LED drive circuit, LED lamp, LED lighting appliance, and LED lighting system

This nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2009-53307 filed in Japan on Mar. 6, 2009, the entire contents of which are hereby incorporated by reference.

1. Field of the Invention

The present invention relates to LED drive circuits for driving an LED (light-emitting diode), and to such LED lamps, LED lighting appliances, and LED lighting systems as use an LED as light sources.

2. Description of Related Art

For their advantages such as low current consumption and long lifetimes, LEDs have been widening their application beyond display apparatuses into lighting equipment and the like. In many pieces of LED lighting equipment, a plurality of LEDs are used to obtain the desired luminance.

Many common pieces of lighting equipment use a commercial AC (alternating-current) 100 V power source, and when consideration is given to cases such as where LED lamps are used in place of common lamps such as incandescent lamps, it is desirable that LED lamps are configured to use, like common lamps, a commercial AC 100 V power source.

For the control of the light of incandescent lamps, phase-control light controllers (generally called incandescent light controllers) are used, which allow easy control of light by means of a variable-resistance device though the control of the power supplied to the incandescent lamp achieved by turning a switching device (commonly, a thyristor device or a triac device) on at a given phase angle of an AC power source voltage. An example of the configuration of an incandescent lamp lighting system provided with an incandescent lamp and a phase-control light controller is shown in FIG. 14 .

The incandescent lamp lighting system shown in FIG. 14 is provided with a phase-control light controller 2 and an incandescent lamp 9 . The phase-control light controller 2 is connected in series between an AC power source 1 and the incandescent lamp 9 . In the phase-control light controller 2 , when the knob (unillustrated) of a potentiometer Rvar 1 is set at a given position, a triac Tri 1 is turned on at the power phase angle corresponding to that position. In the phase-control light controller 2 , a noise prevention circuit is also provided which is constituted by a capacitor C 1 and an inductor L 1 , and the noise prevention circuit reduces the terminal noise that returns from the phase-control light controller 2 to the power line.

An example of the voltage and current waveforms at relevant points in the incandescent lamp lighting system shown in FIG. 14 is shown in FIG. 15A , and an enlarged diagram of the period P in FIG. 15A is shown in FIG. 15B . In FIGS. 15A and 15B , V OUT2 , I 2 , and I 9 respectively indicate the waveform of the output voltage of the phase-control light controller 2 , the waveform of the current passing through the triac Tri 1 in the phase-control light controller 2 , and the waveform of the current passing through the incandescent lamp 9 . In the example shown in FIGS. 15A and 15B , immediately after the triac Tri 1 is triggered and turned on, the current passing through the triac Tri 1 undulates (swings up and down) several times; when it swings down for the first time, the current passing through the triac Tri 1 becomes negative and lower than the holding current, and this means that the triac Tri 1 is momentarily turned off immediately after being turned on. Nevertheless, flickering is small, and light control can be done as normally.

It is however known that, with incandescent lamps of lower wattages, flickering and blinking prevent normal light control.

For the control of the light of LED lamps that use an AC power source, it is desirable, as for the control of the light of incandescent lamps, to use phase-control light controller. Now, a conventional example of an LED lighting system that can control the light of LED lamps that use an AC power source is shown in FIG. 16 . In FIG. 16 , such parts as find their counterparts in FIG. 14 are identified by common reference signs, and no detailed description of such parts will be repeated.

The LED lighting system shown in FIG. 16 is provided with a phase-control light controller 2 , an LED drive circuit including a diode bridge DB 1 and a current limit circuit 5 , and an LED module 3 . The phase-control light controller 2 is connected in series between an AC power source 1 and the LED drive circuit.

An example of the voltage and current waveforms at relevant points in the LED lighting system shown in FIG. 16 is shown in FIG. 17A , and an enlarged diagram of the period P in FIG. 17A is shown in FIG. 17B . In FIGS. 17A and 17B , V OUT2 , I 2 , and I 3 respectively indicate the waveform of the output voltage to the phase-control light controller 2 , the waveform of the current passing through a triac Tri 1 in the phase-control light controller 2 , and the waveform of the current passing through the LED module 3 . In the example shown in FIGS. 17A and 17B , immediately after the triac Tri 1 is triggered and turned on, the current passing through the triac Tri 1 undulates (swings up and down) several times; thus, when the triac Tri 1 is turned on at a given phase angle, a wavefoini as if oscillating results, and light control cannot be done normally. As shown in FIG. 17B , which is an enlarged view of the period P in FIG. 17A , after the current passing through the triac Tri 1 undulates in the positive and negative directions several times, the triac Tri 1 is turned off, and thereafter it is triggered again; thus, the current passing through the triac Tri 1 undulates in the positive and negative directions several times, and then the triac Tri 1 is turned off—so repeats the same sequence of events. How this occurs is as follows: when the current passing through the triac Tri 1 turns from positive to negative, it becomes equal to or lower than the holding current; after the triac Tri 1 is turned off, it does not respond for a certain period, and even after this period has elapsed, the current passing through the triac Tri 1 remains lower than the holding current until it is triggered next time.

