[Diese Seite ist auch auf deutsch verfügbar]

JarLight Mark 3 LED flashlight (white)

The "JarLight" is a small flashlight based on a white light emitting diode (LED). It is powered by a single battery cell. This combination enables a very compact case at a very high light power and long-life. Not only of the battery but also of the LED.
To generate a voltage of 4 volts out of a single 1.2 volt cell it is necessary to make use of a little circuit, based on the LT1073-5 IC, a coil, a diode and a capacitor. It's easy to build and you find the circuit further down.

Comparison to a Maglite Solitaire

To compare the features I used a MagLite Solitaire because this flashlight is comparable in size and power (one cell only). The photographs show the light-cones of the two flashlights as seen from the side and as a reflection of the circle on a white sheet of paper.

Two features are noticeable:

• The colour temperature of the white LED is much higher than that of the Maglite. The light appears to be much whiter and more natural.
• The intensity of the JarLight is much higher as well

Beside the light-power the battery-usage is interesting too. I have charged one and the same 750mAh micro-accumulator cell (size AAA) with a microprocessor controlled battery charger and used it for the test.

The results:

JarLight Mark 3:	5 hours
MagLite Solitaire:	3.5 hours

The circuit and the JarLight Mark 3

Above you see the circuit schematics of the JarLight. The LT1073-5 IC is being produced by Linear Technology. You can find a verbose datasheet on their pages too out of which I derived the circuit above. The coil with 82 micro Henry can of course be substituted by a serial combination of two smaller coils. I use two inductivities of 10µH and 68µH successfully.
According to the datasheet of the diode must be a very fast one. So the 1N5818 Schottky-diode is recommended. The capacitor is not necessary for using the circuit above as a LED driver but it produces a nice after-glow when switching off the current.
The LED I used is a 5mm white LED with a rating of 5.6 Cd and an opening angle of 20°.

On the right side you see the inner "life" of the JarLight. IC, inductivities, diode and capacitor find their place on a small circuit board. The inductivities are "cloaked" in resistance-casing right.

The small white box is a plug that can be used to recharge the 750mAh accu cell without opening the casing.

And if you got some questions left you can ask them in my forum. I will try to answer them!

Here you can find the follow-up models of the Mark 3. The site is written in german but the pictures are speaking for themselves ;-)

To the experimental corner-Forum