JP2011009474A - Light emitting diode driving apparatus, and luminaire, lighting device for vehicle interiors and lighting device for vehicles employing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress overcurrent flowing in a light emitting diode, and to reduce variation of light flux rising characteristics of the light emitting diode caused by a temperature.SOLUTION: A light emitting diode driving apparatus has: a DC-DC converter 2 that converts a DC voltage V1 output from a DC power supply 1 into a desired output voltage V2, and applies the voltage to a light emitting unit 3 having light emitting diodes LED1-5; a current restricting circuit 9 provided in a path of an output current Io supplied from the DC-DC converter 2 to the light emitting unit 3, which restricts the maximum value of the output current Io supplied to the light emitting unit 3; and a current control circuit 7 that controls so that the rising characteristics of the output current Io supplied to the light emitting unit 3 at the start of output of the DC-DC converter or at the load connection becomes substantially constant, based on a temperature of the light emitting unit 3.

Description

  The present invention relates to a light emitting diode driving device that drives a light emitting diode as a light source, and a lighting fixture, a vehicle interior lighting device, and a vehicle lighting device using the light emitting diode driving device.

  In recent years, instead of halogen lamps and discharge lamps, light-emitting diodes have been increasingly adopted in automobile interior lights (room lamps), headlamps (headlights), taillights (rear combination lamps), and Europe. It is being used for a light source such as a running light (a headlamp for improving visibility from an oncoming vehicle in the daytime).

  However, when the light emitting diode driving device is started or when a load is connected, an overcurrent flows through the light emitting diode, and chip deterioration due to disconnection of bonding wires or current concentration has become a problem.

  Therefore, a conventional example of a light emitting diode driving device in which overcurrent flowing through the light emitting diode is suppressed is shown (for example, Patent Document 1).

  The light emitting diode driving device according to the conventional example includes a current limiting resistor configured by a fixed resistor in a circuit connecting the light emitting diode driving device and the light emitting diode in order to suppress an overcurrent flowing through the light emitting diode. This current limiting resistor suppresses overcurrent flowing through the light emitting diode when the light emitting diode driving device is started or when a load is connected, thereby protecting the light emitting diode.

JP 2007-126041 A

  When a forward voltage Vf lower than a certain threshold voltage Vth is applied to the light emitting diode, almost no current flows, but when the forward voltage Vf exceeds the threshold voltage Vth, a current flows suddenly.

  Further, the threshold voltage Vth has a property of fluctuating with temperature. FIG. 7 shows the temperature characteristics of the forward current If with respect to the forward voltage Vf applied to the light emitting diode. Y1 shows the characteristic of the forward current If with respect to the forward voltage Vf at 25 ° C. When the forward voltage Vf is lower than 0.75V, the forward current If hardly flows. However, when the forward voltage Vf exceeds 0.75V, the forward current If suddenly increases. That is, the threshold voltage Vth of Y1 is 0.75V.

  Next, the characteristic of the forward current If with respect to the forward voltage Vf at 85 ° C. is indicated by Y2. The threshold voltage Vth of Y2 is 0.6V, which is lower than the threshold voltage Vth (25V) at 25 ° C. shown in Y1. A characteristic of the forward current If with respect to the forward voltage Vf at −25 ° C. is indicated by Y3. The threshold voltage Vth of Y3 is 0.92 V, which is higher than the threshold voltage Vth (25 V) at 25 ° C. shown in Y1.

  Therefore, the threshold voltage Vth decreases as the light emitting diode becomes hot, and the threshold voltage Vth increases as the light emitting diode becomes cold.

  FIG. 8A shows the forward voltage Vf, the power consumption W, and the forward resistance Rf generated when a forward current If flows through the light emitting diode at 2 A.

  From FIG. 7, the forward voltage Vf at each temperature when the forward current If is 2 A is 0.7 V at 85 ° C., 0.85 V at 25 ° C., and 1.02 V at −25 ° C. Therefore, the value of the power consumption W of the light emitting diode at each temperature is 1.4 W at 85 ° C., 1.7 W at 25 ° C., and 2.04 W at −25 ° C., and the forward resistance Rf of the light emitting diode at each temperature. The value is 0.35Ω at 85 ° C., 0.425Ω at 25 ° C., and 0.51Ω at −25 ° C. Using this result, FIG. 8B shows the temperature characteristics of the forward voltage Vf and the forward resistance Rf. The characteristic of the forward voltage Vf with respect to temperature is indicated by Y4 using the first axis in FIG. 8B, and the characteristic of the forward resistance Rf with respect to temperature is indicated by Y5 using the second axis.

  When a constant current is passed through the light emitting diode, the forward voltage Vf and the forward resistance Rf become smaller as the temperature of the light emitting diode becomes higher, and the forward voltage Vf and the forward resistance Rf become larger as the temperature of the light emitting diode becomes lower.

  FIG. 8B shows the temperature characteristics of a current limiting resistor formed of a fixed resistor provided in the conventional light emitting diode driving device as Y6. Y6 does not vary depending on the temperature of the light emitting diode, and shows a constant resistance value.

  Here, in the light emitting diode driving device of the conventional example, it is assumed that five light emitting diodes having the above characteristics are connected in series. The combined resistance when five light emitting diodes at each temperature are connected is derived as shown in equations (1) to (3).

Combined resistance at 85 ° C. = 0.35 (Ω) × 5 = 1.75 (Ω) (1)
Combined resistance at 25 ° C. = 0.425 (Ω) × 5 = 2.125 (Ω) (2)
Synthetic resistance at −25 ° C. = 0.51 (Ω) × 5 = 2.55 (Ω) (3)
The resistance value of the entire load of the light emitting diode driving device of the conventional example is a value obtained by adding the combined resistance of the forward resistance Rf of the light emitting diode and the current limiting resistance composed of a fixed resistance, and the resistance of the entire load at 85 ° C. The value is minimized. Therefore, when the output voltage of the light emitting diode driving device is constant, the output current becomes maximum at 85 ° C.

  Therefore, in the conventional LED driving device, when 85 ° C. is the maximum operating temperature, the resistance of the current limiting resistor configured by a fixed resistor is taken into consideration at 85 ° C. when the forward resistance Rf of the LED is the lower limit. It is necessary to decide the value.

  However, when the temperature of the light emitting diode fluctuates, there is a problem that the light beam rise characteristic of the light emitting diode is degraded. Since the forward resistance Rf of the light emitting diode when the temperature of the light emitting diode is lower than 85 ° C. is larger than the resistance value at 85 ° C., the output current is suppressed more than necessary. As a result, the luminous flux rise characteristic of the light emitting diode is degraded. Further, when the temperature of the light emitting diode is lower or when the number of light emitting diodes is larger, the luminous flux rising characteristics of the light emitting diode are further deteriorated.

