METHOD OF USING A HIGH REACTANCE, INDUCTOR TRANSFORMER TO PASSIVELY REDUCE FLICKERING, CORRECT POWER FACTOR, CONTROL LED CURRENT, AND ELIMINATE RADIO FREQUENCY INTERFERENCE (RFI) FOR A CURRENT-DRIVEN LED LIGHTING ARRAY INTENDED FOR USE IN STREETLIGHT MESH NETWORKS

Abstract

A circuit for powering an LED lighting array, the circuit comprising: a transformer for receiving AC line current and stepping down the voltage; one of a rectifier bridge or tapped secondary windings of the transformer paired with steering diodes, for providing a varying DC current; an inductor for receiving the varying DC current so as to smooth out the varying DC current with respect to both voltage and current; and a electrical connection for directing the smoothed-out DC current to the LED lighting array to power the LEDs.

Claims

1. An LED area lighting fixture, the LED area lighting fixture comprising: at least two low voltage LEDs; and a passive magnetic energy storage device electrically connected to the at least two low voltage LEDs, wherein the passive magnetic energy storage device operates at 50 hertz or 60 hertz and protects the low voltage LEDs from power line disturbances via its inductive reactance, and further wherein the passive magnetic energy storage device has a designed-in controlled impedance and a magnetic energy storage characteristic designed to stabilize the wattage delivered to the LEDs.

2. An LED area lighting fixture according to claim 1 further comprising an AC rated film capacitor electrically connected to an alternating current voltage difference within the fixture.

3. An LED area lighting fixture according to claim 2 further comprising 2 or 4 power diodes used to obtain a pulsating DC voltage waveform from an AC voltage waveform, and wherein the passive magnetic energy storage device stores between 0.04 and 10 Joules of magnetic energy.

4. An LED area lighting fixture according to claim 1 wherein energy is added to the passive magnetic energy storage device between 100 and 1000 times per second, and is phased to a power line sine wave voltage.

5. An LED area lighting fixture according to claim 1 wherein the passive magnetic energy storage device comprises an inductor.

6. An LED lighting fixture power supply, the LED lighting fixture power supply comprising a galvanically-isolated, controlled leakage reactance ballasting transformer, operating at 50 Hz or 60 Hz, and acting as, or electrically connected to, an inductive energy storage device.

7. An LED lighting fixture power supply according to claim 6 further comprising an AC rated film capacitor electrically connected to an alternating current voltage difference within the LED lighting fixture power supply.

8. An LED lighting fixture power supply according to claim 7 further comprising 2 or 4 power diodes used to obtain a pulsating DC voltage waveform from an AC voltage waveform, and wherein the ballasting transformer or inductive energy storage device stores between 0.04 and 10 Joules of magnetic energy.

9. An LED lighting fixture power supply according to claim 6 wherein the inductive energy storage device comprises an inductor.

10. An LED lighting fixture, the LED lighting fixture comprising: a fixture body; and a ballasting transformer, wherein at least one of the windings of the ballasting transformer is center-tapped, and further wherein the center tap is electrically connected to the fixture body.

11. An LED lighting fixture according to claim 10 further comprising an AC rated film capacitor electrically connected to an alternating current voltage difference within the LED lighting fixture.

12. An LED lighting fixture according to claim 11 further comprising (i) 2 or 4 power diodes used to obtain a pulsating DC voltage waveform from an AC voltage waveform, and (ii) an inductive energy storage device storing between 0.04 and 10 Joules of magnetic energy.

13. An LED lighting fixture according to claim 12 wherein the inductive energy storage device comprises an inductor.

14. An LED lighting fixture, the LED lighting fixture comprising: a fixture body; and a plurality of LED strings each having two ends, wherein all of the LED strings are inherently and passively operated under 42 Vrms over the fixture body voltage, and further wherein one end of each string is electrically connected to the fixture body for heatsinking.

15. An LED lighting fixture according to claim 14 further comprising an AC rated film capacitor electrically connected to an alternating current voltage difference within the LED lighting fixture.

16. An LED lighting fixture according to claim 15 further comprising (i) 2 or 4 power diodes used to obtain a pulsating DC voltage waveform from an AC voltage waveform, and (ii) an inductive energy storage device storing between 0.04 and 10 Joules of magnetic energy.