Due to differences in lighting characteristics between incandescent lamps and LEDs, failure of normal light control as described above is more likely to occur in LED lighting systems than in incandescent lamp lighting systems.

JP-A-2006-319172 discloses an LED lighting system as shown in FIG. 18 . The LED lighting system shown in FIG. 18 is provided with a phase-control light controller 2 , a diode bridge DB 1 , a current holding means, a rectifying-and-smoothing means, and a LED module 3 . The phase-control light controller 2 is connected in series between an AC power source 1 and the diode bridge DB 1 , and the current holding means and the rectifying-and-smoothing means are provided between the diode bridge DB 1 and the LED module 3 .

The current holding means is composed of resistors R 181 to R 186 , Zener diodes ZD 1 and ZD 2 , transistors Q 181 and Q 182 , and a capacitor C 181 . In the current holding means, when the source voltage outputted from the AC power source 1 is equal to or lower than 100 V, the transistor Q 182 is on, and passes a current corresponding to the holding current of a triac Tri 1 in the phase-control light controller 2 ; when the source voltage is not equal to or lower than 100 V, the transistor Q 182 is off. The transistor Q 182 passes a current (about 30 mA) such that the current through the triac Tri 1 in the phase-control light controller 2 is not equal to or lower than the holding current.

In the current holding means described above, however, the period during which the corrector current of the transistor Q 182 passes is the period after the transistor Q 182 turns on until the transistor Q 181 turns on, and the transistor Q 181 turns on when, after the triac Tri 1 in the phase-control light controller 2 turns on, the Zener diode ZD 1 turns on. Thus, for example, if the triac Tri 1 in the phase-control light controller 2 conducts abruptly, or if the source voltage of the AC power source 1 becomes high, the on-state period of the transistor Q 182 may be so short and accordingly the period during which the current that does not become equal to or lower than the holding current of the triac Tri 1 passes may be so short that the triac Tri 1 cannot turn on.

An object of the present invention is to provide LED drive circuits that prevent the flickering and blinking of an LED that may occur when an LED is used with phase-control light controllers, and to provide LED lamps, LED lighting appliances, and LED lighting systems employing such LED drive circuits.

To achieve the above object, according to the invention, an LED drive circuit that receives an alternating-current voltage and drives an LED is provided with: a current extractor which extracts a current from the current supply line through which an LED drive current is supplied to the LED; and a timing adjuster which adjusts the current extraction start timing and the current extraction duration in the current extractor (the first configuration).

In the first configuration described above, the timing adjuster may be provided with a voltage detection circuit which monitors the input voltage to the LED drive circuit or a voltage obtained by rectifying the input voltage so that the current extraction in the current extractor is controlled according to the result of the monitoring by the voltage detection circuit (the second configuration).

In the second configuration described above, the timing adjuster may be provided with a comparator which compares the result of the monitoring by the voltage detection circuit with a set voltage so that the current extraction in the current extractor is controlled according to the result of the comparison by the comparator. The comparator may have hysteresis.

In the second configuration described above, the timing adjuster may be provided with a first transistor of which the base is connected to the output of the voltage detection circuit, the current extractor may be provided with a second transistor of which the base is connected to the collector of the first transistor, and the timing adjuster may be further provided with a capacitor which is connected between the bases of the first and second transistors.

In the first configuration described above, the timing adjuster may be provided with a voltage variation detection circuit which detects a variation in the input voltage to the LED drive circuit or a voltage obtained by rectifying the input voltage so that the current extraction in the current extractor is controlled according to the result of the monitoring by the voltage variation detection circuit (the third configuration).

In the third configuration described above, the timing adjuster may be provided with a resistor, a capacitor, and a first transistor of which the base is connected to the node between the resistor and the capacitor, and the current extractor may be provided with a second transistor of which the base is connected to the collector of the first transistor.

In the third configuration described above, the timing adjuster may be provided with a serial circuit having a capacitor and a resistor connected in series in this order from the high-potential side to the low-potential side, and the current extractor may be provided with a transistor of which the base is connected to the node between the capacitor and the resistor.

In the third configuration described above, there may be further provided an unnecessary lighting preventer which prevents the LED from being lit by an unnecessary current.

The current extractor may be provided with a constant-current source which is connected to the emitter of the second transistor, or the transistor, provided in the current extractor so that the second transistor or the transistor provided in the current extractor is driven on a constant-current basis.

To achieve the above object, according to the invention, an LED lamp is provided with: an LED drive circuit of any one of the configurations described above; and an LED connected to the output side of the LED drive circuit.

To achieve the above object, according to the invention, an LED lighting appliance is provided with an LED lamp configured as described above.

