Power supply for driving LCD dimming device

Abstract

Gradually changing the degree of cloudiness in the liquid crystal layer. [Solution] The power supply 20 for driving the liquid crystal dimming device includes a DC / DC circuit section 40 that transforms and outputs a DC voltage, and a DC / AC circuit section 60 that converts the DC voltage output from the DC / DC circuit section 40 into an AC voltage and outputs it to the liquid crystal dimming device 11. The DC / AC circuit section 60 includes an inverter circuit 61 that converts the DC voltage output from the DC / DC circuit section 40 into a pseudo-sinusoidal AC voltage by the switching operation of switching elements 62 to 65, and a DC / AC control section 72 that can change the voltage value of the AC voltage by controlling the ON time of the switching elements 62 to 65.

Description

Technical Field

[0001] The present disclosure relates to a power supply for driving a liquid crystal dimming device.

Background Art

[0002] The power supply for driving a liquid crystal dimming device disclosed in Patent Document 1 includes a DC / DC converter, a peak voltage generation unit, and a DC / AC inverter. The DC / DC converter converts the input DC voltage into a DC voltage with a first voltage value and outputs it. The peak voltage generation unit generates a plurality of DC voltages with different voltage values from the DC voltage output from the DC / DC converter. The DC / AC inverter converts the DC voltage output from the peak voltage generation unit into an AC voltage and outputs it to the liquid crystal dimming device. The liquid crystal dimming device changes the clouding rate according to the voltage value of the AC voltage.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, the clouding rate of the liquid crystal dimming device cannot be gradually changed.

Means for Solving the Problems

[0005] A power supply for driving a liquid crystal dimming device that solves the above problems is a power supply for driving a liquid crystal dimming device that changes the cloudiness of a liquid crystal layer by supplying power to the liquid crystal dimming device having a liquid crystal layer, and comprises a DC / DC circuit section that transforms and outputs a DC voltage, and a DC / AC circuit section that converts the DC voltage output from the DC / DC circuit section into an AC voltage and outputs it to the liquid crystal dimming device, wherein the DC / AC circuit section comprises an inverter circuit that converts the DC voltage output from the DC / DC circuit section into a pseudo-sinusoidal AC voltage by the switching operation of a switching element, and an output variable section that can change the voltage value of the AC voltage by controlling the ON time of the switching element.

[0006] The output variable unit can change the voltage value of the AC voltage output to the liquid crystal dimming device. The degree of cloudiness of the liquid crystal layer changes depending on the voltage value of the applied AC voltage. Therefore, the degree of cloudiness of the liquid crystal layer can be changed by changing the voltage value of the AC voltage applied to the liquid crystal layer. By changing the voltage value of the AC voltage in steps, the degree of cloudiness of the liquid crystal layer can be changed gradually.

[0007] Regarding the power supply for driving the above-mentioned liquid crystal dimming device, the output variable unit may change the voltage value more gradually in the recognition range in which the change in the cloudiness rate of the liquid crystal layer is easily recognizable to a person, compared to ranges other than the recognition range.

[0008] Regarding the power supply for driving the liquid crystal dimming device described above, the liquid crystal dimming device is provided by the vehicle, and the power supply for driving the liquid crystal dimming device may include a communication circuit for communicating with the vehicle. [Effects of the Invention]

[0009] According to the present invention, the degree of cloudiness of the liquid crystal layer can be gradually changed. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a circuit diagram of the power supply for driving the liquid crystal dimming device. [Figure 2]Figure 2 shows an example of a pseudo-sine wave output by the DC / AC circuit section. [Figure 3] Figure 3 shows the relationship between AC voltage and the cloudiness rate of a liquid crystal dimming device. [Modes for carrying out the invention]

[0011] An embodiment of a power supply for driving a liquid crystal dimming device will be described. As shown in Figure 1, the vehicle 10 includes a liquid crystal dimming device 11, a battery 15, and a vehicle ECU 16.

