| 摘要 |
PROBLEM TO BE SOLVED: To provide an electric circuit controlling voltage input to a constant voltage circuit so as not to greatly change and controlling a calorific value in the constant voltage circuit. SOLUTION: A plurality of series-connected diodes 8 and a plurality of NPN transistors 7 are provided between a battery 2 and the constant voltage circuit 4, wherein the number of diodes 8 placed between emitters and collectors of the plurality of NPN transistors 7 is increased one by one from 1 to N. And, the NPN transistor 7 to be turned on is determined depending on how much higher a voltage of the battery 2 is than 20 V. Specifically, 20 V is subtracted from the voltage of the battery 2, and the result divided by a forward voltage drop Vf for a single diode 8 makes the number of diodes 8 to be passed through between the battery 2 and the constant voltage circuit 4. Consequently, the NPN transistor 7 with the number of diodes 8 connected between its emitter and collector is set as the one to be turned on among the plurality of NPN transistors 7. COPYRIGHT: (C)2007,JPO&INPIT
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