TW202249534A - LED driving system with high light conversion efficiency with a control unit to proceed a dimming operation according to a dimming command current to make the average current of the pooled current of LED load be equal to the dimming command current - Google Patents

Abstract

A LED driving system with high light conversion efficiency is disclosed, which has: a full bridge switch circuit, a capacitor-inductor series circuit, a transformer, a first diode, a second diode, a first inductor, a second inductor, an output capacitor, a LED load, a voltage feedback circuit, a control unit, and a gate driver, wherein the control unit is used to perform a dimming operation according to a dimming command current to make an average current of the pooled current of LED load equal to the dimming command current. The dimming operation includes: finding out one of the intervals of the dimming command current in five current intervals (0, I 1], (I 1, I 2], (I 2, I 3], (I 3 ,I 4] and (I 4,I 5], so as to enable one selected PWM signal combination of five PWM signal combinations (PWM1), (PWM1,PWM2), (PWM2,PWM3), (PWM3 ,PWM4), (PWM4,PWM5); and performing a negative feedback control calculation program to generate a duty cycle D to determine the pulse width of each PWM signal in the selected PWM signal combination, wherein D is a non-negative real number not greater than 1.

Description

LED drive system with high light conversion efficiency

The invention relates to an LED drive system, in particular to an LED drive system with high light conversion efficiency.

In the past 100 years, lighting sources have been continuously improved and developed, from early carbon filament lamps to tungsten filament lamps to fluorescent lamps. The emergence of Solid-State Lighting (SSL) has brought a new concept of light source to the world. Compared with the light source in the past, LED has the advantages of energy saving, long life, high color rendering, and fast start-up. With the development of science and technology, the luminous efficiency of LEDs is gradually improving, and the cost has become more affordable. Therefore, the light sources used in street lights, screen displays, and indoor lighting are gradually converting from traditional light sources to LED light sources. According to the report "Energy Savings Forecast of Solid-State Lighting in General Illumination Applications" (Energy Savings Forecast of Solid-State Lighting in General Illumination Applications) updated by the U.S. Department of Energy at the end of 2019, LED Accounted for 31%, while metal halide (Metal Halide) and high-pressure sodium lamps accounted for 25% in total, linear fluorescent lamps accounted for 27%, and the rest of halogen lamps and incandescent lamps accounted for 15%. It is predicted that in 2025, LED will reach 92% installation rate, and LED lighting equipment will reach 98% installation rate in 2035.

The illuminance-current curve of most LEDs is not linear. Taking CREE CXA2540 as an example, its illuminance-current curve is shown in Figure 1. It can be seen from Figure 1 that when the forward conduction current is smaller, the ratio of illuminance to current will be greater, and it will gradually decrease as the current rises. Since digital dimming uses the length of current conduction time to change the average current, Therefore, for dimming, the current through the LED will switch between zero and the rated value, instead of changing the maximum value of its forward current, so the luminous efficiency is not optimal. Taking the characteristic curve at 25 ^o C as an example, when the current is 2100 mA, the corresponding relative illuminance (Relative Luminous Flux) is about 162%. 83.3% relative illuminance, instead of about 110% relative illuminance of the original feature.

There have been a lot of researches on the technology of LED drivers before: Some literatures propose to connect a linear current regulator to each group of LEDs, and add a feed-forward voltage regulator, using the feed-forward voltage regulator feedback This method improves the efficiency of the circuit, but the effect of improving the efficiency is not obvious. The efficiency of this technology is greatly affected by the consistency of the characteristics of the LEDs in the same string; Control at the highest forward conduction voltage value, make the voltage difference of one group of LEDs close to zero to reduce loss, and use phase shift pulse width modulation (Phase Shift Pulse Width Modulation, PSPWM) to limit the change of output current to One group of LED currents is between the maximum current to reduce the electromagnetic interference caused by high pulsating currents caused by general pulse width modulation control; there are also literatures that digital PWM dimming, dual pulse width dimming, and critical voltage dimming After the dimming technology is realized, we can compare it. After the comparison, we can also know that the threshold voltage dimming has good efficiency, but the linearity of the dimming curve is poor due to its slow response speed; there are also literatures that propose the use of analog circuits The method detects the voltage between the gate and the drain, realizes the adaptive adjustment of the output voltage, and then improves the efficiency; there are also literatures that change the current detection resistor and the reference voltage value of the linear constant current circuit and set the forward current of the seven-segment LED , and use digital PWM dimming to operate the LED at seven different forward current values, operate at low forward current during low-illuminance dimming, and operate at high forward current during high-illuminance dimming, thereby improving LED luminescence efficiency; there are also literatures that propose a multilevel pulse width modulation (Multilevel Pulse Width Modulation, MPWM) dimming method to improve the low luminous efficiency of digital PWM dimming; Floating Output, SIMFO) to improve the single inductor multiple output circuit (Single Inductor Multiple Output, SIMO) low dimming frequency problem, and propose the average current correction (Average Current Correction, ACC) to improve the current deviation caused by the different forward conduction voltage of multiple LED strings ; There are also literatures that use half-bridge non-resonant converters as LED drive circuits, so that the circuit switches can be soft-cut to improve circuit efficiency. There are also literatures that use the synchronous integration method to achieve output voltage self-adaptation to improve efficiency, and propose changing the dimming frequency to solve the problem of poor linearity of the circuit's low-illuminance dimming curve; there are even literatures that use adaptive current control to switch multiple strings of LEDs forward The current is controlled at the maximum forward current to reduce the conduction loss of the switch.

