Phase-cut dimming circuit

Abstract

The phase-cut dimming circuit includes an AC power supply, a light source load connected to the AC power supply in series, a charging unit and a capacitor, and a switch unit. The charging unit is configured to receive a PWM control signal and conduct according to the PWM control signal to charge the capacitor, so that the voltage across the capacitor changes according to the conduction of the charging unit. The first end of the switch unit is connected to the connection point between the light source load and the charging unit, the second end of the switch unit is connected to the connection point between the charging unit and the capacitor, and the third end of the switch unit is connected to the connection point between the capacitor and the AC power supply. The switch unit is configured to conduct when the voltage across the capacitor reaches a threshold voltage, so that a loop is formed between the light source load, the AC power supply, and the first end and the third end of the switch unit, thereby realizing dimming of the light source load. The user can change the time it takes for the capacitor to be charged to reach the threshold voltage for the switch unit to conduct by controlling the duty cycle of the PWM control signal, thereby realizing brightness adjustment of the light source load.

Description

Technical Field

[0001] The present invention relates to the technical field of circuits, and in particular to a phase-cut dimming circuit. Background Art

[0002] Lamps are indispensable tools in people's daily lives. In practical applications, users often need to adjust the brightness of the lamp according to their preferences or needs.

[0003] Although, there are circuits that can change the brightness of lamps, such as Figure 1 As shown, this circuit has an AC power supply for providing AC voltage, a lamp connected to the AC power supply in series, a sliding rheostat, a resistor and a capacitor, and a two-terminal AC device and a bidirectional thyristor. The first anode of the bidirectional thyristor is connected between the lamp and the sliding rheostat, the second anode of the bidirectional thyristor is connected between the AC power supply and the capacitor, one end of the two-terminal AC device is connected between the resistor and the capacitor, and the other end of the two-terminal AC device is connected to the gate of the bidirectional thyristor. The two-terminal AC device will be turned on according to the voltage across the capacitor, thereby triggering the bidirectional thyristor to turn on. When the resistance value of the sliding rheostat is changed, the charging time taken for the capacitor to reach the conduction voltage of the two-terminal AC device will also change, so that the bidirectional thyristor can be turned on at different phases, thereby changing the brightness of the lamp.

[0004] However, this circuit can only adjust the brightness of the lamp by manually adjusting the resistance of the sliding rheostat. It is not only complicated to operate and has poor accuracy, but also cannot be adjusted online or remotely operated. It can no longer meet the development needs of digitalization and intelligence. Summary of the invention

[0005] In view of the above problems, the present invention is proposed to provide a phase-cut dimming circuit that overcomes the above problems or at least partially solves the above problems.

[0006] An object of the present invention is to provide a phase-cut dimming circuit in which the brightness of a light source load can be remotely adjusted.

[0007] A further object of the invention is to reduce the cost of such circuits.

[0008] The present invention provides a phase-cut dimming circuit, comprising an AC power supply for providing an AC voltage, a light source load, a charging unit and a capacitor connected in series in sequence to the AC power supply, and a switch unit; the charging unit is configured to receive a PWM (Pulse Width Modulation) control signal, and is turned on according to the PWM control signal to charge the capacitor, so that the voltage across the capacitor changes according to the turning on of the charging unit; the switch unit has a first end, a second end and a third end, the first end of the switch unit is connected to a connection point between the light source load and the charging unit, the second end of the switch unit is connected to a connection point between the charging unit and the capacitor, and the third end of the switch unit is connected to a connection point between the capacitor and the AC power supply, and the switch unit is configured to be turned on when the voltage across the capacitor reaches a threshold voltage, so that a loop is formed between the light source load, the AC power supply and the first end and the third end of the switch unit, thereby realizing dimming of the light source load.

[0009] Optionally, the PWM control signal includes a first PWM sub-control signal and a second PWM sub-control signal; the charging unit includes: a first charging sub-unit, configured to be turned on according to the first PWM sub-control signal within a half cycle of the AC voltage to charge the capacitor; and a second charging sub-unit, connected in parallel with the first charging sub-unit, configured to be turned on according to the second PWM sub-control signal within another half cycle of the AC voltage to charge the capacitor.

