lighting equipment

Abstract

To provide to obtain a lighting device capable of reducing energy consumption.SOLUTION: A lighting device includes a series circuit in which a light source unit, a switching element, and a current detection resistor are connected in series, a power supply circuit that is supplied with power from an AC power supply, and generates an output voltage including a ripple component based on the AC power supply between both the ends of the series circuit to cause the light source unit to light, and a controller which has a first mode and a second mode as operation modes, and controls the switching element and the control unit that controls the power supply circuit and the power supply circuit. In the first mode, the controller changes the impedance of the switching element so that the voltage generated in the current detection resistor matches a target voltage, and in the second mode, the controller makes the impedance of the switching element smaller than that in the first mode, and controls the power supply circuit so that the voltage generated in the current detection resistor matches a target voltage.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 discloses an LED driver that converts AC input power into desired DC output power and supplies it to an LED load. The LED driver includes a switching element that is on / off controlled, a ripple current reduction unit, and a control circuit. The ripple current reduction unit is connected in series with the LED load and reduces the current ripple flowing through the LED load. The control circuit controls the DC output power to a predetermined value by controlling the on / off of the switching element based on a feedback voltage at the connection point between the LED load and the ripple current reduction unit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-164633 Summary of the Invention [Problem to be solved by the invention]

[0004] In an LED driver such as that disclosed in Patent Document 1, a power conversion circuit performs power factor correction to suppress harmonic currents in the AC power supply from the voltage obtained by rectifying the AC power supply. Even if the output voltage of the power conversion circuit contains ripple components, the ripple current reduction unit can prevent the ripple components from being superimposed on the LED current. Specifically, the ripple components are suppressed by full-wave rectifying the AC power supply, resulting in a frequency component twice that of the AC power supply. Superimposing a frequency component twice that of the AC power supply on the LED current can cause a flickering phenomenon known as optical flicker in imaging devices such as surveillance cameras.

[0005] However, in the control described in Patent Document 1, a loss calculated from the ripple voltage and LED current occurs in the ripple current reduction section. This loss is considered necessary for removing the ripple component. However, light flicker caused by the ripple component cannot be detected by the human eye. Therefore, if the lighting device is used in an environment where light flicker does not have an effect, the loss in the ripple current reduction section becomes unnecessary loss. This may result in a loss that reduces the energy consumption achieved by using LED lighting.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a lighting device that can reduce energy consumption. [Means for solving the problem]

[0007] The lighting device according to the present disclosure includes: a series circuit in which a light source unit, a switching element, and a current detection resistor are connected in series; a power supply circuit that receives power from an AC power source and generates an output voltage including a ripple component based on the AC power source across both ends of the series circuit to light up the light source unit; and a control unit that has a first mode and a second mode as operation modes and controls the switching element and the power supply circuit, wherein in the first mode, the control unit changes the impedance of the switching element so that a voltage generated across the current detection resistor matches a target voltage, and in the second mode, the control unit changes the impedance of the switching element so that a voltage generated across the current detection resistor matches a target voltage. is in the fully on state. A lighting device characterized in that the impedance of the switching element is made smaller than in the first mode, and the power supply circuit is controlled so that the voltage generated across the current detection resistor matches a target voltage. [Effects of the Invention]

[0008] In the lighting device according to the present disclosure, when the control unit is in the second mode, the impedance of the switching element is set to be smaller than when the control unit is in the first mode, thereby reducing energy consumption. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a circuit block diagram of a lighting device according to a first embodiment. [Figure 2] 5A and 5B are diagrams illustrating current and voltage waveforms of the lighting device according to the embodiment. [Figure 3] FIG. 10 is a circuit block diagram of a lighting device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] The lighting device according to each embodiment will be described with reference to the drawings. The same or corresponding components are designated by the same reference numerals, and the repeated description may be omitted.

[0011] Embodiment 1 FIG. 1 is a circuit block diagram of a lighting device 100 according to a first embodiment. The lighting device 100 includes a lighting device 10 and a light source unit 30. The lighting device 10 includes a rectifier DB that rectifies commercial power supply AC, which is an AC power source, and a capacitor C1 that charges the rectified voltage. The voltage generated in the capacitor C1 is a full-wave rectified pulsating voltage. The lighting device 10 also includes a flyback circuit that converts this pulsating voltage to a voltage and charges the capacitor C2. The flyback circuit corresponds to the power supply circuit of the lighting device 100.

