Hysteresis comparator circuit consuming a small current

DETAILED DESCRIPTION It is a general object of the present invention to provide an improved and useful hysteresis comparator circuit in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a hysteresis comparator circuit and a waveform generating circuit which can reduce a power consumption of a DC/DC converter so as to improve a power consumption efficiency when the DC/DC converter is operated with a relatively small load.
In order to achieve the above-mentioned objects, there is provided according to the present invention a hysteresis comparator circuit adapted to be connected to a reference voltage source providing a reference voltage, the hysteresis comparator circuit comprising: a hysteresis comparator comparing an input voltage with one of a first threshold voltage and a second threshold voltage different from the first threshold voltage; and a hysteresis voltage generating circuit comprising a plurality of capacitors so as to selectively generate one of the first threshold voltage and the second threshold voltage by controlling a state of electric charge stored in each of the capacitors, the electric charge stored in the capacitors being provided from the reference voltage source.
According to the above-mentioned invention, the first and second threshold voltages which provide a hysteresis characteristic can be generated by the plurality of capacitors without using a plurality of resistors as in the conventional circuit.
Thus, an electric power consumed by the hysteresis comparator circuit is only a current to charge the capacitors.
Thus, the electric power consumed by the hysteresis comparator circuit according to the present invention can be smaller than an electric power consumed by the conventional hysteresis comparator circuit using a plurality of resistive elements in which a current continuously flows through the resistive elements.
Accordingly, by applying the above-mentioned hysteresis comparator circuit to a waveform generating circuit of a DC/DC converter, a conversion efficiency of the DC/DC converter can be improved when the DC/DC converter is operated with a small load