However, the light conversion efficiency of the existing technical solutions is still insufficient. Therefore, a novel LED driving system is urgently needed in the art.

The main purpose of the present invention is to disclose an LED drive system with high light conversion efficiency, which can improve the luminous efficiency of LED modules through a multi-stage PWM current modulation scheme.

In order to achieve the aforementioned purpose, a LED driving system with high light conversion efficiency is proposed, which has:

A full-bridge switching circuit has: two input terminals for coupling with the positive and negative terminals of an input voltage, and four control terminals for respectively connecting with a first switch control signal, a second switch control signal, and a third switch control signal signal and a fourth switch control signal are coupled; a first output terminal is coupled to the positive terminal when the first switch exhibits an active potential and is coupled to the negative terminal when the second switch exhibits an active potential; and A second output terminal is coupled to the positive terminal when the third switch exhibits an active potential and is coupled to the negative end when the fourth switch exhibits an active potential;

a capacitor-inductor series circuit, one end of which is coupled to the first output end of the full-bridge switch circuit;

A transformer having a primary winding and a secondary winding, the primary winding is connected in parallel with a magnetizing inductance and one end thereof is coupled to the other end of the capacitance-inductance series circuit, and the other end thereof is connected to the full bridge switching circuit The second output end of the secondary coil is coupled, and the secondary coil has a first output end and a second output end;

a first diode having a first anode and a first cathode, the first anode is coupled to a voltage reference terminal, the first cathode is coupled to the first output terminal of the secondary coil;

a second diode having a second anode and a second cathode, the second anode is coupled to the voltage reference terminal, the second cathode is coupled to the second output terminal of the secondary coil;

a first inductor coupled between the first output terminal of the secondary coil and a voltage output terminal;

a second inductor coupled between the second output terminal of the secondary coil and the voltage output terminal;

an output capacitor coupled between the voltage output terminal and the voltage reference terminal;

An LED load, coupled between the voltage output terminal and the voltage reference terminal, is composed of an LED module, a voltage stabilizing circuit, a set of current sources and a current sensor in series, wherein the voltage stabilizing The circuit is used to generate a fixed voltage to bias the set of current sources. The set of current sources has five gating-controlled constant current sources I ₁ , I ₂ , I ₃ , I ₄ and I ₅ . The five gating-controllable constant current sources control their current output according to five gating signals, and the collected current of the group of current sources flows through the current sensor to generate a current feedback signal;

a voltage feedback circuit for generating a voltage feedback signal according to a voltage across the output capacitor;

A control unit, used to execute a firmware program to perform a dimming operation according to a dimming command current to make an average current of the sink current equal to the dimming command current, the dimming operation includes: feedback signal according to the voltage Performing a first negative feedback control calculation program on the difference with a reference voltage to generate a first switch signal, a second switch signal, a third switch signal and a fourth switch signal; and in five current intervals ( 0,I ₁ ], (I ₁ ,I ₂ ], (I ₂ ,I ₃ ], (I ₃ ,I ₄ ] and (I ₄ ,I ₅ ] to find out the interval to which one of the dimming command currents belongs, To enable one of the five PWM signal combinations (PWM1), (PWM1, PWM2), (PWM2, PWM3), (PWM3, PWM4), (PWM4, PWM5) to select one of the PWM signal combinations, and according to the current feedback signal Perform a second negative feedback control calculation program on the difference with the dimming command current to generate a duty cycle D to determine the pulse width of each PWM signal in the selected PWM signal combination, D is a non-negative real number not greater than 1 ;as well as

a gate driver, used to generate the first switch control signal, the second switch control signal, the third switch signal according to the first switch signal, the second switch signal, the third switch signal and the fourth switch signal The control signal and the fourth switch control signal generate five gate control signals according to the five PWM signals.

In one embodiment, the voltage feedback circuit includes a voltage dividing circuit and an optical coupling circuit.

In one embodiment, the control unit includes an analog-to-digital converter for performing an analog-to-digital conversion operation on the voltage feedback signal and the current feedback signal to generate a first input digital signal and a second input digital correspondingly Signal.

In one embodiment, the control unit includes a filtering operation module to perform filtering operation on the first input digital signal and the second input digital signal to generate a third input digital signal and a fourth input digital signal correspondingly .

In one embodiment, the control unit includes a proportional-integral-derivative operation module to execute the first negative feedback control calculation program on the third input digital signal, and execute the first negative feedback control calculation program on the fourth input digital signal Two negative feedback control calculation programs.

In one embodiment, the control unit includes a pulse width modulation module to generate the first switching signal, the second switching signal, the third switching signal, the fourth switching signal and five of the PWM signals .

In order to enable your review committee members to further understand the structure, features and purpose of the present invention, drawings and detailed descriptions of preferred specific embodiments are hereby attached.

Please refer to FIG. 2 , which shows a block diagram of an embodiment of the high light conversion efficiency LED driving system of the present invention.

As shown in Figure 2, the LED driving system with high light conversion efficiency in this case has a full bridge switch circuit 100, a capacitor-inductor series circuit 110, a transformer 120, a first diode 130, and a second diode 140 , a first inductor 150 , a second inductor 160 , an output capacitor 170 , an LED load 180 , a voltage feedback circuit 190 , a control unit 200 and a gate driver 210 .

