Lighting devices and lighting fixtures

Abstract

This system enables high-precision dimming of lighting devices and fixtures with a simple and inexpensive circuit configuration. [Solution] According to the embodiment, the lighting device 5 comprises a power conversion unit 8 having a switching element 41, an inductor 43, and an output capacitor 44, which converts input power supplied from a DC power supply or AC power supply into a desired DC current supply power and supplies it to the light source 2a; a control circuit 110 which receives a dimming signal and outputs a drive signal to the power conversion unit 8 accordingly; and a feedback voltage processing circuit 120 which has a non-inverting amplifier circuit 130 and outputs a supply voltage, which is the voltage of the supply power, to the control circuit 110. The feedback voltage processing circuit 120 has an offset voltage source 124 which adds a positive offset voltage to the supply voltage, and an inverting side input resistor 126 which has one end connected to the inverting input of the non-inverting amplifier circuit 130 and the other end connected to the offset voltage source 124.

Description

Technical Field

[0001] Embodiments of the present invention relate to a lighting device and a lighting fixture.

Background Art

[0002] As a lighting device for a light source such as an LED, for example, an example having an error amplifier unit is known. The error amplifier unit compares a feedback voltage based on the current flowing through the light source with a reference voltage, and adjusts the amplification factor and the amplification speed based on the magnitude of the deviation. Here, an increase in the absolute value of the difference between the feedback voltage and the reference voltage enables more accurate adjustment of the response speed on the load side including the light source of the error amplifier unit.

[0003] In such a lighting device, when adjusting the light source, on the lower limit side of dimming, the magnitude of the voltage generated in the current detection resistor becomes small, and it may be difficult to detect the voltage and perform high-precision dimming. However, increasing the current detection resistor enables an increase in the detection voltage, but it causes an increase in the loss of the circuit.

[0004] There is known a countermeasure technique including an arithmetic unit that performs offset correction by subtracting an offset voltage from a voltage amplified by an amplifier after inputting an offset voltage output from an offset circuit and a voltage based on a direct current flowing through a light source. However, in this case, the circuit configuration and arithmetic processing of the arithmetic unit become complicated. Therefore, in a lighting device and a lighting fixture, it is desired to enable high-precision dimming with a simpler and less expensive circuit configuration.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The embodiment of the present invention aims to provide a lighting device and lighting fixture that enable high-precision dimming with a simple and inexpensive circuit configuration. [Means for solving the problem]

[0007] To achieve the above objective, the lighting device according to the embodiment comprises a power conversion unit having at least one switching element, an inductor, and an output capacitor, which converts input power supplied from an AC or DC power source into DC supply power and supplies the supply power to a light source; a control unit having a dimming signal and outputting a drive signal to the power conversion unit in accordance with the dimming signal; and a feedback voltage processing circuit having a non-inverting amplifier circuit and feeding back a feedback voltage corresponding to the supply voltage, which is the voltage of the supply power, to the control unit, wherein the feedback voltage processing circuit comprises an offset voltage source that adds a positive offset voltage to the supply voltage and inputs it to the non-inverting input of the non-inverting amplifier circuit; and an inverting side input resistor, one end of which is connected to the inverting input of the non-inverting amplifier circuit and the other end of which is connected to the offset voltage source. [Effects of the Invention]

[0008] According to embodiments of the present invention, it is possible to provide a lighting device and lighting fixture that enable high-precision dimming with a simple and inexpensive circuit configuration. [Brief explanation of the drawing]

[0009] [Figure 1] This is a block diagram showing an example configuration of a lighting fixture including a lighting device according to an embodiment. [Figure 2] This graph shows the dependence of the amplification voltage of the feedback circuit of the lighting device according to the embodiment on the light source current. [Figure 3] This graph illustrates the operational amplifier offset voltage of the lighting device according to the embodiment. [Figure 4]This graph shows the dependence of the feedback voltage of the feedback circuit in a lighting device on the light source current in a reference example. [Modes for carrying out the invention]

[0010] The following describes the lighting device and lighting fixture according to the embodiment of the present invention with reference to the drawings. Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the ratio of the sizes of the parts, etc., are not necessarily the same as those of actual objects. Furthermore, even when representing the same part, the dimensions and ratios may differ between drawings. Also, parts that are identical or similar to each other are denoted by a common reference numeral, and overlapping explanations are omitted.

