# Interleaved Boost Converter with ZVT-ZCT for the Main Switches and ZCS for the Auxiliary Switch
## 1 Introduction  
Generally, the traditional switching power supply operates under hard switching. However, due to the parasitic components, large electromagnetic interference and high switching loss will happen the instant the switch is turned on/off. Accordingly, the soft switching concept is presented [1; 2; 3; 4; 5]. Based on an auxiliary inductor connected in series with the switch, this inductor will oscillate with the parasitic capacitor during the turn-off period, and, as soon as the voltage across the parasitic capacitor resonates to zero, the switch will be turned on. This behavior is called zero-voltage switching (ZVS) at turn-on. Moreover, as soon as the current in the auxiliary inductor resonates to zero, the switch will be turned off. This behavior is called zero-current switching (ZCS) at turn-off. However, although the switching loss is reduced based on ZVS or ZCS or both, high resonant voltage stress or high resonant current stress is generated so as to select proper components, thereby increasing the corresponding circuit cost. In addition, since the turn-on and turn-off intervals are determined by the resonant period, the variable-frequency control is chosen so as to stabilize the output voltage, thereby making the filter design difficult. As seen in the half-resonant drawbacks, the active clamp [6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27], the zero-voltage transition (ZVT) [21; 22; 23; 24; 25; 26; 27] and the zero-current transition (ZCT) [28; 29; 30] are presented. As the voltage clampis applied to the non-isolated power supply, the parasitic inductance of the line and the leakage inductance of the transformer are used as the auxiliary inductance, which will oscillate with the auxiliary capacitance. Via this way, the switch can reach soft switching during the resonant period. As the auxiliary switch is turned off, the current in the auxiliary inductance flows through the input terminals, thereby making the body diode of the main switch turn on, and hence the main switch has soft switching and the energy stored in the auxiliary inductance is transferred to the input terminals. By doing so, the overall efficiency is increased. As the active clamp technique is applied to the non-isolated power converter [31], one auxiliary inductance, one auxiliary capacitance, and one auxiliary switch are used to form a resonant loop, and, during the resonant period, the soft switching of the main switch and auxiliary switch can be achieved. Via this way, the voltage stress on the main switch is reduced in addition to the switching loss. However, the switching frequency is varied according to output load and input voltage, and an auxiliary inductance is inserted in the power path. Consequently, although the soft switching of the main switch can be achieved, the low-pass filter is designed difficultly, and the conduction loss is severe as this converter operates under the half or rated load. As the ZVT or ZCT technique is applied to the power supply, one auxiliary resonant circuit is connected in parallel with the main switch. Before the main switch is turned on or off, the auxiliary switch is turned on and hence the resonance occurs, forcing the voltage on the main switch or the current in the main switch to be zero. Since the resonance circuit does not locate in the main power path, the conduction loss is reduced and hence the overall efficiency is increased. The literatures [32; 33; 34] employ ZVT and ZCT simultaneously, so that the switching loss can be reduced and hence the overall efficiency can be enhanced. On the one hand, in order to upgrade the output current as well as to improve the efficiency, the multiphase converter, along with interleave control, is widely used. The fact that the AC components of the inductor currents for multiple phases are cancelled to some extent makes the output current ripple reduce as well as the frequency of the output current ripple increase.