NL2003677C2

NL2003677C2 - Ballast device for a dimming circuit.

Info

Publication number: NL2003677C2
Application number: NL2003677A
Authority: NL
Inventors: Riccardo Arthur Wet; Franciscus Adrianus Steur
Original assignee: Online Services B V
Priority date: 2009-10-20
Filing date: 2009-10-20
Publication date: 2011-04-21

Description

TITLE: Ballast device for a dimming circuit.

FIELD OF THE INVENTION

5 The invention relates to a high-frequency switching-mode ballast device for a dimming circuit.

BACKGROUND OF THE INVENTION

With the progress in lighting technology (and under continuous global 10 pressure to develop more energy-efficient transducers) other kind of lamps has become popular, namely fluorescent lamps (F-L) and, lately, the high-power light-emitting diodes (LED-L) lamps. Both these lamps are no longer, such as the incandescent lamp, made of a simple, single resistive element but consist of several components of very different and disparate electrical 15 properties themselves. Therefore, the total load that they present to the AC sinusoidal supply is very different from the simplex behaviour of a pure resistor. This calls for novel designs of ballast devices for dimming circuits.

In addition, the present and growing demand for compact H-B LED lamp’s 20 constant current devices-controllers has motivated several well known electronic manufacturing firms to design, produce, and make commercially available Integrated Circuits (ICs) exclusively for this specific purpose.

As these ICs are custom-made and differ from each other in the topology of 25 their respective working principles and power handling, the application designer has a very restricted choice when intending to design an in-house, brand-new, competitive and well-spread range of modern solid-state luminaries for household, commerce and industry.

2

The so called ballast has evolved from the already mentioned electromagnetic to the sophisticated electronic types of today. Specifically, for the operational low-voltage halogen-incandescent luminaries they have even adopted the general commercial term of electronic transformers, with its 5 implied meaning of simple voltage-down-converters (nominally 230 Volts AC

household mains potential being in this case a relative high-voltage source.).

Thanks mainly to the amalgamation of the active components into integrated-circuits (ICs) and SMD (Surface-Mounted Devices) passive 10 components generally available today, this LEDS lamps controllers have become very compact and attractive for being implemented within the tight enclosures of household-type incandescent and Compact Fluorescent Lamps (CFLs) of similar geometry and volume; so its increasing desirability.

15 These electronic device-drivers are in fact no more than very efficient SMPS (Switching-Mode Power-Supplies) in miniature. They are implemented in various general and well documented topologies, and new ones are being constantly developed as the requirements evolve with the availability of newer light transducers of different physical and electric properties and new 20 electronic design techniques and manufacturing integration.

SUMMARY OF THE INVENTION:

The present invention aims to offer a price -and performance-25 competitive ballast device for a dimming circuit that do not rely on sourcescarce and relative expensive ICs: as their core, their source-power interface, as well as all their enhanced features. In addition it is aimed to offer a standard topology from end to end design that can be applied and easily extrapolated to a complete range and type of lamps of diverse power and 30 applications 3

In accordance with some aspects of the invention, a high-frequency switching-mode ballast device for a dimming circuit is provided, the ballast device comprising: a bridge rectifier section having an AC input and a DC bridge rectifier 5 output; a high frequency oscillator circuit including a main ballast coil assembly, coupled to the DC bridge rectifier output; a power factor corrector circuit comprising at least one capacitor, coupled in parallel to the DC bridge rectifier output; the power factor corrector circuit including a flyback diode 10 coupled in parallel over said at least one capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will further be elaborated with reference to the following Figures: 15 Fig 1: Block diagram of the dimmable LED lamp

Fig 2: Detailed circuit diagram of a 3W dimmable LED lamp according to the block diagram of Figure 1.

Fig. 3: Standard circuit diagram of a conventional 11W CFL.

Fig. 4: Integrated Power Factor corrector device.

20 In the figures, similar or corresponding elements will be addressed using the same reference numerals.

DETAILED DESCRIPTION OF EMBODIMENTS Great progress have been made in the last part of the old century by the 25 lighting industry in order to meet the new trend, especially in the field of fluorescent lamps: steadily the original the so-called electromagnetic ballast had made way for more efficient electronic types, and even the modern fluorescent tubes themselves have today a much better lumen-per-watt energy-conversion ratio.

