Assuming the ripple portion of the current signal does not have a significant crest factor, a decent digital multimeter accross a shunt (both shall be calibrated units) will provide acceptable data. If the unit cannot maintain a current level, than the load must be reduced. In general, hi-frequency ripple on a DC output should not contribute significantly to output current or voltage data for (non-abnormal) Type Tests. If it does, something may be wrong with test conditions or the unit being tested.
The requirements of this test is to determine maximum current available on an output. It is important to be aware the some PC power supplies have cross-regulation problems for certain load combinations; so it is up to the tester to determine what load configuration will enable a max continuous current for each output; and exact test conditions shall be recorded on the TRF. Please note that data for the overload Type Test is not recorded using this test configuration. R/S, Brian have been asked by my TUV office to measure the actual output current for each of the 5-7 voltages on my PC power supplies. The purpose of this is to baseline the maximum output current in terms of maximum power, not instantaneous current, for each of the various motherboards we use. On the surface it seemed like a simple exercise of putting a DC current meter in series with each of the outputs. Given that the current demand for each of these outputs is dynamic, corresponding with the processing activity, does it make sense to measure this output current with a True RMS meter? If this is the case, I would assume that the True RMS meter takes the measurement based on some type of a time weighted average or sample time. Do any of you have a feel for how this is calculated? How do manufacturers of these PC supplies address the maximum output current ratings for each voltage. Does this rating take into account PEAK demands for current (or over current)?