17. An LED lighting fixture according to claim 16 wherein the inductive energy storage device comprises an inductor.

18. An LED lighting fixture, the LED lighting fixture comprising a metallic fixture body and at least one LED, wherein the LED lighting fixture is operated on a grounded AC grid line voltage, and further wherein one side of the at least one LED is electrically connected directly to the metallic fixture body.

19. A circuit for powering an LED lighting array, the circuit comprising: a transformer for receiving AC line current and stepping down the voltage; one of a rectifier bridge or tapped secondary windings of the transformer paired with steering diodes, for providing a varying DC current; an inductor for receiving the varying DC current so as to smooth out the varying DC current with respect to both voltage and current; and a electrical connection for directing the smoothed-out DC current to the LED lighting array to power the LEDs.

20. A circuit according to claim 19 wherein the circuit further comprises at least one of a parallel leakage core leg on the transformer, and an AC capacitor provided on a winding of the transformer, to correct the power factor of the circuit and to address third harmonic issues.

21. A circuit according to claim 19 further comprising an LED lighting array.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts, and further wherein:

[0038] FIG. 1 is a schematic view showing one form of the present invention;

[0039] FIG. 2 is a schematic view showing another form of the present invention;

[0040] FIG. 3 is a schematic view showing still another form of the present invention;

[0041] FIG. 4 is a schematic view showing still another form of the present invention;

[0042] FIGS. 5A-5D are schematic views showing prior art constructions;

[0043] FIG. 5E is a schematic view showing another form of the present invention; and

[0044] FIG. 5F is a schematic view showing still another form of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0045] It has occurred to Applicant that, given the lower power requirements of LED lighting, and given the fact that the cost and size of magnetic components (2-3 times larger than the cost and size for non-magnetic components for the same light output) are tolerated in the millions of gas-discharge lamps (of 175 to 400 watt size) currently in use, a high-volume-production, magnetic component, rated at only 40% of the current KVA size, may be used without incurring prohibitive cost issues. This is especially true when considering the costs associated with (i) all of the capacitors and power electronic components required for the high frequency switcher type LED lighting, (ii) required heat-sinking of the semiconductor components of the LED lighting, (iii) preventing those components from radiating RFI, (iv) the surge suppression required to properly protect a high frequency, all-electronic switcher approach from 4 KV transients of high power, and (v) insulating the LEDs for long term use in damp environments at high voltages while heatsinking them. Furthermore, even when all of the foregoing is provided for high frequency switcher type LED lighting, there is no question that the reliability of all of these fragile components is less than an essentially bulletproof ballast transformer or ballast inductor which is used in the new, isolated, lower voltage magnetic energy storage lighting design of the present invention. Significantly, mercury vapor lamps using a passive magnetic reactor ballast system, from the late 1930's, still function well (albeit with improved mercury vapor-style lamps).

[0046] Given this insight, Applicant has recognized that one can take advantage of the galvanic isolation and arbitrary voltage ratios of a specially-designed high reactance transformer or transformer/DC inductor fixture configuration to provide a novel circuit for driving an LED lighting array. See the various embodiments shown in FIGS. 1, 2, 3, 4 and 5E, and which are discussed in further detail below. The novel circuit provides the following improvements, among others.

[0047] (1) Easily Heat-Sinkable.

[0048] One side of the LED and power supply can be solidly bolted or grounded (uninsulated) to the aluminum housing of the lighting fixture, heat-sinking the LED array very well; by operating in small, center-tapped winding groups of LEDs (FIG. 1 or FIG. 2), the current can be easily stabilized over a typical range of nominal input voltages due to the inherent energy storage or ballasting action of a transformer or inductor designed to do exactly this. One known way is to provide a parallel magnetic leakage core leg, known from gas-discharge ballasts (note: much less dynamic range is needed here, inasmuch as LEDs are very stable relative to gas-discharge lamps and have no warmup or high voltage startup issues). By using comparatively inexpensive steering, bridge or rectifier diodes, or groups of LEDs with multiple secondary windings, one side of the LED or array can always be the earthed (grounded) side, connected to the structure, simplifying conduction cooling. Even if connected in series, the aggregate voltage at any exposed place can be held below the 42 Vrms which Underwriters Laboratory (UL) considers hazardous (i.e., about ten LEDs in series). This magnetic energy storage principle at 60 Hz allows various combinations of series parallel LED diodes, multiple windings, or both, without actively switching series/parallel configurations or connections. The LED diode current can be made close to optimal and is unrelated numerically to the peak line current (set by the transformer ratio or inductor design). Various fully-exposed, lightly-insulated heat sink arrangements can be envisioned. It should be appreciated that there are no high voltages on the diodes (a critical fact) due to the thorough galvanic isolation and step-down ratio.

