Power balancing device, LED driver circuit and lighting arrangement

Abstract

Current balancing device for operating multiple LED loads (10A, 10B) with an input transformer (20) which has a primary winding (W1) and a secondary winding with center tap (W a , W b ) having a secondary winding having a first end terminal (A), a center tap (NP) and an opposite second end terminal (B), and having the primary winding for receiving an alternating current voltage (v in ) is trained, a compensating choke (30) with a core and a first winding (L a ), which are between the first terminal (A) of the secondary winding and a first rectifier diode (D a ) is connected in series, a second winding (L b ), which have reversed polarity between the first terminal (A) of the secondary winding and a second rectifier diode (D b ) is connected in series, a third winding (L c ), which are located between the second terminal (B) of the secondary winding and a third rectifier diode (D c ) is connected in series, and a fourth winding (L d ), which with reverse polarity between the second terminal (B) of the secondary winding and a fourth rectifier diode (D d ) is connected in series, wherein the first and third rectifier diodes (Da, Dc) are connected to a first LED load output (C) and the second and fourth rectifier diodes (Db, Dd) are connected to a second LED load output (D) or wherein the first and fourth rectifier diodes (Da, Dd) are connected to a first LED load output (C) and the second and third rectifier diodes (Db, Dc) are connected to a second LED load output (D), characterized in that the compensating choke further comprises a fifth winding (L e) which can be selectively short-circuited to cancel a current equalization process of the equalization choke, and the current equalization device further comprises a control circuit (100) designed to control the fifth winding (L e ), in response to the detection of an overvoltage at the first LED load output (C) and / or second LED load output (D) or at the fifth winding (L) e ), optionally short-circuiting, wherein the control circuit includes a switching element (S1) which can be controlled to short-circuit the end terminals of the fifth winding (L e ) connects them to short-circuit the fifth winding, and wherein the control circuit includes at least one capacitor (C B ) in series with the switching element (S1).

Description

Field of invention

[0001] The present invention relates to LED lighting and in particular to current balancing in LED driver circuits. Background of the invention

[0002] Solid-state lighting (SSL), also known as LED lighting, uses light-emitting semiconductor devices, such as inorganic light-emitting diodes (LEDs) and organic light-emitting diodes (OLEDs), to convert electricity into light for illumination. The acronym LED is used broadly here to encompass all types of light-emitting semiconductor devices, including conventional LEDs, organic LEDs (OLEDs), laser diodes, and the like.

[0003] An LED is a current-controlled device whose luminance, or brightness, is proportional to its forward current when the LED is forward-biased. An LED is forward-biased when the supply voltage to the LED matches the LED's forward voltage or forward knee voltage (Vf). The LED is driven by an LED current source or driver, which converts an AC or DC input power into a suitable DC output voltage so that the light emitted by the LED(s) has the desired brightness, color temperature, and / or other desired characteristics. The driver's output voltage must match the LED's forward voltage rating to forward-bias and illuminate the LED.When several LEDs are connected in series, the Vf and thus the required output voltage of the driver increases according to the number of LEDs connected in series.

[0004] A luminaire, also known as a lighting fixture or fixture, is the entire assembly containing the light source (the lamp) that provides illumination. All luminaires have a housing and one or more light sources. In addition to the light source, a luminaire may include a power supply, a reflector, a lens, a diffuser, a lamp holder (base), and electrical connection components. The electrical system of a luminaire can provide power, control, or other electrical functions, such as cables, sockets, switches, drivers, connectors, circuits, and sensors. Optical components can include diffusers, lenses, prismatic elements, waveguides, reflectors, refractors, louvers, etc.

[0005] The light source for LED luminaires is often referred to as an LED array or LED module, which can refer to an arrangement of LEDs (components) or LED dies (or LED chips) on a printed circuit board or substrate, often with optical elements to provide a desired light distribution pattern. In many applications, one or more LED chips or LED packages are mounted within an LED module. The LED module typically has electrical interfaces for coupling to the load side of a power source, which is usually an LED driver.

[0006] US 2010 / 0301982A1 concerns a constant current source with multiple outputs that includes a high-frequency transformer. The high-frequency transformer has a magnetic core, a primary winding, and multiple secondary windings. The multiple secondary windings and the primary winding are arranged separately, and each secondary winding forms a parasitic current transformer with the primary winding.

