A hybrid dimming system for light emitting diodes

Abstract

The present invention discloses a hybrid dimming system for light emitting diodes, which relates to the technical field of light emitting diode dimming. The system comprises: a mode conversion module, a current reference module, a PWM processing module and a current driving module; the mode conversion module is mainly responsible for processing the structure switching between exponential dimming and linear dimming. 2 The C dimming code is input by this module. The present invention realizes high-precision LED current driving by combining the PTAT current or CTAT current generated by the current reference module with a feedback loop composed of a precision resistor and an operational amplifier. In particular, in the zero-temperature drift LED current driving realized in an analog manner, the system adopts a zero-temperature drift current source, which effectively offsets the influence of temperature changes on the LED current and ensures the stability and consistency of the LED current. This design not only improves the stability and reliability of LED light emission, but also extends the service life of the LED and reduces the risk of light decay and failure due to current fluctuations.

Description

Technical Field

[0001] The invention relates to the technical field of light emitting diode dimming, and in particular to a hybrid dimming system of light emitting diodes. Background Art

[0002] LED backlight technology is widely used in the field of consumer electronics. In order to meet the complex and ever-changing market needs, a variety of dimming methods have emerged. Among them, linear dimming and exponential dimming are the two more common dimming methods. The characteristic of linear dimming is that the output LED current is proportional to the input code or input PWM duty cycle, and the LED brightness changes linearly, while the exponential dimming is that the output LED current is exponentially related to the input code or input PWM duty cycle, and the LED brightness changes exponentially. In addition, the dimming control mode is also I 2 There are many ways of dimming, such as C dimming, PWM dimming and hybrid dimming. Different scenarios will have different requirements for the maximum peak current of LED. Therefore, it is necessary to control the maximum peak current range through external signals. Building a universal and scalable dimming system that can meet multiple dimming requirements at the same time is a necessary condition for integrated design.

[0003] In traditional technologies, there are many deficiencies in zero-drift LED current driving implemented by analog methods, hybrid dimming systems implemented by analog methods, compatibility with three different architectures, and realization of arbitrary base exponential dimming. First, in terms of zero-drift LED current driving implemented by analog methods, traditional technologies often find it difficult to ensure that the current value is completely unaffected by temperature, resulting in LED brightness fluctuating with temperature changes. Secondly, in terms of hybrid dimming systems implemented by analog methods, traditional technologies usually need to build complex circuit structures to achieve the integration of multiple dimming functions, which not only increases costs but also reduces the reliability and stability of the system. In addition, in terms of compatibility with three different architectures, traditional technologies often lack flexibility and are difficult to adapt to the needs of different application scenarios. Finally, in terms of realizing arbitrary base exponential dimming, traditional technologies usually require complex calculations and control logic, which not only increases the complexity of the system but also limits the application scope of the dimming system.

[0004] Therefore, a hybrid dimming system of light emitting diodes is developed to solve the above-mentioned problems. Summary of the invention

[0005] The purpose of the present invention is to make up for the shortcomings of the prior art and provide a hybrid dimming system for light-emitting diodes. The system mainly includes a mode conversion module, a current reference module, a PWM processing module and a current driving module. The mode conversion module is responsible for processing the structural switching of exponential dimming and linear dimming. The current reference module provides PTAT or CTAT current for the system. The PWM processing module is responsible for processing the PWM dimming signal and extracting duty cycle information. The current driving module realizes LED current output. By designing appropriate resistance values ​​and proportional coefficients, the system can realize exponential function dimming with any base number, with high flexibility and accuracy.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: a hybrid dimming system for light emitting diodes, the system comprising: a mode conversion module, a current reference module, a PWM processing module and a current driving module;

[0007] The mode conversion module is mainly responsible for processing the structure switching between exponential dimming and linear dimming. 2 C dimming code is input by this module, and the internal structure will be adjusted accordingly in different hybrid dimming systems;

