This application is based on Japanese Patent Application No. 2010-284943 filed on Dec. 21, 2010, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an LED drive circuit that drives an LED (light-emitting diode) and an LED illumination component using the same.
2. Description of the Prior Art
An LED is characterized by its low current consumption, long life, and so on, and its range of applications has been expanding not only to display devices but also to illumination apparatuses and the like. An LED illumination apparatus often uses a plurality of LEDs in order to attain desired illuminance.
A general-use illumination apparatus often uses a commercial alternating current power source, and considering a case where an LED illumination component is used in place of a general-use illumination component such as an incandescent lamp, it is desirable that, similarly to a general-use illumination component, an LED illumination component also be configured to use a commercial alternating current power source.
Furthermore, in seeking to perform light control of an incandescent lamp, a phase-control light controller (referred to generally as an incandescent light controller) is used in which a switching element (generally, a thyristor element or a triac element) is switched on at a certain phase angle of an alternating current power source voltage and that thus allows light control through control of power supply to the incandescent lamp to be performed easily with a simple operation of a volume element. It is known, however, that in performing light control of a low-wattage incandescent lamp by use of a phase-control light controller, connecting the incandescent lamp to the light controller leads to the occurrence of flickering or blinking, so that the light control cannot be performed properly.
It is desirable that in seeking to perform light control of an LED illumination component that uses an alternating current power source, an existing phase-control light controller for an incandescent lamp be connectable as it is to the LED illumination component. By changing only an illumination component to an LED illumination component while using existing light control equipment therewith, compared with a case of using an incandescent lamp, power consumption can be reduced considerably. Furthermore, this can also secure compatibility without requiring the light control equipment to be changed to a type dedicated to an LED illumination component and thus reduces equipment cost.
Now,
When the phase angle of the phase-control light controller 2 is increased to decrease resulting brightness of the LEDs, if an output voltage of the diode bridge DB1 becomes smaller than a forward voltage (VF) obtained when the LED array 4 starts to glow, the LED array 4 no longer glows, and there occurs an abrupt decrease in current flowing through the light controller. Due to this abrupt decrease, the current flowing through the light controller falls below a level of an on-state holding current of the triac Tri1 in the light controller, so that the triac Tri1 is switched off to halt an output of the light controller and thus to bring about an unstable state, which results in the occurrence of brightness flickering of the LED array 4. Furthermore, when the triac Tri1 is switched from an off-state to an on-state through phase control of the output of the light controller, the LEDs are switched from an off-state to an on-state, so that there occurs an abrupt decrease in impedance of the LEDs. This might cause ringing to occur at an edge of an output voltage of the light controller, where the output voltage varies abruptly. For the above-described reason, in an LED illumination system adapted for use with a phase-control light controller, in order to prevent the triac Tri1 from being switched off when LEDs are not glowing, a current drawing circuit that forcibly passes a holding current is used. In this case, however, a drawn current is all converted to heat, which leads to deterioration in efficiency of the LED illumination system and also requires heat radiation measures to be taken.
In a case where a conventional incandescent lamp load is connected, since a filament of tungsten or the like constitutes the load, even if the triac Tri1 of the phase-control light controller 2 is switched from an off-state to an on-state, there hardly occurs a variation in impedance, and thus a low impedance state is maintained. Thus, there occurs no abrupt variation in current flowing through the phase-control light controller 2, so that a stable light control operation can be performed as long as an alternating current power source has a voltage value of around 0 V.
