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    • 专利摘要:
    A step-down converter (101) for a light-emitting diode (110) comprises a first switch (201, 205, 291) and a second switch (202, 206, 292) connected between a supply voltage terminal (211) and ground (215) in series with the first switch (201, 205, 291) is connected. The buck converter (101) also includes a storage inductor (212) connected in series between the supply voltage terminal (211) and an output terminal (219) with the first switch (201, 205, 291). The step-down converter (101) also includes the output terminal (219), which is set up to output a load current (702) to the light-emitting diode (110) based on an inductor current (701) through the storage inductor (212). The step-down converter (101) also comprises a controller which is set up to operate the first switch (201, 205, 291) and the second switch (202, 206, 292) alternately and periodically in the conductive state depending on a dimming signal.
    公开号:AT17349U1
    申请号:TGM293/2016U
    申请日:2016-11-29
    公开日:2022-01-15
    发明作者:
    申请人:Tridonic Gmbh & Co Kg；
    IPC主号:
    专利说明:

    description
    DOWN CONVERTER FOR ONE LED
    TECHNICAL AREA
    Various examples of the invention generally relate to a step-down converter for a light emitting diode having a first switch and a second switch which are alternately and periodically operated in the conducting state by a controller. In particular, various examples of the invention relate to a buck converter in which the controller operates the first switch and the second switch in response to a dimming signal.
    BACKGROUND
    [0002] Luminaires typically have an operating device for operating light-emitting diodes. The operating device typically includes a buck converter, which is set up to reduce the amplitude of a DC supply voltage for operating the light-emitting diode. In addition, the step-down converter can be set up to change the operation of the light-emitting diode depending on a dimming signal which indicates the desired brightness of the luminaire.
    Conventional step-down converters typically have a switch which is connected in series with a storage inductor between a supply voltage connection and an output connection. During an on-time of the switch - i.e. during which the switch is operated in the conducting state - an inductor current flows through the storage inductor which is fed by the supply voltage and energy is stored in the storage inductor. During an off-time of the switch--during which the switch is operated in the non-conductive state--an inductor current flows, which is fed by the energy previously stored in the storage inductor.
    [0004] Fundamentally different modes of operation of the step-down converter are known. For example, in what is referred to as discontinuous mode, the inductor current may drop to zero during the switch off time. In an operating mode referred to as continuous mode, the inductor current does not drop to zero during the off-time of the switch. In between there is still the so-called borderline mode, which corresponds to the transition between intermittent operation and continuous operation.
    In reference implementations of buck converters, it may be necessary to enable intermittent operation in response to the dimming signal. In particular, it may be necessary in connection with a low desired brightness of the lamp to activate intermittent operation with a particularly long switch off time. Then the brightness of the lamp is modulated with a comparatively low frequency. The LED is typically switched off temporarily, i.e. the load current can drop to zero. Such operation of the lamp is sometimes also referred to as pulse width modulation. This can have various negative effects on the area around the lamp: for example, interference with optical devices can occur.
    [0006] In reference implementations of buck converters, it may also be necessary to switch between discontinuous operation and limit operation depending on the dimming signal. In particular, this can mean that, depending on the dimming signal, there is a particularly sharp jump in the frequency at which the switch is switched. This can require complicated and costly control technology.
    SUMMARY OF THE INVENTION
    [0007] Therefore, there is a need for improved step-down converters and techniques for stepping down a supply voltage for a light emitting diode. In particular, there is a
    allowed for such techniques that address at least some of the above disadvantages and limitations.
    [0008] This object is solved by the features of the independent patent claims. The features of the dependent claims define embodiments.
    In one example, a buck converter for a light emitting diode includes a first switch and a second switch. The second switch is connected in series with the first switch between a supply voltage terminal and ground. The buck converter also includes a storage inductor. The storage inductor is connected in series with the first switch—for example between the supply voltage connection and an output connection. The output connection is set up to output a load current to the light-emitting diode based on an inductor current through the storage inductor. The buck converter also includes a controller. The controller is set up to operate the first switch and the second switch alternately and periodically in the conductive state as a function of a dimming signal.
