The power supply for PIC is either 5V or 3.3V. Let us begin with simple 5V regulated power supply. Figure 1 illustrates Proteus simulation for the 5V supply. Note that the supply voltage to the 7805 has to be at least 2V from the regulated voltage. Thus, in this case, the supply voltage has to be 7V and above.
In some cases, you might want to use it with PIC24F and also dsPIC devices that needs 3.3V. Thus, it is better to have both 3.3V and 5V.

PIC24F and also dsPIC devices Figure 1: 5V using 7805

Figure 2 and figure 3 shows a simple circuit that will provide 5V and 3.3V. Here, a voltage divider is used to convert the 5V to 3.3V. The switch, SW1 can be replaced with a 3-pin connector. Thus, this will enable you to have, 5V, 3V and GND on the 3 pins.

Figure 2 shows direct output 5V from the regulator while Figure 3 shows the output from the regulator is passed through a voltage divider to get 3.3V.

Direct output from regulatorFigure 2: Direct output from regulator

Output from a regulator through a voltage divider

Figure 3: Output from a regulator through a voltage divider

Conclusion
Having 5V and 3.3V, power supply could be very handy. IC’s such as PIC24F would require 3.3V while Max232 requires 5V. Therefore, in this case, you would require both 5V and 3.3V

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