| 摘要 |
A current detecting circuit is provided to improve detection precision by canceling offset voltage of an operational amplifier and to add voltage drop degree by integrating the voltage drop degree at a current detecting resistor. A current detecting circuit for detecting current flowing in a current detecting resistor(Rs), by difference between voltages of both ends of the current detecting resistor is composed of a first capacitor(Cf) of which one end receives upper and lower voltages of the current detecting resistor through first and second switches(S1,S2); a third switch(S3) switching the state for determining whether to supply reference voltage(VREF) to the other end of the first capacitor; and an operational amplifier(OP) having a minus input stage receiving voltage corresponding to the voltage of the other end of the first capacitor and a plus input stage receiving reference voltage, and obtaining difference between the voltage inputted to the minus input stage and the reference voltage. While the first and third switches are turned on and the second switch is turned off, the first capacitor is charged with voltage corresponding to difference between the lower voltage of the first capacitor and the reference voltage. While the first and third switches are turned off and the second switch is turned on, voltage corresponding to the sum of difference between the upper and lower voltages and the reference voltage is obtained from the other end of the first capacitor. Difference between voltages of both ends of the current detecting resistor is detected by subtracting the reference voltage from the voltage corresponding to the sum of difference between the upper and lower voltages and the reference voltage.
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