NL2005041C2 - High-frequency switching-mode ballast device for a dimming circuit. - Google Patents

Description

TITLE: High-frequency switching-mode ballast device for a dimming circuit. FIELD OF THE INVENTION

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

BACKGROUND OF THE INVENTION

With the progress in lighting technology (and under continuous global pressure to develop more energy-efficient transducers) other kind of lamps 10 have become popular, namely fluorescent lamps (F-L) and, lately, the highbrightness 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 properties themselves. Therefore, the total load that they present to 15 the AC sinusoidal supply is veiy different from the simplex behaviour of a pure resistor. This calls for novel designs of ballast devices for dimming circuits.

The so called ballast has evolved from the earlier electro-magnetic to the 20 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 implied meaning of simple voltage-down-converters (nominally 230 Volts AC household mains potential being in this case a relative high-voltage source.).

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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 2 newer light transducers of different physical and electric properties and new electronic design techniques and manufacturing integration.

SUMMARY OF THE INVENTION: 5 The present invention aims to incorporate a novel but simple front-end electronic adaptive-switching feedback circuit to optimize the inherent starting low Power-Factor, to compensate for the necessary energy-reserve needed while dimming and to reduce overall components count, as compared with more complex and active and/or passive power-factor correction designs 10 incorporated in more expensive CFL designs.

In accordance with a first aspect of the invention a high-frequency switching-mode ballast device is provided for a dimming circuit according to the features of claim 1.

In accordance with some aspects of the invention, a high-frequency 15 switching-mode ballast device for a dimming circuit is provided, the ballast device comprising: a bridge rectifier section having an AC input; a DC bridge rectifier output and a reservoir capacitor switched in parallel to the DC bridge rectifier output; 20 a high frequency oscillator circuit including a ballast coil assembly, coupled to the DC bridge rectifier output; and further comprising a power factor corrector device arranged as a frequency-modulated electronic switch in series with the reservoir capacitor to switch the reservoir capacitor with increasing frequency; and a frequency modulator circuit 25 coupled with ballast coil assembly to switch the reservoir capacitor with the driving frequency of the ballast coil assembly.

The overall effect of the power factor corrector circuit is to extend as much as possible the -otherwise severely restricted- angle of conducted current drawn from the supply fine.

3

The overall effect of this power factor corrector device is to make the power deliver to the lamp enough at all times to achieve a smooth and continuous transition in fully dimmed and undimmed condition, without seriously compromising the overall performance of the dimmable lamp.

5 Furthermore, the power factor corrector device is suited to be implemented in a dimming circuit as well as in a ballast device.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will further be elaborated with reference to the following 10 Figures:

Figure 1: Block diagram of a dimming circuit for a LED lamp;

Figure 2: Schematic working diagram according to the invention;

Figure 3: exemplary circuit diagram for Figure 2;

Figure 4: schematic chart of capacity versus frequency; 15 Figure 5: Detailed circuit diagram of CFL lamp;

Figure 6: Block diagram of Figure 1 including the LED lamp;

Figure 7: Detailed circuit diagram of a dimmable LED lamp according to the block diagram of Figure 6

20 DETAILED DESCRIPTION OF EMBODIMENTS

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 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 25 resistive load is equal to 1). When the PF<1, the voltages and current waves are out-of-phase, and only part of the energy supplied is consumed by the load, the rest being cyclically absorbed and then reflected back, at the frequency of the AC supply (in standard reticulation distribution, meaning 50 or 60 Hz).

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Whereas incandescent lamps are purely-resistive loads, Fluorescent Lamps and high-brightness LED lamps include some substantial capacitive reactance themselves. Accordingly, their Power Factor is poor due to the resulting V/I phase-shift, and the part of the total power supply available to 5 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.

As this type of dimmer is advanced, it greatly distorts the incoming voltage 10 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 V/I phase-shift, a dramatic reduction of the originally inherent poor PF that this type of lamps have, and finally, an increased loss of the really available power.

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This vicious-circle manifests itself as mild to severe flickering of the lamps as the dimmer control is advanced, and is most-evident when attempting to dim 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 20 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.

Therefore, a purely inductive or purely capacitive load results in a relative 25 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 0, the less real power is available in the load transducer circuit to do work efficiently.

30 5

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

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

5 30) Passive Power Factor Correction compensator integrated network device.

