Discharge circuit, discharge current control method and lighting circuit

Abstract

The invention provides a bleeder circuit, a bleeder current control method and a lighting system, after alternating current input voltage passes through a dimmer and a rectifying circuit, bus voltage after phase cutting is obtained, and the bleeder circuit comprises a current generating circuit used for generating bleeder current; the bleeder control circuit is used for controlling the magnitude of the bleeder current according to the magnitude of the bus voltage; wherein the dimmer works in a back-cut dimming mode, and after the dimmer is turned off, when the bus voltage is greater than a first threshold value, the current generation circuit generates a first bleeder current; when the bus voltage is smaller than a first threshold value, the current generating circuit generates second bleeder current, and the second bleeder current is larger than the first bleeder current. According to the invention, the leakage loss can be saved, and the bus voltage can be quickly reset to zero when the bus voltage is close to the valley bottom.

Description

Technical Field

[0001] The present invention relates to the field of lighting, and in particular to a discharge circuit, a discharge current control method and a lighting circuit. Background Art

[0002] Dimming with a dimmer is a common dimming method. The dimmer is connected in series between the AC input and the rectifier circuit, and the phase control method is used to achieve dimming, that is, the dimmer is controlled to conduct in every half cycle of the sine wave to obtain the same conduction phase angle. By adjusting the chopping phase of the dimmer, the conduction phase angle can be changed to achieve dimming.

[0003] The dimmer working modes generally include front-cut dimming mode, rear-cut dimming mode and digital dimming mode. The schematic diagram of the discharge circuit in the rear-cut dimming mode is as follows: Figure 1 As shown, the AC input voltage AC is converted into a bus voltage Vbus through a dimmer and a rectifier circuit. The discharge circuit is connected to the output end of the rectifier circuit, and includes an operational amplifier U1 and switch tubes M1 and R1 connected in series. The operational amplifier U1 performs operational amplification on the reference voltage VREF and the sampling signal Vcs representing the load current to drive the switch tube M1. When the load is not turned on, the output signal of the operational amplifier U1 is greater than zero, driving the switch tube M1 to turn on, and generating a discharge current I on the switch tube M1 and the resistor R1. BLD The corresponding working waveform is as follows: Figure 2 shown.

[0004] Since the reference voltage VREF and the resistor R1 are fixed, the discharge current I BLD is also fixed. When the internal capacitance of the post-cut dimmer is large enough, if the discharge current I BLD If the resistor R1 is too small, the bus voltage Vbus may not be reset to 0V before the next cycle, which will affect the control of the next cycle. BLD , which will increase the discharge loss. Therefore, the existing discharge circuit makes the dimmer compatibility not good enough and the dimming not flexible enough. Summary of the invention

[0005] The object of the present invention is to provide a discharge circuit, a discharge current control method and a lighting circuit, which solve the problem of poor compatibility of the dimmer in the dimmer post-cut mode in the prior art.

[0006] The present invention provides a discharge circuit, wherein the AC input voltage is passed through a dimmer and a rectifier circuit to obtain a bus voltage after phase cutting, comprising:

[0007] A current generating circuit, connected to the output end of the rectifier circuit, for generating a discharge current;

[0008] A discharge control circuit, connected to the control end of the current generating circuit, and used to control the magnitude of the discharge current according to the magnitude of the bus voltage;

[0009] In which, the dimmer operates in the post-cut dimming mode. After the dimmer is turned off, when the bus voltage is greater than a first threshold, the current generating circuit generates a first discharge current; when the bus voltage is less than the first threshold, the current generating circuit generates a second discharge current, and the second discharge current is greater than the first discharge current.

[0010] Optionally, after the dimmer is turned on and the load is not turned on, if the bus voltage is greater than a first threshold, the current generating circuit generates the first discharge current; if the bus voltage is less than the first threshold, the current generating circuit generates the second discharge current.

