BELINEA 10 55 70, Руководство по обслуживанию

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Part 1.
Version
3.1. Switching Power Supply
The switching power supply used in this display is a
mode type. The power supply provides seven
outputs and Please
refer to schematic diagram for details of the circuit layout. The
input voltage is from with an input
frequency of as shown in Figure
The current first passes through the control circuit and
is regulated to DC by the bridge diodes and filter
capacitor During rectification a large current surge is
generated and as has a very low impedance while being
charged the fuse, on/off switch and bridge diode are all liable
to be damaged. For this reason, a
resistor
is added before the bridge diode in order to limit the large
current surge generated during the charging of the capacitor.
During rectification, Cl2 is charged through R7, R12 and
When Cl2 is charged to
3842A starts to operate (for
details, of the functions of this IC, please refer to the relevant
data sheet) and outputs a pulse signal from Pin 6 to set the
transistor Q6 in the ON state. At this time, transformer
which is connected in parallel, starts to store power. When the
current passing through the resistor R45, and the supplemen-
tary current from R39,
and R27 (Pin 4 to Pin 3) into Pin
3 of IC2 reaches 1.1 V, IC2 is reset, causing the energy stored
by transformer to reach the rated value. In order to prevent
the transformer from being saturated and causing damage to
the transistor, when transistor
is in the OFF state, the
energy stored in the transformer T3 is released into secon-
dary coil and is regulated through the various output loops and
and converted to the required DC output. In addition to
this, at the appropriate time, the windings pin 1 pin2 supply
Pin 7 of IC2 with a fixed power supply for normal operation.
Also, when windings
pin3 are in power saving active
state, power is supplied to Pin 7 of IC2 for normal operation.
In any of the above cased, the output pulse is terminated and
the FET is turned off, causing the voltage on the output of the
FET to rise rapidly, and the voltage across the winding of the
primary to reverse in polarity, thus tending to reset the flux
within the core. At this point, the diodes
D22 and
D24 on the secondary supply winding become forward biased
and begin to conduct, thus transferring energy from primary
to the secondary, and charging the secondary capacitors.
There is also secondary winding the primary side of the power
supply which, through diode
and recharges the control
IC reservoir capacitor C12. This supply then keeps the IC
running. In the event of a secondary short circuit, the supply
fails to recharge, thus the voltage across Cl2 drops to a
threshold limit below which the IC cuts out and returns to its
low current load operation.
During normal operation, the supply rails charge until the
error amplifier realized by IC4 on the secondary begins to turn
on the opto-coupler,
At this point, the photo-transistor
of this opto-coupler on the primary side begins to conduct.
draining current from the primary control IC supply through
diode D6. This reverse biased the gate of the thyristor
As
POWER
RECTIFIER
FILTER CIRCUIT
7 5 v
- › ,
-15v
5 v
i
FM MONITOR H.V. FEEDBACK
Figure Switching Power Supply Block Diagram