16
The conclusion is evident: with a PFC, peak currents are
drastically lowered.
But, I hear you say, apart from the additional cost incurred by
such a system, and the satisfaction of conforming to the new
regulations, how is the end-user going to be affected?
Figure 5
A typical example will help explain more clearly all the advantages of such a configuration:
A stereo power amplifier delivering 100 Watts on each of its outputs, in class AB mode,
consumes about 350 Watts from the AC-supply. Using a typical 110V mains source, this
equates to 3.18 Amperes-RMS or 4.5 Amperes-peak being drawn from the wall socket…
if
the amplifier behaves as a pure resistance
.
Many high quality power amplifiers available today operate in the region shown in Figure 3,
“With a large filtering capacitance”.
Under these conditions, the peak current reached during each half-period of the AC-power
cycle is plus and minus 50 Amperes! This current passes through every socket, plug,
connection and cable feeding the power supply. It won’t be long before they overheat and
make doubtful connections. Perhaps the insulation will degrade and in some cases catch fire.
In addition, these highly “spiked” currents are wonderful generators of nasty harmonics that
could well disturb other equipment nearby.
In the USA (and other 110V countries) in order to avoid these risks, users of power thirsty
equipment often are forced to install dedicated 220V branch circuits from the main local
transformer panel.
The PFC helps to resolve this costly inconvenience, and even if it has a
repercussion on the equipment price, it is easy to understand its advantages.
The MPA is equipped with one PFC per channel. Each PFC supports up to 500 W.
The MPA is fitted with two AC mains power fuses which are installed in the holder to the right
of the AC mains power switch on the rear panel. As a security measure, two fuses are
provided, one is on the Live line of the supply and the second is in the Neutral line. The
correct fuses, according to the AC mains supply voltage available, must be installed in the
fuse holder before the MPA is used.
For 94 V– 135V operation two 10A fuses should be installed
For 186V – 264V operation two 5A fuses should be installed
