Transistor Output Non-Inverting Tri-State Switch
In this example we use NPN Darlington transistors for the output switches.
When the EN pin is HIGH the output is the same as DIN. With EN pin low output is floating or Hi-Z.
This is a 5-volt TTL circuit but would be identical if using CMOS gates and a higher voltage up to 15-volts.
The problem becomes connecting to a 5-volt microcontroller. One must use some kind of logic voltage shift circuit.
See examples at Optocouplers for TTL-CMOS Logic Level Shifting.
Fig. 2 Transistor Output Non-Inverting Tri-State Switch truth table.
Fig. 3 Examples of creating AND-OR gates from NAND-NOR gates.
Fig. 4 H-bridge motor control based on tri-state switches.
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