JP7207695B2 - lighting equipment - Google Patents

Description

The present invention relates to a lighting device using LEDs (Light Emitting Diodes).

When LEDs and drive circuits are mounted in a small housing, the area of the circuit board is reduced, and it is necessary to reduce the number of mounted parts or to make the parts smaller (see, for example, Patent Document 1). In addition, heat builds up easily in a small housing, so safety measures against heat generation are important.

JP 2017-107777 A

In order to suppress the heat generation, the drive current of the LED may be reduced, but the performance of the LED cannot be sufficiently exhibited, and the luminance is also lowered.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and an object of the present invention is to provide a compact, highly efficient, and highly safe lighting device.

In order to solve the above problems, a lighting device according to one aspect of the present invention includes a DC/DC converter that converts an input DC voltage and outputs a constant voltage, and an output voltage of the DC/DC converter is applied. An LED, a constant current circuit connected in series with the LED, and a control circuit that controls current flowing through the LED using the constant current circuit. The output voltage of the DC/DC converter is set to a predetermined value higher than the forward voltage drop of the LED, and the power supply voltage of the control circuit is supplied from the output voltage of the DC/DC converter.

Any combination of the above constituent elements, and conversion of expressions of the present invention between devices, methods, systems, etc. are also effective as aspects of the present invention.

According to the present invention, it is possible to realize a compact, highly efficient, and highly safe lighting device.

It is a figure which shows the circuit structure of the illuminating device which concerns on embodiment of this invention. FIG. 2 is a diagram showing a configuration example of an operation reception unit in FIG. 1; It is a figure which shows the usage example of the illuminating device which concerns on embodiment of this invention. It is a figure which shows the circuit structure of the illuminating device which concerns on a modification.

FIG. 1 is a diagram showing a circuit configuration of a lighting device 1 according to an embodiment of the invention. The illumination device 1 includes an LED 20 and a lighting control circuit 10 that controls lighting of the LED 20 . The LED 20 may be installed on the same substrate as the lighting control circuit 10, or may be installed on another substrate.

A DC power supply and a dimming signal are supplied to the lighting device 1 from the outside. In the example shown in FIG. 1, a DC voltage of 24 V is supplied from the outside through two wires, a power supply line and a ground line. The power line is connected to the power terminal VIN of the lighting device 1 , and the ground line is connected to the ground terminal GND of the lighting device 1 . Also, a dimming signal is supplied from the outside through the control signal line. The transmission side of the control signal line is connected to the dimming controller, and the receiving side of the control signal line is connected to the dimming terminal DIM of the illumination device 1 . For example, the user can set the dimming value (0 to 1) of the LED 20 by rotating/sliding the operation knob of the dimming controller to a predetermined position. 0 is off and 1 is full on.

In the lighting device 1, a diode D1, a polyswitch F1 and a first resistor R1 are inserted in the input stage of a first power supply line W1 (24V line in the example shown in FIG. 1) connected to a power supply terminal VIN. The diode D1 is a reverse-connection prevention diode that is connected in such a direction that the power supply terminal VIN side becomes an anode. When an operator or user mistakenly connects the ground wire to the power terminal VIN of the lighting device 1 and the power wire to the ground terminal GND, the reverse current does not flow in the lighting device 1 . The polyswitch F1 is an element whose resistance value rises sharply when the temperature exceeds a predetermined value. When the temperature rises due to heat dissipation due to overcurrent or the like, the polyswitch F1 suppresses the current and protects the parts in the lighting device 1 from overcurrent and the like. do.

The first resistor R1 is a low resistor for suppressing rush current. The resistance value of the first resistor R1 is set to a value that has little effect on the current in the normal range of use and has the effect of suppressing overcurrent such as inrush current. As a countermeasure against inrush current, it is common to insert an NTC (Negative-Temperature-Coefficient) thermistor in the preceding stage of the DC/DC converter. However, since the NTC thermistor becomes hot in a steady state, it becomes a heat source in the lighting device 1 having a small housing. In the prototype circuit, the inrush current of 9A was successfully reduced to 3A by inserting a low resistance of appropriate value.

