Lighting device

Abstract

To provide a lighting device capable of suppressing variations in the intensity of light emitted from a light source.SOLUTION: A lighting device includes a DC power supply V1, a switching element Q1 connected between the low potential output end of the DC power supply V1 and the cathode of a light emitting diode LD1 of a light source 12 having the light emitting diode LD1 whose anode is connected to the high potential output end of the DC power supply V1, a capacitor C1 connected between the anode and cathode of the light emitting diode LD1, an inductor L1 interposed between the cathode of the light emitting diode LD1 and the switching element Q1, and a diode D1 whose anode is connected to the other end of the inductor L1 opposite to the one end connected to the light emitting diode LD1 and whose cathode is connected to the anode of the light emitting diode LD1.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a lighting device. [Background technology]

[0002] A power supply device has been proposed that includes a rectifier circuit that rectifies AC from a commercial AC power source to DC, a boost chopper circuit that boosts the voltage of the DC power input from the rectifier circuit, a step-down chopper circuit that steps down the DC constant voltage input from the step-up chopper circuit, and a switching element connected to the output end of the step-down chopper circuit (see, for example, Patent Document 1). In this power supply device, the switching element operates to repeatedly short-circuit and open the output ends of the step-down chopper circuit, thereby lighting an LED (Light Emitting Diode) light source connected in parallel to the switching element. Then, the ratio of the time that the output ends are short-circuited in the cycle of the switching element repeatedly shorting and opening the output ends of the step-down chopper circuit, that is, the on-duty, is changed to perform dimming control of the LED light source. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-13241 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, in the power supply device described in Patent Document 1, when the above-mentioned on-duty becomes small, the ripple of the current flowing through the LED light source becomes large, causing the intensity of the light emitted from the LED light source to vary.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a lighting device capable of suppressing variations in the intensity of light emitted from a light source. [Means for solving the problem]

[0006] In order to achieve the above object, a lighting device according to the present invention comprises: A DC power source; a switching element connected between a cathode of a light-emitting diode of a light source having an anode connected to a high-potential output terminal of the DC power supply and a low-potential output terminal of the DC power supply; a capacitor connected between the anode and the cathode of the light emitting diode; an inductor interposed between the cathode of the light emitting diode and the switching element; a diode having an anode connected to an end of the inductor opposite to the end connected to the light-emitting diode and a cathode connected to the anode of the light-emitting diode. Effect of the Invention

[0007] According to the present invention, a capacitor is connected between the anode and cathode of the light-emitting diode, thereby smoothing the current flowing through the light-emitting diode. Also, when the switching element is in the off state, a current accompanying the release of energy stored in the inductor is supplied to the light-emitting diode through the diode, thereby suppressing a decrease in the current flowing through the light-emitting diode. Therefore, since the variation in the current flowing through the light-emitting diode can be suppressed regardless of the on / off state of the switching element, the variation in the intensity of the light emitted from the light source having the light-emitting diode can be suppressed. [Brief description of the drawings]

[0008] [Figure 1] 1 is a circuit diagram of a lighting device according to an embodiment of the present invention. [Diagram 2] 4 is a diagram showing a time profile of a voltage value of a PWM signal output from a driver of a lighting device according to an embodiment, and a time profile of a current value at each of three measurement positions. FIG. [Diagram 3]4 is a diagram showing a time profile of a voltage value of a PWM signal output from a driver of a lighting device according to an embodiment, and a time profile of a current value at each of three measurement positions. FIG. [Figure 4] 4 is a diagram showing a time profile of a voltage value of a PWM signal output from a driver of a lighting device according to an embodiment, and a time profile of a current value at each of three measurement positions. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a lighting device according to an embodiment of the present invention will be described with reference to the drawings. The lighting device according to the present embodiment dims a light source having a light emitting diode (hereinafter referred to as "LED (Light Emitting Diode)").

[0010] The lighting device according to the present embodiment includes, for example, a DC power source V1, a switching element Q1, a capacitor C1, an inductor L1, and a diode D1, as shown in FIG. 1. The DC power source V1 is a power supply circuit that outputs DC power by rectifying and smoothing AC power supplied from a battery or an AC power source. The switching element Q1 is, for example, an enhancement type N-channel MOSFET (metal-oxide-semiconductor field-effect transistor), and is connected between a cathode of the LEDLD1 of a light source 12 having an LEDLD1, the anode of which is connected to an output terminal on the high potential side of the DC power source V1, and an output terminal on the low potential side of the DC power source V1. A driver 11 is connected to a gate of the switching element Q1, and the switching element Q1 is turned on and off by a PWM (Pulse Width Modulation) signal input from the driver 11. The capacitor C1 is connected between the anode and cathode of the LEDLD1. The inductor L1 is inserted between the cathode of the LEDLD1 and the switching element Q1. The anode of the diode D1 is connected to the other end of the inductor L1 opposite to the end connected to the LEDLD1, and the cathode is connected to the anode of the LEDLD1. The light source 12 also has a resistor R1 connected in series with the LEDLD1. The inductor L1 is for limiting the occurrence of an overcurrent when the switching element Q1 switches to the on state. The diode D1 is for preventing the occurrence of an overvoltage due to the energy stored in the inductor L1 when the switching element Q1 switches from the on state to the off state.

