ABB MMCO-2 - Page 11

I
.
L
.
41
-
121.2
6.4
.
POWER
SUPPLY
CIRCUITRY
CAUTION
Referring
to
the Power
Supply
Internal
Schematic
Figure
22
:
Battery
may
explode
if
mistreated
.
DO NOT
RECHARGE
.
Dispose
of
used
battery
promptly
,
in
a
location
where
people
are
not
exposed
to
the
battery
.
DO NOT
disassemble
or
dispose
of
battery by
using
fire
.
Keep
away
from
children
.
A
switching
dc
to
dc
voltage
converter
steps
the
48
-
125
Vdc
(
250
Vdc
for
250
V
option
)
down
to
21
volts
dc
for
output
relay
operation
and
5
volts
for
digital
cir
-
cuitry
.
A
linear
voltage
conversion
to
26
V
is also
gen
-
erated
.
The
active
power
elements
in
the
power
supply
are
Q
1
which
linearly
generates
the
26
V
out
-
put
,
Q
3
which switches
L
1
to
generate
the
21
V
out
-
put
and
Q
4
which switches
L
2
to
generate
the
5
V
output
.
Referring
to
Power
Supply
Module
Internal
Sche
-
matic
,
Figure
22
:
The
ranging
chip
U
3
along
with
discrete
components
Q
6
,
D
6
and
R
43
serves
to reset
the
microprocessor
if
the
“
Deadman
”
signal
is
not
toggled
by
the
micropro
-
cessor
.
This insures
that the
system
will
reset
if
the
software
is
not
functioning
properly
.
OP
amp
U
2.2
and associated
discrete
circuitry
generates
the
OP
Amps
U
1
is used
to
control the
switching regula
-
tor
and
OP
Amp
U
2.1
is used
to
generate
the
5
V
ref
-
erence
and
to
calibrate
the
relay
pickup
level
.
Both
Op
amps
U
2.1
and U
1
are
powered
by
the
26
Volts
generated
on
the Power
Supply
Module
.
“
Inhibit
”
signal
which
prevents
writing
to
RAM
(
U
8
and real
-
time clock
chip
U
9
,
Microprocessor
Module
Schematic
,
Figure
20
)
on
power up
and
power
down
via the
memory
select
chip
U
11
.
The inhibit
signal
also disables
the
relay
outputs
during
power up
or
down conditions
via
relay
driver
chip
Q
1
(
I
/
O
Internal
Schematic
Figure
26
)
.
6.5
.
USER
INTERFACE CIRCUITRY
Referring
to
the
Display
Module Internal
Schematic
Figure
24
:
The
display
consists
of
a
16
X
2
character
alphanu
-
meric
LCD
display
module
(
LD
1
)
which
is
driven
directly by
the
microprocessor
(
U
2
on
Microproces
-
sor
Schematic
,
Figure
20
)
.
A
temperature
compensa
-
tion circuit
consisting
of
Op
Amp
U
1
and
temperature
sensor
U
2
is
used
to
bias
the
display
for
good
read
-
ability
over
the
-
20
C
to
+
60
C
temperature
range
.
Potentiometer
R
13
which is accessible
through
the
front
panel
is used
to
adjust
the
display
for
best read
-
ability
under various
lighting
conditions and
viewing
angles
.
It
is
factory
set
for
normal
lighting
conditions
and
viewing angles
.
A
voltage
inverter
chip
(
U
4
)
is
used
to
supply
the
negative supply voltage
for
the
display
bias
circuitry
.
Red
LED LE
1
(
TRIP
)
and
amber
LED LE
2
(
MONITOR
)
are
driven
by
the micro
-
processor
through
mosfet
transistors
Q
1
and
Q
2
.
The switches
on
the
front
panel
board
are
input
into
a
parallel
to
serial
shift
register
(
U
8
)
and
their
values
are
read
from
the
shift
register
serially by
the
micro
-
processor
.
6.3
.
RELAY
INPUT
/ OUTPUT CIRCUITRY
Referring
to
the
I
/
O
Internal
Schematic
Figure
26
:
The
trip
relays
(
K
1
,
K
3
)
,
annunciator
relays
(
K
2
,
K
4
)
and alarm
relay
(
K
5
)
are
driven
by
the
microproces
-
sor
via
relay
driver
chip
Q
1
.
All
the
relay
contacts
are
normally
open
except
for
the alarm
relay
(
K
5
)
which
has
a
normally
-
closed
contact
.
The alarm
relay
(
K
5
)
is
energized
(
open
contacts
)
when there is
no
alarm
condition
.
A
reed
relay
(
K
6
)
is monitored
by
the
microprocessor
and is used
to
detect
breaker
trip
current
flow
.
The Inhibit
signal
,
along
with
associated
diodes
and resistors and
relay
driver
chip
Q
1
,
is used
to
disable
the
output
relays
on
loss
of
battery
power
to
the
relay
.
Two
optoisolators
(
U
1
,
U
2
)
and associ
-
ated discrete
components
function
as
isolated
inputs
to
the
relay
for
either the directional control
input
option
or
the
remote reset
option
.
11
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