[0010] Optionally, the first charging subunit includes: a first NMOS tube, the gate of the first NMOS (N-Metal-Oxide-Semiconductor) tube is used to obtain the first PWM sub-control signal, the drain of the first NMOS tube is connected to the light source load, and the source of the first NMOS tube is connected to the capacitor.

[0011] Optionally, the first charging subunit further includes a first diode; the source of the first NMOS tube is connected to the capacitor through the first diode, and the cathode of the first diode is connected to the capacitor.

[0012] Optionally, the first charging subunit further includes: a first current limiting resistor connected between the source of the first NMOS tube and the anode of the first diode.

[0013] Optionally, it is characterized in that the second charging subunit includes: a second NMOS tube, the gate of the second NMOS tube is used to obtain the second PWM sub-control signal, the source of the second NMOS tube is connected to the light source load, and the drain of the second NMOS tube is connected to the capacitor.

[0014] Optionally, the second charging subunit further includes a second diode; the drain of the second NMOS tube is connected to the capacitor through the second diode, and the anode of the second diode is connected to the capacitor.

[0015] Optionally, the second charging subunit further includes: a second current limiting resistor connected between the drain of the second NMOS tube and the cathode of the second diode.

[0016] Optionally, the first PWM sub-control signal and the second PWM sub-control signal are the same control signal or different control signals.

[0017] Optionally, a ratio of a frequency of the AC voltage provided by the AC power supply to a frequency of the PWM control signal is 0.0005 to 0.006.

[0018] Optionally, the switching unit includes: a bidirectional thyristor, a first anode of which is connected between the light source load and the charging unit, and a second anode of which is connected between the capacitor and the AC power supply; and a bidirectional trigger diode, one end of which is connected between the charging unit and the capacitor, and the other end of which is connected to the gate of the bidirectional thyristor.

[0019] The present invention provides a phase-cut dimming circuit, which includes an AC power supply for providing an AC voltage, a light source load, a charging unit and a capacitor connected in series in sequence to the AC power supply, and a switch unit. The charging unit is configured to receive a PWM control signal, and is turned on according to the PWM control signal to charge the capacitor, so that the voltage across the capacitor changes according to the conduction of the charging unit. The switch unit has a first end, a second end and a third end, the first end of the switch unit is connected to a connection point between the light source load and the charging unit, the second end of the switch unit is connected to a connection point between the charging unit and the capacitor, the third end of the switch unit is connected to a connection point between the capacitor and the AC power supply, and the switch unit is configured to be turned on when the voltage across the capacitor reaches a threshold voltage, so that a loop is formed between the light source load, the AC power supply and the first end and the third end of the switch unit, thereby realizing dimming of the light source load. The user can change the on-duty cycle of the charging unit by controlling the duty cycle of the PWM control signal to change the time it takes for the capacitor to be charged to reach the threshold voltage of the switch unit, thereby controlling the bidirectional trigger diode to conduct at different phases, thereby triggering the bidirectional thyristor to conduct, so that the working time of the light source load can be adjusted within a single cycle of the AC voltage, thereby achieving brightness adjustment of the light source load. Since the PWM control signal can be provided remotely (such as provided by a remote communication control circuit), it can be adjusted and operated remotely to meet the development needs of digitalization and intelligence. In addition, this phase-cut dimming circuit is simple to operate, which is convenient for users to accurately adjust the brightness of the light source load.

[0020] Furthermore, the first charging subunit obtains the first PWM sub-control signal through the gate of the first NMOS tube, and the second charging subunit obtains the second PWM sub-control signal through the gate of the second NMOS tube. Since the NMOS tube is simpler in structure and easier to manufacture than the PMOS tube (PMOS is positive channel Metal Oxide Semiconductor, PMOS tube is P channel Metal-Oxide Semiconductor Field Effect Transistor), the cost of this phase-cut dimming circuit is lower.

