Zalman 300W ZM300A-APF Quiet Power Supply
When was the last time
you gave more than a passing thought to your power supply? If it works, good.
If it can supply 300 Watts, super. If it makes noise.... you live with
it right? The answer to that last question doesn't always have to
be no, and in the case of the Zalman ZM300A-APF the answer
most certainly is "quiet."
Zalman have founded their company on the concept of providing cooling and
related products which adhere to their own CNPS (Computer Noise Prevention System)
standards. So as we opened up the box for the ZM300A-APF a low noise
power supply greeted us.
From the outside there is no difference between
this power supply and any other you can see except for the lack of a 115V-250V
selector switch (this power supply has circuitry which doesn't require it). The
ATX 2.03 compatible power supply is Pentium 4 compliant and supplies a healthy
300W of juice to the computer.
Zalman's power supply comes with one internal
exhaust fan, (7) molex connectors, (2) FDD connectors, a 24-pin ATX connector,
and a 6-pin & 4-pin Pentium 4 auxiliary power connector.
Additionally, to make powering all those
case fans we have these days easier, this goes against the low-noise mantra just slightly,
Zalman also include a rather handy Molex-to-four 3-pin fan headers connector. Two
of those fan headers supply 12V, and two supply a lower voltage for
quieter cooling possibilities (5V).
Along with the power supply come a fairly detailed set of instructions. Within
the booklet are a set of good technical explanations behind the ZM300A. I think
it's worth quoting two of the sections here for a better understanding of what goes
into making a reliable, and good power supply. Wattage and noise levels are only
one facet after all. The most important component can be the internal circuitry
which is almost always transparent to the user.
Power Factor Correction (PFC) - In a conventional power
supply with switching regulators, a rectifying circuit that converts AC
input source into a DC source for the primary circuit is used. In this
rectifying circuit, a capacitor with a large capacitance is used to soften
transient response and reduce ripple so that the switching regulator is
not over-stressed. However, the peak charge of the capacitor becomes
greater with greater capacitance, and this leads to non-linear bursts of
peak over current into the primary circuit.
Such peaks of current distort output voltage, create harmonic
frequencies, and reduce power factor. There is now an international
standard for controlling harmonics and PFC is mandatory for home
appliances consuming over 70W or more power in Europe. PFC circuitry is
classed as either Active or Passive.
Active PFC uses switching regulator technology called boost-up. Using
active elements such as IC, FET and diodes to create the PFC circuit. This
circuit has a theoretical power factor of over 95%, accepts a full range
(90VAC-260VAC) of AC input, and reduces total harmonics noticeably.
However, it needs a complicated EMI filter and an input source circuit,
and is costly to build. The ZM300A-APF is based on this technology.
The other system is called Passive PFC and this uses passive elements
such as an iron core inductor on the input source to create a countering
reactance. While this can easily be applied to existing power circuitry
without much modification, the power factor is low (60-80%), the AC input
must be chosen (115VAC/230VAC), and the harmonics produced from the
difference between the capacitance and the inductance are hard to control.
There can be large amounts of electromagnetic noise with this system from
the 115VAc input source.
Ripple Voltage - One of the other important factors in
choosing a power supply is the level of DC ripple voltage. A
ripple is normally defined as the peak-to-peak voltage caused by an imperfect
rectification of an AC source. In the case of the typical
switching regulator, ripple factors from the low-frequency AC input source, the high-frequency switching,
and impulse noise contribute to the DC output ripple.
This ripple and impulse noise can be reduced to below regulation limit
by inductive canceling within the rectifier circuit, but if the output
ripple exceeds the limits and is carried into the system, the logic level
of active elements becomes unstable and the system can
The power cables are nice
and long at about 55 cm which is great for those tall tower cases. For those users there
is always the concern of power cables not reaching the lower components. With the ZM300A's its fan running
at 1200 RPM for an internal temperature of 40 degrees Celsius or below, the heatsink
is almost impossible to hear.
When the internal temperature rises to between
50-60 degrees Celsius the fan speed rises up to the 1500RPM mark. Above that
point the fan will increase to 2000RPM to ensure proper cooling levels are