logic-gates
I have been looking at AND gates and noticed there are a couple different ways to build them. I am wonder when each of the circuits is better than the other:
or
Also with the first circuit I am a little confused about how it works. If x and y are 5v then q3 will turn off. Why is this?
Also, if X and Y are 0v what prevents the current from just flowing directly from the power source into Z making it 5v?
Using an inverter is not going to work. You need to use shoot-through protection: -
The OR gate output needs to be inverted so an alternative is to use a NOR gate. It's going to work best when both AND and NOR/OR are schmitt trigger input types. For a quick simulation make the resistor 1k and the capacitor 10nF - this will give a "dead" area of about CR or 10us but clearly the time of the dead area is dependent on the application.
See also this stack exchange page.
It's pretty "brave" to connect (what I think are) 16V (18V abs max) logic chips directly to a 12V automotive supply. Automotive standards call for survival of transients much larger than that. At least you have a diode to prevent negative transients from zapping things.
Please give manufacturer part numbers not distributor numbers.
The NAND will get powered by the protection diodes whenever either input is high.
There is no current limiting- it's not for sure the wimpy little BAV21 diodes will survive charging the 10uF caps, nor is it clear what exactly discharges them.
There should be a series resistor on the SSR LED to limit the current.
I agree with @brhans comment- just stick a W04M in there and be done with it.
simulate this circuit – Schematic created using CircuitLab
Best Answer
Really wide question and neither is really great.
Option A is better if you want to drive something low.. like pulling current down through an LED connected to 5v.
simulate this circuit – Schematic created using CircuitLab
Option B is better for the converse if you want to supply current to some load.
simulate this circuit