CN103124460A - LED driving circuit - Google Patents
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- CN103124460A CN103124460A CN 201310007773 CN201310007773A CN103124460A CN 103124460 A CN103124460 A CN 103124460A CN 201310007773 CN201310007773 CN 201310007773 CN 201310007773 A CN201310007773 A CN 201310007773A CN 103124460 A CN103124460 A CN 103124460A
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Abstract
The invention provides an LED driving circuit which comprises a DC-DC conversion circuit, a voltage division circuit, a driving module and a controller. The DC-DC conversion circuit is used for receiving a power voltage and converting the power voltage into an LED lamp voltage by the aid of a PWM (pulse width modulation) signal; the voltage division circuit is used for outputting a voltage detection signal reflecting the LED lamp voltage; the driving module is used for outputting a PWM switching control signal and a duty ratio adjusting control signal, and the controller comprises a PWM module and is used for receiving the voltage detection signal, the PWM switching control signal and the duty ratio adjusting control signal so as to output the PWM signal. Compared with the prior art, the LED driving circuit has the advantages that a ripple upper limit threshold value and a ripple lower limit threshold value of the LED lamp voltage are taken as reference voltages and are associated with the maximum duty ratio and the minimum duty ratio of the PWM signal, the PWM signal is directly outputted according to the duty ratio adjusting control signal, on or off of the PWM signal is more rapidly adjusted when the output voltage is changed without waiting for passing of the signal through an integral closed-loop control circuit, and accordingly, response speed is higher.
Description
Technical Field
The present invention relates to a driving circuit, and more particularly, to a Light Emitting Diode (LED) driving circuit.
Background
Currently, there is a strong demand for energy saving around the world, and LEDs (light emitting diodes) are increasingly popular and used in the industry because of their advantages of long service life, small size, low power consumption, low operating temperature, and the like. Accordingly, the LED driving circuit is a circuit for driving the LED to emit light. Generally, when driving an LED, the final objective is to control the current flowing through the LED to reach or be as close to a preset current value as possible, and to make the LED stable without being affected by power voltage, temperature, forward bias difference, and other factors, so as to prevent the LED from being used for too short time or damaged.
In the prior art, an LED driver usually determines whether an output Voltage of the LED driver reaches a rated LED lamp Voltage by using a divided feedback Voltage, and designs the feedback Voltage as a key basis for Over Voltage Protection (OVP) and Under Voltage Protection (UVP). When the voltage is stabilized, the LED driver makes the LED current constant and performs dimming control. Therefore, in the control architecture, the LED driver must feed back the voltage to the DC-DC conversion circuit for voltage control, and the low frequency signal for dimming must interfere with the DC-DC conversion circuit through the feedback circuit. In addition, when the LED load varies instantaneously, the structure is also prone to cause voltage offset and slow response speed, resulting in unnecessary loss.
In view of the above, a problem to be solved by the related art in the industry is how to design an LED driving circuit to solve the above defects, effectively reduce the ripple of the output voltage of the DC-DC conversion circuit, and increase the response speed of the system.
Disclosure of Invention
In view of the above-mentioned drawbacks of the LED driving circuit in the prior art, the present invention provides a novel LED driving circuit.
According to an aspect of the present invention, there is provided a driving circuit including:
a DC-DC conversion circuit for receiving a power voltage and converting the power voltage into an LED lamp voltage by a Pulse Width Modulation (PWM) signal;
a voltage divider circuit, disposed at an output end of the DC-DC conversion circuit, for outputting a voltage detection signal reflecting the voltage of the LED lamp;
the driving module is used for outputting a PWM switch control signal and a duty ratio regulation control signal; and
and the controller comprises a PWM module, and the PWM module receives the voltage detection signal, the PWM switch control signal and the duty ratio regulation control signal so as to output the PWM signal to the DC-DC conversion circuit.
Preferably, the voltage dividing circuit includes a first resistor and a second resistor connected in series, one end of the first resistor is electrically connected to the output end of the DC-DC conversion circuit, and one end of the second resistor is electrically connected to a ground end.
Preferably, when the LED lamp voltage is between a lower threshold and an upper threshold of the ripple, the PWM module outputs the PWM signal with a fixed duty ratio.