The full-bridge switch circuit 100 has two input terminals A, B for coupling with the positive and negative terminals of an input voltage _Vin , and four control terminals for respectively connecting with a first switch control signal S ₁ and a second switch control signal S _2. A _third switch control signal S3 and a _fourth switch control signal S4 are coupled, a first output terminal C is coupled to the positive terminal when the _first switch S1 presents an active potential and the second The switch S2 is coupled to the negative terminal when it exhibits an action potential, and a _second output terminal D is coupled to the positive end when the _third switch S3 exhibits an action potential and the _fourth switch S4 exhibits an action Potential when coupled with the negative terminal.

Among them, the full-bridge phase-shift converter has two more main power switches S ₃ and S ₄ than the half-bridge phase-shift converter, so the output power capability can be improved.

One terminal of a capacitor-inductor series circuit 110 is coupled to the first output terminal C of the full-bridge switch circuit 100 .

A transformer 120 has a primary winding and a secondary winding, the primary winding is connected in parallel with a magnetizing inductance and one end thereof is coupled to the other end of the capacitor-inductance series circuit 110 and the other end thereof is connected to the full-bridge switch The second output terminal of the circuit 100 is coupled to D, and the secondary coil has a first output terminal E and a second output terminal F.

A first diode 130 has a first anode and a first cathode, the first anode is coupled to a voltage reference terminal, and the first cathode is coupled to the first output terminal E.

A second diode 140 has a second anode and a second cathode, the second anode is coupled to the voltage reference terminal, and the second cathode is coupled to the second output terminal F.

A first inductor 150 is coupled between the first output terminal E and a voltage output terminal O.

A second inductor 160 is coupled between the second output terminal F and the voltage output terminal O.

An output capacitor 170 is coupled between the voltage output terminal O and the voltage reference terminal.

An LED load 180 is coupled between the voltage output terminal O and the voltage reference terminal, and is composed of an LED module 181 and a voltage stabilizing circuit (a negative feedback circuit composed of an amplifier 182 and an NMOS transistor 183) , a group of current sources 184 and a current sensor 185 are connected in series, wherein the voltage regulator circuit is used to generate a fixed voltage V _r to bias the group of current sources 184, the group of current sources 184 has five Small to large gating-controllable constant current sources I ₁ (composed of NMOS transistor 184a1 and resistor 184a2 connected in series), I ₂ (composed of NMOS transistor 184b1 and resistor 184b2 connected in series), I ₃ (composed of NMOS transistor 184c1 connected in series with resistor 184c2), I ₄ (formed in series with NMOS transistor 184d1 and resistor 184d2), and I ₅ (formed in series with NMOS transistor 184e1 and resistor 184e2), the five gating-controllable constant current sources Its current output is controlled according to five gate control signals VG ₁ -VG ₅ , and the sink current i _out of the group of current sources flows through the current sensor 185 to generate a current feedback signal I _FB .

A voltage feedback circuit 190 includes a voltage dividing circuit 191 and an optical coupling circuit 192 for generating a voltage feedback signal V _FB according to a voltage V _out across the output capacitor 170 .

A control unit 200 stores a firmware program for executing the firmware program to perform a dimming operation according to a dimming command current C _DIM so that an average current of the sink current i _out is equal to the dimming command current C _DIM , The dimming operation includes: performing a first negative feedback control calculation procedure according to the difference between the voltage feedback signal V _FB and a reference voltage (not shown in the figure) to generate a first switch signal, a second switch signal, _{a third switch signal} and _{a fourth} switch signal _; and (I ₄ , I ₅ ] to find out one of the intervals of the dimming command current C _DIM , so as to enable five PWM signal combinations (PWM1), (PWM1, PWM2), (PWM2, PWM3), (PWM3, PWM4 ), (PWM4, PWM5) in one selected PWM signal combination, and according to the difference between the current feedback signal I _FB and the dimming command current C _DIM , a second negative feedback control calculation program is performed to generate a duty The period D is used to determine the pulse width of each PWM signal in the selected PWM signal combination, and D is a non-negative real number not greater than 1.

The control unit 200 includes an analog-to-digital converter 201, a filtering operation module 202, a proportional-integral-differential operation module 203, and a pulse width modulation module 204, wherein the analog-to-digital conversion The device 201 is used to perform an analog-to-digital conversion operation on the voltage feedback signal V _FB and the current feedback signal I _FB to generate a first input digital signal and a second input digital signal correspondingly; the filter operation module 202 is used to filter the first input digital signal and the second input digital signal to generate a third input digital signal and a fourth input digital signal; the proportional-integral-differential operation module 203 is For executing the first negative feedback control calculation program on the third input digital signal, and executing the second negative feedback control calculation program on the fourth input digital signal; and the pulse width modulation module 204 is used to generate the first switch signal, the second switch signal, the third switch signal, the fourth switch signal and the five PWM signals.

The gate driver 210 is used for generating the first switch control signal S ₁ , the second switch control signal S ₂ , The third switch control signal S ₃ and the fourth switch control signal S ₄ generate five gate control signals VG ₁ -VG ₅ according to the five PWM signals.

The principle of the present invention will be described below:

1. LED Driver System Architecture

In this embodiment, the LED module 181 is composed of 10 sets of LED lamps connected in parallel, and the control unit 200 is realized by a TMS320F280049C digital signal processor released by Texas Instruments.

