Pulse-width modulated control of a clocked circuit with adjustable power transmission

Abstract

Operating device (1) for light source, in particular converter for at least one LED, comprising a control unit (14) designed to control a clocked circuit (20), such as e.g.a PFC circuit, to be controlled by means of a pulsed signal (52) which is supplied directly or indirectly to a switch of the clocked circuit (20) as a control signal, wherein the control unit is designed to generate the pulsed signal: - which changes in a dimming range above a predetermined threshold value in that the on-time of the pulses changes at a preferably fixed frequency of the pulses, and - which changes in a dimming range below a predetermined threshold value in that the off-time of the pulses increases stepwise towards lower dimming values ​​and in the ranges of constant off-time the on-time changes continuously and in the range of jumps of the steps of the off-time the on-time increases stepwise with a sawtooth shape, wherein a k-factor is increased in the area of ​​the sawtooth shape of the time.

Description

The invention relates to a method and an operating device for lighting means for carrying out the method for pulse-width-modulated actuation of a clocked circuit, in particular a power factor correction circuit (PFC circuit), in use in operating devices for lighting means, that is to say for example for direct or indirect actuation of an LED path.Pulse-width modulated (PWM) controls are based on a modulation type in which a technical variable (e.g. electrical voltage) changes between two values. At a constant frequency, the duty cycle (pulse duration versus period duration) of a square-wave pulse is modulated, i.e. the width of the pulse forming it. However, PWM controls are also known in which the frequency of the pulses can change. In the context of the present invention, this further definition of PWM is used.A pure pulse width modulated signal is generated, for example, by comparing a linearly increasing or decreasing signal (triangular or sawtooth voltage) with the analog input signal which, depending on its value, lies a short time or a long time above it. At the intersections, the output signal is switched between two logic levels. It thus has the advantage, like a digital signal, that it can only assume-here: two-discrete values, but its duty cycle can be continuously changed.If, therefore, during operation of dimmable lighting, a lower light power is predefined by a dimming value specification or another load specification, the duty cycle of the pulse width modulation (referred to below as PWM modulation or as PWM regulation) is preferably reduced at a constant frequency until a predefined minimum value is reached for the time at which the first logic level has been set. This time is referred to below as t on- time, since up to this point in time typically the (load) switch (e.g. an FET) of a clocked circuit (e.g. a PFC circuit) is switched on. The minimum value for t on alone cannot be undershot, since it is defined by physical boundary conditions (e.g. by resolution and control limits of the associated control circuit and by the time constants of AD converters etc.).Thus, if a further load reduction is to be achieved after the minimum value of the t on- time has been reached, this is effected according to the present state of the art by extending the remaining time of the period, i.e. until the beginning of the subsequent pulse. This time is referred to below as t off- time, since the (load) switch is switched off up to this point in time. By extending the t off- time, there is an increase in the so-called K factor which indicates the ratio of the "non-current flow time" divided by the "current flow time".In the PFC circuit technology ("power factor correction", PFC), the current flow time is the time in which current flows through the input-side inductance (charging and discharging current I L). The term "non-current flow time" refers to the time during which no current flows.While the PWM control in a high load region has to cope with only t on- time control, in a low load region, the t on- time control must be "frozen" at the t on- minimum value and changed to control by changing the turn-off time t off. The latter makes very high demands on the circuit technology and cannot be implemented without continuously recurring faults in the operating sequence.German laid-open specification DE 10 2014 220 099 A1 describes a clocked electronic energy converter having an electronic switching element, at least two electrical energy stores, a connection for connecting an electrical energy source, a connection for connecting an electrical energy sink, a clock generator for driving and operating the electronic switching element in switching operation, and a setting unit which is designed to provide a first signal for setting a power to be transmitted of the energy converter. In this case, the clock generator is designed to set the power to be transmitted of the energy converter in the second power range by means of the switch-on time (ton) of the electronic switching element, and in a second power range in which the power to be transmitted of the energy converter is smaller than in the first power range, to set the power to be transmitted of the energy converter in the second power range by means of a combination of the switch-on time (t on) and the supplementary switch-off time (t off_add) wherein the