Design of High Power ZVS Piezoelectric Transformer and Current Balance Structure
Date Issued
2009
Date
2009
Author(s)
Ho, Chung-Chun
Abstract
Driving paralleled T5 lamps with disk-type piezoelectric transformers (PT) is the main focus of this thesis. Two kinds of piezoelectric transformer were designed and studied in this thesis. The first one is a single output disk-type piezoelectric transformer which is used with current balanced circuit. The second one is a four output disk-type piezoelectric transformer. Although the second kind is more complex, it can drive four paralleled T5 14W lamps directly without any current balance circuit. The purpose of this research is to substitute conventional electromagnetic ballasts with electronic ballasts using a piezoelectric transformer and driving multiple paralleled T5 lamps. Although the design of driving multiple paralleled lamps is more difficult to design, it could significant lower the cost of ballasts. The power range of piezoelectric transformer based ballast was about 10~20W before, but the power of the disk type piezoelectric transformer in this paper can reach 52.8W. his thesis also analyzes the electronic characteristics with equivalent circuit of piezoelectric transformer with the two-ports network model. The impedance matching point was derived from equivalent circuit model. To achieve Zero voltage switching (ZVS) condition is one of the main focus in this thesis. To achieve the ZVS condition, a small inductor was series inserted in front of piezoelectric transformer. The optimal value of the small inductor is decided by the resonant frequency of the PT. Specifically, the resonant frequency resonant tank composed of the small inductor and the input intrinsic capacitor of the piezoelectric transformer should be set between one to three times of resonance of piezoelectric transformer. A ZVS inverter based on disk-type piezoelectric transformer has been implemented. The result showed that two kinds of piezoelectric transformers can both light up four T5 14W fluorescent lamps successfully. The efficiency of the four output piezoelectric transformer is 88.9%, which is higher than the efficiency of single output piezoelectric transformer with a capacitors based current balance circuit ─ 82.3%. But the output power of the single output piezoelectric transformer with a capacitor based current balance circuit is 52.8W, which is larger than 50.4W, the total output power of four output piezoelectric transformers. And the current is more balanced in the single output piezoelectric transformer with a capacitor based current balance circuit, but almost the same with the other. The result in the thesis shows that driving multiple T5 lamps in parallel with piezoelectric transformera and current balance circuits to substitute conventional electromagnetic ballast is possible.
Subjects
disk-type
piezoelectric transformer
driving in parallel
T5 lamp
four output
ballast
ZVS
Type
thesis
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