Modeling and IC-based control of high frequency electronic ballasts

High-frequency electronic ballasts bring up several advantages over low-frequency counterparts including higher efficiency, better light quality, smaller size, and more advanced control features. However, high-frequency operation increases costs and control complexity, leading to continuous research efforts on the design, modeling, control, and drive of high frequency ballasts. This work addresses small-signal modeling and IC-based control of high frequency electronic ballasts, providing theoretical analyses as well as practical IC controller design for the ballast system.;Two approaches are proposed to model the small-signal envelope dynamics in resonant ballasts. The direct modeling approach yields a general mathematical model closely tied to the resonant tank without any network transformation. The phasor transformation approach constructs an equivalent small-signal phasor model that can be solved as any other conventional circuit to find the envelope dynamics. It is found that the two modeling approaches yield the same low frequency salient features for the envelope transfer functions. The dynamic interaction between the ballast and the fluorescent lamp is also studied for full operation range. Based on the results from dynamic analyses, a closed-loop controller design example is demonstrated that improves the transient performance at low dimming levels.;A dual low voltage IC (LVIC) based gate driver is proposed, which brings the advantages of low cost IC fabrication and high frequency operation. A coupling capacitor is placed between low side and high side ICs to perform three functions: high voltage isolation, charge pump power supply, and communication path. A CMOS switch is implemented on each IC to actively steer the current for charge pump power supply and to generate and detect the signaling and handshaking currents for communication. The key switching functions and the charge pump power supply are examined by use of a discrete test-bed. The IC solution of the gate driver is implemented through the AMS 0.8mum HV CMOS process, and is verified by analog simulation.;A digital phase control scheme for resonant inverters and ballasts is proposed to regulate the phase angle between the midpoint voltage and the inductor current, which provides several benefits over traditional frequency control including self-tuning to the resonance, less sensitivity for near resonance operation, and inherent non-ZVS protection. The controller adjusts the power switches on/off timing referred to the inductor current zero crossing to achieve desired phase. The control scheme is realized in a simple state machine and verified through an FPGA-based prototype. Around the phase controller, a two-loop digital ballast control system is built to regulate the lamp current. The control IC is designed through the AMS 0.8mum 5V CMOS process and verified by the experimental results.