I need to use an NPN transistor to switch between no current and ground to control an SN74LS08N AND gate. I want a circuit to function as a switch, so that when the switch circuit is being powered, nothing will be outputted as a result, which is how you make the AND gate receive a 1. When it isn't powered, the switch circuit will be connected to ground, which is how you make the AND gate receive a 0.
6
-
1\$\begingroup\$ "but output a signal from ground when the signal is a 0" ????? Ground, ideally, has no signal - it is the 0V reference - a constant 0V. I honestly don't understand what you want. Do you mean you want the output to be 0V when the input is 0V? Do you want the output to be an open circuit ("nothing") when the input is some non-zero current? \$\endgroup\$– Alfred CentauriCommented May 3, 2014 at 3:52
-
\$\begingroup\$ Sounds like you want a PNP instead. \$\endgroup\$– Ignacio Vazquez-AbramsCommented May 3, 2014 at 3:52
-
\$\begingroup\$ need more details...states are No current and GND ---> how they will control AND gate...elaborate ..? \$\endgroup\$– user19579Commented May 3, 2014 at 4:16
-
1\$\begingroup\$ You want to control an AND gate, that much is clear, but what are you trying to accomplish with the transistor? The only real reason to hang a transistor in front of some logic is if you need to massage an input that is not at logic levels so it can drive the logic. It almost sounds like you are trying to use the transistor to invert something, but you didn't specify that something. Come back with something like "I want the AND gate input to be a logic low when the input is blah volts or more", and so on, and you will get better results. \$\endgroup\$– JustJeffCommented May 3, 2014 at 4:28
-
\$\begingroup\$ You'll have to add a lot more detail on what you are trying to accomplish. "switch between no current and ground" is unclear. "to output nothing when it is given current" unclear what you are asking. "output a signal from ground when the signal is a 0" unclear. Please elaborate. \$\endgroup\$– jippieCommented May 3, 2014 at 8:04
|
Show 1 more comment
1 Answer
\$\begingroup\$
\$\endgroup\$
You probably want something like this. When input is low, pullup will keep second transistor active. When signal gets high, first transistor will conduct and "connect" second one to ground thus turning it off.
simulate this circuit – Schematic created using CircuitLab
