Driver for a load and corresponding light emitting diode, led, based lighting device and method

Abstract

A driver for driving a load, wherein the driver comprises a dual boost converter comprising: an output capacitance comprising a first output capacitor connected in series with a second output capacitor; a first switch connected to a power input stage via a first inductor and arranged to control charging of the first output capacitor via a first diode; and a second switch connected in series with the first switch and connected to a power input stage via a second inductor and arranged to control charging of the second output capacitor via a second diode; wherein a centre tap of the series connected first and second output capacitors is connected to a centre tap of the series connected first and second switches.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to the field of drivers. In particular, the present disclosure relates to an improved driver allowing the use of lower voltage rated components. BACKGROUND

[0002] Drivers can be available in design specifications for medium voltage (120-240V) to high voltage (up to about 400V) alternating current, AC, mains voltages for driving a load, e.g. one or more light sources, such as light emitting diodes, LEDs, or high intensity discharge, HID, light sources.

[0003] These drivers can typically comprise two power converter stages connected in series, i.e. a first power converter stage for power factor correction, PFC, and a second power converter stage for controlling the AC or DC (i.e. direct current, DC, for LEDs; alternating current, AC, for HIDs) in the load. The first power converter stage can typically comprise a boost converter in order to generate a DC output voltage higher than its input voltage (e.g. 650V DC output voltage) to be used as a supply voltage for the load.

[0004] Certain electronic components have a maximum voltage rating. For example, gallium nitride, GaN, semiconductors can have a maximum voltage rating of e.g. 600-650V. Such semiconductors can therefore not be applied in a power converter stage operating at 650V DC voltage. This is especially the case when derating of components is considered in order to meet certain constraints or desires (e.g. extended lifetime) or in case of temporary mains fluctuations caused by e.g. a lightning strike. SUMMARY

[0005] The inventors expect to safely apply such electronic components in a driver. In particular, the inventors' insight is that by providing the involved components with a reduced voltage, thereby respecting the maximum voltage rating, the output voltage of the boost converter is safe for components limited to the maximum voltage rating.

[0006] Accordingly, according to a first aspect of the present application, a driver for driving a load is provided. The driver comprises a dual boost converter. The dual boost converter comprises an output capacitance comprising a first output capacitor connected in series with a second output capacitor. The dual boost converter further comprises a first switch connected to a power input stage via a first inductor and arranged for controlling charging of said first output capacitor via a first diode. The dual boost converter further comprises a second switch connected in series with said first switch. The second switch is further connected to the power input stage via a second inductor and arranged for controlling charging of said second output capacitor via a second diode. A center tap of said series connected first and second output capacitor is connected to a center tap of said series connected first and second switch.

[0007] By providing two series connected output capacitors and two corresponding series connected switches, the voltage provided to certain components can be reduced compared to a situation in which only a single output capacitor and corresponding switch are used. This allows the driver to comply with the maximum rated voltage of these certain components. In other words, the voltage can be reduced significantly, e.g. halved, allowing safe application of such components.

[0008] A bus voltage, e.g. 600 V DC or 650 V AC, can not be reduced by the driver according to the present disclosure. However, the bus voltage is split over the components placed in series, such that the bus voltage is not on a single component having a relatively low maximum rated voltage.

[0009] As used herein, a dual boost converter comprises two boost converters. A boost converter, also known as a step-up converter, is a DC-to-DC (DC-DC) converter whose output (load) voltage is greater than its input (supply or mains) voltage.

[0010] As used herein, a center tap of two components is any node defining a point between the two components, such that each of the two components is connected to the point. In other words, a center tap of components A and B can at the same time be a center tap of components C and D, if each of components A, B, C and D is connected to the center tap.

[0011] In some embodiments, in which the second power converter stage comprises a plurality of power converters supplied from a dual boost converter, the driver can have a problem of discharging the first and second output capacitors of the dual boost converter unequally, because the power levels of the individual power converters of the second power converter stage can not be exactly equal or approximately equal, even if the set points of those power converters are equal. This discharging can lead to an asymmetry of the voltages on the first and second output capacitors, which in turn can lead to one or more of these voltages exceeding the maximum rated voltage of one or more components, e.g. electrolytic capacitors or GaN-based components, which can damage the driver.