[0021] Based on the following detailed description of specific embodiments of the present invention in conjunction with the accompanying drawings, those skilled in the art will become more aware of the above and other objects, advantages and features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0023] Figure 1 It is a circuit diagram of a circuit capable of adjusting the brightness of a lamp in the prior art;

[0024] Figure 2 is a structural block diagram of a phase-cut dimming circuit according to an embodiment of the present invention;

[0025] Figure 3 is a circuit diagram of a phase-cut dimming circuit according to an embodiment of the present invention;

[0026] Figure 4 is a relevant waveform diagram when a phase-cut dimming circuit receives a PWM control signal with a first duty cycle according to an embodiment of the present invention;

[0027] Figure 5 4 is a related waveform diagram when a phase-cut dimming circuit receives a PWM control signal with a second duty cycle according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] Figure 1 FIG. 1 is a circuit diagram of a circuit 10 for adjusting the brightness of a lamp 120 in the prior art. Figure 1 As shown, the circuit 10 has an AC power supply 110 for providing an AC voltage, a lamp 120, a sliding rheostat 130, a resistor 140 and a capacitor 150 connected in series in sequence to the AC power supply 110, and the circuit 10 also has a two-terminal AC device 160 (a two-terminal AC device is also called a bidirectional trigger diode, and in order to distinguish the prior art from the solution of this embodiment, it is called a two-terminal AC device in the prior art) and a bidirectional thyristor 170 (a bidirectional thyristor is also called a bidirectional thyristor, and in order to distinguish the prior art from the solution of this embodiment The first anode of the bidirectional thyristor 170 is connected between the lamp 120 and the sliding rheostat 130, the second anode of the bidirectional thyristor 170 is connected between the AC power supply 110 and the capacitor 150, one end of the two-terminal AC device 160 is connected between the resistor 140 and the capacitor 150, and the other end of the two-terminal AC device 160 is connected to the gate of the bidirectional thyristor 170. The two-terminal AC device 160 will be turned on according to the voltage across the capacitor 150, thereby triggering the bidirectional thyristor 170 to turn on. When the resistance value of the sliding rheostat 130 is changed, the charging time taken by the capacitor 150 to reach the turn-on voltage of the two-terminal AC device 160 will also change, so that the bidirectional thyristor 170 can be turned on at different phases, thereby changing the brightness of the lamp 120. However, this circuit 10 can only adjust the brightness of the lamp 120 by manually adjusting the resistance of the sliding rheostat 130. It is not only complicated to operate and has poor precision, but also cannot be adjusted online and remotely operated, and can no longer meet the development needs of digitalization and intelligence.

[0029] This embodiment provides a phase-cut dimming circuit 20. Figure 2is a structural block diagram of a phase-cut dimming circuit 20 according to an embodiment of the present invention. Figure 3 is a circuit diagram of a phase-cut dimming circuit 20 according to an embodiment of the present invention. The phase-cut dimming circuit 20 includes an AC power supply 200 for providing an AC voltage, a light source load 300, a charging unit 400 and a capacitor 600 sequentially connected in series to the AC power supply 200, and a switch unit 500.

[0030] The AC power supply 200 can adopt an industrial frequency sinusoidal AC power supply, such as a mains power supply. The charging unit 400 is configured to receive a PWM (Pulse Width Modulation) control signal, and is turned on according to the PWM control signal to charge the capacitor 600, so that the voltage across the capacitor 600 changes according to the conduction of the charging unit 400. Specifically, the PWM control signal can be a high-frequency square wave control signal with an adjustable duty cycle, and its frequency can be much greater than the operating frequency (50Hz or 60Hz) of the industrial frequency AC power supply. For example, the frequency of the PWM control signal can be 10kHz to 100kHz. It can be understood by those skilled in the art that when the PWM control signal is at a high level, the charging unit 400 will be turned on to charge the capacitor 600. When the PWM control signal is at a low level, the charging unit 400 will be turned off, and the capacitor 600 cannot be charged. The duty cycle refers to the proportion of the time occupied by the high level in one cycle of the PWM control signal to the cycle.

