EP3440892A1 - Method of reducing the harmonic content of the currents sunk by led strings driven by an integrated "direct ac" power supply and apparatuses associated to the method - Google Patents

Method of reducing the harmonic content of the currents sunk by led strings driven by an integrated "direct ac" power supply and apparatuses associated to the method

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Publication number
EP3440892A1
EP3440892A1 EP16731678.5A EP16731678A EP3440892A1 EP 3440892 A1 EP3440892 A1 EP 3440892A1 EP 16731678 A EP16731678 A EP 16731678A EP 3440892 A1 EP3440892 A1 EP 3440892A1
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EP
European Patent Office
Prior art keywords
led
initial
segment
power supply
led segment
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EP16731678.5A
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German (de)
French (fr)
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EP3440892B1 (en
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Adrian Ioan RUS
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Individual
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Individual
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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/40—Details of LED load circuits
    • H05B45/44—Details of LED load circuits with an active control inside an LED matrix
    • H05B45/48—Details of LED load circuits with an active control inside an LED matrix having LEDs organised in strings and incorporating parallel shunting devices
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/30—Driver circuits
    • H05B45/355—Power factor correction [PFC]; Reactive power compensation
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/30—Driver circuits
    • H05B45/36—Circuits for reducing or suppressing harmonics, ripples or electromagnetic interferences [EMI]

Definitions

  • the invention relates to a method of reducing the harmonic content of currents sunk from the AC grid by light emitting diodes strings driven by low power constant current integrated power supplies (this type of power supplies will be referred to as "Direct AC"), not compliant with the EN61000-3-2 harmonic standard, in order to become compliant with said harmonic standard and therefore to became scalable, i.e. to allow parallel connection of multiple power supplies in order to obtain higher power supplies compliant too with said harmonic standard, and also relates to a series of apparatuses compliant to said harmonic standard.
  • LED is the abbreviation of the light emitting diode.
  • LED lighting technology is maturing fast, in the last 2 years becoming commercially available over 10 direct AC integrated circuits (abbreviated: IC).
  • Direct AC technology is attractive because of its low cost, of its simplicity allowing the manufacturing of complete light engines on single printed circuit boards, because of lack of reactive components and due to its good electric parameters: high electrical efficiency (typically 90%) and good power factor (typically higher than 0.95).
  • Figure 3 exhibits the time domain variation of the current sunk by the apparatus in Figure 1 and Figure 4 exhibits its harmonic content together with the individual harmonic limits, as they are set by the EN61000-3-2 harmonic standard. Acknowledging the standard is only recommended for powers lower than 25W but is mandatory for powers higher than 25W, a lighting apparatus having a rated power higher than 25W and manufactured by simply scaling of any number of not compliant and low power direct AC integrated power sources, is still not compliant and not usable.
  • the not compliant harmonic content is mainly due to the fact that given technological and practical reasons, the ratios of currents sunk by the integrated circuit from the grid is fixed, having the first step/current jump of higher value relative to next steps, Which condition a relatively tight ratio of number of LEDs that make up each of the 4 LED segments.
  • Each LED segment includes one LED device or a plurality of LED? devices, which are connected to each other in series. Needless to say, a plurality of LED devices can be connected to each other in series inside a LED package as the LED segment.
  • Each LED segment can include an arbitrary number of LED devices (at least one LED device).
  • the LED device can be a single LED chip, or a single package including a plurality of collectively-arranged LED chips.
  • that fixed currents ratio requires the approximate number of LEDs of each constituent segment Si, ...,S 4 as following: S! contains about 55 LEDs, S 2 contains about 18 LEDs, S 3 contains about 16 LEDs and S 4 contains about 6 LEDs.
  • S! contains about 55 LEDs
  • S 2 contains about 18 LEDs
  • S 3 contains about 16 LEDs
  • S 4 contains about 6 LEDs.
  • the example is not limitative, and the LED segments may also contain other combinations of numbers of LEDs.
  • the fixed ratios of sunk currents (61/77/94/100) in conjunction with the high level of the first sunk current, requires on one hand the LED segment Si to contain a large number of LEDs, which in turn determines the apparatus to start sinking current later, with a delay greater than 1 .3ms from the zero crossing of sine grid voltage, and on the other hand, it makes the first step / current jump, corresponding to segment Si to be much higher (about 3-fold) than the following steps/levels of sunk current; both effects (late entry into conduction and the first current step of higher value relative to next steps) contribute decisively to the increased levels of odd harmonics of the sunk current, thus exceeding the limits imposed by EN61000-3-2 standard.
  • the technical problem solved by the invention is the decrease of the harmonic content of the currents sunk by direct AC power sources driving LED strings below the limits required by EN61000-3-2 standard.
  • the method according to the invention of reducing the harmonic content of the currents sunk by at least one primary direct AC power supply integrated circuits driving a LED string circuit divided into several LED segments, comprises the steps of adding to the circuit at least one secondary direct AC power supply integrated circuits and reshaping the shape of current sunk by the primary and the secondary direct AC power supply integrated circuits by transforming the LED string from a LED string divided in an initial lower number of LED segments into a LED string divided in a higher number of LED segments, through splitting the first initial LED segment into several additional LED segments and separately driving the additional LED segments by the at least one secondary direct AC power supply integrated circuits.
  • the life time of the power supply has the same order of magnitude to the lifetime of the LEDs.
  • Figure 1 is a circuit schematic diagram showing a known light engine with the LED string driven by a 4 LED segments low power integrated direct AC power supply.
