JP7380174B2 - Lighting devices and luminaires - Google Patents

Description

The present disclosure relates to lighting devices and lighting fixtures.

Patent Document 1 discloses a power supply device that generates a DC voltage by boosting the output of an AC power source rectified by a diode bridge using a boost chopper circuit. This power supply device includes a current limiting element that prevents inrush current from being inserted into a supply path that supplies the output of the diode bridge to the boost chopper circuit. Further, the power supply device includes a switching element that short-circuits the current limiting element after suppressing the inrush current. As the inductor of the boost chopper circuit, one having a secondary winding wound with the same polarity as the primary winding is used. The switching element is turned on using the voltage induced in the secondary winding. This eliminates power loss due to resistance and reduces power loss.

Japanese Unexamined Patent Publication No. 7-147770

In the power supply device of Patent Document 1, when a short-circuit failure occurs in the load, there is a risk that current may continue to flow to the load through the switching element.

The present disclosure was made in order to solve the above-mentioned problems, and an object of the present disclosure is to obtain a lighting device and a lighting fixture that can suppress overcurrent during a short circuit.

A lighting device according to the present disclosure includes a pair of current supply lines that receive power from a DC power supply, a first switching element, and a coil electrically connected to the high potential side of the pair of current supply lines. a step-up chopper circuit that receives power from the DC power supply via the pair of current supply lines and lights up the light source by turning on and off the first switching element; and the high potential side of the pair of current supply lines. a current limiting element provided in the current limiting element, a first terminal electrically connected to one end of the current limiting element, a second terminal electrically connected to the other end of the current limiting element, and the first terminal. and a control terminal for switching between a conductive state or a cutoff state between the second terminal and the second terminal, and a voltage adjustment circuit that supplies a control terminal voltage to the control terminal, When the output voltage of the step-up chopper circuit is higher than the power supply voltage of the DC power supply, the adjustment circuit receives current from the coil and controls the second switching element when the first switching element is in the OFF state. the voltage regulating circuit generates a voltage at the control terminal that brings the second switching element into a conductive state ; is a first capacitor that receives current from the coil and generates the control terminal voltage at the control terminal; an anode is electrically connected to the coil; and a cathode is electrically connected to the positive electrode of the first capacitor. It includes a diode connected thereto, and a voltage dividing circuit that divides the voltage across the first capacitor and outputs the control terminal voltage .
A lighting device according to the present disclosure includes a pair of current supply lines that receive power from a DC power supply, a first switching element, and a coil electrically connected to the high potential side of the pair of current supply lines. a step-up chopper circuit that receives power from the DC power supply via the pair of current supply lines and lights up the light source by turning on and off the first switching element; and the high potential side of the pair of current supply lines. a current limiting element provided in the current limiting element, a first terminal electrically connected to one end of the current limiting element, a second terminal electrically connected to the other end of the current limiting element, and the first terminal. and a control terminal for switching between a conductive state or a cutoff state between the second terminal and the second terminal, and a voltage adjustment circuit that supplies a control terminal voltage to the control terminal, When the output voltage of the step-up chopper circuit is higher than the power supply voltage of the DC power supply, the adjustment circuit receives current from the coil and controls the second switching element when the first switching element is in the OFF state. the voltage regulating circuit generates a voltage at the control terminal that brings the second switching element into a conductive state; includes a second capacitor electrically connected between the coil-side terminal of the first terminal and the second terminal, and the control terminal.

In the lighting device according to the present disclosure, when the output voltage of the boost chopper circuit becomes equal to or lower than the power supply voltage due to a short circuit in the light source, the second switching element enters the cutoff state. Therefore, the current limiting element can suppress overcurrent at the time of short circuit.

1 is a circuit block diagram of a lighting fixture according to Embodiment 1. FIG. FIG. 3 is a diagram illustrating a voltage waveform of the lighting device according to the first embodiment. It is a figure explaining the voltage waveform at the time of a short circuit.

A lighting device and a lighting fixture according to each embodiment will be described with reference to the drawings. Identical or corresponding components may be given the same reference numerals and repeated descriptions may be omitted.

