Specifications

54 Matrox Mura MPX Series – System Builder’s Guide
Power supply sizing for Matrox Mura
MPX-based systems
When assembling a system based on Mura MPX Series products, the power supply must be sized to
provide power for the entire system, including the CPU, all add-in cards, and any peripherals
connected. To determine the power supply size, you must consider not only the power requirements
of all devices but also the power rails from which the current is being drawn.
Each power supply provides different voltages with varying current load capacities, depending on
system usage. For example, a -12V supply (still used in some systems) supports less than 1A of load,
whereas a +12V supply, which bears the brunt of the load in modern systems, can easily exceed 50A
capacity in many mid-sized power supplies. The remaining voltages (typically, +3.3V, +5V, and
+5VSB) fall between these extremes in terms of current load capacity.
Mura cards, being PCI Express-based, draw power primarily from the +12V supply. Although a small
amount of power (approximately 0.1A) is drawn from the +3.3V supply, the power supply must have
sufficient capacity on the +12V supply rail. Since each Mura SKU has slightly different power supply
requirements, using the largest possible current requirement to size the power supply will ensure the
power supply is adequate, regardless of the SKUs installed.
To properly size the power supply, the power requirements of all the devices must be added together
separately for each supply rail and then the appropriate power supply selected. For example, the Mura
MPX-4/4 SKU (4 outputs, 4 inputs) consumes approximately 3.5A from the +12V supply. Seven
Mura MPX-4/4 cards would therefore consume approximately 24.5A (or 7 x 3.5A) from this supply.
This +12V current requirement is in addition to any pre-existing requirements of the motherboard
and/or system (for example, CPU, motherboard, hard disk drives, etc.). In other words, if the base
system requires 15A from the +12V supply with no Mura cards installed, once the Mura cards are
installed the power supply must provide 15A + 24.5A (or 39.5A) on the +12V rail for adequate power
supply.
A merely “adequate” power supply, however, isn’t sufficient. Most power supplies operate at optimal
efficiency at 50-60% of their rated power load. Continually operating beyond this may cause excessive
thermal generation and lead to premature aging of the electronic components. It’s common practice
to ensure that the power supply can supply additional current beyond what’s required for the system
configuration in typical use. For maximum efficiency and reliability, make sure to provide a
minimum 50% margin on the power supply rating. In the example above, a system requiring 39.5A
on the +12V rail would require approximately 475W. Assuming another 50W for the +3.3V rail and
10W for the +5V rail, the total system requirements are approximately 475W + 50W + 10W, for a total
of 535W. A 50% margin on the power supply means specifying a supply of 800W that can supply at
least 60A on the +12V supply.