I made this simple power supply, as I need +5V and -5V to power operational amplifiers.
The original idea was to use the 78xx/79xx family regulators because they are easy to use. They have only three pins and there is no need of external components. I ended using the LM371 for the +5V supply and 7905 for the negative supply. The use of LM371 with a variable resistor gives you the flexibility of regulating the positive supply to be equivalent (in absolut value) to the negative, that is fixed.
This power supply is part of a bigger Arduino project. I will add the links to the following stages later.
Step 1: Simulation
I made a simulation with CUQS (Ubuntu based) just to check that the capacitor used will provide very low ripple. I used 1,000uF to filter the output of the diodes, and checked that they are correct.
In CUQS software I used two AC sources to simulate the output of a center taped transformer.
Step 2: Materials
Here is the list of the components I have used to build the supply:
- 01 x transformer 9V+9V center tap
- 04 x rectifier diodes 1N4001 or equivalent
- 02 x 1,000uF electrostatic capacitor
- 01 x LM7905 three terminal negative voltage regulator
- 01 x LM317T adjustable voltage regulator
- 01 x 1k resistor 1/8W or 1/4W (R3)
- 01 x 10k trimmer or potentiometer (R4)
Notes: In my case the transformer is 220V to 9+9V center tap, but it could be any voltage, center tapped. You have to check not to exceed maximun input voltage to both regulators, LM7905 and LM317T. You can find the datasheets of these components very easy in the Internet.
Step 3: Schematics
Here is the schematic of the circuit. It is very simple and can be adapted to any other voltage you need. You can use 7908 or 7912 to make +8V/-8V or +12V/-12V power supplies. Remember to check the voltage of the transformer to assure it complies with the specifications of the voltage regulators.
Step 4: Mounting Components
I mount all the components in a stripboard. I leave space for the next project, that is mounting and wiring the operational amplifiers. You can use any printed board you want. You can also use a breadboard for prototiping. I use a three pin connector for the transformer. I did not use a connector for the output voltage. If your project is just the power supply, I recommend you put a connector for the output. I don't have the need as I'm going to mount everything on the board.