[0011] Optionally, after the dimmer is turned on, when the load is turned on, if the load current is less than the set current, the current generating circuit generates a third discharge current;

[0012] When the bus voltage is greater than a first threshold value, the set current is equal to the first discharge current, and the sum of the third discharge current and the load current is equal to the first discharge current; when the bus voltage is less than the first threshold value, the set current is equal to the second discharge current, and the sum of the third discharge current and the load current is equal to the second discharge current.

[0013] Optionally, both the first discharge current and the second discharge current are negatively correlated with the bus voltage.

[0014] Optionally, the current generating circuit includes a first resistor and an adjustment tube, and the first resistor and the adjustment tube are connected in series;

[0015] When the dimmer is turned off, the first adjustment tube is turned on, and the discharge current flowing through the first adjustment tube is controlled according to the bus voltage.

[0016] Optionally, after the dimmer is turned on and the load is not turned on, the first adjustment tube is turned on, and a discharge current flowing through the first adjustment tube is controlled according to the bus voltage.

[0017] Optionally, the discharge control circuit includes a reference voltage generating circuit and a first operational amplifier, the dimmer operates in a post-cut dimming mode, and the reference voltage generating circuit generates a reference voltage according to the bus voltage;

[0018] The first input end of the first operational amplifier is connected to the output end of the reference voltage generating circuit, the second input end of the first operational amplifier receives a sampling signal, the output end of the first operational amplifier is connected to the control end of the first adjustment tube, and the size of the sampling signal represents the size of the load current or represents whether the dimmer is turned on.

[0019] Optionally, the reference voltage generating circuit is configured to generate a first reference voltage when the bus voltage is greater than a first threshold value; and to generate a second reference voltage when the bus voltage is less than the first threshold value, wherein the first reference voltage is less than the second reference voltage.

[0020] Optionally, the first reference voltage and the second reference voltage are both negatively correlated with the bus voltage.

[0021] Optionally, it further includes a dimming mode judgment circuit, which detects the bus voltage and judges the working mode of the dimmer according to the bus voltage;

[0022] When it is determined that the dimmer operates in the post-cut mode, the dimming mode determination circuit outputs an enable signal to the discharge control circuit, and the discharge control circuit is enabled.

[0023] Optionally, within N consecutive half-wave cycles, if the dimming mode judgment circuit detects that the duration of the bus voltage dropping from the first voltage to the second voltage in each half-wave cycle is less than a set time, it is determined that the dimmer is operating in the post-cut dimming mode; wherein N is an integer greater than or equal to 2.

[0024] The present invention also provides a discharge current control method, wherein the AC input voltage passes through a dimmer and a rectifier circuit to obtain a bus voltage after phase cutting, and a discharge path is established between the output end of the rectifier circuit and the ground end. The dimmer operates in a post-cut dimming mode. After the dimmer is turned off, when the bus voltage is greater than a first threshold, a first discharge current is generated on the discharge path; when the bus voltage is less than the first threshold, a second discharge current is generated on the discharge path, and the second discharge current is greater than the first discharge current.

[0025] Optionally, after the dimmer is turned on and the load is not turned on, if the bus voltage is greater than a first threshold, the first discharge current is generated on the discharge path; if the bus voltage is less than the first threshold, the second discharge current is generated on the discharge path.

[0026] Optionally, after the dimmer is turned on, when the load is turned on, if the load current is less than the set current, a third discharge current is generated on the discharge path;

[0027] When the bus voltage is greater than a first threshold value, the set current is equal to the first discharge current, and the sum of the third discharge current and the load current is equal to the first discharge current; when the bus voltage is less than the first threshold value, the set current is equal to the second discharge current, and the sum of the third discharge current and the load current is equal to the second discharge current.

[0028] Optionally, both the first discharge current and the second discharge current are negatively correlated with the bus voltage.

