CN212967040U

CN212967040U - Light modulation device and electronic equipment

Info

Publication number: CN212967040U
Application number: CN202022047801.7U
Authority: CN
Inventors: 张兴德; 胡锋
Original assignee: Guangzhou Shiyuan Electronics Thecnology Co Ltd; Guangzhou Shikun Electronic Technology Co Ltd
Current assignee: Guangzhou Shiyuan Electronics Thecnology Co Ltd; Guangzhou Shikun Electronic Technology Co Ltd
Priority date: 2020-09-17
Filing date: 2020-09-17
Publication date: 2021-04-13
Anticipated expiration: 2030-09-17

Abstract

The embodiment of the disclosure provides a dimming device and electronic equipment, wherein the dimming device comprises an LLC resonance conversion circuit, a duty ratio regulating circuit, a rectification filter circuit, a load circuit and a control circuit. The LLC resonant conversion circuit, the duty ratio regulating circuit, the rectification filter circuit, the load circuit and the control circuit are sequentially connected to form a circulation loop. In this framework, behind LLC resonance converting circuit, before the rectification filter circuit, increased duty cycle regulating circuit, utilize duty cycle regulating circuit to adjust effective duty cycle, and then adjust the energy of an output load circuit, ensure that the wide range that also can realize load energy changes in the less within range of switching frequency change, solved the LLC backlight drive circuit that traditional PWM adjusted luminance, scintillation and the problem of adjusting luminance abnormal sound when shooing the backlight screen.

Description

Light modulation device and electronic equipment

Technical Field

The embodiment of the disclosure relates to the technical field of circuits, in particular to a dimming device and an electronic device.

Background

With the rapid development of the technology, the light emitting brightness and the light emitting efficiency of the Light Emitting Diode (LED) are greatly increased, and electronic devices with high-power LED backlight display power sources have come into play.

At present, a backlight driving circuit of a high-power LED backlight display power supply generally adopts a resonant conversion circuit (LLC) topology, and adjusts the frequency by a Pulse Frequency Modulation (PFM) technique, that is, realizes stable constant current output by changing the frequency. Aiming at an LED backlight driving circuit of an LLC topology, if an analog dimming technology is adopted, the frequency is smaller when a load is larger, and the frequency is larger when the load is smaller, so that the frequency variation range is large in the process of adjusting the backlight from bright to dark; meanwhile, the larger the variation range of the backlight voltage is, the larger the variation range of the frequency thereof is. The too large frequency variation range can cause the switching speed of the switching device to not follow up, cause the abnormal operation of the electronic equipment, and also bring about the Electromagnetic Interference (EMI) problem, which is difficult to solve. Therefore, Pulse Width Modulation (PWM) dimming is often used for LED backlight driving circuits of LLC topology. However, PWM dimming is prone to cause problems of LED screen flickering and abnormal sound during dimming.

Therefore, how to adjust the light, and reduce the frequency variation range when adjusting the light and when changing the backlight voltage for the LED backlight driving circuit adopting the LLC topology is a problem to be solved.

SUMMERY OF THE UTILITY MODEL

The embodiment of the disclosure provides a dimming device and electronic equipment, which realize analog dimming of a backlight driving circuit of an LLC topology by improving an LLC circuit, and improve the working reliability of the electronic equipment.

The present disclosure provides a dimming device, including:

the LLC resonant conversion circuit is used for converting the direct-current voltage into alternating-current voltage and inputting first energy to the duty ratio regulation circuit by utilizing the alternating-current voltage;

the duty ratio adjusting circuit is used for reducing the duty ratio of the first energy to obtain second energy;

the rectification filter circuit is used for converting the alternating current signal corresponding to the second energy into a direct current signal and supplying power to the load circuit by utilizing the direct current signal;

the load circuit is an LED backlight load connected with the rectifying and filtering circuit;

the control circuit is used for generating a feedback voltage according to the feedback current of the load circuit, controlling the output driving frequency according to the feedback voltage and further controlling the first energy by using the driving frequency;

the LLC resonant conversion circuit, the duty ratio adjusting circuit, the rectification filter circuit, the load circuit and the control circuit are sequentially connected to form a circulation loop.

In one possible design, the duty cycle adjustment circuit includes: a first inductance and a first capacitance, wherein:

a first end of the first inductor is connected with a first output end of the LLC resonant conversion circuit, and a second end of the first inductor is connected with a first end of the first capacitor;

the second end of the first capacitor is connected with the second output end of the LLC resonant conversion circuit, the first end of the first capacitor is further connected with the first input end of the rectification filter circuit, and the second end of the first capacitor is further connected with the second input end of the rectification filter circuit.

In a possible design, the resonant frequency corresponding to the first inductor and the first capacitor is 1-3 times of the resonant frequency formed by the primary resonant inductor and the primary resonant capacitor of the LLC resonant conversion circuit.

In a possible design, the inductance value of the first inductor is 0.5-3 times of the primary resonant inductor of the LLC resonant conversion circuit, and the capacitance value of the first capacitor is 0.2-0.8 times of the primary resonant capacitor of the LLC resonant conversion circuit.

