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Basic AC-DC Power Supplies
31 questions By Tony R. Kuphaldt
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Question 7 of 31
An essential part of an AC-DC power supply circuit is the filter, used to separate the residual AC (called the “ripple” voltage) from the DC voltage prior to output. Here are two simple AC-DC power supply circuits, one without a filter and one with:
Draw the respective output voltage waveforms of these two power supply circuits (Vunfiltered versus Vfiltered). Also identify the type of filter circuit needed for the task (low pass, high pass, band pass, or band stop), and explain why that type of filter circuit is needed.
Reveal answer
A low pass filter is the kind needed to filter “ripple voltage” from the power supply output.
Notes:Many years ago, when I was first learning about power supplies, I tried to power an automotive radio with voltage from a battery charger. The battery charger was a simple power supply suitable for charging 12-volt automotive batteries, I reasoned, so what harm would there be in using it to power an automotive radio? After a few moments of LOUD humming from the radio speaker, my rhetorical question was answered by a puff of smoke from the radio, then silence.
Part of the problem was the output voltage of the battery charger, but a large part of the problem was the fact that the charger’s output was unfiltered as well. For the same reasons my radio did not function properly on unfiltered, rectified AC, many electronic circuits will not function on it either.
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Question 8 of 31
Observe the following two waveforms, as represented on an oscilloscope display measuring output voltage of a filtered power supply:
If both of these waveforms were measured on the same power supply circuit, at different times, determine which waveform was measured during a period of heavier “loading” (a “heavier” load being defined as a load drawing greater current).
Reveal answerThe left-hand waveform was measured during a period of heavier loading.
Notes:Ask your students what the term “loading” means in this context. Some of them may not comprehend the term accurately, and so it is good to review just to make sure.
More importantly, discuss with your students why the ripple is more severe under conditions of heavy loading. What, exactly, is happening in the circuit to produce this kind of waveform? If it is necessary for us to maintain a low amount of ripple under this heavy loading, what must we change in the power supply circuit?
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Question 9 of 31
What does it mean if a power supply has a DC output with 5% ripple?
Reveal answerThis means the peak-to-peak ripple voltage is equal to 5% of the DC (average) voltage.
Notes:The purpose of this question is to get students to look up the formula for calculating ripple voltage percentage. Notice how I did not simply ask them to regurgitate a formula; rather, I presented a realistic figure for them to interpret. When at all possible, try to format your questions in this sort of practical context!
i m using power supply for CCTV PTZ Camera with his adaptor rating of 230v AC input & 24V AC Output ,2A load current. what would be the power consumption is their from the main supply line? means is it taking 2 amp from main line of it would be from the adaptor itself?