[0029] The present invention further provides a lighting circuit, comprising a dimmer and a rectifier circuit, wherein an AC input voltage passes through the dimmer and the rectifier circuit to obtain a bus voltage after phase cutting, and further comprising any one of the above-described discharge circuits, wherein the discharge circuit is connected to the output end of the rectifier circuit;

[0030] and a subsequent driving circuit connected between the discharge circuit and the load, for controlling the magnitude of the load current. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the schematic diagram of the existing lighting circuit;

[0032] Figure 2 It is a working waveform diagram of the existing discharge circuit;

[0033] Figure 3 This is a schematic diagram of the lighting circuit of the present invention;

[0034] Figure 4 is a schematic diagram of a reference voltage generating circuit of the present invention;

[0035] Figure 5 It is a working waveform diagram of the discharge circuit of the present invention. DETAILED DESCRIPTION

[0036] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitution, modification, equivalent method and scheme made on the spirit and range of the present invention.

[0037] In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without these detailed descriptions.

[0038] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the accompanying drawings are all simplified and not in exact proportions, in order to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0039] like Figure 3As shown, the schematic diagram of the lighting circuit of the present invention is illustrated, including a dimmer, a rectifier circuit, a discharge circuit, a post-stage driving circuit and a load. When the dimmer adopts a thyristor dimmer, the dimmer generally works in the front-cut mode, and the conduction of the dimmer needs to maintain the current; when the dimmer is implemented by an ordinary MOS tube, the dimmer generally works in the back-cut mode. The rectifier circuit diagram shows a rectifier bridge, and the load is a lamp bead, etc. The dimmer is connected between the AC input power supply and the rectifier circuit, and the AC input voltage AC is obtained through the dimmer and the rectifier circuit to obtain the bus voltage Vbus. The discharge circuit is connected to the output end of the rectifier circuit to establish a discharge path between the output end of the rectifier circuit and the ground end, which is used to generate a discharge current I BLD In one implementation, after the dimmer is turned off, the discharge circuit is turned on. Furthermore, when the load is not turned on, the discharge circuit is also turned on. When the discharge circuit is turned on and a discharge current is generated, the discharge current I is controlled according to the magnitude of the bus voltage Vbus. BLD In one implementation, when the bus voltage Vbus is greater than the first threshold value, the discharge current is the first discharge current, and when the bus voltage Vbus is less than the first threshold value, the discharge current is the second discharge current, and the second discharge current is greater than the first discharge current; further, according to the size of the bus voltage Vbus, the discharge current is not limited to being divided into two intervals of the first discharge current and the second discharge current. The discharge current can also be divided into more intervals according to the size of the bus voltage Vbus. Accordingly, the smaller the bus voltage Vbus is, the larger the discharge current in the corresponding interval is; further, the discharge current is negatively correlated with the bus voltage Vbus, the larger the bus voltage Vbus is, the smaller the discharge current is, and the smaller the bus voltage Vbus is, the larger the discharge current is, which is equivalent to the above-mentioned first discharge current and second discharge current being negatively correlated with the bus voltage. Furthermore, when the load is turned on, if the load current is less than the set current, the discharge circuit is also turned on to generate a third discharge current, and the sum of the third discharge current and the load current reaches the set current; in one implementation, when the bus voltage Vbus is greater than the first threshold, the set current is equal to the first discharge current, and when the bus voltage Vbus is less than the first threshold, the set current is equal to the second discharge current, and the second discharge current is greater than the first discharge current. In addition, the first discharge current and the second discharge current can also be set in the above manner.

