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Building a Fixed-Output Regulator using the LM78XX Integrated Circuit

You_are_a_cunt

If you've read my previous rant on odd-ball power adapters, you'll know why I encountered the sudden need for a voltage regulator and today I'm going to, well, show you how to build one.

Since I'm currently tied up with moving to a new apartment, pictures will be scarce but I promise to update with my abominable soldering and PCB layout skills.

 

Applies to: any LM78XX Fixed-Output Regulator but it will be made specific for the LM7808. Details later on.

Difficulty: Easy

Time needed: 10-30 minutes, depending on skill

Part list:

  • 1x LM7808 IC
  • 1x 330 nF capacitor
  • 1x 100 nF capacitor
  • 1x small pre-drilled PCB
  • 1x heatsink (more details on this later on)
  • 1x 12V/1A power supply (I used one from an old router, since the plug fit my switch and I didn't feel like having to modify that too)
  • 1x bolt or screw to fasten the IC to the heatsink
  • thermal compound (any thermal goo will do since we only have to dissipate about 4W of excess heat)
  • a fairly small amount of spare wire (single thread, preferably, since it's easier to work with)

Total cost:

I am unsure of regional costs and individual part costs, but for two of each of the components (IC and capacitors) and the smallest PCB they had at the ripoff electronics store I only paid about $2.5. Since I already had the rest, your mileage may vary. You will probably want to also buy a rather small heatsink (I didn't have any suitable sized ones in my junkbin so I'm temporarily using one off an old dead GPU and I'll be switching it once I get to salvage something from my dad's storage unit)

Tools required:

  • Soldering iron/station (whichever you have)
  • Solder (as long as it's not too thick, any solder will do, but I highly recommend you use the leaded one)
  • Small saw (if your PCB is too large, you'll want to cut it down to a more appropriate size, since this project is quite small)
  • Screwdriver for your screw/bolt
  • Solder pump (in case you mess up your soldering. Not required but nice to have, just in case)
  • Multimeter (not necessary but good to have so you can verify that you've done everything right)

Relevant datasheets:

Fairchild LM78XX IC
Schematic(s):

Spoiler

LM7808.png

 

 

The actual guide

The reason for this particular application is to reduce the input voltage (in this case, 12V) to a more appropriate output voltage (8V for the LM7808) so we don't set things on fire through the magic of overvolting and using non-spec power supplies. In my rant post I mentioned that my switch needs a 7.5V input and the closest (and easiest to achieve) value I could come up with was 8V. You'll notice there's a 0.5V difference which is far less than the 4.5V overhead I would have had to deal with if I used the 12V adapter without modifying it.

I said I'd clear up on the LM7808.

The LM78XX series of three-terminal positive regulators is available in the TO-220 package and with several fixed output voltages, making them useful in a wide range of applications. Each type employs internal current limiting, thermal shut-down and safe operating area protection. If adequate heat sinking is provided, they can deliver over 1A output current. Although designed primarily as fixed-voltage regulators, these devices can be used with external components for adjustable voltages and currents. (Fairchild datasheet for the LM78XX series)

In short, the LM78XX series allows you to lower an input voltage into an output voltage suitable for your particular application. The LM78XX comes in a few flavors, the only difference between them being the outputted voltage (5, 6, 8, 9, 10, 12, 15, 18 and 14 V). You'll find this info and other, more advanced info in the supplied datasheet. You'll also find a list of typical applications, which also where I confirmed my initial capacitor values (Figure 6).

It should be noted that I added a heatsink to the parts list. This is because we want the IC to stay within operating temperature as to not have it shut down when it reaches 125C. The IC gets hot because it basically transforms excess voltage into heat.

We will be using the two capacitors (330 nF on input and 100 nF on output) to filter out unwanted spikes or drops in current, making the regulator more stable.

The TO-220 package looks like this:

387941090_920.jpg

Pinout:

1: Input (this goes on the positive rail. Current comes in through this pin)

2: GND (Ground; this goes on the negative - or ground - rail)

3: Output (this goes on the positive rail. Current goes out through this pin)

Please be mindful of this pinout. It does NOT work both ways. In is in, out is out.

