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Q10066 PC power supply for PCI DAP and iDSC system

Tags: Help, PC power supply, power requirements

Applies to: PC power supply

How should I select a PC power supply for my DAP system?

PCI DAP boards and iDSC boards require current at +5V or +12V, or both, from the power supply in the PC. Any DAP-powered accessory boards also draw current from the same power supply through the DAP board. To determine whether the PC power supply is sufficient for your system, follow the steps below.

1. Determine the current requirements of the DAP/iDSC boards and any DAP-powered accessory boards (i.e. not in an industrial enclosure with a built-in power supply).

2. Add up the current required at +5V and +12V (if any) separately.

3. Determine the rated +5V and +12V output current rating of the power supply in question. Subtract the total(s) calculated from #2. This is the remaining current for PC operation.

4. Calculate the total current required for the motherboard, processor, PC backplane, disk drive(s), and any other components for the PC to operate. Verify that the remaining current from #3 is sufficient for the PC. If not, you will need a larger power supply.

Let's take the following two-DAP configuration as an example. The DAP boards and most of the expansion boards have power consumption in the spec sheet on our web site or/and in the product manuals.

• 2 x DAP 5216a/627 - 2 x 7A @ +5V = 14A

• MSIE010-08 - 2 x 232mA @ +5V for the interface board MSXB033 = 0.46A

• 4 x MSXB078-01-E3P - 4 x 30mA @ +5V = 0.12A

• 2 x MSCBL076-01 - none

• 2 x MSCBL054-01-L36 - none

The total current required by the two DAP boards and their accessory is about 14.6A @ +5V. Let's say the PC in question has a 500W supply with the following specs

• DC Output - +3.3V@25A, +5V@25A, +12V@36A, -12V@0.3A, +5VSB@2.5A

Subtracting the 14.6A required by the DAP system, the remaining current available for the PC at +5V is then roughly 6.6A. Verify that the total current required by the PC components (according to their specs) at +5V does not exceed 6.6A.

Notes:

• Most PC power supplies have a maximum power rating for the sum of power drawn from 3.3V and 5V combined. In addition to calculating the 5V current available, you must also verify that your system does not draw more than the total power allowed on the combination of 3.3V and 5V.

• Any current you draw in your application circuits must also be accounted in your power budget. The main places where you will draw current are from the power supplies, DAC outputs, digital outputs, and sensor voltage or current excitation outputs from the DAP or accessory boards.

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