An adjustable power supply is a power source that does not have a fixed output voltage or current. The power supply output can be Alternating Current (AC) or Direct Current (DC). The output may be adjustable over a broad or narrow range of voltage, current or both. The output frequency may also be adjustable in an AC supply. Adjustable power supplies are often used in scientific laboratories, classrooms and as components in other types of electrical equipment.
The power supply input voltage for an adjustable power supply is usually the main AC line voltage of the region where the supply is being used. It may also be able to handle other common line voltages as well. For example, many power supplies can operate from either 120 volts AC (VAC) or 240 VAC.
A linear power supply uses a transformer to step the AC line voltage down to an often lower AC voltage. In a DC power supply, this lower voltage is then converted to DC with a rectifier and filtered to provide a smoother output. Many DC linear supplies also include power supply regulator circuitry to provide an exact stabilized voltage or current. A linear supply can also be an adjustable power supply. Common DC lab supplies can be varied from 0 to 30 volts DC (VDC), up to currents of several amperes.
A programmable supply is another type of adjustable power supply. The output voltage of some supplies can be varied by adjusting the voltage on a special input signal. Others can be programmed digitally through common serial or instrumentation interfaces. Programmable power supplies are often available in a variety of types, able to produce DC or AC in different current, voltage and frequency ranges. A programmable supply is usually fairly sophisticated, including its own processor as well as power monitoring and limiting circuitry.
High voltages can also be provided by an adjustable power supply. Electron microscopes and chemical analysis equipment often utilize supplies which can be varied up to 30,000 VDC. The current on this type of supply is generally limited to just a few milliamperes. The power on some X-ray equipment is frequently adjustable up to 50,000 VDC.
On some high-voltage AC power supplies, the output frequency is also adjustable. The power output can be three-phase instead of the single-phase common to lower voltage supplies. A voltage multiplier can be used with an AC adjustable power supply to produce a range of even higher DC voltages as well.