Large-signal Model
In the forward active region the Early effect modifies the collector current and the forward common-emitter current gain, as typically described by the following equations:
Where
- is the collector–emitter voltage
- is the thermal voltage ; see thermal voltage: role in semiconductor physics
- is the Early voltage (typically 15 V to 150 V; smaller for smaller devices)
- is forward common-emitter current gain at zero bias.
Some models base the collector current correction factor on the collector–base voltage VCB (as described in base-width modulation) instead of the collector–emitter voltage VCE. Using VCB may be more physically plausible, in agreement with the physical origin of the effect, which is a widening of the collector–base depletion layer that depends on VCB. Computer models such as those used in SPICE use the collector–base voltage VCB.
Read more about this topic: Early Effect
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