[0012] The liquid crystal dimming device 11 is used, for example, as a dimmable glass placed in a side window or sunroof. The liquid crystal dimming device 11 is constructed, for example, by sandwiching a liquid crystal film 12 between two pieces of glass. The liquid crystal film 12 comprises a liquid crystal layer 13 and a coating layer 14 provided on both sides of the liquid crystal layer 13. The coating layer 14 is made of, for example, ITO (Indium Tin Oxide). The liquid crystal layer 13 contains liquid crystal molecules. The orientation of the liquid crystal molecules changes depending on the voltage applied to the liquid crystal layer 13 via the coating layer 14. This changes the degree of cloudiness of the liquid crystal layer 13.

[0013] The battery 15 is the power source for the electrical components of the vehicle 10. The battery 15 is a secondary battery, such as a lead-acid battery or a lithium-ion secondary battery. The vehicle's ECU (Electronic Control Unit) 16 outputs commands in response to user operations. The user is the occupant of the vehicle 10.

[0014] Vehicle 10 is equipped with a power supply 20 for driving the liquid crystal dimming device. The power supply 20 for driving the liquid crystal dimming device is located between the battery 15 and the liquid crystal dimming device 11. The power supply 20 for driving the liquid crystal dimming device converts the DC voltage output by the battery 15 into an AC voltage and outputs it to the liquid crystal dimming device 11, thereby supplying power to the liquid crystal dimming device 11.

[0015] The liquid crystal dimming device driving power supply 20 comprises a first input terminal 21 and a second input terminal 22. The first input terminal 21 is electrically connected to the positive terminal of the battery 15. The second input terminal 22 is electrically connected to the negative terminal of the battery 15.

[0016] The power supply 20 for driving the liquid crystal dimming device includes an input filter 30. The input filter 30 includes a coil 31, a capacitor 32, and an electrolytic capacitor 33. The coil 31 is connected to the first input terminal 21. The capacitor 32 and the electrolytic capacitor 33 are provided in parallel with the first input terminal 21 and the second input terminal 22.

[0017] The power supply 20 for driving the liquid crystal dimming device includes a DC / DC circuit section 40. The DC / DC circuit section 40 transforms the DC voltage input from the battery 15 via the input filter 30 and outputs it. The DC / DC circuit section 40 includes a transformer TS, a first switching element 45, a second switching element 46, a rectifier circuit 47, an electrolytic capacitor 50, a diode 51, a capacitor 52, a DC / DC control section 53, and a switch 54.

[0018] The transformer TS comprises a primary coil 41 and secondary coils 43 and 44. The primary coil 41 includes an intermediate tap 42. The first end of the primary coil 41 is connected to the first switching element 45. The second end of the primary coil 41 is connected to the second switching element 46. The intermediate tap 42 is connected to coil 31.

[0019] The rectifier circuit 47 includes a first diode 48 and a second diode 49. The anode of the first diode 48 is connected to the first end of the secondary coil 43. The anode of the second diode 49 is connected to the second end of the secondary coil 43. The cathodes of the first diode 48 and the second diode 49 are connected to each other. The cathode of the first diode 48 and the cathode of the second diode 49 are electrically connected to the first end of the electrolytic capacitor 50. The anode of the first diode 48 and the anode of the second diode 49 are electrically connected to the second end of the electrolytic capacitor 50. When the secondary coil 43 has an intermediate tap 55 and the intermediate tap 55 is connected to the second end of the electrolytic capacitor 50, the anode of the first diode 48 and the anode of the second diode 49 are electrically connected to the second end of the electrolytic capacitor 50.

[0020] The first end of the secondary coil 44 is connected to the anode of the diode 51. The cathode of the diode 51 is connected to the first end of the capacitor 52. The second end of the secondary coil 44 is connected to the second end of the capacitor 52.

[0021] The DC / DC control unit 53 controls the first switching element 45 and the second switching element 46. The DC / DC control unit 53 is, for example, an IC (Integrated Circuit). The DC / DC control unit 53 is connected to the connection point between the coil 31 and the intermediate tap 42 via the switch 54. The DC / DC control unit 53 is driven by the DC voltage output from the input filter 30.

[0022] The DC / DC control unit 53 turns on the first switching element 45 and the second switching element 46 alternately. When the first switching element 45 is on, current flows from the intermediate tap 42 toward the first end of the primary coil 41. When the second switching element 46 is on, current flows from the intermediate tap 42 toward the second end of the primary coil 41.

