Bicycle tail light

You want to learn more about DC to DC boost converters? Here is a good and practical application of such converters, an LED tail light for your bicycle. Why do you need a boost converter for that you might ask, when you can simply have a battery power up some LEDs. Well, this way you greatly increase efficiency, you increase the number of LEDs you can drive and thus increase the perceived power of light. And yes, you will learn about them.

This project makes use of the National Semiconductor LM3410 chip. This chip provides a current regulation rather than a voltage regulation and makes it suitable when working with LEDs. This current regulation is done by switching a NMOS gate at constant frequency of 525Khz ( you can also chose 1.6Mhz) and varying the duty cycle, the so called pulse width modulation. Given a constant frequency varying the pulse width results in varying the mean value in time. The regulation is done by providing a feedback current that causes a voltage drop on a resistor which in turn is fed into a comparator.

The output of this comparator goes to the PWM comparator where it faces the output of the amplifier that reads the switched current through an inductor. The result will be a PWM signal attacking the NMOS gate and thus providing a steady mean output current value. The current sensing amplifier also provides an output for switched current limiting. Some nice features of LM3410 makes things easier, it’s internally compensated,  has a very low stand-by current, has dimming possibilities and thermal shutdown.

As the author states in his article you have to be careful when choosing components. Since the operation frequency is pretty high the diodes through which the inductor discharges must be high speed or you risk blowing the chip. Taking things a step forward he added a PIC12F683 microcontroller to provide some light effects selected by a pressing a button.

If we look closer at this project we can see it can be further developed, using the dimming possibility of LM3410 you can also turn it into a stop light. Whenever you break light intensity goes higher. Another development is to adapt it to be used with a dynamo. Have fun.

Bicycle Tail Light: [Link]