[0011] Figure 1 is a block diagram showing an example configuration of a lighting fixture 3 including a lighting device 5 according to an embodiment. The lighting fixture 3 has a light source module 2 and a lighting device 5 that supplies DC current to it.

[0012] The light source module 2 has one or more light sources 2a and a connection part 2b. The light source module 2 is detachably connected to the lighting device 5 via the connection part 2b.

[0013] Figure 1 illustrates the case where there is one light source 2a, but the number of light sources 2a can be any number. When there are multiple light sources 2a, each light source 2a may be connected in series or in parallel. Alternatively, multiple light sources 2a may be arranged in a combination of series and parallel connections.

[0014] For example, a light-emitting diode (LED) can be used as the light source 2a. The light source 2a may also be, for example, an organic light-emitting diode (OLED), an inorganic electroluminescent light-emitting element, an organic electroluminescent light-emitting element, or other electroluminescent light-emitting elements. Alternatively, the light source 2a may be, for example, a light bulb.

[0015] The lighting device 5 converts the input power supplied from the power source 1, which is either a DC power source or an AC power source, into a desired supply power, and supplies this DC current to the light source module 2.

[0016] Here, power source 1 is a source of AC power, such as a commercial power supply or a private generator. Power source 1 may also be a DC power source. If power source 1 is a DC power source, the lighting device 5 converts the DC power into another DC power with a different current or voltage value and supplies it to the light source module 2.

[0017] The lighting device 5 is used in common for multiple types of light source modules 2, for example, that differ in at least one of the brightness and color (color temperature) of the light they emit. This suppresses the increase in manufacturing costs of the lighting fixture 3 compared to, for example, manufacturing a dedicated lighting device for each of the multiple types of light source modules 2.

[0018] The lighting device 5 converts the AC power supplied from the power source 1 into DC power corresponding to the light source module 2, and supplies the converted DC power to the light source module 2. This causes the lighting device 5 to light up the light source module 2.

[0019] The lighting device 5 includes a power conversion unit 8 and a control unit 100.

[0020] The power conversion unit 8 is a power path from receiving AC power from the power source 1 to supplying DC power to the light source module 2, and is composed of elements for power conversion. The control unit 100 controls the operation of the elements for power conversion in the power conversion unit 8.

[0021] The power conversion unit 8 has a full-wave rectifier circuit 10, a high-frequency removal capacitor 11, a power factor correction circuit 20, a smoothing capacitor 30, a converter 40, and a connection part 50 that is detachably connected to the connection part 2b of the light source module 2.

[0022] When the power source 1 is a DC power source, the full-wave rectifier circuit 10, the high-frequency removal capacitor 11, the power factor correction circuit 20, and the smoothing capacitor 30 may not be provided.

[0023] In the following description, in the arrangement from the full-wave rectifier circuit 10 connected to the power source 1 to the connection part 50 connected to the light source module 2, the upstream side means the side relatively closer to the power source 1, and the downstream side means the side relatively closer to the light source module 2.

[0024] The full-wave rectifier circuit 10 rectifies the AC power input from the power source 1 and converts it into rectified power. For example, a diode bridge combining four rectifying elements is used for the full-wave rectifier circuit 10. That is, the full-wave rectifier circuit 10 is a full-wave rectifier. The rectified power is, for example, pulsating DC power.

[0025] The full-wave rectifier circuit 10 has a pair of input terminals 10a, 10b, a high-potential output terminal 10c, and a low-potential output terminal 10d. The input terminals 10a, 10b convert the power from the power source 1 into rectified power and output it from the high-potential output terminal 10c and the low-potential output terminal 10d. The potential of the low-potential output terminal 10d is set to a reference potential (for example, ground potential). The potential of the high-potential output terminal 10c is set to a potential higher than the potential of the low-potential output terminal 10d.

