Patent ID: 7511472

Claim:
A power measuring apparatus, comprising: a voltage transformer, for converting an input voltage signal into an output voltage signal, comprising: a pulse width modulation unit, for generating a pulse width modulation signal according to a voltage reference signal and a voltage feedback signal; and a switch unit, coupled to the pulse width modulation unit for deciding whether or not to output the input voltage signal so as to generate the output voltage signal according to the pulse width modulation signal; a voltage-current measuring circuit, comprising: an inductor, having a first end for receiving the output voltage signal and a second end for generating the voltage feedback signal; a first resistor, having a first end coupled to the first end of the inductor; a first capacitor, having a first terminal coupled to a second end of the first resistor and a second terminal coupled to the second end of the inductor; and a second capacitor, having a first terminal coupled to the second end of the inductor and a second terminal coupled to a ground terminal; and an operation unit, for conducting an operation on the voltage feedback signal and a terminal current signal between the first terminal and the second terminal of the first capacitor so as to calculate a power, wherein the operation unit comprises: a current amplifier, having a first terminal and a second terminal respectively coupled to the first terminal and the second terminal of the first capacitor for converting the terminal current signal into a one-phase current signal; a voltage amplifier, having a first terminal for receiving the voltage feedback signal and a second terminal coupled to the ground terminal to gain the voltage feedback signal; a first analog-to-digital converter, for converting the one-phase current into a digital current signal; a first multiplier, for multiplying the digital current signal by a number and generating a total output current signal; and a second analog-to-digital converter, for converting the gained voltage feedback signal into a digital voltage signal; and a second multiplier, for multiplying the total output current signal by the digital voltage signal to obtain the power signal.