Preferably, when the LED lamp voltage is lower than the lower threshold of the ripple thereof, the duty ratio of the PWM signal is increased to a maximum value by the duty ratio adjustment control signal.
Preferably, when the voltage of the LED lamp is higher than the upper threshold of the ripple thereof, the duty ratio of the PWM signal is reduced to a minimum value by the duty ratio adjustment control signal.
Preferably, the LED lamp voltage further includes an overvoltage threshold and an undervoltage threshold, the overvoltage threshold is higher than the upper threshold of the ripple, and the undervoltage threshold is lower than the lower threshold of the ripple.
In one embodiment, when the voltage of the LED lamp is higher than the overvoltage threshold, the PWM switch control signal stops outputting the PWM signal.
In one embodiment, when the LED lamp voltage is lower than the under-voltage threshold, the PWM switch control signal stops outputting the PWM signal.
Preferably, the PWM module includes: an error amplifier, a first input end of which is used for receiving the voltage detection signal, a second input end of which is electrically connected to a reference voltage, and an output end of which is used for outputting an error voltage signal; a PWM modulator electrically connected to the error amplifier for receiving the error voltage signal and a carrier signal and outputting a reference PWM signal; and a PWM controller for receiving the reference PWM signal, the PWM switching control signal, and the duty ratio adjustment control signal, thereby outputting the PWM signal to the DC-DC conversion circuit.
Preferably, the carrier signal is a sawtooth signal.
The LED driving circuit outputs a voltage detection signal reflecting the voltage of the LED lamp through the voltage division circuit, outputs a PWM (pulse width modulation) switch control signal and a duty ratio regulation control signal by using the driving module, and receives the voltage detection signal, the PWM switch control signal and the duty ratio regulation control signal by using the PWM module of the controller so as to output the PWM signal to the DC-DC conversion circuit. Compared with the prior art, the LED lamp voltage regulation circuit has the advantages that the upper limit threshold and the lower limit threshold of the ripple wave of the LED lamp voltage are used as the reference voltage, the correlation comparison is carried out on the maximum duty ratio and the minimum duty ratio of the PWM signal, the PWM signal is directly output according to the duty ratio regulation control signal, the PWM signal can be quickly adjusted to be turned on or turned off when the output voltage changes, the adjustment is not needed after the signal passes through an integral closed-loop control loop, the response speed is higher, the frequency of the corresponding output PWM signal is not changed, the design specification of an output capacitor is further reduced, the cost is saved, and the occupied space is reduced.
Drawings
The various aspects of the present invention will become more apparent to the reader after reading the detailed description of the invention with reference to the attached drawings. Wherein,
fig. 1 shows a schematic structure diagram of an LED driving circuit in the prior art;
FIG. 2 is a schematic diagram showing the control timing sequence of the LED lamp voltage output by the DC-DC conversion circuit and the PWM signal output by the controller in the LED driving circuit of FIG. 1;
FIG. 3 is a schematic diagram of an LED driving circuit according to an embodiment of the present invention;
fig. 4 is a waveform diagram illustrating an overvoltage threshold, a ripple upper threshold, a ripple lower threshold, an undervoltage threshold of the LED lamp voltage, the LED lamp current, and a PWM signal output by the controller in the LED driving circuit of fig. 3; and
fig. 5 is a block diagram illustrating a structure of an embodiment of a PWM module in the LED driving circuit of fig. 3.
Detailed Description
In order to make the present disclosure more complete and complete, reference is made to the accompanying drawings, in which like references indicate similar or analogous elements, and to the various embodiments of the invention described below. However, it will be understood by those of ordinary skill in the art that the examples provided below are not intended to limit the scope of the present invention. In addition, the drawings are only for illustrative purposes and are not drawn to scale.
As mentioned above, in the LED driving circuit, the current flowing through a single LED or each LED in a LED string determines the brightness of light, and the magnitude of the current also determines the forward voltage drop. According to the voltage-current curve characteristics of the LED, when the voltage applied to two ends of the LED fluctuates slightly, the current changes dramatically, and at the moment, the current is easily overlarge, so that the LED is damaged unrecoverably. Therefore, controlling the LED lamp voltage alone is not sufficient to stabilize the light emission luminance, and constant current control is necessary. In this case, current matching between different leds becomes a critical issue.
