WO2021128743A1

WO2021128743A1 - Led constant current drive system and method

Info

Publication number: WO2021128743A1
Application number: PCT/CN2020/094377
Authority: WO
Inventors: 刘军; 吴泉清
Original assignee: 华润矽威科技（上海）有限公司
Priority date: 2019-12-23
Filing date: 2020-06-04
Publication date: 2021-07-01
Also published as: EP3863379A9; CN113099579B; CN113099579A; EP3863379A1; EP3863379A4

Abstract

An LED constant current drive system and method. The system comprises: a constant current control module (21), which is connected to the negative electrode of an LED load; an energy storage capacitor (Co), which discharges to the LED load when the bus voltage is less than the voltage of the energy storage capacitor (Co); a discharging voltage detection module (22), which determines the magnitude of the discharging voltage of the energy storage capacitor (Co) on the basis of the voltage of the negative electrode of the LED load so as to obtain a control signal; a bus voltage detection module (23), which detects the bus voltage to obtain a first detected voltage; and a charging current control module (24), which adjusts the charging current of the energy storage capacitor (Co) on the basis of the control signal and the first detected voltage. When the bus voltage is less than the turn-on voltage of an LED, the energy storage capacitor (Co) discharges. When the bus voltage is greater than the turn-on voltage of the LED, the bus voltage supplies power to the LED load and simultaneously charges the energy storage capacitor (Co). When the bus voltage is less than the voltage of the energy storage capacitor (Co), the energy storage capacitor (Co) discharges. Therefore, it is ensured that power factor and system efficiency are considered when outputting LED flicker-free.

Description

LED constant current driving system and method

Technical field

The present invention relates to the field of system design, in particular to an LED constant current driving system and method.

Background technique

Under normal circumstances, the overall efficiency of a single-segment linear LED driver is determined by the LED conduction voltage and the input voltage, which satisfies:

Among them, V _LED is the LED turn-on voltage, and V _IN is the input voltage.

Figure 1 shows a common single-segment linear LED drive structure 1. The AC input voltage AC IN is converted into an input voltage V _IN by the rectifier module 11, the positive pole of the series LED is connected to the output terminal of the rectifier module 11, and the negative pole of the series LED is connected The constant current control chip 12, the sampling end of the constant current control chip 12 is grounded via the sampling resistor 13, and the adjustable module 14 is connected in parallel to both ends of the rectifier module 11. Since the number of LEDs in series is fixed, when the input voltage V _IN exceeds the LED forward voltage drop V _LED , the excess voltage is borne by the constant current control tube below the LED (set in the constant current control chip 12, not shown in the figure) , V _IN -V _LED is the voltage on the constant current control tube; the _{higher the input voltage V IN, the} lower the efficiency Eff of the system. The electrolytic capacitor C in the adjustable module 14 can store energy, thereby ensuring that the output LED does not flicker, but it will cause the power factor PF of the system to be low.

In order to improve the power factor PF, a switch tube can be connected in series under the input electrolytic capacitor C to control the charging voltage of the electrolytic capacitor C. When the voltage is high, it will be turned off, so that the voltage on the electrolytic capacitor C will be reduced, thereby expanding the conduction of the input current. Through angle to get a higher power factor PF. Fig. 2 is an LED driving scheme with an external switch, the switch tube N1 is connected in series with the bottom plate of the electrolytic capacitor C; Fig. 3 is an LED driving scheme with a built-in switch, the switch tube is located inside the constant current control chip 12. Not shown in the figure. The solutions shown in Figure 2 and Figure 3 _{only do a simple switching action for the input voltage V IN} , that is, it can only be turned on or off, and only one direction can be selected between the high efficiency and high power factor of the system. Those who can't take account of it, cannot achieve the best combination.

Therefore, how to balance the efficiency and power factor in LED control has become one of the problems to be solved urgently by those skilled in the art.

Summary of the invention

In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide an LED constant current driving system and method to solve the problem that efficiency and power factor cannot be balanced in the prior art.

