Dimming signal generation device and illumination control system using same

The present invention relates to a dimming signal generation device suitable for a solid-state light source lighting device for turning on a solid-state light source such as a light emitting diode (LED) and an illumination control system using the same.

Conventionally, there has been proposed an LED lighting device which converts an AC power into a DC power to dim up and down an LED according to a dimming signal supplied from the outside (see, e.g. Japanese Patent Publication No. 4,636,102). In this conventional example, it is controlled such that the LED is turned on or off at a predetermined dimming level during a predetermined time period immediately after the supply of the AC power. After the lapse of the predetermined time period, the LED is dimmed up or down according to the dimming signal supplied from the outside.

Meanwhile, a dimming signal generation device which continuously outputs a dimming signal for a while even after power is cut off has been disclosed as the prior art in FIG. 2 of Japanese Patent Application Publication No. H3-57196. In FIG. 1 of Japanese Patent Application Publication No. H3-57196, as its improved technology, there is disclosed an embodiment of the dimming signal generation device that has been modified such that the dimming signal is blocked before a source voltage of a discharge lamp lighting device is attenuated after the power is cut off.

In the technology disclosed in Japanese Patent Publication No. 4,636,102, the LED can be controlled to be turned on or off at the predetermined dimming level during the predetermined time period immediately after the supply of AC power. However, in a case where a plurality of lighting devices are controlled by one dimming signal generation device as shown in FIG. 4 , it was necessary to provide a countermeasure circuit to each lighting device, resulting in an increase in the cost of the entire illumination control system.

Further, in order to solve such problem of the illumination control system, there has been proposed modifying the dimming signal generation device rather than the lighting device in Japanese Patent Application Publication No. H3-57196. However, since the dimming signal generation device is used in combination with the discharge lamp lighting device that requires a preheating operation when the power supply is turned on, it was not a configuration in which the dimming signal can be supplied immediately after the power supply is turned on.

In view of the above, the present invention provides a dimming signal generation device in which a light output more than a desired level is not generated immediately after power-up even when it is used in combination with a solid-state light source lighting device, and an illumination control system using the same.

In accordance with an aspect of the present invention, there is provided a dimming signal generation device which outputs a square wave voltage signal having an on-duty corresponding to a dimming level to a dimming signal line from a time point when a predetermined time period has elapsed after power-up, wherein a specific voltage is outputted to the dimming signal line for the predetermined time period after the power-up.

In the dimming signal generation device, the specific voltage may be a voltage corresponding to a lights-off state or a predetermined dimming state.

Preferably, the predetermined time period is longer than a start-up time period of a solid-state light source lighting device connected to the dimming signal line after power-up.

In accordance with another aspect of the present invention, there is provided an illumination control system including the dimming signal generation device as described above; and a solid-state light source lighting device which shares a power source with the dimming signal generation device, wherein the solid-state light source lighting device controls a solid-state light source such that an illuminance is lower as the on-duty cycle of the square wave voltage signal received via the dimming signal line increases.

With the present invention, even if it is used in combination with the solid-state light source lighting device having a short start-up time period after power-up, unpleasant flash does not occur immediately after power-up or in sudden power cut-off. Further, it is possible to dim a plurality of solid-state light source lighting devices using one dimming signal generation device, without increasing the overall cost of the illumination control system.

The objects and features of the present invention will become apparent from the following description of embodiments, given in conjunction with the accompanying drawings, in which:

FIG. 1 is a circuit diagram of a dimming signal generation device in accordance with an embodiment of the present invention;

FIG. 2 is an explanatory diagram of an operation of the dimming signal generation device in accordance with the embodiment of the present invention;

FIG. 3 is a circuit diagram of a solid-state light source lighting device used in combination with the dimming signal generation device in accordance with the embodiment of the present invention;

FIG. 4 is a circuit diagram showing an entire configuration of an illumination control system using the dimming signal generation device in accordance with the embodiment of the present invention;

FIG. 5 is an explanatory diagram of an operation of a conventional example; and

FIG. 6 is an explanatory diagram of the operation of the conventional example.

Hereinafter, an embodiment of the present invention will be described in more detail with reference to accompanying drawings which form a part hereof. Throughout the drawings, like reference numerals will be given to like parts.

