| 摘要 |
PURPOSE:To obtain a line signal receiving circuit upon which the influence of an AC induced noise is difficult, by providing an AC induced signal by-passing filter circuit consisting of a capacitor and a resistance between the anode and the cathode of a photocoupler. CONSTITUTION:When the AC induced noise is applied and a current LAC flows in from an input terminal SR, a current IFAC' flows to the anode of a photocoupler PC; however, a current ICAC is by-passed through a capacitor C because the by-pass circuit consisting of the capacitor C exists. Values of the capacitor C and a resistance R2' are selected properly to set the value of the current I'FAC to a value smaller than a threshold current IFTH required for turning on the photocoupler PC thereby obtaining the line receiving circuit which is not affected by the AC induced noise. |
