Why Overvoltage, Overcurrent, and Short Circuit Protection are Important in Power Supplies

In the context of a power supply, “overvoltage” refers to a situation where the output voltage exceeds its specified rated value; that is, the supply starts to deliver a higher voltage than intended. There are several reasons why a PSU may experience overvoltage, including external voltage surges or spikes, or components failing inside the PSU. If the overvoltage is not corrected, it could result in damage to the PSU, damage to the load, or both. In a worst-case scenario, overvoltage may create a fire hazard.

Industrial power supplies incorporate an overvoltage protection (OVP) circuit, which automatically shuts down the output when it detects an overvoltage condition. In high-end industrial power supplies, the OVP circuit typically includes two feedback loops. In this setup, if the primary feedback regulation fails, the backup overvoltage lockout will disable the power supply.

In the context of a power supply, the term “overcurrent” refers to a situation where the current flowing out of the power supply exceeds its maximum rated limit; in other words, the supply begins to deliver more current than intended. There are two main causes of overcurrent. The first occurs when the load attempts to draw more current than the supply is designed to provide. This is often a temporary issue, such as a heavy load requiring extra power during startup. To mitigate this, most industrial AC-to-DC power supplies can supply short-term overcurrent, typically ranging from 120% to 140% for a few seconds.

The second cause of overcurrent is a short circuit on the power supply’s output. This could result from several factors, including damaged wires, loose connections between wires, exposed conductors touching, or a fault in the load that inadvertently creates a path for current to flow with very low resistance. If an overcurrent condition persists, it may cause overheating of the power supply components, leading to potential damage to both the power supply and the load.

Industrial power supplies are equipped with an overcurrent protection (OCP) feature that automatically reduces or cuts off the output current once it reaches a preset limit, preventing damage to the device. High-end industrial power supplies often offer adjustable overcurrent protection modes, including hiccup and tripping (foldback) modes. In this context, foldback protection refers to a method where the output voltage lowers alongside the current, reducing the overall power delivered to the load. In the case of hiccup protection, when an overcurrent condition occurs, the power supply temporarily shuts off its output, then restarts, repeating this cycle until the overload is cleared. This "hiccupping" allows the system to attempt recovery from the overcurrent condition.

The RACPRO1 family of DIN-rail power supplies was recently introduced to address the most demanding industrial applications. The RACPRO1-T240, -T480, and -T960 provide 240, 480, and 960 watts, respectively (Figure 1).

The RECOM AC/DC, DC/DC, and EMC Book of Knowledge provides an extensive collection of insights and best practices necessary to implement successful AC/DC power supply designs. Chapter 12 discusses strategies to reduce housekeeping power consumption along with some measuring techniques.

Also, RECOM’s Energy Efficiency in AC/DC Power Supplies: Quick Guide to the Essentials blog offers a helpful introduction to Ecodesign regulations, which are a set of standards and guidelines established by governments or regulatory bodies to ensure that products are designed to minimize their environmental impact throughout their life cycles. These regulations primarily focus on improving energy efficiency and promoting sustainability by reducing waste, emissions, and resource consumption.

The RACPRO1 webpage provides more information about this exciting new DIN-rail mounted power supply family.