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

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

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 15 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 most popular brightness controller for incandescent luminaries, hence their wide use in the average household, worldwide.

20 Importantly, in the present context of sourcing variable power to the relative much lower power LED lamps, is the -also generally stated in the 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.

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In the present invention design, a fixed resistor of relative medium K-ohms value may help 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 light-30 controlling TRIAC-core products commercially available in the marketplace: 6 their average response becomes smoother, less prone to flickering, less noisy, a more reliable operational life-span can be expected, and their general performance becomes more predictable.

5 Its contribution is therefore four-fold: - To present a constant pure-resistive component to offset, at least partially, the reactively 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 10 geometry span-travels.

- 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 15 design principles.

- 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 20 corrector device described above- to keep the overall harmonic distortion incheck, as well.

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

25 This is implemented as a high-voltage full diode-bridge rectifier topology BR1 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 7 (30) POWER-FACTOR CORRECTOR.

A Power-Factor Corrector (PFC) is an electronic sub-circuit 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 non-10 linearity factor, the worse the harmonic distortion will be.

Very strict International Standards 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 15 distribution lines (110/220VAC) and that includes all luminaries.

According to an aspect of the present invention, the power factor corrector device (30) is arranged as a frequency-modulated electronic switch in series with a reservoir capacitor to switch the reservoir capacitor with increasing 20 frequency; and a frequency modulator circuit coupled with ballast coil assembly to switch the reservoir capacitor with the driving frequency of the ballast coil assembly which will be further elaborated below.

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

25

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.

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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.

5

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 10 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.

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

Figure 2 shows a schematic working diagram according to the invention. From left to right, a resistive minimum load interface 10 is 20 provided parallel over the dimmed AC-mains (dimmer not shown). The load interface is part of the rectifier 20 as substantially described above. In addition a block 25 may be arranged to provide Electro magnetic Compatibility measures. Furthermore, a power factor corrector device 30 is provided, in accordance with the above and as claimed in the annexed claims, 25 and further elaborated in the below. Finally, device 40 represents high-frequency DC to AC self-oscillating inverter to be coupled to a dimmable lamp, in particular, a high brightness LED or CFL lamp (see embodiments below).

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In more detail, Figure 2 shows as an electronic switch to switch on reservoir capacitor 33 (Cl) as a high voltage adaptive solid-state electronic switch.

The purpose of the frequency-modulated electronic switch 31 in series to 5 ground with the reservoir electrolytic capacitor 33 (Cl) may be any of: a) to present the input impedance to the lamp with a relative high power factor at start-up and at high settings of the dimmer; b) to assure enough power-reserve to avoid flickering of the lamp due to lack of D.C. current at low settings of the dimmer; 10 c) to allow for the relevant pass margins to be attained related to Total Harmonic Distortions and Electro Magnetic Interferences.

As the Power Factor degrades inversely with the value of the reservoir capacitor (as the input impedance becomes more capacitive-reactive), a 15 compromise has to be found for he smallest value of Cl that will assure a reliable striking and (full-brightness) running D.C. power-delivery to the driving stages of the CFL. That value is usually in the order of a few micro-Farads for the “low-wattage” range of standard commercial lamps.

20 The present frequency modulated high voltage switch 31 functions to progressively “boost” the charge in the existing single reservoir capacitor in order to avoid the collapse of the lamp’s arc and its sub-sequent attempts at re-striking.

25 As an alternative and deemed to be covered by the scope of the present invention this can be achieved if the average D.C. charge on the reservoir capacitor can be controlled by means of a pulse width controlled series-modulator 10

Advantageously, a frequency modulated switch 31 is applied, as the running frequency of the self-starting oscillator topology (as normally used in most of standard CFL designs) tend to vary inversely with the changing of the H.V.

D.C. bus voltage: the lower the bus voltage, the higher the oscillator 5 frequency and vice-versa.

As the dimmer is exercised across its range, a proportional time-modulator-device is set that controls the average charge of the reservoir capacitor that tends to normalize the average D.C power to the load resulting in a smooth 10 decreasing/increasing (but continuous) D.C. current delivery to the lamp’s driver.

