An
LED driver circuit operating from the
AC power line providing high efficiency, good line and
load regulation, high
power factor, low
line current harmonics, low conducted EMI, high LED utilization, and lamp dimming compatibility, while consisting of a minimal number of components. No inductors, nor capacitors (including electrolytics), nor
high current switching transistors are employed. The top of a string of series connected LED segments is connected to the output of a
rectifier, which in turn is connected to an AC
sine wave power source. The string is tapped at various locations, including the bottom of the string. Each segment can consists of any number of serial or parallel connected LEDs. Current control elements or regulators sink current at each tap and are sequentially turned on and off one at a time, tracking the rectified
sine wave voltage.
Voltage across each
regulator and current when conducting is individually controllable.
Power loss in the regulators is minimized by keeping
regulator voltage to a minimum. The regulators may control current in a multitude of ways, including a
constant current, or a current dependent on
voltage across the regulators including a
resistor, or a combination. The driver is self-commutating, with the sequencing of the current control elements an inherent feature closely integrated with the current control elements and providing optimal performance over variable operating conditions. Given the large number of design variables, the
driver circuit can be optimized for various performance criteria including input
voltage range, line /
load regulation, output power / current, efficiency,
power factor,
line current harmonics,
dimmer compatibility, and LED utilization.