    In some examples, a buck converter with a first switch and a second switch according to the example above is also referred to as a synchronous converter.
    Sometimes the first switch is also referred to as a high-side switch because it is arranged at potential. Correspondingly, the second switch is sometimes also referred to as a low-side switch because it is arranged between potential and ground. For example, it would be possible for the first switch and/or the second switch to be implemented by a semiconductor switch element. Examples of such semiconductor switching elements include: a transistor; a bipolar transistor; a field effect transistor; a metal oxide field effect transistor; an insulated gate field effect transistor.
    [0012] For example, one side of the storage inductor can be connected to a point which is arranged between the first switch and the second switch. The second side of the storage inductor can be connected to the output connection. The storage choke can be implemented as a coil with multiple windings. The storage choke can provide an inductance. Based on the law of induction, the voltage across the storage inductor (inductor voltage) can be equal to the inductance of the storage inductor multiplied by the change in the inductor current over time. In other words, the storage inductor can counteract particularly rapid changes in the inductor current.
    The output terminal may, for example, comprise a smoothing capacitor, which causes the load current, which is output to the light-emitting diode, to correspond to a time-average value of the inductor current. As a result, the inductor current can be smoothed and a more uniform brightness of the light-emitting diode can be achieved. The output connection could, for example, also have a plug contact, soldering contact, clamping contact, etc., in order to establish an electrical connection of the light-emitting diode.
    The controller can be implemented, for example, as an application-specific integrated circuit (ASIC) or as a microcontroller. The controller could also be implemented as an FPGA or processor. The controller could also be implemented, at least in part, by analog circuitry. The controller could receive the dimming signal via a communication interface, for example.
    By using the first switch and the second switch to generate the load current, the brightness of the light-emitting diode can be flexibly controlled depending on the dimming signal. In particular, it may not be necessary to activate intermittent operation when the light-emitting diode is of low brightness. For example, it would be possible for continuous operation to be activated throughout - i.e. for all brightness levels of the dimming signal.
    For example, it would be possible for the controller to be configured to operate the second switch in the conductive state for an on-time. The on-time of the second switch can be dimensioned in such a way that the polarity of the inductor current changes from positive to negative
    alternates and the voltage at the midpoint of the two switches (midpoint voltage) swings, i.e. e.g. from positive to negative polarity or with respect to another reference voltage, such as a bus voltage. This can mean that the second switch is operated in the conducting state until the direction of the inductor current reverses. For example, the inductor current could be supplied with negative polarity by discharging a capacitor of the output terminal.
    [0017] Because the inductor current has a negative polarity at least at times, a particularly small dimensioned time average value of the inductor current can be achieved. As a result, in turn, a small-sized load current can be output to the light-emitting diode. As a result, low levels of brightness can also be achieved for corresponding dimming signals for the light-emitting diode. In particular, low levels of brightness can be achieved without interrupting the operation of the light-emitting diode using the pulse-width modulation method. A discontinuous mode can be avoided. Disturbing influences on the environment - i.e. flickering of the light-emitting diode, for example - can be reduced or avoided.
    [0018] In some examples, the controller may be configured to implement a dead time during which the first switch and the second switch operate in the non-conducting state. For example, the dead time can provide a certain safety range so that short circuits are avoided. For example, the first switch can first be switched to the non-conductive state before the second switch is switched to the conductive state ("break before make"). A corresponding dead time can be dimensioned to be particularly short and can be in the range from 100 ns to 1000 ns, for example.
    In other examples, it may be desirable for the dead time to be lengthened or made comparatively long. For example, the dead time could be no less than 5% of the second switch on-time, optionally no less than 10% of the second switch on-time, further optionally no less than 25% of the second switch on-time. What can be achieved in this way is that after the second switch has been switched to the non-conductive state—and the first switch is continuously operated in the non-conductive state—the inductor current decreases and finally disappears. It is then possible for the controller to be set up to switch the first switch from the non-conducting state to the conducting state in a time-synchronized manner with the swing in the mid-point voltage (zero voltage switching, ZVS). In this way, the first switch can optionally be switched without current (zero current switching). Such a current-free switching of the first switch has the advantage of low power loss. As a result, the power consumption of the buck converter can be reduced.
