Control circuit and method for dimming device and dimming device

Abstract

The embodiment of the invention provides a control circuit and method for a dimming device and the dimming device. The control circuit includes: a dimming signal transmission circuit configured to be coupled to gates of a first field effect transistor and a second field effect transistor of the dimming device; a first turn-off signal section coupled to a gate of the first field effect transistor, and outputting a first turn-off signal at a predetermined time before the first current zero crossing point to turn off the first field effect transistor such that a current flows from a body diode of the first field effect transistor before the first current zero crossing point; and a second turn-off signal section coupled to the gate of the second field effect transistor, turning off the second field effect transistor at a predetermined time before the second current zero crossing so that the current flows from the body diode of the second field effect transistor before the second current zero crossing. Therefore, voltage spikes generated when the dimming device and the inductive load are connected can be eliminated.

Description

Technical Field

[0001] Embodiments of the present disclosure generally relate to the field of dimmers, and more particularly to a control circuit and method for a dimming device, and a dimming device. Background Art

[0002] A dimmer is a device or system used to control the brightness of a light. It can adjust the brightness of a lighting device by changing the voltage, current or power supplied to the lamp. Dimmers also play an important role in energy conservation and environmental protection. By effectively reducing the power output of the lamp, dimmers can significantly reduce power consumption and extend the life of the lamp.

[0003] The configuration of the dimmer needs to consider the type of load and maintain a stable output. Loads usually include resistive loads and non-linear loads, which in turn include inductive loads and capacitive loads. Therefore, it is critical for dimmers to adapt to various types of loads. For example, when an inductive load is connected, a leading edge dimmer is suitable. Before returning the switch to the off state, it is usually necessary to let the current half-cycle load current drop to a level close to zero to avoid excessive levels of inductive voltage spikes, which may damage the electrical components of the device. Summary of the invention

[0004] An object of the embodiments of the present disclosure is to provide a control circuit, method and dimming device for a dimming device, so as to at least partially solve the above problems and other potential problems.

[0005] In a first aspect of the present disclosure, a control circuit for a dimming device is provided, comprising: a dimming signal transmission circuit, configured to be coupled to the gates of a first field effect transistor and a second field effect transistor of the dimming device to transmit a dimming control signal from a control unit to control the on and off of the first field effect transistor and the second field effect transistor; a first shutdown signal unit, coupled to the gate of the first field effect transistor, and adapted to output a first shutdown signal to shut down the first field effect transistor at a predetermined time before a first current zero crossing during a negative half cycle of a waveform output by a main AC power source of a load circuit in response to control of the control unit, so that a current flows through a body diode of the first field effect transistor before the first current zero crossing; and a second shutdown signal unit, coupled to the gate of the second field effect transistor, and adapted to shut down the second field effect transistor at a predetermined time before a second current zero crossing during a positive half cycle of a waveform output by a main AC power source of a load circuit in response to control of the control unit, so that a current flows through the body diode of the second field effect transistor before the second current zero crossing.

[0006] In an embodiment of the present disclosure, the first shutdown signal unit and the second shutdown signal unit respectively output the first shutdown signal and the second shutdown signal at a predetermined time before the first current and the second current cross the zero point, so as to shut down the first field effect transistor and the second field effect transistor, thereby avoiding the generation of voltage spikes generated when the dimming device and the inductive load are connected.

[0007] In some embodiments, the dimming control signal becomes a low level signal at a first current zero-crossing point and a second current zero-crossing point of the main AC power source to turn off the first field effect transistor and the second field effect transistor.

[0008] In some embodiments, the first shutdown signal unit includes: a first transistor, the base of the first transistor is coupled to the first shutdown output port of the control unit to receive a control signal from the control unit, the collector of the first transistor is coupled to the gate of the first field effect transistor, and the emitter of the first transistor is grounded.

[0009] In some embodiments, the second shutdown signal unit includes: a second transistor, the base of the second transistor is coupled to the second shutdown output port of the control unit to receive a control signal from the control unit, the collector of the second transistor is coupled to the gate of the second field effect transistor, and the emitter of the second transistor is grounded.