In order to achieve the above objectives and other related objectives, the present invention provides an LED constant current drive system, the LED constant current drive system at least includes:

LED load, its positive pole is connected to the bus voltage;

A constant current control module, connected to the negative electrode of the LED load, for performing constant current control on the LED load;

An energy storage capacitor, the upper plate of which is connected to the anode of the LED load, and is used to discharge the LED load when the bus voltage is less than the voltage on the energy storage capacitor;

A discharge voltage detection module, connected to the negative electrode of the LED load, judges the discharge voltage of the energy storage capacitor based on the negative electrode voltage of the LED load, and obtains a control signal;

A bus voltage detection module, which detects the bus voltage to obtain a first detection voltage;

The charging current control module is connected to the discharge voltage detection module, the output terminal of the bus voltage detection module and the bottom plate of the energy storage capacitor, and adjusts the energy storage based on the control signal and the first detection voltage The charging current of the capacitor.

In order to achieve the above objectives and other related objectives, the present invention provides an LED constant current driving method. The LED constant current driving method at least includes:

When the bus voltage is less than the turn-on voltage of the LED, the energy storage capacitor discharges the LED load, and performs constant current control on the LED load based on the constant current control module;

When the bus voltage is greater than the turn-on voltage of the LED, the bus voltage supplies power to the LED load, and performs constant current control on the LED load based on the constant current control module; at the same time, the bus voltage is the Charging the energy storage capacitor;

When the bus voltage is less than the voltage of the energy storage capacitor, the energy storage capacitor discharges the LED load, and performs constant current control on the LED load based on the constant current control module.

The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, purposes and advantages of this application will become apparent from the description, drawings and claims.

Description of the drawings

Figure 1 shows a schematic diagram of a single-segment linear LED drive structure in the prior art.

Fig. 2 shows a schematic diagram of an LED driving scheme of an external switch in the prior art.

Fig. 3 shows a schematic diagram of an LED driving scheme with a built-in switch in the prior art.

FIG. 4 shows a schematic diagram of the structure of the LED constant current driving system of the present invention.

FIG. 5 shows a schematic diagram of the waveform of the LED constant current driving method of the present invention.

Detailed ways

The following describes the implementation of the present invention through specific specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

Please refer to Figure 4 to Figure 5. It should be noted that the illustrations provided in this embodiment only illustrate the basic idea of the present invention in a schematic manner. The figures only show the components related to the present invention instead of the number, shape, and shape of the components in actual implementation. For the size drawing, the type, quantity, and proportion of each component can be changed at will during actual implementation, and the component layout type may also be more complicated.

Example one

As shown in FIG. 4, this embodiment provides an LED constant current driving system 2, and the LED constant current driving system 2 includes:

LED load, constant current control module 21, energy storage capacitor Co, discharge voltage detection module 22, bus voltage detection module 23, and charging current control module 24.

As shown in Figure 4, the LED load is connected to the bus voltage Vin.

Specifically, in this embodiment, the bus voltage Vin is provided by a rectifier module 25, and the rectifier module 25 rectifies the alternating current power AC to obtain the bus voltage Vin. The rectifier module 25 includes a rectifier bridge structure BD1 and a fuse F1. The rectifier bridge structure BD1 includes two groups of diodes connected in parallel, and each diode group includes two diodes connected in series. The AC power source AC is connected through the fuse F1. Between the two diodes of each diode group. The bus voltage Vin is the rectified voltage after sinusoidal voltage rectification.

Specifically, the anode of the LED load is connected to the output terminal of the rectifier module 25, the LED load includes a plurality of LED lights connected in series, and the LED load may also be a series-parallel structure of multiple LED lights. This embodiment is limited. When the voltage at both ends of the LED load reaches its turn-on voltage, the LEDs in the LED load light up and play a role of lighting.

As shown in FIG. 4, the constant current control module 21 is connected to the negative electrode of the LED load, and is used to perform constant current control on the LED load.

Specifically, in this embodiment, the constant current control module 21 includes: a first power switch Q1, a first sampling unit 211, and a first operational amplification unit 212. The drain of the first power switch Q1 is connected to the negative electrode of the LED load, the source is grounded through the first sampling unit 211, and the gate is connected to the output terminal of the first operational amplifier unit 212. As an example, the first sampling unit 211 in this embodiment includes a first sampling resistor Rcs, one end of the first sampling resistor Rcs is connected to the source of the first power switch Q1, and the other end is grounded. The inverting input terminal of the first operational amplifying unit 212 is connected to the source of the first power switch Q1, the non-inverting input terminal is connected to the reference voltage Vref, and the output terminal is connected to the gate of the first power switch Q1, The first operational amplifying unit 212 compares the sampling voltage of the source of the first power switch Q1 with the reference voltage Vref to control the current flowing through the LED load, thereby realizing constant current control.

