LED constant current driving system

Abstract

The application provides a LED constant current driving system, comprising: a voltage input module providing an input voltage; a first diode, an anode of which is connected with the input voltage, and a cathode of which is connected with an upper plate of an electrolytic capacitor and a positive pole of an LED load; a leakage current control module providing a leakage current for maintaining a thyristor conduction; a constant current control module performing adaptive ripple elimination control on a current flowing through the LED load; a charging current control module performing control on a charging current of the electrolytic capacitor to realize frequency flash elimination control of the LED load; and a minimum clamping current setting circuit. The system has high efficiency, the minimum clamping current setting circuit is simple and has low cost; the overvoltage compensation technology of a compensation loop is adopted to enable the LED output to remain without frequency flash at low input voltage; the reference voltage is adjusted when the thyristor is dimmed, and the system reliability is improved; and the functional modules are commonly controlled and can be integrated in one chip.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit design, and in particular to an LED constant current driving system. Background Technology

[0002] In LED driver applications using SCR dimming, there is a holding current requirement for the SCR to conduct. Once the input current is less than the holding current, the SCR will turn off and then restart, which will cause the LED to flicker. Therefore, an external discharge circuit is generally required to meet the holding current requirement of the SCR, so that the SCR can conduct continuously within the operating range and avoid LED flickering.

[0003] In linear LED driver SCR dimming, to achieve high system efficiency, high-voltage current reduction technology is used to reduce losses at high input voltages. At the highest input voltage, the LED current may drop below the SCR's holding current. Typically, the bleed current is turned off at this point due to system efficiency considerations. Therefore, the SCR may restart due to insufficient holding current, causing LED flickering. Thus, it is necessary to clamp the minimum current during high-voltage current reduction to ensure it is not lower than the SCR's holding current. Figure 1 As shown.

[0004] Figure 2 This is a block diagram of an existing SCR dimming LED driver application. A bleeder circuit 11 is connected to the input voltage to meet the SCR's holding current requirement. A voltage detection circuit 13 is connected to the lower plate of the electrolytic capacitor Co and receives the input voltage. A high-efficiency linear drive circuit 12 achieves constant current control of the LED based on the output signal of the voltage detection circuit 13, and the high-efficiency linear drive circuit 12 can easily achieve minimum conduction current. To meet the ERP flicker reduction requirement, a ripple reduction circuit 14 is added in series in the LED control loop to filter out the ripple of the LED output current, thus achieving flicker reduction. However, this ripple reduction circuit will lose some efficiency. Since the ripple reduction circuit 14 is superimposed on the LED output current control transistor, its reference ground cannot be shared with the LED control circuit below. Therefore, it must be made as a separate chip and then packaged with the LED control circuit chip inside the chip, increasing the chip's complexity and cost.

[0005] Figure 3 This is a block diagram of an improved SCR dimming LED driver application. The ripple reduction circuit (implemented using a high-efficiency linear drive circuit 15) and the constant current control circuit (implemented using an LED constant current control circuit 16) are separated and connected in parallel, thereby improving system efficiency. However, in this scheme, because the LED constant current circuit and the capacitor charging / discharging circuit are separate, there are two current control circuits. Furthermore, the current in the LED constant current control circuit changes with SCR dimming, making it difficult to simply implement a minimum current clamping circuit.

[0006] Therefore, how to simplify the implementation of the minimum clamping circuit while ensuring system efficiency and reducing costs has become one of the problems that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an LED constant current driving system to solve the problems of low system efficiency, high cost, and difficulty in implementing minimum current clamping circuit in the prior art.

[0008] To achieve the above and other related objectives, the present invention provides an LED constant current driving system, which includes at least: a voltage input module, a first diode, an LED load, an electrolytic capacitor, a discharge current control module, a constant current control module, and a charging current control module;

[0009] The voltage input module receives AC signals and converts the AC signals into DC input voltage;

[0010] The anode of the first diode is connected to the output terminal of the voltage input module, and the cathode is connected to the upper plate of the electrolytic capacitor and the positive terminal of the LED load.

[0011] The discharge current control module is connected to the output terminal of the voltage input module and provides the discharge current to maintain the conduction of the thyristor;

[0012] The constant current control module is connected to the negative terminal of the LED load and performs adaptive ripple-reducing control on the current flowing through the LED load.

[0013] The charging current control module is connected to the lower plate of the electrolytic capacitor and the constant current control module to control the charging current of the electrolytic capacitor to achieve flicker control of the LED load; and controls the minimum clamping current based on the output current of the LED load to ensure that the minimum clamping current is not less than the holding current of the thyristor.

