JP2006147360A - Light-emitting diode lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an LED lighting device capable of lighting all LEDs in equal brightness, lighting the other LED even if one LED gets into trouble, and lighting LEDs with high efficiency and small heat radiation at operation. <P>SOLUTION: The device is provided with LED circuits each having a coil and an LED connected in series and a switching element connecting a plurality of LED circuits in parallel with a power source. A constant current circuit detects that a current flowing in each LED circuit reaches a given value, and controls the on/off-operation of the switching element. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an LED lighting device for lighting a light emitting diode (hereinafter referred to as LED).

When an LED is used as a light source, for example, in a headlamp for a vehicle, since each LED has a small light emission amount, a plurality of LEDs are simultaneously turned on to obtain brightness suitable for the headlamp.
Some conventional LED lighting devices apply a voltage obtained by boosting a power supply voltage by a booster circuit to an LED unit in which a plurality of LEDs are connected in series. The LED unit is connected to a booster circuit that applies a boosted voltage at one end, and a constant current circuit is connected to the other end, and the current flowing through the LED unit is controlled by the constant current circuit. The constant current circuit is connected to a voltage detection circuit that detects a voltage from the current flowing through the constant current circuit. The voltage detection circuit compares the detected voltage with a reference voltage taken from the power supply, and generates a boost control signal. The booster circuit adjusts the voltage applied to the LED unit based on the boost control signal, and keeps the current flowing through the LED unit constant (see, for example, Patent Document 1).

  When a plurality of LEDs are connected in series in this way, the current flowing through each LED can be made constant with a simple circuit configuration, and the amount of light emission can be reduced by eliminating the influence of variations in the voltage drop in the forward direction of each LED. Can be arranged equally. When a plurality of LEDs are connected in series, all the LEDs are turned on by one lighting circuit. If the forward voltage drop of one LED is about 2 V, for example, a voltage several times the voltage drop, that is, It is necessary to apply a voltage corresponding to a multiple of the number of 2V LEDs to the LED unit. For this reason, a booster circuit that outputs a high voltage is required, and the booster circuit is configured using expensive circuit elements having a high rated voltage. In addition, when a high-brightness LED is used, the forward voltage drop of one high-brightness LED is about 3 V, so that the booster circuit becomes more expensive.

  Further, as a conventional LED lighting device, there is one in which a plurality of LEDs are connected in parallel and a constant current circuit is provided for each LED. This is because each LED has a constant current circuit that operates based on the resistance value of the thermistor in order to prevent the current from concentrating to flow in the LED with the smallest resistance among the LEDs connected in parallel. By controlling the current flowing through each LED, uneven brightness of each LED is suppressed (for example, see Patent Document 2).

Japanese Patent Laying-Open No. 2003-187614 (page 3, FIG. 1) Japanese Patent Laid-Open No. 11-298044 (pages 3 and 4 and FIG. 1)

  Since the conventional LED lighting device is configured as described above, an LED unit in which a plurality of LEDs are all connected in series requires a booster circuit that generates a large voltage. When this occurs, all the LEDs cannot be lit. In addition, in the case where a plurality of LEDs are connected in parallel, a plurality of constant current circuits for controlling the currents flowing through the individual LEDs are required, which complicates the circuit configuration and causes power loss due to the resistance and transistors of each constant current circuit. Becomes larger. In particular, a high-intensity LED used for a headlamp or the like flows a large current, and when a plurality of high-intensity LEDs are used, the heat generation of the circuit element that performs current control increases, so an expensive circuit element is used. There has been a problem that the circuit configuration becomes complicated and the cost becomes high.

  The present invention has been made to solve the above-described problems, and can turn on all LEDs with uniform brightness and turn on other LEDs even when a failure occurs in one LED. Another object of the present invention is to obtain an LED lighting device that turns on an LED with high efficiency while generating little heat during operation.

  In the LED lighting device according to the present invention, an LED circuit in which a coil and an LED are connected in series, a switching element that connects a plurality of LED circuits in parallel to a power source, and a current flowing through each LED circuit has a predetermined value. And a constant current circuit for controlling on / off of the switching element.

