Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It only takes a minute to sign up.
Sign up to join this community
I only have 5 PNP transistors and I want to build two AND gates. (for a T Flip-Flop) What would be the simplest way to make an AND gate using PNP transistors? (It can't use more than 2 transistors)
This is the only way I found, but it uses way too many transistors.
A good way to build gates with limited numbers of transistors is to use RTL (resistor-transistor logic) techniques. For example, here is a NAND gate, which can be converted into an AND gate with an inverter:
simulate this circuit – Schematic created using CircuitLab
The fan-in and fan-out capabilities of this type of logic are not great, which is why it was abandoned once the development of ICs made the incremental cost of transistors essentially negligible. But it can be used to build moderately complex logic circuits if you don't care too much about the speed.
You could do this for a simple gate:
The function of this gate is LOW OR LOW = LOW. From DeMorgan's theorem, I can invert all inputs and outputs and change the gate type, so I get HIGH and HIGH = HIGH.
The image quality is not particularly good. Both collectors go to ground and I have not shown series input resistors. I would probably use about 100 ohms for starters. Both the pullup resistors go to the power rail.
