FIELD OF INVENTION The invention generally in t e field of power control of domestic and industrial luminaries of old and next generation technologies. More specifically the invention refers to an electronic circuit means for dimming a lamp-.

BACKGROUND TO THE INVENTION

Dimmers for incandescent lamps have been available in the marketplace for several decades now, and although rather noisy and prone to mechanical and electrical failure, have been the most accepted -albeit restricted- price/performance option for the general public.

This basic kind of dimmers have as their core-control element a specific designed electronic gated-switching device (a semiconductor thyhstor) commonly named as a "TRIAG". This inac is generally made to .switch on and off the load at certain angle of the AC mains cycle by a simple R-C delay network loosely reference to the points of its reverse voltage polarity change, or so called "zero-crossing".

At full brightness the resultant energy that the dimmer applies to the load Is closely related to the sinusoidal wave-front at its input side, but as the dimmer is advanced, its conduction angle becomes restricted and this results in a chopped AC voltage with several negatives consequences if the impedance of the load is not perfectly "resistive".

I The light source of incandescent lamps are generally made of a material ("tungsten") with- the physical properties of a linear resistive element: means that, when a certain instantaneous voltage Is applied to them, an Instantaneous directly proportional currant Is generated across the light-emitting element and with a co-related phase of that of the applied voltage, thus voltage and current are always "m-phase".

In an incandescent lamp the load-element converts the exciting electrical AC energy into heat and light whose power delivery is averaged fairly well by its highly resistive native properties, therefore a smooth transition of lumen. Intensity can be expected across the full range of different settings of the iriae-based, also called "phase-cut" dimmer. With the progress in lighting technology (and under continuous global pressure to develop more energy-efficient transducers) other kinds of lamps have become popular, namely fluorescent lamps (F-L) and, lately, the high-power light-emitting diodes (LED-L) lamps. Both these lamps are no longer made of a simple, single resistive element but consists of several components (sometimes a few dozen) with very different and disparate electrical 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.

With the newer light sources the impedance (Z) becomes "complex', meaning that other factors are affecting it. The power supply Is therefore now presented with a combination load of "resistive" AND "reactive" elements. This 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 the so called "power-factor" of that specific load. Power factor (PF),1s defined as the cosin of the phase-angle between the ad'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 ail the energy that is supplied is consumed by the bad (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 AC supply (in standard reticulation distribution, meaning 50 or BO Hz). 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 0, the less real power is available in the load transducer circuit to do work efficiently.

Whereas incandescent lamps are purely-resistive loads, FLs and high-power LEDs amps Include some substantial capacitive reactance themselves. Their PF is "poor" due to the resulting V/l 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 generall not suitable for dimming these "poor" PF lamps. As this phase-cut 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 grate V/1: phase- shift, a dramatic reduction of the originaily inherent "poor" PF that this type of lamps have, and finally, an ncreased 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 them below 50% (of their nominal maximum power output).

Various attempts have been made to provide dimmable FL and high-power LED lamps.

These are -already available in the market-place, although at a price premium.

In. contrast, the object of the present Invention is to provide electronic means to control the luminance of the standard, so-called ^{' '} "non-dimmabie" tamps, in a fashion that is simple, reliable and cost-effective. It will be highly desirable If the consumer could bu "off-the-shelf non-dimmable lamps to be used with a better- engineered centralized dimmer thai is common ^" to all kinds- of different generation luminaries present in one room and that could be generally available as a. good price/performance alternative against the cost of upgrading to multiple, costly premium-priced "dimmable" lamps.

■ SU MA Y OF THE PRESENTED INVSMTIOM

A-s was outlined in the above paragraphs, the main shortcoming of the present, so called, "state of the art", iriac-based dimmers Is their Inherent progressive distortion of the Incoming sinusoidal energy that the public utility supplies to the general public, as the dimmer Is advanced to restrict the power delivered to- the lamps. Therefore any means to counter-act that ποη- esirab!e side-effect of conventional dimming must be pursued and welcome by both the consumer and the utility supplier. The Invention presented here aims to satisfy the public requirement for "energy- saving" solutions and to draw benefit from commercial and industrial initiatives to reduce energy consumption.

Thus, according to the Invention, there is provided a general purpose dimmer with an inherently Improved power factor (PF) over any of the present phase-cut variety, said dimmer being configured to appear to the incoming sinusoidal energy as progressively more "resistive" as the dimmer is advanced and it further restricts the power through It Thus, the Invention provides a dynamtc-adaptive-resisllve-behaviour at the core of its power-factor compensation technique as described below and illustrates In the examples that follow.

