An ideal BJT acts as an open switch when:

Question

Examoogle · Accepted Answer

The correct answer is Option D: V CE = V CC and I c = 0. An ideal BJT operates as an open switch in the cutoff region, where both the base-emitter and base-collector junctions are reverse-biased. In this state, the collector current $I_{c} = 0$, and the full supply voltage $V_{cc}$ drops across the collector-emitter terminals.

Step-by-Step Solution & Concepts:
An ideal BJT operates as an open switch in the cutoff region, where both the base-emitter and base-collector junctions are reverse-biased. In this state, the collector current $I_{c} = 0$, and the full supply voltage $V_{cc}$ drops across the collector-emitter terminals.

Working Principle: When the base current $I_{b} = 0$, the BJT is in cutoff mode. The device exhibits infinite resistance between the collector and emitter, effectively acting as an open circuit in series with the load. Since $I_{c} = 0$, the voltage drop across any load resistance is zero, resulting in $V_{ce} = V_{cc} - I_{c}R_{L} = V_{cc}$.

Key Formulas: $V_{ce} = V_{cc} - I_{c}R_{L}$ — collector-emitter voltage equation; $I_{c} = \beta I_{b} + I_{ceo}$ — collector current equation; $V_{ce(	ext{cutoff})} = V_{cc}$ — output voltage in cutoff state

Key Points: Cutoff region is characterized by $I_{b} = 0$ and $I_{c} = 0$.; Saturation region is characterized by $V_{ce} \approx 0$ and maximum $I_{c}$.; An ideal switch in the OFF state has infinite impedance.; A BJT switch provides electrical isolation in the cutoff state.

Advantages: High switching speed compared to electromechanical relays.; No moving parts leading to higher reliability.

Disadvantages: Non-zero power dissipation in the ON state ($V_{ce(	ext{sat})} 	imes I_{c}$).; Requires continuous base drive to maintain ON state.

Applications: Digital logic gates (TTL/CMOS).; Power electronic converters and motor drives.

Additional Info: Option A: Represents an active or saturation state depending on load.. Option B: $V_{ce} = V_{bc}$ implies a specific active region bias point.. Option C: Represents the saturation state, where the BJT acts as a closed switch ($V_{ce} \approx 0$).

Answer: D is correct — In the cutoff region, the BJT draws no collector current and blocks the full supply voltage, simulating an open switch.

Exam Tip: Remember: For BJT as a switch, Cutoff means OFF ($I_{c} = 0, V_{ce} = V_{cc}$) and Saturation means ON ($V_{ce} \approx 0, I_{c} = I_{c(	ext{max})}$).

Examoogle · Answer

Option A: V BE = V CC and I B = 50 \mu A

Examoogle · Answer

Option B: V CE = V BC and I c = 10 mA

Examoogle · Answer

Option C: V CE = 0 and I c = 10 mA

Correct Answer

Solve 10,000+ More Questions with AI Tutor

Discussion (0)

Correct Answer

Solve 10,000+ More Questions with AI Tutor

Related Questions

Discussion (0)