[0007] CN 201708990 U discloses an open-circuit protection circuit. The open-circuit protection circuit comprises two load branch circuits of a constant current drive circuit, a voltage regulator, an open-circuit detection unit, and a short-circuit unit. Two terminals of the voltage regulator are connected to two terminals of the same polarity of the two load branch circuits. The other terminals of the two load branch circuits are equipotentially balanced.

[0008] Sometimes it is desirable to operate two or more LED loads with a single LED driver. For example, an LED driver might be designed to power two or more LED luminaires, or a luminaire might have two or more LED loads, such as parallel-connected LED strings. Each LED string has two or more LED devices connected in series. Due to differences in LED parameters, aging, and temperature changes, using parallel LED strings inevitably leads to a current imbalance problem (meaning the load current is not evenly distributed across the parallel LED strings), which in turn affects the luminous intensity and even the color of each string. Most importantly, however, the lifespan of the LED strings (and therefore the LED system) is drastically reduced if the current imbalance causes one or more LED strings to exceed their rated current values.

[0009] One solution to the current imbalance is to use a multi-channel LED driver to regulate the current of each LED string. This method requires a more complex circuit and is more expensive, as each LED string needs its own separate current control and driver circuitry. Brief description of the invention

[0010] One objective of the present invention is a new current balancing circuit for controlling multiple LED loads, so that the aforementioned disadvantages are mitigated or overcome.

[0011] The objectives of the invention are achieved by a current balancing device, an LED driver circuit, and an LED lighting arrangement, as described in the independent claims. Preferred embodiments of the invention are disclosed in the dependent claims.

[0012] One aspect of the invention is a current balancing device for operating multiple LED loads with an input transformer having a primary winding and a secondary winding with a center tap, wherein the secondary winding has a first end terminal, a center tap and an opposite second end terminal, and wherein the primary winding is configured to receive an alternating current voltage, a compensating choke with a core and a first winding which is connected in series between the first end terminal of the secondary winding and a first rectifier diode, a second winding, which is connected in series with reverse polarity between the first end terminal of the secondary winding and a second rectifier diode, a third winding connected in series between the second end terminal of the secondary winding and a third rectifier diode, and a fourth winding, which is connected in series with reverse polarity between the second end terminal of the secondary winding and a fourth rectifier diode, wherein the first and third rectifier diodes are connected to a first LED load output and the second and fourth rectifier diodes are connected to a second LED load output, or wherein the first and fourth rectifier diodes are connected to a first LED load output and the second and third rectifier diodes are connected to a second LED load output, and a fifth winding, which can optionally be short-circuited to cancel a current equalization process of the equalizing choke, and a control circuit designed to selectively short-circuit the fifth winding in response to the detection of an overvoltage at the first LED load output and / or second LED load output or at the fifth winding.

[0013] The control circuit includes a switching element that can be controlled to connect the end terminals of the fifth winding together in order to short-circuit the fifth winding.

[0014] Furthermore, the control circuit includes at least one capacitor in series with the switching element.

[0015] In one embodiment, one end terminal of the fifth winding is connected to the center tap of the input transformer, and the other end terminal of the fifth winding can be connected to the center tap via the switch in order to selectively short-circuit the fifth winding.

[0016] In one embodiment, the control circuit includes means for measuring an output voltage at the first LED load output and / or an output voltage at the second LED load output and means for comparing the same with a reference voltage, and the control circuit is designed to short-circuit the fifth winding if, as a result of the comparison, it is determined that one of the output voltages is an overvoltage.

[0017] In one embodiment, the control circuit includes devices for measuring a voltage at one end of the fifth winding and devices for comparing this voltage with a reference voltage, and the control circuit is designed to short-circuit the fifth winding if, as a result of the comparison, it is determined that the measured voltage is an overvoltage.

[0018] Another aspect of the invention is an LED driver circuit with a current balancing device according to the first aspect and circuit breakers in a half-bridge or full-bridge topology for generating the alternating current voltage.

[0019] In one embodiment, a resonant circuit is connected between the power switches and the current equalization device.

[0020] Another aspect of the invention is an LED lighting arrangement with a current balancing device according to the first aspect and a first LED load connected to the first LED load output, and a second LED load connected to the second LED load output.

[0021] In one embodiment, the arrangement includes power switches in a half-bridge or full-bridge topology for generating the alternating current voltage.

