Make Your Own Lab Power Supply for Less Than $25

Hi and welcome to my Instructable.

This is my first instructable, my first language is Spanish, so I'm still practicing my English, so if there is any question you can send a message, I hope you like it

Power supplies are necessary in any electronic project, I was looking for one on amazon, I found it in prices of $ 69.99 to $300.00 so I say to myself that with my knowledge about electronics I can make one cheaper that the one's that I found on amazon, so I will show you how I make my own power supply for just $25

Step 1: Materials and Equipment

The materials:

• 1 - Transformer 120 V to 36 V (You can use one of 24 Volts too) ---- $5.00 to $10.00
• 2 - Electrolytic Capacitors 4700 uF 50 V ---- $0.50 to $1.50
• 1 - Bridge Rectifier (Depends on the transformer current) ------ $2.00
• 1 - Voltage Regulator LM317 ------ $0.5 to $1.00
• 1 - Voltage Regulator 7805 ------ $0.5 to $1.00
• 1 - Voltage Regulator 7812 ------$0.5 to $1.00
• 1 - Voltage Regulator 7912 ------- $0.5 to $1.00
• 1 - PCB Cooper ----- $1.00
• 1 - Resistor of 240 ohms ----- $0.1
• 1 - Ceramic Capacitor 10uF 25 V ---- $0.3
• 2 - Potentiometers 10 Kohms and 1 Kohm ------ $0.5
• 2 - Diodes 1N4002 ----- $1.00
• 1 - Power switch ----- $ 0.2
• 5 - Output's GND and Voltage (see the picture) ----- $1.00
• 4 - Heat Sinks ------- $ 2.00

The equipment:

• Multimeter
• Soldering gun

Step 2: Circuit Design

For the circuit design, we will need to know how power sources work, so we are going to divide circuit into sections like this:

1. Transformer
2. Rectifier
3. Filter
4. IC regulator
5. Load

Warning: We are working with AC Voltage so be careful if you need help ask someone who has experience with electronic

For the first step the Transformer that I bought gives 36 V 2A output this voltage is AC, so we have a sine wave output that we need to rectifier, for that we need the full bridge rectifier, in the picture I show you how to make this connection, so we now we have a DC output know, but this voltage is not constant so we need to add a filter on it, so we have a linear voltage output, for that we will need the capacitor of 4700 uF 50 Volts, int he pictures It show how the signal is almost linear, but with the capacitor that of 4700 uF the voltage drop caused because of the capacitor is almost invisible, so we don't have to worry about it.

So the next step we need the Voltage Regulators (LM317, LM7805, LM7812, LM7912), so we need a little explanation about this integrates:

• LM317: It is integrated circuit that regulated voltage depending on a resistor configurations as it shown in the pictures, the formula to calculate the output voltage can be found on the datasheet of the integrated, in our case we will use two potentiometers that allow us to regulated the voltage output

• LM7805 and LM7812: All the information about integrates LM78XX are shown in the pictures, basically this regulated positive voltage input into 5 V, 12 V, 15 V, etc..., depending on the name of the integrated for example the integrated LM7812 gives an output of 12 V

• LM7912: The same as the integrates of the LM78XX, but the input of these integrates must be negative voltage and the output will be negative output, it follow the same connection as the LM7812

To design the circuit I used Multisim, I followed the picture where we can see the full connection with the LM7812 and LM7912, this circuit implement the transformer, the rectifier, the filter and the regulator, in the pictures simulator I added a load which is a 1 kohm resistor to show to you the output voltage, just one more thing be careful with the polarity of the capacitor, connected as you see in the picture, if you don't connected right it will explode, I attach the simulator file so you can use it.

Note: The transformer has 3 wires, the one in the middle is the GND the other 2 wires are connect to the rectifier, you will see that you rectifier has two outputs, these have on the integrates a + sign and a - sign, so you have to make your connection as it shown on the pictures to make sure that anything blows up, the diodes can be added to the LM7805, LM7812 and LM7912 just like the LM317 just to poretect the circuit from a short cut

Step 3: Making the PCB and Welding

To design the PCB I used PCB Wizard, I attach the file that I created also the image of it, to printed on the PCB plate I used this method that I found on youtube but if you have other methods to make the PCB, you are free to use it.

Method:

As you can see in the image, my PCB didn't look complete so I took a sharpie and completed the circuit, the holes on the PCB were made with a Dremel.

One's we have our circuit printed we need to welding the plate, the final PCB is shown in the picture.

Step 4: Making the Box

For the box I used one that I found in thingiverse, to make this box you will need a laser machine, if don't have one, you can create your own box for your power supply, be creative !

http://www.thingiverse.com/thing:265763

Step 5: Assembling

One´s we have the PCB and the boxes we can assembling all to make our power supply, finally I added heat sinks to the voltage regulator to avoid voltage drop due to the temperature depending on the load, I hope you find this instructable useful, if you have any question, feel free to ask