[0014] Optionally, the voltage input module includes a rectifier unit and a thyristor; the AC terminal of the rectifier unit is connected to the AC signal, and the DC terminal outputs the input voltage; the thyristor is connected in series with the AC terminal of the rectifier unit.

[0015] Optionally, the charging current control module includes: a high voltage current reduction unit, a second diode, a third diode, a minimum current setting unit, a first power switch, a first resistor, a first operational amplifier, and a feedback unit;

[0016] The anode of the second diode is connected to the lower plate of the electrolytic capacitor, and the cathode is connected to the first terminal of the first power switch; the second terminal of the first power switch is grounded through the first resistor.

[0017] The cathode of the third diode is connected to the anode of the second diode, and the anode is grounded;

[0018] The high voltage drop current unit provides a reference voltage to the first input terminal of the first operational amplifier based on the output current of the LED load, and controls the reference voltage to decrease as the input voltage increases;

[0019] The minimum current setting unit is connected to the first input terminal of the first operational amplifier and is used to limit the minimum clamping current;

[0020] The feedback unit is connected to the constant current control module, the second input terminal of the first operational amplifier, and the second terminal of the first power switch, and is used to feed back the output current of the LED load to the charging and discharging path of the electrolytic capacitor.

[0021] The output terminal of the first operational amplifier is connected to the control terminal of the first power switch.

[0022] Alternatively, the high-voltage current-reducing unit includes a first constant current source, a fourth diode, a second resistor, and a second constant current source;

[0023] The input terminal of the first constant current source is connected to a compensation voltage generated based on the output current of the LED load, and the output terminal is connected to the anode of the fourth diode;

[0024] The cathode of the fourth diode is grounded via the second resistor; the cathode of the fourth diode outputs the reference voltage.

[0025] The input terminal of the second constant current source is connected to the output terminal of the first constant current source, the output terminal is grounded, and the control terminal is controlled by the input voltage. The second constant current source increases as the input voltage increases.

[0026] Alternatively, the minimum current setting unit includes a third resistor, a current setting circuit, and a third constant current source;

[0027] One end of the current setting circuit is connected to the input terminal of the third constant current source, and the other end is grounded via the third resistor;

[0028] The output terminal of the third constant current source is connected to the first input terminal of the first operational amplifier.

[0029] Alternatively, the feedback unit includes a current feedback circuit, a fourth constant current source, and a fourth resistor;

[0030] The current feedback circuit generates a feedback signal for the output current of the LED load;

[0031] The input terminal of the fourth constant current source is connected to the output terminal of the current feedback circuit, and the fourth constant current source is controlled based on the feedback signal.

[0032] One end of the fourth resistor is connected to the output terminal of the fourth constant current source and the second input terminal of the first operational amplifier, and the other end is connected to the second terminal of the first power switch.

[0033] Alternatively, the constant current control module includes a second power switch, a fifth resistor, a second operational amplifier, a compensation unit, and a reference voltage setting unit;

[0034] The first terminal of the second power switch is connected to the negative terminal of the LED load, and the second terminal is grounded via the fifth resistor;

[0035] The reference voltage setting unit generates a reference voltage;

[0036] The first input terminal of the second operational amplifier is connected to the reference voltage, the second input terminal is connected to the second terminal of the second power switch, and the output terminal is connected to the control terminal of the second power switch.

[0037] The compensation unit is connected to the first terminal of the second power switch and generates a compensation voltage to control the charging current of the electrolytic capacitor based on the voltage at the first terminal of the second power switch.

[0038] Alternatively, the compensation unit is also connected to the control terminal of the second power switch, and generates a compensation voltage to control the charging current of the electrolytic capacitor based on the voltage of the first terminal and the control terminal of the second power switch.

[0039] Alternatively, the reference voltage setting unit is also connected to the output terminal of the compensation unit, and the reference voltage is reduced when the compensation voltage is greater than a first preset value.

[0040] Alternatively, the constant current control module further includes a phase detection unit; the phase detection unit detects the phase cut of the thyristor based on the conduction time after the thyristor is turned on; the reference voltage setting unit is connected to the output terminal of the phase detection unit and reduces the reference voltage based on the phase cut of the thyristor; when the duty cycle of the thyristor phase cut is greater than a second preset value, the reference voltage is maintained; when the duty cycle of the thyristor phase cut is less than the second preset value but greater than a third preset value, the reference voltage is reduced as the duty cycle of the thyristor phase cut decreases; when the duty cycle of the thyristor phase cut is less than the third preset value, the reference voltage is adjusted to zero; wherein, the third preset value is less than the second preset value.

[0041] As described above, the LED constant current driving system of the present invention has the following beneficial effects:

[0042] 1. The LED constant current drive system of the present invention separates the LED frequency reduction circuit and the constant current output control circuit and connects them in parallel, which can improve the efficiency of the system.

