Lighting control device, lighting device, and vehicle lamp

Abstract

To provide a lighting control device capable of lighting a light source regardless of switching element characteristics or a driving voltage of a constant current circuit, and capable of reducing a voltage of a lighting start voltage.SOLUTION: A lighting control device 3 includes a constant current circuit 4 connected in series to a light source 2 whose one end is connected to a current path connected to a power supply, for keeping a current flowing through the light source 2 in constant. The constant current circuit 4 includes: a constant current control circuit for generating a control signal for supplying a current with a constant magnitude to the light source 2; a switching element having a control end to which the control signal is inputted, for keeping the current flowing through the light source constant; and a bypass circuit 6 including a resistor 61 connected in parallel between two current input / output terminals of the switching element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a lighting control device, a lighting device, and a vehicle lamp. [Background technology]

[0002] In a lighting control device for a lighting device such as a vehicle lamp, in order to drive a light source configured by connecting light emitting elements such as LEDs (Light Emitting Diodes) in series, a driving voltage is supplied from a voltage supply circuit and constant current control is performed by providing a constant current circuit in the light source.

[0003] Patent Document 1 discloses an LED driving device that includes a step-up / step-down circuit section that is connected in series to an LED element and that steps up or steps down the power supply voltage and applies it to the LED element as an element applied voltage; a constant current circuit section that is connected in series to the LED element and has a field effect transistor (FET) as a switching element that keeps the current flowing through the LED element constant; and a control section that controls the step-up / step-down circuit section and the constant current circuit section, where the control section controls the step-up / step-down circuit section to adjust the element applied voltage based on a control table that associates the element applied voltage with the constant current obtained by the constant current circuit section so that the drain-source voltage of the FET is below a predetermined value, thereby suppressing heat generation in the FET at high voltages and achieving precise dimming. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-18691 Summary of the Invention [Problem to be solved by the invention]

[0005] The LED driver starts up when the power switch is turned on, and the control unit and constant current circuit unit are driven by applying a power supply voltage. When the constant current circuit is driven and the FET is turned on, current flows through the LED and the LED lights up. However, unless a power supply voltage above the threshold at which the constant current circuit unit can be driven is applied, no gate-source voltage is applied, and if the gate-source voltage does not reach a state that turns the FET on, no current flows through the LED and the LED does not light up.

[0006] The present invention has been made in view of the above, and has as its object to enable a light source to be turned on regardless of the switching element characteristics or the drive voltage of the constant current circuit, and to enable a reduction in the lighting start voltage. [Means for solving the problem]

[0007] The lighting control device of the present invention comprises a constant current circuit connected in series to a light source having one end connected to a current path leading to a power source, and which keeps the current flowing through the light source constant; the constant current circuit comprises a constant current control circuit which generates a control signal for supplying a constant magnitude of current to the light source; a switching element which has a control end to which the control signal is input and which keeps the current flowing through the light source constant; and a bypass circuit which includes a resistor connected in parallel between the two current input / output ends of the switching element. [Effects of the Invention]

[0008] According to the present invention, by providing a bypass circuit consisting of a resistor connected in parallel between the two current input / output terminals of the switching element, current flows through the bypass circuit even when the switching element is closed. This allows the light source to be turned on regardless of the switching element characteristics or the drive voltage of the constant current circuit, and the lighting start voltage can be reduced. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a block diagram showing a configuration of a vehicle lamp according to an embodiment of the present invention; [Figure 2] FIG. 1 is a block diagram showing an example of the configuration of a constant current control IC. [Figure 3] In a vehicle lamp according to an embodiment of the present invention, (a) is a diagram showing the operating characteristics of a constant current control IC and the current-voltage characteristics of a light source when the input voltage changes, and (b) is an enlarged view of a portion of (a). [Figure 4] In a conventional vehicle lamp, (a) is a diagram showing the operating characteristics of a constant current control IC when the input voltage changes, and the current-voltage characteristics of the light source, and (b) is an enlarged view of a portion of (a). DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vehicle lamp according to an embodiment of the present invention will now be described with reference to the accompanying drawings. In the drawings, the same or equivalent parts are designated by the same reference numerals.