[0023] When current flows through the primary coil 41, voltages are generated in the secondary coils 43 and 44, respectively. The voltage generated in the secondary coil 43 is rectified by the rectifier circuit 47, resulting in a DC voltage output. The voltage generated in the secondary coil 44 is rectified by the diode 51, resulting in a DC voltage output.

[0024] The power supply 20 for driving the liquid crystal dimming device includes a DC / AC circuit section 60. The DC / AC circuit section 60 converts the DC voltage output from the DC / DC circuit section 40 into an AC voltage and outputs it to the liquid crystal dimming device 11. The DC / AC circuit section 60 includes an inverter circuit 61, a resistor 66, coils 67, 68, a capacitor 69, drive circuits 70, 71, a DC / AC control section 72, and a switch 73.

[0025] The inverter circuit 61 comprises four switching elements 62-65. The inverter circuit 61 is a circuit in which the four switching elements 62-65 are connected in a full bridge configuration. The four switching elements 62-65 include a first upper arm switching element 62, a first lower arm switching element 63, a second upper arm switching element 64, and a second lower arm switching element 65. The first upper arm switching element 62 and the first lower arm switching element 63 are connected in series with each other. The second upper arm switching element 64 and the second lower arm switching element 65 are connected in series with each other. The first terminal of an electrolytic capacitor 50 is connected to each of the upper arm switching elements 62 and 64. The second terminal of an electrolytic capacitor 50 is connected to each of the lower arm switching elements 63 and 65 via a resistor 66. The inverter circuit 61 converts the DC voltage output from the DC / DC circuit section 40 into an AC voltage by the switching operation of the switching elements 62-65.

[0026] A coil 67 is connected to the first connection point P1, which is the connection point between the first upper arm switching element 62 and the first lower arm switching element 63. A coil 68 is connected to the second connection point P2, which is the connection point between the second upper arm switching element 64 and the second lower arm switching element 65. Capacitors 69 are connected to the two coils 67 and 68.

[0027] The DC / AC control unit 72 controls the switching elements 62-65 by outputting control signals to the drive circuits 70 and 71. The DC / AC control unit 72 is, for example, a microcontroller. The DC / AC control unit 72 is connected to the cathode of the diode 51 via a switch 73. The DC / AC control unit 72 is driven by the voltage rectified by the diode 51.

[0028] The drive circuit 70 switches the first upper arm switching element 62 and the first lower arm switching element 63 ON and OFF in accordance with the control signal. When the drive circuit 70 turns the first upper arm switching element 62 ON, it turns the first lower arm switching element 63 OFF. When the drive circuit 70 turns the first upper arm switching element 62 OFF, it turns the first lower arm switching element 63 ON.

[0029] The drive circuit 71 switches the second upper arm switching element 64 and the second lower arm switching element 65 ON and OFF in accordance with the control signal. When the drive circuit 71 turns the second upper arm switching element 64 ON, it turns the second lower arm switching element 65 OFF. When the drive circuit 71 turns the second upper arm switching element 64 OFF, it turns the second lower arm switching element 65 ON.

[0030] The DC / AC control unit 72 controls the first upper arm switching element 62 and the second lower arm switching element 65 to be turned ON simultaneously. In this case, the potential of the first connection point P1 becomes higher than the potential of the second connection point P2, and a positive voltage is generated between the first connection point P1 and the second connection point P2.

[0031] The DC / AC control unit 72 simultaneously turns on the second upper arm switching element 64 and the first lower arm switching element 63. In this case, the potential at the first connection point P1 becomes lower than the potential at the second connection point P2, and a negative voltage is generated between the first connection point P1 and the second connection point P2. In this way, the DC / AC control unit 72 converts the DC voltage to an AC voltage.

[0032] The power supply 20 for driving the liquid crystal dimming device includes an output filter 80. The output filter 80 includes two coils 81 and 82 and four capacitors 83 to 86. Coil 81 is connected to coil 67. Coil 82 is connected to coil 68. The two coils 81 and 82 are, for example, common mode choke coils.

[0033] Two capacitors 83 and 84 are connected in series between the first end of coil 81 and the first end of coil 82. The connection point of the two capacitors 83 and 84 is grounded. Two capacitors 85 and 86 are connected in series between the second end of coil 81 and the second end of coil 82. The connection point of the two capacitors 85 and 86 is grounded.