[0043] 2. The LED constant current drive system of the present invention compensates the LED constant current output current to the capacitor charging and discharging control circuit through current feedback, thereby fixing the minimum input clamping current of the system as a whole, which is not lower than the thyristor holding current, and will not be too high to cause a decrease in system efficiency.

[0044] 3. The reference voltage of the LED constant current drive system of the present invention adopts the current superposition method, which will not affect the control of the system loop compensation.

[0045] 4. The minimum clamping current of the LED constant current drive system of the present invention can be set by an external resistor, which is convenient for application.

[0046] 5. The LED constant current driving system of the present invention detects the drain and gate voltages of the LED constant current control tube, ensuring that the output is flicker-free while the drain voltage is at its lowest, thereby reducing losses and improving system efficiency.

[0047] 6. The LED constant current drive system of the present invention adopts overvoltage compensation technology in the compensation loop, so that the LED output can still remain flicker-free when the input voltage is low, and can be adaptive without external settings.

[0048] 7. The phase detection module of the LED constant current drive system of the present invention controls the reference voltage, so that there is no flicker output when the thyristor dims while suppressing capacitor charging, controlling the instantaneous turn-on power consumption of the MOSFET, and improving system reliability.

[0049] 8. The LED constant current drive system of the present invention has common ground control for each functional module, which can be integrated into a single chip, reducing system cost. Attached Figure Description

[0050] Figure 1 This is a schematic diagram illustrating the principle of clamping the minimum current when the high voltage drops the current.

[0051] Figure 2 This is a schematic diagram of a structure for an LED driver application using silicon controlled rectifier (SCR) dimming.

[0052] Figure 3 This is another schematic diagram of an LED driver application for silicon controlled rectifier (SCR) dimming.

[0053] Figure 4 The diagram shown is a structural schematic of the LED constant current driving system of the present invention.

[0054] Figure 5 The diagram shown illustrates the principle of the compensation voltage adjustment reference voltage according to the present invention.

[0055] Figure 6 The diagram shown illustrates the principle of adjusting the reference voltage using a thyristor phase cut according to the present invention.

[0056] Component designation explanation

[0057] 11. Bleeding circuit

[0058] 12 High-efficiency linear drive circuit

[0059] 13 Voltage Detection Circuit

[0060] 14 Ripple Reduction Circuit

[0061] 15 High-efficiency linear drive circuit

[0062] 16 LED constant current control circuit

[0063] 2 LED constant current drive system

[0064] 21 Voltage Input Module

[0065] 211 Rectifier Unit

[0066] 212 thyristor

[0067] 22 Discharge Current Control Module

[0068] 23 Constant Current Control Module

[0069] 231 Reference Voltage Setting Unit

[0070] 231a Current Setting Circuit

[0071] 232 Compensation Unit

[0072] 232a Voltage Detection Circuit

[0073] 232b compensation circuit

[0074] 233 Phase Detection Unit

[0075] 24 Charging Current Control Module

[0076] 241 High Voltage Current Reduction Unit

[0077] 242 Minimum Current Setting Unit

[0078] 242a Current Setting Circuit

[0079] 243 Feedback Unit

[0080] 243a Current Feedback Circuit

[0081] 25. Discharge bus voltage detection module Detailed Implementation

[0082] The following specific examples illustrate the implementation of the present invention. 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.

[0083] Please see Figures 4-6 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0084] like Figure 4 As shown, this embodiment provides an LED constant current driving system 2, which includes: a voltage input module 21, a first diode D1, an LED load, an electrolytic capacitor Co, a discharge current control module 22, a constant current control module 23, and a charging current control module 24.

[0085] like Figure 4 As shown, the voltage input module 21 receives an AC signal AC and converts the AC signal AC into a DC input voltage Vin.

[0086] Specifically, in this embodiment, the voltage input module 21 includes a rectifier unit 211 and a silicon controlled rectifier (SCR) 212. The AC terminal of the rectifier unit 211 is connected to the AC signal AC, and the DC terminal outputs the input voltage Vin. The SCR 212 is connected in series to the AC terminal of the rectifier unit 211. As another implementation of the present invention, the voltage input module 21 further includes a fuse F1, which is connected in series to the AC terminal of the rectifier unit 211.

[0087] like Figure 4 As shown, the anode of the first diode D1 is connected to the output terminal of the voltage input module 21, and the cathode is connected to the upper plate of the electrolytic capacitor Co and the positive terminal of the LED load.

[0088] like Figure 4 As shown, the discharge current control module 22 is connected to the output terminal of the voltage input module 21, providing a discharge current to maintain the conduction of the thyristor.