  The present invention has been made in view of the above-described reasons, and an object thereof is to suppress an overcurrent flowing through the light-emitting diode and reduce a variation in the light-emission rise characteristic of the light-emitting diode due to temperature, and the same An object of the present invention is to provide a lighting device, a vehicle interior lighting device, and a vehicle lighting device using the above.

  According to the first aspect of the present invention, a DC-DC converter that converts a DC voltage output from a DC power source into a desired DC voltage and applies it to a light-emitting unit including one or more light-emitting diodes, and light emission from the DC-DC converter. A resistance means provided in a path of a current supplied to the light-emitting section, for limiting the maximum value of the current supplied to the light-emitting section, and based on the temperature of the light-emitting section, at the start of output of the DC-DC converter or load connection And a light emitting portion current control means for controlling the rising characteristic of the current supplied to the light emitting portion to be substantially constant.

  According to the present invention, in the light emitting diode driving device, an overcurrent flowing through the light emitting diode is suppressed, and fluctuation of the light-emission rise characteristic of the light emitting diode due to temperature at the time of starting the output of the DC-DC converter or connecting the load is reduced. Can be made.

  According to a second aspect of the present invention, in the first aspect of the present invention, the temperature detecting unit includes a temperature sensing element that detects a temperature of the light emitting unit, the resistance unit includes a variable resistor, and the light emitting unit current control is performed. The means increases the resistance value of the variable resistor as the temperature of the light emitting unit becomes higher, and decreases the resistance value of the variable resistor as the temperature of the light emitting unit becomes lower, based on the detection result of the temperature detecting means. The load of the DC-DC converter is controlled to be substantially constant when the output of the converter is started or when the load is connected.

  According to the present invention, it is possible to detect the temperature of the light emitting diode accurately by detecting the temperature of the light emitting diode using the temperature sensing element, and based on the detection result, the current limit configured by the variable resistor. By controlling the resistance value of the unit, it is possible to reduce the variation of the light-emission rise characteristic of the light-emitting diode due to the temperature when starting the output of the DC-DC converter or when connecting the load.

  According to a third aspect of the present invention, in the first aspect of the present invention, the temperature detecting unit includes a temperature sensing element that detects the temperature of the light emitting unit, the resistance unit includes a transistor, and the light emitting unit current control unit is provided. Based on the detection result of the temperature detecting means, the resistance at both ends of the transistor is increased as the temperature of the light emitting portion becomes higher, and the resistance at both ends of the transistor is decreased as the temperature of the light emitting portion becomes lower. It is characterized in that the load of the DC-DC converter is controlled to be substantially constant at the time of starting the output or when the load is connected.

  According to this invention, the temperature of the light emitting diode can be detected by detecting the temperature of the light emitting diode using the temperature sensitive element, and the current limiting unit configured by the transistor is based on the detection result. By controlling the resistances at both ends of the LED, it is possible to reduce fluctuations due to temperature in the luminous flux rising characteristics of the light emitting diodes when starting the output of the DC-DC converter or when connecting the load.

  According to a fourth aspect of the present invention, in the first aspect of the present invention, the temperature detecting unit includes a temperature sensing element that detects the temperature of the light emitting unit, and the light emitting unit current control unit is based on a detection result of the temperature detecting unit. The output voltage of the DC-DC converter is reduced as the temperature of the light emitting unit becomes high, and the output voltage of the DC-DC converter is increased as the temperature of the light emitting unit becomes low. Alternatively, the rising characteristic of the current supplied to the light emitting unit when the load is connected is controlled to be substantially constant.

  According to the present invention, by controlling the output voltage of the DC-DC converter based on the temperature of the light-emitting unit, the temperature of the light-emitting diode light-emission rise characteristic at the start of the output of the DC-DC converter or when the load is connected. The fluctuation due to can be reduced.

  According to a fifth aspect of the present invention, in the first aspect of the invention, the storage means stores the output voltage of the DC-DC converter before the output of the DC-DC converter stops or before the load becomes no load. Based on the temperature of the light emitting unit estimated from the stored output voltage of the DC-DC converter, the light emitting unit current control means decreases the output voltage of the DC-DC converter as the light emitting unit becomes hot, By increasing the output voltage of the DC-DC converter as the temperature of the light emitting unit becomes low, the rising characteristic of the current supplied to the light emitting unit at the start of the output of the DC-DC converter or when the load is connected is controlled to be substantially constant. It is characterized by doing.

  According to the present invention, it is not necessary to provide a temperature sensing element for detecting the temperature of the light emitting diode, and the temperature of the light emitting diode can be estimated. Therefore, the number of parts constituting the light emitting diode driving device can be reduced, and the cost can be reduced. Can be lowered.

  A sixth aspect of the present invention is the method according to the fifth aspect of the present invention, wherein charging is performed when current is supplied from the DC-DC converter to the light emitting unit, and current supplied from the DC-DC converter to the light emitting unit is stopped. A light-emitting section current control means based on the temperature of the light-emitting section estimated from the output voltage of the DC-DC converter stored in the storage means and the voltage across the capacitor. The output voltage of the DC-DC converter is decreased as the temperature of the light emitting unit is increased, and the output voltage of the DC-DC converter is increased as the temperature of the light emitting unit is decreased. The rising characteristic of the current supplied to the light emitting unit when the load is connected is controlled to be substantially constant.

  According to the present invention, the temperature of the light emitting diode can be estimated even when the stop time is long.

  The invention of claim 7 is the invention of claim 6, further comprising an ambient temperature detection means for detecting an ambient temperature, and the output voltage of the DC-DC converter stored in the storage means, and the voltage across the capacitor. Based on the temperature of the light emitting part estimated from the detection result of the ambient temperature detecting means, the light emitting part current control means decreases the output voltage of the DC-DC converter as the light emitting part becomes hot, and the light emitting part By increasing the output voltage of the DC-DC converter as the temperature becomes lower, the rising characteristic of the current supplied to the light emitting unit at the start of the output of the DC-DC converter or when the load is connected is controlled to be substantially constant. It is characterized by.

  According to the present invention, the temperature of the light emitting diode can be estimated even when the ambient temperature changes at the time of stoppage.

  The invention of claim 8 is a light emitting diode driving device according to any one of claims 1 to 7, a light emitting unit comprising one or more light emitting diodes, a light emitting diode driving device, and an instrument for holding the light emitting unit. And a main body.

  According to the present invention, in the lighting fixture, it is possible to suppress an overcurrent flowing through the light emitting diode, and to reduce fluctuations in the light-emission rise characteristic of the light emitting diode due to temperature.

  A ninth aspect of the invention includes the light-emitting diode driving device according to any one of the first to seventh aspects, and a light-emitting unit in which one or more light-emitting diodes are provided in a vehicle interior.

  According to the present invention, in the vehicle interior lighting device, it is possible to suppress the overcurrent flowing through the light emitting diode and to reduce the variation of the light beam rise characteristic of the light emitting diode due to the temperature.

  A tenth aspect of the present invention includes the light emitting diode driving device according to any one of the first to seventh aspects, and a light emitting unit in which one or a plurality of light emitting diodes irradiate light around a vehicle. To do.

