Synchronous step-down converter for operating one or more lamps, associated method and control gear

Abstract

Synchronous buck converter (11) for operating one or more lighting means (13), wherein the synchronous buck converter (11) is designed to be operated in a first operating mode or in a second operating mode, wherein in the first operating mode of the synchronous buck converter (11) the current flowing through the synchronous buck converter (11) alternately increases and decreases, and wherein in the second operating mode the current profile of the current flowing through the synchronous buck converter (11) oscillates over a predetermined period of time, wherein the synchronous buck converter (11) has a first switch (111) and a second switch (112) for controlling the current flowing through the synchronous buck converter (11), and the synchronous buck converter (11) is designed such that in the second operating mode the first switch (111) and the second switch (112) are switched off.

Description

[0001] The present invention relates to a synchronous buck converter for operating one or more lighting devices, a method for operating a synchronous buck converter for operating one or more lighting devices, and an operating device for operating one or more lighting devices. The one or more lighting devices comprise, for example, one or more light-emitting diodes (LEDs).

[0002] The document US 2008 / 0 224 625 A1 discloses a driver circuit for light-emitting diodes.

[0003] The document US 2006 / 0 017 421 A discloses a method and a device for controlled switching of the operation of a buck converter between synchronous mode and standard mode, so that an increase in the voltage of a system bus during charging of a battery by the buck converter can be prevented.

[0004] Document US 2008 / 0012540 A discloses a current reversal prevention circuit used in a synchronous buck converter.

[0005] The document DE 10 2012 007 479 A1 discloses a method for controlling a power factor correction circuit, a power factor correction circuit and an operating device for a lighting device.

[0006] The document LI RUQI ET AL: "Small-signal characterization of synchronous buck converters under light load conditions", 2015 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE), IEEE, September 20, 2015 (2015-09-20), pages 193–200. XP032800577, DOI:10.1109 / ECCE.2015.7309688 discloses a small-signal characterization of synchronous buck converters under light load conditions.

[0007] The document Jerome Johnson: “Improving Buck Converter Light-Load Efficiency”, POWER SUPPLY DESIGN 18, May 1, 2025 (2015-05-01), pages 1-3, XP055824051 discloses an improvement in the efficiency of buck converters at light loads.

[0008] Synchronous buck converters are well known. Compared to a standard or conventional buck converter, the diode in a synchronous buck converter is replaced by a switch, so the synchronous buck converter has a second switch in addition to the primary switch. Since the synchronous buck converter is constructed from two switchable switches, the second switch must be operated in push-pull fashion to the primary or first switch. If the first switch becomes conductive, the second opens, and vice versa.

[0009] Since a diode always causes a voltage drop in the forward direction, considerable losses occur across it and thus across a standard or conventional buck converter. Synchronous buck converters, on the other hand, have significantly lower losses, which is why they have the advantage of not being affected by short-term bursts in the signal. However, with a synchronous buck converter that drives one or more light sources, the problem is that even a small timing deviation or fluctuations when switching the switches on and off can lead to visually visible flickering of one or more light sources (e.g., one or more LEDs) powered by the synchronous buck converter due to the high current amplitude.

[0010] It is therefore the object of the present invention to enable an improved supply of current to one or more lighting means.

[0011] This object is achieved according to the invention by the features of the independent claims. The dependent claims specify further embodiments of the invention.

[0012] The present invention is based in particular on the idea of ​​reducing the presence of high amplitudes in the synchronous buck converter by introducing a further operating mode in which the amplitudes are reduced during current rise and fall, and especially during current fall. According to the present invention, a decay of the current flow is implemented in the second operating mode.

[0013] According to one aspect of the present invention, a synchronous buck converter according to independent claim 1 is provided for operating one or more lighting means, wherein the synchronous According to one embodiment, the current flowing through the synchronous buck converter increases after a change from the second operating mode to the first operating mode.

[0014] The synchronous buck converter has a first switch and a second switch for controlling the flow of current flowing through the synchronous buck converter.

[0015] According to one embodiment, the synchronous buck converter is designed such that in the first operating mode, the current flowing through the synchronous buck converter increases by switching on the first switch and switching off the second switch and decreases by switching off the first switch and switching on the second switch.

