The challenge of electronic components derating verification
Derating of a component is a desired reduction of a component utilization range.
Even if it sounds strange not to use a component at 100% of its capabilities, it brings a great benefit to the final product: it allows having a long term reliability.
Even when used normally, a component is under stress. The stresses can be electrical, thermal or other. Reducing the stress allows increasing safety margin between the component usage and its limits (given in the datasheet).
On the other side, it can lead to over-design, over-cost and over-sizing. The derating should be defined in order to find the best compromise between performance, size, and costs.
The derating factor is defined as follows:
- The operating value is evaluated under normal conditions of the product
- The maximum rating value is the value that should not be exceeded, otherwise damaging or destructing the device (most of the time given in the datasheets)
Derating factors are defined for components families.
For example, for a general purpose diode, derating factors applies to:
- The forward current
- The reverse voltage
- Dissipated power
- Operating temperature (case temperature, junction temperature, etc…).
Your derating factors may come from different sources. Some are internally defined, based on the experience, other are defined by standard we have to comply with. As an example in the space industry, the standard ECSS-Q-ST-30-11C specifies derating requirements applicable to the electronic components by defining the load ratio (or limit) for each parameter.
For signal/switching, rectified and Schottky diode the applicable derating factors are listed below:
- Forward current: 75%
- Reverse voltage: 75%,
- Dissipated power: 50%,
- Junction temperature: 110°C (or Tj max – 40°C).
For all parameters of each component, you have to compare its operating value with the derated values (Maximum rating value x Derating factor). The operating value should be calculated on the full range of temperature, taking in account the normal environment of the product.
Components deratings verification quickly generates a very fastidious work: for a product with 800 components, you can have an average of more than 2000 values to calculate and to check!
This verification may generate changes:
- Modification of components to have higher maximum ratings
- Reduction of the stresses on the components by modifying the product specification
That’s why it is recommended to perform this verification as early as possible. It should also be performed for any changes on the design.
Components derating verification represents a huge amount of work and it can be a bottleneck in the design planning.
We have seen it is generally done with Excel spreadsheets, with the designer filling different cells one by one.
How is it done on your side?