US Patent 7323850 Current detection circuit and switching power supply using the same

A current detection circuit of the present invention has a switching device 1; an auxiliary switching device 2; an offset voltage source comprising an offset resistor device 7 and a current source circuit 8; a compensation circuit, comprising a differential amplifier 4 and a compensation transistor 5, for adjusting the output current of the auxiliary switching device 2 so that the potential obtained by subtracting the voltage drop across the offset resistor device 7 from the output potential of the switching device 1 is equal to the output potential of the auxiliary switching device 2, being configured that the detection level of the current flowing in the switching device 1 is shifted by an offset amount.