  • Figure 2 is a circuit schematic diagram showing the known scaling method, used to increase the rated power
  • Figure 3 is a graph showing the time variation of the current sunk by the apparatus in Figure 1
  • Figure 4 is a graph showing the frequency spectrum of the current in Figure 3
  • Figure 5 is a circuit schematic diagram showing the wiring of a first preferred embodiment of a LED lighting apparatus according to the invention, having its first initial LED segment ST divided into four additional LED segments
  • Figure 6 is a graph showing the time domanin variation of the current sunk by the apparatus in Figure 5
  • Figure 7 is a graph showing the frequency spectrum of the current in Figure 6
  • Figure 8 is a circuit schematic diagram showing the wiring of a second preferred embodiment, consisting of the scaling of the power supply in Figure 5 according to the invention, having its first initial LED segment Si divided into four additional LED segments
  • Figure 9 is a circuit schematic diagram showing the wiring of a third preferred embodiment as an alternative example of scaling of the power supply in Figure 5, according to the invention, having its first initial LED segment Si divided into three additional LED segments
  • Figure 10 is a circuit schematic diagram showing the wiring of a fourth preferred embodiment as an alternative example of scaling of the power supply in Figure 5, according to the invention, having its first initial LED segment Si divided into two additional LED segments
  • the method of reducing the harmonic content of the current sunk by at least one primary direct AC power supply integrated circuits IC I L IC1 2 ,..., IC1 n driving a LED string circuit divided into several LED segments is comprising the steps of adding to the circuit at least one secondary direct AC power supply integrated circuits ⁇ C2i , IC2 2 ,..., IC2 n and reshaping the shape of the, current sunk by the primary together with the secondary direct AC power supply integrated circuits IC1 i, IC1 2 ,..., IC1 n ; IC2i , IC2 2 ,..., IC2 n by transforming the LED string from a LED string divided in an initial lower number of LED segments Si , S 2 , S 3 , S into a LED string divided in a higher number of LED segments; through splitting the first: initial LED segment Si into several additional LED segments S-m , Si ⁇ , Sif3, Sif 4 and separately driving the additional LED segments Sm , S
  • the method according to the invention is not limited to a particular split in additional LED segments.
  • the first initial LED segment Si can be split into two, or three, or four, or more additional LED segments.
  • Figure 5 exhibits the wiring diagram of a first preferred embodiment of a LED lighting apparatus powered directly from the public grid, associated to the method according to the invention and comprising:
  • a bridge rectifier PR whose "positive" output is series connected to the anode of a string of series connected LEDs divided into four initial LED segments Si , S 2 , S 3 , S 4 , a primary direct AC integrated power supply IC1 whose internal current sources are connected respectively to the anode of the first LED of the second initial LED segment S 2 , respectively to the anode of the first LED of the third initial LED segment S 3 , respectively to the anode of the first LED of the fourth initial LED segment S 4 , respectively to the cathode of the last LED of the string (i.e. of the fourth initial LED segment S 4 ), in which the GND pin of the primary direct AC integrated power supply IC1 , the cold end of its current set resistor R1 and the "negative" output of the bridge rectifier PR are connected to ground,
  • the initial LED segments Si, S 2 , S 3 and S 4 are successively and sequentially switched in by the primary direct AC integrated power supply IC1 and at the decrease of voltage U A B below the respective threshold voltages of the initial LED segments, the initial LED segments S 4 , S3, S 2 and Si are successively and sequentially switched out by the primary direct AC integrated power supply ICT
  • the apparatus also comprising a circuit element Z fitted between the first initial LED.
  • segment S-t and the second initial LED segment S 2 thus the initial LED string becoming split in: a first LED segment Sm, a second LED segment Si f2 , a third LED segment Si f3 , a fourth LED segment S1f4, the circuit element Z, a fifth LED segment S 2 , a sixth LED segment S3 and: a seventh LED segment S ,
  • the apparatus further comprising a secondary direct AC integrated power supply IG2 whose internal current sources are. connected to the taps between the first LED segment Sm and the second LED segment Si f2 respectively between the second LED segment Si f2 and the third LED segment S 1f3 , respectively between the third LED segment Si f3 and the fourth LED segment Sif4, respectively between the fourth LED segment Si f4 and the circuit element Z, where the GND pin of the secondary direct AC integrated power supply IC2, together with the cold end of its set resistor R2 are connected to the tap between the circuit element Z and the fifth LED segment S 2 .
  • a secondary direct AC integrated power supply IG2 whose internal current sources are. connected to the taps between the first LED segment Sm and the second LED segment Si f2 respectively between the second LED segment Si f2 and the third LED segment S 1f3 , respectively between the third LED segment Si f3 and the fourth LED segment Sif4, respectively between the fourth LED segment Si f4 and the circuit element Z, where the GND pin of the secondary direct AC integrated power
  • the circuit element Z on which falls the minimum voltage required to bias the internal circuitry of the direct AC integrated power supply IC2, may be a resistor, a few volts reverse polarized zenner diode or even a forward biased LED.
  • the aditional LED segments Sm, Si f2 , Si f3 , and Si f4 are successively and sequentially switched in by the secondary direct AC integrated power supply IC2, and at the decrease of voltage UAB below the respective threshold voltages of LED segments, after the successive and sequential switch out of the initial LED segments S 4 , S 3 , S 2 and Si (Si now split in additional LED segments S-m, Si f2 , Sif3, Si f4 ) by the primary direct AC integrated power supply IC1 , the aditional LED segments Si f4 , S-
  • the level of sunk current levels is selected the number of LEDs consisting each additional LED segment, so that the current sunk by the apparatus to vary in steps, approximately linearly over time, as seen in Figure 6.
  • the number of LEDs in each additional segment resulting in the sunk current variation as shown in Figure 6 is: Sm contains 15 LEDs, Si f2 contains 18 LEDs, Sif3 contains 9 LEDs, Si f4 contains 6 LEDs and circuit element Z contains 1 single LED.
  • the division of the LED segment S ! in four additional LED segments as shown above is not unique, several divisions being possible, as well as several levels of set currents sunk by IC2; the frequency harmonics of sunk current given the variation indicated above are compliant to harmonic standard.
  • Each LED segment can include an arbitrary number of LED devices (at least one LED device).
  • the LED device can be a single LED chip, or a single package including a plurality of collectively-arranged LED chips.
  • the LED segments may also contain other numbers of LEDs, including but not limited to an equal numbers of LEDs in each initial LED segment (except for S-i) and any additional LED segment.
  • the initial LED segment Si may include 54 LED chips divided in 4 additional LED segments as following: aditional LED segment S-m includes 21 LEDs, and each of the following additional LED segments Sif2, Sif 3 and Sif 3 includes 10 LEDs, or all LED segments may include an equal number of LEDs.
