This paper proposes an analytical model of maximum operating frequency of class-D zero-voltage-switching (ZVS) inverter. The model includes linearized drain-source parasitic capacitance and any duty ratio. The nonlinear drain-source parasitic capacitance is equally linearized through a charge-related equation. The model expresses the relationship among frequency, shunt capacitance, duty ratio, load impedance, output current phase, and DC input voltage under the ZVS condition. The analytical result shows that the maximum operating frequency under the ZVS condition can be obtained when the duty ratio, the output current phase, and the DC input voltage are set to optimal values. A 650 V/30 A SiC-MOSFET is utilized for both simulated and experimental verification, resulting in good consistency.

This paper presents an analysis-based design method for designing the class-Φ22 wireless power transfer (WPT) system, taking its subsystems as a whole into account. By using the proposed design method, it is possible to derive accurate design values which can make sure the class-E Zero-Voltage-Switching/Zero-Derivative-Switching (ZVS/ZDS) to obtain without applying any tuning processes. Additionally, it is possible to take the effects of the switch on resistance, diode forward voltage drop, and equivalent series resistances (ESRs) of all passive elements on the system operations into account. Furthermore, design curves for a wide range of parameters are developed and organized as basic data for various applications. The validities of the proposed design procedure and derived design curves are confirmed by LTspice simulation and circuit experiment. In the experimental measurements, the class-Φ22 WPT system achieves 78.8% power-transmission efficiency at 6.78MHz operating frequency and 7.96W output power. Additionally, the results obtained from the LTspice simulation and laboratory experiment show quantitative agreements with the analytical predictions, which indicates the accuracy and validity of the proposed analytical method and design curves given in this paper.

This paper presents a high step-up DC-DC converter for low voltage sources such as solar cells, fuel cells and battery banks. A novel non isolated Zero-Voltage Switching (ZVS) interleaved DC-DC boost converter condition is introduced. In this converter, by using coupled inductor and active clamp circuit, the stored energy in leakage inductor is recycled. Furthermore, ZVS turn on condition for both main and clamp switches are provided. The active clamp circuit suppresses voltage spikes across the main switch and the voltage of clamp capacitor leads to higher voltage gain. In the proposed converter, by applying interleaved technique, input current ripple and also conduction losses are decreased. Also, with simple and effective method without applying any additional element, the input ripple due to couple inductors and active clamp circuit is cancelled to achieve a smooth low ripple input current. In addition, the applied technique in this paper leads to increasing the life cycle of circuit components which makes the proposed converter suitable for high power applications. Finally an experimental prototype of the presented converter with 40 V input voltage, 400 V output voltage and 200 W output power is implemented which verifies the theoretical analysis.

In this paper, a new single soft switched forward converter with a self driven synchronous rectification (SDSR) is introduced. In the proposed converter, a soft switching condition (ZCS turn on and ZVS turn off) is provided for the switch, by an auxiliary circuit without any extra switch. In additional, this auxiliary circuit does not impose high voltage or current stresses on the converter. Since the proposed converter uses SDSR to reduce conductive loss of output rectifier, the rectifier switches are switched under soft switching condition. So, the conductive and switching losses on the converter reduce considerably. Also, implementing control circuit of this converter is very simple, due to the self-driven method employed in driving synchronous rectification and the converter is controlled by pulse width modulation (PWM). The experimental results of the proposed converter are presented to confirm the theoretical analysis.

Design equations for satisfying off-nominal operating conditions of the class E amplifier with a nonlinear shunt capacitance for a grading coefficient of 0.5 and the duty cycle D=0.5 are derived. By exploiting the off-nominal class E operation, various amplifier parameters such as input voltage, operating frequency, output power, and load resistance can be set as design specifications. As a result of the analysis in this paper, the following extension of the usability of the class E amplifier was achieved. With rising up the dc supply voltage, the shunt capacitance which achieves the off-nominal operation can be increased. This means that a transistor with higher output capacitance can be used for ZVS operation. This also means that maximum operating frequency which achieves ZVS can be increased. An example of a design procedure of the class E amplifier is given. The theoretical results were verified with an experiment.