Generally, the existing LED circuit connections roughly include the following four types: one is to adopt parallel LEDs to provide constant drive voltage and open loop load current control. The connection method uses the resistor connected in series with the LED load to determine the load current, although the input voltage can be changed at will, the load regulation rate is poor, and the current matching effect is poor; and the other is to adopt parallel LEDs to provide constant driving voltage and load current control with closed-loop feedback. According to the connection method, the load current is determined by using the feedback resistor, the LED branch circuits connected with the feedback resistor in series can be accurately controlled by the current, but the current of each other branch circuit needs to be adjusted by the output voltage, so that the current matching degree is not good; thirdly, a current mode of the parallel LEDs is adopted, the current mode is more suitable for the parallel LEDs, the current matching characteristic of the current mode is better, the damage of a single LED cannot influence other normal work, but the number of the LEDs applicable to the mode is more limited; and fourthly, current control with series-parallel LEDs and closed-loop feedback is adopted. That is, the connection method is to connect a plurality of LEDs in series to form an LED string, and then connect different LED strings in parallel to form a series-parallel LED network. In the connection mode, the LEDs connected in series have excellent current matching, and from the point of statistics and probability, the LED lamp strings connected in parallel and the main LED lamp string have better current matching, because the matching degree of the sum of the forward voltage drops of the LEDs connected in series is better than that of the forward voltage drops of the single LED.
Furthermore, LED dimming technology (dimming control) mainly includes three types: PWM dimming, analog dimming, and digital dimming. Taking PWM dimming as an example, based on the characteristic that human eyes are not sensitive enough to brightness flicker, when an LED is loaded, it is dark, and if the frequency of light and dark exceeds 100Hz, the human eyes see the average brightness instead of the flicker of the LED. The brightness can be adjusted by adjusting the ratio of bright time to dark time. A particular advantage of PWM dimming is that the current color does not shift because the current through the LED does not change while the brightness is adjusted.
The LED driving circuit concerned by the invention adopts the current control of series-parallel LEDs with closed-loop feedback and the PWM dimming control. Fig. 1 shows a schematic structure diagram of an LED driving circuit in the prior art.
Referring to fig. 1, the LED driving circuit includes a DC-DC conversion circuit 10, a driving module 20, and a controller 30. The DC-DC conversion circuit 10 is configured to receive a power voltage Vin and convert the power voltage Vin into an LED lamp voltage VLED according to a Pulse Width Modulation (PWM) signal from the controller 30. The driving module 20 is electrically connected to one or more LED strings and the controller 30. The LED lamp voltage VLED output by the DC-DC conversion circuit 10 is processed by the voltage divider circuit to obtain a voltage detection signal FB1, and the voltage detection signal FB1 is sent to the controller 30. When the voltage is stabilized, the driving module 20 makes the LED current constant and performs dimming control.
Therefore, under the control structure, the LED driving circuit must provide the feedback signal FB2 from the driving module 20 to the DC-DC conversion circuit 10 to control the voltage of the LED lamp, which will cause the low frequency signal for dimming to interfere with the DC-DC conversion circuit 10 through the controller 30. In addition, when the LED load varies instantaneously, the structure is prone to LED lamp voltage drift and slow response speed, which causes unnecessary circuit loss.
Fig. 2 is a schematic diagram showing a control timing sequence of the LED lamp voltage output by the DC-DC conversion circuit and the PWM signal output by the controller in the LED driving circuit of fig. 1.
With reference to fig. 1 and 2, according to the control sequence, the output voltage Vout (also referred to as LED lamp voltage) of the DC-DC conversion circuit 10 varies in close relation to the PWM signal received by the switching tube inside the circuit from the controller 30. The over-voltage protection threshold of the output voltage Vout is not set to correspond to the voltage V1, and the under-voltage protection threshold of the output voltage Vout corresponds to the voltage V2.
When the output voltage Vout is between V1 and V2, the circuit is in normal operation, the PWM pulse is turned on, and the PWM pulse is used as the gate driving signal VGSContinuously applied to the switching tube. When the output voltage Vout is lower than V2, the circuit is under-voltage protection, the PWM pulse is turned off, and the gate of the switch tube does not provide any driving signal. When the output voltage Vout is higher than V1, the circuit is under overvoltage protection, the PWM pulse is also turned off, and the gate of the switch tube does not provide any driving signal. Therefore, the LED driving circuit controls the PWM signal to be turned on or off only according to the over-voltage threshold V1 and the under-voltage threshold V2, and once the LED load suddenly changes, the LED driving circuit must wait for the signal to pass through the entire single closed-loop control loop before being adjusted, so that the response speed is slow.
