Patent ID: 8368363

Claim:
A current sensing circuit configured to sense current flowing through a switching transistor of a non-insulated switching regulator, wherein the non-insulated switching regulator includes: the switching transistor being configured to perform switching in accordance with a first control signal input to a control terminal and to supply current supplied from a power input terminal to an inductor, and a rectifier element being configured to carry current supplied from the inductor when the switching transistor is turned off, and wherein the non-insulated switching regulator is configured to convert the input voltage to a predetermined constant voltage and to output the predetermined constant voltage as an output voltage from an output terminal, the current sensing circuit, comprising: a voltage divider circuit portion configured to divide and output a voltage across the switching transistor; a first transistor including a first current input terminal and a first output terminal, wherein the first current input terminal is connected to an output terminal of the voltage divider circuit portion, and wherein a predetermined first load is connected between the first current output terminal and the ground; a first impedance element including first and second ends, wherein the first end is connected to the power input terminal and configured to be supplied with input voltage from the power input terminal, and wherein an impedance of the first impedance element varies in accordance with a second control signal; a second transistor including a second current input terminal and a second current output terminal, wherein the second current input terminal is connected to the second end of the first impedance element, and wherein a predetermined second load is connected between the second current output terminal and the ground; a third transistor including a third current input terminal and a third current output terminal, wherein the third current input terminal is connected to the second end of the first impedance element, and wherein a first constant current source is connected between the third current output terminal and the ground; and a first voltage comparing circuit portion configured to compare a voltage at a connecting portion between the first transistor and the predetermined first load and a voltage at a connecting portion between the second transistor and the predetermined second load, and to output a signal indicating a comparison result of currents flowing through the switching transistor, wherein control terminals of the first transistor, the second transistor, and the third transistor are connected to each other and a connecting portion of the control terminals is connected to a connecting portion between the third transistor and the first constant current source.