This paper presents the analysis of a new multi-oscillated current resonant type DC-DC converter. Current resonant converters have several remarkable features such as high efficiency, small size, low cost and low noise, and are frequently employed in many portable electronic systems such as personal computers, cellular phones and flat panel displays. The current resonant type converter generally employs pulse frequency modulation for constant voltage control in the output. For this reason, the magnetizing current through the converter not only causes a power loss under a light load, but also a loss during stand-by. Therefore, this type of converter has a problem in that the required smaller size cannot be achieved, because an auxiliary source is necessary for stand-by. In order to solve these problems, a new current resonant type power supply is proposed in which two driving methods are employed. In these driving methods, one MOSFET as a main switch is driven by an auxiliary winding of the transformer and another MOSFET as a main switch is driven by the driving IC with a low withstand voltage. Good agreement of the observed and simulated waveforms was confirmed. In addition, eight distinct states and four distinct operating modes, which compose of the sequence of states, were clarified by experimental and simulated analysis.

A systematic approach to the analysis and design of a bi-directional Cuk converter for the cell voltage balancing control of a series-connected lithium-ion battery string is presented in this paper. The proposed individual cell equalizers (ICE) are designed to operate at discontinuous-capacitor-voltage mode (DCVM) to achieve the zero-voltage switching (ZVS) for reducing the switching loss of the bi-directional DC/DC converters. Simulation and experimental results show that the proposed battery equalization scheme can not only enhance the bi-directional battery equalization performance, but also can reduce the switching loss during the equalization period. Two designed examples are demonstrated, the switch power losses are significantly reduced by 52.8% from the MOSFETs and the equalization efficiency can be improved by 68-86.9% using the proposed DCVM ZVS battery equalizer under the specified cell equalization process. The charged/discharged capacity of the lithium-ion battery string is increased by using the proposed ICEs equipped in the battery string.

In this paper, a novel type of the step-up high frequency transformer linked full-bridge soft-switching phase-shift PWM DC-DC power converter with ZVS and ZCS bridge legs is proposed for small scale fuel cell power generation systems, automotive AC power supplies. A tapped inductor filter with a freewheeling diode is implemented in the proposed soft-switching DC-DC power converter to minimize the circulating current in the high-frequency step-up transformer primary side and high-frequency inverter stage. Using a tapped inductor filter with a freewheeling diode makes possible to reduce the circulating current without any active switches and theirs gate-drive circuits. The operating principle of the proposed DC-DC power converter with each operation mode during a half cycle of the steady state operation is explained. The optimum design of the tapped inductor turns ratio is described on the basis of the circuit simulation results. Developing 1 kW 100 kHz prototype with power MOSFETs and 36 V DC source verifies the practical effectiveness of the proposed soft-switching DC-DC power converter. The actual efficiency of the proposed DC-DC power converter is obtained 94% for the wide load and output voltage variation ranges.

A DC-DC converter using two transformers is proposed. One transformer delivers the energy to a load when a switch is on and the other transfers the flyback energy to a load when a switch is off. The primary windings of the two transformers function as choke inductance alternately, and thus the output voltage control by means of the duty ratio and the zero-voltage-switching are possible without an additional inductor. The breadboarded prototypes of the single output and the two outputs have confirmed the principles of operation and demonstrated the high conversion efficiency.

A class E low dv/dt PWM synchronous rectifier regulating the output voltage at a fixed frequency is presented, analyzed and verified experimentally. This rectifier is derived from the class E low dv/dt rectifier by replacing the controlled switch (MOSFET with its anti-parallel diode) with the rectifier diode in class E low dv/dt rectifier, and by using the synchronized PWM signal to control the output voltage at desired value. The ZVS condition of the controlled switch can be maintained from full-loaded to open-loaded. The experimental results measured at switching frequency 1 MHz are in good agreement with the theoretical prediction.

Steady-state characteristics of the push-pull inverter with a piezoelectric transformer are analyzed. The piezoelectric transformer operating in the 3rd-order longitudinal vibration mode is used in place of a conventional magnetic transformer to produce a high output voltage to light up a cold cathode fluorescent lamp. The circuit operation, the load characteristics, the efficiency and the ZVS conditions are analyzed using equivalent circuits. These analytical results are confirmed by experiments. An example of the output current control is also shown.

This paper presents a new type of zero-voltage-switched (ZVS) push-pull dc-dc converter with two synchronous rectifiers in the secondary circuit. ZVS is realized using the magnetizing current of the transformer as a constant current source during the commutation. The output voltage is controlled by PWM with a constant switching frequency. The circuit operation is described using equivalent circuits. The steady-state and dynamic characteristics are analyzed and confirmed experimentally.