) ＞ 90% 滿載有效工作週期(D _eff) 0.7 The power stage circuit of the LED driver adopts a Phase Shift Full Bridge Converter (Phase Shift Full Bridge Converter) with soft switching characteristics. As shown in Figure 3, the main components of the primary side are power switches S ₁ , S ₂ , S ₃ , S ₄ and the resonant inductance L _r and the blocking capacitor C _b used to block DC to avoid unbalanced transformer core flux, the secondary side is the output diode D ₁ , D ₂ and the output inductance L ₁ , L ₂ Stream output architecture and output capacitor C _o . Figure 4 shows the control signals of the four power switches of the phase-shifted full-bridge converter and the corresponding theoretical waveforms of the primary-side current i _p and the transformer primary-side voltage _VAB . From Figure 4, it can be seen that the upper and lower bridge switching signals of the same arm There is obviously a dead time interval, and this dead time interval can make the power switch parasitic capacitance and resonant inductance complete resonance to achieve zero voltage switching. It can be seen from the corresponding current waveforms that there are two nonlinear resonant intervals t ₁ ~ t ₂ and t ₃ ~ t ₄ before the zero-voltage switching of S ₁ and S ₄ . Table 1 shows the design specifications of the phase-shift full-bridge converter circuit used in the present invention. The output voltage is based on the voltage-current relationship of the selected CREE CXA2540 LED. When the temperature is 25 ^o C and the current is 1100 mA, the voltage across It is about 37 V, plus the resistance of the linear constant current circuit and the voltage drop between the sink and the source of the power switch, so the output voltage is set to 40 V, and the input voltage is set to 200 V. In this case, ten CXA2540 LED modules are connected in parallel. The maximum output current is 11 A. Table 1. Phase-Shifted Full-Bridge Converter Design Specifications project value Input voltage (V _in ) _200Vdc Output voltage (V _o ) _40Vdc Output voltage ripple (V _ripple ) ＜ 1% Maximum output current (I _o,max ) 12A Maximum output power (P _out ) 480W Switching frequency (f _s ) 75 kHz expected efficiency (

) > 90% Effective duty cycle at full load (D _eff ) 0.7

2. Dimming principle and illumination measurement environment setting

2.1 digital PWM dimming

Traditional digital PWM dimming achieves dimming effect by changing the current conduction time per unit time to change its average value. If the operating frequency is too low, human eyes will feel flickering. According to previous literature research, the operating frequency is generally set between 100 and 400 Hz. In this case, 200 Hz is used as the PWM dimming frequency. When driving the LED, it will be driven with a constant current, which can not only stabilize the conduction current of the LED, but also improve the characteristics of the LED when the constant voltage is driven. situation. The linear steady current structure is composed of operational amplifier and field effect transistor. As shown in Figure 5, the field effect transistor is operated in the linear region, and V _r is a dimming signal with variable amplitude. When the non-reverse input of the operational amplifier When the terminal voltage is high potential, the field effect transistor is turned on, which is equivalent to a variable resistor, and the output current is fed back to the operational amplifier through the current detection resistor R _s for comparison; when the non-inverting input terminal voltage is low voltage At this time, the field effect transistor is cut off, and this mechanism is used to control the average current flowing through the LED to achieve the dimming function.

2.2 The proposed multi-stage current dimming method

)時，如同數位PWM調光，LED順向電流會在I ₁與零之間作切換，並藉由改變其責任週期進行調光，如圖7a所示，D ₁越大照度越高；第二段(

)時，LED順向電流會在I ₂與I ₁之間作切換，利用改變I ₂與I ₁之間的責任週期比例進行調光，如圖7b所示，其中D _dim1= 1 – D _dim2，D _dim2越大照度越高。數位PWM調光與二段式電流調光之照度-電流曲線如圖8所示，由圖8可知二段式電流調光之發光效率較佳。 2.2.1 多段式調光之各段電流值推導 The LED forward current of the traditional digital PWM dimming will be switched between the rated forward current and zero, and the dimming can be obtained by changing the PWM duty cycle to obtain different average current values, as shown in Figure 6, where D _dim The larger the value, the higher the illuminance. The dimming of the proposed multi-stage current dimming method will be divided into multiple stages. Taking the two-stage dimming as an example, the first stage (

), like digital PWM dimming, LED forward current will switch between I ₁ and zero, and dimming is performed by changing its duty cycle, as shown in Figure 7a, the larger D ₁ is, the higher the illuminance; Second paragraph (

), LED forward current will switch between I ₂ and I ₁ , dimming by changing the duty cycle ratio between I ₂ and I ₁ , as shown in Figure 7b, where D _dim1 = 1 – D _dim2 , the bigger D _dim2 is, the higher the illuminance. The illuminance-current curves of digital PWM dimming and two-stage current dimming are shown in Figure 8. From Figure 8, it can be seen that the luminous efficiency of two-stage current dimming is better. 2.2.1 Derivation of the current value of each stage of multi-stage dimming

(1) As shown in Figure 9, the present invention actually uses five-stage current dimming, and defines the LED forward current from small to large as I ₁ to I ₅ , and assumes that the LED illuminance curve is a line before determining the LED forward current. The quadratic curve of the zero-crossing point and define the illuminance L _n as

(1)

(2) If the area surrounded by five forward currents is defined as A, it can be seen from Figure 9 that A can be divided into a triangle and four trapezoids, and the area A can be calculated as

(2)

(3) And L ₁ to L ₅ are calculated according to formula (1) and substituted into formula (2) to obtain the area A as

(3)

(4) Then, make partial differentials for I ₁ to I ₅ in formula (3), and make the result of the partial differential equal to zero, then you can find out the value of the segmental current that maximizes the area A, and sort them out to get each The relationship between LED forward current is

(4)

