Silicon controlled rectifier detection circuit, LED driving system and bleeder current control method

Abstract

The invention provides a silicon controlled rectifier detection circuit, an LED driving system and a bleeder current control method, and the circuit comprises a bus voltage detection module which generates a pulse signal corresponding to a jump edge of a bus voltage; the pulse voltage detection module is used for generating a front switching or back switching judgment signal of the silicon controlled rectifier and triggering a reset signal; the counting module is used for counting the period of the bus voltage and resetting the counting result when the reset signal is valid; and the discharge control module generates a first control signal when the counting result is smaller than a preset value, and generates a second control signal when the counting result is larger than or equal to the preset value, the first control signal controls a subsequent circuit to perform discharge current control, and the second control signal controls the subsequent circuit to turn off the discharge current. The front-cut dimmer and the rear-cut dimmer are identified, and the compatibility of the silicon controlled rectifier is improved; misjudgment caused by a large phase angle of the silicon controlled rectifier is avoided; the anti-interference performance is high; the system is simple in design and small in chip area.

Description

Technical Field

[0001] The present invention relates to the field of integrated circuit design, and in particular to a thyristor detection circuit, an LED drive system and a discharge current control method. Background Art

[0002] In the LED driver application of thyristor dimming, once the input current is less than the holding current of the thyristor, the thyristor will shut down and restart, causing the LED to flicker. Therefore, an external bleeder circuit is generally required to meet the holding current requirement of the thyristor, so that the thyristor is always turned on within the working range to avoid LED flickering. Especially in linear LED driving, since the LED lamp voltage is relatively high, in order to ensure the reliable conduction of the thyristor when the input voltage is lower than the LED lamp voltage, a large bleeder current needs to be provided. However, when the system is not connected to the thyristor, this bleeder current is not needed, which will cause greater losses. Therefore, the system needs a mechanism to determine whether to connect the thyristor to determine whether to conduct the bleeder current.

[0003] Usually, when the system is connected to the thyristor, the input voltage Vin will be cut off, and the conduction time (Ton, Ton1, Ton2) will be less than the cycle time. Therefore, one method is to detect whether the duty cycle of the input voltage (the duration when Vin is greater than or equal to the detection voltage Vdetect) meets the requirements, and use this to detect whether to connect the thyristor and determine whether to add the discharge current IBleed. Figure 1 As shown, if the on-time duty cycle is greater than or equal to the preset duty cycle, it is determined that the thyristor is not connected, and if the on-time duty cycle is less than the preset duty cycle, it is determined that the thyristor is connected. Because the input voltage Vin sometimes changes, the on-time duty cycle obtained for a fixed detection voltage Vdetect will change. Some thyristors have a very large opening angle. If the detection voltage Vdetect is not set properly, the difference between the on-time duty cycle of the thyristor connected and the thyristor not connected will be very small, resulting in wrong judgment and unreliable detection.

[0004] In addition, thyristor dimmers are divided into front-cut and rear-cut types, and have different requirements for the discharge current IBleed, such as Figure 1 As shown, for the leading dimmer, the discharge current IBleed is required in the periods t7-t8 and t9-t11; and for the trailing dimmer, the discharge current IBleed is only required in the period t15-t16. Therefore, the system needs to be optimized for the leading and trailing dimmers respectively, and the conventional method of detecting the on-time duty cycle cannot distinguish between the leading and trailing dimmers.

[0005] Therefore, how to improve the reliability of thyristor detection and optimize the front-cut dimming and the back-cut dimming respectively has become one of the problems that need to be solved urgently by those skilled in the art.

[0006] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present invention and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because these solutions are described in the background technology section of the present invention. Summary of the invention

[0007] In view of the shortcomings of the prior art described above, an object of the present invention is to provide a thyristor detection circuit, an LED drive system and a discharge current control method, which are used to solve the problems of poor dimming detection reliability and failure to distinguish between front-cut dimming and back-cut dimming in the prior art.