Embodiment 1.
FIG. 1 is a circuit block diagram of a lighting fixture 100 according to the first embodiment. The lighting fixture 100 includes a lighting device 10 and a light source section 50. A direct current power supply DC is supplied to the lighting device 10 from the outside. The lighting device 10 includes a connection part CN1 to which a DC power supply DC is connected. Further, the lighting device 10 supplies power to the light source section 50 to light the light source section 50. The lighting device 10 includes a connection part CN2 to which the light source part 50 is connected.

The light source section 50 includes a plurality of light sources 51 connected in series. The light source 51 is, for example, an LED. The number of light sources 51 included in the light source section 50 may be one or more. Further, the plurality of light sources 51 may be connected in parallel or in series and parallel.

The lighting device 10 includes a pair of current supply lines 11 and 12 that receive power from a direct current power source DC. Of the current supply lines 11 and 12, the current supply line 11 is on the high potential side, and the current supply line 12 is on the low potential side.

The lighting device 10 includes a boost chopper circuit 30. The boost chopper circuit 30 is a lighting circuit section for converting the DC power supply DC into power. The boost chopper circuit 30 boosts the power supply voltage of the DC power supply DC. A light source unit 50 that is turned on at a voltage higher than the power supply voltage of the DC power supply DC is connected to the output of the boost chopper circuit 30. The boost chopper circuit 30 includes a coil L1, a first switching element Q1, and a diode D1.

The first switching element Q1 includes a first terminal, a second terminal, and a control terminal for switching between the first terminal and the second terminal to a conductive state or a disconnected state. The first switching element Q1 is, for example, a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). When the first switching element Q1 is a MOSFET, the first terminal is a drain terminal, the second terminal is a source terminal, and the control terminal is a gate terminal.

One end of the coil L1 is electrically connected to the current supply line 11. The other end of the coil L1 and the anode of the diode D1 are connected to the first terminal of the first switching element Q1. A second terminal of the first switching element Q1 is connected to the current supply line 12. A control terminal of the first switching element Q1 is connected to the lighting control IC 40.

The cathode of diode D1 is connected to the positive electrode of capacitor C1. The negative electrode of capacitor C1 is connected to one end of resistor R1. The other end of the resistor R1 is connected to the second terminal of the first switching element Q1. Further, the high potential side of the light source section 50 is connected to the positive electrode of the capacitor C1. The low potential side of the light source section 50 is connected to the negative electrode of the capacitor C1. The capacitor C1 rectifies the high frequency voltage output from the diode D1 and supplies it to the light source section 50. Capacitor C1 is a smoothing capacitor.

The lighting control IC 40 is composed of, for example, a microcomputer. The lighting control IC 40 controls the lighting state of the light source section 50 by controlling on/off of the first switching element Q1. The P1 terminal of the lighting control IC 40 is connected to the control terminal of the first switching element Q1. Thereby, the lighting control IC 40 drives the first switching element Q1. Further, the P2 terminal of the lighting control IC 40 is connected to one end of the resistor R1. Thereby, the lighting control IC 40 detects the voltage applied to the resistor R1.

A current that flows to the capacitor C1 and the light source section 50 flows through the resistor R1. Therefore, the average value of the current flowing through the light source section 50 can be detected by the resistor R1. The current flowing through the resistor R1 is converted into a voltage and detected at the P2 terminal of the lighting control IC 40. The lighting control IC 40 switches the first switching element Q1 so that the voltage generated across the resistor R1 becomes a predetermined voltage. Thereby, constant current control can be performed so that the average current flowing through the light source section 50 is constant.

In this way, the boost chopper circuit 30 receives power from the DC power supply DC via the pair of current supply lines 11 and 12, and lights up the light source 51 by turning on and off the first switching element Q1.

Note that the connection position to the resistor R1 may be between the low potential side of the light source section 50 and the negative electrode of the capacitor C1. At this position, the current flowing purely through the light source section 50 can be detected.

A protection circuit 20 is provided on the current supply line 11 . The protection circuit 20 includes a current limiting element R2, a second switching element Q2, and a voltage adjustment circuit 22. The current limiting element R2 is provided on the current supply line 11.

