Electronics Engineering (ELEX) Board Practice Exam

How much will the Q-point (I_C, V_CE) change when B_DC increases from 85 to 100 and V_BE decreases from 0.7 V to 0.6 V?

1. 15.1% and 10.6%

2. 18.6% and 15.1%

3. 12.4% and 14.3%

4. 20.0% and 16.5%

The correct answer is: 18.6% and 15.1%

The Q-point, or quiescent point, in a transistor circuit represents the operating point of the transistor when no input signal is present. It is defined by the collector current (I_C) and collector-emitter voltage (V_CE). Understanding how variations in biasing conditions, such as changes in base current (B_DC) and base-emitter voltage (V_BE), affect I_C and V_CE is crucial for analyzing transistor performance. When the base current increases from 85 to 100, this results in a higher level of charge carriers in the transistor, allowing it to conduct more current. In a typical transistor model, the collector current I_C is heavily influenced by the base current due to the transistor's current gain (beta). The increase in base current leads to a proportional increase in I_C, making the change in I_C significant. Simultaneously, the reduction in V_BE from 0.7 V to 0.6 V also has a notable impact. The base-emitter voltage influences the amount of input drive, effectively determining if the transistor is in its active region or in saturation. A decrease in V_BE typically enhances the carrier injection into the base, which also results in an increase in I_C. Together