  According to the present invention, a switching element that connects a plurality of LED circuits in which a coil and an LED are connected in series with each other in parallel to a power supply, and that the current flowing through each LED circuit is detected to be a predetermined value, Since a constant current circuit for controlling on / off is provided, if a coil having a uniform inductance is used, the current flowing through each LED circuit becomes equal, and a uniform current can be supplied to the LEDs. In addition, since current control is performed by turning on and off the switching element, the circuit configuration with less power loss increases the efficiency of the power supply and generates less heat. In addition, since power is supplied to a plurality of LED circuits connected in parallel, even if one circuit is disconnected, power is supplied to the other LED circuits. There is an effect that it is possible to avoid the danger of doing.

An embodiment of the present invention will be described below.
Embodiment 1 FIG.
1 is a circuit diagram showing a configuration of an LED lighting device according to Embodiment 1 of the present invention. A power source 1 such as a battery applies a voltage VB to the anode of the diode 2 and the drain of the switching element 3. The switching element 3 is composed of, for example, an N-channel MOS field effect transistor. The cathode of the diode 2 is connected to one end of the resistor 4 and one end of the capacitor 5. The other end of the resistor 4 is connected to the gate of the switching element 3 and the collector of the transistor 6. Connected to the switching element 3 is a bootstrap drive circuit composed of a diode 2, a resistor 4, and a capacitor 5. The transistor 6 illustrated in FIG. 1 is an NPN bipolar transistor.
The other end of the capacitor 5 is connected to the source of the switching element 3, the cathode of the flywheel diode 14, and the coils 15a to 15n. The anode of the flywheel diode 14 is grounded.

  The coils 15a to 15n are n coils (n is a positive integer), and one end of each is connected to the source of the switching element 3 and the other end of the capacitor 5 as described above. The other end of the coil 15a is connected to the anode of the LED 16a, the other end of the coil 15b is connected to the anode of the LED 16b, and the other end of the coil 15n is connected to the anode of the LED 16n. For example, two LEDs connected in series are connected to the coils 15a to 15n to form an LED circuit. The cathode of the LED 16a is connected to the anode of the LED 17a, the cathode of the LED 16b is connected to the anode of the LED 17b, the cathode of the LED 16n is connected to the anode of the LED 17n, and an LED (not shown) is also connected in the same manner. The cathodes of the LEDs 17 a to 17 n are connected to the inverting input terminal of the comparator (comparison means) 10. Of the LEDs not shown in the figure, the cathode of the LED that is the subsequent stage of the series connection is also connected to the inverting input terminal of the comparator 10.

  The coil 15a, the LED 16a, and the LED 17a are connected in series to the power supply 1, the coil 15b, the LED 16b, and the LED 17b are connected in series, and the coil 15n, the LED 16n, and the LED 17n are connected in series. Are also connected in series. That is, a plurality of circuits in which a coil and two LEDs are connected in series are configured, and a plurality of circuits configured by the series connection, for example, n in parallel as illustrated in FIG. 1, are connected in parallel. Note that the number of LEDs connected to each coil is not limited to the two illustrated.

The comparator 10 is configured to have a hysteresis characteristic by applying positive feedback. A resistor 12 as a feedback resistor is connected between the positive input terminal and the output terminal of the comparator 10. One end of a resistor (current detection means) 20 is connected to the inverting input terminal. The other end of the resistor 20 is grounded. In addition to the resistor 12 described above, one end of the resistor 11 and one end of the resistor 13 are connected to the positive input terminal of the comparator 10. The voltage VB of the power source 1 is applied to the other end of the resistor 11, and the other end of the resistor 13 is grounded. In addition to the resistor 12 described above, one end of the resistor 9 and the input terminal of the inverter 8 are connected to the output terminal of the comparator 10. The voltage VB of the power source 1 is applied to the other end of the resistor 9. The output terminal of the inverter 8 is connected to one end of the resistor 7, and the other end of the resistor 7 is connected to the base of the transistor 6. The emitter of transistor 6 is grounded.
The comparator 10, the resistor 12, the resistors 11 and 13 that determine the voltage Vth, the resistor 20 of the shunt resistor, the resistor 9 that pulls up the output terminal of the comparator 10, the flywheel diode 14, the inverter 8, and the resistor 7. The transistor 6 forms a constant current circuit.