[0010] In some embodiments, the control circuit also includes: a zero-crossing detection circuit, coupled to the load loop and suitable for detecting the first current zero-crossing point and the second current zero-crossing point, and coupled to the control unit so that the control unit outputs at least a dimming control signal based on the detection signal of the zero-crossing detection circuit.

[0011] In a second aspect of the present disclosure, a method for controlling a dimming device is provided, comprising: during a period in which a waveform output by a main AC power supply of a load circuit controlled by the dimming device is in a negative half-cycle, outputting a first shutdown signal at a predetermined time before a first current crosses zero to shut down a first field effect transistor of the dimming device, so that current flows through a body diode of the first field effect transistor before the first current crosses zero; during a period in which a waveform output by a main AC power supply of the load circuit is in a positive half-cycle, outputting a second shutdown signal at a predetermined time before a second current crosses zero to shut down a second field effect transistor of the dimming device, so that current flows through a body diode of the second field effect transistor before the second current crosses zero; and outputting a dimming control signal from a dimming signal output port to control the on and off of the first field effect transistor and the second field effect transistor.

[0012] In some embodiments, outputting the dimming control signal from the dimming signal output port includes: changing the dimming control signal to a low level signal at a current zero-crossing point of the main AC power source to turn off the first field effect transistor and the second field effect transistor.

[0013] In some embodiments, outputting a first shutdown signal includes: outputting a high-level first shutdown signal at a predetermined time before the first current crosses zero, so as to turn off the first field effect transistor by converting the electrical signal acting on the gate of the first field effect transistor into a low-level signal through the first transistor.

[0014] In some embodiments, outputting the second shutdown signal includes: outputting a high-level second shutdown signal at a predetermined time before the second current crosses the zero point, so as to turn off the second field effect tube by converting the electrical signal acting on the gate of the second field effect tube into a low-level signal through the second transistor.

[0015] In some embodiments, the method further includes: acquiring a current zero-crossing point from a zero-crossing detection circuit; and outputting at least a dimming control signal based on a detection signal of the zero-crossing detection circuit regarding the current zero-crossing point.

[0016] In a third aspect of the present disclosure, a dimming device is provided, comprising: a first field effect transistor and a second field effect transistor, which are connected in series in a load loop controlled by the dimming device and respectively include a gate, a source and a drain, and the sources of the first field effect transistor and the second field effect transistor are connected; and a control circuit according to the first aspect, coupled to the first field effect transistor and the second field effect transistor.

[0017] It should be understood that the content described in this content section is not intended to limit the key features or important features of the embodiments of the present disclosure, nor is it intended to limit the scope of the present disclosure. Other features of the present disclosure will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and other features, advantages and aspects of the embodiments of the present disclosure will become more apparent with reference to the following detailed description in conjunction with the accompanying drawings. In the accompanying drawings, the same or similar reference numerals represent the same or similar elements, wherein:

[0019] Figure 1 A schematic diagram of a control circuit according to an embodiment of the present disclosure is shown;

[0020] Figure 2 Shows Figure 1 A simulation schematic diagram of a control circuit of an embodiment shown;

[0021] Figure 3 A flowchart showing a method of controlling a circuit according to an embodiment of the present disclosure; and

[0022] Figure 4 A schematic block diagram of a dimming device according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0023] The preferred embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the preferred embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0024] As used herein, the term "including" and its variations mean open inclusion, i.e., "including but not limited to". Unless otherwise stated, the term "or" means "and / or". The term "based on" means "based at least in part on". The terms "an example embodiment" and "an embodiment" mean "at least one example embodiment". The term "another embodiment" means "at least one additional embodiment". The terms "first", "second", etc. may refer to different or the same objects.

[0025] As briefly mentioned above, with the development of digital technology, dimmers have also played an important role in energy conservation and environmental protection. For example, a phase-controlled dimmer, also known as a dimming switch or electronic dimmer, is a device used to control the brightness of a lamp. The dimmer achieves dimming by changing the voltage supplied to the bulb by the AC power supply. The phase-controlled dimmer uses zero-crossing detection technology to accurately detect and record the zero point position of the sine wave. When the user sends a dimming signal through a knob, switch, or remote control, the phase-controlled dimmer receives the signal and decodes it.