[0089] Specifically, in this embodiment, the sixth resistor R6 and the seventh resistor R7 used for adjusting the current in the discharge current control module 22 are located outside the chip for easy adjustment; in actual use, the sixth resistor R6 and the seventh resistor R7 can be located inside the discharge current control module 22 of the chip, and are not limited to this embodiment.

[0090] like Figure 4 As shown, the constant current control module 23 is connected to the negative terminal of the LED load and performs adaptive ripple control on the current flowing through the LED load.

[0091] Specifically, in this embodiment, the constant current control module 23 includes a second power switch Q2, a fifth resistor R5, a second operational amplifier OP2, a reference voltage setting unit 231, and a compensation unit 232.

[0092] More specifically, the first terminal of the second power switch Q2 is connected to the negative terminal of the LED load, and the second terminal is grounded via the fifth resistor R5. As an example, the second power switch Q2 is implemented using an NMOS transistor. In this case, the first terminal of the second power switch Q2 is the drain, the second terminal is the source, and the control terminal is the gate. In actual use, the type of the second power switch Q2 can be set as needed, and the ports can be adjusted adaptively; these will not be elaborated upon here.

[0093] More specifically, the reference voltage setting unit 231 generates a reference voltage Ref. As an example, the reference voltage setting unit 231 includes a sixth resistor R6 and a current setting circuit 231a, the sixth resistor R6 being connected to the current setting circuit 231a, the current setting circuit 231a generating the reference voltage Ref based on the sixth resistor R6.

[0094] More specifically, the first input terminal of the second operational amplifier OP2 is connected to the reference voltage Ref, the second input terminal is connected to the second terminal of the second power switch Q2, and the output terminal is connected to the control terminal of the second power switch Q2. In this embodiment, the non-inverting input terminal of the second operational amplifier OP2 is connected to the reference voltage Ref, and the inverting input terminal is connected to the second terminal of the second power switch Q2; in actual use, the relationship between the polarity of the input signal and the corresponding input port can be adjusted as needed, and is not limited to this embodiment. The second operational amplifier OP2 controls the second power switch Q2 to turn on or off to provide a constant current output, and the output current of the LED load is ILED = VRef / R5, where VRef is the voltage value of the reference voltage Ref.

[0095] More specifically, the compensation unit 232 is connected to the first terminal of the second power switch Q2 and generates a compensation voltage based on the voltage at the first terminal of the second power switch Q2. In this embodiment, the compensation unit 232 includes a voltage detection circuit 232a and a compensation circuit 232b. The voltage detection circuit 232a detects the voltage at the first terminal of the second power switch Q2 and provides the detection result to the compensation circuit 232b to generate a corresponding compensation voltage. The compensation voltage is used to control the charging current of the electrolytic capacitor Co, ensuring that the charging amount of the electrolytic capacitor Co in each power frequency cycle is such that the drain voltage of the constant current output of the second power switch Q2 is not too high during discharge, thereby improving the overall efficiency of the system. At the same time, it ensures that the discharge of the electrolytic capacitor Co is not insufficient at the bottom of the input voltage, avoiding power frequency flicker caused by the drop in the output current of the LED load. As an example, when the voltage at the first terminal of the second power switch Q2 is greater than a first set value, the compensation voltage is reduced; when the voltage at the first terminal of the second power switch Q2 is less than a second set value, the compensation voltage is increased. In another implementation of the present invention, the voltage detection circuit 232a further detects the voltage at the control terminal of the second power switch Q2, and generates a control compensation voltage based on the voltage at the first terminal and the control terminal of the second power switch Q2. For example, when the voltage at the control terminal of the second power switch Q2 is greater than a third set value, the compensation voltage is rapidly increased.

[0096] When the input voltage is low, the charging current of the electrolytic capacitor Co is also limited due to the internal circuitry limiting the compensation voltage. At the bottom of the input voltage range, the electrolytic capacitor Co may not discharge sufficiently, causing the output current of the entire LED load to drop, resulting in power frequency flicker. Therefore, as another implementation of the invention, the reference voltage setting unit 231 is also connected to the output terminal of the compensation unit 232. When the compensation voltage Vcomp is greater than a first preset value, the reference voltage Ref is reduced; this causes the average output current of the LED load to decrease, instead of dropping at the bottom of the input voltage range (the compensation voltage remains balanced throughout the entire power frequency cycle). Figure 5As shown, the normal operating range of the compensation voltage Vcomp is 0 to VA (the value of VA is determined according to the actual application). VB is the first preset value. Within the range of VB to VC, the reference voltage Ref changes in the opposite direction to the compensation voltage Vcomp (where VC>VB>VA). VD is the highest clamping voltage set internally by the compensation circuit. When the input voltage is relatively low (below the typical operating voltage range), the control loop will also increase the compensation voltage (>VB). At this time, the output current will decrease (the value of the reference voltage Ref decreases), so the charging and discharging ripple of the electrolytic capacitor Co will also decrease (Co*ΔV=ILED*t_Discharge, ΔV is the ripple, and t_Discharge is the discharge time; since the electrolytic capacitor Co and the discharge time t_Discharge remain unchanged, the output current ILED decreases, so the ripple ΔV also decreases). As long as the ripple voltage range is within the voltage adjustment range of the constant current control module 23, the constant current control module 23 can still output a constant current, but the output current is smaller than the rated current, thereby realizing the flicker elimination function.

