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A current collector (often called a "pickup") is a device used in trolleybuses, trams, electric locomotives and EMUs to carry electric power from overhead lines, electric third rails, or ground-level power supplies to the electrical equipment of the vehicles.
When no signal is applied, a DC current I C will flow in the collector circuit due to the battery. This is known as zero signal collector current. [1] The value of zero signal collector current should be at least equal to the maximum collector current due to AC signal alone.
The collector–emitter current can be viewed as being controlled by the base–emitter current (current control), or by the base–emitter voltage (voltage control). These views are related by the current–voltage relation of the base–emitter junction, which is the usual exponential current–voltage curve of a p–n junction (diode).
The transistor continuously monitors V diff and adjusts its emitter voltage to equal V in minus the mostly constant V BE (approximately one diode forward voltage drop) by passing the collector current through the emitter resistor R E. As a result, the output voltage follows the input voltage variations from V BE up to V +; hence the name ...
The pantograph is a common type of current collector; typically, a single or double wire is used, with the return current running through the rails. Other types of current collectors include the bow collector and the trolley pole.
Some models base the collector current correction factor on the collector–base voltage V CB (as described in base-width modulation) instead of the collector–emitter voltage V CE. [3] Using V CB may be more physically plausible, in agreement with the physical origin of the effect, which is a widening of the collector–base depletion layer ...
Collector current and emitter current are related by I c = α I e with α ≈ 1, so the increase in emitter current with temperature is opposed, and the operating point is kept stable. Similarly, if the transistor is replaced by another, there may be a change in I c (corresponding to change in β-value, for example).
2N2222A in metal TO-18 package with the emitter, base and collector identified as E, B, and C respectively. Cross section of 2N2222 in metal TO-18 package, showing connection wires between external pins and die. The 2N2222 is a common NPN bipolar junction transistor (BJT) used for general purpose low-power amplifying or switching applications.