High efficiency minimum headroom and CV control at low PWM dim level

Abstract

The invention relates to a driver for driving a load. The driver comprises an input for receiving an input voltage, a rectifier for rectifying the input voltage to a rectified voltage, a power converter for converting the rectified voltage into a bus voltage, a current regulator couplable in series with the load and arranged to regulate a current through the load by pulse width modulating the current through the load, a controller adapted to receive a dimming signal and arranged for controlling the current regulator based on the received dimming signal, a headroom sensor for sensing a voltage over the current regulator, wherein the controller is arranged to control the power converter to regulate the voltage over the current regulator based on the sensed voltage over the current regulator. The controller is arranged to determine a duty cycle for the pulse width modulation based on the dimming signal, wherein the controller is further arranged to control the power converter to regulate the voltage over the current regulator by using the dimming signal for regulating the voltage over the current regulator.

Description

[0001] High efficiency minimum headroom and CV control at low PWM dim level

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a driver for driving a load. The invention further relates to a system comprising the driver and the load.

[0004] BACKGROUND OF THE INVENTION

[0005] High power factor single stage LED drivers are often used in low-cost LED lighting products. For an improved lighting performance, a second stage can be used to smoothen out the LED current. A linear current regulator may be provided for smoothening out the LED current. Such linear current regulator is compact and low cost compared with a switching mode second stage. Linear current regulators with a headroom control have been introduced for some years and applied in various LED products. The headroom control dynamically adjusts the output voltage of a constant voltage driver to match the required voltage for driving the LED string, so that the loss in the linear current regulator is kept low. A typical control method is to sense the (average) voltage at the MOSFET drain node, of the linear current regulator and then provides this to a feedback control loop. The loop maintains a constant (average) drain voltage. This principle works quite ok for most applications. The desired average drain voltage is a design parameter chosen by the circuit designer. Usually this is the voltage across the current sense resistor at the source of the MOSFET, plus the required voltage drop across the MOSFET for proper operation in linear mode, plus half of the peak-peak ripple voltage.

[0006] When the average drain voltage is provided as a feedback parameter, the circuit can’t respond to a dynamic ripple voltage at the drain when a PWM dimming method is applied to the LED current instead of analog dimming. When the LED is turned OFF, the voltage at the drain will rise significantly due to high dynamic resistance of a heavily underdriven LED. If the average drain voltage is used as the feedback parameter, the headroom will be too low to maintain the LED current at the desired level. This is because the ripple voltage at the drain now contains both the double-mains frequency ripple and the ripple resulting from PWM dimming. The feedback loop tries to force to a constant average drain voltage and the headroom would be too low. As a result, the LED will appear dimmed. It is desired to prevent the LEDs to appear dimmed because of the too low headroom when PWM dimming is applied.

[0007] SUMMARY OF THE INVENTION

[0008] It is an objective of the invention to provide a driver that allows a dimming with PWM that does not suffer from the uncontrolled voltage and potential loss of light at deeper dimming levels.

[0009] To overcome this concern, in a first aspect of the invention, a driver for driving a load is provided. The driver comprises:

[0010] - an input for receiving an input voltage;

[0011] - a rectifier for rectifying the input voltage to a rectified voltage;

[0012] - a power converter for converting the rectified voltage into a bus voltage;

[0013] - a current regulator couplable in series with the load and arranged to regulate a current through the load by pulse width modulating the current through the load;

[0014] - a controller adapted to receive a dimming signal and arranged for controlling the current regulator based on the received dimming signal, wherein the dimming signal represents a dimming range comprising a first dimming range and a second dimming range, the first dimming range being lower than the second dimming range;

[0015] - a headroom sensor for sensing a voltage over the current regulator, wherein the controller is further arranged to control the power converter to regulate the voltage over the current regulator based on the sensed voltage over the current regulator; wherein the controller is arranged to determine a duty cycle for the pulse width modulation based on the dimming signal, wherein the controller is further arranged to control: within the first dimming range the power converter (1) to operate in a constant voltage mode, and within the second dimming range the power converter to regulate the voltage over the current regulator by using the dimming signal for regulating the voltage over the current regulator.

