Protection Features Evaluation

Every PSU should be equipped with a protections set that will not only protect the PSU, but the whole system it feeds. You can learn more about PSU protections by reading through the corresponding section of our "A Detailed Look Into PSUs" article.

In a snap, the most important protections for PSUs are the following:

• Over Current Protection (OCP)
• Over Power Protection (OPP)
• Over Temperature Protection (OTP)
• Over/Under Voltage Protection (OVP/UVP)
• Short Circuit Protection (SCP)
• No-load Operation (NLO)
• Surge & Inrush Protection (SIP)

We should note here that OCP isn't usually offered in single +12V rail PSUs, especially high capacity ones. In such units, OPP takes over. OTP is very important, and we won't mess with OVP/UVP until we find a way to safely evaluate it.


The over-power protection feature is set to normal levels, while OCP is high on all rails, especially at 5VSB where it should be set much lower.

FSP neglected mentioning it, but OTP is present and properly configured. OTP is essential, especially in server-oriented PSUs with high power density. Lastly, there is fan-failure protection as well, which we confirmed to work as it should. The module will shut down should the fan of one of these modules break or simply disconnect. There is also short-circuit protection on all rails, and the power-good signal is accurate since it drops before the rails go out of spec.

Since this frame hosts two power modules, one of which will fully take over should the other break down, we had to run some tests to check on transitioning times, and on how smoothly the transition actually takes place in terms of +12V output. This wasn't easily done, but our advanced (and very expensive) scope allowed us to do so successfully. For the following tests, we applied a full load (500 W) to the PSU.


Here's the moment we cut power to the first module. As you can see in the screenshot above, the total time between the drop in power and the second module stabilizing the +12V rail is 70.2 ms. FSP used large bulk caps to facilitate a smooth transition. The long hold-up time is a major advantage in this particular case.


The peak voltage overshoot is 40.6mV, while the voltage drop reaches 203.7mV. This means that the +12V rail stays within spec during the transition.


We noticed the first effect on the +12V rail's output 26.6 ms after removing power from the first module. This is very close to the power module's hold-up time, and we believe this is the moment the second module kicks in.


The peak of the voltage overshoot happens 39 ms after we remove power from the first module.


The voltage drop starts 48.8 ms after the power cut. Naturally, the second power module needs some time to adjust its operation to the transient load. The peak of the voltage drop is 53.8 ms after removing power to one of the modules.


Here's the last scope screenshot. The transient recovery time is 21.4 ms, which is normal, and as you can see from the scope screenshot above, ripple at +12V slightly increases afterward because the module has to deliver 500 W on its own from now on out, instead of only half that amount, which was the case when both modules were operating.