  According to the present invention, in the vehicular lighting device, it is possible to suppress an overcurrent flowing through the light emitting diode and reduce a variation in temperature of a light beam rising characteristic of the light emitting diode.

  As described above, according to the present invention, there is an effect that the overcurrent flowing through the light emitting diode can be suppressed and the variation of the light beam rise characteristic of the light emitting diode due to the temperature can be reduced.

1 is a circuit configuration diagram showing a first embodiment of the present invention. It is a circuit block diagram which shows 2nd Embodiment same as the above. It is a circuit block diagram which shows 3rd Embodiment same as the above. It is a circuit block diagram which shows 4th Embodiment same as the above. It is a circuit block diagram which shows 5th Embodiment same as the above. It is a circuit block diagram which shows 6th Embodiment same as the above. It is a graph which shows the electric current with respect to the forward voltage of a light emitting diode. (A) Table showing temperature characteristics of light emitting diode, (b) Graph showing temperature characteristics of forward voltage and resistance of light emitting diode.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
As a first embodiment of the present invention, FIG. 1 shows a schematic circuit configuration diagram. In the present embodiment, a DC power source 1 such as an automobile battery that outputs a DC voltage V1, and a DC that is supplied from the DC power source 1 via a power switch SW and converts the DC voltage V1 into a desired DC output voltage V2. The DC-DC converter 2 is connected to the DC-DC converter 2 via the output terminals A and B and the output terminals A and B. The output voltage V2 is applied. Light emitting unit 3, voltage detection circuit 4 for detecting output voltage V2 applied from DC-DC converter 2 to light emitting unit 3, and current detection circuit for detecting output current Io supplied from DC-DC converter 2 to light emitting unit 3 5, a voltage control circuit 6 that controls the output voltage V 2 by controlling the operation of the DC-DC converter 2, a current control circuit 7 that controls the output current Io, and a light emitting unit 3. A temperature sensing element 8 which is kicked, and is configured overcurrent flowing through the light emitting portion 3 by the suppressing current limiting circuit 9.

  The DC-DC converter 2 is a conventionally well-known flyback type, and is composed of a power MOSFET or the like. The switching element Q1 that is turned on / off by the voltage control circuit 6 and one end of the primary winding are the power switch SW. Is connected to the positive electrode of the DC power source 1 via the transformer T, and the other end of the primary winding is connected to the negative electrode of the DC power source 1 via the switching element Q1, and one end of the secondary winding of the transformer T. And a smoothing capacitor C0 connected between the cathode of the diode D1 and the other end of the secondary winding. That is, when the switching element Q1 is turned on by the voltage control circuit 6, current flows through the primary winding and energy is stored in the transformer T, and energy stored in the transformer T when the switching element Q1 is turned off. Is supplied from the secondary winding to the smoothing capacitor C0 via the diode D1. Then, the voltage control circuit 6 performs PWM control of the switching element Q1 to increase / decrease the DC voltage V1 output from the DC power source 1 and output a desired output voltage V2.

  The light emitting unit 3 is composed of light emitting diodes connected in series, and the light emitting unit 3 of the present embodiment includes five light emitting diodes LEDs 1 to 5.

  The voltage detection circuit 4 includes voltage dividing resistors R1 and R2 connected in series between the outputs of the DC-DC converter 2 (both ends of the smoothing capacitor C0), and a voltage detection value Vx (= R2 / R) obtained by dividing the output voltage V2. (R1 + R2) × V2) is output to the voltage control circuit 6.

  The current detection circuit 5 is inserted between the light emitting unit 3 and the voltage detection circuit 4 and includes one end of a detection resistor R3 connected to the negative electrode of the DC power supply 1, and a voltage drop generated at both ends of the detection resistor R3 is output current. This is output to the voltage control circuit 6 as a current detection value Vy (= R3 × Io) of Io.

  Based on the voltage detection value Vx output from the voltage detection circuit 4, the voltage control circuit 6 includes a reference current setting unit 61 that outputs a reference value Vx2 corresponding to a reference current having a predetermined value for the power consumption of the light emitting unit 3. The output voltage control unit 62 that outputs a control signal based on the reference value Vx2 and the current detection value Vy output from the current detection circuit 5, and the on-duty of the switching element Q1 based on the control signal of the output voltage control unit 62 A PWM control unit 63 that outputs a PWM signal for adjusting the ratio, and a driver unit 64 that turns on and off the switching element Q1 at an on-duty ratio corresponding to the PWM signal output from the PWM control unit 63. Yes. The control signal output from the driver unit 64 is connected to the gate of the switching element Q1 via the gate resistor R4, and controls the output voltage V2 of the DC-DC converter 2 by controlling the operation of the switching element Q1.

  The current limiting circuit 9 includes a current limiting resistor R5 that is inserted between the light emitting unit 3 and the current detecting circuit 5 and configured by a variable resistor. The current limiting resistor R5 prevents overcurrent generated when the DC-DC converter 2 is started or when the light emitting unit 3 is disconnected from the output terminals A and B of the DC-DC converter 2 and connected to a load such as chattering that is reconnected. Suppress.

  The basic operation of this embodiment will be described below.

  When the power switch SW is turned on, the voltage control circuit 6 operates the DC-DC converter 2 to output the DC output voltage V2, and the output current Io flows to the light emitting unit 3. The voltage control circuit 6 controls the output voltage V2 of the DC-DC converter 2 by PWM control of the switching element Q1 so that the current detection value Vy of the current detection circuit 5 matches the reference value Vx2.

  For example, if the rated value of the forward voltage Vf of the light emitting diodes LED1 to LED5 of the light emitting unit 3 is 3.5V, the output voltage V2 of the DC-DC converter 2 is set to 3.5V × 5 = 17.5V in a steady state. If set, an output current Io having a rated value can be passed through the light emitting unit 3.

  In addition, since the DC-DC converter 2 in this embodiment can perform either a step-up operation or a step-down operation by the voltage control circuit 6, when the DC voltage V1 of the DC power source 1 is a 12V automobile battery, the DC-DC The converter 2 is boosted to set the output voltage V2 to 17.5V. When the DC voltage V1 is a 24V or 48V automobile battery, the DC-DC converter 2 is stepped down to set the output voltage V2 to 17.5V, so that the light emitting unit is irrelevant to the DC voltage V1 of the DC power supply 1. 3 can be driven at a constant current.

  In addition, the present embodiment includes a current control circuit 7 that controls the output current Io of the DC-DC converter 2 in order to reduce fluctuations due to temperature changes in the luminous flux rising characteristics of the light-emitting diodes LEDs 1 to 5.

  The current control circuit 7 includes a current limiting resistor R5 configured by a variable resistor, a temperature calculating unit 71 that detects the temperature of the light emitting unit 3 using the temperature sensing element 8, and a resistor that controls the resistance value of the current limiting resistor R5. A command unit 72 is included.