[0022] In one embodiment, the arrangement includes a resonant circuit connected between the power switches and the current equalization device. Brief description of the drawings

[0023] The invention will now be described in more detail by means of exemplary embodiments with reference to the accompanying drawings, in which Fig. Figure 1 shows a schematic representation of an exemplary LED driver circuit for multiple LED loads; and Fig. 2 shows a circuit diagram illustrating an exemplary control circuit according to an embodiment of the invention for switching off the current equalization process. Description of exemplary embodiments of the invention

[0024] An LED driver circuit typically has a power input, which is connected to receive input power, such as an input voltage and current, and power output terminals that can be connected to one or more LED light sources. The LED driver circuit is usually configured to control the output power delivered to the LED light source and thus its light intensity. The LED driver circuit can be designed to supply a required output (load) voltage and a constant output (load) current of a suitable magnitude to the LED light source, ensuring that the light emitted by the LED has the desired intensity, brightness, color temperature, and / or other desired characteristics.

[0025] Fig. Figure 1 shows a schematic representation of an example LED driver circuit for multiple LED loads, in this example for two LED loads 10A and 10B. Each LED load 10A and 10B can drive any number N of series-connected LEDs D. 11 , D 12 , D 13 , ... and D N The load contains N, where N is an integer greater than 1. Such LED loads are often called LED arrays or LED strings. The number N can be different for each of the multiple loads. The 10A load is supplied with an output voltage V. out1 and an output current I o1 The load 10B is driven by an output voltage V. out2 and an output current I o2 driven.

[0026] The LED driver circuit for multiple LED loads comprises a center-tapped transformer 20, a current-balancing choke 30, and a diode rectifier 40. An alternating current (AC) voltage v inis fed into the primary winding W1 of transformer 20. A center-tapped transformer is a type of transformer whose secondary winding has a center tap, meaning an additional wire is connected exactly in the middle of the transformer's secondary winding. The center tap provided on the secondary winding divides the secondary winding into two separate halves W. a and W b , so that two separate secondary voltages v a and v b relative to a central tap, often referred to as the neutral point (NP) or ground. The two voltages v a and v b , which are from the secondary windings W a and W b The generated signals are phase-shifted by 180° relative to each other. When a first (for example, positive) half-wave of an AC input voltage v occurs... in , the secondary voltage v aThe transformer with center tap 20 becomes positive and the secondary voltage v becomes negative. When a second (for example, negative) half-wave of an AC input voltage v occurs... in , the secondary voltage v a of the transformer with center tap 20 negative and the secondary voltage v b The result is positive. The transformer 20 can be a step-up transformer or a step-down transformer, or the number of turns in the primary and secondary windings can be the same. A filter capacitor Cs can be connected between the end terminals A and B of the secondary windings.

[0027] There are embodiments in which the end terminals A and B of the secondary windings are connected to the rectifier 40 via the current equalization choke 30, so that the first half-wave of the input voltage corresponds to a current I a to the anode of diode D a and a current Ib to the anode of the diode D bleads to, and the second half-wave leads to a current I c to the anode of diode D c and a current Id to the anode of the diode D d The cathodes of the diodes D a and D d are connected to each other via a first load output C, so that the currents I a and I d a fully rectified first output current I o1 A 10A load is generated for the first LED. Similarly, the cathodes of the diodes D b and D c connected to each other to a second load output D, so that the currents I b and I c a fully rectified second output current I o2 For the second LED load 10B, the LED load 10A is connected between the first output C and the neutral point NP (ground), and the LED load 10B can be connected between the second output D and the neutral point NP. Smoothing capacitors Cs can be provided at the load outputs C and D.

[0028] The exemplary current balancing choke 30 has four windings L a , L b , L c , L d the windings are wound on a common magnetic core. The turns ratio of the choke 30 is one, meaning the number of turns is the same in all four windings. The windings L a and L b are wound with opposite or reversed polarities, therefore their currents carry I a and I b to opposite magnetic fluxes. The opposite fluxes cancel each other out, and the resulting net magnetic flux is zero, and the currents I a and I b are the same. The same applies to the windings L. c and L d , which are wound with opposite or reversed polarities, and the currents I c and I dare equal. The overall result is that the LED loads 10A and 10B have the same output or load currents I. o1 and I o2 have, even if their tensions V out1 and V out2 are different.

[0029] This allows current balancing for operating multiple LED loads with a single inductor or transformer, eliminating the need for separate current control for each LED load. Since the current balancing circuit requires only passive components, such as the balancing inductor, production costs can be reduced and system reliability improved.

[0030] One problem that arises with the current-balancing choke approach is that if one of the LED loads or one of the load wires fails (i.e., if the LED load output is open), the current-balancing choke can cause a very high overvoltage at the open LED load output. Such a high overvoltage can lead to serious damage to the components of the LED driver circuit. In some applications, it may also be necessary that an LED driver circuit with current balancing not be used for a single LED load, i.e., with other LED load outputs open (unconnected).

