In electronics, derating (or derating) is the operation of a
device at less than its rated maximum capability to prolong its life. Typical examples include operations below the maximum power rating, current rating, or voltage rating.
In electronics
Power semiconductor devices have a maximum power dissipation rating usually quoted at a case temperature of . The datasheet for the device also includes a ''derating curve'' which indicates how much a device will dissipate without getting damaged at any given case temperature, and this must be taken into account while designing a system.
As can be seen from the derating curve image for a hypothetical
bipolar junction transistor
A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. A bipola ...
, the device (rated for 100 W at ) cannot be expected to dissipate anything more than about 40 W if the ambient temperature is such that the temperature at which the device's case will stabilize (after
heat-sinking) is . This final case temperature is a function of the
thermal resistance
Thermal resistance is a heat property and a measurement of a temperature difference by which an object or material resists a heat flow. Thermal resistance is the reciprocal of thermal conductance.
* (Absolute) thermal resistance ''R'' in kelvi ...
between the device's case and the heat-sink; and the heat-sink and the ambient (this includes the heat-sinks temp/watt rating - with lower values implying better cooling characteristics).
Some capacitors' voltage capability is reduced at higher temperatures because the softened dielectric (e.g., a polymer) is softened further by the heat, and its breakdown field strength is reduced. Derating curves are included in data sheets for such capacitors.
Derating can also provide a safety margin for transient voltages or currents (spikes) that exceed normal operation or prolong life. For example, the life of electrolytic capacitors is dramatically increased by operating them below their maximum temperature rating.
In electrical installations
All
dimmers rely on heat conduction and convection to keep the electronic components cool. Similarly, power wiring (e.g., house wiring) not surrounded by an air space (e.g., inside a conduit) needs to have its current-limiting device (e.g., circuit breaker or fuse) adjusted so as not to carry as much current through that circuit. Derating is the reduction of the maximum capacity (load) a unit can reliably handle when
fin
A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...
s/side sections are removed.
See also
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Safe operating area
For power semiconductor devices (such as BJT, MOSFET, thyristor or IGBT), the safe operating area (SOA) is defined as the voltage and current conditions over which the device can be expected to operate without self-damage.
SOA is usually presente ...
*
Underclocking
Underclocking, also known as downclocking, is modifying a computer or electronic circuit's timing settings to run at a lower clock rate than is specified. Underclocking is used to reduce a computer's power consumption, increase battery life, red ...
References
* {{cite web , url= http://www.onsemi.com/pub/Collateral/MJL0281A-D.PDF , format= pdf , title= Complementary NPN−PNP Power Bipolar Transistors , work= Datasheet , id= MJL0281A , publisher= OnSemi
Electrical engineering