JP2004127724A - Lighting circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lighting circuit reducing the possibility of generating overpower even if the transmission line for supplying power to the light source is short-circuited to a ground potential. <P>SOLUTION: The lighting circuit for lighting a light source for a vehicle comprises a voltage generating part for generating a supply voltage supplying to the light source, a detecting resistor mounted in series between the voltage generating part and the light source, and a control part controlling the supply voltage generated by the voltage generating part according to the potential between the voltage generating part and the detecting resistor. The power source, the voltage generating part and the detecting resistor are connected in a loop, and the connection between the detecting resistor and the light source, or the connection between the voltage generating part and the light source is grounded. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lighting circuit for lighting a light source.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, when power is supplied to a light source to turn on the light source, constant power is supplied to the light source in order to emit light with a constant light amount. For example, there is a lighting circuit that detects power supplied to a light source, feeds back the detected power, and supplies a constant power to the light source (for example, see Patent Document 1).
[0003]
A conventional lighting circuit includes a power generation unit that generates power, a high-voltage supply unit that provides a high potential to the light source, a low-voltage supply unit that provides a low potential to the light source, and a detection unit that detects a supply current supplied to the light source. A control unit that controls the power generated by the power generation unit based on the detected supply current. The low-voltage supply unit is provided with a resistor for detecting a supply current in series. The one end of the resistor and the generator are grounded, and the detector detects the supply current by detecting the potential of the other end of the resistor.
[0004]
[Patent Document 1]
JP-A-2001-215913 (pages 2-4, FIGS. 7-8)
[0005]
[Problems to be solved by the invention]
However, in the configuration of the conventional lighting circuit described above, when a portion other than between the power generation unit and the resistor is short-circuited to the ground potential, the supply current cannot be correctly detected. Here, the portion other than between the power generation unit and the resistor occupies most of the power transmission line in the lighting circuit, and it is difficult to prevent short circuit for all of them. If the supply current cannot be detected correctly, the power generation unit generates overpower, and the circuit may be destroyed.
[0006]
For example, when the high voltage supply unit is short-circuited to the ground potential, the supply current generated by the power generation unit flows from the high voltage supply unit to the ground potential, and the detection unit detects the supply current as zero. For this reason, the control unit controls the power generation unit so that the power generation unit generates more supply current. However, even in the case of such control, since the supply current detected by the detection unit is zero, the control unit eventually generates the current to the limit of the output capability of the power generation unit. . Therefore, the power generation unit may be thermally destroyed.
[0007]
Also, in the low-voltage supply unit, when the light source and the resistor are short-circuited to the ground potential, the supply current similarly detected by the detection unit is zero. Is generated. Therefore, the power generation unit may be thermally destroyed. Further, an overcurrent may be supplied to the light source, and the light source may be destroyed.
[0008]
In addition, when the current is generated to the limit of the output capability of the power generation unit and the temperature of the light source or the like is increased, there is a possibility of ignition, and particularly, the lighting of a vehicle or the like equipped with flammable fuel is turned on. It is dangerous in case.
[0009]
[Means for Solving the Problems]
In order to solve the above-described problems, according to a first embodiment of the present invention, there is provided a lighting circuit for lighting a light source for a vehicle, comprising: a voltage generating unit configured to generate a supply voltage to be supplied to the light source; A detection resistor provided in series between the light source and the light source, and a control unit for controlling a supply voltage generated by the voltage generation unit based on a potential between the voltage generation unit and the detection resistance, , A voltage generation unit, and a detection resistor are connected in a loop, and a lighting circuit is provided in which the detection resistor and the light source or the voltage generation unit and the light source are grounded. I do.
[0010]
The lighting circuit is provided between the voltage generating unit and the detecting resistor, and is connected so that a forward current flows from the voltage generating unit to the current detecting resistor. May be further provided.
[0011]
The voltage generation unit includes a coil that receives a DC voltage, and a switching element that generates a supply voltage according to the DC voltage by repeatedly switching whether or not to supply a current to the coil. The supply voltage generated by the switching element may be controlled by controlling the time ratio at which the element is turned on or off.
[0012]
The voltage generator repeats whether a primary coil receiving a DC voltage from an external power supply, a secondary coil provided to form a transformer with the primary coil, and whether or not to supply a current to the primary coil. By switching, the secondary coil has a switching element that generates a supply voltage according to the DC voltage, and the control unit controls the time ratio at which the switching element is turned on or off to generate the supply voltage in the secondary coil. The supplied supply voltage may be controlled.
[0013]
Note that the above summary of the present invention does not list all of the necessary features of the present invention, and a sub-combination of these features may also be an invention.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described through embodiments of the present invention. However, the following embodiments do not limit the invention according to the claims, and all of the combinations of the features described in the embodiments are not limited thereto. It is not always essential to the solution of the invention.
[0015]
FIG. 1 shows an example of a configuration of a lighting circuit 100 according to an embodiment of the present invention. The lighting circuit 100 lights a light source 32 by applying a negative voltage to a light source 32 for a vehicle such as an automobile. The light source 32 is, for example, a light emitting diode. Further, the lighting circuit 100 may light the plurality of light sources 32.
[0016]
The lighting circuit 100 includes a voltage generation unit 50, a detection resistor 66, a capacitor 64, a diode 62, and a control unit 60. The light source 32, the voltage generator 50, and the detection resistor 66 are connected in a loop, and the space between the detection resistor 66 and the light source 32 is grounded.
[0017]
The voltage generation unit 50 generates a supply voltage to be supplied to the light source 32. In this example, the voltage generator 50 is a flyback switching regulator having a transformer 56, and boosts or drops the voltage received from the external power supply 200 and outputs the boosted or dropped voltage. The voltage generator 50 has a transformer 56, a capacitor 52, and a switching element 54.
[0018]
The transformer 56 includes a primary coil 72 that is provided in a loop with the power supply 200 and receives a power supply voltage generated by the power supply 200, and a secondary coil 74 that supplies power to the light source 32.
[0019]
The switching element 54 is provided between the primary coil 72 and the power supply 200, and repeatedly switches whether or not to supply the power supply current generated by the power supply 200 to the primary coil 72. , And an output current corresponding to the output voltage. Capacitor 52 smoothes the power supply current generated by power supply 200.
[0020]
In another example, the voltage generator 50 may be another type of switching regulator. For example, by providing a coil in series between the power supply 200 and the light source 32 and repeatedly switching whether or not to supply a current to the coil, a switching regulator that supplies a voltage obtained by stepping down the power supply voltage to the light source 32 is used. There may be. In this case, the voltage generation unit 50 generates a supply voltage according to the DC voltage by repeatedly switching between a coil that receives the DC voltage and whether or not to supply a current to the coil, and a switching element 54 that supplies the voltage to the light source 32. Having.
[0021]
The detection resistor 66 is provided in series between the voltage generator 50 and the light source 32. The diode 62 is provided between the secondary coil 74 and the light source 32 and regulates the direction in which current flows. In this example, the diode 62 is disposed between the secondary coil 74 and the detection resistor 66 and provided so that a forward current flows from the secondary coil 74 to the detection resistor 66.
[0022]
The connection between the detection resistor 66 and the light source 32 is connected to the ground potential. Further, the control unit 60 controls the supply current and the supply voltage generated by the voltage generation unit 56 based on the potential between the voltage generation unit 56 and the detection resistor 66.
[0023]
The supply current flowing through the detection resistor 66 can be detected from the potential applied to the control unit 60 between the voltage generation unit 56 and the detection resistor 66. The control unit 60 controls the voltage generation unit 56 based on the applied potential such that the supply current generated by the voltage generation unit 56 is constant. That is, the control unit 60 controls the supply voltage generated in the secondary coil 74 by controlling the time ratio at which the switching element 54 is turned on or off.
[0024]
The capacitor 64 is provided between the high-voltage terminal and the low-voltage terminal of the light source 32 in parallel with the light source 32 in order to smooth the supply current supplied to the light source 32. In this example, one end of the capacitor 64 is connected to the light source 32, and the other end is connected between the detection resistor 66 and the diode 62.