[0026] The full-wave rectifier circuit 10 may also be a half-wave rectifier or the like. Alternatively, the rectified voltage may be a full-wave rectified pulsating current or a half-wave rectified pulsating current. For example, a Schottky barrier diode is used in the full-wave rectifier circuit 10. This improves the responsiveness of the full-wave rectifier circuit 10.

[0027] The high-frequency rejection capacitor 11 removes the high-frequency components of the rectified high-frequency power and smooths the rectified high-frequency power, thereby converting it into pulsating power.

[0028] In the example shown in Figure 1, the power factor correction circuit 20 includes an inductor 21, a switching element 22, and a diode 23. Specifically, the power factor correction circuit 20 is a boost chopper. That is, the forward upstream end (anode side) of the diode 23 is connected to the downstream side of the inductor 21, and one end of the switching element 22 is connected to the connection point between the inductor 21 and the diode 23. Note that the power factor correction circuit 20 is not limited to a boost chopper; other configurations are also possible as long as the power factor of the input power can be improved.

[0029] The power factor correction circuit 20 improves the power factor by controlling the on / off state of a switching element 22 based on the output from the high-frequency rejection capacitor 11 and the full-wave rectified voltage from the full-wave rectifier circuit 10.

[0030] The switching element 22 has electrodes 22a, 22b, and 22c. One end of the inductor 21 is electrically connected to the high-potential output terminal 10c. The other end of the inductor 21 is electrically connected to electrode 22a. Electrode 22b is electrically connected to the low-potential output terminal 10d. The anode of the diode 23 is electrically connected to electrode 22a. The cathode of the diode 23 is electrically connected to one end of the smoothing capacitor 30. The other end of the smoothing capacitor 30 is electrically connected to the low-potential output terminal 10d.

[0031] Electrode 22c is electrically connected to the control unit 100. Electrode 22c is a so-called control electrode. The switching element 22 switches in response to a signal from the control unit 100. The power factor correction circuit 20 improves the power factor, for example, by switching the switching element 22 and bringing the shape of the envelope of the input current closer to the half-waveform of a sinusoidal voltage.

[0032] The switching element 22 is, for example, an n-channel FET. For example, electrode 22a is the drain, electrode 22b is the source, and electrode 22c is the gate. Alternatively, the switching element 22 may be, for example, a p-channel FET or a bipolar transistor.

[0033] The smoothing capacitor 30 converts the power after power factor correction into DC power by smoothing the output voltage after power factor correction. The smoothing capacitor 30 supplies the DC power to the converter 40.

[0034] The converter 40 converts the DC power from the smoothing capacitor 30 into a desired DC current supply power and supplies this DC current to the light source 2a.

[0035] The converter 40 has a first input terminal 31, a second input terminal 32, a first output terminal 45a, and a second output terminal 45b. The first input terminal 31 is electrically connected to one end of the high-potential side of the smoothing capacitor 30. The second input terminal 32 is electrically connected to the low-potential output terminal 10d of the smoothing capacitor 30. As a result, DC power is supplied to the converter 40 from the smoothing capacitor 30.

[0036] The converter 40 consists of a step-down chopper, an output capacitor 44 downstream of the step-down chopper, and a current sensing resistor 46 that detects the load current and converts it into a supply voltage. In the example shown in Figure 1, the converter 40 includes a switching element 41, a diode 42, an inductor 43, and an output capacitor 44. Specifically, the converter 40 has a step-down chopper in which the inductor 43 is connected downstream of the switching element 41, and the forward downstream end of the diode 42 is connected to the connection point between the switching element 41 and the inductor 43. Note that the converter 40 is not limited to a step-down chopper, and may have other circuits as long as it can convert the input DC power into DC power having a desired DC current.

[0037] The switching element 41 has electrodes 41a, 41b, and 41c. Electrode 41a is electrically connected to the first input terminal 31. Electrode 41b is electrically connected to the cathode of diode 42. The anode of diode 42 is electrically connected to the low-potential output terminal 10d. One end of inductor 43 is electrically connected to electrode 41b. The other end of inductor 43 is electrically connected to the first output terminal 45a. The second output terminal 45b is electrically connected to the low-potential output terminal 10d (second input terminal 32). Electrode 41c of the switching element 41 is a so-called control electrode, and it controls the switching element 41 by command from the control unit 100.

