# Output power efficiency of voltage converter

Hi everyone,
I am considering about the output power of voltage converter. Is the working principle of voltage converter the same with the working principle of transformer, which means if I use step up converter, output current will be smaller than input one while output voltage will be greater then input one? I know that voltage converter use voltage regulator and other electronic components, not using coil and laminated steel as transformer. For example, if I want output of 24V - 7A, what is the minimum of input current while input voltage is 12V? Thanks

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Hi Minh

easy enough to work out.
24V @ 7A = 168W
If we assume converter is 85% efficient
We need 198W input
198W @ 12V = 16,5A.
A fairly hefty supply. Also a fairly hefty converter. Remember there is 30W disappeared somewhere due to converter efficiency. Only one place it can go. Heat which has to be dissipated somehow by the converter.
Cheers Bob
PS

It is laminated iron

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A voltage converter often is a transformer, but with extra bits. Transformers only work with alternating current (AC) so converters have to take Direct Current (DC), convert it to AC, put it through the transformer, turn the AC back to DC at the new voltage.
In the picture, the wire wound doughnut is most likely a transformer with an input winding and an output winding.
Buck and boost converters work by a different principle using an inductor (which could be a wire wound doughnut) as a temporary store of energy. The input puts a pulse of energy into the inductor which stores it as a magnetic field, then the magnetic field collapses transferring energy to the output. They look just like a transformer but usually have only one winding.
What Robert93820 says is correct for either case. Energy in = Energy Out + Energy Lost (usually as heat). Energy (Watts) = Volts x Amps

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