Dimming device

Abstract

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Description

Dimming device The present invention relates to a dimming device for dimming an illumination load. Conventionally, a dimming device for dimming an illumination load has been known (for example, Patent Document 1). The dimming device described in Patent Document 1 includes a pair of terminals, a control circuit unit, a control power supply unit that supplies a control power supply to the control circuit unit, and a dimming operation unit that sets a dimming level of the illumination load. Between the pair of terminals, the control circuit unit and the control power supply unit are each connected in parallel. Also, between the pair of terminals, a series circuit of an AC power supply and an illumination load is connected. The illumination load includes a plurality of LED (Light Emitting Diode) elements and a power supply circuit that lights each LED element. The power supply circuit includes a smoothing circuit of a diode and an electrolytic capacitor. The control circuit unit includes a switch unit that phase-controls an AC voltage supplied to the illumination load, a switch drive unit that drives the switch unit, and a control unit that controls the switch drive unit and the control power supply unit. The control power supply unit is connected in parallel to the switch unit. The control power supply unit converts the AC voltage of the AC power supply into a control power supply. The control power supply unit includes an electrolytic capacitor that accumulates the control power supply. The control unit is supplied with the control power supply from the control power supply unit through the electrolytic capacitor. The control unit includes a microcomputer. The microcomputer performs reverse phase control to cut off power supply to the illumination load in the middle of the period for each half cycle of the AC voltage according to the dimming level set by the dimming operation unit. Japanese Patent Application Laid-Open No. 2013-149498 An object of the present invention is to provide a dimming device that can cope with more types of loads. A dimming device according to a first aspect of the present invention comprises a pair of input terminals, a bidirectional switch, a phase detection unit, an input unit, a power supply unit, and a control unit. The pair of input terminals are electrically connected between a load that lights up when energized and an AC power supply. The bidirectional switch is configured to switch between interrupting and passing bidirectional current between the pair of input terminals. The phase detection unit detects the phase of the AC voltage of the AC power supply. The input unit receives a dimming level that specifies the magnitude of the light output of the load. The power supply unit is electrically connected between the pair of input terminals and generates a control power supply from the power supplied by the AC power supply. The control unit operates by receiving the control power supply from the power supply unit. The control unit controls the bidirectional switch based on the detection signal from the phase detection unit, such that the bidirectional switch is in the off state from the start of the half-cycle of the AC voltage until a first time has elapsed, the bidirectional switch is in the on state from the first time until a second time has elapsed according to the dimming level, and the bidirectional switch is in the off state from the second time until the end of the half-cycle. Furthermore, a dimming device according to a second aspect of the present invention comprises a bidirectional switch, a phase detection unit, a power supply unit, and a control unit. The bidirectional switch is connected in series with a load to an AC power supply and controls the phase of the AC voltage supplied to the load. The phase detection unit detects the phase of the AC voltage of the AC power supply. The power supply unit is connected in parallel with the bidirectional switch and has a capacitive element that performs a conversion operation to convert the AC power supply into a predetermined control power supply and stores the control power supply. The control unit receives the control power supply from the power supply unit through the capacitive element and divides each half-cycle period of the AC voltage into a first period, a second period, a third period, and a fourth period based on the phase detected by the phase detection unit. In the first period and the fourth period, the control unit controls the bidirectional switch to be non-conductive to interrupt the power supply to the load and causes the power supply unit to perform the conversion operation. During the second period, the control unit controls the bidirectional switch to conduct, thereby supplying power to the load and causing the power supply unit to stop the conversion operation. During the third period, the control unit controls the bidirectional switch to deconduct, thereby cutting off the power supply to the load. This is a schematic circuit diagram showing the configuration of the dimming device according to Embodiment 1. This is a timing chart showing the operation of the dimming device according to Embodiment 1. This is a timing chart used for comparison between the dimming device according to Embodiment 1 and a comparative example. This is a schematic circuit diagram showing the configuration of the dimming device according to Modification 1 of Embodiment 1. This is a schematic circuit diagram showing the configuration of the dimming device according to Modification 2 of Embodiment 1. This is a timing chart showing the operation of the dimming device according to Modification 2 of Embodiment 1. This is a schematic circuit diagram showing the configuration of the dimming device according to Embodiment 2. (Embodiment 1) (1.1) Composition The dimming device 1 of this embodiment will now be described. However, the configuration described below is merely one example of the present invention, and the present invention is not limited to the following embodiment. Even in embodiments other than this one, various modifications can be made according to the design, etc., as long as they do not depart from the technical idea of ​​the present invention. As shown in Figure 1, the dimming device 1 of this embodiment includes a pair of input terminals 11 and 12, a bidirectional switch 2, a phase detection unit 3, an input unit 4, a power supply unit 5, a control unit 6, a switch drive unit 9, diodes D1 and D2, and a stop unit 13. A pair of input terminals 11 and 12 are electrically connected between the load 7, which lights up when power is supplied, and the AC power supply 8. The bidirectional switch 2 is configured to switch between interrupting and conducting bidirectional current between the pair of input terminals 11 and 12. The phase detection unit 3 detects the phase of the AC voltage Vac of the AC power supply 8. The input unit 4 receives a dimming level that specifies the magnitude of the light output of the load 7. The power supply unit 5 is electrically connected between the pair of input terminals 11 and 12 and generates a control power supply using power supplied from the AC power supply 8. The control unit 6 operates by receiving control power from the power supply unit 5. Based on the detection signal from the phase detection unit 3, the control unit 6 controls the bidirectional switch 2 so that it is in the OFF state from the start of half a cycle of the AC voltage Vac until the first time point when the first time has elapsed. The control unit 6 controls the bidirectional switch 2 so that it is in the ON state from the first time point until the second time point when the second time point corresponding to the dimming level has elapsed. Furthermore, the control unit 6 controls the bidirectional switch 2 so that it is in the OFF state from the second time point until the end of half a cycle. Here, the expression "from point A" includes point A. For example, "from the first point" includes the first point. On the other hand, the expression "up to point A" does not include point A, but means up to the point immediately preceding point A. For example, "up to the first point" does not include the first point, but means up to the point immediately preceding the first point. Also, the "input terminal" referred to here does not have to have a physical form as a component (terminal) for connecting wires, etc., and may be, for example, a lead of an electronic component or a part of a conductor included in a circuit board. The dimmer 1 is a two-wire dimmer and is used in a state where it is electrically connected in series with the load 7 to the AC power supply 8. The load 7 lights up when power is supplied. The load 7 comprises an LED element as a light source and a lighting circuit that lights up the LED element. The AC power supply 8 is, for example, a single-phase 100V, 60Hz commercial power supply. The dimmer 1 can be applied to a wall switch, for example. The bidirectional switch 2 consists of two elements, for example, a first switch element Q1 and a second switch element Q2, which are electrically connected in series between input terminals 11 and 12. For example, each of the switch elements Q1 and Q2 is a semiconductor switch element consisting of an enhancement-type n-channel MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor). Switch elements Q1 and Q2 are connected in reverse series between input terminals 11 and 12. In other words, the sources of switch elements Q1 and Q2 are connected to each other. The drain of switch element Q1 is connected to input terminal 11, and the drain of switch element Q2 is connected to input terminal 12. The sources of both switch elements Q1 and Q2 are connected to the ground of the power supply unit 5. The ground of the power supply unit 5 is the reference potential for the internal circuit of the dimmer 1. The bidirectional switch 2 can switch between four states by the on and off combination of switch elements Q1 and Q2. The four states are a bidirectional off state where both switch elements Q1 and Q2 are off, a bidirectional on state where both switch elements Q1 and Q2 are on, and two types of unidirectional on states where only one of switch elements Q1 or Q2 is on. In the unidirectional on state, the pair of input terminals 11 and 12 conduct in one direction from the on switch element Q1 to the off switch element via the parasitic diode of the off switch element. For example, when switch element Q1 is on and switch element Q2 is off, it is a first unidirectional on state where current flows from input terminal 11 to input terminal 12. Also, when switch element Q2 is on and switch element Q1 is off, it is a second unidirectional on state where current flows from input terminal 12 to input terminal 11. Therefore, when an AC voltage Vac is applied between input terminals 11 and 12 from an AC power supply 8, during the half-cycle when the AC voltage Vac is positive, i.e., when input terminal 11 is positive, the first unidirectional ON state becomes the "forward ON state," and the