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PDF AN1523 Data sheet ( Hoja de datos )
| Número de pieza | AN1523 | |
| Descripción | 11W FLYBACK CONVERTER | |
| Fabricantes | ST Microelectronics | |
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AN1523
APPLICATION NOTE
11W FLYBACK CONVERTER FOR AUXILIARY POWER
SUPPLY APPLICATION USING THE L6590
by Claudio Spini
This document describes an 11W Switch Mode Power Supply reference design, dedicated to Consumer
Applications, e.g. TV chassis auxiliary power supply, low cost Set-top box or digital equipment. The
board accepts full range input voltage (90 to 265Vrms) and delivers 2 output voltages. It is based on the
monolithic controller L6590, integrating the controller and a POWERMOS and working at fixed frequen-
cy, PWM mode and including a stand-by function to minimize the power consumption during light load
operation. It incorporates also all the protections, offering a complete and very compact solution for low
power SMPS.
Introduction
Low power SMPS are today very popular in consumer applications for example like low-cost cable, terrestrial
decoders or high end TV chassis and the manufacturers need to design circuits with good performance, small
size with high cost effectiveness. An integrated monolithic solution controlling the SMPS like the L6590 makes
it a very suitable device, able to satisfy all the requirements of a compact and flexible solution, integrating all the
necessary functions to obtain a robust design just adding few external components. In this proposed reference
design, the board is thru-hole technology, without any heat sink. A specific application circuit fully tested is pro-
posed and the test results, including thermal and EMI, are enclosed in this document. The transformer data are
included too, making it a good way to achieve a very short time to market solution.
SMPS Main characteristics
q INPUT AND OUTPUT VOLTAGES:
INPUT VOLTAGE:
Vin: 90 ÷ 264 Vrms
f: 45÷ 66 Hz
OUTPUT VOLTAGES AT FULL LOAD:
Vout
Iout
Pout
STABILIT Y
[V] [A] [W]
5 1.4 7.5 ±2%
12 0.3 3.6 ±5%
POUT (W) = 11.1
q STAND BY:
During the stand-by operation the power consumption from the mains has to be≤1W, when the circuit
delivers 50mA from the 5V output and the 12V is unloaded.
q PROTECTIONS:
Overload ad short circuit on both outputs, with auto-restart at short removal. An OVP circuit for open-
loop protection.
q SAFETY:
In acc. with EN60065, creepage and clearance minimum distance is 4.8mm
q EMI:
In acc. with EN50022 Class B
March 2002
1/24
1 page  
AN1523 APPLICATION NOTE
Output voltage measurement and efficiency calculation @normal operation
In the following table the output voltage cross regulation is measured and the overall efficiency of the converter
is calculated at both the nominal input voltages. The output voltages have been measured after the load con-
nector.
full load
5V 12V
Vout
[V]
4.99
@Iou t
[A]
1.400
Vout
[V]
12.11
@Iout
[A]
0.304
PoutTOT
[W]
10.67
115Vac
Pin
[W]
15.12
η
70.6%
half load
5.01
0.650
11.97
0.15
5.05
7.00
72.2%
full load
5V 12V
Vout
[V]
4.99
@Iou t
[A]
1.400
Vout
[V]
12.11
@Iout
[A]
0.304
PoutTOT
[W]
10.67
220Vac
Pin
[W]
14.90
η
71.6%
half load
5.01
0.650
11.99
0.15
5.05
6.90
73.3%
The output voltages are within the tolerances in all conditions, at both full and half load. The efficiency calculated
is good for this kind of converters, then the power dissipation is low and even this affect positively the long-term
reliability of the circuit.
Output voltage measurement and efficiency calculation @stand-by operation
Like in the previous section, the output voltage and the efficiency have been checked and the input power has
been measured. It is clearly visible that with the required stand-by load (5V@50mA and 12V@0mA) the input
power consumption is well below 1W at both the input voltage range. Besides, the circuit has been characterised
at both the nominal input voltage values for different output load, giving very interesting results:
5V
Vout
[V]
5.02
5.02
5.02
5.02
5.02
@Iout
[mA]
10
30
50
80
100
12V
Vout
[V]
11.92
12.35
12.65
13.06
13.27
@Iout
[mA]
0
0
0
0
0
PoutTOT
[W]
0.050
0.151
0.251
0.402
0.502
115Vac
Pin
[W]
0.288
0.430
0.579
0.795
0.941
η
17.4%
35.0%
43.3%
50.5%
53.4%
5/24
5 Page 
AN1523 APPLICATION NOTE
Short-Circuit Tests @ Full Load
The short circuit tests have been done in two phases, making the test shorting by a power switch the output
electrolytic capacitor or making the short by the active load option. This gives an idea about the circuit behaviour
with a hard short (at very low impedance) or with a ”soft” short that could happen on the STB main board, having
slightly higher impedance. All the tests have been done at maximum, nominal and minimum input voltage. For
all conditions the drain voltage is always below the BVDSS, while the mean value of the output current has a
value close to the nominal one, thus preventing component melting for excessive dissipation in case of long term
shorts. The auto-restart is correct at short removal in all conditions.
Figure 19. SHORT ON +5V
Vin = 88 Vrms - 50 Hz @FULL LOAD
Figure 20. SHORT ON +5V
Vin = 265 Vrms - 50 Hz @FULL LOAD
CH1:
CH2:
CH4:
VPIN1 – DRAIN VOLTAGE
VPIN3 - Vcc
ISHORT CIRCUIT
Figure 21. SHORT ON +12V
Vin = 88 Vrms - 50 Hz @FULL LOAD
CH1:
CH2:
CH4:
VPIN1 – DRAIN VOLTAGE
VPIN3 - Vcc
ISHORT CIRCUIT
Figure 22. SHORT ON +12V
Vin = 265 Vrms - 50 Hz @FULL LOAD
CH1:
CH2:
CH4:
VPIN1 – DRAIN VOLTAGE
VPIN3 - Vcc
ISHORT CIRCUIT
CH1:
CH2:
CH4:
VPIN1 – DRAIN VOLTAGE
VPIN3 - Vcc
ISHORT CIRCUIT
11/24
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet AN1523.PDF ] | |
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