WO2018184920A1

WO2018184920A1 - Dimming of lamps

Info

Publication number: WO2018184920A1
Application number: PCT/EP2018/057791
Authority: WO
Inventors: Andre Mitterbacher; Fabio Romano; Dietmar Klien
Original assignee: Tridonic Gmbh & Co Kg
Priority date: 2017-04-05
Filing date: 2018-03-27
Publication date: 2018-10-11

Abstract

The invention relates to a device (1) for producing a pulse-width modulation signal (S1) for controlling the power output of a drive circuit for lamps (1), with a device (10) for converting the first dimming signal into a digital second dimming signal (S2) with a lower resolution, a control circuit (6) for generating the PWM signal on the basis of the converted second dimming signal (S2), and a regulating device (5) designed to temporally vary the dimming value of the first dimming signal (S1) in order to counteract the error, averaged over time, which occurs as a result of the lower resolution of the dimming value of the second dimming signal (S2) compared with the dimming value of the first dimming signal (S1).

Description

The present invention relates to a device and a method for generating a pulse width modulation signal (PWM signal) for controlling the output power of a driver circuit or a switching regulator and the brightness of driven by the driver circuit or the switching regulator bulbs, and a control gear for light-emitting diodes with such a device.

An operating device for supplying one or more light-emitting diodes is known from WO

2013/152368 AI known. Such operating devices are mainly used to provide a desired power supply for the light source, such as a light emitting diode (LED) or more in series and / or parallel connected LEDs. Additional functions, such as dimming the lamps, changing / adjusting the color of the light or compensating for fluctuations in the input voltage, may be provided in the operating device.

The light emission of a light emitting diode depends on the current flow through the light emitting diode. For brightness control or brightness control, light-emitting diodes are therefore typically operated in a mode in which the current flow through the light-emitting diode is controlled or regulated by the operating device.

In the pulse width modulation (PWM), the control or regulation of the brightness via a change in the width / duration of current pulses usually constant amplitude within a predetermined period T. The power delivered in a period results from the amplitude and the duty cycle (English "duty cycle period), so that the individual pulses are not perceived by the human eye, the period should not be too large or the frequency should not be too low

Driver circuits may have a switching frequency of several MHz, wherein the control circuit for driving the resonant converter generates a pulse width modulation signal having a frequency of, for example, 25 kHz. Such a high frequency or low period duration of the pulse width modulation signal requires a very high clock frequency for counting the pulse width stages within the period in digital control circuits, such as a MikrocontroUer, in which the pulse width and thus the dimming value can be changed in the smallest possible steps. With a frequency of 25 kHz and a resolution of 16 bit, for example, within a period of 40 2 ¹⁶ steps must be counted, which corresponds to a clock frequency of 25 kHz × 2 ¹⁶ = 1638.4 MHz.

Microcontrollers with such a high clock frequency and resolution are expensive. When using a microcontroller with a lower resolution, on the other hand, there is a risk that brightness jumps due to the coarse gradation (dim levels) are perceptible in the case of a desired continuous or at least multistage change of the dimming value.

In order to prevent this, DE 10 2011 004452 A1 proposes to reduce the period so that one or more pulses with a different length can be inserted between two pulses of the same length (same duty cycle). In this way, over the period of the original period by the mixture of pulses with

different rough grading produces a mean dimming value with a finer gradation. As described above, however, the demands on the clock frequency increase at one

Reducing the period or increasing the frequency, which is an expensive

MikrocontroUer (control circuit) makes necessary. In addition, the pulses to be inserted must be calculated by the control circuit. The invention has for its object to provide devices and methods that reduce the problems described. In particular, it is an object to provide an apparatus and a method which allow regulation or control of the output power with a high resolution / accuracy and a cost-effective design. This object is achieved according to the features of the independent claims. The invention is further developed by the features of the dependent claims.

According to the present invention, an apparatus for generating a PWM signal for the control of the output according to an input side first control signal (dimming signal) comprises means for converting the first dimming signal to a digital second one Dimming signal with a lower resolution, a control circuit for generating the PWM signal based on the converted second dimming signal and a controller. The controller temporally varies the dimming value of the first dimming signal by the average of the error due to the lower resolution of the dimming value of the second dimming signal versus the dimming value of the first dimming signal

counteract.

The first dimming signal may be a digital or analogue signal indicating the desired brightness of a lighting device or the color of a light to be emitted by a lighting system, and e.g. be specified by an operator or a controller. It has a high resolution as a digital signal or an infinite fine resolution as an analogue signal. The PWM signal is used to drive a driver circuit which generates the current or voltage pulses corresponding to the PWM signal and delivers them to the light source. In order to enable a construction with a cost-effective control circuit, the first dimming signal from the converting device generates the digital second dimming signal with a lower resolution and processes the low-resolution signal from the control circuit. The correction of the resolution of the original dimming value or the error resulting therefrom lost by the use of the low-resolution second dimming signal is carried out by means of the control device.

