# Power consumption of a PCB

Discussion in 'General Electronics Discussion' started by andrewm37, Sep 28, 2012.

1. ### andrewm37

4
0
Sep 28, 2012
Hy!

I designed a PCB and now I would like to determine the current consumption and the power dissipation. I know that there is there factors that define these things: static, dynamic, switching. Static is quite easy for example I have a MOSFEt and a do this : Ps= IDss*V
Dynamic is when I Pd=Cpd*V^2*fout , and I have problem with the switching one:
The equation states this: Ps= CL*V^2*fout. Where CL is the load capacitance. I have 2 0.1u, 1 10u and 1 10p cap connected to my P-mos to reduce inrush. What i did is that I added these caps as paralell ( ~10.2u) and substituted it back to the equation as CL. My V is 5Volt and fout is ~ 25 Mhz (1/ton). This gave me a huge dissipation : 6375 W , I am sure I miscalculated something. Any suggestion. This is the P-mos datasheet:
And this is where I got the info how to calculate power consumtion:
http://www.ti.com/lit/an/scaa035b/scaa035b.pdf

2. ### davennModerator

13,810
1,944
Sep 5, 2009
Hi Andrew
Welcome to the forums

your capacitance is going to be 10.10001uF .... for practical purposes the 10pF is so small in value it doesnt really add anything significant to the overall capacitance
its only 0.00001 uF

can you not just do some basic current measurements ?

Dave

3. ### andrewm37

4
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Sep 28, 2012
How do you mean that?

4. ### CocaCola

3,635
5
Apr 7, 2012
Like this, the 'lamp' represents your circuit...

5. ### andrewm37

4
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Sep 28, 2012
Yes, but I would like to measure it in theory chip by chip.

6. ### wingnut

242
9
Aug 9, 2012
Have you tried a simulator like LTspice?

7. ### andrewm37

4
0
Sep 28, 2012
Yes but not for measuring power. According to the datasheet the power can be calculated if you know certain parameters like Cin Cload Cpd Icc Fout and of course the supply voltage.
But I'm stuck where I wrote that in my original thread.

8. ### wingnut

242
9
Aug 9, 2012
Your maths is correct to get 6375W, so there must be something wrong with your data or equation for Ps surely?