[0016] The synchronous buck converter is designed such that in the second operating mode the first switch and the second switch are turned off.

[0017] According to one embodiment, the first switch is switched off when changing from the first operating mode to the second operating mode.

[0018] According to one embodiment, the first switch is switched on when changing from the second operating mode to the first operating mode.

[0019] According to one embodiment, the current flowing through the synchronous buck converter increases up to a first limit value and / or decreases up to a second limit value in the first operating mode.

[0020] According to one embodiment, the current flowing through the synchronous buck converter in the first operating mode increases until the expiration of a first time period and / or decreases until the expiration of a second time period.

[0021] According to one embodiment, the synchronous buck converter is designed to be connectable to the one or more lighting means and, when connected to the one or more lighting means, is designed to supply the one or more lighting means with the current flowing through the synchronous buck converter.

[0022] According to one embodiment, the one or more lighting means comprise one or more light-emitting diodes, LEDs.

[0023] According to one aspect of the present invention, a method according to independent claim 14 is provided for operating a synchronous buck converter which is designed to operate one or more lighting means, wherein the method comprises operating the synchronous buck converter in a first operating mode or in a second operating mode, wherein in the first operating mode of the synchronous buck converter, current flowing through the synchronous buck converter alternately increases and decreases, and wherein in the second operating mode the

[0024] Current waveform of the current flowing through the synchronous buck converter oscillates over a predetermined period of time.

[0025] According to one embodiment, the operating device comprises a synchronous buck converter for operating the one or more light sources, and the synchronous buck converter is a synchronous buck converter as indicated above and / or as shown in more detail below.

[0026] According to one embodiment, the operating device has a controller which is designed to control the synchronous buck converter.

[0027] According to one embodiment, the controller controls the operation of the synchronous buck converter in the first operating mode and in the second operating mode, a change in the operation of the synchronous buck converter from the first operating mode to the second operating mode, and a change in the operation of the synchronous buck converter from the second operating mode to the first operating mode.

[0028] The present invention reduces the average current amplitude. This eliminates or at least significantly reduces flickering in light sources such as LEDs, which is visually visible (especially at low dimming levels). This allows for improved current supply to one or more light sources through a synchronous buck converter, as the current exhibits a more stable change in current levels.

[0029] Further features, advantages and characteristics of the present invention will now be explained with reference to the figures of the accompanying drawings and the detailed description of exemplary embodiments. Fig. 1 shows an embodiment of an operating device for operating lamps according to an embodiment of the present invention, Fig. 2 shows an exemplary current profile through a synchronous buck converter in two operating modes of the synchronous buck converter according to an embodiment of the present invention,

[0030] In the following, components with identical or similar functions are designated by identical reference numerals in the figures. Furthermore, it should be noted that the embodiments explained herein can be combined with one another, unless a combination is explicitly excluded.

[0031] Fig. 1 shows an exemplary embodiment of an operating device 1 for operating one or more lighting means 13 according to an embodiment of the present invention.

[0032] According to one embodiment, the one or more light-emitting diodes (LEDs) comprise one or more light-emitting diodes (LEDs). The LEDs can be configured in various ways, and the present invention is not limited to any particular configuration of the LEDs. According to one embodiment, the LEDs comprise inorganic and / or organic LEDs. The arrangement of the LEDs can also be configured in various ways. Thus, according to one embodiment, the LEDs are connected in series, while according to another embodiment, the LEDs are connected in parallel. According to another embodiment, the LEDs are connected in more complex arrangements, for example, in several series circuits connected in parallel. Fig. 1 shows three light sources, e.g., LEDs 13, as an example. However, the present invention is not limited to this example and allows the use of any number of light sources, such as LEDs 13, ie, the use of at least one light source (e.g., at least one LED).

[0033] The operating device 1 or the operating circuit 1 serves to operate one or more lighting devices 13 (e.g., LEDs). In particular, the operating device 1 serves to supply one or more lighting devices 13, such as LEDs, with power. A supply voltage V in The supply voltage V in is, for example, a direct voltage or a rectified alternating voltage. According to one embodiment, the operating device comprises a power factor correction circuit (not shown) which determines the supply voltage V in provides.

