the transistor as a switch

[sonaiko]

I have 2 nodes that has 13v RMS voltage difference in the idle situation.
I want to control those 2 nodes by PC such that when i produce a 5v from my parallel port a short circuit between those 2 nodes must happen.

how can i do that?
I will ask again in a different way:
- 2 nodes, have 13v RMS in the usual state (normal state).
- when i turn on a voltage source i have (PC parallel port) with 5v i want the two nodes to be shorted.
- else (when im supplying 0v) from my PC, i want them to have their 13v RMS difference.

can u help me guys?
I thought of using the transistor as a switch, putting a 1v between B and E so that it is ON, and i put the 5v from PC between E and B (+ve is on E side) so it becomes OFF when i supply the 5v. But it doesnt work becoz the terminals will have the baising value not the origional value they have.

what should i do plz help?

 

[Screech]

can u help me guys?
I thought of using the transistor as a switch, putting a 1v between B and E so that it is ON, and i put the 5v from PC between E and B (+ve is on E side) so it becomes OFF when i supply the 5v. But it doesnt work becoz the terminals will have the baising value not the origional value they have.

what should i do plz help?

Your idea of how to turn on and off transistors is wrong.

 

[Screech]

THIS pic might be of interest

 

[audioguru]

An optically isolated Triac will join together two AC signals if you can tolerate the voltage drop.
A relay will do the trick even better. :lol:

 

[Nigel Goodwin]

what should i do plz help?

For a start, how about actually telling us EXACTLY! what you are wanting to do?. This 'nodes' rubbish is no use whatsoever!.

An obvious simple solution is to use a transistor driver feeding a relay, which would work for almost anything - but you still need to select a suitable relay!.

 

[Screech]

For a start, how about actually telling us EXACTLY! what you are wanting to do?. This 'nodes' rubbish is no use whatsoever!.

I can't stop laughing. :lol:

 

[Phasor]

An optically isolated Triac will join together two AC signals if you can tolerate the voltage drop.
A relay will do the trick even better. :lol:

Or a Solid State Relay, if you want faster response.

 

[kazakhan]

The following link might help.
**broken link removed**