Furthermore, in a case of the conventional example shown in
Moreover,
There has recently been invented an LED illumination component that, in order to be adaptable for use with a phase-control light controller, draws a current so that the light controller is prevented from malfunctioning due to a triac included therein being switched off and thus suppresses the occurrence of flickering even when used in combination with an already-existing phase-control light controller. It has been disadvantageous, however, that, in this case, brightness and the color temperature do not vary in the same manner as in a case where an incandescent lamp or a halogen lamp is connected to the phase-control light controller, so that a feeling of strangeness is caused. For example, in a case where an incandescent lamp is connected to a phase-control light controller, there is a characteristic that a high color temperature is obtained at high brightness, and as the phase angle is increased by operating a volume element of the phase-control light controller, the color temperature decreases. In a case where a white LED is connected to a phase-control light controller, the color temperature of light unfavorably stays substantially constant regardless of brightness. Furthermore, also regarding a variation in brightness with a variation in phase angle of a phase-control light controller, an incandescent lamp is turned off gradually at low illuminance, whereas an LED illumination component adapted for use with a light controller varies largely in brightness at low illuminance and thus is disadvantageous in that delicate control of brightness can hardly be achieved.
There is a type of LED illumination component capable of adjusting the color temperature and the light amount by use of a dedicated light controller. This type, however, requires installation work for installing the dedicated light controller. Furthermore, since an existing illumination apparatus such as an incandescent lamp is intended in illumination design, connecting an LED illumination component to already-existing equipment might result in a failure to operate illumination as intended by the original illumination design, causing a human working under the illumination to feel uncomfortable. Also from the viewpoint of utilizing already-existing equipment and design resources of illumination design, the market has been demanding an LED illumination component that, when connected to a light controller, presents substantially the same light control and color control characteristics as those of an existing illumination component (an incandescent lamp, a halogen lamp, or the like).
It is an object of the present invention to provide an LED drive circuit and so on that, when an already-existing phase-control light controller is used, can provide light control and color control characteristics approximate to those of an existing illumination component (for example, an incandescent lamp) and thus enable light control and color control unlikely to cause a feeling of strangeness. Furthermore, it is also an object of the present invention to suppress the occurrence of flickering of an LED due to a malfunction of a phase-control light controller and to reduce a color deviation and a difference in brightness of an LED illumination component attributable to its individual variability.
The present invention provides an LED drive circuit to which a light control signal phase-controlled by a phase-control light controller is inputted and that controls a light emission portion having a plurality of LED loads that emit light of different color tones. The LED drive circuit includes a light control/color control portion that, based on the light control signal inputted, adjusts a current to be passed through each of the LED loads thereby to perform light control and color control of the light emission portion.
According to this configuration, in a case of using an already-existing phase-control light controller, light control and color control characteristics approximate to those of an existing illumination component (for example, an incandescent lamp) can be obtained, and thus light control and color control unlikely to cause a feeling of strangeness are enabled.
Furthermore, the LED drive circuit may have a configuration in which the LED loads are a white LED load and a red LED load.
Furthermore, the LED drive circuit may have a configuration in which the light control/color control portion decreases a light amount and a color temperature of the light emission portion as a phase angle of the light control signal increases.
Furthermore, the LED drive circuit may have a configuration in which a phase angle detection portion is further provided that detects a phase angle of the light control signal, and the phase angle detection portion detects the phase angle by detecting an average voltage of the light control signal.
Furthermore, the LED drive circuit may have a configuration in which a phase angle detection portion is further provided that detects a phase angle of the light control signal, and the phase angle detection portion detects the phase angle by comparing the light control signal with a reference voltage, generating a pulse signal based on a result of the comparison, and detecting a duty ratio of the generated pulse signal.
Furthermore, the LED drive circuit may have a configuration in which a detection portion is further provided that detects a light amount and a color temperature of the light emission portion, and based on the light amount and the color temperature detected by the detection portion, the light control/color control portion performs light control and color control so that the light emission portion attains a target light amount and a target color temperature that correspond to the light control signal.
Furthermore, the LED drive circuit may have a configuration in which the light control/color control portion makes each of the LED loads emit light in a time-divided manner.
Furthermore, the LED drive circuit may have a configuration in which the LED loads are the same and constant in light emission period and variable in light emission intensity.
Furthermore, the LED drive circuit may have a configuration in which the LED loads are the same and constant in light emission intensity and variable in light emission period.
Furthermore, the LED drive circuit may have a configuration in which the detection portion has a light amount sensor and integrates, using, as an integration time, a light emission period of each of the LED loads starting from a light emission timing thereof, an output of the light amount sensor thereby to detect a light amount of the each of the LED loads.