[0026] According to the brightness level set by the user, the phase-controlled dimmer will open the circuit to supply power to the bulb near the zero point of the next AC cycle. This can reduce the risk of shock and damage caused by the sudden application of high voltage and maintain precise control of the output energy of the bulb. By continuously delaying the opening time, a gradual effect at different brightness levels can be achieved. Compared with traditional linear cutting methods (such as variable resistors), phase-controlled dimmers provide a wider range, smoother and more precise brightness selection range. In addition, it also has the advantages of lower power consumption, easy installation and operation. Phase-controlled dimmers are widely used in home, commercial and industrial lighting systems, providing users with customized lighting experience and achieving the goals of energy conservation and environmental protection.

[0027] However, when a conventional phase-controlled dimmer is configured with an inductive load, a spike voltage problem occurs. This is because an inductive load (such as an inductor) will react with self-induction when the power supply is disconnected, causing the current to fail to drop to zero quickly. Therefore, the current that has not completely disappeared will continue to pass through the load before the next half-wave of the AC cycle begins. In this case, when the phase-controlled dimmer is turned on again to provide power to the load, there is a high peak voltage (also called a spike voltage) that exceeds the expected and designed parameters within the normal operating range. This may cause damage, overheating, or even failure of lamps or other equipment.

[0028] To solve this problem, there are two traditional solutions. The first method is to use a series current sense resistor and a precision operational amplifier device to determine when the load current drops to a low enough level so that the switch can be turned off at a minimum voltage spike level. However, since the current sense resistor increases the total resistance of the dimming device, this method has the disadvantage of easily causing the dimming device to consume more power. The second method is to use a non-zero current MOSFET turn-off method. For example, for loads with only marginal inductance (e.g., typical core-based 25LV lighting), the MOSFET can be turned off at a time point corresponding to the zero crossing of the power supply voltage. However, this method is only applicable to loads with only small inductive loads, and cannot be used for larger inductive loads or purely inductive loads.

[0029] In order to solve or at least partially solve the above-mentioned problems or other potential problems of the phase-controlled dimmer of the conventional solution, the embodiments of the present disclosure provide a control circuit, method and dimming device for a dimming device. In the control circuit, during the period when the waveform output by the main AC power supply of the load circuit is in the negative half cycle, the first shutdown signal unit outputs a first shutdown signal at a predetermined time before the first current crosses the zero point, so as to realize the shutdown of the first field effect transistor. During the period when the waveform output by the main AC power supply of the load circuit is in the positive half cycle, the second shutdown signal unit outputs a second shutdown signal at a predetermined time before the second current crosses the zero point, so as to realize the shutdown of the second field effect transistor, so that the current flows from the body diode (also called "anti-parallel diode") of the first field effect transistor or the second field effect transistor before the first current or the second current crosses the zero point. Thereby suppressing and absorbing the self-inductive energy generated by the inductive load, such as the generation of the voltage spike generated when the dimming device and the inductive load are connected, and protecting the lamp or other equipment from damage caused by the high peak voltage, and ensuring the correct connection and grounding to ensure the stability and safety of the system.

[0030] Figure 1 A schematic diagram of a control circuit according to an embodiment of the present disclosure is shown; Figure 2 Shows Figure 1 The simulation diagram of the control circuit shown in the figure is as follows. Figure 1 to Figure 2 To describe the principle of the present disclosure in detail. Figure 1 , Figure 1 FIG. 1 is a schematic diagram showing a structure of a control circuit 100 for a dimming device according to an embodiment of the present disclosure. Figure 1 As shown, the control circuit 100 for the dimming device described herein generally includes a dimming signal transmission circuit, a first shutdown signal unit and a second shutdown signal unit. The dimming signal transmission circuit, the first shutdown signal unit and the second shutdown signal unit are all coupled to the control terminals (i.e., gates) of the two field effect transistors of the dimming device to respectively control the conduction and shutdown of the two field effect transistors. The first shutdown signal unit and the second shutdown signal unit respectively turn off the corresponding field effect transistors at a predetermined time (e.g., 2ms) before the current crosses the zero point. This working mode can ensure that the current half-cycle load current drops to zero at the zero point, thereby effectively avoiding the damage to the lamp or other equipment caused by the high peak voltage of the dimming device. In addition, the dimming device in the present disclosure also has the advantages of low power consumption, easy installation and operation, etc.

