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step up DC/DC and start up

Discussion in 'Electronic Design' started by merco, Feb 10, 2009.

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  1. merco

    merco Guest

    In my last project i did this step up

    Ok IC8 isn't needed, but can't change the Jpg now...

    I put an on/off button before SL1.
    The positive rail (from batteries) is connected directly to the
    positive SL1 (+) , and the negative rail is connected to the button
    and then to the (-) batteries.

    I see that often (always) is difficult to let the circuit start (my 90
    led's bingo with internal speaker :lol: )

    After a lot of on/off swithces , randomly, the circuit start working.

    I notice that if i detach and reattach the SL1 connector from the
    batteries, the circuit starts better.

    Why ?
    Must I use a different button ?
    Something wrong in the design ?
    Too much current request at startup ?

    Thank you
  2. tomrei

    tomrei Guest

    A, why don't you use the shutdown pin on the Max756,
    B, why did you connect the Feedback pin to ground???!!!

    if you still need help,
    tell me about the input voltage output voltage, and load current,
    output ripple, load step (if you know them) and i may come up with a
    solution for you.

    yours Ren
  3. merco

    merco Guest

    A=> i don't know,How can i use It?
    B=> i don't know, i have seen a lot of schematic like that on the net.

    I had to use Max756, because i have a lot of it.
    Input voltage are 3 Ni-Mh cells, current max (with all leds and
    speaker on <=250mA),
    output ripple very low (i use it to supply a PIC)
  4. merco

    merco Guest

    I'm sorry, but before (near batteries) or after the switch ?
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