[0012] Therefore, the inventors additionally also desire to further improve the lifetime of the driver. Another insight of the inventors is to prevent an uneven discharging of the first and second output capacitors in order to prevent exceeding the maximum rated voltage of the driver components.

[0013] Accordingly, in particularly preferred embodiments, the driver comprises a controller arranged for controlling the first and second switches for balancing the voltages on the first and second output capacitors such that the voltages are close to each other.

[0014] In this way, it can be ensured that the voltages on each of the first and second output capacitors remain within a desired operating range.

[0015] Therefore, particularly preferred embodiments are based on the idea of ensuring that the voltage on the first output capacitor and the voltage on the second output capacitor remain substantially equal, thereby dividing the total boost voltage of the dual boost converter in such a way that each individual voltage on the first and second output capacitors remains low enough so that low rated (voltage) components, like Gallium Nitride, GAN, power semiconductors, can be used.

[0016] Note that the controller can control the first and second switches by providing specific control signals to the first and second switches, wherein the duty cycles of the control signals determine the operating characteristics of the corresponding boost converter.

[0017] Therefore, the controller can modify each duty cycle of the control signals provided to the first and second switches.

[0018] In one embodiment, the controller is arranged for controlling the first and second switches in such a way that the voltage on the center tap is controlled to a predefined voltage level.

[0019] As used herein, assuming that the center tap of the first and second output capacitors connected in series is connected to the center tap of the first and second switches connected in series, the two center taps are directly connected or are the same node and thus at the same voltage.

[0020] In this way, it can be ensured that the voltage over each of the first and second output capacitors is kept within a predictable operating range.

[0021] In an embodiment, the driver further comprises a first DC-DC converter arranged for converting the voltage present on the first capacitor into an output voltage for driving a first load. The driver further comprises a second DC-DC converter arranged for converting the voltage present on the second capacitor into an output voltage for driving a second load. In this way, the driver can drive at least two loads.

[0022] In an embodiment, the output of the first load is connected to the center tap of the series connected first and second output capacitors.

[0023] In this way, it is ensured that the first load draws power from the first capacitor, while the second load draws power from the second capacitor.

[0024] In a particular embodiment, the controller is further arranged for receiving a first measurement value which is a measure of the amount of power consumed by, for example, the voltage over the first load, and the controller is further arranged for receiving a second measurement value which is a measure of the amount of power consumed by, for example, the voltage over the second load, and the controller is arranged for controlling the first and second switches based on the received first and second measurement values.

[0025] In this way, the voltage can be balanced in a direct way.

[0026] In a further developed embodiment, the controller is further arranged for receiving a first measurement value which is a measure of the amount of current through the first load, and the controller is further arranged for receiving a second measurement value which is a measure of the amount of current through the second load, and the controller is arranged for controlling the first and second switches based on the received first and second measurement values. It should be noted that the use of a measure of the amount of current in addition to the above described measure of the amount of power consumed can advantageously improve the quality of the control, for example, with a better response speed and / or a better overshoot / undershoot.

[0027] In an embodiment, the controller is further arranged for controlling the first and second switches with a first duty cycle, and for controlling the first and second DC-DC converters with a second duty cycle, wherein the first duty cycle is higher or lower than the second duty cycle. The operating frequencies of the first and second DC-DC converters are preferably equal, but their starting phases can be different.

[0028] In one example, the controller is even further arranged for controlling the first and second switches at a first operating frequency, and for controlling the first and second DC-DC converters at a second operating frequency, wherein the first operating frequency is higher than, lower than, or equal to the second operating frequency.

[0029] In this way, the required size of the inductors LI and L2 can be optimized by the driver.