supplementary switch-off time (t off_add) is constant.The invention is therefore based on the object of specifying a method and an operating device for pulse-width-modulated actuation of a clocked circuit, in particular of a power factor correction circuit (PFC circuit), which method and operating device make possible problem-free and fault-free dimming in the range of low or very low load of arbitrary lighting paths.This object is achieved according to the present invention by the features of the independent claims. The central idea of the invention is further developed in a particularly advantageous manner by the dependent claims.According to the invention, an operating device for lighting means is claimed, in particular a converter for at least one LED, which converter has a control unit which is designed to actuate a clocked circuit, such as a PFC circuit, by means of a pulsed signal. According to the invention, the signal changes in a dimming range above a predetermined threshold value in that, with a preferably fixed frequency of the pulses, the switch-on time duration t on of the pulses changes, and in a dimming range below a predetermined threshold value in that the switch-off time duration t off of the pulses increases stepwise in the direction of low dimming values and the switch-on time duration t on changes continuously in the regions of constant switch-off time duration and the switch-on time duration t on increases stepwise in the region of the jumps of the steps of the switch-off time duration t off with a sawtooth-shaped profile, wherein a k-factor is increased in the region of the sawtooth-shaped profile of the t on- time.Alternatively, an operating device for lighting means is claimed, in particular a converter for at least one LED, which converter has a control unit which is designed to actuate dimmable operation of the lighting means, wherein the control unit is designed to output a pulsed signal. This signal changes in a dimming range above a predetermined threshold value in that, with a preferably fixed frequency of the pulses, the switch-on time duration t on of the pulses is changed. Furthermore, the signal changes in a dimming range below a predefined threshold value in that the switch-off time duration t off of the pulses is at least partially continuously increased in the direction of low dimming values and the switch-on time duration t on is continuously decreased with a sawtooth-shaped profile, wherein a k-factor is increased in the range of the sawtooth-shaped profile of the t on- time.According to the invention, the control unit of such an operating device can have a PWM modulator to which a predefined signal for the switch-off time duration t off of the pulses is fed from a controller, wherein the PWM modulator regulates the switch-on time duration t on as a function of a feedback signal which directly or indirectly reflects a parameter of the operation of the lighting means.According to the invention, the controller of such an operating device has an interface for receiving a dimming signal.Furthermore, a method is claimed according to the invention for operating a PFC circuit for operating lighting means, in particular at least one LED, wherein the switch of the PFC circuit is clocked by a signal. This method is characterized in that in a dimming range above a predetermined threshold value, the signal changes in that, with a preferably fixed frequency of the pulses, the switch-on time duration t on of the pulses changes.Furthermore, the clocked signal can change in a dimming range below a predetermined threshold value in that the switch-off time duration t off of the pulses increases stepwise in the direction of low dimming values, the switch-on time duration t on changes continuously in the regions of constant switch-off time duration, and the switch-on time duration t on increases stepwise with a sawtooth profile in the region of the jumps of the stages of the switch-off time duration t off a k-factor being increased in the region of the sawtooth profile of the t on- time.Further advantages, features and characteristics of the present invention are explained in more detail below on the basis of exemplary embodiments with reference to the accompanying drawings. FIG. 1 shows a lighting system with an actively clocked power factor correction circuit (PFC) according to a possible embodiment, FIG. 2 shows a circuit diagram of an actively clocked power factor correction circuit according to a possible exemplary embodiment, FIG. 3 shows currents and voltages for explaining the mode of operation of the actively clocked power factor correction circuit according to the exemplary embodiment of FIG. 2 in a possible operating mode, FIG. 4 shows the principle of the simplest embodiment of a feedback-based PFC circuit according to the prior art, FIG. 5 shows the principle of a K-factor-based feedback of a PFC circuit according to the prior art, FIG. 6 shows the pulse curve of a K-factor-based PFC circuit according to the prior art, FIG. 7 shows the dependence of t on or the K factor on the load in a PFC circuit according to the prior art, FIG. 8 shows the principle of an external K-factor-based feedback of a PFC circuit according to the invention, FIG. 9 shows the dependence of t on or the K factor on the load in a PFC circuit according to the present invention.One field of application of the invention is operating devices with power factor correction. A power factor