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What's The Difference Between Regulated & Unregulated Power Supplies?

industrial power supplyIn a general sense, a power supply is any device that supplies energy (power!) to an electrical circuit. Taken this way, batteries are power supplies for flashlights and power plants are power supplies for the electrical grid.

But that’s not usually what we have in mind when we talk about power supplies. Usually, we use “power supply” to indicate a circuit or a device that adapts available power to the specific needs of one device or a set of similar devices. In most non-industrial settings, the available power, or input power, is AC, and the output power is DC.

Power supplies can be standalone units (like the “bricks” we plug into walls for laptops), built-in (like in refrigerators, microwaves, and TV’s), or hybrid (like the built-in, yet self-contained power supplies used in desktop computers).

Power supplies are categorized two ways, regulated and unregulated.

Regulated Power Supplies

Regulated power supplies have voltage regulators on their output. The regulator ensures the output voltage will always stay at the rated value of the power supply, regardless of the current that the device is consuming. This works as long as the device is not drawing more than the rated output current of the power supply. In fancy electrical terms, a regulated power supply provides a constant output voltage, independent of the output current. A regulated power supply with multiple regulators can offer multiple output voltages for operating different devices.

Unregulated Power Supplies

The output voltage of an unregulated power supply is not regulated. Unregulated power supplies are designed to produce a certain voltage at a particular current. That is, to use the fancy electrical terms again, unregulated power supplies provide a constant amount of power (voltage x current). The output voltage will decrease as the output current increases, and vice versa; thus, an unregulated power supply should always be matched as closely as possible to the voltage and current requirements of the device it is powering.

Unregulated power supplies by their nature do not produce a clean (i.e. constant) voltage. Without a regulator to stabilize the output voltage, any change in input voltage will be reflected on the output voltage. These small changes in the output voltage are called “ripple voltage” and are, essentially, electrical noise. If the power supply and load requirements are closely matched, there is usually not a problem. However, if the ripple voltage is large enough in relation to the output voltage, it will impact the behavior of circuits and devices.

To reduce the impact of ripple voltage, a filter capacitor can be placed across the positive and negative outputs of the power supply. The capacitor, which resists changes to voltage, will act like a regulator, smoothing the output voltage and allowing for normal operation.

So which is the better choice? It depends on your needs. Unregulated power supplies are less expensive, but can only supply power as clean as the available input power. If you are powering equipment with sensitive electronics, clean power is an absolute requirement. If you need a power supply that can offer multiple DC output voltages, then one regulated power supply with multiple outputs will be a better option than multiple supplies with single outputs.

Contact us if you have any questions about the power supply for your APG level sensor or pressure transducer.


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Take a closer look at APG's DCR-1006A

top image credit: U.S. Army Corps of Engineers Detroit District via flickr cc

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