# Single-Switch Non-Isolated Resonant DC-DC Converter for Single-Input Dual-Output Applications
This way, resonant switching converters are an extension of hard-switching converters, but the switch is complemented with a high-frequency \(L\)-\(C\) tank circuit to provide resonant operation on the main switch, facilitate zero-current or zero-voltage switching and avoid simultaneous high current and high voltage in the switch device. This allows for quasi-resonant techniques and zero-voltage or zero-current switching on the main switch of DC-DC converters to be applied in traditional single-inductor converters, such as CSC (Canonical Switching Cell), Boost, Buck and Buck-Boost single-inductor converters, as well as in well-known two-inductor topologies such as Zeta, Cuk and SEPIC, in their different versions \(L\)-type and \(M\)-type (depending on how the \(L\)-\(C\) tank and switch are interconnected) and in half-wave and full-wave implementations (depending on whether the resonant action is performed over half cycle or full cycle), in order to obtain ZVS or ZCS conditions. These configurations and topologies are well established in the literature and were developed several decades ago [15; 16; 17]. In the same way, the advantages and limitations of quasi-resonant converters are also well established. QRCs provide reduced EMI (radiated and conducted) due to the low \(dv/dt\) and \(di/dt\) produced (no higher peak currents),sinusoidal waveforms that facilitate the turn-off process and voltage control by changing the switching frequency and zero current and/or zero voltage across the switches during switching transitions, thus substantially reducing switch losses. In addition, the parasitic components \(L\) and \(C\) can be incorporated as parts of the resonant circuit. Their main limitations are due to the fact that they require variable switching frequencies for regulation, which is very often considered a drawback of resonant converters. On-state currents and off-state voltages are higher than those found in non-resonant configurations of the same power. In general terms, ZVS-QRCs are more widely used than ZCS-QRCs, mainly because of the parasitic junction capacitances associated with the semiconductor switch that can be incorporated as part of the required resonant capacitor. Also, in ZCS-QRCs, the charge stored in the parasitic capacitance associated with the semiconductor switch is dissipated in the switch itself during the conduction state. \(L\)-type and \(M\)-type configurations have similar behavior. The resonant capacitor in \(M\)-type configurations is exposed to a lower peak voltage, although it is bipolar. The main advantage of the ZCS-QR \(L\)-type converters is that, for some configurations, the resonant capacitor can be associated with the parasitic junction capacitance of the freewheel diode. To regulate the output voltage against input voltage and load variations, ZCS-QRCs require constant on-time control, while constant off-time control needs to be employed for ZVS-QRCs. With respect to half-wave and full-wave versions, for the same conditions, full-wave operation requires a lower switching frequency (higher switching period) and provides better load regulation than half-wave versions. ZCS-QRCs for half-wave operation mode require a unidirectional switch, while for full-wave operation, a bidirectional switch is required. In the same way, ZVS-QRCs require a bidirectional switch for half-wave operation and a unidirectional switch for full-wave operation. This causes the implementation of full-wave versions of ZVS-QRCs with MOSFET switches (and also ZCS-QRCs in half-wave versions) to require the use of an additional diode in series with the MOSFET to make them unidirectional, which is not very effective and increases the number of devices required. However, the advantages and disadvantages of each configuration and topology must be analyzed and compared individually for each specific case and application.