Thinking of making a power supply that can give you 12 V and current of 500 mA? Then you’re at the right place. I’ll show you the easy steps to design a power supply that can give you the DC output voltage you want with input as 230 V AC. I’ve also made the power supply to power up my Arduino board and the relay.
The input voltage of an Arduino can vary from 7 -12 Volts. For the 12 V power supply design, I’ve used a simple full wave bridge rectifier circuit. A Full Wave Bridge Rectifier is a circuit, which converts an AC voltage into a pulsating dc voltage using both half cycles of the applied AC voltage. The full wave bridge rectifier circuit is very reliable, cheaper, and the resulting output is much easier to smooth. The designing of the circuit would cost you less than ₹150(less than $5).
You can use the same power supply for Arduino board as well as for the relay. Firstly, make the bridge rectifier for 12 volt power supply and then connect a LM7807 voltage regulator IC in parallel with the output and you’ll get the 7 volt output. As the IC is connected in parallel with the 12V output, so the input to the IC is 12V (the voltage regulator IC’s input should be more than 4 – 5 Volts than the output, like for LM7812 the input is 18 V) .The following components are required-
- Step Down Transformer – A single phase 230:18 V step down transformer is required for 12v dc power supply. Likewise, to design a 5 V power supply you may use the 230:10. There are three wire in the transformer and 9-0-9 (considering the 18 v) is written on it. So, you’re needed to connect the outermost wires of the transformer (which are of same colors).
- Diode – Four Diodes are used in the circuit for rectification and a single diode is used as freewheeling diode. All diodes are 1N4007.
- Voltage Regulator IC– LM 7812 a voltage regulator IC is used in the 12V DC Power supply. Similarly, for 5 volt power supply just replace the LM 7812 with LM 7805.
- Capacitances– capacitances are used for reducing ripples in DC power supply as per specifications. A 1000 µF and a 10 µF capacitances. All these items are easily available at electronics shop.
- Copper wires– For AC mains they should have the current capacity of more than 1 A.
- Jumper wires– For connection purposes.
- Soldering iron
- Soldering wire
- General Purpose PCB
- Two pin plug
- Adapter Jack- The adapter jack is used to connect the power supply with the Arduino board.
- Heat sink (optional) – For the high current outputs from the power supply and for proper heat dissipation from the voltage regulator. The heat sink may be connected to the Voltage regulator IC.
- LED- You can also connect the led with a limiting resistor for the indication of power supply.
- Limiting resistor- Limiting resistors are used to limit the current flow through the LED.
Understanding the Polarity of a Diode
To connect the diode in the right manner first you must understand the polarity of the diode.The diode (1N4007 datasheet) has two polarity anode and cathode the current flows through the diode from anode to cathode when the diode is in forward biased mode. The diode has a grey line in anyone of the sides and that side is cathode and the other one is anode.
Connecting the IC LM7812
LM 7812 a voltage regulator IC is used in the 12V DC Power supply. You can see the LM7812 <datasheet where it is mentioned that the maximum dropout voltage Vd is listed as 2.5 volts, meaning you need a minimum of 14.5 volts input to the device to guarantee an output of 12 volts. And the maximum input voltage is 27 V. Here we’ve taken a 18 V input to the voltage regulator which is in the suitable range. The pin configuration of the IC is given below-
How to calculate the value of limiting resistance
In order to determine the current limiting resistor’s value you need to determine the three values and put the values in the given formula-
I = LED forward current in Amps (found in the LED datasheet)
Vf = LED forward voltage drop in Volts (found in the LED datasheet)
Vcc = Supply voltage (let’s say 12 v)
R = (Vcc – Vf)/I
Note- Always use the limiting resistors value greater than calculated.
How to connect the adapter jack
To connect the power supply to an Arduino board you’ll need an adapter jack. For connecting the adapter jack you need to heed a little. For common adapter jacks the positive is connected to the tip (i.e. the inner side is positive) and the sleeve is connected to the ground (i.e. the outer side is negative). But for the adapter jacks for the music system the case is opposite.
Circuit Diagram Of Full Wave Bridge Rectifier
Working Of Full Wave Bridge Rectifier
When 230 V Ac mains is supplied to the transformer it steps down the voltage to 18 v. 18 v ac is supplied to the diodes of the bridge rectifier which converts the ac into dc for both the cycles (for each cycle the two diodes conducts and voltage drops across the diodes is 0.7*2=1.4 V). Through a filtering capacitor the supply goes to the positive pin of LM7812 IC which regulate the voltage to 12V and the output of the IC is filtered by the capacitor and the output is taken.
After you have all the above required items, plan the layout of the power supply and carefully solder all the components. The resulting system will be a 12 volt power supply with 700mA and check the output of the power supply with a multimeter.
Still got any doubts ask me in the comment section. Suggestions for the article are welcomed. Thank you for reading.