RADIOMETER TCM3 - Page 77

TCM3
and
TCM30
Service
Manual
2.
TCM3
Power Supply PCB, continued
Switching
Transformers
(continued)
Switching
Generator
Integral
Regulator on
901-644
Integral
Regulator on
901-832
annano +
Stage
Description
TO
Oi
is
activated
and
i,
increases
linearly,
The
EMF
induced
in
the
secondary
is
negative
at
terminal
6.
The
EMF
in
winding
3
is
negative
at
terminal
4.
C12
is
charged
through
CR13
and
R32.
Г
T1
O1
is
cut-off.
Back
EMF
is
induced
in
the
primary
winding.
i,
flows
in
the
loop:
Primary
terminal
2
-
CR12
-
CR20-
CR
11-
~
primary
terminal
1.
i,
decreases
and
an
EMF
is
induced
in
winding
3.
i;
flows
in
the
loop:
Terminal
4
-
CR10
-
CR11
-
Charging
capacitor
-
ground
-
terminal
3.
The
EMF
in
the
secondary
is
positive
at
terminal
6
and
the
capacitor
is
charged.
ip is zero and i; decreases,
aya
i
is
zero
and
i,
decreases.
The
emf
induced
in
the
primary
is
positive
at
terminal
2.
Q3
is
now
cut-off
and
permits
a
current
to
flow
in
the
regulator
feed-back
loop
R1
-
Q2
-
R6.
T4
js
is
zero
and
u,,
us
and
u,
are
decreasing.
The
transformer
becomes
energyless.
TS
Anew cycle commences,
The
generator
consists
of
the
saw-tooth
oscillator
QA
la,
the
comparator
QA1b,
the
drivers
QD1
and
the
FET
Q1.
‘The
comparator
acts
as
a
pulse-width
modulator
where
the
output
signal
from
QA2b
controls
the
duty
cycle
of
the
generator
signal.
This PCB is found in TCM3 below RUN 22.
The
regulator
is
built
up
around
QA2a
and
QA2b
and
controls
the
generator
pulse
duty
cycle
and
hence
the
transformer
secondary
voltage
in
the
following
manner:
Manual
adjustment
by
means
of
potentiometer
R33.
Automatic
regulation
by
means
of
the
feed
back
loop:
Transformer
secondary
-
transformer
primary
-
R1
-
Q2
-
CR2.
Compensation
for
voltage
drop
in
the
secondary
rectifier
diode
via
CR9.
+5
VDC
regulator.
If
the
external
power
is
removed,
(J1,
terminal
1 -
3
or
J5,
terminal
6
-
1)
the
integral
regulator
will
reduce
the
secondary
voltage.
This
PCB
is
found
in
TCM3
of
RUN
22
onwards
and
in
TCM30.
This
board
does
not
include
the
potentiometer
R33.
Instead,
the
secondary
voltage
is
automatically
regulated
via
the
opto-coupler
OP4.
Continued on next page