A transformerless galvanically isolated switched capacitor LED driver

The design and test of a capacitor-isolated LED driver, suitable for screw-in, residential lighting applications, is reported. The design relies on a pair of high voltage isolation capacitors, comprising part of a series resonant tank. The series resonant tank is integrated with a balanced ladder step-down switched capacitor front-end, enabling the series resonant conversion stage to function conveniently with any line voltage, while still preserving the efficient voltage regulation capability of the resonant stage. Dimming and power control are effected with a low frequency PWM control loop. The tested prototype delivers 15.5 W at 425 mA at rated power into a string of 12 LEDs at 92% efficiency. Efficiency exceeding 85% is maintained over more than a 10:1 dimming range, and also over a wide range of line voltages.