The second switching element Q2 includes a first terminal, a second terminal, and a control terminal for switching between the first terminal and the second terminal to a conductive state or a disconnected state. The second switching element Q2 is, for example, a MOSFET. The second switching element Q2 is connected between the coil L1 and the DC power supply DC. The second switching element Q2 has a first terminal connected to the DC power supply DC side, and a second terminal connected to the coil L1 side.

The second switching element Q2 and current limiting element R2 are connected in parallel. A first terminal of the second switching element Q2 is electrically connected to one end of the current limiting element R2. The second terminal of the second switching element Q2 is electrically connected to the other end of the current limiting element R2. A control terminal of the second switching element Q2 is electrically connected to the voltage adjustment circuit 22. The voltage adjustment circuit 22 supplies a control terminal voltage, which will be described later, to a control terminal.

The voltage adjustment circuit 22 includes a diode D2 whose anode is electrically connected to the coil L1. Diode D2 is supplied with current from coil L1. Coil L1 is divided into winding N1 and winding N2. The anode of diode D2 is connected to the connection point of winding N1 and winding N2.

Further, the voltage adjustment circuit 22 includes a capacitor C2. The capacitor C2 has a positive electrode electrically connected to the cathode of the diode D2, and a negative electrode electrically connected to a portion of the current supply line 11 between the coil L1 and the second switching element Q2.

Furthermore, one end of the resistor R3 is connected to the cathode of the diode D2. One end of the resistor R4, the positive electrode of the capacitor C3, and the control terminal of the second switching element Q2 are connected to the other end of the resistor R3. Capacitor C3 and resistor R4 are connected in parallel. Capacitor C3 and resistor R4 are electrically connected between the control terminal and the second terminal of second switching element Q2.

Note that the capacitor C3 is provided to prevent malfunction of the second switching element Q2. Capacitor C3 is connected for voltage stabilization, and may have a small capacitance.

FIG. 2 is a diagram illustrating a voltage waveform of the lighting device 10 according to the first embodiment. It is assumed that a direct current power supply DC is turned on to the lighting device 10 by a switch (not shown) or the like. When the power is turned on, the second switching element Q2 is in an off state. For this reason, a current flows from the DC power supply DC through a loop including the current limiting element R2, the coil L1, the diode D1, and the capacitor C1. This charges the capacitor C1.

This current is a so-called rush current. Inrush current is suppressed by the impedance of current limiting element R2. In this way, the current value when the power is turned on can be controlled by the current limiting element R2.

Note that if the boost chopper circuit 30 does not operate, a voltage higher than that of the DC power supply DC will not be supplied to the light source section 50. Therefore, no current flows through the light source section 50, and the light source section 50 cannot be lit.

Next, the lighting control IC 40 is activated. This causes the boost chopper circuit 30 to operate. The lighting control IC 40 may be started and operated using, for example, the voltage generated in the capacitor C1 as a power source.

Until time T1 in FIG. 2, the boost chopper circuit 30 has not started operating. Therefore, no voltage is applied to the control terminal of the first switching element Q1. Therefore, the first switching element Q1 is off. In FIG. 2, the voltage at the control terminal of the first switching element Q1 is shown as Vg.

At this time, since the boost chopper circuit 30 is not boosting the voltage, no potential difference is generated in the coil L1. In FIG. 2, the voltage of coil L1 is shown as VL1. Further, no voltage is generated in capacitors C2 and C3 until time T1. In FIG. 2, voltages across capacitors C2 and C3 are shown as C2 voltage and C3 voltage, respectively.

At time T1, the first switching element Q1 starts switching. From time T1 to time T2, the first switching element Q1 is in an on state. At this time, the first terminal of the first switching element Q1 becomes the ground potential. As a result, -VDC is applied to the coil L1. VDC is a power supply voltage of a direct current power supply DC.

At this time, the potential at the connection point between the winding N1 and the winding N2 is lower than the potential at the cathode side of the diode D2. Therefore, no current flows through the diode D2. The potential on the cathode side of the diode D2 corresponds to the potential of the portion of the current supply line 11 between the second switching element Q2 and the coil L1.

