Blocking Oscillator Type Power Supply - Loewe Q2500B Serviceanleitung

Technology of Q 2500 colour TV set
W8613
VH-JSTws 7R92 3pol
3
from BB R8134
2
1
W8611
2pol sw 7R92
2
to BB
1
2
Mains
1
W8103
2pol ge 7R92
The rectified secondary voltage is applied to
pin 2 of the relay winding L 8101. via protec-
tive resistor R 106. The cold end is open since
Q114 is non-conducting and the receiver is in
standby mode. This is indicated by illumina-
tion of the red LED.
Transistor Q 8114 is blocked, if the working
contact is open, the device is in standby,
which is indicated by illumination of the red
LED.
If the processor receives an ON command
from the infrared detector it sets its appropri-
ate switch output to low level. This is then fed
to the base of Q 8111 via pin 5 in plug W 8181
which is blocked. Via R 813, U5 SB makes
transistor Q 8114 switch. The cold end of the
relay coil is earthed, the working contact is
closed and the main voltage flows to the main
power supply circuit via pin 1 of W 8613,
thereby switching the receiver on.
Dokument Q 2500
Q2500 Operating Control
MP03
D8133
DF08S
C8133
4u7/400V
I8131
VIPER12
C8136
47n
MP02
MP01
B8103
R10
C8118
S8101
100n
T8101
Standby transformer
3 5
MP04
4
D8121
BYG20D
1
R8138
D8138
0R
LL4148
2 8
C8106
D8131
470u
LL4148
C8132
I8122
TLP621(BL)-D4
10u
4 1
C8123
100n
3 2
I8123
TL431ACLP
L8101
Overtravel contact
2.2 Blocking oscillator type power
supply
The voltage supply in the Q 2400 chassis is
drawn once again from a free-running block-
ing oscillator type power supply. TDA 4605 is
used as the control and regulating circuit. In
terms of its function, this IC resembles the
well-known TDA 4601.
It has, however, a different type of output
stage. The 4605 is designed to control a field
effect transistor.
This circuit uses a BUZ 91 MOS-FET as the
switching transistor. Since control of field ef-
fect transistors requires virtually no current,
reducing the need for heat dissipation, it has
been possible to eliminate the heat sink in the
TDA 4605 control IC and house the circuit in a
dual-in-line package.
13
L8106
C8107
FE_PE
100n
C8103
R8123
C8104
1k2 100n
100u
R8124
1k5
R8126
12k
U5SB
D8106
Standby-LED
LL4148
Overtravel
R8204
R8111
1k
22k
D8114
22k
LL4148
R8219
1k
D8204
C12V
© Loewe ProCollege
W8181
JST sw s
8
7
6
ON/OFF
5
4
3
2
1
D8207
D8201
red
C12V
D8202
green
C12V
D8207