If you are relatively new to electronics, don't freak out just yet. This circuit might look a bit crazy, but I promise you, it is simpler than it looks. What you are looking at here is basically a rectifier.
So what is a rectifier? What does it do? Well, if I slow down time here just a little bit, a rectifier will turn an AC power source, as you can see here, with a back and forth motion of electrons.
Into a DC power source where if you look here the electrons are moving forward in one direction only through the LEDs in only one direction and that is due to the magical wonders of diodes. This is one of the most useful ways of using diodes in any circuit and you'll find them in pretty much every single circuit you look at and especially power supplies because power supplies like the transformer that you plug into the ac socket that is what is responsible for turning alternating current into direct current to power your devices so if we look at the circuit here i've basically got an ac power supply so it's running at 240 volts ac at 60 hertz or pulsing back and forth 60 times a second. And I'm running it through a resistor, not something you would normally do, but for the sake of simplicity, I'm using the resistor to reduce the current, just enough to power these LEDs. The only thing turning this alternating current into direct current are these four diodes. Now if you look at the way that they are arranged, you might be able to see what's happening here.
So here we are, I've actually slowed it down into super super slow motion so that you can actually see the operation. Because a diode will only allow current to flow in one direction, that means I can basically make the alternating current flow through all of these diodes in a way that when the electrons actually flow out to the rest of the circuit... They're always flowing in one direction but you can see they they are not alternating back and forth. They are simply going straight forward in one direction with very small pauses as the ac supply hits zero on the wave and so that means I can power these LEDs because if they were actually being powered from alternating current these LEDs would be flashing and would look absolutely horrendous. Now the easiest way to see how this is working is by following the flow of electrons.
So I'm gonna slow this down even more so we can follow the electrons even easier. We can actually follow the electrons on each part of the wave to see what's happening. As the electrons are now about to move the other way, watch what happens.
So here we go, the electrons will start moving this way and It won't pass through this diode because this diode is in the direction which will not allow current to flow. So instead the current now flows through here and through this diode pushing all the electrons up here. And as the current starts to change now you can see that it's flowing through this diode and again going up in this direction. So that means on each half of the AC wave, the electrons are being pushed in that one direction because only one diode here will allow current to flow on each alternating wave.
And the same happens on the returning end as well. So it followed it from this side and there are another two diodes to obviously complete the circuit, which means that when current flows backwards this way, it goes all the way up here round to the LEDs, through the LEDs and back through this diode and back to the AC power supply and when the current starts to flip the other way you can see it goes in this direction all the way up here through the LEDs and returns to the AC power supply in this direction. so in effect that really useful property of diodes that allows current to flow in only one direction means that we can place the diodes in a particular way that alternating current can be changed into direct current to power devices which can only run, or run more efficiently, on direct current.
And so this is actually a very simplified version of what you would find in pretty much any power supply that converts alternating current from your home electrical supply to direct current to power your devices.