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DC to DC converter

Discussion in 'General Electronics Discussion' started by zapped, Nov 22, 2010.

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  1. zapped

    zapped

    7
    0
    Nov 22, 2010
    Hi all.
    I am new to this forum and to electronics.
    Can someone help me with a with a schematic for a DC to DC converter.
    I need to convert the voltage from 9Volt battery and get from 27 to 36 volts.
    I have just built a circuit that requires 27 to 36 volts.
    I have been using 9volt batteries wired in series.
    They are just too large and costly.
    All help appreciated.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    What current is required by your circuit?

    I ask you this because DC-DC converters are (at best) constant power, so if you require 27V at 10 mA, you will draw at least 30mA from a 9V battery. Added to that is the problem of efficiency (nothing is perfect) meaning that your actual current draw might be 50 or 60mA.

    A 216 size 9V battery is only capable of driving only comparatively light loads, so it may not be able to provide the power required.

    It will actually be cheaper to use 3 9V batteries in series because they will last more than 3 times longer than a single battery. You're also not likely to get much better than a DC-DC converter about the size of one of these batteries, especially if you build it yourself.
     
  3. zapped

    zapped

    7
    0
    Nov 22, 2010
    The current needed is very little as the circuit will operate for a month or more running it 2 hours a day. this is with three 9v in series
    I want to us a rechargeable battery.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Quantitatively, how much current?

    You may have to measure it.
     
  5. zapped

    zapped

    7
    0
    Nov 22, 2010
    Okay I will do that tomorrow and get back to you. As the batteries are dead now.
    Thank you for your reply
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Here is a cheap pre-built boost converter.

    It has a quiescent current of 15mA, which is quite high for a small 9V battery.

    It may be OK if the regulator is not left running, but let's wait until we hear what current is required.

    If we consider a 9V NiMH battery to have approx 250 mAhr capacity, then the quiescent current would discharge the battery in around 15 hours, so about a week at 2 hours a day. However this does not include any allowance for the current the load draws (and which you're finding out)
     
  7. zapped

    zapped

    7
    0
    Nov 22, 2010
    HI Steve,
    This circuit is drawing 2.55mA at full power.
    I am using a 24mm 100k 1/2 watt linear taper potentiometer as a out put control.
    I am going to change it to 16mm 100k 1/4 watt so that I can use a smaller encloser.
    Thank you for the link I like that circuit.But that circuit will not fit in my encloser as I only have 18.50mm to work with and it is 22mm. The heat sink put it over the max height of 18.50.I am thinking that maybe the heat sink is not needed at the small current I am drawing? I am wanting design both circuits on the same pcb.
    So at this point what are your thoughts about this?
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    OK, with those boost regulators, you would probably draw 25mA from a 9V battery. That would exhaust them in about 8 hours, or 4 days of 2 hr/day.

    Probably not ideal.

    Even in the best case, you would not expect a single rechargeable 9V battery to last longer than 12 days as 2 hours per day.

    To get anywhere near this performance you would need a very efficient boost regulator. Three rechargeable batteries would get you a month without any worries (at 2 hours per day).

    Perhaps you can tell us more about this circuit you are powering. Maybe there are alternative ways to design it to run at 9V and at lower current?

    edit: Yes, you are right, the heatsink could be removed at this very low power. It may also be possible to tweak component values to make the device more efficient at low powers and for this particular range of voltages.
     
  9. zapped

    zapped

    7
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    Nov 22, 2010
    I have a schematic of the circuit in pdf file how do I post it?
     
  10. Resqueline

    Resqueline

    2,848
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    Jul 31, 2009
    Maxim has a nice selection page that presents a dozen small IC's that might be up to the task if you dial in the voltages you need.
    National also has a search page that comes up with LM2733, LM3478, LM3481, LM3488, & LM5000 as possible small chips for the task.

    How big is that pdf?
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Use the attachment thingy in the advanced editor (only works for a smallish pdf)

    For a larger pdf, upload it to http://pdfcast.org/ and include a link for us.
     
  12. zapped

    zapped

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    Nov 22, 2010
    It is 33BK
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Click on "Go Advanced", then click on the paperclip and upload your pdf file. Then post your comment (you'll need to say something too)
     
  14. zapped

    zapped

    7
    0
    Nov 22, 2010
    This is the new schematic.
    Every one needs this!!
    This has been a life saver.
     

    Attached Files:

  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It would help if you could give exact specifications for the requirements of the output.

    Colloidal silver is just magic thinking rubbish, so I doubt that the actual output matters much at all.

    I would recommend you build a circuit using 4000 series CMOS operating from 9V. It will have a very low current draw and will probably operate for your desired time from a single battery.

    But I need a technical description (using standard scientific terms) of the required output.
     
  16. barathbushan

    barathbushan

    223
    0
    Sep 26, 2009
    Use this IC here
    http://www.national.com/mpf/LM/LM2577.html#Overview
    Outputs upto 40vdc can be drawn

    There are many such stepup/stepdown/inverter buck boost IC's available , if you know your specific voltage and current requirements , use this webapp

    http://webench.national.com/webench...I&err=I&sync=I&disty=&submit.x=62&submit.y=13

    to find out which IC is suitable for your requirements
     
  17. davenn

    davenn Moderator

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    Sep 5, 2009
    it begs the question ..."why do you need to run it off 27V ??
    why not run it off 9V with the appropriate changes in values of resistors etc

    I also and trying to figure out what the cct is supposed to achieve ?

    As Steve said a technical description would be good :)

    Dave
     
  18. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    The complexity of D1, D2 CR1, the capacitor, etc seems there only to cause the LED to flash alternate colours when nothing is plugged into the socket. However, on closer examination, it also probably loads down the output of U1B somewhat, which probably alters the frequency of oscillation. An attached load (depending on its characteristics and the setting of the pot) will also load down the output to some variable degree but with slightly different effects.

    Also the symbol for CR1 is wrong. I assume this is a back-to-back style dual colour LED. The symbol should reflect that.

    Bi-phasic is some really quite interesting gobbldygook. It's generating an AC square wave by virtue if the fact that the 2 op-amps are essentially being used to drive the load push-pull.

    Gee, I was at least hoping for something other than 0 or 180 degrees!
     
  19. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Fyi, the device is obviously supposed to drive an AC current through a human body, attaining som biological/physical effect, hence it needs a considerable voltage level.
    The LED is there only for checking the function before plugging oneself in. There's a second ("isolated") part of the circuit that delivers DC to the body for another effect.
     
  20. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I'm not entirely sure about that. Here is a document that describes 2 circuits that appear very close to functionally identical. One is described as purifying blood, the other as enhancing plant growth and generating colloidal silver.

    I am fairly certain that reducing the voltage to 9V will have absolutely no effect on the efficacy of this circuit, certainly with regard to its curative properties against HIV. ;-)
     
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