[0034] The power supply 20 for driving the liquid crystal dimming device includes a first output terminal 23 and a second output terminal 24. The first output terminal 23 is connected to coil 81. The second output terminal 24 is connected to coil 82. The two output terminals 23 and 24 are connected to the liquid crystal dimming device 11. The AC voltage output from the DC / AC circuit section 60 has its noise reduced by the output filter 80. The AC voltage with noise reduced by the output filter 80 is then applied to the liquid crystal dimming device 11 from the two output terminals 23 and 24. This changes the cloudiness of the liquid crystal layer 13.

[0035] The power supply 20 for driving the liquid crystal dimming device includes a communication circuit 90 that communicates with the vehicle 10. The communication circuit 90 includes two photocouplers 91, 92. The photocoupler 91 includes a photodiode 93 and a phototransistor 94. The photocoupler 92 includes a photodiode 95 and a phototransistor 96. The photodiodes 93, 95 are connected to the vehicle ECU 16. The phototransistors 94, 96 are connected to the DC / AC control unit 72. The phototransistor 94 turns ON when it receives the light emitted by the photodiode 93. The phototransistor 96 turns ON when it receives the light emitted by the photodiode 95. The photocouplers 91, 92 may be replaced with insulating elements such as isolators.

[0036] <Control performed by the DC / AC control unit> The DC / AC control unit 72 can output an AC voltage with an arbitrary voltage value from the DC / AC circuit unit 60 by changing the ON time of the switching elements 62 to 65. The DC / AC control unit 72 is an output variable unit.

[0037] Figure 2 is a schematic diagram showing the AC voltage output from the DC / AC circuit 60 as a dashed line and the voltage between two connection points P1 and P2 as a solid line. As shown in Figure 2, the AC voltage output from the DC / AC circuit 60 fluctuates depending on the voltage between the two connection points P1 and P2. The AC voltage is the average voltage of the voltage between the two connection points P1 and P2 at predetermined time intervals. Therefore, changing the voltage range between the two connection points P1 and P2, that is, the time during which a positive voltage is present and the time during which a negative voltage is present, changes the AC voltage. The AC voltage also changes depending on the time during which no voltage is present between the two connection points P1 and P2. The range of the positive voltage changes depending on the ON time of the first upper arm switching element 62 and the second lower arm switching element 65. The range of the negative voltage changes depending on the ON time of the second upper arm switching element 64 and the first lower arm switching element 63. The time during which no voltage is present between the two connection points P1 and P2 varies depending on the OFF time of the four switching elements 62 to 65. Therefore, by controlling the four switching elements 62 to 65 using PWM (Pulse Width Modulation), the voltage value of the AC voltage can be changed to any desired value.

[0038] The AC voltage output from the DC / AC circuit section 60 is a pseudo-sine wave. A pseudo-sine wave is a waveform in which the voltage changes between positive and negative during one period, and at least a part of it changes linearly. Multiple control periods of PWM control are included in half a period of the pseudo-sine wave. That is, multiple ON and OFF switching events occur in half a period of the pseudo-sine wave. In other words, multiple ON and OFF switching events occur in half a period of the pseudo-sine wave due to the ON and OFF switching of the switching elements 62 to 65, causing the voltage between the two connection points P1 and P2 to change between positive, negative, and absent.

[0039] The DC / AC control unit 72 can switch the liquid crystal layer 13 between a transparent state and an opaque state by controlling the AC voltage output from the DC / AC circuit unit 60. The user can switch between the transparent and opaque states of the liquid crystal layer 13. The user can also select a switching mode when switching between the transparent and opaque states. The switching modes include a normal mode and a gradual change mode.

[0040] For example, vehicle 10 is equipped with a user-operable control panel. By operating the control panel, the user can select whether the liquid crystal layer 13 is transparent or opaque. The user can also select whether the switching mode is normal mode or gradual mode by operating the control panel.

[0041] The vehicle ECU 16 switches between outputting a high-level signal or a low-level signal to the photocoupler 91 depending on whether the user has selected a transparent or opaque state. When a high-level signal is output to the photocoupler 91, the photodiode 93 lights up, which turns on the phototransistor 94. When the phototransistor 94 is turned on, a high-level signal is input to the DC / AC control unit 72. In this way, the input from the photocoupler 91 to the DC / AC control unit 72 switches between a high-level signal and a low-level signal.