[0016] The term dimming level can be explained as follows. When the dimming level is low, a low amount of current is provided to the load, when the dimming level is high, a large amount of current is provided to the load. The dimming level may a direct derivative of the dimming signal. The driver has a power converter that is used for providing a bus voltage. The bus voltage is provided to the load and the current regulator. This bus voltage is used by the current regulator to regulate the current through the load. The voltage that drops over the current regulator is referred to as the headroom voltage. A minimum headroom voltage is required for the current regulator to operate properly. A too large headroom voltage on the other hand may result in additional undesired power losses. The headroom is therefore tightly regulated to be not too large and also not too low. The current regulator is operated using a PWM control. This means that the current through the load is interrupted by an off time based on the duty cycle of the pulse width modulation signal. As an example, a switch may be provided in series with the load. The switch is turned on and off with the PWM control. The duty cycle of the PWM determines the relation between the on-time and the off-time of the switch. The duty cycle is also considered to define the on-time of the switch. At smaller duty cycles, present at lower dimming levels, the switch will be on for a very short amount of time. This amount of time eventually becomes so short that the switch is unable to properly close. When sensing the headroom voltage, the not properly closing of the switch results in a sensed larger headroom voltage than what would otherwise, when proper closing, be present. The controller will therefore regulate the headroom voltage to a lower value. This reduction of headroom voltage will cause the headroom voltage to be too low for proper operation of the current regulator and further worsen the conduction behaviors of the switch. This may eventually result into a undervoltage level triggering causing the driver to restart. Preferably, the headroom voltage is sensed and averaged to provide a simple control.

[0017] It is an insight of the inventors that it is desired to provide the dimming signal as a control parameter in the control loop for controlling the power converter. Therefore, the headroom voltage is not only regulated by its desired voltage and sensed headroom voltage, but also based on the dimming signal and therefore also the dimming level. The feedback of the dimming signal can be regarded as a compensation for the introduced error of the headroom voltage caused by the dimming signal and therefore the PWM control. The introduction of the dimming signal in the control loop for controlling the power converter may then cause the headroom voltage to be increased within the first dimming range. This can be done by operating the power converter in a constant voltage mode by controlling the average of Vbus provided by the power converter, thereby providing the increased headroom voltage and ensure stable operation by neglecting the variation on Vdrain that typically occur at low load conditions while the linear current source ensures stable light output. During the second dimming range, the headroom voltage may be regulated to be at the optimum level to allow the current regulator to operate properly at highest possible efficiency.

[0018] In a further example, the current regulator is arranged to operate in a linear operation mode when the dimming signal is below a threshold.

[0019] Dimming even further down, using PWM control for dimming may not provide a reliable steady light output anymore because the duty cycle becomes too small. It may therefore be desired to, when the driver receives a very low dimming level, to change over to a linear operation mode for the current regulator. The current regulator provides a linear current regulation to lower the amplitude of the current through the load. This may be combined with a PWM current regulation. Lowering the current amplitude allows the duty cycle to be increased while allowing a similar average current to be provided to the load. Dimming at very deep dimming levels is then also performed in an accurate way, while at higher dimming levels, the PWM regulation as previously mentioned may be implemented when the dimming level is above the threshold.

[0020] In another example, the current regulator is arranged to operate below the threshold combined with the PWM.

[0021] At deeper dimming, the current regulator can be operated using PWM and linear current regulation. The linear current regulator can be used to lower the current amplitude allowing the duty cycle to be increased to maintain the same average current and allowing a better controllability of the control of switch in the current regulator.

[0022] In another example, the current regulator is arranged to operate in a linear operation mode when the dimming signal is below a threshold and arranged to operate using the pulse width modulation when above the threshold.

[0023] The current regulator provides a linear current regulation to lower the amplitude of the current through the load. Preferably this is done without a PWM regulation below the threshold. Above the threshold, the aforementioned PWM control may be implemented, and no linear current regulation may be implemented. This allows at even further dimming only linear current regulation, resulting in a stable deeper dimming of the load current.

[0024] In another example, the controller is arranged to control the power converter to adjust the voltage over the current regulator as a monotonical non-increasing function to the dimming signal.

[0025] Preferably, the headroom voltage increases when the dimming level decreases (lower current to the load). This means that the headroom voltage increases monotonically with a reduction of the dimming level. The other way around, when the dimming level increases (larger current to the load), the headroom voltage is lowered. Since at higher dimming levels, the duty cycle is large enough for the switch to close properly, an increase in headroom voltage may not be required. A decrease in dimming level results in a reduction of the duty cycle and therefore increasing the need for introducing the correction with the dimming signal in the control loop.