The general purpose dimmer may thus Include a hybrid Power Facto Correction (RFC) network having two parts

- a passive or static P ^' FG; and

- an active or dynamic RFC.

The network may act at the source of the power.

The passive or static RFC may be embodied by a permanent fixed resistor of a relative high value placed In parallel with the load port of the dimmer. This may give the new dimmer a better overall resistive-load character that mainly acts as a starting RF improving device when the dimmer is generally not advanced (typically right after power-up) and there is no initial significant restriction of the current delivered to the load through it. The active or dynamic PFG may be embodied by a senslng-adapiiye-swlfchmg network of active and passive components, placed in parallel with the toad port of the dimmer, so that it acts to bring a progressive-compensation PF-correction effect, as the dimmer is progressively advanced, restricting more and more the power delivery to the load.

According to an embodiment of the invention, an electronic circuit means for improving a power factor of a load In response to a dimmer, in particular during dimming of a lamp with a variable phase cut dimmer, Is provided. The electronic circuit means comprises network, which is connected parallel to the dimmer and the load, including a static part and a dynamic part, wherein the dynamic part Is embodied by a network of active and passive components being placed in parallel with the load and restricting the power delivery to the load as the dimmer Is progressively advanced.

The static pari may be embodied by a resistor. The resistor of the static part may be selected in the range between IDkQ and 1 Mil, preferably in the range between iOOkO and SOOkO.

The network of the dynamic part may include a first active component with a first power resistor and a second active component with a second power resistor which are controlled so as to distribute the current through the respective power resistors according to a voltage at the output port of the dimmer.

The voltage at the output port of the dimmer may be rectified by a rectifier preferably by a full-diode bridge so as to retrieve a peak voltage.

A control voltage may be formed from the peak voltage, which is connected to a voitage-divkllng network. The output of the voltage-dividing network may be connected to a first terminal of zener diode. A second terminal of the zener diode may be connected to a control terminal of the second active component. A control terminal of the first active component may be connected to the second power resistor and the second active component. The first power resistor may be connected to the second power resistor and the first active component.

The first active component may be formed as a bipolar transistor. The second active component may be formed as a FET.

The first power resistor may be selected with a resistivity being lower than the resistivity of the second power resistor. The voltage divider may he designed as such that the zene diode Inverse- blocking voltage value is broken for high voltages at the output port of the dimmer.

The first active component may be conductiv for low voltages at the output port of the dimmer. The second active component may foe conductiv for high voltages at the output port of the dimmer. The first active component: and the second active component may foe conductive for intermediate voltages at the output port of the dimmer. The dynamic par may be connected to a change-over switch so as to select AC- driven or DC-driven loads.

A DC-link may be included between the dynamic part and the change-over switch. The DC-link may comprise a diode and a, preferably polarised, capacitor. The invention can be further described, without limiting the scope of the Invention, with reference to the accompanying figures referred to herebelow.

BRIEF DESCRIPTION OF THE DRAWI GS

Figure 1 depicts a schematic diagram of an embodiment of the invention.

Figure 2 depicts the schematic diagram of Fig. 1 in more detail.

Figure 3 depicts the schematic diagram of Fig. 2 in more detail.

Figure 4 depicts schematic diagram of a further embodiment of the invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION The- below is a non-limiting explanation of the embodiments of the invention.

Figure i refers;

Generally speaking, there are two techniques for the Improvement of the PF of any AG load or "power-factor-correction" (RFC): "active RFC" and the "passive RFC". We intend, to present here in this document a new kind of integrated RFC (permanently attached to this new dimmer) we'll call "a hybrid-technique RFC" (2), that means a combination of active and passive components combined and acting together as a "PFOimproving network" which acts "at-source ^* . meaning: 'INTEGRATED AND EMBODIED WITH THE DIMMER" (I).

Figure 2 refers:

In the scope of this present invention this hybrid network have two parts: one "passive" or "static" and other thai is "active" or "dynamic". The passive/static part (3) is embodied b a permanent fixed resistor of a relative high value placed- in parallel ^' with the load port of the new dimmer according to the present Invention. This gives the new dimmer a better overall resists ve-ioad character that mainly acts as a starting PF improving device when the dimmer is generally not advanced (typically right after power-up) and there is no initial significant restriction of the current delivered to the load through It.

The active/dynamic part (4) is embodied by a senslng-adaptive-swltching network of active and passive components, placed In parallel with the load port of the new dimmer, that acts to bring a "progressive-compensation PF-correction" effect, as the dimmer is progressively advanced, restricting more and more the power delivery to the load.