  The temperature calculation unit 71 detects the temperature of the light emitting unit 3 by passing a current through the temperature sensing element 8 including a thermistor disposed in the vicinity of the light emitting unit 3 and measuring the voltage across the thermistor.

  The resistance command unit 72 determines the output state of the DC-DC converter 2 based on the fluctuation of the current detection value Vy of the current detection circuit 5. For example, when the current detection value Vy becomes lower than a predetermined value, it is determined that the DC-DC converter 2 is stopped by turning off the switch SW or the no-load state where the light emitting unit 3 is disconnected from the DC-DC converter 2. Further, when the current detection value Vy exceeds a predetermined value, it is determined that the DC-DC converter 2 is started by turning on the switch SW or a load connection state in which the light emitting unit 3 is connected to the DC-DC converter 2. Further, when the current detection value Vy is equal to or greater than a predetermined value and the fluctuation range is within a predetermined range for a certain time, it is determined that the DC-DC converter 2 is in a steady state.

  Also, the resistance command unit 72 controls the resistance value of the current limiting resistor R5 configured by a variable resistor based on the temperature of the light emitting unit 3 detected by the temperature calculation unit 71, thereby starting the DC-DC converter 2. The fluctuation due to the temperature change of the luminous flux rising characteristics of the light-emitting diodes LED1 to 5 at the time of connection or load is reduced.

  Specific control of the resistance value of the current limiting resistor R5 will be described below.

  As shown in FIG. 8B of the conventional example, the temperature characteristic of the forward resistance Rf of the light emitting diodes LED1 to LED5 decreases as the temperature of the light emitting diodes LED1 to LED5 increases. Thus, the forward resistance Rf of the light emitting diode increases as the temperature of the light emitting diodes LED1 to LED5 decreases.

  Therefore, when the DC-DC converter 2 is started or connected to a load, the temperature calculation unit 71 detects the temperature of the light emitting unit 3 with the temperature sensing element 8, and the resistance command unit 72 detects the forward resistance Rf of the light emitting diodes LED1 to LED5. Based on the temperature characteristics, the current limiting resistance R5 is increased as the temperature of the light emitting unit 3 is increased, and the current limiting resistance R5 is decreased as the temperature of the light emitting unit 3 is decreased. Controls the resistance value of R5.

  By controlling the resistance value of the current limiting resistor R5 as described above, the forward resistance Rf of the light emitting diodes LED1 to 5 even if the temperature of the light emitting unit 3 varies and the forward resistance Rf of the light emitting diodes LED1 to 5 varies. And the current limiting resistor R5 are added, the resistance value of the entire load of the DC-DC converter 2 becomes substantially constant.

  Therefore, even when the temperature of the light emitting unit 3 fluctuates, the output current Io of the DC-DC converter 2 can be made substantially constant when the DC-DC converter 2 is started or when a load is connected. 5 can be reduced due to temperature changes.

  In addition, when the output current Io of the DC-DC converter 2 is steady, the resistance command unit 72 of the current control circuit 7 controls the resistance value of the current limiting resistor R5 to 0Ω, so that unnecessary power is generated by the current limiting resistor R5. Loss can be suppressed. In addition, by configuring the current limiting resistor R5 with a variable resistor, there is no need to provide a bypass circuit for bypassing the current limiting resistor R5, so that the number of parts constituting the light emitting diode driving device can be reduced and the cost can be reduced. Can do.

(Embodiment 2)
As a second embodiment of the present invention, FIG. 2 shows a schematic circuit configuration diagram. In the present embodiment, a DC power source 1, a DC-DC converter 2, a light emitting unit 3, a voltage detection circuit 4, a current detection circuit 5, a voltage control circuit 6, a current control circuit 7, a temperature sensing element 8, and a current limiting circuit 9 It is configured. Note that the DC power supply 1, the DC-DC converter 2, the light emitting unit 3, the voltage detection circuit 4, the current detection circuit 5, the voltage control circuit 6, and the temperature sensing element 8 have the same configuration as in the first embodiment, and are identical. The reference numerals are attached and the description is omitted.

  The current limiting circuit 9 in the present embodiment is inserted between the light emitting unit 3 and the current detection circuit 5 and includes an NPN transistor Q2. The collector terminal of the transistor Q2 is connected to the light emitting unit 3 via the output terminal B, and the emitter terminal is connected to the detection resistor R3, so that the transistor Q2 becomes a part of the current path of the output current Io. Then, by using the active region of the transistor Q2, overcurrent that occurs when the DC-DC converter 2 is started or when a load is connected is suppressed.

  In addition, the present embodiment includes a current control circuit 7 that controls the output current Io of the DC-DC converter 2 in order to reduce fluctuations due to temperature changes in the luminous flux rising characteristics of the light-emitting diodes LEDs 1 to 5.

  The current control circuit 7 includes a transistor Q2, a temperature calculation unit 71 that detects the temperature of the light emitting unit 3 using the temperature sensing element 8, a base current command unit 73 that controls a base current output to the base terminal of the transistor Q2. It consists of

  The temperature calculation unit 71 detects the temperature of the light emitting unit 3 by passing a current through the temperature sensing element 8 including a thermistor disposed in the vicinity of the light emitting unit 3 and measuring the voltage across the thermistor.

  The base current command unit 72 determines the output state of the DC-DC converter 2 based on the fluctuation of the current detection value Vy of the current detection circuit 5. For example, when the current detection value Vy becomes lower than a predetermined value, it is determined that the DC-DC converter 2 is stopped by turning off the switch SW or the no-load state in which the light emitting unit 3 is disconnected from the DC-DC converter 2. When the detection value Vy exceeds a predetermined value, it is determined that the DC-DC converter 2 is started by turning on the switch SW or a load connection state in which the light emitting unit 3 is connected to the DC-DC converter 2. Further, when the current detection value Vy is equal to or greater than a predetermined value and the fluctuation range is within a predetermined range for a certain time, it is determined that the DC-DC converter 2 is in a steady state.

  Further, the base current commanding unit 73 controls the resistance between the collector and the emitter of the transistor Q2 by controlling the base current of the transistor Q2 based on the temperature of the light emitting unit 3 detected by the temperature calculation unit 71, and the DC -The fluctuation | variation by the temperature change of the luminous flux rise characteristic of light emitting diode LED1-5 at the time of starting of the DC converter 2 or a load connection is reduced.

  A specific control of the transistor Q2 by the base current command unit 73 will be described below.

  As shown in FIG. 8B of the conventional example, the temperature characteristic of the forward resistance Rf of the light emitting diodes LED1 to LED5 decreases as the temperature of the light emitting diodes LED1 to LED5 increases. Thus, the forward resistance Rf of the light emitting diode increases as the temperature of the light emitting diodes LED1 to LED5 decreases.

