| 摘要 |
PURPOSE:To attain sure battery warning by detecting a battery voltage automatically even when the battery voltage differs and using a reference voltage in response to the battery voltage so as to operate a comparator circuit. CONSTITUTION:When an input voltage is 12V, since a transistor (TR) Q2 is of an input voltage discriminating circuit 6 is turned off, a TR Q1 of a switch circuit 5 is also turned off. In this case, an output voltage V2 of a reference voltage generating circuit 3 is the voltage division of 5V by resistors R3 and (R4+R5). When an input voltage Vin is sufficiently large, a voltage V1 inputted to a non-inverting input of a comparator 4 is larger than a voltage V2 given to an inverting input of the comparator 4. Thus, the output of the comparator 4 goes to a high level. As a result, no warning lamp D is lighted. When the input voltage Vin is decreased due to battery discharge or the like, the voltage V1 is smaller than the voltage V2, resulting that the comparator 4 is inverted to a low level and the warning lamp D is lighted.
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