Derating
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- This article is about electronics. For the adjustment of engines for longer engine life see engine tuning.
In electronics, derating (or de-rating or de-tuning) is the operation of a device at less than its rated maximum power in order to prolong its life.
In electronics
Derating in Electronics usually relates to each of the main variables in the circuit voltage(V), power(P) and current(I). Derating refers to creation of a buffer zone between the maximal rating from the manufacture and the actual stress level applied on the component. Derating is a compulsory procedure in some reliability standards(MIL) and requires a stress analysis in order to be applied. For example: Power electronic devices have a maximum power dissipation rating usually quoted at a case temperature of 25 °C (77 °F). 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, the device (rated for 100 W at 25 °C (77 °F)) 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 stabilise (after heat-sinking) is 65 °C (149 °F). This final case temperature is a function of the thermal resistance between the device's case and the heat-sink; and the heat-sink and the ambient (this includes the heat-sink's temp/watt rating - with lower values implying better cooling characteristics).
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 fins/side sections are removed.
References
Datasheet of power transistor MJL0281A on OnSemi (PDF)
Derating for Electronic Design
MIL 217F reliability standard section 3.4.4
