| 摘要 |
<P>PROBLEM TO BE SOLVED: To prevent a reverse leakage current flowing from an external power supply to an internal battery through an FET parasitic diode in a power supply circuit that provides a switchover function between the internal battery and the external power supply and uses the FET as an isolating switch for the internal battery when the external power supply is used. <P>SOLUTION: When an external power supply EXS is used, a backflow prevention circuit CCP, which is connected in parallel to an internal battery BAT1 and is comprised of a series circuit of a current setting resistor R4 and a field effect transistor FET4, is operated by the external power supply EXS. Then, a current I4 flowing into the current setting resistor R4 of this backflow prevention circuit CCP toward a ground terminal is set greater than a leakage current I2'[I4=V_BAT1/R4;I4>I2'] flowing backward through a parasitic diode D2 of a FET2 from the external power supply EXS. <P>COPYRIGHT: (C)2012,JPO&INPIT |