[0031] The following will be combined Figure 1 To describe the specific structure of the control circuit. Figure 1 As shown, the dimming signal transmission circuit is configured to be coupled to the gates of the first field effect transistor 113 and the second field effect transistor 114 of the dimming device to transmit the dimming control signal from the control unit. The dimming control signal corresponds to Figure 2 The "3Gate on" signal in the control unit can be used to control the on and off of the first field effect transistor 113 and the second field effect transistor 114. In some embodiments, the first field effect transistor 113 and the second field effect transistor 114 in the present disclosure may include a metal-oxide semiconductor field effect transistor (also known as a MOSFET or MOS transistor), and a PMOS transistor may be used, which is not limited in the present disclosure. In the present disclosure, the dimming signal transmission circuit may include: a transmission line from the dimming signal output port 110 of the control unit to the gates of the first field effect transistor 113 and the second field effect transistor 114, and a plurality of resistors (e.g. Figure 1 Specifically, the resistor 111 and the resistor 123 are connected in series between the dimming signal output port 110 of the control unit and the gate of the coupled first field effect transistor 113 through a transmission line, and the resistor 112 and the resistor 133 are connected in series between the dimming signal output port 110 of the control unit and the gate of the second field effect transistor 114 through a transmission line, so as to control the transmission of the dimming signal.

[0032] In some embodiments, the source of the first field effect transistor 113 is coupled to the source of the second field effect transistor 114. A load circuit is provided between the drain of the first field effect transistor 113 and the drain of the second field effect transistor 114. The load circuit is a circuit including the main AC power supply 140, the resistive load 150 and the inductive load 160 (or referred to as the resistive part and the inductive part of the load). The on and off of the load circuit is realized by controlling the on and off of the first field effect transistor 113 and the second field effect transistor 114.

[0033] In some embodiments, the first shutdown signal unit is coupled to the gate of the first field effect transistor 113, and can, under the control of the control unit, output the first shutdown signal at a predetermined time (for example, 2ms or any other appropriate time) before the current zero crossing point (hereinafter referred to as the first current zero crossing point) of the negative half cycle during the negative half cycle of the waveform output by the main AC power supply of the load circuit, thereby turning off the first field effect transistor 113 so that the current flows through the body diode 1131 of the first field effect transistor 113 before the first current zero crossing point.

[0034] like Figure 2 As shown, the dimming control signal (3Gate on signal) becomes a low level signal at the first current zero crossing point and the second current zero crossing point of the main AC power source to turn off the first field effect transistor 113 and the second field effect transistor 114 .

[0035] In some embodiments, the first shutdown signal unit includes a first transistor 122. The base of the first transistor 122 is coupled to the first shutdown output port 120 of the control unit to receive the first shutdown signal (eg, Figure 2 4off1 signal shown in FIG), the collector of the first transistor 122 is coupled to the gate of the first field effect transistor 113, and the emitter of the first transistor 122 is grounded. In this way, at a predetermined time before the first current crosses the zero point, the first shutdown output port 120 of the control unit outputs a high-level first shutdown signal (e.g. Figure 2 4off1 signal shown in FIG), the collector and emitter of the first transistor 122 will be turned on, thereby pulling down the level of the gate of the first field effect transistor 113 to achieve the effect of turning off the first field effect transistor 113. At this time, the current will flow through the body diode 1131 of the first field effect transistor 113 until the current passes through the zero point.

[0036] Since the first field effect transistor 113 is turned off before the first current reaches the zero point, the current flows through the body diode 1131 of the first field effect transistor 113 before the first current passes through the zero point. Since the body diode 1131 is the anti-parallel diode of the first field effect transistor, the first current is prevented from flowing in the opposite direction, so that when power is provided to the load again, the high peak voltage generated by the first current can be suppressed.