The DC/DC converter 11 is a step-down constant voltage DC/DC converter, and the input terminal VIN of the DC/DC converter 11 is connected to the first power supply line W1 (24V line). An output terminal SW of the DC/DC converter 11 is connected to a second power supply line W2 connected to a load. In the example shown in FIG. 1, an LED 20, a constant current circuit 13, a control circuit 12, and an operation receiver 14 are connected as loads.

A divided voltage of the voltage of the second power supply line W2 is input to the feedback terminal FB of the DC/DC converter 11 . More specifically, a second resistor R2 and a third resistor R3 are connected in series between the second power supply line W2 and the ground potential. The second resistor R2 and the third resistor R3 are connected to the output side of the inductor L1 inserted in the second power supply line W2. A voltage dividing point of the second resistor R2 and the third resistor R3 is connected to the feedback terminal FB of the DC/DC converter 11, and the voltage of the voltage dividing point is input to the feedback terminal FB.

The DC/DC converter 11 internally includes switches, drivers, comparators, and error amplifiers as main components. The switch is connected in the wiring between the input terminal VIN and the output terminal SW. For example, a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) can be used for the switch. The error amplifier amplifies the error between a predetermined reference voltage and the voltage input to the feedback terminal FB to generate an error signal. The comparator compares a predetermined carrier wave (triangular wave) signal and an error signal input from the error amplifier to generate a PWM signal. The driver controls on/off of the switch according to the PWM signal input from the comparator.

When the voltage of the second power supply line W2 corresponding to the divided voltage input to the feedback terminal FB becomes lower than the target value, the DC/DC converter 11 controls to increase the duty ratio of the switch, and the second power supply When the voltage of the supply line W2 becomes higher than the target value, the duty ratio of the switch is controlled to be lowered. Such voltage feedback control maintains the voltage output from the output terminal SW of the DC/DC converter 11 at the target value.

In this embodiment, the target value is set to about 3.5 to 3.6V. The target value is set to a value higher than the forward voltage drop Vf of the LED 20 by a predetermined value. The predetermined value is determined based on the voltage drop caused by the constant current circuit 13 .

An output filter is connected to the output terminal SW of the DC/DC converter 11 . In the example shown in FIG. 1, the output filter is composed of an LC filter. Specifically, the inductor L1 is inserted in the second power supply line W2 connected to the output terminal SW of the DC/DC converter 11 . A first capacitor C1 is connected between the second power supply line W2 and the ground line. A first capacitor C1 is connected to the output side of the inductor L1.

A Schottky barrier diode SB1 is connected between the second power supply line W2 and the ground line. The Schottky barrier diode SB1 is a commutation diode (free wheel diode) that is connected so that its anode faces the ground line and its cathode faces the second power supply line W2. Schottky barrier diode SB1 is connected to the input side of inductor L1. Schottky barrier diode SB1 commutates the energy stored in inductor L1 to the load while the switch in DC/DC converter 11 is off. In the example shown in FIG. 1, the Schottky barrier diode SB1, which has a low forward voltage drop Vf and excellent switching characteristics, is used as the commutation diode, but a general PN junction diode may be used. .

The DC/DC converter 11 shown in FIG. 1 employs a boot startup type DC/DC converter. A second capacitor C2 is connected between the boost terminal BST terminal of the DC/DC converter 11 and the output terminal SW. The second power supply line W2 and the boost terminal BST terminal of the DC/DC converter 11 are connected via the second diode D2. The second diode D2 is connected in such a direction that the second power supply line W2 side is the anode and the boost terminal BST terminal is the cathode. The second capacitor C2 is charged from the second power supply line W2 through the second diode D2. The voltage of the boost terminal BST is higher than the voltage of the output terminal SW by the voltage of the second capacitor C2.

