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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

    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...

  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.

  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

    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.

  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.

    - 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

    Thanks for the help.
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