Patent ID: 8018216
Filing Date: 2011-09-13
Classification: F02D,H02M

Abstract:
1. A power supply voltage booster comprising: a coil including one end supplied with a power supply voltage; a switching device including two output terminals connected in series to a path between an other end of the coil and a reference electrical potential lower than the power supply voltage; a diode including an anode connected to a current path that connects the other end of the coil and a one of the output terminals of the switching device, the one located closer to the coil; a capacitor having a first terminal and a second terminal, the capacitor connected in series to a path between cathode of the diode and the reference electrical potential; and a controller configured to perform a voltage-boost switching control for repeatedly switching the switching device between an ON position and an OFF position to produce a counter-electromotive force in the coil according to a control condition, and charges the capacitor with the counter-electromotive force so that a voltage higher than the power supply voltage is produced in the first terminal of the capacitor, the first terminal being farther away from the reference electric potential than the second terminal, wherein the controller changes the control condition for the voltage-boost switching control to increase an amount of the counter-electromotive force applied per fixed time to charge the capacitor when the power supply voltage becomes low; during the voltage-boost switching control, the controller detects a charging current flowing into the capacitor from the coil when the switching device is in the OFF position, and turns the switching device from the OFF position to the ON position when the controller determines that the current decreases to a switch-on threshold value, and the controller changes the switch-on threshold value, as the control condition, in accordance with the power supply voltage to increase the switch-on threshold value when the power supply voltage becomes low.