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3.3 <-> 5 V power conversion — Parallax Forums

3.3 <-> 5 V power conversion

RaymanRayman Posts: 14,162
edited 2007-12-11 03:45 in Propeller 1
I got in some LM3351 (http://www.national.com/mpf/LM/LM3351.html) Switched Cap Voltage Converters...

These can convert from 5 to 3.3 V or from 3.3 to 5 V with 95% efficiency!· Just needs 4 external caps to work...

These come in a very tiny package (I'll show you a picture of my DIP adapter that challenged my soldering skills!), but I think would be much better for battery powered apps than a regular voltage regulator...
Power3p3To5V.JPG
1152 x 864 - 120K

Comments

  • Fred HawkinsFred Hawkins Posts: 997
    edited 2007-12-10 22:22
    Grain of salt warning, electronic nubie here.

    This·chip seems to cover the range of 9v down to 5v to duplicate the usual prop arrangement: http://www.national.com/pf/LM/LM3475.html

    The ancillary hardware is more complicated than Rayman's chip.

    Interesting pdfs at the bottom of this page.
  • deSilvadeSilva Posts: 2,967
    edited 2007-12-10 22:27
    This looks impressive! However there are MANY more inductorless charge pumps on the market now, some even in DIP packages. The 50mA of the LM3351 is a little bit weak... (though not when considering its size!)

    Searching the web discloses many alternatives as www.chipcatalog.com/Microchip/MCP1252-33X50.htm

    Post Edited (deSilva) : 12/10/2007 10:54:35 PM GMT
  • rjo_rjo_ Posts: 1,825
    edited 2007-12-11 01:52
    Rayman,

    Another friendly word of caution... I just fried some precious bits because my bread-board was getting worn and stuff started to wiggle around on me. I had a new bread board sitting right next to it... I was a day late moving everything over. AND I think you are going to want to save your circuits... they will make a nice display.

    I also have a request... I need a really cheap, really well regulated 5 Volt power supply. I actually don't know how well regulated it needs to be but it seems to me that +/- .01% should do it. Mike told me that there were regulated ADC chips out there that would suit my needs, but I want to use Parallax products as much as possible... and the ADC I want to use requires a good reference voltage.

    The guys here like you and I'm sure that you would get any help you might need.

    There is going to be a market for this. So it wouldn't be a waste of your time.

    Thanks,


    Rich
  • deSilvadeSilva Posts: 2,967
    edited 2007-12-11 02:02
    Note that 0.01% is nearly 14 bits...
  • RaymanRayman Posts: 14,162
    edited 2007-12-11 02:02
    rj0_:· As I recall, I got a 2.5 V reference IC for a circuit I made before...· I think this is what's typically used...
  • Mike GreenMike Green Posts: 23,101
    edited 2007-12-11 02:17
    The LM385 is a good temperature compensated voltage reference. Look for datasheets and application notes on National Semiconductor's website (www.national.com).
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2007-12-11 02:59
    Ditto to both comments about separate voltage references. The +5V main supply never makes a good voltage reference, regardless of how good its initial specs may be. Considering the variable loading and all that switching noise on Vdd, a separate, temperature-compensated reference is always the better bet if you need accuracy. You can, however, drive a 2.5V reference from Vdd, if you observe some simple rules regarding filtering and supply routing.

    -Phil
  • rjo_rjo_ Posts: 1,825
    edited 2007-12-11 03:45
    Ray and Mike,

    The reason I love this forum is that it brings back the excitement I use to have watching Michael Jordan play basketball. Except no-one ever had to remind Michael Jordan of exactly how good he was or just how rare his talent really was.

    There are a lot of guys like that around here. But you guys are so modest that sometimes I think you need to be reminded.

    I found http://www.national.com/mpf/LM/LM385-ADJ.html#Datasheet

    The LM385 comes in a TO-92 package, so hooking it up shouldn't be a problem. And at .26 cents... I think that meets my budget requirements. It is adjustable from 1.24 to 5.3 Volts... There is even a sample circuit that is almost but not quite what I need.

    I searched the Parallax site and it doesn't look like they are offering it. So, I'm breaking my own rules in ordering from someone else... but what are rules for?

    I've looked at National Semiconductor's website before... it is awesome. But the options available are flabbegasting.

    For instance the LM385 comes in 4 different flavors in just the TO-92 package, with prices ranging from .26 to 1.13 in quantities of 1K.

    AND what is truly flabbergasting to the non-engineer in me is that...the LM385 is temperature sensitive... and temperature is an analog of the unknown that I am trying to measure. So, the whole thing is being to feel like an engineering joke[noparse]:)[/noparse]

    Rationally speaking. I'm not the one that should be doing this. I'm sure I can pull it off, if it is the only thing I do for the rest of my life... or I might get lucky in the first half dozen iterations... but I wouldn't bet on it. For instance, there is a temperature graph... is that ambient room temperature?... probably not, but the ambient temperature is probably a factor.

    I'll give it a try... and let you know. I'm going to order a thousand... So, don't go away[noparse]:)[/noparse]

    I am predicting abject failure... and my plan B is to offer the chips to someone else if they will make something available to the community.


    Rich
    ILMP
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