Standalone Voltage Regulator

Simple RegulatorStandards are very important and also very annoying.  Anyone who has worked with digital logic will tell you that to do anything you need a stable 5 volt (or 3.3 volt) DC supply.  The problem is, due to standards in battery form factor and voltage, you can’t really go to the corner store and buy a five volt battery.  Now, even if you could, you really wouldn’t want to since digital electronics don’t really deal well with dips in voltage.  What you really want is some kind of a power supply that will maintain 5 volts DC given a range of input; enter the 5 volt DC Standalone Voltage Regulator.

Theory

The LM7805 voltage regulator is a common solid state device that steps DC voltage down from voltages higher than 5v down to 5v DC.  The great part about the 7805 is that it is very common and very cheap, about $1.50 at your local RadioShack (Part # 276-1770) and even cheaper online and in bulk (About 32¢).  The 7805 is self contained and doesn’t require any peripheral components to work, just send 8v-40v to the input, connect ground and bingo, 5v at the output. While this direct wire method might work for some simple circuits,  any significant circuit or high speed logic should have its Vcc source filtered to eliminate any noise and reduce voltage fluctuation.  This how-to builds a Standalone Voltage Regulator with power filter capacitors.  Also, what circuit is complete without a cool LED to show it is working.  Our circuit will also have a “Power On” indicator LED.  To round out the project, the entire circuit will be built on a pre-etched PCB available at almost any RadioShack, no wire-wrap, no etching, just building.  Here we go.

Parts

Part RadioShack Part#
22 Gauge solid breadboard wire Kit: #276-173
Dual General-purpose IC PC Board #276-159
LM7805 Regulator #276-1770
100uF Electrolytic Capacitor #272-1044
0.1uF Ceramic Capacitor #272-1434
330 Ohm Resistor #271-012
5mm LED #276-309
TO-220 Heatsink #276-1363
PCB Standoffs (Optional) #276-1381

Tools

  • Soldering iron and solder
  • Heat clamp (Optional but very useful,Eg)
  • These instructions
  • Multi-meter
  • Voltage source capable of 8v-40v DC (9V battery will work, with a snap of course)

Circuit

Here is the circuit for the project drawn using Kicad.

Regulator Circuit

Orientation

Regulator Keyhole LayoutsThe regulator circuit will be built on one side of the single IC board, this leaves the other side for other simple circuits you might want.   The two sides of the the single IC board are almost mirrors of each other, but be careful, they are not mirrors,  to build this project we first have to make sure the board is setup the correct way.  The General-purpose IC board comes in a set of two, looking at one of the boards you should see a single small hole next to one of the larger mounting holes, we are going to use this hole as a key for our layout.  If you line up the keyhole and other mounting holes with the image at right (Keyholes are in red) you will be able to build the circuit just as it appears in the assembly diagrams.  Please take time to orient the board, if you don’t, the circuit will not work.

Assembly

Step
Image
1 Measure and cut jumper wires to connect the end holes of the spans shown in the image.  The wire should cover a total of three (3) holes, jumping over the middle one (1) to connect the two outer holes.  If you are using a pre-cut jumper kit the wires are all the same and are commonly colored red.Either solder down these wires or continue on to the next step if you plan to solder all the jumpers at once. Position of 3 hole jumpers (Red)
2 Measure and cut a jumper wire to connect the end holes of the spans shown in the image.  The wire should cover a total of five (5) holes, jumping over the middle three (3) to connect the two outer holes.  If you are using a pre-cut jumper kit the wire is commonly colored yellow.Either solder down this wire or continue on to the next step Regulator Jumpers (Yellow)
3 Measure and cut a jumper wire to connect the end holes of the spans shown in the image.  The wire should cover a total of four (4) holes, jumping over the middle two (2) to connect the two outer holes.  If you are using a pre-cut jumper kit the wire is commonly colored orange.Either solder down this wire or continue on to the next step Regulator Jumpers (Orange)
4 Measure and cut a jumper wire to connect the end holes of the spans shown in the image. The wire should cover a total of six (6) holes, jumping over the middle four (4) to connect the two outer holes. If you are using a pre-cut jumper kit the wire is commonly colored green.Either solder down this wire or continue on to the next step Regulator Jumpers (Green)
4.5 If you have not soldered down the jumper wires do so now. The easiest way to do this is put a piece of paper or card over the top of the board and flip the entire board over on the table to show the underside and traces.
5 Insert the 0.1uF ceramic capacitor in the two holes indicated on the image and solder it in place. Regulator 0.1uf Cap
6 Using pliers, bend one lead of the 330 ohm resistor down parallel to the body of the resistor. [Example]