  • the AC grid voltage passes through zero. It is also considered that at the AB terminals it is applied a 230Vef and 50Hz sinusoidal AC voltage.
  • the LEDs threshold voltage is about 2.8V and respectively the forward directional (anode to cathode) voltage drop at nominal current is about 3.2V.
  • the apparatus does not sink any current from the grid.
  • the UAB voltage By increasing the voltage UAB between 0 Volts and up to 42V (the threshold voltage of LED segment S-m is 42V, 15LED x cca. 2.8V) the apparatus does not sink any current from the grid.
  • the UAB voltage By further increasing the UAB voltage over the threshold voltage of Sm , through LEDs that constitute the segment Sm it starts flowing a current determined by the voltage to current characteristic of the 15 LEDs constituting the segment S m ⁇ the current flowing through the circuit closes to the ground via the internal current source of IC2 which is connected between its terminals; ⁇ and Rext, through the set resistor R2, through the : internal current source of IC1 which is connected between its terminals ⁇ and Rext and ⁇ • through ; the set resistor R1
  • the variation (increase) of the UAB voltage translates into the variation (increase) of the voltage drop at the IC2 terminals.
  • the threshold voltage of LED segment Si f2 about 50.4V, 18LED x 2.8V
  • the LED segment Sif 2 starts flowing a current passing through the internal current source of IC2 connected between the terminal ⁇ 0 ⁇ 2 and R ex t, through resistor R2 and closing to the ground on the same route as the current sunk by IC2 through ⁇ 0 ⁇ ⁇
  • the current sunk through the terminal ⁇ decreases by an equal amount so that at U A B voltage the current sunk by the terminal ⁇ 0 ⁇ drops to zero.
  • the current flowing through the additional LED segments Sm and Si f2 of the initial LED segment S-i, Sm and Si f2 now connected in series increases up to the current level set and limited ⁇ 0 ⁇ 2 , namely 23.3mA.
  • the current passing through the circuit element Z also closes to the ground via the terminal IOUTI-ICI, Rext and ' resistor R1 so the sum of the current flowing through the circuit element Z and 30mA will be limited to the first level set by IC1 which in this exemplary embodiment is 36,7mA. .
  • the primary direct AC power supply IC1 operates classically, successively sinking the current in well-established constant levels through the already switched in additional LED segments that constitute the initial LED segment S1 , as well as through the sequentially switched in initial LED segments S 2 -S 4 .
  • the apparatus both successively switching out the initial LED segments as well as the additional LED segments that constitute the initial LED segment Si in reverse order, and sinking a descending current in the same well established constant levels and at the same well-established moments in time.
  • Figure 6 exhibits the time domain variation of the current sunk by the apparatus in Figure 5
  • Figure 7 exhibits the frequency spectrum of the current sunk by the apparatus in Figure 5 where it is seen that its harmonics are lower than the limits set by EN61000-3-2
  • Figure 8 exhibits a circuit schematic diagram showing the wiring of a second preferred embodiment consisting of the scaling of the power supply in Figure 5, according to the invention, having its first initial LED segment Si divided into four additional LED segments.
  • Figure 9 is a circuit schematic diagram showing the wiring of a third preferred embodiment of a LED lighting apparatus powered directly from the public AC grid as an alternative example of scaling the power supply in Figure 5, associated with the method according to the invention which differs from the wiring diagram shown in Figure 8 as follows:
  • the first initial LED segment Si is divided into three additional LED segments Sm ,
  • circuit element Z is serially connected between the second initial LED segment S2 and the third initial LED segment S3
  • all LED segments Sifi , Sif2, Sif 3 , S 2 , S 3 and S 4 may have an equal number of LEDs.
  • Sm , Sif2, Sif3, S2, S3 and S 4 may each have 14 LEDs; the number of LEDs in the LED segments is not limited to 14, it varies between 13 and 16 depending on the maximum grid voltage; thus, at rated power, the direct forward voltage drop for all the LEDs connected in series in the string has to be equal to or slightly smaller than the maximum, peak voltage, of the grid at nominal voltage.
  • Figure 10 is a circuit schematic diagram showing the wiring of a fourth preferred embodiment as an alternative example of scaling of the power supply in Figure 5, associated with the method according to the invention which differs from the diagram in Figure 8 as follows:
  • the first initial LED segment Si is divided into 2 additional LED segments Sm, Sif2
  • circuit element Z is serially connected between the third initial LED segment S 3 and the fourth initial LED segment S 4
  • each of Si f1 , Sif 2 , S 2 , S 3 and S 4 can consist of 19 LEDs.
  • the internal current sources of the at least one secondary direct AC power supply integrated circuits IC2i, IC2 2 ,..., IC2 n are connected to the taps between the first LED segment Sm and the second LED segment Si f2 , respectively between the second LED segment S-i f2 and the third LED segment Si f3 /S 2 , respectively between the third LED segment S 1f3 /S 2 and the fourth LED segment Si f4 /S 2 /S 3 , respectively between the fourth LED segment Si f /S 2 /S 3 and the circuit element
  • the total number of the primary direct AC power supply integrated circuits IC11. IC1 2 , - ⁇ > may differ from the total number of the secondary direct AC power supply integrated
  • Z is connected between the last LED segment driven by the secondary direct AG power supply integrated circuits (loiru in that case) and their GND pin, together with the cold terminal of the set resistor of these secondary direct AC power supply integrated circuits.
  • the advantage of splitting the initial LED segment Si into four additional segments Si f i,Si f2 , Si f3 ,Si f4 is obtaining maximum performances in terms of the harmonic content of the current sunk; namely, the harmonic content of the current sunk is the lowest possible.
  • the harmonic content of the current sunk remains in accordance with the EN61000-3-2 standard but the cost of the associated apparatuses is much lower given the possibility of using exclusively cheaper multichip packaged LEDs.

