Electrical – BJT as switch to let AC through

acbjtswitchestransistors

I am wondering if this is possible, because all the textbook cases I have seen of using the BJT with an AC source involves an AC input and then an amplified AC output… what i would like to do is use it as a switch to either block the AC or let it through. This is because I want to control the AC with 5v logic. Is this possible? I could always use an actual switch to turn on and off the AC but..well isnt the BJT suppose to be able to do the job if configured properly… or does "BJT as a switch" not REALLY mean a switch.

Ignore the values of the components i paid them no mind i just wanted to graphically represent what i am considering.

The AC is going to be small voltage signal out of a function generator, not mains.
Example

Best Answer

No this is not possible, at least not with a circuit like this.

Transistors can be used to amplify AC signals but only such that the current will never be smaller than zero. That's why in (AC) amplifiers transistors transistors are biased with a certain DC current, for example 10 mA.

Then we can vary that 10 mA by for example a 5 mA AC signal. So the actual current through the transistor will actually vary between 5mA and 15 mA.

Here's an explanation.

This is called biasing a transistor.

You could switch off the biasing and that would stop the transistor from amplifying the signal. That could work for small audio signals for example.

To switch a large AC signal you need a more elaborate circuit. It depends on the properties of the AC signal what kind of circuit you would need.

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