Unregulated DC Power Adapters

Regulated or un-regulated: what does it mean?
A voltage regulator is a device (usually an electronic circuit) that controls or maintains the constant voltage output of a power supply. Some (more expensive) DC voltage output power adapters have voltage regulators built in, while most do not.

Unregulated DC output power adapters are still the most common type of power adapter in use today. Unregulated, or "non-regulated" simply means the power adapter is not subject to the control or authority of a voltage regulator. With unregulated power adapters, or any other unregulated DC power supply, the DC output voltage is dependent upon an internal voltage reduction transformer, and related to the amount of current used by the electrical load. (The load is the device receiving power from the adapter).

Example: A given unregulated power adapter has an output rating of 9 volts DC at 500ma (500 milliamps = 0.5 Amps).
This rating means that the unregulated voltage output of the power adapter will be 9 volts DC when it is under the full rated load of 500ma. Many people are surprised when they plug an unregulated power adapter into a wall outlet and measure the DC output voltage of the power adapter with a volt meter. While the adapter is providing no power to a load device, the measured output voltage is several volts higher than the rated voltage of the power adapter. Often, people jump to the conclusion that something is wrong with the power adapter, while the simple explanation is that the power adapter has no voltage regulator, and this is normal. But if the same unregulated power adapter is connected to a load which draws 500ma of current, the measured output voltage of the power adapter would drop to the rated 9 volt DC output level as it should.

The second important concept to understand about any power adapter, whether regulated or unregulated, is that the rated output current of the adapter should not be exceeded by the maximum current requirement of the load.

Example:  If a power adapter has an output current rating of 500ma, it should never be connected to a load that will draw more than 500ma of current from the adapter. Drawing more than the rated current output from an unregulated power adapter will certainly cause the actual output voltage to drop below the rated value, and overloading any power adapter in this way will lead to overheating and premature failure of the adapter. Overloading a power adapter may cause a fire hazard and depending on the power sensitivities of the load, may cause damage to the load as well. Most power adapters made today, have built in overload protection (essentially an internal fuse to prevent the adapter from going up in a puff of smoke), but overloading the adapter may still cause it permanent damage. Appropriate external fuse protection can be added if the extra precaution is warranted.

A third concept about unregulated power adapters which for most applications is less important, but still helpful for people to understand, is that unregulated DC output power adapters do not produce a pure and "clean" DC voltage. But if the power adapter selected is closely matched to the power requirements of the load, the purity of the DC voltage produced is more than adequate for many jobs (with few exceptions).

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