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Clarification about step up modules/converters

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malium:
Hello,

just a quick one. DC step up converter based on LM2577, it trades of A for V, right? If I have 5A input to the converter, and boost from 3,7V to 12V, I am still gonna end with 0,5A on the output, no matter what?

Thanks!

Dave:
Think of power.
You have 3,7V * 5A = 18,5W going in. Your switching converter has a certain efficiency, for example 85%, so output power will be 18,5W * 0,85 = 15,7W. Your output voltage will be 12V, so your maximum output current will be 15,7W / 12V = 1,3A.

malium:
Dear neighbour from Slovenia, many, many thanks! I suspected that, but their datasheets confused me there for the moment :)

Thanks again!

fcb:
Vout * Iout * Efficiency = Vin * Iin

So if you are drawing 5A @ 3.7v you are using 18.5W (watts!), so at 12v (assuming 100% efficiency) your load is drawing 18.5/12 = 1.54A

Efficiency is more likely to be around 70-80%.

Also, it's more conventional to design for the output current rather than the input current.

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