 

 

Since I'm at work (and actually supposed to be working, since it's Monday), I'll stop here and I'll update later today. I'll also provide pictures of my first attempt at making this with a later revision coming sometime this weekend or next week.

 

footnotes:

This guide can also be found on my personal blog and will be updated here and on my blog at the same time

revisions and edits:

  • added total cost of parts

Remember kids, the only difference between screwing around and science is writing it down. - Adam Savage

 

PHOΞNIX Ryzen 5 1600 @ 3.75GHz | Corsair LPX 16Gb DDR4 @ 2933 | MSI B350 Tomahawk | Sapphire RX 480 Nitro+ 8Gb | Intel 535 120Gb | Western Digital WD5000AAKS x2 | Cooler Master HAF XB Evo | Corsair H80 + Corsair SP120 | Cooler Master 120mm AF | Corsair SP120 | Icy Box IB-172SK-B | OCZ CX500W | Acer GF246 24" + AOC <some model> 21.5" | Steelseries Apex 350 | Steelseries Diablo 3 | Steelseries Syberia RAW Prism | Corsair HS-1 | Akai AM-A1

D.VA coming soon™ xoxo

Sapphire Acer Aspire 1410 Celeron 743 | 3Gb DDR2-667 | 120Gb HDD | Windows 10 Home x32

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Diskord Apple MacBook A1181 Mid-2007 Core2Duo T7400 @2.16GHz | 4Gb DDR2-667 | 120Gb HDD | Windows 10 Pro x32

Firebird//Phoeniix FX-4320 | Gigabyte 990X-Gaming SLI | Asus GTS 450 | 16Gb DDR3-1600 | 2x Intel 535 250Gb | 4x 10Tb Western Digital Red | 600W Segotep custom refurb unit | Windows 10 Pro x64 // offisite backup and dad's PC

 

Saint Olms Apple iPhone 6 16Gb Gold

Archon Microsoft Lumia 640 LTE

Gulliver Nokia Lumia 1320

Werkfern Nokia Lumia 520

Hydromancer Acer Liquid Z220

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Update: moving basically just ate all my spare time. Postponing the rest of the guide and the pictures for the weekend or mid-next week

Remember kids, the only difference between screwing around and science is writing it down. - Adam Savage

 

PHOΞNIX Ryzen 5 1600 @ 3.75GHz | Corsair LPX 16Gb DDR4 @ 2933 | MSI B350 Tomahawk | Sapphire RX 480 Nitro+ 8Gb | Intel 535 120Gb | Western Digital WD5000AAKS x2 | Cooler Master HAF XB Evo | Corsair H80 + Corsair SP120 | Cooler Master 120mm AF | Corsair SP120 | Icy Box IB-172SK-B | OCZ CX500W | Acer GF246 24" + AOC <some model> 21.5" | Steelseries Apex 350 | Steelseries Diablo 3 | Steelseries Syberia RAW Prism | Corsair HS-1 | Akai AM-A1

D.VA coming soon™ xoxo

Sapphire Acer Aspire 1410 Celeron 743 | 3Gb DDR2-667 | 120Gb HDD | Windows 10 Home x32

Vault Tec Celeron 420 | 2Gb DDR2-667 | Storage pending | Open Media Vault

gh0st Asus K50IJ T3100 | 2Gb DDR2-667 | 40Gb HDD | Ubuntu 17.04

Diskord Apple MacBook A1181 Mid-2007 Core2Duo T7400 @2.16GHz | 4Gb DDR2-667 | 120Gb HDD | Windows 10 Pro x32

Firebird//Phoeniix FX-4320 | Gigabyte 990X-Gaming SLI | Asus GTS 450 | 16Gb DDR3-1600 | 2x Intel 535 250Gb | 4x 10Tb Western Digital Red | 600W Segotep custom refurb unit | Windows 10 Pro x64 // offisite backup and dad's PC

 

Saint Olms Apple iPhone 6 16Gb Gold

Archon Microsoft Lumia 640 LTE

Gulliver Nokia Lumia 1320

Werkfern Nokia Lumia 520

Hydromancer Acer Liquid Z220

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