From time T2 to time T3, the first switching element Q1 is in an off state. When the first switching element Q1 is in the off state, a voltage applied to the light source section 50 is generated at the first terminal of the first switching element Q1. The voltage applied to the light source section 50 is the output voltage V1 of the boost chopper circuit 30. The output voltage V1 is higher than the power supply voltage VDC of the DC power supply DC.

At this time, V1-VDC is applied to the coil L1. However, since the output voltage V1 is sufficiently higher than the forward voltage VF of the diode D1, the forward voltage VF of the diode D1 is ignored. Therefore, the potential at the connection point between the winding N1 and the winding N2 is higher than the potential at the cathode side of the diode D2. Therefore, capacitor C2 is charged via diode D2, and a voltage is applied to capacitor C2.

The voltage applied to the capacitor C2 is a voltage obtained by dividing V1-VDC by the turns ratio of the winding N1 and the winding N2 of the coil L1. Here, the forward voltage VF of the diode D2 is ignored.

Resistors R3 and R4 connected in series form a voltage divider circuit. A voltage obtained by dividing the voltage of the capacitor C2 by resistors R3 and R4 is applied to the capacitor C3. The voltage across the capacitor C3 becomes the control terminal voltage of the second switching element Q2. In this way, the voltage dividing circuit divides the voltage across the capacitor C2 and outputs the control terminal voltage to the second switching element Q2.

The control terminal voltage is applied to the control terminal of the second switching element Q2. The control terminal voltage is higher than the on-voltage Vth of the second switching element Q2. The on-voltage Vth is also called a threshold value. Therefore, the voltage at the control terminal of the second switching element Q2 exceeds the on-voltage Vth, and the second switching element Q2 is turned on.

In this way, the second switching element Q2 is rendered conductive by the drive voltage obtained by the switching operation of the boost chopper circuit 30 while the first switching element Q1 is off. Further, the capacitor C2 receives current from the coil L1 and generates a control terminal voltage at the control terminal of the second switching element Q2.

At time T3, the first switching element Q1 is turned on again. From time T3 to time T4, the first switching element Q1 is in an on state. At this time, similarly to the period from time T1 to time T2, the potential at the connection point between the winding N1 and the winding N2 is lower than the potential at the portion of the current supply line 11 between the second switching element Q2 and the coil L1. low. However, the current is blocked by the diode D2, and no current flows from the capacitor C2 to the diode D2 side. Therefore, the capacitor C2 is discharged only to the resistors R3 and R4.

At this time, the voltage of the capacitor C2 decreases by ΔV during the on period of the first switching element Q1. Along with this, the voltage of capacitor C3 decreases. Here, even if the voltage of the capacitor C2 decreases by ΔV, the control terminal voltage of the second switching element Q2 is maintained at or above the on-voltage Vth. Therefore, the second switching element Q2 can continue to be in the on state from time T3 to time T4.

At time T4, the first switching element Q1 is turned off again. From time T4 to time T5, the first switching element Q1 is in an off state. At this time, as from time T2 to time T3, V1-VDC is applied to the coil L1, and the potential of the anode of the diode D2 becomes higher than the potential of the cathode. Therefore, capacitor C2 is charged via diode D2, and a voltage is applied to capacitor C2. After that, the same operation is repeated.

In this way, after the inrush current is suppressed by the current limiting element R2, the second switching element Q2 is turned on by the lighting operation of the boost chopper circuit 30. Therefore, a stable voltage can be supplied to the boost chopper circuit 30 while suppressing the loss in the current limiting element R2.

If there is no second switching element Q2 in parallel with current-limiting element R2, current flows through current-limiting element R2 even during steady operation. Therefore, unnecessary loss may occur and energy consumption may increase. In this embodiment, energy consumption can be suppressed by the second switching element Q2.

In this embodiment, in the case of steady operation, the voltage adjustment circuit 22 receives current from the coil L1 when the first switching element Q1 is in the off state, and adjusts the control terminal voltage to bring the second switching element Q2 into the conductive state. generate. Here, steady operation indicates a state in which the output voltage V1 of the boost chopper circuit 30 is higher than the power supply voltage VDC of the DC power supply DC.