The control device may in this case be designed to cumulate the errors continuously determined for at least some pulses of the PWM signal and the dimming value of the first dimming signal for the next duty cycle corresponding to a difference between the dimming value of the first dimming signal and to change the currently accumulated error.

If the difference is very small, the accumulation can extend over many pulses before there is a change in the duty cycle for the error correction at a pulse, which can lead to a low-frequency variation of the power output by the driver circuit or the light intensity. To prevent this, the controller may be configured to vary the dimming value of the first dimming signal or the duty cycle so that at least the duty cycles of some previous pulses change. In particular, the control device is adapted to the dimming value of the first dimming signal or the

Duty cycle to vary so that the duty cycle to the exact set

Mean value fluctuates over time ("dithering" of the duty cycle) The dithering can be done over the entire time course of the PWM signal or only for certain periods of time.

The conversion device can for this purpose have a delta-sigma modulator whose

Quantizer the digital dimming value of the first supplied to the delta-sigma modulator

Convert or convert the dimming signal to the lower resolution. The delta-sigma modulator can be a first-order or higher-order digital-to-digital converter. If the first dimming signal is an analog signal, it can be converted for conversion into a digital dimming signal with a higher resolution than the second dimming signal.

The duty cycle to be set is proportional to the ratio between the dimming value indicated by the first dimming signal and the maximum possible dimming value, so that the error is also determined based on the first dimming signal and the actual duty cycle indicating PWM signal can be. For this purpose, the control circuit or the conversion device determines on the basis of the analog or digital dimming value of the first

Dimming signal, a target duty cycle, wherein the controller determines a deviation between the target duty cycle and the duty cycle indicated by the PWM signal and changes the dimming value of the first dimming signal to counteract the determined deviation in the time average.

The control device may in this case be designed to cumulate at least some of the continuously determined deviations and to change the dimming value of the first dimming signal for the next duty cycle according to a difference between the desired duty cycle and the currently accumulated deviation.

The controller may include a first order or higher order delta-sigma modulator that determines and gradually compensates for the deviation between the desired duty cycle and the duty cycle indicated by the PWM signal. The device may be configured such that the period of the pulses of the PWM signal can be changed.

The device may be designed such that the period duration of the PWM signal is modulated between two limit values, the limit values being a modulation stroke of the

Period duration define, and the modulation is preferably load-dependent. According to the present invention, a control device for light emitting diodes on one of the devices described. According to the present invention, a method for generating a PWM signal for controlling the output of at least one light source based on a first dimming signal comprises the steps of:

- converting the first dimming signal into a digital second dimming signal with a lower resolution, and

Generating the PWM signal on the basis of the converted second dimming signal, the dimming value of the first dimming signal being temporally varied in order to compensate for this by the lower resolution of the dimming value of the second dimming signal compared to the dimming value Counteract the value of the first dimming signal occurring errors in the time average. The invention will be explained in more detail with reference to the accompanying drawings. Show it:

Fig. 1 shows a circuit of a control device for LEDs after a first

Embodiment according to the present invention,

Fig. 2 is a simplified circuit of the control device after a second

Embodiment according to the present invention,

3 is a simplified circuit of the control device according to a third embodiment of the present invention,

4 shows a simplified circuit of the control device according to a fourth embodiment according to the present invention, FIG. 5 shows a simplified circuit of the control device according to a fifth embodiment according to the present invention,

Fig. 6 shows a circuit of a control device for LEDs after a sixth

Embodiment according to the present invention, and Fig. 7 is a simplified diagram for illustrating the method.

Components with the same functions are identified in the figures with the same reference numerals.

Fig. 1 shows a simplified circuit of a control device for lighting means 1 according to a first embodiment according to the present invention. The operating device comprises a rectifier 2, a driver circuit 3 and a device 4 for generating a PWM signal for the driver circuit 3. The device 4 has, according to the present invention, a control device 5 with a converter and a control circuit 6.

The operating device 1 serves to operate the light-emitting device 1 that can be coupled to the operating device 1, which is preferably a light-emitting diode or a composite of a plurality of light-emitting diodes.

For this purpose, the operating device 1 generates a pulse-width-modulated current from the AC voltage supplied at the terminal 7 based on the digital dimming signal S 1 supplied at the terminal 8, the rectifier 2 rectifying the AC voltage and outputting the rectified AC voltage or a direct current to the driver circuit 3 which generates therefrom the pulse width modulated current in accordance with the output from the control circuit 6 PWM signal S3.

The rectifier 2 may include a power factor correction circuit and the driver circuit 3 may include an LLC resonant converter or other DC-DC converter.

