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The -8V is regulated to -5.5V via transistor 7304 and
zenerdiode 6308, and is switched 'off', with transistor
7305, during Standby Mode.
The -32V is not switched 'off' during Standby Mode.
2.3 Operation
Mains Input Circuit
The bridge rectifier (D6110-D6113), direct after the mains
filter 5115, rectifies the mains voltage, after which C2116
smooths it. The DC voltage across this capacitor is the DC
input voltage (HV= approximately 300 V), to pin 9 of
transformer T5190 and pin 1 of IC7130.
Start-up Circuitry
The rectified voltage from the bridge rectifier is connected
to pin 1 via L5130. It will charge the VCC capacitor
(C2131).
When this voltage, (at pin 13 of 7130), reaches the start-
up threshold of min 15 V, the control circuit starts to
operate.
After start-up, IC 7130 requires a sinking current, which
the start-up circuitry cannot deliver. Therefore, a take-over
circuitry (a coupled winding of transformer L5190) is
present. The voltage here will take over the supply voltage
at pin 13 of the IC.
If the take-over circuit does not function, the IC will switch
'off' again at the minimal operating voltage of +8 V. The
whole operation cycle will repeat itself with audible hiccup
sound if take-over is not present.
Secondary Voltage Sensing
The secondary voltage regulating circuit is comprised of
opto-coupler 7190 (which isolates the error signal from the
control IC on the primary side), and a reference
component 7290 (TL431) with the following functions:
• A very stable and accurate reference diode.
• A high gain amplifier.
TL431
R
2.5V
Fig. 4
When the output voltage increases (due to a reduction in
the load), the voltage across R3290+R3291 increases to
above the internal reference voltage of 2.5 V. Item 7290
will conduct and the current through the opto-coupler will
increase. This results in an increase of the voltage at pin 4
of 7130, which will reduce the 'on' time of FET 7125. In the
event of an output voltage decrease (due to an increase in
the load), the control circuit will operate in the opposite
way.
K
A
Primary Current Sensing
The current through FET 7125 will result in a voltage drop
across R3120/21/22 (RSENSE). This line goes to pin 11 of
7130, which is the current sense input. The higher the
input voltage, the more the primary current is limited. In
this way, the maximum output power of the power supply
is limited.
Under-voltage Protection
If the supply voltage at pin 13 drops below 7.2 V (typical),
e.g. due to a shorted secondary voltage or excessive load,
the drive pulse at pin 12 is disabled and the controller will
switch 'off'.
Over-voltage Protection
An internal over-voltage protection circuitry continuously
monitors the VCC pin. If, after start-up, this voltage
exceeds 40 V, the internal latch circuit is triggered, the
output buffer is disabled, and the SMPS goes into over-
voltage protection.
Now a complete restart sequence is required.
Note: If the event of the over-voltage situation remains
present, the SMPS will go in sequence of protection, start-
up, protection and the cycle repeats. This effect is highly
audible.
3. Control and Display
3.1 Control
The most important component on this board is the (slave)
microprocessor (item 7113/7101). It runs on an 8MHz
system clock generated by a ceramic resonator.
After the RESET pulse (active LOW), the STB_CTRL line
(pin 21, item 7113/7101) will release the reset of the host
uP (on the mono board) via the switched 3V3 supply (see
circuit around item 7605 on mono board).
Other slave processor functions are:
• Generation of a scanning grid for the keys.
• Generation of the display grid and segment scanning.
• Generation of a square signal to generate the filament
voltage for FTD display.
• Input for RC5/6 remote control protocol. The logic is
HIGH > 4.5V and LOW < 0.3V.
Key Matrix
When a key on the local keyboard is pressed, the signal at
the scanning pins of the microprocessor goes from +5V to
0V.
Circuit IR Receiver
The IR controller in the slave processor handles both RC5
and RC6 signals. The logic is +5V for 'high' and 0V for
'low'.
FTD Display
The slave uP drives the 11-segment FTD. It provides a
negative DC switching drive voltage. As the display
consists of eleven segments, there are eleven grid signals
(G1-G11) controlling each respective grid.
DVD-S530/DV-S5550
23
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