[0008] The current reference module provides a specific PTAT current or CTAT current for the mode conversion module, and is controlled by the PWM processing module in a specific mixed mode. The generated bandgap reference PTAT current is connected to the resistor and the positive input of the operational amplifier, and is connected to the gate of the adjustment tube MOS through the output of the operational amplifier, and the source is connected to the negative input of the operational amplifier and the resistor. After proportional amplification, the PTAT current of the required size of the circuit can be obtained;

[0009] The PWM processing module is responsible for processing the PWM dimming signal, extracting the duty cycle information in the PWM signal through chopping and filtering, and integrating it into the hybrid dimming system. The current in the current reference module is affected differently in different hybrid dimming systems.

[0010] The current driving module is used for the final driving stage to realize LED current output. The connection mode and related parameters will be adjusted accordingly in different hybrid dimming systems.

[0011] Furthermore, the mode conversion module includes two identical PNPs, bipolar D1 and bipolar D2, the base of bipolar D1 is connected to the collector, and the current source I MIN-IN Connected to the positive input of operational amplifier OP1, current source I MIN-IN It is a zero temperature drift current source. The output of the op amp OP1 is connected to the gate of the adjustment tube MOSM1. The source of the adjustment tube MOSM1 is connected to the negative input of the op amp OP1 and the regulating resistor group R code , regulating resistor group R code Available through I2 The C input code controls the overall resistance value, which can be calculated using the PTAT current calculation formula: R code =code×R st , where code is I 2 C input value, R st is a single step resistance value, the positive input of op amp OP2 is connected to the regulating resistor group R code The other end is connected to the PTAT current in the current reference module. The output of the op amp OP2 is connected to the gate of the adjustment tube MOSM2. The source of the adjustment tube MOSM2 is connected to the collector of the bipolar D2 and the negative input of the op amp OP2. The drain of the adjustment tube MOSM2 is connected to the resistor R F .

[0012] Furthermore, the bandgap reference PTAT current I generated in the reference module PTAT-Bandgap , connected to resistor R1 and the positive input of operational amplifier OP4, the output of operational amplifier OP4 is connected to the gate of adjustment tube MOSM4, the source of adjustment tube MOSM4 is connected to the negative input of operational amplifier OP4 and resistor R2, and the PTAT current I required by the circuit is obtained through appropriate ratio amplification. PTAT , the PTAT current can be calculated by the resistance value calculation formula of the regulating resistor group, the formula is: Where V T is the thermal voltage, R BG is the resistance for constructing PTAT current in the bandgap reference, and m is the proportionality coefficient.

[0013] Furthermore, the bipolar current is calculated in the reference module by a bipolar current characteristic formula, which is: Among them I s is the bipolar reverse saturation current, V T is the thermal voltage, V BE is the voltage between the base and emitter of the bipolar.

[0014] Furthermore, the PWM processing module is responsible for processing the PWM signal. The chopping unit CHOPPER receives the PWM signal, performs chopping processing on the reference signal output from the mode conversion module, and then inputs it to the filtering unit LPF for filtering processing, and inputs the reference with PWM duty cycle information into the current driving module.

[0015] Furthermore, the current driving module is an LED driving circuit, the PWM processing module output reference is connected to the positive input of the operational amplifier OP3, the gate of the operational amplifier OP3 is connected to the gate of the adjustment tube MOSM3, and the source of the adjustment tube MOSM3 is connected to the LED sampling resistor R sense And the negative terminal input of the operational amplifier OP3, the drain of the adjustment tube MOSM3 is connected to the light-emitting diode LED, and multiple LEDs can be connected in series at the same time.

[0016] Furthermore, the LED current output by the current driving module is calculated by an LED current calculation formula, which is:

[0017] Among them I PTAT represents the PTAT current, V T Represents thermal voltage, V BE Represents the voltage between the base and emitter of the bipolar, which is one of the parameters for calculating the bipolar current. F and R sense Both represent resistance, D PWM Indicates the duty cycle of the PWM signal, I MIN-IN Indicates CTAT current, code is I 2 C input value, ensure R st and R BG The resistor type is the same, and I MIN-IN is also the CTAT current, then I 2 C-index dimming and PWM linear dimming have zero temperature drift.

