1. Field of the Invention
The present invention relates to an LED (Light-Emitting Diode) drive circuit that drives an LED, and to an LED illumination component, an LED illumination device and an LED illumination system that use an LED as a light source.
2. Description of the Related Art
An LED has features of a low current consumption, a long life and the like, and is spreading its applications not only to display devices but also to illumination devices and the like. In illumination apparatuses, to obtain a desired illumination, a plurality of LEDs are often used.
A general illumination apparatus often uses a commercial 100 VAC power source, and considering a case and the like where an LED illumination component is used instead of a general illumination component such as an incandescent lamp or the like, it is desirable that like a general illumination component, an LED illumination component also has a structure to use a commercial 100 VAC power source.
Besides, to perform light control of an incandescent lamp, a phase-control light controller (generally called a incandescent light controller) is used, which is able to easily perform light control so as to control power supply to the incandescent lamp with only a volume element by turning on a switching element (generally, a TRIAC element) at a phase angle of an alternating-current power source voltage.
To perform light control of an LED illumination component that uses an alternating-current power source, usually, a phase-control light controller is used as in a case where light control of an incandescent lamp is performed. Here, a conventional example of an LED illumination system that is able to perform light control of an LED illumination component that uses an alternating-current power source is shown in FIG. 19
The LED illumination system shown in FIG. 19 includes: a phase-control light controller 2; an LED drive circuit 101; and an LED module 3. The phase-control light controller 2 is connected between and in series with an alternating-current power source 1 and the LED drive circuit 101. If a light-control knob (not shown) of a control circuit CNT1 is set to a predetermined position, the phase-control light controller 2 turns on a TRIAC Tra1 at a power-source phase angle that corresponds to the set position. Besides, in the phase-control light controller 2, a noise prevention circuit is composed of a capacitor C1 and an inductor L1 and reduces terminal noise that is returned from the phase-control light controller 2 to the power-source line.
In the LED illumination system shown in FIG. 19, when the TRIAC Tra1 is in an off state, power supply from the alternating-current power source 1 to the LED drive circuit 101 should be cut off; however, the alternating-current power source 1 and the LED drive circuit 101 are always connected to each other by the capacitor C1 of the noise prevention circuit of the above phase-control light controller 2. Accordingly, even if the TRIAC Tra1 is in the off state, a current is supplied to the LED as shown in FIGS. 20A and 20B. Here, in FIGS. 20A and 20B, VIN2 is an input voltage waveform to the phase-control light controller 2; VOUT2 is an output voltage waveform from the phase-control light controller 2; and I3 is a current waveform that flows in the LED module 3.
Because the TRIAC Tra1 of the phase-control light controller 2 is in the off state, only a leakage current that flows through the capacitor C1 is supplied to the LED drive circuit 101, so that a current limiting circuit of the LED drive circuit 101 does not operate; however, there is a problem that the LED module 3 is turned on by the leakage current and slightly emits light. Besides, because the LED module 3 is slightly lighting because of the leakage current that flows through the capacitor C1, a forward voltage VF is generated in the LED module 3; accordingly, in FIG. 20A, a rising voltage of the TRIAC Tra1 is delayed, and a time span in which a drive current is supplied to the LED module 3 becomes short, so that a problem arises that the LED module 3 becomes dim and the light control range becomes narrow.
Besides, as another conventional example of the LED illumination system that is able to perform light control of an LED illumination component which uses an alternating-current power source, as shown in FIG. 21, there is an LED illumination system that includes a phase-control light controller 2′ that has a firefly lighting function with a neon lamp. Here, in FIG. 21, the same parts as those in FIG. 19 are indicated by the same reference numbers and the explanation of them is skipped.
In the LED illumination system shown in FIG. 21, a series circuit (hereinafter, called a firefly circuit) of a neon lamp NL1 and a current limiting resistor Re1 is connected in parallel with the TRIAC Tra1; if the TRIAC Tra1 is selected by an external switch S1 to supply an LED drive current to the LED module 3, the neon lamp NL1 is turned off; if the firefly circuit is selected by the switch S1 not to supply the LED drive current to the LED module 3, electricity is supplied to the firefly circuit to indicate where the phase-control light controller 2′ is. As in the LED illumination system shown in FIG. 21, even if the capacitor C1 of the noise prevention circuit is not connected in parallel with the TRIAC Tra1, a slight current is supplied to the LED drive circuit 101 via the firefly circuit when the TRIAC Tra1 is in the off state; accordingly, a problem arises that the LED module 3 slightly emits light and the rising voltage of the TRIAC Tra1 is delayed.
Here, as a solution to the above problems, a solution is known, in which as shown in FIG. 22, a leakage current that flows in the LED module 3 is curbed by connecting an impedance Z1 (a resistor, a capacitor, a neon lamp or the like) in parallel with a power input portion of an LED drive circuit 102 (e.g., JP-A-2004-296205). However, in the structure shown in FIG. 22, a current IZ1 (=an input power-source voltage VZ1/an impedance value ZZ1 of the impedance Z1) flows through the impedance Z1 even for a time the TRIAC Tra1 is turned on and input power is supplied to the LED drive circuit 102. Accordingly, a problem arises that the power loss is large and the power efficiency decreases.