A line power-supply for LED lighting using piezoelectric transformers in Class-E topology

An up to 5 Watts wide range power supply LED driver demonstrator with a Piezoelectric Transformer (PT) has been built to show the static and dynamic behavior as an off-line power supply [1],[2],[5],[6],[7]. The target of the power converter controller using a PT, with 2.3 mm thickness and 17 mm diameter at frequency of 155-175 kHz, designed in a resonant circuit of Class-E topology, is to maintain a constant output current of 290mA/DC with variable output voltage drop at wide input voltage range of 85-250 V/AC. Also, the ZVS (Zero-Voltage-Switching) condition is achieved over the full operation range. The used 1200 V Fieldstop IGBT (1 A-Type) shows losses around 200 mW over the full operating range for constant output current. The paper shows the regulation method for off-line power supplies using PT in Class-E topology in constant current mode regulation (CCMR). The regulation algorithm has been programmed in C language operated by a 32-bit DSP (TMS320F2812). Besides, in the Class-E application, the duty cycle of the switching frequency needs to be controlled in order to achieve the ZVS during the operation at different load and input condition [1]. This goal is achievable only by Phase Locked Loop (PLL) feedback in a satisfying way [3]. To solve this problem, the idea of PT with an auxiliary tap has been applied, and it is shown in Fig.3. The application is suited for low size LED line adapters, to be integrated in bulb sockets. The results are applicable for any controller design of resonant PT stepdown topologies. The several suited optimum control concept is investigated in this paper, considering the circuit expense being minimized.