As shown in Figure 10, the structure of the linear constant current circuit in this case is that 10 CXA2540 LED modules share 5 current detection resistors. Table 2 shows the electrical specifications of CXA2540, which generally operate at a typical forward current value of 1100 mA, and The total current value of 10 CXA2540s is 11 A. Therefore, in this case, the maximum current value I ₅ is set to 11 A, and it is substituted into formula (4), and the required five-stage currents I ₁ to I ₅ are respectively 2.2 A, 2.2 A, 4.4A, 6.6A, 8.8A and 11A. Table 2. Electrical Specifications of CXA2540 Electrical parameters value Forward conduction current (mA) 1100 (typ.) Forward conduction voltage (V) 36.2 (typ.) Color Rendering Index (CRI) 95 color temperature(K) 3000

2.2.2 Current Sense Resistor Design

In Figure 10, the reference voltage V _r is originally set to 3.3 V, and the required five-segment currents I ₁ to I ₅ derived from the previous section are 2.2 A, 4.4 A, 6.6 A, 8.8 A, and 11 A, respectively. Calculate R ₅ = 0.3 Ω, R ₄ = 0.375 Ω, R ₃ = 0.5 Ω, R ₂ = 0.75 Ω, R ₁ = 1.5 Ω, because the current flowing through the above resistors is very large, so the current detection in this case The resistance is realized by using cement resistance with a large error range in series and parallel connection, and this also causes the actual value of the five-stage forward current in this case to deviate. The actual value R ₅ = 0.383 Ω, R ₄ is obtained after the actual RLC measuring instrument is used to measure = 0.422 Ω, R ₃ = 0.523 Ω, R ₂ = 0.78 Ω, R ₁ = 1.41 Ω, in order to make the maximum forward current value I ₅ adjusted to close to 11 A, so adjust V _r to 4 V, and actually measured to The corrected forward current values I ₁ to I ₅ are 2.9 A, 5.3 A, 7.5 A, 9.3 A, and 10.5 A, respectively. 2.2.3 Selection of the number of current segments

(%)]為

(5) This case defines the percentage increase of luminous efficiency [

(%)]for

(5)

(6) Among them, A _n is the area enclosed by the illuminance-current curve of the multi-stage current dimming method, A _PWM is the area enclosed by the illuminance-current curve of the digital PWM dimming method, and A _LED is the area enclosed by the LED illuminance-current curve The enclosed area, and substituting the actual value of the 25 ^o C illuminance-current curve in Figure 1 into (1), and solving the simultaneous equations, the 25 ^o C illuminance-current curve equation can be obtained as

(6)

至

分別為6%、7.15%、7.54%、7.74%、7.83%，由這些數據可得知，段數越高發光效率提升百分比會越高，但是隨著段數變高其提升效果會變得越不明顯，而從第五段至第六段時發光效率提升百分比已不到0.1%，因此本案選用五段式電流調光法。 Then do the integral calculation of formula (6) from 0 integration to the maximum current of 1100 mA to get A _LED is 66.7, and the triangle area A _PWM surrounded by the illuminance-current curve of the digital PWM dimming method can be obtained after calculation. is 61.33, and then according to the above-mentioned segmental current derivation method, the segmental current values of the two-stage to six-stage current dimming methods are respectively derived, and substituted into the formula (3) to obtain the segmental current values The illuminance value corresponding to the current, and then calculate the area A ₂ to A ₆ surrounded by the illuminance-current curve of the two-stage to six-stage current dimming method is 65.36, 66.1, 66.36, 66.49, 66.55, and finally A _n . Substituting A _PWM and A _LED into formula (5), you can get the luminous efficiency improvement percentage of two-stage to six-stage current dimming method

to

They are 6%, 7.15%, 7.54%, 7.74%, and 7.83%, respectively. From these data, it can be known that the higher the number of segments, the higher the percentage of luminous efficiency improvement, but as the number of segments increases, the improvement effect will become more It is not obvious, and the luminous efficiency improvement percentage from the fifth stage to the sixth stage is less than 0.1%, so the five-stage current dimming method is used in this case.

2.3 Illuminance measurement environment settings

When measuring the illuminance, in order to avoid the influence of other ambient light sources, a wooden box with a length of 55 cm, a width of 35 cm, and a height of 30 cm was selected as the test space. There is a 4 cm square hole on the side for wiring, and it is used for measuring When measuring, seal the gap with adhesive tape to make it opaque. Since the maximum brightness of 10 CXA2540 exceeds 50830 lumens, the illuminance meter is installed on the side of the box (the illuminance meter used in this invention is TES-1339R) to prevent the illuminance value from exceeding the measurable range of the illuminance meter.

3. Controller firmware design

In this case, the TMS320F280049C digital signal processor launched by Texas Instruments was selected as the digital controller for the LED driver and five-segment current dimming control. The system architecture diagram is shown in Figure 2. The sampling circuit is used to sample the output voltage and current, and the signal is sent to the digital filter for filtering through analog/digital conversion, and then the filtering result is calculated through PID compensation, and finally the PWM module outputs the PWM signal to the power switch to control the phase shift Full-bridge converter and linear constant current circuit can achieve digital control. The overall firmware program flow is shown in Figure 12. The program can be divided into two parts: the main program and the analog-to-digital converter interrupt. When the program starts, first declare the variables required by the program, initialize the core modules such as the system CLK, set the ADC and GPIO modules, then set and enable the PWM module, and then enter an infinite loop to perform dimming Subroutine and wait for ADC interrupt to occur.