Next, the operation will be described.
As described above, the bootstrap drive circuit including the diode 2, the resistor 4, and the capacitor 5 is connected to the switching element 3. When shifting the N-channel switching element 3 to the ON state, it is necessary to apply a voltage higher than the voltage VB to the gate. The voltage VB of the power supply 1 is applied to the capacitor 5 through the diode 2, and voltage energy is stored in the capacitor 5. When the transistor 6 is controlled to be in the OFF state in order to turn on the switching element 3, the current flowing from the diode 2 to which the voltage VB of the power source 1 is applied to the transistor 6 through the resistor 4 is cut off. A voltage from the power source 1 through the diode 2 and the resistor 4 is applied to the gate of the switching element 3. At this time, the voltage energy accumulated in the capacitor 5 moves to the gate of the switching element 3 via the resistor 4, further increases the gate voltage of the switching element 3, and the switching element 3 is turned on.

When the switching element 3 is turned on, the voltage VB of the power source 1 is applied to one end of the coils 15a to 15n via the switching element 3. Since the coils 15a to 15n are connected in parallel to the power supply 1, the voltage output from the switching element 3 is similarly applied to the coils 15a to 15n.
For example, a current as described later flows in the coil 15a to which the voltage is applied in this way, and this current flows in the LED 16a and the LED 17a connected in series to the coil 15a. The currents that flow through the LEDs 16 a and 17 a merge with the currents that flow through the other LEDs, and return to the power supply 1 through the resistors 20. Therefore, a voltage representing the total amount of current flowing through all the LEDs is generated at both ends of the resistor 20. This voltage, that is, the voltage at the connection point A shown in FIG. 1 is input to the inverting input terminal of the comparator 10 as the voltage VI.

FIG. 2 is an explanatory diagram illustrating the operation of the LED lighting device according to the first embodiment. This figure shows the voltage applied to each coil by the ON / OFF operation of the switching element 3, and the voltage VI at the connection point A and the voltage Vth at the connection point B of the circuit shown in FIG. In the figure, the vertical axis represents the magnitude of the voltage, and the horizontal axis represents the elapsed time. The voltage VI represented by a solid line is a voltage input to the inverting input terminal of the comparator 10 as described above. The total amount of current flowing out from the LEDs 17a to 17n connected in parallel is converted by the resistor 20 acting as a shunt resistor. It appears as a size.
A voltage Vth represented by a broken line in the figure is a voltage input to the positive input terminal of the comparator 10 and is a reference voltage to be compared with the voltage VI. A voltage obtained by dividing the voltage VB by the resistors 11 and 13 is applied to the positive input terminal of the comparator 10, and a voltage component fed back by the resistor 12 is added to this voltage. Since the comparator 10 to which the positive feedback is applied by the resistance 12 of the feedback resistor has a hysteresis characteristic in the comparison operation, the voltage Vth including the feedback component is the high potential level H and the low potential level as illustrated in FIG. It has two values of L.

  When a pulse voltage is applied to the coil, the current flowing through the coil changes like a triangular wave, and specifically changes like an integrated waveform that increases with time. The voltage VI shown in FIG. 2 indicates the magnitude of the sum of currents flowing through the LEDs 16a and 17a connected in series, the LEDs 16b and 17b connected in series to the LEDs 16n and LED 17n connected in series, and this voltage VI Continues to increase while the switching element 3 is in the ON state. Thus, by controlling the ON time of the switching element 3, the current flowing through the coils 15a to 15n can be adjusted to an arbitrary value.