It should be noted that the reference voltage Vref is an internal fixed value or externally provided. When the reference voltage Vref is an internal fixed value, the resistance of the first sampling resistor Rcs can be changed to adjust the LED load. Output current. The connection relationship between the input terminal and the output terminal of the first operational amplifier unit 212 can be adjusted, and the same logical relationship can be realized by adding an inverter, which is not limited to this embodiment.

As an implementation of the present invention, the constant current control module 21 further includes a dimming unit 213. The input end of the dimming unit 213 receives the dimming control signal DIM, and the output end is connected to the first operational amplifier unit 212. Based on the dimming control signal DIM, adjust the magnitude of the reference voltage Vref to realize dimming control. The dimming control signal DIM includes but is not limited to an analog signal or a pulse width modulation signal (PWM), which will not be repeated here.

It should be noted that any system structure that can realize constant current control is applicable to the present invention and is not limited to this embodiment.

As shown in Figure 4, the upper plate of the energy storage capacitor Co is connected to the anode of the LED load. When the bus voltage Vin is less than the voltage VCo on the energy storage capacitor Co, the energy storage capacitor Co The LED load is discharged.

Specifically, the upper plate of the energy storage capacitor Co is connected between the rectifier module 25 and the LED load, and the lower plate is connected with the charging current control module 24. When the bus voltage Vin is greater than the storage When the voltage VCo on the energy capacitor Co, the bus voltage Vin charges the energy storage capacitor Co, and at the same time, the bus voltage Vin supplies power to the LED load. When the bus voltage Vin is less than the voltage VCo on the energy storage capacitor Co, the energy storage capacitor Co supplies power to the LED load.

As shown in FIG. 4, the discharge voltage detection module 22 is connected to the negative electrode of the LED load, and the discharge voltage of the energy storage capacitor Co is determined based on the negative electrode voltage of the LED load to obtain a control signal.

Specifically, the discharge voltage detection module 22 includes: a first detection unit 221 and a comparison unit 222. The detection unit 221 is connected to the negative electrode of the LED load, and detects the negative electrode voltage of the LED load to obtain a second detection voltage. The comparison unit 222 is connected to the output terminal of the detection unit 221, and determines the magnitude of the discharge voltage of the energy storage capacitor Co based on the second detection voltage.

More specifically, in this embodiment, the detection unit 221 includes a first resistor R1 and a second resistor R2, and the first resistor R1 and the second resistor R2 are connected in series between the negative electrode of the LED load and the ground. In time, the second detection voltage is obtained by voltage division.

More specifically, the comparison unit 222 includes a first comparator CMP1 and a second comparator CMP2. The non-inverting input terminal of the first comparator CMP1 is connected to the second detection voltage, and the inverting input terminal is connected to the first preset voltage Ref1 to output a first control signal. When the second detection voltage is greater than the first preset voltage Ref1, the first comparator CMP1 outputs a high level, and the first control signal is valid; when the second detection voltage is less than the first When the voltage Ref1 is preset, the first comparator CMP1 outputs a low level, and the first control signal is invalid. The inverting input terminal of the second comparator CMP2 is connected to the second detection voltage, and the non-inverting input terminal is connected to the second preset voltage Ref2 to output a second control signal. When the second detection voltage is greater than the second preset voltage Ref2, the second comparator CMP2 outputs a low level, and the second control signal is invalid; when the second detection voltage is less than the second When the voltage Ref2 is preset, the second comparator CMP2 outputs a high level, and the second control signal is valid. Wherein, the first preset voltage Ref1 is greater than the second preset voltage Ref2.

It should be noted that the connection relationship between the input terminals and output terminals of the first comparator CMP1 and the second comparator CMP2 can be adjusted, and the same logic relationship can be realized by adding an inverter, which is not limited to this embodiment .

As shown in FIG. 4, the bus voltage detection module 23 is connected to the bus voltage Vin, and detects the bus voltage Vin to obtain the first detection voltage V _LN .

