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  • EEVblog #240 – Power Supply Design Part 8

    Posted on January 31st, 2012 EEVblog 18 comments


    PART 7: http://www.youtube.com/watch?v=s8b4h_UybLE
    After some Arduino hurdles, Dave troubleshoots his DAC SPI driver code in “real time”, and takes a peek at an issue with the LCD I2C bus. As well as showing off his PSU PCB for the first time.
    The PCB is from Circuit Labs in New Zealand:
    http://www.pcbzone.net

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    18 responses to “EEVblog #240 – Power Supply Design Part 8” RSS icon

    • While debugging the Software you missed one SPI_CLK at 12:57

    • The way I understand that datasheet, the accuracy is given in units of LSB for each of the part options, so one LSB of the 10-bit part = 4 LSB of the 12-bit part, so the 12-bit part should still have (slightly) higher accuracy, or am I missing something? Sounds like they just bin them at the factory based on which spec they fulfill…

    • It looks that what you see in the scope is ACKs of I2C bus.
      During ACK the line must be released by the master (HIGH,pullups) and the slave must pull down the SDA line during the acknowledge clock pulse. So something is happening with the slave and how it putlls down SDA.

    • I’ve had issues with Newhaven products, too. It is almost always some timing related issue, and their data sheets are often wrong wrt timing.

      Check out their forums as their userbase are always coming up with fixes.

    • How about sharing your code with us?

    • Since you’re only using 10 of the 12 DAC bits anyway, you could multiply by two in software instead of using the 2x gain, and cut your error in half. Just move one of those two “shift out zero” calls to the end.

    • I am waitnig for this part, when you realize, this is not a really precision device. :)
      My Microchip DAC cant go to 0V, I have to pull down the outputs. I use them with trimmers at the outpus, so I can set the max value.

      • Today tried mi mcu controlled psu with this dac, after bradbordig. It is shame. The increments are not uniform either :(

        From 0 to 16:

        9.4
        9.8
        9.9
        9.8
        11.1
        11.2
        11.1
        11.2
        9.1
        9.2
        9.2
        9.2
        11.2
        11.3
        11.2
        11.3

        It sould be 10 always, but not.

    • Dave is definitely not a software guy, as he mentions in one of his very old blogs. But for multiple mislabeled variables like that, it is much easier to use the edit menu and do a find and/or replace function to rename your label, plus it should be able to find all your mislabeled variables. It’s not a big deal in tiny amount of code, but if you have 10s of thousand lines of code, according to Murfy, you will miss some.

      “It’s simple, easy, I like it”

    • Dave, your power supply series is fantastic! I only wish your blog was around back when I was going for my BSEE. Please keep up the great work! I’d like to make a suggestion for a future video. I realize this is just a single power supply circuit, but I’m wondering how hard it would be to power an opamp with +-6v with it. I just finished watching an older video where you described the types of instruments you should buy if you’re assembling a basic lab and you stressed how important a dual power was to have on hand. This project seems to have everything a person could ever want, except for the dual supply capability.

    • Can someone please help me understand how the differential amplifier (that senses current) has suddenly been disappeared from REV B to REV C and been replaced with a set of op amps? And why isnt this explained in the video?
      I tried. failed to spot why.

    • Hi Dave.

      Great project there !

      Was wondering if you could perhaps do a video (or series of videos if required) to tell us how you might select proper standards for this supply (ISO, IEC, CE, UL, etc..) and then possibly make ammendments to the circuit, parts, schematic, pcb layout, enclosure, etc. for ensuring that the supply will pass appropriate standards.

      I am just venturing into the standards and compliance arean and there are quite a few gray areas, and i think there would be quite a few on your blog facing the same issues. I know there are respected companies and consultants for this kind of work, but on the lighter side, such videos might be very informative and educational for a design engineer.

      Just as they say, a proper designer needs to have a know-how of the manufacturing & assembly processes, i believe it goes the same for a designer to have the proper knowledge of standards compliance, how to search for applicable standards for a particular project, what tests need to be performed and what ranges / limits, how to re-structure a basic schematic / layout for better compliance, etc.

      Thanks.

      Regards,
      Zeeshan

    • Hey Dave,
      I am currently an EE student and you have inspired me to build my own power-supply following in your footsteps to learn more about digital power supplies. I have built and tested and mine works but I have been using a LC filter and PWM for the control. Since this video came out I have been thinking and debating on changing to a DAC such as in this video. I have made the now decided to go with it and learn more about the MCP49XX chips. Unfortunately there are not really any tutorials that explain how to use such a device. I was hoping that coming to you here I could seek some answers and maybe you could do a more in-depth tutorial on how to use them.

      Your videos have taught me tons and pushed me to greater limits do to your inspiration. Thank you,

      An eager to learn EE student named Mike

    • Any updates on your PSU projects? We didn’t see anything for a long time.

    • Hi Dave
      Many many thanks for your excellent blog! One learns so many things and all that with lots of laughs and good humor…

      The idea of a battery powered rechargeable power supply with voltage + current control and Arduino environment is fantastic!

      One question: Would an additional simple function generator functionality (square, sine, and triangle wave @ 0.1 to ???KHz) with similar voltage and current regulation be difficult to implement? That would be an ideal tool for beginners like me. There would also be some room for a somewhat smaller board next to the batteries at the top of the box if necessary…

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