JP4647674B2 - Lighting circuit - Google Patents

Description

  The present invention relates to a lighting circuit. In particular, the present invention relates to a lighting circuit for lighting a vehicular lamp including a light emitting diode.

  Conventionally, a switching regulator that supplies electric power to a light source of a vehicular lamp is known (see, for example, Patent Document 1). The output voltage of the switching regulator is controlled based on the current flowing through the light source, for example.

Japanese Patent Laid-Open No. 2001-215913 (page 3, FIG. 7)

  The vehicle is equipped with highly flammable fuel such as gasoline. Therefore, high safety is required in a switching regulator mounted on a vehicle.

  However, for example, when the output of the switching regulator is short-circuited or grounded, the load of the switching regulator becomes heavy, so that the switching regulator may break down from excessive power load, generate heat, or generate smoke.

  In addition, when the output is opened due to disconnection or the like, for example, in a flyback type switching regulator, the output voltage may increase excessively, causing danger such as electric shock of the user, leakage from high voltage, In some cases, there was a risk of smoking or ignition due to discharge.

  Then, an object of this invention is to provide the lighting circuit which can solve said subject. This object is achieved by a combination of features described in the independent claims. The dependent claims define further advantageous specific examples of the present invention.

  In other words, according to the first aspect of the present invention, the lighting circuit for lighting a vehicle lamp including a light emitting diode is configured to apply an output voltage based on a power supply voltage received from a DC power supply provided outside to the light emitting diode. Based on at least one of a switching regulator that supplies a supply current to the light emitting diode, an output voltage, a supply current, or a power supply voltage of the switching regulator, an abnormality detection unit that detects an abnormality in the lighting circuit, An output control unit configured to control the output voltage of the switching regulator based on the output voltage of the switching regulator, and to reduce the output voltage of the switching regulator when the abnormality detection unit detects an abnormality.

  The vehicular lamp includes n light emitting diodes (n is an integer of 2, 3, 4,..., 2 or more) connected in parallel, and the abnormality detection unit includes n light emitting diodes. When at least one disconnection is detected as an abnormality, and the abnormality detection unit detects the abnormality, the output control unit reduces the output voltage of the switching regulator to reduce the supply current to a large value of (n−1) / n. It may be reduced.

  Further, when the abnormality detection unit detects an abnormality, the output control unit may stop the switching regulator. The abnormality detection unit may detect that the output voltage of the switching regulator changes to a value higher than a predetermined value as an abnormality.

  In addition, the abnormality detection unit detects that the power supply voltage changes to a value outside the predetermined range as an abnormality, and the output control unit stops the switching regulator when an abnormality is detected, and the abnormality is detected. If it is no longer possible, the switching regulator may be restarted.

  Further, a smoothing capacitor is provided for smoothing a change in the smoothed voltage based on at least one of the output voltage, supply current, or power supply voltage of the switching regulator, and the abnormality detection unit detects an abnormality based on the smoothed voltage. You can.

  The above summary of the invention does not enumerate all the necessary features of the present invention, and sub-combinations of these feature groups can also be the invention.

  Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the invention according to the claims, and all combinations of features described in the embodiments are included. It is not necessarily essential for the solution of the invention.

  FIG. 1 shows an example of a circuit configuration of a vehicular lamp 10 according to an example of an embodiment of the present invention. The vehicular lamp 10 of this example turns on the light emitting diode 30 safely based on electric power received from a DC power supply 112 provided outside such as a vehicular battery. The vehicular lamp 10 includes a light source block 58 and a lighting circuit 102.

  The light source block 58 includes a plurality of light source units 60 connected in parallel and a plurality of resistors 106 connected in series with the respective light source units 60. The light source unit 60 includes one or more light emitting diodes 30 connected in series. Further, the resistor 106 generates a voltage based on the current flowing through the light source unit 60 in accordance with the supply current at both ends. Therefore, when one or a plurality of light emitting diodes 30 included in the light source unit 60 is disconnected, the voltage across the resistor 106 decreases.

