Simple 5V DC Power Supply
Figure 1: Simple Regulated 5V DC Power supply circuit diagram
In any electronic products or projects there is always a source of power for the system to work. This is called a power supply.
The source of this power can come from different sources like the mains AC voltage, a battery or even from a renewable power source like a solar panel wind turbine or fuel cell to name just a few.
The most common source of power is usually the mains AC, with this power, we need a transformer to convert the 220V 50Hz mains or the 120V 60Hz if you are living in the United States of America to a lower voltage required by the electronic circuit, this can be typically between 6V and 12V when 5V regulated DC is needed.
We are not going into the theoretical details here, I am going to discuss in this article only the basics for you to be able to build a simple power supply to power your microcontroller.
Here are the main components in this project:
- Capacitors and
- Voltage regulator
1. Power Source
The first thing to choose is the power source, this can be 220V AC mains stepped down with a transformer or we can use a 9V battery or even a solar panel depending on our application.
For our 7805 voltage regulator IC to work properly, it’s input voltage should be at least 2V greater than the required output voltage.
In this case as we are using a 5V regulator (5V required at the output), the input voltage should be close to at least 7V.
A 6V transformer with current rating of 500mA (since 6*√2 = 8.48V) can be used or any other power source supplying more than 7V like a 9V battery, solar panel etc.
- Any transformer which can supply a secondary peak voltage of up to 35V can be used with this 7805 voltage regulator but as the voltage increases as is the power dissipation across the regulator which may require a heat sink if there is a huge power dissipation.
- For a portable devices, a 9V battery can be used, this will decrease the cost as they will be no need to use the diode rectifiers.
2. Rectifying circuit
The purpose of a bridge rectifier is to convert the stepped down AC voltage into a DC (direct current) voltage. The bridge rectifier is composed of diodes D1 to D4 offering a full wave rectification.
1N4004 diodes are used as they are capable of withstanding a higher reverse voltage of 400V and a forward current of 1A. These specifications are enough for this application, the 1N4001 and 1N4007 diodes can also be used.
3. 7805 Voltage Regulator
The 78xx (sometimes prefixed by some letters like: L78xx, LM78xx, MC78xx…) series is a family of fixed linear voltage regulator integrated circuits. These regulators are commonly used in electronic circuits requiring a regulated power supply due to their simplicity. They are easy to use, they require very few additional components (2 capacitors) and they are not expensive.
In this family, the xx replaces two digits, these digits indicates the output voltage, for example the 7805 has a 5 volt regulated output voltage while the 7812 has 12 volts, the 7815 produces 15 volts and so on.
The 78xx series are positive voltage regulators, this simply means that they produce a voltage that is positive relative to a common ground in contrast to the related 79xx series which are negative voltage regulators.
If a positive and a negative regulated voltage is required, the 78xx and 79xx ICs can be used together in the same circuit.
Figure 2: The 7805 regulator connection
Figure 2 above shows the connection of a 7805 regulator extracted from the 7805 datasheet, only two additional capacitors are required, the datasheet prescribes to use a 0.1μF capacitor at the output side to avoid transient changes in the voltages due to changes in load and a 0.33μF at the input side of regulator to avoid ripples if the filtering is far away from regulator.
In the circuit diagram on figure 1, 100μF capacitor is used at the input side to avoid ripples.
- The input voltage range can vary from 7V to 35V
- Output current rating: 1A
- Output voltage range from 5.2V to 4.8V
Figure 3 below shows the pinout of the 7805 voltage regulator.