Hello Instructables Community!
LET'S BUILD A DIGITAL DC-DC POWER SUPPLY TOGETHER!
Before we get started, let me tell you a little about this kit. I have a digital DC-DC power suppy that I use daily. However, it cost a bunch of money that I didn't want to spend and it is limited to an output current of 500mA. This supply has a current limit of 1.5A, as that is what the LM317 IC is designed to output. I decided that while I'll stick with my current power supply, there may be people out there who are looking for a simple and practical solution for their Arduino projects and such. I hope you all enjoy this instructable! If you have any questions, I'll do my very best to help! I'm also going to offer hardware kits for this project, so read on to find out where they can be found!
This circuit is made to work with a wall transformer or a battery. You can use either. There is no on-board AC-DC rectification, so don't apply 120VAC to the input by mistake! The power supply for the digital voltage display should be kept under 18v. If you're going to use a wall wart AC-Dc transformer, I suggest a 12v-14v @ 1A transformer. You can use a 9v battery if you'd like =) We will talk more about that in a while.
When you feed DC voltage to the input terminal block, it acts to supply power to the digital voltage display, as well as the variable DC voltage LM317 regulator circuit. The LM317 is the key behind this device. The LM317 is a 3-pin chip that acts to offer a variable DC voltage based on the resistance of the on-board variable resistor. The voltage at the output terminal block is variable and is displayed for you on the 4-digit 0-20VDC digital display. Please note that this design has limitations. Mainly that the output is not protected from shorts. If you short your output pins together for a short time, the circuit will likely be okay. However, this can cause permanent damage to the LM317, in which case you'd need to replace it. Be very careful not to short the output pins. If you can get your hands on a fuse, you can easily protect your supply. Place the fuse in series with the positive lead on the input DC line of the device. Otherwise, be careful. As well, this supply does not read out load current. On top of that, the kit does not come with banana wires. The neat thing about this project is that you can customize it to your liking. We do sell parts and a kit for this project in our hobby electronic stores that can be found here: http://www.electroniclessons.com and http://www.engineeringshock.com
Here is a video that gives you a demonstration: