What is exactly happening when AC power is being converted to DC energy?
In: Technology
A simple explanation using water as an example.
One cycle of the pump will put some water in a bucket, and then stop flowing. Each cycle of the pump will dump some water in the bucket.
The bucket has a hole in it that can allow water to flow out of it at a certain rate based on the gravity and the pressure of the water accumulating in the bucket.
If the pump can provide enough water to the bucket so that a steady flow of water exits the hole, we have achieved the goal.
The pump keeps pumping in water each cycle (AC), the bucket (capacitor and inductance) accumulates it and allows it to flow out at a steady rate and pressure (DC)
There are different ways to achieve this with components.
There’s a few steps
Usually the first step is an AC/AC transformer which reduces the voltage closer to the final voltage.
Then some one-way valves (diodes or rectifiers) are wired in such a way as to change the electrons from moving both ways to moving one way only. However it’s still pulsing on and off.
Then there is usually a filter which smooths out the pulsing. This usually consists of one or more capacitors, which are kind of like batteries, or an electron-balloon.
Finally there is usually a regulator which acts like an automatically adjusting variable resistor designed to maintain a constant output voltage. This is much more important for electronics than, say, a fan.
Some of the fancier regulators (switching regulators) actually convert the DC back to AC and then back to DC again; this is more efficient, because instead of acting like a variable resistor, it’s merely turning on and off very fast, which has the same effect, but without heating up the resistor. (although it can heat up the switching transistors)
This is one of those things that’s much harder to explain with just words, so I’m going to invest about a hundred seconds in MSpaint to make some bad images that will help a great deal.
First off, DC, or direct current, is electricity that flows in one direction.
AC, or alternating current is simply electricity that switches directions on a regular basis. Household AC switches 60 times per second.
AC starts out looking like this on a device called an oscilloscope. You can see it smoothly changes from one direction (positive, or +) to the other (negative, or -):
Using a pretty simple circuit, you can ‘cut off’ one side and send it all in one direction, so that it looks like this:
That circuit just uses a few components called diodes, which only allow electricity to flow in one direction through it.
The problem is that it isn’t very smooth. It’s more like very fast bursts of DC current, so we need to try and fill in those gaps.
To do that, we use a component called a capacitor. That device is like a tiny battery. When there is current going through it, it charges up. When there isn’t, it discharges. We can use these to sort of fill in those gaps, like so:
The better a job done by the capacitors, the more it looks like a straight line, the closer to pure DC it gets.
There are more modern ways of converting AC to DC with much more accurate results using transistors, but this classic way has been around for a very long time.
AC – electrons moving back and forth in the circuit
DC – electrons moving in one direction
AC-DC – using a circuit made of diodes (which function as a one way street for current) you make a circuit, where both the positive and negative phase of the AC is contributed to positive part of DC. (Effectively making an abs(ac) funtion. Then you just smooth this output using filter (capacitor and resistor) and you get a DC
AC power is like a kid on a swing going back and forth. A diode is like a zip tie that can only go in one way but with electricity instead of the plastic rope. Imagine the swinger uses their feet to push the zip tie rope along, but the zip tie rope is up high a little ways, so the swinger has to swing really high to reach it. This turns the back and forth power(AC) into pulling power(DC).
The first step is to step it down to the right voltage, using a transformer to go from 120V AC, to 12V AC. Then, AC power goes back and forth, 60 times a second, So you take a bridge rectifier to make all the AC power go forward. Then you add a capacitor to smooth out the humps in the voltage, and you have 12V DC power
AC is electricity that goes from positive voltage to negative voltage over and over again. Each time it does this, we call that a cycle. The number of cycles per second are called hertz.
DC is electricity that is always a positive voltage.
There are 2 components you need to know about to converting AC to DC. The first is called a diode. A diode only allows electricity to flow one direction through it. Since AC voltage goes positive to negative, the current flows backward and forward. We want to stop that. The second component is a capacitor. More on that later.
So, imagine a sine wave of electricity, that is AC. The diode chops off the bottom half of the wave, or the negative part. What you have now is like hills of positive voltage with 0 volts between them. This is called pulsing DC. We want to make the pulses smooth, so that the voltage is constant.
This is where the capacitor comes in. The capacitor charges and then slowly releases that charge. So it charges up from the pulse of DC and the releases a longer slowly decreasing voltage that bridges the gap between the hills. Its still not perfectly constant, but its much closer to a constant voltage and most DC items don’t really care about the noise.
Extra credit: there are circuits you can build called full-bridge rectifiers that flip the negative part of the wave to positive and add it to the positive wave so that there is no time when the voltage is at zero and the hills are closer together. This is both more efficient and has less noise. These are made with 4 diodes in a clever arrangement.
I think your question can be answered by studying the physics behind AC and DC, it will be a more complete answer that what we could write in such short time.
Imagine the energy as some water. Now imagine a big glass of water – something like a water tank full of water with a hole in the bottom with a continuous output flow. This is your D.C. current. Now, imagine that you bury this water tank in the sand on a beach and that each wave that arrives fill it a little bit (and you still have a the water going out of this tank). Well, the waves are you A.C. current entering in pulses in your tank. When an A.C. to D.C convertet is designed, its basically a calculation on how much you can bury your tank in the and the size of your tank (voltage and capacitance value for the capacitors) in order to have a more or less stable output flow out of the tank – also depending on the frequency of the waves arriving.
It always bothered me that devices that used batteries require them to be installed with the correct polarity. Just a couple diodes and that would allow the battery to be installed in any direction. Especcially things that only need one battery.
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