In particular, as the dimmer goes toward its lower settings, although the D.C. bus voltage decreases, the reservoir capacitor is allowed to charge 15 progressively more per unit of time, (as is brought more and more “in-circuit” by its F.M. driving signal) and the boost-current is increased to provide enough D.C. current to maintain the CFL operating without flicker .

The F.M.-driven solid-state switch 31 can be provided by a standard high 20 voltage transistor, of the same type as used in the driver stage 40.

The open-loop control signal 311 for the H.V. solid-state switch 31 is derived from the load section of the self-starting oscillator 40, in particular, ballast coil assembly 45 that drives the dimmable lamp.

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In more detail, and as exemplary embodiment, Figure 3 illustrates the frequency modulator circuit 32 coupled to ballast coil 45 of driver circuit 40. While the coil may be provided as single ballast coil, it may also be a subsidiary coil since it’s purpose is to drive the switch 31 in synchronicity 30 with the driver frequency of the driver circuit 40.

11

It may be designed as a small isolating high frequency transformer (the same ring-core type as used to drive the bases of the output transistors) in series before the ballast coil, samples the continuously (inversely proportional) variable frequency of the lamp’s oscillator, as the dimmer is exercised down 5 and up its range.

The original H.F. frequency is doubled by a standard full-wave rectifier bridge BR2 (fast-recovery diodes might be used for better efficiency...) and after current calibrated/limited by a series resistor, applied to the base of the 10 H.V. switching transistor.

The resulting switching driving signal is therefore a series of pulses of continuous variable frequency (as the D.C bus voltage changes according to the setting of the dimmer) that in conjunction with the H.V. switching 15 transistor realizes an adaptive F.M.’s “time-modulator” that “boost”, as required, the charge of the small-value reservoir capacitor.

In particular, it is shown that the power factor corrector device is arranged as a frequency-modulated electronic switch 31 in series with the 20 reservoir capacitor 33 to switch the reservoir capacitor 31 with increasing frequency; and a frequency modulator circuit 32 coupled with ballast coil assembly 45 to switch the reservoir capacitor 31 with the driving frequency of the ballast coil assembly 45.

25 Figure 4 further illustrates this as a schematic chart of capacity versus frequency (no units). It can be shown that the capacity is effectively increased when the frequency increases - that is, when the dimmer is activated towards fully dimmed condition. Especially when needed, the capacity is switched on and only a very small residual capacity is maintained in the non-30 dimmed condition, compliant with the THD/EMC constraints.

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CFL EMBODIMENT

A CFL is composed of a few dozen different electronic components, but basically can be thought-of a miniature high-frequency switching-mode power 5 supply (HFSMPS) 100 driving a light-transducer low-pressure gas tube 60. The overall input impedance of the CFLs are far removed from the theoretical pure-resistive concept, (vis-a-vis: the incandescent paradigm) as their Power Supply (PS) front-end are made (on purpose) highly capacitive due to the need for reservoir or smoothing DC capacitors of very significant value, as 10 any good AC/DC/AC frequency converter design must have for its intended stable and reliable long-term operation.

This relatively significant capacitive character of the input impedance of the classical front-end of the PS of any standard fluorescent lamps tends not only 15 to lower their PF, but as a direct consequence (due to their added full bridge rectifier-diodes standard configuration and conductive behaviour), distorts the incoming Current supply waveform itself, proportionally increasing the Total Harmonics Distortion (THD).

20 Block 25 of Figure 5 is a schematic illustration of a low pass filter including an L-R High Frequency Low-Pass Filter (HF-LPF) 25 including an inductor LI that is configured in series with the total circuit load’s current-return-path 130.

25 Harmonic distortion can be measured with specialized relative low-frequency response analyzers (up to the 40th Harmonic of the fundamental Mains frequency, -50 or 60 Hz.-, that means roughly up to 25KHz or so.). The current pass-specification usually keeps a special watch for the third and the fifth ones, still within the realm of very low frequencies, indeed.

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The inductor LI is implemented as a HF-choke made of a copper-wire coil wounded around a ferrite core, and the resistor is a low-value, high-power one.

5 TUBE’S FILAMENTS HEATING.

The filaments 65 are necessary to help start the ionization process of the compound heavy-metal and complex gas structures inside the tube’s rarefied low-pressure vacuum that finally starts to break its initial high impedance state (due to the initial presence of a high-voltage differential potential) in 10 order for an arc to develop across its length and thus starts the lamp 60 (strike phase).