second unidirectional ON state becomes the "reverse ON state." On the other hand, during the half-cycle when the AC voltage Vac is negative, i.e., when input terminal 12 is positive, the second unidirectional ON state becomes the "forward ON state," and the first unidirectional ON state becomes the "reverse ON state." Here, the bidirectional switch 2 is in the ON state when both the "bidirectional ON state" and the "forward ON state" are ON, and in the OFF state when both the "bidirectional OFF state" and the "reverse ON state" are OFF. The phase detection unit 3 detects the phase of the AC voltage Vac applied between the input terminals 11 and 12. Here, "phase" includes the zero-crossing point of the AC voltage Vac and the polarity of the AC voltage Vac (positive polarity, negative polarity). The phase detection unit 3 is configured to output a detection signal to the control unit 6 when it detects the zero-crossing point of the AC voltage Vac. The phase detection unit 3 includes a diode D31, a first detection unit 31, a diode D32, and a second detection unit 32. The first detection unit 31 is electrically connected to the input terminal 11 via the diode D31. The second detection unit 32 is electrically connected to the input terminal 12 via the diode D32. The first detection unit 31 detects the zero-crossing point when the AC voltage Vac transitions from a negative polarity half-cycle to a positive polarity half-cycle. The second detection unit 32 detects the zero-crossing point when the AC voltage Vac transitions from a positive polarity half-cycle to a negative polarity half-cycle. In other words, the first detection unit 31 determines that a zero-crossing point has occurred when it detects that the voltage with the input terminal 11 as the positive terminal has transitioned from a state below a specified value to a state above a specified value. Similarly, the second detection unit 32 determines that a zero-crossing point has occurred when it detects that the voltage with the input terminal 12 as the positive terminal has transitioned from a state below a specified value to a state above a specified value. The specified value is a value (absolute value) set around 0 [V]. For example, the specified value for the first detection unit 31 is around a positive number [V], and the specified value for the second detection unit 32 is around a negative number [V]. Therefore, the detection point of the zero-crossing point detected by the first detection unit 31 and the second detection unit 32 is slightly delayed from the zero-crossing point (0 [V]) in the strict sense. The input unit 4 receives a signal representing the dimming level from the operation unit operated by the user and outputs it to the control unit 6 as a dimming signal. The input unit 4 may or may not process the received signal when outputting the dimming signal. The dimming signal is a numerical value that specifies the magnitude of the light output of the load 7, and may include an "OFF level" that turns off the load 7. The operation unit can be any device that receives user input and outputs a signal representing the dimming level to the input unit 4, such as a variable resistor, rotary switch, touch panel, remote controller, or communication terminal such as a smartphone. The control unit 6 controls the bidirectional switch 2 based on the detection signal from the phase detection unit 3 and the dimming signal from the input unit 4. The control unit 6 controls the switch elements Q1 and Q2 separately. Specifically, the control unit 6 controls the switch element Q1 with a first control signal and controls the switch element Q2 with a second control signal. The control unit 6 primarily consists of, for example, a microcomputer. The microcomputer performs its function as the control unit 6 by executing a program stored in its memory using its CPU (Central Processing Unit). The program may be pre-stored in the microcomputer's memory, provided on a recording medium such as a memory card, or provided via a telecommunications line. In other words, the program is a program that causes the computer (in this case, the microcomputer) to function as the control unit 6. The switch drive unit 9 includes a first drive unit 91 that drives (on / off controls) the switch element Q1 and a second drive unit 92 that drives (on / off controls) the switch element Q2. The first drive unit 91 receives a first control signal from the control unit 6 and applies a gate voltage to the switch element Q1. In this way, the first drive unit 91 controls the on / off state of the switch element Q1. Similarly, the second drive unit 92 receives a second control signal from the control unit 6 and applies a gate voltage to the switch element Q2. In this way, the second drive unit 92 controls the on / off state of the switch element Q2. The first drive unit 91 generates the gate voltage with reference to the potential of the source of the switch element Q1. The second drive unit 92 does the same. The power supply unit 5 includes a control power supply unit 51 that generates a control power supply, a drive power supply unit 52 that generates a drive power supply, and a capacitive element (capacitor) C1. The control power supply is the power supply for the operation of the control unit 6. The drive power supply is the power supply for driving the switch drive unit 9. The capacitive element C1 is electrically connected to the output terminal of the control power supply unit 51 and is charged by the output current of the control power supply unit 51. The power supply unit 5 is electrically connected to the input terminal 11 via diode D1 and to the input terminal 12 via diode D2. As a result, the AC voltage Vac applied between the input terminals 11 and 12 is full-wave rectified by a diode bridge composed of the pair of diodes D1 and D2 and the parasitic diodes of the respective switch elements Q1 and Q2, and supplied to the power supply unit 5. The drive power supply unit 52 smooths the full-wave rectified AC voltage Vac to generate a drive power supply. The drive power supply unit 52 supplies the drive power supply to the switch drive unit 9 and the control power supply unit 51. The drive power supply is, for example, 10V. The control power supply unit 51 steps down the drive power supply supplied from the drive power supply unit 52 to generate a control power supply and outputs it to the capacitive element C1. The control power supply is, for example, 3V. The control power supply unit 51 may generate the control power supply directly from the full-wave rectified AC voltage Vac without going through the drive power supply unit 52. In other words, the power supply unit 5 generates a control power supply and a drive power supply using power supplied from the AC power supply 8. The stop unit 13 stops the generation of control power in the power supply unit 5 during the stop period. In this embodiment, the stop unit 13 stops the generation of control power in the power supply unit 5 by electrically disconnecting the power supply unit 5 or by controlling the semiconductor switch element included in the power supply unit 5. In the example in Figure 1, the stop unit 13 forms a series circuit with the power supply unit 5, and the series circuit of the stop unit 13 and the power supply unit 5 is electrically connected in parallel with the bidirectional switch 2 between a pair of input terminals 11 and 12. As will be explained in detail in the section "(1.2.2) Dimming Operation", the stop period is a set period that excludes at least the period during which the bidirectional switch 2 is in the bidirectional off state. Specifically, the stop unit 13 is a switch electrically connected between the connection point of a pair of diodes D1 and D2 and the power supply unit 5, and turns off upon receiving a disconnection signal from the control unit 6, electrically disconnecting the power supply unit 5 from the input terminals 11 and 12. Furthermore, the dimming device 1 of this embodiment includes a mask unit 61. When the mask unit 61 receives a detection signal from the phase detection unit 3, it disables the detection signal for a certain length of mask time. In this embodiment, the mask unit 61 is provided integrally with the control unit 6 as a function of the control unit 6. As will be explained in detail in the section "(1.2.2) Dimming Operation", the mask unit 61 disables the detection signal from the phase detection unit 3 during the mask time, thereby making the control unit 6 less susceptible to the effects of erroneous detection of zero-crossing points by the phase detection unit 3. It is preferable that the mask unit 61 disables the detection signals of the first detection unit 31 and the second detection unit 32 separately. The lighting circuit for load 7 reads the dimming level from the waveform of the AC voltage Vac, which is phase-controlled by the dimmer 1, and changes the magnitude of the light output of the LED element. Here, the lighting circuit includes, for example, a circuit for ensuring current, such as a bleeder circuit. Therefore, it is possible to supply current to load 7 even during periods when the bidirectional switch 2 of the dimmer 1 is not conducting. (1.2) Operation (1.2.1) Startup operation First, the startup operation of the dimming device 1 in this embodiment when power is turned on will be described. According to the dimming device 1 with the above configuration, when an AC power supply 8 is connected between input terminals 11 and 12 via a load 7, the AC voltage Vac applied from the AC power supply 8 between input terminals 11 and 12 is rectified and supplied to the drive power supply unit 52. The drive power generated by the drive power supply unit 52 is supplied to the switch drive unit 9 and also to the control power supply unit 51. When the control power generated by the control power supply unit 51 is supplied to the control unit 6, the control unit 6 starts up. When the control unit 6 is activated, it determines the frequency of the AC power supply 8 based on the detection signal from the phase detection unit 3. Then, according to the determined frequency, the control unit 6 refers to a numerical table stored in memory and sets various parameters such as time (for example, the mask time and stop period described later). If the dimming level input to the input unit 4 is at the "OFF level", the control unit 6 maintains the bidirectional switch 2 in a bidirectional off state, thereby maintaining the impedance between the pair of input terminals 11 and 12 in a high impedance state. As a result, the load 7 remains off. (1.2.2) Dimming operation Next, the dimming operation of the dimming device 1 of this embodiment will be explained with reference to Figure 2. Figure 2 shows the AC voltage "Vac", the first detection signal "ZC1", the first masking process "MASK1", the second detection signal "ZC2", the second masking process "MASK2", the first control signal "Sb1", the second control signal "Sb2", and the cutoff signal "Ss1". Here, the first detection signal ZC1 is a detection signal by the first detection unit 31, and the second detection signal ZC2 is a detection signal by the second detection unit 32. The first masking process MASK1 is a masking process (invalidation process) of the first detection signal ZC1 by the mask unit 61, and the second masking process MASK2 is a masking process of the second detection signal ZC2 by the mask unit 61. Here, the first detection signal ZC1 is considered to have been generated when the first detection signal ZC1 changes from an "H" level to an "L" level. Furthermore, the generation of the second detection signal ZC2 is determined when the second detection signal ZC2 changes from an "H" level to an "L" level. In other words, the first detection signal ZC1 and the second detection signal ZC2 are signals that change from an "H" level to an "L" level when a zero-crossing point is detected. First, the operation of the dimming device 1 during a half-cycle in which the AC voltage Vac is positive will be explained. The dimming device 1 detects the zero-crossing point of the AC voltage Vac, which serves as the reference for phase control, using the phase detection unit 3. When the AC voltage Vac transitions from a half-cycle in which it is negative to a half-cycle in which it is positive, the first detection unit 31 outputs a first detection signal ZC1 when the AC voltage Vac reaches a specified positive value "Vzc". Upon receiving the first detection signal ZC1, the control unit 6 sets the first control signal Sb1 and the second control signal Sb2 to "OFF" signals. As a result, during the first period T1 from the start of the half-cycle (zero-crossing point) t0 to the first time point t1 after the first hour has elapsed, both switch elements Q1 and Q2 are turned off, and the bidirectional switch 2 is in a bidirectional off state. In this embodiment, the time at which the first detection signal ZC1 is generated is defined as the "detection point," and the sum of the period from the start of the half-cycle (zero-crossing point) t0 to the detection point and the period until a certain amount of time (for example, 300 [μs]) has elapsed from the detection point is defined as the first period T1. In other words, in this embodiment, the control unit 6 controls the bidirectional switch 2 to be in a bidirectional off state not only after the detection point, but also during the period from the start of the half-cycle (zero-crossing point) t0 to the detection point. Here, if the frequency of the AC voltage Vac is constant, the time from the start of the half-cycle (zero-crossing point) t0 to the detection point is a constant length of time, so the first hour (the time from the start of the half-cycle t0 to the first time point t1) in this embodiment is a constant length of time. At a certain time interval (for example, 300 μs) after the detection point, i.e., at the first time point t1, the control unit 6 sets the first control signal Sb1 and the second control signal Sb2 to "ON" signals. The second time point t2 is the point in time when two hours have elapsed since the first time point t1, according to the dimming signal. At the second time point t2, the control unit 6 maintains the second control signal Sb2 as an "ON" signal while setting the first control signal Sb1 to an "OFF" signal. As a result, during the second period T2 from the first time point t1 to the second time point t2, both switch elements Q1 and Q2 are turned on, and the bidirectional switch 2 is in a bidirectional on state. Therefore, during the second period T2, power is supplied from the AC power supply 8 to the load 7 via the bidirectional switch 2, and the load 7 lights up. The third time point t3 is a certain time (for example, 300 [μs]) before the end point (zero-crossing point) t4 of the half-cycle. At the third time point t3, the control unit 6 sets the first control signal Sb1 and the second control signal Sb2 to "OFF" signals. As a result, during the third period T3 from the second time point t2 to the third time point t3, only switch element Q1 of the switch elements Q1 and Q2 is turned off, and the bidirectional switch 2 is turned on in the reverse direction (i.e., turned off). Therefore, during the third period T3, power from the AC power supply 8 to the load 7 is cut off. During the fourth period T4, from the third time point t3 to the end of the half-cycle (zero-crossing point) t4, both switching elements Q1 and Q2 are turned off, and the bidirectional switch 2 is in a bidirectional off state. Furthermore, the operation of the dimming device 1 during a half-cycle when the AC voltage Vac is negative is basically the same as that during a half-cycle when it is positive. In a negative polarity half-cycle, the first period T1 is defined as the period from the start point (zero-crossing point) t0 (t4) of the half-cycle to the first time point t1, when the first time has elapsed. In this embodiment, the time at which the second detection signal ZC2 is generated is defined as the "detection point," and the first period T1 is defined as the sum of the period from the start point (zero-crossing point) t0 (t4) of the half-cycle to the detection point and the period until a certain time (e.g., 300 [μs]) has elapsed from the detection point. The second time point t2 is the time when the second time corresponding to the dimming signal has elapsed from the first time point t1, and the third time point t3 is a certain time (e.g., 300 [μs]) before the end point (zero-crossing point) t4 (t0) of the half-cycle. That is, when the AC voltage Vac reaches the specified negative polarity value "-Vzc", the second detection unit 32 outputs the second detection signal ZC2. Upon receiving the second detection signal ZC2, the control unit 6 sets the first control signal Sb1 and the second control signal Sb2 to "OFF" signals. As a result, the bidirectional switch 2 is in a bidirectional off state during the first period T1. Then, at the first time point t1, the control unit 6 sets the first control signal Sb1 and the second control signal Sb2 to "ON" signals. At the second time point t2, the control unit 6 maintains the first control signal Sb1 as an "ON" signal while setting the second control signal Sb2 to an "OFF" signal. As a result, during the second period T2 from the first time point t1 to the second time point t2, both switch elements Q1 and Q2 are turned on, and the bidirectional switch 2 is in a bidirectional on state. Therefore, during the second period T2, power is supplied from the AC power supply 8 to the load 7 via the bidirectional switch 2, and the load 7 lights up. At the third time point t3, the control unit 6 sets the first control signal Sb1 and the second control signal Sb2 to "OFF" signals. As a result, during the third period T3 from the second time point t2 to the third time point t3, only switch element Q2 of the switch elements Q1 and Q2 is turned off, and the bidirectional switch 2 is turned on in the reverse direction (i.e., turned off). Therefore, during the third period T3, power from the AC power supply 8 to the load 7 is cut off. The dimming device 1 of this embodiment dims the load 7 by alternately repeating the positive-polarity half-cycle operation and the negative-polarity half-cycle operation described above for each half-cycle of the AC voltage Vac. The bidirectional switch is in the off state from the start point (zero-crossing point) t0 of the half-cycle to the first time point t1, and the bidirectional switch is also in the off state from the second time point t2 to the end point (zero-crossing point) t4 of the half-cycle. Therefore, focusing on two consecutive half-cycles, the bidirectional switch is in the off state from the second time point t2 of the first half-cycle to the first time point t1 of the next half-cycle (i.e., the second half-cycle). Here, the time from the first time point t1 to the second time point t2 (second time) is the time corresponding to the dimming level input to the input unit 4. Therefore, the time during which the input terminals 11 and 12 conduct during a half-cycle is defined according to the dimming level. That is, the second time is defined to be shorter when the light output of the load 7 is reduced, and longer when the light output of the load 7 is increased. Therefore, it is possible to change the magnitude of the light output of the load 7 according to the dimming level input to the input unit 4. In addition, there are periods (first period T1 and fourth period T4) before and after the zero-crossing point of the AC voltage Vac during which the bidirectional switch 2 is in a bidirectional off state. Therefore, the dimming device 1 can use these periods to ensure power supply from the AC power source 8 to the power supply unit 5. In this embodiment, power supply from the AC power source 8 to the power supply unit 5 can be ensured during at least one of the first period T1 and the fourth period T4. Furthermore, if the user operates the control unit to maximize the optical output of load 7, priority may be given to securing the first period T1 and the fourth period T4, while controlling the second period T2 to be shorter than the length required to maximize the optical output. By the way, the dimming device 1 of this embodiment is equipped with a mask unit 61, which, after receiving a zero-crossing point detection signal, performs a masking process that disables subsequent zero-crossing point detection signals for a certain length of masking time. That is, after the mask unit 61 receives the first detection signal ZC1 from the first detection unit 31, it turns on the first masking process MASK1 and disables the first detection signal ZC1 until the masking time has elapsed. Similarly, after the mask unit 61 receives the second detection signal ZC2 from the second detection unit 32, it turns on the second masking process MASK2 and disables the second detection signal ZC2 until the masking time has elapsed. The length of the masking time is set based on half a cycle of the AC voltage Vac. Here, as an example, the masking time is set to a time slightly shorter than twice half a cycle (i.e., one cycle). In Figure 2, the first detection signal ZC1 and the second detection signal ZC2 during the disabled period are shown by dashed lines. As a result, once a zero-crossing point is detected, masking is applied up to the vicinity of the next zero-crossing point. For example, even if a zero-crossing point is falsely detected due to noise at 1 / 4 of a period after the initial detection, the detection signal generated by the false detection will be invalidated by the masking process. Therefore, the control unit 6 is less susceptible to the effects of false zero-crossing point detection by the phase detection unit 3. Furthermore, the dimming device 1 of this embodiment controls the stop unit 13 with a cutoff signal Ss1. During the stop period, the stop unit 13 stops the generation of control power in the power supply unit 5 by electrically cutting off the power supply unit 5 or by controlling the semiconductor switch elements included in the power supply unit 5. That is, the control unit 6 turns off the stop unit 13 by setting the cutoff signal Ss1 to an "OFF" signal during the stop period, thereby electrically disconnecting the