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參數(shù)資料
| 型號： | TDA8140 |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | HORIZONTAL DEFLECTION POWER DRIVER |
| 中文描述： | 水平偏轉(zhuǎn)功率驅(qū)動器 |
| 文件頁數(shù)： | 6/10頁 |
| 文件大?。?/td> | 191K |
| 代理商： | TDA8140 |
OFF PHASE
CONTROL
INPUT
t
I
0
ON PHASE
t
I
p0
I
0
t
don
I
n0
t
S
I
S0
t
S
dI
0
dt
=
I
S0
8
Figure 6
During the active deflection phase the collector
current of the power transistor is linearly rising and
the driving circuitry must be adapted to 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
we give a comparison between the typical real base
current and the ideal base current waveform and
the collector waveform.
The marked area represents a useless base cur-
rent which gives an additional power dissipation on
the power transistor.
Furthermore during the turn-ON and turn-OFF tran-
sient phase of the chassis the power transistor is
extremely stressed when the conventional network
cannot guarantee the saturation ; for this reason,
generally, the driving circuit must be carefully de-
signed and is different for each deflection system.
The new approach, using the TDA 8140, over-
comes 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 I
b
can be easily generated by a feed-
back transconductance amplifier g
m
which senses
the deflection current across the resistor R
s
at the
emitter of the power transistor and delivers :
I
b
= R
S
.
g
m
.
I
e
The transconductance must only fulfill the condi-
tion :
1
1
+
β
min
1
Where
β
min
is the minimum current gain of the
transistor. This method always ensures the correct
R
S
<
gm
<
1
R
S
base current and acts time independent on princi-
ple.
For the turn-OFF, the base of the power transistor
must be discharged by a quasi linear time decreas-
ing 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 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.
I
C
I
C
t
t
I
BIAS
Base Bias Current
D
I
t
S
Off Phase
On Phase
Off Phase
Real Base Current
Ideal Base Current
8
Figure 5 :
Waveforms of Collector and
Base Current
TDA8140
6/10
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| TDA8143 | 制造商:STMicroelectronics 功能描述:TV HOR. DRIVER - Bulk |
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| TDA8146 | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:EAST/WEST CORRECTION FOR RECTANGULAR TV-TUBES |
| TDA8153 | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:RGB VIDEO OUTPUT AMPLIFIER |
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