Cross-Load Tests And Infrared Images
Our cross-load tests are described in detail here.
To generate the following charts, we set our loaders to auto mode through our custom-made software before trying more than 1,000 possible load combinations with the +12V, 5V and 3.3V rails. The load-regulation deviations in each of the charts below were calculated by taking the nominal values of the rails (12V, 5V and 3.3V) as point zero.
Load Regulation Charts
Toward the end of the hot-box tests, we took some photos of the PSU with our modified FLIR E4 camera that delivers 320x240 IR resolution (76,800 pixels).
The thermal images shown above were taken during the overload test with an ambient temperature exceeding 47 C (116 F). As you can see, the temperature levels of the RM750i's internals were very high.
We also took some thermal images with the top cover removed and at 28 C (82 F) ambient temperature, with the PSU delivering 50 percent of its max-rated capacity for 10 minutes. We followed the above procedure simply out of curiosity, since we wanted to check how hot the +12V FETs would get, given the lack of an actual heat sink. As you will see, their temperatures stayed at low levels (65 C, or 149 F) taking into account the fanless operation. The very high operating temperature (90 C, or 194 F) of the NTC thermistor made quite an impression on us. On one hand, this means that very low energy levels are lost on it, since the higher its temperature, the lower its resistance. However, in a hot restart and with the APFC caps fully discharged, it won't provide efficient protection against large inrush currents.