Thinking about dual supply for portable system

Discussion in 'The Projects Forum' started by Crowbar, Dec 20, 2006.

  1. Crowbar

    Thread Starter Active Member

    Dec 19, 2006
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    I'm working on portable signal processing unit for 3-axis fluxgate magnetometer. 1-axis Analog part consists of preamplifier, switchable HPF, fixed LPF, programmable gain amplifier with in-out offset control. I was thinking a lot about supply(dual supply +/-5V 60mA max for each rail). As I said, system is portable and is be powered from 8.4V accumulator- therefore voltage converter must be used. I see some ways:
    1)Use Regulator 8.4v->5v then DC-DC converter(Traco etc.) with LC filters (here we have problems with ripple noise)
    2)Use Regulator with Inverter(here we have problems with Inverter cause at higher load voltage dropout is around 650mV)

    So I need some advice on voltage converters- what will be better to use in my signal processor in order not to lose overall system characteristics and perfomance.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    They all involve charge pumping or DC - AC - DC conversion. Any hope for using two batteries? It's bulkier, but lots quieter.
     
  3. Crowbar

    Thread Starter Active Member

    Dec 19, 2006
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    Two 8.4 accumulators(like standard 9V battery) needs some space,
    and we can have some problems with diiferent discharging of them. When I read DC-DC converters datasheets(ripple noise is quite big~75mv p-p) I began thinking of external 12V acc, but they are so bulky :)
     
  4. Crowbar

    Thread Starter Active Member

    Dec 19, 2006
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    Suppose we use battery supply and virtual ground circuit(2 resistors+2 cap+BUF634)- will this scheme work from stabilized mains adapter?
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    You make a real ground using two batteries by electrically connecting one battery's positive terminal to the other's negative. That point is common to both, and becomes the circuit ground.

    Without seeing a schematic of your "stabilized mains adapter" I cannot answer that part of your question.
     
  6. Crowbar

    Thread Starter Active Member

    Dec 19, 2006
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    I asked such question, cause finale device should work from batteries and from mains(using simple adapter 220->12V)
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    You may find that something more elaborate than an unregulated wall transformer will be necessary. Also, a battery charging circuit.

    So far, this is all very hypothetical. Posting a circuit and the power requirement of your magnetometer would be useful.
     
  8. Crowbar

    Thread Starter Active Member

    Dec 19, 2006
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    Can't post a cirquit- It's is redrawing now. Sensor must be powered from stabilized 5v, also I'm using precision voltage references (2.5V and 5v) for offset control, all other cirquit blocks are powered form +/-5v(~35mA each rail)
     
  9. Crowbar

    Thread Starter Active Member

    Dec 19, 2006
    32
    0
    Hm, finally I've decided to use 8.4 battery with voltage inverter followed by 6v linear regulator.
     
  10. Crowbar

    Thread Starter Active Member

    Dec 19, 2006
    32
    0
    Another Imlementation, What's your opinion? [​IMG].
     
  11. mcj74

    New Member

    Jan 10, 2007
    6
    0
    Hi Crowbar. Drawing 120mA from a single 9V battery is going to deplete it very quickly. I agree with the first reply, your best bet is to use two 9V batteries and the 7805/7905 linear regulators. Simple, and low-noise.

    Keep in mind there are other choices than 9v batteries - check out some of the NiMH and Li-ion packs sold at www.allelectronics.com for example.

    Also, the 1uF caps might not be enough if you demand REALLY clean power. Try 10uF tantalum caps, that ought to do the trick. :)
     
  12. Crowbar

    Thread Starter Active Member

    Dec 19, 2006
    32
    0
    Two battaries take lot place. Yes, there will be some noise but op amp's that I'm using at the rest of cirquit have high PSRR.
     
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