Patent ID: 6977513

Claim:
A bidirectional-switch current detection circuit for a direct current power source, comprising: (a) a main bidirectional switch comprising two main transistors connected in series and being reversed in polarity with respect to one another, each main transistor comprising a respective parasitic diode connected thereto in parallel, the main bidirectional switch being insertable into a current path of the power source; (b) a mirror bidirectional switch comprising two mirror transistors connected in series and being reversed in polarity with respect to one another, each main transistor comprising a respective parasitic diode connected thereto in parallel; (c) a sensing resistor; (d) a feedback amplifying unit comprising two high impedance inputs and an output, wherein the output is coupled to the sensing resistor and wherein the main bidirectional switch and the mirror bidirectional switch are connected in parallel between the feedback amplifying unit and a connection point included, with the main bidirectional switch, in the current path of the power source, wherein each of the main bidirectional switch and the mirror bidirectional switch is connected to a respective one of the high impedance inputs at the feedback amplifying unit, and wherein the output of the feedback amplifying unit is connected through the sensing resistor to the high impedance input that is connected to the mirror bidirectional switch; and (e) a current detecting unit detecting a voltage across the sensing resistor, thereby carrying out detection of current in the main bidirectional switch; wherein each mirror transistor is formed such that a mirror current flowing therein, which is smaller than a main current flowing in a main transistor having the same polarity as that mirror transistor, is in a specified mirror ratio of the mirror current to the main current, when electric potentials of main electrodes of that mirror transistor and the main transistor having the same polarity are made equal.