The input and output protection circuit of digital integreted circuit

Published:2011/7/7 7:32:00 Author:Sophia | Keyword: Input and output, protection circuit, digital integreted circuit | From:SeekIC

Signal low level UIL of TTL circuit is less than or equal to 0.8V, high UIH is great than or equal to 2.0v. If external digital signal level it receives is within this range, there will be no proplem. In the actual circuit, due to various reasons, the input signal level will be high. Therefore, the input of the digital circuit should be protected from the circuit damaged. Figure is the most common protection circuit. In this circuit, the resistor R is the current limiting resistor, and diode VD1 and VD2 are used to limit the input signal level of digital circuit. The greater R-value, the better the protection, but the voltage drop on input current will be greater. Therefore. For TTL circuits, R should be 100Ω; for CMOS circuits, R is 1kΩ,which will be more appropriate.



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