  The lighting circuit 102 includes a switching regulator 114, a resistor 118, an abnormality detection unit 120, an output control unit 116, a capacitor 122, a capacitor 126, a diode 134, and a diode 124.

  The switching regulator 114 includes an NMOS transistor 130 and a transformer 128. The NMOS transistor 130 is a switch that switches whether to supply the power supply voltage received from the DC power supply 112 to the primary coil of the transformer 128 by being connected in series with the primary coil of the transformer 128.

  The transformer 128 outputs an output voltage based on the power supply voltage received by the primary coil from the secondary coil. In this example, the transformer 128 outputs a positive voltage from the high voltage output terminal by grounding the low voltage output terminal of the secondary coil. The switching regulator 114 supplies the supply current to the plurality of light emitting diodes 30 by applying the positive voltage to the plurality of light emitting diodes 30 to light the light emitting diodes 30.

  Here, for example, if a supply current is generated by applying a power supply voltage to a resistor connected in series with the light source block 58, heat loss in the resistor increases, and the power consumption of the vehicular lamp 10 increases. . However, in this example, the switching regulator 114 generates a supply current. Therefore, according to this example, the vehicular lamp 10 with high power efficiency can be provided.

  In this example, the switching regulator 114 is a flyback switching regulator. In another example, the switching regulator 114 may be a switching regulator of another method such as a forward method or a step-down type. The switching regulator 114 may have a coil that supplies the current received from the DC power supply 112 to the light source block 58 instead of the transformer 128.

  The resistor 118 is connected in series with the light source block 58 and generates a current detection voltage at both ends, which is a voltage based on a supply current flowing through the light source block 58. Further, the abnormality detection unit 120 detects an abnormality of the vehicular lamp 10 based on the output voltage of the switching regulator 114, the information indicating the disconnection of the light emitting diode 30, the supply current, and the power supply voltage.

  The output control unit 116 controls the ratio at which the NMOS transistor 130 is turned on or off based on the current detection voltage generated by the resistor 118. Thereby, the output control unit 116 controls the output voltage of the switching regulator 114 based on the supply current.

  Here, when the abnormality detection unit 120 detects an abnormality, the output control unit 116 reduces the output voltage of the switching regulator 114. For example, the output control unit 116 stops the switching regulator 114. According to this example, the light emitting diode 30 can be turned on safely.

  For example, when the vehicular lamp 10 includes n light emitting diodes 30 (n is an integer of 2, 3, 4...) Connected in parallel, the abnormality detection unit 120 At least one disconnection of the n light emitting diodes 30 is detected as an abnormality. When the abnormality detection unit 120 detects the abnormality, the output control unit 116 reduces the supply current to approximately (n−1) / n by reducing the output voltage of the switching regulator 114. Good. In this case, the vehicular lamp 10 can cause the light emitting diodes 30 that are not disconnected to emit light with appropriate brightness.

  FIG. 2 shows an example of the circuit configuration of the abnormality detection unit 120. The abnormality detection unit 120 includes a disconnection detection unit 212, an output voltage monitoring unit 202, a hold unit 204, a supply current monitoring unit 208, a power supply voltage monitoring unit 206, and an abnormality signal output unit 210.

  The disconnection detection unit 212 detects disconnection of the light emitting diode 30 (see FIG. 1) connected in series with the resistor 106 based on the voltage across the resistor 106 and provides the detection result to the abnormal signal output unit 210. In addition, since various circuits are known as circuit configurations for detecting such disconnection, description thereof is omitted.

  The output voltage monitoring unit 202 includes a comparator 302, a comparator 304, and a plurality of resistors. Each of the comparators 302 and 304 keeps the output high impedance when the voltage received at the positive input is higher than the voltage received at the negative input, and outputs the output when the voltage received at the positive input is lower than the voltage received at the negative input. Ground. The comparator 304 supplies the output to the hold unit 204.

