THOMSON 29DF45E "SCENIUM" CHASSIS ICC20 POWER DEFLECTION PANEL OVERVIEW.

The left sided POWER PANEL of the Thomson ICC20 contains POWER SUPPLY AND LINE DEFLECTION AT 31250HZ + EHT AND FRAME DEFLECTION AT 100HZ.


TDA8177 VERTICAL DEFLECTION BOOSTER


DESCRIPTION
Designed for monitors and high performance TVs,
the TDA8177 vertical deflection booster delivers
flyback voltages up to 70V.
The TDA8177 operates with supplies up to 35V
and provides up to 3APP output current to drive the
yoke.
FEATURES SUMMARY
■ POWER AMPLIFIER
■ FLYBACK GENERATOR
■ THERMAL PROTECTION
■ OUTPUT CURRENT UP TO 3.0APP
■ FLYBACK VOLTAGE UP TO 70V (on Pin 5)
■ SUITABLE FOR DC COUPLING
APPLICATION


Power Supply is based on 2 Sections:

- St-By supply with VIPer20

- Main Supply with TEA2262.


VIPer20A SMPS PRIMARY I.C.

DESCRIPTION
VIPer20/20A, made using VIPower M0
Technology, combines on the same silicon chip a
state-of-the-art PWM circuit together with an
optimized high voltage avalanche rugged Vertical
Power MOSFET (620V or 700V / 0.5A).
Typical applications cover off line power supplies
with a secondary power capability of 10Win wide
range condition and 20W in single range or with
doubler configuration. It is compatible from both
primary or secondary regulation loop despite
using around 50% less components when
compared with a discrete solution. Burst mode
operation is an additional feature of this device,
offering the possibility to operate in stand-by
mode without extra components.


OPERATION DESCRIPTION:
CURRENT MODE TOPOLOGY
The current mode control method, like the one
integrated in the VIPer20/20A uses two control
loops - an inner current control loop and an outer
loop for voltage control. When the Power
MOSFET output transistor is on, the inductor
current (primary side of the transformer) is
monitored with a SenseFET technique and
converted into a voltage VS proportional to this
current. When VS reaches VCOMP (the amplified
output voltage error) the power switch is switched
off. Thus, the outer voltage control loop defines
the level at which the inner loop regulates peak
current through the power switch and the primary
winding of the transformer.
Excellent D.C. open loop and dynamic line
regulation is ensured due to the inherent input
voltage feedforward characteristic of the current
mode control. This results in an improved line
regulation, instantaneous correction to line
changes and better stability for the voltage
regulation loop.
Current mode topology also ensures good
limitation in the case of short circuit. During the
first phase the output current increases slowly
following the dynamic of the regulation loop. Then
it reaches the maximum limitation current
internally set and finally stops because the power
supply on VDD is no longer correct. For specific
applications the maximum peak current internally
set can be overridden by limiting the voltage
excursion externally on the COMP pin. An
integrated blanking filter inhibits the PWM
comparator output for a short time after the
integrated Power MOSFET is switched on. This
function prevents anomalous or premature
termination of the switching pulse in the case of
current spikes caused by primary side capacitance
or secondary side rectifier reverse recovery time.

STAND-BY MODE
Stand-by operation in nearly open load condition
automatically leads to a burst mode operation
allowing voltage regulation on the secondary side.
The transition from normal operation to burst
mode operation happens for a power PSTBY given
by:
Where:
LP is the primary inductance of the transformer.
FSW is the normal switching frequency.
ISTBY is the minimum controllable current,
corresponding to the minimum on time that the
device is able to provide in normal operation. This
current can be computed as:
tb + td is the sum of the blanking time and of the
propagation time of the internal current sense and
comparator, and roughly represents the minimum
on time of the device. Note that PSTBY may be
affected by the efficiency of the converter at low
load, and must include the power drawn on the
primary auxiliary voltage.
As soon as the power goes below this limit, the
auxiliary secondary voltage starts to increase
above the 13V regulation level forcing the output
voltage of the transconductance amplifier to low
state (VCOMP < VCOMPth). This situation leads to
the shutdown mode where the power switch is
maintained in the off state, resulting in missing
cycles and zero duty cycle. As soon as VDD gets
back to the regulation level and the VCOMPth
threshold is reached, the device operates again.
The above cycle repeats itself indefinitely,
providing a burst mode of which the effective duty
cycle is much lower than the minimum one when in
normal operation. The equivalent switching
frequency is also lower than the normal one,
leading to a reduced consumption on the input
mains lines. This mode of operation allows the
VIPer20/20A to meet the new German ”Blue
Angel” Norm with less than 1W total power
consumption for the system when working in
stand-by. The output voltage remains regulated
around the normal level, with a low frequency
ripple corresponding to the burst mode. The
amplitude of this ripple is low, because of the
output capacitors and because of the low output
current drawn in such conditions. The normal
operation resumes automatically when the power
gets back levels which are higher than PSTBY.
HIGH VOLTAGE START-UP CURRENT
SOURCE
An integrated high voltage current source provides
a bias current from the DRAIN pin during the startup
phase. This current is partially absorbed by
internal control circuits which are placed into a
standby mode with reduced consumption and are
also provided to the external capacitor connected
to the VDD pin. As soon as the voltage on this pin
reaches the high voltage threshold VDDon of the
PSTBY