To achieve the above object, according to the invention, an LED lighting system is provided with: an LED lamp or an LED lighting appliance configured as described above; and a light control unit which is connected to the input side of the LED lamp or the LED lighting appliance, the light control unit including a phase-control light controller.

FIG. 1 is a diagram showing an example of the configuration of an LED lighting system according to the invention;

FIG. 2 is a diagram showing an embodiment of the LED lighting system shown in FIG. 1 ;

FIG. 3 is a diagram showing an example of the configuration shown in FIG. 2 ;

FIG. 4A is a diagram showing a specific example of the configuration shown in FIG. 3 ;

FIG. 4B is a diagram showing another specific example of the configuration shown in FIG. 3 ;

FIG. 5A is a diagram showing an example of operating waveforms in the LED lighting systems shown in FIGS. 2 to 4 ;

FIG. 5B is an enlarged diagram of part of FIG. 5A ;

FIG. 6A is a diagram showing an example of operating waveforms in the LED lighting systems shown in FIGS. 2 to 4 ;

FIG. 6B is a diagram showing an example of operating waveforms in the LED lighting systems shown in FIGS. 2 to 4 ;

FIG. 6C is a diagram showing an example of operating waveforms in the LED lighting systems shown in FIGS. 2 to 4 ;

FIG. 7 is a diagram showing another embodiment of the LED lighting system shown in FIG. 1 ;

FIG. 8 is a diagram showing a specific example of the configuration shown in FIG. 7 ;

FIG. 9 is a diagram showing another specific example of the configuration shown in FIG. 7 ;

FIG. 10 is a diagram showing yet another specific example of the configuration shown in FIG. 7 ;

FIG. 11 is a diagram showing yet another specific example of the configuration shown in FIG. 7 ;

FIG. 12A is a diagram showing an example of operating waveforms in the LED lighting systems shown in FIGS. 7 to 11 ;

FIG. 12B is an enlarged diagram of part of FIG. 12A ;

FIG. 13 is a diagram showing an LED lighting system according to the invention, obtained by additionally providing the configuration shown in FIG. 7 with an unnecessary lighting prevention circuit;

FIG. 14 is a diagram showing an example of the configuration of an incandescent lamp lighting system;

FIG. 15A is a diagram showing an example of the voltage and current waveforms at relevant points in the incandescent lamp lighting system shown in FIG. 14 ;

FIG. 15B is an enlarged diagram of part of FIG. 15A ;

FIG. 16 is a diagram showing a conventional example of an LED lighting system;

FIG. 17A is a diagram showing an example of the voltage and current waveforms at relevant points in the LED lighting system shown in FIG. 16 ;

FIG. 17B is an enlarged diagram of part of FIG. 17A ;

FIG. 18 is a diagram showing another conventional example of an LED lighting system;

FIG. 19 is a diagram showing the configuration of an LED lighting system provided with an unnecessary lighting prevention circuit of Example 1;

FIG. 20 is a diagram showing a specific example of the LED lighting system shown in FIG. 19 ;

FIG. 21 is a diagram showing a configuration obtained by replacing the comparator in the LED lighting system shown in FIG. 20 with a comparator with hysteresis;

FIG. 22 is a diagram showing another specific example of the LED lighting system shown in FIG. 19 ;

FIG. 23 is a diagram showing a configuration obtained by replacing the constant-current source in the LED lighting system shown in FIG. 22 with a resistor;

FIG. 24A is a diagram showing an example of operating waveforms in the specific examples shown in FIGS. 20 to 23 ;

FIG. 24B is a diagram showing an example of operating waveforms in the specific examples shown in FIGS. 20 to 23 ;

FIG. 24C is a diagram showing an example of operating waveforms in the specific examples shown in FIGS. 20 to 23 ;

FIG. 25 is a diagram showing yet another specific example of the LED lighting system shown in FIG. 19 ;

FIG. 26 is a diagram showing a specific example in which MOS transistors are used in the LED lighting system shown in FIG. 19 ;

FIG. 27 is a diagram showing the configuration of an LED lighting system provided with an unnecessary lighting prevention circuit of Example 2;

FIG. 28 is a diagram showing a specific example of the LED lighting system shown in FIG. 27 ;

FIG. 29 is a diagram showing an example of the configuration of a current limit circuit;

FIG. 30 is a diagram showing an example of an outline of the structure of an LED lamp according to the invention; and

FIG. 31 is a diagram showing examples of an outline of the structure of other LED lamps according to the invention.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

An example of the configuration of an LED lighting system according to the invention is shown in FIG. 1 . In FIG. 1 , such parts as find their counterparts in FIG. 14 are identified by common reference signs, and no detailed description of such parts will be repeated. The LED lighting system according to the invention shown in FIG. 1 is provided with a phase-control light controller 2 , an LED module 3 , and an LED drive circuit 4 . The LED drive circuit 4 is an example of an LED drive circuit according to the invention, and includes a diode bridge DB 1 , a current limit circuit 5 , a timing adjustment circuit 6 , and a bypass circuit 7 . In the LED lighting system according to the invention shown in FIG. 1 , an AC power source 1 , the phase-control light controller 2 , the diode bridge DB 1 , the current limit circuit 5 , and the LED module 3 , which comprises one or more LEDs, are connected in series, and the timing adjustment circuit 6 and the bypass circuit 7 are provided between the diode bridge DB 1 and the current limit circuit 5 .

