EP3457814A1

EP3457814A1 - Dimming control optimization system

Info

Publication number: EP3457814A1
Application number: EP17191257.9A
Authority: EP
Inventors: Sen-Tai Yang
Original assignee: Yu Jing Energy Tech Co Ltd; Yu Jing Energy Technology Co Ltd
Current assignee: Yu Jing Energy Tech Co Ltd; Yu Jing Energy Technology Co Ltd
Priority date: 2017-09-15
Filing date: 2017-09-15
Publication date: 2019-03-20
Anticipated expiration: 2037-09-15
Also published as: EP3457814B1

Abstract

A dimming control optimization system includes a light-emitting sampling module, an integrator module, an error amplifying module, a comparator module, a dimming module, and a power supply converting module. The light-emitting sampling module obtains and transmits a brightness signal of an illuminator to the integrator. The integrator module integrates the brightness signal to generate a direct-current (DC) sampling signal. The error amplifying module receives the sampling signal and an external dimming reference voltage to generate an output compensation voltage signal. The comparator module determines if the output signal from the error amplifying module has reached a transitioning threshold and output the compensation voltage of the error amplifying module or a threshold voltage as a control reference signal. The dimming module receives the control reference signal and a finite-peak periodic continuous wave input signal to generate a dimming signal to be sent to the power supply converting module. The power supply transitioning module synchronizes the control reference signal and the dimming signal to allow the dimming control optimization system to control analog dimming of the illuminator for medium and high brightness and to enter into a fixed-frequency digital dimming for low brightness without transition gaps during the transitioning between the two dimming modes.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a dimming control optimization system, and more particularly, to a dimming control optimization system without flickering during transition between analog dimming and digital dimming.