HIGH VOLTAGE START-UP CURRENT
SOURCE
An integrated high voltage current source provides
a bias current from the DRAIN pin during the startup
phase. This current is partially absorbed by
internal control circuits which are placed into a
standby mode with reduced consumption and are
also provided to the external capacitor connected
to the VDD pin. As soon as the voltage on this pin
reaches the high voltage threshold VDDon of the
starts switching.
The start up current generator is switched off, and
the converter should normally provide the needed
current on the VDD pin through the auxiliary
winding of the transformer, as shown on figure 15.
In case of abnormal condition where the auxiliary
winding is unable to provide the low voltage supply
current to the VDD pin (i.e. short circuit on the
output of the converter), the external capacitor
discharges itself down to the low threshold voltage
VDDoff of the UVLO logic, and the device gets back
to the inactive state where the internal circuits are
in standby mode and the start up current source is
activated. The converter enters an endless start
up cycle, with a start-up duty cycle defined by the
ratio of charging current towards discharging when
the VIPer20/20A tries to start. This ratio is fixed by
design from 2 to 15, which gives a 12% start up
duty cycle while the power dissipation at start up is
approximately 0.6 W, for a 230 Vrms input voltage.
This low value of start-up duty cycle prevents the
stress of the output rectifiers and of the
transformer when in short circuit.
The external capacitor CVDD on the VDD pin must
be sized according to the time needed by the
converter to start up, when the device starts
switching. This time tSS depends on many
parameters, among which transformer design,
output capacitors, soft start feature and
compensation network implemented on the COMP
pin. The following formula can be used for defining
the minimum capacitor needed:
where:
IDD is the consumption current on the VDD pin
when switching. Refer to specified IDD1 and IDD2
values.
tSS is the start up time of the converter when the
device begins to switch. Worst case is generally at
full load.
VDDhyst is the voltage hysteresis of the UVLO
logic. Refer to the minimum specified value.
Soft start feature can be implemented on the
COMP pin through a simple capacitor which will
also be used as the compensation network. In this
case, the regulation loop bandwidth is rather low,
because of the large value of this capacitor. In
case of a large regulation loop bandwidth is
mandatory, the schematics in figure 16 can be
used. It mixes a high performance compensation
network together with a separate high value soft
start capacitor. Both soft start time and regulation
loop bandwidth can be adjusted separately.
If the device is intentionally shut down by putting
the COMP pin to ground, the device is also
performing start-up cycles, and the VDD voltage is
oscillating between VDDon and VDDoff.
This voltage can be used for supplying external
functions, provided that their consumption doesn’t
exceed 0.5mA. Figure 17 shows a typical
application of this function, with a latched shut
down. Once the ”Shutdown” signal has been
activated, the device remains in the off state until
the input voltage is removed.


TEA2262 SWITCH MODE POWER SUPPLY CONTROLLER


DESCRIPTION
The TEA2262 is a monolithic integrated circuit for
the use in primary part of an off-line switching
mode power supply using a MOS power transistor.
All functions required for SMPS control under normal
operating, transient or abnormal conditions
are provided.
The capability of working according to the ”masterslave”
concept, or according to the ”primary regulation”
mode makes the TEA2262 very flexible and
easy to use. This is particularly true for TV receivers
where the IC provides an attractive and low
cost solution (no need of stand-by auxiliary power
supply).