[0011] FIG. 1 is a block diagram showing the configuration of a vehicle lamp 1. The vehicle lamp 1 includes a light source 2 and a lighting control device 3 that controls the lighting of the light source 2. The light source 2 is a light-emitting string made up of light-emitting elements 21 and 22 connected in series. The light-emitting elements are LEDs. The number of light-emitting elements making up the light source is not limited to this, and may be one, or a string made up of three or more light-emitting elements, and the number of light-emitting elements making up the light source can be set as appropriate. Here, it is assumed that each light-emitting element is the same and has the same forward voltage, but it may also be a combination of light-emitting elements with different emission colors, for example.

[0012] The lighting control device 3 includes a constant current circuit 4, which performs constant current control to cause a constant current to flow through the light source 2. The constant current circuit 4 includes a constant current control IC 41 that constitutes a constant current control circuit, a field effect transistor (FET) 42 that is a switching element, and a detection resistor 5. The vehicle lamp 1 is connected to a power supply battery (not shown), and receives an input voltage V , which is a DC voltage, from the power supply battery. in The input voltage V inis supplied as a drive voltage for driving the light source 2 and the constant current control IC 41. The constant current circuit 4 is connected to the light source 2, and supplies the light source 2 with a current whose magnitude corresponds to the control signal supplied from the constant current control IC 41.

[0013] The constant current control IC 41 is connected to the gate G, which is the control terminal of the FET 42, and controls the current between the drain D and source S, which are current input / output terminals, by supplying a control signal to the control terminal. The constant current control IC 41 is also connected to a detection resistor 5. The detection resistor 5 is connected between the source S of the FET 42 and ground, and the constant current control IC 41 detects the drive current of the light source 2 from the voltage generated across the detection resistor 5. The constant current control IC 41 feeds back the voltage of the detection resistor 5 and compares it with an internal reference voltage. The constant current control IC 41 controls the current between the drain D and source S by supplying the comparison result to the gate G of the FET 42 as a control signal.

[0014] 2, the constant current control IC 41 includes an operational amplifier 410. The power supply terminal of the operational amplifier 410 receives an input voltage V from a power supply battery as a drive voltage. in is input to the non-inverting input terminal. A reference voltage generator 411 is connected to the non-inverting input terminal. The reference voltage generator 411 generates a reference voltage and outputs it to the non-inverting input terminal. A detection resistor 5 is connected to the inverting input terminal, and a voltage generated across the detection resistor 5 is input as a detection signal for detecting the drive current of the light source 2. The operational amplifier 410 compares the reference voltage input from the reference voltage generator 411 with the detection signal, and outputs a control signal from the output terminal based on the comparison result. The output terminal of the operational amplifier 410 is connected to the gate G of the FET 42, and a control signal is input to the gate G to control the current flowing between the drain D and source S. A current flows between the drain D and source S in accordance with the control signal, thereby forming a current path 7 that passes a constant current through the light source 2.

[0015] Returning to FIG. 1 , a bypass circuit 6 is provided in which a resistor 61 is connected in parallel between the drain D and source S of the FET 42. The bypass circuit 6 forms a current path 8, which is a bypass path through which current can flow without passing through the FET 42. By passing a current through a path that passes through the resistor 61 in addition to the current path 7 through which the current passes within the FET 42, it becomes possible to light the light source 2 even when the current path 7 is not formed. Therefore, the bypass circuit 6 including the resistor 61 reduces the light-on start voltage of the light source 2. The voltage reduction achieved by adding the bypass circuit 6 will be described below.

[0016] In the vehicle lamp 1, the light source 2 can be turned on by satisfying the following voltage formula. Input voltage V in =Voltage V across the light-emitting element 21 L1 +Voltage V across light-emitting element 22 L2 +Voltage across resistor 61 V R +Voltage across sense resistor 5, V S ···(1)

[0017] Equation (1) can be substituted as follows when the drive current of the light source 2 flowing through the current path 8 is I: Input voltage V in = Driving current I of light source 2 × (resistance value R of light emitting element 21) L1 +Resistance value R of light emitting element 22 L2 +Resistance value R of resistor 61 R +Resistance value of detection resistor 5 R S ) ···(2) Here, the light emitting elements 21 and 22 have current-voltage characteristics, and a current flows according to the applied voltage. According to this current-voltage characteristic, a resistance value R L1 , R L2 In other words, the light emitting elements 21 and 22 have a characteristic that their resistance value changes depending on the voltage applied thereto.