  Therefore, for example, when the output voltage of the switching regulator 114 becomes higher than a predetermined upper limit output voltage due to a failure such as the output of the switching regulator 114 being open, the comparator 302 grounds the negative input of the comparator 304. In this case, the comparator 304 keeps the output at high impedance. Further, even when the output voltage of the switching regulator 114 becomes lower than the predetermined lower limit output voltage, which is lower than the upper limit output voltage due to a failure such as a short circuit of the output of the switching regulator 114, the comparator 304 Keep the output in high impedance.

  On the other hand, when the output voltage of the switching regulator 114 is a voltage between the lower limit output voltage and the upper limit output voltage, the comparator 304 grounds the output. As a result, the output voltage monitoring unit 202 detects that the output voltage of the switching regulator 114 changes to a value higher than the upper limit output voltage or a value lower than the lower limit output voltage as an abnormality, and transmits the detection result to the hold unit 204. To do. According to this example, the output voltage monitoring unit 202 can detect an abnormality based on an open or short of the output of the switching regulator 114.

  The hold unit 204 includes an NPN transistor 308, a capacitor 310, an NPN transistor 306, and a plurality of resistors. When the output voltage monitoring unit 202 detects an abnormality in the output voltage of the switching regulator 114, the NPN transistor 308 is turned on, and the collector current is supplied to notify the abnormality signal output unit 210 that the abnormality has been detected. .

  Capacitor 310 smoothes changes in the base voltage of NPN transistor 308, which is a voltage based on the output voltage of switching regulator 114, thereby preventing malfunction of NPN transistor 308 in response to a short-time error signal such as noise. To do. As a result, when the output voltage monitoring unit 202 continuously detects an abnormality in the output of the switching regulator 114 for a predetermined monitoring time or longer, the hold unit 204 detects that the abnormality has been detected. This is transmitted to the signal output unit 210.

  Further, when the output voltage monitoring unit 202 detects an abnormality in the output voltage of the switching regulator 114, the NPN transistor 306 is turned on, and the potential of the negative input of the comparator 304 is lowered by flowing a collector current.

  Thereby, the comparator 304 keeps the output in high impedance regardless of the output voltage of the switching regulator 114. That is, the NPN transistor 308 feeds back a signal based on the output signal of the output voltage monitoring unit 202 to the output voltage monitoring unit 202, thereby fixing the value of a signal output from the output voltage monitoring unit 202 thereafter.

  Note that, when the output voltage monitoring unit 202 detects an abnormality, the NPN transistor 306 is preferably turned on before the NPN transistor 308. In this case, the hold unit 204 can reliably fix the value of the signal output from the output voltage monitoring unit 202.

  The supply current monitoring unit 208 includes an NPN transistor 320 and an NPN transistor 318. The NPN transistor 320 is turned off when the supply current drops below a predetermined lower limit current value by receiving the current detection voltage generated by the resistor 118 at the base terminal.

  When the NPN transistor 320 is turned off, the NPN transistor 318 is turned on to flow the collector current, thereby lowering the negative input of the comparator 304. Accordingly, the supply current monitoring unit 208 detects that the supply current is lower than the lower limit current value as an abnormality, and detects that the abnormality is detected via the output voltage monitoring unit 202 and the hold unit 204. 210. In this case, the capacitor 310 smoothes the voltage change based on the supply current.

  The power supply voltage monitoring unit 206 includes a diode 340, a diode 336, a comparator 322, an NPN transistor 326, an NPN transistor 328, a comparator 324, an NPN transistor 334, an NPN transistor 332, an NPN transistor 330, and a plurality of resistors. The diode 340 supplies the output of the power supply voltage monitoring unit 206 to the abnormal signal output unit 210. The diode 336 discharges the capacitor 310 when the NPN transistor 206 detects a power supply voltage abnormality.

  The comparator 322 and the comparator 324 have the same or similar functions as the comparator 302. Comparator 322 receives a predetermined upper limit power supply voltage as a reference voltage. When the power supply voltage becomes higher than the upper limit power supply voltage, the comparator 322 notifies the abnormality signal output unit 210 of abnormality of the power supply voltage by turning on the NPN transistor 326. Further, in this case, the NPN transistor 328 is turned on to flow the collector current, thereby lowering the potential of the reference voltage received by the comparator 322 to a predetermined lower limit upper voltage.