[0034] The operating device 1 or operating circuit 1 includes a synchronous step-down converter 11 (also known as a "step-down regulator," "buck converter," or "step-down converter") as a converter. The step-down converter 11 lowers the voltage from the input to the output of the step-down regulator 11. The current is increased from the input to the output of the step-down regulator 11.

[0035] The synchronous buck converter 11 has a first switch 111 and a second switch 112, wherein the second switch 112 replaces the diode of the conventional or standard buck converter. The first and second switches 111, 112 are controllable. According to further embodiments, the first and / or second switches 111, 112 are designed as power switches, field-effect transistors, bipolar transistors, or transistors with an insulated gate electrode. The present invention allows various suitable embodiments of the first and second switches 111, 112 of the synchronous buck converter 11. By switching the first and second switches 111, 112, current i is supplied via the synchronous buck converter 11. L from the supply voltage V into the at least one light source 13 (e.g., LED). The synchronous down converter 11 has energy storage: a coil 113 and, if necessary, a capacitor 114, which supply the at least one light source 13 (e.g., LED) with current i L in the phases of operation of the synchronous buck converter 11 in which the first switch 111 is switched on or open.

[0036] Usually the current flows i L In the switched-on state of the first switch 111, the current is generated by the at least one illuminant 13 (e.g., LED) and by the coil 113, which is thereby magnetized. The coil 113 is charged with energy. The second switch 112 is usually switched off in this state. After the first switch 111 is switched off, the second switch 112 is switched on, and the coil 113 drives the current i flowing through it. Lfurther through the at least one light source (e.g., LED) 13 and the second switch 112. The energy stored in the magnetic field of the coil 113 discharges. In parallel, the capacitor 114 can be charged when the first switch 111 is initially switched on. During the off phase of the first switch 111, the capacitor 114 can discharge and contributes to the current flow through the at least one light source 13 (e.g., LED). With appropriate dimensioning of the capacitor 114, this can lead to a smoothing of the current through the at least one light source 13 (e.g., LED).

[0037] In the embodiment of the Fig. 1, the first switch 111 and the coil 113 are connected in series between the input and the output of the synchronous buck converter 11. When the at least one light source 13 (e.g., LED) is connected to the synchronous buck converter 11, the first switch 111, the coil 113, and the at least one light source 13 (e.g., LED) are connected in series according to the present embodiment. The capacitor 114 is connected in parallel to the at least one light source 13 (e.g., LED) and the coil 113 (when the second switch 112 is closed). The capacitor 114 is connected in parallel to the output terminals 115, 116 according to the present embodiment, so that the capacitor 114 is connected in parallel to the at least one light source (e.g., LED). The capacitor 114 is an optional element of the synchronous buck converter 11. The capacitor 114 can be formed by the supply line to the lamp 13 or can be integrated on an LED module.

[0038] The operating device 1 further comprises a controller or a control circuit 12, which is designed to control the synchronous buck converter 11. In particular, the controller 12 is designed to control the first and second switches 111, 112 of the synchronous buck converter 11, which Fig. 1 is represented by the arrows leading from the controller 12 to the switches 111, 112.

[0039] According to one embodiment, the controller 12 operates the first and second switches 111, 112 of the synchronous buck converter 11 in a pulsed mode, so that an output current is provided in the form of pulse packets. For example, in this embodiment, pulse packets are generated at lower dimming levels to adjust the average current intensity and thus the brightness perceived by the eye.

[0040] The present invention allows for various configurations of the controller 12. For example, according to one embodiment, the controller 12 is a semiconductor integrated circuit or comprises a semiconductor integrated circuit. According to further embodiments, the controller 12 is configured as a processor, a microprocessor, a controller, a microcontroller, an application-specific integrated circuit (ASIC), or a combination of the aforementioned units.