[0040] Specifically, the discharge circuit includes a current generating circuit 01 and a discharge control circuit 02. The current generating circuit 01 is connected to the output end of the rectifier circuit, and includes a first resistor R1 and a switch tube M1 connected in series. When the switch tube M1 is turned on, a discharge current I BLD , Figure 3In the schematic diagram, the switch tube M1 is controlled to be on and off according to the sampling signal Vcs representing the load current. When the sampling signal Vcs is greater than the set value, it represents that the load is turned on, and the load current is greater than the set current, and the switch tube M1 is controlled to be turned off; when the sampling signal is less than the set value, it represents that the load current is less than the set current or the load is turned off, and the switch tube M1 is controlled to be turned on, and the discharge current I is controlled according to the bus voltage and the sampling signal. BLD In another way, the sampling signal is used to indicate whether the dimmer is turned off (not shown in the figure). For example, when the sampling signal is zero, it indicates that the dimmer is turned off, and the switch tube M1 is controlled to be turned on to generate a discharge current. If the sampling signal is greater than zero, it indicates that the dimmer is turned on, and the switch tube M1 is controlled to be turned off. The discharge control circuit 02 is used to control the state (conduction degree) of the switch tube M1 according to the bus voltage Vbus to control the discharge current I BLD The size of the mode judgment circuit includes a mode judgment circuit, a reference voltage generating circuit and a first operational amplifier U01. The mode judgment circuit is used to judge whether the dimmer works in the front-cut dimming mode or the rear-cut dimming mode according to the bus voltage Vbus. When it is judged that the dimmer works in the rear-cut dimming mode, an enable signal EN is output to enable the reference voltage generating circuit. Further, if it is known that the dimmer is a rear-cut dimmer, it is no longer necessary to judge the working mode of the dimmer, and the reference voltage generating circuit is directly enabled to work; if the working mode of the dimmer is unknown, it is necessary to judge the working mode of the dimmer. When it is determined that the dimmer works in the rear-cut working mode, the reference voltage generating circuit is enabled. Therefore, the mode judgment circuit is not necessary, and whether it is needed depends on the specific circuit situation. One implementation method of the mode judgment circuit is to detect the bus voltage Vbus. In N consecutive half-wave cycles (N is an integer greater than or equal to 2), if it is detected that the time taken for the bus voltage to drop from the first voltage to the second voltage in each half-wave cycle is less than the set threshold time, then it is determined that the dimmer works in the rear-cut dimming mode. In addition, if the mode determination circuit determines that the dimmer operates in the leading cutting mode, another solution for controlling the discharge current is adopted, which is not further limited in the present invention.

[0041] The reference voltage generating circuit receives the bus voltage Vbus and generates a reference voltage VREF according to the magnitude of the bus voltage Vbus. The first operational amplifier U1 receives the reference voltage VREF at its in-phase input terminal, receives the sampling signal Vcs representing the load current at its inverting input terminal, and connects its output terminal to the control terminal of the switch tube M1. In another way, the sampling signal received at the inverting input terminal of the first operational amplifier U1 represents whether the dimmer is turned on or not. The reference voltage VREF is obtained according to the bus voltage Vbus as follows. In one implementation, when the bus voltage Vbus is greater than the first threshold, the reference voltage is the first reference voltage, and when the bus voltage Vbus is less than the first threshold, the reference voltage is the second reference voltage, which is greater than the first reference voltage; further, when the bus voltage Vbus is less than the first threshold and greater than the second threshold, the second reference voltage is the first voltage, and when the bus voltage Vbus is less than the second threshold, the second reference voltage is the second voltage, which is greater than the first voltage; further, the reference voltage VREF is negatively correlated with the bus voltage Vbus, that is, the first reference voltage and the second reference voltage are both negatively correlated with the bus voltage. Furthermore, the reference voltage VREF can be divided into multiple intervals according to the bus voltage Vbus. The smaller the bus voltage Vbus is, the larger the reference voltage VREF in the corresponding interval is, so that when the switch tube M1 is turned on, the corresponding discharge current I BLD The bigger.

