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PDF WS3412AH Data sheet ( Hoja de datos )
| Número de pieza | WS3412AH | |
| Descripción | Non-isolated Buck APFC Offline LED Driver | |
| Fabricantes | WINSEMI | |
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WS3412AH ProductDescription
Features
Specially Optimized for the EMI
Internal 600V Power MOSFET
Active PFC for High Power Factor and Low THD
Critical Conduction Mode Operation
System Efficiency up to 95%
Without auxiliary winding
Excellent Line and Load Regulation
±3% LED Output Current Accuracy
Thermal Regulation Function
LED Short/Open Protection
Current Sensing Resistor Open Protection
Auto Fault Recovery
Available in SOP7 Package
Applications
E27 LED Bulb, Spot Light
PAR30, PAR38 Lamp
T8/T10 LED String
Other LED Lighting
Typical Application
Non-isolated Buck APFC Offline LED Driver
Description
The WS3412AH is a high precision non-isolated buck
driver with active PFC, specially designed for universal input
offline constant current LED lighting. The driver with on-chip
PFC circuit achieves high power factor and low THD.
Operating in critical conduction mode, the power MOSFET
switching loss is reduced and the inductor is fully utilized.
The WS3412AH integrates a 600V power MOSFET. With
few external components, the LED output current can be
precisely controlled.
The WS3412AH offers rich protection functions to
improve the system reliability, including LED open circuit
protection, LED short circuit protection, CS resistor open
circuit protection and cycle by cycle current limit. All the
protection functions are auto-recovery. The system reliability
is further improved by the thermal regulation function. The
output current is reduced when the driver is over temperature.
The WS3412AH has ultra low start up current and ultra
low operating current.
The WS3412AH is available in SOP7 Package.
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1 page  
WS3412AH ProductDescription
Application Information
The WS3412AH is a high precision Active PFC driver
integrating 600V power MOSFET, specially designed for
non-isolated buck offline constant current LED lighting.
Operating in critical conduction mode, the driver achieves
high power factor, low THD and high efficiency.
Start Up
After system powered up, the VCC pin capacitor is
charged up by the start up resistor. When the VCC pin voltage
reaches the turn on threshold, the internal circuits start
working. The COMP pin voltage is pulled up to 1.5V quickly,
then the WS3412AHstarts switching. The system works at
10k Hz frequency at the beginning, the COMP voltage rises
up gradually, and the inductor peak current also rises up. The
LED current hence achieves a soft start without overshoot.
After the output voltage is built up, the VCC power is supplied
by the output voltage through a diode.
The maximum value of the startup current is 100uA. For
the application of 85VAC —264VAC, the startup resistor can
be calculated by the equation:
Rst
Vin _ min
I st _ max
85V
100uA
850KΩ
Constant Current Control
The WS3412AH utilizes floating ground structure. The
inductor current is sensed during the whole switching cycle,
thus it achieves high precision output current control and also
excellent line and load regulation.
The current in LED can be calculated by the equation:
IO
VCS
RCS
200mV
Rcs
Rcs is the current sensing resistor.
Feedback Network
The WS3412AH senses the output current zero crossing
information through the feedback network, the FB falling
threshold voltage is set to 0.2V with 0.15V hysteresis. The FB
pin is also used to detect output OVP, the threshold voltage is
1.6V. The ratio of FB upper resistor to lower resistor can be
set as:
RFBL
RFBL RFBH
1.6V
VOVP
Where,
RFBL: The lower resistor of the feedback network
RFBH: The upper resistor of the feedback network
VOVP: Output over voltage setting point
The minimum VOVP should be set about 1.3Vo.It is
recommended that the FB lower resistor is set to
3.3KΩ—5.1KΩparalleled with a 22pF ceramic capacitor.
Protection Functions
The WS3412AH offers rich protection functions to
improve the system reliability.
When the LED is open circuit, the output voltage will
gradually rise up. The output voltage is sensed by the FB pin
when power MOSFET is turned off. When FB voltage reaches
the OVP threshold, it will trigger fault logic and the system
stops switching.
When the LED is shorted circuit, the system will work
under 10k Hz switching frequency. Meanwhile, the output
voltage is low and the VCC pin cannot be charged up by the
output voltage, so the VCC pin voltage will gradually
decrease and finally reaches the UVLO threshold.
After the system enters into fault condition, the VCC
voltage will decrease until it reaches UVLO threshold. Then
the system will re-start again. If the fault condition is removed,
the system will resume normal operation.
When the output is short circuit or the inductor is
saturated, the CS peak voltage will be relatively high. When
CS voltage reaches the internal limitation (1V), the power
MOSFET will be turned off instantaneously. This cycle by
cycle current limitation can help protecting the power
MOSFET, the inductor and the output diode.
Thermal Regulation
The WS3412AH integrates thermal regulation function.
When the system is over temperature, the output current is
gradually reduced; the output power and thermal dissipation
are also reduced. The system temperature is regulated and
the system reliability is improved. The thermal regulation
temperature is set to 150℃ internally.
PCB Layouts
The following guidelines should be followed in
WS3412AH PCB layout:
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WINSEMI MICROELECTRONICS
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5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet WS3412AH.PDF ] | |
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