FIG. 3 is an explanatory diagram illustrating the operation of the LED lighting device according to the first embodiment. This figure shows the change with time of the current flowing through each coil when, for example, a pulse voltage output from the switching element 3 is applied. The current flowing through the coil increases while the pulse voltage is applied. When the voltage applied to the coil is V and the inductance of the coil is L, the increase in the energization current of the coil can be expressed by V / L. The slope of the waveform of the energization current of the coil that increases while the switching element 3 is in the ON state shown in FIG. 3 corresponds to this V / L. The energization current of the coil in which the LEDs are connected in series is expressed by the following formula (1).
Energizing current = (Voltage applied to coil-LED forward voltage) x ON time
/ Inductance of coil (1)
In the circuit shown in FIG. 1, the “voltage applied to the coil” in the equation (1) corresponds to the voltage output from the switching element 3, and is, for example, the voltage applied to the coil 15a. In addition, the “LED forward voltage” in Equation (1) is, for example, the voltage across the LDE 16a and the LED 17a connected in series, that is, the voltage between the anode of the LED 16a and the cathode of the LED 17a. Thus, the current flowing through the coil 15a and the other coils 15b to 15n increases with the elapsed time that the switching element 3 is in the ON state, and becomes larger as the ON time becomes longer.

  The flywheel diode 14 connected to the source of the switching element 3 and the coils 15a to 15n returns the current flowing out from each LED to the coils 15a to 15n when the switching element 3 changes from the ON state to the OFF state. Thus, it is suppressed that the currents flowing through the LEDs 16a to 16n and the LEDs 17a to 17n rapidly decrease. The current recirculated by the flywheel diode 14 decreases with time, and the current flowing through each LED when the switching element 3 is turned off gradually decreases as the voltage VI shown in FIG.

  When the inductances of the coils 15a to 15n are set to the same value, the currents flowing through the two LEDs connected in series, for example, the LED 16a and the LED 17a, the LED 16b and the LED 17b, can be made uniform. The currents flowing through the connected LEDs can be set to the same value. Specifically, the peak currents flowing through the LEDs connected in parallel can be made uniform. As the coils 15a to 15n, for example, coils whose inductance is changed by adjusting the insertion amount of the core member inserted in the coil may be used so that the light emission amounts of the respective LEDs are made uniform.

The comparator 10 compares the voltage Vth with the voltage VI and outputs the comparison result as a voltage. As shown in FIG. 1, the output terminal of the comparator 10 is pulled up via the resistor 9. A positive feedback is applied to the positive input terminal of the comparator 10 from the pulled-up output terminal by the resistor 12, and the voltage Vth of the level H shown in FIG.
When the output terminal of the comparator 10 is at a high potential, the output signal of the comparator 10 is inverted by the inverter 8, converted into a low potential signal, and input to the base of the transistor 6 via the resistor 7. The transistor 6 that has input a low-potential output signal to the base is turned off, and the ground connection of the gate of the switching element 3 is opened. Then, the gate voltage of the switching element 3 rises, the switching element 3 is turned on, and a voltage is applied to the coils 15a to 15n. Then, current begins to flow through the coils 15a to 15n, the LEDs 16a to 16n, and the LEDs 17a to 17n, and this current gradually increases due to the action of the coils 15a to 15n.

  Since the voltage VI indicates the current flowing through the coils 15a to 15n, the LEDs 16a to 16n, and the LEDs 17a to 17n, the voltage VI gradually increases when the switching element 3 is turned on. The comparator 10 inverts the output voltage to a low potential when the increasing voltage VI becomes larger than the voltage Vth of the level H. Then, the inverted output voltage is fed back to the positive input terminal of the comparator 10 through the resistor 12, and the voltage Vth of the level L is applied.

  When the output signal of the comparator 10 becomes low potential, the inverter 8 inverts this output signal and inputs a high potential signal to the base of the transistor 6. The transistor 6 is turned on, the gate of the switching element 3 is grounded, the gate voltage drops, and the switching element 3 is turned off. When the switching element 3 is turned off, the currents flowing through the LEDs 16a to 16n and the LEDs 17a to 17n decrease due to the action of the coils 15a to 15n as described above, and the voltage VI decreases and becomes lower than the voltage Vth of the level L. . Then, the comparator 10 inverts the output voltage, returns to the initial state in which a high potential signal is output, and the switching element 3 is turned on.

In this way, the comparator 10 compares the voltage Vth, which alternately represents the two reference voltages of level H and level L, generated by applying positive feedback to the comparator 10, and the voltage VI that changes with time, and based on this comparison result. When the ON / OFF operation of the switching element 3 is controlled, the pulse voltage applied to the coils 15a to 15n has a pulse width related to the temporal change of the voltage VI.
Further, as described above, the current flowing through the LEDs 16a to 16n and the LEDs 17a to 17n is determined by the pulse width of the pulse voltage, that is, the time during which the switching element 3 is in the ON state. Feedback control is performed so as to be within a certain range.
The constant current circuit including the above-described comparator 10 feeds back the voltage VI, that is, the value of the current flowing through each LED in this manner, and performs the self-excited oscillation operation using the hysteresis characteristic to turn on / off the switching element 3. The light emitting operation is stabilized by turning off and supplying a constant current to each LED by the switching operation of the switching element 3.

As described above, according to the first embodiment, the switching element 3 is turned ON / OFF by comparing the voltage VI indicating the current flowing through each LED with the comparator 10 with hysteresis and the voltage Vth indicating the two reference voltages alternately. Since the current flows through the LEDs 16a to 16n and the LEDs 17a to 17n connected in series to the coils 15a to 15n, respectively, the power consumption is suppressed because there are no resistors or transistors that limit the current flowing through the LEDs. Thus, there is an effect that heat generation of the circuit can be reduced.
In addition, since a plurality of LEDs are connected and operated in parallel with the power supply 1, even when one LED is disconnected, current can be supplied to the other LEDs, and all the LEDs are turned off simultaneously. This has the effect of avoiding the danger of sudden turn-off.

Embodiment 2. FIG.
FIG. 4 is a circuit diagram showing a configuration of an LED lighting device according to Embodiment 2 of the present invention. The same reference numerals are used for the same or corresponding parts as shown in FIG. One end of the resistor 30 is connected to the power source 1 and applied with the voltage VB. The other end of the resistor 30 is connected to one end of the resistor 31 and the inverting input terminal of the comparator 34. One end of the resistor 32 is connected to the power source 1 and applied with the voltage VB. The other end of the resistor 32 is connected to the cathode of the Zener diode 33 and the positive input terminal of the comparator 34. The anode of the Zener diode 33 is grounded. The output terminal of the comparator 34 is connected to one end of the resistor 35 and the base of the transistor 36. A voltage VB is applied to the other end of the resistor 35. This resistor 35 is a pull-up resistor connected to the output terminal of the comparator 34. The transistor 36 is composed of, for example, an NPN-type bipolar transistor. The collector is connected to the gate of the switching element 3, the other end of the resistor 4, and the collector of the transistor 6, and the emitter is grounded. The resistors 30 to 32 and 35, the Zener diode 33, the comparator 34, and the transistor 36 constitute power supply voltage detection means.
The resistors 30 to 32 are for reducing the voltage VB to a voltage range that the comparator 34 can input. When the voltage VB is a normal voltage, the voltage divided by the resistor 30 and the resistor 31 is the same voltage VB. The respective resistance values are set to be higher than the Zener voltage of the Zener diode 33 via the resistor 32. The rest is configured in the same manner as the circuit shown in FIG.

Next, the operation will be described.
Description of operations similar to those of the LED lighting device shown in FIG. 1 is omitted, and operations that characterize the LED lighting device according to Embodiment 2 will be described. When the voltage VB of the power supply 1 decreases, the current flowing through each LED decreases. The voltage VI representing this current cannot rise until it becomes equal to the voltage Vth of the level H, the comparison result of the comparator 10 becomes constant, the output signal is not inverted, and the base of the transistor 6 has a low potential. The state where the output signal is input continues. The gate of the switching element 3 is always in a state where the ground connection is opened. In such a state, the bootstrap circuit including the resistor 4 and the capacitor 5 cannot operate normally, and the switching element 3 is in an incomplete ON state, causing troubles such as heat generation and increased power consumption. To do.