The bypass circuit 7 extracts a current from the current supply line through which an LED drive current is supplied to the LED module 3 , and passes the extracted current through a bypass line. The timing adjustment circuit 6 adjusts the timing with which the bypass circuit 7 starts to extract current (hereinafter also referred to as the “current extraction start timing”) and the period for which the bypass circuit 7 keeps extracting current (hereinafter also referred to as the “current extraction duration”).

Here, the undulation wavelength of the current I 2 passing through the triac Tri 1 which undulates immediately after the triac Tri 1 turns on as shown in FIG. 17B depends on the resonance wavelength 2π√{square root over (LC)} of a capacitor C 1 and an inductor L 1 constituting a noise prevention filter in the phase-control light controller 2 (L represents the inductance value of the inductor L 1 , and C represents the capacitance value of the capacitor C 1 ). Accordingly, the timing adjustment circuit 6 needs to adjust the current extraction duration in such a way that the current I 2 passing through the triac Tri 1 does not become lower than the holding current of the triac Tri 1 for a period corresponding to several cycles of that resonance wavelength.

Moreover, since the current I 2 passing through the triac Tri 1 undulates immediately after the triac Tri 1 turns on as shown in FIG. 17B , the bypass circuit 7 needs to start to extract current immediately after the triac Tri 1 turns on.

Moreover, the current value of the current extracted by the bypass circuit 7 needs to be set with consideration given to the fact that the bypass circuit 7 extracts not only a current that passes through the triac Tri 1 but also a current that does not directly pass through the triac Tri 1 .

With the above-mentioned factors taken into consideration, the current extraction duration, the current extraction start timing, and the current value of the current extracted by the bypass circuit 7 are adjusted or set; in this way, it is possible to keep the triac Tri 1 in the phase-control light controller 2 from turning off for a period corresponding to several cycles of the undulation wavelength at which the current I 2 passing through the triac Tri 1 undulates.

Next, an embodiment of the LED lighting system shown in FIG. 1 is shown in FIG. 2 . In the configuration shown in FIG. 2 , the timing adjustment circuit 6 includes a voltage detection circuit 6 A which monitors the output voltage of the diode bridge DB 1 , and based on the output voltage of the diode bridge DB 1 as detected by the voltage detection circuit 6 A, the current extraction start timing and the current extraction duration are adjusted.

Next, an example of the configuration shown in FIG. 2 is shown in FIG. 3 . In FIG. 3 , the AC power source 1 and the phase-control light controller 2 are omitted from illustration. Division resistors R 31 and R 32 , a comparator COMP 31 , a constant-voltage source VS 31 , and a time setter 8 constitute an example of the timing adjustment circuit 6 (see FIG. 2 ), and the division resistors R 31 and R 32 constitute an example of the voltage detection circuit 6 A (see FIG. 2 ).

The comparator COMP 31 compares the midpoint voltage of the division resistors R 31 and R 32 with the constant voltage outputted from the constant-voltage source VS 31 .

When the midpoint voltage of the division resistors R 31 and R 32 is lower than the constant voltage outputted from the constant-voltage source VS 31 , the output signal of the comparator COMP 31 turns the bypass circuit 7 on, and thus the bypass circuit 7 extracts a current from the current supply line through which the LED drive current is supplied to the LED module 3 . When the triac Tri 1 in the phase-control light controller 2 turns on and the output voltage of the diode bridge DB 1 rises, the source voltage is supplied to the comparator COMP 31 ; thus, the comparator COMP 31 starts to operate, and makes the bypass circuit 7 extract current. That is, immediately after the triac Tri 1 turns on, the bypass circuit 7 starts to extract current.

By contrast, when the midpoint voltage of the division resistors R 31 and R 32 is equal to or higher than the constant voltage outputted from the constant-voltage source VS 31 , in principle, the output signal of the comparator COMP 31 turns the bypass circuit 7 off, and thus the bypass circuit 7 does not extract a current from the current supply line through which the LED drive current is supplied to the LED module 3 . However, when the triac Tri 1 in the phase-control light controller 2 turns on and the output voltage of the diode bridge DB 1 rises, after the midpoint voltage of the division resistors R 31 and R 32 is detected to be higher than the constant voltage outputted from the constant-voltage source VS 31 until the time by the time setter 8 , the bypass circuit 7 extracts current, and after the time set by the time setter 8 has elapsed, the bypass circuit 7 turns off.

