Panasonic EURO 4 Chassis, Technical Manual

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Chapter 4 EURO 4D Supplement
2.7. Voltage Stabilisation
2.7.1. 12V Supply
A 14V supply which is fed from the transformer T4801
is fed to pin 1 of IC4851 which is used to produce a
stabilized 12V supply output from pin 3.
This stabilised 12V supply is then fed to the V-Board
containing the DVB digital processing IC’s via
connectors W3 pin 6 to V9.
2.7.2. 9V Supply
The stabilised 12V supply produced by IC4851 and
fed to the V-Board just mention is also used to produce
a 9V supply.
The 9V supply is produced by feeding the 12V (fed to
V-Board as just mention) back out from the V-Board
via connector V6 pin 5 to the H-Board and connector
H6 pin 5. Here on the H-Board the 12V supply is used
to supply the Video and Audio switching ICs IC3401
and IC3151, the 12V supply is also fed to connector
H11 pin 2 where the 12V supply is fed to the E-Board
via connector E28 pin 2. Once on the E-Board this 12V
supply is then fed to IC3801 pin 1 which produces a
stabilised 9V supply output via pin 3 of IC3801. This
9V supply is then is used by the tuner / IF stage.
2.7.3. 5V Supply
A supply of approximately 6V is output from
transformer T4801 and fed to the collector of
transistor Q4856. Transistor Q4856,
which is
connected as a series regulator. inconjunction with
IC4853 produces a regulated 5V supply.
The 5V supply fed from the emitter junction of Q4856
is monitored by IC4853, via the regulator (R) terminal.
The regulator input being connected to the 5V supply
via a voltage divider consisting of resistors R4871 /
R4872.
If any load variations are detected by IC4853, the
cathode (K) terminal output will increase or decrease
the base bias of transistor Q4856. The base bias
being fed from the 12V line via R4866. By adjusting
this base bias of Q4856 by a greater or lesser degree
the 5V supply is stabilised.
At start-up to ensure that the 3.3V supply rises before
the 5V supply transistor Q4858 is used. As the
supplies being to rise at switch ON transistor Q4858
is biased into conduction by the rising 12V supply line
which is fed via resistor R4866. At this point the
capacitor C4873 is charging keeping the base of
Q4858 at a lower potential then its emitter, this
ensures that Q4858 conducts removing the base bias
of transistor Q4856 thus preventing the 5V supply
from being output. However once capacitor C4873
has charged the base potential rises biasing OFF
Q4858, this in turn allows transistor Q4856 to be
biased into conduction and supplying a stabilised 5V
supply. This delay in the output of the 5V supply is long
enough to allow the 3.3V supply to become
established.
2.7.4. 5V CA (Conditional Access) Supply
This 5V CA (Conditional Access) supply is produced
by feeding a 6V supply from transformer T4801 to
IC4852 pin 5. Output from pin 3 of IC4852 is a
stabilised 5V supply which is fed to connector W3 pins
11 and 12, from here the supply is then fed to the
V-Board and the conditional access module.