[0042] The vehicle ECU 16 switches between outputting a high-level signal or a low-level signal to the photocoupler 92 depending on whether normal mode or slow-change mode is selected. When a high-level signal is output to the photocoupler 92, the photodiode 95 lights up, turning on the phototransistor 96. When the phototransistor 96 is turned on, a high-level signal is input to the DC / AC control unit 72. This switches whether a high-level signal or a low-level signal is input to the DC / AC control unit 72.

[0043] The DC / AC control unit 72 performs control according to the combination of signals input from photocoupler 91 and signals input from photocoupler 92. As shown in Figure 3, the haze rate of the liquid crystal layer 13 changes depending on the voltage value of the AC voltage applied to the liquid crystal dimming device 11. The voltage value of the AC voltage is the RMS value. In the following explanation, the voltage value refers to the RMS value of the AC voltage. The haze rate is the haze value and is defined as the ratio of the diffuse transmittance [%] to the total light transmittance [%]. The method for determining the haze is specified, for example, by JIS K 7136 or ISO 14782.

[0044] The degree of cloudiness can be reduced by increasing the voltage applied to the liquid crystal dimming device 11. This switches the liquid crystal layer 13 between a transparent state and an opaque state. The transparent state of the liquid crystal layer 13 is, for example, a state in which the cloudiness of the liquid crystal layer 13 is lower than a first predetermined value. The first predetermined value is, for example, 10% to 15%. The opaque state of the liquid crystal layer 13 is, for example, a state in which the cloudiness of the liquid crystal layer 13 is higher than a second predetermined value. The second predetermined value is, for example, 85% to 90%. When the cloudiness of the liquid crystal layer 13 is changed, the recognition range A1 in which the change in the cloudiness of the liquid crystal layer 13 is easily recognizable by humans is, for example, in the range of 20% to 80%.

[0045] When the phototransistor 94 of the photocoupler 91 turns OFF, a low-level signal is input to the DC / AC control unit 72, and the liquid crystal layer 13 changes from a transparent state to an opaque state, the DC / AC control unit 72 stops applying AC voltage to the liquid crystal dimming device 11. When changing the liquid crystal layer 13 from an opaque state to a transparent state, the DC / AC control unit 72 applies AC voltage to the liquid crystal dimming device 11.

[0046] <Normal Mode> When the user has selected the normal mode, that is, when the phototransistor 96 of the photocoupler 92 is turned ON and a high-level signal is input to the DC / AC control unit 72, the DC / AC control unit 72 switches between transparent and opaque states by switching whether or not to apply an AC voltage to the liquid crystal dimming device 11.

[0047] When switching the liquid crystal layer 13 from a transparent state to an opaque state, the DC / AC control unit 72 sets the target value of the voltage applied to the liquid crystal dimming device 11 to 0[V]. That is, when switching the liquid crystal layer 13 from a transparent state to an opaque state, the DC / AC control unit 72 controls the system to immediately stop the application of AC voltage to the liquid crystal dimming device 11, even though AC voltage is currently being applied to it.

[0048] When switching the liquid crystal layer 13 from an opaque state to a transparent state, the DC / AC control unit 72 sets the target value of the voltage applied to the liquid crystal dimming device 11 to the voltage value corresponding to the transparent state. That is, when switching the liquid crystal layer 13 from an opaque state to a transparent state, the control unit 72 controls the system so that the voltage value corresponding to the transparent state is immediately applied to the liquid crystal dimming device 11, even though no AC voltage is currently applied to the device.

[0049] <Gradual change mode> When the user has selected the slow-change mode, that is, when the phototransistor 96 of the photocoupler 92 is turned OFF and a low-level signal is input to the DC / AC control unit 72, the DC / AC control unit 72 gradually changes the voltage value applied to the liquid crystal dimming device 11.

[0050] When switching the liquid crystal layer 13 from a transparent state to an opaque state, the DC / AC control unit 72 gradually reduces the target voltage value applied to the liquid crystal dimming device 11 to 0. In other words, the rate of voltage reduction is slower in the gradual change mode compared to the normal mode. Because the time until the application of the AC voltage stops is longer, the time until the transparent state becomes opaque is also longer.