[0042] For example, the dimmer conduction angle is 120 degrees, the bus voltage Vbus peak is 311V, and the load conduction voltage is 200V. When the bus voltage drops below 200V / the dimmer is turned off, the load does not conduct, generating a discharge current I BLD , so that when the dimmer is turned off, the bus voltage can be quickly pulled to zero with low loss. When the bus voltage drops below 200V but is greater than 100V, the reference voltage is set smaller, which is the second reference voltage, to control the discharge current I BLD is smaller, thereby reducing the loss generated in the current generating circuit 01; when the bus voltage Vbus further drops below 100V, the reference voltage Vbus is set to be a little larger, which is the first reference voltage, and the discharge current I is controlled by the reference voltage BLD The present invention takes into account that the internal capacitor on the dimmer will store energy, and the bus voltage after phase cutting may not drop to zero quickly after the dimmer is turned off, so a discharge current I is required. BLDThe bus voltage Vbus is quickly reset to zero to avoid problems such as misjudgment affecting subsequent control when entering the next half-wave cycle due to the bus voltage Vbus not rising from zero. When the bus voltage Vbus is high, a small discharge current is generated to reduce the discharge loss. When the bus voltage Vbus is low, a large discharge current is generated. The bus voltage is quickly pulled down to zero. When the bus voltage Vbus is low, even if the discharge current is larger, the loss generated on the first resistor R1 is limited, and no large loss will be generated. When the load is not turned on, the present invention is not limited to dividing the discharge current into two intervals. According to the size of the bus voltage Vbus, the discharge current can also be divided into multiple intervals (greater than two intervals). The larger the bus voltage Vbus is, the larger the discharge current in the corresponding interval is, which further optimizes the performance of the discharge circuit and improves the compatibility of the dimmer.

[0043] For example, when the dimmer conduction angle is small, such as 60 degrees, after the dimmer is turned on, when the load is not turned on / the load current is small, a discharge current will also be generated to avoid the bus voltage Vbus being artificially high and affecting subsequent detection and control. The present invention can also control whether to generate a discharge current according to the load current during the entire half-wave cycle, referring to Figure 5 The waveform shows that after the dimmer is turned on, when the load is not turned on / the load current is small, a larger discharge current is generated when the bus voltage is small, and a smaller discharge current is generated when the bus voltage is large, which can not only avoid the bus voltage Vbus being artificially high before the load is turned on, but also reduce the discharge loss; after the dimmer is turned off, the load is turned off, and the need to generate a discharge current is determined by detecting the load current size. There is no need to detect the turn-off moment of the dimmer, and there is no need to worry about the discharge delay caused by the discharge current generated after the dimmer is detected to be turned off, so that the bus voltage can be quickly reset to zero with a lower discharge loss.

[0044] like Figure 4As shown in the figure, a schematic diagram of an embodiment of the reference voltage generation circuit of the present invention is illustrated, which includes a comparator U02 and a reference voltage selection circuit. One input terminal of the comparator U02 receives the bus voltage Vbus, and the other input terminal receives the first voltage VZ. The output terminal of the comparator is connected to the input terminal of the reference voltage selection circuit. The reference voltage selection circuit selects and outputs the first reference voltage VREF1 or the second reference voltage VREF2 according to the relationship between the bus voltage Vbus and the first voltage VZ. When Vbus > VZ, the first reference voltage VREF1 is selected for output; when Vbus < VZ, the second reference voltage VREF2 is selected for output, where VREF1 < VREF2. In this embodiment, according to the magnitude of the bus voltage Vbus, the reference voltage VREF is the first reference voltage VREF1 or the second reference voltage VREF2. The schematic diagram of the reference voltage generation circuit of the present invention is not limited to this embodiment. The reference voltage VREF can also be divided into multiple intervals with different magnitudes, or output after linear adjustment according to the bus voltage Vbus (the larger the bus voltage Vbus, the smaller the reference voltage VREF). There are various ways to generate the reference voltage VREF, and the present invention does not limit this.

