EasyManua.ls Logo

Valleylab Force FX-C - Page 70

Valleylab Force FX-C
214 pages
Save Page as PDF
Print Icon
To Next Page IconTo Next Page
To Next Page IconTo Next Page
To Previous Page IconTo Previous Page
To Previous Page IconTo Previous Page
Loading...
Power
Supply/RF
Board
4-20
The
SYS_ECON signal from
the
microcontroller controls
the
output
voltage leveL
This
0 to S V dc
signal
sets
the
reference for the
PWM
control
loop.
An
external
op-amp
(U7B)
is
used
for
gain
and
integration, since
common
mode
voltage limitations
in
US's
internal
op-amp
preclude
its
use
over
the
full
range
of
0 to S
V.
The
internal
op-amp
is
connected
as
a
follower.
SYS_ECON is
compared
to
the
feedback
voltage
from
the
output
divider
(R34, R3S,
and
R49),
and
an
error
signal (ECON) is
sent
to
the
PWM
microcontroller.
In
addition
to
the
error
signal, U7B
and
the
associated R-C
networks
provide
lead-lag
loop
compensation
to increase
the
bandwidth
of
the
regulator
beyond
that
of
the
output
L-C filter.
Note:
U7 A is
used
for
random
gain
switching
in
the
Spray
mode
and
is
configured for
unity
gain
in
all
other
modes.
The
output
of
US
is a
pair
of
180
0
out-of-phase signals
that
are
pulse
width
modulated
by
comparing
ECON
with
the
internal
oscillator
ramp
waveform.
At
the
start
of
an
oscillator cycle,
an
output
is
turned
on.
It
turns
off
when
the
ramp
voltage crosses
the
ECON
level.
The
two
output
signals from US (pins
11
and
14) feed
the
MOSFET
drivers
(U3Aand
U3B).
R36
and
C42
set
the
US oscillator frequency to
approximately
170 kHz.
C4S controls
the
ramp-up
of
the
pulse
width
at
power
on
for
slow
start
control. Transformer
T2
limits
the
power
transformer
primary
current,
protecting
against
faults
in
the
OC/OC
switcher
power
stage
and
faults
in
circuitry dovvnstream
of
the
switcher.
The
output
of
T2 is rectified (CR3-
CR6), filtered (R30
and
C30),
and
fed
to
the
current
limit
pin
(pin 9
of
US).
During
an
overcurrent
condition
the
US
current
limit
function resets
the
slow
start
circuit, resulting
in
the
output
cycling from
on
to
off
until
the
current
falls.
Pin
9
of
US is also
used
for
remote
shut
dovvn
of
the
DC/DC
switcher
through
U6A
and
CR8.
The
shut
dmvn
signal
comes
from
the
main
microcontroller
on
the
Control
board.
The
resistor
divider
on
the
high
voltage
DC
output
formed
by
RS2
and
R53 is
used
for
dosage
error
sensing.
Force
FXTM-C
Service
Manual

Table of Contents

Related product manuals