correction (PFC) is used to eliminate or at least reduce harmonic currents in an input current. Harmonic currents can occur in particular in the case of nonlinear consumers, such as rectifiers with subsequent smoothing in power supplies, since in the case of such consumers the input current is shifted in phase and distorted non-sinusoidally in spite of the sinusoidal input voltage. The higher-frequency harmonics occurring in this case can be counteracted by an active or clocked power factor correction circuit connected upstream of the respective device.For power factor correction circuits, a circuit topology is frequently used which is based on a boost converter, also referred to as a boost converter or boost converter. In this case, an inductance or coil supplied with a rectified alternating voltage is charged or discharged with an input current by switching on / off a controllable switch. The discharge current of the inductance flows via a diode to the output of the converter coupled to an output capacitance, so that a DC voltage increased compared to the input voltage can be tapped at the output. Other types of converters may also be used. Power factor correction circuits may operate in different modes of operation. In particular, operation with a continuous current through the aforementioned inductance is (so-called "continuous conduction mode". CCM), a discontinuous conduction mode (DCM) operation, or a boundary area continuous and discontinuous conduction mode (BCM) operation. In BCM operation, a drop in coil current to zero during the coil discharge phase may take as a reason to start a new switching cycle and turn the switch back on to recharge the coil. Over the duration of the time during which the switch is switched on in each case, the power factor correction circuit can be controlled or regulated. In DCM operation, on the other hand, after a zero crossing of the coil current during the discharge phase, a predefined additional waiting time will first be allowed to wait until the switch is closed again.DE 10 2004 025 597 A1 describes a power factor correction circuit in which an output direct voltage is derived during the switch-off time duration of the switch.When operating a power factor correction circuit in DCM mode, the waiting time before the converter is switched on again can be selected depending on a load, i.e. depending on an output power of the power factor correction circuit, in order to maintain a predefined bus voltage. If the switch is switched on again immediately after this time has elapsed, this can lead to irregularities in the coil current. If the switch-on time is selected only as a function of the predefined waiting time and independently of the behavior of the power factor correction circuit, increased dissipation and thus heating of the switching means can also occur. It is an object to provide methods and apparatuses which offer improvements in view of the aforementioned problems. It is an object to specify methods and devices for power factor correction in which operation over a relatively wide range of loads is possible. It is also an object to provide methods and devices in which the dynamic behavior of the power factor correction circuit during the period in which the switch is in the off state can be taken into account in the determination of the switch-on time.In methods and devices according to exemplary embodiments, a power factor correction circuit for a lighting means can be operated in a plurality of operating modes. Depending on a load, which can be detected via the output power, for example, one operating mode can be selected from a plurality of operating modes. In a first operating mode, which can be a DCM operating mode, a minimum waiting time is determined between the switching off of the switching means and a renewed switching on of the switching means. A switch-on time for the switching means is determined not only as a function of the minimum waiting time, but also as a function of a voltage dropping across the switching means. This allows consideration of the dynamic behavior of the power factor correction circuit during the off state of the switching means for determining the switch-on time. In a power factor correction circuit according to one exemplary embodiment, a control device is configured to carry out the corresponding method.The switching means can be a power switch, in particular an FET or MOSFET, and the voltage dropped across the switching means can be the drain-source voltage of the power switch while the power switch is switched to the off state.The control device of the power factor correction circuit can define the switch-on time as a function of the time-dependent behavior of the voltage dropping across the drain-source path of the power switch. The controller of the power factor correction circuit may define time slots corresponding to allowable on-times, each of which is at the times at which the voltage dropping across the drain-source path of the power switch approaches or crosses a local minimum. That is, the switch is only turned on when not only the minimum waiting time has elapsed but the voltage at the switching means is in a "valley". Such a procedure is also referred to as "valley switching". The control device of the power factor correction circuit can obtain information about the voltage at the drain-source path of the switching means or its change in various ways. In one configuration, the current