GENERAL DESCRIPTION
The TEA2262 is an off-line switch mode power
supply controller. The synchronization function
and the specific operation in stand-by mode make
it well adapted to video applications such as TV
sets, VCRs, monitors, etc...
The TEA2262 can be used in two types of architectures:
– Master/slave architecture. In this case, the
TEA2262 drives the power transistor according
to the pulse width modulated signals generated
by the secondary located master circuit. A pulse
transformer provides the feedback (see Figure
5).
– Conventional architecture with linear feedback
signal (feedback sources : optocoupler or
transformer winding) (see Figure 6).
Using the TEA2262, the stand-by auxiliary power
supply, often realized with a small but costly 50Hz
transformer, is no longer necessary. The burst
mode operation of the TEA2262 makes possible
the control of very low output power (down to less
than 1W) with the main power transformer.
When used in a master/slave architecture, the
TEA2262and also the power transistor turn-off can
be easily synchronized with the line transformer.
The switching noise cannot disturb the picture in
this case.
As an S.M.P.S. controller, the TEA2262 features
the following functions:
– Power supply start-up (with soft-start)
– PWM generator
– Direct power transistor drive (±1A)
– Safety functions : pulse by pulse current
limitation, output power limitation, over and
under voltage lock-out.
S.M.P.S. OPERATING DESCRIPTION
Starting Mode - Stand By Mode
Power for circuit supply is taken from the mains
through a high value resistor before starting. As
long as VCC of the TEA2262 is below VCC start,
the quiescent current is very low (typically 0.5mA)
and the electrolytic capacitor across VCC is linearly
charged. When VCC reaches VCC start (typically
11.8V), the circuit starts, generating output pulses
with a soft-starting. Then the SMPS goes into the
stand-by mode and the output voltage is a percentage
of the nominal output voltage (eg. 80%).
During starting phase, in order to avoid transformer
magnetization (specially at high frequency), the
frequency oscillator is divided by four.
At switch-on, C0 charging current is divided by
four. It recover its normal value when the voltage
on soft-start capacitor reach 2.5V.
The current also recover its standard value when
the soft-start capacitor is discharged because of a
burst operating mode (starting in stand-by).
In other words, the charging current will become
and stay at its normal value, as soon as one of the
following events occurs:
– VC1 rearch 2.5V
– C1 is discharged by burst operating mode
For this the TEA2262 contains all the functions required
for primary mode regulation: a fixed frequency
oscillator, a voltage reference, an error
amplifier and a pulse width modulator (PWM).
For transmission of low power with a good efficiency
in stand-by, an automatic burst generation system
is used, in order to avoid audible noise.
Normal Mode (secondary regulation)
The normal operating of the TV set is obtained by
sending to the TEA2262 regulation pulses generated
by a regulator located in the secondary side
of the power supply (TEA5170 for example).
This architecture uses the ”Master-slave Concept”,
advantages of which are now well-known
especially the very high efficiency in stand-by
mode, and the accurate regulation in normal
mode.
Stand-by mode or normal mode are obtained by
supplying or not the secondary regulator. This can
be ordonnered for example by a microprocessor in
relation with the remote control unit.
Regulation pulses are applied to the TEA2262
through a small pulse-transformer to the IN input
(pin 2). This input is sensitive to positive square
pulses. The typical threshold of this input is 0.85V.
The frequency of pulses coming from the secondary
regulator can be lower or higher than the frequency
of the starting oscillator.
The TEA2262 has no soft-starting system when it
receives pulses from the secondary.The soft-starting
has to be located in the secondary regulator.
Due to the principle of the primary regulation, pulses
generated by the starting system automatically
disappear when the voltage delivered by the
SMPS increases.

Stand-by Mode - Normal Mode Transition
During the transition there are simultaneously
pulses coming from the primary and secondary
regulators.
These signals are not synchronized and some
care has to betaken to ensure the safety of the
switching power transistor.
A very sure and simple way consist in checking the
transformer demagnetization state.
– A primary pulse is taken in account only if the
transformer is demagnetized after a conduction
of the power transistor required by the
secondary regulator.
– A secondary pulse is taken in account only if the
transformer is demagnetized after a conduction
of the power transistor required by the primary
regulator.
With this arrangement the switching safety area of
the power transistor is respected and there is no
risk of transformer magnetization.
The magnetization state of the transformer is
checked by sensing the voltage across a winding
of the transformer (generally the same which supplies
the TEA2262). This is made by connecting a
resistor between this winding and the demagnetization
sensing input of the circuit (pin 1).
SECURITY FUNCTIONS (see flow-chart below)
Undervoltage detection. This protection works in
association with the starting device ”VCC switch”
(see paragraph Starting-mode - standby mode). If
VCC is lower than VCCstop (typically 8.5V) output
pulses are inhibited, in order to avoid wrong operation
of the power supply or bad power transistor
drive.
Overvoltage detection. If VCC exceeds VCCmax
(typically 15.7V) output pulses are inhibited and
the external capacitor C2 is charged as long as
VCC is higher than VCC stop. Restarting of the
power supply is obtained by reducing VCC below
VCCstop except if the voltage across C2 reaches
VC2 (typically 2.55V) (refer to ”Restart of the power
supply” paragraph).In this last case, the circuit is
definitively stopped.
Current limitation of the power transistor. The
current is measured by a shunt resistor. A double
threshold system is used:
– When the first threshold (VIM1) is reached,
the conduction of the power transistor is
stopped until the end of the period : a new
conduction signal is needed to obtain
conduction again.
– Further more as long as the first threshold is
reached (it means during several periods), an
external capacitor C2 is charged. When the
voltage across the capacitor reaches VC2
(typically 2.55V) the output is inhibited.This is
called the ”repetitive overload protection”. If
the overload diseappears before VC2 is
reached, C2 is discharged, so transient
overloads are tolerated.
– Second current limitation threshold (VIM2).
When this thresholdis reached the output of
the circuit is immediatly inhibited. This
protection is helpfull in case of hard overload
for example to avoid the magnetization of the
transformer.
Restart of the power supply. After stopping due
to VIM2, VCCmax or VCCstop triggering, restart of
the power supply can be obtained by the normal
operating of the ”VCC switch” VCC switch sequency
from VCCstop to VCCstart . After stopping due to
VC2 threshold reaching, the circuit is definitively
stopped.
In this case it is necessary to reduce VCC below
approximately 5V to reset the circuit. From a practical
point of view, it means that the power supply
has to be temporarily disconnected from any power
source to get the restart.