[0025]
With the above configuration and operation, substantially constant power can be supplied to the light source 32. Therefore, the light source 32 can emit light with a substantially constant light amount.
[0026]
Further, even if one end of the light source 32 and the detection resistor 66 are short-circuited to the ground potential, the operation of the lighting circuit 100 is not affected because the portion is already at the ground potential. Further, even when the other end of the light source 32 and the voltage generation unit 56 are short-circuited, the supply current generated by the voltage generation unit 56 flows through the detection resistor 66. The current actually generated by the generator 56 can be correctly detected. Therefore, the control unit 60 can control the voltage generation unit 56 with high accuracy. That is, the number of locations that must not be short-circuited to the ground potential can be significantly reduced as compared with the conventional lighting circuit, and operation can be performed more accurately. Further, by providing the detection resistor 66 near the secondary coil 74, the area that must not be short-circuited to the ground potential can be further reduced.
[0027]
In addition, the lighting circuit 100 in the present example can easily and accurately detect the supply current because the potential applied to the control unit 60 for detecting the supply current is close to the ground potential. Further, since the supplied current can be detected by comparing the detected potential with the ground potential, a differential circuit or the like is not required, and the supplied current can be detected with a simple circuit configuration.
[0028]
In the present example, the space between the detection resistor 66 and the light source 32 is grounded. However, in another example, the space between the voltage generator 56 and the light source 32 may be grounded. That is, of the two transmission lines connecting the voltage generator 56 and the light source 32, the transmission line without the detection resistor 66 may be grounded. Also in this case, similarly, the number of locations that must not be short-circuited to the ground potential can be significantly reduced as compared with the conventional lighting circuit. In this case, the control unit 60 may control the voltage generation unit 56 based on the potential difference between both ends of the detection resistor 66, and may control the voltage generation unit 56 based on the potential difference between one end of the detection resistor 66 and the ground potential. The voltage generator 56 may be controlled.
[0029]
FIG. 2 shows another example of the configuration of the lighting circuit 100. The configuration of the lighting circuit 100 in this example is different from the configuration of the lighting circuit 100 described with reference to FIG. The configuration and function of the components other than the diode 62 are the same as those described with reference to FIG.
[0030]
In this example, the diode 62 is provided so that a forward current flows from the detection resistor 66 to the secondary coil 74. For example, as shown in FIG. 2, the diode 62 is disposed on a transmission line on which the detection resistor 66 is not provided among the two transmission lines connecting the secondary coil 74 and the light source 32, and And a light source 32 is provided so that a forward current flows.
[0031]
In the lighting circuit 100 according to the present embodiment, similarly to the lighting circuit 100 described with reference to FIG. 1, even if the connection between one end of the light source 32 and the detection resistor 66 is short-circuited to the ground potential, the relevant portion is not affected. Since it is already at the ground potential, the operation of the lighting circuit 100 is not affected. Further, even when the other end of the light source 32 and the voltage generation unit 56 are short-circuited, the supply current generated by the voltage generation unit 56 flows through the detection resistor 66, so that the control unit 60 The supply current generated by the voltage generation unit 56 can be detected. Therefore, the lighting circuit 10 can operate with high accuracy.
[0032]
FIG. 3 illustrates an example of a partial configuration of the lighting circuit 100. FIG. 3A illustrates an example of a configuration of a part of the lighting circuit 100. The lighting circuit 100 in this example further includes a diode 68 for preventing a reverse current in addition to the configuration of the lighting circuit 100 described in FIG. 1 or FIG.
[0033]
The diode 68 is provided between the low voltage terminal of the power supply 200 and the voltage generation unit 50, and prevents a reverse current flowing from the low voltage terminal of the power supply 200 to the voltage generation unit 50. For example, even when the lighting circuit 100 described with reference to FIG. 1 further includes the diode 68, the potential between the detection resistor 66 and the light source 32 is substantially equal to the ground potential. Therefore, the lighting circuit 100 can be protected, and as described with reference to FIG. 1, a region that must not be short-circuited to the ground potential can be reduced, and the lighting circuit 100 can operate accurately. The same applies to the case where the lighting circuit 100 described with reference to FIG.
