Transistor cutoff and saturation

[pjbullock]

Hi Guys,

I want to use a transistor as a switch not an amplifier, therefore I need to use cutoff and saturation. What components do I need to do this and can someone suggest a circuit, please?

Thx

PJ.

[David]

This is very simple, and merely consists of putting sufficient base current into the transistor, which will cause the transistor to switch between cut off and saturation. The detail depends on exactly what you are using the switch for. I would recommend that you get a good book on electronics and peruse that to expand your knowledge. Various books have been recommended on this site.

[Fractal Cat]

Hi,

I'm trying to create a temperature alarm using a transistor and a thermistor. I want to be able to just turn the transistor to fully on and fully off so that the LED
indicator is either on or off; it shouldn't increase in intensity in a linear fashion, It is either completely on or off and nowhere in between.

Thx

PJ.

[Pauldf]

It may be worth looking up darlington pairs, these use two transistors to create a very high gain which is what you sound like you want.
I know we used to use BC108 and BFY51 transistors in this configuration but you can get darlington transistors such as the TIP110

The other option is to build a comparator circuit using op amps.