Tektronix FG 5010 User Manual

Theory
of
Operation -
FG
5010
ticipating
the proper
time
to
switch
at
the
Transistor
Bridge
output .
Loop
Capacitors
Refer
to
Diagram
12 in
this and
following
discussions
.
The
Loop
Capacitor
stage
consists
of
four
relays , five
fixed
capacitors
, an
inductor
and an
adjustable
capacitor .
The ca
pacitance
values
are
arranged in
decades , so
that
five
fre
quency
decades
are
possible by
selecting
the
proper
amount
of
capacitance .
Relays
K1331 ,
K1323 ,
K1322 ,
and
K1321 , all
driven
by one
of the
Digital
Control
Latches ,
se
lect
the
proper
amount
of
capacitance
for
the
selected
fre
quency
.
The
first
three
of
the
relays
also
control
the
selection
and
application
of the
shrink
current to
the
Level
Detector , which is illustrated on Diagram 14. The loop ca
pacitance for the
highest
frequency range is actually
two
capacitors ,
one of
which is
adjustable
.
Capacitor
C1432
is
adjusted to
bring the
highest
frequency
range
within
specification
.
The
Loop
Capacitors
are
connected
through test
jumper
P1435 to the
Transistor
Bridge
circuit
,
which
furnishes the
current for
charging
and
discharging
the
capacitors . This
junction also
connects to
the input of
the
Triangle Buffer ,
the
interface
between the
Loop
Capacitors and
the driven
circuits . The other connection to the Loop Capacitors is to
the
Phase Clamp
Circuits , depicted on
Diagram 14.
This
input is
used when
triggered ,
gated ,
or
burst modes
are
selected . In those
modes , current
is
steered away from
the
Loop
Capacitors to hold
the loop out
of the free
-
running
mode ,
which
permits the
gating ,
trigger , and
burst
logic
cir
cuits to control the start and stop of the loop .
Triangle
Buffer
The
Triangle
Buffer provides
the
high -
impedance
inter
face
required
to isolate
the
Loop
Capacitors
from the
driven
circuits . The
buffer is a unity
- gain
amplifier that
consists of
the
following
components :
field -
effect
transistors
Q1232A
and
Q1232B ,
transistors
Q1231 ,
Q1234 ,
Q1230 ,
and
Q1332 ;
Zener
diodes
VR1240 ,
VR1220
, and
VR1230 ;
and
related
components .
The
triangle -
wave
output
of
the Loop
Capacitor
circuit
is
applied
to the
gate
of
Q1232B
and
Q1232A ,
which
is a to
tem - pole amplifier configuration . Temperature compensa
tion
transistors
Q1234 and
Q1231 act
to maintain
a
constant
drain
-
source
voltage
across Q1232B
and
Q1232A ,
respectively , which
maintains
a constant power
dissipation
.
Thermistor RT1230 maintains a constant source impedance
on
the base
of
Q1230
,
which is driven
by the
source
of
4-12
Q1232B
.
The
Zener
diodes in
the
emitter
and collector
cir
cuits
of
emitter follower Q1230
limit the
power
dissipation
across
the
transistor . From Q1230
, the triangle
wave is ap
plied
to
the
base of
Q1332
,
the
output
emitter
follower
.
Power
dissipation
of
Q1332
is
reduced by
VR1240 in
the
collector
circuit of
the
transistor .
The
triangle
wave is
taken
from the
emitter of
Q1332
, then
applied to the
Triangle
Se
lector and
Level Detector
circuits .
Level Detector
The
purpose
of
the Level
Detector
is to
determine
the
switching
point at
which
the charge
current
to
the
Loop Ca
pacitors
, is
reversed and
to
produce
the
square
wave
that
triggers that
event
. The
square
wave is
passed
through to
the
HF
Square
Wave Buffer
to be
applied to
other
circuits ,
and for use as the output high - frequency square wave .
The
Level
Detector
consists of
transistor array
U1351A ,
transistors
Q1341 ,
Q1342 , and
Q1233 , plus
related
compo
nents
. The circuit
is
configured to be a
Schmitt trigger stage
,
with
some
refinements . The
main
part
of
the
circuit is
U1351A , which
operates
as a differential
comparator
stage
that
has a
constant -
current
sink
.
Zener
diode
VR1351
sets
the
bias for
the current - sink
transistor
in U1351A
, resulting
in
a
standing
current
through
the
conducting
half of
the
dif
ferential
pair
of
4 mA
.
Transistors
Q1341
and Q1342
form a
controlled
differential amplifier that
provides
the
positive
feedback to
make the
driving stage
operate as
a Schmitt
trigger
circuit
,
sets the
upper trip
point
for the
circuit
,
and
makes provision for the Schmitt Defeat Circuit input by way
of
Q1233 ,
the
remaining
transistor .
The
triangle
- wave
signal
is
applied
to pin
4 of
U1351A
, to
be
compared against
the
voltage
at pin
1.
This voltage
, the
trip
point for the
Schmitt
trigger
circuit , is
variable
due to
the
shrink
current that is
injected into
the
circuit to
adjust the
upper
and
lower
points .
Assume that
the pin 4
input is more
positive
than the pin
1
input . This
means that
the
applied triangle
wave
signal is
moving
negative
. (
Also , for the
purpose
of
simplification , as
sume
that no shrink
current is
applied for the
moment
. ) At
this
time , the left
transistor of
U1351A
is cut
off , the
right
is
conducting ,
Q1341 is
cut off ,
and
Q1342 is
conducting .
Nor
mally
the
SCHFEAT
line at the
base of
Q1233 is high
, so
this
transistor
is not
conducting . The
pin 13 output
of
U1351A is
at a low state
, so the
Transistor
Bridge
circuit is
operating
in
the
down
-
current
mode .
When the
applied
triangle - wave
signal at pin
4 of
U1351A
passes
the voltage
at pin
1 ,
the left -
hand
transistor
begins
U
(
U
U
U
U
U
U

Tektronix FG 5010 Specifications

General

Brand	Tektronix
Model	FG 5010
Category	Portable Generator
Language	English