Patent ID: 7902905

Claim:
A voltage supply circuit comprising: a booster circuit; and a ripple filter circuit that has a first resistor connected to a first output terminal at one end thereof, a first switch circuit connected between the other end of the first resistor and a second output terminal, and a second switch circuit connected between the first output terminal of the booster circuit and the first switch circuit, wherein, if an output voltage at the first output terminal is equal to a first voltage, the first switch circuit is turned on, and the second switch circuit is turned off, if the output voltage at the first output terminal is equal to a second voltage higher than the first voltage, the first switch circuit is turned on, and the second switch circuit is turned on, and the booster circuit has a pump circuit having a plurality of charge pump circuits that boost a voltage supplied from a power supply and output the boosted voltage to the first output terminal; a pump controlling circuit that outputs a first clock signal for operating the pump circuit to control the operation of the pump circuit; a first variable resistor connected to the first output terminal at one end thereof; a second variable resistor connected to the other end of the first variable resistor at one end thereof; a third variable resistor connected to the other end of the second variable resistor at one end thereof; a limiter circuit that is connected between the other end of the third variable resistor and a ground potential, composed of a variable resistor, and capable of adjusting a current flowing through the first variable resistor, the second variable resistor and the third variable resistor; a first comparator that receives a first monitor voltage at the other end of the first variable resistor at an inverting input terminal thereof and a reference voltage at a non-inverting input terminal thereof; a second comparator that receives a second monitor voltage at the other end of the second variable resistor at an inverting input terminal thereof and the reference voltage at a non-inverting input terminal thereof; and a third comparator that receives a third monitor voltage at the other end of the third variable resistor at an inverting input terminal thereof and the reference voltage at a non-inverting input terminal thereof; and the pump controlling circuit controls the pump circuit to reduce a number of active charge pump circuits according to one of output signals of the first comparator and the second comparator, controls the pump circuit to reduce a frequency of a second clock signal for operating the active charge pump circuits by reducing a frequency of the first clock signal according to the other of the output signals of the first comparator and the second comparator, and brings the pump circuit into an inactive state according to an output signal of the third comparator.