[Moved] why npn tr not suitable as switch

[ajays2539]

hello, need help,, why npn tr not suitable as switch for analog signals

 

[Audioguru]

Where is your schematic??

 

[BradtheRad]

Spec tables list some transistors as 'switch' and some as 'amplifier'. This is not necessarily binding in all cases.

A transistor can be turned into a switch by operating it at very high gain.

Often the analog signal will need to be conditioned. You need to add the right amount of bias. Etc.

 

[BrunoARG]

Every NPN transistor can work both as switch and as amplifier. Depending of the device model you will find different characteristics as gain, bandwith (commonly the PGB product between these), response times and junction capacitances.

At the beginning of the datasheet is easy to know what the transistor is designed to work as, the manufacturer gives you information about it.

Some BJT transistors are faster than FET when switching, but as I told you before, it depends of the model.

Which transistor do you suppose that can't work as switch? How fast is your application?

 

[Audioguru]

Ajays, you said you want to use an NPN transistor "as a switch for analog signals".
Do you want to switch the audio signal from an MP3 player and the audio signal from an FM tuner to an amplifier? Then we use a Cmos Bilateral switch (like a CD4066) , not a transistor.