Power Supplies A to Z : "d"

We've included this handy glossary to help with the terminology & abbreviations relating to power products. Pick a letter below to begin, or download the glossary to refer to it whenever you like.

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Abbreviation for Decibel.


Abbreviation for Direct Current.

dc Component

The dc part of an ac wave.

dc-dc converter

A circuit or device that changes dc input voltage/current to a different dc output voltage/current. Normally the output of a dc/dc converter is isolated from the input. Non isolated versions are available (usually called Point of Load Converters). TDK-Lambda's PSS, PSD, PXD, PXE, PXF and PL series are excellent examples of dc-dc converters.


SI prefix multiplier. Multiplies by 101. So 100 daF = 100 x 101 F = 1000F. Written as 'deca'. Abbreviated to 'da'.

Decay Time

See Fall Time.


SI prefix multiplier. Multiplies by 10-1. So 100 dF = 100 x 10-1 F = 10F. Written as 'deci'. Abbreviated to 'd'.


The numerical expression of the relative loudness of two signals, such as sound. The difference in decibels between two signals is ten times the common logarithm of the ratio of their powers. Abbreviated to dB.


Power supply decoupling is used to compensate for the impedance of the output of the power supply and the interconnecting leads. This impedance may prevent the power supply reacting quickly to the rapidly changing loads that are common in modern electronic equipment. Decoupling of the output should be carried out with electrolytic capacitors for medium frequencies and ceramic capacitors for high frequencies. The capacitors should be connected as closely as possible to the load for the best results.


The ratio of mass of material to its own volume. See also Power Density.


1) operating components or devices at lower stress levels than maximum specified capabilities in order to reduce the occurrence of stress-related failures.

2) Reduced output power available from a power supply under certain conditions (especially elevated temperature).

Design Life

Expected length of time of acceptable performance under specified conditions.

Design Validation Testing (DVT)

Testing performed at various stages throughout a product's development cycle to ensure that the initial design specifications are achieved. The DVT will usually involve performing many varied tests, including i) functional testing, ii) reliability testing, iii) ESD testing, iv) EMC testing, v) environmental testing.

Design Verification Test (DVT)

See Design Validation Testing.

Differential Mode Noise

The component of noise that is measured between two lines with respect to a common reference point. The value is the difference of the noise components on the two lines. This excludes common-mode noise.

Differential Voltage

The difference in voltages at two points.


Acronym for Deutsches Institut für Normung e.V. (German Institute for Standardisation).

DIN Rail

Standardised metal rail (35mm wide shown here). Used to mount building automation electronics, industrial control electronics, power supplies, circuit breakers, etc. usually inside equipment racks. Other sizes exist including:

15mm (EN 50045, BS 6273) where dimension a = 15mm, b = 8.5mm, c = 5.5mm, d = 1mm

G type asymmetric DIN rail (EN 50035, BS 5825) (differnet profile to below)

DIN Rail - EN 50022, BS 5584

DIN Rail Power Supply

A Power Supply that mounts directly onto a DIN Rail. TDK-Lambda's DLP, DPP and DSP ranges are excellent examples of Din Rail Power Supplies displaying many of the attributes useful for this type of power supply: compact size, high efficiency, convection cooled, etc.).


A component containing a cathode and an anode that allows current flow in one direction (anode to cathode) and blocks flow from the other (cathode to anode).

Schematic Symbol for a Diode

Direct Current (dc)

Flow of current in one direction. Written: dc.

Distributed Power Architecture (DPA)

A system power architecture where the ac supply into the system is converted by a Front End Power Supply into a safe voltage (usually 12V, although 48V is common) which is then converted by dc-dc converters or point of load converters locally to the load requiring the (usually) lower voltage. Benefits of Distributed Power Architecture (DPA) are spreading the power losses throughout the system (which reduces the need for additional cooling, such as heatsinking or blown air), distribution of a higher voltage bus (such as 12V) will be more efficient that distributing 3.3V (or lower) from a centralised power supply. See also Bus Converter. TDK-Lambda has a range of products suitable for designing into a Distributed Power Architecture (DPA). These include the NV-350 FEP (350W front end power supply), FPS (1000W – 3000W front end power supply) and a full range of dc/dc converters such as the PA range [up to 700W], bus converters and non isolated point of load converters (such as the PL range [available with up to 20A outputs]).

Distributed-power Open Systems Alliance

(DOSA) - formed to ensure future DC/DC product compatibility and standardization within the increasingly fragmented power converter market. The goal of the alliance is to establish customer interface standards early in the development cycle, which include form factors, footprints, pin-outs, feature sets and other parameters that will permit alternative sourcing. The alliance will cover a broad range of power converters including non-isolated (POL), isolated applications, and intermediate bus converters.


Acronym for Distributed-power Open Systems Alliance.

Double Insulation

An insulation system comprised of basic insulation and supplementary insulation. Generally, if equipment is double insulated, it does not need to be earthed. See also Reinforced Insulation.

Symbol for double insulated devices


Abbreviation for Distributed Power Architecture


A change in output over a period of time independent of input, environment or load or other factors.

Duty Cycle

In a recurring event, the ratio of on time to off time.


Abbreviation for Design Validation Testing

Dynamic Load

A load that changes from one level to another. To be fully specified, both the size and rate of change must be stated.

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