power supply unit 5 from the input terminals 11 and 12. The stop period is a set period excluding at least the period when the bidirectional switch 2 is in the bidirectional off state (first period T1, fourth period T4). In other words, the stop period is set within the second period T2 when the bidirectional switch 2 is in the bidirectional on state, and the third period T3 when the bidirectional switch 2 is in the unidirectional on state (reverse on state). Here, as an example, the stop period is set to start at a point set between the first time point t1 and the second time point t2 and end at the third time point t3. That is, the stop period is set within the period during which power may be supplied from the AC power supply 8 to the load 7. As a result, during the shutdown period, the dimming device 1 can maintain a high impedance between input terminals 11 and 12, proportional to the disconnection of the power supply unit 5 from the input terminals 11 and 12. In other words, the dimming device 1 supplies power from the AC power supply 8 to the power supply unit 5 when the bidirectional switch 2 is in the bidirectional off state, and maintains a high impedance between input terminals 11 and 12 during the period when it does not supply power to the power supply unit 5 (shutdown period). For example, during the third period T3 when the bidirectional switch 2 is in the reverse on state, maintaining a high impedance between input terminals 11 and 12 prevents power from being supplied to the load 7 due to leakage current. This allows the magnitude of the light output of the load 7 to change in response to fine changes in the dimming level, improving the responsiveness of the load 7. (1.3) Summary of the dimming device according to Embodiment 1 As described above, the dimming device 1 according to this embodiment comprises a bidirectional switch 2, a phase detection unit 3, a power supply unit 5, and a control unit 6. The bidirectional switch 2 is connected in series with the load 7 to the AC power supply 8 and controls the phase of the AC voltage Vac supplied to the load 7. The phase detection unit 3 detects the phase of the AC voltage Vac of the AC power supply 8. The power supply unit 5 is connected in parallel with the bidirectional switch 2 and has a capacitive element C1 that converts the AC power supply 8 into a predetermined control power supply and stores the control power supply. The control unit 6 receives control power from the power supply unit 5 through the capacitive element C1 and divides each half-cycle period of the AC voltage Vac into a first period T1, a second period T2, a third period T3, and a fourth period T4 based on the phase detected by the phase detection unit 3. In the first period T1 and the fourth period T4, the control unit 6 controls the bidirectional switch 2 to be non-conductive to cut off the power supply to the load 7 and causes the power supply unit 5 to perform the conversion operation. In the second period T2, the control unit 6 controls the bidirectional switch 2 to be conductive to supply power to the load 7 and causes the power supply unit 5 to stop the conversion operation. In the third period T3, the control unit 6 controls the bidirectional switch 2 to be non-conductive to cut off the power supply to the load 7. In this context, "non-conductive control" refers to control that turns the bidirectional switch 2 to the OFF state. "Conductive control" refers to control that turns the bidirectional switch 2 to the ON state. "Conversion operation" refers to the operation in the power supply unit 5 that converts the AC power supply 8 into a predetermined control power supply, that is, the operation that generates the control power supply using the power supplied from the AC power supply 8. Furthermore, the dimming device 1 may also include a stop unit 13 that switches between executing and stopping the conversion operation of the power supply unit 5. In this case, for example, during the third period (T3), in addition to the control unit 6 controlling the bidirectional switch 2 to deconduct and interrupting the power supply to the load 7, the stop unit 13 may also stop the conversion operation of the power supply unit 5. (1.4) Comparison with Comparative Example In the following, a different inverse phase control method from this embodiment will be used as a comparative example, and the differences between the control method of this embodiment and the control method of the comparative example will be explained with reference to Figure 3. Although the operation of the control unit 6 (control method of the bidirectional switch 2) in the comparative example shown here differs from that of this embodiment, the circuit configuration is the same as that of this embodiment. Therefore, components similar to those in this embodiment will be denoted by the same reference numerals below. Figure 3 shows the AC voltage "Vac", the first control signal "Sa1" and the second control signal "Sa2" of the comparative example, and the first control signal "Sb1" and the second control signal "Sb2" of this embodiment. The dimming device in the comparative example alternately turns on the first control signal Sa1 and the second control signal Sa2 in the same period as the AC voltage Vac. In this comparative example, the bidirectional switch 2 conducts during the period when the switch element Q1 and Q2 that is on the higher potential side of the AC voltage Vac is ON. In other words, in the comparative example, in Figure 3, so-called inverse phase control is realized, in which the pair of input terminals 11 and 12 conduct during the period Ta1 from the zero-crossing point of the AC voltage Vac to the middle of the half-cycle. Therefore, the conduction time of the bidirectional switch 2 can be adjusted by adjusting the phase difference between the first control signal Sa1 and the second control signal Sa2 and the AC voltage Vac. Therefore, when comparing this embodiment with the comparative example described above, the two differ in the following two points. [Difference 1] As shown by [X] in Figure 3, in this embodiment there is a period (second period T2) during which the bidirectional switch 2 is in a bidirectional ON state, whereas in the comparative example there is no such period during which the bidirectional switch 2 is in a bidirectional ON state. In other words, in the comparative example, the pair of input terminals 11 and 12 become conductive when the bidirectional switch 2 is in a unidirectional ON state (forward ON state), whereas in this embodiment, the pair of input terminals 11 and 12 become conductive when the bidirectional switch 2 is in a bidirectional ON state. Thus, in the dimming device 1 of this embodiment, the bidirectional switch 2 becomes bidirectional ON when the pair of input terminals 11 and 12 become conductive, so the conductivity loss in the bidirectional switch 2 can be kept smaller compared to the comparative example where the bidirectional switch 2 is in a unidirectional ON state. [Difference 2] As shown by [Y] in Figure 3, in this embodiment, there are periods (first period T1, fourth period T4) before and after the zero-crossing point of the AC voltage Vac during which the bidirectional switch 2 is in a bidirectional off state, whereas in the comparative example, such periods do not exist. In other words, in the comparative example, the pair of input terminals 11 and 12 conduct during the period Ta1 from the zero-crossing point of the AC voltage Vac to the middle of the half-cycle, so the opportunity to supply power from the AC power source 8 to the power supply unit 5 is secured only in the latter half of the half-cycle. However, depending on the type of load 7, such as a load 7 employing a capacitor-input type lighting circuit, current may not flow to the load 7 in the latter half of the half-cycle of the AC voltage Vac. Therefore, in the comparative example, sufficient current cannot be supplied to the power supply unit 5 during the period when the pair of input terminals 11 and 12 do not conduct, and there is a possibility that sufficient power cannot be supplied from the AC power source 8 to the power supply unit 5. As a result, in the comparative example, there is a possibility that the supply of control power from the power supply unit 5 to the control unit 6 cannot be maintained. In contrast, the dimming device 1 of this embodiment keeps the bidirectional switch 2 in a bidirectional off state during the period from the start point (zero-crossing point) t0 of the half-cycle to the first time point t1 (first period T1), so that this period can be used to supply power to the power supply unit 5. Although the dimming device 1 of this embodiment basically employs reverse phase control, by providing a period (first period T1) in the first half of the half-cycle of the AC voltage Vac during which the bidirectional switch 2 is non-conductive, the opportunity to supply power from the AC power source 8 to the power supply unit 5 can be secured in the first half of the half-cycle. Therefore, the dimming device 1 of this embodiment can maintain power supply from the power supply unit 5 to the control unit 6 in response to a wider variety of loads 7 compared to the comparative example. Furthermore, the dimming device 1 also keeps the bidirectional switch 2 in the bidirectional off state during the period from the third time point t3 to the end point t4 of the half cycle (the fourth period T4), so this period can also be used to supply power to the power supply unit 5. In other words, by providing a period (the fourth period T4) in which the bidirectional switch 2 is non-conductive even in the latter half of the half cycle, the dimming device 1 can ensure that the opportunity to supply power from the AC power source 8 to the power supply unit 5 is also secured in the latter half of the half cycle. (1.5) Advantages In addition to the inverse phase control method (trailing edge method), there is also the forward phase control method (leading edge method), in which a pair of input terminals 11 and 12 conduct during the period from the middle of the half-cycle of the AC voltage Vac to the zero-crossing point. The inverse phase control method starts supplying power to the load 7 equipped with LED elements as a light source from the zero-crossing point, thus minimizing current waveform distortion at the start of power supply. This has advantages such as increasing the number of loads 7 (lights) that can be connected to the dimmer and suppressing the generation of humming noise. The dimming device 1 of this embodiment basically employs an inverse phase control method, but provides an opportunity to supply power from the AC power source 8 to the power supply unit 5 in the first half of the half-cycle of the AC voltage Vac. For this reason, since power supply to the load 7 starts at the first time point t1, which is one hour after the zero-crossing point, the current waveform distortion may be greater than that of the inverse phase control method in the comparative example above. However, since the absolute value of the AC voltage Vac at the first time point t1 is not that