My Circuit

Zener diode ZD1 senses the supply, and should the supply rise above 6 V, Ql will turn on. In turn, Q2 conducts clamping the rail. Subsequent events depend on the source supply. It will either shut down, go into current limit or blow its supply fuse. None of these will damage the TTL chips. The rating of Q2 depends on the source supply, and whether it will be required to operate continuously in the event of failure. Its current rating has to be in excess of the source supply. Over voltage protection for logic Circuit Diagram

We can construct simply logic functions for our hypothetical lamp circuit, using multiple contacts, and document these circuits quite easily and understandably with additional rungs to our original “ladder.” If we use standard binary notation for the status of the switches and lamp (0 for unactuated or de-energized; 1 for actuated or energized), a truth table can be made to show how the logic works: Now, the lamp will come on if either contact A or contact B is actuated, because all it takes for the lamp to be energized is to have at least one path for current from wire L 1 to wire 1. What we have is a simple OR logic function, implemented with nothing more than contacts and a lamp. We can mimic the AND logic function by wiring the two contacts in series instead of parallel: Now, the lamp energizes only if contact A and contact B are simultaneously actuated. A path exists for current from wire L 1 to the lamp (wire 2) if and only if both switch contacts are closed. The logi...

Introduction Logic states  True  False 1 0 High Low +Vs 0V On Off Logic gates process signals which represent   true   or   false . Normally the positive supply voltage +Vs represents true and 0V represents false. Other terms which are used for the true and false states are shown in the table on the right. It is best to be familiar with them all. Gates are identified by their function: NOT, AND, NAND, OR, NOR, EX-OR and EX-NOR. Capital letters are normally used to make it clear that the term refers to a logic gate. Note that logic gates are not always required because simple logic functions can be performed with switches or diodes: Switches in series (AND function) Switches in parallel (OR function) Combining IC outputs with diodes (OR function) Logic gate symbols There are two series of symbols for logic gates: The  traditional symbols  have distinctive shapes making them easy to recognise so...