    It would be possible for a regulated operation of the first switch and the second switch to be implemented by the controller. This means that the controller could implement a closed loop. What can thereby be achieved is that the brightness of the light-emitting diode can be set particularly precisely and stably by generating the load current.
    For example, the controller could be set up to operate the first switch and the second switch in a regulated manner. The corresponding control circuit can take into account the time average value of the inductor current as a controlled variable. Alternatively or additionally, it would also be possible to take the load current into account as a controlled variable. The corresponding control loop could also take into account a reference variable that is determined based on the dimming signal. For example, it would be possible to use a look-up table to determine the command variable based on the dimming signal in such a way that it can be directly compared with the load current as the controlled variable. In this way it can be possible to set the desired brightness particularly precisely in accordance with the dimming signal.
    For example, the controller could be set up to operate the first switch and the second switch in a regulated manner. The corresponding control circuit can take into account at least one peak value of the inductor current as a manipulated variable. For example, the peak value of the inductor current with positive polarity could be taken into account as a manipulated variable. Alternatively or additionally, it would also be possible to take into account the peak value of the inductor current with negative polarity as a manipulated variable, which means that operation is in a particularly good
    driving point can be reached. Alternatively or additionally, it would be possible, for example, to take into account the duty cycle of the on-time of the first switch and/or the second switch as a manipulated variable. Alternatively or additionally, it would also be possible, for example, to take into account the on-time of the first switch and/or the second switch as a manipulated variable. Alternatively or additionally, it would also be possible, for example, to take into account the off time of the first switch and/or the second switch as a manipulated variable.
    It can sometimes be desirable to keep the peak value of the inductor current constant with negative polarity. In this way, current-free switching of the first switch can be achieved—and at the same time the dead time can be dimensioned comparatively small and fixed.
    It can thus be achieved that the voltage at the midpoint of the two switches can swing around and voltage-free switching on of the first switch is ensured.
    In some examples, it may be desirable for the controller to be set up to operate the first switch and the second switch in a regulated manner, with the peak value of the inductor current being taken into account as a manipulated variable when the polarity is positive, but the peak value of the inductor current when the polarity is negative is kept constant. With a fixed peak value of the inductor current in the case of negative polarity, the voltage-free switching of the first switch can be implemented in a particularly simple manner. In particular, a period of time between the switching of the second switch from the conducting state to the non-conducting state and the switching of the first switch from the non-conducting state to the conducting state can also be kept constant at a fixed peak value of the inductor current with negative polarity.
    For regulated operation, the step-down converter can have a sensor circuit, for example. Using the sensor circuit, it may be possible to obtain a measurement signal that is indicative of the controlled variable. For example, the measurement signal could be indicative of the inductor current. For example, the measurement signal could be indicative of the time average value of the inductor current: a low-pass filter could be provided in the sensor circuit for this purpose, for example. Alternatively or additionally, however, it would also be possible for the measurement signal to be indicative of the inductor current with a large bandwidth, which corresponds to the change in the inductor current due to the law of induction based on the inductance of the storage inductor. Alternatively or additionally, it would also be possible for the measurement signal to be indicative of an inductor voltage across the storage inductor. The sensor circuit can be set up, for example, to bring about a zero point offset between the measurement signal and the inductor current. It can thereby be achieved that the measurement signal has only positive or only negative polarity. A zero crossing of the measuring signal can be avoided - despite the zero crossing of the inductor current. Such a zero offset can be implemented, for example, by providing a further current source that provides a reference current. Such a zero offset could also be achieved, for example, with a suitable voltage divider. Because the measurement signal has only positive polarity or only negative polarity, a particularly simple regulation based on the measurement signal can be implemented.
    In another example, an operating device for a lamp comprises the buck converter according to the various examples described herein. Yet another example relates to the luminaire with the control gear having the buck converter.
    [0028] For example, the operating device could also have an AC/DC converter. The AC/DC converter can be set up to convert an AC supply voltage into the DGC supply voltage, which is then fed to the step-down converter. In other examples, however, it would also be possible for the operating device to receive the DC supply voltage directly.