[0037] Similarly, in some embodiments, the second shutdown signal unit is coupled to the gate of the second field effect transistor 114, and can, under the control of the control unit, shut down the second field effect transistor 114 at a predetermined time before the current zero crossing point (hereinafter referred to as the second current zero crossing point) of the positive half cycle when the waveform output by the main AC power supply of the load circuit is in the positive half cycle, so that the current flows through the body diode 1141 of the second field effect transistor 114 before the second current zero crossing point.

[0038] In some embodiments, the second shutdown signal unit includes a second transistor 132. The base of the second transistor 132 is coupled to the second shutdown output port 130 of the control unit to receive the second shutdown signal (eg, Figure 2 The collector of the second transistor 132 is coupled to the gate of the second field effect transistor 114, and the emitter of the second transistor 132 is grounded. In some embodiments, the first shutdown output port 120 and the second shutdown output port 130 of the control unit can be the same port on the control unit or different ports.

[0039] Similar to the case of the first transistor 122, at a predetermined time before the second current crosses the zero point, the second shutdown output port 130 of the control unit outputs a high-level second shutdown signal (eg Figure 2 5off2 signal shown in FIG), the collector and emitter of the second triode 132 will be turned on, thereby pulling down the level of the gate of the second field effect transistor 114 to achieve the effect of turning off the second field effect transistor 114. At this time, the current will flow through the body diode 1141 of the second field effect transistor 114 until the current passes through the zero point.

[0040] Similar to the first shutdown signal unit, since the second field effect transistor 114 is turned off before the current reaches the zero point, the current flows through the body diode 1141 of the second field effect transistor 114 before the second current passes through the zero point. Since the body diode 1141 is the anti-parallel diode of the second field effect transistor 114, the second current is prevented from flowing in the opposite direction, so that when power is provided to the load again, the high peak voltage generated by the second current can be suppressed.

[0041] In some embodiments, the first transistor 122 and the second transistor 132 in the present disclosure may be NPN transistors. A resistor 121 may be provided between the base of the first transistor 122 and the first shutdown signal output port 120 of the control unit, and a resistor 131 may be provided between the base of the second transistor 132 and the second shutdown signal output port 130 of the control unit. As mentioned above, the predetermined time before the first current zero crossing point and the second current zero crossing point in the present disclosure may be 2 milliseconds (ms), and may also be set to 3 milliseconds, 5 milliseconds or any other appropriate time, which is not limited in the present disclosure.

[0042] Therefore, the present invention controls the first field effect transistor 113 and the second field effect transistor 114 to be turned off respectively when the waveform output by the main AC power supply of the load circuit is in the positive half cycle and the negative half cycle respectively through the first transistor 122 and the second transistor 132, so as to avoid the generation of high peak voltage when the current passes through the zero point when the dimming device is connected to the inductive load.

[0043] In some embodiments, the control circuit further includes: a zero-crossing detection circuit, coupled to the load circuit, and adapted to detect the first current zero-crossing point and the second current zero-crossing point, and coupled to the signal input unit 170 of the control unit, so that the control unit outputs at least a dimming control signal based on the detection signal of the zero-crossing detection circuit. In addition, in some embodiments, the control unit may also output the first shut-off signal or the second shut-off signal mentioned above at a predetermined time before the current zero-crossing point according to the first current zero-crossing point and the second current zero-crossing point detected by the zero-crossing detection circuit to effectively prevent the generation of a high peak voltage.

[0044] In some embodiments, the zero-crossing detection circuit in the embodiment of the present disclosure may include a first diode 115, a second diode 116, a resistor 172, a resistor 173, and a third diode 171. The cathode of the first diode 115 is connected to the cathode of the second diode 116, and both are connected in parallel with the load circuit. The resistor 172 and the resistor 173 are connected in series. Specifically, one end of the resistor 172 is connected between the cathodes of the first diode 115 and the second diode 116, the other end of the resistor 172 is connected to one end of the resistor 173, and the other end of the resistor 173 is grounded. The positive pole of the third diode 171 is connected between the resistor 172 and the resistor 173, and the negative pole of the third diode 171 is connected to the signal input unit 170 of the control unit.

