Fluke 93 Service Manual page 66

3-32
CIRCUIT
DESCRIPTIONS
3.4.8
BATTERY CHARGER
- Introduction
Seo
figufG 3.18.
The
battery
charger
consists of
a
switched
mode
power
supply
and
some
auxiliary
clrculiry.
Whenever
the
Scope Meter
Is
connected
to the
line
voltage
(via
the
separ^e power
adapter/battery
charger PM6907), the instrument switches over
to line
voltage operation automatically.
If
a
NiCd
battery
pack
Is
Installed,
the
ScopeMeter
wilt
charge
this
If
line
voltage
Is
present. Special
circuitry
prevents discharge
of
the
batteries
when
the Instrument
Is
not
being used.
-
Detailed
circuit
description
See
figure
3.18
and
circuit
diagram
A2c
(figure
1
0.7).
HF
Fitter
The
input
voltage
(between
8V
and 20V)
first
passes
MF
FILTER Z2501 and
is
used
to diive
a
flyback
converter.
POWffi
SUPPLY
Figure
3.
16
Schematic diagram
battery
charger
Une
voitage detection
When
the
ScopeMeter
is
operated
on
line
voltage, transistor
V2521
will
be
driven by the
(filtered)
Input voltage.
The
signal
MAINVOLTHT
will
become
"low" to indicate that
the Instrument
is
operated
from
the
line
voltage.
The
related signal
MAINS-D
(connector
XI
201,
pin
5)
is
connected
to
the
microprocessor analog
input 19.
When
the signal
MAINS-0
Is
"high",
the
microprocessor
will
not
switch
off
the
ScopeMeter, as
in
battery operated
mode.