Design of Stacked Switched Capacitor energy buffers for offline LED drivers.

摘要

Light Emitting Diode (LED) lamps are becoming the preferred lighting option for a large number of applications due to their high efficiency and long life. Since LED lamps require a power electronic driver to operate from ac line, the LED driver must also have a long life to take full advantage of the LED's longevity. However, the life of offline LED drivers is constrained by the use of limited-life electrolytic capacitors, as twice-line-frequency energy buffers, in them. Twice-line-frequency energy buffering is needed in all high power factor power electronic interfaces between single-phase ac and dc. The recently proposed Stacked Switched Capacitor (SSC) energy buffer architecture with film or ceramic capacitors can increase the life of single-phase ac-dc converters by eliminating electrolytic capacitors, while keeping the passive volume of the relatively lower energy density film/ceramic capacitors in check. This thesis presents a methodology for further increasing the effective energy density of enhanced unipolar SSC energy buffers by optimizing the capacitance ratio of the capacitors used in the energy buffer. It is shown that the relative enhancement in energy density depends on the required ripple ratio and the number of supporting capacitors in the energy buffer. The presented methodology is validated using a 1-2 enhanced unipolar SSC energy buffer designed for an 8-W offline LED driver. This thesis also develops a method for precharging the capacitors in the SSC energy buffer that does not require a separate precharge circuit and presents new ground-referenced gate drive circuits suitable for low voltage enhanced unipolar SSC energy buffers.