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Linear power supply design

Discussion in 'Power Electronics' started by Markeh, Feb 3, 2014.

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  1. Markeh

    Markeh

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    Feb 3, 2014
    I'm trying to do a project where I'm creating a linear power supply for a pre-amp of an audio circuit. The main focus on the project is the power supply itself.

    I'm needing some help explaining how this circuit works (Attached), mainly why there is use of electrolytic capacitors in parallel to the capacitors. I've altered the circuit to get a 40v output from a 230v input.

    Also, how do I add overcurrent and overvoltage protection?

    If anyone can break it down into simple terms I would be appreciative, I'm not a huge electronics boffin and this is just a small part of a course.
     

    Attached Files:

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    What sort of over-current and over-voltage protection do you mean?

    one answer is using a fuse and varistors.
     
  3. Markeh

    Markeh

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    Feb 3, 2014
    Thanks for taking a look, I'd be wanting to incorporate a varistor within this circuit somewhere.
     
  4. jcurrie

    jcurrie

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    Feb 22, 2011
    the LM317 is rated at 37v max.
    jc
     
  5. duke37

    duke37

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    Jan 9, 2011
    The electrolytic capacitors are used to smooth low frequencies but they are ineffective at high frequencies so they are paralled with small low inductance capacitors.

    Why do you need over 1A (or 40V) to drive a preamp circuit?
     
  6. Markeh

    Markeh

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    Feb 3, 2014
    Thanks jc, I did read it was up to 40v, I'm currently getting 20V maximum going across the IC, would this be acceptable?

    Thanks for your input duke, I've never seen the two coupled together before, I've just chosen that circuit as a starting point, would reducing the current requirements be easier?
     
  7. Markeh

    Markeh

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    Feb 3, 2014
    I'm actually having a problem at the moment with the fuse randomly blowing, have I got a mistake in the software or is the circuit not right?
     

    Attached Files:

  8. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    You have a very large capacitor on the output of the rectifier. A 4.7mF at startup could try and draw 20Amps or more from your circuit because it will have a very low ESR. I would reduce the value to say 1000uF and make sure you use an anti-surge type of fuse, I would move the fuse to before the rectifier, and reduce its value to say 1.5Amps. Your only driving a small load.
    Adam
     
  9. duke37

    duke37

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    Jan 9, 2011
    If you are using less than 1A, you do not need a booster transistor.
    The TIP42A is the wrong way round.
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Not really.

    Attaching a capacitive load to the output of the power supply could momentarily place the full voltage across the device. It may not destroy it the first time (depending on the size of the capacitor) but it may cause cumulative damage that eventually results in failure.

    In addition to this, the extra voltage you have is wasted as heat. It is best to have your input voltage maybe 4 to 6 volts higher than the output voltage (but this does depend on load current) not 20V.
     
  11. Markeh

    Markeh

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    Feb 3, 2014
    Thank you all for your input, I've made some good changes. How would I set up overvoltage protection?
     
  12. Markeh

    Markeh

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    Feb 3, 2014
    Can someone please show me how to get overvoltage protection on this circuit? I've tried a few varistors across the supply and after the rectifier, but I still can't get it to switch to ground on overvoltage
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    If you recall, you asked this question earlier and I responded by asking you "what sort of over-voltage protection do you mean".

    You're simply not going to get an answer until you tell us what you mean.

    You might also think to explain why this might be required and what events would precipitate its activation.
     
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