[0008] To achieve the above-mentioned object and other related objects, the present invention provides a thyristor detection circuit, which at least includes:

[0009] Bus voltage detection module, pulse voltage detection module, counting module and discharge control module;

[0010] The first end of the bus voltage detection module is connected to the bus voltage, and the second end is connected to the reference voltage, and is used to detect the transition edge of the bus voltage and generate a corresponding pulse signal;

[0011] The pulse voltage detection module is connected to the output end of the bus voltage detection module, generates a leading cutting judgment signal or a trailing cutting judgment signal of the thyristor based on the pulse signal, and triggers a reset signal when detecting that the leading cutting judgment signal or the trailing cutting judgment signal is valid;

[0012] The counting module is connected to the output end of the pulse voltage detection module, counts the cycle of the bus voltage, and resets the counting result to zero when the reset signal is valid;

[0013] The discharge control module is connected to the output ends of the pulse voltage detection module and the counting module, and generates a first control signal according to the front-cut judgment signal or the back-cut judgment signal when the counting result is less than a preset value, and generates a second control signal when the counting result is greater than or equal to the preset value, wherein the first control signal controls the subsequent circuit to perform discharge current control, and the second control signal controls the subsequent circuit to shut off the discharge current.

[0014] Optionally, the bus voltage detection module includes a first capacitor and a first resistor; one end of the first capacitor serves as the first end of the bus voltage detection module, and the other end is connected to one end of the first resistor; the other end of the first resistor serves as the second end of the bus voltage detection module; and the connection node between the first capacitor and the first resistor serves as the output end of the bus voltage detection module.

[0015] Optionally, the thyristor detection circuit further includes a second resistor, which is connected in series between the bus voltage and the first end of the bus voltage detection module.

[0016] Optionally, the potential of the reference voltage is equal to or higher than the reference ground.

[0017] More optionally, the pulse voltage detection module includes a first comparator, a second comparator and a logic unit;

[0018] The first comparator receives the output signal of the bus voltage detection module, and outputs a valid leading edge judgment signal when the voltage value of the pulse signal is greater than a first preset voltage;

[0019] The second comparator receives the output signal of the bus voltage detection module, and outputs a valid post-cut judgment signal when the voltage value of the pulse signal is less than a second preset voltage;

[0020] The logic unit is connected to the output terminals of the first comparator and the second comparator, and generates the reset signal based on the leading cut judgment signal and the trailing cut judgment signal;

[0021] The first preset voltage is greater than the reference voltage, and the second preset voltage is less than the reference voltage.

[0022] Optionally, the thyristor detection circuit further includes a counting clock generating module; the counting clock generating module is connected to the bus voltage, generates a timing clock based on the power frequency cycle of the bus voltage, and provides the timing clock to the counting module.

[0023] More optionally, the counting clock generating module includes a voltage dividing unit and a third comparator; the voltage dividing unit divides the bus voltage; the third comparator is connected to the output end of the voltage dividing unit, and compares the output signal of the voltage dividing unit with a reference signal to obtain the timing clock.

[0024] To achieve the above-mentioned object and other related objects, the present invention further provides an LED driving system, the LED driving system at least comprising:

[0025] Voltage input circuit, LED constant current control circuit and the above-mentioned thyristor detection circuit;

[0026] The voltage input circuit receives an AC voltage and converts the AC voltage into a bus voltage;

[0027] The thyristor detection circuit is connected to the output end of the voltage input circuit, and is used to detect whether the thyristor is connected, and to generate a leading cutting judgment signal or a trailing cutting judgment signal of the thyristor when the thyristor is connected;

[0028] The LED constant current control circuit is connected to the voltage input circuit and the output end of the thyristor detection circuit, realizes constant current output of the LED based on the bus voltage, and realizes thyristor dimming control based on the output signal of the thyristor detection circuit.

[0029] Optionally, the LED constant current control circuit is a linear drive structure or a switch type drive structure.

[0030] In order to achieve the above-mentioned object and other related objects, the present invention further provides a discharge current control method, which is implemented based on the above-mentioned thyristor detection circuit, and the discharge current control method at least includes:

[0031] Power on, generating discharge current;

[0032] Counting the cycle of the bus voltage and detecting the transition edge of the bus voltage;

[0033] If the leading or trailing judgment signal of the thyristor is detected, the counting result is reset to zero, and the discharge current is controlled according to the leading or trailing judgment result;

[0034] If the leading cutting judgment signal or the trailing cutting judgment signal of the thyristor is not detected, the counting continues until the preset value is reached, and the discharge current is turned off.

[0035] As described above, the thyristor detection circuit, LED drive system and discharge current control method of the present invention have the following beneficial effects:

[0036] 1. The thyristor detection circuit, LED drive system and discharge current control method of the present invention can identify the front-cut and rear-cut dimmers according to the jump signal, thereby improving the compatibility of thyristors; and will not cause erroneous judgment of not connecting the thyristor due to the large phase angle of the thyristor.

