BP2833D 查看數據表（PDF） - Bright Power Semiconductor
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BP2833D Datasheet PDF : 8 Pages
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晶丰明源半导体
BP2833D
Non-isolated Buck Offline LED Driver
I LED
IPK
2
Where, IPK is the peak current of the inductor.
Inductor Selection
The BP2833D works under inductor current critical
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 IPK
VIN VLED
Where,
L is the inductance value
VIN is the DC bus voltage after the rectifier bridge
VLED is the voltage on the LED
small, the tOFF may be smaller than the minimum off
time, 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.
Over Voltage Protection
The over voltage protection can be programmed by
the ROVP pin resistor. The ROVP pin voltage is
0.5V.
When the LED is open circuit, the output voltage
increases gradually, and the demagnetization time
gets shorter. The demagnetization time at OVP----
Tovp can be calculated by the open circuit protection
voltage:
After the power MOSFET is switched off, 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:
t off
L IPK
VLED
The inductance can be calculated by the equation:
L VLED (VIN VLED )
f IPK VIN
Tovp L Vcs
Rcs Vovp
Where，
Vcs is the CS pin turn off threshold (400mV)
Vovp is the open circuit protection voltage
And then the Rovp resistor value can be calculated
by the equation:
Rovp 15*Tovp*106 （kohm）
Protection Function
The f is the 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 BP2833D is
set at 3us and 240us, respectively. Referring to the
equation of tOFF calculation, if the inductance is too
The BP2833D offers rich protection functions to
improve the system reliability, including LED
open/short protection, CS resistor short protection,
VCC under voltage protection, thermal regulation.
When the LED is open circuit, the system will
trigger the over voltage protection and stop
switching.
When the LED short circuit is detected, the system
works at low frequency (5kHz), and the CS pin turn
BP2833D_EN _DS_Rev.1.0
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