The Extremely Simple Digital Dc-dc Power Supply

http://www.instructables.com/id/THE-EXTREMELY-SIMPLE-DIGITAL-DC-DC-POWER-SUPPLY/

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THE EXTREMELY SIMPLE DIGITAL DC-DC POWER SUPPLY!by EngineeringShock on June 25, 2011

Table of Contents

THE EXTREMELY SIMPLE DIGITAL DC-DC POWER SUPPLY! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Intro: THE EXTREMELY SIMPLE DIGITAL DC-DC POWER SUPPLY! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Step 1: What You'll Need! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Step 2: The Schematic Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Step 3: Putting It All Together . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Step 4: Applications - What Can I Do With My Power Supply??? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Step 5: Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

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Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6


Author:EngineeringShock engineeringshock.com + More!Hi there!My name is Patrick, and I am an electronics engineering technician who works full time as a lab tech, and part time as an electronics engineer/salesman. Iown an ebay store, and two websites, which I share with my business partner. We sell all sorts of unique electronic components and modules for students,hobbyists, and inventors. All of my fun circuits are posted on youtube. My user name is "patrickikis". If you want to know more, I'm happy to share =)Thanks!Pat

Intro: THE EXTREMELY SIMPLE DIGITAL DC-DC POWER SUPPLY!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 tospend 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'llstick 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 allenjoy 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 canbe found!

THE BREAKDOWN: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 bymistake! 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 @ 1Atransformer. 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. Mainlythat 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 causepermanent 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 caneasily 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 notread 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 sellparts and a kit for this project in our hobby electronic stores that can be found here: http://www.electroniclessons.com and http://www.engineeringshock.comHere is a video that gives you a demonstration:


Step 1: What You'll Need!HERE IS A LIST OF WHAT YOU'RE GOING TO NEED:

COMPONENTS:1x 0-20VDC Digital Voltage Display Module1x LM317 Voltage Regulator IC1x On/Off Switch (Included in http://www.engineeringshock.com kit, but not seen in image)2x Terminal Blocks1x Heat Sink for LM3171x 5k Ohm Variable Resistor2x 200 Ohm Resistor2x 100uf Electrolytic Capacitors (Rated for 20v or higher)2x 0.1uf Ceramic Capacitors (Rated for 20v or higher)1x 7cm-9cm PCB1x DC Power Source (Battery of Wall Transformer) - Not included in http://www.engineeringshock.com kit.TOOLS REQUIRED:1) Soldering Iron2) Lead Solder3) A Hand Drill4) A Drill Bit (I used 1/16)5) About two hours of time, give or take. This is based on your electronic background, and soldering experience.6) A Multimeter to troubleshoot, in case you have any problems along the way =)

Step 2: The Schematic DiagramAs you can see, there really isn't too much to this schematic. We will be begin from the left-hand side.

The Input Terminal Block:This is where you're going to connect your input DC source. In the video, I mention that 18VDC is fine, but I suggest keeping it to 14v or under. if you are looking for ahigher voltage, you can use a 18VDC source at the input. In all likelihood, most of you are going to want to use this for digital applications, or perhaps for poweringamplifier circuits. Anyhow, through the terminal block, there are two capacitors in parallel with the line. The 100uf capacitor is a smoothing capacitor. While the DCsource is likely coming from an already smooth DC source, you never know! This capacitor isn't 100% necessary, but I do recommend that you use it. The 0.1ufcapacitor is a decoupling capacitor. It is used to filter out unwanted high frequency signals that might find their way to your circuit.. It is good practice to have both ofthese capacitors in parallel with the DC input line. The positive DC input line feeds voltage to the input of the LM317 chip (Pin#3), and to the digital voltage readout. The Digital Voltage Readout:The digital voltage readout has four pins on its rear. Pin#1 is connected to the voltage reference (Our output voltage), pin#2 and pin#4 are connected to the ground line,and pin#3 is connected to the DC input supply. This device requires a power supply at pin#3 of anywhere between 6VDC-18VDC. Nice range, eh? This supply powersthe circuitry on the device. As long as their is power at this pin, you will see the voltage display light up. If thre is no votlage connected to the reference pin (Pin#1), thenthe display will read 00.00v. Again, our reference pin is reading the voltage at the ouput terminal block. The voltage at the output terminal block will be displayednumerically on the voltage readout.