[0037] 2. The thyristor detection circuit, LED drive system and discharge current control method of the present invention utilize a counting module to eliminate occasional spike interferences such as power on / off and voltage mutations, and have strong anti-interference properties.

[0038] 3. The capacitance of the capacitor for detecting the bus voltage in the thyristor detection circuit and LED drive system of the present invention is very small and can be integrated into the chip together with the resistor, thus simplifying the system design.

[0039] 4. The thyristor detection circuit, LED drive system and discharge current control method of the present invention utilize the jump caused by the opening of the thyristor to generate a reset signal, so that the counting module cannot output the shutdown signal of the discharge current, thereby judging the connection of the thyristor. A large capacitor is no longer needed to filter and time the industrial frequency signal, which can significantly reduce the chip area and external capacitance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram showing voltage and current when there is no thyristor, thyristor is cut in front, and thyristor is cut in the back.

[0041] Figure 2 Shown is a structural schematic diagram of the thyristor detection circuit of the present invention.

[0042] Figure 3 Shown is a structural schematic diagram of the pulse voltage detection module of the present invention.

[0043] Figure 4 Shown is a schematic structural diagram of the LED driving system of the present invention.

[0044] Figure 5 It is a schematic flow chart of the discharge current control method of the present invention.

[0045] Figure 6 Another structural schematic diagram of the thyristor detection circuit of the present invention is shown.

[0046] Component number description

[0047] 1. Silicon controlled rectifier detection circuit

[0048] 11 Bus voltage detection module

[0049] 12 pulse voltage detection module

[0050] 121 First comparator

[0051] 122 Second comparator

[0052] 123 Logic Unit

[0053] 13 Counting module

[0054] 14 Discharge control module

[0055] 15 Counting clock generation module

[0056] 151 Third comparator

[0057] 16 clamp units

[0058] 2 Voltage input circuit

[0059] 21 Rectifier module

[0060] 22 SCR

[0061] 3 LED constant current control circuit

[0062] 31 drive control module DETAILED DESCRIPTION

[0063] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0064] See also Figure 2 to Figure 6 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0065] Embodiment 1

[0066] like Figure 2 As shown, this embodiment provides a thyristor detection circuit 1, and the thyristor detection circuit 1 at least includes:

[0067] A bus voltage detection module 11 , a pulse voltage detection module 12 , a counting module 13 and a discharge control module 14 .

[0068] like Figure 2 As shown, the first end of the bus voltage detection module 11 is connected to the bus voltage HVin, and the second end is connected to the reference voltage Vref, and is used to detect the transition edge of the bus voltage HVin and generate a corresponding pulse signal.

[0069] Specifically, in this embodiment, the bus voltage detection module 11 includes a first capacitor C1 and a first resistor R1. One end of the first capacitor C1 serves as the first end of the bus voltage detection module 11, and the other end is connected to one end of the first resistor R1; the other end of the first resistor R1 serves as the second end of the bus voltage detection module 11; the connection node between the first capacitor C1 and the first resistor R1 serves as the output end of the bus voltage detection module 11. The first capacitor C1 is used to detect the change of the bus voltage HVin, and a voltage signal Vs is generated on the first resistor R1, and the capacitor current satisfies: where i C1is the current of the first capacitor, C1 is the capacity of the first capacitor, VC1 is the voltage on the first capacitor; according to the capacitor current formula, the output voltage Vs of the bus voltage detection module 11 satisfies: When a thyristor is connected, a jump voltage will be generated when the thyristor is turned on and off, and the time for the voltage change is in the ns level. The first capacitor C1 only needs a very small capacity to generate a relatively large peak voltage on the first resistor R1 and be detected by the system. Therefore, the first capacitor C1 can be integrated into the chip, thereby reducing peripheral devices and simplifying the system circuit.

[0070] It should be noted that if the bus voltage HVin is directly detected, the first capacitor C1 may need to be set as a high-voltage capacitor, but the cost of integrating high-voltage capacitors is relatively high; therefore, as another implementation of the present invention, the bus voltage HVin is divided by resistors and then connected to the first capacitor C1 at a lower voltage point. Figure 2 As shown, the thyristor detection circuit 1 further includes a second resistor R2 , and the second resistor R2 is connected in series between the bus voltage HVin and the first end of the bus voltage detection module 11 .