[0030] In a further contemplated embodiment, the operating frequency is synchronized with the mains power frequency of the driver, preferably an integer multiple of said mains power frequency.

[0031] In this way, the duty cycle of the operating frequency can be made proportional to the instantaneous mains amplitude, in order to mitigate electromagnetic interference.

[0032] In one embodiment, at least one of the first and second DC-DC converters comprises a Gallium Nitride, GaN, semiconductor.

[0033] In this way, the size and cost can be reduced compared to a driver comprising semiconductors made of conventional materials.

[0034] In a further developed embodiment, at least one of the first and second DC-DC converters comprising a GaN semiconductor can operate at a frequency of at least 150 kHz, preferably higher than 300 kHz, most preferably higher than 1 MHz.

[0035] In this way, the size requirements of the electronic components of the driver can be reduced to smaller sizes, which can result in lower costs.

[0036] In one embodiment, the dual boost converter is further configured to perform power factor correction.

[0037] In this way, the circuitry of the boost converter can be used more efficiently.

[0038] In one embodiment, the dual boost converter is arranged to boost the input voltage of said power input stage to at least 640 V DC.

[0039] In this way, a high power load can be supplied.

[0040] Further, according to another aspect of the invention, there is provided a light emitting diode, LED, based lighting device arranged for emitting light, wherein said LED based lighting device comprises a driver according to any of the embodiments as described above.

[0041] The skilled person will understand that the considerations and advantages applicable to the driver will apply to the lighting device with the necessary modifications.

[0042] In an embodiment, the first and the second load are LED-based loads.

[0043] In this way, convenience can be increased in terms of power consumption and lifetime.

[0044] In a further developed embodiment, the LED-based loads are heterogeneous loads.

[0045] In this way, more different loads can be selected.

[0046] Further, according to another aspect of the application, there is provided a method of operating a driver according to any of the embodiments described above, the driver comprising at least the controller described above. The method comprises the step of controlling, by the controller, the first and second switches for balancing the voltages on the first and second capacitors such that the voltages are close to each other.

[0047] Note that according to the application, the voltage on the first capacitor and the voltage on the second capacitor do not necessarily have to be equal. According to the disclosure, the voltages on these capacitors can differ from a predefined headroom voltage. In this case, the controller can not actively try to make the two voltages equal. As soon as the difference between the two voltages exceeds the predefined headroom voltage, the controller can start working, i.e. can start balancing the voltages. The predefined headroom voltage can for example be 20% of the nominal rated voltage of the capacitors.

[0048] The skilled person will understand that considerations and advantages applicable to the driver will apply to the lighting device with the necessary modifications. BRIEF DESCRIPTION OF DRAWINGS

[0049] Exemplary embodiments will now be described in more detail with reference to the following drawings:

[0050] Figure 1 schematically illustrates an electrical scheme of a driver according to some embodiments; and

[0051] Figure 2 schematically illustrates an electrical scheme of a driver according to some embodiments. DETAILED DESCRIPTION

[0052] Drivers for driving loads such as LEDs or HIDs can be specified for single- or three-phase AC supply voltages (typically 347V, 400V or 480V AC supply). Example applications for these drivers can be in luminaires, in particular in horticulture applications. These drivers can typically comprise two power stages connected in series, wherein the first power input stage can typically comprise a boost converter for power factor correction (PFC) and total harmonic distortion (THD) control. The boost converter can thus generate a controlled DC output voltage of e.g. 650V or even 678V DC, which is higher than the amplitude of the maximum AC supply voltage. The second stage can be arranged to control the AC current in a HID lamp or the DC current of an LED luminaire. This second stage can have the same high DC voltage rating.

[0053] Therefore, new and advanced power gallium nitride (GaN) power semiconductors with a maximum voltage rating of typically 600V or 650V cannot be directly used in a single DC-DC converter powered by a 650V DC bus voltage, taking into account the voltage derating required for a long product lifetime.