Specifically, in this embodiment, the bus voltage detection module 23 includes a third resistor R3 and a fourth resistor R4, and the third resistor R3 and the fourth resistor R4 are connected in series with the output terminal of the rectifier module 25 Between the ground and the ground, the first detection voltage V _{LN is} obtained by voltage division. The bus voltage detection module 23 may be integrated inside the chip or arranged outside the chip.

As shown in FIG. 4, the charging current control module 24 is connected to the discharge voltage detection module 22, the output terminal of the bus voltage detection module 23, and the lower plate of the energy storage capacitor Co, based on the control signal and The first detection voltage V _LN adjusts the charging current of the energy storage capacitor Co.

Specifically, the charging current control module 24 includes a second power switch Q2, a second sampling unit 241, a compensation unit 242, a subtraction unit 243, and a second operational amplification unit 244.

More specifically, the drain of the second power switch Q2 is connected to the bottom plate of the energy storage capacitor Co, the source is grounded through the second sampling unit 241, and the gate is connected to the second operational amplifying unit 244 The output terminal of is used to adjust the charging current of the energy storage capacitor Co. As an example, the second sampling unit 241 in this embodiment includes a second sampling resistor Rs, one end of the second sampling resistor Rs is connected to the source of the second power switch Q2, and the other end is grounded.

More specifically, the input terminal of the compensation unit 242 is connected to the discharge voltage detection module 22, and a corresponding compensation voltage Vcomp is generated based on the output signal of the discharge voltage detection module 22. In this embodiment, the compensation unit 242 includes a compensation voltage generating circuit 242a, a compensation capacitor Ccomp, a first current source I1 and a second current source I2. The compensation voltage generating circuit 242a is connected to the upper plate of the compensation capacitor Ccomp, and the lower plate of the compensation capacitor Ccomp is grounded. One end of the first current source I1 is grounded, the other end is connected to the upper plate of the compensation capacitor Ccomp, and the control end is connected to the first control signal. When the first control signal is valid, the first current source I1 Is turned on to discharge the compensation capacitor Ccomp; one end of the second current source I2 is connected to the upper plate of the compensation capacitor Ccomp, the other end is connected to the working voltage VDD, and the control end is connected to the second control signal. When the second control signal is valid, the second current source I1 is turned on to charge the compensation capacitor Ccomp; the compensation voltage Vcomp is adjusted based on the charge and discharge of the first current source I1 and the second current source I2 Value. The compensation capacitor Ccomp can be arranged outside the chip, or integrated into the chip using digital filtering technology to reduce external components and simplify the system.

More specifically, the subtraction unit 243 is connected to the output terminal of the compensation unit 242 and the bus voltage detection module 23 to obtain the difference between the compensation voltage Vcopm and the first detection voltage V _LN .

More specifically, the inverting input terminal of the second operational amplifier unit 244 is connected to the source of the second power switch Q2, the non-inverting input terminal is connected to the output terminal of the subtracting unit 243, and the output terminal is connected to the second power switch Q2. The gate of the second power switch Q2, the second operational amplifying unit 244 compares the sampling voltage of the source of the second power switch Q2 with the output voltage of the subtracting unit 243 to realize the comparison of the energy storage capacitor Adjustment of the charging current of Co.

It should be noted that the connection relationship between the input terminal and the output terminal of the second operational amplifying unit 244 can be adjusted, and the same logical relationship can be realized by adding an inverter, which is not limited to this embodiment.

As an implementation manner of the present invention, the compensation unit 242 further includes a third comparator CMP3 and a third current source I3. The non-inverting input terminal of the third comparator CMP3 is connected to the gate of the first power switch Q1, and the inverting input terminal is connected to the third preset voltage Ref3 to output a third control signal; when the first power switch When the gate voltage of the tube Q1 is greater than the third preset voltage Ref3, a high level is output, and the third control signal is valid. One end of the third current source I3 is connected to the upper plate of the compensation capacitor Ccomp, the other end is connected to the operating voltage VDD, and the control end is connected to the output end of the third comparator CMP3; when the third control signal When valid, the third current source is turned on.

It should be noted that the connection relationship between the input terminal and the output terminal of the third comparator CMP3 can be adjusted, and the same logical relationship can be realized by adding an inverter, which is not limited to this embodiment.