The LM317 Varaible DC-DC Regulator:As mentioned before, the input supply pin for the LM317 is pin#3. The postiive DC supply voltage is connected here. Pin#2 is the output pin. There is a 200 Ohmresistor tied in parallel with pin#2 and pin#1, and a 5k Ohm variable resistor between pin#1 and ground. This variable resistor adjusts the voltage at the output. Whenyou adjust the variable resistor, the output votlage goes up or down depending on which direction you're turning the variable resistor. The lowest output voltage that theLM317 can support at the output is 1.2v and the highest output voltage is 37v. However, we're never going to go that high, as our input voltage will be less than 18v toprotect the digital readout.. The LM317 can support up to 1.5A of current, but it needs to be heat sinked. In this case, a heat sink DOES come with the kit =)The Output Terminal Block:Like the input terminal block, there are two capacitors of the same values in parallel with the output line. This is used for the same purpose. I do suggest you implementthem. You will also notice that the reference pin from the readout is connected to the positive line of the outputer terminal block. We talked about this before. Thisterminal block is where you will connect your load. It may be a digital circuit..... It may be an analog circuit... The possibilities are endless!


Step 3: Putting It All TogetherWhen it comes to putting this all together, there really is no right way or wrong way. I soldered each of the big components on first, such as the heat sink, the terminalblocks, the variable resistor, and the digital voltage display.

IMPORTANT NOTE!!!When you're about to place your heat sink and terminal block into your PCB, you may notice that the leads are too big for the board. In this case you're going to need ahand drill with a small drill bit. I Used a 1/16 bit.

Once you place all of the larger components into the board, drop the LM317 into an area of slots in front of the heat sink. DO NOT SOLDER THE LM317 YET! First, usethe screw to screw the LM317 into the heat sink. For those if you who don't know anything about heat sinks, they are used to dissipate heat created by current runningthrough the IC. It helps to keep the IC cool, and acts as protection.

Once you have the LM317 screwed tightly against the heat sink, solder the leads to the board. Now, solder the switch and all of the passive components to the board. From here, all you have to do is make all of the connections on the bottom of the board, and you're set.

Please note that I am very experienced in soldering. Don't feel discouraged if you're having trouble soldering paths like I did. If you are having problems, use jumpersand wires. It doesn't have to look neat to be cool!


Step 4: Applications - What Can I Do With My Power Supply???Well.... It is a DC power supply, so the world is your oyster! I use my power supply every day. Mainly for design purposes, but I play with my hobby kits from time totime.

WHAT CAN I DO WITH THIS???

Tune the output to 5v to work with TTL ICs!

Charge super capacitors with your new variable power supply! Please keep in mind to limit that charge to the super capacitors before you do so!

Power with your arduino!

Use it to power small motors!

Use it to power your own circuit designs!

Build the Eye of Thundera and Destroy Mumm-Ra!

THE POSSIBILITIES ARE ENDLESS!

Step 5: ConclusionsThis kit is great for people with little electronics background. It doesn't take a weekend to build, and it can be used as a effective lab tool!All in all, I'm very happy with this device. I hope you enjoyed reading the instructable. If you try to solder the paths like I have, take your time and be careful. It would bea good to have a solder sucker handy =)Thanks again everyone! Have an educational day!


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Comments9 comments Add Comment

mattman2 says: Aug 3, 2011. 5:19 AM REPLYawesome thanks for replying, nice instructable by the way

mattman2 says: Jul 29, 2011. 3:09 PM REPLYjust wondering could you use capacitor with more than 100 UF or less cause that's all I have available

EngineeringShock says: Aug 2, 2011. 10:50 AM REPLYYes, that is fine =)

mattman2 says: Jul 30, 2011. 5:20 AM REPLYI was also thinking that if the display dosn`t have a separate source of power or the power consumption is not subtracted out of it the reading would beinaccurate.

gormly says: Jul 29, 2011. 1:42 PM REPLYHi Patrick, love your videos.

Is this the same as the kit on your website?I want to biuld one for a project using two 3000mAH batteries at 3.7v each, connected in series for 7.4v and be able to vary output from 3 to 5v.I have most of these parts already.


greyhawk83 says: Jul 10, 2011. 9:41 AM REPLYPatrick, All your instructables are very educational, enjoyable-great work.My question about super capacitor is how large do they get and do you carry them?

MROHM says: Jul 2, 2011. 3:08 PM REPLYI Would HIGHLY RECOMMEND Patrick's E/bay store as I have purchased 4 Kits from him and all 4 kits worked when completed,,,,and some of theInstructions were even in Chinese!!! Do you have any ideal how much a Store Bought Variable Power Supply Costs????Like a Horror Movie,,,Very VeryScary!!!

Electronics Man says: Jun 30, 2011. 4:38 PM REPLYVery nice!!!!!!!

rtty21 says: Jun 27, 2011. 7:01 AM REPLYnice instructable!

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The Extremely Simple Digital Dc-dc Power Supply