  As a result, the NPN transistor 328 gives hysteresis to the reference voltage received by the comparator 322. Therefore, after the power supply voltage becomes higher than the upper limit power supply voltage, the comparator 322 fixes the output until the power supply voltage becomes lower than the lower limit upper voltage.

  Each of the comparator 324, the NPN transistor 334, and the NPN transistor 330 has the same or similar function as the comparator 322, the NPN transistor 326, and the NPN transistor 330. The comparator 324 receives, as a reference voltage, a predetermined lower limit power supply voltage during a period when the NPN transistor 330 is on, and a predetermined increase lower limit voltage that is higher than the lower limit power supply voltage during a period when the NPN transistor 330 is off. receive. The comparator 324 receives a voltage lower than the upper limit power supply voltage as the lower limit power supply voltage. The comparator 324 may receive a voltage lower than the decrease upper limit voltage as the increase lower limit voltage.

  Further, when the power supply voltage becomes lower than the lower limit power supply voltage, the NPN transistor 332 is turned on to notify the abnormality signal output unit 210 of the abnormality of the power supply voltage.

  That is, the power supply voltage monitoring unit 206 detects that the power supply voltage changes to a value outside the range from the lower limit power supply voltage to the upper limit power supply voltage as an abnormality. In addition, after the abnormality signal output unit 210 detects an abnormality in the power supply voltage, when the power supply voltage changes to a normal range between the lower limit voltage and the lower increase voltage, the abnormality signal output unit 210 detects that the power supply voltage is abnormal. Will not be detected. Note that when an abnormality in the power supply voltage is detected, the output control unit 116 may stop the switching regulator 114. When the abnormality is no longer detected, the output control unit 116 may restart the switching regulator 114.

  Here, when the output voltage decreases in response to the stop of the switching regulator 114, if the output voltage monitoring unit 202 detects the decrease as an abnormality, the hold unit 204 fixes the output of the output voltage monitoring unit 202. It becomes. In this case, even when the power supply voltage returns to the normal range, the switching regulator 114 does not return to operation.

  However, in this example, when an abnormality in the power supply voltage is detected, the diode 336 discharges the capacitor 310, so the hold unit 204 does not fix the output of the output voltage monitoring unit 202. Therefore, according to this example, the output control unit 116 can restart the switching regulator 114 in response to the return of the power supply voltage to the normal range.

  When the switching regulator 114 stops, the switching regulator 114 may receive a power supply voltage that varies due to the impedance of the wiring. Depending on the fluctuation, the power supply voltage monitoring unit 206 may not detect the abnormality of the power supply voltage. In this case, since the output control unit 116 restarts the switching regulator 114, the switching regulator 114 repeats the stop and restart of the operation in a short cycle. However, the power supply voltage monitoring unit 206 of this example detects an abnormality in the power supply voltage based on the threshold voltage having hysteresis. Therefore, according to this example, the switching regulator 114 can be stably controlled.

  In another example, the comparator 322 may receive the same voltage as the upper limit power supply voltage as the lower limit upper voltage. The comparator 324 may receive the same voltage as the lower limit power supply voltage as the rising upper limit voltage. In this case, the power supply voltage monitoring unit 206 detects an abnormality in the power supply voltage based on the threshold voltage without hysteresis. The output control unit 116 may cause the light emitting diode 30 to blink in the cycle by repeatedly stopping and restarting the operation of the switching regulator 114 in a short cycle according to the fluctuation of the power supply voltage caused by the impedance of the wiring. In this case, the abnormality detection unit 120 can notify the user of an abnormality in the DC power supply 112 by the blinking.

  The abnormality signal output unit 210 outputs and controls information indicating the abnormality when any one of the disconnection detection unit 212, the output voltage monitoring unit 202, the supply current monitoring unit 208, or the power supply voltage monitoring unit 206 detects an abnormality. Supplied to the unit 116. According to this example, the abnormality of the vehicular lamp 10 (see FIG. 1) can be detected appropriately. Moreover, the switching regulator 114 can be appropriately controlled according to the detection result of the abnormality.

