(110–220, 117–220, 110–230, etc.) Converters for devices Mains converters Another requirement is to provide low-voltage electricity to a device from mains electricity; this would be done by what is usually called a power supply. Most modern electronic devices require between 1.5 and 24 volts DC; lower-powered devices at these voltages can often work either from batteries or mains. Some devices incorporate a power supply and are simply plugged into the mains. Others use an external power supply comprising either a transformer and rectifier, or electronic circuitry. Switched-mode power supplies have become widespread in the early twenty-first century; they are smaller and lighter than the once-universal transformer converters, and are often designed to work from AC mains at any voltage between 100 and 250 V. Additionally, because they are typically rectified to operate at a DC voltage, they are minimally affected by the frequency of the mains (50 vs 60 Hz). Details on operation are given in the article on power supplies. Mobile converters Voltage converters can be used in vehicles with 12 V DC outlets. A simple voltage dropper can be used to reduce the voltage for low-power devices; if more than 12V is required, or for high-powered devices, a switched-mode power supply is used. The output will usually be DC in the range 1.5–24 V. Power supplies that output either 100–120 V AC or 210–240 V AC are available; they are called inverters, due to the conversion from DC to AC rather than the voltage change. The output frequency and waveform of an inverter may not accurately replicate that supplied by mains electricity, although this is not usually a problem. See also Electric power conversion Extra-low voltage High voltage Low voltage Transformer References Electric power systems components