Research On Multiple Constant Current Outputs Switching Converters With High Power Factor

Multiple outputs ac/dc power converter has been becoming popular with fast development of consumer electronics and light emitting diode (LED) lighting, such as LED backlight, general lighting, current balancing for multiple LED string driving, RGB LED lighting, etc. IEC61000-3-2 Class C for lighting equipment establishes a strict requirement for input current harmonic content of power converter. Power factor correction (PFC) is usually used to provide sinusoidal input current. Hence, the research of multiple outputs ac/dc power converter with low cost and high power factor is important.In order to achieve high power factor (PF) and to accurately regulate output currents of multiple output ac/dc converter, conventional multiple output ac/dc power converter consisting of two-stage power conversion is utilized, where PFC pre-regulator provides dc bus voltage, and the parallel connected dc-to-dc regulators are used to regulate output output current from bus voltage. The circuit configuration of multiple output ac/dc converters with multiple inductors and controllers is complex and suffers from high cost. Moreover, the two-stage power conversion converters including PFC pre-regulator and dc-to-dc suffer from low efficiency, high volume and cost. In order to solve the above problems, single-inductor dual-output Buck PFC converter is proposed in this dissertation. Control strategy and corresponding characteristics operating in discontinuous conduction mode (DCM) and critical conduction mode (CRM) are analyzed. An inductor multiplexing method nearing the zero-crossing point was proposed, which reduces the switch frequency and makes inductor easier for multiplexing nearing the zero-crossing point. Independent regulation and high power factor can be achieved together in this converter by multiplexing single inductor. Compared with conventional two-stage multiple output solution, this solution benefits with significant overall cost saving, small size and light weight of equipment and device. Due to single stage power conversion, this PFC converter also benefits with high efficiency.The conventional topologies of single-inductor multiple-output (SIMO) switching converter need active floating switches for multiplexing control. The driving circuit for those floating switches is complex. Especially, the output current sampling circuit is also complex for SIMO buck-boost topology. In order to solve the above problems, single-inductor dual-output buck-boost PFC converter with active switches common-source connected and corresponding control method are proposed. Control strategy and characteristics of the proposed converter are analyzed. Common-source connected switches can be driven as "low side" using common-connected point as signal ground, which benefits from simple driving. The switching currents of multiplexing switch are sample for output current, which benefits from simple sampling. The research result presents that high efficiency and high power factor can be achieved in SIDO buck-boost PFC converter. Unity power factor can be achieved in DCM SIDO buck-boost PFC converter. The power factor of CRM SIDO buck-boost PFC converter is relative to the output voltage and power ratio of each output. The input currents of SIDO buck-boost PFC converter are easy to meet IEC 61000-3-2 C standard.In order to further decrease the volume and cost of multiple constant output converters, a novel high-efficiency high power factor multi-channel LED driver based on current bus with time-multiplexing current sharing control scheme is proposed and analyzed. The current bus is provided by the output of a high-efficiency converter with high power factor. Each LED string connects this current bus and its desired sharing current can be controlled by the turn on duty of its time-multiplexing switch. The time multiplexing method of current bus with complementary mode and synchronous mode are proposed. Complementary mode, whose channel current can be flexible adjust, is very suible for LED color dimming application. Synchronous mode, whose LED utilization in each channel can be improved effectively, is very suitable for current ballacing application. With this control method, the bus voltage can be controlled to a self-adaptive level to meet each channel LED current require, which simplifies control and improves efficiency. Furthermore, it needs only one output filter capacitor with the proposed control scheme, which makes circuit volume small and cost low.For large power rating and high-luminance LED driver applications, the current balancing technique is necessary for LED driver when several LED strings connected in parallel. Although single-stage SIMO PFC converter and constant current bus with time-multiplexing current sharing control scheme can achieve current balancing for each LED string, but they need more active switches and the control methods of these converter are complex. In this dissertation, a resonant single-stage multiple-output LED driver with power factor correction and passive current sharing is proposed and analyzed when magnetizing inductor current operating in DCM and CRM. The research result presents that the power factor of this converter is similar to boost PFC converter. Unity power factor can be achieved when magnetizing inductor current operats in CRM and isn't affected by the resonance current. By control one output current, the other output currents of the proposed multiple-string LED driver can be controlled via passive current balancing, which makes the control of proposed LED driver simple. Furthermore, the proposed LED driver is a single-stage single-switch converter. It uses only one active switch and one magnetic component. Compared with conventional two-stage multi-output converters, the proposed converter benefits with low cost, small size, high efficiency and light weight.In order to verify the theoretical analysis, a mass of simulation results are provided, and corresponding prototypes in laboratory are built to present experimental results. Simulation and experimental results have a good agreement with the theoretical analysis which presentes in this dissertation.