For the high-side switching elements of the switches in the DC/DC converter 11, N-channel MOSFETs are used instead of P-channel MOSFETs. The voltage input to the boost terminal BST is used as the drive voltage for the high-side N-channel MOSFET. Since the N-channel MOSFET has a higher driving capability than the P-channel MOSFET, the size of the switch can be reduced and the cost can be reduced. In the case of a DC/DC converter that does not adopt the boot startup method, the boost terminal BST terminal is not provided, and the second diode D2 and the second capacitor C2 are unnecessary.

An LED 20 and a constant current circuit 13 are connected in series between the second power supply line W2 and the ground potential. The constant current circuit 13 keeps the current flowing through the LED 20 constant and dims the LED 20 based on the PWM signal supplied from the control circuit 12 .

The constant current circuit 13 includes a first transistor S1, a second transistor S2, a fourth resistor R4 and a fifth resistor R5. In the example shown in FIG. 1, an N-channel MOSFET is used as the first transistor S1, and an NPN-type bipolar transistor is used as the second transistor S2.

A first transistor S1 and a fourth resistor R4 are connected in series between the LED 20 and the ground potential. The fourth resistor R4 is a high resistor for detecting the current flowing through the LED20. Specifically, the source terminal of the first transistor S1 is connected to the ground potential through the fourth resistor R4, and the drain terminal is connected to the cathode terminal of the LED20. A drive signal line from the control circuit 12 is connected to the gate terminal (control terminal) of the first transistor S1. A fifth resistor R5 is inserted in the drive signal line. The control circuit 12 supplies a drive voltage to the gate terminal of the first transistor S1 through the drive signal line. The drive voltage is set to a value at which the first transistor S1 operates in a linear region (unsaturated region).

The emitter terminal of the second transistor S2 is connected to the ground potential, and the collector terminal is connected to the node between the fourth resistor R4 on the drive signal line and the gate terminal of the first transistor S1. The base terminal (control terminal) of the second transistor S2 is connected to the node N1 between the source terminal of the first transistor S1 and the fourth resistor R4.

In an NPN-type bipolar transistor, when the base-emitter voltage becomes higher than the threshold voltage, the base current begins to flow, and the collector current proportional to the base current flows. A typical silicon transistor has a threshold voltage of about 0.6 V at room temperature.

When a collector current flows through the second transistor S2, conduction is established between the drive signal line of the first transistor S1 and the ground potential, and the second transistor S2 becomes a resistance component between the drive signal line and the ground potential. In this state, a voltage generated by dividing the drive voltage output from the control circuit 12 by the fifth resistor R5 and the second transistor S2 is supplied to the gate terminal of the first transistor S1.

As described above, the base potential of the second transistor S2 is determined by the potential of the node N1. The potential of the node N1 is determined by the resistance value of the fourth resistor R4 and the current value flowing through the LED 20 and the fourth resistor R4. As the current flowing through the LED 20 and the fourth resistor R4 increases, the potential of the node N1 rises and the base potential of the second transistor S2 rises. When the base-emitter voltage exceeds the threshold voltage, a base current proportional to the base-emitter voltage and a collector current proportional to the base current flow. As the base-emitter voltage increases, the collector current increases, and as the collector current increases, the gate potential of the first transistor S1 decreases. In the linear region of the first transistor S1, the drain current changes in proportion to the gate potential.

The designer sets the resistance value of the fourth resistor R4 to a resistance value according to the target value of the current flowing through the LED 20 . The target value is set, for example, to a value within the range of 400mA to 700mA. When the current flowing through the LED 20 exceeds the target value, the potential of the node N1 increases and the drain current of the first transistor S1 decreases. This also reduces the current flowing through the LED 20 . On the other hand, when the current flowing through the LED 20 falls below the target value, the potential of the node N1 drops and the drain current of the first transistor S1 increases. As a result, the current flowing through the LED 20 also increases. As described above, the current flowing through the LED 20 can be maintained at the target value.

