Datasheet

NCL30051
http://onsemi.com
8
DETAILED OPERATING DESCRIPTION
EMI
Filter
AC Input
HBoost
HDRVhi
HVS
HDRVlo
PDRV
PGND
VCC
PCT
HV
OSC
GND
VREF
PFBPCS
PZCD
PControl
Logic
PWM
Z
Z
VREF
VDD
VDD
Secondary Side
Compensation
(CCCV)
2.5 V
DR1
DR2
C
out
V
out
T1
L
R
Q
H
Q
L
C
bulk
V
bulk
D
BST
Q
BST
L
BST
VCC
2.5 V
1
2
3
4
56
7
8
9
1012
11
13
14
15
16
Figure 2. Simplified Application Block Diagram
OVERVIEW
The NCL30051 is a combination of a PFC boost
controller and a half−bridge resonant controller optimized
for off-line LED lighting solutions. This device integrates
all the features needed to implement a highly efficient and
small form factor LED driver. It contains a critical
conduction mode (CrM) power factor correction (PFC)
controller and a half−bridge resonant (HBR) controller
with a built−in 600 V driver. The half−bridge stage operates
at a fixed frequency − greatly simplifying the control
implementation. Output (current or voltage) regulation can
be achieved by adjusting the PFC stage output voltage
based on a control signal generated external to the
NCL30051.
This device includes an enable input on the PFC
feedback pin, open feedback loop protection and PFC
overvoltage and undervoltage detectors. Other features
included in the NCL30051 are a 600 V startup circuit and
an adjustable frequency oscillator. The controllers are
properly sequenced, simplifying the system design.
THEORY OF OPERATION
The NCL30051 provides an innovative control
mechanism compared to traditional two stage power
conversion architectures. This unique regulation scheme
offers extreme simplicity for certain applications, but at the
same time places constraints that have to be taken into
account during the converter design.
Traditional 2-stage converters have independent control
loops for the PFC stage and the step-down stage, allowing
each converter output to be regulated on its own. The PFC
stage is often designed for critical conduction (CrM) or
continuous conduction mode (CCM) operation and the
step-down stage is typically a current-mode/voltage-mode
PWM controller geared for forward or flyback
applications. More recently, some solutions such as the
NCP1910 CCM PFC two stage combo from ON
Semiconductor have become available which incorporates
the half-bridge resonant converter topology which offers
significant efficiency and EMI advantages. However, this
HBR topology involves varying the switching frequency to
regulate the output and hence adds further complexity to
such combination controllers.
In contrast, the NCL30051 simplifies the overall
approach significantly by implementing the HBR approach
for the second stage converter at a fixed frequency. This
simply means that the second-stage converter now operates
in a non-regulating fixed-ratio voltage conversion mode.
The implication of this approach is that output regulation
control has to be provided by adjusting the output of the
PFC front-end converter. The benefits of this approach can
be summarized as follows: