3DQDVRQLF
50
Chapter
4
EURO 4D Supplement
The DVB power supply relay RL4801 is controlled by
the DVB microcontroller and transistors Q4852,
Q4851.
Transistor Q4851 is fed a supply voltage of
approximately 7V from the junction of resistors R861,
R862 and diode D868 of the standby power supply.
This 7V supply is then fed via resistor R4863 and the
relay winding of the DVB relay RL4801 to the collector
of Q4851.
When the DVB decoder is in operation a Low level is
applied to the base of transistor Q4852 fed from the
DVB microcontroller via connector W4 pin 3. This
LOW level switches OFF Q4852 resulting in a HIGH
level being fed via resistor R4855 to the base of
Q4851. This HIGH level which is now applied to the
base of transistor Q4851 is biased into conduction,
resulting in current flow taking place via the DVB relay
RL4801 and the collector / emitter junction of
transistor Q4851, this current flow causing the
normally open relay contact to close. When the relay
contact closes the mains A.C. supply is fed to the
bridge rectifier D4802. Here the A.C. supply is fully
rectified before being smoothed by capacitor C4809.
This supply voltage of approximately 350V is then split
into two paths.
1.
The first path feeds the supply voltage via the
primary windings P2 / P1 of transformer T4801
to pin 3 of IC4801 and the drain terminal of the
internal FET transistor. Which at present has no
gate control voltage preventing the operating
voltage from being subjected to any load.
2.
The second path the supply voltage takes from
the bridge rectifier D4802 is via the start-up
circuit made up of resistors R4802 / R4803, the
operation of which is discussed in the following
section.
Summary of Contents for EURO 4 Chassis
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