Fig. 3 is a schematic diagram of an LED driving circuit according to an embodiment of the invention. Referring to fig. 3, the LED driving circuit of the present invention includes a DC-DC conversion circuit 40, a driving module 50, a controller 60 and a voltage divider circuit 70.
The DC-DC conversion circuit 40 is used for receiving a power voltage and converting the power voltage into an LED lamp voltage by a pwm signal. Here, the pulse modulation signal comes from the PWM module 62 of the controller 60. The voltage divider circuit 70 is disposed at the output end of the DC-DC converter circuit 40 for outputting a voltage detection signal reflecting the LED lamp voltage. In one embodiment, the voltage divider circuit 70 includes a first resistor R1 and a second resistor R2 connected in series. One end of the first resistor R1 is electrically connected to the output end of the DC-DC converter circuit 10. The other end of the first resistor R1 is connected to one end of the second resistor R2. The other end of the second resistor R2 is electrically connected to a ground terminal.
The driving module 50 is used for outputting a PWM switch control signal and a duty ratio adjustment control signal. Specifically, the LED lamp voltage output by the DC-DC conversion circuit 40 is designed to be four thresholds, that is, an overvoltage threshold, an undervoltage threshold, an upper ripple threshold of the LED lamp voltage, and a lower ripple threshold of the LED lamp voltage. The PWM signal is turned on or off through the PWM switch control signal, and further protection and corresponding processing are carried out on the overvoltage state or the undervoltage state which possibly occurs in the circuit. And judging whether the ripple of the LED lamp voltage is lower than a ripple lower limit threshold or higher than a ripple upper limit threshold through the duty ratio regulation control signal, further controlling the ripple size of the LED lamp voltage, and reducing the model selection specification of an output capacitor of the DC-DC conversion circuit 40. In practice, the driving module 50 may be a current sink (current sink) circuit.
The controller 60 includes a PWM module 62. The PWM module 62 receives two feedback signals, wherein one of the feedback signals is a voltage detection signal from the voltage divider circuit 70; the other path of feedback signal is a PWM switching control signal and a duty ratio adjustment control signal, and comes from the driving module 50. Therefore, the LED driving circuit of the present invention can also be referred to as a dual feedback control circuit.
Fig. 4 is a waveform diagram illustrating an overvoltage threshold, a ripple upper threshold, a ripple lower threshold, an undervoltage threshold of the LED lamp voltage, the LED lamp current, and a PWM signal output by the controller in the LED driving circuit of fig. 3.
Referring to fig. 4, V1 denotes an overvoltage threshold value of the LED lamp voltage, V2 denotes an undervoltage threshold value of the LED lamp voltage, V3 denotes an upper ripple threshold value of the LED lamp voltage, V4 denotes a lower ripple threshold value of the LED lamp voltage, and ILED denotes the LED lamp current. As can be seen from the figure, the overvoltage threshold V1 is higher than the upper threshold V3 of the ripple, and the undervoltage threshold V2 is lower than the lower threshold V4 of the ripple. When the lamp voltage VLED is between the ripple upper threshold V3 and the ripple lower threshold V4, the PWM module outputs a PWM signal with a fixed duty cycle.
When the lamp voltage VLED is lower than the ripple lower threshold V4, the PWM module increases the duty cycle of the PWM signal to a maximum value by the duty cycle adjustment control signal. In other words, two adjacent pulses in the PWM signal almost overlap, and the pulse width corresponds to a high potential. When the lamp voltage VLED is higher than the ripple upper threshold V3, the PWM module decreases the duty cycle of the PWM signal to a minimum value by the duty cycle adjustment control signal. That is, two adjacent pulses in the PWM signal also almost overlap, except that the pulse width at this time corresponds to the low potential.
Fig. 5 is a block diagram illustrating a structure of an embodiment of a PWM module in the LED driving circuit of fig. 3.
Referring to fig. 5, in this embodiment, the PWM module 60 includes an error amplifier 621, a PWM modulator 623, and a PWM controller 625.