2. Description of the Prior Art

Dimming generally can be divided into analog dimming and digital dimming. Analog dimming adjusts the brightness of a light directly with a stable voltage or current. The voltage or current output by a controller can be adjusted based on whether the intensity of the light output is depended on voltage or current. Digital dimming uses pulse width modulation (PWM) to split a cycle of a light into intervals where the light is "on" and "off" under a constant voltage or current. The brightness of the light is proportional to the ratio of the "on" period to the "off" period. There is also hybrid dimming methods, for example, where analog dimming is used for high to medium brightness and digital dimming for below medium brightness.
Since analog dimming relies on the light emitting signal as a feedback. In low brightness, a low feedback signal may affect the stability and accuracy of the control. Moreover, analog dimming results in different color temperatures at high and low brightness. For applicant with stringent color requirements, analog dimming is not suitable for low brightness. Digital dimming has potential drawbacks, including audible noises if the dimming frequency is within the audio range. If the dimming frequency is too low, flickers may be observed. Digital dimming may also cause multiple harmonics and distortions in the power lines, which is not conductive to specifications that have stringent requirements for power factor correction (PFC) and total harmonic distortion (THD). Integrated hybrid dimming thus has the advantages of both of these approaches. Of course, the architectures of some control circuits cannot obtain a balance between low brightness control and efficiency due to its gain curve, this type of control circuits may be forced into a burst mode at low brightness. However, the frequency of this burst mode is not controllable as frequency is increasingly lowered with an increasingly lower brightness. It is inevitable that the dimming frequency enters the visible range.
As a result, methods that combine digital and analog dimming have been proposed, for example, in TW Patent Publication No. I501006 titled "Backlight Unit and Method for Driving the Same", it is characterized in that: a backlight unit includes: a LED array having a plurality of LEDs; a voltage generating unit for generating a driver voltage in response to a switch signal for driving the LEDs; an amplifying unit for feeding back the driver voltage and amplifying the driver voltage to output an amplified signal; a stabilizer for stabilizing the amplified signal; a comparator for comparing the amplified signal with a reference waveform in order to apply the switch signal to the voltage generating unit; a first switching unit for switching a current of the LED array in response to a PWM dimming signal from a timing controller; and a second switching unit for switching the switch signal from the comparator in response to the PWM dimming signal. However, in this publication, in the aspect of PWM dimming, shortage of instantaneous voltage is not addressed, resulting in large errors in PWM dimming.
Moreover, in TW Patent Publication No. M359771 titled "Dual Dimming Backlight Driver", it is characterized in that: a dual dimming backlight driver performs digital dimming upon receiving a PWM dimming signal. The PWM dimming signal includes an enabled period and a disabled period in a cycle, and a duty cycle is a ratio of the enabled period to a cycle. During the enabled period, the driver converts a DC voltage into an output AC voltage to drive a backlight source to illuminate, and during the disabled period, the driver inhibits the backlight source such that it does not illuminate. In addition, when the duty cycle is greater than a threshold duty cycle, in the enabled period, a lamp current is fixed at a first current based on a difference between a feedback voltage and a first voltage, whereas when the duty cycle is determined to be less than or equal to the threshold duty cycle, the first voltage is adjusted to a second voltage, and in the enabled period, the lamp current is fixed at a second current based on a difference between the feedback voltage and the second voltage. The second current is smaller than the first current. Therefore, this application is based on digital dimming, in particular, when the duty cycle is less than or equal to the threshold duty cycle, i.e. when the average brightness is lower than a certain level, the lamp current is reduced by digital dimming to further lower the average brightness, thereby increasing brightness contrast. However, in this application, the backlight control has non-linear issue at low brightness as the "on" period of the light is limited due to the on-time of PWM being too short. Moreover, although digital and analog dimming are used in this application, there is no solution proposed for the step-like variations occurring during switching of the two dimming modes.
Furthermore, in CN Patent Publication No. CN106535412A titled "Port-Sharing Digital/Analog Dimmer", it is characterized in that: a port-sharing digital/analog dimmer includes: a comparator module, buffer modules, a gate logic module, wherein the comparator module includes first and second comparators A1 and A2, the first comparator A1 is configured for processing digital dimming and controlling the status of an enabled port EN of the second comparator A2 through buffer modules B1 and B2 and a capacitor C, the second comparator A2 is configured for processing analog dimming. A dimming signal processed by the two comparators is then passed through an OR gate and an AND gate of the gate logic module. The advantage of this application is that the input port for the digital dimming and analog dimming is integrated, so that one input port provides both analog and digital functions. It is simple in structure and saves chip footprint and packaging cost. However, this publication only has digital and analog modes in the input dimming signals, but the actual output control signal is still just digital (PWM).
In view of the shortcomings in the prior art, the present invention is proposed to provide improvements that address these shortcomings.

SUMMARY OF THE INVENTION

One main objective of the present invention is to provide a dimming control optimization system that will not produce flickering during transitions between analog and digital dimming.
Another objective of the present invention is to provide a dimming control optimization system that uses the same compensation voltage to control analog dimming for medium and high brightness and to enter into a fixed-frequency digital dimming for low brightness.
Still another objective of the present invention is to provide a dimming control optimization system that introduces a finite-peak periodic continuous wave input signal and synchronizes the dimming signal with the periodic continuous wave input signal.
In order to achieve the above objectives and efficacies, the technical means employed by the present invention may include:

a light-emitting sampling module for obtaining a brightness signal of an illuminator;
an integrator module electrically connected with the light-emitting sampling module for receiving and integrating the brightness signal to generate a direct-current (DC) sampling signal;
an error amplifying module electrically connected with the integrator module for receiving the sampling signal and a dimming reference voltage provided externally to generate an output signal;
a comparator module for determining if the output signal of the error amplifying module has reached a transitioning threshold and outputting the compensation voltage outputted by the error amplifying module or a threshold voltage as a control reference signal;
a dimming module for receiving a finite-peak periodic continuous wave input signal and the control reference signal to generate a dimming signal; and
a power supply transitioning module electrically connected with the comparator module and the dimming module for synchronizing the periods of the control reference signal and the dimming signal to output a dimming control signal for adjusting the brightness of the illuminator,
wherein when the comparator module outputs the control reference signal including the compensation voltage, the control reference signal and the finite-peak periodic continuous wave input signal are inputted into the dimming module, which generates the dimming signal to be transmitted to the power supply transitioning module, the power supply transitioning module synchronizes the periods of the control reference signal and the dimming signal to allow the dimming control optimization system to control analog dimming of the illuminator for medium and high brightness and to enter into a fixed-frequency digital dimming for low brightness without transition gaps during the transitioning between the two dimming modes

