| 摘要 |
PROBLEM TO BE SOLVED: To prevent saturation in transistors forming a differential circuit to feed a reference voltage, by keeping the potentials of the transistors equal to such ones that the transistors are not brought into saturation when their power supply is on, and by cutting off the driving current to the differential circuit from a current source when the power supply is off. SOLUTION: In a saturation preventing circuit 3, keeping the collector potentials of the transistors Q21, Q22, to a reference voltage BV, equal to such ones that the transistors Q21, Q22 are not brought into saturation states when their power supply is in ON-state, the driving current of a differential amplifier 2A is stopped when the power supply is off. Thereby, the npn transistor Q21 of the differential amplifier 2A whereto the reference voltage BV is fed can be prevented from being saturated. Therefore, in a circuit used by a single power supply, the saturations of the transistors forming a differential circuit with a reference voltage can be prevented. Thereby, noises can be prevented from being outputted from an input terminal to having originally high impedance. |
