Question

A semiconductor switch needs to block voltage $V$ of only one polarity ($V > 0$) during OFF state as shown in figure (i) and carry current in both directions during ON state as shown in figure (ii). Which of the following switch combination(s) will realize the same? \begin{center} \includegraphics[width=0.5\textwidth]{10.jpeg} \end{center}

• A. A
• B. B
• C. C
• D. D

Hint:

In power electronics, to achieve bidirectional current with unidirectional blocking, we use a unidirectional switch (e.g., IGBT or MOSFET) connected with an anti-parallel diode. This is widely used in choppers, inverters, and AC voltage controllers.

Answer 1

The Correct Option is A

Step 1: Requirement analysis.
We need a switch which satisfies two properties: 1. OFF state: Must block positive voltage ($V > 0$) but need not block negative voltage. 2. ON state: Must conduct current in both directions (bidirectional current). This is a common requirement in power electronics, such as AC controllers, where the device must allow bidirectional current flow but block only one polarity of voltage.

Step 2: Evaluate each option.
- (A) Consists of a semiconductor switch (like a transistor or IGBT) with an anti-parallel diode. - In ON state: Switch + diode allow bidirectional current flow. - In OFF state: The switch blocks positive voltage, diode blocks negative polarity. Requirement satisfied. - (B) Switch and diode in series. - This blocks both polarities, not suitable since requirement is to block only $V > 0$. - (C) Two anti-parallel switches with additional diode. - Too complex; not needed. Also blocks both polarities incorrectly. - (D) Parallel diode pair with switch. - In OFF state, diodes may conduct in undesired direction. Incorrect.

Step 3: Conclusion.
The simplest and correct realization is option (A): a switch with an anti-parallel diode. % Final Answer \[ \boxed{\text{Option (A)}} \]