NCL30030 Datasheet, PDF (12/32 Pages) ON Semiconductor – Combination Power Factor Correction

NCL30030
DETAILED OPERATING DESCRIPTION
INTRODUCTION
The NCL30030 is a combination critical mode (CrM)
power factor correction (PFC) and quasi−resonant (QR)
flyback controller optimized for high performance LED
driver applications.
HIGH VOLTAGE STARTUP CIRCUIT
The NCL30030 integrates a high voltage startup circuit
accessible by the BO/HV pin. The BO/HV input is also used
for monitoring the ac line voltage and detecting brown−out
faults. The startup circuit is rated at a maximum voltage of
700 V to support higher voltages used in commercial
lighting such as 277 and 347 VAC.
A startup regulator consists of a constant current source
that supplies current from the ac input terminals (V_in) to the
supply capacitor on the V_CC pin (C_CC). The startup circuit
current (I_start2A) is typically 3.75 mA. I_start2A is disabled if
the VCC pin is below V_CC(inhibit). In this condition the
startup current is reduced to I_start1A, typically 0.5 mA. The
internal high voltage startup circuit eliminates the need for
external startup components. In addition, the startup
regulator helps increase the system efficiency as it uses
negligible power in the normal operation mode.
Once C_CC is charged to the startup threshold, V_CC(on),
typically 17 V, the startup regulator is disabled and the
controller is enabled. The startup regulator will remain
disabled until V_CC falls below the minimum operating
voltage threshold, V_CC(off), typically 8.8 V. Once reached,
the PFC and flyback controllers are disabled reducing the
bias current consumption of the IC. The startup circuit is
then are then enabled allowing V_CC to charge back up.
A dedicated comparator monitors V_CC when the QR stage
is enabled and latches off the controller if V_CC exceeds
V_CC(OVP), typically 28 V.
The controller is disabled once a fault is detected. The
controller will restart the next time V_CC reaches V_CC(on) and
all non−latching faults have been removed.
The supply capacitor provides power to the controller
during power up. The capacitor must be sized such that a
V_CC voltage greater than V_CC(off) is maintained while the
auxiliary supply voltage is building up. Otherwise, V_CC will
collapse and the controller will turn off. The operating IC
bias current, I_CC4, and gate charge load at the drive outputs
must be considered to correctly size C_CC. The increase in
current consumption due to external gate charge is
calculated using Equation 1.
I_{CC(gatecharge)} + f @ Q_G
(eq. 1)
where f is the operating frequency and Q_G is the gate charge
of the external MOSFETs.
LINE VOLTAGE SENSE
The BO/HV pin provides access to the brown−out and line
voltage detectors. The brown−out detector detects mains
interruptions and the line voltage detector determines the
presence of either 120 V or 230 V ac mains. Depending on
the detected input voltage range device parameters are
internally adjusted to optimize the system performance.
This pin can connect after the rectifier bridge to achieve
full wave rectification as shown in Figure 3. A diode is used
to prevent the pin from going below ground. A low value
resistor in series with the BO/HV pin can be used for
protection. A low value resistor is needed to reduce the
voltage offset while sensing the line voltage.
AC
Input
EMI
Filter
BO/HV
NCL30030
Figure 3. Brown−out and Line Voltage Detectors
Configuration
The flyback stage is enabled once V_BO/HV is above the
brown−out threshold, V_BO(start), typically 111 V, and V_CC
reaches V_CC(on). The high voltage startup is immediately
enabled when the voltage on V_BO/HV crosses over the
brown−out start threshold, V_BO(start), to ensure that device is
enabled quickly upon exiting a brown−out state. Figure 4
shows typical power up waveforms.
www.onsemi.com
12