Abstract

The invention relates to a method of reducing the harmonic content of the current sunk by at least one primary direct AC power supply integrated circuits (IC11, IC12,..., IC1n) driving a LED string circuit divided into several LED segments comprising the steps of : a) adding to the circuit at least one secondary direct AC power supply integrated circuits (IC21, IC22,..., IC2n) reshaping the shape of the current sunk by the primary together with the secondary direct AC power supply integrated circuits (IC11, IC12,..., IC1n; IC21, IC22,..., IC2n) by transforming the LED string from a LED string divided in an initial lower number of LED segments (S1, S2, S3, S4) into a LED string divided in a higher number of LED segments, through splitting the first initial LED segment (Si) into several additional LED segments (S1f1, S1f2, S1f3, S1f4) and separately driving the additional LED segments (S1f1, S1f2, S1f3, S1f4) by the at least one secondary direct AC power supply integrated circuits (IC21, IC22,...,IC2n).

Description

Method of reducing the harmonic content of the currents sunk by LED strings driven by an integrated "Direct AC" power supply
and apparatuses associated to the method
The invention relates to a method of reducing the harmonic content of currents sunk from the AC grid by light emitting diodes strings driven by low power constant current integrated power supplies (this type of power supplies will be referred to as "Direct AC"), not compliant with the EN61000-3-2 harmonic standard, in order to become compliant with said harmonic standard and therefore to became scalable, i.e. to allow parallel connection of multiple power supplies in order to obtain higher power supplies compliant too with said harmonic standard, and also relates to a series of apparatuses compliant to said harmonic standard. According to the present invention, hereinafter the term "LED" is the abbreviation of the light emitting diode.
It should be appreciated, however, that the embodiments described below are illustrations of LED driving apparatuses used therein to give a concrete form to technical ideas of the invention, and the LED driving apparatuses of the invention are not specifically limited to the description below. Furthermore, it should be appreciated that the members shown in claims attached hereto are not specifically limited to members in the embodiments. Unless otherwise specified, any dimensions, materials, shapes and relative arrangements of the parts described in the embodiments are given as an example and not as a limitation.
LED lighting technology is maturing fast, in the last 2 years becoming commercially available over 10 direct AC integrated circuits (abbreviated: IC). Direct AC technology is attractive because of its low cost, of its simplicity allowing the manufacturing of complete light engines on single printed circuit boards, because of lack of reactive components and due to its good electric parameters: high electrical efficiency (typically 90%) and good power factor (typically higher than 0.95).
Since the power supplied by the available direct AC ICs does not exceed 20W, in order to achieve higher rated power it is known the scaling method, i.e. the parallel connection of several small power sources. When the harmonic content of currents sunk by the direct AC integrated power supplies exceeds the limits imposed by the harmonic standard (EN61000- 3-2), the scaling method cannot be applied for powers higher than 25W. Figure 1 exhibits the electric diagram of a LED light source driven by a 10W and 4 LED segments direct AC integrated power supply and Figure 2 exhibits the known method of scaling of several direct AC power sources in order to obtain higher-power sources. Figure 3 exhibits the time domain variation of the current sunk by the apparatus in Figure 1 and Figure 4 exhibits its harmonic content together with the individual harmonic limits, as they are set by the EN61000-3-2 harmonic standard. Acknowledging the standard is only recommended for powers lower than 25W but is mandatory for powers higher than 25W, a lighting apparatus having a rated power higher than 25W and manufactured by simply scaling of any number of not compliant and low power direct AC integrated power sources, is still not compliant and not usable. The not compliant harmonic content is mainly due to the fact that given technological and practical reasons, the ratios of currents sunk by the integrated circuit from the grid is fixed, having the first step/current jump of higher value relative to next steps, Which condition a relatively tight ratio of number of LEDs that make up each of the 4 LED segments. Each LED segment includes one LED device or a plurality of LED? devices, which are connected to each other in series. Needless to say, a plurality of LED devices can be connected to each other in series inside a LED package as the LED segment. The time domain variation of current sunk by the direct AC integrated power supply as shown in Figure 3 is characteristic to a series of common, cheap and very popular integrated power supplies, characterized by the following currents ratio: Ιουτι/Ιουτ2/Ιουτ3/Ιουτ4 = 61/77/94/100. Each LED segment can include an arbitrary number of LED devices (at least one LED device). The LED device can be a single LED chip, or a single package including a plurality of collectively-arranged LED chips. In this embodiment, that fixed currents ratio requires the approximate number of LEDs of each constituent segment Si, ...,S4 as following: S! contains about 55 LEDs, S2 contains about 18 LEDs, S3 contains about 16 LEDs and S4 contains about 6 LEDs. The example is not limitative, and the LED segments may also contain other combinations of numbers of LEDs.
For a power of 10W, the set resistor R = 15 ohms is selected in accordance with the datasheet, and therefore the levels of sunk currents become: Ιουτι= 36.7mA, 'OUT2- 46.7mA, louT3- 56.7mA and Ιουτ4- 60.0mA.
The fixed ratios of sunk currents (61/77/94/100) in conjunction with the high level of the first sunk current, requires on one hand the LED segment Si to contain a large number of LEDs, which in turn determines the apparatus to start sinking current later, with a delay greater than 1 .3ms from the zero crossing of sine grid voltage, and on the other hand, it makes the first step / current jump, corresponding to segment Si to be much higher (about 3-fold) than the following steps/levels of sunk current; both effects (late entry into conduction and the first current step of higher value relative to next steps) contribute decisively to the increased levels of odd harmonics of the sunk current, thus exceeding the limits imposed by EN61000-3-2 standard.
The technical problem solved by the invention is the decrease of the harmonic content of the currents sunk by direct AC power sources driving LED strings below the limits required by EN61000-3-2 standard.
The method according to the invention, of reducing the harmonic content of the currents sunk by at least one primary direct AC power supply integrated circuits driving a LED string circuit divided into several LED segments, comprises the steps of adding to the circuit at least one secondary direct AC power supply integrated circuits and reshaping the shape of current sunk by the primary and the secondary direct AC power supply integrated circuits by transforming the LED string from a LED string divided in an initial lower number of LED segments into a LED string divided in a higher number of LED segments, through splitting the first initial LED segment into several additional LED segments and separately driving the additional LED segments by the at least one secondary direct AC power supply integrated circuits.