    In another example, a method includes receiving a dimming signal for a light emitting diode. The method further includes, in response to the dimming signal, alternately and periodically operating a first switch of a buck converter and a
    second switch of the buck converter in the conducting state. In this case, the second switch—for example between a supply voltage connection of the step-down converter and ground—is connected in series with the first switch. The method also includes outputting a load current to the light emitting diode via an output terminal of the buck converter. This is based on a choke current of a storage choke of the step-down converter. The storage inductor is connected in series with the first switch between the supply voltage connection and the output connection.
    For such a method, effects can be achieved that are comparable to the effects that can be achieved for a buck converter according to various examples described herein.
    The features set out above and features described below can be used not only in the corresponding combinations explicitly set out, but also in other combinations or in isolation, without departing from the scope of protection of the present invention.
    BRIEF DESCRIPTION OF THE FIGURES
    FIG. 1 schematically illustrates an operating device of a lamp with a buck converter according to various embodiments.
    [0033] FIGS. 2A and 2B schematically illustrate the buck converter with a first switch and a second switch and a storage inductor according to various embodiments.
    FIG. 3 schematically illustrates the operation of the first switch and the second switch alternately and periodically in the conducting state according to various embodiments.
    FIG. 4 schematically illustrates the operation of the first switch and the second switch alternately and periodically in the conducting state according to various embodiments, wherein in the example of FIG. 4 a dead time is provided.
    [0036] FIGS. 5A and 5B schematically illustrate the buck converter with a first switch and a second switch and a storage inductor and a sensor circuit according to various embodiments.
    FIG. 6 is a flow diagram of a method according to various embodiments.
    FIG. 7 is a flow diagram of a method according to various embodiments.
    DETAILED DESCRIPTION OF EMBODIMENTS
    The properties, features and advantages of this invention described above, and the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the exemplary embodiments, which are explained in more detail in connection with the drawings.
    The present invention is explained in more detail below using preferred embodiments with reference to the drawings. In the figures, the same reference symbols designate the same or similar elements. The figures are schematic representations of various embodiments of the invention. Elements depicted in the figures are not necessarily drawn to scale. Rather, the various elements shown in the figures are presented in such a way that their function and general purpose can be understood by those skilled in the art. Functional units can be implemented in hardware, software, or a combination of hardware and software.
    Techniques related to converting a DC supply voltage are described below. The techniques described herein relate in particular to stepping down the DC supply voltage, i.e. step-down. The techniques described herein can be used in particular in connection with the operation of light-emitting diodes. In other examples, however, it would also be possible for the techniques described herein to be used in other areas of application. Examples include charge storage, power supplies for electronic devices, or other forms of light sources, etc.
    In various examples, the supply voltage is converted as a function of a dimming signal for the light-emitting diode. The dimming signal can be indicative of a desired brightness of the light-emitting diode. In this case, the conversion can output a specific load current to the light-emitting diode, it being possible for the load current to be greater (lower) for greater (lower) desired brightnesses.
    The various techniques described herein are described in particular in relation to a particular buck converter architecture: This buck converter architecture uses a first switch placed at potential and a second switch placed between potential and ground. In comparison to other architectures of step-down converters that only use a diode instead of the second switch, particularly energy-efficient operation can be achieved in this way: in particular, the voltage drop across the diode can be avoided by using the second switch.
    The techniques described herein make it possible to implement different brightnesses for the light-emitting diode without using pulse width modulation. This can prevent the light-emitting diode from flickering at low levels of brightness. Additionally, the techniques described herein may allow for simple control that does not require switching between continuous or limit operation of the buck converter and intermittent operation of the buck converter.
    FIG. 1 illustrates aspects relating to an operating device 100 for a light-emitting diode 110. For example, the operating device 100 could be part of a lamp. The lamp could further include a housing, heat sink, battery backup, etc.
