Design and Implementation of a Line-Frequency Parallel/Series Automatic Switching LED Driver

Abstract

In this thesis a line-frequency parallel/series automatic switching LED driver is proposed Based on the topology of the parallel/series automatic switching LED driver a dual input-voltage-level LED driver and a valley-fill LED driver are further presented The parallel/series automatic switching mechanism employed in the proposed LED driver utilizes the input voltage as the control signal With the increasing of the input voltage the connection of two LED strings automatically changes from parallel to series Since the number of the turned-on LEDs is reduced by half with low input voltage value the forward-conduction time for LEDs is increased which further improves power factor (PF) and crest factor (CF) For the purpose of compatibility with the RMS input voltages of 110 V and 220 V the dual input-voltage-level mechanism is added into the proposed LED driver Moreover the proposed LED driver can be applied with a valley-fill circuit in order to improve the flicker problem Finally two prototype circuits of dual input-voltage-level LED driver and valley-fill LED driver are built to verify the performances such as PF CF dual input voltage and the improvement in flicker problem

Date of Award	2014 Aug 11
Original language	English
Supervisor	Tsorng-Juu Liang (Supervisor)