17-05-2017, 06:50 PM
(17-05-2017, 06:14 PM)ppppenguin Wrote: One of the most important things to understand about transistors is that they are voltage amplifiers, not current amplifiers. Yes a change in base current will give a bigger change in collector current but base current is actually a nuisance, something that we have to put up with. Designers have to make their circuits work despite base current which will vary a lot with teperature and between different devices.
Many people have written that transistors are current amplifiers. They are wrong. Any article that claims this should be taken with a large pinch of salt as the author clearly doesn't understand how transistors work.
I'm sorry but I have to disagree, the relationship between collector current and base current is reasonably linear over quite a wide range.
On the other hand the relationship between base voltage and collector voltage is not...
The base current is exponentially related to the base voltage (wrt the emitter) and for a linear collector load (e.g. a resistor) the collector voltage will be a linear function of the collector current.
Thus the voltage gain of a transistor is an exponential function.
( Without a collector load the voltage gain would depend on the transistors output resistance and feedback voltage (Early effect).)
I would agree that a FET may be regarded as a voltage amplifier in similar fashion to a valve but not a Bipolar transistor.
Jim
