Question

A DC chopper operates on 230 V DC and frequency of 400 Hz, feeds an R-L load. If the output voltage of chopper is 150 V, the ON time of the chopper is _______.

• A. 3.84 msec
• B. 2.5 msec
• C. 1.63 msec
• D. 0.65 msec

Hint:

Use: \( V_o = \alpha V_{in} \) and \( T = \frac{1}{f} \), then \( T_{on} = \alpha T \)

Answer 1

The Correct Option is C

Step 1: Understand the relationship for chopper output voltage
\[ V_o = \alpha \cdot V_{in} \] Where:
- \( V_o = 150 \, V \),
- \( V_{in} = 230 \, V \)
- \( \alpha \) = duty cycle \( = \frac{T_{on}}{T} \)
Step 2: Find duty cycle
\[ \alpha = \frac{V_o}{V_{in}} = \frac{150}{230} \approx 0.652 \] Step 3: Use frequency to get total period
\[ f = 400 \text{ Hz} \Rightarrow T = \frac{1}{f} = \frac{1}{400} = 2.5 \, ms \] Step 4: Find \( T_{on} \)
\[ T_{on} = \alpha \cdot T = 0.652 \times 2.5 = 1.63 \, ms \] Conclusion:
Option (3) is correct.