Dual voltage power supply


[Melanie] had some time this weekend so she whipped up a dual voltage power supply from parts on hand. This design plugs right into a breadboard and, unlike the last breadboard power supply we saw, provides two voltages at one time. 5v is delivered to one power bus while 3.3v goes to the other. Her design uses two linear low voltage drop regulators from the LF00 family (PDF datasheet) to accomplish this. Nice work!


  1. macegr says:

    I did a similar one last year: http://www.flickr.com/photos/macetech/2813231588/

    I used jumper blocks so that either rail could be switched to 5V or 3.3V. And randomly added an AVR-ISP breakout.

  2. I really liked the adafruit design but like a lot of folks needed both voltages for some of my comm designs. This is a great idea and will be pretty darn handy..

  3. jimmys says:

    Come on. This is just the app notes for LFxx regulators. Here’s what lost out to “two regs on one power supply” from the website-

    Beebthernet: getting ethernet on to my BBC Microcomputer

    Bit Banging SPI In 6502 Assembler: During my adventures with my BBC Micro and external hardware I found I needed to read/write to an SPI bus. I ended up writing a bit banging routine to communicate in SPI Mode 0 with the device.

  4. sansan says:

    And the hack is????? C’mon!

  5. strider_mt2k says:

    Needs heatsinks.

    -and technically you’d want to mechanically secure those regs against vibration-induced failure as well, but I’m “that” guy. Sorry.

    It’s clean and gets the job done. Nothing bad here.

  6. medix says:

    @sansan: It seems that the word ‘hack’ is rather loosely defined these days.

    @strider_mt2k: Are you implying that this breadboard will be used as a ‘final’ prototype? Having a breadboard pretty much negates the need for vibration proofing, and even then only if the part is to see extended service in an environment fraught with.. well, vibration. Just curious..

  7. medix says:

    I should add that vibration-induced failure seems to be far less likely if the solder used is **NOT** lead-free. The RoHS crap seems to hold up horribly under *any* kind of stress..

    Go figure.

  8. therian says:

    Seriously it just a voltage regulator, should we call every soldering job a hack ? then I made 5 hacks last weak

  9. tristan says:

    oh yeah… I made a dual op-amp. (2x 741, http://www.national.com/ds/LM/LM741.pdf) I was thinking about soldering it on a breadboard, but the package it comes in is pretty nice, and if you only need one don’t add the other to your project…

  10. Dave says:

    Nice plug and play board. I need one of these in my box of goodies… Also nice to see one more girl hacker.

    Most of you guys seem to think power supplies have nothing to do with hacking… Not sure what to say about that but, this board is perfect for digital logic and many times you need to have both 5v and 3.3v. The other kit boards by ladyada and others seem to have overlooked this need.

  11. not_starman says:

    Why couldn’t this be done with a potential divider?

  12. incognito53 says:

    wait… we have females frequenting and designing on this board? zomg!

  13. Noobius says:

    This does seem rather simple to be mentioned on a site like hack-a-day, but then we do see a billion arduino hacks -.-‘

    As for the ROHS solder, I agree it is the worst piece of crap to work with ever. I’m glad for once to live in a country that doesn’t give a crap about the law. We can still get solder with lead in it here in Romania ^^

  14. cyanide says:

    in b4 3 voltage supplies

  15. Paul says:

    Well I’m interested in this – I know it might not seem like a hack to all you seasoned hardware hackers, but as someone who only discovered electronics + Arduino’s in the last few months, this is actually valuable information.

    Thanks for sharing Melanie.

  16. Drone says:

    At least it’s not an Arduino that blinks a light.

  17. Cyberspice says:

    Love the sarcastic comments guys. In the end where do you get examples of use of chips other than the data sheet or application note?

    I’ve just gotten back in to electronics this year after a long long hiatus. I’m having to build back from scratch and things have moved on. So in order to play with various of the funky new chips I wanted a dual voltage power supply and had some bits. Thought some people may be interested in it.


  18. nebulous says:

    @ Cyberspice
    It’s a nice and useful power supply. I could use one myself.

    It isn’t really a hack, though. The sarcasm is for the site, not for you.

  19. ClutchDude says:

    Just out of curiosity…Where should I go to find projects like this if Hack-A-Day is not the place?

    Don’t get me wrong, I enjoy the occasional over-my-head project. However, projects like this are more useful to me in terms of practicability and are likely to be used in other projects.

    Thanks for the work and making it easier to find.

  20. Ben Ryves says:

    However much of a hack this is or not, I certainly hope we see more of the Beebthernet project..!

  21. JD says:

    As much as I agree that this isn’t an overly complex build, nor a hack, it is important to “n00bs” to be able to actually SEE a circuit physically with actual components and values, as opposed to just staring at an app note schematic. Those of us that work in the industry can almost visualize layout of a schematic in our heads, but that is NOT true for the vast majority of the readers here.

    So, not a hack, but well worth showing it off. What I wouldn’t mind is if Hack-a-day blasted out 20 of these stories a day, with a few really good hacks, as opposed to only 5 total posts a day.

  22. lol3supplies says:

    How about one with 12v,5v,3,3v? I could really use a 3 voltage supply. >.>

  23. strider_mt2k says:


    Like I said, I’m “that” guy.

    Indeed fine as-is!
    I just like to bulletproof everything I dunno why.

  24. ApprenticeWizard says:


    Vibration resistance is *especially* important here. You are using a prototyping board, which (likely as not) will be handled, jostled, plugged to, unplugged to, and generally roughed up. Pad-per-hole board is not your friend in terms of holding the pads to the board under heat.


    This is a modification of a breadboard. It has the added bonus that it is both reversible and generally useful, qualities that not every entry on this site can claim. It has decent documentation and referencing, and some thought in implementation; again not something every entry here can boast. Lambasting this because it is simple is quite short-sighted: simplicity is a laudable goal. Too, make suggestions as to improvements and additions instead of whining that it is too simple or easy.


    Using a divider would be unwise unless you have specific and/or very low current requirements. Changing the load across the (lower) divider resistor would change your voltage. Simply put, if you attach a load to the divider point, it is the same thing as placing an impedance in parallel with the lower resistor. Two regulators from the same source will maintain their voltages despite loading (within specification). Also, the divider would always draw power, which would decrease efficiency of the circuit.

    A suggestion for an addition to this circuit would be some current limiting. As this is a prototype, risk is high that a short could occur. A simple implementation can be found here:


    the design limits current by sensing the voltage drop across the resistor and using that to turn off the transistor. The sense resistor could either be fixed (for general safety) or adjustable depending on circuit needs.

  25. Rachel says:

    @Dave & @incognito53

    We’re not as rare as you might think. I’ve done plenty of hacking on my website, but so far nothing has made hackaday.

  26. texas chainsaw airways says:

    Is this your doing?!? What kind of horrors were you exposed to as a child? You do know that ‘hacking’ in this context does not mean ‘dismemberment’, right?

    Having said all that, nice work.


  27. Rachel says:

    *Giggle* Yep! I don’t think I was exposed to any horrors, though I don’t have any memory before the age of five… Besides, the insects were never dismembered, only…gassed and adhered….


  28. Cyberspice says:


    That fly plane is amazing. You are a genius! But are they bees? They look like wasps to me!

  29. Rachel says:

    Aww, thanks. Technically they’re Polistes dominula, or the common European paper wasp, but I’ve always called flying yellow stinging insects “bees”.

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