  In order to avoid such a state, the LED lighting device shown in FIG. 4 uses the comparator 34 or the like to turn off the switching element 3 when the voltage VB becomes lower than a predetermined value. A voltage obtained by dividing the voltage VB by the resistor 30 and the resistor 31 is input to the inverting input terminal of the comparator 34. The Zener voltage of the Zener diode 33 from the voltage VB through the resistor 32 is input to the positive input terminal of the comparator 34 as a reference voltage.

  When the input voltage V + at the positive input terminal is smaller than the input voltage V− at the inverting input terminal, the output voltage of the comparator 34 is saturated to a low potential. Further, when the input voltage V + is larger than the input voltage V−, the output voltage is saturated to a high potential. If the voltage divided by the resistor 30 and the resistor 31 is V− and the Zener voltage of the Zener diode 33 is V +, the voltage V− is grounded by the Zener diode 33 if the voltage VB is a predetermined value or more. An output signal having a lower potential than the voltage V + of the positive input terminal is output from the comparator 34 to the base of the transistor 36. At this time, the transistor 36 is turned off, and the gate voltage of the switching element 3 is controlled by the ON / OFF operation of the transistor 6.

  When the voltage VB decreases and falls below a predetermined value, the voltage divided by the resistors 30 and 31 also decreases. The comparator 34 compares the voltage V− input at this time with the voltage V +, and outputs a high potential output signal to the base of the transistor 36 when the voltage V− becomes smaller than the voltage V +. Then, the transistor 36 is turned on, the gate of the switching element 3 is grounded, and the switching element 3 is turned off.

  As described above, according to the second embodiment, the switching element 3 is turned off when the voltage VB of the power supply 1 becomes smaller than a predetermined value by the comparator 34 having the Zener diode 33 connected to the input terminal. When the voltage VB of the power source 1 is lowered and the switching operation of the switching element 3 is stopped, the current supplied to each LED can be cut off, and the occurrence of a failure such as heat generation of the circuit can be prevented. is there.

Embodiment 3 FIG.
FIG. 5 is an explanatory diagram showing lighting fixtures such as a ceiling lamp and a stand in which the LED lighting device of the present invention according to the first or second embodiment is applied to lighting control of a large number of LEDs constituting the light source. The same reference numerals are used for portions that are the same as or correspond to those shown in FIGS. 1 and 4 and description thereof is omitted. The illuminating device 40 includes an illuminating lamp main body 41 including LEDs 16a to 16n and LEDs 17a to 17n as light sources, and a control unit 42 having a circuit configuration similar to that of the LED lighting device described in the first embodiment or the second embodiment. Prepare.
The controller 42 operates in the same manner as the LED lighting device described in the first embodiment or the second embodiment, and controls the lighting of the large number of LEDs 16a to 16n and the LEDs 17a to 17n.

  FIG. 6 is an explanatory view showing a liquid crystal display device using a large number of LEDs as a backlight. The same reference numerals are used for the same or corresponding parts as those shown in FIG. 1, FIG. 4 and FIG. Is omitted. The liquid crystal display device 50 includes a liquid crystal panel 51 and a backlight 52 behind the liquid crystal panel 51. The backlight 52 includes LEDs 16 a to 16 n and LEDs 17 a to 17 n and a control unit 42, and the LEDs 16 a to 16 n and the LEDs 17 a to 17 n are arranged so as to illuminate the liquid crystal panel 51 uniformly. The control unit 42 operates in the same manner as that described in the first embodiment or the second embodiment, and controls lighting of a large number of LEDs 16a to 16n and LEDs 17a to 17n arranged as the backlight 52.

