An Integrated Multilevel Converter With Sigma–Delta Control for LED Lighting

Abstract

High brightness LEDs have become a mainstream lighting technology due to their efficiency, life span, and environmental benefits. As such, the lighting industry values LED drivers with low cost, small form factor, and long life span. Additional specifications that define a high quality LED driver are high efficiency, high power factor, wide-range dimming, minimal flicker, and a galvanically isolated output. The flyback LED driver is a popular topology that satisfies all these specifications, but it requires a bulky and costly flyback transformer. In addition, its passive methods for cancelling AC power ripple require electrolytic capacitors, which have been known to have life span issues. This dissertation details the design, construction, and verification of a novel LED driver that satisfies all the specifications. In addition, it does not require a flyback transformer or electrolytic capacitors, thus marking an improvement over the flyback driver on size, cost, and life span. This dissertation presents an integrated circuit (IC) LED driver, which features a pair of generalized multilevel converters that are controlled via sigma-delta modulation. The first is a multilevel rectifier responsible for power factor correction (PFC) and dimming. The PFC rectifier employs a second order sigma-delta loop to precisely control the input current harmonics and amplitude. The second is a bidirectional multilevel inverter used to cancel AC power ripple from the DC bus. This ripple-cancellation module transfers energy to and from a storage capacitor. It uses a first order sigma-delta loop with a preprogrammed waveform to swing the storage capacitor voltage. The system also contains an output stage that powers the LEDs with DC and provides for galvanic isolation. The output stage consists of an H-bridge stack that connects to the output through a small toroid transformer. The IC LED driver was simulated and prototyped on an ABCD silicon test chip. Testing and verification indicates functional performance for all the modules in the LED driver. The driver exhibits moderate efficiency at half voltage. Although the part was only testable to half voltage, loss models predict that its efficiency would be much higher at full voltage. The driver also meets specifications on the line current harmonics and ripple cancellation. This dissertation introduces multilevel circuit techniques to the IC and LED research space. The prototype's functional performance indicates that integrated multilevel converters are a viable topology for lighting and other similar applications. i Dedication Dedicated to my family and friends, who have been unwavering in their love and support. Contents Contents ii List of Figures iv List of Tables ix

A comprehensive review on various non-isolated power converter topologies for a light-emitting diode driver

“…To reduce the cost and complexity of the system, single-stage topologies fed LED drivers are developed. A 48 V, resonant DC-DC converter with switched capacitor was developed (Gerber et al, 2019). Dimming control is deployed using a variable inductor, as shown in Figure 6A.…”

Adoption Pathways for DC Power Distribution in Buildings

“…Eliminating those capacitors can significantly increase the driver's life span. Also, because DC voltage levels are generally better matched to the LED string voltage, DC drivers do not require an internal flyback transformer, which can lead to additional cost savings [34].…”

Reconfigurable Hybrid-Switched-Capacitor-Resonant LED Driver for Multiple Mains Voltages

“…A PFC rectifier interfaces the 120-V AC line voltage to the input of the HSCR converter, converting the ac source voltage to about 170 V dc . One example of the PFC rectifier front-end implementation that works with the proposed HSCR converter can be found in [10]. The HSCR converter consists of two main building blocks: a two-phase balanced 4:1 step-down power train and an LC-resonant output stage.…”