| 摘要 |
To provide a current estimation circuit that can achieve a reduction in cost, a miniaturization, and a suppression of switching loss, and estimate an inductor current with a high degree of accuracy, despite a variation in the inductance value of the inductor. A current flowing through a switching element (5) is detected by current detection means (8), and a capacitor (201) is charged by a signal voltage corresponding to the current. A reduction factor of a terminal voltage of the capacitor in an off period of the switching element (5) is calculated based on an amplification factor of the terminal voltage of the capacitor, an absolute value of an instantaneous value of an input power supply voltage, and an instantaneous value of a direct current output voltage, and the capacitor is discharged so that the terminal voltage of the capacitor decreases by the reduction factor in an off period of the switching element (5). A current flowing through an inductor (4) is estimated from the terminal voltage of the capacitor.
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