Transistor

A Transistor can be thought of as a device that is active in only one direction: it can draw more or less current through its load resistor (sometimes referred to as a pull-up resistor).


It can either Source Current or it can Sink Current, it cannot do doth.

Since the Transistor is a Current device, any signal Voltage must first be converted to a Current.

Voltage to Current Convertor

First, you must convert the input voltage to a current by using a Voltage to Current Convertor -- a resistor.

Current to Voltage Convertor

Next, convert the output current into a voltage by using a Current to Voltage Convertor in the collector circuit -- also a resistor.



Note voltage to current convertor in the base circuit, a.k.a. current limiting resistor. This following animation is illustrating current limiting resistor...


The results when driving the transistor's base directly with no voltage to current convertor: