WO2012107791A1

WO2012107791A1 - Light-source driver, lighting apparatus and vehicle

Info

Publication number: WO2012107791A1
Application number: PCT/IB2011/000476
Authority: WO
Inventors: Wim Teulings; Antoine Capel
Original assignee: Freescale Semiconductor Inc
Current assignee: NXP USA Inc
Priority date: 2011-02-07
Filing date: 2011-02-07
Publication date: 2012-08-16
Anticipated expiration: 2013-08-07

Abstract

A light-source driver (64) comprises at least one light-source (52), and a converter circuit (66) comprising a first (68) and a second input terminal (70) connectable to a power source (54), a first (72) and a second output terminal (74) connected to the at least one light-source, a first (76) and a second inductive member (78), a capacitive member (80) and a first (82) and a second switching member (84). The first input terminal is connected to a first terminal of the first inductive member having a second terminal connected to a first terminal of the first switching member and to a first terminal of the capacitive member; and a second terminal of the first switching member is connected to the first output terminal and to a first terminal of the second switching member having a second terminal connected to a second terminal of the capacitive member and to a first terminal of the second inductive member having a second terminal connected to the second input terminal and the second output terminal.

Description

Title: Light-source driver, lighting apparatus and vehicle

Description Field of the invention

This invention relates to a light-source driver, a lighting apparatus and a vehicle.

Background of the invention

Light-sources, such as light bulbs or light emitting diodes, may be connected to a source of electrical power for being stimulated to radiate electromagnetic energy in a range of the spectrum visible to the human eye. Adjacent parts of the spectrum, such as infrared or ultraviolet, may also be regarded as light. If the light-source requires provision of electrical current or voltage at a level different to that the available electrical power source, such as a battery, a dynamo, a photovoltaic cell etc., that is any current source or voltage source, is capable of providing, the light source may be used as part of a light-source driver, having a converter circuit coupled between the electrical power source and the light-source.

As schematically shown in FIG. 1 , the basic structure of a lighting apparatus 10 contains a light-source 12 and an electrical power source 14, but may contain additional circuitry such as a converter circuit 16, or switches or fuses (not shown). The light-source 12 may for example be a single light emitting diode (LED). In the shown example, the light-source is given by a set of LEDs 18, 20, 22, for example high-brightness LEDs whose anodes are connected together. Due to the spread in forward voltage of the different LEDs, it is difficult to apply the same supply voltage across all the LEDs. For that reason, each LED has a small regulator in series with it, regulating the LED-current to the desired level. Since the anodes of all the LEDs are connected together, but not the cathodes, this configuration is referred to as a quasi-parallel connection, with the LED anodes, in order to have favourable heat evacuation properties, being thermally and electrically directly connected, and the cathodes being connected through a dissipative current regulator circuit 24 for regulating the probably differing LED forward voltages.

For minimizing wasted energy, the converter circuit 16 may for example be a switched mode power supply. Voltage regulation may for example be provided by varying the ratio of on to off time of a switch inside converter circuit 16. Spectral ripples in the input voltage received by the converter circuit 16, for example caused by electromagnetic interference (EMI), for example when the power source 14 is connected through long, unshielded power lines 26, 28, may be filtered by an input filter, for example consisting of an inductor 30 and a capacitor 32.

The lighting apparatus 10 may for example be an automotive lighting apparatus, for example containing headlamps and/or rear lamps of a car. The electrical power source 14, shown in FIG. 1 as a voltage source, may for example be a battery. Two long supply lines 26, 28 connect the battery to the light-source driver 34. The length of these lines or cables can for example be several meters, and thereby be at risk of emitting and receiving electromagnetic radiation when the spectral contents of the current that is carried by the lines is high. The shown input filter is used to limit the spectral contents. In the shown basic form, this filter may comprise a capacitor 32 and an inductor 30. Size and volume of these components may be considerable, since the inductor 30 should be able to carry high supply currents without saturating the magnetic material of its core. The value of the capacitor 32 is dependent on the shape of the current drawn by the converter circuit. Often, the value of this capacitor 32 is high and a polarized, electrolytic capacitor is used.

