When it comes to working with power supplies (Figure 1), there are many considerations design engineers must take into account to avoid common issues such as input under and overvoltages. This article will take a deeper look at five key power supply problems, how to know when they arise, and the best ways to address or mitigate them. Figure 1. Power supplies are often overlooked when they work well, but as soon as the quality of their performance degrades, it becomes almost impossible to ignore them

　　Temperature Issues

　　Falling either under or over the recommended temperature range for a power supply is another common issue that can cause problems for a power supply. Thermal limits ensure that the power supply safely operates within a range where you can account for its performance.

　　Figure 2. Operating a power supply outside of a safe operating temperature 

 as shown in the temperature derating curve can lead to unpredictable behavior.

　　Outside of the minimum and maximum operating temperature, reliability, regulation, EMI, and efficiency can quickly become problems. Many components inside the power supply, such as the transistors, operate at temperatures close to their thermal limits. Operating the power supply beyond its rated temperature can cause these devices to fail.

　　Some power supplies allow for an extended temperature range if the output power is decreased or derated. The datasheets for these power supplies will contain derating curves, such as the one shown in Figure 2, that show the maximum temperature for specific load conditions. Derating may be required at lower temperatures as well. At very low temperatures, the values of some components, especially electrolytic capacitors, can be significantly different than under normal conditions. This can result in increased ripple voltages and start-up issues.