Design and Characterization of a Secondary Side Smart-Power Integrated Active Asynchronous Voltage Clamp


IEICE TRANSACTIONS on Electronics   Vol.E98-C   No.6   pp.518-527
Publication Date: 2015/06/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E98.C.518
Type of Manuscript: PAPER
Category: Electronic Circuits
power conversion,  clamping,  snubber,  smps,  

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As is well known in the design of transformer isolated converters, the transformer leakage inductance causes a large voltage overshoot on the secondary side switching nodes at every switch transition, unless measures are taken to limit the peak voltage stress. Since the peak voltage stress in smart-power integrated converters, where the power devices are integrated on the same die as the controlling logic and supporting circuits, is the major determining factor for the required silicon area for the implementation, this is a major roadblock for the affordable integration of this type of converter. Therefore, any cost-effective smart-power synchronous rectifier requires a voltage clamping circuit that minimizes the voltage stress, while still maintaining the potential advantages of smart-power converters, i.e. minimizing the number and size of the discrete components in the converter. We present an integrated asynchronous active clamping circuit, that can clamp the overshoot voltage to arbitrary voltages while optimizing the efficiency by only being active when required. Because of the asynchronous operation, the size of the required external components is minimized. Measurements on the smart-power IC implementation of the asynchronous active clamp circuit combined with a secondary side synchronous rectifier for a 1 MHz full bridge converter confirm the reduction in voltage stress and the optimization of the efficiency.