FIG. 1 is a circuit diagram of a dimming signal generation device 1 in accordance with an embodiment of the present invention. A commercial AC power supply is connected to power supply terminals a 1 and a 2 . Further, connected to dimming signal output terminals a 3 and a 4 are dimming signal input terminals b 3 and b 4 of a solid-state light source lighting device 2 via a dimming signal line 10 (see FIG. 4 ).

A feature of the present embodiment is addition of a voltage output circuit 11 surrounded by a dashed line in FIG. 1 . A portion except for the voltage output circuit 11 is the same as the conventional dimming signal generation device as shown in FIG. 2 of Japanese Patent Application Publication No. H3-57196. The dimming signal generation device outputs a square wave voltage signal having a duty cycle corresponding to a dimming level to the dimming signal line 10 from a time point (t 9 of FIG. 2 ) when a predetermined time period has elapsed after the power supply is turned on (power-up). As shown in FIG. 1 , the voltage output circuit 11 is a circuit which outputs a specific voltage to the dimming signal line 10 for a predetermined time period (t 7 -t 9 of FIG. 2 ) after power-up.

Hereinafter, a circuit configuration of FIG. 1 will be described. An Ac voltage between the power supply terminals a 1 and a 2 is stepped down by a step-down transformer T 1 , and is full-wave rectified by a diode bridge DB 2 to charge a capacitor C 1 . A voltage of the capacitor C 3 is converted into a constant voltage by a three-terminal regulator IC 1 , and is charged in a capacitor C 4 to serve as a DC power source E 2 supplying a low DC voltage (e.g., about 12 V). A triangular wave generation circuit 12 being powered by the DC power source E 2 applies a triangular wave voltage at a predetermined frequency (e.g., about 1 kHz) to an inverting input terminal of a comparator 13 .

A voltage of the DC power source E 2 is divided by a variable resistor VR 2 and trimmer potentiometers VR 1 and VR 3 and is applied as a reference voltage to a non-inverting input terminal of the comparator 13 . The trimmer potentiometers VR 1 and VR 3 are adapted to determine upper and lower limits of the reference voltage obtained from the variable resistor VR 2 .

An output terminal of the comparator 13 is connected to a base of a transistor Tr 2 through a resistor R 4 . An emitter of the transistor Tr 2 is connected to a negative electrode of the capacitor C 4 , and a collector of the transistor Tr 2 is connected to a positive electrode of the capacitor C 4 through a resistor R 5 and also connected to a base of a transistor Tr 3 . A collector of the transistor Tr 3 is connected to the positive electrode of the capacitor C 4 , and an emitter of the transistor Tr 3 is connected so the negative electrode of the capacitor C 4 through a resistor R 6 and also connected to a base of a transistor Tr 4 through a resistor R 7 . A collector of the transistor Tr 4 is connected to the positive electrode of the capacitor C 4 , and an emitter of the transistor Tr 4 is connected to the negative electrode of the capacitor C 4 through a resistor R 8 . Then, a dimming signal is obtained from both terminals of the resistor R 8 .

In other words, the transistor Tr 4 and the resistors R 4 and R 5 constitute a common-emitter inverting amplifier circuit. The transistor Tr 3 , the resistor R 6 , the transistor Tr 4 and the resistors R 7 and R 8 constitute a common-collector (emitter follower) impedance conversion circuit.

Further, since the impedance conversion circuit is arranged at an output stage of the dimming signal generation device 1 , it is possible to reduce an impedance in the dimming signal line even when the dimming signal line 10 connected between the solid-state light source lighting device 2 and the dimming signal generation device 1 becomes longer, which prevents attenuation of the dimming signal.

Next, an operation of the dimming signal generation device 1 will be described. If the triangular wave voltage outputted from the triangular wave generation circuit 12 is equal to or lower than the reference voltage, the output terminal of the comparator 13 becomes a high level. Accordingly, the transistor Tr 2 is turned on, and the collector potential of the transistor Tr 2 drops, so that the dimming signal becomes a low level.

On the other hand, if the triangular wave voltage outputted from the triangular wave generation circuit 12 is higher than the reference voltage, the output terminal of the comparator 13 becomes a low level. Accordingly, the transistor Tr 2 is turned off, and the collector potential of the transistor Tr 2 rises, so that the dimming signal becomes a high level. Thus, the dimming signal consisting of a square wave voltage signal is obtained.

