# System Output Calculations

Discussion in 'General Electronics Chat' started by sgonzalez90, Feb 22, 2014.

1. ### sgonzalez90 Thread Starter New Member

Feb 5, 2014
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When analyzing system designs for example a PCB layout with hundreds of components...passive and active devices....how do I calculate the total output power?

I thought perhaps the best method would be to analyze datasheets for active devices...use the (typically) max power output, or output resistance...or voltages/currents and with just KCL/KVL sum up all values...

Is there perhaps a reference on this? I know my power calculations...but I'm fairly new to large scale designs and would like to refine this skill.

2. ### studiot AAC Fanatic!

Nov 9, 2007
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513
Have you thought about power supply voltage x power supply current?

3. ### ScottWang Moderator

Aug 23, 2012
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To collecting all the datasheets of parts that you have used.
According to the datasheets to calculating the current of each part.
Adding all the current of parts, and plus some more current about 20%~50% for backup request, 300%~500% for the motor if the system needed.

4. ### sgonzalez90 Thread Starter New Member

Feb 5, 2014
8
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So you are saying look at the max output power parameters or typical of the power supply?

As an alternative, would it be practical to calculate the Thevenin equivalent circuit and calculate load from these parameters?

Thanks

5. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
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It would help if you were more clear about what you are trying to do.

Gauge the power requirements of an existing board or the requirements of a design.

In the old days up to about TTl and LSI chips there were rules one could follow, but these days there are so many different types these rules have largely been forgotten.

It is surely simpler to build or simulate the circuit and measure?

6. ### crutschow Expert

Mar 14, 2008
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3,083
By "output power" to you mean the total power from the power supply consumed by all the components in the circuit? The easy way is to simulate the circuit and measure the power consumed. The old way is to calculate the power of each and every device and add them all together, which is a lot of grunt work.

7. ### sgonzalez90 Thread Starter New Member

Feb 5, 2014
8
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I basically have a system schematic of an old PCB with various components with no available models...so I'm basically just looking to find the total output power for the circuit under no load and then under full load.

8. ### studiot AAC Fanatic!

Nov 9, 2007
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The more information you supply the better will be the quality of the help.

So post your schematic and any other useful info.