[0045] like Figure 2As shown, 1Vin represents the voltage signal of the main AC power supply, which is distributed in a sinusoidal waveform, 2Current is the current diagram of the load circuit, 3Gate on is the waveform diagram of the dimming control signal, 4off1 is the waveform diagram of the first shutdown signal, 5off2 is the waveform diagram of the second shutdown signal, Diode current is the current waveform diagram of the body diode, V_dimmer is the load voltage waveform diagram, and ZCD is the output signal waveform diagram of the zero-crossing detection circuit. Figure 2 It can be concluded that near the zero point of the next AC cycle (i.e., the predetermined time of the first current zero point or the second current zero point mentioned above), after the control operation of the control circuit described above, no high peak voltage appears at the position near the current zero point in the load voltage waveform. Therefore, the control circuit disclosed in the present invention effectively eliminates the problem of voltage spikes generated when the dimming device is connected to the inductive load.

[0046] Figure 3 A flow chart of a method for controlling a circuit according to the present disclosure is shown. In some embodiments, the method 300 may be implemented by a processor of the control unit or other suitable device mentioned above. For ease of understanding, the specific examples, numbers or values ​​mentioned in the following description are merely exemplary and are not intended to limit the scope of protection of the present disclosure.

[0047] Ginseng Figure 3 As shown, in box 310, the control unit outputs a first turn-off signal to turn off the first field effect transistor of the dimming device at a predetermined time before the first current crosses zero during the waveform output by the main AC power supply of the load circuit controlled by the dimming device is in the negative half cycle, so that the current flows through the body diode of the first field effect transistor before the first current crosses zero. In box 320, the control unit outputs a second turn-off signal to turn off the second field effect transistor of the dimming device at a predetermined time before the second current crosses zero during the waveform output by the main AC power supply of the load circuit is in the positive half cycle, so that the current flows through the body diode of the second field effect transistor before the second current crosses zero. In box 330, the control unit outputs a dimming control signal from the dimming signal output port 110 to control the on and off of the first field effect transistor and the second field effect transistor.

[0048] In some embodiments, the control unit changes the dimming control signal into a low level signal at a current zero-crossing point of the main AC power source to turn off the first field effect transistor and the second field effect transistor.

[0049] In some embodiments, the control unit outputs a high-level first shutdown signal at a predetermined time before the first current crosses zero, so as to turn off the first field effect transistor 113 by converting the electrical signal acting on the gate of the first field effect transistor 113 into a low-level signal through the first transistor.

[0050] In some embodiments, the control unit outputs a high-level second shutdown signal a predetermined time before the second current crosses zero, so as to turn off the second field effect tube by converting the electrical signal acting on the gate of the second field effect tube into a low-level signal through the second transistor.

[0051] In some embodiments, the control unit obtains a current zero-crossing point from a zero-crossing detection circuit, and outputs at least a dimming control signal based on a detection signal of the zero-crossing detection circuit regarding the current zero-crossing point.

[0052] Figure 4 FIG. 4 is a schematic block diagram of a dimming device 400 suitable for implementing an embodiment of the present disclosure. Figure 4 As shown, the dimming device 400 includes a first field effect transistor 113, a second field effect transistor 114 and a control circuit 100. The first field effect transistor 113 and the second field effect transistor 114 are connected in series in a load loop controlled by the dimming device, and respectively include a gate, a source and a drain. The sources of the first field effect transistor 113 and the second field effect transistor 114 are connected. The control circuit 100 is coupled to the first field effect transistor 113 and the second field effect transistor 114 in the manner described above, thereby effectively avoiding the high peak voltage generated when the dimming device 400 is connected to an inductive load, thereby effectively ensuring the safe use of the load and the device.