[0051] When switching the liquid crystal layer 13 from an opaque state to a transparent state, the DC / AC control unit 72 gradually increases the target voltage value applied to the liquid crystal dimming device 11 from 0. In other words, the rate at which the voltage value increases is slower in the gradual change mode compared to the normal mode. Because it takes longer for the voltage value to reach the value corresponding to the transparent state, the time it takes for the opaque state to become transparent is also longer.

[0052] Furthermore, in this embodiment, the DC / AC control unit 72 slows down the rate of change of the voltage value in the recognition range A1 compared to ranges other than the recognition range A1. The rate of change of the voltage value includes at least one of the rate of decrease and the rate of increase of the voltage value. In this embodiment, the haze rate is 80% when the voltage value is 15[V]. The haze rate is 20% when the voltage value is 25[V]. Therefore, in this embodiment, the voltage value corresponding to the recognition range A1 is between 15[V] and 25[V]. The voltage value corresponding to the recognition range A1 may differ depending on the type of liquid crystal dimming device 11. In other words, in this embodiment, the voltage value corresponding to the recognition range A1 is set to be between the voltage value at which the haze rate is 80% and the voltage value at which the haze rate is 20%.

[0053] When the DC / AC control unit 72 switches the liquid crystal layer 13 from a transparent state to an opaque state, it decreases the target voltage value at a first decrease rate when the voltage value is higher than 25[V]. When the voltage value drops from a state higher than 25[V] to 25[V], the DC / AC control unit 72 decreases the target voltage value at a second decrease rate. When the voltage value falls below 15[V], the DC / AC control unit 72 decreases the target voltage value at a third decrease rate. The second decrease rate is slower than the first decrease rate and the third decrease rate. For example, if the DC / AC control unit 72 decreases the target voltage value at predetermined intervals, the decrease in the target value in the range of 15[V] to 25[V] should be smaller compared to other ranges. The first decrease rate and the third decrease rate may be the same or different.

[0054] When the DC / AC control unit 72 switches the liquid crystal layer 13 from an opaque state to a transparent state, it increases the target voltage value at a first rate of increase when the voltage value is lower than 15[V]. When the voltage value rises from lower than 15[V] to 15[V], the DC / AC control unit 72 increases the voltage value at a second rate of increase. When the voltage value rises above 25[V], the DC / AC control unit 72 increases the target voltage value at a third rate of increase. The second rate of increase is slower than the first and third rates of increase. For example, if the DC / AC control unit 72 increases the target voltage value at predetermined intervals, the increase in the target value in the 15[V] to 25[V] range should be smaller than in other ranges. The first rate of increase and the third rate of increase may be the same or different.

[0055] [Effects of this embodiment] (1) The DC / AC control unit 72 can change the voltage value output to the liquid crystal dimming device 11 by performing PWM control. The degree of cloudiness of the liquid crystal layer 13 changes depending on the voltage value applied to the liquid crystal dimming device 11. Therefore, the degree of cloudiness of the liquid crystal layer 13 can be changed by changing the voltage value applied to the liquid crystal dimming device 11. By changing the voltage value in steps, the degree of cloudiness of the liquid crystal layer 13 can be changed gradually.

[0056] (2) The DC / AC control unit 72 changes the voltage value more gradually in the recognition range A1, where the change in the cloudiness of the liquid crystal layer 13 is easily recognizable to humans, compared to ranges other than recognition range A1. This makes it possible to make humans recognize that the cloudiness is changing gradually, while also speeding up the switching speed between the transparent and opaque states.

[0057] (3) The power supply 20 for driving the liquid crystal dimming device is equipped with a communication circuit 90 that communicates with the vehicle ECU 16. This allows the switching mode to be changed according to the user's operation. (4) The DC / AC circuit section 60 outputs a modified sine wave. When a square wave is output to the liquid crystal dimming device 11, an inrush current flows due to the capacitive component of the liquid crystal dimming device 11, causing noise to be generated. In contrast, by outputting a modified sine wave, the voltage can be applied to the capacitive component more gradually compared to a square wave. Therefore, the inrush current can be suppressed, and noise can be reduced.

