From: Rob & Liz Ward <wards_at_paradise.net.nz>
Date: Sat, 29 Dec 2001 08:06:16 +1300

10k resistor fixed. Excellent.

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.

I think T3 should be PNP, not NPN.

Are you sure C12 is correctly wired?

The long wires from D8 to conn. SV1 (pins 31,32) seem wrong also - circular.

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

Good luck.

Rob


----- Original Message -----
From: "Andrew Jamieson" <ajamiesn_at_mira.net>
To: <jukebox_at_cool.haxx.se>
Sent: Saturday, December 29, 2001 12:51 AM
Subject: Re: Getting rid of that damn noise.


>
> > Ok. I have finally seen the schematic. One comment - the MC34063 chip
> (U15)
> > on the i/f and power sheet is a switch-mode power supply chip from
> Motorola
> > (an old trashy chip in my opinion - there are much nicer ones than this
> > part). It looks as if they are using it in a buck configuration (step
> > down) - acting purely as a battery charger (6V?). The short between pins
7
> &
> > 8 mean there is no current limiting for the switcher.
>
> Yeah. Hmmm ....
>
> This is weird.
>
> The 10k resistor (on the high side of T3 and the 34063 supply) seems to be
> the current limiter for the battery charger. This seems a bit high, but
the
> energy supplied by the inductor may be doing something I'm not factoring
in
> (in fact there must be something I am missing, cos my calcs say the
> batteries would take ~ 3111 hours to charge with a 9V source and a 10K
feed
> resistor!).
>
> The comp input of the switcher seems to be connected up to a strange
circuit
> that connects to one of the A/D inputs of the CPU (AN1), and also PB5, and
> then fed back to the comp circuit via a couple of resistors and a diode.
So
> what's it do?
>
> Well, it seems that the state of PB5 determines if the switcher is on or
> not. Set PB5 high, and the switcher will turn off (as comp will go high).
> Set it low, and the switcher will turn on (assuming there is a drain of
the
> voltage left by setting PB5 high (PB5 won't pull it low because of the
> diode) - this may be a big assumption, and the switcher could take awhile
to
> turn off after changing the state of PB5). Therefore, the battery charger
> can be controlled by the CPU.
>
> BTW: with no direct feedback from the switcher output to comp, there is
> absolutely no voltage regulation; the switcher is being used more as a
> current source than a voltage source.
>
>
>
>
Received on 2001-12-28