  In this example, the capacitor 310 smoothes a change in voltage based on either the output voltage of the switching regulator 114 or the supply current. In another example, the capacitor 310 may smooth a change in voltage based on a power supply voltage or the like. The abnormality detection unit 120 may detect an abnormality based on these smoothed voltages. In this case, it is possible to prevent erroneous detection of fluctuations in these voltages based on noise or the like as abnormalities.

  In another example, the abnormality detection unit 120 includes only one of these instead of including the output state monitoring unit 202, the supply current monitoring unit 208, the power supply voltage monitoring unit 206, and the disconnection detection unit 212. May be. In this case, the vehicular lamp 10 can be provided at a low cost by reducing the number of parts of the abnormality detection unit 120.

  For example, the abnormality detection unit 120 may have a configuration in which the supply current monitoring unit 208, the power supply voltage monitoring unit 206, and the disconnection detection unit 212 are deleted from the configuration illustrated in FIG. The monitoring unit 202, the supply current monitoring unit 208, the hold unit 204, and the disconnection detection unit 212 may be deleted.

  Further, the abnormality detection unit 120 may have a configuration in which the output state monitoring unit 202, the power supply voltage monitoring unit 206, and the disconnection detection unit 212 are deleted from the configuration illustrated in FIG. In this case, the hold unit 204 may have a configuration in which parts other than the configuration that gives the input to the comparator 304 and the comparator 304 are deleted from the configuration shown in FIG.

  In still another example, the abnormality detection unit 120 is replaced with the output state monitoring unit 202, the supply current monitoring unit 208, the power supply voltage monitoring unit 206, and the disconnection detection unit 212. The structure which has one may be sufficient. According to this example, the vehicular lamp 10 having a combination of necessary monitoring functions can be provided.

  FIG. 3A shows another example of the circuit configuration of the output voltage monitoring unit 202. In this example, the output voltage monitoring unit 202 includes an NPN transistor 402, an NPN transistor 404, a Zener diode 406, and a plurality of resistors.

  When the output voltage of the switching regulator 114 becomes lower than a predetermined lower limit output voltage, the NPN transistor 402 is turned off, and the abnormality of the output voltage is transmitted to the hold unit 204. Further, when the output voltage of the switching regulator 114 becomes higher than a predetermined upper limit output voltage, a current flows through the Zener diode 406, whereby the NPN transistor 404 is turned on. In this case, the NPN transistor 404 transmits the abnormality of the output voltage to the hold unit 204 by turning off the NPN transistor 402. According to this example, the output voltage monitoring unit 202 can appropriately detect an abnormality in the output voltage of the switching regulator.

  Note that the base terminal of the NPN transistor 402 is electrically connected to the collector terminal of the NPN transistor 306. Thereby, when the output voltage monitoring unit 202 detects an abnormality, the hold unit 204 fixes the output of the output voltage monitoring unit 202.

  FIG. 3B shows still another example of the circuit configuration of the output voltage monitoring unit 202. In this example, an NPN transistor 402, an NPN transistor 404, a Zener diode 406, an NPN transistor 410, and a plurality of resistors are included. In FIG. 3B, the configuration denoted by the same reference numeral as in FIG. 3A has the same or similar function as the configuration in FIG. In this example, the base terminal of the NPN transistor 402 is connected to a pull-up resistor, and when the NPN transistor 404 is off, the NPN transistor 402 is turned on.

  The base terminal of the NPN transistor 410 receives the output voltage of the switching regulator 114 via the Zener diode 412 and the resistor downstream from the NPN transistor 404. In this case, the base terminal of the NPN transistor 410 receives a voltage lower than the base voltage of the NPN transistor 306. As a result, the NPN transistor 410 detects that the output voltage of the switching regulator 114 is higher than the stop voltage higher than the upper limit output voltage as an abnormality. In this case, it is possible to appropriately detect that the output voltage of the switching regulator 114 increases excessively.