The control circuit 6 generating the PWM signal S3 may be a semiconductor integrated circuit or may comprise a semiconductor integrated circuit. The control circuit 6 can be used as a processor, a microprocessor, a controller, a microcontroller or a

Application specific integrated circuit (ASIC) or a combination of said units The high-resolution digital first dimming signal Sl having a resolution of, for example, 16 bits received at the terminal 8 is received by the converter contained in the controller 5 (Digital / digital converter) converted into a processable by the control circuit 6 digital dimming signal S2 with a lower compared to the dimming signal Sl resolution of, for example, 10 bits.The control circuit 6 generates in a conventional manner on the basis of the dimming signal S2 displayed 10-bit dimming the PWM signal S3, wherein a duty cycle is selected for a current pulse corresponding to the displayed 10-bit dimming value and the number of discrete selectable duty cycles corresponds to the number of possible discrete dimming values of the 10-bit dimming signal S2. The event that has a duty cycle selected according to the 10-bit dimming value of the dimming signal S2 and transmitted to the driver circuit 3 with the PWM signal S3 is displayed to the control device 5 with a signal S4. The controller 5 then determines, for this 10-bit dimming value, an error with respect to the 16-bit dimming value of which the 10-bit dimming value is generated by the converter (quantization error) varies the 16-bit dimming value to counteract the determined error, for example by adding the signed error value, converts the varied 16-bit dimming value to a new 10-bit dimming value and outputs the new 10-bit dimming value in the dimming signal S2 to the

Control circuit 6, based on the duty cycle is selected for the next current pulse.

The error to be corrected causes a too high or too low power output of the driver circuit 3 or an excessively high or too low brightness of the operated lighting device compared to the dimming value indicated by the dimming signal S1. If the error is or becomes so large that the varied 16-bit dimming value reaches the next higher or lower quantization level of the converter, the 10-bit dimming value also changes with constant dimming signal Sl and is at least partially equal to time means the error. In this way, a mean dimming value is obtained with the finer gradation of the dimming signal Sl.

In order to prevent low-frequency change of the 10-bit dimming value and thus low-frequency variation of light intensity, the control device is designed to vary the 10-bit dimming value by adding this to the 16-bit dimming value to be set a higher frequency varies over time ("dithering").

The error determination and the correction can be done for all determined by the control circuit 6 duty cycles or only at times in which the dimming signal Sl is constant or changing only slowly. The controller 5 may cumulate the errors and vary the 16-bit dimming value according to the currently accumulated error. Fig. 3 shows such a control device 4, which has a delta-sigma modulator. The dimming signal Sl received at the terminal 8 is supplied via an adder 9 to a quantizer 10, which converts the 16-bit dimming value into a 10-bit dimming value and to the control circuit 6 (not shown) via the terminal 11 spends.

The error between the 16-bit dimming value obtained by the adder 9 and the 10-bit dimming value output to the control circuit 6 is determined by a differentiating element 12 and supplied to an integrator 13.

The integrator 13 sums the errors of a plurality of successively output to the control circuit 6 10-bit dimming values and outputs this sum to the adder 9, which adds the accumulated error value to the 16-bit dimming value received via the terminal 8 and outputs this sum to the quantizer 10 as an input. With each cycle indicated by the signal S4 of the controller, the input value (16-bit dimming value) of the controller 6 can be varied to counteract the error in the average time due to the conversion to a lower resolution.

The control device 4 shown in FIG. 2 represents a first-order delta-sigma modulator. However, it is also possible to use a modulator of a higher order in order to avoid variations in brightness caused by the variation. 3 shows a control device 4 with a second-order delta-sigma modulator, FIG. 4 shows another control device 4 with a first-order delta-sigma modulator, and FIG. 5 shows another control device 4 with a second-order delta-sigma modulator ,

FIG. 6 shows a circuit of a control device for light-emitting diodes after a fourth

Embodiment according to the present invention, in which the error on the basis of the dimming signal Sl and the actual duty cycle indicative PWM signal S3 is determined by the controller 4.

The dimming signal S 1 may be an analog signal, which from the control device 4 as a varied analog signal S2 to the control circuit 6, which it in a low-resolution

Digital signal (e.g., 10-bit signal), output, or high-resolution

Digital signal which, as described above, is converted by controller 4 into a low-resolution digital signal S2 after variation / correction. It is also possible the high resolution Generate digital signal by means of an additional A / D converter from the analog dimming signal Sl.

The controller 4 determines a target duty ratio and the deviation (error) between the target duty ratio and the duty ratio indicated by the PWM signal S3 or an actual dimming based on the analog or digital dimming value of the dimming signal S 1 Value based on the duty ratio indicated by the PWM signal S3 and the deviation (error) between the actual dimming value and the analogue or digital dimming value of the dimming signal Sl.

