GRUNDIG Super Color P37-342 Chassis CUC 3400 details 2

Chassis CUC 3400 details 2
Line transistor driver TDA8140 (SGS)
uController SDA2010-a025 (SIEMENS)
Display driver UAA2022 (MOTOROLA)
The program memory was contained in the RF Tuner Unit.
Sound amplifier stage with TDA1905 (SGS)


TDA8140 HORIZONTAL DEFLECTION POWER DRIVER
DESCRIPTION
The TDA 8140 is a monolithic integrated circuit designed
to drive the horizontal deflectionpower transistor.
The current source characteristic of this device is
adapted to the on-linear current gain behaviour of
the power transistor providing a minimum power
dissipation. The TDA8140 is internally protected
against short circuit and thermal overload.

During the active deflection phase the collector
current of the power transistor is linearly rising and
the driving circuitry mustbe adaptedto the required
base current in order to ensure the power transistor
saturation.
According to the limited components number the
typical approach of the present TVs provides only
a rough approximation of this objective ; in Figure 5
wegive a comparisonbetweenthe typical real base
current and the ideal base current waveform and
the collector waveform.
The marked area represents a useless base current
which gives an additional power dissipation on
the power transistor.
Furthermoreduring the turn-ONand turn-OFFtransient
phase of the chassis the power transistor is
extremely stressed when the conventionalnetwork
cannot guarantee the saturation ; for this reason,
generally, the driving circuit must be carefully designed
and is different for each deflection system.
The new approach, using the TDA 8140, overcomes
these restrictions by means of a feedback
principle.
As shown in Figure 5, at each instant of time the
ideal base current of the power transistor results
from its collector current divided by such current
gain which ensure the saturation ; thus the required
base current Ib can be easily generated by a feedback
transconductanceamplifier gm which senses
the deflection current across the resistor Rs at the
emitter of the power transistor and delivers :
Ib = RS . gm . Ie
The transconductance must only fulfill the condition
:
1
1 + bmin V 1
RS
<>
RS
Where bmin is the minimum current gain of the
transistor. This method always ensures the correct
base current and acts time independent on principle.For the turn-OFF, the base of the power transistor
must be discharged by a quasi linear time decreasing
current as given in Figure 6.
Conventional driver systems inherently result into
a stable condition with a constant peak current
magnitude.
This is due to the constant base charge in the
turn-ON phase independent from the collector current
; hence a high peak current results into a low
storage time of the transistor because the excess
base charge is a minimum and vice versa. In the
active deflection the required function, high peak
current-fast switch-OFF and low peak current-slow
switch-OFF, is obtained by a controlled base discharge
current for the power transistor ; the negative
slope of this ramp is proportional to the actual
sensed current.
As a result, the active driving system even improves
the sharpnessof vertical lines on the screen
compared with the traditional solution due to the
increasedstability factor of the loop representedas
the variation of the storagetime versus the collector
peak current.



TDA1905 5W AUDIO AMPLIFIER WITH MUTING

DESCRIPTION
The TDA1905 is a monolithic integrated circuit in
POWERDIP package, intended for use as low
frequency power amplifier in a wide range of applications
in radio and TV sets:
– muting facility
– protection against chip over temperature
– very low noise
– high supply voltage rejection
– low ”switch-on” noise
– voltage range 4V to 30V
The TDA 1905 is assembled in a new plastic package,
thePOWERDIP, that offers the same assembly
ease, space and cost saving of a normal dual in-line
packagebutwith apower dissipationofup to6Wand
a thermal resistance of 15°C/W (junction to pins).


THERMAL SHUT-DOWN
The presence of a thermal limiting circuit offers the following advantages:
1) An overload on the output (even if it is permanent), or an above limit ambient temperature can be easily
tolerated since the Tj cannot be higher than 150 °C.
2) The heatsink can have a smaller factor of safety compared with that of a conventional circuit. There is
no possibility of device damage due to high junction temperature.
If for any reason, thejunction temperatureincreases upto 150°C, the thermalshut-down simply reduces
the power dissipation and the current consumption.
The maximum allowable power dissipation depends upon the size of the external heatsink (i.e. its thermal resistance.