flowing through the inductance of the power factor correction circuit can be detected and the point in time at which the voltage at the drain-source path of the switching means has an extreme can be determined as a function of a comparison of the current through the coil with a reference value. The control device can be supplied with a corresponding measurement signal which indicates the current in the coil or its zero crossings. The measurement signal may be generated to indicate zero crossings of the coil current and its direction. A local minimum or trough of the voltage at the switching means can be detected as a function of a zero crossing of the coil current in a specific direction.For detecting the zero crossing of the current, a corresponding detection circuit can be provided, with which, for example, the coil current is detected over one winding and compared with a reference value.The control device of the power factor correction circuit can transition between the first operating mode and a second operating mode depending on the load or output power of the power factor correction circuit. The second operating mode may be a CCM operation or a BCM operation. In the second operating mode, the power factor correction circuit can be controlled or regulated by setting the on-time during which the switching means is switched on in each case. In the first operating mode, the power factor correction circuit can be controlled or regulated by setting the minimum waiting time. In the first operating mode, the on-time during which the switching means is switched on in each case can be selected to be equal to the value which corresponds to the minimum value of the on-times permissible in the second operating mode. The minimum waiting time can only be defined and used in the first operating mode for the control of the power factor correction circuit.When the controller of the power factor correction circuit detects that the load or output power falls below a threshold value, the controller may automatically switch from the second operating mode to the first operating mode.The power factor correction circuit according to embodiments can be used in particular for power factor correction for an AC / DC converter, so that in this case the input voltage is a rectified AC voltage and the output voltage is a DC voltage. The power factor correction circuit according to embodiments may be constructed according to the topology of a boost converter, so that the discharge current of the inductance is supplied via a diode to the output terminal coupled to an output capacitance. The described methods and configurations can also be applied to other converter topologies. In each of the exemplary embodiments, in the first operating mode, for example in the DCM operating mode, a switch-on time can be selected such that cumulatively the following three conditions are fulfilled: the minimum waiting time has expired; the current through the inductance is at a zero crossing; and the drain-source voltage of the switching means has dropped to a local minimum.The control device can be designed in the form of an integrated circuit, in particular an application specific integrated circuit (ASIC). The control device can have a common measurement input for detecting a measurement variable corresponding to the coil current or a zero crossing of this current, which is also used for determining the time windows which correspond to a local minimum or the voltage dropping across the switching means.The method and power factor correction circuit can be used in an operating device for a lighting means, for example for an electronic ballast for fluorescent lighting means or for an LED converter. In this application, embodiments of the invention make it possible to adapt over a wide range of different power levels or components of the respectively used operating device and, in the process, to achieve energy-efficient switching even in a DCM operating mode.FIG. 1 shows a block diagram representation of a lighting system 1, which has an operating device 2 and a lighting means 3 operated by the latter, for example one or more LEDs or OLEDs. The operating device 2 can be connected to a bus 4 or a wireless communication system in order to receive dimming commands and / or output status messages.The operating device 2 can be designed, for example, as an electronic ballast (EVG) for a gas discharge lamp, fluorescent lamp or another fluorescent lighting means or as an LED converter. The operating device 2 has a rectifier 10 for rectifying a supply voltage, for example the mains voltage. The operating device 2 has a circuit 1 for power factor correction with an associated control device 14.The power factor correction circuit provides an output voltage for downstream components of the operating device 2, which is also referred to as bus voltage Vbus. A further voltage conversion and / or dimming functions can be achieved, for example, via a DC / DC converter 12, which can be designed as an LLC resonant converter, and / or an output driver 13.The operation of the power factor correction circuit and its controller 14 will be described in more detail with reference to FIGS. 2 and 3.Generally, the controller 14 may control the power factor correction circuit into a plurality of modes of operation including at least a discontinuous conduction mode (DCM) mode of operation as the first mode of operation and a second mode of operation. The second