    The operating device 100 includes an AC/DC converter 104 which is set up to convert an AC supply voltage 151 into a DC supply voltage 152 . The AC supply voltage 151 is received via a power connection 153 . For example, the AC supply voltage 151 could have an amplitude in the range of 100V to 300V. For example, the AC/DC converter 104 could include a rectifier bridge circuit (not shown in FIG. 1). The AC/DC converter 104 is optional: in other examples, the operating device 100 could receive a DC supply voltage directly.
    The operating device 100 also includes a DC/DC converter 101. The DC/DC converter 101 is set up to convert the DC supply voltage 152. In particular, the DC/DC converter 101 is set up to step down the DC supply voltage. Therefore, the DC/DC converter 101 is referred to as buck converters 101 hereinafter. The light emitting diode 110 is operated based on the DC supply voltage. For this purpose, a load current can be provided by the step-down converter 101 and output to the light-emitting diode 110 .
    The down converter 101 is driven by a controller 102 . For example, controller 102 could implement regulated operation of buck converter 101 . Thereby, the operation of the light emitting diode 110 can be stabilized. In addition, the operation of the light-emitting diode 110 can be controlled by external specifications.
    In the example of FIG. 1, the controller 102 receives a dimming signal 161 via a communication interface 103. In the example of FIG. 1, the dimming signal 161 is received via a dedicated transmission medium 162, e.g. a DALI interface. In other examples, however, it would also be possible for the dimming signal 161 to be received via the mains connection 153 (not shown in FIG. 1). For example, the dimming signal 161 on the
    AC supply voltage 151 are modulated. An example would be phase cut modulation.
    The controller 102 can control the operation of the light-emitting diode 110 depending on the dimming signal 161 as an external specification or control variable. For example, the controller 102 could control the step-down converter 101 in such a way that the load current assumes different values depending on the dimming signal 161 .
    The dimming signal can also be specified, for example, by a resistor connected to the operating device 100, with the resistance value preferably specifying the rated current of the light-emitting diode. A potentiometer could also be connected as a variable resistor, which would also make it possible to change or set the nominal current.
    FIG. 2A and 2B illustrate aspects related to buck converter 101. In particular, FIG. 2A shows the buck converter 101 in more detail. FIG. 2A is a circuit diagram of the buck converter 101.
    The step-down converter 101 is set up to receive the DC supply voltage 152 via a supply voltage connection 211 . A field effect transistor 201 with a free wheeling diode 205 implements a switch 291. A field effect transistor 202 with a free wheeling diode 206 implements a switch 292. The switch 291 and the switch 292 are connected between the supply voltage terminal 211 and ground 215 in series.
    The step-down converter 101 also includes a storage inductor 212. The storage inductor 212 and the switch 291 are connected in series between the supply voltage connection 211 and an output connection 219 for the light-emitting diode 110. In FIG. 2a also illustrates an inductor current 701 through the storage inductor 212. An orientation of the inductor current 701 towards the output terminal 219 (as represented by the corresponding arrow in FIG. 2a) is hereinafter referred to as the positive polarity of the inductor current 701.
    The output terminal 219 has a smoothing capacitor 213 with a resistor 214 . Therefore, the load current 702, which is provided based on the inductor current 701 of the light-emitting diode 110, corresponds to a time average value of the inductor current 701.
    In FIG. 2A also shows that a control signal 601 is present at a control contact of the field effect transistor 201 of the switch 291. By means of the control signal 601 it is possible to operate the switch 291 either in the conductive state or in the non-conductive state. Furthermore, it is possible to switch the switch 291 from the conductive state to the non-conductive state and to switch it from the non-conductive state to the conductive state. For example, the control signal 601 can be generated by the controller 102 . This allows the controller 102 to selectively operate the switch 291 in the conductive state or in the non-conductive state.
    In FIG. 2a also shows that a control signal 602 is present at a control contact of the field effect transistor 202 and thus of the switch 292. By means of the control signal 602 it is possible to operate the switch 292 selectively in the conducting state or in the non-conducting state. Furthermore, it is possible to switch the switch 292 from the conducting state to the non-conducting state and to switch it from the non-conducting state to the conducting state. For example, control signal 602 may be generated by controller 102 . This allows the controller 102 to selectively operate the switch 292 in the conductive state or non-conductive state.
