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NPN TRANSISTOR BASE EMITTER COLLECTOR SERIES

Transistor Action More on transistor regions The base-emitter voltage V BE varies slightly with the collector-emitter voltage V CE at constant collector current I C : ΔV BE ≈ -0.001ΔV CE.The base-emitter voltage V BE is temperature dependent, decreasing about 2.1 mV/C.

NPN TRANSISTOR BASE EMITTER COLLECTOR SERIES

The effective AC series resistance of the emitter is about 25/I C ohms.

An increase in base-emitter voltage V BE by about 60 mV will increase the collector current I C by about a factor of 10.

A base emitter voltage V BE of about 0.6 v will "turn on" the base-emitter diode and that voltage changes very little, < +/- 0.1v throughout the active range of the transistor which may change base current by a factor of 10 or more.

The value of β is not highly dependable since it depends on I C, V CE, and the temperature.īase-Emitter Junction Details Some useful "rules of thumb" which help in understanding transistor action are (from Horowitz & Hill): A further useful relationship is I C=βI B This relationship is stable over a wide range of voltages and currents. The saturation current is characteristic of the particular transistor (a parameter which itself has a temperature dependence).

The collector current is related to this voltage by the Ebers-Moll relationship (sometimes labeled the Shockley equation): The base-emitter voltage V BE can be considered to be the controlling variable in determining transistor action. In saturation (collector a few tenths of a volt above emitter), large current useful for " switch on" applications.In the active region (some collector current, more than a few tenths of a volt above the emitter), useful for amplifier applications.Cut off (no collector current), useful for switch operation.Transistor Operating Details Transistor OperationA transistor in a circuit will be in one of three conditions