In a possible design, the dimming device further includes:

the rectification filter circuit includes: first diode, second electric capacity and third electric capacity, wherein:

the negative electrode of the first diode is connected with the positive electrode of a first load, the negative electrode of the first diode is also connected with the first end of the second capacitor, the positive electrode of the first diode is the second input end of the rectifying and filtering circuit, and the first load is contained in the load circuit;

the second end of the second capacitor is grounded;

the anode of the second diode is connected with the first end of the third capacitor, and the anode of the second diode is connected with the cathode of a second load, wherein the second load is contained in the load circuit;

and the second end of the third capacitor is connected with the anode of the second load, the second end of the third capacitor is a first input end of the rectification filter circuit, and the second end of the third capacitor is grounded.

In one possible design, when the first inductor, the first capacitor, the first diode, the second capacitor, and the first load form a closed path, the LLC resonant conversion circuit supplies power to the first load;

when the first inductor, the first capacitor, the second diode, the third capacitor and the second load form a closed path, the LLC resonant conversion circuit supplies power to the second load.

In one possible design, the duty cycle adjusting circuit further includes: a second inductance and a fourth capacitance, wherein:

a first end of the second inductor is connected with a third output end of the LLC resonant conversion circuit, and a second end of the second inductor is connected with a first end of the fourth capacitor;

and the second end of the fourth capacitor is connected with the fourth output end of the LLC resonant conversion circuit, the first end of the fourth capacitor is also connected with the third input end of the rectification filter circuit, and the second end of the fourth capacitor is also connected with the fourth input end of the rectification filter circuit.

In one possible design, the rectifying and filtering circuit further includes: third diode, fourth diode, fifth electric capacity, sixth electric capacity and seventh electric capacity, wherein:

the cathode of the third diode is connected with the anode of a third load, the cathode of the third diode is further connected with the first end of the fifth capacitor, the anode of the third diode is connected with the cathode of the fourth diode, the anode of the third diode is a fourth input end of the rectifying and filtering circuit, and the third load is included in the load circuit;

a second end of the fifth capacitor is connected with a first end of a seventh capacitor, a second end of the fifth capacitor is also connected with a negative electrode of a third load, and a second end of the seventh capacitor and a second end of the second inductor are grounded;

the anode of the fourth diode is connected with the first end of the sixth capacitor, the anode of the fourth diode is connected with the cathode of a fourth load, and the fourth load is contained in the load circuit;

the first end of the sixth capacitor is connected with the anode of the fourth diode, the second end of the sixth capacitor is connected with the second end of the second inductor, and the second end of the sixth capacitor is further connected with the anode of the fourth load.

In a possible design, the dimming device further includes: and the second end of the first capacitor is connected with the second input end of the rectifying and filtering circuit through the current-sharing device.

In a possible design, the control circuit includes a controller and a detection resistor, a first end of the detection resistor is connected to the negative electrode of the first load, a second end of the detection resistor is grounded, and the negative electrode of the first load is connected to the controller.

In one possible design, the rectifying and filtering circuit includes: first diode, second diode, third diode, fourth diode and second electric capacity, wherein:

the anode of the first diode is connected with the second input end of the rectifying and filtering circuit, the anode of the first diode is also connected with the cathode of the second diode, the cathode of the first diode is connected with the anode of a first load, and the load circuit comprises the first load;

the anode of the second diode is grounded;

the cathode of the third diode is connected with the anode of the first load, and the anode of the third diode is connected with the first input end of the rectification filter circuit;

the anode of the fourth diode is grounded, and the cathode of the fourth diode is connected with the first input end of the rectifying and filtering circuit;

and the first end of the second capacitor is connected with the anode of the first load, and the second end of the second capacitor is grounded.

In one possible design, the LLC resonant conversion circuit includes: go up half-bridge MOS pipe, lower half-bridge MOS pipe, third inductance, eighth electric capacity and isolation transformer, wherein:

the grid electrode of the upper half-bridge MOS tube is connected with a first driving pin of the control circuit, the drain electrode of the upper half-bridge MOS tube is connected with an input voltage, and the source electrode of the upper half-bridge MOS tube is connected with the first end of the third inductor;

the grid of the lower half-bridge MOS tube is connected with a second driving pin of the control circuit, the drain electrode of the lower half-bridge MOS tube is connected with the source electrode of the upper half-bridge MOS tube, and the source electrode of the lower half-bridge MOS tube is grounded;

the second end of the third inductor is connected with the first end of the isolation transformer;

a first end of the eighth capacitor is connected with a source electrode of the lower half-bridge MOS tube, and a second end of the eighth capacitor is connected with a second end of the isolation transformer;

the third end of the isolation transformer forms a first output end of the LLC resonant conversion circuit;

and the fourth end of the isolation transformer forms a second output end of the LLC resonant conversion circuit.

In a second aspect, an embodiment of the present disclosure provides an electronic device, where the electronic device includes a dimming device implemented in any possible manner of the first aspect, and an electronic device body, and the dimming device is disposed on the electronic device body.