Since the reference voltage can be set to a voltage ranging from a high voltage to a low voltage by operating the variable resistor VR 2 , an on-duty of the dimming signal can be set to a value ranging from a minimum value (e.g., 5%) to a maximum value (e.g., 95%).

Next, a circuit configuration of the voltage output circuit 11 that is the feature of the present invention will be described. Connected to an output terminal of the step-down transformer T 1 are anodes of diodes D 3 and D 4 . A constant-voltage circuit is provided between cathodes of the diodes D 3 and D 4 connected in common and a negative electrode of the diode bridge DB 2 , and the constant-voltage circuit includes a resistor R 3 , a Zener diode ZD 1 and a transistor Tr 1 . An output of the constant-voltage circuit is inputted to a cathode of a diode D 6 through a diode D 5 . The diodes D 5 and D 6 constitute an OR circuit such that an output voltage of the voltage output circuit 11 or an output voltage of the DC power source E 2 , whichever is greater, is supplied to the collectors of the transistors Tr 3 and Tr 4 .

Herein, a Zener voltage of the Zener diode ZD 1 is set to be slightly lower than the voltage of the DC power source E 2 , and, in a period during which the voltage of the DC power source E 2 is low immediately after power-up, a voltage through the transistor Tr 1 is supplied to the dimming signal output terminals a 3 and a 4 via the transistors Tr 3 and Tr 4 . After that, when the voltage of the DC power source E 2 rises and becomes stable, the diode DC becomes a cut-off state, and the dimming signal is generated by the voltage of the DC power source E 2 supplied through the diode D 6 .

FIG. 2 is an explanatory diagram of the operation of this embodiment. Referring to FIG. 2 , the power turns on at a time point t 7 . Immediately after that, a power supply voltage slightly lower than the voltage of the DC power source E 2 is supplied from a cathode of the diode D 5 via the voltage output circuit 11 . Since the transistor Tr 2 is not turned on until the voltage of the DC power source E 2 is supplied at a time point t 9 such that the triangular wave generation circuit 12 and the comparator 13 can operate, a voltage from the voltage output circuit 11 is outputted to the dimming signal output terminals a 3 and a 4 through the emitter follower circuit consisting of the transistors Tr 3 and Tr 4 .

The voltage output circuit 11 has a feature that there is no time delay after power-up because it does not have the smoothing capacitors C 3 and C 4 , unlike the DC power source E 2 , although there is a period during which a voltage is not outputted in the vicinity of the zero-cross of the AC power source. The output voltage of the voltage output circuit 11 has a voltage waveform in which a peak of the waveform of a ripple voltage obtained by stepping down and full-wave rectifying the AC power source is clamped by the Zener diode ZD 1 , and can be used as a pseudo PWM signal corresponding to a lights-out state or a predetermined low luminance lighting state although it has a low frequency (100 Hz or 120 Hz) compared to the frequency (1 kHz) of an original dimming signal.

With the dimming signal generation device 1 of the present invention, as shown in FIG. 2 , the voltage of the voltage output circuit 11 is outputted to the dimming signal line 10 in a predetermined time period t 7 -t 9 after power-up. Accordingly, even if the solid-state light source lighting device 2 begins to operate at a timing t 8 of FIG. 2 , the operation can be started in a lights-out state or a predetermined low luminance lighting state during a time period t 8 -t 9 , and unpleasant flash does not occur. That is, the predetermined time period t 7 -t 9 is longer than a start-up time period t 7 -t 8 of the solid-state light source lighting device 2 .

FIG. 3 illustrates a configuration of the solid-state light source lighting device 2 used in combination with the dimming signal generation device 1 shown in FIG. 1 . Further, FIG. 4 illustrates an overall configuration of an illumination control system using the dimming signal generation device 1 shown in FIG. 1 and the solid-state light source lighting device 2 shown in FIG. 3 .

The power supply terminals a 1 and a 2 of the dimming signal generation device 1 are connected to AC power lines and connected to a commercial AC power source Vs (e.g., AC 100 V, 50/60 Hz) through a power switch SW as shown in FIG. 4 . Further, the dimming signal output terminals a 3 and a 4 of the dimming signal generation device 1 are connected to the dimming signal line 10 and connected to the dimming signal input terminals, b 3 and b 4 of the solid-state light source lighting device 2 as shown in FIG. 4 .