[0026] In another example, the monotonical non-increasing function is a step function.

[0027] A simple implementation of the monotonical non-increasing function is to provide a step of the headroom voltage when the dimming level is low enough i.e., below the threshold.

[0028] In another example, the driver comprises a sensor for sensing the regulated bus voltage.

[0029] The sensor may be used for generating a control signal for controlling the power converter in an optimized way. The sensor may also be used for determining an overvoltage in the event that the load or the driver has a defect. The sensor may further be used when the power converter is controlled using a constant voltage control mode.

[0030] In another example, the controller comprises a comparator or an operational amplifier arranged for comparing the sensed regulated bus voltage with a reference voltage.

[0031] The controller may have a comparator or an operational amplifier. The comparator may be used for comparing the sensed regulated bus voltage with a reference voltage. If the sensed regulated bus voltage exceeds the threshold, this may be an indication of an overvoltage and the driver may respond to this by going into an overvoltage protection mode. The operational amplifier may be used to provide a regulation of the regulated bus voltage when e.g., the power converter is operated in the constant voltage control mode. The operational amplifier may also be used for sensing an overvoltage.

[0032] In another example, the controller comprises a further operational amplifier arranged for comparing the sensed voltage over the current regulator with the dimming signal.

[0033] A further operational amplifier may be provided for comparing the sensed voltage over the current regulator with the dimming signal. This allows the dimming signal to be incorporated in the feedback loop for regulating the power converter. The output of the comparison by the operational amplifier can then be used as the control signal for the power converter. In another example, the dimming signal is provided as an average signal for regulating the voltage over the current regulator.

[0034] Preferably, the dimming signal is provided as an average signal. This may be used for use with the further operational amplifier or any other feedback circuitry. The advantage of the average signal is that it allows a simpler, low speed, regulation of the power converter.

[0035] In a further example, a system is provided. The system comprises the driver according to any of the preceding examples and the load.

[0036] Preferably, a system uses the provided insights of the invention. The system then has a more reliable dimming of the current to the load while allowing PWM to be implemented during dimming.

[0037] In a further example, the load is a lighting load.

[0038] Preferably, the load is a lighting load. The system may then be a lighting system. The lighting load can be dimmed down more reliably without a risk of light artefact because of an improper operation of the current regulator.

[0039] In a further example, the load comprises at least one of an LED or a laser diode.

[0040] The light output of LEDs and laser diodes is mainly dependent on the amount of current flowing through them. By more reliably regulating the current to the load, the light output is also more accurately regulated.

[0041] In a further example, the system is a luminaire or a lamp.

[0042] BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Examples of the invention will now be described with reference to the accompanying drawings, in which:

[0044] Fig. 1 shows an example of a circuit diagram of a commonly used driver.

[0045] Fig. 2 shows an example of circuit diagram of a driver.

[0046] Fig. 3 shows an example of circuit diagram of a part of a controller.

[0047] Fig. 4 shows another example of circuit diagram of a part of the controller.

[0048] Fig. 5 shows another example of circuit diagram of a part of the controller.

[0049] Fig. 6 shows an example of a graph showing the relation between the dimming level and the headroom voltage.

[0050] Fig. 7 shows another example of a graph showing the relation between the dimming level and the headroom voltage. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] The invention will be described with reference to the Figures.

[0052] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should also be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

[0053] Figure 1 shows an example of a circuit diagram of a driver that is commonly used. The driver may receive a mains voltage. A rectifier B is used to rectify the mains voltage into a rectified voltage. A power converter 1 converts the rectified voltage into a bus voltage. The load LED is coupled to the bus to receive the bus voltage. In series with the load LED is a current regulator. The current regulator has a series arrangement of a MOSFET M with a sense resistor R in series with the load LED. A controller 2 provides a control signal for controlling the MOSFET M based on a dimming signal Dim level. Preferably, the controller 2 provides a PWM signal to the gate of the MOSFET M. The PWM signal is then made dependent on the dimming signal Dim level. A voltage over the current regulator is sensed. The voltage over the current regulator is also referred to as the headroom voltage. The headroom voltage is provided to a comparator or operational amplifier, Op-Amp. The headroom voltage is compared with a reference voltage representing the desired headroom voltage. A control signal is then generated by the comparator or Op-Amp to the power converter 1. The power converter 1 therefore regulates the headroom voltage corresponds to the desired headroom voltage by providing a suitable bus voltage.