The dimming device and the electronic equipment provided by the disclosure, wherein the dimming device comprises an LLC resonance conversion circuit, a duty ratio adjusting circuit, a rectification filter circuit, a load circuit and a control circuit. The LLC resonant conversion circuit, the duty ratio regulating circuit, the rectification filter circuit, the load circuit and the control circuit are sequentially connected to form a circulation loop. In the framework, a duty ratio adjusting circuit is added behind the LLC resonant conversion circuit and in front of the rectifying and filtering circuit, the effective duty ratio is adjusted by the duty ratio adjusting circuit, and then the energy output to the load circuit is adjusted, so that the wider backlight load voltage range can be matched in a smaller frequency variation range, and the inherent flicker problem and the abnormal sound problem when the display screen is photographed by a mobile phone adopting the PWM dimming technology can be avoided by adopting the analog dimming technology in the smaller frequency variation range.

Drawings

In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present disclosure, and for those skilled in the art, other drawings can be obtained according to the drawings without inventive exercise.

Fig. 1 is a schematic structural diagram of a dimming device provided by the present disclosure;

fig. 2 is a schematic circuit diagram of a dimming device provided in an embodiment of the present disclosure;

fig. 3 is a schematic circuit diagram of another dimming device provided in the embodiments of the present disclosure;

fig. 4 is a circuit schematic diagram of another dimming device provided in the embodiments of the present disclosure;

fig. 5 is a circuit schematic diagram of another dimming device provided in the embodiments of the present disclosure;

fig. 6 is a circuit schematic diagram of another dimming device provided in the embodiments of the present disclosure;

fig. 7 is a circuit schematic diagram of another dimming device provided in the embodiments of the present disclosure.

Detailed Description

To make the objects, technical solutions and advantages of the embodiments of the present disclosure more clear, the technical solutions of the embodiments of the present disclosure will be described clearly and completely with reference to the drawings in the embodiments of the present disclosure, and it is obvious that the described embodiments are some, but not all embodiments of the present disclosure. All other embodiments, which can be derived by a person skilled in the art from the embodiments disclosed herein without making any creative effort, shall fall within the protection scope of the present disclosure.

Fig. 1 is a schematic structural diagram of a dimming device provided by the present disclosure. Referring to fig. 1, the dimming device 100 includes: the control circuit comprises an LLC resonant conversion circuit 11, a duty cycle regulation circuit 12, a rectifying and smoothing circuit 13, a load circuit 14 and a control circuit 15. Wherein:

the LLC resonant converting circuit 11 is configured to convert the dc voltage into an ac voltage, and input the first energy to the duty ratio adjusting circuit 12 by using the ac voltage. In the process, the LLC resonant conversion circuit 11 converts the input dc voltage into an ac voltage through switching control of a certain frequency, and the ac voltage passes through the resonant network and the transformer, and then inputs the first energy to the duty ratio adjustment circuit 12. Wherein the resonant network comprises a capacitance and an inductance, such as the third inductance L3 and the eighth capacitance C8, etc., hereinafter.

And the duty ratio regulating circuit 12 is used for reducing the duty ratio of the first energy to obtain second energy.

And the rectifying and filtering circuit 13 is configured to supply power to the load circuit according to the second energy, that is, convert an ac signal corresponding to the second energy into a dc signal, and supply power to the load circuit by using the dc signal.

And the load circuit 14 is an LED backlight load connected with the rectifying and filtering circuit 13. Taking a television using an LED light bar as a backlight module as an example, the load circuit 14 is an LED light bar. When the television adopts 2 paths of LED light bars, the load circuit 4 comprises 2 loads, namely, each path of LED light bar is one load. When the television employs 4 LED light bars, the load circuit 14 includes 4 loads. When the television employs 1 LED light bar, the load circuit 14 includes a load.

And the control circuit 15 is configured to generate a feedback voltage according to the feedback current of the load circuit 14, control an output driving frequency according to the feedback voltage, and further control the first energy by using the driving frequency.

The LLC resonant conversion circuit 11, the duty ratio adjusting circuit 12, the rectifying and filtering circuit 13, the load circuit 14, and the control circuit 15 are connected in sequence to form a circulation loop.

Based on the structure shown in fig. 1, after the LLC resonant conversion circuit 11 and before the rectification filter circuit 13, the duty ratio adjusting circuit 12 is added, and the duty ratio adjusting circuit 12 is used to adjust the effective duty ratio, thereby adjusting the energy output to the load circuit 14, so that a wider backlight load voltage range can be matched within a smaller frequency variation range, and an analog dimming technique can be implemented within a smaller frequency variation range.

In addition, during the process of displaying the picture on the display screen of the television, the user may shoot the display screen by using a mobile phone or the like. If the television uses the PWM dimming technique, the screen of the television is not constantly bright, but is switched between bright and dark at a certain frequency, and the switching process cannot be perceived by human eyes. However, the shutter speed is much faster than the dimming frequency when the phone is taking a picture, so that the phone taking frequency and the display dimming frequency are not synchronized. At the moment, the phenomenon of bright and dark flashing which cannot be seen by the eyes can be captured in the shooting process of the mobile phone; meanwhile, if the television adopts PWM dimming, the dimming frequency falls within the sensing frequency range of human ears, and a large piezoelectric effect is generated on some magnetic devices, so that the problem of abnormal sound is caused. By adopting the dimming scheme provided by the disclosure, the problems can be solved.

The dimming device provided by the embodiment of the disclosure comprises an LLC resonance conversion circuit, a duty ratio adjusting circuit, a rectification filter circuit, a load circuit and a control circuit. The LLC resonant conversion circuit, the duty ratio regulating circuit, the rectification filter circuit, the load circuit and the control circuit are sequentially connected to form a circulation loop. In the framework, a duty ratio adjusting circuit is added behind the LLC resonant conversion circuit and in front of the rectifying and filtering circuit, the effective duty ratio is adjusted by the duty ratio adjusting circuit, and then the energy output to the load circuit is adjusted, so that the wider backlight load voltage range can be matched in a smaller frequency variation range, and the inherent flicker problem and the abnormal sound problem when the display screen is photographed by a mobile phone adopting the PWM dimming technology can be avoided by adopting the analog dimming technology in the smaller frequency variation range.

As shown in fig. 2, in the dimming device 100 shown in fig. 1, the duty cycle adjusting circuit 12 includes a first inductor L1 and a first capacitor C1. One end of the first inductor L1 is connected to the first output end of the LLC resonant converting circuit 11, and the second end of the first inductor L1 is connected to the first end of the first capacitor C1. A second end of the first capacitor C1 is connected to the second output end of the LLC resonant conversion circuit 11, a first end of the first capacitor C1 is further connected to the first input end of the rectifying and filtering circuit 13, and a second end of the first capacitor C1 is further connected to the second input end of the rectifying and filtering circuit 13.

Illustratively, the duty cycle adjusting circuit 12 includes an LC circuit formed by a first inductor L1 and a first capacitor C1, and the LC circuit has a free-wheeling characteristic, and the longer the free-wheeling time is, the stronger the capability of automatically adjusting the duty cycle is. The effective duty ratio adjusting range is narrowed due to the fact that the values of the first inductor L1 and the first capacitor C1 are too small, and therefore the corresponding switching frequency change range is larger when the load is changed, but circulation currents formed between the L1C1 are small, the temperature of the device is low, and the efficiency is high. The effective duty ratio adjustment range is enlarged due to the overlarge values of the first inductor L1 and the first capacitor C1, so that the corresponding switching frequency change range is smaller and more stable during load conversion, but a larger circulating current is formed, and the temperature of the device is overhigh and the efficiency is reduced. In consideration, in order to achieve balance efficiency and an effective duty ratio adjustment range, in the embodiment of the present disclosure, a resonant frequency corresponding to the first inductor and the first capacitor is 1 to 3 times a resonant frequency formed by the primary resonant inductor and the primary resonant capacitor of the LLC resonant conversion circuit 11.

The inductance value of the first inductor L1 is determined according to the inductance value of the third inductor L3, the capacitance value of the first capacitor C1 is determined according to the capacitance value of the eighth capacitor C8, the third inductor L3 is a primary resonant inductor in the LLC resonant conversion circuit, and the eighth capacitor C8 is a primary resonant capacitor in the LLC resonant conversion circuit. For example, the inductance of the first inductor L1 is 0.5-3 times that of the third inductor L3, and the capacitance of the first capacitor C1 is 0.2-0.8 times that of the eighth capacitor C8.

Therefore, the duty ratio can be automatically adjusted based on the duty ratio adjusting circuit of the dimming device, so that the dimming device stably works.

In the above embodiment, if the load circuit 14 includes a plurality of loads, the dimming device 100 further includes a current equalizing device 16, and the current equalizing device 16 is a current equalizing capacitor. At this time, one end of the duty ratio adjusting circuit 12 is connected to one end of the rectifying and smoothing circuit 13 through the current equalizing device 16. The number of current sharing devices 16 is related to the number of loads. For example, if the load circuit 14 includes a two-way load, the dimming device 100 further includes a current equalizing device 16, and the current equalizing device 16 is used for equalizing the voltage difference between the two-way load; if the load circuit 14 includes 4 loads, the dimming apparatus 100 further includes 2 current sharing devices 16, and one current sharing device 16 is provided for each two loads. For another example, if the load circuit 14 includes only one load, the dimming device 100 does not include the current sharing device 16. The current equalizing device 16 is used for balancing the voltage difference of the multiple loads to ensure that the current of each load is kept consistent, i.e. the current of each load is the same.

Fig. 2 is a schematic circuit diagram of a dimming device according to an embodiment of the present disclosure. The load circuit of the dimming device comprises two loads, namely a first load LED1 and a second load LED2, wherein the anode of the first load LED1 is shown as an LED1+ in the figure, and the cathode of the first load LED1 is shown as an LED 1-in the figure. The anode of the second load LED2 is shown as LED1+ and the cathode of the second load LED2 is shown as LED 1-.

Referring to fig. 2, the rectifying-filtering circuit 13 includes a first diode D1, a second diode D2, a second capacitor C2, and a third capacitor C3. Wherein: the cathode of the first diode D1 is connected to the anode of the first load (LED1+), the cathode of the first diode D1 is further connected to the first end of the second capacitor C2, the anode of the first diode D1 is the second input end of the rectifying-filtering circuit 13, and the first load is included in the load circuit 14. The second terminal of the second capacitor C2 is connected to ground. The anode of the second diode D2 is connected to the first end of the third capacitor C3, and the anode of the second diode D2 is connected to the cathode of the second load (LED2-), which is included in the load circuit 14. The second terminal of the third capacitor C3 is connected to the anode (LED2+) of the second load, the second terminal of the third capacitor C3 is the first input terminal of the rectifying-filtering circuit, and the second terminal of the third capacitor C3 is grounded.

Referring to fig. 2 again, the LLC resonant conversion circuit 11 includes: upper half-bridge MOS pipe Q1, lower half-bridge MOS pipe Q2, third inductance L3, eighth electric capacity C8 and isolation transformer T1, wherein: the gate (G) of the upper half-bridge MOS transistor Q1 is connected to the first driving pin of the control circuit 15, the drain (D) of the upper half-bridge MOS transistor Q1 is connected to the input voltage (shown as VDC), and the source (S) of the upper half-bridge MOS transistor Q1 is connected to the first end of the third inductor L3.

The gate (G) of the lower half-bridge MOS transistor Q2 is connected to the second driving pin of the control circuit 15, the drain (D) of the lower half-bridge MOS transistor Q2 is connected to the source (S) of the upper half-bridge MOS transistor Q1, and the source of the lower half-bridge MOS transistor Q2 is grounded. The second end of the third inductor L3 is connected to the first end (shown as (r)) of the isolation transformer T1.

A first terminal of the eighth capacitor C8 is connected to the source of the lower half-bridge MOS transistor Q2, and a second terminal of the eighth capacitor C8 is connected to a second terminal (e.g., the second terminal of the isolation transformer T1).

A third end (shown as the third end in the figure) of the isolation transformer T1 forms a first output end of the LLC resonant conversion circuit; the fourth terminal (shown as (r)) of the isolation transformer T1 forms a second output terminal of the LLC resonant converter circuit.

Based on the above framework, the working principle of fig. 2 is: when the first inductor L1, the first capacitor C1, the first diode D1, the second capacitor C2, and the first load LED1 form a closed path, the LLC resonant conversion circuit 12 powers the first load LED 1. When the first inductor L1, the first capacitor C1, the second diode D2, the third capacitor C3 and the second load LED2 form a closed path, the LLC resonant conversion circuit 12 supplies power to the second load LED 2.

For example, referring to fig. 2, the upper half-bridge MOS transistor Q1, the lower half-bridge MOS transistor Q2, the third inductor L3, the eighth capacitor C8, and the primary winding portion of the isolation transformer T1 form a primary side circuit of the overall circuit. The current sharing device 16, the first diode D1, the second diode D2, the second capacitor C2, the third capacitor C3, the first inductor L1, the first capacitor C1, the first load LED1, the second load LED2 and the detection resistor Rs form a secondary side circuit.

In the first half cycle of the whole cycle, the upper half-bridge MOS transistor Q1 is turned on, the lower half-bridge MOS transistor Q2 is turned off, the input voltage VDC is positively charged through the upper half-bridge MOS transistor Q1, the third inductor L3, the isolation transformer T1 and the eighth capacitor C8, the third inductor L3 and the eighth capacitor C8, and the voltage is transformed and transmitted to the secondary side circuit through the isolation transformer T1. The secondary winding of the secondary side circuit, the first inductor L1, the first capacitor C1, the current equalizing device 16, the first diode D1, the second capacitor C2, the anode LED1+ of the first load LED1, the cathode LED 1-of the first load LED1, and the detection resistor Rs form a closed path to supply power to the first load LED 1. The first diode D1 and the second capacitor C2 form a rectifying and filtering loop.

In the lower half cycle of the whole cycle, the upper half-bridge MOS transistor Q1 is turned off, the lower half-bridge MOS transistor Q2 is turned on, and the input voltage VDC is cut off, at this time, the energy stored in the third inductor L3 and the eighth capacitor C8 in the upper half cycle starts reverse resonance discharge, and the voltage is transmitted to the secondary side circuit through the isolation transformer T1 by transformation via the eighth capacitor C8, the isolation transformer T1, the third inductor L3 and the lower half-bridge MOS transistor Q2. The secondary winding of the secondary side circuit, the first inductor L1, the first capacitor C1, the current sharing device 16, the second diode D2, the anode LED2+ of the second load LED2, the cathode LED 2-of the second load LED2, and the detection resistor Rs form a closed path to supply power to the second load LED 2. The second diode D2 and the third capacitor C3 form a rectifying and filtering loop.

The current sharing device 16 shares current for the first load LED1 and the second load LED 2. The current sharing principle is as follows: the current equalizing device 16 is a current equalizing capacitor, and the current equalizing capacitor is an alternating current device and can be charged and discharged. In a complete charging and discharging period, the charging and discharging current is balanced. If the charge and discharge are not uniform, the voltage of the capacitor will continue to rise, possibly causing the capacitor to be destroyed. Therefore, the current of each load can be balanced by using the charge-discharge charge balance principle of the capacitor. At this time, the LLC resonant converter 11, the duty ratio adjusting circuit 12, the current equalizing device 16, the rectifying and filtering circuit 13, the load circuit 14, and the control circuit 15 are connected in sequence to form a circulation loop.

For example, referring to fig. 2, if the fourth terminal (e.g., (r) in the figure) of the isolation transformer T1 is positive, the third terminal (e.g., (r) in the figure) is negative. After the current flows through the first inductor L1 and the first capacitor C1, the current reaches the current sharing device 16 to charge the current sharing device 16. At this time, the left side of the current equalizing device 16 is positive, and the right side is negative. The current is filtered by a rectifying and filtering loop formed by the first diode D1 and the second capacitor C2 to supply power to the first load LED1, that is, the current reaches the LED1+ from the LED1+, flows through the detection resistor Rs, and then reaches the third terminal of the isolation transformer T1 (see the third point in the figure). In this process, power is supplied to the LED1 load.

