Constrained to a particular current, the LED will settle in at its Vf for that current and the rest of the voltage from the battery will be converted to heat by the regulator chips. Because any voltage beyond the required amount is wasted as heat, supplying a higher voltage is less efficient and the board becomes more efficient as the input voltage approaches the output voltage.
As the voltage supplied drops below the Vf of the LED plus some overhead for the chips, the driver drops out of regulation and goes into direct drive and the light will start to dim. These drivers can also have modes by using a microcontroller utilizing PWM for lower modes and flashing modes.
The FET is basically a switch with very low resistance lower than running the full current through the microprocessor and can be turned on and off by the microprocessor using PWM. This multichannel approach lets the driver limit the current to mA instead of unlimited through the FET and use PWM as needed to work from there. Also the mA channel gives more uniform low levels whereas the levels from the FET vary with battery strength.
Increasing the voltage is done by a 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. 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. A buck circuit is similar to the boost circuit above, but in reverse. It takes a higher voltage and reduces it down to the voltage desired.
This is used in flashlights with multiple cells in series, for instance when there are two 3V CR batteries or 2 3. The buck circuit is also quite efficient, but typically requires at least a 0. Good luck finding one at a reasonable price though. In addition to regulating the voltage, the driver controls brightness levels and how the user switches between those by monitoring button clicks and presses.
Therefore some drivers offer various modes and some do not. Some offer different packages of modes that are available either by the user pressing buttons or they can be hard wired by soldering bridges on the driver board. The size of the driver itself is also important. The most common size is 17mm which works well in most P60 drop-ins and many lights powered by an li-ion battery.
However, smaller lights uses smaller diameter boards that are harder to find. There are also larger circuit boards of around 25mm used on larger flashlights. See Popular drivers for some specific drivers available.
The light emitting diodes are low energy, lighting devices with a long lifespan and low energy consumption, hence the requirement for specialized power supplies. Without the correct LED light driver the LEDs would become too hot and unstable resulting in failure and bad performance. Individual LED bulbs operate at voltages ranging from about 1. The domestic bulbs may consist of several bulbs, in series and parallel combinations and which requires a total voltage of between 12 and 24 V DC. This means converting the high AC mains voltage which ranges from Volts to Volts, to the required low DC voltage.
The drivers ensure that the voltage and current to the LED bulbs remains within the operating range of the LEDs regardless of fluctuations in the mains supply. The protection avoids providing too much voltage and current that would degrade the LEDs or too low current that would reduce the light output. These are commonly used in domestic LED bulbs to make it easy when replacing the bulbs; the internal drivers are usually housed in the same case as the LEDs.
The external drivers are housed separately from the LEDs and usually used for applications such as outdoor, commercial, roadways lighting. These types of lights require separate drivers which are easier and cheaper to replace. In most of these applications the manufacturer specifies the type of the LED driver to use for particular light assembly.
Most of the LED bulb failures are due to the failure in the driver, and it is easier to replace or repair the external driver compared to the internal driver.
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