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ericmar
Joined: 14 Apr 2004
Posts: 279
Location: Singapore
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 20 Dec 2006 8:02 Power Consumption? Or Current Consumption? |
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Dear all,
May I know how do we normally calculate the power consumption or rather current consumption of a circuit design? Do we sum up the maximum supply current of each component on the circuit to estimate the maximum current consumption?
How many percent extra current should we supply for the circuit? For e.g. if a circuit requires 15V(at)2A, should we only supply it 15V(at)2A or say, 15V(at)3A which is 50% extra in terms of supply current.
Thanks,
Eric Mar
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Sal
Joined: 29 Nov 2005
Posts: 310
Helped: 37
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20 Dec 2006 16:03 Power Consumption? Or Current Consumption? |
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Hi
For simple circuits you find the circuit impedance Z, then appy very know formulas for power calculataion P= V^2/Z, where V is the supply voltage and P is the power consumption. Now, if the circuits are complex, with CIs and other components, we use the Z parameters where a circuit is seen as a black box and the Z parameters are obtained.
About the guard current, it pretty depends on the circuit nature, it is different for a circuit which makes some filtering to other which may control a motor. Cost and extra power are traded off in this matter.
Sal
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ericmar
Joined: 14 Apr 2004
Posts: 279
Location: Singapore
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20 Dec 2006 17:48 Re: Power Consumption? Or Current Consumption? |
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| Sal wrote: |
Hi
For simple circuits you find the circuit impedance Z, then appy very know formulas for power calculataion P= V^2/Z, where V is the supply voltage and P is the power consumption. Now, if the circuits are complex, with CIs and other components, we use the Z parameters where a circuit is seen as a black box and the Z parameters are obtained.
About the guard current, it pretty depends on the circuit nature, it is different for a circuit which makes some filtering to other which may control a motor. Cost and extra power are traded off in this matter.
Sal |
Hi Sal,
Can u give me an example? Just a simple circuit will do.
Thanks,
Eric Mar
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Kral
Joined: 28 Mar 2005
Posts: 1182
Helped: 187
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20 Dec 2006 19:41 Re: Power Consumption? Or Current Consumption? |
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ericmar,
One approach is to assume the difference between typical current and max current is the 3sigma limit. Then add the RSS values of the deviations to the nominal current. Example:
Component 1:
Inom1 = 1.0
Imax1 = 1.2
Component 2:
Inom2 = 1.5
Imax2 = 1.75
Component 3:
Inom3 = 0.5
Imax3 = 0.6
Rssdev = Sqrt[(1.2-1)^2 + (1.75-1.5)^2 + (0.6-0.5)^2]
Rssdev = Sqrt(.2^2 + .25^2 + .1^2)
Rssdev = sqrt(.04 + .0625 + .01)
Rssdev = .3354
So your upper 3 sigma limit would be 1.0 + 1.5 + 0.5 + .3354 = 3.2254
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This approach gives a more realistic estimate of your actual requirements than does using the max rating of each component.
Regards,
Kral
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ericmar
Joined: 14 Apr 2004
Posts: 279
Location: Singapore
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21 Dec 2006 3:14 Re: Power Consumption? Or Current Consumption? |
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| Kral wrote: |
ericmar,
One approach is to assume the difference between typical current and max current is the 3sigma limit. Then add the RSS values of the deviations to the nominal current. Example:
Component 1:
Inom1 = 1.0
Imax1 = 1.2
Component 2:
Inom2 = 1.5
Imax2 = 1.75
Component 3:
Inom3 = 0.5
Imax3 = 0.6
Rssdev = Sqrt[(1.2-1)^2 + (1.75-1.5)^2 + (0.6-0.5)^2]
Rssdev = Sqrt(.2^2 + .25^2 + .1^2)
Rssdev = sqrt(.04 + .0625 + .01)
Rssdev = .3354
So your upper 3 sigma limit would be 1.0 + 1.5 + 0.5 + .3354 = 3.2254
.
This approach gives a more realistic estimate of your actual requirements than does using the max rating of each component.
Regards,
Kral |
Hi Kral,
Sorry for my innocence. But this is the 1st time i heard abt the 3sigma limit! U hv taught me sth new. Thanks a lot.
Regards,
Eric Mar
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El-Hadidy
Joined: 23 Feb 2006
Posts: 63
Helped: 1
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22 Dec 2006 20:31 Re: Power Consumption? Or Current Consumption? |
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Hello Eric,
The consumption used is always the "Power Consumption". Practically there is nothing called "current consumption".
The current is normally dependent on the impedance of your circuit. So, when you have a 15V, 2A supply, the voltage will be constant(15V) but the current will depend on the impedance of the circuit. You have to ensure your circuit will drive a maximum of 2A.(i.e. impedance of 7.5 Ohm).
Thanks
El-Hadidy
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safwatonline
Joined: 19 Nov 2005
Posts: 1418
Helped: 172
Location: EGYPT
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22 Dec 2006 20:54 Power Consumption? Or Current Consumption? |
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| they are equivelant as P=VI ,so if u have P consumed then for ur supply V u have a consumed current I=P/V
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ericmar
Joined: 14 Apr 2004
Posts: 279
Location: Singapore
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26 Dec 2006 3:01 Power Consumption? Or Current Consumption? |
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How do I find out the power consumption of an IC if the datasheet only specifies its Supply Voltage, Quiescent Current, etc. without Supply Current?
Thanks,
Eric Mar
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shwoo
Joined: 19 Apr 2006
Posts: 107
Helped: 13
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26 Dec 2006 6:56 Re: Power Consumption? Or Current Consumption? |
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You need to be more specific. For example, amplifiers will consume more
current if you push more power out of the IC. Digital logic IC's will
consume more current at higher frequency.
Regards,
S. H.
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26 Dec 2006 6:56 Ads |
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Kral
Joined: 28 Mar 2005
Posts: 1182
Helped: 187
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27 Dec 2006 13:37 Re: Power Consumption? Or Current Consumption? |
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Eric
There are a couple of things to try. First go to the websites of several vendors. Datasheets from some vendors are very sketchy. Second, contact the vendor via the "contact us" feature of its web page. Ask for the information. It's usually available, even though it doesn't appear on the datasheet. As a last resort, call the vendor and ask for an Applications Engineer.
Regards,
Kral
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