| 摘要 |
PURPOSE:To prevent the production of an abnormal current flowing through an input pin without lowering the static dielectric strength of the input pin by connecting the 3rd diode in series with the protection diode in opposite polarity connected between power voltage terminal at the high potential side and the input pin in an input protection circuit comprising protection diodes. CONSTITUTION:The 3rd diode d3 in reverse polarity is connected to the protection diode d2 provided to the power supply voltage VCC. Thus, even when a voltage in excess of the forward voltage Vth of the diode d2 and the power supply voltage VCC is applied to an input terminal 1, no current flows through the diodes d2, d3. Thus, even with a signal of a TTL level given to the input terminal 1, no fault current flows from the input terminal 1 up to the power voltage VCC. When a very high voltage due to static electricity is applied to the input terminal 1, a breakdown voltage takes in the Zener diode d3 and a large current flows toward the power voltage VCC momentarily and the destruction of the input TR Q1 is prevented.
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