[0031] According to one aspect of the invention, to overcome or mitigate this problem, the current balancing choke 30 is equipped with an additional (fifth in the illustrated example) winding L. eThe device is equipped with a terminal that can be selectively short-circuited to cancel a current equalization process of the equalizing choke 30. Furthermore, a control circuit 100 is provided, which is designed to detect an overvoltage at the first LED load output C and / or the second LED load output D or at the fifth winding Le of the equalizing choke and selectively short-circuit the fifth winding Le in response to the overvoltage detection. Short-circuiting the fifth winding L e The magnetic path in the core is short-circuited and the magnetic fluxes in the compensating inductor 30 are reduced to zero. Therefore, the currents I a , I b , I c and I d no longer balanced and equal, the currents of the open load output C or D are zero and the overvoltage at the open load output is avoided.

[0032] In some embodiments, a controllable switch S1, such as a semiconductor switch, is provided to short-circuit the fifth winding L of the choke 30. e is not short-circuited and the connections of the fifth winding L e are not coupled to each other when switch S1 is off (open) in normal balancing operation. The fifth winding L e is short-circuited and the connections of the fifth winding L e They are coupled together when switch S1 is turned on (closed) and the current equalization process is canceled. A DC blocking capacitor C B can be connected in series with switch S1 and the fifth winding L e be switched on.

[0033] In one embodiment, an end connection of the fifth winding L econnected to the neutral point NP of the transformer with center tap 20, and the other end terminal of the fifth winding can be connected to the neutral point NP via the switch S1 to connect the fifth winding L e Optionally, short-circuit.

[0034] In embodiments, the control circuit 100 can be arranged such that it controls the output voltages V out1 and V out2 The circuit measures the output voltage and compares it to a reference voltage REF. If, based on the comparison, it is determined that one of the output voltages is overvoltage, the control circuit 100 can activate switch S1 via a switch control signal. on / off Control on and off. The reference REF can be a user-defined parameter.

[0035] In embodiments, the control circuit 100 can be arranged such that it applies a voltage V LE at one end of the fifth winding L e(at the open end) and compares it to a reference voltage REF. If, based on the comparison, it is determined that the voltage V LE If an overvoltage occurs, the control circuit 100 can activate switch S1 via a switch control signal. on / off Control on and off. The reference REF can be a user-defined parameter.

[0036] Fig. Figure 2 shows a circuit diagram illustrating an exemplary control circuit 100 according to an embodiment of the invention. An operational amplifier A1 and the resistors R3, R4, and R5 form a comparator. A reference voltage REF is applied to an inverting (-) input of the amplifier A1. The output voltage V out1 The output C is measured across a resistor R1 and a diode D6. Similarly, the output voltage V is measured. out2 The measured output voltages V are measured at output D via a resistor R2 and a diode D7. out1 and Vout2 are applied to a non-inverting input of amplifier A1. A capacitor C2 can be provided at the non-inverting input. If both output voltages V out1 and V out2 If the voltages are smaller than the reference voltage REF, then the output voltage of the comparator and the switch control signal are balanced. on / off low, which controls switch S1 to turn off. If one of the output voltages V out1 and V out2 If the reference voltage REF is higher than the reference voltage, then the output voltage of the comparator and the switch control signal are balanced. on / off high, which controls switch S1 to turn on and short-circuit the fifth winding.

[0037] In some embodiments, a source for the AC input voltage v can be used. in Circuit breakers in a half-bridge topology or a full-bridge topology are included. Fig.Figure 1 shows a simplified schematic representation of a half-bridge 50 with power switches M1 and M2. Power switches can be any suitable semiconductor devices, such as power MOSFETs. The switches M1 and M2 are controlled to switch at a switching frequency f. s The bridge alternately switches on and off. This allows it to generate a DC input voltage V. dc a high-frequency square wave voltage.

[0038] In embodiments, the square wave voltage is supplied by the power switch bridge 50 as an AC input voltage v. in connected to transformer 20.

[0039] In certain embodiments, a resonant circuit 60 is provided between the power switch bridge 50 and the transformer 20, thus forming an LLC resonant converter. The high-frequency square wave voltage is input to the resonant circuit 60, which eliminates the harmonics of the square wave voltage and produces a sinusoidal voltage as the AC input voltage v. in outputs to transformer 20.