    In some examples, the controller 102 is set up to operate the switch 291 and the switch 292 alternately and periodically in the conductive state depending on the dimming signal 161 .
    Figure 2B shows an alternative implementation of a buck converter. In contrast to FIG. 2A, in FIG. 2B the light-emitting diode 110 with the parallel capacitor 213 is not connected to the ground point 215 but to the supply voltage connection 211. The storage inductor 212 is magnetized during the on time of the switch 292.
    The phase of the positive increase in the inductor current 701 is the on time of the switch 292. The freewheeling phase, i.e. the phase of demagnetization of the storage inductor 212, takes place via the switch 291. The time phase of the negative increase in the inductor current 701 is the on time of the switch 291 .
    FIG. 3 illustrates aspects related to operating the switches 291, 292 alternately and periodically in the conducting state. FIG. 3 schematically illustrates the timing of the control signal 601 and the control signal 602. FIG. 3 also schematically illustrates the resulting time profile of the inductor current 701.
    From FIG. 3 that switch 291 is operated in the conducting state during repeated on-times 651 . The switch 291 is operated in the non-conductive state during repeated off times 652 . The switch 292 is accordingly operated in the conducting state during repeated on-times 661 . The switch 292 is operated in the non-conductive state during repeated off times 662 . In the example of FIG. 3 shows the period duration 670 with which the switches 291, 272 are periodically operated in the conductive state.
    From FIG. 3 that switch 292 is in the conducting state whenever switch 291 is in the non-conducting state. Also, whenever switch 292 is in the non-conducting state, switch 291 is in the conducting state. Accordingly, the switches 291, 292 are alternately operated in the conductive state.
    In particular, the on-time 661 of the switch 292 is dimensioned such that the polarity of the inductor current 701 changes from positive to negative at the time 755 . By implementing the inductor current 701 with an at least temporarily negative polarity, it can be achieved that the time mean value 712 (horizontal dashed line in FIG. 3) of the inductor current 701—and thus the load current 702—assumes particularly low values close to zero. As a result, low levels of brightness of the light-emitting diode 110 can be achieved.
    In the example of FIG. 3 it might be possible to provide a dead time between the switching of the switches 291, 292 (not shown in FIG. 3). Such dead time can avoid short circuits. Such a dead time to avoid short circuits can be dimensioned to be particularly short: in particular, the switches 291, 292 are switched essentially at the same values of the inductor current 701. In the example in FIG. 3, these values of the inductor current 701, at which the switches 291, 292 are switched, correspond to peak values 751, 752 of the inductor current 701 (compare vertical dashed lines in FIG. 3). In some examples it may also be possible to provide a longer dead time.
    FIG. 4 illustrates aspects related to operating the switches 291, 292 alternately and periodically in the conducting state. The example of FIG. 4 corresponds in principle to the example in FIG. 3. However, in the example of FIG. 4 a comparatively long dead time 671 is provided. In the example of FIG. 4, the dead time 671 is approximately 25% of the on time 661 and approximately 20% of the off time 652. During the dead time 671, both the switch 291 and the switch 292 are operated in the non-conductive state. Therefore, the switch 292 is switched from the conducting state to the non-conducting state at a different value of the inductor current 701 than the switch 291, which is switched from the non-conducting state to the conducting state. In particular, the switch 291 is switched from the non-conducting state to the conducting state in time synchronization with the transition of the midpoint voltage of both switches 291 and 292. Alternatively or additionally, the switch 291 can be switched from the non-conductive state to the conductive state in a time-synchronized manner with a zero crossing 753 of the inductor current 701 . There is also an optional dead time between the on time 651 and the off time 652 (not shown in FIG. 4). This dead time between turning off switch 291 and turning on switch 292 can be dimensioned in order to avoid a short circuit through both switches 291 and 292 .
    The operation of the switches 291, 292 - for example according to the implementations
    of the FIGs. 3 and 4 - can be regulated in some examples. For example, the time mean value 712 of the inductor current 701 could be taken into account as a controlled variable since this can be directly proportional to the load current 702. For example, the dimming signal 161 or a variable derived from it could be taken into account as a reference variable. A deviation between the reference variable and the controlled variable can then be minimized by suitable operation 291, 292.
