There are two types of electric current commonly used in electrical systems and components: AC (alternating current) and DC (direct current). Mains power supply is AC, but most electronic equipment requires a DC current.
An AC adaptor is a device which takes an AC current and changes it in some way, either to a different type of AC current or to a DC current. In most cases an AC adaptor means an AC to DC converter.
AC adaptors include the following circuits:
- Rectification: The main conversion to DC. The circuit passes only one polarity of the AC voltage, or generates an absolute value for the waveform.
- Filtering: Removes the alternating portion of the rectified signal. In most cases this portion is not needed and may cause problems (e.g. hum).
- Regulation: Provides a stable output, and may limit the current.
AC adaptors may be included as part of the internal circuitry of a device, or the device may require an external AC adapter. When connecting an external adapter, it is important to use the correct type — the wrong adapter can cause damage. In most cases it is safest to use the adapter supplied by the manufacturer — only do otherwise if you're very confident you've got it right.