When does a transistor work as an inverter?

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MPPGCL JE Electrical 19 March 2019 Shift 2 Official Paper

Answer 1

Quiescent point of a transistor

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When no signal is applied, the transistor voltage and current conditions are as indicated at the quiescent point (Q point) on the dc load line.
When an AC signal is applied, the transistor voltage and current vary above and below point Q.
The load line is drawn between collector current lC and collector voltage VCE for different values of base current lg.
When a value for the maximum possible collector current is considered, that point will be present on the Y-axis, which is nothing but the saturation point.
When a value for the maximum possible collector-emitter voltage is considered, that point will be present on the X-axis, which is the cutoff point.
When a transistor is operated between cut-off and saturation region, it works as an inverter.
When a line is drawn joining these two points, such a line can be called a Load line. This line, when drawn over the output characteristic curve, makes contact at a point called an Operating point or quiescent point, or Q-point.

Operating modes of BJT

The transistor operates in four operating modes. These are as follows: