A RECTIFYING ARRANGEMENT OF A DRIVER FOR AN LED LIGHTING UNIT

Abstract

A rectifying arrangement for an LED driver comprising a rectifying circuit and a clamping arrangement provides a low-impedance path between input terminals of the rectifying circuit in response to an abnormal operation of the rectifying arrangement, such as an open circuit of one rectifying branch of the rectifying arrangement. The low-impedance path is maintained for a plurality of cycles of an AC power supply provided to the rectifying circuit, and can be maintained on a (semi-)permanent basis.

Claims

1. A rectifying arrangement, adapted to be used with an electromagnetic ballast with an inductor (L1), for an LED driver of an LED lighting unit, the rectifying arrangement comprising: a rectifying circuit comprising: an input arrangement formed of two input terminals (I.sub.1, I.sub.2) configured to connect to an alternating current, AC, power source; an output arrangement formed of one or more output terminals; and rectifying circuitry connected between the input and output arrangement and configured to rectify an AC voltage received at the input arrangement from the AC power source to provide output DC voltage at the output arrangement, and a clamping arrangement connected between the two input terminals of the input arrangement of the rectifying circuit, wherein the clamping arrangement is configured to, in response to an abnormal operation of the rectifying circuit, wherein the abnormal operation of the rectifying circuit is an open circuit of one rectifying branch of the rectifying circuit such that the electromagnetic ballast could only output current in one polarity of the AC cycles which causes the clamping arrangement to receive an increased input voltage from the electromagnetic ballast, exceeding a threshold magnitude, due to voltage induction caused by the open circuit of the one rectifying branch of the rectifying circuit: provide a low-impedance path between the two input terminals of the input arrangement; and continually maintain the low-impedance path between the two input terminals for at least a plurality of continuous cycles of the AC current received at the input arrangement.

2. The rectifying arrangement of claim 1, wherein the clamping arrangement is configured, before an abnormal operation of the rectifying circuit occurs, to not provide a low-impedance path between the two input terminals of the input arrangement.

3. The rectifying arrangement of claim 1, wherein the clamping arrangement is configured to, in response to the abnormal operation of the rectifying circuit, continually maintain the low-impedance path between the two input terminals for a substantially permanent period of time.

4. The rectifying arrangement of claim 1, wherein the clamping arrangement is configured to permanently maintain the low-impedance path between the two input terminals in response to the abnormal operation of the rectifying circuit.

5. The rectifying arrangement of claim 1, wherein the threshold magnitude is larger than 1.25 times the forward voltage of the LED lighting unit.

6. The rectifying arrangement of claim 1, wherein the clamping arrangement comprises a bidirectional conductive and non-recoverable component which comprising diode for alternating current (DIAC) type or Thyristor Surge Suppressors; (TSS) type component connected between the two input terminals of the rectifying circuit.

7. The rectifying arrangement of claim 1, wherein the rectifying circuitry comprises a bridge rectifier including four rectifying branches, wherein at least one branch comprises at least two diodes, and wherein the abnormal operation of the rectifying circuit comprises an open circuit of one rectifying branch.

8. The rectifying arrangement of claim 1, further comprising a capacitor connected to the output arrangement and configured to smooth an output DC current provided by the output arrangement.

9. The rectifying arrangement of claim 8, wherein the one or more output terminals comprise two output terminals, and the capacitor is connected between the two output terminals.

10. An LED lighting unit to be used with an electromagnetic ballast for a gas discharge lamp, comprising: a rectifying arrangement adapted to be used with an electromagnetic ballast with an inductor, for an LED driver of an LED lighting unit, the rectifying arrangement comprising: a rectifying circuit comprising: an input arrangement formed of two input terminals configured to connect to an alternating current, AC, power source; an output arrangement formed of one or more output terminals; and rectifying circuitry connected between the input and output arrangement and configured to rectify an AC voltage received at the input arrangement from the AC power source to provide output DC voltage at the output arrangement, and a clamping arrangement connected between the two input terminals of the input arrangement of the rectifying circuit, wherein the clamping arrangement is configured to, in response to an abnormal operation of the rectifying circuit, wherein the abnormal operation of the rectifying circuit is an open circuit of one rectifying branch of the rectifying circuit such that the electromagnetic ballast could only output current in one polarity of the AC cycles which causes the clamping arrangement to receive an increased input voltage from the electromagnetic ballast, exceeding a threshold magnitude, due to voltage induction caused by the open circuit of the one rectifying branch of the rectifying circuit: provide a low-impedance path between the two input terminals of the input arrangement; and continually maintain the low-impedance path between the two input terminals for at least a plurality of continuous cycles of the AC current received at the input arrangement; and an LED arrangement, comprising one or more LEDS, configured to receive power from the output arrangement of the rectifying arrangement.

11. The LED lighting unit of claim 10, further comprising an LED driver configured to convert the output DC voltage to a different DC voltage for powering the LED arrangement.

12. An LED lighting arrangement comprising: a rectifying arrangement, and adapted to be used with an electromagnetic ballast with an inductor, for an LED driver of an LED lighting unit, the rectifying arrangement comprising: a rectifying circuit comprising: an input arrangement formed of two input terminals configured to connect to an alternating current, AC, power source; an output arrangement formed of one or more output terminals; and rectifying circuitry connected between the input and output arrangement and configured to rectify an AC voltage received at the input arrangement from the AC power source to provide output DC voltage at the output arrangement, and a clamping arrangement connected between the two input terminals of the input arrangement of the rectifying circuit, wherein the clamping arrangement is configured to, in response to an abnormal operation of the rectifying circuit, wherein the abnormal operation of the rectifying circuit is an open circuit of one rectifying branch of the rectifying circuit such that the electromagnetic ballast could only output current in one polarity of the AC cycles which causes the clamping arrangement to receive an increased input voltage from the electromagnetic ballast, exceeding a threshold magnitude, due to voltage induction caused by the open circuit of the one rectifying branch of the rectifying circuit: provide a low-impedance path between the two input terminals of the input arrangement; and continually maintain the low-impedance path between the two input terminals for at least a plurality of continuous cycles of the AC current received at the input arrangement; and an AC power source configured to receive a mains AC power from a mains supply and provide an AC power to the input arrangement of the rectifying arrangement, wherein said AC power source comprises an electromagnetic ballast for a gas discharge lamp.

13. The LED lighting arrangement of claim 12, further comprising an LED arrangement, comprising one or more LEDS, configured to receive power from the output arrangement of the rectifying arrangement.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0045] FIG. 1 is a block diagram illustrating components of an embodiment;

[0046] FIG. 2 provides partial waveforms for understanding a concept of the disclosure;

[0047] FIG. 3 is a circuit diagram illustrating an embodiment; and

[0048] FIG. 4 is a circuit diagram illustrating an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0049] The invention will be described with reference to the Figures.

[0050] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

[0051] The invention provides a rectifying arrangement for an LED driver. A clamping arrangement provides a low-impedance path between input terminals of the rectifying arrangement in response to an abnormal operation of the rectifying arrangement, such as an open circuit. The low-impedance path is maintained for a plurality of cycles of an AC power supply provided to the rectifying circuit, and can be maintained on a (semi-) permanent basis.

[0052] FIG. 1 is a block diagram conceptually illustrating different components of an embodiment. In particular, FIG. 1 illustrates an LED lighting arrangement 10, comprising a lighting unit 100 and an AC power source 190.

[0053] The lighting unit 100 is formed of a rectifying arrangement 110, an LED driver 120 and an LED arrangement 130 (comprising a plurality of LEDs, not shown). The LED lighting arrangement 10, the lighting unit 100 and the rectifying arrangement 110 provide different embodiments. In some embodiment, the driver 120 could be a switched mode power supply, a shunt switch power supply, or even a direct connection, without power conversion, that directly connects the LED arrangement 130 to the output 113 of the rectifying arrangement 110.

[0054] The AC power source 190 is configured to provide an AC power (e.g. an AC current, AC voltage or AC signal) to the lighting unit 100, and in particular to the rectifying arrangement 110. The AC power source may, for example, receive a mains AC power from a mains supply V1, and convert the mains AC power to the AC power provided to the lighting unit. The AC power source may have been initially designed for a gas discharge lamp, such as a high-intensity discharge (HID) lamp or fluorescent lamp.

[0055] In preferable examples, the AC power source 190 may comprise an electromagnetic (EM) ballast having an inductor L1 (e.g. with an inductance of 5h), configured for use in converting a mains AC power to an AC power for powering a gas discharge lamp.

[0056] The rectifying arrangement 110 of the lighting unit 100 is configured to receive the AC power from the AC power source 190 at an input interface 111. The input interface comprises at least two input terminals: a first terminal I.sub.1 and a second terminal I.sub.2. The input interface 111, and therefore the rectifying arrangement 110, may therefore receive a differential input from the AC power source 190.

[0057] The rectifying arrangement 111 is configured to rectify an AC voltage received at the input arrangement 111 to provide output DC voltage at an output arrangement 112. The rectifying is performed by rectifying circuitry 113, connected between the input arrangement 111 and the output arrangement 112.

[0058] The output arrangement 112 comprises one or more output terminals: e.g. a first output terminal O.sub.1 and (optionally) a second output terminal O.sub.2). The power provided at the output arrangement is a DC voltage. If there are two terminals, the DC voltage may be a voltage between the two terminals. If there is a single terminal, the DC voltage maybe a voltage between the single terminal and a ground/reference voltage (e.g. an Earth).

[0059] As previously noted, the rectifying of the AC power is performed by rectifying circuitry 113. Various forms of rectifying circuitry could be used, e.g. a half-bridge rectifier, a full-bridge rectifier. The rectifying circuit may, for example, employ a plurality of diodes to rectify (i.e. place all half-cycles in a same polarity) the AC power received form the AC power source 190.

[0060] The input interface 111, the output interface 112 and the rectifying circuitry together form a rectifying circuit.

[0061] The rectifying arrangement 110 further comprises a clamping arrangement 115, which is connected between the two input terminals I.sub.1, I.sub.2 of the input arrangement 111.

[0062] The clamping arrangement 115 is configured to, in response to an abnormal operation of the rectifying circuit 110, provide a low-impedance path between the two input terminals of the input arrangement; and continually maintain the low-impedance path between the two input terminals for at least a plurality of continuous/consecutive/successive cycles of the AC current received at the input arrangement.

[0063] In other words, if an abnormal operation of the rectifying arrangement occurs, the clamping arrangement may effectively short circuit the two input terminals together, by providing a low-impedance path between the two input terminals. In the context of the present disclosure, “low-impedance” is relative to the impedance of other components of the lighting unit (and in particular, other paths of the rectifying arrangement).

[0064] Preferably, the low impedance path has an impedance of below 100Ω or, more preferably, below 50Ω, or even more preferably, below 20Ω. In particularly preferable examples, the impedance is negligible.

[0065] Thus, the clamping arrangement 115 may respond to an abnormal operation of the rectifying arrangement by providing a low impedance path between the input terminals of the input arrangement, to effectively short circuit the input terminals in both positive and negative polarity of the AC output from the AC power source 190. This enables a symmetrical AC output from the AC power source 190 and avoid a DC component in it, preventing the inductor being saturated and overcurrent. It also avoids a high-voltage potential existing between the input terminals when an abnormal operation of the rectifying arrangement occurs, or quickly dissipates any high-voltage potential induced when an abnormal operation of the rectifying arrangement occurs.

[0066] The clamping arrangement is configured to continually maintain the low-impedance path between the two input terminals for at least a plurality of continuous (i.e. consecutive or successive) cycles of the AC current received at the input arrangement. In particular examples, the clamping arrangement may be configured to (semi-)permanently provide the low impedance path between the two input terminals.

[0067] Thus, the low-impedance path may be maintained for a period of time greater than the time taken for a number of cycles of the input power to occur. This can be achieved through appropriate selection of electrical components for connecting the two input terminals to one another.

[0068] In some examples, the clamping arrangement may be analogous to a fuse, except that instead of switching from acting as a closed circuit to acting as an open circuit, the clamping arrangement may instead switch from acting as an open circuit to acting as a closed circuit. Thus, the clamping arrangement may effectively permanently (without external intervention) act as a short circuit, i.e. provide a low-impedance path, even if the rectifying arrangement is powered off and on again.

[0069] As one example, some forms of diodes for alternating current (DIAC) or Thyristor Surge Suppressors can be configured to permanently (e.g. irreversibly) become low-impedance when some electronic condition is met (e.g. a voltage across the component exceeds a threshold magnitude). One example is the K1050SA DIAC.

[0070] In some examples, the clamping arrangement may comprise a component (such as a bidirectional diode) that is configured to undergo permanent and bidirectional damage/breakdown (e.g. if a voltage difference across the component exceeds some threshold magnitude). This permanent damage may cause the component to become (semi-)permanently conductive. This characteristic can be exploited.

[0071] In yet other examples, the clamping arrangement may comprise a component that becomes conductive when heated, e.g. a thermistor. A high voltage differential across this component may cause it to heat up, resulting in a low-impedance path. The heat may be retained by the component for a plurality of cycles of the AC power, causing the low-impedance path to be provided for a plurality of cycles.

[0072] These are only some examples, and the skilled person would be readily capable of using other variants.

[0073] The abnormal operation of the rectifying arrangement 110 may be an sudden open circuit of one rectifying branch of the rectifying circuitry 113 during the operation, which causes voltage between the input terminals I.sub.1, I.sub.2 exceeding a threshold voltage. This voltage exceeding the threshold voltage can result from the sudden change in current flow (as no current can flow in the open circuit) in the inductor L1. A sudden change in current flow in the inductor L1 can result in a large voltage being induced by the inductor L1 of the AC power source 190 (following Faraday's law).

[0074] FIG. 2 provides partial waveforms to improve a conceptual understanding of this phenomenon. FIG. 2 illustrates the effect of a sudden open circuit in the rectifying arrangement illustrated in FIG. 1 (assuming that the clamping arrangement 190 is omitted).

[0075] A first waveform 210 illustrates a voltage V.sub.V1 (peak amplitude is +/−400V) across the supply V1 of the AC power source 190. A second waveform 220 illustrates a voltage V.sub.L across the inductor L1 of the AC power source 190. the V.sub.L is a little less, for example 50V (the forward voltage of LEDs) than the V.sub.V1 in normal operation, and its peak amplitude is +/−350V for example. A third waveform illustrates a current I.sub.L through the inductor L1 of the AC power source 190. A fourth waveform illustrates a voltage between the two input terminals I.sub.1, I.sub.2 of the input interface of the rectifying arrangement 110, which is equal to V.sub.V1−V.sub.L in normal operation, for example the forward voltage 50V of the LEDs.

[0076] At a time T.sub.1 in the negative polarity of the voltage V.sub.V1, the V.sub.V1 is −380V and the V.sub.L is −330V. There is a sudden/abrupt stop in the current through the inductor L1 (see the third waveform 230), caused by a break in the rectifying arrangement. Curve 230 shows this and the current goes to zero. This causes a corresponding change/reverse in the voltage output by the inductor, i.e. a reverse voltage is induced, see the second waveform 220. The reverse voltage could be as large as above +100V or just a medium voltage of around +60V, depending on the inductance and dI/dt. Throughout this period, the voltage across the supply V1 is maintained, as it is a mains supply voltage, as illustrated by the first waveform 210, say it is −380V. The change in the voltage across the inductor induces a corresponding change in the voltage between the two input terminals I.sub.1, I.sub.2, see the fourth waveform. V.sub.V1−V.sub.L=−380V−60V=−440V. Thus, a voltage of an extremely large magnitude is induced across the input terminals I.sub.1, I.sub.2 of the rectifying arrangement.

