The importance of over temperature protection design

Power supplies usually come with multiple protection circuit designs including over voltage protection (OVP), under voltage protection(UVP), over current protection (OCP), over power protection (OPP), over temperature protection (OTP), and short circuit protection (SCP). Most suppliers of this product skip some of these, e.g., OCP and OTP, in their product due to lower probability of occurrence. We noticed some posts on the Internet concerning computer burnout and scorched power supplies. Fortunately no fire accidents were reported. Most FSP products are designed with OTP to power off the power supplies when internal temperature is too high. Otherwise, components in the power supply may get burnt and lead to a fire due to over temperature.

Most power supplies are safety certified. Usually they are tested and certified under conditions of output at full load, but not always at high ambient temperature. A test standard of 35°C is normal as internal temperature of most computers is at this level. Some suppliers may get a safety certification at ambient temperature of 25°C for cost saving while those more concerned about quality may test at temperature of 40°C. Still other manufacturers test their power supplies at temperature of 50°C to set them the top server grade specification compliant.

Most FSP power supplies are designed with safety certification at ambient temperature of 40°C. Products featuring OTP are subject to vigorous internal design verification process. Under conditions of rated lower or upper limit of input voltage at full load and ambient temperature beginning at the safety specification value, the test goes by raising temperature in steps of 5°C upward until the OTP mechanism is enabled. The product then goes through a full range of inspections including identifying any of its key components suffers temperature over its rated upper limit and none of them were burnt out before triggering the protection mechanism. See the table below for the test results of our flagship product—650W power supplies with OTP:

AC input: 90Vac/264Vac

Frequency: 47Hz/63Hz

Ambient temperature: Start from 45°C till OTP occur, 5°C/step

Load:

Loading	+5V	+12V	-12V	+3.3V	+5Vsb
Full	11.96A	44.8A	0.25A	11.96A	2.07A

 

( UNIT:℃)

The increasing popularity of virtual reality (VR) products is leading to fast growing demands for advanced computers of compact size, which suffers worse ventilation compared to their tower counterparts with larger volume and radiation space. High-end graphics card built in these computers raise their internal ambient temperature above 35°C. It is beyond our worst imagination for systems built with power supplies without OTP feature. Gamers, please pay special attention to this electric specification most often neglected.