[0018] For example, in equation (2), if you want to pass a drive current of 1 mA through resistor 61, the required V inThe voltage value is determined as follows: Driving current I of light source 2 × resistance value R of light emitting element 21 L1 =Voltage V across the light-emitting element 21 L1 = Voltage value when a current of 1 mA is applied to the light emitting element 21, which is determined from the current-voltage characteristics of the light emitting element 21 Driving current I of light source 2 × resistance value R of light emitting element 22 L2 =Voltage V across the light-emitting element 22 L2 = Voltage value when a current of 1 mA is applied to the light emitting element 22, which is determined from the current-voltage characteristics of the light emitting element 22 V L1 , V L2 The current-voltage characteristics of V differ depending on the light-emitting element used. L1 , V L2 =2V. Drive current I of light source 2 × resistance value R of resistor 61 R = 1mA x resistance value R of resistor 61 R Here, the resistance value R of resistor 61 R is usually several kΩ, so for convenience, let us assume that it is 1 kΩ. R is set to 1V. Drive current I of light source 2 × resistance value R of detection resistor 5 S = 1mA × resistance value of detection resistor 5 R S Here, the resistance value R of the detection resistor 5 S is usually several ohms, so for convenience, let us assume it is 1 ohm, and the voltage across the detection resistor 5, V S is set to 1mV.

[0019] From the above, the input voltage V in When we calculate V in =V L1 +V L2 +V R +V S =2+2+1+0.001=5.001(V) This becomes: The LED will light up even at about 0.1mA, so if we calculate it in the same way, we get V in becomes even lower, and even below 4V is possible.

[0020] The resistor 61 is added between the drain D and source S of the FET 42, and there are two paths through which current passes: one through the resistor 61 and one through the FET 42. Which path the current passes through is determined by changes in the resistance value between the drain D and source S within the FET 42. The current flowing between the drain D and source S within the FET 42 is controlled by a control signal input to the gate G. The FET 42 continuously changes the resistance value between the drain D and source S from 0 to infinity according to the voltage applied as the control signal. In the OFF state, when the control signal has not yet reached a level that turns the FET 42 ON, the drain D and source S are in an open state, and the resistance value is equivalent to infinity. Then, when the control signal reaches a predetermined value, the FET 42 turns ON, and the resistance value changes to 0Ω.

[0021] In this way, in the OFF state before the control signal reaches a level that turns FET 42 ON, the resistance value between drain D and source S is infinite, but because there is a bypass circuit 6 including resistor 61, current flows through this bypass circuit 6, and the resistance value between drain D and source S becomes the resistance value of resistor 61. Then, when the control signal reaches a predetermined value, FET 42 turns ON, and the resistance value changes to 0Ω.

[0022] When a current passes through the FET 42, the OFF / ON control between the drain D and source S of the FET 42 is performed by the potential difference between the gate G and source S. Therefore, the current flowing through the current path 7 depends on the characteristics (OFF / ON voltage threshold) between the gate G and source S of the FET 42 and the drive voltage of the constant current control IC 41 that supplies voltage to the gate G of the FET 42. Both of these depend on the input voltage V that is effective for turning ON the gate G and source S. in Otherwise, no current will flow. Generally, the drive voltage of the constant current control IC is dominant. If the drive voltage of the constant current control IC is 6V, the input voltage V in If the voltage is not 6V or higher, no current will flow through the path in the FET 42.

[0023] FIG. 3(a) shows the input voltage V in When the input voltage V is changed from 0 to 14V, in 3(b) shows an enlarged view of the portion enclosed by the dotted ellipse in FIG. 3(a). For comparison, a conventional lighting control device not provided with a bypass circuit 6 was used to control the input voltage V in When the input voltage V is changed from 0 to 14V, in FIG. 4(a) shows the characteristics of the control signal to gate G, which is the output voltage of constant current control IC 41, and the current-voltage characteristics of light-emitting elements 21 and 22, and FIG. 4(b) shows an enlarged view of the part surrounded by the dotted ellipse in FIG. 4(a).

