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I got a Samsung phone charger some time ago. The text on it says 5.3V/2.0A, and when I plug a USB meter on it, the meter reads 5.3V 0.0A. The meter itself consumes a maximum of 0.02W (so 0.004A - safe to ignore).

When I plug in a load that is made up of simply a 5 ohm resistor (labelled 5V/1A), the voltage goes up to 5.45V to 5.50V. When i plug in another 2.5 ohm load (two 5V/1A resistors in parallel), the charger raises its output to 5.55V to 5.60V.

I know it's designed to compensate the resistance of charging cables and it's named "loss compensation", but after dismantling a charger, I found no special parts compared to another Apple one without such a feature.

How is that implemented?

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They use a chip like this one: -

enter image description here

It uses an internal current monitor to adjust the target output voltage: -

enter image description here

There are many ways to skin a cat and this is just one of them. Others can look at the rate of discharge of the output capacitor to estimate output current and make an adjustment.

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