Excitation current detection circuit and semiconductor device

Abstract

An excitation current detection circuit is disclosed. A transformer comprises a primary winding, an auxiliary winding, and a secondary winding. A first voltage detector detects a positive voltage of an auxiliary winding voltage. A second voltage detector detects a negative voltage of the auxiliary winding voltage. A first voltage controlled oscillator generates a first clock with a frequency proportional to the positive voltage during a period when the auxiliary winding voltage is the positive voltage. A second voltage controlled oscillator generates a second clock with a frequency proportional to the negative voltage during a period when the auxiliary winding voltage is the negative voltage. A counter outputs a counter value, which is added in one of cycles of the first clock and the second clock and subtracted in the other cycle of the first clock and the second clock as a detected value of an excitation current.