DESIGN, ANALYSIS AND CONTROL OF INTERLEAVED FLY-BACK

CONVERTER FOR LED LIGHTING SYSTEM

INTRODUCTION:-

• Applications of LEDs are increasing due to its high luminous efficacy , ease to drive , absence of mercury problems and long lifetime.

• Outdoor lights should comply with IEC61000-3-2 standard regarding PF and THD i.e. required PF is higher than 0.9 and THD should be less than 10%.

LED DRIVERS

• An LED driver is a self-contained power supply that controls the amount of current and voltage supplied to an LED light.

• An LED constant current driver monitors the loop current of each LED and automatically adjusts the generated DC voltage output to the minimum value needed to produce the highest forward voltage.

TOPOLOGIES OF LED DRIVERS

The available topologies for LED drivers are:

• Buck converter

• Buck-Boost converter

• Tapped-Buck converter

• Fly-back converter

BUCK CONVERTER

• Advantages:-

1. the lowest component count, a very simple (low cost) magnetic component (an inductor) and the highest efficiency. 

2.a viable choice for non-isolated designs.

BUCK CONVERTER

• Disadvantages:

1. this type cannot provide functional isolation.

2.For buck conversion to work, the input voltage needs to be higher than the output voltage.

BUCK CONVERTER

BUCK-BOOST CONVERTER

• Buck-boost conversion is the next alternative – component count is similar to buck design sand efficiency is also very high.

• They have a similar problem with isolation and duty cycle limited input/output voltage ratio as buck converters

BUCK-BOOST CONVERTER

TAPPED-BUCK CONVERTER

• the winding structure allows a turns-ratio type adjustment of output voltage and current making tapped buck converters good for standard designs

• It is appropriate to consider the tapped buck converter as analogous to a non-isolated fly-back converter

TAPPED-BUCK CONVERTER

FLY-BACK CONVERTER

• The converter can be implemented as either isolated or non-isolated.

• Due to imperfect coupling between primary and secondary windings, as well as primary parasitic capacitance, the more complex winding arrangement leads to increased cost and power losses

FLY-BACK CONVERTER

• Fly-back converters are overwhelmingly used for isolated LED bulb designs

• Higher-efficiency Power Factor Correction(PFC) converters that are available today.

FLY-BACK CONVERTER

BEST LED DRIVER

LED power supply is used in an application that can be considered to be uniquely challenging based on the following factors:-

• Internal ambient temperatures

• Size requirements

• Input considerations

• Cost considerations

BEST LED DRIVER

• The decision process to select between different topologies, selection strategy assumes the following order for designs: Buck →Buck Boost →Tapped Buck → Fly-back. The order is weighted; highest efficiency and lowest cost being the most desirable requirements.

CLASSIFICATION OF LIGHTING SYSTEMS:

• According to output power rating , power stage to drive an LED can be classified into single stage and two stage structures.

• Single stage structure for LED power supply unit combines the power factor correction(PFC) part and dc-dc converter part in one stage.

• In two stage structure , the first stage is the ac-dc converter for PFC and the second stage is the dc-dc converter for regulating the output voltage or current.

TWO STAGE STRUCTURE:-

•  In a critical conduction mode(CRM) boost converter for PFC it shows poor PF and THD under light load condition due to the negative drain current for valley switching.

• However this structure needs a large number of components and two kinds of control ICs so that it costs a lot and shows low efficiency due to two processes of input power.

• So , the two stage structure cannot cover the wide output power range of LED lighting applications.

SINGLE STAGE STRUCTURE:-

• single stage structure has low component count , low cost , a simple control circuit, high efficiency.

• Single stage structure has long life and high reliability compared with two stage structure.

PROPOSED CONTROL METHOD:-

• Generally CRM fly-back converter is widely used as single stage structure due to its high efficiency due to valley switching

• But it shows poor PF and THD under light load condition due to valley switching of the CRM control method

• DCM interleaved fly-back converter has good PF,THD under light load condition but shows low efficiency due to high RMS current.

• to achieve high efficiency and good PF,THD in wide output power range , this method proposes a pulse duty cycle pulse frequency modulation(PDPFM) control method for an interleaved single stage fly-back(ISSF) converter.

Interleaved single stage fly-back converter

OBJECTIVES:-

• To design a AC-DC converter of high efficiency for wide input voltage and output load ranges.

• To achieve high power factor(PF) and low Total Harmonic Distortion(THD) for wide output power range for the proposed converter.

SCOPE OF THE PROJECT

• In the first phase , the simulation of interleaved fly-back converter for LED lighting systems is performed.

• Finally , in second phase the simulated results are verified practically.