The solid-state light source lighting device 2 includes, as shown in FIG. 3 , power supply terminals b 1 and b 2 , dimming signal input terminals b 3 and b 4 , and load terminals b 5 and b 6 . If a plurality of solid-state light source lighting devices 2 are controlled by one dimming signal generation device 1 , as shown in FIG. 4 , the power supply terminals b 1 and b 2 of each of the solid-state light source lighting devices 2 are connected to the power supply terminals a 1 and a 2 of the dimming signal generation device via the AC power lines, and the dimming signal input terminals b 3 and b 4 of each of the solid-state light source lighting devices 2 are connected to the dimming signal output terminals a 3 and a 4 of the dimming signal generation device 1 via the dimming signal line 10 , The load terminals b 5 and b 6 of each of the solid-state light source lighting devices 2 are connected to each solid-state light source 3 .

Hereinafter, a configuration of the solid-state light source lighting device 2 will be described. Connected to the power supply terminals b 1 and b 2 is a step-up chopper circuit 4 via a filter circuit FL and a full-wave rectifier DB. The step-up chopper circuit 4 includes a switching element Q 1 , an inductor L 1 , a diode D 1 , a smoothing capacitor C 1 and a current detection resistor R 1 . The switching element Q 1 is turned on/off at a high frequency by a chopper control circuit 84 , so that a predetermined DC voltage Vdc is stored in the smoothing capacitor C 1 .

In the circuit configuration of FIG. 3 , the step-up chopper circuit 4 and the chopper control circuit 84 may be omitted. Alternatively, the DC voltage Vdc may be generated by using only the smoothing capacitor C 1 .

The DC voltage Vdc of the smoothing capacitor C 1 is converted by a step-down chopper circuit 5 . The step-down chopper circuit 5 includes a switching element Q 2 , an inductor L 2 , a diode D 2 , a smoothing capacitor C 2 and a current detection resistor R 2 . The switching element Q 2 is turned on/off at a high frequency by a chopper control circuit 83 , so that a DC voltage obtained by stepping down the input DC voltage Vdc is charged in the smoothing capacitor C 2 and a DC current is supplied to the solid-state light source 3 . The solid-state light source 3 is a semiconductor light emitting element such as a light emitting diode (LED) or organic electroluminescence (EL) element.

The chopper control circuit 83 is controlled by a microcomputer 82 , and adjusts a light output of the solid-state light source 3 by varying an on-pulse width of the switching element Q 2 according to the dimming signal, or lights of the solid-state light source 3 by stopping a switching operation of the switching element Q 2 .

In this embodiment, the step-down chopper circuit 5 is used as a switching circuit for controlling the DC current flowing in the solid-state light source 3 . However, switching circuits having other configurations such as a flyback converter circuit, step-up chopper circuit, and step-up/step-down chopper circuit may be used.

The solid-state light source lighting device 2 shown in FIG. 3 is installed together with the solid-state light source 3 in an illumination apparatus. As shown in FIG. 4 , the illumination apparatus has a dimming function in which dims up and down the solid-state light source 3 according no the dimming signal inputted from the dimming signal generation device 1 through the dimming signal line 10 .

A plurality of illumination apparatuses, each including the solid-state light source lighting device 2 shown in FIG. 3 , may be connected in parallel to the commercial AC power supply Vs as shown in FIG. 4 . In this case, an illumination control system may be configured such that the dimming signal common to each of the illumination apparatuses is provided from the dimming signal generation device 1 , and dimming of all the illumination apparatuses provided in the floor is controlled by the single dimming signal generation device 1 .

The dimming signal transmitted via the dimming signal line 10 from the dimming signal generation device 1 is formed of, e.g., a square wave voltage signal having a frequency of about 1 kHz and amplitude of about 10 V. An on-duty (percentage of a high level period in one cycle) of the square wave voltage signal varies depending on the dimming level. For example, it is controlled such that if the on-duty ranges from 0 to x 1 (%), the light output becomes 100% (full-lighting state), if the on-duty ranges from x 1 to x 2 (%), the light output decreases as the on-duty increases, and if the on-duty ranges from. x 2 to 100 (%), the light output becomes 0%/((lights-out state). As described earlier (see, e.g., Japanese Patent Application Publication H3-57196), the dimming signal is widely used in the field of the inverter type fluorescent lamp lighting device. For example, x 1 and x 2 may be 5% and 95% (x 1 =5% and x 2 =95%).