[0012] Next, the configuration of the flyback circuit will be explained. The positive terminal of capacitor C1 is connected to the primary winding of transformer T1, and the other end of the primary winding is connected to the drain of switching element Q1. Switching element Q1 is, for example, a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). The source of switching element Q1 is connected to the negative terminal of capacitor C1. The negative terminal of capacitor C1 is connected to the circuit reference potential GND of the anode terminal of rectifier DB.

[0013] The gate of the switching element Q1 is connected to the P1 terminal of the lighting control IC 12. The lighting control IC 12 outputs a gate signal to the switching element Q1. The switching element Q1 is an element for driving a flyback circuit. The lighting control IC 12 corresponds to a power supply circuit control unit that controls the flyback circuit, which is a power supply circuit.

[0014] Transformer T1 has a secondary winding magnetically coupled to its primary winding. One end of the secondary winding is connected to the anode of diode D1, and the other end is connected to GND. The cathode of diode D1 is connected to the positive terminal of capacitor C2, and the negative terminal of capacitor C2 is connected to GND.

[0015] The positive electrode of capacitor C2 is connected to the anode side of the LED provided in light source unit 30. Light source unit 30 is composed of multiple LEDs. In FIG. 1, light source unit 30 has four LEDs connected in series. Light source unit 30 may have one or more LEDs. Furthermore, the multiple LEDs provided in light source unit 30 may be connected in series, in parallel, or in a series-parallel configuration. Hereinafter, light source unit 30 may be referred to as an LED.

[0016] The cathode side of the LED is connected to the drain of the switching element Q2. The drain of the switching element Q2 is also connected to the P2 terminal of the lighting control IC12 via resistor R4. The P2 terminal of the lighting control IC12 is the voltage feedback detection terminal of the flyback circuit. Resistor R4 is a current limiting resistor. One end of the current detection resistor R1 is connected to the source of the switching element Q2, and the other end of the current detection resistor R1 is connected to GND.

[0017] The gate of the switching element Q2 is connected to the output terminal of the comparator AMP1 via a resistor R3. A voltage V1 generated from the P3 terminal of the lighting control IC 12 is applied to the positive terminal of the comparator AMP1. The voltage V1 is variable. For example, the voltage V1 can be generated by an integrating circuit consisting of a resistor and a capacitor (not shown) based on the duty of a PWM (Pulse Width Modulation) signal output from the P3 terminal.

[0018] An LED current flows through current detection resistor R1, which converts the LED current to a voltage. The negative terminal of comparator AMP1 is connected to the connection point between the source of switching element Q2 and current detection resistor R1 via resistor R2. Capacitor C3 is connected between the negative terminal and output terminal of comparator AMP1. Capacitor C3 is a phase compensation capacitor. Resistor R2 is provided for current limiting and integration with capacitor C3. Switching element Q2 is driven according to the comparison result of comparator AMP1.

[0019] Furthermore, the resistor R2 is connected to the P4 terminal of the lighting control IC 12. The P4 terminal of the lighting control IC 12 is a current feedback detection terminal of the flyback circuit.

[0020] An operation switching signal is input to the P5 terminal of the lighting control IC 12 from the operation mode switching unit 20, which switches between a first mode and a second mode (described later). The operation mode switching unit 20 is, for example, a slide switch provided on the outer casing of the lighting device 100 or a communication unit that receives a signal. The operation switching signal is input to the P5 terminal by, for example, switching the slide switch or receiving an infrared remote control signal. The operation switching signal is a trigger signal that allows the user to switch the operation mode.

[0021] The switching element Q2, comparator AMP1, capacitor C3, and resistor R3 correspond to the current limiting circuit 14, which will be described later. The voltage V1 is the target command value for the current limiting circuit 14. The comparator AMP1 corresponds to the impedance control unit, which will be described later. Hereinafter, the lighting control IC 12 and the impedance control unit may be collectively referred to as the control unit. The control unit has a first mode and a second mode as its operating modes, and controls the switching element Q2 and the flyback circuit.

[0022] Fig. 2 is a diagram showing current and voltage waveforms of the lighting device 100 according to the embodiment. The operation of the lighting device 100 will be described using the time chart shown in Fig. 2. First, the operation from time T0 to T1 will be described. During this period, the current limiting circuit 14 is on, and the operation mode of the control unit is the first mode.

[0023] A pulsating voltage is applied to capacitor C1 from the commercial power supply AC via rectifier DB. This pulsating voltage is also called a full-wave rectified voltage. This voltage is applied to switching element Q1 via the primary winding of transformer T1. Switching element Q1 performs switching operation. When switching element Q1 turns on, energy is generated in the primary winding of transformer T1. When switching element Q1 turns off, a voltage proportional to the turns ratio is generated in the secondary winding.

[0024] The high-frequency secondary winding voltage obtained by turning switching element Q1 on and off in this way is rectified by diode D1 and charged as a smooth voltage to capacitor C2. As shown in Figure 2, the voltage of capacitor C2 contains the frequency of the pulsating voltage applied to capacitor C1, i.e., a frequency component twice that of the commercial AC power supply.

[0025] The P2 terminal is a detection terminal that detects the drain voltage of the switching element Q2. The lighting control IC12 controls the drain voltage of the switching element Q2 to be constant based on the voltage of the P2 terminal. The drain voltage of the switching element Q2 is equal to the sum of the voltage of the current detection resistor R1 and the drain-source voltage of the switching element Q2. The drain voltage of the switching element Q2 is also equal to the voltage of the capacitor C2 minus the LED voltage.

[0026] The lighting control IC12 controls the drive voltage output from the P1 terminal according to the voltage detected from the P2 terminal, thereby controlling the on-time of the switching element Q1. If the voltage at the P2 terminal is lower than a reference voltage stored in the lighting control IC12, the lighting control IC12 lengthens the on-time of the drive voltage output from the P1 terminal. Conversely, if the voltage at the P2 terminal is higher than the reference voltage, the lighting control IC12 shortens the on-time of the drive voltage output from the P1 terminal. By actively repeating these operations, the drain voltage of the switching element Q2 can be maintained at a constant voltage. In this way, in the first mode, the lighting control IC12 performs constant voltage control of the flyback circuit based on the drain voltage of the switching element Q2.

[0027] The lighting control IC12 controls the switching element Q1 with a constant on-width during the commercial power cycle, achieving a high power factor. The capacitance of capacitor C1 must be set so that the voltage generated across capacitor C1 is a pulsating voltage. As a result, a ripple voltage containing twice the frequency of the commercial AC power source is generated across capacitor C2. However, by controlling the switching of the flyback circuit with a constant on-width, the input current can be controlled to follow the input voltage, enabling high power factor control.

[0028] A series circuit is connected in parallel with the capacitor C2. The series circuit is made up of the light source 30, the switching element Q2, and the current detection resistor R1. The flyback circuit receives power from the AC commercial power supply and generates an output voltage across the series circuit that includes a ripple component based on the AC commercial power supply. This turns on the light source 30.

[0029] Here, the lighting control IC 12 may perform constant voltage control so that the voltage of capacitor C2 is constant. In other words, the P2 terminal may detect the voltage of capacitor C2. The drain voltage of switching element Q2 is equal to the voltage of capacitor C2 minus the LED voltage. Furthermore, the LED voltage is generally a design factor. Therefore, constant voltage control of the drain voltage of switching element Q2 can be said to be equivalent to constant voltage control of the voltage of capacitor C2.

[0030] On the other hand, constant voltage control of the drain voltage of switching element Q2 reduces losses during current control by switching element Q2. When constant voltage control of capacitor C2 voltage is used, the voltage of capacitor C2 must be set taking into account the maximum LED voltage value, taking into account temperature characteristics and individual variations. Therefore, if the LED voltage is lower than expected due to temperature characteristics and individual variations, the voltage that switching element Q2 must handle may increase.