large, the effect of the current waveform distortion is negligibly small. On the other hand, there is the advantage that the control power necessary for the operation of the control unit 6 can be reliably secured and stably operated. Furthermore, in this embodiment, the dimming device 1 sets the bidirectional switch 2 to the reverse ON state during the period from the second time point t2 to the third time point t3 (third period T3), thereby reducing false detections by the phase detection unit 3. That is, depending on the load 7, the absolute value of the voltage across the load 7 may exceed the absolute value of the AC voltage Vac, and as a result, a voltage with the opposite polarity to the AC voltage Vac (hereinafter referred to as "reverse polarity voltage") may be applied to the pair of input terminals 11 and 12. For example, such a reverse polarity voltage is likely to occur in loads 7 where the voltage across the load 7 is not easily reduced, such as loads 7 equipped with relatively large capacity buffer capacitors. When a reverse polarity voltage occurs, the phase detection unit 3 may mistakenly detect a zero-crossing point at a point other than the zero-crossing point of the AC voltage Vac. There are also loads 7 in which a reverse polarity voltage may or may not occur depending on the dimming level, and in such loads 7, the zero-crossing point will change abruptly when the dimming level changes. During the third period T3, the bidirectional switch 2 is in the reverse ON state, which suppresses the generation of such reverse polarity voltages, thereby reducing erroneous detections by the phase detection unit 3 caused by reverse polarity voltages. Of course, even during the period when the bidirectional switch 2 is in the reverse ON state (the third period T3), the pair of input terminals 11 and 12 are not conductive, so by setting the cutoff signal to an "ON" signal, this period can be used to supply power to the power supply unit 5. The dimming device 1 can maintain power supply from the power supply unit 5 to the control unit 6, thereby preventing abnormal operation such as flashing or flickering of the load 7. In the control of the bidirectional switch 2 in this embodiment, it is possible to control it to a "forward-only on state" instead of a "bidirectional on state," and conversely, to control it to a "bidirectional on state" instead of a "forward-only on state." Furthermore, it is possible to control it to a "reverse-only on state" instead of a "bidirectional off state," and conversely, to control it to a "bidirectional off state" instead of a "reverse-only on state." In other words, it is sufficient that the state of the bidirectional switch 2 remains unchanged, whether on or off. Furthermore, as in this embodiment, it is preferable that the bidirectional switch 2 is configured to be switchable between a bidirectional off state that interrupts bidirectional current between input terminals 11 and 12, a bidirectional on state that allows bidirectional current to pass through, and a unidirectional on state that allows current to pass through in one direction. In this case, it is preferable that the control unit 6 is configured to control the bidirectional switch 2 so that it is in the reverse on state from the second time point t2 to the third time point t3, which is between the second time point t2 and the end of the half-cycle. The "reverse on state" is a unidirectional on state in which the bidirectional switch 2 allows current to flow from the input terminal on the lower potential side of the AC power supply 8 to the input terminal on the higher potential side of input terminals 11 and 12. With this configuration, the generation of reverse polarity voltage is suppressed from the second time point t2 to the third time point t3, so that erroneous detection by the phase detection unit 3 caused by reverse polarity voltage can be reduced. Furthermore, as in this embodiment, it is preferable that the power supply unit 5 has a capacitive element C1. With this configuration, the power supply unit 5 can store the power supplied from the AC power supply 8 in the capacitive element C1 during periods when the input terminals 11 and 12 are not conducting. Therefore, even during periods when the input terminals 11 and 12 are conducting, the power supply unit 5 can secure the control power supply for the control unit 6. However, the presence of the capacitive element C1 in the power supply unit 5 is not an essential configuration for the dimming device 1, and the capacitive element C1 may be omitted as appropriate. Also, as in this embodiment, it is preferable that the first time is a time of a constant length. According to this configuration, the control unit 6 may control the bidirectional switch 2 to the bidirectional off state during a period (first period T1) from the start point (zero crossing point) t0 of the half cycle until a first time of a constant length has elapsed. Therefore, compared with the case where the length of the first time changes, the processing of the control unit 6 becomes simpler. Although the processing of the control unit 6 becomes complicated, it is also possible to make the length of the first time different between the first period T1 in the positive half cycle and the first period T1 in the negative half cycle. As in this embodiment, it is preferable that the phase detection unit 3 is configured to output a detection signal when detecting the zero crossing point of the AC voltage Vac. In this case, it is preferable that the dimming device 1 further includes a mask unit 61 that invalidates the detection signal for a mask time of a constant length when receiving the detection signal from the phase detection unit 3. The mask unit 61 in this embodiment is not an essential configuration of the dimming device 1, and the mask unit 61 may be appropriately omitted. Also, as in this embodiment, it is preferable that the dimming device 1 further includes a stop unit 13 that stops the generation of the control power supply in the power supply unit 5 during the stop period. The stop period is a period set excluding at least the period during which the bidirectional switch 2 is in the off state. The stop unit 13 in this embodiment is not an essential configuration of the dimming device 1, and the stop unit 13 may be appropriately omitted. Also, as in this embodiment, it is preferable that the bidirectional switch 2 includes switch elements Q1 and Q2 electrically connected in series between a pair of input terminals 11 and 12. (1.6) Modified Example (1.6.1) Modified Example 1 As shown in FIG. 4, the dimming device 1A according to the first modified example of the first embodiment is different from the dimming device 1 of the first embodiment in the part corresponding to the bidirectional switch 2. Hereinafter, the same components as those in the first embodiment will be denoted by the same reference numerals and the description will be appropriately omitted. In this modification example, the bidirectional switch 2A includes a switch element Q3 with a double-gate structure. The switch element Q3 is a semiconductor element with a double-gate (dual-gate) structure using a wide-bandgap semiconductor material such as GaN (gallium nitride). Further, the bidirectional switch 2A includes a pair of diodes D3 and D4 connected in so-called reverse series between the input terminals 11 and 12. The cathode of the diode D3 is connected to the input terminal 11, and the cathode of the diode D4 is connected to the input terminal 12. The anodes of both diodes D3 and D4 are electrically connected to the ground of the power supply unit 5. In this modification example, the pair of diodes D3 and D4 together with the pair of diodes D1 and D2 constitute a diode bridge. According to the configuration of this modification example, the bidirectional switch 2A can further reduce the conduction loss compared to the bidirectional switch 2. (1.6.2) Modification Example 2 As shown in FIG. 5, the dimming device 1B according to the second modification example of the first embodiment is different from the dimming device 1 of the first embodiment in that the control unit 6B is configured to estimate the zero-crossing point of the AC voltage Vac more than half a cycle ahead based on the detection signal of one zero-crossing point. The circuit configuration of the dimming device 1B is the same as that of the dimming device 1 of the first embodiment. Hereinafter, the same components as those in the first embodiment will be denoted by common reference numerals and the description thereof will be omitted as appropriate. The phase detection unit 3 is configured to output a detection signal when detecting the zero-crossing point of the AC voltage Vac, which is the same as that in the first embodiment. In this modified example, the control unit 6B estimates a virtual zero-crossing point at least half a cycle ahead of the AC voltage Vac each time it receives a detection signal from the phase detection unit 3 based on the frequency of the AC voltage Vac, and generates a virtual signal at the timing of the virtual zero-crossing point. Specifically, as shown in Figure 6, the control unit 6B generates a first virtual signal Si1 when a waiting time Tzc equivalent to one cycle of the AC voltage Vac has elapsed from the time it receives the first detection signal ZC1. Similarly, the control unit 6B generates a second virtual signal Si2 when a waiting time Tzc equivalent to one cycle of the AC voltage Vac has elapsed from the time it receives the second detection signal ZC2. Here, the waiting time Tzc is set to be slightly longer than one cycle of the AC voltage Vac so that the first virtual signal Si1 is not generated before the next first detection signal ZC1. Furthermore, to prevent the second virtual signal Si2 from occurring before the next second detection signal ZC2, the waiting time Tzc is set to be slightly longer than one cycle of the AC voltage Vac. The control unit 6B then uses the logical OR of the first detection signal ZC1 and the first virtual signal Si1 as a trigger signal to determine the control timing of the bidirectional switch 2. Similarly, the control unit 6B uses the logical OR of the second detection signal ZC2 and the second virtual signal Si2 as a trigger signal to determine the control timing of the bidirectional switch 2. Therefore, even if the phase detection unit 3 fails to detect a zero-crossing point, the control unit 6B can use the virtual signal generated at the virtual zero-crossing point as a trigger signal instead of the detection signal from the phase detection unit 3 to determine the control timing of the bidirectional switch 2. The control unit 6B may be configured to estimate two or more virtual zero-crossing points for each detection signal of a zero-crossing point. In this case, the control unit 6B generates a virtual signal each time a waiting time Tzc has elapsed since receiving the detection signal. Here, the waiting time Tzc may be varied such that the first waiting time Tzc is slightly longer than one period of the AC voltage Vac, and subsequent waiting times Tzc are approximately the same