30 4

The race is on for a lighting source with the least disadvantages and the most efficient input-power lumen-output ratio. The modern LED lamps seem to fulfil that requirement. Their main properties, vis a vis older technologies are: 5 - mechanical compactness and robustness, light and packing-friendly, - lower operating voltage, less inherent operational stress, - no brittle glass or vacuum enclosure required for normal operation, - no direct heated metal transducer used, 10 - no mercury, amalgam or foreign catalyst required for energy conversion, - inherent solid-state reliability and longer estimated working life, - best lumen-watt ratio than incandescent and fluorescent lamps, - no toxic residual chemicals precautions needed when replaced, disposed, - availability in different primary colours and power ratings, 15 - steadily getting better as price-performance specifications evolve, - solid-state’s lower manufacturing risks, - growing general consumer’s budget-conscious acceptability, - progressive tightening of official efficient legislation worldwide.

20 Although they seem to be a good bet for the future (as far as lighting-delivery transducers technology and range of applications is concerned), the developing engineer has to be aware of certain inherent limitations and restrictions for implementing successful commercial LAMPS, such as: 25 - normal low DC operational voltages coupled with relative high currents, - point of source light transducer might need added distribution optics, - concentrated energy will need some sort of thermal management, - versatility, longer life and efficiency must not compromise real and perceived manufacturing, distribution and retail final cost barriers in order to 30 make the technology, appeal-able and viable.

5

Therefore the challenge is to translate the obvious potential advantages of the LEDS LAMPS into a real-world competitive and popular price-performance product.

5

As the cost of the original High-Brightness (H-B) LED devices have come down in price dramatically in the last couple of years, the focus have been put squarely in the design and implementation of suitable low-cost drivers to match them, coupled with the desired goal of making a modern, more 10 efficient and longer-lasting direct-replacement product for the ubiquitous household incandescent bulb.

The Power factor (PF), is defined as the cosine of the phase-angle between the load’s voltage and current waves, which is a unit-less number between 1 and 15 0. When the PF=1, the voltage and current waves are in perfect sync, and all the energy that is supplied is consumed by the load (the PF of a purely resistive load is equal to 1). When the PF<1, the voltages and current waves are out-of-step, and only part of the energy supplied is consumed by the load, the rest being cyclically absorbed then reflected back, at the frequency of the 20 AC supply (in standard reticulation distribution, meaning 50 or 60 Hz).

Whereas incandescent lamps are purely-resistive loads, Fluorescent Lamps and high-power LEDs lamps include some substantial capacitive reactance themselves. Accordingly, their Power Factor is poor due to the resulting V/I 25 phase-shift, and the part of the total power supply available to do real work is therefore somehow compromised by the presence of a concurrent reactive power term. Phase-cut dimmers are generally not suitable for dimming these poor PF lamps.

6

As this type of dimmer is advanced, it greatly distorts the incoming voltage wave-front progressively, and the higher harmonics elements so generated tend to increase even further the original reactance value-part of the load (at the nominal mains frequency), which leads to an even grater Vfl phase-shift, 5 a dramatic reduction of the originally inherent poor PF that this type of lamps have, and finally, an increased loss of the real available power.

This vicious-circle manifest itself as mild to severe flickering of the lamps as the dimmer control is advanced, and is most-evident when attempting to dim 10 them below 50% (of their nominal maximum power output). The reactive part of the load, capacitive and/or inductive (Xc and/or XI), induces a phase-shift between the supplied voltage wave-front and its consequential resultant load-current. The relative amount of phase-shift that thus occurs is a magnitude so called power-factor of that specific load.

15

Therefore, a purely inductive or purely capacitive load results in a relative phase-shift of minus/plus 90 degrees and a PF=0. Purely inductive or pure capacitive loads consume no power on average, but merely cyclically absorb and reflect the input power totally. Importantly then, the closer the PF is to 20 0, the less real power is available in the load transducer circuit to do work efficiently.

Turning now to Figure 1, the block diagram of the dimming circuit, coupled to AC mains is divided into four areas: 25 10) Triac-dimmer minimum-load interface.

20) Low-frequency AC to DC rectifier-converter.