A transistor has a characteristic that the threshold voltage decreases as the temperature increases. As the temperature increases, the threshold voltage decreases from 0.6V to 0.5V. Conversely, when the temperature decreases, the threshold voltage increases from 0.6V to 0.7V. Therefore, when the temperature rises, the target value of the current flowing through the LED 20 is lowered due to the lowering of the threshold voltage. That is, the amount of current drawn by the first transistor S1 increases, and the current flowing through the LED 20 decreases. Thus, the constant current circuit 13 includes a temperature protection function that automatically reduces the current flowing through the LED 20 when the temperature rises.

The control circuit 12 receives a dimming signal for the LED 20 input from the dimming terminal DIM, and dims the LED 20 by controlling the first transistor S1 according to the received dimming signal. The dimming signal may be given as a digital signal from the dimming controller, or may be given as an analog signal.

For example, the control circuit 12 dims the LED 20 by supplying a PWM signal to the gate terminal of the first transistor S1 through the drive signal line according to the input dimming signal. Instead of supplying the PWM signal to the gate terminal of the first transistor S1, the control circuit 12 may adjust the level of the drive voltage in an analog manner to dim the LED 20. FIG.

The control circuit 12 is composed of, for example, a microcontroller. The power supply voltage of the microcontroller is supplied from the output voltage of the DC/DC converter 11 . As described above, in this embodiment, the output voltage of the DC/DC converter 11 is maintained at approximately 3.5-3.6V. Therefore, the control circuit 12 should use a microcontroller that operates with a power supply voltage of 3.5 to 3.6V or less.

As described above, the high-resistance fourth resistor R4 is connected between the first transistor S1 and the ground potential. The control circuit 12 can detect the current flowing through the LED 20 with high accuracy by monitoring the voltage at the node N1 between the first transistor S1 and the fourth resistor R4.

In the example shown in FIG. 1, a low-pass filter is installed between the node N1 and the control circuit 12. FIG. The low pass filter includes a sixth resistor R6 and a third capacitor C3. A sixth resistor R6 is inserted in a signal line connecting the node N1 and the control circuit 12, and a third capacitor C3 is connected between the signal line and the ground potential. The low-pass filter can convert the voltage at the node N1 into a smooth analog voltage. When the LED 20 is PWM-dimmed, the voltage at the node N1 turns on/off at high speed, but the control circuit 12 can detect the voltage at the node N1 as a smooth analog voltage by inserting a low-pass filter.

As described above, the constant current circuit 13 has the effect of decreasing the current flowing through the LED 20 when the temperature is high and increasing the current flowing through the LED 20 when the temperature is low. For example, when the lighting device 1 is activated in a low-temperature environment, a large current flows through the LEDs 20 . When the current starts to flow, the second transistor S2 is warmed by the heat generated by the current, and the current flowing through the LED 20 decreases. However, the large current that flows during startup in a low-temperature environment cannot be suppressed only by the feedback control by the second transistor S2. can't

Therefore, in the present embodiment, feedback control by the control circuit 12 is also used. The control circuit 12 feedback-controls the first transistor S1 so that the monitored voltage of the node N1 maintains the target voltage corresponding to the target current flowing through the LED20. The control circuit 12, for example, adjusts the duty ratio of the PWM signal supplied to the gate terminal of the first transistor S1 to match the voltage of the node N1 with the target voltage. The control circuit 12 may adjust the voltage of the node N1 to the target voltage by adjusting the level of the driving voltage supplied to the gate terminal of the first transistor S1 in an analog manner.

The control circuit 12 performs feedback control of the first transistor S1 when the voltage of the monitored node N1 is higher than the target voltage, and performs feedback control of the first transistor S1 when the voltage of the node N1 is lower than the target voltage. You can stop it. That is, control is applied in the direction of decreasing the current flowing through the LED 20 only when a current larger than the target current is flowing through the LED 20 . When a current smaller than the target current flows through the LED 20, it may be due to the above-described temperature protection function of the constant current circuit 13. No control is applied in the direction of increasing current.

