To achieve more accurate detection of voltage from a commercial AC source than ever before even if the voltage from the commercial AC source is distorted.
A zero-cross and voltage detection circuit 120 generates a pulse wave with a duty ratio corresponding to a peak value of output voltage from a diode bridge 2 or DC voltage from a primary electric field capacitor 3. A CPU 29 receives the pulse wave, obtains the duty ratio of the pulse wave and estimates the voltage from a commercial AC source 1 from the duty ratio. The peak value of the output voltage of the diode bridge 2 or the DC voltage from the primary electric field capacitor 3 is hardly affected by distortion. Therefore, the invention enables more accurate detection of the voltage from the commercial AC source 1 than ever before.
Shiro Takayanagi
Yasuhiro Otsuka
Shuji Kimura
Osamu Shimoyama
Nagakawa Yukimitsu
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