[0031] The switch unit 500 has a first end, a second end and a third end. The first end of the switch unit 500 is connected to the connection point between the light source load 300 and the charging unit 400, the second end of the switch unit 500 is connected to the connection point between the charging unit 400 and the capacitor 600, and the third end of the switch unit 500 is connected to the connection point between the capacitor 600 and the AC power supply 200. The switch unit 500 is configured to be turned on when the voltage across the capacitor 600 reaches a threshold voltage, so that a loop is formed between the light source load 300, the AC power supply 200, and the first end and the third end of the switch unit 500, thereby realizing dimming of the light source load 300. It can be understood by those skilled in the art that when the switch unit 500 is turned on, the first end and the third end of the switch unit 500 are both turned on, and when the AC voltage of the AC power supply 200 passes through zero, the first end and the third end of the switch unit 500 are both turned off. It can be understood by those skilled in the art that the second end can be a control end, and the control end is used to control the first end and the third end to be turned on, or to control the first end and the third end to be turned off. The threshold voltage refers to the conduction trigger voltage of the switch unit 500, which is related to the components of the selected switch unit. Those skilled in the art can understand that by changing the duty cycle of the PWM control signal, the conduction duty cycle of the charging unit 400 within one cycle of the AC voltage can be changed, and the time for the capacitor 600 to be charged to reach the threshold voltage for the switch unit 500 to conduct will change accordingly, so that the switch unit 500 can be turned on at different phases of the AC voltage.

[0032] In the phase-cut dimming circuit 20 of the present embodiment, the user can change the conduction duty cycle of the charging unit 400 by controlling the duty cycle of the PWM control signal to change the time for the capacitor 600 to be charged to reach the threshold voltage of the switch unit 500, thereby controlling the bidirectional trigger diode 550 to conduct at different phases, thereby triggering the bidirectional thyristor 540 to conduct, so that the working time of the light source load 300 in a single cycle of the AC voltage is adjustable, and the brightness of the light source load 300 is adjusted. Since the PWM control signal can be provided remotely (such as provided by a remote communication control circuit), it can be adjusted online and remotely operated to meet the development needs of digitalization and intelligence. In addition, the phase-cut dimming circuit 10 is simple to operate, which is convenient for users to accurately adjust the brightness of the light source load 300.

[0033] The PWM control signal may include a first PWM sub-control signal and a second PWM sub-control signal. The charging unit 400 may include a first charging sub-unit 410 and a second charging sub-unit 420 .

[0034] The first charging subunit 410 is configured to be turned on according to the first PWM sub-control signal in a half cycle of the AC voltage to charge the capacitor 600. It can be understood by those skilled in the art that in this half cycle, when the first PWM sub-control signal is at a high level, the first charging subunit 410 is turned on, and the capacitor 600 is reversely charged. When the first PWM sub-control signal is at a low level, the voltage across the capacitor 600 remains unchanged. In this half cycle, the capacitor 600 is alternately in a state of charging and voltage remaining unchanged. When the voltage across the capacitor 600 reaches the threshold voltage, the bidirectional trigger diode 550 triggers the bidirectional thyristor 540 to turn on, thereby starting the light source load 300. At this time, the capacitor 600 will be quickly discharged through the second terminal and the third terminal of the switch unit 500, and the light source load 300 will remain in the started state until the AC voltage passes zero.

[0035] The second charging subunit 420 is connected in parallel with the first charging subunit 410, and is configured to be turned on according to the second PWM sub-control signal in another half cycle of the AC voltage to charge the capacitor 600. It can be understood by those skilled in the art that in the other half cycle, when the second PWM sub-control signal is at a high level, the second charging subunit 420 is turned on, and the capacitor 600 is charged, and when the second PWM sub-control signal is at a low level, the voltage across the capacitor 600 remains unchanged. In this way, the capacitor 600 is alternately in a state of charging and voltage remaining unchanged. When the voltage across the capacitor 600 reaches the threshold voltage, the bidirectional trigger diode 550 is turned on, and the bidirectional trigger diode 550 triggers the bidirectional thyristor 540 to turn on, thereby starting the light source load 300. At this time, the capacitor 600 is quickly discharged through the second end and the third end of the switch unit 500, and the light source load 300 remains in the started state until the AC voltage passes zero.

[0036] This configuration makes it possible to adjust the charging or discharging speed of the capacitor 600 by controlling the PWM control signal during the entire cycle of the AC voltage.

[0037] The first charging subunit 410 may include a first NMOS (N-Metal-Oxide-Semiconductor) tube 411, the gate of the first NMOS tube 411 is used to obtain a first PWM sub-control signal, the drain of the first NMOS tube 411 is connected to the light source load 300, and the source of the first NMOS tube 411 is connected to the capacitor 600.