The control circuit 12 monitors the voltage of the first power supply line W1 connected to the input terminal VIN of the DC/DC converter 11 (24 V in the example shown in FIG. 1). A seventh resistor R7 and an eighth resistor R8 are connected in series between the first power supply line W1 and the ground potential. A voltage dividing point of the seventh resistor R7 and the eighth resistor R8 is input to the control circuit 12 . The control circuit 12 detects the voltage of the first power supply line W1 based on the input voltage dividing point voltage.

The control circuit 12 turns off the constant current circuit 13 to cut off the current flowing through the LED 20 when the voltage of the first power supply line W1 becomes lower than a first set value (for example, about 17 to 18 V). Specifically, the control circuit 12 reduces the gate voltage of the first transistor S1 to turn off the first transistor S1. The DC/DC converter 11 has the property of increasing the input current to secure the energy to be output when the input voltage drops. As the input current to the DC/DC converter 11 increases, heat generation increases and current consumption also increases.

When the voltage of the first power supply line W1 becomes higher than a second set value (for example, about 19 to 21 V) after the voltage of the first power supply line W1 becomes lower than the first set value, the control circuit 12 sets the constant voltage. The current circuit 13 is turned on to unblock the current flowing through the LED 20 . It should be noted that when restoring, it is desirable to restore with a soft start. The second set value is set to a value obtained by adding a predetermined margin (for example, about 2V) to the first set value. A region between the second set value and the first set value becomes a dead zone, and it is possible to prevent the LED 20 from chattering between the ON mode and the OFF mode.

FIG. 2 is a diagram showing a configuration example of the operation reception unit 14 in FIG. The operation reception unit 14 is an operation reception unit using a magnetic sensor. In the configuration example shown in FIG. 2, the operation reception section 14 includes a Hall element 14a, a differential amplifier 14b and an A/D converter 14c. The Hall element 14a is an element that uses the Hall effect to convert a magnetic field into a voltage and output the voltage. The output voltage (3.5 to 3.6 V in this embodiment) of the DC/DC converter 11 is supplied to the Hall element 14a as a power supply voltage, and a constant current flows through the Hall element 14a.

The differential amplifier 14b amplifies the voltage output from the Hall element 14a. The A/D converter 14 c converts the analog voltage output from the differential amplifier 14 b into a digital value and outputs the digital value to the control circuit 12 . If the control circuit 12 has an analog input port, the A/D converter 14c is unnecessary.

The user can also perform light control of the LED 20 using the operation assisting tool 30 in addition to light control of the LED 20 using the light control controller. A magnet 30a is attached to the operation assisting tool 30, and the operation assisting tool 30 can generate a magnetic field. The Hall element 14a outputs a voltage corresponding to the detected magnetic field when the operation assisting tool 30 approaches. The control circuit 12 detects the approach of the operation assisting tool 30 based on the voltage input from the operation reception section 14 . For example, when the input voltage exceeds a predetermined set voltage, it is recognized as one approach by the operation assisting tool 30 .

For example, in the control circuit 12, the maximum current value that can be supplied to the LED 20 is set in multiple stages. For example, six modes of 0%, 20%, 40%, 60%, 80%, and 100% of the preset maximum current value that can be passed through the LED 20 may be set. The control circuit 12 sequentially switches modes each time the approach of the operation assisting tool 30 is detected.

FIG. 3 is a diagram showing a usage example of the lighting device 1 according to the embodiment of the present invention. A single lighting system may be constructed by arranging a plurality of lighting devices 1 in a line. In the system configuration example shown in FIG. 3, power is supplied from the external power source 2 to each of the plurality of lighting devices 1 via the power line 4a and the ground line 4b. The external power source 2 may be, for example, an AC/DC converter connected to a commercial power system, or may be a storage battery. Further, a dimming signal is supplied from the dimming controller 3 to each of the plurality of lighting devices 1 via the control signal line 4c.

