Which device can be used in a chopper circuit?

Question

Examoogle · Accepted Answer

All of the mentioned

Explanation: A chopper is a static power electronics device that converts fixed DC voltage to variable DC voltage using high-speed switching. Various semiconductor devices like BJTs, MOSFETs, and GTOs are used as switches because they can be turned on and off at controlled intervals to regulate the output voltage.

Working Principle: The chopper acts as a high-speed switch. By controlling the 'on' time ($T_{on}$) and 'off' time ($T_{off}$), the average output voltage $V_o$ is controlled. These devices are used in their saturation region for conduction and cut-off region for non-conduction, enabling efficient power conversion.

Key Formulas: $V_o = V_s \cdot \alpha$ — Relationship between output voltage, input voltage, and duty cycle $\alpha$; $f = \frac{1}{T_{on} + T_{off}}$ — Chopping frequency formula

Key Points: Choppers are DC-to-DC converters used in traction, electric vehicles, and battery chargers.; The selection of the device depends on power levels, switching frequency, and cost.; MOSFETs are typically preferred for high-frequency low-power applications.; GTOs and IGBTs are suitable for high-power industrial applications.

Advantages: High efficiency due to switching operation; Compact size and light weight; Fast dynamic response

Disadvantages: Generation of electromagnetic interference (EMI); Output contains ripples requiring filter circuits

Applications: Electric traction control; DC motor speed control (Ward Leonard replacement); Switch-mode power supplies (SMPS)

Additional Info: BJT (Bipolar Junction Transistor) has high switching losses at high frequencies.. MOSFET (Metal Oxide Semiconductor Field Effect Transistor) offers the fastest switching speed but limited power handling.. GTO (Gate Turn-Off Thyristor) is a fully controlled device capable of switching high current and voltage.

Answer: D is correct — All listed semiconductor devices (BJT, MOSFET, and GTO) can function as the primary switching element in a chopper circuit.

Exam Tip: Always remember that choppers require forced commutation or self-commutated devices; since BJTs, MOSFETs, and GTOs all allow control over turn-off, they are valid candidates.

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