Step 1: Car to Portable MP3 Player Power Supply
Open up your lamp and look for a small ferrite core transformer (some brands might have two, so try different brands or sizes)
Step 2: MP3 PSU:Stuff You'll Need
-NE 555 (Timmer- oscillator IC)
-two 1N4001 or 1N4148 diodes or any similar (for low frequency)
-10k trimpot or potencimeter
-100n ceramic or polyester capacitor
-10n ceramic or polyester capacitor
-1000u X 25 V polarized capacitor
-Any N-Channel enhanced mode Mosfet for 5 A or greater current
-470 Ohm resistor
-A Schotsky diode (This is the most important item, since is should be a diode that can switch at high frequencies, thus the "fast recovery" tag) I got this from a deceased laptop power adaptor. They are very common.
-FROM YOUR LAMP, remove the xtransformed and if it is is still in goog shape, use it. If not, you can still use the core and rewind some 200 turns of magnet wire (30 or 32 AWG). Inductance of this coil should be in the mH range.
Step 3: Schematic
Step 4: End Result.
Step 5: Adjust Your Output Voltage
Step 6: Joule Thief
This circuit is known for its alias "Joule Thief". This is simply a self oscillating Boost DC-DC converter.
Using the toroidal ferrite core found on some flourescent lamps, you can wind the transformer needed for this gadget.
This is what you'll need:
-Any small signal NPN or PNP (bipolar transistor) like BC548.
-A 1.5 V battery
-The toroid from your lamp.
-1 meter long piece of magnet wire.
Step 7: Winding
Cut the ends and using a Ohmmeter, identify the ends of L1 and L2.
Solder the end of L1 to the begginig of L2. So polarity on L1 and L2 are oposite. (for more detail go to these link: http://www.evilmadscientist.com/article.php/joulethief)
This is how it works:
When the transistor conducts, current flows thru L1 and the the LED is off (fig. a). This creates a magnetic field on the coil and makes L2 shut off the transistor. When this happens (fig. b), the energy of the magnetic field induces a voltage on the coil called "back emf" and this ADDS up with the battery so you have 3 V or more (it like adding batteries in series).
Because this cycle occurs at high frequencies (kHz, depending on your inductor and transistor, etc), the LED seems to be all the time ON.