[0054] The current regulator is used to provide a dimming of the current through the load LED. By applying a PWM signal to the gate of the MOSFET M, the dimming of the current through the load can be regulated accurately. When reducing the current at deeper dimming levels, the duty cycle becomes very small. Eventually, the duty cycle is too small for the MOSFET M to fully close. This results in a residual headroom voltage to be present when the PWM signal is high i.e., the MOSFET M is supposed to be closed. This residual voltage results in a flawed headroom voltage measurement, causing the power converter 1 to interpret that a larger headroom voltage is present than is actually present. The power converter 1 will therefore lower the bus voltage to compensate for the sensed higher headroom voltage. This will eventually result in a headroom voltage that is too low for the current limiter to operate properly. The MOSFET M may then not close fully. Therefore, the problem may cause a cascade voltage reduction by the power converter 1 until the power converter goes into an undervoltage lockout protection.

[0055] Figure 2 shows an example of a circuit diagram of a driver. The driver may receive a mains voltage. The mains voltage is rectified into a rectified voltage by a rectifier Bl. The rectified voltage is provided to a power converter 1. The power converter 1 provides a bus voltage Vbus. The load LED is provided with the bus voltage Vbus. In series with the load LED is a current regulator. The current regulator has a series arrangement of a MOSFET Ml with a sense resistor RS, which is then coupled in series with the load LED. A controller is used for controlling the power converter 1 and the current regulator. The headroom voltage Vdrain is measured and provided to the controller 2. The controller 2 also receives a dimming signal Dim_level. The dimming signal represents a dimming range comprising a first dimming range and a second dimming range, the first dimming range being lower than the second dimming range. Figures 6 and 7 show examples of such dimming ranges. The controller 2 uses the dimming signal Dim_level and the sensed headroom voltage Vdrain for controlling both the power converter 1 and the current regulator. The controller 2 may provide a PWM signal Dim to the gate of the MOSFET ML The PWM signal may then be directly proportional to the dimming signal Dim level. The PWM signal causes the MOSFET to reduce the average current through the load LED. In the event that the load LED is an LED, the reduction of the average current directly translates into a reduction of the light output.

[0056] The controller 2 is also used to generate a feedback signal FB for the power converter 1. The feedback signal FB provides the required information for the power converter 1 to control the bus voltage Vbus to the desired level. The headroom voltage Vdrain is sensed by the controller 2 and used to generate the feedback signal FB. The headroom voltage Vdrain is the main parameter that requires to be controlled. To avoid the aforementioned undervoltage lockout protection of the power converter 1, it is not sufficient to use only the headroom voltage Vdrain. Within the second dimming range, the controller 2 therefore also incorporates the dimming signal Dim level for modifying the feedback signal so that a compensation for the PWM disturbance is provided for the power converter 1. The feedback signal FB is therefore a combined signal based on the sensed headroom voltage Vdrain and the dimming signal Dim level. This combination provides a stable regulation of the headroom voltage Vdrain allowing the headroom voltage Vdrain to be kept as low as possible for improved efficiency and allowing a good operation of the current regulator over the dimming range. Within the second dimming range, the control as used in the second dimming range may cause oscillations in the current to the load occur when further dimming down. It is therefore recommended to operate in a first dimming range, lower than the second dimming range, the power converter 1 may be operated in a constant voltage mode. This means that the control for the power converter is simplified in the first dimming range, preventing the oscillation to occur since a different control is used. The headroom voltage is not regulated and will therefore vary based in the dimming level within the first dimming range. Even presence of small oscillation in the output voltage are do not impact the light output not control as they would be filtered by the linear current regulator. The voltage provided by the power converter 1 therefore needs to be large enough. Figure 6 and 7 show examples of how the compensation over the dimming range can be performed in more detail. The driver may have a sense resistor RS for sensing the current through the current regulator and therefore also the load LED. At further deep dimming, it may be desired to operate the current regulator into its linear operation mode instead of using a PWM control. This means that the MOSFET Ml operates in its linear mode and therefore acts as a linear current limiter. In this case, the dimming signal Dim level may not be required for providing a compensation into the feedback signal FB.