  In this example, the collector terminal of the NPN transistor 410 is electrically connected to the abnormal signal output unit 210 without passing through the NPN transistor 404. Therefore, in this example, when the NPN transistor 410 is turned on, the output control unit 116 (see FIG. 1) immediately stops the output of the switching regulator 114. In this case, it is possible to prevent the output voltage of the switching regulator 114 from further rising after the abnormality is detected. According to this example, the output voltage monitoring unit 202 can appropriately detect an abnormality in the output voltage of the switching regulator.

  The NPN transistor 410 is turned on when the output voltage of the switching regulator 114 exceeds 60V, for example. In this case, the vehicular lamp 10 can be operated safely.

  FIG. 4 shows another example of the circuit configuration of the hold unit 204. In this example, the hold unit 204 includes an NPN transistor 308, a capacitor 310, a diode 430, a PNP transistor 420, and a plurality of resistors. 4, the configuration denoted by the same reference numeral as in FIG. 2 has the same or similar function as the configuration in FIG.

  When the NPN transistor 308 is turned on according to the output of the output state monitoring unit 202, the PNP transistor 420 is turned on, thereby increasing the base voltage of the NPN transistor 308 and holding the NPN transistor 308 on. As a result, the hold unit 204 fixes the value of the signal output from the NPN transistor 308. Therefore, according to this example, when the output state monitoring unit 202 detects an abnormality, the hold unit 204 can continuously supply a signal indicating the detection of the abnormality to the abnormality signal output unit 210.

  FIG. 5 shows another example of the circuit configuration of the lighting circuit 102. 5, the configuration denoted by the same reference numeral as in FIG. 1 has the same or similar function as the configuration in FIG. In this example, the transformer 128 outputs a negative voltage from the low voltage output terminal by grounding the high voltage output terminal of the secondary coil via the resistor 118.

  Therefore, in this example, the lighting circuit 102 further includes an inversion unit 440. The inversion unit 440 inverts the sign of the output voltage of the switching regulator 114 received from the low voltage output terminal of the secondary coil of the transformer 128 and supplies the inverted sign to the abnormality detection unit 120. The inversion unit 440 may supply the output state monitoring unit 202 with the output voltage with the sign inverted. In this case, the abnormality detection unit 120 can appropriately detect an abnormality in the output voltage of the switching regulator 114.

  In this example, the inverting unit 440 includes an operational amplifier 442 whose positive input is grounded and whose output is fed back to the negative input. The operational amplifier 442 receives the output voltage of the switching regulator 114 via a resistor as a negative input, and supplies the output to the abnormality detection unit 120.

  FIG. 6 shows another example of the circuit configuration of the vehicular lamp 10. In this example, the output control unit 116 controls the NMOS transistor 130 based on the output voltage of the switching regulator 114 to cause the switching regulator 114 to output a predetermined voltage. Further, the abnormality detection unit 120 detects an abnormality in the output voltage of the switching regulator 114 and detects the abnormality. Therefore, the light emitting diode 30 can be safely turned on also in this example.

  The light source block 58 includes a plurality of light source units 60 and resistors 602 connected to the plurality of light source units 60 in series. In this example, some light source units 60 include a different number of light emitting diodes 30 than other light source units 60. In addition, some of the light source units 60 include light emitting diodes 30 of different colors from the light emitting diodes 30 included in other light source units 60. Therefore, in this example, the sum of forward voltage drops accompanying light emission (hereinafter referred to as forward voltage sum) of the light emitting diodes 30 included in the light source unit 60 is less than the other light source units 60 in some light source units 60. large.

  The resistor 602 supplies the light source unit 60 with a current corresponding to the output voltage of the switching regulator 114 and the forward voltage sum of the light source unit 60. The plurality of resistors 602 may have different resistance values. In this case, the resistor 104 can supply an appropriate current to each light source unit 60.

  Here, the output control unit 116 causes the switching regulator 114 to output a voltage larger than the forward voltage sum in any of the light source units 60. Therefore, according to this example, all the light emitting diodes 30 can be appropriately lit. Except for the above points, in FIG. 6, the components denoted by the same reference numerals as those in FIG. 1 have the same or similar functions as those in FIG.

