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This shows a current source, a device that provides a constant amount of current (1.4mA in this case), regardless of the position of the switch. The transistor's base voltage is fixed at 1.98V by a voltage divider, which causes a fixed amount of current to flow through the base (14µA). The collector current will be 100x that, as long as the collector voltage is not too low relative to the base.

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Generated Sat Nov 15 2014