[0041] The synchronous buck converter 11 is designed to be operated in a first operating mode or in a second operating mode. In the first operating mode of the synchronous buck converter 11, the current i flowing through the synchronous buck converter 11 increases and decreases. L . The decrease and increase of the current i L occur alternately. According to one embodiment, the current i LWhen the current falls, it initially flows towards zero and then flows in a negative direction. If the current i L in the first operating mode and reaches the zero line or when the current i L in the first operating mode and has a predetermined distance from the zero line, a change from the first operating mode to the second operating mode is made according to the embodiment. According to a further embodiment, this occurs after a predetermined number of decreases or increases of the current i L in the first operating mode.

[0042] In the second operating mode, the current waveform of the current flowing through the synchronous buck converter 11 oscillates i Lfor a predetermined period of time. According to one embodiment, this predetermined period of time is predetermined by a predetermined number of decay cycles. After the predetermined period of time has elapsed, the operation of the synchronous buck converter 11 changes from the second operating mode to the first operating mode.

[0043] The inventive operation of the synchronous buck converter 11 is described in Fig. 2 by illustrating the different current waveforms in the two operating modes of the synchronous buck converter 11.

[0044] Fig. Figure 2 shows an exemplary current profile through the synchronous buck converter 11 in the two operating modes of the synchronous buck converter 11 according to an embodiment of the present invention. It should be noted that the number and duration of the different phases in the respective operating modes are merely exemplary and serve to better understand the present invention.

[0045] In Fig. 2, the horizontal axis represents the time sequence and the vertical axis represents the height or level of the current. The horizontal axis intersects the vertical axis in the embodiment of the Fig. 2 at a zero point. Thus, the horizontal axis in Fig. 2 also a zero line.

[0046] The current curve in the first operating mode is in Fig. 2 is divided into three phases by way of example, although the present invention is not limited to this exemplary division. The first and second phases of the first operating mode show the alternating increase and decrease of the current i flowing through the synchronous buck converter 11. L .

[0047] In the first phase of the first operating mode, the current flowing through the synchronous buck converter 11 increases i LThis is achieved by switching on the first switch 111 and by switching off the second switch 112. The switching on and off of the switches 111, 112 is controlled accordingly by the controller 12. According to one embodiment, the current i L until an upper limit or threshold, also referred to as the upper shutdown threshold, is reached. According to another embodiment, the current i L until a predetermined time period has elapsed. If the upper limit is reached or the predetermined time period has elapsed, the flow of current i L lowered (see the second period of the first operating mode in Fig. 2). This is achieved according to the present embodiment by turning off the first switch 111 and turning on the second switch 112.

[0048] As already mentioned, the first and second switches 111, 112 are controlled according to the present embodiment by the controller 12. With regard to the first operating mode, the controller 12 is designed to check whether the rising current i L has reached the upper limit or whether the predetermined time period has elapsed. If the upper limit is exceeded by the increasing current i L has been reached or the predetermined time period has elapsed, the controller 12 controls the synchronous buck converter 11 to change the current direction in the first operating mode. For example, the controller 12 controls the first switch 111 to turn on the first switch 111 and the second switch 112 to turn off the second switch 112.

[0049] In the second phase of the first operating mode, the current flowing through the synchronous buck converter 11 decreases i LThis is achieved by turning off the first switch 111 and turning on the second switch 112. As explained, the switching on and off of the switches 111, 112 is controlled by the controller 12. According to one embodiment, the current i L until a lower limit or threshold, also referred to as the lower shutdown threshold, is reached. According to another embodiment, the current i L until a predetermined time period has elapsed. If the lower limit has been reached or the predetermined time period has elapsed, the flow of current i L to rise (see the third period of the first operating mode in Fig. 2). This is achieved according to the present embodiment by turning on the first switch 111 and turning off the second switch 112.

[0050] As already mentioned, the first and second switches 111, 112 are controlled according to the present embodiment by the controller 12. With regard to the first operating mode and the decreasing current profile, the controller 12 is designed to check whether the decreasing current i L has reached the lower limit or whether the predetermined time period has elapsed. If the lower limit is reached by the decreasing current i L has been reached or the predetermined time period has elapsed, the controller 12 controls the synchronous buck converter 11 to change the current direction in the first operating mode. For example, the controller 12 controls the first switch 111 to turn on the first switch 111 and the second switch 112 to turn off the second switch 112.

