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Boost converter for battery widget

Discussion in 'Electronic Design' started by Richard H., Aug 21, 2007.

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  1. Richard H.

    Richard H. Guest

    To step-up a single-cell 1.5v battery to ~3.3v, is there a better option
    than using a boost regulator like an LM2623?

    I'm trying to hack out power options for a simple battery-operated LED
    gizmo, and it's turning out more complex than the gadget itself.

    BTW, load is <1mA to ~100mA depending on LED duty cycle, with a lot of
    "off" time. (The power needs to stay on, but the microcontroller will be
    quiescent - I'm not sure that a simple transistor+inductor scheme will
    give much battery life.)

  2. colin

    colin Guest

    depends how well it is designed,
    if it reduces the frequency of operation at idle it can
    increase the efficiency becuase it lowers switching losses.
    a hysteretic type would be ideal for this.
    some others go into whats called burst mode.

    you would need a very low power controller,
    ive not had to look for such before.

    maybe you could use the led pwm if its high enough frequency.

    an alternative is the capacitor charge pump.
    100ma is quite a bit, there are many wich are fairly low power,
    not sure about 100ma.

    depends what idle power consumption you can tolerate.
    if its only a few microamps its difficult.

    I used one of those micropwer op amps in a rf sniffer probe,
    didnt have space for an on/off switch as well as a battery.
    but got it down to 5 yrs life with no switch.

    Colin =^.^=
  3. jack

    jack Guest

    why not consider a super-capacitor and d.c-d.c converter -- the converter
    can loaf along with a very low duty cycle

    linear tech had a very low loss dc-dc converter application note which
    appeared in EDN in the Spring.
  4. Richard H.

    Richard H. Guest

    Yep, I'd planned to put an electrolytic near the load; it hadn't crossed
    my mind to consider a super cap there. That could be a good match.
    I'll look for the appnote.

    Now, maybe a dumb question, but... DC-DC converter seems to be a generic
    term in this area, with 'boost' and 'step-up' being more specific
    synonyms (but I could be reading this all wrong). By DC-DC, do you mean
    a linear regulator? Don't they generally have lower efficiency and
    higher quiescent current? (This gadget won't have a power switch in
    most cases, so the supply itself can't draw too much current when the
    LEDs are idle.)

  5. Richard H.

    Richard H. Guest

    Hmmm. The application here is something along the lines of Activate ->
    blink LEDs for a while -> shutoff until re-activated. Activation is
    likely to be manual (maybe a pushbutton or capacitive sensor) but maybe
    also periodic timer (which could be another microcontroller in the power

    So, it's possible between cycles to fully quiesce the power regulator
    for max battery life. I'm not sure an MCU will be required, but either
    way perhaps triggering shutdown on the regulator or cutting off its
    power completely with a MOSFET. (But then this calls for a separate
    low-power stage to feed the control circuitry. Seems a lot for a
    battery widget, but maybe not.)
  6. Chuck Harris

    Chuck Harris Guest

    Though technically a linear regulator is a DC-DC converter, so is a resistor.
    The term is not usually used for such devices.

    Usually a DC-DC converter implies a device that through some switching technique
    increases, or decreases the supplied voltage to some other level.

    Generally, it is not practical to raise the DC supply voltage without some kind
    of switching, or AC creating device, be it a motor-generator, an inverter,
    or some scheme of charging capacitors in parallel, and discharging them in series...

  7. colin

    colin Guest

    just another thought, you could have the micro drive the LED via a mosfet
    and inductor
    therby doing the boost conversion from the batery voltage,
    there wont be a need for a current limit resistor.

    it then makes the micro supply a lot easier.

    Colin =^.^=
  8. R&D

    R&D Guest

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