| 摘要 |
PROBLEM TO BE SOLVED: To optimize an output current and to reduce power source noise and output noise by controlling a P-channel transistor in accordance with a second power source potential change. SOLUTION: A first power source VCCA 1 is fixed to 3 v and a second power source VCCB 2 is set to vary between 3 and 5 v. A P-channel transistor PB1 16 is controlled by a control circuit, so that it is turned on only when the potential of the VCCB 2 is between 3 and 5 v and a P-channel transistor PB2 15 is turned on only when the potential of the VCCB 2 is 3 v. Also, a P-channel transistor P5 (5) is arranged, is turned off, when the potential of the VCCB 2 changes from 3 to 5 v and current is made to flow to a GND 6 from the VCCB 2. Furthermore, a P-channel transistor P6 (8) is equipped between a P-channel transistor P3 (7) and an N-channel transistor N3 (9). Even if transistors 7 and 9 are turned on when the potential of the VCCB 2 changes from 5 to 3 v, the transistor 8 is turned off and will not cause current to flow to the GND 6 from the VCCA 1.
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