If the fourth terminal (e.g., (r) in the figure) of the isolation transformer T1 is negative, the third terminal (e.g., (c) in the figure) is positive. The current passes through the first inductor L1, the LED2+ of the second load LED2, the LED2-, and then to the anode and cathode of the second diode D2. And then to the current share device 16. At this time, the left side of the current sharing device 16 is negative, and the right side of the current sharing device 16 is positive, which is equivalent to reversely charging the current sharing device 16, that is, discharging the current sharing device 16, and finally, the current reaches the fourth terminal of the isolation transformer T1. In this process, power is supplied to the LED2 load.

The two working processes are respectively the power supply process of the first load LED1 and the second load LED2, and respectively represent a charging and discharging process on the capacitor, the average charging current is the current of the first load LED1, and the average discharging current is the current of the second load LED 2. According to the charge balance principle in one cycle of charge, the following principle is known: if the charging current is inconsistent with the discharging current, the voltage on the capacitor cannot be completely released in the discharging process on the assumption that the charging current is large. At this time, a certain direct current voltage is stored on the capacitor, so that the next charge-discharge period is caused, and the charging current is small in the charging process. Therefore, the two currents are ensured to be consistent through self-adaptive adjustment until the charging and discharging currents are consistent.

In the above fig. 2, the sense resistor Rs is shown in the load circuit 14 for convenience. In practice, however, the control circuit 15 includes a controller and a sense resistor Rs, i.e. the sense resistor Rs is part of the control circuit 15. The first end of the detection resistor Rs is connected with the cathode LED 1-of the first load LED1, the second end of the detection resistor Rs is grounded, and the cathode LED 1-of the first load LED1 is connected with the controller in the control circuit.

Referring to fig. 2, the cathode LED 1-of the first load LED1 and the cathode LED 2-of the second load LED2 are not connected together, i.e., the first load LED1 and the second load LED2 are not connected in a common cathode manner. The negative LED 1-of the first load LED1 is connected to the sensing resistor Rs, which is connected to ground. While the anode LED2+ of the second load LED2 is directly grounded. By adopting the non-common-cathode connection mode, compared with a common-cathode or common-anode connection mode, each independent half-wave rectification filter circuit does not need two serially-connected rectifier diodes, but only needs one rectifier diode to realize the double-path LED load backlight current-sharing function, so that the diodes can be saved, and the dimming device is simple in structure and low in cost.

Referring to fig. 2, the sensing resistor Rs only senses the current of the first load LED1, which is converted into a voltage value by the sensing resistor Rs, and the voltage is inputted to a feedback loop control module (not shown) in the controller. Then, the controller compares the converted voltage with a reference voltage (Vref) to obtain a comparison result. The comparison result is amplified by an operational amplifier, and the controller controls the driving frequency according to the output result of the operational amplifier. In the control process, taking the first load LED1 as an example, when the conversion voltage is large, that is, the current on the first load LED1 is too large, the driving frequency is increased, so that the output energy of the isolation transformer T1 is changed, and the current on the first load LED1 is reduced. When the conversion voltage is small, i.e., the current on the first load LED1 is too low, the driving frequency is decreased, thereby changing the output energy of the isolation transformer T1, so that the current on the first load LED1 increases.

Referring to fig. 2, the dimming control signal is an analog dimming signal, for example, the dimming control signal is a dc level with adjustable amplitude; for another example, the dimming control signal is a high-low level pulse width signal with a certain frequency, the high-low level pulse width signal is filtered into a direct current level, and the direct current level controls the magnitude of the reference voltage (Vref) through a circuit inside the controller, so as to adjust the magnitude of the backlight brightness, thereby implementing the dimming function. The luminance is brightest, the reference voltage (Vref) is maximum, and the backlight current is maximum, and when the luminance is darkest, the reference voltage (Vref) is minimum, and the backlight current is minimum. Taking the first load LED1 as an example, when the amplitude of the dimming control signal is maximum, the reference voltage (Vref) is maximum, and the load current of the first load LED1 is maximum at this time. As the magnitude of the dimming control signal decreases, the reference voltage (Vref) gradually decreases, and the current of the first load LED1 linearly decreases, so that the brightness of the first load LED1 decreases, thereby reaching an analog dimming function of the LED 1.

According to the above, it can be seen that: the sense resistor Rs senses only the current of the first load LED1, and compares the sensed current with the reference voltage Vref in the feedback loop control module to control the frequency of the controller, so that the current of the first load LED1 is constant. The second load LED2 or the first load LED1 implements a constant current function through the current share device 16. Therefore, the current control of the two-way load can be realized only by detecting the first load LED1, and the method is simple, reliable and low in cost.

Referring to fig. 2, the rectifying-filtering circuit 13 includes a half-wave rectifying-filtering circuit formed by a first diode D1 and a second capacitor C2, and a half-wave rectifying-filtering circuit formed by a second diode D2 and a third capacitor C3. The two separate half-wave rectifier filter circuits power the first load LED1 and the second load LED2, respectively.

