| 摘要 |
In order to avoid a ripple voltage and to ensure that an adequate voltage is applied to a load even when a supply voltage is low, the duty ratio of a PFM type switching regulator is provided with a supply voltage dependency. A control circuit for a PFM type switching regulator according to a first embodiment comprises a first circuit for producing a first output signal based on a difference between a fed back portion of a regulated output voltage of a PFM type switching regulator and a first reference voltage; and a second circuit for producing a second output signal based on a second reference voltage, the second output signal being used for modulating the first output signal and including a pulse signal having successive pulses the width of which is dependent upon the value of the second reference voltage so that the duty cycle of the PFM type voltage regulator is dependent upon the second reference voltage. The second reference voltage varies depending upon the value of a power supply voltage of the PFM type switching regulator so that the duty ratio is increased when the power supply voltage decreases and the duty ratio decreases when the power supply voltage increases.
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