Circuit Descriptions, Abbreviation List, and IC Data Sheets
9.
For the power supply of the FBX, a separate DC/DC converter
is used, generating 3.3 V.
9.3
Power Supply
9.3.1
Block diagram
The architecture of the power supply is made flexible by
separating the different function blocks as much as possible.
Figure 9-4 Block diagram power supply
Block A
This block contains the AC power entrance part together with
the filtering. It is supplied directly from the AC power cord. The
AC power input has a polarization for the USA together with a
polarized AC power cord; the neutral of the chassis
is
connected to the AC power neutral in the USA.
Block B
This block contains the relay switch and relay control. The relay
switches the AC power voltage to the rectifier and voltage
doubler. The relay is powered by the +5V2_RELAY and driven
by the +5V_SW. This voltage is derived from the +5V2 and is
driven by the STAND_BY line (this line is active "low" in the
"Semi-standby" and the "On" state.
Block C
The AC power voltage is rectified and doubled here (see
description below).
Rectifier/Doubler
The circuit involves component 7805 (Sanken STR83145) that
senses the AC input voltage. This device also includes a
thyristor.
If the voltage is less than 140 V_ac, the 7805 thyristor switches
"on", and the combination (rec closed switch) acts as a
voltage doubler (sum of voltages over C2815 and 2816).
If the voltage is above 149 V_ac, the 7805 thyristor stays open
and we have a classical rectification.
Notes:
•
In order to prevent accidental problems with voltage
overshoot or sink, once the thyristor "opens", it cannot be
closed, unless the AC power voltage is back to zero.
•
Resistors 3806, 3807, 3808, 3810, 3811, and 3812 are
present in order to allow the discharge of capacitors 2815
and 2816 in case of no-load condition.
Protection
If the voltage on one (or both) of the two main electrolytic
capacitor's (C2815, C2816) becomes too high (in case of over-
voltage for instance), the circuit goes into protection. In case of
an over-voltage on C2816, the voltage across 2816 exceeds
460 V_dc, and the voltage across 3810 becomes more than
15.7 V (via divider 3810/3811/3812). This implies that transistor
7802 goes into conduction. This will activate transistor 7803.
The emitter of this transistor is connected to the gate of thyristor
7804. When 7803 conducts, then 7804 goes into conduction
between the live AC line and the DC ground. The high current
flow will immediately blow fuse 1400.
Block D
This block contains an LLC supply. The output voltages are
+12V, which de8V6, the +24V for the LCD lamps, and
the +12V_SOUND and -12V_SOUND. The relay switch
controls the supply for this block (see also description of block
B).
Note:
See the FM24 manual for a more detailed description.
Block E
This block contains the standby supply. This supply generates
a stab5V2 output. This voltage is connected to the ON/
OFF switch and delivers the +5V_RELAY to the SSP and to the
relay when the functional switch is "on". The 3V3 supply for the
OTC, ROM, and RAM is derived from the +5V_RELAY via a
stabilizer on the SSP. A reset circuit resets the OTC as long as
the +5V2 is not stabilized.
When the ON/OFF switch is switched "off":
1.
The relay is switched "off".
2.
The OTC is reset.
3.
The standby line becomes "high".
4.
The main supply is switched "off".
The V_TUN (50 V stabilized, on SSB converted to 33 V) is a
secondary voltage of the standby supply.
Note:
See the FM24 manual for a more detailed description.
Block OTC
The OTC controls the supply. The OTC is powered by the 3V3
derived from the +5V2, and is powered when the ON/OFF
switch is "on". In standby, the STANDBY line disconnects the
+5V_SW from the +5V2, and the relay is switched "off".
In "Semi-standby" or "On" state, the STANDBY line is "low" and
the +5V_SW is connected. The relay is activated, and the main
supply can start up.
Block POR (Power On Reset)
The POR mutes the audio output amplifier and switches "off"
the backlight lamps. After a POR, the software must start the
set. There must be a delay of 1 s after switching "off" (the lamps
need this delay).
The OTC receives the POR signal via input pin 99 (P1-6/INT3).
This POR signal is generated in the following cases:
•
When the standby supply (+5V2) starts up (this is when the
AC power cord is connected).
•
By switching "off" the ON/OFF switch (as long as the switch
is "off").
•
When the main voltage drops.
9.3.2
DC/DC Converter (diagram B12)
This circuit on the SSP provides the 3V3 voltage for the Feature
Box and PIP/DW (if present).
A DC/DC converter has the following advantages:
•
The DC/DC converter is directly on the SSB near the
circuits that needs to be powered with the 3.3 V.
•
Circuits in the FBX and the DW part need some high
current by low voltage, so there is no risk of having power
dips or voltage losses in connections between the Power
Supply and the SSB panel.
The circuit used is a so-called "synchronous buck converter".
Some characteristics:
•
Input parameters: 12.5 V / 330 mA.
•
Output parameters: 3.42 V
±
0.15 V / 1.2 A.
•
Switching frequency: approx. 60 kHz.
•
Efficiency: approx. 90%.
•
Inhibit (+5V) and fast turn-off (3V3_FAULT) control inputs.
110-230V
Block D
LCD aux
Supply
Block E
Stand By
Supply
OTC
Stby LED
+5Vsw
+5V2
Audioprotect
+24V lamp
+12V
+8V6
+12V Sound
-12V Sound
Stby
ON/OFF
switch
V tuner
5Vrelay
RE
SE
T
3V3
Block C
Rectifier
Doubler
Block A
Input filter
Block B
Relay Switch
Relay Control
CL 36532053_055.eps
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FTL13U_AA_AB_312278513481.book Page 140 Thursday, December 30, 2004 1:50 PM