As shown in FIG. 2, a lighting apparatus with a prior art light-source driver is shown. Only components different from FIG.1 are described. The light-source driver contains a Buck converter 36, i.e. a step-down DC to DC converter, driving the set of LEDs 18, 20, 22. It alternates between connecting the inductor 38 to the source voltage via switch 40 in order to store energy in the inductor 38 and discharging the inductor 38 into the light-source, i.e. the load, by means of a current through a freewheeling diode 42. A capacitor 44 serves as an output filter for smoothing the current supplied to the light-source 12. The Buck converter requires the input filter 30, 32. As shown in FIG. 3, unfiltered input current 46 at switch 40 is discontinuous over time, with current 48 at inductor 38 giving current 50 through the light-source. A Buck converter LED driver circuit is shown in US 7,750,616.

In Capel et al. "A versatile zero ripple topology", Power Electronics Specialists Conference, 1988, PESC '88 Record, a light weight zero ripple DC to DC converter for high power space applications is shown, wherein a Buck converter is modified in that the input filter is integrated in an advantageous way in the converter topology such that the input current becomes continuous instead of discontinuous.

Summary of the invention

The present invention provides a light-source driver, a lighting apparatus and a vehicle as described in the accompanying claims.

Specific embodiments of the invention are set forth in the dependent claims.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

Brief description of the drawings

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. In the drawings, like reference numbers are used to identify like or functionally similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale.

FIG. 1 schematically shows an example of a lighting apparatus with a first prior art light- source driver.

FIG. 2 schematically shows an example of a lighting apparatus with a second prior art light- source driver.

FIG. 3 schematically shows a diagram of an example of converter circuit input and output current over time according to the second prior art light-source driver. FIG. 4 schematically shows an example of a lighting apparatus with a first embodiment of a light-source driver.

FIG. 5 schematically shows an example of a lighting apparatus with a second embodiment of a light-source driver.

FIG. 6 schematically shows a diagram of an example of converter circuit input and output current over time according to the second embodiment of a light-source driver.

FIG. 7 schematically shows an embodiment of a vehicle having a lighting apparatus.

Detailed description of the preferred embodiments

Because the illustrated embodiments of the present invention may for the most part, be implemented using electronic components and circuits known to those skilled in the art, details will not be explained in any greater extent than that considered necessary as illustrated, for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention.

Referring to FIG. 4, an example of a lighting apparatus 60 with a first embodiment of a light- source driver 64 is schematically shown. The light-source 64 driver may comprise at least one light- source 52, and a converter circuit 66 comprising a first 68 and a second input terminal 70 connectable to a power source 54, a first 72 and a second output terminal 74 connected to the at least one light-source 52, a first 76 and a second inductive member 78, a capacitive member 80 and a first 82 and a second switching member 84; wherein the first input terminal 68 is connected to a first terminal of the first inductive member 76 having a second terminal connected to a first terminal of the first switching member 82 and to a first terminal of the capacitive member 80; and a second terminal of the first switching member 82 is connected to the first output terminal and to a first terminal of the second switching member 84 having a second terminal connected to a second terminal of the capacitive member 80 and to a first terminal of the second inductive member 78 having a second terminal connected to the second input terminal 70 and the second output terminal 74.

The naming convention "first" and "second terminal" of a component may comprise that first and second terminal do not refer to the same terminal. The term "connected" may refer to an electrically conductive connection.

Input filter functionality is integrated in the converter circuit, providing an improved dynamic behaviour, which may allow for example, when being used as part of a light-source driver for an automotive lighting application, a fast, but overshoot-free start up, which may be helpful e.g. for dimming.

The lighting apparatus 60 may for example be an automotive lighting apparatus, including a headlamp of a car, connected to a power source 54, which may for example be a car battery, connected to the first and second input terminals 68, 70 of the converter circuit 66 via long supply lines 56, 58. The power source 54 may for example be any voltage supply or current supply.

