Single-Inductor-Dual-Output Flyback Converter In Pseudo Continuous Conduction Mode

Mobile phones and other portable electronic equipments usually need a number of different levels of supply voltage. The conventional multiple-output switching converter has the disadvantage of excessive magnetic components and large size and serious cross-regulation. Single-Inductor-Multi-Output(SIMO) converter only needs one inductor to achieve accurate adjustment of all outputs, with size and cost of the converter reduced, which makes it as one of the most suitable and cost-effective solution for multiple output power supplies. At present, the study of SIMO converter is focused on the non-isolated topologies, which is not suitable when isolation between inputs and outputs is needed. It is necessary that SIMO is applied to isolation switch converters.Single-Inductor-Dual-Output (SIDO) Flyback converter is anlysised as an example of the SIMO isolation converters. The working principles and cross gregulation of SIDO Flyback converter are anlysised when inductance current is in independent charging timing and sharing charge timing. In sharing timing, there will be cross-regulation between different outputs. Working in DCM, the cross-regulation can be eliminated in independent timing, while the ripple of inductance current is large.SIDO Flyback converter topology in pseudo-continuous conduction mode (PCCM) is derived. Both independent charging timing and sharing charge timing are discussed. In sharing timing, there will be cross regulation between different outputs. In independent charging timing, the freewheeling duration helps to avoid the cross-regulation and wide the power range of the converter. Switch voltage stress analysis showes that the freewheeling switch and main power switch forms a half-bridge structure, which can reduce the voltage stress on the main power switch. The PCCM SIDO Flyback converters can be applied to drive the LED strings as current source. Finally, the performance of PCCM SIDO converter is verified by experimental results.Mixed Conduction Mode (MCM) is proposed, for the needs of different outputs. CCM-PCCM is discussed as an example of MCM, the working principle is discussed. There is only one freewheling duration in a working cycle in MCM, improving the efficiency. Fixed-frequency modulation and frequency modulation are provided for the regulation of CCM-PCCM SIDO Flyback converter. The cross regulation is analysed. The PCCM branch avoids cross regulation on the CCM one with both modulation methods; the CCM branch brings transient cross regulation on PCCM one with fixed frequency modulation, while the CCM branch brings both transient and steady cross regulation on PCCM one with frequency modulation. The control strategies are provided for both Fixed-frenquency and frenquency modulation. Simulation results are presented to verify the validity of CCM-PCCM SIDO flyback converter.