[0031] Next, the operation of the current limiting circuit 14 in the first mode will be described. The voltage charged in capacitor C2 is supplied to the series circuit formed by the LED, switching element Q2, and current detection resistor R1. Switching element Q2 is driven by comparator AMP1, which forms an inverting amplifier circuit. Comparator AMP1 performs feedback control on switching element Q2 based on the result of comparing voltage V1 with the voltage generated across current detection resistor R1. In other words, comparator AMP1 controls switching element Q2 so that the detected voltage across current detection resistor R1 is constant and equal to voltage V1.

[0032] The voltage generated across current detection resistor R1 is the product of the LED current and the resistance of current detection resistor R1. The lighting control IC12 generates voltage V1 as the target value of the LED current and outputs it from terminal P3. In other words, in the first mode, the control unit changes the impedance of switching element Q2 so that the voltage generated across current detection resistor R1 matches the target voltage. In this way, comparator AMP1 functions as an impedance control unit that controls the impedance of switching element Q2. In other words, comparator AMP1 performs current limiting control by operating as a constant current regulator.

[0033] The voltage applied between the drain and source of the switching element Q2 is the voltage applied to capacitor C2 minus the LED voltage and the voltage applied to current detection resistor R1. As shown in Figure 2, the impedance of switching element Q2 is adjusted to limit the current, including the ripple voltage contained in the voltage of capacitor C2. This makes it possible to remove the ripple component from the LED voltage, and therefore the LED current.

[0034] In this way, the ripple component can be removed from the LED current by the current limiting circuit 14. At this time, a loss equivalent to the product of the drain-source voltage and the LED current occurs in the switching element Q2.

[0035] Next, we will explain the operation after time T1. During this period, the current limiting circuit 14 is off, and the control unit is in the second operating mode. At this time, current limiting is not performed by the impedance of the switching element Q2. The lighting control IC 12 generates a voltage V1 that is higher than the target value of the LED current, and outputs it from the P3 terminal.

[0036] Furthermore, from time T1 onwards, the lighting control IC12 controls the flyback circuit so that the voltage generated across the current detection resistor R1 matches the target voltage. The P4 terminal was not directly related to feedback control from time T0 to T1. From time T1 onwards, the lighting control IC12 detects the voltage generated across the current detection resistor R1 from the P4 terminal and performs constant current control of the LED current based on the detected voltage. Furthermore, the P2 terminal was a detection terminal for constant voltage control from time T0 to T1, but from time T1 onwards it is no longer directly related to feedback control. However, high power factor control remains in place so that the on-width of the switching element Q1 remains constant relative to the commercial power cycle.

[0037] Comparator AMP1 drives switching element Q2 based on the comparison result between voltage V1 and the voltage across current detection resistor R1. In the second mode, voltage V1 is set to a voltage higher than the voltage across current detection resistor R1, so a high voltage is applied to the gate of switching element Q2. From time T0 to time T1, switching element Q2 is in a so-called half-on state in which its impedance is adjusted. However, after time T1, the impedance of switching element Q2 decreases, and switching element Q2 enters a so-called fully-on state. In other words, in the second mode, the control unit reduces the impedance of switching element Q2 compared to the first mode. At this time, the voltage between the drain and source becomes approximately zero.

[0038] At this time, the voltage of capacitor C2 drops by an amount substantially equal to the voltage ΔV generated between the drain and source of switching element Q2 in the first mode, as shown in Figure 2. In other words, the output voltage of the flyback circuit is smaller in the second mode than in the first mode.

[0039] In addition, in the second mode, the impedance of the switching element Q2 is not adjusted. Therefore, the LED voltage is superimposed with the ripple voltage generated in the capacitor C2. In other words, a ripple component is generated in the LED current. In this way, in the second mode when the current limiting circuit 14 is off, a ripple component is generated in the LED current, while the loss of the switching element Q2 is minimized.

[0040] As described above, this embodiment can reduce the energy consumption of the lighting device 100. Furthermore, it is possible to select between lighting that suppresses light flicker and lighting that is highly efficient and has a high energy-saving effect without removing ripple components. The operation mode can be switched by, for example, the user operating a trigger signal for switching the operation mode.