[0038] The switching element 41 is, for example, an n-channel field-effect transistor (FET). For example, electrode 41a is the drain, electrode 41b is the source, and electrode 41c is the gate. Alternatively, the switching element 41 may be, for example, a p-channel FET or a bipolar transistor. Electrode 41c switches the switching element 41 on or off according to a command from the control unit 100.

[0039] The output capacitor 44 has a first electrode 44a and a second electrode 44b. The first electrode 44a is electrically connected to the first output terminal 45a. The second electrode 44b is electrically connected to the second output terminal 45b. The output capacitor 44 is connected in parallel between the first output terminal 45a and the second output terminal 45b. The output capacitor 44 smooths the current flowing between the first electrode 44a and the second electrode 44b of the output capacitor 44 through the switching operation of the switching element 41. As a result, DC power is output from the first output terminal 45a and the second output terminal 45b.

[0040] In this example, the converter 40 is a step-down chopper circuit as described above. The converter 40 converts DC power to another DC power by stepping down the voltage of the input power. Thus, the converter 40 is, for example, a constant current circuit and supplies a substantially constant DC current to the light source 2a of the light source module 2.

[0041] The first output terminal 45a is the high-potential output terminal, and the second output terminal 45b is the low-potential output terminal. The potential of the first output terminal 45a is higher than the potential of the second output terminal 45b. The potential of the first electrode 44a is set higher than the potential of the second electrode 44b. The first electrode 44a is, for example, the anode, and the second electrode 44b is, for example, the cathode. Conversely, the potential of the second output terminal 45b may be higher than the potential of the first output terminal 45a.

[0042] The configuration of the converter 40 described above is not limited to the step-down chopper circuit described above. The converter 40 may be configured in any other way as long as it can convert DC power to another DC power.

[0043] The control unit 100 receives a dimming signal, which is a request for dimming level from an external source, and controls the switching element 41 of the converter 40 so that the converter 40 supplies a DC current to the light source module 2 according to the dimming level.

[0044] The control unit 100 includes a control circuit 110 and a feedback voltage processing circuit 120 that feeds back a feedback voltage corresponding to the converted supply voltage in the converter 40 to the control circuit 110.

[0045] The control circuit 110 includes a reference value generation unit 111, a control calculation unit 112, and a drive signal generation unit 113.

[0046] The reference value generation unit 111 receives a dimming signal from the dimming signal unit 4, converts and corrects it as needed, and generates a reference value for control calculations in the control calculation unit 112. The dimming signal is input to the reference value generation unit 111 via wired or wireless connection from, for example, a remote control, a switch on the wall, or an operating unit on the lighting fixture 3 (lighting device 5). Here, the dimming signal is a signal that can appropriately represent the dimming degree, such as a PWM signal with a duty cycle corresponding to the dimming degree, or an AC voltage whose conduction angle is controlled by a dimmer. The signal output from the reference value generation unit 111 has the offset voltage Vs component, which will be described later, added to it to become the reference value. Here, the offset voltage Vs component may be read from an external input by the control circuit 110 and stored in the control circuit 110. Alternatively, the control circuit 110 may receive the signal from the offset voltage Vs generation part, which will be described later, as the offset voltage Vs component.

[0047] The control calculation unit 112 calculates a feedback signal by performing conversions such as AD conversion of the amplified voltage (A·Vf, described later), which is the feedback voltage, as needed. Furthermore, the control calculation unit 112 compares the feedback signal with a reference signal, which has the dimming degree converted as needed and the offset voltage Vs added, using a comparator (not shown), for example, to perform control calculations so that the feedback signal matches the reference signal. Specifically, for example, the control calculation unit 112 calculates the deviation between the feedback signal and the reference signal, performs PI calculations, etc., and calculates a control signal. Note that the offset voltage Vs is not limited to being added to the reference signal, but may also be subtracted from the feedback signal.

