# Why doesn't the RMS current and voltage give me average power?

Apologies for the multiple bridge rectifier questions.

I have a 230V/9V 10VA transformer, and I want to know how much DC current I can draw from this circuit. From this I assume that the $I_{rms\_max} = 1.1A$.

I ran the simulation for various values of C1 and R1, and this seems to give the greatest possible DC current (I think).

Because this was going to be fed to a boost converter, I allowed 2V ripple.

The following values were obtained from LTspice:

• $V1_{rms} = 9V$
• $I_{V1(rms)} = 0.96A$ <- Less than 1.1A
• $V_{out(rms)} = 10.15V$
• $I_{R1(rms)} = 0.40A$

This gives me:

$$\eta = \frac{P_{out}}{P_{in}} = \frac{10.15*0.4}{9*0.96} = 47\%$$

However, this is the power graph:

The average values of the graphs give me 4.9W and 4.13W, which gives me an efficiency of 84%.

Which value is correct?