[0051] The rise and fall of the current i L, as defined by the first phase and the second phase of the first operating mode in Fig. 2, a predetermined number of times (e.g., N times, where N is a positive integer) can be repeated. When the predetermined number of repeated increases and decreases in the current have been reached in the first operating mode, the switch from the first operating mode to the second operating mode is made. This can also be done by the controller 12. The controller 12 checks, e.g., whether the predetermined number of repeated increases and decreases in the current have been reached in the first operating mode, and upon reaching the predetermined number, initiates the switch from the first operating mode to the second operating mode.

[0052] The first operating mode is switched to the second operating mode when the current increases in the first operating mode and reaches the zero line, or when the current increases in the first operating mode and is at a predetermined distance from the zero line. This can also be detected by the controller 12. If the zero line is reached or the increasing current is at a predetermined distance from the zero line, the second operating mode is switched to (see in Fig. 2 the transition from the third phase of the first operating mode to the second operating mode). In the second operating mode, the current profile of the current flowing through the synchronous buck converter 11 oscillates over a predetermined period of time. In order for the synchronous buck converter 11 to operate in the second operating mode, according to the present embodiment, the first switch 111 is turned off and the second switch 112 is turned off or left off. The corresponding control of the switches 111, 112 is carried out, for example, by the controller 12. Furthermore, the controller 12 is designed, according to the present embodiment, to check whether the predetermined period of time has elapsed. The predetermined period of time is predetermined, for example, by a predetermined number of decay cycles. If the predetermined period of time has elapsed (e.g.If the predetermined number of decay cycles is reached, which can also be determined by the controller 12, a change from the second operating mode to the first operating mode is made. According to the present embodiment, this can also be controlled by the controller 12.

[0053] To switch from the first operating mode to the second operating mode, according to the present embodiment, the first switch 111 is turned on, while the second switch 112 is turned off or remains off. The corresponding control of the switches 111, 112 is carried out by the controller 12 according to the present embodiment.

[0054] The further course of the first operating mode and the subsequent change from the first operating mode to the second operating mode and back are still carried out as discussed above.

[0055] The first operating mode of the synchronous buck converter 11 is, according to one embodiment, a synchronous borderline mode.

[0056] According to a further embodiment of the present invention, the first switch 111 is in the phase of the first operating mode in which the change from the first operating mode to the second operating mode will take place (see in Fig. 2, the third phase of the first operating mode with the first switch 111 switched on and the second switch 112 switched off. If the first switch 111 remains open, the negative current flow (with the decreasing amplitude in the third phase of the first operating mode) is taken over by a body diode of the switch 111 if the switch 111 is configured as a field-effect transistor (FET).

[0057] According to one embodiment, the synchronous buck converter is operated in the two operating modes at low dimming values ​​for the one or more LEDs (e.g., an LED array), since brightness fluctuations are particularly noticeable in this range. At low dimming values, the eye is often particularly sensitive to brightness fluctuations. Furthermore, the relative brightness change corresponding to a change by one clock rate is often greater at low dimming values ​​than at higher dimming values.

[0058] As explained above, the present invention relates to a synchronous buck converter 11 for operating one or more lighting devices 13, wherein the synchronous buck converter 11 is configured to be operated in a first operating mode or in a second operating mode, wherein in the first operating mode of the synchronous buck converter 11, the current flowing through the synchronous buck converter 11 alternately increases and decreases, and wherein in the second operating mode, the current profile of the current flowing through the synchronous buck converter 11 oscillates over a predetermined period of time. Furthermore, the invention relates to a corresponding method for operating one or more lighting devices 13 and to an operating device 1 having the synchronous buck converter 11 and configured to operate the one or more lighting devices 13. List of reference symbols 1 operating device 11 Synchronous buck converter 111 first switch 112 second switch 113 Coil 114 Capacitor 115 Output connector 116 Output connector 12 Control 13 one or more light sources (e.g. LEDs)