[0045] As Figure 5 shown in the figure, a working waveform diagram of a discharge circuit of the present invention is illustrated, corresponding to the dimming device operating in the post-cut dimming mode. When the bus voltage Vbus is less than the first threshold VZ and less than the load voltage VF, the reference voltage VREF is VREF1, the load is not conducting and there is no current, and the discharge circuit is conducting, and the discharge current I BLD has a magnitude of I BLD1 . As the bus voltage Vbus increases, when the bus voltage Vbus is greater than the first threshold VZ and less than the load voltage VF, the reference voltage VREF is VREF2, VREF2 is less than VREF1, the load is not conducting and there is no current, the discharge circuit is conducting, and the discharge current I BLD has a magnitude of I BLD2 , and I BLD2 is less than I BLD1 . As the bus voltage Vbus further increases, when the bus voltage Vbus is greater than the load voltage VF, the load conducts, the discharge circuit is turned off, and the reference voltage VREF is zero (the reference voltage VREF can also be maintained, but the difference between the reference voltage VREF and the current sampling signal VCS is not sufficient to drive the discharge circuit to conduct), and the discharge current I BLD is zero. After the bus voltage Vbus drops from the peak value, when the dimming device is turned off, the bus voltage drops to Vtra, and the bus voltage Vbus drops rapidly after the dimming device is turned off. After the dimming device is turned off, the load is turned off, there is no current in the load, and when the bus voltage Vbus is greater than the first threshold VZ, the reference voltage VREF is VREF2, the discharge circuit is conducting, and a discharge current I BLD2As the bus voltage Vbus further drops below the first threshold VZ, the reference voltage VREF becomes VREF1, and the discharge current I BLD Rise to I BLD1 When the bus voltage Vbus is zero, the discharge current I BLD This waveform is explained by taking the reference voltage VREF as a two-stage type and the discharge current as a two-stage type as an example, that is, according to the size of the bus voltage Vbus, when the load is not turned on, VREF is VREF1 or VREF2, and the corresponding discharge current is I BLD1 or I BLD2 According to the above description of the present invention, the discharge circuit of the present invention can also generate the discharge current in other ways, such as from the discharge current I BLD It decreases linearly with the increase of bus voltage Vbus, not like Figure 5 In the post-cut dimming mode, the present invention adjusts the discharge current according to the bus voltage, which can not only reduce the discharge loss when the bus voltage is large, but also quickly reset the bus voltage to zero voltage when the bus voltage is small, avoiding other problems caused by the bus voltage not dropping to zero at the end of the half-wave cycle.

[0046] Although the embodiments are described and illustrated separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that the embodiments can be replaced and integrated. If the content is not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0047] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. A discharge circuit, wherein the AC input voltage is converted into a bus voltage after phase cutting after passing through a dimmer and a rectifier circuit, characterized in that: include: A current generating circuit, connected to the output end of the rectifier circuit, for generating a discharge current; A discharge control circuit, connected to the control end of the current generating circuit, and used to control the magnitude of the discharge current according to the magnitude of the bus voltage; In which, the dimmer operates in the post-cut dimming mode. After the dimmer is turned off, when the bus voltage is greater than a first threshold, the current generating circuit generates a first discharge current; when the bus voltage is less than the first threshold, the current generating circuit generates a second discharge current, and the second discharge current is greater than the first discharge current.

2. The discharge circuit according to claim 1, characterized in that: After the dimmer is turned on and the load is not turned on, if the bus voltage is greater than a first threshold, the current generating circuit generates the first discharge current; if the bus voltage is less than the first threshold, the current generating circuit generates the second discharge current.

3. The discharge circuit according to any one of claim 2, characterized in that: After the dimmer is turned on, when the load is turned on, if the load current is less than the set current, the current generating circuit generates a third discharge current; When the bus voltage is greater than a first threshold value, the set current is equal to the first discharge current, and the sum of the third discharge current and the load current is equal to the first discharge current; when the bus voltage is less than the first threshold value, the set current is equal to the second discharge current, and the sum of the third discharge current and the load current is equal to the second discharge current.

4. The discharge circuit according to claim 1, characterized in that: The first discharge current and the second discharge current are both negatively correlated with the bus voltage.