[0077] For the sake of improved understanding, the skilled person would readily recognized that the voltage (V.sub.L) across an inductor can be modelled using the following equation:

[00001]$\begin{array}{cc}{V}_L=L_L\frac{{\mathrm{dI}}_L}{dt}& \left(1\right)\end{array}$

[0078] where V.sub.L is the voltage across the inductor, L.sub.L is the inductance of the inductor and

[00002]$\frac{{\mathrm{dI}}_L}{dt}$

or dI.sub.L/dt is the instantaneous change in current through the inductor. From the above, it will be appreciated that a sudden step change in current, e.g. caused by an open circuit in the rectifying arrangement, will induce a large reverse voltage output by the inductor (and thereby between the input terminals I.sub.1, I.sub.2 of the rectifying arrangement 110).

[0079] Put another away, the abnormal operation of the rectifying arrangement may be the occurrence of an open circuit in the rectifying arrangement. The input voltage at I.sub.1 and I.sub.2 is the V1 voltage minus L1 voltage. Since L1 voltage reverses, it causes an amplitude-increased input voltage across the input terminals from an electromagnetic ballast due to voltage induction.

[0080] Specifically, where the rectifying arrangement comprises at least one rectifying branch, the abnormal operation may be the occurrence of an open circuit in one of the branches an increased input voltage from the electromagnetic ballast due to voltage induction.

[0081] Other causes for a sudden voltage increase between the input terminals will be apparent to the skilled person.

[0082] One or more electronics components that (semi-) permanently breakdown when a voltage exceeding a threshold magnitude is present across the component(s) may be used to provide a low-impedance path between the input terminals in both polarities of the AC output in response to an abnormal condition of the rectifying arrangement. Thus, the clamping arrangement may comprise one or more of these electronic components. Suitable examples of such electronic components have previously been described.

[0083] The threshold voltage may be determined, for example, based on a forward voltage of the connected LED arrangement and/or of the (maximum) voltage provided by the AC power source (when there is no abnormal operation).

[0084] The threshold voltage may be no less than 1.25 times, for example, no less than 1.5 times, for example no less than 2 times the maximum voltage of the AC power that the AC power source is configured to supply, when no abnormal operation takes place (e.g. during normal operation). This provides a safe margin that the normal operation would not trigger the protection.

[0085] The threshold magnitude may be no less than 1.25 times, for example, no less than 1.5 times, for example no less than 2 time the forward voltage of the LED lighting unit.

[0086] Optionally the threshold magnitude is less than 300V. In EM ballast, if the output current is suddenly stopped, the induced voltage plus the input voltage (meaning the output overvoltage at the ballast output) is usually larger than 300V. Therefore, setting the threshold magnitude less than 300V can accurately detect this overvoltage event caused by current stopped by open circuit.

[0087] It will be apparent that, before the abnormal operation of the rectifying arrangement, the clamping arrangement may be configured to not provide a low-impedance path between the two input terminals of the input arrangement. Thus, before an abnormal operation, the clamping arrangement may effectively act as an open circuit connection.

[0088] The rectifying arrangement 110 may further comprise a capacitor C.sub.O connected to the output arrangement O.sub.1, O.sub.2 and configured to smooth an output DC current provided by the output arrangement. This capacitor may be connected between two output terminals of the output arrangement.

[0089] The LED driver 120 may be configured to receive the DC power output at the output arrangement 112 of the rectifying arrangement, and convert the DC power into a suitable DC power for powering the LED arrangement 130. Suitable LED drivers would be readily apparent to the skilled person and may comprise, by way of example, a switched mode power supply, a voltage divider, a buck and/or boost converter and so on. The LED driver 120 may be further configurable to control an operation of the LED arrangement (e.g. to selectively provide power to certain LEDs of the LED arrangement).

[0090] The LED arrangement 130 comprises one or more LEDs configured to draw power from the DC power provided by the output arrangement 112 of the LED arrangement. The LED arrangement may comprise any suitable arrangement or array of LEDs, as would be appreciated by the skilled person. For example, the LED arrangement 130 may comprise a string of LEDs, two or more parallel strings of LEDs, an LED array and so on.

