Abstract
The flyback converters are widely used in low power applications. The switch typically requires 600 V breakdown voltage in order to perform large step-down voltage. Thus, slight variation on the switch control can either permanently damage the switch or decrease the efficiency of the power conversion. In order to achieve higher power efficiency, the previous literature suggested operating the flyback converter in the discontinuous current mode (DCM). It is then required to understand the critical conditions of the DCM through analyzing the dynamic behavior and discontinuous current mechanism. This paper started from the current waveform analyses, proceeded to the derivation of zero current switching (ZCS) formulation, and finally reached the necessary conditions for the DCM. The entire DCM operation was divided into three phases that subsequently affect the result of the zero voltage switching (ZVS) and then to the ZCS. The experiment shows a power efficiency of over 96% when the output power is around 65 W. The switch used in this paper is a Gallium Nitride High-Electron-Mobility Transistor (GaN HEMT) that is advantageous at the high breakdown voltage up to 800 V. The important findings from the experiments include that the output power increases with the increasing input DC voltage and the duty cycle is rather linearly decreasing with the increasing switching frequency when both the zero voltage switching (ZVS) and ZCS conditions are satisfied simultaneously.
Highlights
The rapid advancement of electric vehicles [1,2,3], military technology [4], grid technology [5,6] and factory automation [7] have led to an increased demand for the dc-dc converter
This paper aims to provide an insight of the discontinuous current mode (DCM) mechanism and zero current theories to reduce the number of experiments, which are organized as follows
The low switching loss strategy proposed in this paper can yield a high efficiency in the DCM operation for a conventional flyback converter with high switching frequency using GaN HEMT
Summary
The rapid advancement of electric vehicles [1,2,3], military technology [4], grid technology [5,6] and factory automation [7] have led to an increased demand for the dc-dc converter. In continuous conduction mode (CCM), the transformer is unable to transfer the complete energy since the part of energy always remains in the core In this mode, the semiconductor switch is stressed at a higher voltage [8,9,10]. Considering these limitations in the CCM operation, the converter is preferred to operate in the discontinuous conduction mode (DCM) This mode of operation brings other challenges for the circuit designer, such as larger filter requirements at the input and output side [21,22,23,24], and increased electromagnetic interference [25,26]. Few studies have presented some methods using divided resonant capacitor [30], the secondary-side resonant method [31], and dynamic resonant period control [32], for mitigating voltage spike and increasing power conversion efficiency to improve the traditional methods, such as RCD clamp circuit, or active clamp circuit
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