operating mode can be selected from a CCM ("continuous conduction mode") operating mode and a BCM ("border conduction mode" or "boundary conduction mode") operating mode. In the first operating mode, an adaptation to different load or different output power can be achieved by setting a minimum waiting time which must pass between the switching off of a switching means and the renewed switching on. The control device 14 controls the switching means in such a way that not only does the expiration of the minimum waiting time enter into the criterion for switching on the switching means, but also the time-dependent behavior of the power factor correction circuit is taken into account. The switching means can be switched on again depending on whether the minimum waiting time has elapsed and a drain-source voltage of the switching means meets a specific criterion. The criterion may include that the drain-source voltage of the switching means reaches a local minimum value as a function of time. This criterion can be checked by supplying the control device 14 with a variable which contains information about zero crossings of the current in a coil of the power factor correction circuit.FIG. 2 is a circuit diagram of the power factor correction circuit 20 according to an embodiment. A supply AC voltage, for example, the line voltage, is converted by a rectifier (not shown in FIG. 2 ) into a rectified AC voltage, which is applied as an input AC voltage Vin between an input terminal of the power factor correction circuit 20 and ground. The input AC voltage Vin is supplied to an inductor 21. The inductor 21 is connected in series with a diode 22 between the input terminal and an output terminal 27 of the power factor correction circuit 20. An output DC voltage Vout is provided at the output terminal 27 coupled to a charging capacitor 23. A further capacitor 25 can be connected between the inductance 21 and ground, which capacitor is connected in parallel with a series circuit of switch 24 and resistor 26. The capacitor 25 can be connected to the same terminal of the diode 22 to which the inductance 21 is also connected.The output DC voltage Vout is used to supply a load which is preceded by the power factor correction circuit 20. The load can be, for example, components of an operating device for a lighting means, such as, for example, a fluorescent lamp, a halogen lamp, a light-emitting diode arrangement, etc. The load may comprise a LLC resonant converter with potential isolation.Connected to the connection between the inductance 21 and the diode 22 is a controllable electronic switch 24, which is a power switch and which can be designed, for example, as a field effect transistor (FET), in particular as a MOSFET. The switch 24 may be connected to ground via a resistor 26, wherein the resistor 26 may serve as a shunt resistor. The switch 24 is switched to the on state and the off state by the controller 14 of the power factor correction circuit 20 using a pulsed signal. The control device 14 has a corresponding output 41 for controlling a control signal, by means of which, for example, the gate voltage of the switch 24 can be controlled directly or indirectly (for example via a driver circuit).When the switch 24 is switched on, the inductance 21 is connected to ground via the switch 24, the diode 8 being blocked, so that the inductance 21 is charged and energy is stored in the inductance 21. If, on the other hand, the switch 24 is switched off, i.e. open, the diode 22 is conductive, so that the inductance 21 can discharge via the diode 22 into the charging capacitor 23 and the energy stored in the inductance 21 is transferred into the charging capacitor 23.The switch 24 is controlled by a control device 14, which can be designed in the form of an integrated circuit, in particular as an ASIC. Power factor correction is achieved by repeatedly turning switch 24 on and off, with the switching frequency for switch 24 being much greater than the frequency of rectified input AC voltage Vin. The power factor correction circuit 20 may operate as a boost converter. The control device 14 can be supplied with various measured variables which can be evaluated for controlling or regulating the power factor correction circuit 20 or other components of the operating device. For example, the control device 14 can detect the output voltage via a voltage divider with resistors 36, 37.The control device 14 can also be supplied with a measured variable which indicates when a current I L in the inductance 21 has a zero crossing or with which sign the zero crossing takes place. The corresponding sensing circuit may include a winding 31 or small coil 31 inductively coupled to the inductor 21. The winding 31 is connected via a diode 32 and a resistor 33 to a node which is connected via a further resistor 34 to a node between the switch 24 and the resistor 26. The signal at input 42 of controller 14 indicates zero crossings of current I L in inductor 21, particularly in the time periods when switch 24 is switched to the off state.The controller 14 generates the pulsed control signal to cyclically switch the switch 24 to the on state (conductive state) and the off state (non-conductive state), respectively. This can be done in different ways, in particular depending on a load or output power. At higher loads or output powers, a second operating mode is used, which can be a BCM operation or a CCM operation. The time during