[0057] Figure 3 shows an example of a part of the controller 2. A comparator or Op- Amp U1 is provided. The bus voltage Vbus is provided via resistors R1 and R2 to the negative input of the comparator or Op-Amp Ul. The bus voltage Vbus is compared with a reference voltage Vbus_set provided to the positive input of the comparator or Op-Amp Ul. An RC circuit having resistor R3 and capacitor Cl may be provided between the negative input and the output of the comparator or Op-Amp Ul. The comparison result may be considered as the error between the sensed bus voltage and the desired bus voltage. The output of the comparator or Op-Amp Ul may be used by the controller 2 to provide the feedback signal FB. In this case, the output may be used for regulating the bus voltage. This may be required in the event of deeper dimming when the current regulator operates as a linear current limiter or when an overvoltage protection needs to be incorporated. The reference voltage may then be a representation of an overvoltage threshold.

[0058] Figure 4 shows another example of a part of the controller 2. A further Op- Amp U2 is provided. The headroom voltage Vdrain is provided via resistor R6 to the positive input of the Op-Amp U2. The dimming signal Dim level is provided via resistor R4 to the negative input of the Op-Amp U2. An RC circuit having resistor R5 and capacitor C2 may be provided between the negative input and the output of the Op-Amp U2. The headroom voltage Vdrain and the dimming level Dim level are provided to the Op-Amp. The output of the Op-Amp U2 is a regulation value for the headroom with a compensation based on the dimming level. At a low dimming level, low load current, the compensation will be higher than at a high dimming level, high load current. A higher compensation may in this example mean that the headroom voltage Vdrain is increased. This may result in additional losses in the current regulator due to the increase of the headroom voltage Vdrain but prevents the headroom voltage Vdrain to become too low due to the small duty cycle. Since this increase in headroom voltage Vdrain occurs at lower dimming levels, the current through the load LED is also reduced and the energy losses may be still relatively low.

[0059] Figure 5 shows a more detailed circuit diagram of a controller 2. The controller 2 may incorporate the circuit as shown in Figure 3 and the circuit as shown in Figure 4. The circuits are combined and can be seen in Figure 5. The output of the Op-Amp U2 is provided to a further circuit via resistor R7. The output of the comparator or Op-Amp U1 is provided to the further circuit via a resistor R8 and diode DI. Resistor R7 may be connected to a base of transistor QI. Resistor R8 may be connected to the collector of transistor QI via an optional resistor RIO. The emitter of the transistor QI may be coupled to ground via an optional resistor R9. An optocoupler U3 is used for generating the feedback signal FB that is provided to the power converter 1. The diode of the optocoupler U3 is coupled to the transistor QI. The transistor QI is used for providing a conductive path for the diode to conduct a predetermined current. The current determines the conductivity of the transistor of the optocoupler U3 and hence a variable feedback signal FB can be generated for the power converter 1. The transistor and surrounding circuitry allow the outputs of the Op-Amp U2 and the comparator or Op-Amp U1 to be combined and provide a single control signal for the optocoupler U3. Therefore, the headroom voltage and the dimming level may be used together to generate the feedback signal FB.

[0060] Figure 6 shows an example of the relation between the dimming level and the amount of compensation that is provided. The dimming signal represents a dimming range, which can be split up in at least two dimming ranges. The first dimming range extends between 0 % to x %, preferably starting from 1 % to x %. The second dimming range extends from x % to 100 %. At the first dimming range, the controller 2 controls the power converter 1 to operate in a constant voltage mode. The voltage provided by the power converter 1 is larger than the sum of the forward voltage of the load LED, the voltage across the MOSFET Ml and the maximum expected ripple at the output of the power converter 1 at light load conditions. At the second dimming range, the controller 2 controls the power converter 1 to regulate its output voltage as to regulate the headroom voltage across the MOSFET Ml. To ensure a proper current control at high output power, the controller 2 may need to use a feedback with a high gain. This however may result in oscillations in the low power range for the power converter 1. Providing a constant voltage control at the first dimming range provides a simple constant voltage control for the power converter 1. Voltage fluctuations of the voltage provided by the power converter 1 at light load condition are small compared to the total output voltage such that the risk of oscillation at the first dimming range is mitigated . In this example, the first dimming range is lower than the second dimming range.