The first and second switching devices 82, 84 may for example be semiconductor switches. The first switching device 82 may for example be an active switch, i.e. a controlled switch, such as a transistor, receiving control signals from a controller (not shown). The second switching device 84 may for example be a passive switch such as a diode, arranged to switch into a conductive state after blocking, i.e. switching to an off- or non-conductive state of switching member 82 to allow flow of a freewheeling current through the light-source 52, which may for example be a set of quasi- parallel LEDs 88, 90, 92 connected to a dissipative current regulator 94, driven by the energy stored by the second inductive member 78. As shown in FIG. 4, the converter circuit 66 may be implemented as a "zero ripple buck converter" and may allow removing or down-sizing a connected input filter to a small capacitor 62, since an input filter is integrated in the converter topology as first inductive member 78 and capacitive member 80. Output filtering may be achieved by a capacitive output member 86 connected between the first and second output terminals 72, 74.

Referring to FIG. 5, an example of a lighting apparatus 60 with a second embodiment of a light-source driver 64 is schematically shown. Only components differing from the lighting apparatus shown in FIG. 4 will be described in detail.

In the shown embodiment, the first 82 and the second switching members 84 may be active switches, such as transistors, e.g. bipolar transistors or MOSFET or any other active semiconductor device, thereby reducing conduction and switching losses, which may occur in a freewheeling diode. In the shown embodiment, no passive diodes may be used for switching. Efficiency of the shown converter circuit using active switches may be for example at least 90%.

The active switches may be controlled by a controller module (not shown). The second switching member 84 may be arranged to be switched synchronously to the first switching member 82. The controller may be arranged to switch the first and second active switches synchronously, in an inverse manner, switching off, i.e. switching in a non-conductive state one of the switches while switching on, i.e. switching in a conductive state, the other. In other words, by the term "synchronous", it is meant that the first and second switching members are opened and closed in opposite phase, such that when one switch conducts, the other is blocked, which may reduce switching and conduction, losses, and may allow to avoid a discontinuous conduction operating mode a classical Buck converter might get in at start up or under small load conditions.

The first and second inductive members 76, 78 may be provided as one magnetically coupled inductive device, e.g. as strongly coupled power inductors. Ripple of the input current provided to the converter circuit 66 may be low or zero when both inductive members 76, 78 are magnetically strongly coupled or coupled without leakage. Strongly coupled power inductors (continuous input current) may be available at a competitive price, for example in surface mounted technology. The controlled light-source driver may behave very similar to or exactly as a DC load. Output current ripple may be strongly or completely removed. As an example, two 22 μΗ single inductors may be replaced with one coupled inductor of 1 1 μΗ per winding, potentially allowing for the selection of a smaller inductor, or one the same size that has lower DC-resistance (DCR) and higher current handling. The selection of one coupled inductor over two single parts may also save board space and can also save cost.

The shown converter circuit 66 may have the same or a very similar DC transfer function compared to a classical Buck converter. A major advantage of the shown light-source driver 64 may be that it draws a continuous DC input current with strongly reduced spectral contents (low or zero ripple) instead of a pulsed, discontinuous input current (cf. FIG. 3), the filtering of which requires an input filter, such as the LC-filter shown in FIG. 2, where the values of the inductor and the capacitor will typically be high if low values of current- and voltage ripple must be achieved. An input filter for continuous input current may be less voluminous. In an embodiment, a ceramic capacitor may be connected to the first 68 and second input terminals 70, i.e. a small and reliable capacitive device may be used instead of a failure sensitive and probably voluminous electrolytic capacitor. Since the ability to withstand a reverse battery connection may be considered a general requirement to any battery-supplied equipment, an electrolytic capacitor may usually be accompanied by an additional protection diode, which may not be required for a ceramic capacitor. The inductor of an input filter must also be able to withstand a high DC current without saturating, and effectively participate to filtering out the AC component of the current drawn. In the shown embodiment, no such inductor for the input filter may be used.

In another embodiment, the first and second input terminals 68, 70 may be directly connected to supply lines 56, 58 from the power source 54. In other words, no external input filter may be used. The shown converter circuit may be able to operate without any input filter connected even in the case of electromagnetic interferences encountered on long unshielded supply lines. This may allow to further reduce the size of the light-source driver.