[0054] The present disclosure relates to the second stage of such a driver. In short, by having two output capacitors connected in series at the output of a dual boost converter, the 650V DC bus voltage can be divided into two times 325V DC. Moreover, each output capacitor of the dual boost converter can supply a DC-DC converter and a load. In this way, two DC-DC converters connected in series can divide the input voltage and power stress by 2. This can allow the use of e.g. new GaN power semiconductors. The use of GaN power semiconductors is advantageous as it allows to significantly increase the switching frequency for miniaturization purposes. Moreover, GaN power semiconductors are characterized by reduced switching losses due to reduced parasitics. Each DC-DC converter can control the power in a group of LEDs.

[0055] However, since the power levels of the two DC-DC converters will never be exactly the same even if the setpoint is the same, such an arrangement can have the problem of unequally discharging the two series connected supply voltage capacitors. This can lead to an imbalance (asymmetry) of the voltage over the two series connected capacitors with the risk of exceeding the maximum voltage rating of components (e.g. electrolyte, GaN power devices), in turn potentially impairing the driver.

[0056] The above problem can be solved by a combination of two power control loops. A first local power control loop can have the same reference control value to regulate the load power of each DC-DC converter to the same nominal value. These loads can for example be a group of LEDs.

[0057] The second power control loop can control the power difference between the two DC-DC converters such that the two series connected supply voltages V DC1 and V DC2 are close to each other and are loaded with the same or approximately the same power level. In this way, the second power control loop can compensate for unequal power levels due to e.g. component tolerances or unequal temperatures that can occur for different power consumptions in case of LEDs.

[0058] Figure 1 An electrical scheme of a driver 100 according to some embodiments is schematically illustrated. The driver 100 is adapted to drive a load (not shown). The driver 100 comprises a dual boost converter comprising: an output capacitance comprising a first output capacitor Cl connected in series with a second output capacitor C2; a first switch Ql connected to a power input stage (not shown) via a first inductor LI and arranged for controlling charging of said first output capacitor Ql via a first diode DI; a second switch Q2 connected in series with said first switch Q2 and connected to the power input stage via a second inductor L2 and arranged for controlling charging of said second output capacitor C2 via a second diode D2; wherein a center tap 102 of said series connected first Cl and second C2 output capacitors is connected to a center tap 101 of said series connected first Ql and second Q2 switches. As can be seen in the figure, a voltage V12 is present across the series connected first Cl and second C2 output capacitors and voltages VI and V2 are present across the first Cl and second C2 output capacitors, respectively.

[0059] In this example, the advantages of the safer operation apply to the first Ql and second Q2 switches as well as to the first Cl and second C2 output capacitors themselves, but the same advantages of the safer operation can also apply to other components (not shown in the figure) connected to the node 102.

[0060] Figure 2 An electrical scheme of a driver 100 according to some embodiments is schematically illustrated.

[0061] The components of the driver 100 as illustrated in Figure 1 are also present in the driver 100 as illustrated in Figure 2 and are denoted with the same numbers and reference signs.

[0062] Furthermore, Figure 2 A grouping 201 of the power input stage and the dual boost converter (with output side 204 on capacitors Cl and C2) supplied by a supply voltage V AC is also illustrated below. The voltage V ACsupplied to the power input stage comprising the EMC filter 210 and the rectifier comprising a set of diodes 206 and capacitor C5, in order to provide power factor correction. In this sense, the dual boost converter is configured to perform power factor correction. In other words, the grouping 201 comprises an AC-DC power factor correction converter that rectifies the AC supply voltage V AC to a controlled DC output voltage V DC . It should be noted that power factor correction is not considered to be essential for the operation of the driver 100.

[0063] The dual boost converter is a dual boost converter in the sense that it comprises two (or more) boost converters, i.e. a first boost converter comprising an inductor LI, a switch Ql, a diode DI and a capacitor CI and a second boost converter comprising an inductor L2, a switch Q2, a diode D2 and a capacitor C2.

