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Does this dc - dc booster have regulated Vout?

Discussion in 'General Electronics Discussion' started by pityocamptes, Sep 13, 2012.

  1. pityocamptes

    pityocamptes

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    Jul 26, 2012
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Yeah. It's a regulator. One of the main purposes is to maintain a fixed output voltage independent of load or supply variations (within reason)
     
  3. pityocamptes

    pityocamptes

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    Jul 26, 2012

    Would it be cheaper to build your own or buy this? I guess I could pull the pot and use a resistor box for fixed Vout. How would I calculate the R1 value for the R2 resistor box. Do I have to pull R1 to get its value for the R2 box?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Why bother? Adjust the trimmer for the voltage you want and then don't touch it again.

    edit: If you can build one for this price, go for it (if price is the main driver).
     
  5. pityocamptes

    pityocamptes

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    Jul 26, 2012
    Also, if I want two Vout's to be 1.5 and 3 volts (my other Vout's would be 4.5, 6, 7.5, etc. I know this booster Vin/Vout is 3.7, should I go to the problem of using a lm350 for the 1.5 and 3 Vout switch segment? Perhaps an easier way? I thought about a Zenier, but not sure how effective. Thoughts? Thanks!!!!
     
  6. pityocamptes

    pityocamptes

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    Jul 26, 2012
    I need multi volts out, based on a resistor switch pack and multi switch.
     
  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I'm sure everyone here would be able to help you a lot better if you gave us all the background information on your project.

    What is the incoming power source?

    What output voltages do you want, and what current rating do you want for them? Do you have specific loads that you want to be able to drive? If so, can you describe them?

    Multiple output voltages is easy to arrange. You'll need a single pole switch, usually rotary, with one position for each output voltage you want, and a voltage divider for each voltage. The divider may contain a trimpot for exact adjustment, or may just contain two resistors.

    All of the voltage dividers are connected across the output voltage, and the centre points (outputs) from the voltage divider are fed to a selector switch, which chooses one of them and passes it to the voltage feedback input on the regulator IC on the board.

    If you want an on/off switch at the input, you can combine this with the rotary switch. You'll need a two-pole switch instead of single-pole for this, and an extra position for "OFF".

    The output voltage is set by a resistor ratio in the feedback path. The operation of the regulator, and calculation of the output voltage setting resistors, are covered in the data sheet http://www.ti.com/lit/ds/symlink/lm1577.pdf - please read it thoroughly.

    Yes it is probably much easier and cheaper to buy that board and add the switchable output voltage feature, assuming that board is suitable for your project in all other respects. If you describe your project, and link to that board, the kind folks here will be able to help you a lot more.
     
    Last edited: Sep 13, 2012
  8. pityocamptes

    pityocamptes

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    Jul 26, 2012

    Thanks. Basically trying to use a solar panel array 5 volts in at 3 amps max to power a couple of backup super caps through the ltc 4425. I want to power low voltage devices like an mp3 player etc. The above booster will power anything above the 4.5 threshold given the min 3.7 volts. To acquire voltages at 1.5 and 3 volts should I use a zenier diode, or voltage regulator for those low voltages or another option that is not power wasteful? Thanks!
     
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    So let me get this straight. You have a 5V solar panel, rated at 3A max, and you're charging a pair of series-connected supercaps from that panel using an LTC4425 supercap charger IC. Now you want to generate several output voltages from the voltage on those supercaps. Right so far?

    And you've found this boost converter using an LM2577 that will convert your supercap voltage to any voltage from about 6V upwards, but not less than that, because it's a boost converter. Right so far?

    So you want to modify the LM2577 board to give you switchable output voltages, and you also want to provide 3V and 1.5V output voltages.

    I would use a separate regulator, powered from the supercaps, that will produce 3V or 1.5V. You could use a buck switching regulator, or a linear regulator (e.g. a low dropout regulator or LDO). A switching regulator will be more efficient but also more complicated and expensive. How much current are you planning to draw from the unit at 1.5V and 3V? If it's not much, an LDO should be fine.
     
  10. pityocamptes

    pityocamptes

    79
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    Jul 26, 2012
    Right all the way around! Thanks! Very low current all the way around. Just trying to offer a multi output port for some of the stuff I have, like one of those multi convertors. OK, I will go with a buck step down, chinese component is cheaper than I can build it for! Thanks again!

    One more question, would you power anything prior to the ltc4425 regulated supercap charger, ie straight from the panels, or would I be asking for problem on an unregulated power source?
     
  11. pityocamptes

    pityocamptes

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    Jul 26, 2012
    Also, the only question, or part I do not understand, and its sort of off topic, but what connects to the PFO leg on the LTC4425??? I have been asking around and no one has gotten back to me. In the datasheet I see a resistor in series on the PFO leg but the resistor does not connect to anything, at least from how I understand it. Any thoughts?
     
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I wouldn't power any device that expects a particular supply voltage (e.g. 6V, 3V etc) from the solar panels directly.

    According to the description of the PFO pin in the datasheet, it's an output that signals when certain bad operating conditions are present. So you don't need to connect it to anything.

    That device is quite complicated internally. I think it would be worth your while to read that data sheet very carefully and thoroughly, and make sure you really understand it fully, and that you are using it the way it was intended to be used.
     
  13. pityocamptes

    pityocamptes

    79
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    Jul 26, 2012
    Thanks! I have been reading it over and over and I am slowly getting it. In one of the example schematics they had a resistor on the PFO leg but it connected to nothing, I am curious as to why, does the resistor have any affect?
     
  14. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    No, the PFO pin is just an output. The chip doesn't care what you connect to it.
     
  15. pityocamptes

    pityocamptes

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    Jul 26, 2012
    OK I have to ask, what sort of output would it be used for, pic controller? Thanks. I found a buck boost convertor that does everything I need!!!!
     
  16. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I have to answer, read the data sheet. Look in the pin descriptions section. There's a description of the PFO pin there, and there's probably a more detailed description later in the applications section.

    Can you point us to the buck-boost converter? I would be interested to see it :)
     
  17. pityocamptes

    pityocamptes

    79
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    Jul 26, 2012
    Thanks.

    http://www.prodctodc.com/dc-345v-to...boost-module-for-solar-power-panel-p-104.html
     
  18. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    That buck-boost converter looks good.
     
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