Question

The chopper circuit shown in figure (i) feeds power to a 5 A DC constant current source. The switching frequency of the chopper is $100 \,\text{kHz$. All the components can be assumed to be ideal. The gate signals of switches $S_{1}$ and $S_{2}$ are shown in figure (ii). The average voltage across the 5 A current source is:} \begin{center} \includegraphics[width=0.5\textwidth]{08.jpeg} \end{center}

• A. 10 V
• B. 6 V
• C. 12 V
• D. 20 V

Hint:

In chopper circuits with constant current loads, the average output voltage is simply the product of duty cycle and input voltage. Always compute the duty ratio from the switching waveform.

Answer 1

The Correct Option is A

Step 1: Identify switching frequency and period.
Switching frequency = $100 \,\text{kHz}$ \[ T = \frac{1}{f} = \frac{1}{100 \times 10^{3}} = 10 \,\mu\text{s} \] So, one complete cycle has a duration of $10 \,\mu\text{s}$.

Step 2: Duty cycle of switch $S_{1$.}
From figure (ii), the gate signal of $S_{1}$ is ON (high) for $5 \,\mu\text{s}$ and OFF for $5 \,\mu\text{s}$. Thus, \[ D = \frac{t_{\text{on}}}{T} = \frac{5}{10} = 0.5 \]

Step 3: Output voltage behavior.
- When $S_{1}$ is ON, the full input voltage (20 V) appears across the load (current source). - When $S_{2}$ is ON, the current source is short-circuited (voltage = 0). Thus, the average output voltage across the current source is: \[ V_{\text{avg}} = D \cdot V_{\text{in}} = 0.5 \times 20 = 10 \,\text{V} \]

Step 4: Verify consistency.
- Since load is a constant current source (5 A), it always demands current regardless of voltage. - The chopper alternates between applying 20 V and 0 V, giving an average of 10 V. % Final Answer \[ \boxed{\text{Option (A): 10 V}} \]