[0038] Compared with a PMOS tube (PMOS, namely positive channel Metal Oxide Semiconductor, PMOS tube, namely P-channel Metal-Oxide Semiconductor Field Effect Transistor), an NMOS tube has a simpler structure and is easier to manufacture, thus making the cost of the phase-cut dimming circuit 20 lower.

[0039] The first charging subunit 410 may further include a first diode 412, the source of the first NMOS tube 411 is connected to the capacitor 600 through the first diode 412, and the cathode of the first diode 412 is connected to the capacitor 600. The first diode 412 can prevent the capacitor 600 from being directly charged through the first charging subunit 410 in another half cycle of the AC voltage when the first charging subunit 410 is not working, thereby ensuring the validity of the second PWM sub-control signal.

[0040] The first charging subunit 410 may further include a first current limiting resistor 413, which is connected between the source of the first NMOS tube 411 and the positive electrode of the first diode 412. The first current limiting resistor 413 may limit the current to prevent the capacitor 600 from charging or discharging too quickly. Specifically, the resistance of the first current limiting resistor 413 may be 10 kΩ to 100 kΩ, and the specific value may be determined according to actual application requirements.

[0041] The second charging subunit 420 may include a second NMOS transistor 421 , a gate of the second NMOS transistor 421 is used to obtain a second PWM sub-control signal, a source of the second NMOS transistor 421 is connected to the light source load 300 , and a drain of the second NMOS transistor 421 is connected to the capacitor 600 .

[0042] Compared with the PMOS tube, the NMOS tube has a simpler structure and is easier to manufacture. Therefore, the cost of the phase-cut dimming circuit 20 is relatively low.

[0043] The second charging subunit 420 may further include a second diode 422, the drain of the second NMOS tube 421 is connected to the capacitor 600 via the second diode 422, and the anode of the second diode 422 is connected to the capacitor 600. The second diode 422 may prevent the capacitor 600 from being directly charged through the second charging subunit 420 in the half cycle of the AC voltage in which the second charging subunit 420 is not working, thereby ensuring the validity of the first PWM sub-control signal.

[0044] The second charging subunit 420 may further include a second current limiting resistor 423, which is connected between the drain of the second NMOS tube 421 and the cathode of the second diode 422. The second current limiting resistor 423 may limit the current to prevent the capacitor 600 from charging or discharging too quickly. Specifically, the resistance of the second current limiting resistor 423 may be 10 kΩ to 100 kΩ, and the specific value may be determined according to actual application requirements.

[0045] The first PWM sub-control signal and the second PWM sub-control signal may be the same control signal or different control signals. That is to say, the first PWM sub-control signal and the second PWM sub-control signal may be sent by the same device or by different devices.

[0046] The switch unit 500 may include a bidirectional thyristor 540 and a bidirectional trigger diode 550. The bidirectional thyristor 540 may be considered as an integration of a pair of common thyristors connected in anti-parallel, and its working principle is the same as that of a common unidirectional thyristor. The bidirectional thyristor 540 has a first anode, a second anode and a gate. Since the bidirectional thyristor 540 itself is well known to those skilled in the art, it will not be described in detail here. The first anode of the bidirectional thyristor 540 (i.e., the first end of the switch unit 500) is connected between the light source load 300 and the charging unit 400, and the second anode is connected between the capacitor 600 and the AC power source 200.

[0047] The bidirectional trigger diode 550 is a three-layer structure, a symmetrical two-terminal semiconductor device, and can be used to trigger the bidirectional thyristor 540. Since the bidirectional trigger diode 550 itself is well known to those skilled in the art, it will not be described in detail here. One end of the bidirectional trigger diode 550 is connected between the charging unit 400 and the capacitor 600, and the other end of the bidirectional trigger diode 550 is connected to the gate of the bidirectional thyristor 540. One end of the bidirectional trigger diode 550 connected between the charging unit 400 and the capacitor 600 and the second anode of the bidirectional thyristor 540 serve as the second end and the third end of the switch unit 500, respectively.