[0097] During SCR dimming, the input voltage decreases due to SCR phase switching, leading to an increase in the compensation voltage. This causes a larger charging current in the electrolytic capacitor Co. If this coincides with a high voltage spike at the moment the SCR turns on, the first power switch Q1, which adjusts the charging current of the electrolytic capacitor Co, can easily break down. Therefore, as another implementation of this invention, the constant current control module 23 further includes a phase detection unit 233, which reduces the reference voltage Ref when the SCR phase switches, thereby maintaining a suitable compensation voltage value. This achieves flicker-free output while reducing the power consumption of the first power switch Q1 at the moment the SCR turns on, improving system reliability. The phase detection unit 233 detects the phase cut of the thyristor based on the conduction time after the thyristor is turned on. For example, the phase detection unit 233 obtains the conduction time after the thyristor is turned on through the discharge bus voltage detection module 25. Before the thyristor phase cut, the discharge bus voltage is at a low level, and the high-level time of the discharge bus voltage after the phase cut starts varies with the dimming state. In actual use, it can also be determined by the time of the detection signal Vs (the voltage across the eighth resistor R8 caused by the sum of the charging current of the electrolytic capacitor and the LED output current) from the discharge current control module 22. The conduction time of the detection signal Vs will change after the thyristor phase cut; only the selected detection signal needs to reflect the conduction time after the thyristor is turned on. Further details are omitted here. The reference voltage setting unit 231 is connected to the output terminal of the phase detection unit 233 and adjusts (reduces) the reference voltage Ref based on the thyristor phase cut. Figure 6As shown, when the duty cycle of the thyristor phase cut (i.e., the proportion of the remaining phase angle after phase cutting) is greater than the second preset value, the reference voltage Ref is maintained, and the adjustment coefficient is 100%; as an example, the second preset value is 80%. When the duty cycle of the thyristor phase cut is less than the second preset value but greater than the third preset value, the reference voltage is reduced as the duty cycle of the thyristor phase cut decreases, and the adjustment coefficient gradually decreases from 100% to 0%; as an example, the third preset value is 30%. When the duty cycle of the thyristor phase cut is less than the third preset value, the reference voltage Ref is adjusted to zero, and the adjustment coefficient is 0%. The third preset value is less than the second preset value. The second preset value and the third preset value can be set according to the actual application environment so that the reference voltage Ref adjusted by the phase detection unit 233 meets the requirements of the NEMA (National Electrical Manufacturers Association) standard curve. Figure 6 The upper dotted line is the upper limit, and the lower dotted line is the lower limit. Anything between the two is acceptable to achieve the purpose of optimizing the dimming effect. I will not go into details here.

[0098] like Figure 4 As shown, the charging current control module 24 is connected to the lower plate of the electrolytic capacitor Co and the constant current control module 23 to control the charging current of the electrolytic capacitor Co to achieve flicker control of the LED load; and controls the minimum clamping current of the LED constant current drive system 2 based on the output current of the LED load to ensure that the minimum clamping current is not less than the holding current of the thyristor.

[0099] Specifically, in this embodiment, the charging current control module 24 includes: a high voltage current reduction unit 241, a second diode D2, a third diode D3, a minimum current setting unit 242, a first power switch Q1, a first resistor R1, a first operational amplifier OP1, and a feedback unit 243.

[0100] More specifically, the anode of the second diode D2 is connected to the lower plate of the electrolytic capacitor Co, and the cathode is connected to the first terminal of the first power switch Q1; the second terminal of the first power switch Q1 is grounded via the first resistor R1. As an example, the first power switch Q1 is implemented using an NMOS transistor. In this case, the first terminal of the first power switch Q1 is the drain, the second terminal is the source, and the control terminal is the gate. In actual use, the type of the first power switch Q1 can be set as needed, and the ports can be adjusted adaptively, which will not be elaborated here.