[0071] like Figure 2 As shown, the pulse voltage detection module 12 is connected to the output end of the bus voltage detection module 11, generates a front-cutting judgment signal or a rear-cutting judgment signal of the thyristor based on the pulse signal, and triggers a reset signal Rset when it is detected that the front-cutting judgment signal or the rear-cutting judgment signal is valid.

[0072] Specifically, the front-cut dimmer generally generates a positive jump after rectification, at which time the output voltage Vs of the bus voltage detection module 11 is a positive spike pulse voltage signal; the rear-cut dimmer generates a negative jump after rectification, at which time the output voltage Vs of the bus voltage detection module 11 is a negative spike pulse voltage signal. In this embodiment, the reference voltage Vref is set as the reference ground; therefore, it is necessary to detect the positive spike pulse and the negative spike pulse separately. Figure 3As shown, in this embodiment, the pulse voltage detection module 12 includes a first comparator 121, a second comparator 122 and a logic unit 123. The first comparator 121 receives the output signal of the bus voltage detection module 11, and outputs a valid front-cut judgment signal CF when the voltage value of the pulse signal is greater than the first preset voltage Vset1; as an example, the positive phase input terminal of the first comparator 121 is connected to the output voltage Vs of the bus voltage detection module 11, and the inverting input terminal is connected to the first preset voltage Vset1, and outputs the front-cut judgment signal CF. The second comparator 122 receives the output signal of the bus voltage detection module 11, and outputs a valid back-cut judgment signal CR when the voltage value of the pulse signal is less than the second preset voltage Vset2; as an example, the positive phase input terminal of the second comparator 122 is connected to the second preset voltage Vset2, and the inverting input terminal is connected to the output voltage Vs of the bus voltage detection module 11, and outputs the back-cut judgment signal CR. In this embodiment, the first preset voltage Vset1 is greater than 0V and is set to ΔV (that is, the pulse signal is a positive peak pulse voltage signal, and is ΔV greater than the reference ground); the second preset voltage Vset2 is less than 0V and is set to -ΔV (that is, the pulse signal is a negative peak pulse voltage signal, and is ΔV less than the reference ground). In actual use, any circuit structure that can detect positive peak pulse voltage signals and negative peak pulse voltage signals is applicable to the present invention, and is not limited to this embodiment. The logic unit 123 is connected to the output ends of the first comparator 121 and the second comparator 122, and generates the reset signal Rset based on the front-cut judgment signal CF or the back-cut judgment signal CR; in this example, the logic unit 123 is implemented using an OR gate, and in actual use, any circuit structure that can implement OR logic is applicable, and will not be described one by one here.

[0073] It should be noted that any circuit structure that can output a judgment signal for cutting the dimmer forward or backward according to the positive or negative properties of the peak pulse voltage when the jump voltage reaches a certain value is applicable to the pulse voltage detection module 12 of the present invention, and is not limited to this embodiment.

[0074] like Figure 2 As shown, the counting module 13 is connected to the output end of the pulse voltage detection module 12, counts the cycle of the bus voltage HVin, and resets the counting result to zero when the reset signal Reset is valid.

[0075] Specifically, when the power is turned on, there will be a positive voltage jump, which is equivalent to the front-cut dimmer signal; when the power is turned off, there will be a negative voltage jump, which is equivalent to the rear-cut dimmer signal; that is, the front-cut judgment signal CF and the rear-cut judgment signal CR output by the pulse voltage detection module 12 are not necessarily the dimming signals of the thyristor, but may also be caused by the power on and off. Therefore, the present invention avoids the interference caused by power mutation or switching spikes through the counting module 13. Since power mutation and switching spikes are occasional situations, the above situation can be eliminated by maintaining several cycles of detection to ensure the accuracy of thyristor detection.

[0076] More specifically, the counting module 13 counts the cycle of the bus voltage HVin. If no front cutting, rear cutting or interference signal is detected in the current cycle (i.e., the front cutting judgment signal CF and the rear cutting judgment signal CR are both invalid), the counting module 13 continues to count, and is locked after counting to the preset value, and is not cleared and counted again until the next reset signal is received. If a front cutting, rear cutting or interference signal is detected in the current cycle (i.e., the front cutting judgment signal CF or the rear cutting judgment signal CR is valid), the counting module 13 is cleared.