As shown in FIG. 3 , a control circuit 8 includes a signal conversion circuit 81 , the microcomputer 82 , the chopper control circuits 83 and 84 . The signal conversion circuit 81 converts the dimming signal formed of the square wave voltage signal (PWM signal) with the variable on-duty into a DC voltage signal having an amplitude corresponding to the on-duty. The signal conversion circuit 81 includes, e.g., a waveform shaping circuit and a smoothing circuit.

The dimming signal transmitted via the dimming signal line 10 from the dimming signal generation device 1 is shaped by the waveform shaping circuit and smoothed by the smoothing circuit to be converted into the DC voltage signal. This DC voltage signal is inputted to the microcomputer 82 from an A/D conversion input terminal thereof and converted into a digital value. The microcomputer 82 includes a data table in an internal memory and sends to the chopper control circuit 83 a control signal of the light output corresponding to the digital value obtained by A/D conversion.

A power ON/OFF detection circuit 7 monitors a voltage between the power supply terminals b 1 and b 2 , and generates a power ON/OFF detection signal to be inputted to the microcomputer 82 of the control circuit 8 . The power ON/OFF detection circuit 7 does not determine the power OFF only by the zero-crossing of the AC source voltage across the power supply terminals b 1 and b 2 . If the voltage across the power supply terminals b 1 and b 2 has continued to be at a low level for, e.g., several cycles to less than twenty cycles, the power OFF is determined to switch the state of the power ON/OFF detection signal.

A control power generation circuit 6 generates a control source voltage Vcc by using the DC voltage Vdc the smoothing capacitor C 1 , and supplies the control source voltage Vcc to the control circuit 8 and the power ON/OFF detection circuit 7 . Even though the state of the power ON/OFF detection signal is switched to a state where the power OFF is detected by an OFF operation of the power switch SW, or a momentary voltage drop or outage in the AC power source Vs, the control source voltage Vcc is supplied while the DC voltage Vdc is outputted from the smoothing capacitor C 1 , and the control circuit 8 and the power ON/OFF detection circuit 7 are operable.

Since the AC power source Vs is shared by the dimming signal generation device 1 , the output of the dimming signal is stopped when the power is OFF. However, since the dimming signal generation device 1 also has an internal power supply circuit (circuit consisting of the capacitors C 3 and C 4 and the three-terminal regulator IC 1 as shown in FIG. 1 ), as shown in FIGS. 2 , 5 and 6 , the dimming signal disappears after a little time delay from the time when the power is OFF. Further, if no countermeasure circuit (voltage output circuit 11 ) as shown in FIG. 1 is provided, the dimming signal is generated after a little time delay (t 1 -t 2 of FIG. 5 , t 4 -t 6 of FIG. 6 ) from the time when the power is ON.

FIG. 5 illustrates an operation when the power is ON and OFF in a conventional example in which no countermeasure is provided in accordance with she present invention. The solid-state light source 3 is turned off and the light output is 0% before the power ON. In this state, the dimming signal is not generated.

When the power is ON at the timing t 1 , the dimming signal generation device 1 connected to the common power source generates the dimming signal after a predetermined time period, i.e., at the timing t 2 . After the dimming signal occurs at the timing t 2 , the solid-state light source 3 is turned on at a light output corresponding to the dimming level specified by the dimming signal. When the power is OFF at the timing t 3 , the microcomputer 82 receives a power OFF detection signal and controls the solid-state light source 3 to be turned off immediately.

Here, what is concerned is the light output during the period t 1 -t 2 . The on-duty of the dimming signal is 0% until the dimming signal occurs at the timing t 2 after the power ON is detected at the timing t 1 . In this case, the light output of the solid-state light source 3 is started from 100%. Accordingly, for example, even if a user performs an operation of the power ON by rotating a dimming knob of the dimming signal generation device 1 from at a low position (low light output), the light output of 100% is generated for a certain short period of time from the power ON.

