hi,
im having a temperature sensor, then in programming part it will on the transistor in the sensor circuit when the temperature is reached the desired value.
so is it the voltage in Transistor will increase to 5V?

 

I think a clearer statement of your problem would help. Also perhaps so help with your english. I am not able to figure out what the question is.

 

I think the OP wants 5V when the temperature hits a certain temperature. Why use a transistor when there are ICs that do this job off the shelf I do not know.

 

sorry, actually i'm trying to say if the output voltage of the temperature sensor is 0.45V.
so, is the the transistor can give an output of 5V if the output voltage of the temperature sensor is go through the transistor?

 

Nope, though you might be able to get a germanium transistors to do it. Silicon diodes have a breakover voltage of .6V (give or take) before they start responding.

Operational amplifiers sound like the ticket to me.

It would help if you could post your concept in a drawing. Schematics are the language of electronics.

If the transistor was already biased on (that pesky 0.6V I mentioned) you could get a transistor circuit to respond very will to the small change you are talking about.

 

i see...thanks a lot ya..