9702 · 21.2
Rectification and smoothing flashcards
Revision flashcards for Cambridge 9702 Rectification and smoothing (syllabus 21.2). Flip, recall, then mark a real past-paper question.
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What is **rectification**?
The process of converting alternating current (AC) into a unidirectional direct current (DC).
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What is the main difference between half-wave and full-wave rectification?
Half-wave uses only one half-cycle of AC, while full-wave converts both half-cycles into positive pulses.
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How many diodes are typically used in a **bridge rectifier** for full-wave rectification?
Four diodes.
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What is the purpose of **smoothing** after rectification?
To reduce the voltage fluctuations (ripple) in the DC output, making it more constant and stable.
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Which electronic component is connected in parallel with the load for smoothing?
A capacitor.
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How does a capacitor achieve smoothing?
It charges when the rectified voltage rises and discharges through the load when the voltage falls, filling in the dips.
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Define the **RC time constant** in the context of smoothing.
It's the product of the load resistance (R) and capacitance (C), indicating how quickly the capacitor charges/discharges.
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What happens to the output ripple if the RC time constant is significantly increased?
A larger RC time constant results in a smaller, reduced voltage ripple, producing a smoother DC output.
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What is a disadvantage of half-wave rectification?
It's inefficient, as half of the input AC power is unused (only one half-cycle passes).
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Why is a full-wave rectified output generally preferred over half-wave?
It's more efficient, converting both AC half-cycles, and produces a higher average output voltage with a smaller ripple frequency.
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What is the frequency of the output ripple for a full-wave rectifier compared to the input AC frequency?
The ripple frequency is double the input AC frequency (f_ripple = 2 * f_in).
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What is the frequency of the output ripple for a half-wave rectifier compared to the input AC frequency?
The ripple frequency is the same as the input AC frequency (f_ripple = f_in).
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For effective smoothing, how should the RC time constant compare to the period of the rectified waveform?
The RC time constant (τ) should be much larger than the period of the rectified waveform (T), i.e., τ >> T.
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What is 'ripple voltage'?
The small variation in voltage (ΔV) in the smoothed DC output, measured as the difference between the maximum and minimum voltage levels.