ABSTRACT
Chapter 3 presents a nonisolated SIMO AC-DC converter, which performs a one-stage AC-DC power conversion. Unlike the conventional two-stage (or multi-stage) AC-DC power converters, this SIMO AC-DC converter does not require an intermediate DC link. Hence, no high-voltage electrolytic capacitor (E-cap) at the DC link is required. The elimination of this E-cap helps extend the operating lifetime of the converter. An interesting application of such SIMO-based converter is to act as an offline AC-DC LED driver for supplying multiple independent LED strings in LCD backlighting for large panel display or general lighting applications. Due to its high compactness, light weight, and low cost, it is especially suitable for space-constrained retrofit lighting applications. In this chapter, the circuit topology and operating principle of this SIMO AC-DC converter are thoroughly discussed. A time-multiplexed PWM controller is introduced, which allows the sharing of a single PWM modulator and subsequent logic elements among the three individual feedback loops for a single-inductor three-string LED driver. It further reduces the controller complexity, minimizes the component count, and lowers the build-of-material cost. The use of time-interleaving control and multiple-energizing phases enables each LED string of the SIMO LED driver to be independently driven and fully coupled from other strings with minimal cross-regulation.