Furthermore, the LED drive circuit may have a configuration further including a low voltage detection portion that detects that a voltage of the light control signal has been lowered, and a current drawing portion that, upon the detection of the lowed voltage by the low voltage detection portion, draws a current from a power supply line for supplying power to the LED loads.
Furthermore, the LED drive circuit may have a configuration further including an edge detection portion that detects an edge of the light control signal, and a current drawing portion that, upon the detection of the edge by the edge detection portion, draws a current from a power supply line for supplying power to the LED loads.
Furthermore, the LED drive circuit may have a configuration in which a detection portion is further provided that detects illuminance and/or a color temperature of external light, and the light control/color control portion makes each of the LED loads emit light in a time-divided manner and adjusts a light amount of each of the LED loads in accordance with a result of the detection performed by the detection portion in a period during which the LED loads do not emit light.
Furthermore, an LED illumination component of the present invention has a configuration including an LED drive circuit having any of the above-described configurations, and the plurality of LED loads that are connected to an output side of the LED drive circuit and emit light of different color tones.
Hereinafter, an embodiment of the present invention will be described with reference to the appended drawings.
The light emission portion 6 is composed of a red LED array R that emits light having a light emission wavelength in the R (red) band, a green LED array G that emits light having a light emission wavelength in the G (green) band, and a blue LED array B that emits light having a light emission wavelength in the B (blue) band. The red LED array R is connected between an output terminal T1 through which an output voltage VOUT is outputted from the LED drive circuit 5 and an R terminal T2. The green LED array G is connected between the output terminal T1 and a G terminal T3. The blue LED array B is connected between the output terminal T1 and a B terminal T4. In order to suppress a loss caused in the LED drive circuit to a minimum level, it is desirable that a difference in forward voltage among the LED arrays R, G, and B be set to be as small as possible.
The LED drive circuit 5, the light emission portion 6, and the diode bridge DB1 constitute an LED illumination component, one example of which is an LED light bulb.
The commercial alternating current power source 1 outputs a sinusoidal alternating current voltage that varies from country to country between 100 V to 250 V, and a frequency of 50 Hz or 60 Hz is used for the power source 1. When an alternating current voltage is inputted to the phase-control light controller 2, in accordance with the rotation or sliding operation for light control of a volume element, a waveform is generated that has a shape obtained by cutting away a certain phase point of an alternating current waveform. By the diode bridge DB1, full-wave rectification of an output waveform of the phase-control light controller 2 is performed, and a ripple waveform having a frequency double an input frequency (100 Hz in a case of an input frequency of 50 Hz, and 120 Hz in a case of an input frequency of 60 Hz) is inputted to an input terminal T0 of the LED drive circuit 5.
The LED drive circuit 5 detects a phase angle of an input voltage VIN having the above-described ripple waveform and controls a current value of a current to be passed through each of the red LED array R, the green LED array G, and the blue LED array B in accordance with the detected phase angle, so that the light emission portion 6 can be adjusted in terms of the light amount and the color temperature.
Now,
The low voltage detection portion 7, upon detecting that the input voltage VIN has become lower than a threshold voltage, i.e. so low that a boosting operation can no longer be performed, outputs a detection signal as a result of the detection to the first current drawing portion 8. The first current drawing portion 8 then draws a current larger than a holding current of the phase-control light controller 2 from a power supply line LN1 for supplying power to the light emission portion 6 and thus can suppress a malfunction of the phase-control light controller 2. Furthermore, since current drawing is performed when the input voltage VIN has been lowered, a decrease in efficiency can be suppressed.
Furthermore, the edge detection portion 9, upon detecting rising of the input voltage VIN, outputs a detection signal as a result of the detection to the second current drawing portion 10. The second current drawing portion 10 then draws, from the power supply line LN1, a pulsating current larger than the current dawn by the first current drawing portion 8 and thus can prevent the phase-control light controller 2 from malfunctioning due to resonance.
