Linear LED Driver Work

A typical linear LED driver includes a full wave bridge rectifier, a ripple filter and a linear regulator. Commercial AC power is rectified into DC power and is smoothed out by a low pass filter to achieve a continuous DC voltage with low ripple current. The rectified and filtered voltage is fed to a linear regulator which consists of an internal reference voltage, an error amplifier, a feedback voltage divider and a pass transistor. The error amplifier continuously compares the difference between the reference voltage and the feedback voltage providist divider. The pass transistor operates in the linear region to adjust the input voltage to the desired output using the error amplifier. In practices a linear regulator intended for driving a long string of LEDs wired in series often incorporates multiple current regulators with which different are set voltage and current steps. The voltage and current steps are made large for the first regulator and small for the last regulator. This makes the LED load roughly sinusoidal in phase with the power line voltage and thus a high power factor (PF) and low total harmonic distortion (THD) are obtained.