In order to achieve the above objectives and efficacies, the technical means employed by the present invention may include:

Based on the above structure, when the comparator is in positive feedback control, the power supply converting module clamps the control reference signal at a positive peak of the dimming signal. The positive peak of the dimming signal is a peak voltage of the periodic continuous wave input signal.

Based on the above structure, when the comparator is in negative feedback control, the power supply converting module clamps the control reference signal at a negative trough of the dimming signal. The negative trough of the dimming signal is a trough voltage of the periodic continuous wave input signal.
Based on the above structure, the periodic continuous wave input signal is a saw-tooth wave, a triangular wave or a sine wave with a stable period, and the finite peak is within the voltage range of the compensation voltage.
Based on the above structure, the error amplifying module, the comparator module and the dimming module are mutually and electrically connected with a compensation capacitor for generating the compensation voltage.
Based on the above structure, the dimming module is connected with a decoupling capacitor, and the voltage on the decoupling capacitor is the finite-peak periodic continuous wave input signal.
The objectives, efficacies and features of the present invention can be more fully understood by referring to the drawing as follows:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram depicting a dimming control optimization system in accordance with an embodiment of the present invention
FIG. 2 is a block diagram depicting a dimming control optimization system in accordance with a preferred embodiment of the present invention.
FIG. 3 is a waveform graph of FIG. 2.
FIG. 4 is a block diagram depicting a dimming control optimization system in accordance with another preferred embodiment of the present invention.
FIG. 5 is a waveform graph of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a block diagram depicting a dimming control optimization system in accordance with an embodiment of the present invention is shown. The dimming control optimization system includes the components as follow.
A light-emitting sampling module 2 is used for obtaining a brightness signal of an illuminator 1.
An integrator module 3 is electrically connected with the light-emitting sampling module 2 for receiving and integrating the brightness signal to generate a DC sampling signal.
An error amplifying module 4 is electrically connected with the integrator module 3 for receiving the sampling signal and a dimming reference voltage provided externally to generate an output signal.
A comparator module 5 is electrically connected with the error amplifying module 4 for determining if the output signal from the error amplifying module 4 has reached a threshold for transition and outputting the compensation voltage of the error amplifying module or a threshold voltage as a control reference signal.
A dimming module 6 is used for receiving a finite-peak periodic continuous wave input signal and the control reference signal to generate a dimming signal. The dimming module 6 is connected with a decoupling capacitor 9. The voltage on the decoupling capacitor 9 is the finite-peak periodic continuous wave input signal. It should be noted that the aforementioned periodic continuous wave input signal can be a saw-tooth wave, a triangular wave or a sine wave with a stable period, and "finite peak" is within the voltage range of the compensation voltage.
A power supply transitioning module 7 is electrically connected with the comparator module 5 and the dimming module 6 for synchronizing the periods of the control reference signal and the dimming signal to output a dimming control signal for adjusting the brightness of the illuminator.
The compensation voltage comes from a compensation capacitor 8. The compensation capacitor 8 is mutually and electrically connected between the error amplifying module 4, the comparator module 5 and the dimming module 6.
Accordingly, the comparator module 5 outputs the control reference signal including the compensation voltage. The control reference signal and the finite-peak periodic continuous wave input signal are inputted into the dimming module 6, which generates the dimming signal to be transmitted to the power supply transitioning module 7. The power supply transitioning module 7 synchronizes the periods of the control reference signal and the dimming signal. This allows the dimming control optimization system to control analog dimming of the illuminator 1 for medium and high brightness and to enter into a fixed-frequency digital dimming for low brightness without transition gaps during the transitioning between the two dimming modes.
Referring to FIGs. 2 and 3, a block diagram and a waveform graph depicting the dimming control optimization system in accordance with a preferred embodiment of the present invention are shown. This embodiment illustrates the implementations of the system when the comparator 5 is in positive feedback. It can be seen from the diagram and the graph, the lower the compensation voltage (V_EA) of the compensation capacitor 8, i.e. the lower the output signal voltage of the error amplifying module 4, the lower the output power of the power supply transitioning module 7. When the compensation voltage (V_EA) approaches the peak (VP) of the periodic continuous wave input signal (Vc) on the decoupling capacitor 9, the power supply transitioning module 7 then clamps the control reference signal at a positive peak value (i.e. the peak (VP)) that the compensation voltage (V_EA) first comes into contact with the periodic continuous wave input signal (Vc). However, the external input voltage still varies with the dimming reference voltage. When the external input voltage is lower than the peak (VP) of the periodic continuous wave input signal (Vc) and higher than the trough (VV) of the periodic continuous wave input signal (Vc), a digital dimming signal T2 (a PWM-controlled signal) is generated. At this time, the power supply transitioning module 7 synchronizes the periods of the control reference signal and the dimming signal, that is, the output of the power supply transitioning module 7 is a PWM-controlled signal. When the power supply converting module 7 is in the "on" periods, the control signal used is the peak (VP).
