How to calculate the efficiency of a switch mode power supply?

[Maniac_XOX]

Homework Statement

I have designed a non isolated circuit meant to input a high voltage with AC, then filter the AC to DC with an inductor, a capacitor and a full wave rectifier.
Then it has to step down the high voltage through a transformer. The circuit has an R-L-C on its input side. It works and fits its purpose but i have to measure its efficiency.

Relevant Equations

P=VI
P= Vrms / Z

I know how to calculate the power output and input by analyzing the current in put and output with multimeters and using the formula P=VI. But P_out is obviously incomparably smaller than P_in so the efficiency would suck this way. Is there a better way to do this??

 

[DaveE]

I think we'll need a schematic. Your description doesn't make sense to me. You rectify and filter HV AC to make DC and then you step it down with a transformer. I must not understand, or, alternatively, your efficiency is 0.

 

[phinds]

And to add to what @DaveE said, you would get zero output from a transformer that has high voltage DC in, which is what you have described, which is why your efficiency would be zero. I agree we need a circuit. You should ALWAYS show a circuit diagram when asking about a circuit.

 

[DaveE]

BTW, the efficiency of sine wave rectifiers is quite difficult to calculate. What people actually do is simulate them. It's very non-linear in the regions where they work well. Even the simulation isn't that easy since you will need good component models, more complicated (or accurate for your parts) than the ones you get in the free libraries.

There's a nice treatment in the appendix this ancient National Semiconductor Audio/Radio Application Notes

 

[Maniac_XOX]

I think we'll need a schematic. Your description doesn't make sense to me. You rectify and filter HV AC to make DC and then you step it down with a transformer. I must not understand, or, alternatively, your efficiency is 0.

I'm not sure I can upload a picture of the schematic, if so how do I do that?