Patent attributes
A power supply voltage booster avoids inadequate step-up capability. In a voltage boosting circuit, a switching device connects and disconnects between the ground potential and one end of the coil, the other end of which is supplied with a supply voltage VB. The switching device is repeatedly turned ON and OFF such that the capacitor is electrically charged from the force in the coil when the switching device is turned off. A charging control circuit turns off the switching device when current flowing through the switching device into the coil is determined to have increased to a switch-off threshold value when the switching device is ON, and turns on the switching device upon determining that the charging current flowing to the capacitor from the coil decreases to a switch-on threshold value when the switching device is OFF. The charging control circuit sets the switch-off threshold value to a larger value as the supply voltage VB is lower. Thus, inadequacy of the step-up capability caused by a drop in the supply voltage VB can be avoided.
