TEA2029 STMICROELECTRONICS [STMicroelectronics], TEA2029 Datasheet - Page 32

• Manufacturer Part Number: TEA2029
• Description: APPLICATION NOTE
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

TEA2028 - TEA2029 APPLICATION NOTE
V.7.2 - General operating principles
A fraction of the 135V output voltage to be regu-
lated is compared to the 1.26V reference voltage.
Resulting error signal is amplified and then applied
to phase modulator ”M
square waveform at line frequency whose duty
cycle depends on the value of input voltage ”V
A second phase modulator ”M
conduction period as a function of voltage on
Pin 15. This function is mandatory for system start-
up.
A 28 s window is used to limit the conduction
period of the primary-connected transistor.
Supply output (Pin 7) and line output (Pin 10) will
be disabled if any information indicating abnormal
operation is applied to safety input (Pin 28). Con-
sequently, all power stages are disabled and the
TV set is thus protected.
V.7.3 - Electrical characteristics of the internal
regulation loop
Figure 63
The phase modulator implemented by a simple
transistor ”T1” will compare in current mode, the
image of amplified input (i
(i
sum of ”i
enters into saturation thus determining the output
conduction period.
A low-pass filter implemented by combination of a
100pF capacitor and the input impedance of tran-
sistor ”T
higher than the line frequency.
- Input Amplification : A
- Modulator conversion gain :
- Overall gain of the internal loop :
32/46
V
(1.26V)
2
B =
dt
REF
) at line frequency. With ”i
dV
OUT
IN
dt
di
OUT
1
1
1
9
”, attenuat es all frequency variations
+ i
1.9 s/mV
V
V
A
IN
2
0.558
- I
V
DC
I
” goes positive, the transistor
V
s
13
/ A
I
1
1
V
1
1
1
”, which will deliver a
) with saw-tooth current
I
dV
2
2
j
di
I
I
f
” rising, as soon as the
DC
f
0
I
1
IN
2
(f
B
” will determine the
0
40 A
= 15kHz)
3.3 A/mV
Low-pass
Filter
T1
- 1
7
t
OUT
9
”.
Figure 64 : Conduction Periode (Pin 7) versus
SMPS WAVEFORMS
For discontinous mode ”flyback” configuration
The primary-connected transistor is turned-off dur-
ing the line flyback.
All interference signals due to switching and sus-
ceptible to affect the video signal will not therefore
be visible on screen.
Figure 65
Regulation Characteristics
The following characteristics have been measured
on a large screen and yield excellent results :
- 135V voltage regulation as a function of mains
- 135 V voltage regulation as a function of load :
This type of power supply offers the following ad-
vantages :
- Overall efficiency enhancement: better than 80%
- Reduction of interferences by synchronizationon
V
LF
V
PRIMARY PULSES
PRIMARY CURRENT
SECONDARY
RECTIFIER DIODE
CURRENT
SECONDARY
WINDING
VOLTAGE
voltage : better than 0.5% for mains voltage vari-
ations of 170V
better than 0.5% for a delivered power of 35W to
120W.
horizontal frequency
13
7
28 s
10 s
Input Voltage (Pin 9)
135V
t
RMS
ON
0
(Pin 7)
9.5mV
to 270V
1.26V
t
ON
2 s
5.2mV
RMS
-1.9 s/mV
(P = 60W at 135V)
28 s (max.)
(Pin 9)
V
IN