Driver: Difference between revisions

If you apply the correct voltage, you don't need a driver at all. Lithium-ion batteries conveniently provide a decent voltage without any further modification. This is quite efficient since all of the power from the battery is delivered to the LED. However a fresh li-ion battery starts at 4.2 volts fully charged and will be 3.6 volts when it needs to be recharged. As power is applied to the LED, it will draw a certain amount of current from the battery. This current increases with the voltage. When the voltage is higher, the LED will be very bright and draw a great deal of current. As voltage decreases the light will dim and draw less current. If a constant brightness is desired, a driver that offers some kind of regulation is required. Also, many LED's are being overdriven by 4.2 volts of a fresh li-ion battery.

Modifying the voltage of a DC power supply is described by Wikipedia in the [http://en.wikipedia.org/wiki/DC_to_DC_converter DC to DC converter] article. Increasing the voltage is done by a [http://en.wikipedia.org/wiki/Boost_converter boost converter] circuit, also called a step-up circuit. The efficiency of a boost converter increases as the voltage supplied gets closer to the output voltage. For instance a flashlight that uses one 1.2V NiMH cell will not be as efficient as one that uses two, since in one case the boost converter is nearly tripling the voltage and in the other is not even doubling it. This is why a flashlight can work using either one or two batteries but will be brighter with two. If the source voltage exceeds the target voltage, some drivers will go into direct drive and some will just burn out. Therefore it is important to match up the driver's voltage range with the batteries you will be using.