[0048] In a specific implementation, the AC power source 200 of the phase-cut voltage regulation circuit 10 is an industrial frequency mains power outputting a sinusoidal AC voltage, the neutral terminal of which is connected to one end of the light source load 300, the other end of the light source load 300 is connected to the charging unit 400, and the charging unit 400 is connected to the live terminal of the AC power source 200 through the capacitor 600. In this case, the first charging subunit 410 is turned on according to the first PWM sub-control signal in the negative half cycle of the AC voltage to charge the capacitor 600, and the second charging subunit 420 is turned on according to the second PWM sub-control signal in the positive half cycle of the AC voltage to charge the capacitor 600.

[0049] In some embodiments, the ratio of the frequency of the AC voltage provided by the AC power supply 200 to the frequency of the PWM control signal is 0.0005 to 0.006. For example, when the frequency of the AC voltage provided by the AC power supply 200 is 50 Hz, the frequency of the PWM control signal can be 10 kHz, 20 kHz, 60 kHz, etc. That is, the frequency of the PWM control signal is much greater than the frequency of the AC voltage provided by the AC power supply 200. The larger the frequency of the PWM control signal, the more times the capacitor 600 is intermittently charged and the voltage across the capacitor 600 remains unchanged when the switch unit 500 is not turned on, and the slower the voltage across the capacitor 600 changes, thereby facilitating the accurate control of the duty cycle of the PWM control signal to change the phase of the AC voltage when the voltage across the capacitor 600 reaches the threshold voltage.

[0050] Figure 4 is a relevant waveform diagram when a phase-cut dimming circuit receives a PWM control signal with a first duty cycle according to an embodiment of the present invention; Figure 5 : is a related waveform diagram when the phase-cut dimming circuit according to an embodiment of the present invention receives a PWM control signal with a second duty cycle. Among them, the waveform represented by A is the waveform of the AC voltage output by the AC power supply 200, and the waveform represented by B is the waveform of the PWM control signal. Since the duty cycle and frequency of the first PWM sub-control signal and the second PWM sub-control signal are consistent, the first PWM sub-control signal and the second PWM sub-control signal are both represented by B. The waveform represented by C is the waveform of the gate voltage of the bidirectional thyristor 540, and its trend is basically consistent with the voltage across the capacitor 600. D represents the voltage waveform across the light source load 300. Among them, Figure 4 The duty cycle of the PWM control signal selected is 75%. Figure 5 The duty cycle of the selected PWM control signal is 50%, and, in order to clearly illustrate this embodiment, Figure 4 as well as Figure 5 The PWM control signal shown uses a smaller frequency.

[0051] like Figure 4 , 5As shown, in the first half period (i.e., the period during which the voltage reaches the voltage peak from the zero point) of the positive half cycle of the sinusoidal AC voltage output by the AC power supply 200 (in the positive half cycle, due to the action of the first diode 412, the current cannot pass through the first charging subunit 410, that is, the first diode 412 is in the cut-off state and the second diode is in the on state) and the second PWM sub-control signal is at a high level, the second charging subunit 420 is turned on, and the capacitor 600 is charged. In the first half period of the positive half cycle of the sinusoidal AC voltage output by the AC power supply 200 and the PWM control signal is at a low level, the voltage across the capacitor 600 remains unchanged. In this way, in the positive half cycle of the sinusoidal AC voltage output by the AC power supply 200, the capacitor 600 will alternately be in a state of charging and keeping the voltage unchanged. When the voltage across the capacitor 600 reaches the threshold voltage (at this time, the threshold voltage is the turning voltage of the bidirectional trigger diode 550) ( Figure 4 a1 represents the moment, Figure 5 At the moment indicated by a2 in the figure), the bidirectional trigger diode 550 will be turned on, and the bidirectional trigger diode 550 will trigger the bidirectional thyristor 540 to be turned on, so that the light source load 300 is started. At this time, the capacitor 600 will be quickly discharged through the second end and the third end of the switch unit 500, and the light source load 300 will remain in the started state until the AC voltage passes through zero ( Figure 4 At the time indicated by b1, Figure 5 b2 in the figure). And, from Figure 4 as well as Figure 5 From the positions of a1 and a2 (a2 lags behind a1), it can be seen that the larger the duty cycle of the second PWM sub-control signal, the larger the conduction duty cycle of the second charging sub-unit 420 (when the second charging sub-unit 420 includes the second NMOS tube 421, the larger the conduction duty cycle of the second NMOS tube 421), causing the capacitor 600 to reach the threshold voltage at a smaller phase of the AC voltage, so that the bidirectional thyristor 540 can be turned on at a smaller phase of the AC voltage, and the longer the working time of the light source load 300 in a single half cycle, the greater the brightness. Conversely, the smaller the duty cycle of the second PWM sub-control signal, the larger the phase when the bidirectional thyristor 540 is turned on, the shorter the working time of the light source load 300 in a single half cycle, and the lower the brightness.

