The proposed circuit (Fig. 1) consists only of a line filter, an
LED bridge, a load inductor, a bi-directional switch, and a
switch control circuit. The line filter prevents injection of high
frequency switching noise to the line. The switch (SW) powers
the LED bridge periodically. The i-th leg of the LED bridge
has an LED string (LEDi, i = 1, 2, 3, and 4) connected in series
with a protection diode (Di). The load inductor (L) limits the
bridge current. The load current iL is measured using a vsense
coil which is wound over L. SW operates at a switching period
TS = 1/fS (where fS is switching frequency) with a duty factor of
D, and controls iL. The control circuit measures iL and
generates the gate voltage vg for SW