By varying the resistance ratio of the division resistors R 31 and R 32 , it is possible to vary the threshold voltage of the comparator COMP 31 , and thereby to vary the timing with which the bypass circuit 7 turns from on to off. However, when the triac Tri 1 in the phase-control light controller 2 conducts abruptly, the bypass circuit 7 turns on and immediately turns off; thus, if the time setter 8 is not provided, the bypass circuit 7 can only extract current for a short period.

The time setter 8 produces a delay in the progress of, after the bypass circuit 7 turns on, the midpoint voltage of the division resistors R 31 and R 32 becoming equal to or higher than the constant voltage outputted from the constant-voltage source VS 31 and turning the bypass circuit 7 off. With this delay, when the triac Tri 1 in the phase-control light controller 2 turns on and the output voltage of the diode bridge DB 1 rises quickly, the bypass circuit 7 extracts current at a predetermined current value for a predetermined period, and thereby prevents the triac Tri 1 in the phase-control light controller 2 from turning off for a period corresponding to several cycles of the undulation wavelength at which the current passing through the triac Tri 1 undulates.

In the comparator COMP 31 , the threshold voltage is the same between when the midpoint voltage of the division resistors R 31 and R 32 turns from lower to higher than the constant voltage outputted from the constant-voltage source VS 31 and when the midpoint voltage of the division resistors R 31 and R 32 turns from higher to lower than the constant voltage outputted from the constant-voltage source VS 31 . Thus, also when the AC voltage outputted from the AC power source 1 is in the middle of falling from its peak voltage of 141 V to 0 V, the bypass circuit 7 may turn on and cause a current that does not contribute to the lighting of the LED module 3 to pass through the bypass circuit 7 . This can be avoided by the use of, instead of the comparator COMP 31 , a comparator with hysteresis such that the threshold voltage when the midpoint voltage of the division resistors R 31 and R 32 turns from higher to lower than the constant voltage outputted from the constant-voltage source VS 31 is lower than the threshold voltage when the midpoint voltage of the division resistors R 31 and R 32 turns from lower to higher than the constant voltage outputted from the constant-voltage source VS 31 . This prevents the bypass circuit 7 from turning on when the AC voltage outputted from the AC power source 1 is in the middle of falling from its peak voltage of 141 V to 0 V, and thus prevents a current that does not contribute to the lighting of the LED module 3 from passing trough the bypass circuit 7 . Thus, higher power efficiency is achieved.

Next, a specific example of the configuration shown in FIG. 3 is shown in FIG. 4A . In FIG. 4A , the AC power source 1 and the phase-control light controller 2 are omitted from illustration. Division resistors R 41 and R 42 correspond to the division resistors R 31 and R 32 ( FIG. 3 ). The division resistors R 41 and R 42 constitute a voltage detection circuit. A transistor Q 41 of which the base is connected to the output of the voltage detection circuit and of which the emitter is connected to the negative-side output of the diode bridge DB 1 , and a resistor R 43 connected between the collector of the transistor Q 41 and the positive-side output of the diode bridge DB 1 , constitute an example of the comparator COMP 31 and the constant-voltage source VS 31 (see FIG. 3 ). The base-emitter voltage of the transistor Q 41 is equivalent to the output voltage of the constant-voltage source VS 31 . A transistor Q 42 of which the base is connected to the collector of the transistor Q 41 and of which the emitter is connected to the negative-side output of the diode bridge DB 1 , and a resistor R 44 connected between the collector of the transistor Q 42 and the positive-side output of the diode bridge DB 1 , constitute an example of the bypass circuit 7 (see FIG. 3 ). A capacitor C 41 connected between the bases of the transistors Q 41 and Q 42 constitutes an example of the time setter 8 (see FIG. 3 ). Furthermore, a capacitor 42 for preventing malfunctioning caused by noise is connected between the base of the transistor Q 41 and the negative-side output of the diode bridge DB 1 .

While the midpoint voltage of the division resistors R 41 and R 42 is lower than the base-emitter voltage of the transistor Q 41 , the transistor Q 41 remains off; accordingly, a current is supplied via the resistor R 43 to the base of the transistor Q 42 , and thus the transistor Q 42 remains on. As a result, the transistor Q 42 extracts a current from the output of the diode bridge DB 1 via the resistor R 44 , at a predetermined current value. By contrast, while the midpoint voltage of the division resistors R 41 and R 42 is equal to or higher than the base-emitter voltage of the transistor Q 41 , the transistor Q 41 remains on; accordingly, no current is supplied to the base of the transistor Q 42 , and thus the transistor Q 42 remains off.

