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Homework Help: Electronics/Power supply assignment questions

  1. Feb 4, 2013 #1
    1. The problem statement, all variables and given/known data

    Hello all, there are three fairly simple electronics related questions of an assignment to be handed in tomorrow, and whilst the initial answers as obvious, I'd greatly appreciate some assistance on elaborating on certain questions:

    1. Explain the reasons for requiring a constant DC voltage for most electronic devices.
    2. Explain why batteries are not an adequate solution to DC power requirements.
    3. Explain the need for conversion of domestic AC supply to DC.

    3. The attempt at a solution
    Obviously for 1: The majority of small, electrical appliances, eg phone chargers and children's toys require a small voltage. What I'm querying however, is the fundamental difference between AC and DC and why such devices could not operate on AC?

    For 2: Life-span as a main answer, is this a correct starting point? Is there any other general difference considering a battery provides a completely flat DC voltage?

    For 3: Well obviously due to safety, and AC is cheaper as a mains source etc. But what would be the consequence of not using AC?

    Any help or advice would be greatly appreciated, thanks for reading!
  2. jcsd
  3. Feb 4, 2013 #2


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    2017 Award

    Staff: Mentor

    Transistors have fixed, different sides - you cannot operate them with AC, or not in the intended way.

    2: I think everywhere where batteries are not an adequate solution, lifetime is an issue. If they would have an infinite lifetime, you could use them nearly everywhere.
    Hint: the power grid would have a poor performance with DC.
  4. Feb 4, 2013 #3
    Brilliant, thanks for your reply and confirmation!
    There's also two more questions I'm slightly apprehensive about, I'm also unsure whether the first refers to a full-wave/half-wave with a capacitor?

    Q1: Explain filter circuits to remove ripples.

    Q2: Explain the use of stabilising circuits for voltage regulation.

    Thanks again
  5. Feb 4, 2013 #4


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    Staff: Mentor

    This is applicable to both full-wave and half-wave, and addresses ripple on the DC at the output. Though I think you could confine your discussion to full-wave, since one of the measures to reduce ripple on a half-wave is to convert it into a full-wave! :smile:

    Stabilize against changing conditions that would tend to cause the DC output voltage to vary.
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