| 摘要 |
PROBLEM TO BE SOLVED: To operate a clamp circuit at all times even if error signal voltage fed back from output reduces by limiting the first drive signal to maximum pulse width based on reference voltage, and the second drive signal to minimum pulse width based on reference voltage. SOLUTION: The error signal voltage V1 which feeds back output voltage is compared by the maximum duty signal voltage V4 based on reference voltage 15 and a comparative circuit 17, and compared by the voltage V3 of a delta wave oscillator 16 and a comparative circuit 18 to drive MOS transistor 5 by a pulse-width modulated drive pulse signal P1. The voltage V2 where the error signal voltage V1 is shifted to a low level by a level shift circuit 21 and the voltage V5 where maximum duty signal voltage V4 is shifted to a low level by a level shift circuit 20 are compared with each other by a comparison circuit 22, and compared by voltage V3 and a comparison circuit 19 so as to become a driving pulse signal P2 to drive a MOS transistor 6. It is thus possible to operate a clamp circuit all at times.
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