As an implementation of the present invention, the LED constant current drive system further includes a working voltage generating module 26, which is connected to the bus voltage Vin, and based on the bus voltage Vin, is the LED constant current The driving system provides working voltage VDD.

The LED constant current drive system of the present invention eliminates the problem of LED flicker based on constant current control. The energy storage capacitor Co supplies power to the LED during the bus voltage valley period, and reduces the charging current of the energy storage capacitor Co when the bus voltage is too high, thereby Take into account the power factor and system efficiency.

Example two

As shown in Figures 4 and 5, this embodiment provides an LED constant current driving method. In this embodiment, the LED constant current driving system of the first embodiment is used to implement the LED constant current driving method of the present invention. In actual use Any hardware circuit or software code that can realize the LED constant current driving method of the present invention is applicable. The LED constant current driving method includes:

When the bus voltage Vin is less than the turn-on voltage of the LED, the energy storage capacitor Co discharges the LED load, and the constant current control module 21 performs constant current control on the LED load.

Specifically, during normal operation, the voltage on the energy storage capacitor Co will not drop very low, so during the valley of the bus voltage Vin, power can be supplied to the inside of the chip. When the bus voltage Vin is less than the turn-on voltage of the LED load, the bus voltage Vin is not enough to turn on the LED load. At this time, the energy storage capacitor Co discharges the LED load, so that all The LED load is lit, and the constant current control module 21 performs constant current control on the current flowing through the LED load.

Specifically, the constant current control module 21 detects the source voltage of the first power switch tube Q1, and compares the source voltage of the first power switch tube Q1 with a reference voltage Vref, and the comparison result is used to control the source voltage of the first power switch tube Q1. The gate of the first power switch Q1 further realizes constant current control to ensure that the current flowing through the LED load is constant to eliminate stroboscopic flicker.

It should be noted that the reference voltage Vref is an internally preset value, the LED output current is adjusted by changing the resistance of the first sampling resistor Rcs, and the reference voltage Vref is an adjustable value provided externally.

As an implementation manner of the present invention, the constant current control module 21 further adjusts the value of the reference voltage Vref based on the dimming control signal DIM to implement dimming control. The dimming control signal DIM includes but is not limited to an analog signal or a PWM signal.

When the bus voltage Vin is greater than the turn-on voltage of the LED, the bus voltage Vin supplies power to the LED load, and performs constant current control on the LED load based on the constant current control module 21; at the same time, the bus voltage Vin charges the energy storage capacitor Co.

Specifically, the bus voltage Vin gradually increases. When the bus voltage Vin is greater than the turn-on voltage of the LED, the bus voltage Vin supplies power to the LED load and charges the energy storage capacitor Co. Through the second power switch Q2, the second operational amplifying unit 244, and the second sampling resistor Rs control the charging current of the energy storage capacitor Co, thereby expanding the conduction angle of the input current and improving the power factor.

Specifically, in this embodiment, the charging current of the energy storage capacitor is adjusted based on the negative electrode voltage of the LED load and the bus voltage Vin. The bus voltage detection module 23 detects the bus voltage Vin, and reduces the charging current of the energy storage capacitor Co to zero when the bus voltage Vin is too high, thereby reducing the loss of the second power switch Q2 , Improve the overall efficiency of the system. In order to ensure the highest system efficiency, the discharge voltage of the energy storage capacitor Co should not be too high, and in order to keep the output LED current constant, the discharge voltage of the energy storage capacitor Co should not be too low. This embodiment is judged by the LED negative voltage The energy storage capacitor Co discharge voltage (VOUT=Vin-VLED). More specifically, the LED negative voltage is detected by the detection unit 221, and when the detected voltage is higher than the first preset voltage Ref1, it indicates that the discharge voltage of the energy storage capacitor Co is relatively high, and the first comparator CMP1 The first constant current source I1 is controlled to be turned on, the compensation capacitor Ccomp is discharged, and the compensation voltage Vcomp is reduced to reduce the charging current of the energy storage capacitor Co, thereby reducing the energy storage capacitor Co Discharge voltage; when the detected voltage is lower than the second preset voltage Ref2, it means that the discharge voltage of the energy storage capacitor Co is relatively low. The second comparator CMP2 controls the second constant current source I2 to turn on, The compensation capacitor Ccomp is charged to increase the compensation voltage Vcomp to increase the charging current of the energy storage capacitor Co, thereby increasing the discharge voltage of the energy storage capacitor Co. In order to optimize system performance, where Ref1>Ref2. After the loop adjustment of the compensation unit 242, it is ensured that the lowest level of the LED negative voltage after the constant current of the LED current will not be too high, which will result in the loss of system efficiency.

