LED flashlight based on a white LED

Description: The JarLight is a compact flashlight utilizing a white light-emitting diode (LED) and powered by a single battery cell. This configuration allows for a highly compact design with significant light output and extended operational life, both for the battery and the LED. To achieve a voltage of 4 volts from a single 1.2-volt cell, a small circuit is required, featuring the LT1073-5 integrated circuit (IC), an inductor, a diode, and a capacitor. The construction of this circuit is straightforward, and a schematic is provided below. For comparison, a MagLite Solitaire was used due to its similar size and power (single cell). Photographs illustrate the light cones produced by both flashlights as viewed from the side and reflected onto a white sheet of paper. Battery efficiency is also notable; a 750mAh AAA micro-accumulator cell was charged using a microprocessor-controlled battery charger for testing. The circuit schematic for the JarLight is displayed above. The LT1073-5 IC is manufactured by Linear Technology, and detailed specifications can be found in their datasheet, which served as a reference for the circuit design. The inductor rated at 82 microhenries can be replaced with a series combination of smaller inductors, such as two inductors of 10 µH and 68 µH, which have been successfully used. According to the diode's datasheet, a fast diode is essential; thus, the 1N5818 Schottky diode is recommended. While the capacitor is not necessary for the circuit's operation as an LED driver, it provides a pleasing afterglow effect when the current is switched off. The internal components of the JarLight, including the IC, inductors, diode, and capacitor, are mounted on a compact circuit board, with the inductors enclosed in resistance casing.

The JarLight circuit is designed for efficiency and simplicity, making it an ideal project for both novice and experienced electronics enthusiasts. The LT1073-5 integrated circuit serves as a step-up converter, allowing the low voltage from the single battery cell to be increased to the required 4 volts for optimal LED operation. The choice of components is critical to the performance of the circuit; the use of a high-speed Schottky diode, such as the 1N5818, minimizes voltage drop and maximizes efficiency during the switching process.

The inductor plays a vital role in energy storage and transfer within the circuit. Using an 82 µH inductor or a combination of smaller inductors ensures that the circuit can maintain the necessary current levels to drive the LED effectively. The capacitor, while not essential for basic operation, enhances the user experience by providing a soft fade-out of the LED light, which can be particularly appealing in low-light environments.

The compactness of the JarLight is further accentuated by its circuit board design, which accommodates all components in a small footprint. This design choice not only contributes to the flashlight's portability but also aids in heat dissipation, ensuring the longevity of the components. The overall construction is robust, and the use of resistance casing for the inductors adds an extra layer of protection and stability.

In conclusion, the JarLight represents a practical application of basic electronic principles, combining efficient component selection and circuit design to create a high-performance, portable lighting solution. The schematic provided serves as a valuable guide for individuals looking to replicate or modify the design for personal use or further experimentation.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. 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.

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. 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 10 µH and 68 µH 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. 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.