    In principle, different manipulated variables could be taken into account in a corresponding regulation. For example, the duty cycle for the operation of the switch 291 in the conducting state and/or for the operation of the switch 292 in the conducting state could be taken into account as a manipulated variable. For example, the peak value 751 of the inductor current 701 with positive polarity and/or the peak value 752 of the inductor current 701 with negative polarity could be taken into account as a manipulated variable. In some examples, it may be desirable for the peak value 752 of the inductor current 701 to be regulated to a constant value in the case of negative polarity in order to reduce the dead time 671 while at the same time enabling the switch 291 to be switched without current.
    The FIGS. 5A and 5B illustrate aspects related to the buck converter 101. The examples of FIGs. 5A and 5B basically correspond to the example of FIG. 2.
    In the example of FIG. 5A also shows a sensor circuit 301 and a sensor circuit 311. The sensor circuit 301 is set up to output a measurement signal at the connection 302 which is indicative of a current value of the inductor current 701 . The inductor current 701 is detected by means of the resistor 214. The sensor circuit 301 is also set up to output a measurement signal at the connection 303 which is indicative of the time average value 712 of the inductor current 701: a low-pass filter is provided for this purpose. Optionally, it would be possible for the sensor circuit 301 to be set up to bring about a zero offset between the measurement signal at the connection 302 and the inductor current 701). As a result, it can be achieved that the measurement signal does not have changing polarities—corresponding to the inductor current 701: this can simplify the determination of the peak values 751, 752 and/or an implementation of the control loop.
    [0070] The zero point offset can be implemented, for example, by means of a current source, which can preferably be integrated into the controller. This example is shown in Figure 5A. Alternatively, for example, the zero point offset can be implemented by means of a pull-up resistor (sometimes also referred to as a pull-up resistor), which is preferably connected to a supply voltage such as the supply voltage Vec of the operating device. This example is shown in Figure 5B.
    The sensor circuit 311 comprises a coil which is inductively coupled to the storage inductor 212. The sensor circuit 311 is set up to output a measurement signal at the connection 312 which is indicative of the inductor voltage and thus also of the voltage at the midpoint of the two switches 291 and 292 . Alternatively, for example, the midpoint voltage of the two switches 291 and 292 can also be measured via a voltage divider which taps off the voltage at the midpoint of the two switches 291 and 292. In the example of FIG. 5A , the voltage at the mid point of the two switches 291 and 292 swings over to the voltage of the supply voltage connection 211 . In the example of FIG. 2B , the midpoint voltage of the two switches 291 and 292 can resonate with the voltage at ground point 215 .
    FIG. 6 is a flow chart of a method according to various examples. First, in block 1001, a dimming signal is received. The dimming signal can be indicative of a desired brightness of a light-emitting diode of a lamp. The dimming signal can be received in analog form or digital form, for example. For example, the dimming signal could be received through phase cut modulation of an AC supply voltage.
    A first switch and a second switch of a step-down converter are then operated alternately and periodically in the conductive state. It would be optionally possible to
    to provide times during which both the first switch and the second switch are operated in the non-conductive state.
    For example, it would be possible for current-free switching of the first switch and/or current-free switching of the second switch to be achieved on the basis of a corresponding dimensioning of the dead times.
    [0075] By switching the switches, an inductor current can be modified by a storage inductor of the step-down converter. In particular, the storage inductor can be alternately charged and discharged by switching the switches.
    Subsequently, in block 1003, a load current is output to the light-emitting diode. For example, the load current can correspond to an average value of the inductor current. The load current is supplied alternately by the supply voltage and the storage choke.
    FIG. 7 is a flow chart of a method according to various examples. FIG. 7 illustrates details related to the regulated operation of the first switch and the second switch. For example, the method of FIG. 7 to be executed as part of block 1002. First, in block 1011, a command variable is determined based on the dimming signal.
    Then, in block 1012, a time average value of the inductor current is determined as the controlled variable. Alternatively or additionally, the load current could also be taken into account as a controlled variable.