[0077] In this embodiment, the period of the bus voltage HVin is the power frequency period, and the power frequency clock is used as the counting clock of the counting module 13. Any method that can obtain the counting clock is applicable to the present invention. Preferably, in order to avoid using large capacitor filtering, in this example, the thyristor detection circuit 1 also includes a counting clock generating module 15; the counting clock generating module 15 is connected to the bus voltage HVin, generates the timing clock based on the power frequency period of the bus voltage HVin, and provides it to the counting module 13. Specifically, the counting clock generating module 15 includes a voltage dividing unit and a third comparator 151; the voltage dividing unit divides the bus voltage HVin, and in this example, the voltage division is achieved by a series structure of a third resistor R3 and a fourth resistor R4; the third comparator 151 is connected to the output end of the voltage dividing unit, and compares the output signal of the voltage dividing unit with the reference signal REF to obtain the timing clock, that is, the clock signal is obtained based on the magnitude relationship between the output signal of the voltage dividing unit and the voltage value of the reference signal REF. It should be noted that the counting clock generating module 15 can be directly connected to the bus voltage HVin, or connected to the bus voltage HVin after voltage division through a resistor (including but not limited to the second resistor R2), as long as voltage division can be achieved, which will not be elaborated here.

[0078] like Figure 2As shown, the discharge control module 14 is connected to the output ends of the pulse voltage detection module 12 and the counting module 13, and generates a first control signal according to the front cutting judgment signal or the back cutting judgment signal when the counting result is less than a preset value, and generates a second control signal when the counting result is greater than or equal to the preset value, wherein the first control signal controls the subsequent circuit to perform discharge current control, and the second control signal controls the subsequent circuit to shut off the discharge current.

[0079] Specifically, the discharge control module 14 generates a control signal Ctl. If a front cut or a rear cut is detected in any cycle, it is considered that a thyristor is connected to the system, and the control signal provides the information of the front cut or the rear cut to the subsequent circuit, so as to realize different discharge current controls in the case of the front cut and the rear cut, and improve the compatibility of the thyristor. If the front cut or the rear cut is still not detected after multiple cycles (the count value reaches the preset value), it is considered that the thyristor is not connected to the system, and the control signal Ctl controls the subsequent circuit to turn off the discharge current, thereby improving the system efficiency.

[0080] It should be noted that the signal output by the discharge control module 14 can be one, which represents the first control signal and the second control signal through different levels, and the signal output by the discharge control module 14 can be two, which are used to represent the first control signal and the second control signal respectively, which are not described one by one here.

[0081] like Figure 4 As shown, this embodiment further provides an LED driving system, which at least includes: a thyristor detection circuit 1, a voltage input circuit 2 and an LED constant current control circuit 3.

[0082] like Figure 4 As shown, the voltage input circuit 2 receives an alternating voltage AC and converts the alternating voltage AC into a bus voltage HVin.

[0083] Specifically, in this embodiment, the voltage input circuit 2 includes a rectifier module 21 and a thyristor 22. The AC end of the rectifier module 21 is connected to the AC voltage AC, and the DC end outputs the bus voltage HVin. The thyristor 22 is connected in series to the AC end of the rectifier module 21. As another implementation of the present invention, the voltage input circuit 2 also includes a fuse F1, which is connected in series to the AC end of the rectifier module 21.

[0084] like Figure 4 As shown, the thyristor detection circuit 1 is connected to the output end of the voltage input circuit 2, and is used to detect whether the thyristor is connected, and to generate a thyristor leading or trailing judgment signal when the thyristor is connected. The specific structure is as described above, and will not be described here one by one.

[0085] like Figure 4 As shown, the LED constant current control circuit 3 is connected to the voltage input circuit 2 and the output end of the thyristor detection circuit 1, realizes the constant current output of the LED based on the bus voltage HVin, and realizes the thyristor dimming control based on the output signal of the thyristor detection circuit 1.

[0086] Specifically, in the present embodiment, the LED constant current control circuit 3 includes a drive control module 31, a diode D1, an LED load and an output capacitor Co. The drive control module 31 receives the bus voltage HVin and the control signal output by the thyristor detection circuit 1 to control the current flowing through the LED load. The anode of the diode D1 is connected to the drive control module 31, and the cathode is connected to the positive electrode of the LED load. The negative electrode of the LED load is connected to the drive control module 31. One end of the output capacitor Co is connected to the anode of the LED load, and the other end is grounded. In actual use, the LED constant current control circuit 3 can be a linear drive structure or a switch-type drive structure, as long as it can accept the discharge control signal and perform corresponding actions, and is not limited to the present embodiment.