[0024] In Figure 3, the line a indicates the voltage value at point A in Figure 1. Here, the voltage value at point A is the input voltage V in The curve b shows the voltage value at point B in FIG. 1. Here, the voltage value at point B indicates the output voltage to the gate G of the constant current control IC 41, and the horizontal axis shows the input voltage V in The vertical axis represents the output voltage of the constant current control IC 41. Curve c represents the current-voltage characteristics of the light emitting elements 21 and 22 when the circuit configuration of FIG.

[0025] On curve b, the input voltage V in When the input voltage V changes from 0 and reaches 6.2V, the output voltage of the constant current control IC 41 starts to rise from 0. In other words, the constant current control IC 41 starts to operate when the power supply voltage reaches 6.2V. Therefore, in If the voltage is less than 6.2V, the constant current control IC 41 is not driven and no control voltage is output to the gate G, so that the drain D-source S of the FET 42 is not turned on. Therefore, no current path 7 passing through the FET 42 is generated in the vehicle lamp 1.

[0026] However, even when the constant current control IC41 starts to operate, the control voltage output from the constant current control IC41 to the gate G does not reach a level that turns the drain D-source S in the FET42 into the ON state, so the FET42 remains in the OFF state.

[0027] Input voltage V in When the input voltage V exceeds 6.2V, the output voltage of the constant current control IC41 increases accordingly. in When the voltage reaches 8.2V, the output voltage of the constant current control IC 41 reaches a level at which the drain D-source S of the FET 42 is turned on, and the FET 42 changes from the off state to the on state.

[0028] As shown above, the input voltage V in When the input voltage V is between 0 and 8.2V, the FET 42 is in the OFF state, and no current flows to the light source 2 through the current path 7. However, between the drain D and the source S, in addition to the path through the FET 42, a bypass circuit 6 including a resistor 61 connected in parallel with the FET 42 is provided as a path for the current to pass. in The current can pass through the bypass circuit 6 until the input voltage V reaches 8.2 V. In the curve c in FIG. 3(b), which is an enlarged view of the area enclosed by the dotted ellipse in FIG. 3(a), in When the input voltage V reaches 2.5V, a current starts to flow through the current path 8 passing through the bypass circuit 6, and the light source 2 starts to light up. Here, the current and voltage are low, so the light source 2 is in a dim light state. In this way, when the input voltage V in Until the voltage reaches 8.2 V, a current flows through the current path 8, and the light source 2 remains lit.

[0029] And the input voltage V inreaches 8.2 V, the output voltage to the gate G of the constant current control IC 41 changes the FET 42 from the OFF state to the ON state. When the FET 42 is turned ON, the resistance value in the FET 42 between the drain D and the source S becomes smaller than the resistance value in the bypass circuit 6, so that current flows through the current path 7 and no current flows through the current path 8, which has a higher resistance value than the current path 7, and the current path is automatically switched from the current path 8 to the current path 7.

[0030] Input voltage V in When the input voltage V in When the voltage reaches 13V, the output voltage of the constant current control IC 41 becomes constant, and the drive current flowing through the light source 2 becomes constant.

[0031] In this way, the lighting control device 3 in this embodiment can start lighting the light source 2 even if the voltage required to drive the constant current control IC 41 has not yet been reached, thereby realizing a lower lighting start voltage.

[0032] Next, for comparison, a case where a conventional lighting control device without the bypass circuit 6 is used will be described with reference to FIG. 4. As in FIG. 3, in the curve b, the input voltage V in When the input voltage V changes from 0 and reaches 6.2V, the constant current control IC41 starts to operate and the output voltage starts to rise from 0. in If the input voltage V is less than 6.2V, the constant current control IC 41 is not driven, and the control voltage is not output to the gate G, so the drain D-source S of the FET 42 is not turned on. in When the input voltage V exceeds 6.2V and the constant current control IC41 starts to operate, in The output voltage of the constant current control IC41 increases according to the input voltage V in When the input voltage V reaches 8.2V, the drive current starts to flow to the light source 2, as shown in curve c. inWhen the voltage reaches 8.2V, the output voltage to the gate G of the constant current control IC 41 changes the FET 42 from the OFF state to the ON state, and a drive current begins to flow between the drain D and the source S. When the drive current begins to flow, the light source 2 begins to light up.