Here, when the triac Tri 1 in the phase-control light controller 2 conducts abruptly, the transistor Q 42 turns on, and immediately the transistor Q 41 turns on and then the transistor Q 42 turns off. Thus, if the capacitor C 41 is not provided, the bypass circuit constituted by the resistor R 44 and the transistor Q 42 can only extract current for a short period.

By correctly setting the capacitance value of the capacitor C 41 , a delay is produced in the progress of, after the transistor Q 42 turns on, the midpoint voltage of the division resistors R 41 and R 42 becoming equal to or higher than the base-emitter voltage of the transistor Q 42 and causing the transistor Q 41 to turn on and the transistor Q 42 to turn off. With this delay, when the triac Tri 1 in the phase-control light controller 2 turns on and the output voltage of the diode bridge DB 1 rises quickly, the bypass circuit constituted by the resistor R 44 and the transistor Q 42 extracts current at a predetermined current value for a predetermined period, and thereby prevents the triac Tri 1 in the phase-control light controller 2 from turning off for a period corresponding to several cycles of the undulation wavelength at which the current passing through the triac Tri 1 undulates.

Next, another specific example of the configuration shown in FIG. 3 is shown in FIG. 4B . In FIG. 4B , the AC power source 1 and the phase-control light controller 2 are omitted from illustration.

As compared with the configuration shown in FIG. 4A , the configuration shown in FIG. 4B is additionally provided with a constant-current source i 41 . The constant-current source i 41 is connected between the emitter of the transistor Q 42 and the negative-side output of the diode bridge DB 1 . The resistor R 44 , the transistor Q 42 , and the constant-current source i 41 constitute an example of the bypass circuit 7 (see FIG. 3 ).

Also in the configuration shown in FIG. 4A , basically, the bypass circuit extracts current at a predetermined current value; however, for example, when the source voltage of the AC power source 1 varies, the current value of the bypass circuit varies. By contrast, in the configuration shown in FIG. 4B , since the constant-current source i 41 is provided, even when, for example, the source voltage of the AC power source 1 varies, the current value of the bypass circuit can be kept constant. Moreover, when the resistance values of the individual resistors and the amplification factors of the individual transistors are sufficient, the current value of the bypass circuit can be changed by the constant-current source i 41 .

Examples of Operating Waveforms in Embodiments 2 to 5

Examples of the operating waveforms in the LED lighting systems shown in FIGS. 2 to 4 are shown in FIGS. 5A , 5 B, 6 A, 6 B, and 6 C.

The waveform of the output voltage V OUT2 of the phase-control light controller 2 , the waveform of the current I 2 passing through the triac Tri 1 in the phase-control light controller 2 , and the waveform of the current I B passing through the bypass circuit are shown in FIG. 5A , and an enlarged diagram of the period P in FIG. 5A is shown in FIG. 5B . FIGS. 5A and 5B show that the triac Tri 1 remains in the on state even after the current passing through the triac Tri 1 undulates.

FIG. 6A shows the waveforms when the light is controlled to be 100% (no delay in phase), FIG. 6B shows the waveforms when the light is controlled to be medium (a medium delay in phase), and FIG. 6C shows the waveforms when the light is controlled to be 0% (the maximum delay in phase), that is, when the light is off. In FIGS. 6A , 6 B, and 6 C, V IN2 , V OUT2 , and I 3 respectively indicate the waveform of the input voltage to the phase-control light controller 2 , the waveform of the output voltage of the phase-control light controller 2 , and the waveform of the current passing through the LED module 3 .

Next, another embodiment of the LED lighting system shown in FIG. 1 is shown in FIG. 7 . In the configuration shown in FIG. 7 , the timing adjustment circuit 6 includes a voltage variation detection circuit 6 B which detects a variation in the output voltage of the diode bridge DB 1 , and according to the variation in the output voltage of the diode bridge DB 1 as detected by the voltage variation detection circuit 6 B, the current extraction start timing and the current extraction duration are adjusted.

Next, a specific example of the configuration shown in FIG. 7 is shown in FIG. 8 . In FIG. 8 , the AC power source 1 and the phase-control light controller 2 are omitted from illustration. A serial circuit of a resistor R 81 and a capacitor C 81 constitutes an example of the voltage variation detection circuit 6 B (see FIG. 7 ). One end of the resistor R 81 is connected to the positive-side output of the diode bridge DB 1 , and one end of the capacitor C 81 is connected to the negative-side output of the diode bridge DB 1 . The serial circuit of the resistor R 81 and the capacitor C 81 , a transistor Q 81 of which the base is connected to the node between the resistor R 81 and the capacitor C 81 , a resistor R 82 connected between the emitter of the transistor Q 81 and the positive-side output of the diode bridge DB 1 , and a resistor R 83 connected between the collector of the transistor Q 81 and the negative-side output of the diode bridge DB 1 constitute an example of the timing adjustment circuit 6 (see FIG. 7 ). A transistor Q 82 of which the base is connected to the collector of the transistor Q 81 and of which the emitter is connected to the negative-side output of the diode bridge DB 1 , and a resistor R 84 connected between the collector of the transistor Q 82 and the positive-side output of the diode bridge DB 1 , constitute an example of the bypass circuit 7 (see FIG. 7 ).