[0087] It should be noted that, in this example, the control signal provided by the thyristor detection circuit 1 is used to provide information on whether the thyristor is connected, and when the thyristor is connected, whether it is cut in front or in the back. The actual discharge current is controlled by the LED constant current control circuit 3. In actual use, all control circuits for the discharge current can also be integrated into the discharge control module 14 of the thyristor detection circuit 1, which will not be described one by one here.

[0088] like Figure 5 As shown, this embodiment also provides a discharge current control method, and the discharge current control method at least includes:

[0089] 1) Power on and generate discharge current.

[0090] Specifically, Figure 4 Taking the LED driving system shown as an example, when the system is powered on, the discharge path in the driving control module 31 is turned on to generate a discharge current.

[0091] 2) Counting the cycles of the bus voltage HVin and detecting the transition edges of the bus voltage HVin.

[0092] Specifically, in this embodiment, the thyristor detection circuit 1 compares the voltage division signal of the bus voltage HVin with the reference signal REF to obtain the duty cycle of the bus voltage HVin and counts. At the same time, the thyristor detection circuit 1 also detects the transition edge of the bus voltage HVin and outputs a corresponding pulse signal when the transition edge is detected.

[0093] 3) If the leading or trailing judgment signal of the thyristor is detected, the counting result is reset to zero, and the discharge current is controlled according to the leading or trailing judgment result.

[0094] Specifically, in this embodiment, the thyristor detection circuit 1 judges the voltage value of the pulse signal. When the amplitude of the pulse signal is greater than the set value, the reset signal is triggered, and the counting module is reset to zero, and it is determined that the system is not connected to the thyristor. At the same time, the thyristor detection circuit 1 generates a corresponding discharge control signal according to the positive and negative attributes of the pulse signal (positive and negative relative to the reference voltage). The LED constant current control circuit 3 then controls the discharge current based on the output signal of the thyristor detection circuit 1 combined with the output current of the LED constant current control circuit 3, which will not be described in detail here.

[0095] 4) If the leading or trailing judgment signal of the thyristor is not detected, the counting continues until the preset value is reached, and the discharge current is turned off.

[0096] Specifically, in this embodiment, if the thyristor detection circuit 1 does not detect a pulse signal, or the amplitude of the pulse signal is less than a set value, the reset signal is not triggered, and the counting module continues to count. After a number of consecutive counting cycles (i.e., a preset value, as an example, the preset value is not less than 2), it is determined that the system is not connected to the thyristor, then the thyristor detection circuit 1 outputs a control signal to shut down the discharge current, and then the LED constant current control circuit 3 shuts off the internal discharge current.

[0097] In the present invention, the voltage-dividing signal of the bus voltage HVin is compared with the reference signal REF to generate a signal that changes with the bus voltage, and count the power frequency cycle of the input voltage. When the thyristor is connected, the judgment signal of the thyristor can be detected in each power frequency cycle, and the counting module will be reset by the reset signal of the pulse voltage detection module, and it is always in a counting state starting from zero, and the LED constant current control circuit is always in a discharge current control state (the system starts in the default discharge current control state). When there is no thyristor, on the one hand, the judgment signal of the thyristor cannot be received (the judgment signal of the front cutting and the back cutting) on ​​the other hand, when the counting module is still not reset by the thyristor judgment signal after several power frequency cycles, the counting module counts to the preset value and considers that the system is not connected to the thyristor, thereby outputting a control signal to turn off the discharge current of the rear-stage LED constant current control circuit. At this time, the counting module is locked until a new reset signal is cleared and counted again.

[0098] Therefore, when there is no thyristor connected, even if the bus voltage jumps or there is a switch spike interference, the system will work for a few more power frequency cycles to output the discharge current to ensure the detection of the thyristor, and then turn off the discharge current after the counting is completed, and finally re-enter the stable state to improve the system efficiency. When the thyristor is connected, since the system defaults to outputting the discharge current when it is turned on, and then the counting module is reset and cleared to zero each time by the thyristor detection signal, it is unable to output the discharge current shutdown signal, thereby avoiding the mistaken shutdown of the discharge current due to inaccurate detection time and improving the compatibility of the thyristor.

