How Does a DC Power Supply Work? DC Power Supplies Explained

Power Supply

The power that comes into a building is in the form of alternating current (AC). AC switches from positive to negative 60 times per second and is carried into the building via the live wire. The return wire is the second wire that takes the current back out of the building to complete the circuit.

How Transformers Work

120 volts is too high for most DC appliances. AC comes into the building at 120 volts and must therefore be reduced with the use of a step-down transformer. The transformer uses two coils of wire to reduce the voltage of the AC. Each coil is connected to its own circuit. The current is sent through the first coil, which creates a magnetic field. The second coil has fewer turns and is placed beside the first; the magnetic field from the first coil creates a lower-voltage current in the second.


Direct current (DC) differs from AC in that it flows in only one direction. DC power supplies have a wire for the positive charge and another for the negative. In order to convert AC into DC, a component called a rectifier is used. The main feature of a rectifier is called a diode. A rectifier is essentially an arrangement of diodes.

How Diodes Work

Diodes only allow current to flow in one direction and thus function in a similar way to the valves used in water pipes. Valves control the direction in which water flows in a pipe. Diodes are basically one-way electrical valves. When current is sent through a diode, half of the wave form gets blocked off, leaving only the other half. This is referred to as half wave rectification.

When the AC switches to negative, the diode lets it go down the negative wire and closes when the AC switches back to positive; at this point, another diode will let it go down the positive wire. The different kinds of rectifiers all function in basically the same way; they utilize diodes to keep negative current separated from positive.

Filtering Electrical Noise

The rectifier changes AC to DC, but it produces a current that pulses; in other words, rectified DC produces a lot of what is sometimes termed electrical noise. In order to get a smoother current, another component that serves as a filter will be necessary. A filter is usually simple and consists of large capacitors. The capacitors used to filter rectified DC function as batteries over a short period, this is because batteries produce current that is steady and that has almost no electrical noise. The filter works by filtering out certain frequencies with the result that the current pulses less.


The DC current from the capacitor will still oscillate a little (this is called ripple), so there is still one more voltage regulating stage necessary. This involves the use of an integrated circuit appropriately called a regulator. The regulator can ensure that the current is at exactly the level that is required.

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The author, Devim Andrey is energetic self motivated writer. He writes creative article on various channels . Now he is working with Abbott Technologies.

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