Fluke 93 - Power

3*34
CIRCUIT DESCRIPTIONS
If th 0 ScopeMeter
is connected
to the line voltage and is
not operallonaJ, the flyback
converter
operates almost
wrthoiJt a load (only
the NICd battery
pack). This irr^plies that
the current floating
through windings
L2504 and
L2505 (averaged In time) is almost
zero. Because of this,
the voltage on
CL+ Is about
30 mA and the voltage on
CL- Is about 170
mV. The battery
pack will be charged with
170 mA.
If the flyback
converter Is operated
normally
(ScopeMeter "ON"), the voltage
on both CL- and
CL+
will rise and the charging current will
decrease to
100 mA.
Battery charge
protection
To prevent charging
of non-rechargeable
batteries, a special
protection circuit Is provided.
For safety
reasons, this circuit
consists of two cascaded
sections. When the
ScopeMeter Is "ON",
the
flyback
converter will
be operative. The produced
voltage POWER-ON
will drive both Feld Effect
Transistors
V2537 and V2538
Open (conductive) via
R2568 and R2569.
Now the battery plus contact
Is
connected
to the ScopeMeter clrcuH
ground, if line voltage
Is present, the voltage -VCH produced
by
the flyback
converter will drive V2534
and V2536, which
prevent transistcfs
V2537 and V2638 from
conducting. The battery plus
contact is disconnected
from ground.
Power ON/OFF
circuitry
During normal operation
the POWER-ON signal
Is-hSV. Transistor
V2542 Is opened
(conductive), so
•Vbat/s equals
-V.CH. If me ScopeMeter
Is operating and me RESPOWHT
(
'reset power
si^>ply")
becomes "high".
V2541 will conduct and V4542 will
stop conducting.
This will disconnect -VbaVs
from
•V_CH.
3.4.9 POWERSUPPLY
•
Introduction
See figure 3.19.
Different
supply voltages are needed for
various ScopeMeter
sections. A second flyback
converter Is
used to convert -V Dal's to
supply
voltages
of -30V, -5V
and -fSV. This voltage, -VbaVs,
is made by the
first flyback
converter (In the battery
charger section)
or comes from the batteries.
-Vbat/s Is 5V If
operated with NICad battery
pack, and 8V if operated
from line voltage.
-
Detailed circuit
description
See figure
3.19 and circuit diagram A2c (figure
10.7).
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