Why (you need this)?
Any circuit needs power, the power supply circuit is necessary to ensure you give reliable power to your circuit (Filtered, Regulated, Protected).
Filtered: mainly by capacitors
Regulated: Stabilized at a know level
Protected: No reverse polarity, no over current
What (do you need)?
Unregulated Power Source (7-30VDC)
(This applies for most power adapters that you buy from the local supermarkets)
|5v Voltage Regulator||1|
|Resistor 300 ohm||1|
The first thing is an ordinary power source which connects to a wall socket (220v) and gives you an output voltage of say 12v
The following power supply gives and adjustable voltage output, I set it to give 10v and checked the output and wire polarity
So the polarity is correct, the wire with white strip is negative and the other is positive, let connect to our breadboard
We need to “regulate” this voltage down to 5v which is the most common supply for digital circuits.
It is always a good idea to add protections to your power supply. It will save you a lot of time and headache when you misconnect some wire here or there.
A diode ensures that your + and – lines are connected correctly, if you reverse the connection, the reversed lines won’t get to your circuit, let us use a general purpose diode such as the 1N4001
A second protection is for over current meaning that if your circuit pulls out too much current (e.g. in case of a short circuit), the power supply should shut-off, otherwise things will get smoky!
Add the PTC as shown:
PTC actually means (Positive Temperature Coefficient) a fancy name, all what it does is simple though, as more current flows through it, the resistance will increase until it becomes like an open circuit.
Once you correct up your wiring and remove the short, the PTC will return to normal condition. It will “Reset” that is why it is called a Resettable Fuse
We are almost done; let us connect the remaining components as shown
5v Voltage Regulator:
Now our power supply is assembled, let us make it more user friendly by adding an LED and taking the voltage to a common rail
Alright, now you can turn on your main 220v or 110v supply and you should see the Power LED ON, otherwise, you need to double check your wiring
In my case I have made a little mistake, have a look:
Opps, I did not place the voltage regulator in the right place, after replacing it:
YAY! it is ON!
The capacitors are needed to stabilize the output (e.g. low pass filter)
The component marked U1 L7805CV is a common 5v voltage regulator, it will take any voltage above 7v and below 30 volts and gives a nice 5v supply
R1 is a 300 Ohm current limiting resistor
If you have any questions, feel free to use the comments section, you can buy the components in Qatar, Oman and UAE from our online store.