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Subject: Re: Getting rid of that damn noise.
From: Joachim Schiffer (gemoin_at_gmx.net)
Date: 2001-12-28


Hi Rob,

I must apologize for the errors in the schematics...
I have just made lists of connections
(for example U11,5 -> U6,5)
and when i was finished, I put them together.
I didn't analyze the circuit (and i don't have the time for that
at the moment), so i didn't notice the bugs.
I also don't have the time to re-check the whole
circuit again (it took a few days...), so it's the best,
if I check single connections, if they look strange.

> The comp would be the feedback i/p (normal operation = 1.25V?). Driving
> this pin high (via the diode D8) stops the switching, and
> using the a/d to read it would tell whether the battery is charged. This
> means the battery charger is logic-levelled controlled - ON or OFF !
>
> This is a rather crude battery charger that would appear (from the current
> circuit) to feed as many volys into the batteries as possible. Please check
> the /COMP wiring for correctness.
>

There were indeed bugs around the /COMP pin.
I have attached a new version of the second pdf.

The values of some Resistors may be wrong, too.
They are sometimes badly printed, and there are
two notations. Sometimes it's 103, sometimes it's
10B or 01C. It's also not easy to read sometimes,
for example if a B looks like a 3...

> I think T3 should be PNP, not NPN.

T3 is labeled FZT849, i think it's definitely NPN.

> Are you sure C12 is correctly wired?

C12 is correctly wired, but there was one additional
connection missing, I fixed it.

Also, i found out, that D12 is a zener diode (2.7 V) and
is connected R20, not to VSUP directly.

> Of course, they could have some weirdo circuit here, but it certainly
> resembles what I would expect.

> Good luck.
Thank you :-)

/Joachim





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