Therefore, before the compensation voltage (V_EA) is in contact with the periodic continuous wave input signal (Vc), a dimming control signal T outputted by the power supply transitioning module 7 is an analog dimming signal T1. At this stage, dimming is controlled in an analog manner.
Before the compensation voltage (V_EA) is in contact with the periodic continuous wave input signal (Vc), the voltage peak of the dimming control signal T is clamped at the peak (VP) of the periodic continuous wave input signal (Vc).
Once the voltage peak of the dimming control signal T is fixed, the period of the dimming control signal T will create a PWM-controlled digital dimming signal T2 due to synchronization of the periods of the control reference signal and the dimming signal by the power supply transitioning module 7. At this stage, dimming is digitally controlled. It can be seen more clearly from FIG. 4, during the transition of the analog dimming signal T1 to the digital dimming signal T2, it is not a direct analog to digital transition, but a progressive transition. Therefore, a dimming control optimization system without flickering during transitioning between analog and digital dimming can be achieved.
Referring to FIGs. 4 and 5, a block diagram and a waveform graph depicting the dimming control optimization system in accordance with another preferred embodiment of the present invention are shown. This embodiment illustrates the implementations of the system when the comparator 5 is in negative feedback. It can be seen from the diagram and the graph, the higher the compensation voltage (V_EA) of the compensation capacitor 8, i.e. the higher the output signal voltage of the error amplifying module 4, the lower the output power of the power supply transitioning module 7. When the compensation voltage (V_EA) approaches the trough (VV) of the periodic continuous wave input signal (Vc) on the decoupling capacitor 9, the power supply transitioning module 7 then clamps the control reference signal at a negative trough value (i.e. the trough (VV)) that the compensation voltage (V_EA) first comes into contact with the periodic continuous wave input signal (Vc). However, the external input voltage still varies with the dimming reference voltage. When the external input voltage is higher than the trough (VV) of the periodic continuous wave input signal (Vc) and lower than the peak (VP) of the periodic continuous wave input signal (Vc), a digital dimming signal T2 (a PWM-controlled signal) is generated. At this time, the power supply transitioning module 7 synchronizes the control reference signal and the dimming signal, that is, the output of the power supply transitioning module 7 is a PWM-controlled signal. When the power supply converting module 7 is in the "on" periods, the control signal used is the trough (VV).
Therefore, before the compensation voltage (V_EA) is in contact with the periodic continuous wave input signal (Vc), a dimming control signal T outputted by the power supply transitioning module 7 is an analog dimming signal T1. At this stage, dimming is controlled in an analog manner.
Before the compensation voltage (V_EA) is in contact with the periodic continuous wave input signal (Vc), the voltage peak of the dimming control signal T is clamped at the trough (VV) of the periodic continuous wave input signal (Vc).
Once the voltage peak of the dimming control signal T is fixed, the period of the dimming control signal T will create a PWM-controlled digital dimming signal T2 due to synchronization of the periods of the control reference signal and the dimming signal by the power supply transitioning module 7. At this stage, dimming is digitally controlled. It can be seen more clearly from FIG. 4, during the transition of the analog dimming signal T1 to the digital dimming signal T2, it is not a direct analog to digital transition, but a progressive transition. Therefore, a dimming control optimization system without flickering during transitioning between analog and digital dimming can be achieved.
In conclusion, the dimming control optimization system of the present invention is capable of using the same compensation voltage to control analog dimming for medium and high brightness and enter into fixed-frequency digital dimming for low brightness without producing flickers during the transition (transition gaps). In view of this, the present invention is submitted to be novel and non-obvious and a patent application is hereby filed in accordance with the patent law. It should be noted that the descriptions given above are merely descriptions of preferred embodiments of the present invention, various changes, modifications, variations or equivalents can be made to the invention without departing from the scope or spirit of the invention. It is intended that all such changes, modifications and variations fall within the scope of the following appended claims and their equivalents.

