# Total power dissipation of a circuit in Ltspice

#### Ikh1

##### Newbie
Hello, I have a circuit with 40+ components and multiple voltage sources. How can I calculate the total power dissipation in Ltspice? I know how to find the dissipation for individual components but is there a way to calculate it at once for the whole CMOS circuit like in pspice. Also, is there a way to get it in text instead of the waveform?

#### KlausST

##### Super Moderator
Staff member
Hi,

not sure how your circuit looks like:

but I guess there is an (or more) electrical input and an (or more) electrical outputs.

then
power_dissipation = input_power - output_power

Klaus

#### Ikh1

##### Newbie
Please can you tell if it applies to this circuit as well?

#### KlausST

##### Super Moderator
Staff member
Hi,

I see no reason why it should not.

For exact calculation you have to take the pulse input also into account.

M5_gate seems to not be connected properly.

Klaus

### Ikh1

Points: 2

#### Ikh1

##### Newbie
Thank you, fixed the M5_gate. I'm confused about how to find the output power.
The input power components would be 2 sine sources as well as pulse input. But what about the output?

#### KlausST

##### Super Moderator
Staff member
Hi,

generally:
P = V x I

for non DC signals you should calculatate the average of P over a useful time. (at least one fullwave)

Independent of: input, output, waveform, frequency, phase shift, overtones, non linearty, ....

Klaus

#### Taihung

##### Junior Member level 3
I often use efficiency report.
Open simulation command, tick []

Result will appear like this:

#### FvM

##### Super Moderator
Staff member
You should mention that the option "Stop simulating if steady state is detected" depends on a special function, which is built into most LT SMPS controller models. As stated in the online help under Circuit Efficiency Calculation
The program will detect the steady state by checking the internal state of the switcher macromodel. It doesn't work when a switching regulator part is not part of the circuit because the steady state detection is implemented in the model -- usually by looking for the the current flowing out of the error amplifier to drop to zero as integrated over a switching cycle.

You can also implement steady state detection by using the EAclk parameter of the OTA special function.

#### Taihung

##### Junior Member level 3
You should mention that the option "Stop simulating if steady state is detected" depends on a special function, which is built into most LT SMPS controller models. As stated in the online help under Circuit Efficiency Calculation

You can also implement steady state detection by using the EAclk parameter of the OTA special function.
Yes, sometime it will not stop until the end of simulation time.
If "stop" by hand, the result will not accurate. But acceptable.