RMS current

Power factor correction circuits are intended to increase the conduction angle of the rectifiers and to make the ac input current waveform sinusoidal and in phase with the voltage waveform. The input waveforms can be seen in Figure C-2. This means that all the power drawn from the power line is real power and not reactive. The net result is that the peak and RMS current drawn from the line is much lower than that drawn by the capacitive input Alter circuit traditionally used. 

Capacitor RMS current depends only on the power, turns ratio, and inductance... 

So what are the temperature multipliers really telling us All they really tell us is how the vendor has designed his capacitor from a thermal point of view, or what exactly is the capacitor s core temperature. As we will see, if we stick to the RMS current rating of the capacitor (without applying temperature multipliers), we don t really need to know the details of the core temperature either. Temperature multipliers were therefore just objects of abuse by some designers in the past. This is perhaps why nowadays most elko datasheets are no longer even carrying that information. 

For the Buck, we see that the input capacitor RMS actually maxes out at D = 50%, whereas the output capacitor RMS current (curve number 12) increases dramatically at low D (high input). Does that really mean that we have to worry about the dissipation in the output capacitor Think about it. The output capacitor in a Buck is barely responsible for any of its losses, since it sees only the smoothened (undulating) inductor current. So yes, as a... 

Figure 12-14 The RMS Current Through the Output Capacitor of a Buck...

Winslow RM. Current status of blood substitute research towards a new paradigm. J Int Med 2003 253 508. 

One method by which transformers may be rated for suitability to handle harmonic loads is by k factor ratings. The k factor is equal to the sum of the square of the harmonic frequency currents (expressed as a ratio of the total RMS current) multiplied by the square of the harmonic frequency numbers ... 

I2 is the ratio between the second harmonic current and the total RMS current. 

The transformer specified should be capable of handling 559 A of total RMS current with a k factor of not less than 4.378. Typically, transformers are marked with k ratings of 4, 9, 13, 20, 30, 40, and 50, so a transformer with a k rating of 9 should be chosen. Such a transformer would have the capability to carry the full RMS load current and handle winding eddy current losses equal to k times the normal rated eddy current losses. 

Feibel RM. Current concepts in retrobulbar anesthesia. Surv Ophthalmol 1985 30 102-110. 

In high-power offline Flybacks, the trace inductances on the secondary side reflect on to the primary side, and can greatly increase the effective primary-side leakage inductance and degrade the efficiency. The situation gets worse when we have to stack several output capacitors in parallel, just to handle the higher RMS currents. Long traces seem inevitable here. This has been discussed in detail previously. 

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