  Therefore, when the DC-DC converter 2 is started or a load is connected, the temperature calculation unit 71 detects the temperature of the light emitting unit 3 with the temperature sensing element 8, and the gate current command unit 73 detects the forward resistance Rf of the light emitting diodes LED1 to LED5. Based on this temperature characteristic, the gate current output to the transistor Q2 is controlled. That is, as the temperature of the light emitting unit 3 becomes higher, the gate current output to the transistor Q2 is reduced and the resistance between the collector and emitter of the transistor Q2 is increased. Further, as the temperature of the light emitting unit 3 becomes lower, the gate current output to the transistor Q2 is increased, and the resistance between the collector and the emitter of the transistor Q2 is decreased.

  By controlling the gate current of the transistor Q2 as described above, the forward resistance Rf of the light emitting diodes LED1 to 5 and the transistor even if the forward resistance Rf of the light emitting diodes LED1 to LED5 varies due to the temperature variation of the light emitting unit 3. The resistance value of the entire load of the DC-DC converter 2 including the resistance between the collector and the emitter of Q2 is substantially constant.

  Therefore, even when the temperature of the light emitting unit 3 fluctuates, the output current Io of the DC-DC converter 2 can be made substantially constant when the DC-DC converter 2 is started or when a load is connected. 5 can be reduced due to temperature changes.

  Further, when the output current Io of the DC-DC converter 2 is steady, the gate current command unit 73 of the current control circuit 7 can suppress unnecessary power loss due to the transistor Q2 by saturating the transistor Q2.

(Embodiment 3)
As a third embodiment of the present invention, FIG. 3 shows a schematic circuit configuration diagram. The present embodiment includes a DC power source 1, a DC-DC converter 2, a light emitting unit 3, a voltage detection circuit 4, a current detection circuit 5, a voltage control circuit 6, a temperature sensing element 8, and a current limiting circuit 9. Note that the DC power source 1, the DC-DC converter 2, the light emitting unit 3, the voltage detection circuit 4, the current detection circuit 5, and the temperature sensitive element 8 have the same configurations as those of the first embodiment, and are denoted by the same reference numerals. Description is omitted.

  The current limiting circuit 9 in the present embodiment includes a current limiting resistor R6 that is inserted between the light emitting unit 3 and the current detecting circuit 5 and is configured with a fixed resistor. When the DC-DC converter 2 is started or a load is connected. Suppresses the overcurrent that occurs.

  Based on the voltage detection value Vx output from the voltage detection circuit 4, the voltage control circuit 6 includes a reference current setting unit 61 that outputs a reference value Vx2 corresponding to a reference current having a predetermined value for the power consumption of the light emitting unit 3. The temperature calculation unit 71 that detects the temperature of the light emitting unit 3 using the temperature sensing element 8, and the output voltage control that outputs the control signal based on the reference value Vx2 and the current detection value Vy output from the current detection circuit 5. Unit 62, a PWM control unit 63 that outputs a PWM signal for adjusting the on-duty ratio of switching element Q1 based on the control signal of output voltage control unit 62, and a PWM signal output from PWM control unit 63 And a driver unit 64 for turning on / off the switching element Q1 at an on-duty ratio. The control signal output from the driver unit 64 is connected to the gate of the switching element Q1 via the gate resistor R4, and controls the output voltage V2 of the DC-DC converter 2 by controlling the operation of the switching element Q1.

  Specific control of the output voltage V2 by the voltage control circuit 6 will be described below.

  The output voltage control unit 62 determines the output state of the DC-DC converter 2 based on the fluctuation of the current detection value Vy of the current detection circuit 5. For example, when the current detection value Vy becomes lower than a predetermined value, it is determined that the DC-DC converter 2 is stopped by turning off the switch SW or the no-load state where the light emitting unit 3 is disconnected from the DC-DC converter 2. Further, when the current detection value Vy exceeds a predetermined value, it is determined that the DC-DC converter 2 is started by turning on the switch SW or a load connection state in which the light emitting unit 3 is connected to the DC-DC converter 2. In addition, when the current detection value Vy is equal to or greater than a predetermined value and the fluctuation range is within a predetermined range for a certain time, the DC-DC converter 2 determines that it is in a steady state.

  When the DC-DC converter 2 is in a steady state, the output voltage control unit 62 controls the control signal based on the reference value Vx2 output from the reference current setting unit 61 and the current detection value Vy output from the current detection circuit 5. Is output to the PWM control unit 63, and the driver unit 64 controls the output current Io to be constant by changing the output voltage V2 of the DC-DC converter 2.

  When the DC-DC converter 2 is turned on by turning on the switch SW, the output voltage control unit 62 outputs a control signal based on the temperature of the light emitting unit 3 detected by the temperature calculation unit 71.

  As shown in FIG. 8B of the conventional example, the temperature characteristic of the forward resistance Rf of the light emitting diodes LED1 to LED5 decreases as the temperature of the light emitting diodes LED1 to LED5 increases. Thus, the forward resistance Rf of the light emitting diode increases as the temperature of the light emitting diodes LED1 to LED5 decreases.

  Therefore, when the DC-DC converter 2 is started, the output voltage control unit 62 controls the output voltage V2 based on the temperature characteristics of the forward resistance Rf of the light emitting diodes LED1 to LED5. That is, using the temperature of the light emitting unit 3 detected by the temperature calculation unit 71, the output voltage control unit 62 controls the output voltage V2 of the DC-DC converter 2 to be smaller as the light emitting unit 3 becomes higher temperature, Control is performed so that the output voltage V2 of the DC-DC converter 2 increases as the temperature of the light emitting unit 3 decreases.

  By controlling the output voltage V2 of the DC-DC converter 2 based on the temperature of the light emitting unit 3 as described above, the temperature of the light emitting unit 3 varies and the forward resistance Rf of the light emitting diodes LED1 to LED5 varies. In addition, the output current Io of the DC-DC converter 2 when the DC-DC converter 2 is started can be made substantially constant.

  Accordingly, it is possible to reduce the fluctuation due to the temperature change of the luminous flux rising characteristics of the light emitting diodes LED1 to LED5 when the DC-DC converter 2 is started.

  Further, even in the load connection state in which the light emitting unit 3 is connected to the DC-DC converter 2, the output voltage control unit 62 of the light emitting unit 3 detected by the temperature calculation unit 71 is the same as the starting state of the DC-DC converter 2. By controlling the output voltage V2 of the DC-DC converter 2 based on the temperature, even if the temperature of the light emitting unit 3 varies and the forward resistance Rf of the light emitting diodes LED1 to LED5 varies, the output of the DC-DC converter 2 The fluctuation due to the temperature change of the luminous flux rising characteristics of the light emitting diodes LED1 to LED5 when the load is connected can be reduced.

(Embodiment 4)
As a fourth embodiment of the present invention, FIG. 4 shows a schematic circuit configuration diagram. The present embodiment includes a DC power source 1, a DC-DC converter 2, a light emitting unit 3, a voltage detection circuit 4, a current detection circuit 5, a voltage control circuit 6, and a current limiting circuit 9. Note that the DC power supply 1, the DC-DC converter 2, the light emitting unit 3, the voltage detection circuit 4, the current detection circuit 5, and the current limiting circuit 9 have the same configurations as those in the third embodiment, and are denoted by the same reference numerals. Description is omitted.