The shown converter may be able to operate with small or even without an output capacitor, contrarily to a classical Buck converter. As shown in FIG. 5, no output capacitive device may be connected between the first 72 and second output terminal 74. A continuous output current may be available. No output filter may be used. The DC behaviour may be similar or identical to bulb lamps. For example, the controller circuit may be retrofitted to a body controller designed to only drive bulb-lamps, which may allow to easily replace bulb lamps by LEDS on a vehicle.

Referring to FIG. 6, a diagram of an example of converter circuit input and output current over time according to the second embodiment of a light-source driver is shown. The converter circuit output current through the light-source 100 as well as the input current through the first inductive member 76 and the second inductive member 78 are continuous over time, each of the three sets of current curves shown refers to a current measured for different coupling factors between first and second inductive members. For the shown diagram, the factor varies from 0.1 to 0.97, with the smallest current ripple for a factor of 0.97.

Referring again to FIG. 4 and FIG. 5, the converter circuit may be arranged to receive a first voltage at the first and second input terminals 68, 70 and to provide a second voltage lower than the first voltage, having the same polarity, at the first and second output terminals 72, 74. The presented converter circuit may be regarded as a DC-DC downconversion circuit, without providing an inverted voltage, which may help avoid circuitry for inverting the converted input voltage.

The at least one light-source 52 may be any load connectable to the converter circuit 66. It may for example be a semiconductor light-source, such as a LED or, as shown in FIG. 4 and FIG. 5, an array of quasi-parallel LEDs 88, 90, 92, which may for example be at set of high-brightness (HB) LEDs. As an example, the array may consist of 1 to 10 High-Brightness LEDs, e.g. for If = 350mA, Vf =3.3V, in quasi parallel connection, but any other type or amount of LEDs (or LEDs with different electrical characteristics) may be used.

Referring to FIG. 7, an embodiment of a vehicle 1 10 having a lighting apparatus 1 12, 1 16 is schematically shown. A lighting apparatus may comprise a lamp module 1 12, and a light-source driver as described before. The lighting apparatus or lighting application may comprise, besides a power source, such as a battery 1 14 at least one lamp module 1 12 or lamp body and for example a body control module or front body module 1 16 connected via power lines. The front body module 1 16 may for example comprise fuses for protecting the lighting apparatus.

A vehicle comprising a lighting apparatus or a light-source driver as described above may be a car. Or it may be any other automotive apparatus comprising a light-source, for example a motorcycle, a train, a ship, a helicopter, a plane etc.

At least one light source 52 may be located inside the lamp module. The converter circuit may for example be located in the front body module. In an embodiment, the converter circuit may be located inside the lamp module 1 12 since the LED temperature can then be monitored and controlled, to avoid preliminary LED damage caused by overtemperature. The light-source driver may be as small as possible, having capacitor and inductor values chosen minimal, while using as few capacitors and inductors as possible. The lamp module may for example be a headlamp of a vehicle, or a rear lamp module 1 18. In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims. The connections as discussed herein may be any type of connection suitable to transfer signals from or to the respective nodes, units or devices, for example via intermediate devices. Accordingly, unless implied or stated otherwise, the connections may for example be direct connections or indirect connections. The connections may be illustrated or described in reference to being a single connection, a plurality of connections, unidirectional connections, or bidirectional connections. However, different embodiments may vary the implementation of the connections. For example, separate unidirectional connections may be used rather than bidirectional connections and vice versa. Also, plurality of connections may be replaced with a single connections that transfers multiple signals serially or in a time multiplexed manner. Likewise, single connections carrying multiple signals may be separated out into various different connections carrying subsets of these signals. Therefore, many options exist for transferring signals.

Although specific conductivity types or polarity of potentials have been described in the examples, it will appreciated that conductivity types and polarities of potentials may be reversed.

Those skilled in the art will recognize that the boundaries between logic blocks are merely illustrative and that alternative embodiments may merge logic blocks or circuit elements or impose an alternate decomposition of functionality upon various logic blocks or circuit elements. Thus, it is to be understood that the architectures depicted herein are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. For example, the output capacitor 86 may be a part of the converter circuit 66 or connected to it.