  FIG. 7A shows another example of the circuit configuration of the light source block 58 in FIG. In FIG. 7A, the configuration denoted by the same reference numeral as in FIG. 6 has the same or similar function as the configuration in FIG. In this example, the light source block 58 includes an NMOS transistor 610, an operational amplifier 612, and a resistor 614 instead of the resistor 602 for each light source unit 60.

  The NMOS transistor 610 is connected downstream of the light source unit 60 in series with the light source unit 60, and controls the current flowing through the light source unit 60 in accordance with the voltage received at the gate terminal. The resistor 614 is connected in series with the light source unit 60 and the NMOS transistor 610 and generates a voltage corresponding to the current flowing through the light source unit 60.

  The operational amplifier 612 receives a predetermined constant voltage at the positive input, receives a voltage generated at the resistor 614 at the negative input, and provides an output to the gate terminal of the NMOS transistor 610. As a result, the operational amplifier 612 maintains the current flowing through the light source unit 60 at a predetermined current value. In this case, the light emitting diode 30 can be lighted more appropriately.

  FIG. 7B shows an example of the circuit configuration of the output control unit 116 in this example. The output control unit 116 includes an operational amplifier 620, a comparator 618, a capacitor 616, and a plurality of resistors.

  The operational amplifier 620 is negatively fed back, and the output voltage of the switching regulator 114 divided by a plurality of resistors received at the negative input is compared with a predetermined constant voltage received at the positive input. Output to input. The comparator 618 controls the NMOS transistor 130 by giving the result of comparing the output of the operational amplifier 620 with a predetermined sawtooth voltage received at the negative input to the gate terminal of the NMOS transistor 130.

  The capacitor 616 is a phase compensation capacitor for the operational amplifier 620 and prevents the operational amplifier 620 from oscillating. Further, since various circuits for generating a sawtooth voltage are known, description thereof is omitted. According to this example, the switching regulator 114 can be appropriately controlled.

  FIG. 8A shows another example of the circuit configuration of the light source block 58 in FIG. In FIG. 8A, the configuration denoted by the same reference numeral as in FIG. 7A has the same or similar function as the configuration in FIG. In this example, the output control unit 116 receives the output voltages of the plurality of operational amplifiers 612 instead of the output voltage of the switching regulator 114, and controls the switching regulator 114 based on these.

  FIG. 8B shows an example of a circuit configuration of the output control unit 116 corresponding to the light source block 58 in FIG. In this example, the output control unit 116 includes a plurality of diodes 622, an operational amplifier 620, a comparator 618, a capacitor 616, and a plurality of resistors. The diode 622 is provided corresponding to each of the plurality of operational amplifiers 612, and supplies the output of the corresponding operational amplifier 612 to the positive input of the operational amplifier 620.

  The negative input of the operational amplifier 620 is electrically connected to a constant voltage source via a resistor. The operational amplifier 620 is negatively fed back, and outputs a result obtained by comparing these to the comparator 618. With respect to the other points, in FIG. 8B, the configuration denoted by the same reference numerals as in FIG. 7B has the same or similar functions as the configuration in FIG.

  In this example, when the current flowing through one of the plurality of light source units 60 is smaller than a predetermined current value, the output control unit 116 controls the gate voltage of the NMOS transistor 130, thereby outputting the output of the switching regulator 114. Increase the voltage. Therefore, according to this example, the switching regulator 114 can be appropriately controlled.

  FIG. 9 shows still another example of the circuit configuration of the light source block 58 in FIG. 9, the configuration denoted by the same reference numeral as in FIG. 8A has the same or similar function as the configuration in FIG.

  In this example, the light source block 58 further includes a plurality of diodes 624 provided corresponding to each of the plurality of light source units 60. The anode of the diode 624 is electrically connected to the gate terminal of the NMOS transistor 610, and the cathode receives a selection signal that is an instruction from the outside of the light source block 58.