The dimming value of the dimming signal Sl is varied / changed according to the determined deviation (error) by the next duty ratio controller 4 to counteract the error on the time average. In Fig. 7 is a highly simplified flow chart is shown, showing the individual steps in carrying out the method described in detail above.

In the described embodiments, the width of the pulses is varied within a constant period. However, it is also possible to vary the width of the pulses tpuise at a constant switch-off time t ₀ ff between the pulses for setting a medium high-resolution dimming value (eg 16-bit dimming value). This leads to a pulse-frequency modulation, wherein the period T = tpuise + t ₀ ff remains constant in the time average for a 16-bit dimming level (dimming level) to be set. Additionally or alternatively, the period T of the pulse width modulation (PWM) of the PWM signal S3 can be modulated. There is then a deviation from a normal pulse width modulation (PWM), since the frequency and thus the period T of the pulses of the PWM signal S3 is changed. For example, the period duration T of the PWM signal S3 can be modulated between two limit values, so that the limit values define a modulation stroke of the period T, and the modulation stroke can be load-dependent, for example, wherein the modulation stroke is adjusted as a function of load by changing the lower and / or the upper limit value becomes. The modulation of the period T can be done for example in triangular form or pseudo-random (pseudo-random).

Claims

claims

A device for generating a PWM signal (S3) for the control of the output power of at least one light source (1) on the basis of a first dimming signal (Sl), comprising

means (5) for converting the first dimming signal into a digital lower-resolution second dimming signal (S2);

a control circuit (6) for generating the PWM signal on the basis of the converted second dimming signal (S2), and

a control device (5), which is designed to vary the dimming value of the first dimming signal (Sl) in time by the lower resolution of the dimming value of the second dimming signal (S2) compared to the dimming value counteract the errors occurring in the time average of the first dimming signal (Sl).

2. Device according to claim 1, wherein

the first dimming signal (Sl) is a digital signal.

3. A device according to claim 2, wherein

the first dimming signal (Sl) is an analogue signal and the device (4) comprises an analogue / digital converter adapted to convert the first dimming signal (Sl) into a digital dimming signal with respect to the second one Dimming signal (S2) higher resolution to convert and supply the converted signal of the conversion device (5).

4. Apparatus according to claim 2 or 3, wherein

the control device (5) is designed to cumulate the continuously determined errors for at least some pulses of the PWM signal (S3) and the dimming value of the first dimming signal (S1) corresponding to a difference between the dimming value of the first dimming Signal (Sl) and the currently accumulated error.

5. Device according to one of claims 2 to 4, wherein

the conversion device (5) has a delta-sigma modulator (9, 10, 12, 13..16) whose quantizer (10) supplies the digital dimming value of the first dimming signal (S1) supplied to the delta-sigma modulator convert or convert to the lower resolution.

6. Apparatus according to claim 5, wherein

the delta-sigma modulator (9, 10, 12, 13 ..16) is a digital / digital converter of first or higher order.

7. Device according to one of claims 1 to 3, wherein

the control circuit (6) or the conversion device (5) is designed to determine a desired duty cycle on the basis of the dimming value of the first dimming signal (SI), and

the control device (5) is designed for the determination of the error

Determine deviation between the target duty cycle and the duty cycle indicated by the PWM signal (S3) and to change the dimming value of the first dimming signal (Sl) to counteract the determined deviation in the time average.

8. Apparatus according to claim 7, wherein

the control device (5) is designed to cumulate the continuously determined deviations for at least some pulses of the PWM signal (S3) and the dimming value of the first dimming signal (S1) corresponding to a difference between the desired duty cycle and the current one change cumulative deviation.

9. Device according to one of claims 1 to 8, wherein

the regulating device (5) is designed to vary in time the dimming value of the first dimming signal (S1) such that the pulse duty factors predetermined by the PWM signal (S3) are reduced by the dimming value of the first dimming signal (S1 ) vary in time.

10. Device according to one of claims 1 to 9, wherein

the period T of the pulses of the PWM signal (S3) is changed.

11. The apparatus of claim 10, wherein

the period duration (T) of the PWM signal (S3) is modulated between two limit values, wherein the limit values define a modulation stroke of the period duration (T), and the modulation stroke is preferably load-dependent.

12. Operating device for light-emitting diodes, comprising a device (1) according to one of claims I to 11.

13. Light, comprising a light-emitting diode module and a control device according to claim 12.

14. A method of generating a PWM signal for controlling the output of at least one light source based on a first dimming signal, comprising the steps of:

Converting the first dim signal into a lower resolution digital second dimming signal, and

Generating the PWM signal based on the converted second dimming signal, wherein

the dimming value of the first dimming signal is varied over time to counteract in the time average the error occurring due to the lower resolution of the dimming value of the second dimming signal compared to the dimming value of the first dimming signal.