[0018] Furthermore, the current driving module is designed according to the requirements. st , R BG The resistance value and the proportionality coefficient m give an exponential function with any base a. The exponential function is: The LED current calculation formula is simplified by exponential function, and the simplified formula is:

[0019] Furthermore, when the PWM processing module intervenes in the current reference module, the current driving module calculates the PTAT current after the duty cycle information is introduced through a formula, and the calculation formula is: Where m is the proportionality coefficient, V T Represents thermal voltage, R BG Resistance value, D PWM Representing the duty cycle of the PWM signal, the output current extreme formula of the LED is: Where a is calculated by exponential function, R F Represents resistance, I MIN-IN represents the CTAT current, R sense Represents resistance, D PWM Indicates the duty cycle of the PWM signal, code is I 2 C input value.

[0020] Furthermore, the current driving module changes bipolar D1 and bipolar D2 into two resistors R with the same single step length as the regulating resistor group in the mode conversion module. st In the design, the connection is switched through an internal switch, and the PTAT current introduced by the bandgap reference is switched to the CTAT current I in the current reference module. CTAT , and the mode conversion module I MIN-IN The current is designed to be CTAT Equal, in the current reference module, the reference zero-temperature current I generated in the reference circuit CTAT-Bandgap I is obtained by proportional amplification by operational amplifier OP4 and resistors R1 and R2. CTAT , in this structure, the LED current calculation formula is: Where R F and R sense Both represent resistance, D PWM Indicates the duty cycle of the PWM signal, code is I 2 C input value.

[0021] Compared with the prior art, the hybrid dimming system of light emitting diodes has the following beneficial effects:

[0022] 1. The present invention realizes high-precision LED current driving by combining the PTAT current or CTAT current generated by the current reference module with a feedback loop composed of a precision resistor and an operational amplifier. In particular, in the zero-temperature drift LED current driving realized in an analog manner, the system adopts a zero-temperature drift current source, which effectively offsets the influence of temperature changes on the LED current and ensures the stability and consistency of the LED current. This design not only improves the stability and reliability of LED light emission, but also prolongs the service life of the LED and reduces the risk of light decay and failure caused by current fluctuations.

[0023] 2. The present invention realizes seamless switching and hybrid dimming between exponential dimming and linear dimming through the coordinated work of a mode conversion module, a current reference module, a PWM processing module and a current driving module. In a hybrid dimming system implemented in an analog manner, the PWM processing module extracts duty cycle information from a PWM signal and integrates it into the hybrid dimming system, thereby realizing precise control of LED brightness. This hybrid dimming method not only improves the flexibility and accuracy of dimming, but also reduces energy consumption and noise during the dimming process, thereby improving the overall performance of the system and user experience.

[0024] 3. By adjusting the internal structure and parameters of the mode conversion module and the current reference module, the system can flexibly switch between different dimming modes to meet the needs of different application scenarios. In addition, the system also realizes exponential dimming with any base. By designing appropriate resistance values ​​and proportional coefficients, an exponential function with any base can be obtained, thereby achieving more precise and flexible control of the LED brightness. This design not only improves the dimming range and accuracy of the system, but also provides users with richer dimming options and a better visual experience.

[0025] Other advantages, objectives and features of the present invention will be set forth in part in the following description and, in part, will be apparent to those skilled in the art based on an examination of the following or may be taught from the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 A control block diagram of a hybrid dimming system for light emitting diodes;

[0028] Figure 2 For I 2 Circuit diagram of hybrid system of C-index dimming and PWM linear dimming;

[0029] Figure 3 For I 2 Circuit diagram of hybrid system of C-index dimming and PWM-index dimming;

[0030] Figure 4 For I 2 C Circuit diagram of the hybrid system of linear dimming and PWM linear dimming. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Embodiment 1:

[0033] I 2C-index dimming and PWM linear dimming hybrid system:

[0034] System structure and connection method: Figure 2 , I 2 As shown in the circuit schematic diagram of the hybrid system of C index dimming and PWM linear dimming, the control switch S1 is opened, S2 is closed, S3 is closed, S4 is opened, and S5 is opened.

