High-frequency Contravariant Constant Flow Source Based On Soft-Switch Technology

Most of the traditional constant current sources are linear power supplies, with the maturity of switching power supply technology, they have been gradually replaced by switching constant current sources. In contrast, switching constant current sources have many advantages such as small size, light weight, high efficiency.Generally, switching constant current sources operate under high-frequency conditions, the switching losses are very large, which will restrict the size and weight to be further reduced. In order to solve this problem, soft switching technology is proposed. This paper first analyzes the causes of swiching losses in the traditional PWM DC/DC converter, then introduces the basic principles and implementation method of soft-switch technology. Focused on the realization of soft switching in full bridge converter, this paper starts a detailed analysis of 12 different process in a complete cycle, at the same time, the inherent shortcomings of phase-shifted full-bridge converter are pointed out : lose ZVS with light loads; duty cycle losses in secondary side; hard switch of secondary rectifier diode and intrinsic parasitic ringing in secondary side. Aiming at these problems, additional resonant inductor and resonant support network can be used to improve converter performance.Base on the above theories, this paper attempts to design a high-frequency and high power contravariant current source, whose output current is continuously adjustable in the range of 10A-200A, and its open-circuit voltage can be arbitrarily set between 1V and 5V. Compared with traditional linear current source, the current source designed in this paper has its own advantages: large output current; large adjustable range for output current; overcoming the intrinsic shortcomings in linear power supply; using soft-switch technology in full-bridge DC/DC converter, to further improve the power efficiency; using synchronous rectification technology for the second side, which significantly reduces the loss of rectifier circuit; adding various protection circuits, to enhance the reliability. This paper mainly finishes the design of phase-shifted full-bridge converter,high frequency transformer,peripheral circuits of control chip UC3875 and current feedback proposal. In addition this paper also designs a assistive device, which can easily achieve high-power switches test. Finally, complete the installation and debugging, give the test results and sample images, to confirm the feasibility of this current source.