EVL6566B-65W-QR STMicroelectronics, EVL6566B-65W-QR Datasheet - Page 6

• Manufacturer Part Number: EVL6566B-65W-QR
• Description: BOARD EVAL SMPS FOR L6566B
• Manufacturer: STMicroelectronics
• Type: Power Factor Correctionr

Specifications of EVL6566B-65W-QR

• Main Purpose: AC/DC, Primary Side
• Outputs And Type: 1, Isolated
• Power - Output: 65W
• Voltage - Output: 700V
• Voltage - Input: 8 ~ 23 V
• Regulator Topology: Flyback
• Frequency - Switching: 100kHz
• Board Type: Fully Populated
• Utilized Ic / Part: L6566B
• Input Voltage: 90 V to 265 V
• Output Voltage: 1.8 V to 12 V
• Board Size: 150 mm x 75 mm
• Product: Power Management Modules
• Dimensions: 150 mm x 75 mm
• Lead Free Status / RoHS Status: Lead free by exemption / RoHS compliant by exemption
• Current - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• For Use With/related Products: L6566B
• Other names: 497-10165

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Circuit description
Circuit description
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-to-rms current ratio and output capacitor size. The nominal switching
frequency, 62 kHz, has been chosen to arrive at 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. An NTC
(R1) limits the inrush current produced by the capacitor charging at plug-in. The MOSFET is
a standard and inexpensive 600 V-2 Ω max, TO-220FP, needing just a small heat sink. The
transformer is a layer type, using a standard ferrite type EER28L. It has been designed
according to the EN60065 and it is manufactured by TDK. The reflected voltage is 70 V,
providing enough room for the leakage inductance voltage spike with still margin for
reliability of the MOSFET. The network D7, R7, C21 clamps the peak of the leakage
inductance voltage spike.
The output rectifiers have been selected according to the maximum reverse voltage,
forward-voltage drop and power dissipation. The rectifiers for 5 V and 12 V 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, as indicated in the bill of material (BOM). 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
outputs in order to filter the high frequency ripple without increasing the output capacitors
and a capacitor (100 nF) has been placed on each output, to limit the spike amplitude.
The output voltage regulation is performed by secondary feedback sensing the 12 V, 5 V
and 3.3 V outputs, while for 1.8 V 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 performance power supplies. It also
integrates all protections needed by a power supply offering a very high degree of flexibility
to the designer.
Furthermore the L6566B has a soft-start (pin#14), disable (pin#8) and 5 V reference voltage
VREF (pin#10) available.
Startup sequence
The L6566B pin #1 (HV) is directly connected to the DC bulk voltage and at startup, an
internal high voltage current source charges C19 and C100 until the L6566B turn-on voltage
threshold is reached, then the high voltage current source is automatically switched off. As
the L6566B starts switching it is initially supplied by the VCC capacitor, and then the
transformer auxiliary winding provides the voltage to power the IC. Because the L6566B
integrated HV startup circuit is turned off, it is not dissipative during normal operation and
has a significant role to reduce the power consumption when the power supply operates at
light load. This contributes significantly to meet worldwide standby standards currently
required.
Doc ID 14630 Rev 2
AN2749