This articular is not relates with above circuit diagram.This is another circuit for understanding.
Our source will not only feed our projects with microcontrollers. Putting a USB plug in the place of the output terminal, and taking care that the polarity is correct, we can use it as a “travel charger” for all those gadgets that recharge your battery from a USB port on the computer.
The maximum current delivered by this source is 1 Amper. However, if we do not use a good heat sink in the LM7805 voltage regulator, we can only require a little more than half of the maximum current, since the heat generated by this component would be excessive. In any case, the LM7805 has an internal thermal protection that will turn it off if its temperature exceeds the safety limits.
If we see the circuit of the source, we notice that the input has two terminals in series. In one of them we must screw the secondary wires of the chosen transformer, and in the other, the key that will serve to turn the source on and off. We must remember that when we turn off the power supply with this key, the transformer will continue to be connected to the mains, so it would be appropriate to unplug it from the wall when we are not using it.
The output of the transformer attacks a bridge of diodes that is responsible for rectifying the input current, and then a capacitor of 470uF / 16V helps eliminate part of the proper curl of this type of rectifier. The heart of the source is the voltage regulator, which has a capacitor of 0.1uF at its input and another at its output, as specified in its datasheet. At the end of this stage we have the 5V regulated.
Another capacitor of 470uF / 16V is responsible for eliminating any small ripple that may have remained, and a LED in series with a limiting resistance is in charge of indicating to us that the source is (or not) on.
We have made a small printed circuit board, only 2.5 x 5.0 centimeters in the side, that you can make in your house following the procedure we have already explained in NeoTeo. Once this is ready, we will make the necessary holes to pass the component pins, remembering that the terminal blocks, the diode bridge and the LM7805 regulator have thicker pins than the others.
Following the guide that provides the figure of the plate without components, we will mount one by one all the elements, being careful not to weld them in an incorrect position. When everything is ready and checked, we will connect it in transformer and the key. We will plug in the power supply and if all is well, when the ignition key is pressed the “Power” LED should light indicating that the power supply is working.
If instead of obtaining 5V at the output of our source we needed another voltage, we could simply change the voltage regulator used (and the transformer, of course). For example, a LM7812 provides 12V dc output. 3V, 5V, 6V, 8V, 9V, 12V and 15V regulators are easily available (and only for a few coins). All have the name “LM78xx” where “xx” is the output voltage. If your project is powered from a 9V battery or battery, simply replace the LM7805 with an LM7809 and you already have a power supply to replace the batteries of your invention.
In case you decide to change the voltage that this power supply delivers, keep in mind that you must replace the resistor that limits the current flowing through the “Power” LED. If you need 9V, you can put an R = 680 ohm, and if you use 12V, an R = 1K could work.
List of components
The list of components needed to build our source is very short, and all items are easy to get at any electronics store. We will need:
1 transformer from 220V to 6V (or from 110V to 6V, depending on the country)
1 50V diode bridge, 1st
3 two-screw terminals (or two terminals and one USB plug for PCBs)
2 470uF / 16V electrolytic capacitors
2 ceramic capacitors of 0.1uF
1 220 ohm 1/8 watt resistor.
1 red 5 millimeter LED
1 Voltage regulator LM7805 in TO220 capsule.
1 key on / off.
As you will see, this is a very simple assembly but also very useful. It will surely be appreciated by those just starting out with this hobby.