In the system configuration shown in FIG. 3, a plurality of lighting devices 1 receive the same dimming signal from the outside. On the other hand, the light control using the operation assistance tool 30 shown in FIG. 2 can individually control light for each lighting device 1 . The dimming value set by the dimming controller 3 is effective within the range of the maximum current value of the LED 20 set by dimming using the operation aid 30 . That is, PWM dimming is performed with the maximum current value set to 100%.

Individual dimming using a magnetic sensor is an effective operation method when the lighting device 1 is mounted in a small housing. If the lighting device 1 is small, it is difficult to install a dimming knob on each lighting device 1 . Also, even if the lighting device 1 is not small, if a dimming knob is installed, the design will be degraded.

As described above, according to the present embodiment, the constant voltage supplied from the DC/DC converter 11 to the LED 20 is used as the power supply voltage for the control circuit 12, thereby generating the power supply voltage for the control circuit 12. regulator can be omitted. As a result, the space for installing the regulator can be saved, and the circuit board can be miniaturized. Also, omitting the regulator leads to cost reduction. It also leads to elimination of loss in the regulator and heat generation from the regulator.

Also, in this embodiment, a constant current circuit 13 is provided to control the current of the LED 20 . Since the voltage applied to the constant current circuit 13 is a low voltage, the loss in the constant current circuit 13 is small and the heat generation is also small. Therefore, highly efficient operation of the lighting device 1 is possible.

Further, the constant current circuit 13 is configured as an analog type using two transistors, a first transistor S1 and a second transistor S2, and dimming is performed by supplying a PWM signal to the gate terminal of the first transistor S1. Thereby, the constant current function and the dimming function can be integrated, and constant current control and dimming control of the LED 20 can be performed with a small number of elements.

Further, the control circuit 12 monitors the voltage at the node N1 between the first transistor S1 and the fourth resistor R4, so that the current flowing through the LED 20 can be detected in real time with high accuracy. Further, the control circuit 12 feedback-controls the first transistor S1 based on the voltage of the node N1 being monitored. Thereby, the feedback control of the first transistor S1 by the second transistor S2 and the feedback control of the first transistor S1 by the control circuit 12 are duplicated, and the current flowing through the LED 20 can be further stabilized. In addition, feedback control by the control circuit 12 can also suppress a large current generated at low temperature start-up, which is difficult to suppress only by the feedback control by the second transistor S2.

Further, the feedback control by the control circuit 12 is performed only in the direction of decreasing the current, so that the temperature protection function in which the constant current circuit 13 automatically reduces the current as the temperature rises can be effectively utilized. Also, by inserting the polyswitch F1 and the low-resistance first resistor R1 in the input stage of the DC/DC converter 11, the inrush current can be suppressed. It also monitors the voltage of the first power supply line W1 and cuts off the current supply to the LED 20 when the voltage drops below the first set value. In this way, a mechanism is introduced at each stage to avoid an abnormal temperature rise, and even if the LED and drive circuit are mounted in a small housing, thermal runaway is suppressed and safety is maintained. In addition, since multiple safety functions are incorporated, even an LED installed in a small housing can operate at a high efficiency by making full use of its capabilities.

The present invention has been described above based on the embodiments. It should be understood by those skilled in the art that the present embodiment is an example, and that various modifications can be made to the combination of each component, and that such modifications are within the scope of the present invention.

FIG. 4 is a diagram showing a circuit configuration of a lighting device 1 according to a modification. In the circuit configuration according to the modification, a regulator 15 is added to the circuit configuration shown in FIG. The regulator 15 steps down the voltage (24 V in the example shown in FIG. 1) of the first power supply line W1 input to the input terminal IN, and outputs the stepped-down voltage from the output terminal OUT. The stepped-down voltage is used as the power supply voltage for the control circuit 12 and the operation reception section 14 . In a variant, the output voltage of regulator 15 need not be the same as the output voltage of DC/DC converter 11 . For example, it may be about 5V.