[0035] The mode conversion module includes two identical PNPs, bipolar D1 and bipolar D2. The base of bipolar D1 is connected to the collector, which is connected to the zero-drift current source and the positive input of the operational amplifier. The current source is a zero-drift current source. The output of the operational amplifier is connected to the gate of the adjustment tube MOS. The source of the adjustment tube MOS is connected to the negative input of the operational amplifier and the regulating resistor group. The regulating resistor group can be adjusted through I 2 The C input code controls the overall resistance value, which can be calculated using the PTAT current calculation formula: R code =code×R st , where code is I 2 C input value, R st is the resistance value of a single step resistor.

[0036] The current reference module provides a specific PTAT current for the mode conversion module. The bandgap reference PTAT current is connected to the resistor and the positive input of the operational amplifier. The output of the operational amplifier is connected to the gate of the adjustment tube MOS, and the source is connected to the negative input of the operational amplifier and the resistor. After proportional amplification, the PTAT current of the required size of the circuit can be obtained. The PTAT current can be obtained by the formula, which is: Where V T is the thermal voltage, R BG is the resistance for constructing PTAT current in the bandgap reference, and m is the proportional coefficient, which can be adjusted by adjusting the ratio of the number of bipolar resistors in the bandgap reference to the ratio of HE resistors.

[0037] The PWM processing module processes the PWM signal, the chopping unit receives the PWM signal, chops the reference signal output from the mode conversion module, and then inputs it to the filtering unit for filtering, and finally inputs the reference with PWM duty cycle information into the current driving module.

[0038] The current driving module is an LED driving circuit, the PWM processing module output reference is connected to the positive input of the operational amplifier, the operational amplifier gate is connected to the MOS gate of the adjustment tube, the MOS source of the adjustment tube is connected to the LED sampling resistor and the negative input of the operational amplifier, and the MOS drain of the adjustment tube is connected to the light-emitting diode LED. Multiple LEDs can be connected in series at the same time.

[0039] Dimming formula derivation, based on the bipolar current formula: Among them Is is the bipolar reverse saturation current, which is determined by the bipolar characteristics. The bipolars with the same structure and area have the same parameters. V τ is the thermal voltage, V BE is the voltage between the base and emitter of the bipolar Figure 2 Under the structure, the output LED current can be calculated as follows: Among them I PTAT represents the PTAT current, V T Represents thermal voltage, V BE Represents the voltage between the base and emitter of the bipolar, which is one of the parameters for calculating the bipolar current. F and R sense Both represent resistance, D PWM Indicates the duty cycle of the PWM signal, I MIN-IN Indicates CTAT current, code is I 2 C input value, ensure R st and R BG The resistor type is the same, and I MIN-IN is also the CTAT current, then I 2 C index dimming and PWM linear dimming have zero temperature drift. R is designed according to the requirements. st , R BG The resistance value and the proportionality coefficient m give an exponential function with any base a. The exponential function is: The LED current calculation formula is simplified by exponential function. The simplified formula is:

[0040] Embodiment 2:

[0041] I 2 C index dimming and PWM index dimming hybrid system:

[0042] System structure and connection method: Figure 3 , I 2 As shown in the circuit diagram of the hybrid system of C index dimming and PWM index dimming, the control switch S1 is closed, S2 is disconnected, S3 is disconnected, S4 is closed, S5 is closed, and the mode conversion module is connected to I 2 C exponential dimming and PWM linear dimming hybrid system are consistent.