As an implementation of the present invention, in order to filter the power frequency ripple, the compensation capacitor Ccomp is relatively large and the loop response is relatively slow. When the output voltage is relatively low, the LED current will decrease. At this time, the first power The gate voltage of the switching tube Q1 will rise relatively high (especially the compensation voltage Vcomp is relatively low when it is just started), and the third comparator CMP3 detects that the gate voltage of the first power switching tube Q1 exceeds the first power switching tube Q1. When the voltage Ref3 is three presets, the third constant current source I3 is controlled to be turned on (in this embodiment, the current flowing through the third current source is greater than the current flowing through the second current source I1>I2) , To quickly increase the compensation voltage Vcomp, increase the charging current of the energy storage capacitor Co, and quickly increase the discharge voltage of the energy storage capacitor Co.

When the bus voltage Vin is less than the voltage of the energy storage capacitor Co, the energy storage capacitor Co discharges the LED load, and performs constant current control on the LED load based on the constant current control module 21.

Specifically, the bus voltage Vin gradually decreases after reaching a peak value. When the bus voltage Vin is less than the voltage of the energy storage capacitor Co, the energy storage capacitor Co discharges the LED load until the bus voltage Vin is again greater than the LED turn-on voltage or the voltage on the energy storage capacitor Co is less than the LED turn-on voltage.

Figure 5 shows the working waveform diagram of the LED constant current driving method of the present invention:

As shown in Figure 5, at t0, the bus voltage Vin starts to rise from zero, Vin<VLED, where VLED is the turn-on voltage of the LED load. At this time, the energy storage capacitor Co discharges the LED load, and the energy storage capacitor The lowest voltage at which the voltage VCo discharges on Co is VLED, the current ICo of the energy storage capacitor Co during discharge is a constant value, the current flowing through the LED load is a constant value, and the negative voltage VLED of the LED load gradually Decrease (the lowest value is VLED-_min).

As shown in FIG. 5, as the bus voltage Vin rises, at time t1, the bus voltage Vin is greater than the turn-on voltage VLED of the LED load, and the bus voltage Vin supplies power to the LEDs while simultaneously supplying energy to the energy storage. The capacitor Co is charged, and the current Iin provided by the bus voltage Vin includes the charging current of the energy storage capacitor Co and the constant current of the LED load. The charging current is determined by the compensation voltage Vcomp and the detection voltage of the bus voltage Vin. The charging current of the energy storage capacitor Co shows a downward trend as the bus voltage Vin increases. In this embodiment, The charging current of the energy storage capacitor Co first decreases and then increases. As the energy storage capacitor Co voltage VCo is charged to the highest voltage VCo_max, the energy storage capacitor Co stops charging. During this process, the negative voltage VLED- of the LED load gradually increases.

As shown in Figure 5, the bus voltage Vin begins to decrease after reaching a peak value. At time t2, the bus voltage Vin is less than the voltage VCo of the energy storage capacitor Co (in this embodiment, the energy storage capacitor The voltage of Co is the highest voltage VCo_max, and for ease of illustration, when different power frequency cycles VCo_max adopt the same level in the figure), the energy storage capacitor Co starts to discharge the LED load until the end of a power frequency cycle at time t3. In this power frequency period, the shadow area of the charging current A of the energy storage capacitor Co in the figure is equal to the shadow area of the discharge current B, where C is the shadow area of the current provided by the bus voltage to the LED.

As shown in Figure 5, t4～t7 and t8～t11 are power frequency cycles of different bus voltages. The charging current changes with the change of the bus voltage. The minimum charging current can drop to zero when the input voltage is high, and passes through the loop. After the circuit is adjusted, the minimum value of the negative electrode voltage of the LED load remains unchanged, VLED-_min, and the loss of the second power switch tube Q2 is minimized while keeping the output LED current constant.

