After plugging my phone in to a power source, it will not begin to charge the battery until I unlock it. My laptop similarly can “ignore” the voltage coming through the power cord.
How do these devices reject/ignore/disregard the voltage coming through the power cord?
In: 3
We became really good at doing DC voltage conversion, typically using buck converters (to reduce voltage) and boost converters (to increase voltage). Think >90% efficient.
Why does it matter? Well, if you want to charge a battery, simply apply a higher voltage than the battery provides, and the current and therefore energy will simply flow towards it. If you want to discharge (aka. use it) simply apply a voltage that is lower than the battery provides, and the current and therefore energy will simply flow back out of it.
How does that voltage conversion works? The simplest one is to double or halve the voltage: use transistors to connect two condensators in series to the input wires (thus adding the voltage), then disconnect them and reconnect them to the output but this time in parallel (thus adding the current, but halving the voltage). You do this with high frequency enough and it looks like a lower voltage power source. It’s also symmetrical in the sense that if the output has higher voltage then your condensators get charged there and discharged in the input side. In practice it’s more efficient to step down the voltage so we tend to have a battery that has higher voltage (19V) than the components of the computer (12V, 5.5V, 3V and 1.1V).
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