  The voltage control circuit 6 of the present embodiment includes a storage device 65 that stores the voltage detection value Vx output from the voltage detection circuit 4 and the voltage detection value Vx stored in the storage device 65. A reference current setting unit 61 that outputs a reference value Vx2 corresponding to a reference current whose power consumption is a predetermined value, and a control signal is output based on the reference value Vx2 and the current detection value Vy output from the current detection circuit 5. The output voltage control unit 62, the PWM control unit 63 that outputs a PWM signal for adjusting the on-duty ratio of the switching element Q1 based on the control signal of the output voltage control unit 62, and the PWM that is output from the PWM control unit 63 The driver unit 64 is configured to turn on and off the switching element Q1 with an on-duty ratio corresponding to the signal. The control signal output from the driver unit 64 is connected to the gate of the switching element Q1 via the gate resistor R4, and controls the output voltage V2 of the DC-DC converter 2 by controlling the operation of the switching element Q1.

  Specific control of the output voltage V2 by the voltage control circuit 6 will be described below.

  The storage device 65 stores the voltage detection value Vx from the present to a certain period before. The output voltage control unit 62 determines the output state of the DC-DC converter 2 based on the fluctuation of the current detection value Vy of the current detection circuit 5. For example, when the current detection value Vy becomes lower than a predetermined value, it is determined that the DC-DC converter 2 is stopped by turning off the switch SW or the no-load state where the light emitting unit 3 is disconnected from the DC-DC converter 2. When the current detection value Vy exceeds a predetermined value, it is determined that the DC-DC converter 2 is started by turning on the switch SW or a load reconnection state in which the light emitting unit 3 is reconnected to the DC-DC converter 2. . In addition, when the current detection value Vy is equal to or greater than a predetermined value and the fluctuation range is within a predetermined range for a certain time, the DC-DC converter 2 determines that it is in a steady state.

  When the DC-DC converter 2 is in a steady state, the reference current setting unit 61 corresponds to a reference current that uses the power consumption of the light emitting unit 3 as a predetermined value based on the latest voltage detection value Vx stored in the storage device 65. The reference value Vx2 is output to the output voltage control unit 62. Then, the output voltage control unit 62 outputs a control signal based on the reference value Vx2 and the current detection value Vy output from the current detection circuit 5 to the PWM control unit 63. The driver unit 64 controls the output current Io to be constant by changing the output voltage V2 of the DC-DC converter 2.

  In addition, when the DC-DC converter 2 is in a start state by turning on the switch SW, the output voltage control unit 62 detects the voltage detection value Vx immediately before the output of the DC-DC converter 2 stored in the storage device 65 is stopped. The temperature of the light emitting unit 3 is estimated based on (hereinafter referred to as the voltage Vx immediately before stopping).

  As shown in FIG. 8B of the conventional example, the temperature characteristic of the forward resistance Rf of the light emitting diodes LED1 to LED5 decreases as the temperature of the light emitting diodes LED1 to LED5 increases. Thus, the forward resistance Rf of the light emitting diode increases as the temperature of the light emitting diodes LED1 to LED5 decreases. Therefore, when the DC-DC converter 2 is started, the output voltage control unit 62 controls the output voltage V2 based on the temperature characteristic of the forward resistance Rf of the light emitting diodes LED1 to LED5.

  That is, the output voltage control unit 62 estimates the temperature of the light emitting unit 3 from the voltage Vx immediately before stop stored in the storage device 65, and the light emitting unit 3 is hot based on the temperature characteristic of the forward resistance Rf of the light emitting diodes LED1 to LED5. The output voltage V2 of the DC-DC converter 2 is controlled so as to become smaller, and the output voltage V2 of the DC-DC converter 2 is controlled to become larger as the light emitting unit 3 becomes lower in temperature.

  By controlling the output voltage V2 of the DC-DC converter 2 based on the temperature of the light emitting unit 3 as described above, the temperature of the light emitting unit 3 varies and the forward resistance Rf of the light emitting diodes LED1 to LED5 varies. In addition, the output current Io of the DC-DC converter 2 when the DC-DC converter 2 is started can be made substantially constant.

  Accordingly, it is possible to reduce the fluctuation due to the temperature change of the luminous flux rising characteristics of the light emitting diodes LED1 to LED5 when the DC-DC converter 2 is started.

  Next, the control of the voltage control circuit 6 during chattering in which the light emitting unit 3 is disconnected from the output terminals A and B of the DC-DC converter 2 and reconnected will be described below.

  Even in the load reconnection state in which the light emitting unit 3 is reconnected to the DC-DC converter 2 by chattering or the like, the output voltage control unit 62 is stored in the storage device 65 in the same manner as in the starting state of the DC-DC converter 2. The temperature of the light emitting unit 3 is estimated based on the voltage detection value Vx immediately before the DC-DC converter 2 is unloaded. Then, by controlling the output voltage V2 of the DC-DC converter 2 based on the temperature of the light emitting unit 3, even if the temperature of the light emitting unit 3 varies and the forward resistance Rf of the light emitting diodes LED1 to LED5 varies. When the load of the DC-DC converter 2 is reconnected, fluctuations due to temperature changes in the luminous flux rising characteristics of the light emitting diodes LED1 to LED5 can be reduced.

  Further, in the present embodiment, since the temperature of the light emitting unit 3 can be estimated based on the voltage detection value Vx stored in the storage device 65, it is necessary to provide a temperature sensitive element that detects the temperature of the light emitting unit 3. Therefore, the number of parts constituting the light emitting diode driving device can be reduced, and the cost can be reduced.

(Embodiment 5)
As a fifth embodiment of the present invention, FIG. 5 shows a schematic circuit configuration diagram. The present embodiment includes a DC power source 1, a DC-DC converter 2, a light emitting unit 3, a voltage detection circuit 4, a current detection circuit 5, a voltage control circuit 6, and a current limiting circuit 9. Note that the DC power source 1, the DC-DC converter 2, the light emitting unit 3, the voltage detection circuit 4, the current detection circuit 5, and the current limiting circuit 9 have the same configuration as in the fourth embodiment, and are denoted by the same reference numerals. Description is omitted.

  The voltage control circuit 6 of this embodiment is characterized in that the voltage control circuit 6 of Embodiment 4 includes a temperature correction signal generation unit 66.

  The temperature correction signal generation unit 66 is configured by a parallel circuit of a capacitor C1 and a discharge resistor R7, and a control voltage V3 is applied thereto. The voltage across the capacitor C1 is output to the output voltage control unit 62 as a temperature correction signal.

