Patent ID: 7932710
Filing Date: 2011-04-26
Classification: H02M

Abstract:
1. A step-up circuit configured to be connected to a first capacitor and a second capacitor, comprising: a power supply terminal which is applied with a voltage source voltage; a first capacitor connecting terminal which is configured to be connected to one electrode of the first capacitor and through which the step-up voltage generated by stepping up the voltage source voltage is output; a first rectifier element which is provided on a current path from the power supply terminal to the first capacitor connecting terminal such that a direction from the power supply terminal toward the first capacitor connecting terminal is a forward direction; a second rectifier element which is provided on a portion of the current path which is between the first rectifier element and the first capacitor connecting terminal such that a direction from the first rectifier element toward the first capacitor connecting terminal is a forward direction; a second capacitor connecting terminal which is configured to be connected to one electrode of the second capacitor and is applied with an oscillating voltage; a third capacitor connecting terminal which is connected to a portion of the current path which is between the first rectifier element and the second rectifier element and configured to be connected to the other electrode of the second capacitor; and a switching element connected to a portion of the current path which is between a connection point, where the third capacitor connecting terminal is connected to the current path, and the power supply terminal, wherein a control terminal for controlling ON and OFF of the switching element is connected to the first capacitor connecting terminal, the switching element is turned ON when a voltage at the first capacitor connecting terminal is higher than a voltage at the third capacitor connecting terminal by a specified voltage or larger, and the switching element is turned OFF when the voltage at the first capacitor connecting terminal is not higher than the voltage at the third capacitor connecting terminal by the specified voltage or larger.