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TDA8143 View Datasheet(PDF) - STMicroelectronics

Part Name
Description
View to exact match
TDA8143
ST-Microelectronics
STMicroelectronics ST-Microelectronics
TDA8143 Datasheet PDF : 9 Pages
1 2 3 4 5 6 7 8 9
TDA8143
Figure 4 : Waveforms of Collector and
Base Current
IC Off Phase On Phase Off Phase
I BIAS
Base Bias Current
IC
Real Base Current
Ideal Base Current
t
t
tS
ID
This is due to the constant base charge in the
turn-ON phase independent from the collector cur-
rent ; 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 dis-
charge current for the power transistor ; the nega-
tive slope of this ramp is proportional to the actual
sensed current.
As a result, the active driving system even im-
proves the sharpness of vertical lines on the screen
compared with the traditional solution due to the
increased stability factor of the loop represented as
the variation of the storage time versus the collector
peak current.
Figure 5
I0
t don
I0
dI0 = IS0
dt t S
Ip0
IS0
ON PHASE
In0
t
OFF PHASE
CONTROL
INPUT
tS
t
CIRCUIT DESCRIPTION
Figure 6 shows the block diagram of the TDA8143,
the circuit consists of an input transconductance
amplifier composed by Q1, Q2, Q3 and Q4.
The symmetrical output current is fed into the load
resistor R1 and R2 ; the two amplifiers V1 and V2
realize a floating voltage to current converter which
can drive 1.2A sink current and 2A source current
for a wide common output range.
So, the overall transconductance results into :
gm
=
R1 + R2
R3
1
R5
A current source I1 generates a drop of 70mV
across the resistor R4 which provides an output
bias current of 140mA ; the control input determines
the turn ON/OFF function.
In the ON phase, Q5 shorts the external capacitor
Ct. Within the input voltage range 0 < Vin < 750mV
the element realizes the transconductance func-
tion ; lower voltages are clamped by the D1/Q6
configuration.
For input voltages higher than 750mV, Q7 limits the
maximum output current at 1.5A peak.
In the turn-OFF mode, Ct will be charged by the
controlled source I2 which is proportional to the
input voltage, by this way, the output current de-
creases quasi linearly and the system stability is
reached.
During the flyback phase, the IC is enabled via the
sync. detector input ; this function with the limited
sink and source current together with the undervol-
tage turn-OFF and a chip temperature sensor en-
sure a complete protection of the IC.
6/9
 

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