Abstract—This paper presents the design and experimental of ring-dot piezoelectric ballasts for a 36-W, T-8 fluorescent lamp. The piezoelectric transformer used in this paper is a radial contour- vibration mode devices with a diameter of 30 mm, a thickness of 2.7- mm and a desired resonant frequency of 80 kHz. The design process can be conducted step-by-step with a set of empirical formulae. Therefore, designed test samples can be implemented for performance evaluation. In this paper, three different pieces of the ring-dot piezoelectric transformer were formed. The tests were carried out by using the implemented piezoelectric transformers as a part of electronic ballasts to drive a 36-W fluorescent lamp. The results show that overall efficiency of the implemented piezoelectric transformers was as high as 96.1% at a resonant frequency of 81.4 kHz. Keywords—Piezoelectric transformer, electronic ballast, ring-dot type, radial contour vibration mode. I. INTRODUCTION NVENTION of piezoelectric transformers (PZT) was first published in 1954 by Rosen, Fish and Rothenberg [1] and granted later the US patent no. 2830274 in 1958. Recently, almost sixty years after the first invention, the piezoelectric transformer has become a potential device to replace a wound- type, magnetic-core transformer in various applications. The piezoelectric transformer is an energy conversion device that can convert electric energy into mechanical vibration energy or vice versa. It must be made from appropriate materials in order to give satisfactorily desired performances. Piezoelectric ceramic materials have special characteristics in which the voltage gain of the piezoelectric transformer is changed significantly due to the applied force at the resonant frequency. Therefore, they are suitable and widely accepted for use as piezoelectric transformers in association with various electrical devices. With special design, the Peerasaksophol, M., is with the School of Electrical Engineering, Suranaree University of Technology, Nakhon Ratchasima, 30000 Thailand (e-mail: tweety-bow@hotmail.com). Srilomsak, S., is with the School of Ceramic Engineering, Suranaree University of Technology, Nakhon Ratchasima, 30000 Thailand (e-mail: sutamsri@sut.ac.th). Laoratanakul, P., is with the Nation Metal and Materials Technology Center (MTEC), Pathumthani, 12120 Thailand (e-mail: pitakl@mtec.or.th). Kulworawanichpong, T., is with the School of Electrical Engineering, Suranaree University of Technology, Nakhon Ratchasima, 30000 Thailand, (corresponding author to provide phone: (+66) 4422-4404, (+66) 4422-4400; fax: (+66) 4422-4601; e-mail: thanatch@sut.ac.th). piezoelectric transformer can perform as a step-up or a step- down transformer without any magnetic core to cause magnetic field interference. At the beginning of the invention of the piezoelectric transformers, it had not been accepted or used in commercial sectors. Until the 1990s, the piezoelectric transformers have been attracted by several Japanese companies to be used as a coreless transformer of portable electronic devices, e.g. notebook, PDA, mobile, etc. The combination with the piezoelectric transformer has led to the considerable reduction in weight and size of the electronic devices. In addition, there is no or less magnetic field interference produced by the piezoelectric transformers. In this paper, the only application to be considered is the replacement of the piezoelectric transformer over heavy and sizable magnetic-core inductors in electronic ballast circuits for 36-W, T-8 fluorescent lamps [2-6]. In this paper, the design and implementation of the ring-dot piezoelectric transformer operating in contour vibration-mode for 36-W, T-8 fluorescent lamp ballasts was proposed. In Section 2, empirical formulae used to calculate the desired structure dimension of the piezoelectric transformers were given. The proposed design procedure was illustrated step-by- step in Section3. The driving circuit for fluorescent lamps was also briefed in this section. In Section 4, simulation and experimental results were discussed. Section 5 gave the conclusion remark and future works. II. RING-DOT PIEZOELECTRIC TRANSFORMER A. Structure and Mode of Operation The piezoelectric transformer is an application of piezoelectric materials that act in both transverse (actuator) and longitudinal (transducer) modes. Although piezoelectric transformers can be formed in many configurations, only radial vibration mode of operation can enable high electric power applications such as electronic ballasts, notebook adapter, etc [7-17]. The piezoelectric transformer in radial vibration mode transfers electrical power from its input port into mechanical power and thereafter converts mechanical power into electrical power at its output port, all in radial direction. The ring-dot type has simple configuration giving the radial vibration mode [18]. Several electronic ballast applications of this type can be found from recent literatures [19-22]. The structure of ring-dot configuration is shown in Fig. 1. Ring-dot Piezo-electric Ballasts for 36-W Fluorescent Lamps Monthakarn Peerasaksophol, Sutham Srilomsak, Pitak Laoratanakul and Thanatchai Kulworawanichpong I International Conference on Advances in Electrical and Electronics Engineering (ICAEE'2011) 169