[0049] (2) Power Factor Optimized.

[0050] Power factor can be addressed by an AC capacitor, by arranging the isolated transformer windings (as always, at least two windings) on separate bobbins, one winding can be a leakage winding (inductive reactive winding, or lagging power factor) and the other winding can be compensated by an AC capacitor network to draw a leading power factor (PF)the sum can be made to be 90% PF or better (normal PF), solving the power factor and harmonic issues. Because the currents are phase-shifted, the harmonics are not as additive, and a major improvement results. The light output from each string of LEDs can be phase-shifted in time, tending to remove or reduce any flicker effects. This phase-shift concept, while not explicitly required, has been previously used in fluorescent lighting, but has not previously been used with low voltage, isolated windings or in LED lighting with one side at earth (ground) potential. Ceramic stacked film capacitors of small size and low voltage can enable this capacitive reactance at low cost.

[0051] (3) No RFI Emitted.

[0052] Because there is no high frequency switching, there is inherently no radiated or conducted RFI. An RFI problem simply does not exista critical advantage for the described mesh network-compatible LED light fixture when viewed as embedded in a digital system, or controlled by adjacent digital networks (e.g., a poletop-mounted LED light fixture controlled by a physically adjacent radio-based mesh network system such as a Wi-Fi network system). Stated another way, low frequency, 60 hertz LED lighting fixtures utilizing the present magnetic energy storage invention do not emit significant RFI. RFI is a significant problem with radio-based mesh network systems (such as Wi-Fi network systems) mounted to poletops adjacent to streetlights. It is almost impossible to adequately shield a 100 watt switching power supply located in proximity to a maximally sensitive broadband radio receiver (such receivers must have sensitivity in the 1-5 V range, and are very wideband by nature). Noise in the receiver will block Wi-Fi-like uses. The present invention allows radio-based mesh network systems (such as next generation Wi-Fi-like network or meshed router systems) to be used adjacent to highly efficient LED streetlights. The present invention provides an LED lighting fixture power supply which produces little or no RFI and is highly reliable.

[0053] The LED power supply can also provide low voltage noise-free DC power to the Wi-Fi mesh network (or to another adjacent system such as a radio system) by a suitable interface such as a plug-and-socket configuration on the streetlight.

[0054] Control modifications of the system, with added not in the critical path parts, allows operation on a dimmer (inherently) or 0-10 volt signals, by add-in electronic boards, isolated from line voltage and powered from the low voltage DC already present. Failure of such add-in electronic boards would not, by design, shut down the basic LED lighting fixture or impact power to the Wi-Fi mesh network.

[0055] (4) Current Smoothed Out.

[0056] The reactance or effective impedance of the transformer or series inductor (choice) may be adjusted (by design) to tolerate LED imbalance issues, keeping currents near optimal. LED life is increased, as there are no startup or surge issues, etc. Further, the inductor reactance keeps the current flowing in the LED junctions even across the AC current zeros, due to power stored in its windings ( LI.sup.2) as a smoothed circulating current, ideal for LED operation.

[0057] (5) Accommodates a Range of Input Voltages.

[0058] Various nominal input ranges are readily accommodated by transformer tappings or variable winding arrangement leads120, 208 and 240, 277 in one design; 377, 480 and 600 in another input coil design. This wide range is difficult to accommodate with solid state PFC designs while keeping efficiency high.

Some Preferred Embodiments

[0059] In FIG. 1, the transformer 11 is energized by an alternating current at the winding 21, which may be tapped to match various voltages. Transformer 11 may be a special high reactance transformer of various known configurations to help with regulation of an inductive current path 41.

[0060] The winding 31 provides a lower voltage (or any voltage) to inject current into the inductive current path shown by arrow 41, a circulating current. The inductive storage element 51 smoothes this current, tending to keep inductive current path 41 constant as shown by typical waveform 61.

[0061] Depending on the power of the LED fixture, inductive storage element 51 may store 0.04-1 joule or 1 Watt/second (without excluding other values) to keep the current circulating even as the fluctuating AC line voltage goes through zero crossings. This also helps with flicker as an engineering tradeoff.