In the conventional inverter type fluorescent lamp lighting device (see Patent Document 2), since a preheating period of filaments of the lamp is set for, e.g., about 1 second after power-up, there is no problem although the light output of 100% is set for a certain short period of time from the power ON, as mentioned above. It is rather preferable to start in the full-lighting state than starting in the dimming state in terms of the life of a hot cathode type discharge lamp. From this point of view, a dimmer designed to be suitable for the conventional inverter type fluorescent lamp lighting device generally has the specifications such that the dimming signal is not outputted (on-duty is set to 0%) for a short period of time corresponding to the preheating period of the fluorescent lamp after detecting the power ON.

However, in an LED dimming lighting device, there is no need for the preheating period during start-up as in the hot cathode type discharge lamp. Thus, the solid-state light source 3 can be turned on at a light output corresponding to the dimming level specified, by the dimming signal immediately after the power ON. Accordingly, there occurs a phenomenon (so-called “on-flash”) in which the light source is momentary brightly lit, on when the power is turned on in the dimming state. A similar phenomenon may occur even in the momentary voltage drop or outage in the power source Vs.

FIG. 6 illustrates an operation of the momentary power outage in the conventional example in which no countermeasure is provided in accordance with the present invention.

At the timing t 3 , when the power OFF is detected, and the microcomputer 82 receives a power OFF detection signal, the microcomputer 82 controls the solid-state light source 3 to be turned of immediately. At the timing t 4 , when the power is restored, and the microcomputer 82 receives a power ON detection signal, the microcomputer 82 controls the solid-state light source 3 to be turned on at a light output corresponding to the dimming level of the dimming signal.

At the timing t 5 , when the on-duty of the dimming signal of the dimming signal generation device 1 becomes 0%, the light output becomes 100%. Then, after the dimming signal occurs at the timing t 6 , the solid-state light source 3 is turned on at a light output corresponding to the dimming level specified by the dimming signal.

Here, what is concerned is the light output during the period t 5 -t 6 . Since the on-duty of the dimming signal is 0% until the dimming signal occurs at the timing t 6 after the dimming signal disappears at the timing t 5 , the light output of the solid-state light source 3 becomes 100%. Accordingly, when the power is restored after a brief outage of the power source Vs while the dimming state is carried out, there occurs a phenomenon in which the light source is briefly brightly lit on.

In order to solve this problem, the present invention is characterized in that, as shown in FIG. 2 , a specific voltage is outputted to the dimming signal line 10 for a predetermined time period t 7 -t 9 after power-up.

By doing this, when the power is ON at the timing t 7 and the operation of the solid-state light source lighting device 2 is started at the timing t 8 in FIG. 2 , the operation can be started in the lights-out state or the dimming state corresponding to the predetermined low luminance during the time period t 8 -t 9 , and unpleasant flash does not occur. Further, even if the power is restored in a short period of time after the power is OFF at the timing t 3 in FIG. 2 , there does not occur a phenomenon in which the light source is briefly brightly lit on.

For example, in a case where the voltage output circuit 11 of FIG. 1 is not provided, if the power is turned off at the timing t 3 and the power is restored at the timing t 4 as shown in FIG. 6 , the light source is turned on at a light output corresponding to the dimming level in the time period t 4 -t 5 . However, since the dimming level becomes 100% in the time period t 5 -t 6 , the momentary flash occurs.

However, in a case where the voltage output circuit 11 of FIG. 2 is provided, a specific voltage is outputted to the dimming signal line 10 during the time period t 5 -t 6 of FIG. 6 , as shown in the time period t 7 -t 9 of FIG. 2 . Accordingly, since the solid-state light source lighting device 2 operates at a light output of the lights-out state or the dimming state corresponding to the predetermined low luminance, unpleasant momentary flash does not occur.

Therefore, even if the power failure occurs while the light source is turned on in the dimming state and then the power is restored immediately, inconvenience caused by temporarily switching to the 100% lighting state does not occur.

In addition, it is preferred that the light, output is set at a predetermined dimming level at which the user does not feel the glare. Further, the light output is preferably set to be a low luminance dimming state which ensures a minimum brightness rather than a complete OFF state. Accordingly, especially in lighting control at night, it is possible to eliminate the anxiety of the user.

While the invention has been shown and described with respect to the embodiments, it will be understood by those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.