Insert the resistor in the two holes indicated on the image and solder it down.

Regulator Resistor
7 LEDs only work when power is applied one way.  All LEDs have positive and negative leads.  The negative lead on most LEDs is the shorter one.  Another way to tell is there is a flat side on the body of the LED, this is the negative lead side. [Diagram]

Insert the LED with the negative lead closest to the resistor in the holes indicated in the image. Solder down the LED.

Regulator LED
8 Electrolytic capacitors, like LEDs, only work one way.  The negative lead of the electrolytic capacitor should have a black line on the body.Insert the 100uF capacitor in the two holes indicated on the image with the negative side furthest from the LED.  Solder the capacitor in place. 100uF Capacitor
9 Insert the two screw terminals in the holes indicated on the image.  Ensure the openings of the terminals are facing away from the circuit.  Solder the terminals in place.

The terminals allow for removable power sources, if you have a power source that you would like permanently connected, such as a power jack or battery snap, solder it in place of the left terminal with the positive lead closest to the top of the board.

Regulator Terminals
10 The final component of the circuit is the 7805 regulator.  As you might imagine the regulator must be inserted in the circuit a very precise way.  Examine the pinout of the LM7805.

Insert the regulator so the correct pins are connected to the correct power sources.  It is very important to insert the regulator correctly.  Measure twice cut once!

Regulator
11 The final layout Regulator Layout Outline
12 Heatsink: The LM7805 can get quite warm under even a small load, and under high loads will go into thermal shutdown. To keep the regulator cool, you should use a small heatsink to disperse the heat. The way the regulator is positioned, most common TO-220 sinks should work. [Image]

Final Check

If you have followed the assembly instructions above your regulator is ready to use, however before you plug in your voltage supply you might want to check for some common mistakes:

  • Trim all leads close to the PCB and solder joint to eliminate shorts
  • Make sure all solder joints are solid, no loose wires
  • Ensure that there are no solder bridges between pads
  • If you are not using PCB standoffs ensure the area is clear and you are not going to accidentally put the exposed PCB traces down on a scrap lead or solder-ball
  • Make sure your input voltage source is at least 8v, the 7805 requires a source 3v greater than the output
  • If you plan to draw more than 500mA you want to use a heat sink and some thermal grease to keep the 7805 from shutting down due to the heat.

To prove the circuit works measure the output of the regulator before connecting it to a circuit.  When you apply power to the circuit, the LED should turn on and a multi-meter should read ~5v at the output.

Checking the voltageFinal Circuit

That’s it! Thanks for reading and leave comments and ideas on this project below!

12 Volt Regulator

The LM7805 is not the only TO-220 form factor regulator out there, there are many others including negative voltages.  Since the LM78XX family has a common footprint it is possible to make a regulator for 5, 6, 8, 9, 10, 12, 15, 18, and 24 volts!  Check out the datasheet for the LM78XX family here:

http://www.digchip.com/datasheets/download_datasheet.php?id=91852&part-number=7812

If you do make a larger regulator, remember to change the current limiting resistor for the LED on the board, if you don’t you WILL burn the LED out.  Here are resistor values for different regulator voltages:

Voltage Estimate Resistance
5 volts 330 Ohm
8 volts 660 Ohm
12 volts 1.1K Ohm
15 volts 1.4K Ohm

Parts Kits

myBitBox.com is partnered with C Code Systems and excited to announce that we are selling complete kits of this project! The kits contain all the parts required to build the Standalone Voltage Regulator including precut jumper wires!