[0048] The drive signal generation unit 113 converts the control signal calculated by the control calculation unit 112 to generate a drive signal that is actually output to the electrode 41c, which is the control electrode of the switching element 41 of the converter 40. Specifically, the drive signal is a signal that changes the on / off period (duty cycle) of the switching element 41, and is, for example, a PWM signal.

[0049] Here, the off state of the switching element 41 is, for example, a state in which substantially no current flows between the main electrodes 41a and 41b. In the off state, for example, a weak current that does not affect the operation of the converter 40 may flow between the electrodes 41a and 41b. In other words, the on state of the switching element 41 is, in other words, a first state in which current flows between the electrodes 41a and 41b, and the off state is a second state in which the current flowing between the electrodes 41a and 41b is smaller than that of the first state. The on and off states of the switching element 22 are the same as those of the switching element 41.

[0050] As described above, the feedback voltage processing circuit 120 converts the supply voltage at the converter 40 and feeds it back to the control circuit 110 as a feedback voltage.

[0051] The feedback voltage processing circuit 120 includes an operational amplifier 121, an input resistor 122, an input capacitor 123, an offset voltage source 124, an offset voltage source resistor 125, an inverting input resistor 126, a voltage divider resistor 127, and an output capacitor 128. The voltage divider resistor 127 has an output voltage divider resistor 127a and a ground voltage divider resistor 127b connected to each other at an intermediate connection section 127c.

[0052] The inductor voltage signal line from the converter 40 is connected to the non-inverting input section 121a of the operational amplifier 121. Here, the inductor voltage signal line consists of an input connection line from the voltage detection point 45c of the converter 40 to the non-inverting input section 121a, an input resistor 122, and an input capacitor 123. The input resistor 122 and the input capacitor 123 constitute an RC filter, which reduces high-frequency components present in the voltage at the voltage detection point 45c of the converter 40.

[0053] An offset voltage line is connected to the summing point 122a between the non-inverting input section 121a and the input resistor 122 of the operational amplifier 121. The offset voltage line includes an offset voltage source 124 and an offset voltage source resistor 125 provided between the positive side of the offset voltage source 124 and the summing point 122a.

[0054] The branch point 125a between the offset voltage source 124 and the offset voltage source resistor 125, and the intermediate connection point 127c of the voltage divider resistor 127 are connected to each other, and an inverting input resistor 126 is provided on the connection line. Here, the inverting input resistor 126 is a variable resistor. In detail, the value RDCn of the inverting input resistor 126 can be set with a range around a value equal to the value RDCp of the offset voltage source resistor 125. Note that Figure 1 illustrates the case where the value RDCn of the inverting input resistor 126 is variable, but it is also possible to make the value RDCp of the offset voltage source resistor 125 variable. Alternatively, both may be variable, or both may be non-variable resistor elements.

[0055] One terminal of the output capacitor 128 is connected to the operational amplifier output section 121x, which is the output side of the operational amplifier 121, and the other terminal is grounded. The output capacitor 128 has the effect of reducing the high-frequency components of the output signal of the operational amplifier 121 and stabilizing the output signal.

[0056] The operational amplifier 121, the input line to the non-inverting input section 121a of the operational amplifier 121, the voltage divider resistor 127, and the input line from the intermediate connection section 127c of the voltage divider resistor 127 to the inverting input section 121b of the operational amplifier 121 constitute a so-called non-inverting amplifier circuit 129. The amplification factor A of the non-inverting amplifier circuit 129 is given by (1 + R1 / R2), where R1 is the resistance value of the output-side voltage divider resistor 127a and R2 is the resistance value of the ground-side voltage divider resistor 127b that constitute the voltage divider resistor 127.

[0057] Figure 2 is a graph showing the dependence of the amplified voltage of the feedback circuit of the lighting device 5 according to the embodiment on the light source current. In Figure 2, the horizontal axis represents the light source current [A], and the vertical axis represents the amplified voltage [V], i.e., the voltage of the operational amplifier output section 121x. Note that the horizontal axis may also represent the voltage of the non-inverting input section 121a. The straight line A1 in Figure 2 shows the dependence of the voltage of the operational amplifier output section 121x on the light source current [A]. In other words, the amplified voltage is the feedback voltage input to the control circuit 110.