length as one period of the AC voltage Vac. Furthermore, the waiting time Tzc for generating the virtual signal can be set based on half a cycle of the AC voltage Vac, and may be set based on half a cycle, three times half a cycle (i.e., 1.5 cycles), four times half a cycle (i.e., 2 cycles) or more, in addition to one cycle. When the waiting time Tzc is set based on an odd multiple of half a cycle, the control unit 6B generates the second virtual signal Si2 when the waiting time Tzc has elapsed based on the first detection signal ZC1. In this case, the control unit 6B also generates the first virtual signal Si1 when the waiting time Tzc has elapsed based on the second detection signal ZC2. Therefore, the control unit 6B can also be configured to generate the first virtual signal Si1 and the second virtual signal Si2 from only one of the first detection signal ZC1 and the second detection signal ZC2. According to this modified configuration, even if the phase detection unit 3 cannot detect the zero-crossing point due to the influence of accidental noise or other factors, or if a shift in the zero-crossing point occurs due to a momentary drop in the AC voltage Vac, the control unit 6B performs stable inverse phase control in synchronization with the period of the AC voltage Vac. (1.6.3) Other variations The following lists modifications of Embodiment 1 other than those described in Modifications 1 and 2 above. The dimming devices of Embodiment 1 and Modifications 1 and 2 described above are not limited to loads 7 using LED elements as light sources, but are also applicable to light sources equipped with capacitor-input type circuits that have high impedance and light up with low current. Examples of this type of light source include organic EL (Electroluminescence) elements. Furthermore, the dimming device is applicable to loads 7 of various light sources, such as discharge lamps. Furthermore, the switch drive unit 9 is not an essential component of the dimming device 1 and may be omitted as appropriate. If the switch drive unit 9 is omitted, the control unit 6 directly drives the bidirectional switch 2. The mask unit 61 is configured to disable the detection signal for a certain length of mask time, and is not limited to being integrated with the control unit 6. In other words, the mask unit 61 may be integrated with the phase detection unit 3, for example, in which case the detection signal can be disabled by the mask unit 61 stopping the operation of the phase detection unit 3 for the duration of the mask period. The mask unit 61 may also be provided separately from the control unit 6 and the phase detection unit 3. Furthermore, the mask time can be any time preset based on half a cycle of the AC voltage Vac, and is not limited to a time slightly shorter than twice a half cycle (i.e., one cycle), as illustrated in Embodiment 1. For example, the mask time may be slightly shorter than half a cycle, or slightly shorter than three times a half cycle (i.e., 1.5 cycles). Alternatively, the mask time may be set based on four times a half cycle (i.e., two cycles) or more. Furthermore, each of the switch elements Q1 and Q2 constituting the bidirectional switch 2 is not limited to enhancement-type n-channel MOSFETs, but may also be, for example, IGBTs (Insulated Gate Bipolar Transistors). Moreover, in the bidirectional switch 2, the rectifier element (diode) for realizing the unidirectional ON state is not limited to parasitic diodes of the switch elements Q1 and Q2, but may be an external diode as in Modification 1. The diode may be built into the same package as each of the switch elements Q1 and Q2. Furthermore, the first time period can be any length of time, and this length can be set as appropriate. For example, if the first period T1 is the sum of the period from the start point (zero-crossing point) t0 of the half-cycle to the detection point and the period from the detection point until a certain delay time has elapsed, the delay time is not limited to 300 [μs], but can be set as appropriate within the range of 0 [μs] to 500 [μs]. Furthermore, the third time point t3 only needs to be before the end point (zero-crossing point) t4 of the half-cycle, and the length from the third time point t3 to the end point t4 of the half-cycle can be set as appropriate. For example, if the time length from the detection point to the third time point t3 is shorter than the half-cycle by a certain specified time, the specified time is not limited to 300 [μs], but can be set as appropriate within the range of 100 [μs] to 500 [μs]. Furthermore, the stop period during which the stop unit 13 electrically disconnects the pair of input terminals 11 and 12 from the power supply unit 5 is a set period that excludes at least the period during which the bidirectional switch 2 is in the bidirectional off state (the first period T1 and the fourth period T4). Therefore, the stop period is not limited to a period that starts at a time between the first time point t1 and the second time point t2 and ends at the third time point t3, as in Embodiment 1. For example, the start of the stop period may be the first time point t1, and the end of the stop period may be before the third time point t3. Furthermore, the stopping unit 13 only needs to be configured to stop the generation of control power in the power supply unit 5 during the stopping period. Therefore, the stopping unit 13 is not limited to a configuration that stops the generation of control power in the power supply unit 5 by electrically disconnecting at least one of the pair of input terminals 11 and 12 from the power supply unit 5, or by controlling the semiconductor switch element included in the power supply unit 5. For example, the stopping unit 13 may be configured to stop the generation of control power in the power supply unit 5 by increasing the input impedance of the power supply unit 5 by stopping the output of the power supply unit 5 (output of control power). In this embodiment, diodes D1 and D2 are not essential components of the dimming device 1, and diodes D1 and D2 may be omitted as appropriate. (Embodiment 2) The dimming device 1C of this embodiment differs from the dimming device 1 of Embodiment 1 in that, as shown in Figure 7, it further includes a voltage detection unit 53 for detecting the voltage of the control power supply (voltage of the capacitive element C1). Hereinafter, components similar to those of Embodiment 1 will be denoted by common reference numerals and their descriptions will be omitted as appropriate. In this embodiment, the first time is not a fixed length of time, but rather the time from the starting point (zero-crossing point) t0 of the half-cycle of the AC voltage Vac until the voltage detected by the voltage detection unit 53 (voltage of the capacitive element C1) reaches a predetermined threshold. In other words, the first time in this embodiment is not a fixed length of time, but a variable length of time that changes according to the value detected by the voltage detection unit 53. Specifically, the voltage detection unit 53 is provided in the power supply unit 5C. The voltage detection unit 53 detects the voltage across the capacitive element C1 of the power supply unit 5C and outputs the detected value to the control unit 6C. After receiving a detection signal from the phase detection unit 3, the control unit 6C compares the detected value from the voltage detection unit 53 with a predetermined threshold value and determines that the first time has elapsed (i.e., it is the first time point t1) when the detected value reaches the threshold value. Here, the threshold value is the voltage across the capacitive element C1 when the capacitive element C1 is charged to a degree that ensures the operation of the control unit 6 at least until the end point (zero-crossing point) t4 of the half-cycle of the AC voltage Vac. As described above, the dimming device 1C of this embodiment further includes a voltage detection unit 53 for detecting the voltage of the control power supply, and the first time is the time from the start of the half-cycle until the voltage detected by the voltage detection unit 53 reaches a predetermined threshold. According to this embodiment, the control unit 6 can turn the bidirectional switch 2 to a bidirectional ON state when the capacitive element C1 is charged to a degree that the control power supply necessary for the operation of the control unit 6 is secured. Therefore, the dimming device 1C of this embodiment can reliably secure the control power supply necessary for the operation of the control unit 6, while minimizing the time from the start of the half-cycle (zero-crossing point) t0 of the AC voltage Vac until conduction occurs between the input terminals 11 and 12. The capacitive element C1 may be a parasitic capacitance, in which case there is no separate capacitive element. Other configurations and functions are the same as in Embodiment 1. The configuration of this embodiment can be applied in combination with each configuration described in Embodiment 1 (including modified examples). (Other embodiments) In the above-described embodiments 1 (including modified versions) and 2, power supply from the AC power source 8 to the power supply unit 5 is ensured before and after the starting point (zero-crossing point) t0 of the half-cycle of the AC voltage Vac (first period T1, fourth period T4), but the invention is not limited thereto. Only after the start point (zero-crossing point) t0 of the half-cycle of the AC voltage Vac (first period T1), power supply from the AC power source 8 to the power supply unit 5 may be ensured for a certain period of time. Alternatively, only before the start point (zero-crossing point) t0 of the half-cycle of the AC voltage Vac (fourth period T4), power supply from the AC power source 8 to the power supply unit 5 may be ensured for a certain period of time. In this case as well, since the first period T1 or the fourth period T4 is set with priority given to ensuring power supply from the AC power source 8 to the power supply unit 5, the second period T2, which supplies power to the load 7 according to the dimming level input to the input unit 4, may not be set. For example, this occurs when the user operates the control unit to maximize the light output of the load 7. By setting the above-mentioned fixed time to ensure sufficient power supply from the AC power source 8 to the power supply unit 5, the control unit 6 can be operated stably while suppressing current waveform distortion. 1, 1A, 1B, 1C light control device 2.2A Bidirectional Switch 3. Phase detection unit 4. Input section 5,5C power supply section 6, 6B, 6C Control Unit 7. Load 8 AC power supply 11 Input terminals 12 Input terminals 13 Stop part 53 Voltage detection unit 61 Mask section C1 Capacitive element Q1 Switching element Q2 Switching element Q3 Switch element t0 is the starting point of the half-period (zero-crossing point). t1 First point in time t2 Second point in time t3 Third point in time t4 Half-period endpoint (zero-crossing point) Vac AC voltage ZC1 First detection signal ZC2 Second detection signal