[0043] In the current reference module, the PWM processing module intervenes in the PTAT current processing. When the PWM processing module intervenes in the current reference module, the current driving module calculates the PTAT current after the duty cycle information is introduced through the formula. The calculation formula is: Where m is the proportionality coefficient, VT Represents thermal voltage, R BG Resistance value, D PWM Indicates the duty cycle of the PWM signal.

[0044] Dimming formula derivation, finally I 2 The dimming formula of the hybrid system of C exponential dimming and PWM exponential dimming can be obtained by the formula, and the output current extreme formula of the LED is: Where a is calculated by exponential function, R F Represents resistance, I MIN-IN represents the CTAT current, R sense Represents resistance, D PWM Indicates the duty cycle of the PWM signal, code is I 2 C input value.

[0045] Embodiment 3: I 2 C Linear dimming and PWM linear dimming hybrid system:

[0046] System structure and connection method Figure 4 , I 2 As shown in the circuit diagram of the hybrid system of linear dimming and PWM linear dimming C, the control switch S1 is opened, S2 is closed, S3 is closed, S4 is opened, and S5 is opened.

[0047] The mode conversion module changes the bipolar D1 and D2 into two resistors R with the same single step length as the control resistor group. st In the design, the connection can be switched through the internal switch, and the PTAT current introduced by the bandgap reference can be switched to the CTAT current I in the current reference module. cτAT , and the mode conversion module I MIN-IN The current is designed to be CTAT Equal, in the current reference module, the reference zero-temperature current I generated in the reference circuit CTAT-Bandgap I is obtained by proportional amplification by operational amplifier OP4 and resistors R1 and R2. CTAT .

[0048] Dimming formula derivation, based on this structure, we can get I 2 The dimming formula of the hybrid system of C linear dimming and PWM linear dimming is: Where R F and R sense Both represent resistance, D PWM Indicates the duty cycle of the PWM signal, code is I 2 C input value.

[0049] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A hybrid dimming system for light emitting diodes, characterized in that: The system includes: a mode conversion module, a current reference module, a PWM processing module and a current driving module; The mode conversion module is mainly responsible for processing the structure switching between exponential dimming and linear dimming. 2 The C dimming code is input from this module. In different hybrid dimming systems, the internal structure will be adjusted accordingly. The module contains two identical PNP bipolar D1 and bipolar D2. The base of bipolar D1 is connected to the collector and the current source I MIN-IN Connected to the positive input of operational amplifier OP1, current source I MIN-IN It is a zero temperature drift current source. The output of the op amp OP1 is connected to the gate of the adjustment tube MOSM1. The source of the adjustment tube MOSM1 is connected to the negative input of the op amp OP1 and the regulating resistor group R code , regulating resistor group R code Available through I 2 The C input code controls the overall resistance value, which can be calculated using the PTAT current calculation formula: R code =code×R st , where code is I 2 C input value, R st is a single step resistance value, the positive input of op amp OP2 is connected to the regulating resistor group R code The other end is connected to the PTAT current in the current reference module. The output of the op amp OP2 is connected to the gate of the adjustment tube MOSM2. The source of the adjustment tube MOSM2 is connected to the collector of the bipolar D2 and the negative input of the op amp OP2. The drain of the adjustment tube MOSM2 is connected to the resistor R F ; The current reference module provides a specific PTAT current or CTAT current for the mode conversion module. In individual mixed modes, it is controlled by the PWM processing module. The generated bandgap reference PTAT current I PTAT-Bandgap , connected to resistor R1 and the positive input of operational amplifier OP4, the output of operational amplifier OP4 is connected to the gate of adjustment tube MOSM4, the source of adjustment tube MOSM4 is connected to the negative input of operational amplifier OP4 and resistor R2, and the PTAT current I required by the circuit is obtained through appropriate ratio amplification. PTAT , the PTAT current can be calculated by the resistance value calculation formula of the regulating resistor group, the formula is: Where V T is the thermal voltage, R BG is the resistance for constructing the PTAT current in the bandgap reference, and m is the proportionality coefficient. At the same time, the module calculates the bipolar current through the bipolar current characteristic formula, which is: Among them I s is the bipolar reverse saturation current, V T is the thermal voltage, V BE is the voltage between the base and emitter of the bipolar; The PWM processing module is responsible for processing the PWM dimming signal, extracting the duty cycle information in the PWM signal through chopping and filtering, and integrating it into the hybrid dimming system. The current in the current reference module is affected differently in different hybrid dimming systems. The current driving module is used for the final driving stage to realize LED current output. The connection mode and related parameters will be adjusted accordingly in different hybrid dimming systems.