ADC interrupt subroutine flow: The ADC interrupt program flow is shown in Figure 13. After entering the ADC interrupt, first sample V _out through the analog-to-digital converter, and send the sampled signal to the digital filter for processing to prevent Influenced by high-frequency noise, after entering the phase shift mode, input the error amount to the PID controller to calculate the PWM phase shift amount, and then limit the upper and lower limits of the phase shift amount calculated by the PID control, so that the phase shift amount will not exceed the setting Then update the phase shift amount of the PWM module, clear the ADC interrupt flag and return to the main program to enter an infinite loop, wait for the next ADC interrupt to occur, and repeat the above actions to achieve the stability of the phase-shifted full-bridge converter. pressure control.

Five-stage current dimming program flow: use the PWM module to generate five pulse signals with a frequency of 200 Hz, and the pulse signals used to control I ₄ and I ₂ must be consistent with the pulses that control I ₁ , I ₃ and I ₅ Wave signals are complementary, and the reference voltage V _r is provided by a power supply. The five-stage control current composed of five current detection resistors is defined as I ₁ to I ₅ from small to large, and the corresponding duty cycle is defined as D _dim1 to D _dim5 , and then passed back through the current sensor The reading value of the ADC module is used to judge the current magnitude, so as to determine how to adjust D _dim1 to D _dim5 . The control flow chart of the dimming program is shown in Figure 14.

(7) Incremental PID controller: Incremental PID control law can be expressed as:

(7)

可表示為

(8) 由第(7)式，可得

(9) Among them, K _P is the proportional gain, integral gain T _i = K _P /K _I , differential gain K _D = K _P . T _d , T _d is the sampling period, e(n) is the current error amount of the system, e(n - 1 ) is the previous error amount of the system, and n is the sampling signal point. control increment

can be expressed as

(8) From formula (7), we can get

(9)

，

，

，則式(9)可改寫為

(10) make

,

,

, then formula (9) can be rewritten as

(10)

，PID輸出結果PID _out等於相移量減

，再與相移量上下限作比較，若輸出結果小於下限相移量或大於上限相移量，則輸出結果分別等於下限或上限值，最後將其結果輸出至PWM產生器。 The incremental PID program flow is shown in Figure 15. The output command value is subtracted from the sampled value to obtain an error amount e(n), and then compared with the previous error amount e(n-1) and the previous two error amounts Substituting e(n-2) into formula (9) for calculation, A, _B , and C can be obtained, and then multiplied by K _P , KI, and K _D in sequence, and then added to obtain the output variation

, the PID output result PID _out is equal to the phase shift minus

, and then compared with the upper and lower limits of the phase shift amount, if the output result is less than the lower limit phase shift amount or greater than the upper limit phase shift amount, the output result is equal to the lower limit or upper limit value respectively, and finally the result is output to the PWM generator.

4. Experimental results and analysis

4.1 PWM dimming measurement

The control group in this case uses the digital PWM control mode to drive the LED, and tests the input power and illuminance values at intervals of 10% of the duty cycle. Figure 16a-16c shows the digital PWM dimming duty cycle of 10%, 50% and 100%. Waveform diagram, the upper part is the voltage waveform of the dimming command, and the lower part is the current flowing through the LED; the experimental data of each dimming command in Table 3, the subsequent measurement of the five-stage dimming method will be based on the illuminance in Table 3, with for a fair comparison. Table 3. Experimental data of digital PWM dimming for each illuminance PWM Duty (%) Output voltage (V) Output current (A) output power(W) Illumination (Lux) Photoelectric efficiency (Lux/W) 10 40 1.11 44.4 6230 140.32 20 40 2.13 85.2 11621 136.40 30 40 3.20 128.0 17752 138.69 40 40 4.25 170.0 23651 139.12 50 40 5.30 212.0 29532 139.30 60 40 6.35 254.0 35506 139.79 70 40 7.40 296.0 41237 139.31 80 40 8.46 338.4 47000 138.89 90 40 9.50 380.0 52820 139.00 100 40 10.5 420.0 58410 139.07

4.2 Five-stage current dimming measurement

Figures 17a-17c are waveform diagrams of the five-stage current dimming method at different equivalent dimming illuminances, the upper part is the voltage waveform of the dimming command, and the lower part is the waveform of the forward current of the LED. Table 4 shows the experimental data of each equivalent illuminance, and the output power of the converter is tested at the interval of the equivalent illuminance of every 10% dimming command of the digital PWM dimming method. Table 5 shows the experimental data of each equivalent output power, taking the output power of every 10% dimming command of the digital PWM dimming method as the interval to test the illuminance value. Table 4. Experimental data of five-stage current dimming and PWM dimming Output voltage (V) Output current (A) output power(W) Illumination (Lux) Photoelectric efficiency (Lux/W) 40 0.94 37.6 6240 165.96 40 1.82 72.8 11685 160.51 40 2.80 112.0 17764 158.61 40 3.80 152.0 23762 156.33 40 4.90 196.0 29731 151.69 40 5.97 238.8 35560 149.91 40 7.13 285.2 41745 146.37 40 8.30 332.0 47593 143.35 40 9.30 372.0 53000 142.47 40 10.50 420.0 58410 139.07 Table 5. Experimental data of five-stage current dimming with the same output power as PWM dimming Average current (A) Output voltage (V) output power(W) Illumination (Lux) Photoelectric efficiency (Lux/W) 1.11 40 44.4 7265 163.63 2.13 40 85.2 13672 160.47 3.25 40 130.0 20451 157.32 4.20 40 168.0 25953 154.48 5.34 40 213.6 32081 150.19 6.38 40 255.2 37715 147.79 7.39 40 295.6 43024 145.55 8.49 40 339.6 48512 142.85 9.53 40 381.2 53741 140.98 10.50 40 420.0 58410 139.07