30) Passive Power Factor Correction compensator integrated network device. 40) High-frequency DC to AC self-oscillating inverter.

7

Referring specifically to the 10 - 40 sections of Figure 1, the following is observed: (10) Triac-dimmer minimum-load interface.

5

Most commercial dimmers are of the phase-cut topology and have at their core a high-voltage AC bipolar gating-controller device, an industry-standard electronic component known as a TRIAC. These dimmers, being low-cost due to their small component count, have historically been -and they still are- the 10 most popular brightness controller for incandescent luminaries, therefore their wide use in the average household, worldwide.

Though their electronic design principle is fairly standard, their actual manufacture implementation still differs quite a lot from brand to brand.

15 Moreover, depending of the particular TRIAC device used, all have a specific -and perhaps diverse- maximum power-handling capability.

More important, in the present context of sourcing variable power to the relative much lower power LED lamps, is the -also generally stated in the 20 product’s packaging- specific minimum load requirement. This is mainly due to an inherent restricting electrical property of all TRIACS devices and it is very well published and understood.

In the present invention design, a fixed resistor of relative medium K-ohms 25 value helps to equalize the performance of many disparate dimmer devices, especially at low brightness levels, as it presents a constant and fixed minimum working load to the wide-spread brands and types of lightcontrolling TRIAC-core products commercially available in the marketplace: their average response become smoother, less prone to flickering, less noisy, a 8 more reliable operational life-span can be expected, and their general performance becomes more predictable.

Its contribution is therefore four-fold: 5 - To present a constant pure-resistive component to offset, at least partially, the re actively inherent characteristic of any CFL’s input impedance.

- To help equalize the performance of the very disparate dimmer electronic designs dimming ranges, and the mechanical variations in their control-pot geometry span-travels.

10 - To present the dimmer’s gating device (the Triac core) with a minimum load current to keep it conducting for a longer angle span, especially at the critical low-brightness dimming settings, when the avoidance of flickering is highly desirable, not only just for aesthetics but also due to sound electronic design principles.

15 - As a perfect resistive element of fixed value, always in parallel with the changing lamp’s reactance (as it is progressively dimmed.) it helps to keep the overall PF as high as possible, and therefore contributes -although partially, as compared to the principal contribution of the power factor corrector device described above- to keep the overall harmonic distortion in-20 check, as well.

(20) Low-frequency AC to DC rectifier-converter.

This is implemented as a high-voltage full diode-bridge rectifier topology 200 25 of standard-grade inverse-recovery response. Its many possible current-capacity rating values are directly proportional to the specific stated AC overall power consumption.

(30) POWER-FACTOR CORRECTOR.

9 A Power-Factor Corrector (PFC) is an electronic sub-circuit 400 needed to help reduce as much as possible the phase-shift between the input Voltage and Current wave fronts due to the presence of a complex/non-linear load.

5 A non-linear load (linear-load= perfect resistor) will generate some sort of spurious, non-desired harmonic (higher multiples.) frequencies that, as they all add-up, will distort somehow, the generally clean sinusoidal fundamental low-frequency Mains supply wave-front (50/60 Hz). The greater the nonlinearity factor, the worse the harmonic distortion will be.

10

Very strict International Standard are being currently enforced world-wide in respect of the electronic pollution limits that apply specifically to any kind of load/appliance/circuit connected to the L.V. Public Utility Supply distribution lines (110/220VAC) and that includes all luminaries.

15

There are two main power factor corrector implementation approaches: they are so called passive and active. Respectively, each presents the design and the manufacturing engineers with their own set of electronic and mechanical advantages and restrictions, notably challenging in the case of the CFLs.

20 But the general idea, or rather common goal, is to make, somehow, the load as to look as much resistive as possible, taking in consideration the best price/performance, mechanical space/electronic complexity, and total design effort/features compromises.

25 According to an aspect of the present invention, a passive power factor corrector has been chosen for its simplicity, robustness, low-cost and, - as the provided comparative tests will confirm - it’s very promising results.

The power factor corrector according to an aspect of the invention is 30 practically realized by the integration within a single component sub- 10 assembly (resembling an ordinary polarized 2-terminal electrolytic capacitor) of an electrical network of 2 capacitors and 3 rectifier diodes, placed just after the bridge rectifier 200, superseding the single reservoir capacitor characteristic of standard Low-PF lamps and at the same classical position.