[0052] In the first half period (i.e., the period when the voltage reaches the voltage valley from the zero point) of the negative half cycle of the sinusoidal AC voltage output by the AC power supply 200 (in the negative half cycle, due to the action of the second diode 422, the current cannot pass through the second charging subunit 420, that is, the first diode 412 is in the on state and the second diode is in the off state) and the PWM control signal is at a high level, the capacitor 600 is reversely charged. In the first half period of the negative half cycle of the sinusoidal AC voltage output by the AC power supply 200 and the PWM control signal is at a low level, the voltage across the capacitor 600 remains unchanged. In this way, in the negative half cycle of the sinusoidal AC voltage output by the AC power supply 200, the capacitor 600 will alternately be in a state of charging and a state of keeping the voltage unchanged. When the voltage across the capacitor 600 reaches the threshold voltage ( Figure 4 The moment represented by c1 is Figure 5 At the moment indicated by c2 in FIG. 1 ), the bidirectional trigger diode 550 is turned on, and the bidirectional trigger diode 550 triggers the bidirectional thyristor 540 to turn on, thereby starting the light source load 300. At this time, the capacitor 600 is quickly discharged through the second end and the third end of the switch unit 500, and the light source load 300 remains in the started state until the AC voltage passes through zero ( Figure 4 At the time indicated by d1, Figure 5 d2 in the figure). And, from Figure 4 as well as Figure 5 From the positions of c1 and c2 (c2 lags behind c1), it can be seen that the larger the duty cycle of the first PWM sub-control signal, the larger the conduction duty cycle of the first charging sub-unit 410 (when the first charging sub-unit 410 includes the first NMOS tube 411, the larger the conduction duty cycle of the first NMOS tube 411), causing the capacitor 600 to reach the threshold voltage at a smaller phase of the AC voltage, so that the bidirectional thyristor 540 can be turned on at a smaller phase of the AC voltage, and the longer the working time of the light source load 300 in a single half cycle, the greater the brightness. Conversely, the smaller the duty cycle of the first PWM sub-control signal, the larger the phase when the bidirectional thyristor 540 is turned on, the shorter the working time of the light source load 300 in a single half cycle, and the lower the brightness.

[0053] The threshold voltage may include a positive threshold voltage and a negative threshold voltage, and the values ​​of the two may be different based on the adopted switch unit 500. For example, in the case where the switch unit 500 includes a bidirectional trigger diode 550 and a bidirectional thyristor 540, the positive threshold voltage and the negative threshold voltage may be the forward break voltage and the reverse break voltage of the bidirectional trigger diode 550, respectively.

[0054] The present embodiment provides a phase-cut dimming circuit 20, which includes an AC power supply 200 for providing an AC voltage, a light source load 300, a charging unit 400 and a capacitor 600 connected in series to the AC power supply 200, and a switch unit 500. The charging unit 400 is configured to receive a PWM control signal, and is turned on according to the PWM control signal to charge the capacitor 600, so that the voltage across the capacitor 600 changes according to the conduction of the charging unit 400. The switch unit 500 has a first end, a second end and a third end. The first end of the switch unit 500 is connected to the connection point between the light source load 300 and the charging unit 400, the second end of the switch unit 500 is connected to the connection point between the charging unit 400 and the capacitor 600, and the third end of the switch unit 500 is connected to the connection point between the capacitor 600 and the AC power supply 200. The switch unit 500 is configured to be turned on when the voltage across the capacitor 600 reaches a threshold voltage, so that the light source load 300, the AC power supply 200 and the first end and the third end of the switch unit 500 form a loop, thereby realizing dimming of the light source load 300. The user can change the conduction duty cycle of the charging unit 400 by controlling the duty cycle of the PWM control signal to change the time when the capacitor 600 is charged to reach the threshold voltage of the switch unit 500, so that the bidirectional trigger diode 550 can be controlled to conduct at different phases, thereby triggering the bidirectional thyristor 540 to conduct, so that the working time of the light source load 300 in a single cycle of the AC voltage is adjustable, and the brightness of the light source load 300 is adjusted. Since the PWM control signal can be provided remotely (such as by a remote communication control circuit), network adjustment and remote operation can be performed to meet the development needs of digitalization and intelligence. In addition, the phase-cut dimming circuit 10 is easy to operate, which is convenient for users to accurately adjust the brightness of the light source load 300.