[0101] More specifically, the cathode of the third diode D3 is connected to the anode of the second diode D2, and the anode is grounded. The second diode D2, the first power switch Q1, and the first resistor R1 form a charging path, and the third diode D3 forms a discharging path.

[0102] More specifically, the high-voltage current-drop unit 241 provides a reference voltage VB to the first input terminal of the first operational amplifier OP1 based on the output current of the LED load, and controls the reference voltage VB to decrease as the input voltage increases. As an example, the high-voltage current-drop unit 241 includes a first constant current source I1, a fourth diode D4, a second resistor R2, and a second constant current source I2. The input terminal of the first constant current source I1 is connected to a compensation voltage generated based on the output current of the LED load, and its output terminal is connected to the anode of the fourth diode D4. In this embodiment, the compensation voltage is provided by the compensation unit 232. As an example, the first constant current source I1 increases as the compensation voltage increases and decreases as the compensation voltage decreases. The cathode of the fourth diode D4 is grounded via the second resistor R2, and the cathode of the fourth diode D4 outputs the reference voltage VB. The input terminal of the second constant current source I2 is connected to the output terminal of the first constant current source I1, and the output terminal is grounded. The control terminal is controlled by the input voltage Vin. The second constant current source I2 increases as the input voltage Vin increases. In this embodiment, the control terminal of the second constant current source I2 is connected to the output terminal of the discharge bus voltage detection module 25, so that the discharge bus voltage reflects the input voltage Vin.

[0103] More specifically, the minimum current setting unit 242 is connected to the first input terminal of the first operational amplifier OP1 and is used to limit the minimum clamping current. As an example, the minimum current setting unit 242 includes a third resistor R3, a current setting circuit 242a, and a third constant current source I3. One end of the current setting circuit 242a is connected to the input terminal of the third constant current source I3, and the other end is grounded via the third resistor R3; the output terminal of the third constant current source I3 is connected to the first input terminal of the first operational amplifier OP1.

[0104] The fourth diode D2 is used to isolate the third constant current source I3 from the second constant current source I2, ensuring that the minimum current setting is not affected by the input voltage. In practical use, the internal connection between the third constant current source I3 and the second constant current source I2 can be modified so that the second constant current source I2 does not interfere with the operation of the third constant current source I3, thereby eliminating the need for the fourth diode D2. This is not limited to this embodiment. The first constant current source I1 generates a voltage across the second resistor R2. The first constant current source I1 is shunted by the second constant current source I2, which is controlled by the input voltage, to achieve the high voltage current reduction function. In extreme cases, the first constant current source I1 is completely shunted by the second constant current source I2, so that only the current provided by the third constant current source I3 is available across the second resistor R2, thereby limiting the minimum clamping current during high voltage current reduction. The current setting circuit 242a controls the third constant current source I3 based on the third resistor R3 and generates a voltage drop across the second resistor R2, thereby limiting the minimum charging current (i.e., the minimum clamping current) of the electrolytic capacitor Co to satisfy:

[0105] It should be noted that if the minimum clamping current is set too high, it will lead to a decrease in the overall efficiency of the system. Therefore, in this embodiment, the third resistor R3 is set externally and can be adjusted by external resistor to optimize system performance.

[0106] More specifically, the feedback unit 243 is connected to the constant current control module 23, the second input terminal of the first operational amplifier OP1, and the second terminal of the first power switch Q1, and is used to feed back the output current of the LED load to the charging and discharging path of the electrolytic capacitor. As an example, the feedback unit 243 includes a current feedback circuit 243a, a fourth constant current source I4, and a fourth resistor R4. The current feedback circuit 243a generates a feedback signal of the output current of the LED load; in this embodiment, the current feedback circuit 243a is connected to the second terminal of the second power switch Q2, converting the voltage at the second terminal of the second power switch Q2 into a feedback signal of the output current of the LED load. The input terminal of the fourth constant current source I4 is connected to the output terminal of the current feedback circuit 243a, and the fourth constant current source I4 is controlled based on the feedback signal. One end of the fourth resistor R4 is connected to the output terminal of the fourth constant current source I4 and the second input terminal of the first operational amplifier OP1, and the other end is connected to the second terminal of the first power switch Q1. When current flows through the LED constant current control circuit, the voltage at the second terminal of the second power switch Q2 satisfies: VsLED=ILED*R5, where ILED is the output current of the LED load. The output current signal of the LED load is fed back to the charging and discharging path of the electrolytic capacitor Co through the current feedback circuit 243a. The fourth constant current source I4 satisfies: I4=VsLED*K2=ILED*R5*K2. The fourth constant current source I4 generates a feedback voltage I4*R4 across the fourth resistor R4. The current generated by this feedback voltage across the first resistor R1 is equal to ILED, thus the control coefficient of the fourth constant current source I4 can be obtained. It should be noted that the control coefficient K2 can be determined by setting the resistance value of the fourth resistor R4, thereby obtaining the current fed back to the first resistor R1, and this embodiment is not limited to this one.

