Every time when we work on circuits, we need something to power up the entire thing. We can easily do this with a battery. But the problem with batteries is, they drain pretty fast or sometimes you might run out of batteries. So, in this blog I'll show you how you can make your own AC 220v to 5v DC stable power supply. I'll explain about circuit components before jumping on the circuit diagram. Before you start reading the entire thing,

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Step 1: Transformer

it's an obvious to use a transformer. A transformer's main job is to transform power. In this case you need a step down transformer. A step down transformer transforms high power into low power. You might know that mains voltage in all countries aren't same. like Bangladesh's 220v and USA's 120v. So, 5v output rated transformer won't always give you 5v. Because output depends on input. In some cases it can be more or less than 5v. So, in this case I'll use a 12v output rated transformer. I'll explain more later. Let me tell you a little bit more about transformers.

A transformer is an electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. A varying current in one coil of the transformer produces a varying magnetic field, which in turn induces a voltage in a second coil. Power can be transferred between the two coils through the magnetic field, without a metallic connection between the two circuits.Transformers are used to increase or decrease the alternating voltages in electric power applications. (Copied from wikipedia) It can be only used on ALTERNATING current.

Step 2: Diodes

A diode is a semiconductor device with two terminals, typically allowing the flow of current in one direction only. It means current can't go on the reverse direction. There is a diode symbol in the first image. On that image I showed you the - and +. As you all know that electron flows from cathode (-) to anode (+). The second image's circuit is a completed circuit because the diode is facing the right direction. Like the third image if I have used the diode on reverse direction, THE BULB WOULDN'T GLOW. Interesting right? This happens because the diode does not let current flow on the other direction. So, there no big difference between the open and the reversed diode circuit. Now, lets just change the power source into AC. AC stands for 'Alternating Current'. In the fifth and sixth image I showed the basic wave from of alternating current. AC current changes it's direction based on it's frequency. Long story short, AC is an electric current that reverses its direction many times a second at regular intervals, typically used in power supplies. Now look at the 4th and 5th image. On the positive half cycle of the AC, the diode is forward biased. That means the LED will glow. (Yea, i switched the bulb into a LED. LED stands for Light Emitting Diode. That means LED is also a diode.) But during the negative, the diode is not forward biased. So, it will end up being an open circuit. That means the LED won't glow. Again when positive half cycle the AC, the diodes is forward biased. And this happens over and over again....... The LED will blink in every 0.02second provided the source the frequency is 50Hz. Although it blinks pretty fast but it's still noticeable.

Step 3: Bridge Rectifier AC to DC

Now, by using 4 diodes we need to make a bridge rectifier. By arranging 4 diodes like the first image we can make a simple AC to DC rectifier. But it can't actually provide DC power. The wave form is still pulsating. In the first image I also showed the the wave form beside the rectifiers. In the 2nd image i arranged the diodes differently. This way it will work. But not perfectly. It leaves a gap when it goes above or below 0. To fix this you actually need to arrange like before. Now, come back to the 1st one. I told you that wave was pulsating. An easy way to fix that is to use a filter capacitor of 1000uf if the mains frequency is 50Hz. Here's link of 'how to choose a capacitor for rectifing AC to DC'. (I did not make the video.) Now, you got your own DC power supply. But you still have a problem. When you add some load and drop some current the wave form will look some thing like the 2nd image. It happens because the capacitor charges and discharges.There's another thing you might forget. We need 5v instead of 12v. So, lets do it in the next step.

Step 4: Voltage Regulator

I'm gonna be using a LM7805 voltage regulator (5v). By the way last two digits actually tell the voltage. The fist picture tells wheres the GND, input and output. I also uploaded a datasheet of that voltage regulator where you can get more information about the voltage regulator. If you don't know much about these then you should google about it. After all google is your best friend when you are working with circuits. Now, make the circuit like i showed you in the 2nd picture. And now you are done.

TO-220.pdf
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Step 5: Why I Used 12v?

Now, I'll tell you why I used 12v instead of 5v output rated transformer. The voltage regulator will constantly supply 5v provided that the input is above 5v. Your transformer's output also depends on it's input. If the input is above 220v the output must be more than 12v and if the input is lower than 220v the output must be lower than 12v. Same thing could happen I had used a 5v output rated transformer. In some cases it wouldn't able to provide 5v. Some times it can be less than that. Long story short, a voltage regulator stabilizes voltage. And if your transformer's output is 5v, it may not always provide 5v. If the transformer's output is 4v then the voltage regulator will give you 4v. And if it is 9v or 10v or 12v then the voltage regulator will always provide 5v stable output. It can't be more than that, provided you are using a 5v voltage regulator.

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