# How I do calculate the power consumption

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#### cheniour

##### Member
what is the method that I applied to calculate the power consumption of this bloc in the paper it's equal 6.7 μW at 1.5 V Welcome to ETO!
What 'paper' are you referring to?
Read the datasheets for the components to find their power consumption.

Assuming that you're not interested in the current consumption of the NAND gates, there are 4 ways the power can go, and you need to add them up.
1. Oscillator consumption from data sheet
2. Power to charge and discharge the 7 pF capacitor at the frequency of the oscillator
3. Current through the variable resistors.
4 . Current taken by the comparator

No. 3 is interesting. If there are two variable resistors, if they are both turned to minimum resistance then the current could be quite large.

@driver300 thank you but how I can calculated the power charge and discharge of the supercapacitor please there is equation that I can used it ?

sorry I means the 7pF capacitor not supercapacitor

The 7pF capacitor is a SUPER tiny value capacitor.
The datasheet for the MCP6543 shows that it will do nothing when powered by your 1.5V supply because its minimum allowed supply is 1.6V.

@driver300 thank you but how I can calculated the power charge and discharge of the supercapacitor please there is equation that I can used it ?
It's not a super capacitor, it's just a capacitor.

In calculating the charge, the first thing to do is to calculate the time constant. That's just RC, so 460,000 * 7E-12 which comes out at 3.22 μs.

Assuming that the oscillator is 32.768 kHz, the time constant of 3.22 μs is a lot smaller than that. That means that the capacitor will be almost completely charged each cycle.

The charge needed to fully charge the capacitor is just 7E-12 * 1.5 = 1.05E-11 Coulombs. The current is the number of Coulombs per second, so that is 1.05E-11 * 32768 = 0.344064 μA. The power is the current times the voltage so that is 0.516096 μW.

I agree with audioguru that 1.5 V is too low to be sure that the comparator works, but that doesn't mean that it definitely won't work at 1.5 V, it means that it might not work or might not meet other parts of its specification.

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