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ADVERTISEMENT FEATURE COVER STORY Derating power supplies
Derating is a protective measure which allows the use of power supplies at high temperatures, at high altitudes, or in alternative mounting orientations. But why is derating necessary? Maximilian Hülsebusch – PULS Power global product marketing & communications manager, explains
components. Above a defined temperature limit the output power must be reduced linearly. The corresponding value can be found in the data sheet. As an example, the 960W (24V, 40A) power
supply QS40.241 requires a derating of 24W/°C above 60°C. If it is required to use the device near its temperature limit of 70°C, only a maximum output of 720W would be advisable to maintain the life expectancy or MTBF. This value must be taken into account when
selecting a power supply – especially if a device requires derating even at lower temperatures. Many commonly used power supplies demand the reduction of the output power from just 40°C, however such temperatures are common in a closed control cabinet without a cooling system. System engineers have four options to solve this problem: 1. Choose a power supply that has a higher temperature limit before it requires derating.
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2. Choose a power supply unit with a higher output power in order to have a sufficient power budget available despite derating.
hile most power supply manufacturers specify ratings for lifetime, output current, and reliability (e.g., MTBF) for
their products, this information only applies under certain environmental conditions. In particular, the temperature limits must be observed so that the components in the power supply do not overheat or wear out prematurely. The means to regulate internal temperature is the so-called ‘derating’. Derating means the reduction of the output
power depending on the ambient conditions. It is therefore a recommended protective measure for electronic components and devices to protect them from high temperatures and prevent failures. The power reduction is precisely specified for each power supply; and the necessary procedure is described in the respective data sheet.
When is Derating necessary for a poWer supply?
There are several environmental conditions that increase the internal temperature of a power supply and become a potential risk, including high ambient temperatures, an installation altitude of more than 2,000m, and mounting orientations that deviate from the recommended installation. Power supplies do not regulate derating
automatically – users have to adapt the device to the ambient conditions of the application during installation. Considering this will avoid system downtimes and damage to the power supply itself. Specifications for the necessary settings
8 DESIGN SOLUTIONS DECEMBER/JANUARY 2023
for power supplies are in their data sheets. The derating curves for adapting the output current depending on the temperature and the installation altitude are also very helpful.
Derating at high ambient temperatures
Nearly all industrial power supplies require derating above a certain ambient temperature in order to protect their electronic
3. Connect multiple identical power supplies in parallel to get the total power required.
4. Install a cooling system. All options mean higher investments
within the planning phase of the system but are usually worth it in terms of higher reliability and longer service life. Even if the system is subsequently
expanded, it must be checked whether the power supply can provide sufficient power
Derating curves related to the altitude for the power supply CP20.241
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