In more detail, the first input terminal of the error amplifier 621 is used for receiving the voltage detection signal VFBA second input terminal electrically connected to a reference voltage VREFThe output end of the voltage-measuring circuit is used for outputting a representative voltage detection signal VFBAnd a reference voltage VREFAn error voltage signal V of the difference ofE. The PWM modulator 623 is electrically connected to the error amplifier 621 for receiving the error voltage signal VEAnd a carrier signal VMAnd outputs a reference PWM signal. The PWM controller 625 receives a reference PWM signal, a PWM switching control signal and a duty ratio adjustment control signal, and outputs the PWM signal to the DC-DC conversion circuit, wherein VGIndicating the potential voltage of the PWM signal.
In one embodiment, the carrier signal VMIs a sawtooth signal.
In addition, when the voltage of the LED lamp is higher than the overvoltage threshold value, the PWM module stops outputting the PWM signal through the PWM switch control signal. When the voltage of the LED lamp is lower than the undervoltage threshold value, the PWM module stops outputting the PWM signal by the PWM switch control signal.
The LED driving circuit outputs a voltage detection signal reflecting the voltage of the LED lamp through the voltage division circuit, outputs a PWM (pulse width modulation) switch control signal and a duty ratio regulation control signal by using the driving module, and receives the voltage detection signal, the PWM switch control signal and the duty ratio regulation control signal by using the PWM module of the controller so as to output the PWM signal to the DC-DC conversion circuit. Compared with the prior art, the LED lamp voltage regulation circuit has the advantages that the upper limit threshold and the lower limit threshold of the ripple wave of the LED lamp voltage are used as the reference voltage, the correlation comparison is carried out on the maximum duty ratio and the minimum duty ratio of the PWM signal, the PWM signal is directly output according to the duty ratio regulation control signal, the PWM signal can be quickly adjusted to be turned on or turned off when the output voltage changes, the adjustment is not needed after the signal passes through an integral closed-loop control loop, the response speed is higher, the frequency of the corresponding output PWM signal is not changed, the design specification of an output capacitor is further reduced, the cost is saved, and the occupied space is reduced.
Hereinbefore, specific embodiments of the present invention are described with reference to the drawings. However, those skilled in the art will appreciate that various modifications and substitutions can be made to the specific embodiments of the present invention without departing from the spirit and scope of the invention. Such modifications and substitutions are intended to be included within the scope of the present invention as defined by the appended claims.
Claims (10)
1. An LED (Light Emitting Diode) driving circuit, comprising:
a DC-DC conversion circuit for receiving a power voltage and converting the power voltage into an LED lamp voltage by a Pulse Width Modulation (PWM) signal;
a voltage divider circuit, disposed at an output end of the DC-DC conversion circuit, for outputting a voltage detection signal reflecting the voltage of the LED lamp;
the driving module is used for outputting a PWM switch control signal and a duty ratio regulation control signal; and
and the controller comprises a PWM module, and the PWM module receives the voltage detection signal, the PWM switch control signal and the duty ratio regulation control signal so as to output the PWM signal to the DC-DC conversion circuit.
2. The LED driving circuit of claim 1, wherein the voltage divider circuit comprises a first resistor and a second resistor connected in series, one end of the first resistor is electrically connected to the output terminal of the DC-DC converter circuit, and one end of the second resistor is electrically connected to a ground terminal.
3. The LED driving circuit of claim 1, wherein the PWM module outputs the PWM signal with a fixed duty cycle when the LED lamp voltage is between a lower threshold and an upper threshold of a ripple of the LED lamp voltage.
4. The LED driving circuit according to claim 1, wherein when the LED lamp voltage is lower than a lower threshold of ripple thereof, the duty ratio of the PWM signal is increased to a maximum value by the duty ratio adjustment control signal.
5. The LED driving circuit according to claim 1, wherein when the LED lamp voltage is higher than an upper threshold of ripple thereof, the duty ratio of the PWM signal is reduced to a minimum value by the duty ratio adjustment control signal.
6. The LED driver circuit of claim 1, wherein the LED lamp voltage further comprises an over-voltage threshold and an under-voltage threshold, the over-voltage threshold is higher than an upper threshold of the ripple, and the under-voltage threshold is lower than a lower threshold of the ripple.
