12 Important Power Supply Terms

Power Supply

A power supply is an optimized, high-power current and voltage output device that supplies electrical energy to automated test equipment. Specialized power sources offer various advantages, including heightened sensitivity and enhanced precision, to provide more efficient power to a multitude of electrical appliances. Common attributes of a power supply include voltage and current levels and stability of output voltage or current under variable conditions (i.e., line and load). Examples of common power supplies include AC (alternating current) and DC (direct current), each with advantages when used in specific conditions and with various electrical appliances.

Constant Current Operation (Current-Controlled Mode)

Constant current operation is equipped on an output channel when a given load endeavors to pull more current than the programmed limit allows. When this mode is enabled, the current that is forced through the load is maintained at this programmed limit. The level of voltage increases or decreases as the load exhibits need for higher or lower levels of power. During constant current operation mode, the output channels of the power supply act as current sources.

Constant Voltage Operation (Voltage-Controlled Mode)

Constant voltage operation is equipped on an output channel as long as the given load does not exhibit need for more current than the programmed limit allows. In this mode, the output voltage maintains constancy regardless of changes in load. If the load does endeavor to pull more current and this amount exceeds the programmed limit, constant current operation automatically ensues.


Isolation refers to the method of separating two portions of a measurement device, both physically and electrically. It directly pertains to completely removing ground paths between two separate electrical systems. The ability to electrically isolate the two parts allows a user to break ground loops and increase the common-mode range of a power supply.

Line Regulation

Line regulation is defined as the measure of a power supply's ability to maintain its output of voltage even under circumstances in which the input line voltage changes. Line regulation is conveyed as a ratio in the form of a percent. This percentage denotes the change in the power supply's output voltage in relation to the change in input voltage.

Linear Power Supply

A linear power supply is a regulated power supply that determines output voltage by decreasing excess voltage in laboratory test equipment, control circuits, data acquisition devices and automatic test equipment. They are utilized to lower load and line regulation, ripple and output noise.

Load Regulation

Load regulation is defined as the measure of an output channel's ability to maintain constancy in the event of various load changes. This specification can be conveyed in one of two ways, depending on the mode of control enabled on the output channel at the time of testing. With constant voltage mode, changes to the load directly cause a change in the output current. With constant current mode, a change in the load results in a variation to the current as it passes through the load.

Output Rating

The output rating of a given transmitter or power supply expresses the available amount of power at the output terminals when the device is connected to its normal load (or an equivalent). Output rating can also refer to the amount of energy that a power supply can transmit over a length of time without overheating. A device's output rating is measured in watts.

Programmable Power Supply

A programmable power supply allows its user to control the output voltage remotely via an analog signal or a computer-controlled interface. The properties of a programmable power supply are adjustable to match the user's specific needs. These programmable features include voltage and current, as well as frequency for AC power supplies. Many power supplies that are programmable also offer adjustable components in the form of overvoltage control, protection from short circuiting and overcurrent programming. Types of programmable power supplies include floor-mounted, wall-mounted, modular and bench top.

Redundant Power Supply

A redundant power supply is an incredibly advanced type of electrical power supply used in a variety of devices, including personal computers, large servers and electronic testing instruments. It includes two or more individual power supply devices within a single unit. Each of these power supplies is capable of supplying its load on a standalone basis so, should one of the main supplies fail, the device being powered will simply switch over to one of the other units to avoid loss of power.

Ripple & Noise

Noise refers to undesirable signals existent on the output channels of a power supply and can belong to one of two categories: normal-mode noise and common-mode noise. Either type can cause unwanted effects in devices that are directly connected to these output channels. When noise and unfiltered AC voltage exist at the output of a fully loaded and operational power supply the resulting periodic normal-mode noise is called ripple. Ripple is unwanted for various reasons, including reduction in test equipment resolution and visible or audible interference in electronic appliances.


A transformer is a unit of electronic equipment that is designed to convey electrical energy from one circuit to another via coils that act as conductors. An electrical current passes through the first or primary wire, creating a magnetic field that extends to the second coil. As this current varies, it causes changes in the magnetic field to which the second coil is exposed. A transformer can be used to either increase or decrease the voltage that is conveyed to a given appliance.