Power Supplies
The block marked 'Filter' in the diagram is to
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filter RF radiation from the output of the power supply
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Correct Answersmooth the rectified waveform from the rectifier
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act as a 50 Hz tuned circuit
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restore voltage variations
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The block marked 'Regulator' in the diagram is to
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regulate the incoming mains voltage to a constant value
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ensure that the output voltage never exceeds a dangerous value
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keep the incoming frequency constant at 50 Hz
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Correct Answerkeep the output voltage at a constant value
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The block marked 'Transformer' in the diagram is to
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transform the incoming mains AC voltage to a DC voltage
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ensure that any RF radiation cannot get into the power supply
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Correct Answertransform the mains AC voltage to a more convenient AC voltage
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transform the mains AC waveform into a higher frequency waveform
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The block marked 'Rectifier' in the diagram is to
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Correct Answerturn the AC voltage from the transformer into a fluctuating DC voltage
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rectify any waveform errors introduced by the transformer
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turn the sinewave output of the rectifier into a square wave
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smooth the DC waveform
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The block marked 'Regulator' in the diagram could consist of
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four silicon power diodes in a regulator configuration
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two silicon power diodes and a centre-tapped transformer
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Correct Answera three-terminal regulator chip
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a single silicon power diode connected as a half-wave rectifier
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In the block marked regulator in the diagram below, a reversed diode may be present across the regulator. Its job is to
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Block negative voltages from appearing at the output
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Blow a fuse if high voltages occur at the output
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Blow a fuse if negative currents occur at the output
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Correct AnswerBypass the regulator for higher voltage at its output compared to its input
Correct answer: bypass the regulator for higher voltage at its output compared to its input
A diode placed reverse-biased across a regulator acts as a protection device. If the input voltage suddenly falls (for example during power-off or a short circuit) while the output capacitor remains charged, the output can temporarily be at a higher voltage than the input. This reverse voltage can damage the regulator.
When this happens, the diode becomes forward biased and safely conducts current around the regulator, preventing excessive reverse voltage across it.
- block negative voltages from appearing at the output is not the function of this diode, negative voltages are normally prevented by the rectifier and regulator stages.
- blow a fuse if high voltages occur at the output is not the intent, the diode protects the regulator rather than acting as an overvoltage fuse trigger.
- blow a fuse if negative currents occur at the output is incorrect, the diode allows reverse current to flow safely instead of forcing a fault.
Therefore, the diode’s purpose is to bypass the regulator when the output voltage becomes higher than the input voltage.
Last edited by jim.carroll. Register to edit