A transistor converts _________

Question

Examoogle · Accepted Answer

DC power into AC power

Explanation: A transistor functions as an active device that, when provided with a DC power supply, modulates the flow of current to produce an amplified AC signal. In amplifier applications, the DC power is effectively converted into the AC power observed in the load circuit, controlled by the small AC signal applied at the input.

Working Principle: The transistor acts as a variable resistor controlled by the input signal. By utilizing a constant DC source (collector supply $V_{CC}$), the transistor varies its internal resistance in response to the base current $i_B$. This control mechanism allows the transistor to transfer energy from the low-power DC source to the output load as an amplified AC signal, a process referred to as the transfer-resistor effect.

Key Formulas: $P_{AC} = \frac{1}{2} I_c^2 R_L$ — AC output power delivered to the load; $P_{DC} = V_{CC} I_c$ — DC power supplied by the collector bias

Key Points: The term 'transistor' is derived from 'transfer resistor'.; Transistors do not create energy; they modulate existing DC power.; The efficiency of this conversion depends on the amplifier configuration (Class A, B, AB, etc.).; Saturation and cutoff modes allow the transistor to function as a switch.

Advantages: High efficiency in switching applications; Compact size and solid-state reliability; Ability to provide high current gain

Disadvantages: Thermal instability if not properly biased; Limited power handling compared to vacuum tubes in certain RF scenarios

Applications: Audio and Radio Frequency Amplifiers; Digital Logic Circuits; Power Electronics Converters

Additional Info: The conversion is governed by the conservation of energy, where the total power supplied equals the sum of the load power and the heat dissipated by the transistor.. Option B (AC to DC) describes a Rectifier circuit, typically involving diodes, not a transistor in its primary role.

Answer: A is correct — A transistor acts as a power converter that utilizes DC bias to produce an amplified AC output signal.

Exam Tip: Always remember that the transistor's primary role as an amplifier is essentially modulating DC flow; focus on the bias point (Q-point) stability to maintain linear conversion.

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