Furthermore, the phase angle detection portion 11 detects the phase angle of the input voltage VIN, namely, the phase angle of the phase-control light controller 2, and the light control/color control portion 13 adjusts a current value of a current to be passed through each of the LED arrays of the respective colors of the light emission portion 6 in accordance with the detected phase angle, so that the light emission portion 6 can output light having a light amount and a color temperature that correspond to the phase angle.
Referring to
Furthermore, referring to
Now, the following describes variations in light amount and in color temperature in a case where an incandescent lamp is connected to the phase-control light controller 2.
Now, the following describes in detail how the light amount and the color temperature are adjusted. A light amount of an LED is in a substantially proportional relationship with a driving current of the LED, and thus a light amount of each of the LED arrays R, G, and B of the respective colors can be controlled using a driving current. Where currents flowing through the LED arrays R, G, and B are indicated as Ir, Ig, and Ib, respectively, the light amounts of the LED arrays are expressed as functions of a driving current, i.e. as
Φr(Ir),
Φg(Ig), and
Φb(Ib), respectively.
A light amount Φ of the light emission portion 6 as a whole is therefore determined as a sum of the light amounts of the LED arrays R, G, and B of the respective colors, i.e. by
Φ=Φr(Ir)+Φg(Ig)+Φb(Ib).
Thus, by controlling a current value of a current to be passed through each of the LED arrays R, G, and B of the respective colors in accordance with the output of the phase angle detection portion 11, brightness can be adjusted.
Next, the following describes control of a color temperature of light emitted from the light emission portion 6. When a given current Io is passed through each of the LED arrays R, G, and B of the respective colors, spectral characteristics of light emitted from the LED arrays of the respective colors can be expressed as functions of a wavelength λ of light, i.e. as
Bo(λ), respectively.
Where currents flowing through the LED arrays R, G, and B of the respective colors are indicated as Ir, Ig, and Ib, respectively, a spectral characteristic P(λ) of a light source as a whole, in which light of the three types of LED arrays is mixed together, is expressed by
P(λ)=(Ir·Ro(λ)+Ig·Go(λ)+Ib·Bo(λ))/Io.
Coordinates on the xy chromaticity diagram of the light source having the above-mentioned spectral characteristic P(λ) can be determined based on color matching functions of tristimulus values shown in
IPD
—
X=□P(λ)·X(λ)·dλ,
IPD
—
Y=□P(λ)·Y(λ)·dλ,
IPD
—
Z=□P(λ)·Z(λ)·dλ.
Coordinates x and y on the xy chromaticity diagram are expressed by
x=IPD
—
X/(IPD—X+IPD—Y+IPD—Z),
and
y=IPD
—
Y/(IPD—X+IPD—Y+IPD—Z),
respectively.
Thus, by making the currents Ir, Ig, and Ib to be passed respectively through the LED arrays R, G, and B of the respective colors vary, coordinates of P(λ) on the xy chromaticity diagram can be shifted.
Since the following expression holds:
P(λ)=((Ir/Ig)·Ro(λ)+Go(λ)+(Ib/Ig)·Bo(λ))·(Ig/Io),
the coordinates x and y of the light source on the xy chromaticity diagram are expressed as functions of (Ir/Ig) and (Ib/Ig), respectively. By maintaining (Ir/Ig) and (Ib/Ig) at constant values, it is possible to make the light amount vary without making the color temperature vary, thereby allowing the light amount and the color temperature to be controlled independently of each other.
As described above, the light control/color control portion 13 adjusts the currents Ir, Ig, and Ib flowing through the LED arrays R, G, and B of the respective colors in accordance with a phase angle detected, thereby to control so that a relationship between the phase angle of the phase-control light controller 2 and the light amount and a relationship between the phase angle of the phase-control light controller 2 and the color temperature are consistent with the light control characteristic shown in
Currents flowing through the R terminal T2, the G terminal T3, and the B terminal T4 are expressed by
I(T2)=VIR/RIR,
I(T3)=VIG/RIG,
and
I(T4)=VIB/RIB,
respectively.