The current sharing device 16 is, for example, a current sharing capacitor, and if the voltage difference between the first load LED1 and the second load LED2 is different, the current sharing function for the two loads can be achieved by using the charge-discharge charge balance principle of the capacitor to make the currents of the first load LED1 and the second load LED2 equal, that is, the two loads are shared.

Referring to fig. 2 again, a duty ratio adjusting circuit 12 is added after the LLC resonant converting circuit 11 and before the rectifying and filtering circuit 13, and the duty ratio adjusting circuit 12 is used to adjust the effective duty ratio, thereby adjusting the energy output to the load circuit 14. When the upper half-bridge MOS transistor Q1 is turned off and the lower half-bridge MOS transistor Q2 is turned on, the first capacitor C1 starts to be charged reversely, and when the charging voltage reaches a certain level, the second diode D2 starts to be turned on, and the isolation transformer T1 supplies power to the second load LED 2. Thereafter, the lower half-bridge MOS transistor Q2 is turned off. After the lower half-bridge MOS transistor Q2 is turned off, the first load LED1 still cannot be supplied with power for a long time before the upper half-bridge MOS transistor Q1 is turned on due to the freewheeling of the first inductor L1 and the first capacitor C1.

When the voltage of the first load LED1 or the second load LED2 drops, certain parameters of the first inductor L1 and the first capacitor C1 change. For example, the voltage is fixed due to the energy coming out of the isolation transformer T1. While the first load LED1 and the first capacitor C1 are in a parallel relationship, the first load LED1 and the first inductor L1 are in a series relationship. Therefore, when the voltage across the first load LED1 drops, the voltage across the first inductor L1 rises, causing the energy stored by the first inductor L1 to be greater. As another example, as the voltage of the LED2 decreases, the voltage across the first inductor L1 increases, causing more energy to be stored by the first inductor L1. Thus, it can be seen that: when the voltage drop of the first load LED1 or the second load LED2 is larger, the freewheeling time of the first inductor L1 and the first capacitor C1 is longer, and the duty ratio is effectively reduced, so that even if the voltage change of the first load LED1 or the second load LED2 is larger, the duty ratio can be automatically adjusted, and the operating frequency of the dimming device is stabilized. It can be seen from this that: if the first inductor L1 and the first capacitor C1 are not added, the change value of the load power directly changes the switching frequency of the upper half-bridge MOS transistor Q1 and the switching frequency of the lower half-bridge MOS transistor Q2. In the embodiment of the present disclosure, by adding the first inductor L1 and the first capacitor C1, the effective duty ratio is changed by using the time delay of storing and releasing energy of the first inductor L1 and the first capacitor C1, so as to achieve the purpose of adjusting the load when the switching frequency is not changed or is changed less.

Referring to fig. 2, the primary circuit of the isolation transformer T1 is a typical LLC half-bridge architecture.

In the above-described configuration shown in fig. 2, the first load LED1 and the second load LED2 are not connected in common. However, the disclosed embodiments are not limited, and in other possible implementations, the first load LED1 and the second load LED2 are connected in a common cathode. For example, please refer to fig. 3.

Fig. 3 is a schematic circuit diagram of another dimming device provided in the embodiments of the present disclosure. Referring to fig. 3, compared to fig. 2, the first load LED1 and the second load LED2 in fig. 3 are connected in a cascode manner, resulting in two more diodes in the rectifying-filtering circuit 13 in fig. 3. If the D2 and the D4 are removed, the LED1 and the LED2 do not form a closed loop and cannot provide power to the LED. For example, the power supply closed loop for LED1 is: the secondary winding 4 pin of T1, I6, D1, LED1+, LED1-, Rs, D4, L1 and the secondary winding 3 pin of T1 cannot form a closed loop if D4 is removed, and the LED1 cannot be powered at this time. Therefore, the rectifying-filtering circuit 13 in fig. 3 has two more diodes D2, D4.

Fig. 4 is a circuit schematic diagram of another dimming device provided in the embodiments of the present disclosure. Referring to fig. 4, compared to fig. 2, the load circuit 14 in fig. 4 includes four loads, i.e., an LED1, an LED2, an LED3, and an LED4, and the four loads in fig. 4 are not connected in a common-cathode manner.

Compared to fig. 2, the duty cycle adjusting circuit 12 further includes: a second inductor L2 and a fourth capacitor C4. A first end of the second inductor L2 is connected to a third output end (indicated as "C") of the LLC resonant converting circuit 11, and a second end of the second inductor L2 is connected to a first end of the fourth capacitor C4. A second end of the fourth capacitor C4 is connected to a fourth output end (e.g., | in the figure) of the LLC resonant conversion circuit 11, a first end of the fourth capacitor C4 is further connected to a third input end of the rectifying and filtering circuit, and a second end of the fourth capacitor C4 is further connected to a fourth input end of the rectifying and filtering circuit.

Further, the rectifying and filtering circuit 13 further includes: a third diode D3, a fourth diode D4, a fifth capacitor C5, a sixth capacitor C6, and a seventh capacitor C7, wherein: the cathode of the third diode D3 is connected to the anode LED3+ of the third load LED3, the cathode of the third diode D3 is further connected to the first end of the fifth capacitor C5, the anode of the third diode D3 is connected to the cathode of the fourth diode D4, the anode of the third diode D3 is the fourth input end of the rectifying and filtering circuit, and the third load LED3 is included in the load circuit.