[0099] Embodiment 2

[0100] In the first embodiment, the reference voltage Vref is set to 0V, which may cause the problem of inconvenient processing of negative voltage (including but not limited to negative peak pulse voltage signals). Therefore, in this embodiment, the reference voltage Vref is set to be greater than 0 (the potential is higher than the reference ground), and the output voltage Vs of the bus voltage detection module 11 is clamped and protected, and the first preset voltage and the second preset voltage in the pulse voltage detection module 12 are adjusted.

[0101] like Figure 6 As shown, the thyristor detection circuit 1 further includes a clamping unit 16, which is connected to the output end of the bus voltage detection module 11 and is used to clamp the output signal of the bus voltage detection module 11. At this time, the range of the output voltage Vs of the bus voltage detection module 11 is transferred from positive and negative voltages to between 0-VZD1 (VZD1 is a clamping voltage point, greater than 0), so it is relatively easier to process.

[0102] Specifically, in this embodiment, the clamping unit 16 is implemented by a voltage regulator diode ZD1, the cathode of the voltage regulator diode ZD1 is connected to the output end of the bus voltage detection module 11, and the anode is grounded. In actual use, any structure that can achieve clamping is applicable.

[0103] like Figure 6 As shown, in this embodiment, the first preset voltage Vset is greater than Vref, and is set to Vref+ΔV (i.e., the pulse signal is a positive peak pulse voltage signal, and is ΔV greater than the reference voltage Vref); the second preset voltage Vset2 is greater than 0V and less than Vref, and is set to Vref-ΔV (i.e., the pulse signal is a positive peak pulse voltage signal, and is ΔV less than the reference voltage Vref). In actual use, any circuit structure that can obtain the front-cut judgment signal CF and the rear-cut judgment signal CR based on the output signal of the bus voltage detection module 11 is applicable to the present invention, and is not limited to this embodiment.

[0104] The other circuit structures and working principles of the thyristor detection circuit, LED driving system and discharge current control method of this embodiment are the same as those of the first embodiment and are not described in detail here.

[0105] In summary, the present invention provides a thyristor detection circuit, an LED drive system and a discharge current control method, comprising: a bus voltage detection module, a pulse voltage detection module, a counting module and a discharge control module; the first end of the bus voltage detection module is connected to the bus voltage, and the second end is connected to the reference voltage, for detecting the transition edge of the bus voltage and generating a corresponding pulse signal; the pulse voltage detection module is connected to the output end of the bus voltage detection module, generates a leading cutting judgment signal or a trailing cutting judgment signal of the thyristor based on the pulse signal, and triggers a reset when detecting that the leading cutting judgment signal or the trailing cutting judgment signal is valid. The counting module is connected to the output end of the pulse voltage detection module, counts the period of the bus voltage, and resets the counting result to zero when the reset signal is valid; the discharge control module is connected to the pulse voltage detection module and the output end of the counting module, and generates a first control signal according to the front cutting judgment signal or the back cutting judgment signal when the counting result is less than the preset value, and generates a second control signal when the counting result is greater than or equal to the preset value, wherein the first control signal controls the subsequent circuit to perform discharge current control, and the second control signal controls the subsequent circuit to shut off the discharge current. The thyristor detection circuit, LED drive system and discharge current control method of the present invention can identify the front-cut and rear-cut dimmers according to the jump signal, thereby improving the compatibility of the thyristor; and there will be no erroneous judgment of not connecting the thyristor due to the large phase angle of the thyristor; the thyristor detection circuit, LED drive system and discharge current control method of the present invention use the counting module to eliminate occasional spike interference such as switching and voltage mutation, and have strong anti-interference performance; the capacitance capacity of the thyristor detection circuit and LED drive system for detecting the bus voltage of the present invention is very small, and can be integrated into the chip together with the resistor to simplify the system design; the thyristor detection circuit, LED drive system and discharge current control method of the present invention use the jump caused by the opening of the thyristor to generate a reset signal, so that the counting module cannot output the shutdown signal of the discharge current, thereby judging the connection of the thyristor, and no longer needing a large capacitor to filter and time the power frequency signal, which can significantly reduce the chip area and external capacitance. Therefore, the present invention effectively overcomes the various shortcomings in the prior art and has a high industrial utilization value.