FIG. 7 is an explanatory view showing a headlamp of a vehicle using a number of LEDs as a light source. For example, the arrangement of each component when the headlamp unit 60 is viewed from the side is shown. The same reference numerals are used for portions that are the same as or correspond to those shown in FIGS. 1 and 4 to 6, and descriptions thereof are omitted. The headlamp unit 60 includes, for example, a reflecting mirror 61, a light shielding wall 62, a lens 63, and LEDs 16a to 16n and LEDs 17a to 17n as light sources. A control unit 42 is provided in the deep part of the headlamp unit 60, and the LEDs 16a to 16n and the LEDs 17a to 17n as light sources connected to the control unit 42 irradiate light in an irradiation range required as a headlamp. In this manner, the orientation and the like are adjusted so as to be arranged inside the reflecting mirror 61.
The circuit provided in the control unit 42 controls the lighting of the LEDs 16a to 16n and the LEDs 17a to 17n as the light sources arranged inside the reflecting mirror 61 as described in the first embodiment or the second embodiment.
Moreover, you may use many LED16a-16n and LED17a-17n for a traffic signal light as a light source like the above.

As described above, according to the third embodiment, the LED lighting device of the present invention in which a large number of LEDs 16a to 16n and LEDs 17a to 17n are used as light sources, and the numerous LEDs 16a to 16n and LEDs 17a to 17n are provided in the control unit 42. By controlling the lighting at, power consumption can be suppressed and heat generation can be reduced.
Further, even when one LED is disconnected, all the LEDs are not turned off at the same time, and there is an effect that it is possible to avoid a danger caused by sudden turn-off.

It is a circuit diagram which shows the structure of the LED lighting device by Embodiment 1 of this invention. FIG. 5 is an explanatory diagram showing the operation of the LED lighting device according to Embodiment 1. FIG. 5 is an explanatory diagram showing the operation of the LED lighting device according to Embodiment 1. It is a circuit diagram which shows the structure of the LED lighting device by Embodiment 2 of this invention. It is explanatory drawing which shows the lighting fixture which applied the LED lighting device of this invention by Embodiment 1 or 2 to lighting control of many LED which comprises a light source. It is explanatory drawing which shows the liquid crystal display device which uses many LED as a backlight. It is explanatory drawing which shows the headlamp of the vehicle which uses many LED as a light source.

Explanation of symbols

  1 power supply, 2 diode, 3 switching element, 4, 7, 9, 11 to 13, 20, 30 to 32, 35 resistor, 5 capacitor, 6, 36 transistor, 8 inverter, 10, 34 comparator, 14 flywheel diode, 15a to 15n coil, 16a to 16n, 17a to 17n LED, 33 Zener diode, 40 illumination device, 41 illumination lamp body, 42 control unit, 50 liquid crystal display unit, 51 liquid crystal panel, 52 backlight, 60 headlamp unit, 61 Reflector, 62 light shielding wall, 63 lens.

Claims (6)

An LED circuit in which a coil and an LED are connected in series;
A switching element for connecting the plurality of LED circuits in parallel to a power source;
An LED lighting device comprising: a constant current circuit that detects that a current flowing through each LED circuit has reached a predetermined value and controls on / off of the switching element.   The constant current circuit includes current detection means for detecting a current flowing through the LED, and comparison means for comparing the detected value of the current detection means with a reference value and inverting the output signal by its own hysteresis characteristic. The LED lighting device according to claim 1.   3. The LED lighting device according to claim 1, wherein an N-channel field effect transistor is used as the switching element, and a bootstrap driving circuit for driving the field effect transistor is provided.   The power supply voltage detection means which detects a power supply voltage and controls a switching element to an OFF state, if the said voltage falls below predetermined value, The power supply voltage detection means in any one of Claims 1-3 characterized by the above-mentioned. LED lighting device.   The LED lighting device according to any one of claims 1 to 4, wherein the coil is an adjustable coil capable of changing an inductance.   The LED lighting device according to any one of claims 1 to 5, wherein a set of LEDs formed of a plurality of LED circuits constitutes a light source of a headlamp of a vehicle.

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