Figure 3 refers:

The passive/static embodiment part (3), according to the presented invention, Is a single resistor (5), Being in the lower 100's of kilo-ohms value ^' ,- it does not need to be of a very high wattage rating, although it can, at times, be subjected to the full amplitude of the AC incoming voltage, and as such has to be rated accordingly (but not more than 2 watts, approximately).

The active/dynamic, part (4) functions as follows:

There is an electronic "progressive analogue curren path selector device" formed by _. the active components (S) and (7) thai work in. "tandem" so as- to distribute the current through two power resistors (8) and (9) according to the amplitude of the peak voltage at the output port of the dimmer.

The AC output voltage is tlrsf rectified by a full-diode bridge (10) to retrieve the said peak voltage. A control voltage is formed from this point and is sensed by the voltage-dividing network (11) and (12). A proportion of the control voltage is therefore applied to the anode of a low-voltage value zener diode ( 3).

As to summarize the functionality of this adaptive RFC we'll describe only three main "situations"; dimmer at maximum, dimmer at minimum and dimmer in intermediate setting.

When the voltage at the output (load) port of the dimmer is at its AXI UM _* the voltage divider is designed as such that the proportional sampled voltage is of such instantaneous magnitude that breaks the zener diode (13) inverse-blocking voltage value most of the time.

"Most of the time ^" -In this Instance- refers to the part of the period of that the instantaneou proportional AC sampled voltage is of enough amplitude as to "break" the zener "barrier.

A significant- periodic - voltage Is then presented at the gate of the FET transistor (7) as to make its resistance from its source to its drain to be of a very low value. Therefore we can safely assume that, most of the time its drain terminal is at (or very near) the 0V potential (or "return" or "common") of the adaptive embodiment (&). The bipolar transistor (6) has, a well, its base terminal at near common potential and it is in a non-conductive state most of the time. And most- of the time the "adaptive resistive network" formed by the series of a lower (8) and a higher- value resisto (9) is of a total HIGH K-ohm- magnitude.

The total power dissipation of the resistive network (8+9) In this situatio (as a result of the common average current path magnitude trough BOTH of them) is therefore divided between the two resistors. Only low-wattage resistors are required in this embodiment.

0 When t e voltage at the output (load) port of the dimmer is at its INIMUM, the voltage divider Is designed such that the proportional sampled voltage is of such instantaneous magnitude that DOES NOT breaks the zener diode {13} inverse- blocking voltage value most of the time.

' vlost of the time" - in this instance - refers to the part of the period of thai the ^• instantaneous proportional AG sampled voltage is of NOT enough amplitude as to "break" the zener "barrier". Little or NOT ENOUGH significant periodic voltage is then presented at the gate of the FET transistor (7) as to make its resistance from its source to its drain to be of a very HIGH value.

Therefore we can safely assume that, most of th time (If not permanently) the FET transistor (7) is in an OFF state and its drain terminal Is MOT near or at the OV potential (or "return" O "common") of the adaptive embodiment (e). The bipolar transistor (8) does NOT have, as well, its base term in a 1 at near common potential and it is now in a conductive state most of the time (if not permanently ON). And most of the time the "adaptive resistive network" formed by the series of a lower (8) and a higher-value resistor (9) is now of a total LOW -onm magnitude.

The total power dissipation of the resistive network (8+9) in this situation is st!!i very low (as a result of mainl low average collector current of the now assumed permanent ON bipolar transistor due to the much lower peak voltage supplied by the dimmer). In this situation, it is clear that only low-wattage resistors are required In this embodiment. in any INTERMEDIATE setting of the dimmer we could safely assume that a smooth transition between both extreme instances occurs as the dimmer Is advanced from its maximum to its minimum setting. The adaptive process necessary to automatically compensate for the PF Is then realized in the embodiment of the present Invention ,· as described above.

Fig. refers;

5

A further variation of the present invention is the integration of a smoothing Delink (14) and switch-over {15} stages that improves the stability of CFL at low levels of dimming and also eaters for those lamps that require to be supplied with a DC voltage,

ID

A provision have been made to Integrate the present invention to be made compatible with the latest generation of analogue and digitally controlled dimmers that use integrated circuits as their core technology, therefore the present invention realizing a true universal power controller lor any kind of luminaries.

15

The smoothing DC-link is realized by an Isolation rectifier diode (16) and polarized capacitor (17), The values of these components are rated according to the different stated maximum power capacity ("wattage") of the universal dimmers embodiments and therefore must be specified accordingly,

20

A double-pole double-throw change-over switch (18) can select the different application lamps, AC-djiven (position "A"), or DC-dhven (position "8").

For a smooth transition, when required, an equalizer power resistor of a few Kilo- 25 ohms (19) is permanently attached as a constant resistive load to the DC-link.