Quasi Resonant Zeta and Other Fourth Order Converters

The Zeta converter has many interesting features. The main switch is in series to the positive terminal of the input source. So no inrush occurs, when the converter is connected to the supply and it can be used as an electronic fuse in case of an error. The output side of the converter is an LC-filter, so only the current ripple of the current through the output coil is flowing through the output capacitor, and the voltage across it is very stable, even with a smaller capacitor. To reduce the switching losses and to smooth the slope of the signals, the zero current switching (ZCS) and the zero voltage switching (ZVS) can be applied. The converter must be extended by a small resonant inductor in series to the electronic switch and a capacitor in parallel (in case of ZVS) to the electronic switch or in parallel to the diode (in case of ZCS). The function of the converter is explained in detail with the help of calculations and with the u-Zi diagram. The considerations are proved with the help of LTSpice simulations. The Sepic and the Cuk converter are also treated as QR converters.