[0033] Thus, the input voltage V in However, the light source 2 can only begin to light up when the voltage required to drive the constant current control IC 41 reaches a voltage sufficient to drive the constant current control IC 41, and the constant current control IC 41 outputs the gate voltage required to turn on the FET 42. If the constant current control IC 41 cannot be driven, the constant current control IC 41 cannot output the gate voltage required to turn on the FET 42. Therefore, the drive voltage of the light source 2 is governed by the drive voltage of the constant current control IC 41. Therefore, to reduce the drive voltage of the light-emitting elements 21 and 22, it is necessary to use a constant current control IC 41 with a lower drive voltage. This narrows the range of available drive voltages, thereby limiting the types of constant current control ICs 41 that can be selected. This limited selection of constant current control ICs 41 can sometimes force compromises in price, size, functionality, and other factors. Furthermore, a diode is connected to the vehicle lamp 1 as a reverse connection protection component to protect against reverse connection of the power battery and the + / - terminals, but when a diode is used, a voltage drop occurs due to the diode, which reduces the drive voltage applied to the constant current control IC 41. This also limits the types of constant current control ICs 41 that can be selected, so it is necessary to change to an expensive component such as a FET to suppress the voltage drop due to the diode.

[0034] In contrast, the lighting control device 3 of the present embodiment, which includes a bypass circuit 6 having a resistor 61 connected in parallel with the FET 42 between the drain D and source S of the FET 42, can lower the light-on start voltage of the light source 2 regardless of the voltage value required to drive the constant current control IC 41. Therefore, there is no need to use a constant current control IC 41 with a lower drive voltage in order to reduce the drive voltage of the light source 2, and the range of usable drive voltages is not narrowed, so there is no limit to the type of constant current control IC 41 that can be selected. Since there is no limit to the type of constant current control IC 41 that can be selected, it is possible to select an optimal constant current control IC 41 taking into consideration price, size, functionality, and the like. Furthermore, since there is no limit to the type of constant current control IC 41 that can be selected, it is possible to avoid replacing the reverse connection protection component with an expensive component such as a FET.

[0035] In the above embodiment, FETs are used as switching elements, but the present invention is not limited to this and bipolar transistors and insulated gate transistors may also be used.

[0036] Furthermore, in the above embodiment, the description has been given of a vehicle lamp, but the invention is not limited to this and the lighting device can also be used for other purposes such as amusement equipment.

[0037] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to the above-described embodiments, but includes the scope of the invention described in the claims and its equivalents. [Explanation of symbols]

[0038] 1...vehicle lamp, 2...light source, 3...lighting control device, 4...constant current circuit, 5...detection resistor, 6...bypass circuit, 7, 8...current path, 21, 22...light emitting element, 41...constant current control IC, 42...field effect transistor (FET), 61...resistor, 410...operational amplifier, 411...reference voltage generation unit

Claims

1. a constant current circuit connected in series to a light source, one end of which is connected to a current path connected to a power source, for making constant a current flowing through the light source; The constant current circuit is a constant current control circuit that generates a control signal for supplying a constant magnitude of current to the light source; a switching element having a control terminal to which the control signal is input, the switching element keeping the current flowing through the light source constant; a bypass circuit including a resistor connected in parallel between two current input / output terminals of the switching element, Lighting control device.

2. The switching element is a transistor. The lighting control device according to claim 1 .

3. The switching element is a field effect transistor, the control terminal is a gate, and the two current input / output terminals are a drain and a source. The lighting control device according to claim 2 .

4. the constant current control circuit is a constant current control IC to which a drive voltage is supplied from the power supply; The lighting control device according to claim 1 .

5. A lighting device comprising the lighting control device according to any one of claims 1 to 4 and the light source.

6. A vehicle lamp constructed using the lighting device according to claim 5.

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