4.3 Photoelectric conversion efficiency comparison

In this section, according to the results of Table 3, Table 4, and Table 5, the illuminance curve and photoelectric conversion efficiency comparison chart of digital PWM dimming and five-stage current dimming are drawn. Figure 18 is a comparison chart of photoelectric conversion efficiency between digital PWM dimming and five-stage current dimming. Figure 19 is a schematic diagram of the illuminance-current curve and the calculation method of the improvement effect. At the same illuminance, the power difference between point A and point B divided by the power value of point B is the percentage of output power reduction (improvement) of the LED drive circuit; at the same When the LED drive circuit outputs power, the illuminance difference between point C and point D divided by the illuminance value at point D is the illuminance increase (improvement) percentage. Table 6 shows the improvement effect of the five-stage current dimming method in the full control stage. Table 6. The improvement effect of the five-stage current dimming method in the full control stage Illumination (Lux) Drive circuit output power reduction (%) Drive output power (W) Illumination increase (%) 6240 15.32 44.4 16.61 11685 14.55 85.2 15.00 17764 12.50 130.0 15.20 23762 10.59 168.0 9.73 29731 7.55 213.6 8.63 35560 5.98 255.2 6.22 41745 3.70 295.6 4.33 47593 1.89 339.6 3.22 53000 2.11 381.2 1.40 average output power improvement 8.2% Illumination Average Improvement 8.9%

V. Conclusion

This case proposes a multi-stage current dimming method with high luminous efficiency, and successfully implements it in the digital signal processor, so that the LED drive circuit can increase the illuminance through the control strategy without increasing the output power, and then according to the actual To verify its correctness and feasibility. This multi-stage dimming method uses changing the current detection resistor of the linear constant current circuit to set the multi-stage forward conduction current value, and uses the duty cycle ratio of the dimming command to control the upper and lower currents to adjust the average value of the LED forward conduction current to achieve the illuminance. The multi-stage current dimming method can make the LED illuminance-current curve close to its original light source characteristics, so its luminous efficiency will be higher than the digital PWM dimming method that makes the LED illuminance-current curve tend to be linear.

With the design disclosed above, the present invention has the following advantages:

1. The LED driving system with high light conversion efficiency of the present invention can improve the luminous efficiency of the LED module through a multi-stage PWM current modulation scheme.

2. In the implementation of the LED drive system with high light conversion efficiency of the present invention at 480 W, compared with the general digital PWM dimming method: under the same illuminance, the output power of the drive circuit is reduced by 8.2% on average; When the output power of the circuit is the same, the illuminance is increased by 8.9% on average.

What is disclosed in this case is a preferred embodiment. For example, any partial changes or modifications derived from the technical ideas of this case and easily deduced by those who are familiar with the technology are within the scope of the patent right of this case.

To sum up, regardless of the purpose, means and efficacy of this case, it shows that it is very different from the conventional technology, and its first invention is practical, and it does meet the patent requirements of the invention. I implore your review committee to understand it clearly and grant a patent as soon as possible. Society is for the Most Prayer.

100: full bridge switch circuit 110: Capacitor-inductor series circuit 120: Transformer 130: the first diode 140: second diode 150: the first inductance 160: Second inductance 170: output capacitance 180: LED load 181: LED module 182: Amplifier 183: NMOS transistor 184: Current source 184a1: NMOS transistor 184a2: resistance 184b1: NMOS transistor 184b2: resistance 184c1: NMOS transistor 184c2: resistance 184d1: NMOS transistor 184d2: resistance 184e1: NMOS transistor 184e2: resistance 185: Current sensor 190: Voltage feedback circuit 191: Voltage divider circuit 192: Optical coupling circuit 200: control unit 201: Analog to Digital Converter 202: Filter operation function module 203:Proportional-integral-differential calculation function module 204: Pulse Width Modulation Module 210: Gate driver

FIG. 1 shows the curves of relative illuminance, current and temperature of a conventional LED. FIG. 2 is a block diagram of an embodiment of an LED driving system with high light conversion efficiency according to the present invention. FIG. 3 shows the topology of a phase-shifted full-bridge power stage circuit. FIG. 4 shows waveforms of main operating points of the phase-shifted full-bridge power stage circuit shown in FIG. 3 . FIG. 5 shows a linear steady flow structure adopted by the present invention. Figure 6 shows an LED forward current for conventional digital PWM dimming. 7a-7b respectively illustrate the first-stage dimming and the second-stage dimming of the multi-stage current dimming LED forward current used in the present invention. FIG. 8 shows a comparison diagram of illuminance-current curves between conventional digital PWM dimming and two-stage current dimming. FIG. 9 shows a dimming curve of the five-stage current dimming method of the present invention. FIG. 10 shows a linear current stabilizing circuit structure adopted in the five-stage current dimming method of the present invention. FIG. 11 is a schematic diagram of an illumination measurement environment for verifying the effectiveness of the present invention. FIG. 12 shows a flowchart of an embodiment of the system firmware of the present invention. FIG. 13 shows a flowchart of an ADC interrupt subroutine of the system firmware in FIG. 12 . FIG. 14 is a flow chart of the five-stage current dimming of the system firmware in FIG. 12 . FIG. 15 shows the incremental PID control flow chart of the ADC interrupt subroutine in FIG. 13 . 16a-16c show different output current waveforms under different duty cycles (10%, 50%, 100%) of an existing digital PWM dimming scheme. 17a-17c show the different output current waveforms of the high light conversion efficiency LED driving system of the present invention under different duty cycles (10%, 50%, 100%). FIG. 18 shows the photoelectric conversion efficiency comparison between the existing digital PWM dimming scheme and the five-stage current dimming scheme of the present invention. FIG. 19 is a schematic diagram of the illuminance-current curve and the calculation method of the improvement effect of the conventional digital PWM dimming scheme and the five-stage current dimming scheme of the present invention.

