Modifying the voltage of a DC power supply is described by Wikipedia in the DC to DC converter article.
Led flashlight driver circuit s 1703 drivers#
These drivers can also have modes by using a microcontroller utilizing PWM for lower modes and flashing modes.
Led flashlight driver circuit s 1703 plus#
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.
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. 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. Eight 350mA chips (using two boards or both sides of one 17mm board) gives 2800mA which is ideal for XM-L2 and XP-L LEDs. Each chip allows 350mA of current through and when wired in parallel, the current adds, so 700mA from 2 chips, 1050mA from 3 chips, and 1400mA from 4 (some drivers have higher binned regulator chips that allow 380mA through). However these drivers have a number of AMC7135 current regulating chips installed.
Though people call this type of driver a linear regulator, linear regulators regulate the voltage. Also, many LEDs are being overdriven by 4.2 volts of a fresh li-ion battery. If a constant brightness is desired, a driver that offers some kind of regulation is required. As voltage decreases the light will dim and draw less current. When the voltage is higher, the LED will be very bright and draw a great deal of current. As power is applied to the LED, it will draw a certain amount of current from the battery. 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. This is quite efficient since all of the power from the battery is delivered to the LED. Lithium-ion batteries conveniently provide a decent voltage without any further modification. If you apply the correct voltage, you don't need a driver at all. 17mm linear regulator driver wchips and microprocessor
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