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34063 questions...

Discussion in 'Electronic Basics' started by zulutime, Jun 1, 2004.

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  1. zulutime

    zulutime Guest

    Adapting a 34063 based dc-dc cell charger for use as a portable
    recharger operating off alkalines, and I could use some expert
    advice...

    1) How much reverse voltage can a 34063 take? What kind of input
    polarity protection is needed?

    2) Is an input cap required when running off batteries?

    Thanks in advance...

    zulutime
     
  2. jan

    jan Guest


    ////

    Hi zulutime,

    You didn't get a response to your problem, looks like you have to find
    a smarter NG. Let me know if you do.

    Jan
     
  3. Most chips can only take a half volt or less. THe usual way to protect
    these is to put a 1N4002 rectifier across the battery leads, with the
    cathode to positive. If the battery voltage is reversed, the rectifier
    conducts heavily and either drains the battery or...

    That's why it's a good idea to have a fuse between the battery and t he
    rectidier.

    For best efficiency you should have a capacitor across the battery,
    preferably a low ESR type.
     
  4. onestone

    onestone Guest

    If there is a strong possibility that a battery may be connected
    reverse polarity I use a small bridge rectifier, then polarity becomes
    irrelevant. other wise I use blocking diode. I prefer to have akeyed
    connector to prevent this.

    I always have an input cap when running off batteries.

    Al
     
  5. Watson A.Name \"Watt Sun - the Dark Remover\" wrote...
    The forward voltage of a 1n4002 diode is 1.4 volts at 20A, so a
    high-current Schottky diode is a better choice for this tough
    form of protection. E.g., an axial-lead 1n5822 (Vf = 1V at 20A),
    or a TO220 part like an MBR1045 (Vf = 0.8V at 20A) or MBR2545CT
    (Vf = 0.75V at 60A with both sections paralleled).

    These Schottky diodes have a low enough voltage drop they can be
    easily used in series for a more relaxed protection scheme. For
    example the 1n5822 only drops 0.4V at 2A.

    Thanks,
    - Win

    (email: use hill_at_rowland-dot-org for now)
     
  6. zulutime

    zulutime Guest

    Thanks much for the responses and advise.

    Some of these converters have a 1N400x reversed across the input, but
    without actually blowing one up, it's impossible to be sure how much
    reverse voltage they can take. A Schottky is a good idea.

    I'm using a 9v snap style connector...keyed, but easy to reverse
    momentarily.

    Thanks for the help.
     
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