    It is then possible to compare the controlled variable with the reference variable. The aim of the regulation can be to minimize deviations between the controlled variable and the reference variable. To do this, one or more control variables can be changed. For example, the peak value of the inductor current could be changed as a manipulated variable with positive polarity. As an alternative or in addition, the peak value of the inductor current could also be changed as a manipulated variable in the case of negative polarity. This occurs in block 1013.
    Of course, the features of the embodiments and aspects of the invention described above can be combined with one another. In particular, the features can be used not only in the combinations described, but also in other combinations or taken on their own, without departing from the field of the invention.
    权利要求:
    Claims (10)
    [1]
    A light emitting diode (110) buck converter (101) comprising:
    - a first switch (201, 205, 291),
    - a second switch (202, 206, 292), which is connected between a supply voltage connection (211) and ground (215) in series with the first switch (201, 205, 291),
    - a storage choke (212) which is connected in series with the first switch (201, 205, 291),
    - An output terminal (219) which is set up to output a load current (702) to the light-emitting diode (110) based on an inductor current (701) through the storage inductor (212), and
    - A controller (102) which is set up to operate the first switch (201, 205, 291) and the second switch (202, 206, 292) in dependence on a dimming signal (161) alternately and periodically in the conductive state.
    [2]
    The buck converter (101) of claim 1, wherein the controller (102) is arranged to operate the second switch (202, 206, 292) in the conducting state for an on-time (661), the on-time ( 661) of the second switch (202, 206, 292) is dimensioned such that the polarity of the inductor current (701) changes from positive to negative.
    [3]
    The buck converter (101) of claim 2, wherein the controller (102) is arranged to implement a dead time during which the first switch and the second switch are operated in the non-conductive state.
    [4]
    4. Buck converter (101) according to any one of the preceding claims, wherein the controller (102) is arranged to switch the first switch (201, 205, 291) time-synchronized with the swing of a midpoint voltage between the first switch (201, 205, 291) and switching the second switch (202, 206, 292) from the non-conductive state to the conductive state.
    [5]
    5. Buck converter (101) according to one of the preceding claims, wherein the controller (102) is set up to operate the first switch (201, 205, 291) and the second switch (202, 206, 292) in a controlled manner with the time average value of the Inductor current (701) as a controlled variable and with a reference variable based on the dimming signal (161).
    [6]
    6. Buck converter (101) according to any one of the preceding claims, wherein the controller (102) is set up to operate the first switch (201, 205, 291) and the second switch (202, 206, 292) in a regulated manner with at least one peak value the inductor current (701) as a manipulated variable.
    [7]
    7. Buck converter (101) according to claim 6, wherein the controller (102) is set up to operate the first switch (201, 205, 291) and the second switch (202, 206, 292) regulated with the peak value of the inductor current ( 701) with positive polarity as a manipulated variable and with a constant peak value of the inductor current (701) with negative polarity.
    [8]
    A buck converter (101) according to any one of the preceding claims, further comprising:
    - a sensor circuit (301) which is set up to output a measurement signal which is indicative of the inductor current (701), the sensor circuit being set up to bring about a zero offset between the measurement signal and the inductor current (701).
    [9]
    9. Method comprising: - receiving a dimming signal (161) for a light-emitting diode (110), - depending on the dimming signal (161): alternating and periodic operation of a first switch (201, 205, 291) of a step-down converter (101) and a second
    switch (202, 206, 292) of the step-down converter (101), which is connected between a supply voltage connection (211) and ground (215) in series with the first switch (201, 205, 291), in the conducting state, and
    - based on an inductor current (701) of a storage inductor (212) connected in series with the first switch (201, 205, 291): outputting a load current (702) to the light-emitting diode (110) via an output terminal (219).
    [10]
    10. The method of claim 9, wherein the method is performed by the down-converter (101) of any one of claims 1-8.
    8 sheets of drawings
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    同族专利:
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    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    DE102016221398.9A|DE102016221398A1|2016-10-31|2016-10-31|DOWN TRANSFORMER FOR ONE LIGHT DIODE|
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