Abstract: A switching amplifier including a PWM circuit 14, a driver 15, a switching output circuit 16 and an LPF 17 is provided with a fluctuation detection circuit 12 for detecting fluctuations in the power supply voltage. The fluctuation detection circuit 12 includes detection resistors 122 and 123 connected in series between a positive power supply 19 and a negative power supply 20. A fluctuating signal RPL occurring at a fluctuation detection terminal 121 is supplied to the inverted input terminal of a differential amplifier 131 of a non-inverted amplifier circuit 13. The non-inverted amplifier circuit 13 inverts the fluctuating signal RPL, mixes the inverted fluctuating signal into the input signal eS, amplifies the mixed signal, and supplying the amplified signal to the PWM circuit 14.

Abstract: A switching amplifier including a PWM circuit 14, a driver 15, a switching output circuit 16 and an LPF 17 is provided with a fluctuation detection circuit 12 for detecting fluctuations in the power supply voltage. The fluctuation detection circuit 12 includes detection resistors 122 and 123 connected in series between a positive power supply 19 and a negative power supply 20. A fluctuating signal RPL occurring at a fluctuation detection terminal 121 is supplied to the inverted input terminal of a differential amplifier 131 of a non-inverted amplifier circuit 13. The non-inverted amplifier circuit 13 inverts the fluctuating signal RPL, mixes the inverted fluctuating signal into the input signal eS, amplifies the mixed signal, and supplying the amplified signal to the PWM circuit 14.

Abstract: In a switching power supply of the present invention, when a voltage output from start-up means is greater than a driving voltage produced by output means, the voltage from the start-up means is provided to control means, whereby the switching power supply can be started up reliably. Furthermore, when the voltage output from the start-up means is less than the driving voltage produced by the output means, the current path is blocked in the start-up means so that no voltage is provided to the control means from the start-up means, whereby it is possible to reduce the power consumption during the steady operation.

Abstract: In a switching power supply of the present invention, when a voltage output from start-up means is greater than a driving voltage produced by output means, the voltage from the start-up means is provided to control means, whereby the switching power supply can be started up reliably. Furthermore, when the voltage output from the start-up means is less than the driving voltage produced by the output means, the current path is blocked in the start-up means so that no voltage is provided to the control means from the start-up means, whereby it is possible to reduce the power consumption during the steady operation.