5 The overall effect of this network is to extend as much as possible the - otherwise severely restricted - angle of conducted Current drawn from the Supply line within the reference of the positive and the negative excursions of the input Voltage mains cycle/period.

10 Accordingly the power factor corrector circuit 400 comprises a two-terminal network of three serially switched diodes; wherein first and second diodes are coupled in parallel with a first polarized capacitor and wherein second and third diodes are coupled in parallel with a second polarized capacitor; the two-terminal network coupled in parallel to the bridge converter. The flyback 15 diodes D4, D5, D6 or steering diodes make the capacitors’ distributed overall charging and discharging process (from the supply and to the load respectively) smoother, predictable, balanced, self-adjusting and more independent of the load’s demands. The overall input Current waveform tends to better follow the input Voltage waveform, and as is greatly improved 20 average shape shows, brings into view a clear indication that the nonlinearity conductive restrictions of the load have been largely overcome. According to an aspect, the present invention accordingly provides a front-end, highly efficient passive high power factor correction.

25 When integrating the electronic components of the capacitive circuit in a single electronic device, an example of which is illustrated in Fig 4, the result of the tight mechanical integration of 5 standard electronic components within this new 2-terminal Power-Factor Correction Device saves footprint space and interconnection tracks and holes on the PCB.

30 11

Accordingly, the power factor corrector circuit 400 is preferably designed as a two pin connectable device. The input impedance of the CFL now becomes less reactive, therefore with a marked and more defined resistive behaviour that was originally predicted if no power factor corrector were to be 5 implemented. Much less energy bounces-back towards the supply-lines: the nasty harmonics are greatly restricted and the harmonic distortion is brought within acceptable specification’s margins.

40) High-frequency DC to AC self-oscillating inverter.

10

The challenge presented by the need of a general-purpose and very compact power converter is magnified by the desire for a cost-effective but reliable SMPS universal design topology that could be applied successfully to a full range of mains-powered luminaries.

15

Although new specific ICs available for this very purpose have started to appear in the marketplace, variations of tried and tested discrete components topologies can work as well as the emerging new-ones, and can be as good for its perceived price-performance competitiveness.

20

One of the most popular and reliable have been the so called DC-bus powered, High-Frequency, Half-Bridge AC Driver configuration, that is one of the group of ideals in order to excite non-linear/complex loads.

Again, modern manufacturing techniques have gravitated to amalgamate 25 and miniaturize the main critical components of general-purpose Half-Bridge Drivers into Integrated Circuits, custom-made by well known power-control oriented design houses, and also manufactured under their licences by several third-party electronics concerns.

12

As the output load impedance of the converter remains relatively fairly constant, and its input power DC-BUS voltage varies with the progressive dimmer operation, a variable current control is developed onto the LED devices themselves, therefore proportionally varying their brightness.

5 A simple design calculation to properly rate all the current-carrying components of the basic topology design core, in order to encompass all the products within a set range of industry-standard power outputs, then becomes a very simple scale and straight-forward proportionality task.

10

According to an aspect, no specialized high voltage IC-driver is used but a discrete high voltage switched mode power supply.

Figure 2 refers to a detailed block diagram showing practical implementation 15 of the device. Accordingly, there is shown a high-frequency switching-mode ballast device 100 for a dimming circuit, the ballast device 100 comprising a bridge rectifier section 200 having an AC input 201; 202 and a DC bridge rectifier output 203; 204; a high frequency oscillator circuit 300 including a main ballast coil assembly 350, coupled to the DC bridge rectifier output 203; 20 204; and further comprising a power factor corrector circuit 400 comprising at least one capacitor C6, C7, coupled in parallel to the DC bridge rectifier output 203; 204; the power factor corrector circuit 400 including a flyback diode D4, D5, D6 coupled in parallel over said at least one capacitor C6, C7.

25 Figure 3 shows a detailed layout scheme for the power factor corrector functional circuit which may be applied in other electrical layouts for improving a power factor.

Figure 4 shows an embodiment, wherein the dimming circuit is arranged for 30 driving a (High Brightness) LED 60.