5. The discharge circuit according to claim 1, characterized in that: The current generating circuit comprises a first resistor and an adjusting tube, wherein the first resistor and the adjusting tube are connected in series; When the dimmer is turned off, the first adjustment tube is turned on, and the discharge current flowing through the first adjustment tube is controlled according to the bus voltage.

6. The discharge circuit according to claim 5, characterized in that: After the dimmer is turned on and the load is not turned on, the first adjustment tube is turned on, and the discharge current flowing through the first adjustment tube is controlled according to the bus voltage.

7. The discharge circuit according to claim 5, characterized in that: The discharge control circuit includes a reference voltage generating circuit and a first operational amplifier, the dimmer operates in a post-cut dimming mode, and the reference voltage generating circuit generates a reference voltage according to the bus voltage; The first input end of the first operational amplifier is connected to the output end of the reference voltage generating circuit, the second input end of the first operational amplifier receives a sampling signal, the output end of the first operational amplifier is connected to the control end of the first adjustment tube, and the size of the sampling signal represents the size of the load current or represents whether the dimmer is turned on.

8. The discharge circuit according to claim 7, characterized in that: The reference voltage generating circuit is configured to generate a first reference voltage when the bus voltage is greater than a first threshold value; and to generate a second reference voltage when the bus voltage is less than the first threshold value, wherein the first reference voltage is less than the second reference voltage.

9. The discharge circuit according to claim 8, characterized in that: The first reference voltage and the second reference voltage are both negatively correlated with the bus voltage.

10. The discharge circuit according to claim 1, characterized in that: It also includes a dimming mode judgment circuit, which detects the bus voltage and judges the working mode of the dimmer according to the bus voltage; When it is determined that the dimmer operates in the post-cut mode, the dimming mode determination circuit outputs an enable signal to the discharge control circuit, and the discharge control circuit is enabled.

11. The discharge circuit according to claim 9, characterized in that: In N consecutive half-wave cycles, if the dimming mode judgment circuit detects that the duration of the bus voltage dropping from the first voltage to the second voltage is less than the set time in each half-wave cycle, it is determined that the dimmer is operating in the post-cut dimming mode; wherein N is an integer greater than or equal to 2.

12. A discharge current control method, wherein the AC input voltage is passed through a dimmer and a rectifier circuit to obtain a bus voltage after phase cutting, characterized in that: A discharge path is established between the output end of the rectifier circuit and the ground end. The dimmer operates in a post-cut dimming mode. After the dimmer is turned off, when the bus voltage is greater than a first threshold, a first discharge current is generated on the discharge path; when the bus voltage is less than the first threshold, a second discharge current is generated on the discharge path, and the second discharge current is greater than the first discharge current.

13. The discharge current control method according to claim 12, characterized in that: After the dimmer is turned on and the load is not turned on, if the bus voltage is greater than a first threshold, the first discharge current is generated on the discharge path; if the bus voltage is less than the first threshold, the second discharge current is generated on the discharge path.

14. The discharge current control method according to claim 12, characterized in that: After the dimmer is turned on, when the load is turned on, if the load current is less than the set current, a third discharge current is generated on the discharge path; When the bus voltage is greater than a first threshold value, the set current is equal to the first discharge current, and the sum of the third discharge current and the load current is equal to the first discharge current; when the bus voltage is less than the first threshold value, the set current is equal to the second discharge current, and the sum of the third discharge current and the load current is equal to the second discharge current.

15. The discharge current control method according to claim 12, characterized in that: The first discharge current and the second discharge current are both negatively correlated with the bus voltage.

16. A lighting circuit, comprising a dimmer and a rectifier circuit, wherein an AC input voltage passes through the dimmer and the rectifier circuit to obtain a bus voltage after phase cutting, characterized in that: It also includes the discharge circuit according to any one of claims 1 to 11, wherein the discharge circuit is connected to the output end of the rectifier circuit; and a subsequent driving circuit connected between the discharge circuit and the load, for controlling the magnitude of the load current.

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