The method according to the invention has the following advantages:
- Allows manufacturing of EN61000-3-2 compliant power supplies by using non-compliant direct AC power supplies
- Allows direct grid connection of apparatuses having the rated power higher than 25W
- It is unlimited scalable in power;
- Maintains the high electric efficiency of the original un-compliant topologies, of over 90%;
- Exhibits an improved, close to unity (0.995) power factor, higher than the power factor of the initial, known and not compliant topologies
- Decreases the time during which LEDs don't lit, when compared with the initial, known and not compliant topologies; - Improves the flicker index when compared to the initial known direct AC not compliant integrated solutions;
- High power supplies can be manufactured on the same printed circuit board where the LEDs are placed, dramatically simplifying the production of the entire high power light engine;
- The life time of the power supply has the same order of magnitude to the lifetime of the LEDs.
LED Lighting apparatuses associated to the invention have the following advantages:
- are unlimited scalable in power as they comply with the EN61000-3-2 harmonic standard;
- are particularly cheap as they use specialized, low power integrated direct AC power supplies.
The method aceording to the invention is detailed below, offering several embodiments of lighting apparatuses employing LEDs in accordance with the method mentioned, in connection with the figures which represent:
Figure 1 : is a circuit schematic diagram showing a known light engine with the LED string driven by a 4 LED segments low power integrated direct AC power supply.
Figure 2: is a circuit schematic diagram showing the known scaling method, used to increase the rated power
Figure 3: is a graph showing the time variation of the current sunk by the apparatus in Figure 1
Figure 4: is a graph showing the frequency spectrum of the current in Figure 3
Figure 5: is a circuit schematic diagram showing the wiring of a first preferred embodiment of a LED lighting apparatus according to the invention, having its first initial LED segment ST divided into four additional LED segments
Figure 6: is a graph showing the time domanin variation of the current sunk by the apparatus in Figure 5
Figure 7: is a graph showing the frequency spectrum of the current in Figure 6
Figure 8: is a circuit schematic diagram showing the wiring of a second preferred embodiment, consisting of the scaling of the power supply in Figure 5 according to the invention, having its first initial LED segment Si divided into four additional LED segments Figure 9: is a circuit schematic diagram showing the wiring of a third preferred embodiment as an alternative example of scaling of the power supply in Figure 5, according to the invention, having its first initial LED segment Si divided into three additional LED segments Figure 10: is a circuit schematic diagram showing the wiring of a fourth preferred embodiment as an alternative example of scaling of the power supply in Figure 5, according to the invention, having its first initial LED segment Si divided into two additional LED segments
Apparatuses in Figures 5, 8, 9 and 10 are all compliant to EN61000-3-2 standard.
According to the invention the method of reducing the harmonic content of the current sunk by at least one primary direct AC power supply integrated circuits IC I L IC12,..., IC1n driving a LED string circuit divided into several LED segments is comprising the steps of adding to the circuit at least one secondary direct AC power supply integrated circuits \C2i , IC22,..., IC2n and reshaping the shape of the, current sunk by the primary together with the secondary direct AC power supply integrated circuits IC1 i, IC12,..., IC1 n ; IC2i , IC22,..., IC2n by transforming the LED string from a LED string divided in an initial lower number of LED segments Si , S2, S3, S into a LED string divided in a higher number of LED segments; through splitting the first: initial LED segment Si into several additional LED segments S-m , Si^, Sif3, Sif4 and separately driving the additional LED segments Sm , Sif2, Sif3, Sif4 by the at least one secondary direct AC power supply integrated circuits IC2 , IC22,..., IC2n.
The method according to the invention is not limited to a particular split in additional LED segments. As non-limiting examples, the first initial LED segment Si can be split into two, or three, or four, or more additional LED segments.
Figure 5 exhibits the wiring diagram of a first preferred embodiment of a LED lighting apparatus powered directly from the public grid, associated to the method according to the invention and comprising:
a bridge rectifier PR whose "positive" output is series connected to the anode of a string of series connected LEDs divided into four initial LED segments Si , S2, S3, S4, a primary direct AC integrated power supply IC1 whose internal current sources are connected respectively to the anode of the first LED of the second initial LED segment S2, respectively to the anode of the first LED of the third initial LED segment S3, respectively to the anode of the first LED of the fourth initial LED segment S4, respectively to the cathode of the last LED of the string (i.e. of the fourth initial LED segment S4), in which the GND pin of the primary direct AC integrated power supply IC1 , the cold end of its current set resistor R1 and the "negative" output of the bridge rectifier PR are connected to ground,
in which at the increase of voltage UAB over the respective threshold voltages of the initial LED segments, the initial LED segments Si, S2, S3 and S4 are successively and sequentially switched in by the primary direct AC integrated power supply IC1 and at the decrease of voltage UAB below the respective threshold voltages of the initial LED segments, the initial LED segments S4, S3, S2 and Si are successively and sequentially switched out by the primary direct AC integrated power supply ICT
in which the first initial LED segment Si is divided into four additional LED segments Sm, Sif2, Sits, Sif , the apparatus also comprising a circuit element Z fitted between the first initial LED. segment S-t and the second initial LED segment S2, thus the initial LED string becoming split in: a first LED segment Sm, a second LED segment Sif2, a third LED segment Sif3, a fourth LED segment S1f4, the circuit element Z, a fifth LED segment S2, a sixth LED segment S3 and: a seventh LED segment S ,
the apparatus further comprising a secondary direct AC integrated power supply IG2 whose internal current sources are. connected to the taps between the first LED segment Sm and the second LED segment Sif2 respectively between the second LED segment Sif2 and the third LED segment S1f3, respectively between the third LED segment Sif3 and the fourth LED segment Sif4, respectively between the fourth LED segment Sif4 and the circuit element Z, where the GND pin of the secondary direct AC integrated power supply IC2, together with the cold end of its set resistor R2 are connected to the tap between the circuit element Z and the fifth LED segment S2.
The circuit element Z, on which falls the minimum voltage required to bias the internal circuitry of the direct AC integrated power supply IC2, may be a resistor, a few volts reverse polarized zenner diode or even a forward biased LED.
