The only de-rating analysis I've ever done is with using MIL-HDBK-217F. Here's a copy. It's getting a tad old now but still covers all the main parts you might use and each component is detailed and explained. It covers all the environmental scenarios from "ground, benign" thru "airborne", "space, flight", "missile launch" and finally the top one "canon launches".
De-rating can be done by inference from this document - it'll guide you how to calculate the expected failure rate of components used in a particular circuit configuration and then you have the option of de-rating that component to either a bigger component of two sharing the same load. Bridge rectifiers, as I remember are one of the more troublesome elements.
EDIT - simple example
For a wire-wound resistor you use section 9.1 of the document and it tells you that the basic reliability of the component is: -
\$\lambda_P = \lambda_b\cdot\pi_T\cdot\pi_P\cdot\pi_S\cdot\pi_Q\cdot\pi_E\$
Then if you look further down the page you can start to choose values that are appropriate for the circuit that component is used in. For instance, I've chosen these: -
- \$\lambda_b = 0.0024\$
- \$\pi_T = 1.5\$ (I've assumed it's at 70degC)
- \$\pi_P = 1.0\$ (I've assumed it's a 1 watt resistor)
- \$\pi_S = 1.5\$ (I've assumed it's running at 50% wattage)
- \$\pi_Q = 1.0\$ (Category M supplier i.e. has an established reliability)
- \$\pi_E = 1.0\$ (I've assumed the application is ground benign i.e. the least onerous application)
\$\lambda_P = 0.0054\$ - this means failure rate per million hours. And if your design has 100 resistors like this then the overall failure rate from the resistors in your design is 0.54 failures every million hours or a MTTF of 1.85 million hours.
Two theories (really one!)
There are basically two ways of looking at an electrical circuit: electromagnetic theory (Maxwell's equations) and the theory of lumped elements.
In fact the theory of lumped parameter circuits, is a simplification of electromagnetic theory, since the latter involves a hard mathematical work for analysis or design of an electrical circuit.
The simplifications.
In the lumped parameter theory, it is assumed that all conductors interconnecting the circuit components are ideal (zero resistance). Another simplification is that all actions of magnetic induction, can be represented by an ideal element, called Inductor. By element called resistor, all energy exchanges that occur irreversibly are represented. Finally, the element called capacitor, represents interactions where electric energy is stored as potential energy.
Ideal components
Obviously, the ideal components do not exist, but while taking into account the condition of the working frequency; a coil, for example, can be modeled with good approximation by an inductor. As the operating frequency increases, the capacitive effect on the coil, due to proximity of the conductors from each other, are made much more noticeable. This capacity is not a capacitor connected to the coil (as concentrated element) but it is distributed on the coil.
When I can apply the theory of lumped parameter?
This theory represents a very good approximation when the physical dimensions of the circuit are much smaller than the shortest wavelength is expected to process. That is, when the higher frequency (shorter wavelength), this theory begins to fail, if the circuit dimensions are comparable with the wavelength. In this case, use the electromagnetic theory.
When the physical size of the circuit, is comparable with the wavelength effects start appearing, such as induced currents, to the full extent of the circuit, and also vary with the distances of the conductors that connect the components. In this case, it can not be considered to all effects of magnetic induction can be represented by a single component (i.e., an inductor), but the inductor, is distributed throughout the circuit. A similar analysis can be plotted for the case of a capacitor.
Summary.
Concentrated Parameters Theory, is a simplification of electromagnetic theory, which applies when the physical dimensions of the circuit are much smaller than the shortest wavelength of work. Three ideal elements are defined to represent the exchange of energy between the electromagnetic field and the medium: resistor, inductor and capacitor. These elements are considered physically implemented by an object (lumped!) And are connected by ideal conductors.
Best Answer
Operating the part at lower values than rated specifications
Running a part at a lower voltage or current means less heat is generated. Powering a 16v max capacitor, at 16v, is stressing it. Running a 20mA led at 20mA will only provide x number of hours of life, while running it at 10mA will provide y hours, where y is greatly larger than x.
Derating can apply to almost anything. Resistors, LEDs, Other Diodes, Capacitors, ICs, CPUs. Another common word for derating, in the context of computers and CPUs, is underclocking. As opposed to overclocking, where you run a cpu at a higher than rated speed, underclocking (aka derating) runs it at a lower speed, allowing for less heat and longer life. Mainly used when modders want to remove noisy fans.
As a note, some devices demand derating in certain situations. Resistors listed as x wattage, expect the resistor to be in free air at ambient temperatures with air movement over it. If you put it in a sealed case, or in heat shrink, or in a hot environment, you NEED to derate it down. Same with Solar Panels. The given rating is for IDEAL sunlight. Average sunlight will derate the output current and voltage.