[0061] Figure 7 shows another example of the relation between the dimming level and the amount of compensation that is provided. The first dimming range extends between 0 % to x %, preferably starting from 1 % to x %. The second dimming range extends from x % to 100 %. At the first dimming range, the controller 2 controls the power converter 1 to operate in a constant voltage mode. The voltage provided by the power converter 1 is larger than the sum of the forward voltage of the load LED, the voltage across the MOSFET Ml, and the maximum ripple voltage at the output of power converter 1. Preferably, an additional headroom voltage is provided to ensure that over the entire first dimming range, the headroom voltage across the MOSFET Ml is sufficient. At the second dimming range, the controller 2 controls the power converter 1 to regulate its output voltage as to regulate the headroom voltage across the MOSFET ML In this example, the first dimming range is lower than the second dimming range. Although figure 7 shows a linear slope of increase headroom voltage over decreasing dimming level, the curve very much depends on the junction area and the scale of the dimming range. For a linear dimming axis, the headroom voltage will show a typical exponential curve. In the examples provided, the dimming signal Dim level used by the controller 2 can be the directly received dimming signal Dim. The dimming signal Dim_level can also be a signal processed by the controller 2 where the received dimming signal Dim is provided as an input. Such an example of a dimming signal Dim level can be the PWM signal provided to the MOSFET ML

[0062] In the examples provided, the switch used for the current regulator is shown as a MOSFET. It is to be appreciated that other switches, that can e.g. operate in the linear operation mode, can also be used. Such a switch may also be a BJT. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A driver for driving a load (LED), the driver comprising:- an input for receiving an input voltage;- a rectifier (Bl) for rectifying the input voltage to a rectified voltage;- a power converter (1) for converting the rectified voltage into a bus voltage (Vbus);- a current regulator couplable in series with the load (LED) and arranged to regulate a current through the load (LED) by pulse width modulating the current through the load (LED);- a controller (2) adapted to receive a dimming signal and arranged for controlling the current regulator based on the received dimming signal, wherein the dimming signal represents a dimming range comprising a first dimming range and a second dimming range, the first dimming range being lower than the second dimming range;- a headroom sensor for sensing a voltage over the current regulator, wherein the controller (2) is further arranged to control the power converter (1) to regulate the voltage over the current regulator based on the sensed voltage over the current regulator; wherein the controller (2) is arranged to determine a duty cycle for the pulse width modulation based on the dimming signal, wherein the controller (2) is further arranged to control: within the first dimming range the power converter (1) to operate in a constant voltage mode, and within the second dimming range the power converter (1) to regulate the voltage over the current regulator by using the dimming signal for regulating the voltage over the current regulator.

2. The driver of claim 1 wherein the current regulator is arranged to operate in a linear operation mode when the dimming signal is below a threshold.

3. The driver according to claim 2, wherein the current regulator is arranged to operate below the threshold combined with the PWM.

4. The driver of claim 1, wherein the current regulator is arranged to operate in a linear operation mode when the dimming signal is below a threshold and arranged to operate using the pulse width modulation when above the threshold.

5. The driver according to any of the preceding claims, wherein the controller (2) is arranged to control the power converter (1) to adjust the voltage over the current regulator as a monotonical non-increasing function to the dimming signal.

6. The driver according to claim 5 wherein the monotonical non-increasing function is a step function.

7. The driver according to any of the preceding claims, further comprising a sensor for sensing the regulated bus voltage.

8. The driver according to claim 6, wherein the controller (2) comprises a comparator or an operational amplifier (Ul) arranged for comparing the sensed regulated bus voltage with a reference voltage.

9. The driver according to any of the preceding claims, wherein the controller comprises a further operational amplifier (U2) arranged for comparing the sensed voltage over the current regulator with the dimming signal.

10. The driver according to any of the preceding claims, wherein the dimming signal is provided as an average signal for regulating the voltage over the current regulator.

11. A system comprising the driver according to any of the preceding claims and the load (LED).

12. The system of claim 11 wherein the load (LED) is a lighting load.

13. The system of any of the claims 11 or 12, wherein the load (LED) comprises at least one of an LED or a laser diode.

14. The system according to any of the claims 11 to 13, wherein the system is a luminaire or a lamp.

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