At the increase of voltage UAB over the respective threshold voltages of additional LED segments, before switching in the first initial segment St (now split in additional LED segments Sm, Sif2, Sif3, Sif4) by the primary direct AC integrated power supply IC1 , the aditional LED segments Sm, Sif2, Sif3, and Sif4 are successively and sequentially switched in by the secondary direct AC integrated power supply IC2, and at the decrease of voltage UAB below the respective threshold voltages of LED segments, after the successive and sequential switch out of the initial LED segments S4, S3, S2 and Si (Si now split in additional LED segments S-m, Sif2, Sif3, Sif4) by the primary direct AC integrated power supply IC1 , the aditional LED segments Sif4, S-|f3, Sif2 and Sm are successively and sequentially switched out by the secondary direct AC integrated power supply IC2.
Considering the fixed ratios of sunk currents, for a 10W power supply the set resistor values are: R1 = 15 ohms and R2 = 30 ohms. These values ensure the maximum leap between any two consecutive sunk constant current levels is less than 10mA, meaning that it provides an quasi linear increasing set of currents I0UTI-IC2, IOUT2-IC2, IOUT3-IC2, IOUT4-IC2, louTi-ici, I0UT2-1C1 , louT3-ici, louT4-ici sunk by the apparatus. The additional current levels corresponding to IC2 and set resistor R2 = 30 ohms are IOUTI-IC2 = 18.3mA, IOUT2-IC2 = 23.3mA, IOUT3-IC2 = 28.3mA and IOUT4-IC2 - 30mA, the initial IC1 levels remaining unchanged i.e. currents: IOUTI-ICI = 36.7mA, 'OUT2-IC1 = 46.7mA, louT3-ici - 56.7mA and Ιουτ4 ici - 60mA. After the level of sunk current levels are determined, it is selected the number of LEDs consisting each additional LED segment, so that the current sunk by the apparatus to vary in steps, approximately linearly over time, as seen in Figure 6. The number of LEDs in each additional segment resulting in the sunk current variation as shown in Figure 6 is: Sm contains 15 LEDs, Sif2 contains 18 LEDs, Sif3 contains 9 LEDs, Sif4 contains 6 LEDs and circuit element Z contains 1 single LED. The division of the LED segment S! in four additional LED segments as shown above is not unique, several divisions being possible, as well as several levels of set currents sunk by IC2; the frequency harmonics of sunk current given the variation indicated above are compliant to harmonic standard.
Each LED segment can include an arbitrary number of LED devices (at least one LED device). The LED device can be a single LED chip, or a single package including a plurality of collectively-arranged LED chips.
The LED driving apparatus built as according to the above mentioned division of initial LED segment Si in four additional LED segments, each including the indicated number of LEDs, is compliant to the current harmonic standard for Ιουτ4 = 30mA.
The example is not limitative, as the LED segments may also contain other numbers of LEDs, including but not limited to an equal numbers of LEDs in each initial LED segment (except for S-i) and any additional LED segment. In another embodiment the initial LED segment Si may include 54 LED chips divided in 4 additional LED segments as following: aditional LED segment S-m includes 21 LEDs, and each of the following additional LED segments Sif2, Sif3 and Sif3 includes 10 LEDs, or all LED segments may include an equal number of LEDs.
It is considered that when connecting the supply voltage UAB at the AB terminals, the AC grid voltage passes through zero. It is also considered that at the AB terminals it is applied a 230Vef and 50Hz sinusoidal AC voltage. We reckon the LEDs threshold voltage is about 2.8V and respectively the forward directional (anode to cathode) voltage drop at nominal current is about 3.2V.
By increasing the voltage UAB between 0 Volts and up to 42V (the threshold voltage of LED segment S-m is 42V, 15LED x cca. 2.8V) the apparatus does not sink any current from the grid. By further increasing the UAB voltage over the threshold voltage of Sm , through LEDs that constitute the segment Sm it starts flowing a current determined by the voltage to current characteristic of the 15 LEDs constituting the segment Sm \ the current flowing through the circuit closes to the ground via the internal current source of IC2 which is connected between its terminals; Ιοϋτι and Rext, through the set resistor R2, through the : internal current source of IC1 which is connected between its terminals Ιουτι and Rext and ■• through; the set resistor R1 As UAB voltage continues to increase, the current flowing H- through Sifi segment also increases until it reaches the maximum value limit IOUTI-IC2 = : 18.3mA of the internal current source. While the voltage UAB further increases, the cu rrent sunk by the apparatus stays constant and limited to those 18.3mA, meaning the forward voltage drop across LED segment S1fi also stays constant. The voltage difference between UAB and the voltage forward directional voltage drop on LED segment Sm is found on IC2, across the terminals loun and GND.
Thus, the variation (increase) of the UAB voltage translates into the variation (increase) of the voltage drop at the IC2 terminals. When the voltage drop at the IC2 terminals reaches the threshold voltage of LED segment Sif2 (about 50.4V, 18LED x 2.8V), through the LED segment Sif2 starts flowing a current passing through the internal current source of IC2 connected between the terminal Ι0υτ2 and Rext, through resistor R2 and closing to the ground on the same route as the current sunk by IC2 through Ι0υτι · According to the internal configuration of IC, as the current sunk through the terminal Ι0υτ2 increases, the current sunk through the terminal Ιουτι decreases by an equal amount so that at UAB voltage the current sunk by the terminal Ι0υτι drops to zero. At the further increase of the UAB voltage the current flowing through the additional LED segments Sm and Sif2 of the initial LED segment S-i, Sm and Sif2 now connected in series, increases up to the current level set and limited Ι0υτ2, namely 23.3mA.
At a further increase of the voltage UAB the current drawn by the apparatus stays constant, as well as the forward directional voltage drop at the terminals of the series connected LED segments S-m and Sif2, the voltage variation being found across the terminals Ιουτ2 and GND of IC2. As UAB voltage further increases, the LED segment Sm begins to lit, and then Sif4, similarly.
Up to this point the operation of the apparatus is typical for the operation of a direct AC integrated power supply with 4 LED segments.