which the switch 24 is turned on can be adjusted to maintain the output voltage at a set point. The time during which the switch 24 is switched on in each case can be selected depending on a load or output power at the output 27. As long as the load or output power is greater than a threshold value, an adjustment of the operation can be made by reducing the on-time, i.e. the time duration during which the switch 24 is switched on in each case. When the load or output power reaches the threshold value, a first operating mode may be activated, which is a DCM operation. After switching the switch 24 into the off state, the switch 24 is not immediately switched on again if the current I L in the inductance 21 has dropped to zero, but a certain minimum waiting time is provided. The on-time may be maintained at a predetermined fixed value in DCM operation, which may be the smallest value selectable for the on-time in BCM operation. An adaptation to different loads or output powers can take place in the first operating mode, i.e. in DCM operation, by adaptation of the minimum waiting time.Incidentally, in the first operation mode, i.e., in the DCM operation, a switch-on time is set not only according to the minimum waiting time but also depending on the time-dependent behavior of the current I L through the inductor 21 and depending on the time-dependent behavior of the voltage dropping between the drain terminal and the source terminal of the switch 24.FIG. 3 illustrates the control of the power factor correction circuit 20 by the control device 14 in the second operating mode, which is illustrated by way of example as BCM operation. By the gate voltage Vg at the switch 24, the switch is switched to the on state and the off state. When the switch is turned to the off state, the inductor 21 discharges and the coil current I L51 decreases. In BCM operation, a new switch-on process can be triggered by the current I L51 dropping to zero at 54 or having a zero crossing. The corresponding control signal 52 then turns on the switch 24 again in order to recharge the inductance 21. In BCM operation, the on-time 55 may be adjusted to keep the bus voltage stable for different loads and / or output powers. Also shown in FIG. 3 is the voltage 53 which drops between the drain terminal and the source terminal of the switch 24 in the BCM mode. While BCM operation is illustrated by way of example in FIG. 3, the second operating mode, which may be activated at larger loads and / or larger output powers, may also be CCM operation. In CCM operation, the switch 24 can be triggered to turn on when the current I L through the inductor 21 reaches a non-zero reference value.FIG. 4 illustrates the principle of the simplest embodiment of a feedback-based PFC circuit according to the prior art. A controller compares the Vbus voltage with a reference value Ref and controls the t on- value by turning on and off the switch 24 so that the output voltage Vout provides a nearly constant dimming value (PWM modulation principle). The PWM modulator thus supplies a clocked, correspondingly modulated signal.This type of dimming value control is robust for the range of high dimming values and is not currently questioned in the prior art. Problems arise-as already indicated in the introduction to the description-at low dimming value specifications, since for physical reasons the t on- value cannot be selected to be arbitrarily small. In order to nevertheless obtain a correspondingly low dimming value-i.e. a correspondingly low output voltage Vout-a zero-current state is generated in the modulation signal which is characterized by the K factor, the duration of the non-zero-current state t active and the switch-on duration of the switch 24 t on by the following equation-see also FIG. 6 :According to the current state of the art, this problem is solved (see FIG. 7 ) in that starting from the minimum value for t on with decreasing load, the K factor is continuously increased (dashed line), i.e. with frozen t on( horizontal solid line), the switch-off time period t off is controlled at the desired low load, with the associated circuit and control technical problems already mentioned in the introduction to the description.The invention solves these problems in that at low load specifications (dimming value specifications) a change of the t on- time continues to take place without dropping below the minimum t on- time. This is done by the t on- time being increased abruptly in sawtooth fashion at least once, preferably several times, in the direction of lower load specification, in order then to drop again, preferably continuously. Thus, the minimum t on- time specification can be maintained and the t on- time can nevertheless be kept variable over the entire load range.The minimum t on- time specification is therefore complied with without freezing the t on- time in the lower load range.The range of the sawtooth-shaped course of the t on- time is preferably effected in a lower load range after (coming from the maximum load in the direction of the lower load) the t on- time has reached the minimum t on- time for the first time.In the region of the sawtooth-shaped course of the t on- time, the k-factor is increased again according to the invention, which preferably takes place in the form of a stepwise (discrete) K-value change.The increasing jump in the K value takes place synchronously with a jump with which the t on- time is increased. In