When the triac Tri 1 in the phase-control light controller 2 turns on and the output voltage of the diode bridge DB 1 rises, a pulse current passes through the capacitor C 81 ; using this pulse current as its base current, the transistor Q 81 turns on; using the collector current of the transistor Q 81 as its base current, the transistor Q 82 turns on. Thus, during the period in which the just-mentioned pulse current is passing, the bypass circuit constituted by the transistor Q 82 and the resistor R 84 extracts a current from the output of the diode bridge DB 1 .

By varying the capacitance value of the capacitor C 81 , it is possible to vary the pulse width of the pulse current. By varying the resistance values of the individual resistors with consideration given to the amplification factors of the individual transistors, it is possible to vary the current value of the pulse current.

Thus, when the triac Tri 1 in the phase-control light controller 2 turns on and the output voltage of the diode bridge DB 1 rises quickly, the bypass circuit constituted by the transistor Q 82 and the resistor R 84 extracts current at a predetermined current value for a predetermined period, and thereby prevents the triac Tri 1 in the phase-control light controller 2 from turning off for a period corresponding to several cycles of the undulation wavelength at which the current passing through the triac Tri 1 undulates.

Next, another specific example of the configuration shown in FIG. 7 is shown in FIG. 9 . In FIG. 9 , the AC power source 1 and the phase-control light controller 2 are omitted from illustration.

As compared with the configuration shown in FIG. 8 , the configuration shown in FIG. 9 is additionally provided with a constant-current source i 91 . Accordingly, the resistors R 91 to R 94 , the capacitor C 91 , and the transistors Q 91 to Q 92 here respectively correspond to the resistors R 81 to R 84 , the capacitor C 81 , and the transistors Q 81 to Q 82 . The constant-current source i 91 is connected between the emitter of the transistor Q 92 and the negative-side output of the diode bridge DB 1 . The resistor R 94 , the transistor Q 92 , and the constant-current source i 91 constitute an example of the bypass circuit 7 (see FIG. 7 ).

Also in the configuration shown in FIG. 8 , basically, the bypass circuit extracts current at a predetermined current value; however, for example, when the source voltage of the AC power source 1 varies, the current value of the bypass circuit varies. By contrast, in the configuration shown in FIG. 9 , since the constant-current source i 91 is provided, even when, for example, the source voltage of the AC power source 1 varies, the current value of the bypass circuit can be kept constant. Moreover, when the resistance values of the individual resistors and the amplification factors of the individual transistors are sufficient, the current value of the bypass circuit can be changed by the constant-current source i 91 .

Next, yet another specific example of the configuration shown in FIG. 7 is shown in FIG. 10 . In FIG. 10 , the AC power source 1 and the phase-control light controller 2 are omitted from illustration.

A serial circuit of a resistor R 101 , a resistor R 102 , and a capacitor C 101 constitutes an example of the timing adjustment circuit 6 and the voltage variation detection circuit 6 B (see FIG. 7 ). One end of the resistor R 101 is connected to the positive-side output of the diode bridge DB 1 , and one end of the resistor R 102 is connected to the negative-side output of the diode bridge DB 1 . The capacitor C 101 is connected between the resistors R 101 and R 102 . A transistor Q 101 of which the base is connected to the node between the capacitor C 101 and the resistor R 102 , of which the collector is connected to the positive-side output of the diode bridge DB 1 , and of which the emitter is connected to the negative-side output of the diode bridge DB 1 constitutes an example of the bypass circuit 7 (see FIG. 7 ).

When the triac Tri 1 in the phase-control light controller 2 turns on and the output voltage of the diode bridge DB 1 rises, a pulse current passes through the capacitor C 101 ; using this pulse current as its base current, the transistor Q 101 turns on. Thus, during the period in which the just-mentioned pulse current is passing, the bypass circuit constituted by the transistor Q 101 extracts a current from the output of the diode bridge DB 1 .

By varying the capacitance value of the capacitor C 101 , it is possible to vary the pulse width of the pulse current. By varying the resistance values of the individual resistors with consideration given to the amplification factor of the transistor Q 101 , it is possible to vary the current value of the pulse current.

Thus, when the triac Tri 1 in the phase-control light controller 2 turns on and the output voltage of the diode bridge DB 1 rises quickly, the bypass circuit constituted by the transistor Q 101 extracts current at a predetermined current value for a predetermined period, and thereby prevents the triac Tri 1 in the phase-control light controller 2 from turning off for a period corresponding to several cycles of the undulation wavelength at which the current passing through the triac Tri 1 undulates.