[0011] The lighting device also includes a current measuring unit (not shown) that measures an average current value of a current flowing through the LEDLD1. The driver 11 generates and outputs a PWM signal based on the average current value of the current flowing through the LEDLD1 measured by the current measuring unit, thereby controlling the amount of light emitted from the LEDLD1.

[0012] Here, if the DC voltage supplied from the DC power supply V1 is 24 V and the resistance value of the resistance component of the light source 12 having the LED LD1 is 10 Ω, it is preferable that the capacitance of the capacitor C1 is 30 μF or more and the inductance of the inductor L1 is 10 μH or more.

[0013] When the switching element Q1 is turned on, the voltage across the resistor R1 and LEDLD1 connected in series approaches the output voltage of the DC power supply V1 and becomes approximately 24V, and a current flows through the resistor R1 and LEDLD1. The voltage across the capacitor C1 is also approximately 24V because it is connected in parallel to the resistor R1 and LEDLD1. Next, when the switching element Q1 is turned off, no current flows from the DC power supply V1 through the resistor R1 and LEDLD1. However, since the capacitor C1 is charged with the output voltage of the DC power supply V1, which is approximately 24V, when the switching element Q1 is turned on, a current discharged from the capacitor C1 flows through the circuit consisting of the capacitor C1, resistor R1, and LEDLD1, and even though the switching element Q1 is turned off, a current flows through the LEDLD1 and the LEDLD1 emits light. By selecting a capacitor C1 with an appropriate capacity, the switching element Q1 can be turned on before the discharge current from the capacitor C1 stops flowing, so that the current flowing through the LEDLD1 is not interrupted. That is, in this embodiment, two types of circuits, a circuit that supplies power to LEDLD1 from a DC power supply V1 and a circuit that supplies power to LEDLD1 from a capacitor C1, are alternately realized in accordance with the on / off operation of the switching element Q1.

[0014] Next, the operation of the lighting device according to the present embodiment will be described. FIGS. 2 to 4 show the time profile of the voltage value of the PWM signal when the on-duty of the PWM signal output from the driver 11 to the switching element Q1 is changed, and the time profile of the current value at each of the measurement positions Pos1, Pos2, and Pos3 in FIG. 1. In addition, in FIGS. 2 to 4, "VG" indicates the time profile of the voltage value of the PWM signal, and "Pos1", "Pos2", and "Pos3" indicate the time profile of the current value at each of the measurement positions Pos1, Pos2, and Pos3, respectively. In FIGS. 2 to 4, the ratios of the times T1, T2, and T3 during which the switching element Q1 is maintained in the on-state to the repetition period Ta when the switching element Q1 repeats the on-off operation are set to 10%, 50%, and 90%, respectively. As shown in FIGS. 2 to 4, it can be seen that the time profiles of the current values ​​at the measurement positions Pos1 and Pos2 change significantly by changing the on-duty of the PWM signal. On the other hand, the time profile of the current value at the measurement position Pos3 was observed to have a low ripple rate regardless of the magnitude of the on-duty of the PWM signal. From these, it can be seen that in the lighting device according to the present embodiment, the current flowing through the LEDLD1 is kept substantially constant regardless of the magnitude of the on-duty of the PWM signal, and therefore the variation in the intensity of the light emitted from the LEDLD1 is suppressed.

[0015] As described above, in the lighting device according to the present embodiment, the capacitor C1 is connected between the anode and cathode of the LEDLD1, thereby smoothing the current flowing through the LEDLD1. In addition, when the switching element Q1 is in the off state, the current accompanying the release of the energy stored in the inductor L1 is supplied to the LEDLD1 through the diode D1, thereby suppressing the decrease in the current flowing through the LEDLD1. Therefore, since the variation in the current flowing through the LEDLD1 can be suppressed regardless of the on / off state of the switching element Q1, the variation in the intensity of the light emitted from the light source 12 having the LEDLD1 can be suppressed.

[0016] Incidentally, in the case of conventional dimming control by PWM of LEDLD1, if a capacitor C1 is connected in parallel with LEDLD1, the duty ratio cannot be controlled and the resolution of the light amount in dimming is reduced, so connecting the capacitor C1 in parallel with LEDLD1 is not considered. In contrast, in this embodiment, the current value of the current flowing through LEDLD1 is measured, and dimming control of the light source 12 is performed based on the average current value of the current flowing through LEDLD1.

[0017] Although the embodiments of the present invention have been described above, the present invention is not limited to the configurations of the above-mentioned embodiments. For example, a P-channel MOSFET, a bipolar transistor, or the like may be used as the switching element Q1.

[0018] Although the embodiments and modifications of the present invention have been described above, the present invention is not limited to these. The present invention includes appropriate combinations of the embodiments and modifications, and appropriate modifications thereto. [Industrial Applicability]

[0019] The present invention is suitable as a lighting device for dimming an LED. [Explanation of symbols]

[0020] 11: driver, 12: light source, C1: capacitor, D1: diode, LD1: LED, Q1: switching element, Pos1, Pos2, Pos3: measurement position, R1: resistor

Claims

[Claim 1] A DC power source; a switching element connected between a cathode of a light-emitting diode of a light source having an anode connected to a high-potential output end of the DC power supply and a low-potential output end of the DC power supply; a capacitor connected between the anode and cathode of the light emitting diode; an inductor interposed between the cathode of the light emitting diode and the switching element; a diode having an anode connected to an end of the inductor opposite to the end connected to the light emitting diode and a cathode connected to the anode of the light emitting diode, Lighting device.

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