| 摘要 |
PROBLEM TO BE SOLVED: To provide a soft start circuit capable of relieving an overshoot of an output voltage when starting a switching type DC-DC converter. SOLUTION: This soft start circuit includes: an error amplifier 1 for inputting a reference voltage V<SB>REF</SB>and a feedback voltage V<SB>FB</SB>; a first counter 9 for increasing the reference voltage V<SB>REF</SB>in stages; a comparator 2 for comparing an error output signal V<SB>ERR</SB>of the error amplifier 1 with a triangular wave; a comparator output signal V<SB>COMP</SB>of the comparator 2 for indicating whether or not increase of the feedback voltage V<SB>FB</SB>follows increase of the reference voltage V<SB>REF</SB>; a second counter 6 which periodically checks the comparator output signal V<SB>COMP</SB>to count up a count value when the increase of the feedback voltage V<SB>FB</SB>does not follow increase of the reference voltage V<SB>REF</SB>; an output MOS transistor M1 in which a conducting state is controlled by the comparator output signal V<SB>COMP</SB>; and an overcurrent protection circuit 3 for controlling an overcurrent of the output MOS transistor M1. COPYRIGHT: (C)2007,JPO&INPIT
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