[0055] The first charging subunit 410 obtains the first PWM sub-control signal through the gate of the first NMOS tube 411, and the second charging subunit 420 obtains the second PWM sub-control signal through the gate of the second NMOS tube 421. Since the NMOS tube is simpler in structure and easier to manufacture than the PMOS tube, the cost of the phase-cut dimming circuit 20 is lower.

[0056] At this point, those skilled in the art should recognize that, although multiple exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived based on the content disclosed in the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and recognized as covering all these other variations or modifications.

Claims

1. A phase-cut dimming circuit, comprising an AC power supply for providing an AC voltage, a light source load, a charging unit and a capacitor connected in series to the AC power supply, and a switch unit; The charging unit is configured to receive a PWM control signal and be turned on according to the PWM control signal to charge the capacitor, so that the voltage across the capacitor changes according to the turning on of the charging unit; The switch unit has a first end, a second end and a third end, the first end of the switch unit is connected to a connection point between the light source load and the charging unit, the second end of the switch unit is connected to a connection point between the charging unit and the capacitor, and the third end of the switch unit is connected to a connection point between the capacitor and the AC power supply, and the switch unit is configured to be turned on when the voltage across the capacitor reaches a threshold voltage, so that a loop is formed between the light source load, the AC power supply, and the first end and the third end of the switch unit, thereby realizing dimming of the light source load; The PWM control signal includes a first PWM sub-control signal and a second PWM sub-control signal; The charging unit comprises: a first charging sub-unit, configured to be turned on according to the first PWM sub-control signal within a half cycle of the AC voltage to charge the capacitor; as well as a second charging subunit, connected in parallel with the first charging subunit, and configured to be turned on according to the second PWM sub-control signal in another half cycle of the AC voltage to charge the capacitor; The switch unit comprises: a bidirectional thyristor, wherein a first anode of the bidirectional thyristor is connected between the light source load and the charging unit, and a second anode of the bidirectional thyristor is connected between the capacitor and the AC power source; and A bidirectional trigger diode, one end of which is connected between the charging unit and the capacitor, and the other end of which is connected to the gate of the bidirectional thyristor; Wherein, the first charging subunit comprises: a first NMOS transistor, wherein a gate of the first NMOS transistor is used to obtain the first PWM sub-control signal, a drain of the first NMOS transistor is connected to the light source load, and a source of the first NMOS transistor is connected to the capacitor; a first diode, wherein the source of the first NMOS tube is connected to the capacitor through the first diode, and the cathode of the first diode is connected to the capacitor; and a first current limiting resistor, connected between the source of the first NMOS tube and the anode of the first diode; The second charging subunit comprises: a second NMOS tube, wherein a gate of the second NMOS tube is used to obtain the second PWM sub-control signal, a source of the second NMOS tube is connected to the light source load, and a drain of the second NMOS tube is connected to the capacitor; a second diode, the drain of the second NMOS tube is connected to the capacitor through the second diode, and the anode of the second diode is connected to the capacitor; and The second current limiting resistor is connected between the drain of the second NMOS tube and the cathode of the second diode.

2. The phase-cut dimming circuit according to claim 1, wherein The first PWM sub-control signal and the second PWM sub-control signal are the same control signal or different control signals.

3. The phase-cut dimming circuit according to claim 1, wherein The ratio of the frequency of the AC voltage provided by the AC power source to the frequency of the PWM control signal is 0.0005 to 0.006.

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