According to the modified example, although the effect of omitting the regulator described above cannot be enjoyed, other effects can be enjoyed. In particular, the constant current circuit 13 is configured as an analog type using two transistors, a first transistor S1 and a second transistor S2, and by controlling the first transistor S1 for dimming, the constant current of the LED 20 can be achieved with a small number of elements. The effect of enabling current control and dimming control can be enjoyed.

In the above embodiments, an example of using a MOSFET as the first transistor S1 has been described. In this regard, bipolar transistors may be used. In addition, when the electric current sent through LED20 is large, it is more preferable to use MOSFET. Although it is possible to use a MOSFET for the second transistor S2, it is preferable to use a bipolar transistor. A MOSFET has a higher threshold voltage than a bipolar transistor. Therefore, when a MOSFET is used, it is necessary to increase the output voltage of the DC/DC converter 11 applied to the LED 20 and the fourth resistor R4 compared to when a bipolar transistor is used. . In bipolar transistors, the base voltage at which collector current begins to flow is more stable, but in MOSFETs, the gate voltage at which drain current begins to flow is relatively unstable. Therefore, the accuracy of maintaining a constant current is higher when a bipolar transistor is used.

Also, in the above-described embodiments, an example in which a DC voltage is supplied from the outside has been described. In this respect, when an AC voltage is supplied from the outside, an AC/DC converter may be installed in front of the DC/DC converter 11 in the lighting device 1 .

In addition, in the circuit configuration shown in FIG. 1, a constant current circuit other than the analog type using the first transistor S1 and the second transistor S2 may be used as the constant current circuit 13 . Moreover, in the circuit configuration shown in FIG. 1, a switch for dimming the LED 20 may be provided separately from the constant current circuit 13 . Even in these cases, the effect of omitting the regulator described above can be enjoyed.

Reference Signs List 1 illumination device 10 lighting control circuit 11 DC/DC converter 12 control circuit 13 constant current circuit 14 operation reception unit 14a hall element 14b differential amplifier 14c A/D converter 20 LED S1 th 1 transistor S2 second transistor F1 polyswitch D1, D2 diode SB1 Schottky barrier diode L1 inductor C1-C3 capacitor R1-R8 resistor W1 first power supply line W2 second power supply line 30 operation aid, 30a magnet, 2 external power supply, 3 dimming controller, 15 regulator.

Claims (10)