As shown in Figure 5, the present invention reduces the charging current of the energy storage capacitor Co when the bus voltage Vin is high by detecting the bus voltage Vin, thereby reducing the charging power consumption of the second power switch Q2 and improving the overall efficiency of the system . Adjusting the voltage division ratio of the third resistor R3 and the fourth resistor R4 can adjust the size of the high-voltage drop current. The larger the peak value of the bus voltage Vin, the smaller the peak value of the charging current of the energy storage capacitor Co, so that in the system There is a compromise between efficiency and power factor.

In summary, the present invention provides an LED constant current driving system and method, including: an LED load, the positive electrode of which is connected to the bus voltage; a constant current control module, connected to the negative electrode of the LED load, and is used to control the LED load. Perform constant current control; an energy storage capacitor, the upper plate of which is connected to the anode of the LED load, and is used to discharge the LED load when the bus voltage is less than the voltage on the energy storage capacitor; a discharge voltage detection module, Connect the negative electrode of the LED load, determine the discharge voltage of the energy storage capacitor based on the negative voltage of the LED load, and obtain a control signal; a bus voltage detection module detects the bus voltage to obtain the first detection voltage; charging The current control module is connected to the output terminal of the discharge voltage detection module and the bottom plate of the energy storage capacitor, and adjusts the charging current of the energy storage capacitor based on the control signal and the first detection voltage. When the bus voltage is less than the turn-on voltage of the LED, the energy storage capacitor discharges the LED load and performs constant current control on the LED load based on the constant current control module; when the bus voltage is greater than the turn-on voltage of the LED, the The bus voltage supplies power to the LED load, and performs constant current control on the LED load based on the constant current control module; at the same time, the bus voltage charges the energy storage capacitor; when the bus voltage is less than the energy storage When the voltage of the capacitor is reached, the energy storage capacitor discharges the LED load, and performs constant current control on the LED load based on the constant current control module. The LED constant current drive system and method of the present invention detect the negative electrode voltage of the LED to control the charging current of the energy storage capacitor, and control the constant current power switch tube to have the lowest loss under the condition of ensuring that the output LED does not flicker; The grid voltage speeds up the loop response speed to ensure fast startup; at the bottom of the input voltage valley, the energy storage capacitor supplies power to the LED. At the same time, the charging current of the energy storage capacitor is reduced when the input voltage is high, and both power factor and system efficiency are considered. , A compromise can be considered; and the peripheral system of the LED constant current driving system of the present invention is the simplest, and the system cost is low. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial value.

The above-mentioned embodiments only exemplarily illustrate the principles and effects of the present invention, but are not used to limit the present invention. Anyone familiar with this technology can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed in the present invention should still be covered by the claims of the present invention.

Claims

An LED constant current drive system, the LED constant current drive system at least includes:

LED load, its positive pole is connected to the bus voltage;

A constant current control module, connected to the negative electrode of the LED load, for performing constant current control on the LED load;

An energy storage capacitor, the upper plate of which is connected to the anode of the LED load, and is used to discharge the LED load when the bus voltage is less than the voltage on the energy storage capacitor;

A discharge voltage detection module, connected to the negative electrode of the LED load, judges the discharge voltage of the energy storage capacitor based on the negative electrode voltage of the LED load, and obtains a control signal;

A bus voltage detection module, which detects the bus voltage to obtain a first detection voltage; and

The charging current control module is connected to the discharge voltage detection module, the output terminal of the bus voltage detection module and the bottom plate of the energy storage capacitor, and adjusts the energy storage based on the control signal and the first detection voltage The charging current of the capacitor.
The LED constant current drive system according to claim 1, wherein the constant current control module comprises a first power switch tube, a first sampling unit and a first operational amplifier unit;

The drain of the first power switch tube is connected to the negative electrode of the LED load, and the source is grounded via the first sampling unit;

The input terminal of the first operational amplifier unit is respectively connected to the source of the first power switch tube and a reference voltage, and the output terminal is connected to the gate of the first power switch tube, and the sampling voltage is compared with the reference voltage. Compare to control the amount of current flowing through the LED load.
The LED constant current driving system according to claim 2, wherein the constant current control module further comprises a dimming unit connected to the first operational amplifier unit, and the dimming unit receives a dimming control signal based on the The dimming control signal adjusts the size of the reference voltage, thereby realizing dimming control.
The LED constant current driving system according to claim 3, wherein the dimming control signal is an analog signal or a pulse width modulation signal.
The LED constant current drive system according to claim 1, wherein the discharge voltage detection module includes a detection unit and a comparison unit;

