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WS9822B Schematic ( PDF Datasheet ) - Winsemi

Teilenummer WS9822B
Beschreibung Non-isolated Buck High Precision Three-stage Dimming LED Driver
Hersteller Winsemi
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Gesamt 11 Seiten
WS9822B Datasheet, Funktion
WS9822B Product Description
Non-isolated Buck High Precision Three-stage Dimming LED Driver
Features
Three-stage switcher dimming: 100%-40%-15%
Compatible PCB with WS3442
Internal 500V Power MOSFET
Critical Conduction Mode Operation
±3% LED Current Accuracy
without Auxiliary Winding for power supplying
Efficiency up to 93%
LED Open and Short Circuit Protection
Thermal Regulation Function to avoid lights flicking
under high temperature.
Typical Applictions
T5/T8 LED Strings
Ceiling Lamps
Bulbs
Other LED Lightings
Description
The WS9822B is a three-stage dimming constant current
LED driver with high precision and is applied to non-isolated
buck LED power system. The WS9822B integrates a switch
dimming circuit and can change the output current through
switch shifting.
The device operates in critical conduction mode and is
suitable for universal input offline LED lighting to dim with
three-stage by switcher.
The WS9822B utilizes proprietary current control method.
It can achieve precise LED output current and excellent line
regulation.
The operating current of the IC is as low as 120uA. So it
doesn’t need the auxiliary winding for supplying the chip,
which brings more simplified designs and lower cost.
The WS9822B adopts intelligent temperature control and
thoroughly solves the problem of LED flickering under high
temperature.
The WS9822B offers multiple protection functions to
improve the system reliability, including LED open circuit
protection, LED short circuit protection, and VCC under
voltage protection.
Typical Application Circuit
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WS9822B Datasheet, Funktion
WS9822B Product Description
Function Description
The WS9822B is a three-stage dimming constant
current LED driver with high precision and is applied to
non-isolated buck LED power system. The WS9822B
integrates a switcher dimming circuit and can change the
output current through shifting external switcher ON/OFF to
perform the dimming function.
The WS9822B is compatible the PCB board with
mainstream non-dimming products in the markets, such as
WS3442, thus it can achieve the seamless upgrades from
non-dimming to ON/OFF dimming.
Switcher Dimming Control
The switcher is opened first and closed again when the
dimming is required, and the output current changes in
accordance with the presetted current. The switching time
should be more than 500mS. The dimming current cyclically
varies in the sequence of 100% to 40% to15%. The reset
time is 5S. So it is a normal dimming if the time interval of the
switch from turn-off to turn-on is less than 5s; otherwise it will
be considered as a reset signal. The output current reaches
up to 100% after the switch is on again whatever the output
stage of the preceding current is.
Start Up
The VCC capacitor will be charged through the start-up
resistor when the system is powered on. When the VCC pin
voltage reaches the turn on threshold, the internal circuits
start operating. The WS9822B integrates the 16V ZENER for
clamping the VCC.
The typical value of the start-up current is 130uA (the
maximum value is 195 uA). For the application of 176VAC
264VAC, the start-up resistor can be calculated by the
equation1:
Rst
Vin _ min 1.414
I st _ max
176V 1.414
195uA
1.27M1
The start-up resistor can be chosen from 720K Ω to
1.2MΩ. Two resistors in 1206 size SMD or 1/4W metal film
resistors can be used in series.
Due to the ultra-low operating current, the auxiliary
winding is not needed to supply the IC.
VCC Capacitor Selection
The Vcc capacitor is used to bypass noise to IC, so that
to assure its stable operation, and should be as close as
possible to the chip.
A 4.7uF/25V electrolytic capacitor can be used to Vcc Pin.
If selecting MLCC, the material of X7R will be used to satisfy
the stability of the capacity under high temperature. Due to
external damage resulted from small volume and brittle texture
of MLCC, it is easy to cause Vcc currents leakage, which will
make the WS9822B unable to start. Strict control measures
are taken in the layout and productive process.
In order to avoid the return flickering and the disorder time,
the Vcc capacitor should be in parallel with discharge resistor,
which value should be chosen from 150KΩ to 240KΩ.
Constant Current Control
Utilizing proprietary current control method, the
WS9822B can achieve precise LED output current with a few
external components. Cycle by Cycle current sense is adopted
in WS9822B, the CS pin is connected to the current sense
comparator, and the voltage on CS pin is compared with the
internal 400mV reference voltage. The MOSFET will be
switched off when the voltage on CS pin reaches the threshold.
The CS comparator includes a 350ns leading edge blanking
time.
The peak inductor current is calculated by the equation
2:
I PK
0.4 (mA)
Rcs
2
Where, RCS is the current sense resistor value.
The current in LED can be calculated by the equation3:
I LED
I PK
2
(mA)
3
Where, IPK is the peak current of the inductor.
Freewheeling Diode
The diode will bear the reverse voltage equal to the
input voltage when the MOSFET is on. A 600V diode was
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