a DC/DC converter that converts an input DC voltage and outputs a constant voltage;
an LED (Light Emitting Diode) to which the output voltage of the DC/DC converter is applied;
a constant current circuit connected in series with the LED;
a control circuit that keeps the current flowing through the LED constant using the constant current circuit and dims the LED according to an input dimming signal ;
The output voltage of the DC/DC converter is set to a predetermined value higher than the forward voltage drop of the LED,
The lighting device, wherein the power supply voltage of the control circuit is supplied from the output voltage of the DC/DC converter. The constant current circuit is
a first transistor inserted between the LED and a predetermined fixed potential and having a control terminal connected to a drive signal line from the control circuit;
a first resistor inserted between the first transistor and the fixed potential;
a second resistor inserted in the drive signal line;
inserted between the fixed potential and a node between the second resistor and the control terminal of the first transistor on the drive signal line, the control terminal being a node between the first transistor and the first resistor; a second transistor connected to
2. The lighting device of claim 1, comprising: 3. The lighting device according to claim 2, wherein the second transistor is an NPN bipolar transistor. a DC/DC converter that converts an input DC voltage and outputs a constant voltage;
an LED (Light Emitting Diode) to which the output voltage of the DC/DC converter is applied;
a constant current circuit connected in series with the LED;
a control circuit that controls the current flowing through the LED using the constant current circuit;
The output voltage of the DC/DC converter is set to a predetermined value higher than the forward voltage drop of the LED,
A power supply voltage of the control circuit is supplied from an output voltage of the DC/DC converter,
The constant current circuit is
a first transistor inserted between the LED and a predetermined fixed potential and having a control terminal connected to a drive signal line from the control circuit;
a first resistor inserted between the first transistor and the fixed potential;
a second resistor inserted in the drive signal line;
inserted between the fixed potential and a node between the second resistor and the control terminal of the first transistor on the drive signal line, the control terminal being a node between the first transistor and the first resistor; a second transistor connected to
a voltage of a node between the first transistor and the first resistor is input to the control circuit;
The lighting device, wherein the control circuit feedback-controls the first transistor so that the voltage of the node becomes a target voltage corresponding to a target current flowing through the LED. 5. The control circuit according to claim 4, wherein the control circuit executes the feedback control when the voltage of the node is higher than the target voltage, and stops the feedback control when the voltage of the node is lower than the target voltage. lighting system. a DC/DC converter that converts an input DC voltage and outputs a constant voltage;
an LED (Light Emitting Diode) to which the output voltage of the DC/DC converter is applied;
a constant current circuit connected in series with the LED;
a control circuit that controls the current flowing through the LED using the constant current circuit;
The output voltage of the DC/DC converter is set to a predetermined value higher than the forward voltage drop of the LED,
A power supply voltage of the control circuit is supplied from an output voltage of the DC/DC converter,
The constant current circuit is
a first transistor inserted between the LED and a predetermined fixed potential and having a control terminal connected to a drive signal line from the control circuit;
a first resistor inserted between the first transistor and the fixed potential;
a second resistor inserted in the drive signal line;
inserted between the fixed potential and a node between the second resistor and the control terminal of the first transistor on the drive signal line, the control terminal being a node between the first transistor and the first resistor; a second transistor connected to
The lighting device, wherein the control circuit controls the first transistor according to an input dimming signal. 7. The control circuit according to claim 6, wherein the control circuit supplies a PWM (Pulse Width Modulation) signal to the control terminal of the first transistor through the drive signal line in accordance with an input dimming signal. A lighting device as described. a DC/DC converter that converts an input DC voltage and outputs a constant voltage;
an LED (Light Emitting Diode) to which the output voltage of the DC/DC converter is applied;
a constant current circuit connected in series with the LED;
a control circuit that controls the current flowing through the LED using the constant current circuit;
The output voltage of the DC/DC converter is set to a predetermined value higher than the forward voltage drop of the LED,
A power supply voltage of the control circuit is supplied from an output voltage of the DC/DC converter,
The control circuit is
when the DC voltage input to the DC/DC converter becomes lower than a first set value, the constant current circuit is turned off to cut off the current flowing through the LED;
When the DC voltage input to the DC/DC converter becomes higher than a second set value that is higher than the first set value by a predetermined value, the constant current circuit is turned on to cancel the interruption of the current flowing through the LED. A lighting device characterized by: 9. The lighting device according to any one of claims 1 to 8, wherein a polyswitch is connected to the input stage of the DC/DC converter. a DC/DC converter that converts an input DC voltage and outputs a constant voltage;
an LED (Light Emitting Diode) to which the output voltage of the DC/DC converter is applied;
a constant current circuit connected in series with the LED;
a control circuit that controls the current flowing through the LED using the constant current circuit;
The output voltage of the DC/DC converter is set to a predetermined value higher than the forward voltage drop of the LED,
A power supply voltage of the control circuit is supplied from an output voltage of the DC/DC converter,
Further comprising an operation receiving unit that includes a hall element and detects the approach of an operation aid that generates a magnetic field,
In the control circuit, a maximum current value that can be passed through the LED is set in multiple stages,
The lighting device according to claim 1, wherein the control circuit sequentially switches the maximum current value each time the approach of the operation assisting tool is detected.

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