the constant K-value ranges, the t on- time is then preferably continuously reduced in the direction of lower load.Depending on a reduced load value specification, the K value specification for the PWM control is thus increased in stages according to FIG. 8, so that thus, toff times that are extended in stages are set (feed forward). Thus, in the range of the K value steps at a constant K value, a continuously changed t on- time regulation can take place depending on the load specification in this range.The K value can be specified from the outside to the control unit which outputs the pulsed signal with variable t on- time, but it can also be generated internally in this control unit, for example by means of a look-up table using a determined load specification (on the basis of a fed-back measured value) or supplied load specification.According to FIG. 9, a dimming value specification is preferably supplied to a (micro)controller μC, which then, depending on the dimming value specification, outputs a K value specification signal of the control unit, which outputs the pulsed signal with variable t on- time.Alternatively, the K value specification can change not in a stepwise manner but also continuously in the range of low loads. This has the advantage that, due to second variable parameters (t on- time and t off- time or K value), the resulting changes naturally turn out to be less drastic compared to the gradual freezing of the K value (K factor).It should be noted that the present invention is a PWM signal in the broader sense, since the frequency of the pulses (modulation frequency) can change at any time depending on the regulation.However, according to the invention, the output signal in the form of a PWM signal with varying frequency must in fact be used for driving the switch of a PFC circuit, which must be taken into account in the technical implementation of this regulation.

Claims

Operating device (1) for lighting means, in particular converters for at least one LED, having a control unit (14) which is designed to drive a clocked circuit (20), such as a PFC circuit, by means of a pulsed signal (52) which is fed directly or indirectly as a drive signal to a switch of the clocked circuit (20), wherein the control unit is designed to generate the pulsed signal: - which changes in a dimming range above a predetermined threshold value in that, at a preferably fixed frequency of the pulses, the switch-on time period t on of the pulses changes, and - which changes in a dimming range below a predetermined threshold value as a result, that the switch-off time duration t off of the pulses increases stepwise in the direction of low dimming values and the switch-on time duration t on changes continuously in the regions of constant switch-off time duration and the switch-on time duration t on increases stepwise with a sawtooth profile in the region of the jumps of the steps of the switch-off time duration t off a k-factor being increased in the region of the sawtooth profile of the t on- time.Operating device (1) for lighting means, in particular converters for at least one LED, having a control unit (14) which is designed to drive dimmable operation of the lighting means which is fed directly or indirectly as a drive signal to a switch of the clocked circuit (20), wherein the control unit is designed to generate the pulsed signal: - which changes in a dimming range above a predetermined threshold value in that, at a preferably fixed frequency of the pulses (52), the switch-on time duration t on of the pulses changes, and - which changes in a dimming range below a predetermined threshold value in that, in the direction of low dimming values, the switch-off time duration t off of the pulses increases at least partially continuously and the switch-on time duration t on is continuously reduced with a sawtooth-shaped profile, wherein a k-factor is increased in the region of the sawtooth-shaped course of the t on- time.Operating device (1) according to Claim 1 or 2, wherein the control unit (14) has a PWM modulator to which a predefined signal (Ref) for the switch-off time duration t off of the pulses is fed from a controller (μC), wherein the PWM modulator regulates the switch-on time duration t on as a function of a feedback signal which directly or indirectly reflects a parameter of the operation of the lighting means.Operating device according to Claim 3, in which the controller (μC) has an interface for receiving a dimming signal.Method for operating a PFC circuit (20) for operating lighting means, in particular at least one LED, wherein the switch (24) of the PFC circuit (20) is clocked by a signal (52), - which changes in a dimming range above a predetermined threshold value in that, with a preferably fixed frequency of the pulses, the switch-on time duration t on of the pulses changes, and - which changes in a dimming range below a predetermined threshold value as a result, that the switch-off time duration t off of the pulses increases stepwise in the direction of low dimming values and the switch-on time duration t on changes continuously in the regions of constant switch-off time duration and the switch-on time duration t on increases stepwise with a sawtooth profile in the region of the jumps of the steps of the switch-off time duration t off a k-factor being increased in the region of the sawtooth profile of the t on- time.

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