What is exactly happening when AC power is being converted to DC energy?
In: Technology
The most important part is the bridge rectifier. We use little electrical one way valves (diodes) so that no matter the input voltage (+ on top or on the bottom) you always get positive voltage on one wire and negative on the other, [the wiki has a nice GIF showing this](https://upload.wikimedia.org/wikipedia/commons/3/34/Diodebridge-eng.gif)
Generally we will put a big capacitor on the output to store the energy. This capacitor takes the ups and downs that are coming into it and stores the energy so it just sits at the peak voltage.
Now you’ve got a constant voltage that you can use to power things or can step down to a low voltage using a DC-DC converter so you can get 5V for your phone or 3V for a little micro controller.
Old style boxes, the really heavy ones, used to put a step down transformer in the front to bring the peak voltage down from 170V (on US 120V power) to the 12 or 24V that they were needing in the end and then they ran that lower voltage through the rectifier and into the capacitor. These are simple and don’t require any fancy electronics but they do require about 5 pounds of iron in the transformer core. Electronics are wayyyy cheaper these days than they used to be so its now cheaper to use the fancy electronics for the DC-DC converter than a big transformer meant for stepping down line voltage at just 50/60 Hz
There are electronic components called diodes. These are sort of like one-way streets for electricity. If you try to pass AC through one of these, only half the wave will get through, say the positive half. This is called a *half-wave rectifier*.
Now, if you do two of these, one in each direction, you can have one stream that gets the positive halves of the waves and a second that takes the negative half. You can then combine these together using some more diodes so that you basically get the full wave, but with all the negative bumps flipped to positive. This is a *full-wave rectifier*.
Sometimes, your circuit uses 3-phase power. There are 3 wires running AC, but ⅓ of a cycle out of step with each other. If you fully rectify this, you get a signal that’s just a slightly bumpy version of DC.
Regardless of single or 3 phase, the next step is to smooth things out as best you can. This can be done using a *low-pass filter*. LP filters let through signals that don’t vary much, and are resistant to quickly changing signals. If you’ve got a sound system with a woofer and a tweeter (low and high speakers), there’s an LP filter making sure the woofer only gets the bass.
A simple LP filter is just a coil of wire, known as an inductor. When you pass a current through it, it generates a magnetic field. This field is resistant to changes in the current. It store energy, and when the supply drops, it gives off some of the stored energy to stabilise it. When the current tries to increase, the inductor takes in some of that energy to ‘charge up’ the magnet. This means the current coming out the inductor will be smoother than what went in.
You use some diodes and a capacitor to “rectify” the signal. They are arranged in such a way that when the voltage is positive, current flows, but current is blocked by the diode when your AC voltage is negative. The capacitor then starts discharging some stored energy it got when the signal was positive, and that keeps your DC voltage constant.
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