The price per kit is $8, which is less than the cost of buying individual parts at the store!  Plus C Code Systems is offering flat rate shipping on all Standalone Regulator orders, no matter the quantity. This kit is perfect for soldering classes, introductory electronics classes, personal circuit development, soldering practice, and microcontroller development .

Show you appreciate this project and help support myBitBox.com!

http://ccodesystems.com/products-page/

15 Comments

  • By David Dukes, February 5, 2009 @ 1:16 pm

    I assume the volts are DC not AC

  • By s1axter, February 5, 2009 @ 1:23 pm

    Yes, input and output voltages are DC.

    There have been some comments on the Make blog about using a heatsink. The LM78XX gets quite warm under load, a heatsink is a smart move. I will update the instructions with some pictures tonight.

  • By Aaron, February 5, 2009 @ 4:33 pm

    shouldn’t you put a diode back across the regulator to prevent damaging the regulator with back current when the input power is disconnected

  • By vic, February 6, 2009 @ 6:45 am

    Aaron, you only need a diode across the regulator if the input can be short-circuited, and the output has some relatively big capacitors. Here the input stays floating if is is disconnected.

    Anyway a small but pretty useful project. What you could do too is modify a standard 3-4.5-6-7.5-9-12V power supply to output a more useful and more stable 3.3V and 5V instead of 3V and 4.5V.

  • By Trencher, February 6, 2009 @ 8:30 am

    Why not throw a rectifier in there and have a idiot proof voltage input as well as being able to use ac wall warts too. Just a thought.

  • By Working Man, February 6, 2009 @ 8:58 pm

    Trencher brings up a very interesting insight- many folks have wall warts for devices they no longer use. The rectifier addition would allow easy adaptation to other devices.

    Thanks for this EZ looking circuit,

    W.M.

  • By Layer, February 11, 2009 @ 1:39 pm

    Nice little project. Very similar to what I’m currently working on. My regulator uses a DC barrel jack for using a wall-wart. Although I do like the idea of throwing a rectifier in there, I currently only have a diode. I’ve also added a power switch. The board is the basis for a modular prototyping system I’m working on, similar to the Arduino/TinkerKit combination. One nice thing about your approach is the cost. I don’t think I could sell mine for less than $12. Anyhoo, just wanted to give you a thumbs-up for getting your stuff out there, whereas I’m forever stuck in the design phase :)

  • By Tatters, December 27, 2009 @ 7:39 pm

    Great project – thanks for posting! I am interested in putting this together but require a total of three power outputs. Are there any changes to the design in order to do this (aside from adding the extra outputs)? Also, do the voltage requirements change because of the extra outputs?

  • By Blue Eyes, February 19, 2010 @ 12:55 pm

    The parts list is missing the screw terminals – RS part # 276-1388.

  • By Austin Litman, May 29, 2011 @ 6:59 pm

    Thanks for the clear & straightforward instructions. I dropped by the Shack, grabbed the boards, and used some parts around the shop. It works great!

  • By Ken, June 23, 2012 @ 11:09 am

    For what it’s worth, the boards currently sold by RadioShack do not have the small key hole as mentioned in the Orientation section. I just looked at the pics to figure out what I needed to do.

Other Links to this Post

  1. C Code Systems » Regulator kits now available — February 4, 2009 @ 7:48 pm

  2. Standalone Voltage Regulator | myBitBox — February 4, 2009 @ 8:07 pm

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  4. help on pinouts on voltage regulator — December 28, 2010 @ 2:16 pm

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