| 摘要 |
PURPOSE:To reduce the size of a device and to achieve economization by eliminating the need for a transformer, etc., by connecting the potential of the 2nd loop of a reference potential setting circuit as an input to a comparing circuit. CONSTITUTION:Since the output transistor (TR) Q of a row selective driving circuit is normally turned on, a current flows through the 1st loop of the ground, a scanning point, a resistance R1, a diode D1, the Q, and a power supply 1 when the scanning point is closed, and no current flows through the 2nd loop of the ground, the scanning point, the resistance, a diode D2, a resistance R2, and a power supply E. Therefore, a detecting circuit generates no output. When a row selecting circuit generates a driving signal to turn off the Q, the 2nd loop conducts and a potential at the connection point of the diode D2 and resistance R2 reaches a positive reference potential set by the resistances R3 and R4, so a comparing circuit COMP generates an output signal meaning that the scanning point is closed. |
