| 摘要 |
PURPOSE:To protect a logic circuit by providing a capacitor between a signal line and an earth of the logic circuit and connecting the 2nd diode to the earth so as to allow the circuit to show a low impedance to a negative surge voltage. CONSTITUTION:A resistor 24 is arranged to discharge an electric charge of a capacitor 23 and a resistor 28 is arranged to limit a current flowing to a contact 4 by the discharge of the capacitor 23 when the contact 4 is closed. When a positive surge is fed to an input terminal 6 of a device 27, since the diode 22 exists in reverse polarity to the positive surge, the surge is absorbed by the capacitor 23 and the surge voltage is divided by the resistor 25 so as to protect the logic circuit 8. When a negative surge is fed to the input terminal 6, the surge path is short-circuited by the diode 21 and the surge is absorbed and blocked by the capacitor 23 and the resistor 25 to protect the logic circuit 8. |
