High‐efficiency power‐feed equipment using a series‐resonant constant‐current converter for use in submarine optical‐fiber transmission systems

Abstract

The saturable-reactor constant-current converter is widely used in cable transmission systems. It has excellent constant-current characteristics, but it is difficult to realize high efficiency due to the large loss in the switching element and the large driving loss of the saturable reactor. Consequently, it cannot be applied to submarine optical-fiber transmission systems, where a large current feed is required. For a constant-current converter to be used instead of the forementioned device in the submarine optical-fiber transmission system, the current variation must be less even in the transient state (the constant-current characteristic must be realized without the control) in addition to achieving high efficiency. This study describes a new constant-current converter design, a series-resonant converter based on the discontinuous current mode, which has excellent constant-current characteristics as well as small driving loss and switching loss. The series-resonant converter is analyzed first, and it is shown that a constant-current characteristic is realized without control. An approach to improvement of efficiency which decreases the on-period loss is described. The proposed high-efficiency technique is applied to the submarine optical-fiber constant-current converter. A technique of reducing the effective current, which is useful in reducing loss in the on-period, is considered. A design method for the maximum normalized frequency ratio is presented. In addition, in the current-feedback driving circuit, which is considered to minimize the loss of the transistor, the minimum-loss driving condition for the transistor is described. As a result, the efficiency of the main circuit of the constant-current converter is improved to 93 percent. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80 (5): 87–97, 1996