[0062] Because of inductive storage element 51 being on at all times, the very non-linear IV characteristic of LEDs 71, 72, etc. is isolated from the line, and a fairly constant current is drawn from the line, improving power factor and reducing harmonics. Further reduction is possible by known methods, like power factor capacitors.

[0063] Furthermore, the active nature of inductive storage element 51 is isolated in an AC sense from the line by the diodes 81. Peaked AC line currents would otherwise reduce the power factor as happens with DC capacitor storage. The AC capacitors 91 are connected in known ways (such as those displayed), and will further improve the power factor as required.

[0064] The diodes 81 (in FIG. 1) or 81 and 101 (in FIG. 2) carry the circulating current during the time the AC line voltage is instantaneously low. The rectified AC voltage pulses 111 can be viewed as pumping the current loop 120 times per second while inductive storage element 51 sustains current 41 between pumps.

[0065] In the embodiment of FIG. 1, the bridge diode array 81 embodies the function of diodes 81 and 101 in FIG. 2, but has always at least two diodes in conduction, adding to losses.

[0066] In the embodiment of FIG. 2, efficiency may be improved for larger power versions depending on the ratio of storage-to-pump diode conduction intervals, due to less diode loss.

[0067] In the embodiment of FIG. 3, the pumping function can be modulated by a synchronized pulse width modulation (PWM) scheme 112 (details not shown) reducing the pump conduction and so offering a dimming function controlled by a 0-10V signal 121.

[0068] This same arrangement, using a field-effect transistor (FET), bipolar junction transistor (BJT) or insulated-gate bipolar transistor (IGBT), at 131, as a control switch for brightness, can also protect against overcurrent in the system by current sense 141, which tends to turn off FET, BJT or IGBT 131 if the current rises above a threshold (excessive line voltage).

[0069] Various series parallel arrangements can be substituted for LEDs 71, 72 as a part of optimization of the design. In reality, many more diodes are in place than the LEDs 71, 72 drawn in the figures.

[0070] In the embodiment of FIG. 4, the function of the controlled pump current (and thus energy per pulse) allowed by FET, BJT or IGBT 131 can be combined with current sense 141 so as to enable a feedback loop via FET, BJT or IGBT 131 that regulates the average current in inductive current path 41 actively, by the known methods outlined in the section entitled (4) Current Smoothed Out above.

[0071] By the concepts shown herein, a novel circuit for powering an LED area light is provided that emits substantially no RFI, enabling use of the circuit (and an LED light array driven by the circuit) with Wi-Fi or mesh networks.

[0072] FIG. 5A (prior art) shows a normal DC bridge power supply with filter capacitor 151, followed by a regulator 161. This results in high third harmonic currents, shown at 171. Third harmonics add in 3 phase systems, and are therefore to be avoided in large area lighting.

[0073] FIG. 5B (prior art) suffers from third harmonics due to the diodes only coming on at voltage peaks. For thermal peak temperature reasons, approximately 2.6 times as many LED diodes are needed on AC direct operation for the same DC light output as the constructions shown in FIGS. 5A, 5D (see below) or 5E (see below). Heat cannot be averaged at line frequency; the DC limit still applies to the peak, and the LED diodes are off between the peaks. The construction of FIG. 5B loses much power in ballast 201.

[0074] FIG. 5C (prior art) is essentially the same as FIG. 5B. It is sometime advocated for lower cost, but now requires approximately 5.4 times as many diodes for the same light output. This construction is used in low power decorative LED lighting.

[0075] FIG. 5D (prior art) is the conventional approach for driving LEDs, still requiring energy storage via electrolytic capacitor 151, and generating copious amounts of RFI. Power factor correction (PFC) schemes also require switching, again generating RFI.

[0076] FIG. 5E is another embodiment of the new concept of the present invention, free of RFI, no electrolytic capacitor, and uses magnetic storage of energy in a low frequency inductive storage element 51, resulting in a smooth current draw 41.

[0077] FIG. 5F shows how the line draw may be shaped and allow a smaller inductor to be used if refreshed more often than once per line cycle.

Modifications of the Preferred Embodiments

[0078] It should be understood that many additional changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the present invention, may be made by those skilled in the art while still remaining within the principles and scope of the invention.