[0106] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may 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 a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A thyristor detection circuit, characterized in that: The thyristor detection circuit at least comprises: Bus voltage detection module, pulse voltage detection module, counting module and discharge control module; The first end of the bus voltage detection module is connected to the bus voltage, and the second end is connected to the reference voltage, and is used to detect the transition edge of the bus voltage and generate a corresponding pulse signal; The pulse voltage detection module is connected to the output end of the bus voltage detection module, generates a leading cutting judgment signal or a trailing cutting judgment signal of the thyristor based on the pulse signal, and triggers a reset signal when detecting that the leading cutting judgment signal or the trailing cutting judgment signal is valid; The counting module is connected to the output end of the pulse voltage detection module, counts the cycle of the bus voltage, and resets the counting result to zero when the reset signal is valid; The discharge control module is connected to the output ends of the pulse voltage detection module and the counting module, and generates a first control signal according to the front-cut judgment signal or the back-cut judgment signal when the counting result is less than a preset value, and generates a second control signal when the counting result is greater than or equal to the preset value, wherein the first control signal controls the subsequent circuit to perform discharge current control, and the second control signal controls the subsequent circuit to shut off the discharge current.

2. The thyristor detection circuit according to claim 1, characterized in that: The bus voltage detection module includes a first capacitor and a first resistor; one end of the first capacitor serves as the first end of the bus voltage detection module, and the other end is connected to one end of the first resistor; the other end of the first resistor serves as the second end of the bus voltage detection module; A connection node between the first capacitor and the first resistor serves as an output end of the bus voltage detection module.

3. The thyristor detection circuit according to claim 1 or 2, characterized in that: The thyristor detection circuit further includes a second resistor, which is connected in series between the bus voltage and the first end of the bus voltage detection module.

4. The thyristor detection circuit according to claim 1, characterized in that: The potential of the reference voltage is equal to or higher than the reference ground.

5. The thyristor detection circuit according to claim 1 or 4, characterized in that: The pulse voltage detection module includes a first comparator, a second comparator and a logic unit; The first comparator receives the output signal of the bus voltage detection module, and outputs a valid leading edge judgment signal when the voltage value of the pulse signal is greater than a first preset voltage; The second comparator receives the output signal of the bus voltage detection module, and outputs a valid post-cut judgment signal when the voltage value of the pulse signal is less than a second preset voltage; The logic unit is connected to the output terminals of the first comparator and the second comparator, and generates the reset signal based on the leading cut judgment signal or the trailing cut judgment signal; The first preset voltage is greater than the reference voltage, and the second preset voltage is less than the reference voltage.

6. The thyristor detection circuit according to claim 1, characterized in that: The thyristor detection circuit also includes a counting clock generating module; the counting clock generating module is connected to the bus voltage, generates a timing clock based on the power frequency cycle of the bus voltage, and provides the timing clock to the counting module.

7. The thyristor detection circuit according to claim 6, characterized in that: The counting clock generating module includes a voltage dividing unit and a third comparator; the voltage dividing unit divides the bus voltage; the third comparator is connected to the output end of the voltage dividing unit, and compares the output signal of the voltage dividing unit with a reference signal to obtain the timing clock.

8. An LED driving system, characterized in that: The LED driving system at least comprises: A voltage input circuit, an LED constant current control circuit and a thyristor detection circuit as claimed in any one of claims 1 to 7; The voltage input circuit receives an AC voltage and converts the AC voltage into a bus voltage; The thyristor detection circuit is connected to the output end of the voltage input circuit, and is used to detect whether the thyristor is connected, and to generate a leading cutting judgment signal or a trailing cutting judgment signal of the thyristor when the thyristor is connected; The LED constant current control circuit is connected to the voltage input circuit and the output end of the thyristor detection circuit, realizes constant current output of the LED based on the bus voltage, and realizes thyristor dimming control based on the output signal of the thyristor detection circuit.

9. The LED driving system according to claim 8, characterized in that: The LED constant current control circuit is a linear drive structure or a switch type drive structure.

10. A discharge current control method, implemented based on the thyristor detection circuit according to any one of claims 1 to 7, characterized in that: The discharge current control method at least comprises: Power on, generating discharge current; Counting the cycle of the bus voltage and detecting the transition edge of the bus voltage; If the leading or trailing judgment signal of the thyristor is detected, the counting result is reset to zero, and the discharge current is controlled according to the leading or trailing judgment result; If the leading cutting judgment signal or the trailing cutting judgment signal of the thyristor is not detected, the counting continues until the preset value is reached, and the discharge current is turned off.

Images