[0053] The embodiments of the present disclosure have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A control circuit for a dimming device, comprising: a dimming signal transmission circuit, configured to be coupled to the gates of the first field effect transistor and the second field effect transistor of the dimming device to transmit a dimming control signal from a control unit to control the on and off of the first field effect transistor and the second field effect transistor; a first shutoff signal unit coupled to the gate of the first field effect transistor and adapted to output a first shutoff signal to shut off the first field effect transistor at a predetermined time before a first current crosses zero during a negative half cycle of a waveform output by a main AC power source of a load circuit in response to control by the control unit, so as to make a current flow through a body diode of the first field effect transistor before the first current crosses zero; as well as A second shutdown signal unit is coupled to the gate of the second field effect transistor and is suitable for shutting off the second field effect transistor at the predetermined time before the second current crosses zero during the positive half cycle of the waveform output by the main AC power supply of the load circuit in response to the control of the control unit, so that the current flows through the body diode of the second field effect transistor before the second current crosses zero.

2. The control circuit according to claim 1, wherein the dimming control signal becomes a low level signal at a first current zero crossing point and a second current zero crossing point of the main AC power supply to turn off the first field effect transistor and the second field effect transistor.

3. The control circuit according to claim 1, wherein the first shutdown signal unit comprises: A first transistor, wherein the base of the first transistor is coupled to the first shutdown output port of the control unit to receive a control signal from the control unit, the collector of the first transistor is coupled to the gate of the first field effect transistor, and the emitter of the first transistor is grounded.

4. The control circuit according to claim 1, wherein the second shutdown signal unit comprises: A second transistor, the base of the second transistor is coupled to the second shutdown output port of the control unit to receive a control signal from the control unit, the collector of the second transistor is coupled to the gate of the second field effect transistor, and the emitter of the second transistor is grounded.

5. The control circuit according to any one of claims 1 to 4, further comprising: A zero-crossing detection circuit is coupled to the load loop and is adapted to detect the first current zero-crossing point and the second current zero-crossing point, and is coupled to the control unit so that the control unit at least outputs the dimming control signal based on the detection signal of the zero-crossing detection circuit.

6. A method for controlling a dimming device, comprising: During the period when the waveform output by the main AC power supply of the load circuit controlled by the dimming device is in the negative half cycle, outputting a first turn-off signal at a predetermined time before the first current crosses zero to turn off the first field effect transistor of the dimming device, so that the current flows through the body diode of the first field effect transistor before the first current crosses zero; During the period when the waveform output by the main AC power supply of the load circuit is in a positive half cycle, outputting a second turn-off signal at the predetermined time before the second current crosses zero to turn off the second field effect transistor of the dimming device, so that the current flows through the body diode of the second field effect transistor before the second current crosses zero; and A dimming control signal is output from the dimming signal output port to control the on and off of the first field effect transistor and the second field effect transistor.

7. The method according to claim 6, wherein outputting the dimming control signal from the dimming signal output port comprises: The dimming control signal is changed into a low level signal at a current zero-crossing point of the main AC power source to turn off the first field effect transistor and the second field effect transistor.

8. The method according to claim 6, wherein outputting the first shutdown signal comprises: A high-level first shutdown signal is outputted at a predetermined time before the first current crosses the zero point, so as to turn off the first field effect transistor by changing the electrical signal acting on the gate of the first field effect transistor into a low-level signal through the first transistor.

9. The method according to claim 6, wherein outputting the second shutdown signal comprises: A high-level second shutdown signal is outputted at a predetermined time before the second current crosses the zero point, so as to change the electrical signal acting on the gate of the second field effect tube into a low-level signal through the second transistor, thereby shutting down the second field effect tube.

10. The method according to any one of claims 6 to 9, further comprising: Obtain the current zero-crossing point from the zero-crossing detection circuit; as well as At least the dimming control signal is output based on the detection signal of the zero-crossing detection circuit regarding the current zero-crossing point.

11. A dimming device, comprising: A first field effect transistor and a second field effect transistor are connected in series in a load loop controlled by the dimming device, and respectively include a gate, a source and a drain, and the sources of the first field effect transistor and the second field effect transistor are connected; as well as The control circuit according to any one of claims 1 to 5, coupled to the first field effect transistor and the second field effect transistor.

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