| Electronics > Beginners |
| Whats the purpose of using 3 transistors in an AND gate? |
| (1/4) > >> |
| Beamin:
What is the purpose of Q3? Wouldn't just two transistors work? Or is it to hold the circuit at ground when not on? To figure this out would you need the values of the R's? |
| oPossum:
It would be a NAND gate without Q3. |
| ledtester:
The transistors will either be off or driven into saturation, so the precise values of the R's are not important. For instance, using 1K for for all of the R's would probably work, or even 10K. The resistor values used will determine the drive capability (fan-out) of the gate. |
| Zero999:
The collector load resistors should have a much lower value, than the base resistors. If the NAND part isn't being used to drive other circuits, then R5 can be omitted. |
| Beamin:
--- Quote from: oPossum on August 20, 2019, 12:51:15 pm ---It would be a NAND gate without Q3. --- End quote --- Im reading about these and the same page where I got the above schematic from says this is how you would make a nand gate which is clearly different. :-// EDIT: here is another picture of an OR gate that might help me figure out whats going on, what is the point of R4 in the ORgate/2nd attachment pic circuit |
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