Bill Turner wrote:
> I wonder if someone could clarify this for me. I've heard this before
> but not quite understood it.
>
> My question is, for the same DC output, why is the RMS current in the
> transformer higher with one type of filter vs another type? I would
> think it would be the same.
To be more precise, the ratio of RMS AC input current to average DC
output current of a rectifier with capacitor input filter is higher
than the ratio of RMS input current to average DC output current of a
rectifier with choke input filter.
RMS is a calculation that tells you the DC that has the same heating
effect as an arbitrary waveform. The S in RMS refers to a squaring
operation on the instantaneous current or voltage, since heat in
resistors is proportional to the square of current through or voltage
across them. To perform an RMS calculation, you need to
instantaneously square at least a half cycle (since the squaring
operation makes the negative and positive half cycles look the same),
then average that squared waveform over its period of time, then take
the square root of that average. Root of the Mean of the Square. The
squaring operation gives appropriate emphasis of the larger peaks,
since these contribute a non proportional (squared) addition to the
total energy per cycle, dumped into any winding resistance this
current passes through.
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