Further, in steady operation, while the first switching element Q1 is in the on state, the supply of current from the coil L1 to the voltage adjustment circuit 22 is cut off. However, while the first switching element Q1 is in the on state, the voltage adjustment circuit 22 maintains the control terminal voltage at or above the threshold value of the second switching element Q2. In other words, the voltage adjustment circuit 22 maintains the second switching element Q2 in a conductive state. Therefore, in steady operation, once the second switching element Q2 is turned on, it can continue to be in the on state.

The turns ratio of the coil L1, the capacitance of the capacitors C2 and C3, the resistance values of the resistors R3 and R4, etc. are set so as to provide the second switching element Q2 with a control terminal voltage equal to or higher than the on-voltage Vth. In addition, the turns ratio of the coil L1, the capacitance of the capacitors C2 and C3, the resistance values of the resistors R3 and R4, etc., maintain the control terminal voltage at or above the on-voltage Vth while the first switching element Q1 is in the on-state. It is set as follows.

Next, the operation when the light source section 50 is short-circuited for some reason will be described. FIG. 3 is a diagram illustrating a voltage waveform at the time of a short circuit. The operation up to time T5 is similar to that described with reference to FIG. Assume that at time T6, a short circuit occurs and the light source section 50 enters a low voltage state. As a result, the output voltage V1 of the boost chopper circuit 30 becomes low. In the example of FIG. 3, the output voltage V1 has decreased to VDC. At the time of short circuit, the output voltage V1 of the boost chopper circuit 30 may be lower than VDC.

At time T7, the first switching element Q1 is turned off. However, since the output voltage V1 of the boost chopper circuit 30 is low, a voltage higher than the power supply voltage VDC is not generated at the first terminal of the first switching element Q1. Therefore, unlike in steady operation, the potential at the connection point between the windings N1 and N2 does not become higher than the potential at the cathode side of the diode D2. Therefore, no current flows through diode D2.

During a short circuit, no current flows through the diode D2 even when the first switching element Q1 is off, so the capacitor C2 is not charged. In this way, when the output voltage V1 of the boost chopper circuit 30 is lower than the power supply voltage VDC, the supply of current from the coil L1 to the voltage adjustment circuit 22 is cut off. Therefore, the capacitor C2 continues to be discharged to the resistors R3 and R4, and the voltage of the capacitor C2 continues to decrease. Along with this, the voltage of capacitor C3 also continues to decrease.

At time T8, the control terminal voltage, which is the voltage of capacitor C3, falls below the on-voltage Vth of second switching element Q2. Therefore, the second switching element Q2 is turned off.

As a comparative example of this embodiment, consider connecting a thyristor in parallel with the current limiting element in order to suppress power loss due to the current limiting element. In the comparative example, the thyristor generates the on-voltage from its own current, ie, the holding current. At this time, even if the voltage of the light source becomes lower than the DC power supply DC due to a failure, the thyristor cannot be turned off, and an overcurrent continues to flow from the DC power supply DC. Therefore, in the comparative example, a protective operation in the event of a short circuit cannot be performed.

On the other hand, in this embodiment, the second switching element Q2 is connected in parallel with the current limiting element R2. A control terminal voltage is supplied from the voltage adjustment circuit 22 to the control terminal of the second switching element Q2. The voltage adjustment circuit 22 generates a control terminal voltage that turns off the second switching element Q2 when the output voltage V1 of the boost chopper circuit 30 is lower than the power supply voltage VDC of the DC power supply DC.

In this way, since the second switching element Q2 is turned off at the time of a short circuit, an overcurrent due to the short circuit flows through the current limiting element R2. Therefore, overcurrent can be suppressed by current limiting element R2. Therefore, even if a short-circuit failure occurs due to some abnormality such as the lifespan of the LED, the safety of the lighting fixture 100 can be ensured.

That is, the second switching element Q2 is normally turned off when the gate trigger signal disappears. Thereby, the above-mentioned function can be realized.

Further, in the lighting device 10 of the present embodiment, it is possible to efficiently suppress inrush current and perform a protective operation in the event of a short circuit failure with a small number of components. This can suppress the complexity of the protection circuit 20 and contribute to downsizing and energy saving of the lighting device 10. Furthermore, by simplifying the protection circuit 20, malfunctions of the protection circuit 20 can be suppressed.