Thus, the LED current setting portion 13a can control a current to be passed through each the LED arrays R, G, and B of the respective colors by controlling VIR, VIG, and VIB in accordance with a phase angle detected.
Furthermore,
Where amplitudes of the pulse voltage sources are indicated as VIR, VIG, and VIB, respectively, and duty ratios thereof as DIR, DIG, and DIB, respectively, average currents of pulsating currents flowing through the R terminal T2, the G terminal T3, and the B terminal T4 are expressed by
I(T2)=DIR·VIR/RIR,
I(T3)=DIG·VIG/RIG,
and
I(T4)=DIB·VIB/RIB,
respectively.
Thus, the LED current setting portion 13a can control a current to be passed through each of the LED arrays R, G, and B of the respective colors by controlling the amplitudes or duty ratios of the pulse voltage sources in accordance with a phase angle detected.
Moreover, through the use of the LED illumination system configured as above, it is also possible to make the color temperature vary dynamically with the phase angle of the light controller. For example, the color temperature of illumination can even be set to be as high as “daylight” or “neutral” when the phase angle of the light controller is small and to be “incandescent” when the phase angle is large and thus can be made to vary in a wider range than in the case of an incandescent lamp, so that a broader range of applications can be achieved. More specifically, for example, with respect to variations in color temperature with the phase angle shown in
The LED arrays R, G, and B of the respective colors in the light emission portion 6 shown in
Now, the following describes in detail how the light amount and the color temperature are adjusted. A light amount of an LED is in a proportional relationship with a driving current of the LED, and thus a light amount of each of the white and red LED arrays can be controlled using a driving current. Where currents flowing through the white and red LED arrays are indicated as Iw and Ir, respectively, the light amounts of the LED arrays are expressed as functions of a driving current, ie. as
Φw(Iw) and
Φr(Ir), respectively.
A light amount Φ of the light emission portion 6 as a whole is therefore determined as a sum of the light amounts of the white and red LED arrays, i.e. by
Φ=Φw(Iw)+Φr(Ir).
Thus, by controlling a current to be passed through each of the LED arrays in accordance with the output of the phase angle detection portion 11, brightness can be adjusted.
Next, the following describes control of the color temperature. When a given current Io is passed through each of the white and red LED arrays, spectral characteristics of light emitted from the LED arrays can be expressed as functions of a wavelength λ of light, i.e. as
Ro(λ), respectively.
Where currents flowing through the white and red LED arrays are indicated as Iw and Ir, respectively, a spectral characteristic P(λ) of a light source as a whole, in which light of the two types of LED arrays is mixed together, is expressed by
P(λ)=(Iw·Wo(λ)+Ir·Ro(λ))/Io.
Coordinates on the xy chromaticity diagram of the light source having the above-mentioned spectral characteristic P(λ) can be determined based on the color matching functions of tristimulus values shown in
IPD
—
X=□P(λ)·X(λ)·dλ,
IPD
—
Y=□P(λ)·Y(λ)·dλ,
IPD
—
Z=□P(λ)·Z(λ)·dλ.
Coordinates x and y on the xy chromaticity diagram are expressed by
x=IPD
—
X/(IPD—X+IPD—Y+IPD—Z),
and
y=IPD
—
Y/(IPD—X+IPD—Y+IPD—Z),
respectively.
By making the currents Iw and Ir to be passed respectively through the white and red LED arrays vary, coordinates of P(λ) on the xy chromaticity diagram can be shifted. When a current to be passed through the red LED array, namely, Ir is decreased, the color temperature increases, and when Ir is increased, the color temperature decreases. In a case where three primary colors of R, G, and B are used as in the first embodiment, it is possible to control so that coordinates on the xy chromaticity diagram lie exactly along the Planckian locus. On the other hand, in a case of making Iw and Ir vary, since the number of parameters used is two, the coordinates of P(λ) on the xy chromaticity diagram cannot be made to lie exactly along the Planckian locus. This, however, often is not a serious issue from a practical standpoint since even when coordinates on the xy chromaticity diagram do not exactly coincide with the Planckian locus, the color temperature of the light source can be defined as long as the coordinates lie within a certain range from the Planckian locus.