  Here, when the diode 624 receives a Low signal as a selection signal, the gate voltage of the NMOS transistor 610 is grounded via the diode 624 and the NMOS transistor 610 is turned off, so that the NMOS transistor 610 is connected in series. The light emitting diode 30 included in the light source unit 60 is not lit. On the other hand, when the diode 624 receives a High signal as a selection signal, the diode 624 does not pass a current, and thus the NMOS transistor 610 passes a current having a predetermined value.

  In this example, the operational amplifier 612 provides the output voltage to the gate terminal of the NMOS transistor 610 via a resistor. The cathode of the diode 624 is grounded via a resistor. In this case, according to the selection signal, the light source unit 60 can be appropriately unselected regardless of the output of the operational amplifier 612. According to this example, the light emitting diode 30 can be selectively turned on based on an instruction from the outside.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. Various changes or improvements can be added to the above embodiment. It is apparent from the description of the scope of claims that embodiments with such changes or improvements can be included in the technical scope of the present invention.

  As apparent from the above description, according to the present invention, the light source of the vehicular lamp can be safely turned on.

An example of the circuit structure of the vehicle lamp 10 which concerns on an example of embodiment of this invention is shown. An example of the circuit structure of the abnormality detection part 120 is shown. The other example of the circuit structure of the output voltage monitoring part 202 is shown. FIG. 3A shows another example of the circuit configuration of the output voltage monitoring unit 202. FIG. 3B shows still another example of the circuit configuration of the output voltage monitoring unit 202. Another example of the circuit configuration of the hold unit 204 is shown. Another example of the circuit configuration of the lighting circuit 102 is shown. The other example of the circuit structure of the vehicle lamp 10 is shown. Another example of the light source block 58 and the output control unit 116 is shown. FIG. 7A shows another example of the circuit configuration of the light source block 58. FIG. 7B shows an example of the circuit configuration of the output control unit 116. Another example of the light source block 58 and the output control unit 116 is shown. FIG. 8A shows another example of the circuit configuration of the light source block 58. FIG. 8B shows an example of the circuit configuration of the output control unit 116. Another example of the circuit configuration of the light source block 58 will be described.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Vehicle lamp, 30 ... Light emitting diode, 58 ... Light source block, 60 ... Light source unit, 102 ... Lighting circuit, 106 ... Resistance, 112 ... DC power supply, 114 ... Switching regulator, 116 ... Output control unit, 120 ... Abnormality detection unit, 128 ... Transformer, 130 ... NMOS transistor, 200 ... Disconnection detection unit, 202 ... Output voltage monitoring , 204 ... Hold unit, 206 ... Power supply voltage monitoring unit, 208 ... Supply current monitoring unit, 210 ... Abnormal signal output unit, 212 ... Disconnection detection unit, 440 ... Inversion unit

Claims (2)

A vehicle lighting circuit for lighting a plurality of light emitting diodes arranged in a vehicle lamp, wherein the vehicle lamp includes at least one light emitting diode, and has a plurality of light source units connected in parallel.
The vehicle lighting circuit is:
A plurality of transistors connected in series to each column of the light source units connected in parallel and controlling a current flowing through the light source unit according to a voltage received by a gate terminal;
A plurality of resistors connected in series to each row of the light source units connected in parallel;
It is connected in series to each row of the light source units connected in parallel, and a predetermined voltage and a voltage generated in the resistor due to a current flowing through the light source unit are supplied to the input, and the light source unit is connected to the light source unit. A plurality of operational amplifiers for providing an output to the gate terminal of the transistor;
A switching regulator that supplies a supply current to the plurality of light emitting diodes by applying an output voltage based on a power supply voltage received from a DC power supply provided outside to the plurality of light source units;
An output control unit for controlling an output voltage of the switching regulator based on the outputs of the operational amplifiers provided to the gate terminals;
The output control unit increases the output voltage of the switching regulator when a current flowing through any of the plurality of light source units is smaller than a predetermined current value.   A selection signal for selecting lighting of the light source unit to which the transistor is connected is applied to each of the gate terminals of the plurality of transistors, and the light source unit is selectively lit according to the selection signal. The lighting circuit for vehicles according to 1.

Images