7. The LED driving circuit according to claim 6, wherein when the LED lamp voltage is higher than the overvoltage threshold, the output of the PWM signal is stopped by the PWM switch control signal.
8. The LED driving circuit according to claim 6, wherein the PWM signal is stopped from being output by the PWM switch control signal when the LED lamp voltage is lower than the under-voltage threshold.
9. The LED driving circuit according to claim 1, wherein the PWM module comprises:
an error amplifier, a first input end of which is used for receiving the voltage detection signal, a second input end of which is electrically connected to a reference voltage, and an output end of which is used for outputting an error voltage signal;
a PWM modulator electrically connected to the error amplifier for receiving the error voltage signal and a carrier signal and outputting a reference PWM signal; and
a PWM controller for receiving the reference PWM signal, the PWM switching control signal, and the duty ratio adjustment control signal to output the PWM signal to the DC-DC conversion circuit.
10. The LED driving circuit according to claim 9, wherein the carrier signal is a sawtooth signal.
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| Application Number | Priority Date | Filing Date | Title |
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| CN 201310007773 CN103124460A (en) | 2013-01-09 | 2013-01-09 | LED driving circuit |
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| Application Number | Priority Date | Filing Date | Title |
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| CN 201310007773 CN103124460A (en) | 2013-01-09 | 2013-01-09 | LED driving circuit |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106900118A (en) * | 2013-09-29 | 2017-06-27 | 赛尔富电子有限公司 | A kind of under-voltage protecting circuit for LED lamp |
| CN109388330A (en) * | 2017-08-07 | 2019-02-26 | 富士电机株式会社 | Power-converting device |
| CN109688659A (en) * | 2018-12-21 | 2019-04-26 | 太仓电威光电有限公司 | LED drive power mould group and the integral LED car light for applying it |
| CN110460377A (en) * | 2019-07-25 | 2019-11-15 | 浙江大学 | A kind of device carrying out LED light communication using driving circuit switching harmonics |
| WO2020107171A1 (en) * | 2018-11-26 | 2020-06-04 | 上海晶丰明源半导体股份有限公司 | Control circuit, driving system, chip, control method and driving method |
| CN111903193A (en) * | 2018-03-28 | 2020-11-06 | 株式会社小糸制作所 | Lighting circuit and vehicle lamp |
-
2013
- 2013-01-09 CN CN 201310007773 patent/CN103124460A/en active Pending
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106900118A (en) * | 2013-09-29 | 2017-06-27 | 赛尔富电子有限公司 | A kind of under-voltage protecting circuit for LED lamp |
| CN109388330A (en) * | 2017-08-07 | 2019-02-26 | 富士电机株式会社 | Power-converting device |
| CN109388330B (en) * | 2017-08-07 | 2023-11-03 | 富士电机株式会社 | power conversion device |
| CN111903193A (en) * | 2018-03-28 | 2020-11-06 | 株式会社小糸制作所 | Lighting circuit and vehicle lamp |
| US11382194B2 (en) | 2018-03-28 | 2022-07-05 | Koito Manufacturing Co., Ltd. | Lighting circuit |
| CN111903193B (en) * | 2018-03-28 | 2024-02-06 | 株式会社小糸制作所 | Lighting circuit and vehicle lamp |
| WO2020107171A1 (en) * | 2018-11-26 | 2020-06-04 | 上海晶丰明源半导体股份有限公司 | Control circuit, driving system, chip, control method and driving method |
| CN113228828A (en) * | 2018-11-26 | 2021-08-06 | 上海晶丰明源半导体股份有限公司 | Control circuit, driving system, chip, control method and driving method |
| US11737180B2 (en) | 2018-11-26 | 2023-08-22 | Shanghai Bright Power Semiconductor Co., Ltd. | Control circuit, chip and control method |
| CN109688659A (en) * | 2018-12-21 | 2019-04-26 | 太仓电威光电有限公司 | LED drive power mould group and the integral LED car light for applying it |
| CN109688659B (en) * | 2018-12-21 | 2024-04-30 | 太仓电威光电有限公司 | LED driving power supply module and integrated LED car lamp applying same |
| CN110460377A (en) * | 2019-07-25 | 2019-11-15 | 浙江大学 | A kind of device carrying out LED light communication using driving circuit switching harmonics |
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Application publication date: 20130529 |