Analysis of a soft switched, low power and high gain capacitor charger

This study presents a soft switched, high gain and high output voltage capacitor charger for low power applications. Unlike the Flyback topology, which is commonly used for high voltage, low power chargers, high leakage of the isolation transformer is allowed here. To obtain high gain, while preserving a relatively low transformer ratio, a multiple stage Cockcroft-Walton (CW) voltage multiplier is used at the output. The combination of a small number of turns and a high switching frequency allows application of planar magnetic technology, significantly simplifying the transformer's manufacturing process and reducing its core size. Despite the high voltage at the output, the voltage at the transformer's secondary is kept relatively low, avoiding the need for an expensive and less reliable transformer's molding process, which is otherwise required to prevent an electrical breakdown. The analytical model for lossy resonant charging, developed in this study is verified by simulations and experiments on a 2kV capacitor charger which is fed by a low voltage source. The experimental results show that the proposed charger is an excellent engineering choice for reduced size, reliable, low power and high voltage applications.