[0091] FIG. 3 is a circuit diagram illustrating components of an LED lighting arrangement 300 comprising a rectifying arrangement 110 according to an embodiment of the invention.

[0092] The LED lighting arrangement 400 again comprises an AC power source 190, comprising an electromagnetic ballast having an inductor L1.

[0093] The rectifying arrangement 110 comprises an input interface 111, having a first I.sub.1 and second I.sub.2 input terminal configured to receive an AC signal from the AC power source 190. The rectifying arrangement comprises a bridge rectifier, formed of four didoes DB1, DB2, DB3 and DB4 that rectify the AC signal from the AC power source 190. The rectified signal is provided at an output terminal O.sub.1. A second output terminal O.sub.2 provides a ground/reference (and may be connected to a ground/reference as illustrated), and can be omitted in some embodiments. The output terminal(s) provide an output interface for the rectifying arrangement. A smoothing capacitor C.sub.3 (previously labelled C.sub.O) smooths an output of the rectifying arrangement, e.g. to provide a substantially constant DC signal).

[0094] An LED arrangement 130, comprising one or more LEDS D2, D3 is configured to draw power from the output O.sub.1 (interface) of the rectifying arrangement 111. In the illustrated example, an LED driver comprises a direct connection between the output of the rectifying arrangement and the LED arrangement 130, although other embodiments may replace this direct connection with another DC-DC converter, e.g. embodied as previously described.

[0095] The rectifying arrangement 110 further comprises a clamping arrangement 115. The clamping arrangement here comprises a bidirectional DIAC, here iconic illustrated as being conceptually formed of two back-to-back diodes DB5, DB6. The operation and purpose of the clamping arrangement has been previously described. Other suitable examples for a clamping arrangement, such as those previously noted, may be substituted for the illustrated clamping arrangement.

[0096] In particular, the clamping arrangement 115 provides, in response to an abnormal condition of the rectifying arrangement (such as one of the diodes DB1-DB4 breaking and forming an open circuit), a low-impedance path between the two input terminals of the input arrangement; and is configured to continually maintain the low-impedance path between the two input terminals for at least a plurality of continuous cycles of the AC current received at the input arrangement. In particular, the clamping arrangement 115 may irreversibly or irrecoverable become conductive (provide a low-impedance path).

[0097] A resistor R1 provides an escape path for current, where appropriate.

[0098] FIG. 4 is a circuit diagram illustrating components of a rectifying arrangement 110 according to an embodiment.

[0099] The circuit diagram also illustrates additional input circuitry 410 for simulating the filament of a fluorescent lamp before the EM ballast. The additional input circuit 410 is illustrated for the purposes of contextual understanding, and is not essential to the underlying concept of the present invention.

[0100] The rectifying circuitry of the rectifying arrangement 110 here comprises a full-bridge rectifier 113 in which one half is placed near end A and the other half is placed near end B, formed of four rectifying branches. The AC power is provided across both ends A and B. A pair of rectifying branches is made conductive during a particular half cycle of an AC power supplied to an input interface connected to the rectifying circuitry, to thereby generate a single-polarity DC power. The operation of a full-bridge rectifier is well known to the skilled person, and shall not be further described for the sake of brevity.

[0101] The rectifying arrangement 110 further comprises a capacitor C.sub.O connected to the output arrangement O.sub.1, O.sub.2 and configured to smooth an output DC current provided by the output arrangement. In the illustrated example, the output arrangement comprises two output terminals, and the capacitor C.sub.O is connected between the two output terminals.

[0102] The rectifying arrangement 110 further comprises a resistor R.sub.O connected between the output terminals of the output arrangement. The resistor R.sub.O stands for the LED load.

[0103] The clamping arrangement 115 here comprises a bi-directional DIAC configured to (semi-)permanently breakdown when a voltage across the DIAC exceeds a threshold magnitude voltage, as previously described. An example of a suitable DIAC is the K1050SA DIAC.

[0104] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. If the term “adapted to” is used in the claims or description, it is noted the term “adapted to” is intended to be equivalent to the term “configured to”. Any reference signs in the claims should not be construed as limiting the scope.