A second end of the fifth capacitor C5 is connected to a first end of a seventh capacitor C7, a second end of the fifth capacitor C5 is further connected to a negative LED 3-of the third load LED3, and a second end of the seventh capacitor C7 and a second end of the second inductor L2 are grounded.

An anode of the fourth diode D4 is connected to the first end of the sixth capacitor C6, and an anode of the fourth diode D4 is connected to a cathode LED 4-of the fourth load LED4, the fourth load LED4 being included in the load circuit.

A first end of the sixth capacitor C6 is connected to the anode of the fourth diode D4, a second end of the sixth capacitor C6 is connected to the second end of the second inductor L2, and a second end of the sixth capacitor C6 is further connected to the anode LED + of the fourth load LED 4.

By adopting the scheme, the analog dimming scheme can be expanded to four paths of LED loads, and the application range of the dimming device is enlarged.

Fig. 5 is a circuit schematic diagram of another dimming device provided in the embodiments of the present disclosure. Referring to fig. 5, compared to fig. 3, the load circuit 14 in fig. 5 includes four loads, i.e., an LED1, an LED2, an LED3, and an LED4, and the four loads in fig. 5 are connected in a common-cathode manner. As can be seen from fig. 5: when the non-cascode method is adopted, 4 rectifier diodes, i.e., the diode D2, the diode D6, the diode D7, and the diode D8 are used more than in fig. 4.

Fig. 6 is a circuit schematic diagram of another dimming device provided in the embodiments of the present disclosure. Referring to fig. 6, only one load, i.e., the first load LED1, exists in the dimming device. In this case, the current equalizing device 16 is not required.

By adopting the scheme, the analog dimming scheme can be expanded to one path of LED load, and the application range of the dimming device is enlarged.

Fig. 7 is a circuit schematic diagram of another dimming device provided in the embodiments of the present disclosure. The difference between this embodiment and the embodiment shown in fig. 1 to 6 is that: in this embodiment, the controller of the control circuit 15 and the feedback loop control module are independently provided. That is, the feedback loop control module can be disposed inside the controller, as well as outside the controller. Moreover, the controller can be flexibly arranged on a primary side line or a secondary side line of the dimming circuit.

Based on the dimming device described in each of the above embodiments, the present disclosure further provides an electronic device, which includes an electronic device body, and a dimming device disposed on the electronic device body.

Finally, it should be noted that: the above embodiments are only used for illustrating the technical solutions of the present disclosure, and not for limiting the same; while the present disclosure has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art will understand that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present disclosure.

Claims

1. A dimming device, comprising:

the duty cycle adjusting circuit is used for reducing the duty cycle of the first energy to obtain second energy;

2. The apparatus of claim 1, wherein the duty cycle adjustment circuit comprises: a first inductance and a first capacitance, wherein:

3. The apparatus of claim 2, wherein the resonant frequency of the first inductor and the first capacitor is 1-3 times the resonant frequency of the LLC resonant conversion circuit primary resonant inductor and primary resonant capacitor.

4. The apparatus of claim 3, wherein the inductance of the first inductor is 0.5-3 times the primary resonant inductance of the LLC resonant conversion circuit, and the capacitance of the first capacitor is 0.2-0.8 times the primary resonant capacitance of the LLC resonant conversion circuit.

5. The apparatus of any of claims 2-4, further comprising:

the second end of the second capacitor is grounded;

6. The apparatus of claim 5,

when the first inductor, the first capacitor, the first diode, the second capacitor and the first load form a closed path, the LLC resonant conversion circuit supplies power to the first load;

7. The apparatus of claim 5, wherein the duty cycle adjustment circuit further comprises: a second inductance and a fourth capacitance, wherein:

8. The apparatus of claim 7,

the rectification filter circuit further comprises: third diode, fourth diode, fifth electric capacity, sixth electric capacity and seventh electric capacity, wherein:

9. The apparatus of claim 5, further comprising:

and the second end of the first capacitor is connected with the second input end of the rectifying and filtering circuit through the current-sharing device.

10. The apparatus of claim 5, wherein the control circuit comprises a controller and a detection resistor, a first terminal of the detection resistor is connected to a negative terminal of the first load, a second terminal of the detection resistor is connected to ground, and the negative terminal of the first load is connected to the controller.

11. The apparatus of claim 2, wherein the rectifying-filtering circuit comprises: first diode, second diode, third diode, fourth diode and second electric capacity, wherein:

the anode of the second diode is grounded;

12. The apparatus according to any of claims 1-4, 11, wherein the LLC resonant conversion circuit comprises: go up half-bridge MOS pipe, lower half-bridge MOS pipe, third inductance, eighth electric capacity and isolation transformer, wherein:

the grid electrode of the lower half-bridge MOS tube is connected with a second driving pin of the control circuit, the drain electrode of the lower half-bridge MOS tube is connected with the source electrode of the upper half-bridge MOS tube, and the source electrode of the lower half-bridge MOS tube is grounded;

13. An electronic device, comprising: an electronic device body, and the dimming device according to any one of claims 1 to 12, the dimming device being provided on the electronic device body.