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3.3: Voltage Source Circuits

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    Multiple power sources can be connected in series or parallel in order to meet the different voltage or current output requirements for various applications:

    • Power sources are connected in series to increase the voltage output.
    • Power sources are connected in parallel to increase the current capacity

    Series Sources

    Voltage sources are sometimes connected in series to produce a higher voltage value. This is common in devices such as flashlights and portable transistor radios, in which 1.5 V battery cells are used.

    To obtain a higher voltage output from series-connected sources, you must observe correct polarity. In Figure \(\PageIndex{1}\), a net voltage of 6 V is obtained if the individual 1.5 V cells are acting in the same direction. This is called series aiding.

    Figure \(\PageIndex{1}\): Battery cells connected in series aiding (CC BY-NC-SA; BC Industry Training Authority)
      Figure \(\PageIndex{2}\): Battery cells connected in series opposing (CC BY-NC-SA; BC Industry Training Authority)
      Figure \(\PageIndex{3}\): Two batteries in parallel (CC BY-NC-SA; BC Industry Training Authority)
      • Three of the cells are connected series aiding to produce 4.5 V.
      • One cell is connected with opposite polarity of 1.5 V.
      • The net voltage is 4.5 V – 1.5 V = 3 V.
        Overall polarity acts in the direction of the largest cell.

    Whenever batteries or other power sources such as transformers or generators are to be connected in parallel, it is very important that the power sources have the following:

    • The same terminal voltages

      A lower voltage source connected to a higher one acts as a load itself, rather than helping share the real load current with the other sources of supply.

    • Properly connected polarity.

      Like terminals of the power sources must be connected together; that is, positive-to-positive and negative-to-negative.