Claims

A dimming control optimization system comprising:
a light-emitting sampling module (2) for obtaining a brightness signal of an illuminator (1);

an integrator module (3) electrically connected with the light-emitting sampling module (2) for receiving and integrating the brightness signal to generate a direct-current (DC) sampling signal;

an error amplifying module (4) electrically connected with the integrator module (3) for receiving the sampling signal and a dimming reference voltage provided externally to generate an output signal;

a comparator module (5) electrically connected with the error amplifying module (4) for receiving the output signal and a compensation voltage to output a control reference signal;

a dimming module (6) for receiving a finite-peak periodic continuous wave input signal and the control reference signal to generate a dimming signal; and

a power supply transitioning module (7) electrically connected with the comparator module (5) and the dimming module (6) for synchronizing the periods of the control reference signal and the dimming signal to output a dimming control signal for adjusting the brightness of the illuminator,

wherein when the comparator module (5) outputs the control reference signal including the compensation voltage, the control reference signal and the finite-peak periodic continuous wave input signal are inputted into the dimming module (6), which generates the dimming signal to be transmitted to the power supply transitioning module (7), the power supply transitioning module (7) synchronizes the periods of the control reference signal and the dimming signal to allow the dimming control optimization system to control analog dimming of the illuminator (1) for medium and high brightness and to enter into a fixed-frequency digital dimming for low brightness without transition gaps during the transitioning between the two dimming modes.
The dimming control optimization system of claim 1, wherein the comparator module (5) is in positive feedback control, the power supply converting module (7) clamps the control reference signal at a positive peak of the dimming signal.
The dimming control optimization system of claim 2, wherein the positive peak of the dimming signal is a peak voltage of the periodic continuous wave input signal.
The dimming control optimization system of claim 1, wherein the comparator module (5) is in negative feedback control, the power supply converting module (7) clamps the control reference signal at a negative trough of the dimming signal.
The dimming control optimization system of claim 4, wherein the negative trough of the dimming signal is a trough voltage of the periodic continuous wave input signal.
The dimming control optimization system of claim 1, wherein the periodic continuous wave input signal is a saw-tooth wave, a triangular wave or a sine wave with a stable period, and the finite peak is within the voltage range of the compensation voltage.
The dimming control optimization system of claim 1, wherein the error amplifying module (4), the comparator module (5) and the dimming module (6) are mutually and electrically connected with a compensation capacitor for generating the compensation voltage.
The dimming control optimization system of claim 1, wherein the dimming module (6) is connected with a decoupling capacitor, and the voltage on the decoupling capacitor is the finite-peak periodic continuous wave input signal.