At the further increase of the UAB voltage the forward directional voltage drop on the four series connected Sm, S^, S1f3 and Si« stays constant, the variation of the voltage UAB being found in the variation of the voltage drop between the Ιουτ4 and GND terminals of IC2. When this voltage drop exceeds some 2,8V, the LED which forms the circuit element Z starts to conduct. The entry into conduction of the circuit element Z leads to the situation in which through the series connected Sifi, Sif2, S1f3 and S-if4 pass both; the current set at 30mA by the IC plus the current flowing through the circuit element Z. The current passing through the circuit element Z also closes to the ground via the terminal IOUTI-ICI, Rext and ' resistor R1 so the sum of the current flowing through the circuit element Z and 30mA will be limited to the first level set by IC1 which in this exemplary embodiment is 36,7mA. .
At a further increase of UAB voltage the primary direct AC power supply IC1 operates classically, successively sinking the current in well-established constant levels through the already switched in additional LED segments that constitute the initial LED segment S1 , as well as through the sequentially switched in initial LED segments S2-S4.
At the decrease of the UAB grid voltage the functioning occurs in reverse, the apparatus both successively switching out the initial LED segments as well as the additional LED segments that constitute the initial LED segment Si in reverse order, and sinking a descending current in the same well established constant levels and at the same well-established moments in time.
Figure 6 exhibits the time domain variation of the current sunk by the apparatus in Figure 5, Figure 7 exhibits the frequency spectrum of the current sunk by the apparatus in Figure 5 where it is seen that its harmonics are lower than the limits set by EN61000-3-2, and Figure 8 exhibits a circuit schematic diagram showing the wiring of a second preferred embodiment consisting of the scaling of the power supply in Figure 5, according to the invention, having its first initial LED segment Si divided into four additional LED segments. By way of example, the commercial optimum number of integrated circuits needed to manufacture a 30W power supply is 4, a 60W power supply is 2x4=8 and a 90W power supply is 4x3=12; it stems from the fact that all direct AC power supply integrated circuits are identical and from the fact that the secondary direct AC power supply integrated circuits sunk a maximum current equal to between one third and a half of the maximum current sunk by the primary direct AC power supply integrated circuits.
• Figure 9 is a circuit schematic diagram showing the wiring of a third preferred embodiment of a LED lighting apparatus powered directly from the public AC grid as an alternative example of scaling the power supply in Figure 5, associated with the method according to the invention which differs from the wiring diagram shown in Figure 8 as follows:
- the first initial LED segment Si is divided into three additional LED segments Sm ,
7 ί ί - the circuit element Z is serially connected between the second initial LED segment S2 and the third initial LED segment S3
As an example, for the wiring diagram in Figure 9, all LED segments Sifi , Sif2, Sif3, S2, S3 and S4 may have an equal number of LEDs. As a preferred example (given by the large availability of the 50V direct forward bias voltage multichip LEDs packageing in a single capsule 14 LED junctions, but without limiting the invention only to this example), Sm , Sif2, Sif3, S2, S3 and S4 may each have 14 LEDs; the number of LEDs in the LED segments is not limited to 14, it varies between 13 and 16 depending on the maximum grid voltage; thus, at rated power, the direct forward voltage drop for all the LEDs connected in series in the string has to be equal to or slightly smaller than the maximum, peak voltage, of the grid at nominal voltage.
Figure 10 is a circuit schematic diagram showing the wiring of a fourth preferred embodiment as an alternative example of scaling of the power supply in Figure 5, associated with the method according to the invention which differs from the diagram in Figure 8 as follows:
- the first initial LED segment Si is divided into 2 additional LED segments Sm, Sif2
- the circuit element Z is serially connected between the third initial LED segment S3 and the fourth initial LED segment S4
As ah example, for the diagram in Figure 10 all LED segments S-m, Sif2, S2, S3 and S4 can consist of an equal number of LEDs. As a preferred example (but without limiting the invention only to this example) each of Sif1, Sif2, S2, S3 and S4 can consist of 19 LEDs. In the embodiments exhibited in Figures 8, 9 and 10, the internal current sources of the at least one secondary direct AC power supply integrated circuits IC2i, IC22,..., IC2n are connected to the taps between the first LED segment Sm and the second LED segment Sif2, respectively between the second LED segment S-if2 and the third LED segment Sif3/S2, respectively between the third LED segment S1f3/S2 and the fourth LED segment Sif4/S2/S3, respectively between the fourth LED segment Sif /S2/S3 and the circuit element
The total number of the primary direct AC power supply integrated circuits IC11. IC12, -■> may differ from the total number of the secondary direct AC power supply integrated
; circuits IC2i; IC22;. ., in all preferred embodiments depicted in Figures 8,9 and 10.
■ All the embodiments presented in Figures 8, 9 and 10 use the same operating mode as they were described for the embodiment in Figure 5.
In all embodiments using 4 LED segments direct AC power supply integrated circuits, Z is connected between the last LED segment driven by the secondary direct AG power supply integrated circuits (loiru in that case) and their GND pin, together with the cold terminal of the set resistor of these secondary direct AC power supply integrated circuits.
It should be apparent to those with an ordinary skill in art that while various preferred embodiments of the invention have been shown and described, it is contemplated that the invention is not limited to the particular embodiments disclosed, which are deemed to be merely illustrative of the inventive concepts and should not be interpreted as limiting the scope of the invention, and which are suitable for all modifications and changes falling within the scope of the invention as defined in the apprehended claims.
The advantage of splitting the initial LED segment Si into four additional segments Sifi,Sif2, Sif3,Sif4 is obtaining maximum performances in terms of the harmonic content of the current sunk; namely, the harmonic content of the current sunk is the lowest possible. In the embodiments where splitting the initial LED segment Si is done in three SKI , Sif2,Sif3 or respectively in two additional segments S-ifi ,Sif2, although maximum performance is not achieved, the harmonic content of the current sunk remains in accordance with the EN61000-3-2 standard but the cost of the associated apparatuses is much lower given the possibility of using exclusively cheaper multichip packaged LEDs.