2. A hybrid dimming system for light emitting diodes according to claim 1, characterized in that: The PWM processing module is responsible for processing the PWM signal. The chopping unit CHOPPER receives the PWM signal, performs chopping processing on the reference signal output from the mode conversion module, and then inputs it to the filtering unit LPF for filtering processing, and inputs the reference signal with PWM duty cycle information into the current driving module.

3. The hybrid dimming system of light emitting diodes according to claim 1, characterized in that: The current driving module is an LED driving circuit, the PWM processing module output reference is connected to the positive input of the operational amplifier OP3, the gate of the operational amplifier OP3 is connected to the gate of the adjustment tube MOSM3, and the source of the adjustment tube MOSM3 is connected to the LED sampling resistor R sense And the negative terminal input of the operational amplifier OP3, the drain of the adjustment tube MOSM3 is connected to the light-emitting diode LED, and multiple LEDs can be connected in series at the same time.

4. The hybrid dimming system of light emitting diodes according to claim 3, characterized in that: The LED current output by the current driving module is calculated by the LED current calculation formula, which is: Among them I PTAT represents the PTAT current, V T Represents thermal voltage, V BE Represents the voltage between the base and emitter of the bipolar, which is one of the parameters for calculating the bipolar current. F and R sense Both represent resistance, D PWM Indicates the duty cycle of the PWM signal, I MIN-IN Indicates CTAT current, code is I 2 C input value, ensure R st and R BG The resistor type is the same, and I MIN-IN is also the CTAT current, then I 2 C-index dimming and PWM linear dimming have zero temperature drift.

5. The hybrid dimming system of light emitting diodes according to claim 4, characterized in that: The current driving module is designed according to the requirements R st , R BG Resistance value and proportionality factor m, get any base a m×Rst The exponential function is: a = e R BG , the LED current calculation formula is simplified by exponential function, and the simplified formula is:

6. The hybrid dimming system of light emitting diodes according to claim 1, characterized in that: The current driving module calculates the PTAT current after the duty cycle information is introduced by a formula when the PWM processing module intervenes in the current reference module. The calculation formula is: Where m is the proportionality coefficient, V T Represents thermal voltage, R BG Resistance value, D PWM Representing the duty cycle of the PWM signal, the output current extreme formula of the LED is: Among them, a is calculated by exponential function, R F Represents resistance, I MIN-IN represents the CTAT current, R sense Represents resistance, D PWM Indicates the duty cycle of the PWM signal, code is I 2 C input value.

7. The hybrid dimming system of light emitting diodes according to claim 1, characterized in that: The current driving module changes bipolar D1 and bipolar D2 into two resistors R with the same single step length as the control resistor group in the mode conversion module. st In the design, the connection is switched through an internal switch, and the PTAT current introduced by the bandgap reference is switched to the CTAT current I in the current reference module. CTAT , and the mode conversion module I MIN-IN The current is designed to be CTAT Equal, in the current reference module, the reference zero-temperature current I generated in the reference circuit CTAT-Bandgap I is obtained by proportional amplification by operational amplifier OP4 and resistors R1 and R2. CTAT , in this structure, the LED current calculation formula is: Where R F and R sense Both represent resistance, D PWM Indicates the duty cycle of the PWM signal, code is I 2 C input value.

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