[0034]
FIG. 3B illustrates another example of the configuration of a part of the lighting circuit. The lighting circuit 100 in this example further includes a transistor 70 for preventing a reverse current and a resistor 78 in addition to the configuration of the lighting circuit 100 described with reference to FIG. 1 or FIG.
[0035]
The transistor 70 is provided in series between the low voltage terminal of the power supply 200 and the voltage generation unit 50, and prevents a reverse current flowing from the low voltage terminal of the power supply 200 to the voltage generation unit 50. The resistor 78 is provided between the gate terminal of the transistor 70 and the high-voltage side transmission line of the lighting circuit 100. When the power supply 200 is reversely connected, a voltage for turning off the transistor 70 is applied to the gate terminal of the transistor 70 via the resistor 78. Also in this example, as in the case described with reference to FIG. 3A, the potential between the detection resistor 66 and the light source 32 is substantially equal to the ground potential. Therefore, the lighting circuit 100 can be protected, and as described with reference to FIGS. 1 and 2, a region that must not be short-circuited to the ground potential can be reduced, and the lighting circuit 100 can operate accurately.
[0036]
As described above, the present invention has been described using the embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments. It is apparent to those skilled in the art that various changes or improvements can be made to the above embodiment. It is apparent from the description of the appended claims that embodiments with such changes or improvements can be included in the technical scope of the present invention.
[0037]
As is clear from the above description, according to the lighting circuit 100 according to the present invention, it is possible to reduce a region in the transmission line that supplies power to the light source, which must not be short-circuited to the ground potential. Therefore, the light source can be accurately turned on.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a configuration of a lighting circuit 100 according to an embodiment of the present invention.
FIG. 2 is a diagram showing another example of the configuration of the lighting circuit 100.
FIG. 3 is a diagram illustrating an example of a partial configuration of a lighting circuit 100. FIG. 3A illustrates an example of a partial configuration of the lighting circuit 100, and FIG. 3B illustrates another example of a partial configuration of the lighting circuit 100.
[Explanation of symbols]
Reference numeral 10: lighting circuit, 50: voltage generator, 52: capacitor, 54: switching element, 56: transformer, 62: diode, 64: capacitor, 66 ... Detection resistor, 68: diode, 70: transistor, 72: primary coil, 74: secondary coil, 78: resistor, 100: lighting circuit, 200: power supply

Claims (4)

A lighting circuit for lighting a light source for a vehicle,
A voltage generation unit that generates a supply voltage to be supplied to the light source;
A detection resistor provided in series between the voltage generator and the light source,
A control unit that controls the supply voltage generated by the voltage generation unit based on a potential between the voltage generation unit and the detection resistor,
The light source, the voltage generation unit, and the detection resistor are connected in a loop, and the detection resistor and the light source or the voltage generation unit and the light source are grounded. A lighting circuit characterized by the above. The detection resistor and the light source are grounded,
The device according to claim 1, further comprising a diode provided between the voltage generation unit and the detection resistor, and connected to allow a forward current to flow from the voltage generation unit to the current detection resistor. Illumination circuit as described. The voltage generator,
A coil for receiving a DC voltage,
A switching element that generates the supply voltage according to the DC voltage by repeatedly switching whether or not to flow a current to the coil,
The lighting circuit according to claim 1, wherein the control unit controls a time ratio at which the switching element is turned on or off, and controls the supply voltage generated by the switching element. The voltage generator,
A primary coil for receiving a DC voltage from an external power supply,
A secondary coil provided to form a transformer with the primary coil;
The secondary coil has a switching element that generates the supply voltage according to the DC voltage by repeatedly switching whether or not to supply a current to the primary coil,
The lighting circuit according to claim 1, wherein the control unit controls the supply voltage generated in the secondary coil by controlling a time ratio at which the switching element is turned on or off.

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