Claims

------04 / 04 / 2561------(OCR) Page 1 of 3 pages Claims 1. A dimming device, consisting of a pair of input terminals designed to be electrically connected between a load designed to illuminate when energized and an AC power source, a bidirectional switch designed to switch the bidirectional current flow and stop flow between the pair of input terminals, a phase detector designed to detect the phase of the AC voltage of the AC power source, and an input device designed to receive the dimming level represented by the value of the dimming. The load's output light, the power supply connected via a pair of input terminals and designed to receive power from the AC power source to generate control power, and the controller designed to receive control power from the power source to be activated. The controller is designed to actuate a directional switch based on a signal from a phase detector to make the directional switch in the closed state from the starting point of half a cycle of AC voltage to the first time point. When the first time point has elapsed,The bidirectional switch is in the open state from time one to time three when two times have elapsed following the dimming level, and the bidirectional switch is in the closed state from time three to the end of half-cycle 2. The dimming device of claim 1, where the bidirectional switch is designed to be switched to any one of the bidirectional closed states in which bidirectional current between the pairs of inputs is stopped, the bidirectional open state in which bidirectional current is conducted, and the one-way open state in which one-way current is conducted.The controller is designed to control a bidirectional switch so that from the time point at the beginning of the cycle to the time point between the time point at the beginning and the end of the half-cycle, the bidirectional switch is in a one-way open state in which the bidirectional switch allows current to flow from the lower input point of the lower input pair on the low-differential side of the AC power supply to the lower input point of the lower input pair on the high-differential side of the AC power supply. Page 2 of 3. The dimming device of claim 1 or 2, where time one is a constant time length.