13

Basically, a LED (Light-Emitting Diode) is a current-driven energy-transducer device and can be driven electrically only by a direct (unipolar or single polarity -generally labelled as DC-) energy-source. Its maximum 5 normalized current has a tight specification and can not otherwise be exceeded without a predictable sure failure: in electronic terms it has a very low dynamic impedance. Therefore the control of its current is the most important requirement for the associated electronic driver.

10 Its normal operating voltage is relative very low (only a few volts) and once is progressively achieved (i.e.: as a slow rise from 0 Volts can testify) it will remain relative constant. Thereafter it will revert to its constant-current drive requirement, so long as it is operated within the range of its maximum specified current limit.

15 H-B LED devices are basically designed for constant current operation to attaint their maximum specified efficiency, therefore there is a general perception that they can not be directly dimmable by voltage drivers means.

20 According to an aspect of the present invention, as opposed to industry standard current driven control topologies, the present invention provides a voltage driven and dimming control design for a LED device. Accordingly, the LED-device according to the invention comprises a ballast device providing a voltage driven dimming control design.

25

For a discussion of block elements 10-40, reference is made to Figure 1. In addition, for driving the HB-LED 60, block element 50 references a high-frequency AC to DC rectifier and ripple-compensation network.

Since the LEDS devices are essentially unipolar in their normal operational 30 drive requirements, a high frequency and efficient AC to DC conversion is 14 implemented in the present invention. The use of an inverse fast-recovery full-wave rectifier diode-bridge configuration aids to this purpose in a simple, compact and robust way, which rating can as well be scaled to each particular LED lamp nominal power output.

5

According to an aspect, the driver is of a fixed frequency, and no frequency control is required.

In order to extend to it’s maximum the dimming performance capabilities of 10 the LED lamps, an optional and proportionally rated relative low voltage electrolytic capacitor could be added in parallel with the output DC polarized terminals of the high-frequency rectifier diode-bridge to aid to minimize any onset of flickering behaviour that could appear on the LED devices at very low brightness levels, if so required. It could, as well, help to the general 15 smoother transitional operation of the dimmer controller itself, as it is exercised throughout its full range.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to 20 be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

Although a specific type and specific power (prototype-quality) LEDs have been constructed to assess the real-world application of the principles 25 disclosed in this document, the integration of all and/or some of the enhancements in order to improve the performance and features over any standard design (as has been the aim of this paper), can be extended and applied successfully across a wide board of all the LEDs, and higher-power electronic ballast that are at the core of all modern and efficient luminaries, 15 of any topology and/or any power whatsoever; the only concern being the assessment of the final values and ratings of the components involved.

Other variations to the disclosed embodiments can be understood and 5 effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The 10 mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in 15 other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.

Claims

A high frequency switching mode ballast (100) for switching, said ballast (100) comprising: 5. a bridge rectifier part (200) with an AC input (201; 202) and a DC bridge rectifier output (203; 204); a high frequency oscillator circuit (300) comprising a main ballast coil assembly (350) coupled to a DC bridge rectifier output (203; 204); further comprising 10. a power factor correction circuit (400) comprising at least one capacitance (C6, C7) connected in parallel with the DC bridge rectifier output (203; 204); said power factor correction circuit (400) comprising a freewheel diode (D4, D5, D6) which is connected in parallel over the at least one capacitance (C6, C7). 15

The ballast as claimed in claim 1, wherein the power factor correction circuit (400) comprises a two-terminal network of three serially-switched feedback dieodes (D4, D5, D6); wherein first and second diodes (D5, D4) are connected in parallel with a first polarized capacitance C7 and wherein second and third diodes (D4, D6) are coupled in parallel with a second polarized capacitance C6; wherein the two-terminal network is connected in parallel with the bridge rectifier.

The ballast of claim 2, wherein the power factor correction circuit is configured as a two-pin linkable component (400).

The ballast of claim 1, further comprising a resistor network (210) connected in parallel with the DC bridge rectifier input (201; 202).

The ballast according to claim 1, wherein the dimming circuit is of a phase cut off type.

The ballast according to claim 6, wherein the dimming circuit comprises a triac.

The ballast of claim 1, further comprising an H-B LED device.