[0058] For example, when the light source current is I0, the operational amplifier output voltage Vx1 is the sum of the amplified signal voltage A·Vf and the offset voltage Vs.

[0059] Here, a supply voltage corresponding to the load current supplied from the converter 40 to the light source module 2 is output to the feedback voltage processing circuit 120 as a voltage signal Vf. The amplified signal voltage A·Vf is the amplified voltage obtained by amplifying the voltage signal Vf by a factor A by the operational amplifier 121. The amplification factor A is the amplification factor of the non-inverting amplifier circuit 129.

[0060] Thus, the output voltage Vx1 of the operational amplifier is the sum of the amplified signal voltage A·Vf, which is obtained by amplifying the voltage signal Vf, and the offset voltage Vs, which is a constant value that does not depend on the amplification factor A.

[0061] The operational amplifier 121 is an electronic circuit, and there are limits to the voltage that can be applied to both the non-inverting input section 121a and the inverting input section 121b. On the other hand, in order to improve the accuracy of control, it is preferable that the amplification factor A of the operational amplifier 121 be as high as possible.

[0062] Figure 3 is a graph illustrating the operational amplifier offset voltage of the lighting device 5 according to the embodiment. The horizontal axis represents the light source current [A], and the vertical axis represents the amplified voltage, i.e., the voltage of the operational amplifier output section 121x [V]. The operational amplifier offset voltage will be described later. Figure 3 shows the characteristics of the non-inverting amplifier circuit 129 alone, without the application of an external offset voltage Vs.

[0063] In an ideal operational amplifier, the voltage applied from the offset voltage source 124 through the offset voltage source resistor 125 to the non-inverting input section 121a should be equal to the voltage applied from the offset voltage source 124 through the inverting input resistor 126 to the inverting input section 121b (a so-called virtual short circuit). The solid line A0 in Figure 3 represents this ideal case.

[0064] However, in actual products, there is a subtle variation in the characteristics of each element of the operational amplifier 121. As a result, a small difference called the operational amplifier offset voltage generally occurs between the voltage of the non-inverting input section 121a and the voltage of the inverting input section 121b.

[0065] In Figure 3, the dashed line B1 represents the case where the voltage of the non-inverting input 121a is higher than the voltage of the inverting input 121b. Similarly, the dashed line B2 represents the case where the voltage of the inverting input 121b is higher than the voltage of the non-inverting input 121a. If the characteristics of the operational amplifier 121 are as shown by the dashed line B2, a dead zone will occur near zero of the light source current where the amplified voltage does not change. In other words, a dead zone will occur near the lower limit of dimming. If a dead zone occurs near the lower limit of dimming in this way, there is a concern that the brightness of the light source 2a will not change even when the dimming level is changed. Furthermore, if the characteristics of the operational amplifier 121 are as shown by the dashed line B1, there is a concern that the light will not turn off (dimming off) even when the dimming level is set to 0%.

[0066] To suppress the occurrence of such phenomena, it has been proposed to apply an offset voltage Vs to the non-inverting input section 121a of the operational amplifier 121.

[0067] Figure 4 is a graph showing the dependence of the feedback voltage of the feedback circuit of the lighting device in the reference example, i.e., the countermeasure technology described above, on the light source current. The horizontal axis represents the light source current [A], and the vertical axis represents the amplification voltage [V]. Line A2 in Figure 4 shows the dependence of the output voltage of the operational amplifier on the light source current [A]. The reference example is one in which an offset voltage Vs (voltage of the offset voltage source 124) is applied only to the non-inverting input section 121a.

[0068] In the example, when the light source current is I0, the operational amplifier output voltage Vx2 is the sum of the amplified signal voltage A·Vf, the offset voltage Vs, and the offset voltage amplification factor ΔV. Here, the amplified signal voltage A·Vf is the amplified voltage obtained by amplifying the voltage signal Vf, which is the voltage supplied from the converter to the light source, by the operational amplifier. The offset voltage amplification factor ΔV is the difference between the amplified value of the offset voltage Vs and the original offset voltage Vs, and is given by (A·Vs-Vs). Here, A is the amplification factor of the amplifier, which in the example will vary depending on the load.