  The control voltage V3 is output from a control power supply (not shown). A control power supply (not shown) generates a control voltage V3 based on the DC voltage V1 output from the DC power supply 1. When the switch SW is turned on, the control power supply (not shown) operates to output the control voltage V3, and when the switch SW is turned off, the control power supply (not shown) stops and the output of the control voltage V3 also stops.

  When the switch SW is turned off and the control voltage V3 is stopped, the constants of the discharge resistor R7 and the capacitor C1 are set so that the discharge curve of the voltage charged in the capacitor C1 approximates the heat dissipation curve of the light emitting diodes LED1 to LED5. Set. Then, when the DC-DC converter 2 is started by turning on the switch SW, the voltage across the capacitor C1 discharged during the stop is measured, so that the light emitting unit 3 immediately before the output of the DC-DC converter 2 is stopped. The LED temperature difference that is the difference between the temperature and the temperature of the light emitting unit 3 at the start can be estimated.

  Specific control of the output voltage V2 by the voltage control circuit 6 will be described below.

  When the DC-DC converter 2 is turned on by turning on the switch SW, the output voltage control unit 62 is connected to the voltage Vx immediately before stop stored in the storage device 65 and both ends of the capacitor C1 of the temperature correction signal generation unit 66. Based on the voltage, the temperature of the light emitting unit 3 at the time of starting is estimated. And the output voltage control part 62 controls the output voltage V2 based on the temperature characteristic of the forward resistance Rf of light emitting diode LED1-5.

  That is, the temperature of the light emitting unit 3 immediately before stopping is estimated from the voltage Vx immediately before stopping stored in the storage device 65. And by detecting the both-ends voltage of the capacitor | condenser C1 of the temperature correction signal generation part 66 at the time of starting of the DC-DC converter 2, the LED temperature difference of the light emission part 3 during a stop can be estimated. Therefore, the temperature of the light emitting unit 3 at the time of starting the DC-DC converter 2 can be estimated by subtracting the LED temperature difference of the light emitting unit 3 during the stop from the temperature of the light emitting unit 3 immediately before the stop. And the output voltage control part 62 is controlled based on the temperature characteristic of the forward resistance Rf of the light emitting diodes LED1 to 5 so that the output voltage V2 of the DC-DC converter 2 decreases as the light emitting part 3 becomes high temperature. The output voltage V2 of the DC-DC converter 2 is controlled to increase as the temperature of the light emitting unit 3 decreases.

  Accordingly, even when the output stop time of the DC-DC converter 2 is long when the DC-DC converter 2 is started, the temperature of the light emitting unit 3 after the stop time has elapsed can be estimated, and light emission is performed as described above. By controlling the output voltage V <b> 2 of the DC-DC converter 2 based on the temperature of the unit 3, it is possible to reduce fluctuations due to temperature changes of the luminous flux rising characteristics of the light-emitting diodes LED <b> 1 to 5 when the DC-DC converter 2 is started. it can.

  Next, the control of the voltage control unit 6 during chattering in which the light emitting unit 3 is disconnected from the output terminals A and B of the DC-DC converter 2 and reconnected will be described below.

  When the light emitting unit 3 is disconnected from the output terminals A and B of the DC-DC converter 2 in the configuration of the temperature correction signal generating unit 66, the capacitor C1 is discharged, and the light emitting unit 3 is connected to the output terminals A and B of the DC-DC converter 2. When connected, the capacitor C1 is charged. Thereby, the LED temperature difference of the light emitting unit 3 while the light emitting unit 3 is out of the output ends A and B of the DC-DC converter 2 can be estimated. Therefore, the output voltage control unit 62 estimates the temperature of the light emitting unit 3 at the time of load reconnection by subtracting the LED temperature difference of the light emitting unit 3 under no load from the temperature of the light emitting unit 3 immediately before the load is removed. can do. Then, by performing the above control based on the temperature characteristics of the light emitting diodes LED1 to 5, the fluctuation due to the temperature change of the luminous flux rising characteristics of the light emitting diodes LED1 to LED5 when the load of the DC-DC converter 2 is reconnected is reduced. be able to.

  Further, in the steady state of the DC-DC converter 2, the control of the output voltage control unit 62 is the same as that of the fourth embodiment, and the same reference numerals are given and the description thereof is omitted.

(Embodiment 6)
FIG. 6 shows a schematic circuit configuration diagram as a sixth embodiment of the present invention. The present embodiment includes a DC power source 1, a DC-DC converter 2, a light emitting unit 3, a voltage detection circuit 4, a current detection circuit 5, a voltage control circuit 6, and a current limiting circuit 9. Note that the DC power source 1, the DC-DC converter 2, the light emitting unit 3, the voltage detection circuit 4, the current detection circuit 5, and the current limiting circuit 9 have the same configuration as in the fourth embodiment, and are denoted by the same reference numerals. Description is omitted.

  The voltage control circuit 6 according to the present embodiment is characterized in that the voltage control circuit 6 according to the fifth embodiment includes a temperature sensitive element 8 and a temperature calculation unit 71.

  The temperature sensitive element 8 of this embodiment is composed of a thermistor and is provided in the light emitting diode driving device to detect the ambient temperature. Further, the temperature calculation unit 71 detects the ambient temperature by flowing a current through the thermistor and detecting the voltage across the thermistor, and outputs the detection result to the output voltage control unit 62. Moreover, the temperature calculation part 71 has memorize | stored the atmospheric temperature from the present to a fixed period before.

  Specific control of the output voltage V2 by the voltage control circuit 6 will be described below.

  In the starting state of the DC-DC converter 2 by turning on the switch SW, the output voltage control unit 62 estimates the temperature of the light emitting unit 3 immediately before stopping from the voltage Vx immediately before stopping stored in the storage device 65. And the LED temperature difference of the light emission part 3 during a stop is estimated by detecting the both-ends voltage of the capacitor | condenser C1 of the temperature correction signal generation part 66. FIG.

  Further, the temperature calculation unit 71 subtracts the ambient temperature at the start of the DC-DC converter 2 from the stored ambient temperature immediately before the output of the DC-DC converter 2 is stopped. The change is output to the output voltage control unit 62 as an atmospheric temperature difference.

  Then, the output voltage control unit 62 subtracts the LED temperature difference of the light emitting unit 3 during the stop from the temperature of the light emitting unit 3 immediately before the stop, and corrects it by using the atmospheric temperature difference of the ambient temperature during the stop. The temperature of the light emitting unit 3 at the start of the DC-DC converter 2 can be estimated. And the output voltage control part 62 is controlled based on the temperature characteristic of the forward resistance Rf of the light emitting diodes LED1 to 5 so that the output voltage V2 of the DC-DC converter 2 decreases as the light emitting part 3 becomes high temperature. The output voltage V2 of the DC-DC converter 2 is controlled to increase as the temperature of the light emitting unit 3 decreases.