Claims

[1] Synchronous buck converter (11) for operating one or more lighting means (13), wherein the synchronous buck converter (11) is designed to be operated in a first operating mode or in a second operating mode, wherein in the first operating mode of the synchronous buck converter (11) current flowing through the synchronous buck converter (11) alternately increases and decreases, and wherein in the second operating mode the current profile of the current flowing through the synchronous buck converter (11) oscillates over a predetermined period of time, wherein the synchronous buck converter (11) has a first switch (111) and a second switch (112) for controlling the current flowing through the synchronous buck converter (11), and the synchronous buck converter (11) is designed such that in the second operating mode the first switch (111) and the second switch (112) are switched off. [2] Synchronous buck converter (11) according to claim 1, wherein in the first operating mode, when the current decreases, the current first decreases towards zero and then flows in a negative direction. [3] Synchronous buck converter (11) according to claim 1 or 2, wherein the synchronous buck converter (11) is configured to switch from the first operating mode to the second operating mode when the current in the first operating mode increases and reaches zero line or when the current in the first operating mode increases and has a predetermined distance from the zero line. [4] Synchronous buck converter (11) according to one of the preceding claims, wherein the synchronous buck converter (11) is designed to change from the second operating mode to the first operating mode after the expiration of the predetermined period of time [5] Synchronous buck converter (11) according to claim 4, wherein the predetermined time period is predetermined by a predetermined number of decay cycles. [6] Synchronous buck converter (11) according to one of the preceding claims, wherein after a change from the second operating mode to the first operating mode, the current flowing through the synchronous buck converter (11) increases. [7] Synchronous buck converter (11) according to one of the preceding claims, wherein the synchronous buck converter (11) is designed such that in the first operating mode, the current flowing through the synchronous buck converter increases by switching on the first switch (111) and switching off the second switch (112) and decreases by switching off the first switch (111) and switching on the second switch (112). [8] Synchronous buck converter (11) according to one of the preceding claims, wherein the first switch (111) is turned off when changing from the first operating mode to the second operating mode. [9] Synchronous buck converter (11) according to one of the preceding claims, wherein the first switch (111) is switched on when changing from the second operating mode to the first operating mode. [10] Synchronous buck converter (11) according to one of the preceding claims, wherein the current flowing through the synchronous buck converter (11) increases up to a first limit value and / or decreases up to a second limit value in the first operating mode. [11] Synchronous buck converter (11) according to one of claims 1 to 9, wherein the current flowing through the synchronous buck converter (11) in the first operating mode increases until the expiration of a first time period and / or decreases until the expiration of a second time period. [12] Synchronous down converter (11) according to one of the preceding claims, wherein the synchronous down converter (11) is designed to be connectable to the one or more lighting means (13) and, when connected to the one or more lighting means (13), is designed to supply the one or more lighting means (13) with the current flowing through the synchronous down converter (11). [13] Synchronous buck converter (11) according to one of the preceding claims, wherein the one or more lighting means (13) comprise one or more light-emitting diodes, LEDs. [14] Method for operating a synchronous buck converter (11) which is designed to operate one or more lighting means (13), wherein the method comprises operating the synchronous buck converter (11) in a first operating mode or in a second operating mode, wherein in the first operating mode of the synchronous buck converter (11) the current flowing through the synchronous buck converter (11) alternately increases and decreases, and wherein in the second operating mode the current profile of the current flowing through the synchronous buck converter (11) oscillates over a predetermined period of time, wherein the synchronous buck converter (11) has a first switch (111) and a second switch (112) for controlling the current flowing through the synchronous buck converter (11), and in the second operating mode the first switch (111) and the second switch (112) are switched off. [15] Operating device (1) for operating one or more lighting means (13), wherein the operating device (1) has a synchronous step-down converter (11) for operating the one or more lighting means (13), and wherein the synchronous step-down converter (11) is a synchronous step-down converter (11) according to one of claims 1 to 13. [16] Operating device (1) according to claim 15, wherein the operating device (1) has a controller (12) which is designed to control the synchronous step-down converter (11). [17] Operating device (1) according to claim 16, wherein the controller (12) controls the operation of the synchronous buck converter (11) in the first operating mode and in the second operating mode, a change in the operation of the synchronous buck converter (11) from the first operating mode to the second operating mode and a change in the operation of the synchronous buck converter (11) from the second operating mode to the first operating mode.

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