The high current burst that immediately follows -as the impedance of the lamp instantly decreases dramatically- excites the mercury gas inside with 15 enough energy as its free electrons are able to release visible light-bearing photons as they collide with the atoms of the phosphor coating inside.

Finally, after a few seconds, when the lamp has reached its optimal balanced temperature, it automatically acquires its natural steady-state phase, developing its specifically-designed public parameters, such as its normal 20 running current, nominal power rating and stated luminance output.

This situation is normally referred to as a CFL’s cold start-up.

The hard-metal filament’s core-base are themselves coated with a chemical 25 substance that favours the emissions of primary-source electrons as to greatly facilitate the reliable but complex series of processes that finally bring the lamp to its strike phase. Therefore their integrity, or otherwise the lack of it, is the weakest link in the tube, and they constitute mainly the initial load when the driving electronics are started as the mains power is initially 14 applied to the lamp: the filaments 65 take an initial substantial stress each time the lamp is powered up.

Eventually, with time and the repeated power-ups, the special chemical 5 coating on the filaments 65 begin to literally peel off due to the normal wear and tear of the inter-collision of atoms and electrons due primarily to the relative big surge start-up and (although at a much lesser rate) the normal arc AC currents (back and forth) from end to end of the tube.

10 This has the effect of start pitting the sensitive coating, exposing the bare hard-metal and, at this stage, the deterioration of the filaments 65 continuing to occur at an accelerated rate, until eventually one (or both) breaks up and an open filament situation develops.

15 As to add further value to the features already described in this specification, it is herewith proposed to add a constant filament heating circuit 140 that will not only facilitate the initial emission of source electrons, but will soft-start the CFLs with much less electronic overall stress, which will help to keep the integrity of their filaments 65 (as their coatings will be less prone to 20 the rate of pitting otherwise occurring with the cold-start situation) and therefore, as a great bonus to the consumer, extends substantially their normal useful life expectancy, more particularly when dimming is applied.

The inductance of the choke and the start capacitance values define the 25 resonant frequency-circuit that builds-up the required high voltage necessary to generate the necessary initial hurst of arc-current that will start the lamp.

As long as the resonance point is not achieved, the lamp will not have a enough high-voltage to start-up; therefore, if for some brief time (while at the 30 same time some current is allowed to pass through both filaments 65) their 15 naturally low cold resistance will steadily increase, automatically pre-heating them by circuit 140 and will start to generate source electrons just prior to the initiation of the ignition phase.

5 To realize that important condition during this initial phase, heating supply current for both filaments 65 is obtained from a transformer configuration built-in within the ballast coil assembly: two independent small-turn coils 140 are added electrically independent and in parallel with each filament.

10 After the lamps strike, and from now-on until the overall mains power supply to the lamp is interrupted, the filaments 65 will always be provided with their heating current, even in the case the lamp has apparently extinguished (due to over-extension of its useful dimming range, or maybe due to a sudden or progressive drop in ambient temperature), as their internal oscillator still 15 will be operational. This can substantially improve a dimmed CFL’s lifetime.

Therefore, a residual AC current will still pass through the filaments 65 (as the driver electronics are still powered, although with lower incoming mains current), as to keep them still in a relative warm situation. A small increase 20 in the input supply mains current (usually just by tweaking upwards the dimmer’s control pot.) will then normally be enough to soft-start and re-ignite the lamp, safely and with no electronic stuttering (no apparent flickering) whatsoever, thus avoiding a filaments 65 wearing, continuous cold restarting, vicious-circle condition of popular previous designs.

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Accordingly, it is shown that the dimmable energy saving lamp preferably comprises a gas tube 60 filament heating circuit. The heating circuit may be provided by small-turn coils that are added electrically independent and in parallel with each filament; arranged in transformer configuration built-in 30 within a ballast coil assembly 45’.

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LED EMBODIMENT

Figure 6 shows a schematic embodiment, wherein the dimming circuit is 5 arranged for driving a (H-B) LED 70.

Basically, a LED 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 normalized current has a tight 10 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.

15 Its normal operating voltage is relatively very low (only a few volts) and once it is progressively achieved (i.e.: as a slow rise from 0 Volts can testify), it will remain relatively 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.

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

25 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.