4. The dimming device of claim 1 or 2, is further composed of a pressure sensor designed to detect the pressure of the control power, where time one is the time from the beginning of the half-cycle to the point in time when the pressure detected by the pressure sensor reaches a predetermined initial value.

5. Dimming devices of any of the claims 1 through 4, where the power supply contains a capacitor 6. Dimming devices of any of the claims 1 through 5,Where the phase detector is designed to output a detection signal when an AC zero-voltage drop is detected, and the dimming device is subsequently incorporated with a camouflage processor designed to shut off the detection signal for a fixed camouflage time when a detection signal is received from the phase detector.

7. The dimming device of any of the claims 1 through 6 is subsequently incorporated with a stopper designed to stop the power supply from generating control power during a stop period; the stop period shall be the period of time from which at least the period of time during which the bidirectional switch is in the off state is not included.

8. The dimming device of any of the claims 1 through 7, where the phase detector is designed to output a detection signal when an AC zero-voltage drop is detected, and the controller is designed to estimate the AC zero-voltage drop after one or more cycles based on a single detection signal.

9. Lighting equipment of any one of the claims 1 through 8,Where a bidirectional switch consists of two switching devices electrically connected in series between a pair of input terminals.

10. The lighting dimming device of any of the claims 1 through 8 is of the type where a bidirectional switch consists of a switching device with a double gate terminal structure.

11. The lighting dimming device consists of a bidirectional switch designed to be connected to an AC power source with a bidirectional switch connected in series with the load. The bidirectional switch is designed to create phase control of the AC voltage of the AC power source to be supplied to the load. Page 3 of 3 shows a phase detector designed to detect the phase of the AC voltage of the AC power source. The power source is connected in parallel with the bidirectional switch. The power source is designed to create a conversion function to convert the AC power supply to AC power. The control unit, a power supply with a capacitor designed to store the control power, and a controller designed to receive the control power through the capacitor from the power supply.The controller is designed to divide each AC voltage cycle into periods one, two, three, and four based on phase detection by a phase detector. The controller is then designed so that between periods one and four, the bidirectional switch is modulated out of conduction to stop the power supply to the load and cause the power source to operate during conversion; between periods two, the bidirectional switch is modulated in conduction to supply power to the load and stop the power source from operating during conversion; and between periods three, the bidirectional switch is modulated out of conduction to stop the power supply to the load.

12. Lighting equipment, consisting of a pair of connectors, with a switching device connected between the pair of connectors.The controller, designed to control the switching device, consists of a pair of input terminals designed to be electrically connected between the load designed to illuminate when energized and the AC power source, and an adjuster designed to adjust the angle of conduction of the switching device. The controller, designed to allow the power source to supply power to the controller during a specified time period from zero AC voltage drop in each AC voltage cycle, modulates the switching device to exit conduction to allow the power source to supply power to the controller. After a specified time period, the switching device is modulated to enter conduction and sequentially modulates the switching device to exit conduction according to the angle of conduction adjusted via the adjuster. During the time period until the next zero AC voltage drop, the switching device remains exit conduction to allow the power source to supply power to the controller.------------Page 1 of 3 pages of Claims 1. The dimming device, consists of a pair of input terminals designed to be electrically connected between the load designed to illuminate when energized and the AC power source,A bidirectional switch is designed to switch the flow of current in both directions between a pair of input terminals; a phase detector is designed to detect the phase of the AC voltage of the AC power supply; an input device is designed to receive the dimming level representing the load's lighting output; a power supply is electrically connected between the pair of input terminals and designed to receive power from the AC power supply to generate control power; and a controller is designed to receive control power from the power supply to activate it. The controller is designed to bidirectional switch based on the detection signal from the phase detector, placing the bidirectional switch in the closed state from the beginning of the AC voltage half-cycle to time point one. After one time elapses, the bidirectional switch is in the open state from time point one to time point two. After two time elapses, the dimming level is reflected in the switch.And the bidirectional switch is in the closed state from time point two to the end of half-cycle point 2. The dimming device of claim 1, where the bidirectional switch is designed to be switched to any of the bidirectional closed states in which bidirectional current between the pair of input terminals is stopped, the bidirectional open state in which bidirectional current is conducted, and the one-way open state in which one-way current is conducted, and page 2 of the number 3 controller page is designed to control the bidirectional switch so that from time point two to time point three, between time point two and the end of half-cycle point, the bidirectional switch is in the one-way open state in the direction in which the bidirectional switch allows current to flow from the input point of the pair of input terminals on the low-voltage side of the AC power supply to the input point of the input terminals on the high-voltage side of the AC power supply 3. The dimming device of claim 1 or 2, where time one is a constant time length 4. Dimming device for claim 1 or 2,It is further comprised of a voltage detector designed to detect the voltage of the control power supply, where time one is the time from the start of the half-cycle to the point in time when the voltage detected by the voltage detector reaches a predetermined initial value.

5. A dimming device of any of claims 1 through 4, where the power supply has a capacitor.

6. A dimming device of any of claims 1 through 5, where a phase detector is designed to output a detection signal when the zero point of AC voltage is detected, and the dimming device is further comprised of a camouflage processor designed to block the detection signal on a fixed camouflage time length when a detection signal is received from the phase detector.

7. A dimming device of any of claims 1 through 6, is further comprised of a stopper designed to stop the power supply from generating control power during the stop period.The pause period shall be the period of time from which at least the period of time during which the bidirectional switch is in the closed state is not included.

8. Dimming device of any of Reputations 1 through 7, in which the phase detector is designed to output a detection signal when the zero point of the AC voltage is detected, and the controller is designed to approximate the zero point of the AC voltage after a half-cycle or more on the basis of one detection signal. Page 3 of Number 3.

9. Dimming device of any of Reputations 1 through 8, in which the bidirectional switch consists of two switching devices electrically connected in series between a pair of input terminals.

10. Dimming device of any of Reputations 1 through 8, in which the bidirectional switch consists of a switching device with a dual gate structure.

11. Dimming device, consisting of a bidirectional switch designed to be connected to an AC power source, with the bidirectional switch connected in series with the load, the bidirectional switch is designed to create phase control of the AC voltage to be supplied to the load.A phase detector is designed to detect the phase of the AC voltage of an AC power source. The power source is connected in parallel with a bidirectional switch. The power source is designed to perform a conversion operation to transform the AC power into a specified controlled power. A capacitor is designed to store the controlled power, and a controller is designed to receive the controlled power through the capacitor from the power source. The controller divides each half-cycle of the AC voltage into periods one, two, three, and four based on the phase detected by the phase detector. Between periods one and four, the controller modulates the bidirectional switch to conduct, stopping the power supply to the load and causing the power source to perform the conversion operation. Between periods two, the bidirectional switch is modulated to conduct, supplying power to the load and stopping the power source from performing the conversion operation.And during the third period, the bidirectional switch modulates out of conduction to stop the flow of power to the load;