[0107] More specifically, the output terminal of the first operational amplifier OP1 is connected to the control terminal of the first power switch Q1, and the charging current of the electrolytic capacitor Co is adjusted by turning the first power switch Q1 on and off. In this embodiment, the non-inverting input terminal of the first operational amplifier OP1 is connected to the output terminals of the high voltage drop current unit 241 and the minimum current setting unit 242 to obtain the control voltage; the inverting input terminal is connected to the output terminal of the feedback unit 243 to obtain the feedback voltage. In actual use, the relationship between the input signal and the polarity of the corresponding input port can be adjusted as needed, and is not limited to this embodiment.

[0108] It should be noted that, due to the feedback function of the feedback unit 243, even if the LED output current changes with the dimming of the thyristor, the minimum input current of the system is clamped at a fixed value, which will not be lower than the holding current of the thyristor, nor will it be too large to cause a decrease in system efficiency.

[0109] It should be noted that the control voltage of the first operational amplifier OP1 is superimposed on the second resistor R2 through the first constant current source I1 and the third constant current source I3, and the feedback voltage is superimposed on the fourth resistor R4 through the fourth constant current source I4. This superposition will not affect the operation of the system loop.

[0110] It should be noted that the LED constant current driving system 2 can be implemented using a chip. In this case, the third resistor R3, the sixth resistor R6, and the seventh resistor R7 (used to adjust the discharge current) can be set outside the chip to facilitate the adjustment of each current.

[0111] In summary, this invention provides an LED constant current driving system, comprising: a voltage input module, a first diode, an LED load, an electrolytic capacitor, a discharge current control module, a constant current control module, and a charging current control module; the voltage input module receives an AC signal and converts the AC signal into a DC input voltage; the anode of the first diode is connected to the output terminal of the voltage input module, and the cathode is connected to the upper plate of the electrolytic capacitor and the positive terminal of the LED load; the discharge current control module is connected to the output terminal of the voltage input module and provides a discharge current to maintain the conduction of the thyristor; the constant current control module is connected to the negative terminal of the LED load and performs adaptive ripple reduction control on the current flowing through the LED load; the charging current control module is connected to the lower plate of the electrolytic capacitor and the constant current control module, controls the charging current of the electrolytic capacitor to achieve flicker reduction control of the LED load; and controls the minimum clamping current based on the output current of the LED load to ensure that the minimum clamping current is not less than the holding current of the thyristor. The LED constant current drive system of this invention separates and connects the LED flicker removal circuit and the constant current output control circuit in parallel, which can improve the system efficiency. The LED constant current output current is compensated to the capacitor charging and discharging control circuit through current feedback, thereby fixing the minimum input clamping current of the entire system. This ensures the current is not lower than the thyristor holding current, nor is it too high, which would reduce system efficiency. The reference voltage uses current superposition, which does not affect the control of the system loop compensation. The minimum clamping current can be set by an external resistor, making it convenient to use. Detecting the drain and gate voltages of the LED constant current control transistor ensures flicker-free output while minimizing the drain voltage, thereby reducing losses and improving system efficiency. The overvoltage compensation technology of the compensation loop ensures that the LED output remains flicker-free even at low input voltages, and can adapt without external settings. The phase detection module controls the reference voltage, ensuring flicker-free output during thyristor dimming while suppressing the instantaneous turn-on power consumption of the capacitor charging control MOS transistor, improving system reliability. All functional modules share a common ground control, allowing integration into a single chip and reducing system cost. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial applicability.

