| 摘要 |
PROBLEM TO BE SOLVED: To provide a ripple filter circuit, that can eliminate ripple components superimposed by a switching regulator which appear at the output terminal of an operational amplifier. SOLUTION: In this ripple filter circuit, a connecting point between a resistor 4 and a capacitor 5 is connected to a base of an NPN transistor(TR) 6, and an emitter of the NPN TR 6 is connected to a constant current source 8 via a resistor 7. The base of a PNP TR 14 is connected to a connecting point between the resistor 7 and a constant current source 8, a collector of the PNP TR 14 is connected to ground, and the emitter is connected to a terminal 3. A capacitor 15 is connected between the terminal 3 and a ground terminal 2, to furthermore improve a ripple suppression ratio. A ripple suppression ratio which becomes higher toward higher frequencies can be obtained, by a characteristics of a low-pass filter by a CR filter consisting of the resistor 4 and the capacitor 5. Eliminating high-frequency ripple components increases the ripple suppression ratio, to decrease the voltage between a power supply terminal and an output terminal and the power supply utilization ratio can be enhanced without narrowing the dynamic range.
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