Step_up_down_dc_dc_converter

Published:2009/7/24 8:52:00 Author:Jessie | From:SeekIC

Positive-output step-up and step-down dc/dc converters have a common limitation in that neither can handle input voltages that can be both greater than (or less than) the output. For example, when convening a 12-V sealed lead-acid battery to a regulated + 12-V output, the battery voltage can vary from a high of 15 to 10 V. By using a MAX641 to drive separate P- and N-channel MOSFETs, both ends of the inductor are switched to allow noninverting buck/boost operation. A second advantage of the circuit over most boost-only designs is that the output goes to 0 V when Shutdown is activated. A drawback is that efficiency is not optimum because the two MOSFETs and diodes increase losses in the charge and discharge path of the inductor. The circuit delivers + 12 V at 100 mA with an 8-V input (70% efficiency).



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