[0058] (5) It is not necessary to provide multiple transformers to change the voltage value. Therefore, compared to cases where the voltage value is changed by providing multiple transformers, manufacturing costs can be reduced.

[0059] (6) The DC / AC control unit 72 can set the voltage value output to the liquid crystal dimming device 11 to any value by performing PWM control. This allows the DC / AC control unit 72 to maintain the liquid crystal layer 13 in a semi-transparent state. The semi-transparent state is a state between the transparent state and the opaque state. The DC / AC control unit 72 may also set the liquid crystal layer 13 to a semi-transparent state in response to a command from the vehicle ECU 16.

[0060] Furthermore, the upper limit of the voltage value that can be applied may differ depending on the type of liquid crystal dimming device 11. Since the voltage value can be set to any desired value by performing PWM control, the voltage value can be controlled so as not to exceed the upper limit. Therefore, it is possible to support multiple types of liquid crystal dimming devices 11.

[0061] [Example of changes] The embodiment can be implemented with the following modifications. The embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0062] ○The power supply 20 for driving the liquid crystal dimming device does not need to have a communication circuit 90. In this case, the DC / AC control unit 72 always switches between the transparent state and the semi-transparent state in a gradual change mode. ○The communication circuit 90 may be a communication device that communicates with the vehicle ECU 16 in accordance with a vehicle communication protocol. The vehicle communication protocol is, for example, CAN (Controller Area Network) or LIN (Local Interconnect Network).

[0063] ○The DC / AC control unit 72 may change the voltage value at the same rate of change in the recognition range A1 and in a range different from the recognition range A1. ○The voltage value corresponding to the recognition range A1 is not limited to being set to a voltage value above which the haze rate is 80% and a voltage value below which the haze rate is 20%. It may also be set to a range of voltage values ​​that result in a desired haze rate, such as a voltage value above which the haze rate is 90% and a voltage value below which the haze rate is 10% and a voltage value above which the haze rate is 70% and a voltage value below which the haze rate is 30%.

[0064] ○The DC / AC control unit 72 may be an IC. ○The photocouplers 91 and 92 may be connected to a switch. The switch is provided to switch between ON and OFF in response to user operation. By connecting a power supply to the switch, switching between ON and OFF will switch between outputting a High-level signal and an OFF-level signal. This will provide the same effect as in the embodiment. The "communication with the vehicle" performed by the communication circuit 90 is not limited to communication with the vehicle ECU 16, but means that user operation is accepted by components provided in the vehicle 10.

[0065] ○The liquid crystal dimming device 11 and the power supply 20 for driving the liquid crystal dimming device do not necessarily have to be installed in the vehicle 10. For example, the liquid crystal dimming device 11 may be used as dimmable glass installed in a building. [Explanation of Symbols]

[0066] A1...Recognition range, 11...Liquid crystal dimming device, 13...Liquid crystal layer, 20...Power supply for driving the liquid crystal dimming device, 40...DC / DC circuit section, 60...DC / AC circuit section, 61...Inverter circuit, 62, 63, 64, 65...Switching elements, 72...DC / AC control section, 90...Communication circuit.

Claims

1. A power supply for driving a liquid crystal dimming device that has a liquid crystal layer, which changes the cloudiness of the liquid crystal layer by supplying power to the device, A DC / DC circuit section that transforms and outputs a DC voltage, The system includes a DC / AC circuit that converts the DC voltage output from the DC / DC circuit into an AC voltage and outputs it to the liquid crystal dimming device, The DC / AC circuit section is An inverter circuit that converts the DC voltage output from the DC / DC circuit into a pseudo-sinusoidal AC voltage by the switching operation of a switching element, A power supply for driving a liquid crystal dimming device, comprising an output variable unit capable of changing the voltage value of the AC voltage by controlling the ON time of the switching element.

2. The output variable unit changes the voltage value more gradually in a range where the change in the cloudiness rate of the liquid crystal layer is easily recognizable to a person, compared to a range other than the recognition range, as described in claim 1.

3. The aforementioned liquid crystal dimming device is installed in the vehicle. The power supply for driving the liquid crystal dimming device according to claim 1, wherein the power supply for driving the liquid crystal dimming device includes a communication circuit for communicating with the vehicle.

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