  Therefore, even when the output stop time of the DC-DC converter 2 is long at the start and the ambient temperature fluctuates during the stop, the temperature of the light emitting unit 3 after the stop time can be estimated. As described above, by controlling the output voltage V2 of the DC-DC converter 2 based on the temperature of the light emitting unit 3, fluctuations due to temperature changes of the luminous flux rising characteristics of the light emitting diodes LED1 to LED5 at the start of the DC-DC converter 2 are reduced. can do.

  Next, the control of the voltage control unit 6 during chattering in which the light emitting unit 3 is disconnected from the output terminals A and B of the DC-DC converter 2 and reconnected will be described below.

  When the light emitting unit 3 is disconnected from the output terminals A and B of the DC-DC converter 2 in the configuration of the temperature correction signal generating unit 66, the capacitor C1 is discharged, and the light emitting unit 3 is connected to the output terminals A and B of the DC-DC converter 2. When connected, the capacitor C1 is charged. Thereby, the LED temperature difference of the light emitting unit 3 while the light emitting unit 3 is out of the output ends A and B of the DC-DC converter 2 can be estimated. Therefore, the output voltage control unit 62 estimates the temperature of the light emitting unit 3 at the time of load reconnection by subtracting the LED temperature difference of the light emitting unit 3 under no load from the temperature of the light emitting unit 3 immediately before the load is removed. can do. Then, by performing the above control based on the temperature characteristics of the light emitting diodes LED1 to 5, the fluctuation due to the temperature change of the luminous flux rising characteristics of the light emitting diodes LED1 to LED5 when the load of the DC-DC converter 2 is reconnected is reduced. be able to.

  Further, in the steady state of the DC-DC converter 2, the control of the output voltage control unit 62 is the same as that of the fourth embodiment, and the same reference numerals are given and the description thereof is omitted.

  Further, the light emitting diode driving device according to the present invention, the light emitting unit 3, and the light emitting diode driving device and the fixture main body holding the light emitting unit 3 constitute a lighting fixture, or the light emitting unit 3 is provided in the interior of a vehicle or the like. The vehicle lighting device (headlight device) in which the light-emitting unit 3 that constitutes the vehicle interior lighting device or the light-emitting unit 3 formed of a series or parallel circuit of high-intensity light-emitting diodes is used as a headlight of a vehicle such as an automobile ) Can also be configured.

DESCRIPTION OF SYMBOLS 1 DC power supply 2 DC-DC converter 3 Light emission part 4 Voltage detection circuit 5 Current detection circuit 6 Voltage control circuit 7 Current control circuit 8 Temperature sensing element

Claims (10)

  A DC-DC converter that converts a DC voltage output from a DC power source into a desired DC voltage and applies it to a light emitting unit including one or more light emitting diodes, and a current supplied from the DC-DC converter to the light emitting unit. Based on the resistance means provided in the path for limiting the maximum value of the current supplied to the light emitting unit and the temperature of the light emitting unit, supplied to the light emitting unit when the output of the DC-DC converter is started or when a load is connected A light emitting diode driving device comprising: a light emitting portion current control means for controlling a rising characteristic of the generated current to be substantially constant.   The temperature detecting means comprises a temperature sensing element for detecting the temperature of the light emitting part, the resistance means is constituted by a variable resistor, and the light emitting part current control means is based on the detection result of the temperature detecting means. The resistance value of the variable resistor is increased as the temperature of the DC-DC converter is increased, and the resistance value of the variable resistor is decreased as the temperature of the light emitting unit is decreased. 2. The light emitting diode driving device according to claim 1, wherein the load of the DC converter is controlled to be substantially constant.   The temperature detecting means comprises a temperature sensing element for detecting the temperature of the light emitting section, the resistance means is constituted by a transistor, and the light emitting section current control means is based on the detection result of the temperature detecting means. The resistance at both ends of the transistor is increased as the temperature increases, and the resistance at both ends of the transistor is decreased as the temperature of the light emitting unit decreases, so that the DC-DC at the time of starting the output of the DC-DC converter or when connecting the load. 2. The light emitting diode driving device according to claim 1, wherein the load of the converter is controlled to be substantially constant.   And a temperature detecting unit configured to detect a temperature of the light emitting unit, wherein the light emitting unit current control unit is configured to detect the DC-DC converter as the temperature of the light emitting unit increases based on a detection result of the temperature detecting unit. The output voltage of the DC-DC converter is increased as the temperature of the light emitting unit becomes lower, so that the current supplied to the light emitting unit at the start of the output of the DC-DC converter or when the load is connected is reduced. 2. The light emitting diode driving device according to claim 1, wherein the rising characteristic is controlled to be substantially constant.   Storage means for storing the output voltage of the DC-DC converter before the output of the DC-DC converter stops or before no load is applied, and is estimated from the output voltage of the DC-DC converter stored in the storage means. Based on the temperature of the light emitting unit, the light emitting unit current control means decreases the output voltage of the DC-DC converter as the temperature of the light emitting unit increases, and the output voltage of the DC-DC converter as the temperature of the light emitting unit decreases. 2. The light emitting diode drive according to claim 1, wherein the rising characteristic of the current supplied to the light emitting unit when the output of the DC-DC converter is started or when the load is connected is controlled to be substantially constant by increasing apparatus.   The storage means includes a capacitor that is charged when current is supplied from the DC-DC converter to the light emitting unit and is discharged when current supplied from the DC-DC converter to the light emitting unit is stopped. Based on the temperature of the light emitting unit estimated from the stored output voltage of the DC-DC converter and the voltage between both ends of the capacitor, the light emitting unit current control means is configured so as to increase the temperature of the light emitting unit. The rise of the current supplied to the light emitting part at the start of the output of the DC-DC converter or when the load is connected by decreasing the output voltage and increasing the output voltage of the DC-DC converter as the light emitting part becomes colder. 6. The light emitting diode driving device according to claim 5, wherein the characteristic is controlled to be substantially constant. An ambient temperature detection means for detecting an ambient temperature, the output voltage of the DC-DC converter stored in the storage means, the voltage across the capacitor, and the detection result of the ambient temperature detection means Based on the temperature of the light emitting section, the light emitting section current control means decreases the output voltage of the DC-DC converter as the temperature of the light emitting section increases, and increases the output voltage of the DC-DC converter as the temperature of the light emitting section decreases. 7. The light emitting diode driving device according to claim 6, wherein the rising characteristic of the current supplied to the light emitting unit when the output of the DC-DC converter is started or when the load is connected is controlled to be substantially constant.
apparatus.   A light-emitting diode driving device according to any one of claims 1 to 7, a light-emitting unit including one or more light-emitting diodes, and a fixture main body that holds the light-emitting diode driving device and the light-emitting unit. Lighting equipment.   8. A vehicle interior lighting device comprising: the light-emitting diode driving device according to claim 1; and a light-emitting unit in which one or more light-emitting diodes are provided in the vehicle interior.   An illumination device for a vehicle, comprising: the light-emitting diode driving device according to any one of claims 1 to 7; and a light-emitting unit that irradiates light around the vehicle with one or more light-emitting diodes.

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