# 34063 questions...

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

1. ### zulutimeGuest

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?

zulutime

2. ### janGuest

////

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. ### Watson A.Name \Watt Sun - the Dark Remover\Guest

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. ### onestoneGuest

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. ### Winfield HillGuest

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. ### zulutimeGuest

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.