Title
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Hugo Dias

01/31/2023, 11:57 AM
Hi guys, What's the best way to get rms vdd potency (Real and Aparent)? I did: let pot= - i(vdd) *vd meas tran pot_rms rms pot from... (or something like that) Obs. : it worked, but i dont know if its the more safe way. Obs. 2: i dont know if i got a Apparent or Real potency with that code shown.
s

Stefan Schippers

01/31/2023, 2:01 PM
You are in the time domain. Do not calculate the
``rms``
value of a power. RMS is the (square root) average of squared values, taking the square of instantaneous power and taking the average is nonsense. If you want to get the average power do:
``let pow = i(v1) * v(a,b)``
``meas tran cap_avg_pow avg pow from=600u to=800u``
If
``a``
and
``b``
are the nodes of a capacitor and
``i(v1)``
is the current flowing into the capacitor in steady state the average power into the capacitor is zero. See example below. Instantaneous power into or out a capacitor is apparent, it has net value zero. See ngspice calculated value (in blue) at the bottom.
1.png