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dc converter

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marios:
hello everybody. i have as a project to find design a dc converter, i have done everything  so far but i can figure out how to find the efficiency i saw the episode where David did something similar but i didnt understand how he did it.
is it just divide output over input and multiply by a hundred??
please help
thank you in advance

Simon:
the efficiency is typically on the datasheet but you can find it by mearuring voltage and current in and out and calculating the percentage (Wo/Wi)*100

neoone:
yep, no more magic there. Of course the efficiency differs with load and over parameters like input voltage so if you have an operating circuit check input and output power in at least few different cases of output current (load) and input voltage (actually it's about changing difference between input and output).

Alex:
Make sure you are using the real power in Simon's formula.

Measure the true RMS voltage and current at the input and calculate Wi. Then repeat for output with a fixed dummy load to calculate Wo. You can change the input voltage or output load and do a sweep for an effciency curve.

If you have overspecified input bypass and output filter capacitors then a simple multimeter can be used as all AC components would have been filtered out, otherwise you should be using an oscilloscope or true-RMS multimeter with high bandwidth.

scrat:
I don't know what the common practice is, but I'd measure RMS input and DC output (at least for voltage).
You usually don't want to take count in the reactive power (which will be with RMS output measurement), otherwise the converter will gain efficiency as the output ripple increases.

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