What is the duty cycle of a chopper?

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Examoogle · Accepted Answer

$\frac{T_{o n}}{T}$

Explanation: 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. 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 Formulas: $D = \frac{T_{on}}{T}$ — Definition of Duty Cycle; $V_{avg} = D \cdot V_s$ — Average Output Voltage 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: Generates electromagnetic interference (EMI) due to high-frequency switching; Requires filtering to reduce output ripple Applications: DC motor speed control in electric vehicles; Switched-mode power supplies (SMPS) Additional Info: 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. Answer: B is correct — The duty cycle is the ratio of the ON time ($T_{on}$) to the total switching period ($T$). 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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