A High-Efficiency, Low-Cost Solution for On-Board Power Converters

Wide-input, low-voltage, and high-current applications are addressed. A single-ended isolated topology which improves the power efficiency, reduces both switching and conduction losses, and heavily lowers the system cost is presented. During each switching cycle, the transformer core reset is provided. The traditional tradeoff between the maximum allowable duty-cycle and the reset voltage is avoided and the off-voltage of active switches is clamped to the input voltage. Therefore, the system cost is heavily reduced and the converter is well suited for wide-input applications. Zero-voltage switching is achieved for active switches, and the power efficiency is greatly improved. In the output mesh, an inductor is included making the converter suitable for high-current, low-voltage applications. Since the active clamp forward converter is the closest competitor of the proposed converter, a comparison is provided as well. In this paper, the steady-state and small-signal analysis of the proposed converter is presented. Design examples are provided for further applications. Simulation and experimental results are shown to validate the great advantages brought by the proposed topology. 1. Introduction On-board power converter technology has extensively matured over the last two years. Until recently, the industry was manufacturing converters from 5？W of power to, at most, 30？W. Today, converter power levels are increasing to 50, 100, 300, and even 400？W in miniature sizes. These are rather dramatic improvements in a relatively short period of time. High-power converters are physically much smaller than their predecessors, achieving energy density levels of 50？W per cubic inch without the required external heat sink. Recently, distributed power architectures for telecommunications and data-computing systems have received a great deal of attention. With the spread of wide-input, low-voltage, and high-current applications, many topologies have been proposed to improve the efficiency, power density, and cost of the whole system. The well-known forward converter is still the most suitable topology for medium power levels, well-suited for low-voltage and high-current applications [1, 2]. Yet, in forward converters an external circuit is required to achieve the core reset. By adding an auxiliary winding, the energy stored in the transformer could be recycled to the input rail but increasing the cost and complexity of the power supply. Otherwise, the energy is lost in the reset circuit, as in the Resistor-Capacitor-Diode (RCD) network [3–5]. The active clamp is