Direct current (DC) is an electric current that flows in one direction only. The electrons move steadily from the negative terminal of the source, through the circuit, and back to the positive terminal.
Sources of DC
Batteries and cells produce DC. A chemical reaction inside the cell maintains a potential difference that drives current in one fixed direction. Solar cells (photovoltaic cells) also produce DC directly from light energy.
DC on an oscilloscope
A steady DC voltage appears as a horizontal straight line on an oscilloscope screen. The height of the line above the centre line gives the voltage (multiply the number of divisions by the Y-gain setting).
Where DC is used
Most electronic devices run on DC. Mobile phones, laptops, and LED circuits all require DC. When a device is plugged into the mains (AC), a rectifier inside the charger converts the AC to DC.
Rectification
A single diode converts AC to half-wave DC by blocking one half of each cycle. Four diodes arranged in a bridge circuit produce full-wave rectification, which uses both halves of the AC cycle. A capacitor can then smooth the output to produce a steadier DC voltage.
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