control system

[weitao]

in control system, why have so many device like transistor? Wat is them function?

[Naty1]

The essence of a control system is feedback to control output. It may be positive or negative as described here:
http://en.wikipedia.org/wiki/Electronic_feedback_loops#Types_of_feedback

It's not directly related to a transister but is rather a circuit configuration.


The transister is used primarily as an amplifier, that is, boosting a weak input to provide a more powerful output.
Here is one brief explanation:
http://www.physlink.com/Education/AskExperts/ae430.cfm

Transisters are widely used in many circuits because of their efficiency....very low heat loss for example.....and fast response times..they replaced vacuum tubes which used a lot more power and could not be made nearly as small as solid state transisters.