPUs, monitors, PCB modules and other electronic devices. . . .
[© EFY Enterprises Pvt. Ltd. All rights reserved]
White
LED Night Light - This simple circuit is designed to
plug into a standard AC electrical outlet. It uses four super bright white light emitting diodes (LED) in
conjunction with a capacitor coupled full wave rectifier circuit. The LEDs are mounted in a box and are angled
slightly to bounce the light off of a nearby wall. . . . [Hobby Circuit designed by David A. Johnson P.E.,
05/27/03]
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