Javalab [Javalab] Lars Drud Nielsen
ldn@oersted.dtu.dk

npn Transistor stage

The circuit is a primitive common-emitter (CE) amplifier comprising an npn-transistor and external basis-, collector- and load resistors.

The transistor is described by a simple model with fixed parameters VBEdiode = 0.6 V, VCEsat = 0.2 V, RCEsat = 50 W (Wakerly: Digital Design, 3rd ed., sec. 3.9.3). The current gain b of the transistor is adjustable.

Find for a fixed set of component parameters the ranges of input voltage that make the transistor cut off, active or saturated, respectively.

Analogue applications: Determine the differential voltage amplification of the circuit when the transistor is in the active range.

Digital applications: Let the base resistance be 5 kohm and the load 500 ohm (example). Find the smallest possible current gain (beta) and a corresponding collector resistance that makes the circuit a functional logical inverter with LOW = 0.0-0.8 V and HIGH = 2.0-5.0 V.

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