Dimmable light-emitting diode driver with cascaded current regulator and voltage source

This study presents a dimmable light-emitting diode (LED) driver consisting of a flyback power factor corrector (PFC) with two secondary windings. The first secondary output is cascaded by a floating buck current regulator with a dimming switch. Then its unregulated output voltage is connected in series with the second secondary output, which acts as a regulated voltage source. Since either secondary output voltage is lower than that of a single-output topology, low voltage-rating film capacitors with longer lifetime can be used instead of electrolytic capacitors. Most of the load power is supplied by the voltage source. Therefore the reduced voltage stress and switching losses on the dimming switch result in high conversion efficiency in a wide dimming range. The operating principles and design considerations of the proposed LED driver are discussed and analysed. A 20-W laboratory prototype with dimming feature is developed and tested. Satisfactory experimental results verify the feasibility of the studied driver.