[0069] In the example, for instance, the calculation unit amplifies the sum of the voltage offset and the light source current using an amplifier, and then performs offset correction by subtracting the offset voltage from the amplified voltage. In this case, the amplified voltage amplified by the calculation unit will include not only the amplified signal voltage A·Vf and the offset voltage Vs, but also the offset voltage amplification component ΔV.

[0070] Therefore, the calculation unit in the example needed to not only correct the constant offset voltage Vs, but also to handle the offset voltage amplification component ΔV, which depends on the amplification factor A. For this reason, the calculation unit in the example requires a circuit to perform the calculations related to this handling. Consequently, the circuit configuration and calculation processing of the calculation unit in the example become complex.

[0071] Furthermore, there is an upper limit to the magnitude of the amplification voltage, for example, due to the characteristics of the control calculation unit 112. Therefore, as shown in Figure 4, if the magnitude of the amplification voltage when the light source current is zero becomes large due to the offset voltage Vs and the offset voltage amplification component ΔV, the range of change in the amplification voltage in response to changes in the light source current becomes smaller. In other words, the amplification factor is forced to decrease. This, for example, reduces the control resolution of the light source current. As a result, the control performance of the dimming level deteriorates.

[0072] To suppress the decrease in the control resolution of the light source current as described above, it has also been proposed to reduce the amplification factor of the non-inverting amplifier circuit 129 in accordance with the increase in the light source current.

[0073] However, in this case, the circuit configurations of the control calculation unit 112 and the non-inverting amplifier circuit 129 become more complex. Furthermore, in this case, it becomes difficult to reduce the resistance value of the current sensing resistor so that an appropriate amplification voltage can be obtained even when the amplification factor is reduced, and there is a concern that it will become difficult to reduce the power consumption of the current sensing resistor.

[0074] On the other hand, in this embodiment, the feedback voltage processing circuit 120 has an inverting input resistor 126, and can apply a voltage corresponding to the offset voltage source 124 to the non-inverting input section 121a and the inverting input section 121b of the operational amplifier 121, respectively. As a result, in this embodiment, it is possible to suppress the inclusion of an offset voltage amplification component ΔV in the operational amplifier output voltage Vx1, as shown in the characteristics of Figure 2.

[0075] Therefore, in this embodiment, the amplification factor A of the operational amplifier 121 can be made larger than in the conventional configuration compared to the reference example. As a result, this embodiment can ensure even greater dimming accuracy compared to the reference example. Furthermore, since accuracy can be ensured even at low loads in this embodiment, it is possible to suppress the need for changes in the amplification factor, such as making the amplification factor at low loads greater than the amplification factor at high loads, as in the reference example.

[0076] In this embodiment, at least one of the offset voltage source resistor 125 and the inverting input resistor 126 is variable. Therefore, the voltage difference between the non-inverting input section 121a and the inverting input section 121b from the offset voltage source 124 can be adjusted so as to cancel out the operational amplifier offset voltage. In other words, a DC voltage is input (applied) to the non-inverting input section 121a and the inverting input section 121b that can produce the same effect as input to an ideal operational amplifier. In this case, it is said that equivalent DC voltage components are superimposed on the non-inverting input section 121a and the inverting input section 121b.

[0077] <Mechanism of action, effect> According to this embodiment configured as described above, the following effects and benefits can be obtained.

[0078] (1) The feedback voltage processing circuit 120 has an offset voltage source resistor 125 on the application line from the offset voltage source 124 to the non-inverting input section 121a. The feedback voltage processing circuit 120 also has a voltage application line from the offset voltage source 124 to the inverting input section 121c with an inverting input resistor 126. As a result, the generation of an offset voltage amplification component ΔV, as in the reference example, can be suppressed in the operational amplifier output voltage. That is, the operational amplifier output voltage Vx1 is the sum of the amplified signal voltage A·Vf, which is obtained by amplifying the voltage signal Vf, and the offset voltage Vs, which is a constant value that does not depend on the amplification factor A.

