What is the duty cycle of a chopper? | Electrical MCQ | Examoogle

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What is the duty cycle of a chopper?

$T o n T o f f$

$T o n T$

$T T o n$

$T o f f \times T o n$

Correct Answer

⚙️ TE • Technical Concept & PrincipleElectricalPower Electronics

Option B

$T o n T$

Quick Summary:

The duty cycle (often denoted by $\alpha$ or $D$ ) of a chopper is defined as the ratio of the time the chopper is in the 'ON' state ( $T_{on}$ ) to the total time period ( $T$ ) of the switching cycle. It represents the fractional portion of the total cycle during which the source is connected to the load.

⚙️TETechnical SolutionConcept & Principle

💡 Explanation

🔢 Key Formulas

$D = \frac{T_{on}}{T}$ — Definition of Duty Cycle

$V_{avg} = D \cdot V_s$ — Average Output Voltage

⚙️ Working Principle

In a DC chopper, a power semiconductor switch (like an IGBT or MOSFET) is toggled ON and OFF at a constant frequency. The total time period $T$ is the sum of the conduction time $T_{on}$ and the non-conduction time $T_{off}$ , where $T = T_{on} + T_{off}$ . By varying $T_{on}$ while keeping $T$ constant (Pulse Width Modulation), the average output voltage $V_{out} = D \cdot V_{in}$ can be controlled linearly.

📌 Key Points

▸
Duty cycle $D$ is a dimensionless parameter ranging from 0 to 1 (or 0% to 100%).
▸
Increasing the duty cycle increases the average output voltage.
▸
The switching frequency $f$ is the reciprocal of the total period: $f = \frac{1}{T}$ .

✅ Advantages

▸
High efficiency due to switching operation
▸
Precise control over average output voltage

❌ Disadvantages / Limitations

▸
Generates electromagnetic interference (EMI) due to high-frequency switching
▸
Requires filtering to reduce output ripple

🛠️ Applications / Uses

▸
DC motor speed control in electric vehicles
▸
Switched-mode power supplies (SMPS)

📄 Additional Information

▸
A duty cycle of 0 means the switch is always open (off), while 1 means it is always closed (on).
▸
Option A is incorrect as it represents the ratio of conduction to non-conduction time, not the total cycle.

📊 Diagram / Illustration

✅

B is correct — The duty cycle is the ratio of the ON time ( $T_{on}$ ) to the total switching period ( $T$ ).

Core Concepts Used

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Power Electronics Chopper Control Pulse Width Modulation

💡 EXAM TIP

Always remember that $T = T_{on} + T_{off}$ . In some advanced problems, $T_{off}$ might be varied to control frequency while $T_{on}$ is kept constant, which changes the duty cycle dynamically.

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