How to build a very low quiescent current 1.4V LDO

Discussion in 'General Electronics Chat' started by praondevou, Jan 4, 2016.

  1. praondevou

    Thread Starter AAC Fanatic!

    Jul 9, 2011
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    Hi,

    First of all, Happy New Year to everybody!! Hope you are doing good.

    Now my problem:
    I want to power a microphone with a button cell. The button cell is a silver oxide one with an initial voltage of 1.55V (new).
    The microphone works down to 0.9V, it's maximum rating is 1.45V though. The microphone consumes not more than 25uA. I want to limit the voltage on the microphone to 1.4V max without adding more than a few uA (< 10). I know it can be done with a comparator and voltage reference and P-FET but current will be higher than just a few uA due to the voltage reference AND the component count is quite high.

    Just putting a schottky in series will not allow me to completely discharge the battery, unfortunately discharge curves for that battery available on the internet vary widely also, some are straight at about 1.3V, some decrease almost linearily...

    Any ideas? Low component count, low additional current, 1.35 to 1.4V maximum output voltage. Ideally I would remove 0.15V when the battery is new and once it arrives at 1.4V it just goes straight through to the load (microphone)

    Thanks

    Link to datasheet: http://store.invensense.com/datasheets/invensense/ICS-40310_ProductSpec_V1 0.pdf
     
  2. crutschow

    Expert

    Mar 14, 2008
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    A small Schottky diode in series should work for you.
    A simulation of one is shown below.
    All the silver oxide battery curves I've seen have a relatively flat output voltage as they discharge, so the amount of battery capacity left should be quite small after it drops to below the operating point of the amplifier with the diode in series.

    I don't know of any low current, low voltage circuit that will do what you want.

    Diode.PNG
     
  3. praondevou

    Thread Starter AAC Fanatic!

    Jul 9, 2011
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    Hi Crutschow,
    Thanks for taking the time to respond. After having a closer look at the various discharge curves I think you are right. I would probably be able to use 80 to 85% of the battery capacity. I will try it out.

    Thanks
     
  4. hp1729

    Well-Known Member

    Nov 23, 2015
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    There must be something for me to learn here. Why power the microphone separately instead of from the circuit it goes to?
     
  5. praondevou

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    "The rest of the circuit" could support way more than 1.55V. The problem is the initial voltage of the battery cell which is higher than the maximum rating of the microphone.
     
    Last edited: Jan 6, 2016
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    So why not power the microphone from the circuit psu, and use an lm317 to drop the voltage to 1.5v, or use two silicon diodes as a voltage regulator?
     
  7. praondevou

    Thread Starter AAC Fanatic!

    Jul 9, 2011
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    The whole circuit is powered by the button cell but only the the microphone has a maximum rating of 1.45V, which I do not want to exceed.

    And a LM317 has a minimum load current requirement of 3.5mA.

    Anyway, I made a practical test and yes, a schottky diode (I used the BAT54) does the job, voltage remains just below 1.45V, tested from 6uA to 31uA. Need to do this at different temperatures now. I was confused about the many different discharge curves...

    Thanks all
     
  8. GopherT

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    Nov 23, 2012
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    A working voltage range of 0.9 to 1.45V seems like this device was designed around a one-cell niCad battery instead of silver oxide technology.

    Here is the voltage discharge curve for NiCd. Max is 1.4 (typically 1.35) and end of life is typically considered 1.1.

    image.jpg
     
  9. praondevou

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    Interesting!! The problem is the battery size though, I want to use a 335 button cell which is the thinnest small diameter battery I could find...
     
  10. crutschow

    Expert

    Mar 14, 2008
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    NiCad is so yesterday...;)
     
    cmartinez and GopherT like this.
  11. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Just like the OP's part if a decent alternative battery cannot be found with a max voltage under 1.45V.
     
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