[0079] In this embodiment, the generation of the offset voltage amplification component ΔV can be suppressed, which widens the range that can be secured as the amplified signal voltage A·Vf component, making it possible to set a larger amplification factor A than in the reference example.

[0080] (2) In this embodiment, since a larger amplification factor A can be achieved than in the reference example, there is no need to implement a mechanism that increases the amplification factor in the region of low light source current. In other words, in this embodiment, the amplification factor A can be kept constant.

[0081] (3) At least one of the offset voltage source resistor 125 of the application line to the non-inverting input section 121a and the inverting side input resistor 126 of the voltage application line to the inverting input section 121b is variable. This makes it possible to superimpose equivalent DC voltages on the non-inverting input section 121a and the inverting input section 121b.

[0082] (4) In this embodiment, no special circuit like that in the reference example is required, and a simple and inexpensive circuit configuration for the control unit 100 can be used to obtain a lighting device 5 and lighting fixture 3 that enable high-precision dimming.

[0083] [Other embodiments] Although embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. Furthermore, the features of each embodiment may be combined. Moreover, the embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. Embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols]

[0084] 1...Power supply, 2...Light source module, 2a...Light source, 2b...Connected part, 3...Lighting fixture, 4...Dimming signal unit, 5...Lighting device, 8...Power conversion unit, 10...Full-wave rectifier circuit, 10a, 10b...Input terminals, 10c...High potential output terminal, 10d...Low potential output terminal, 11...High frequency rejection capacitor, 20...Power factor correction circuit, 21...Inductor, 22...Switching element, 22a, 22b, 22c...Electrodes, 23...Diode, 30...Smoothing capacitor, 31...First input terminal, 32...Second input terminal, 40...Converter, 41...Switching element, 41a, 41b, 41c...Electrodes, 42...Diode, 43...Inductor, 44...Output capacitor, 44a...First electrode, 44b...Second electrode, 45a...First output terminal, 45b... Second output terminal, 45c...voltage detection point, 46...current detection resistor, 50...connection point, 100...control unit, 110...control circuit, 111...reference value calculation unit, 112...control calculation unit, 113...drive signal generation unit, 120...feedback voltage processing circuit, 121...operational amplifier, 121a...non-inverting input unit, 121b...inverting input unit, 121x...operational amplifier output unit, 122...input side resistor, 122a...adding point, 123...input side capacitor, 124...offset voltage source, 125...offset voltage source resistor, 125a...branching point, 126...inverting side input resistor, 127...voltage divider resistor, 127a...output side voltage divider resistor, 127b...ground side voltage divider resistor, 127c...intermediate connection unit, 128...output side capacitor, 129...non-inverting amplifier circuit

Claims

1. A power conversion unit having at least one switching element, an inductor, and an output capacitor, which converts input power supplied from an AC or DC power source into DC supply power and supplies the supply power to a light source, A control unit having a control circuit that receives a dimming signal and outputs a drive signal to the power conversion unit in accordance with the dimming signal, and a feedback voltage processing circuit that has a non-inverting amplifier circuit and feeds back a feedback voltage corresponding to the supply voltage, which is the voltage of the supplied power, to the control circuit, Equipped with, The aforementioned feedback voltage processing circuit is An offset voltage source is provided, which adds a positive offset voltage to the supply voltage and inputs it to the non-inverting input section of the non-inverting amplifier circuit. An inverting input resistor, one end of which is connected to the inverting input of the non-inverting amplifier circuit and the other end of which is connected to the offset voltage source, A lighting device characterized by having the following features.

2. The lighting device according to claim 1, characterized in that the amplification factor of the non-inverting amplifier circuit is constant.

3. The lighting device according to claim 2, characterized in that, in the feedback voltage processing circuit, at least one of the offset voltage source resistor connected to the non-inverting input section of the non-inverting amplifier circuit and the inverting input resistor is variable.

4. The light source described in claim 1, A lighting device according to any one of claims 1 to 3, Equipped with lighting fixtures.

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