The detection unit is connected to the negative electrode of the LED load, and detects the negative electrode voltage of the LED load to obtain a second detection voltage;

The comparison unit is connected to the output terminal of the detection unit, and determines the magnitude of the discharge voltage of the energy storage capacitor based on the second detection voltage.
The LED constant current driving system according to claim 5, wherein the comparison unit includes a first comparator and a second comparator;

The input terminals of the first comparator are respectively connected to the second detection voltage and the first preset voltage, and output a first control signal when the second detection voltage is greater than the first preset voltage;

The input terminals of the second comparator are respectively connected to the second detection voltage and a second preset voltage, and output a second control signal when the second detection voltage is less than the second preset voltage.
The LED constant current driving system according to claim 1, wherein the charging current control module includes a second power switch tube, a second sampling unit, a compensation unit, a subtraction unit, and a second operational amplification unit;

The drain of the second power switch tube is connected to the bottom plate of the energy storage capacitor, and the source is grounded via the second sampling unit;

The input terminal of the compensation unit is connected to the discharge voltage detection module, and a corresponding compensation voltage is generated based on the output signal of the discharge voltage detection module;

The subtraction unit is connected to the output terminal of the compensation unit and the bus voltage detection module to obtain the difference between the compensation voltage and the first detection voltage;

The input terminal of the second operational amplifier unit is connected to the output terminal of the subtraction unit and the source of the second power switch tube, and the output terminal is connected to the gate of the second power switch tube to realize the Adjustment of the charging current of the energy storage capacitor.
7. The LED constant current driving system according to claim 7, wherein the compensation unit comprises a compensation voltage generating circuit, a compensation capacitor, a first current source and a second current source;

The compensation voltage generating circuit is connected to the upper plate of the compensation capacitor, and the lower plate of the compensation capacitor is grounded;

One end of the first current source is grounded, and the other end is connected to the upper plate of the compensation capacitor;

One end of the second current source is connected to the upper plate of the compensation capacitor, and the other end is connected to a working voltage;

The control terminals of the first current source and the second current source are respectively connected to the output terminal of the discharge voltage detection module, and the compensation voltage is adjusted based on the charging and discharging of the first current source and the second current source. value.
The LED constant current driving system according to claim 8, wherein the compensation unit further comprises a third comparator and a third current source;

The input terminal of the third comparator is respectively connected to the gate of the power switch tube in the constant current control module and the third preset voltage;

One end of the third current source is connected to the upper plate of the compensation capacitor, the other end is connected to the operating voltage, and the control end is connected to the output end of the third comparator;

When the gate voltage of the power switch tube is greater than the third preset voltage, the third current source is turned on.
The LED constant current driving system according to claim 1, wherein the LED constant current driving system further comprises a working voltage generating module, the working voltage generating module is connected to the bus voltage, and based on the bus voltage, the LED Constant current drive system provides working voltage.
An LED constant current driving method, the LED constant current driving method at least includes:

When the bus voltage is less than the turn-on voltage of the LED, the energy storage capacitor discharges the LED load, and performs constant current control on the LED load based on the constant current control module;

When the bus voltage is greater than the turn-on voltage of the LED, the bus voltage supplies power to the LED load, and performs constant current control on the LED load based on the constant current control module; at the same time, the bus voltage is the Charging the energy storage capacitor;

When the bus voltage is less than the voltage of the energy storage capacitor, the energy storage capacitor discharges the LED load, and performs constant current control on the LED load based on the constant current control module.
11. The LED constant current driving method of claim 11, wherein the charging current of the energy storage capacitor is adjusted based on the negative electrode voltage of the LED load and the bus voltage.
The LED constant current driving method according to claim 12, wherein the charging current of the energy storage capacitor is adjusted based on the magnitude of the bus voltage, the greater the peak value of the bus voltage, the greater the charging current of the energy storage capacitor The smaller the peak value.
The LED constant current driving method according to claim 1, wherein when the gate voltage of the power switch tube in the constant current control module is greater than a preset voltage, the charging current of the energy storage capacitor is increased.
11. The LED constant current driving method according to claim 11, wherein the charging current of the energy storage capacitor has a trend of first decreasing and then increasing.