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The paper presents a new topology of the pulse current source required in contemporary electrochemical processes (e.g. pulse plating). The main design challenge is generation of pulses with current slopes (di/dt) as high as possible. A buck converter is the most appropriate topology for generation of a constant current, but it doesn't fulfill the demands for a dynamic operation. The slope of the pulsed load current can be essentially improved if two or more converters are connected in series or parallel according to U. Lettau (1993). A complex control algorithm and interdependence between the slope of the pulse current and its ripple in the steady state are the main disadvantages of such connection. These two drawbacks are bypassed with a proposed topology of the pulse current source. The source consists of the input buck converter and the bridge inverter with a current fed transformer. The function of the bridge inverter differs from the usual bridge operation. The operating mode, in which the energy is carried to the load, is called transfer mode. The idle mode is the other possible mode in which all transistors in the bridge are turned on at the same time and the load current is zero. The load current is controlled indirectly by the DC input current (iL). Since the main inductor is placed into a DC link, the slope of the output current is limited only by stray inductances of the transformer and load. Stray inductances slow down commutation process, which is reflected in over-voltages on the bridge transistors. In order to avoid the destruction of those transistors, a clamping diode DZ is added in the input circuit. Additional advantages of the proposed topology are isolated output stage and modularity. Experimental results obtained from a laboratory pulse current source confirm an outstanding dynamic performance.
EUROCON 2003. Computer as a Tool. The IEEE Region 8 (Volume:2 )
Date of Conference: 22-24 Sept. 2003