Tektronix 465M User Manual

3
As Q552 turns on.
current is
drawn through
T550 and L554.
This current
induces
positive feedback
into
the feedback coil of
L554 and turns
on Q552 harder.
The
voltages induced into the
feedback
coils of T550 and
L554
hold Q552
on.
^
As
the magnitude
of the
current in T550
and
L554
increases,
the rate of change
of
the
current
decreases.
When
the
rate
of change of the
current
reaches about zero,
the voltage induced
in the feedback
windings
of T550 and
L554 becomes insufficient
to
hold
Q552 on.
Q552 begins
to
turn off.
Note that
at
this
instant
the voltage
across the
secondary of
L554 is
0
volts.
^
As
Q552
is turning
off,
the magnetic field
around
L554 starts collapsing.
This induces
a voltage in
the feedback
winding of
L554 which
sp>eeds up
the turnoff
of
Q552.
^
The collapsing magnetic
field of
L554
induces
a
voltage
in
L554
which forces
the emitter of
Q556 more
positive. This voltage
causes the
emitter of Q556
to go
more positive than
pin 4
of
T550.
As
a
result, Q556 turns
on and places
L554 in parallel
with the primary winding
of
T550.
_7
The current
produced
by the collapsing
magnetic
field of L554
flows through
Q556 and the
pri-
mary
winding
of T550. This transfers
the energy
stored in
L554 to T550 and
increases the
efficiency of
the circuit.
The
amount of energy
stored in
L554 is controlled
by
the
high voltage
regulator.
^
As
the oscillation
cycle
continues,
the
voltage
across
L554
decreases
until it is
not
sufficient
to
hold
Q556
on.
Therefore
Q556 turns
off.
9 The cycle continues
until pin
3 of
T550
again
becomes
sufficiently
positive to turn
on
Q552. Then
the
sequence
just described
repeats.
(b)
High
Voltage Regulator.
The
high voltage reg-
ulator consists of
Q544,
Q548,
and associated circuitry.
Figure
FO-9
shows the high voltage regulator circuitry.
The
high
voltage regulator controls
the output of the high volt-
age oscillator
by controlling the energy in the
primary
circuit.
To fully understand the high
voltage regulator, read
the
previous
High
Voltage
Oscillator
discussion
before
con-
tinuing
with
this
discussion.
J[The
high voltage regulator controls the
point
during
an
oscillation cycle that
Q552 is turned
on.
Assume
the
—2
kV
supply starts
to go
more
negative
(too
much
energy
is
transferred
to the secondary circuit of T550).
AIR FORCE
T033A1-13-496-1
NAVELEX 0969-LP-170-0010
Operation
Instructions
^
As the
—2
kV
supply goes more negative
it
pulls the base
of 0554 less positive. The collector
of Q544
goes more positive
which
decreases the collector
current of
Q548. Transistor Q548 supplies charge current
to C548. Be-
cause the collector current of Q548 is decreased,
C548
charges more
slowly. As a
result,
the voltage on
pin 3 of
T550 will
not
become positive enough
to
turn
on Q552
until later in the oscillation cycle
(see
Figure
4-13).
There-
fore
less
energy
is stored in
L554
and transferred
to the pri-
mary of T550 when Q556 turns
on. This decreases
the
a-
mount of energy
transferred
to
the
secondary
of T550
which causes the
—2
kV supply
to go
less
negative.
^
If
the
—2
kV
supply goes less
negative,
Q544
and Q548 turn
on harder charging
C548
faster.
The voltage
on pin
3 of T550 becomes
positive
enough
to turn
on Q552
earlier in
the oscillation
cycle. Therefore
more
energy
is
stored in
L554
and
transferred
to the primary
of T550
when Q556 turns on.
As
a
result,
more energy
is
transfer-
red
to the secondary
circuit of
T550 and
the
-2
kV supply
goes more negative.
4 In the event
the high
voltage
regulator
mal-
functions, VR552,
VR553,
and CR552
provide
over-
voltage
protection. If
the peak
voltage on
pin
8 of
T550
exceeds
about
-t200
volts,
VR552
conducts.
When
VR552
and VR553
conduct they
turn on
Q552
which
draws
enough
current
to
open
fuse
F558.
(c)
High
Voltage Rectifier.
Figure
4-14
shows
a
simplified diagram of the high voltage rectifier. Figure
FO-9 shows the high voltage rectifier and associated
circuitry.
J^The
high voltage rectifier
is contained
within
U550. The circuit half
wave
rectifies the
—2
kV peak
ac
signal
at
pin 9 of T550. The rectified and
filtered voltage
is
supplied
to
the crt cathode,
dc
restorer,
FOCUS
control,
and the high voltage regulator.
^
The heater supply winding
of T550
is re-
ferenced
to the
—2
kV supply. This prevents
breakdown
between
the heater and the cathode due
to a large
voltage
difference between them.
(d)
High
Voltage
Multiplier.
Figure
FO-9 shows
the high voltage multiplier. The circuit is
a
standard
voltage
multiplier consisting of diodes and capacitors. The
multi-
plication factor is 3. The multiplier is contained within
module U550. The output of the multiplier supplies the
positive
anode voltage
for the crt.
(e) DC Restorer. The
dc restorer is contained
with-
in
U550.
Figure
4-1
5
shows
a
simplified
diagram
of the
circuit.
4-25

Tektronix 465M Specifications

General

Brand	Tektronix
Model	465M
Category	Test Equipment
Language	English