[0040] In various embodiments, the output current I o1 and / or I o2 by controlling the switching frequency f s The bridge is controlled by 50. A current feedback loop can be provided from the output.

[0041] In some embodiments, a source for the DC input voltage V can be used. dc Essentially any power supply or power source designed and capable of delivering a direct current (dc) voltage V dcto supply to bridge 50. Normally, the DC input voltage V can dc converted from a mains voltage (such as 230 VAC, 50 Hz).

[0042] The description and accompanying figures are intended only to illustrate the principles of the present invention by means of examples. Various alternative embodiments, variations, and modifications are obvious to a person skilled in the art based on this description. The present invention is not intended to be limited to the examples described herein, but may vary within the scope and in accordance with the appended claims.

Claims

[1] Current balancing device for operating multiple LED loads (10A, 10B) with an input transformer (20) which has a primary winding (W1) and a secondary winding with center tap (W a , W b ) having a secondary winding having a first end terminal (A), a center tap (NP) and an opposite second end terminal (B), and having the primary winding for receiving an alternating current voltage (v in ) is trained, a compensating choke (30) with a core and a first winding (L a ), which are between the first terminal (A) of the secondary winding and a first rectifier diode (D a ) is connected in series, a second winding (L b ), which have reversed polarity between the first terminal (A) of the secondary winding and a second rectifier diode (D b ) is connected in series, a third winding (L c ), which are located between the second terminal (B) of the secondary winding and a third rectifier diode (D c ) is connected in series, and a fourth winding (L d ), which with reverse polarity between the second terminal (B) of the secondary winding and a fourth rectifier diode (D d ) is connected in series, wherein the first and third rectifier diodes (Da, Dc) are connected to a first LED load output (C) and the second and fourth rectifier diodes (Db, Dd) are connected to a second LED load output (D) or wherein the first and fourth rectifier diodes (Da, Dd) are connected to a first LED load output (C) and the second and third rectifier diodes (Db, Dc) are connected to a second LED load output (D), characterized by , that the compensating choke also has a fifth winding (L e) which can be selectively short-circuited to cancel a current equalization process of the equalization choke, and the current equalization device further comprises a control circuit (100) designed to control the fifth winding (L e ), in response to the detection of an overvoltage at the first LED load output (C) and / or second LED load output (D) or at the fifth winding (L) e ), optionally short-circuiting, wherein the control circuit includes a switching element (S1) which can be controlled to short-circuit the end terminals of the fifth winding (L e ) connects them to short-circuit the fifth winding, and wherein the control circuit includes at least one capacitor (C B ) in series with the switching element (S1). [2] Current balancing device according to claim 1, wherein an end terminal of the fifth winding (L e) is connected to the center tap (NP) of the input transformer and the other end terminal of the fifth winding (L e ) can be connected via the switch (S1) to the center tap (NP) to selectively short-circuit the fifth winding. [3] Current balancing device according to any one of the preceding claims, wherein the control circuit (100) includes means for measuring an output voltage (V) out1 ) at the first LED load output (C) and / or an output voltage (V) out2 ) at the second LED load output (D) and means for comparing the same with a reference voltage (REF), and wherein the control circuit (100) is designed to control the fifth winding (L e ) to short-circuit if, based on the comparison, it is determined that one of the output voltages (v out1 , v out2 ) is an overvoltage. [4] Current balancing device according to any one of claims 1 or 2, wherein the control circuit (100) includes devices for measuring a voltage (V) LE ) at one end of the fifth winding (L e ) and means for comparing this voltage with a reference voltage (REF), wherein the control circuit (100) is designed to control the fifth winding (L e ) to short-circuit if, based on the comparison, it is determined that the measured voltage (V) LE ) is an overvoltage. [5] LED driver circuit with a current balancing device according to any one of claims 1 to 4 and Circuit breakers (M1, M2, 50) in a half-bridge or full-bridge topology to generate the AC voltage. [6] LED driver circuit according to claim 5, comprising a resonant resonant circuit (60) connected between the power switches and the current equalization device. [7] LED lighting arrangement with a current balancing device according to any one of claims 1 to 4 and a first LED load (10A) connected to the first LED load output (C), and a second LED load (10B) connected to the second LED load output (D). [8] LED lighting arrangement according to claim 7 with power switches (M1, M2, 50) in a half-bridge or full-bridge topology for generating the AC voltage. [9] LED lighting arrangement according to claim 8, comprising a resonant resonant circuit (60) connected between the power switches (50) and the current equalization device.

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