DC Voltage Sources

If the polarity of an electrical energy source does not change over time, it is called a direct current source. If the magnitude of the voltage is invariable, the source is termed as being a fixed voltage source. The following graphic depicts the circuit diagram symbol for such a source.


Galvanic Elements

The principle of a galvanic elements involves using electro-chemical processes to generate a voltage. Such an element contains two materials of differing conductivity (e.g. zinc and carbon) that are used as electrodes immersed in a so-called electrolyte.  Elements of this kind are called primary elements. The magnitude of the voltage produced by a galvanic element depends on the materials used for the electrodes.

Among the examples of such galvanic elements are common household batteries. These are available nowadays in a variety of shapes and forms (e.g. as cylindrical batteries, button cells or in block form - see right). A typical voltage output is 1.5 V or some multiple of this number (e.g. 9V).



Unlike primary elements, so-called accumulator batteries can be recharged on many occasions. They are defined as secondary galvanic elements. The best known is the lead accumulator usually used as the starter battery in motor vehicles (see right). Such batteries usually provide a voltage of 12 V. Most types of household battery are also available in a rechargeable accumulator form nowadays.  accumulators.jpg


Mains Power Supplies

mains power supply or transformer provides power supplied from the AC mains network (which has a specified voltage, currently defined in Europe as 230 V). This usually involves using a transformer to step the voltage down to the required voltage for the appliance and to ensure galvanic isolation (for safety reasons it is usually forbidden to have a direct connection to the mains), In a stabilised power supply, a closed-loop controller (voltage stabiliser) will ensure that the output voltage remains generally constant in spite of changing load or input. Such power supplies are also available in many forms, e.g. the adjustable laboratory power supply shown here (above right) or the fixed voltage supply that is often used for toys or music and games equipment (bottom right). Other forms include plug in power supplies or the power supply in a computer that provides various different but constant voltage outputs.  mains-power-supplies.jpg

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