WS9441P Datasheet, PDF (6/9 Pages) List of Unclassifed Manufacturers – Non-isolated BuckOffline LED Driver

WS9441P Product Description
External PWM Dimming
The WS9441P integrates an external dimming pin
which inputs PWM signal and can dim by changing the duty
cycle of the PWM signal. The testing dimmable curve of a
80V/220mA driver under 175~264Vac application is shown
as below:
The duty cycle of the PWM signal
Inductor Selection
The WS9441P works in a inductor critical current
conduction mode. When the power MOFET is switched on,
the current in the inductor rises up from zero. The on time of
the MOSFET can be calculated by the equation:
t_on

L  I _PK
V_IN  V_LED
Where,
L is the inductance value,
IPK is the peak current of the inductor,
VIN is the DC bus voltage after the rectifier bridge,
VLED is the voltage on the LED.
After the power MOSFET is also switched off and the
current in the inductor decreases. When the inductor current
reaches zero, the power MOSFET is turned on again by IC
internal logic. The off time of the MOSFET is given by the
equation:
t_off

L  I _PK
V_LED
The inductance can be calculated by the equation:
L  ^{VLED  (VIN VLED )}
f  I _PK V_IN
Where, f is the maximum system switching frequency,
which is proportional to the input voltage. So the minimum
switching frequency is set at lowest input voltage, and the
maximum switching frequency is set at highest input voltage.
The minimum and maximum off time of WS9441P is set at
4.5us and 310us, respectively. Referring to the equation of Toff
calculation, if the inductance is too small, the Toff may be
smaller than the minimum off time, the system will operate in
discontinuous conduction mode and the output current will be
smaller than the designed value. If the inductance is too large,
the Toff may be larger than the maximum off time, the system
will operate in continuous conduction mode and the output
current will be higher than the designed value. So it is
important to choose a proper inductance.
Thermal Regulation
The WS9441P integrates thermal regulation function.
When the system is under higher 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.
Over Voltage Protection
The over voltage protection of the WS9441P can be
programmed by the ROVP pin resistor. The ROVP pin voltage
is 0.5V.
When the LED is open circuit, the period of the output
voltage increases gradually, the demagnetization time gets
shorter. The demagnetization time at OVP---- Tovp can be
calculated by the open circuit protection voltage by the
equation:
Tovp  ^{L  V CS}
R _CS  V _OVP
Where，
Vcs is the CS pin turn off threshold (0.4V);
Vovp is the open circuit protection voltage.
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