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EVL6566B-40WSTB Datasheet, PDF (3/5 Pages) STMicroelectronics – Set-top box
EVL6566B-40WSTB
2
Description
Description
The board implements a reference design of a 40W Switch Mode Power Supply dedicated
to Set-Top Box, DVD and Auxiliary SMPS for Flat TV or small size Flat screen equipment.
The board accepts wide range input voltage (90 to 265Vrms) and delivers 4 voltages. It is
based on the L6566B, a new current mode fixed frequency or QR controller. High efficiency
and low standby consumption are the main characteristics of this board. This joined to
minimal part count required and low cost approach of the global solution makes it a very
interesting solution for powering Digital Consumer Equipment, capable of meeting
worldwide standby rules.
The topology of this converter is the classical Flyback, working in continuous and
discontinuous conduction mode with fixed frequency, capable of achieving the best trade-off
between the peak/rms current ratio and output capacitors size. The nominal switching
frequency, 62 KHz, has been chosen to get a compromise between the transformer size and
the harmonics of the switching frequency, optimizing the input filter size and its cost. The
input EMI filter is a classical Pi-filter, 1-cell for differential mode noise. The MOSFET is a
standard and inexpensive 600V-2Ωmax, TO-220FP, needing a just small heat sink. The
transformer is a layer type, using a standard ferrite type EER28L. It has been designed
according to the EN60065. The reflected voltage is 70V, providing enough room for the
leakage inductance voltage spike with still margin for reliability of the MOSFET.
The output rectifiers have been selected according to the maximum reverse voltage, forward
voltage drop and power dissipation. The rectifiers for 5V and 12V outputs are Schottky, low
forward voltage drop type, hence dissipating less power with respect to standard types.
They are housed in TO-220 package. A small heat sink for both devices is required. The
other two output rectifiers are Schottky too but with a smaller package. The snubber R2 and
C7 damps the oscillation produced by the diode D2 at MOSFET turn-on. A small LC filter
has been added on all output in order to filter the high frequency ripple without increasing
the output capacitors and a capacitor (100nF) has been placed on each output, to limit the
spike amplitude.
The output voltage regulation is performed by secondary feedback sensing the 12V, 5V and
3.3V outputs, while for 1.8V output the regulation is achieved by the transformer coupling.
The feedback network uses a TS2431 as error amplifier which drives an optocoupler
SFH617A-4, insuring the required insulation between primary and secondary. The opto-
transistor modulates directly the voltage on COMP pin of the L6566B.
The controller, the new L6566B, is an extremely versatile current mode primary controller
embedding all functions needed to get very high performances power supplies. It integrates
also all protections are needed by a power supply offering a very high degree of flexibility to
the designer.
Table 1.
Vout
1.8V
3.3V
5V
12V
Output voltages
IoutMAX
IoutMIN
PMAX
1.73A
0.20A
3.1 W
0.5A
0.03A
1.65 W
2.4A
0.3A
12 W
1.9Avg, 2.9Apk
0.05A
34.8 W
POUT (W) = 40W Avg / 51W pk
Stability
±7%
±5%
±10%
±8%
Doc ID 018852 Rev 1
3/5