[0064] The switches Ql and Q2 are here illustrated as N-type metal oxide semiconductor nMOS, but can be of any suitable type. The same applies to the switches Q3 and Q4. The switches Ql and Q2 can be controlled with a gate pulse, i.e. CTRLl, from the controller, similar to the operation of a single switch in a known boost converter.

[0065] Furthermore, Figure 2 A first DC-DC converter 202 (in this case a buck converter) and a second DC-DC converter 203 (also in this case a buck converter) are also illustrated. The first DC-DC converter 202 is arranged for converting the voltage VI present on the first output capacitor CI to an output current for providing to a first load (here denoted as LEDl). The second DC-DC converter 203 is arranged for converting the voltage V2 present on the second output capacitor C2 to an output current for providing to a second load (here denoted as LED2). In this particular example, the first load is an LED and is therefore denoted as LEDl, while the second load is also an LED and is therefore denoted as LED2. It will be appreciated that LEDl can also comprise a set of LEDs, and additionally or alternatively, LED2 can also comprise a set of LEDs. Furthermore, the first and second loads can also be another type, such as a HID lamp, with the necessary modifications.

[0066] Other DC-DC converters, such as resonant converters (LLC, LCC), can be used instead of buck converters.

[0067] The first DC-DC converter 202 illustrated here includes a diode D3, an inductor L3 and a capacitor C3, and a local power controller 221 operating a switch Q3. Similarly, the second DC-DC converter 203 illustrated here includes a diode D4, an inductor L4 and a capacitor C4, and a local power controller 222 operating a switch Q4. To control the power (or current) level in LED1 and LED2 as desired, the local power controllers 221 and 222 can be provided with a nominal power level 230, for example from a lighting control according to the Digital Lighting Interface Alliance (DIIA) standard, such as Digital Addressable Lighting Interface (DALI) or Sensor Ready (SR). In this way, the power of each DC-DC converter can be controlled to a setpoint.

[0068] The details of the arrangement of these components within the respective DC-DC converters are left to the skilled person, noting that in this example, DC-DC converters are used in order to cooperate with the corresponding LED load.

[0069] The DC-DC converter 202 and the DC-DC converter 203 can have input capacitors C1 and C2 of the same or approximately the same value, for example within 95%. In this case, the equal impedance of the two capacitors divides the output voltage of the PFC converter front end into two equal DC voltages. The input voltages of the two DC-DC converters are only equal at the start of operation. After that, the two capacitors are charged by one output current of the PFC converter front end and discharged by the input current of each DC-DC converter individually.

[0070] In this example, as in the example of Figure 1 The advantages of the safer operation apply in this example to the first Q1 and second Q2 switches and to the first C1 and second C2 output capacitors themselves, but the same advantages of the safer operation can also apply to other components connected to the node 102, such as the DC-DC converter 202 and the DC-DC converter 203.

[0071] In Figure 2 In this example, the output 207 of the first load LED1 is connected to the center tap 102 of the series-connected first C1 and second C2 output capacitors, as in the example of

[0072] In some embodiments, as illustrated here, there is a second controller CTRL2 to control V DC2 = V DC / 2, in this example, the setpoint is slightly manipulated by adding or subtracting ΔP for the DC-DC converters 202, 203, so that the two supply voltages of the DC-DC converter 202 and the DC-DC converter 203 approach each other, or ideally are the same as each other.

[0073] In a particular embodiment, the controller can be arranged for controlling the first and second switches for balancing the voltages on the first and second output capacitors such that the voltages approach each other to a predefined voltage ratio. The predefined voltage ratio can be expressed as at least one of the voltages divided by the sum of the voltages. In other words, the individual voltages VI and V2may be balanced to a voltage ratio different from 50%-50%, for example to a voltage ratio of 60%-40% respectively (or vice versa). In this case, the controller may, for example, balance the voltage VI to 60% of the voltage V12and the voltage V2to 40% of the voltage V12(or vice versa), which can still allow for safe application of some components. Any other voltage ratio value in the range of 40% to 60% can also be used.

