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Voltage regulator step up/down

Discussion in 'General Electronics Discussion' started by Anon_LG, Feb 20, 2016.

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  1. Anon_LG


    Jun 24, 2014
    I purchased a photovoltaic panel from maplin, maximum voltage output of 18.5 volts. I need to use a step up/down voltage regulator, I think this should be sufficient. I need to limit the maximum voltage that reaches the regulator to a maximum of 11 volts per the specification. Would this be best done with a zener connected between positive and ground before the regulator, this then links to a shutdown FET? This would of course only allow the regulator to operate when the panel is less than nominal.

    My favourite option is attached, though I have doubts over it's functionality, dissipation and plausibility. Z1 has a breakdown of 11 volts, U1 is a simple voltage regulator of probably about 5 volts, but alternatively this could be replaced with a few diodes, totaling a voltage drop of 8 volts. The hatched box is a dc-dc converter, the same as I have linked to above. MOSFET1 is a P channel depletion (had to look that up, normally on/off at negative/positive/zero voltages, difficult to remember). The gate is connected to the output of the zener, so when this circuit section is activated, the direct connection is disconnected, protecting the adjustable converter from the raised voltages. D1 and D2 are blocking diodes, I am unsure whether this is necessary, but I could raise the voltage to compensate.

    Whether diodes or a regulator would be used where vreg is on the diagram, both would present problems. The fixed regulator becomes inefficient at low loads and the diodes drop the voltage to a minimum of 4 volts, which will drop the efficiency of the adjustable regulator at high loads (as shown in the diagrams supplied on the polulu page). So mostly it is a case of whether the output would drive a high load or a low load. I find it more likely that it would be a low load.

    Or would all of this be too complex and instead should locate a converter with an improved voltage spec?


    Attached Files:

    Last edited: Feb 20, 2016
  2. davenn

    davenn Moderator

    Sep 5, 2009
    you do realise that solar panels voltage rating is the open circuit voltage ? ... it drops substantially under load

    and can you please post a proper file and NOT a zip file

  3. Anon_LG


    Jun 24, 2014
    Ok, I had forgotten this. If I measure the internal resistance will this enable me to accurately determine the voltage under load?

    I will attempt to upload the image as a non compressed version, I was forced to compress the image as the site reported that "the contents did not match the description" I could not produce the image on my computer as it is coming to a stage of wear that makes it difficult to use, my tablet must now be used for most of my work, this is an inconvenience. I located the image in another section of my internal storage, this time it functioned.

    The diagram is attached below, I can not obtain a suitable schematic editor for my tablet and so it is drawn.

    However now that you mention it, the circuit is more than likely obsolete.

    *Edit: The box quotes an open circuit voltage of 21 volts and voltage at max power of 17.5 (not 18.5) at maximum power. What conditions does "maximum power" assume?

    *Second edit: It appears this is not the case and experimentation is required, although thinking about it, all that my circuit does is provide a fail safe, protecting against the extremes quoted of the maximum output voltages.


    Attached Files:

    Last edited: Feb 21, 2016
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