About DC Power Supply

The humble "wall wart" DC supply powers many consumer gadgets.

Toasters, motors, and light bulbs run well on the alternating current (AC) from your household outlet, but electronic devices need direct current (DC). Engineers solved this problem by developing the DC power supply, a circuit that converts AC to DC. In 2011, hundreds of different DC supply designs provide power for computers, cellphones, radios, and televisions.

Linear

The simplest DC power supplies combine a transformer, rectifier, capacitor, and regulator. The transformer reduces the voltage from the 60-Hz,110-volt AC standard to between 3 and 24 volts, depending on what the equipment needs. The rectifier converts the lower-voltage AC to DC, though the DC has electrical noise that the capacitor and regulator remove. Engineers call these designs "linear power supplies," as they use components that respond without abrupt changes.

Switching

Though more complex than a linear power supply, a "switching supply" is lighter, more compact, and more efficient. Instead of working directly from 60 Hz AC, it first increases the frequency to more than 100,000 Hz. Because of this, the power supply can use a smaller, lighter transformer that also runs cooler. It has the rectifier and other parts in common with the linear supply, but needs additional components to produce the high frequencies. Energy-efficient electronics or portable equipment typically have switching DC power supplies. Equipment sensitive to the high-frequency noise produced by switching supplies may use linear power supplies

Consumer

If you have a cellphone, laptop computer or MP3 player, you have handled a DC power supply, perhaps without knowing it. The thick power-adapter plugs that power these devices convert the AC from the outlet to DC at a voltage that the equipment can use. These DC power supplies plug into the wall and have a thin cable that connects to the device. Many appliances, such as stereos, televisions and desktop computers, have their DC power supplies inside them. All these power supplies produce fixed DC voltages set specifically for the equipment.

Professional

Technicians, engineers, and scientists use DC power supplies to run their electronic projects. They use power supplies with knobs and displays to adjust voltage and current. Because they may work with many kinds of electronic circuits, such versatile power supplies simplify their work areas. Benchtop power supplies have additional features, such as multiple outputs and overload protection.

References

• Electronics Club: Power Supply
• Agilent: Single and Multiple Output Bench Power Supply