Claims

1. Method of reducing the harmonic content of the current sunk by at least one primary direct AC power supply integrated circuits (IC1 i, IC12,..., IC1n) driving a LED string circuit divided into several LED segments
characterized in that it comprises the steps of :
a) adding to the circuit at least one secondary direct AC power supply integrated circuits (IC2t, IC22 IC2n),
b) reshaping the shape of the current sunk by the primary together with the secondary direct AC power supply integrated circuits (IC1 i, IC12,■·, IC1 n ; IC2i, IC22,..., IC2n) by transforming the LED string from a LED string divided in an initial lower number of LED segments (Si, S2, S3, S4) into a LED string divided in a higher number of LED segments, through splitting the first initial LED segment (S-i) into several additional LED segments (Sin, Sif2, Sif3, Sif4) and separately driving the additional LED segments (SKI , Sif2, Sif3, Sif4) by the at least one secondary direct AC power supply integrated circuits (IC2i, IC22,..., IC2n).
2. Method according to claim 1 , characterized in that the splitting of the first initial LED segment (Si) is made into two, or three, or four, or more additional LED segments.
3. LED lighting apparatus driven directly from the public AC grid, comprising:
- a bridge rectifier (PR) whose "positive" lead is series connected to the anode of a series connected LED string divided into several initial LED segments (Si, S2, S3, S4)
- at least one primary direct AC power supply integrated circuits (ICI-1 , IC12,..., IC1 n) whose internal current sources are connected respectively to the anode of the first LED constituent of the initial second LED segment (S2), respectively to the anode of the first LED constituent of the initial third LED segment (S3), respectively to the anode of the first LED constituent of the fourth initial LED segment (S4), respectively to the cathode of the last LED constituent of the fourth initial LED segment (S4)
- in which the GND pin of the at least one primary direct AC power supply integrated circuits (IC1 i, IC12,..., IC1n) together with the cold end of its current set resistor (R1 i , R12,..., R1n) and together with the "negative" lead of the bridge rectifier (PR) are connected to the ground in which
at the increase of the voltage (UAB) over the respective threshold voltages of the initial LED segments (Si), (S2), (S3) and (S4), said initial LED segments are successively and sequentially switched in by the at least one primary direct AC power supply integrated circuits (ICI 1 , IC12,..., IC1 n)
and at the decrease of the voltage (UAB) under the respective threshold voltages of the initial LED segments, the initial LED segments (S4), (S3), (S2), and (S-i) are successively and sequentially switched out by the at least one primary direct AC power supply integrated circuits (IC1 i , IC12,..., IC1 n)
characterized in that
- the first initial LED segment (Si) is divided into at least two additional LED segments (Sm ,
Slf2, S-|f3, Sif4),
- a circuit element (Z) is series connected between the first initial LED segment (Si) and the fourth initial LED segment (S4),
- the LED string circuit thus consisting, in order, of at least: a first LED segment (S-m), a second LED segment (Sif2), a third LED segment (S1f3; S2), a fourth LED segment (Sif ; S2; S3), the circuit element (Z), a fifth LED segment (S4; S3; S2),
the apparatus further comprising -
- at least one secondary - direct AC power supply integrated circuits (IG2t,. IC22,. ., ' IC2n) in which
- the internal current sources of the at least one secondary direct AC power supply integrated circuits (IC2-I , IC22,..., IC2n) are connected to the taps between the first LED segment (Sifi) and the second LED segment (Sif2), respectively between the second LED segment (Sif2) and the third LED segment (S-if3; S2), respectively between the third LED segment (Sif3; S2) and the fourth LED segment (Si«; S2; S3), respectively between the fourth LED segment (Sif4; S2; S3) and the circuit element (Z)
- the GND pin of the at least one secondary direct AC power supply integrated circuits (IC2i , IC22,..., IC2n) together with the cold end of its current set resistor (R2i , R22,..., R2n) are connected together to the tap between the circuit element (Z) and the fifth LED segment (S4; S3; S2)
4. LED lighting apparatus according to claim 2, characterized in that the initial LED segment (S1 ) is divided into two additional LED segments (Sin, Sif2) and the circuit element (Z) is series connected between the third initial LED segment (S3) and the fourth initial LED segment (S4).
5. LED lighting apparatus according to claim 2, characterized in that the initial LED segment (S1) is divided into three additional LED segments (S-m, Sif2, Sif3) and the circuit element (Z) is series connected between the second initial LED segment (S2) and the third initial LED segment (S3).
6. LED lighting apparatus according to claim 2, characterized in that the initial LED segment (S1 ) is divided into four additional LED segments (Sm, Si^, Sif3, Sif4) and the circuit element (Z) is series connected between the fourth LED segment (Sif4) and the second initial LED segment (S2).
7. LED lighting apparatus according to claims 2 or 3, characterized in that the total number of the first direct AC power supply integrated circuits (IC1 i, IC12,...,IC1n), may differ from the total number of secondary direct AC power supply integrated circuits (IC2-i, IC22,...,IC2n).
EP16731678.5A 2016-04-05 2016-04-05 Led lighting apparatus driven directly from the public ac grid Active EP3440892B1 (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/RO2016/000014 WO2017176141A1 (en) 2016-04-05 2016-04-05 Method of reducing the harmonic content of the currents sunk by led strings driven by an integrated "direct ac" power supply and apparatuses associated to the method

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US9398656B2 (en) * 2012-05-16 2016-07-19 Beijing EffiLED Opto-Electronics Technology Co., Ltd. Device and method for driving an LED light
CN103209506B (en) * 2013-04-25 2015-02-18 合肥云杉光电科技有限公司 Low-voltage bypass electricity taking method for alternating current direct driving light-emitting diode (LED) and integrated circuit
KR101610617B1 (en) * 2013-05-23 2016-04-08 주식회사 실리콘웍스 Led lighting apparatus
CN104780646B (en) * 2014-01-15 2018-06-05 四川新力光源股份有限公司 A kind of LED drive circuit for supporting controllable silicon light modulation
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CN109156056B (en) 2020-10-30
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WO2017176141A1 (en) 2017-10-12

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