30 17

For a discussion of block elements 10-40, reference is made to Figure 1. In addition, for driving the HB-LED 70, block element 50 references a high-frequency AC to DC rectifier and ripple-compensation network.

Since the LED devices are essentially unipolar in their normal operational 5 drive requirements, a high frequency and efficient AC to DC conversion is 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.

10

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

In order to extend to its maximum dimming performance capabilities of the 15 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 generally 20 smoother transitional operation of the dimmer controller itself, as it is exercised throughout its full range.

Figure 7 refers to a detailed block diagram showing practical implementation of the device. Accordingly, there is shown a high-frequency switching-mode 25 ballast device 200 for a dimming circuit, the ballast device 200 comprising a bridge rectifier section 20 having an AC input 201; 202 and a DC bridge rectifier output 203; 204; a high frequency oscillator circuit 40 including a ballast coil assembly 45, coupled to the DC bridge rectifier output 203; 204; and further comprising a power factor corrector circuit 30 as specified 30 previously.

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While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is 5 not limited to the disclosed embodiments.

Although a specific type and specific power (“prototype-quality”) CFL can be constructed “ad-hoc” to assess the real-world application of the principles disclosed in this document, the integration of all and/or some of the 10 enhancements can be favourably combined with any standard design (as has been the aim of this document), and can be extended and applied successfully across a wide-board of all “production-ready” CFLS, and higher-power electronic ballast, as well, that are at the core of all modern and energysaving luminaries, (including the h.v. LED ones), of any topology and/or any 15 power; the only obvious concern being the correct assessment of the proportional extrapolation final values -and ratings- of the components involved.

Other variations to the disclosed embodiments can be understood and 20 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 fulfil the functions of several items recited in the claims. The 25 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. Any reference signs in the claims should not be construed as limiting the scope.

Claims (14)

A high frequency switching mode ballast (100, 200) for a dimming circuit, the ballast (100, 200) comprising: 5. a bridge rectifier section (20) having an AC input; a DC bridge rectifier output; and a reservoir capacity (33) connected in parallel to the DC bridge rectifier output; - a high frequency oscillator circuit (40) with a ballast coil assembly (45) coupled to the DC bridge rectifier output; and further comprising - a power factor correction circuit (30) arranged as a frequency modulated electronic switch (31) in series with the reservoir capacity (33) to switch the reservoir capacity with increasing frequency; and a frequency modulator circuit (32) coupled to the ballast coil assembly (45) to switch the reservoir capacity 15 with the drive frequency of the ballast coil assembly (45). The ballast according to claim 1, further comprising a resistor network (10) coupled in parallel to the DC bridge rectifier input. 20 The ballast as claimed in claim 1, wherein the dimming circuit is of a phase-cut off type. The ballast device according to claim 1, wherein the dimming circuit 25 comprises a triac. The ballast device according to claim 1, further comprising an LED device (70). A dimmable energy-saving lamp comprising a lighting device and a high-frequency switching mode switching device (100) according to one of claims 1 to 5. A dimmable energy-saving lamp according to claim 6, wherein the lighting device is an LED device (70). A dimmable energy-saving lamp comprising: - a light-converting low-pressure gas tube (60) comprising filaments (65) adapted to start the tube-light conversion process; - a high frequency switching mode ballast (100) according to any one of claims 1-5. 10 The dimmable energy-saving lamp according to claim 8, further comprising a low-pass filter (25) comprising an induction element L1 connected in parallel to the power factor correction circuit (30) to provide a low-pass filter. 15 The dimmable energy-saving lamp according to claim 8, further comprising a resistor network (10) coupled in parallel to the DC bridge rectifier input to couple to a dimming circuit. The dimmable energy-saving lamp according to claim 8, further comprising a gas tube (60) filament heating circuit (140). 12. The dimmable energy-saving lamp according to claim 11, wherein the heating circuit is supplied by small rotary coils (140) arranged electrically independently in parallel to each filament; arranged in transformer configuration and built-in within the ballast coil assembly (45 '). A dimming circuit comprising: - a phase-cut-off dimmer section to be connected to AC mains voltage; and - a high frequency switching mode ballast (100, 200) according to any one of claims 1 to 5. The dimming circuit of claim 13, further comprising a DC-AC conversion section coupled to the power factor correction circuit and providing AC output points for the dimming circuit.