[0112] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An LED constant current driving system, characterized in that, The LED constant current drive system includes at least: Voltage input module, first diode, LED load, electrolytic capacitor, discharge current control module, constant current control module and charging current control module; The voltage input module receives AC signals and converts the AC signals into DC input voltage; The anode of the first diode is connected to the output terminal of the voltage input module, and the cathode is connected to the upper plate of the electrolytic capacitor and the positive terminal of the LED load. The discharge current control module is connected to the output terminal of the voltage input module and provides the discharge current to maintain the conduction of the thyristor; The constant current control module is connected to the negative terminal of the LED load and performs adaptive ripple-reducing control on the current flowing through the LED load. The charging current control module is connected to the lower plate of the electrolytic capacitor and the constant current control module to control the charging current of the electrolytic capacitor to achieve flicker control of the LED load; and controls the minimum clamping current based on the output current of the LED load to ensure that the minimum clamping current is not less than the holding current of the thyristor. The charging current control module includes: a high voltage current reduction unit, a second diode, a third diode, a minimum current setting unit, a first power switch, a first resistor, a first operational amplifier, and a feedback unit. The anode of the second diode is connected to the lower plate of the electrolytic capacitor, and the cathode is connected to the first terminal of the first power switch; the second terminal of the first power switch is grounded through the first resistor. The cathode of the third diode is connected to the anode of the second diode, and the anode is grounded; The high voltage drop current unit provides a reference voltage to the first input terminal of the first operational amplifier based on the output current of the LED load, and controls the reference voltage to decrease as the input voltage increases; The minimum current setting unit is connected to the first input terminal of the first operational amplifier and is used to limit the minimum clamping current; The feedback unit is connected to the constant current control module, the second input terminal of the first operational amplifier, and the second terminal of the first power switch, and is used to feed back the output current of the LED load to the charging and discharging path of the electrolytic capacitor. The output terminal of the first operational amplifier is connected to the control terminal of the first power switch.

2. The LED constant current driving system according to claim 1, characterized in that: The voltage input module includes a rectifier unit and a thyristor; the AC terminal of the rectifier unit is connected to the AC signal, and the DC terminal outputs the input voltage; the thyristor is connected in series with the AC terminal of the rectifier unit.

3. The LED constant current driving system according to claim 1, characterized in that: The high-voltage current reduction unit includes a first constant current source, a fourth diode, a second resistor, and a second constant current source. The input terminal of the first constant current source is connected to a compensation voltage generated based on the output current of the LED load, and the output terminal is connected to the anode of the fourth diode; The cathode of the fourth diode is grounded via the second resistor; the cathode of the fourth diode outputs the reference voltage. The input terminal of the second constant current source is connected to the output terminal of the first constant current source, the output terminal is grounded, and the control terminal is controlled by the input voltage. The second constant current source increases as the input voltage increases.

4. The LED constant current driving system according to claim 3, characterized in that: The minimum current setting unit includes a third resistor, a current setting circuit, and a third constant current source; One end of the current setting circuit is connected to the input terminal of the third constant current source, and the other end is grounded via the third resistor; The output terminal of the third constant current source is connected to the first input terminal of the first operational amplifier.

5. The LED constant current driving system according to claim 1, characterized in that: The feedback unit includes a current feedback circuit, a fourth constant current source, and a fourth resistor; The current feedback circuit generates a feedback signal for the output current of the LED load; The input terminal of the fourth constant current source is connected to the output terminal of the current feedback circuit, and the fourth constant current source is controlled based on the feedback signal. One end of the fourth resistor is connected to the output terminal of the fourth constant current source and the second input terminal of the first operational amplifier, and the other end is connected to the second terminal of the first power switch.

6. The LED constant current driving system according to any one of claims 1-5, characterized in that: The constant current control module includes a second power switch, a fifth resistor, a second operational amplifier, a compensation unit, and a reference voltage setting unit; The first terminal of the second power switch is connected to the negative terminal of the LED load, and the second terminal is grounded via the fifth resistor; The reference voltage setting unit generates a reference voltage; The first input terminal of the second operational amplifier is connected to the reference voltage, the second input terminal is connected to the second terminal of the second power switch, and the output terminal is connected to the control terminal of the second power switch. The compensation unit is connected to the first terminal of the second power switch and generates a compensation voltage to control the charging current of the electrolytic capacitor based on the voltage at the first terminal of the second power switch.

7. The LED constant current driving system according to claim 6, characterized in that: The compensation unit is also connected to the control terminal of the second power switch, and generates a compensation voltage to control the charging current of the electrolytic capacitor based on the voltage of the first terminal and the control terminal of the second power switch.

8. The LED constant current driving system according to claim 6, characterized in that: The reference voltage setting unit is also connected to the output terminal of the compensation unit, and the reference voltage is reduced when the compensation voltage is greater than the first preset value.

9. The LED constant current driving system according to claim 6, characterized in that: The constant current control module further includes a phase detection unit; the phase detection unit detects the phase cut of the thyristor based on the conduction time after the thyristor is turned on; the reference voltage setting unit is connected to the output terminal of the phase detection unit and reduces the reference voltage based on the phase cut of the thyristor; when the duty cycle of the thyristor phase cut is greater than a second preset value, the reference voltage is maintained; when the duty cycle of the thyristor phase cut is less than the second preset value but greater than a third preset value, the reference voltage is reduced as the duty cycle of the thyristor phase cut decreases; when the duty cycle of the thyristor phase cut is less than the third preset value, the reference voltage is adjusted to zero; wherein, the third preset value is less than the second preset value.

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