| 摘要 |
PURPOSE:To prevent a negative voltage from being applied to an input terminal of an IC connected to a DC pulse circuit, by clamping a negative voltage produced in this circuit comprising a switching element, a capacitor and a resistor. CONSTITUTION:When a potential at a point C goes to a low potential, a transistor TRTR1 turns on, and a TRTR2 turns off, then the voltage of diodes D2, D1 goes to zero, and the potential at a point A goes to a positive side. When the point C goes to a high potential, the TRTR1 is turned on, then a voltage Vcc is applied to the diode D1 through a resistor R3, a current flows to a grounding point VSS through the diode D1, and the anode potential of the diode D1 is increased by the forward voltage drop of the diode D1. On the other hand, the anode of the diode D2 is connected to a point E, the cathode is connected to the point A going to be drawn to the negative polarity with the discharge of the capacitor C, allowing to clamp the potential at the point A to the cathode potential of the diode D2. |