[0041] Furthermore, the lighting device 100 can switch between operation modes without replacing parts, etc. Therefore, the lighting device 100 can be configured for any purpose, contributing to the standardization of parts and resource conservation.

[0042] In this embodiment, the lighting control IC 12 and the impedance control unit are provided as separate control units. However, this is not limiting, and the lighting control IC 12 and the impedance control unit may be a single control unit. The lighting control IC 12 is, for example, a microcomputer. The lighting control IC 12 has, for example, a processor and a memory. The processor reads and executes a program stored in the memory to achieve the above-mentioned control. The memory stores, for example, the target voltage and reference voltage for the above-mentioned constant current control and constant voltage control.

[0043] These modifications can be applied as appropriate to the lighting devices according to the following embodiments. Note that the lighting devices according to the following embodiments have many points in common with embodiment 1, so the following description will focus on the differences from embodiment 1.

[0044] Embodiment 2 FIG. 3 is a circuit block diagram of a lighting device 200 according to embodiment 2. The difference from FIG. 1 is that the lighting control IC 12 does not have a P4 terminal. In embodiment 1, in the second mode, the lighting control IC 12 performs constant current control of the LED current from the flyback circuit using a signal detected from the P4 terminal. In this embodiment, although the lighting control IC 12 also performs constant current control of the LED current from the flyback circuit in the second mode, it detects the LED current from the P2 terminal.

[0045] In other words, in the first mode, the lighting control IC 12 performs constant voltage control of the flyback circuit based on the drain voltage detected from the P2 terminal, and in the second mode, the lighting control IC 12 detects the voltage generated across the current detection resistor R1 using the P2 terminal and performs constant current control of the flyback circuit. In the second mode, the impedance of the switching element Q2 is small. Therefore, it is possible to detect the voltage across the current detection resistor R1 using the drain voltage of the switching element Q2.

[0046] Even when the switching element Q2 is fully on, it has an on-resistance between its drain and source. However, this value is a design factor. In general, the current detection resistor R1 is often set to a value significantly larger than the on-resistance of the switching element Q2. This allows the detection terminal for the LED current and the detection terminal for the drain voltage of the switching element Q2 to be shared. In this way, the configuration of the lighting device 200 can be simplified in this embodiment.

[0047] The technical features described in each embodiment may be used in appropriate combination. [Explanation of symbols]

[0048] 10 lighting device, 14 current limiting circuit, 20 operation mode switching unit, 30 light source unit, 100 lighting device, 200 lighting device, AC commercial power supply, AMP1 comparator, C1, C2, C3 capacitor, D1 diode, DB rectifier, Q1, Q2 switching element, R1 current detection resistor, R2, R3, R4 resistors, T1 transformer

Claims

1. a series circuit in which a light source unit, a switching element, and a current detection resistor are connected in series; a power supply circuit that receives power from an AC power supply, generates an output voltage including a ripple component based on the AC power supply across both ends of the series circuit, and lights up the light source unit; a control unit having a first mode and a second mode as operation modes and controlling the switching element and the power supply circuit; Equipped with In the first mode, the control unit changes the impedance of the switching element so that the voltage generated across the current detection resistor matches a target voltage; In the second mode, the control unit controls the power supply circuit so that the switching element is fully on, reducing the impedance of the switching element compared to the first mode, and the voltage generated across the current detection resistor matches a target voltage.

2. 2. The lighting device according to claim 1, wherein the output voltage of the power supply circuit is smaller in the second mode than in the first mode.

3. The lighting device according to claim 1 , further comprising an operation mode switching unit for switching between the first mode and the second mode.

4. 4. The lighting device according to claim 1, wherein the control unit includes an impedance control unit that controls an impedance of the switching element, and a power supply circuit control unit that controls the power supply circuit.

5. 5. The lighting device according to claim 1, wherein the control unit has a detection terminal that detects a drain voltage of the switching element, and in the first mode, performs constant voltage control of the power supply circuit based on the drain voltage.

6. 6. The lighting device according to claim 5, wherein in the second mode, the control unit detects a voltage generated in the current detection resistor by the detection terminal and performs constant current control on the power supply circuit.

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