As distinct from the configuration shown in FIG. 8 , the configuration shown in FIG. 10 achieves the amplification of the above-mentioned pulse current with a transistor in a single stage, hence with a very simply circuit configuration, and thus at low cost.

Next, yet another specific example of the configuration shown in FIG. 7 is shown in FIG. 11 . In FIG. 11 , the AC power source 1 and the phase-control light controller 2 are omitted from illustration.

As compared with the configuration shown in FIG. 10 , the configuration shown in FIG. 11 is additionally provided with a resistor R 113 and a constant-current source i 111 . Accordingly, the resistors R 111 to R 112 , the capacitor C 111 , and the transistor Q 111 here respectively correspond to the resistors R 101 to R 102 , the capacitor C 101 , and the transistor Q 101 . The resistor R 113 is connected between the collector of the transistor Q 111 and the positive-side output of the diode bridge DB 1 . The constant-current source i 111 is connected between the emitter of the transistor Q 111 and the negative-side output of the diode bridge DB 1 . The resistor R 113 , the transistor Q 111 , and the constant-current source i 111 constitute an example of the bypass circuit 7 (see FIG. 7 ).

Also in the configuration shown in FIG. 10 , basically, the bypass circuit extracts current at a predetermined current value; however, for example, when the source voltage of the AC power source 1 varies, the current value of the bypass circuit varies. By contrast, in the configuration shown in FIG. 11 , since the constant-current source i 111 is provided, even when, for example, the source voltage of the AC power source 1 varies, the current value of the bypass circuit can be kept constant. Moreover, when the resistance values of the individual resistors and the amplification factor of the transistor Q 111 are sufficient, the current value of the bypass circuit can be changed by the constant-current source i 111 .

As distinct from the configuration shown in FIG. 9 , the configuration shown in FIG. 11 achieves the amplification of the above-mentioned pulse current with a transistor in a single stage, hence with a very simply circuit configuration, and thus at low cost.

Examples of Operating Waveforms in Embodiments 6 to 10

Examples of the operating waveforms in the LED lighting systems shown in FIGS. 7 to 11 are shown in FIGS. 12A and 12B . The waveform of the output voltage V OUT2 of the phase-control light controller 2 , the waveform of the current I 2 passing through the triac Tri 1 in the phase-control light controller 2 , and the waveform of the current I B passing through the bypass circuit are shown in FIG. 12A , and an enlarged diagram of the period P in FIG. 12A is shown in FIG. 12B . FIGS. 12A and 12B show that the triac Tri 1 remains in the on state even after the current passing through the triac Tri 1 undulates.

In controlling the light of an LED module in an LED lighting system by use of a phase-control light controller, just because LEDs are low-current-consumption devices, a triac in the phase-control light controller may fail to turn on normally. This inconvenience can be effectively overcome by either of the LED drive circuit shown in FIG. 2 and the LED drive circuit shown in FIG. 7 .

In cases where a phase-control light controller is used, however, there is also the problem of an unnecessary current passing through an LED module 3 and causing it to light unnecessarily. Here, an unnecessary current denotes one that may be supplied to, but is unnecessary to, the LED module 3 during a period in which the LED module 3 needs to be kept from lighting. What counts as such here is the current that, when the triac in the phase-control light controller is off, originates from a capacitor forming a filter according to its capacitance value and the AC frequency.

In the LED drive circuit shown in FIG. 2 , the timing adjustment circuit 6 and the bypass circuit 7 also function as a circuit capable of preventing the LEDs from being lit by an unnecessary current (an unnecessary lighting prevention circuit). This overcomes the problem of the LEDs lighting unnecessarily.

By contrast, in the LED drive circuit shown in FIG. 7 , the timing adjustment circuit 6 and the bypass circuit 7 do not function as a circuit capable of preventing the LEDs from being lit by an unnecessary current (an unnecessary lighting prevention circuit). Thus, to overcome the problem of the LEDs lighting unnecessarily, it is necessary to provide an unnecessary lighting prevention circuit separately.

Additionally providing the LED drive circuit shown in FIG. 7 with an unnecessary lighting prevention circuit 10 gives a configuration as shown in FIG. 13 . The unnecessary lighting prevention circuit 10 is provided with a current extractor (unillustrated) which extracts a current from the current supply line through which the LED drive current is supplied to the LED module 3 . When the input current to the LED drive circuit according to the invention is an unnecessary current, through the current extraction by the current extractor, the LED module 3 is prevented from lighting. Preferably, the unnecessary lighting prevention circuit 10 is provided with a function of making the current extractor extract a smaller amount of current when the input current to the LED drive circuit according to the invention is switched from an unnecessary current to the LED drive current. The LED drive current denotes the current that is supplied to the LED module 3 during a period in which the LED module 3 needs to be lighting. Now, specific examples of the unnecessary lighting prevention circuit 10 will be described.