AN826 データシートの表示（PDF） - STMicroelectronics
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AN826 Datasheet PDF : 7 Pages
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APPLICATION NOTE
250W HIGH POWER FACTOR SUPPLY FOR TV
INTRODUCTION
This application has been designed to provide a
complete supply for colour TV. The system has
been configured using a Flyback DC-DC con-
verter with an upstream PFC section in order to
improve the characteristics of the whole supply.
The architecture of the system consists of a
L4981A controller with the relevant circuitry for
the PFC section, and of a TEA2261 synchro-
nised, in master-slave configuration, with a
TEA5170 at 15 kHz switching frequency. When
the supply is in stand-by condition, the TEA2261
controller operates in burst mode.
System block diagram. (fig.1)
System Main Features:
Input Voltage Range: 176 to 270 Vac
Rated Output Power: 250W
Power Factor at max. Output Power: 0.98
Input Power in Stand-by mode: 3W
DC Preregulated Voltage: 400
Efficiency: > 80%
Operating Frequency: 15kHZ Synchronised
Figure 1.
(only Fly-Back Section)
Minimum Output Power Synchronised : 8.5 W
Others: Short Circuit, Overload and Open Load
Protection.
DESCRIPTION.
How to use the demoboard:
The evaluation board is provided with a multi-con-
tact switch (sw.1) which allows to simulate the
TVC operations. The procedure is very simple:
1) Put the switch (1) in s-by position and then
switch on the board.
In this condition no pulses are coming from the
TEA5170 I.C. , T1 is in on state grounding C9 (at
soft start pin of L4981) and so the PFC section is
not working. It is possible to test the voltage at the
output of the step-up (PFC) section C23. It must
be about 308 V (depending on the mains volt-
age). The outputs of the converter should be
measured, and the values can be adjusted with
P1 placed at the primary side.
Here below the schematic diagram is shown in
Fig 2a, PCB and components layout in Fig. 2b.
220V
EMI
FILTER
AN826/01297
PFC
(L4981A)
+400V
FLY BACK
DC-DC CONV
(TEA2261-
TEA5170)
+135(B+)
+15
+14
-14
+7.5
D95IN236A
1/7
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