BW6562A Datasheet, PDF (12/15 Pages) Bruckewell Technology LTD – High PFC LED Driver

BW6562A High PFC LED Driver
shape the input current by drawing a quasi-sinusoidal
current to be in-phase with the line voltage. A simplified
circuit, shown in Figure 3, can explain the operation as
follows :
Figure 3. ZCD Pin Synchronization without Auxiliary
Winding
The output of the multiplier is fed into the non-inverting
pin of the internal PWM comparator. As the output from
multiplier, a sinusoidal reference for PWM, equals to the
voltage on the current sense CS pin (#4), the MOSFET
will be turned off. As a consequence, the peak inductor
current will be enveloped by a rectified sinusoid. After
the MOSFET is turned off, the boost inductor discharges
its stored energy to the load until zero current is
detected and turns on MOSFET again.
In case there is no auxiliary winding on the boost
inductor, a solution can be implemented by simply
connecting the ZCD pin to the drain of the power
MOSFET through an RC network as shown in Figure 3.
In this way the high-frequency edges experienced by the
drain will be transferred to the ZCD pin, hence arming
and triggering the ZCD comparator.
The AC mains voltage is rectified by a diode bridge and
delivered to the boost converter which boosts the rectified
input voltage to a higher regulated DC bus V_O.
The error amplifier compares a portion of the output
voltage with an internal reference and generates a signal
error proportional to the difference between them. The
bandwidth of the internal error amplifier is set to be
narrow within 20kHz, the output would be a DC value
over a given half-cycle. Output of E/A fed into multiplier,
multiplied by portion of the rectified mains voltage, will
generate a scaled rectified sinusoid whose peak
amplitude depends on the rectified mains peak voltage as
well as the value of error signal.
Also in this case the resistance value must be properly
chosen to limit the current sourced/sunk by the ZCD pin.
In typical applications with output voltages around 400V,
recommended values for these components as 22pF (or
33pF) for C_ZCD and 330kΩ for R_ZCD. With these values
proper operation is ensured even with few volts
difference between the regulated output voltage and the
peak input voltage.
© 2012 Bruckewell Technology Corp., Ltd.
12
www.bruckewell-semi.com/