[0074] In a practical embodiment, the presence of the insights of the present disclosure can be tested by applying an asymmetric load and by measuring the voltage V DC2 The presence of the insights of the present disclosure can be tested by applying an asymmetric load and by measuring the voltage V

[0075] In a particular embodiment, when two or more TLEDs are connected in series to a power supply, not feedback but feedforward can advantageously be used for tubular LEDs (TLEDs).

[0076] In one embodiment, the main power supply of the driver is a three-phase connected through a three-phase rectifier bridge.

[0077] In this way, the output power of the converter can be raised above 3000W, which is typically the limit for single-phase converters.

[0078] In one embodiment, the driver comprises at least one additional capacitor connected in series to the first and second capacitors. The driver further comprises at least one respective additional power converter connected in series to the first and second power converters and in parallel to each respective additional capacitor.

[0079] In this way, even more numbers of loads can be supplied. In a particular embodiment, three capacitors and three respective power converters can be provided for three loads (groups) to advantageously drive separate colors (groups), for example, red, green and blue light sources (groups).

Claims

1. A driver (100) for driving a first load (LED1) and a second load (LED2), wherein the driver (100) comprises: a dual boost converter comprising: - an output capacitor comprising a first output capacitor (Cl) connected in series with a second output capacitor (C2); - a first switch (Ql) connected to a power input stage via a first inductor (LI) and arranged for controlling charging of the first output capacitor (Cl) via a first diode (Dl); - the first inductor (LI) and the first diode (Dl); - a second switch (Q2) connected in series with the first switch (Ql) and connected to the power input stage via a second inductor (L2) and arranged for controlling charging of the second output capacitor (C2) via a second diode (D2); - the second inductor (L2) and the second diode (D2); wherein a center tap of the first output capacitor and the second output capacitor connected in series is connected to a center tap of the first switch and the second switch connected in series, wherein the driver further comprises: - a first DC-DC converter (202) arranged for converting a voltage present on the first output capacitor (Cl) to a first output current for providing to the first load (LED1); - a second DC-DC converter (203) arranged for converting a voltage present on the second output capacitor (C2) to a second output current for providing to the second load (LED2).

2. The driver according to claim 1, wherein the driver further comprises: - a controller arranged for controlling the first switch and the second switch for balancing the voltage on the first output capacitor and the second output capacitor such that the voltages are close to each other.

3. The driver according to claim 2, wherein the controller is arranged for controlling the voltage on the center tap to a predefined voltage level.

4. The driver according to any of the preceding claims, wherein an output of the first load is connected to the center tap of the first output capacitor and the second output capacitor connected in series.

5. The driver according to claim 1 or 2, wherein the controller is further arranged for receiving a first measurement value, the first measurement value being a measure of the amount of current passing through the first load, and the controller is arranged for receiving a second measurement value, the second measurement value being a measure of the amount of current passing through the second load, and wherein the controller is arranged for controlling the first switch and the second switch based on the received first and second measurement values.

6. The driver according to claim 5, wherein the controller is further arranged for controlling the first switch and the second switch with a first duty cycle, and for controlling the first DC-DC converter and the second DC-DC converter with a second duty cycle, wherein the first duty cycle is higher or lower than the second duty cycle.

7. The driver according to claim 1 or 2, wherein at least one of the first DC-DC converter and the second DC-DC converter comprises a gallium nitride, GaN, semiconductor.

8. The driver according to claim 7, wherein the at least one of the first DC-DC converter and the second DC-DC converter comprising the GaN semiconductor is adapted to operate at a frequency of at least 150 kHz.

9. The driver according to claim 1 or 2, wherein the dual boost converter is further configured to perform power factor correction.

10. The driver according to claim 1 or 2, wherein the dual boost converter is arranged to boost an input voltage of the power input stage to at least 640 V DC.

11. A light emitting diode, LED, based lighting device arranged for emitting light, wherein the LED based lighting device comprises a driver according to claim 1 or 2.

12. The LED based lighting device according to claim 11, wherein the first load and the second load are LED based loads.

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