Any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being "operably connected," or "operably coupled," to each other to achieve the desired functionality.

Furthermore, those skilled in the art will recognize that boundaries between the above described operations merely illustrative. The multiple operations may be combined into a single operation, a single operation may be distributed in additional operations and operations may be executed at least partially overlapping in time. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments.

Also for example, in one embodiment, the illustrated examples may be implemented as circuitry located on a single integrated circuit or within a same device. For example, the converter circuit 66 and light-source may be located within the same device. Alternatively, the example may be implemented as any number of separate integrated circuits or separate devices interconnected with each other in a suitable manner. For example, the converter circuit 66 may be located in a different module than but connected to the light-source 52.

Also for example, the examples, or portions thereof, may implemented as soft or code representations of physical circuitry or of logical representations convertible into physical circuitry, such as in a hardware description language of any appropriate type.

Also, the invention is not limited to physical devices or units implemented in nonprogrammable hardware but can also be applied in programmable devices or units able to perform the desired device functions by operating in accordance with suitable program code, such as mainframes, minicomputers, servers, workstations, personal computers, notepads, personal digital assistants, electronic games, automotive and other embedded systems, cell phones and various other wireless devices, commonly denoted in this application as 'computer systems'.

However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word 'comprising' does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the terms "a" or "an," as used herein, are defined as one or more than one. Also, the use of introductory phrases such as "at least one" and "one or more" in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an." The same holds true for the use of definite articles. Unless stated otherwise, terms such as "first" and "second" are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

While the principles of the invention have been described above in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

Claims

1 . A light-source driver (64) comprising

at least one light-source (52), and a

converter circuit (66) comprising

a first (68) and a second input terminal (70) connectable to a power source (54), a first (72) and a second output terminal (74) connected to said at least one light- source,

a first (76) and a second inductive member (78),

a capacitive member (80) and

a first (82) and a second switching member (84); wherein said first input terminal is connected to

a first terminal of said first inductive member having a second terminal connected to

a first terminal of said first switching member and to

a first terminal of said capacitive member; and

a second terminal of said first switching member is connected to said first output terminal and to

a first terminal of said second switching member having a second terminal connected to

a second terminal of said capacitive member and to

a first terminal of said second inductive member having a second terminal connected to said second input terminal and said second output terminal.

2. The light-source driver as claimed in claim 1 , wherein said first and said second switching members (82, 84) are active switches.

3. The light-source driver as claimed in claim 2, wherein said second switching member (84) is arranged to be switched synchronously but in opposite phase to said first switching member.

4. The light-source driver as claimed in any of the preceding claims, wherein said first and second inductive members (76, 78) are provided as one magnetically coupled inductive device.

5. The light-source driver as claimed in any of the preceding claims, wherein a ceramic capacitor (62) is connected to said first and second input terminals.

6. The light-source driver as claimed in any of claims 1 to 4, wherein said first and second input terminals are directly connected to supply lines (56, 58) from said power source.

7. The converter circuit as claimed in any of the preceding claims, wherein no output capacitive device is connected between said first (72) and second output terminal (74).

8. The light-source driver as claimed in any of the preceding claims, wherein said converter circuit is arranged to receive a first voltage at said first and second input terminals (68, 70) and to provide a second voltage lower than said first voltage, having the same polarity, at said first and second output terminals (72, 74).

9. The light-source driver as claimed in any of the preceding claims, wherein said at least one light source (52) is a semiconductor light-source.

10. A lighting apparatus (1 12, 1 16), comprising

a lamp module (1 12), and

a light-source driver as claimed in any of the preceding claims.

1 1. The lighting apparatus as claimed in claim 10, wherein said at least one light-source is located inside said lamp module.

12. The lighting apparatus as claimed in claim 10 or claim 1 1 , wherein said converter circuit is located inside said lamp module.

13. The lighting apparatus as claimed in any of claims 10 to 12, wherein said lamp module is a headlamp of a vehicle.

14. A vehicle (1 10), comprising a lighting apparatus as claimed in any of claims 10 to 13 or a light-source driver as claimed in any of claims 1 to 9.