100: full bridge switch circuit

110: Capacitor-inductor series circuit

120: Transformer

130: the first diode

140: second diode

150: the first inductance

160: Second inductance

170: output capacitance

180: LED load

181: LED module

182: Amplifier

183: NMOS transistor

184: Current source

184a1: NMOS transistor

184a2: resistance

184b1: NMOS transistor

184b2: resistance

184c1: NMOS transistor

184c2: resistance

184d1: NMOS transistor

184d2: resistance

184e1: NMOS transistor

184e2: resistance

185: Current sensor

190: Voltage feedback circuit

191: Voltage divider circuit

192: Optical coupling circuit

200: control unit

201: Analog to Digital Converter

202: Filter operation function module

203:Proportional-integral-differential calculation function module

204: Pulse Width Modulation Module

210: Gate driver

Claims (6)

A LED drive system with high light conversion efficiency, which has: a full bridge switch circuit, with: two input terminals for coupling with the positive and negative terminals of an input voltage, and four control terminals for respectively connecting with a first switch control signal, A second switch control signal, a third switch control signal and a fourth switch control signal are coupled; a first output terminal is coupled with the positive terminal when the first switch presents an action potential and the second switch presents a second output terminal is coupled to the positive terminal when the third switch exhibits an active potential and is coupled to the negative terminal when the fourth switch exhibits an active potential; a capacitance-inductance series circuit, one end of which is coupled to the first output end of the full-bridge switch circuit; a transformer having a main coil and a secondary coil, the main coil being connected in parallel with a magnetizing inductance and one end It is coupled with the other end of the capacitance-inductance series circuit, and its other end is coupled with the second output end of the full bridge switch circuit. The secondary coil has a first output end and a second output end. output end; a first diode having a first anode and a first cathode, the first anode is coupled to a voltage reference end, the first cathode is connected to the first output end of the secondary coil Coupling; a second diode having a second anode and a second cathode, the second anode is coupled to the voltage reference end, the second cathode is coupled to the second output end of the secondary coil coupling; a first inductor, coupled between the first output end of the secondary coil and a voltage output end; a second inductor, coupled between the second output end of the secondary coil and the voltage between the output terminals; an output capacitor, coupled between the voltage output terminal and the voltage reference terminal; an LED load, coupled between the voltage output terminal and the voltage reference terminal, consisting of an LED module, A voltage stabilizing circuit, a group of current sources and a current sensor are connected in series, wherein the voltage stabilizing circuit is used to generate a fixed voltage to bias the group of current sources, and the group of current sources has five Large gating-controllable constant current sources I ₁ , I ₂ , I ₃ , I ₄ and I ₅ , the five gating-controllable constant current sources control their current output according to five gating control signals, and the set of current sources The collection current flows through the current sensor to generate a current feedback signal; a voltage feedback circuit is used to generate a voltage feedback signal according to a voltage across the output capacitor; a control unit is used to execute a toughness The body program performs a dimming operation according to a dimming command current to make an average current of the sink current equal to the dimming command current. The dimming operation includes: performing a dimming operation according to the difference between the voltage feedback signal and a reference voltage The first negative feedback control calculation program is used to generate a first switch signal, a second switch signal, a third switch signal and a fourth switch signal; and in five current intervals (0, I ₁ ], (I ₁ ,I ₂ ], (I ₂ ,I ₃ ], (I ₃ ,I ₄ ] and (I ₄ ,I ₅ ], find out the interval of one of the dimming command currents, so that five PWM signal combinations (PWM1 ), (PWM1 ,PWM2), (PWM2,PWM3), (PWM3,PWM4), (PWM4,PWM5) selected PWM signal combination, and according to the difference between the current feedback signal and the dimming command current for a second The negative feedback control calculation program is used to generate a duty period D to determine the pulse width of each PWM signal in the selected PWM signal combination, D is a non-negative real number not greater than 1; and a gate driver is used for according to the first the switch signal, the second switch signal, the third switch signal and the fourth switch signal generate the first switch control signal, the second switch control signal, the third switch control signal and the fourth switch control signal, and The five gate control signals are generated according to the five PWM signals. According to the LED driving system with high light conversion efficiency described in item 1 of the scope of the patent application, the voltage feedback circuit includes a voltage divider circuit and an optical coupling circuit. The LED driving system with high light conversion efficiency as described in item 1 of the scope of the patent application, wherein the control unit includes an analog-to-digital converter to perform analog-to-digital conversion operations on the voltage feedback signal and the current feedback signal to correspond to A first input digital signal and a second input digital signal are generated. The LED driving system with high light conversion efficiency as described in item 3 of the scope of the patent application, wherein the control unit includes a filtering operation module to perform filtering operation on the first input digital signal and the second input digital signal to generate corresponding A third input digital signal and a fourth input digital signal. The LED driving system with high light conversion efficiency as described in item 4 of the scope of the patent application, wherein the control unit includes a proportional-integral-differential calculation function module to perform the first negative feedback control calculation on the third input digital signal program, and execute the second negative feedback control calculation program on the fourth input digital signal. The LED driving system with high light conversion efficiency as described in item 1 of the scope of the patent application, wherein the control unit includes a pulse width modulation module to generate the first switching signal, the second switching signal, and the third switching signal , the fourth switch signal and the five PWM signals.

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