Power Consumption? Or Current Consumption?

[ericmar]

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@2A, should we only supply it 15V@2A or say, 15V@3A which is 50% extra in terms of supply current.

Thanks,
Eric Mar

 

[Sal]

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

 

[ericmar]

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

 

[Kral]

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

 

[ericmar]

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

 

[El-Hadidy]

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

 

[safwatonline]

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

 

[ericmar]

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

 

[shwoo]

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.

 

[Kral]

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

 

[Tamas888]

The energy consumption is E = P*T, P are [V] and [A] and T is .
And if I have a battery I know it uses 1800mAh -> it [A] and ..
where is the [V]? I know it's a constans
T

 

[Kral]

Tamas888
The ampere-hour rating of a battery is an indication of the charge, not the energy, that a battery is capable of storing.
.
I = Coulombs/second
so coulombs/second X seconds = coulombs = charge.
.
Ampere hours is used insted of ampere seconds for convenience. It results in a smaller number.
Regards,
Kral