As an expression for calculating a color temperature based on coordinates on the xy chromaticity diagram, McCamy's formula is known and given as follows:
Color temperature=449n3+3525n2+6823.3n+5520.33,
where
n=(x−0.3320)/(0.1858−y).
Using this expression, a color temperature can be determined based on coordinates on the xy chromaticity diagram.
Furthermore, since the following expression holds:
P(λ)=(Wo(λ)+(Ir/Iw)·Ro(λ))/(Iw/Io),
by maintaining (Ir/Iw) at a constant value, it is possible to make the light amount vary without making the color temperature vary, thereby allowing the light amount and the color temperature to be controlled independently of each other. As described above, the currents Ir and Iw flowing respectively through the white and red LED arrays are controlled in accordance with a phase angle detected by the phase angle detection portion 11, and thus a relationship between the phase angle of the phase-control light controller 2 and the light amount and a relationship between the phase angle of the phase-control light controller 2 and the color temperature approximate respectively to the light control and color control characteristics of an incandescent lamp can be obtained, so that compared with the case of using the three types of LED arrays R, G, and B, cost reduction can be achieved.
Now, the following describes detection of a light amount and a color temperature by the color sensor 14.
x=IPD
—
X/(IPD—X+IPD—Y+IPD—Z),
y=IPD
—
Y/(IPD—X+IPD—Y+IPD—Z).
Moreover, since Y(λ) has a spectral characteristic consistent with a standard luminosity factor, the light amount of the light source can be estimated using IPD_Y.
Furthermore, even if spectral sensitivity characteristics of the light-receiving elements of the color sensor 14 are not compliant with the tristimulus values, they can be transformed to coordinates on the xy chromaticity diagram by coordinate transformation using a transformation matrix.
As described above, coordinates on the xy chromaticity diagram (namely, a color temperature) and a light amount are measured by the color sensor 14, and based on the color temperature and light amount thus measured, the light control/color control portion 13 controls a current value of a current to be passed through each of the LED arrays R, G, and B of the respective colors so that the light emission portion 6 attains a target light amount and a target color temperature that correspond to a phase angle. Thus, a color deviation and a difference in brightness of an LED illumination component attributable to its individual variability can be reduced.
Then, the light control/color control portion 13 integrates, at the respective light emission timings of the LED arrays R, G, and B and using the respective light emission periods thereof as integration times, outputs of the light amount sensor 15 that has sensitivity in R, G, and B regions and thus has a wide range of spectral sensitivity characteristics thereby to detect respective light amounts of the LED arrays R, G, and B. The light amounts thus detected are summed, and thus a light amount of a light emission portion 6 is detected. Furthermore, the LED arrays R, G, and B are made to emit light in a time-divided manner, and the light thus emitted is inputted to the light amount sensor 15. Where average outputs of the light amount sensor 15 obtained in this case are indicated as Ipd_R, Ipd_G, and Ipd_B, respectively, using a transformation matrix experimentally determined beforehand, coordinates on the xy chromaticity diagram (a color temperature) can be approximately determined by the following expressions.
Based on the light amount and color temperature thus detected, the light control/color control portion 13 adjusts the light emission intensity of each of the LED arrays R, G, and B while maintaining the light emission period thereof constant so that the light emission portion 6 attains a target light amount and a target color temperature that correspond to a phase angle. This enables extremely precise control of a light amount and a color temperature, and a color deviation and a difference in brightness of an illumination component attributable to its individual variability can be reduced.
Furthermore, as a modification example of the above-described embodiment, the LED arrays of the respective colors may be set so that currents of the same level are passed therethrough, with the on-periods thereof made to vary. Thus, as shown in
A configuration may be adopted in which, as shown in
Number | Date | Country | Kind |
---|---|---|---|
2010-284943 | Dec 2010 | JP | national |