Download offline soft-switched led driver based on an integrated

OFFLINE SOFT-SWITCHED LED DRIVER BASED ON AN INTEGRATED
BRIDGELESS BOOST ASYMMETRICAL HALF-BRIDGE CONVERTER
ABSTRACT:
This paper proposes an offline single-stage light emitting diode (LED) driver based on a
novel approach to reduce low-frequency ripple in LED arrays supplied from mains, while
assuring high input power factor (PF). The proposal employs a series resonant dc–dc converter
integrated into a bridgeless boost power factor correction (PFC) stage. The resonant stage works
to reduce the low-frequency ripple transmitted from the output of the PFC stage to the LEDs
with only small power losses. This solution achieves three main goals: 1) reduction of the bulk
capacitance used at the dc bus, allowing for the use of long-life film capacitors; 2) increase in the
overall efficiency of the LED driver owing to the low switching and conduction losses in the
shared switching network; and 3) assuring high input PF. Experimental results of a driver
without electrolytic capacitors for a 100-W street lighting LED luminaries are presented,
showing overall efficiency in excess of 92%, input PF greater than 0.97, and line current
harmonic content in compliance with the IEC 61000-3-2 standard.
INTRODUCTION:
While LEDs can have a lifespan ranging from 50 000 to 70–000 h, under some circumstances,
the life of the LED driver circuitry could be shorter than that of the devices being driven.
Thus, one current approach to make the lifespan of the driver compatible with that of the LEDs is
to remove from the power circuitry critical and short-life components, such as the bulky
electrolytic capacitors, which commonly sit at the output of the input stage (the dc bus).
Thus, research effort is currently being focused in replacing these components for the more
reliable metalized film capacitors, of smaller capacitance and longer lifespan
One effective approach to reduce the bulk capacitance enough to employ film capacitors is to use
two cascaded dc–dc conversion stages: one for power factor correction (PFC) and the other for
LED power control (PC), both sharing a common dc bus with a high-frequency decoupling
capacitor, such as the one schematically.
This introduces the bus voltage as an additional degree of freedom in the design of the converter,
allowing the use of smaller capacitances.
Many recent works have stemmed from such
approach, some of them integrating both stages into a single-stage power converter, thus
reducing the number of components.
The main drawback in these cases is that the reprocessing of power by each stage reduces the
overall driver efficiency. One alternative to increase efficiency while still reducing capacitance is
to use two no cascaded converters, each of them processing only part of the power delivered to
the load .
This allows for reduced redundant power processing, thus increasing efficiency, but
results in complex converter topologies and intricate control schemes.
EXISTING SYSTEM:
One effective approach to reduce the bulk capacitance enough to employ film capacitors
is to use two cascaded dc–dc conversion stages: one for power factor correction (PFC) and the
other for LED power control (PC), both sharing a common dc bus with a high-frequency
decoupling capacitor. This introduces the bus voltage as an additional degree of freedom in the
design of the converter, allowing the use of smaller capacitances. Alternative to increase
efficiency while still reducing capacitance is to use two non cascaded converters, each of them
processing only part of the power delivered to the load. This allows for reduced redundant power
processing, thus increasing efficiency, but results in complex converter topologies and intricate
control schemes
PROPOSED SYSTEM:
The proposed driver consists of two separate converters, which are integrated to form a
single-stage solution. The first converter is the PFC stage, which is composed of a BLB rectifier
working in discontinuous conduction mode (DCM). This stage synthesizes a quasi-sinusoidal
current to the power grid, thus resulting in a high PF and low total harmonic distortion (THD) of
the input current. The second converter is the PC stage, composed of an asymmetrical HB
(AHB) SRC with a full-wave high-frequency bridge rectifier feeding the LEDs. The PC stage is
mainly responsible for stepping down the voltage from the dc bus and regulating the LED array
current.
ADVANTAGES:

Low-frequency ripple in LED arrays.

Reduction of the bulk capacitance.
 Assuring high input PF.
BLOCK DIAGRAM:
TOOLS AND SOFTWARE USED:

MPLAB – microcontroller programming.

ORCAD – circuit layout.

MATLAB/Simulink – Simulation
APPLICATIONS:

Street lighting.
CONCLUSION:
This paper has presented an LED driver based on an integration between a BLB PFC
converter and an AHB SRC. The goals of achieving high conversion efficiency, high PF, and
low enough ripple on the output current were achieved, without the need for electrolytic
capacitors in the power circuitry. The 92.4% global efficiency (PFC + PC) achieved with the
prototype is fairly high when compared with what has been recently proposed in the LED driving
literature, particularly when compared with other integrated converters, in which the switching
losses are greater because of increased voltage and current stresses on the shared MOSFETs. The
high efficiency is, thus, mostly due to the use of soft switching for bothMOSFETs and the
reduced conduction losses in the bridgeless PFC stage. It is also remarkable that no special
semiconductors were required to achieve such a high efficiency level (e.g., CoolMOS
MOSFETs, Scotty diodes, SiC or GaN devices, etc.).
REFERENCES:
[1] A. Laubsch, M. Sabathil, J. Baur, M. Peter, and B. Hahn, “High-power and high-efficiency
InGaN-based light emitters,” IEEE Trans. Electron Devices, vol. 57, no. 1, pp. 79–87, Jan. 2010.
[2] F. Li, D. Chen, X. Song, and Y. Chen, “LEDs: A promising energy-saving light source for
road lighting,” in Proc. Asia-Pac. Power Energy Eng. Conf., 2009, pp. 1–3.
[3] C. R. B. S. Rodrigues et al., “An experimental comparison between different technologies
arising for public lighting: LED luminaires replacing high pressure sodium lamps,” in Proc.
IEEE ISIE, 2011, pp. 141–146.
[4] P. S. Almeida, J. M. Jorge, D. Botelho, D. P. Pinto, and H. A. C. Braga, “Proposal of a low
cost LED driver for a multistring street lighting luminaire,” in Proc. IEEE IECON, 2012, pp.
4586–4590.