As the current limiting element R2, it is preferable to use a positive temperature coefficient thermistor whose impedance increases when current flows and generates heat. In this case, the current limiting element R2 generates heat due to the overcurrent, so that transient current can be suppressed. Further, the current limiting element R2 may be a resistive element.

Further, the lighting control IC 40 may detect that the light source section 50 has short-circuited and stop the boost chopper circuit 30. Thereby, the safety of the lighting fixture 100 can be improved.

Further, the time from time T6 to time T8 can be set by the turn ratio of coil L1, the capacitance of capacitors C2 and C3, the resistance values of resistors R3 and R4, etc. The time from time T6 to time T8 is the time from when the short circuit occurs until the second switching element Q2 is turned off. For example, the smaller the resistance values of the resistors R3 and R4, the shorter the time from time T6 to time T8.

In this embodiment, the anode of diode D2 is connected, for example, to the midpoint of coil L1. However, the present invention is not limited to this, and the anode of the diode D2 may be connected to the wiring that connects the coil L1 and the diode D1. Further, components such as the capacitor C3 and the resistors R3 and R4 may not be provided as long as the function of the voltage adjustment circuit 22 can be ensured.

The lighting device 10 of this embodiment is supplied with DC power. Therefore, power consumption can be reduced. The lighting device 10 is not limited to this, and the lighting device 10 may be powered from a commercial power source. In this case, for example, the lighting device 10 includes a rectifier circuit, and the pair of current supply lines 11 and 12 are connected to the output of the rectifier circuit. Further, a plurality of lighting fixtures 100 may be set for one power supply system. Further, the DC power source DC may be a battery, the output of a rectifier circuit, the output of a DC power supply circuit, or the like.

Note that the technical features described in this embodiment may be used in combination as appropriate.

10 lighting device, 11, 12 current supply line, 20 protection circuit, 22 voltage adjustment circuit, 30 step-up chopper circuit, 50 light source section, 51 light source, 100 lighting fixture, C1, C2, C3 capacitor, CN1, CN2 connection section, D1 , D2 diode, DC DC power supply, 40 lighting control IC, L1 coil, N1, N2 winding, Q1 first switching element, Q2 second switching element, R1 resistor, R2 current limiting element, R3, R4 resistor

Claims (7)

a pair of current supply lines receiving power from a DC power supply;
It has a first switching element and a coil electrically connected to the high potential side of the pair of current supply lines, receives power from the DC power supply via the pair of current supply lines, and a boost chopper circuit that lights up a light source by turning on and off a first switching element;
a current limiting element provided on the high potential side of the pair of current supply lines;
a first terminal electrically connected to one end of the current limiting element; a second terminal electrically connected to the other end of the current limiting element; and a connection between the first terminal and the second terminal. a second switching element having a control terminal for switching to a conduction state or a cutoff state;
a voltage adjustment circuit that supplies a control terminal voltage to the control terminal;
Equipped with
When the output voltage of the step-up chopper circuit is higher than the power supply voltage of the DC power supply, the voltage adjustment circuit receives current from the coil when the first switching element is in an OFF state, and adjusts the voltage to the second switching element. generates the control terminal voltage that causes the voltage to be in the conducting state, and generates the control terminal voltage that causes the second switching element to be in the cutoff state when the output voltage of the boost chopper circuit is equal to or lower than the power supply voltage ;
The voltage regulation circuit is
a first capacitor that receives current from the coil and generates the control terminal voltage at the control terminal;
a diode whose anode is electrically connected to the coil and whose cathode is electrically connected to the positive electrode of the first capacitor;
a voltage dividing circuit that divides the voltage across the first capacitor and outputs the control terminal voltage;
A lighting device comprising : 2. The lighting device according to claim 1, wherein when the output voltage of the step-up chopper circuit is equal to or lower than the power supply voltage, supply of current from the coil to the voltage adjustment circuit is cut off. 3. The lighting device according to claim 1, wherein the diode is supplied with current from the coil . a pair of current supply lines receiving power from a DC power supply;
It has a first switching element and a coil electrically connected to the high potential side of the pair of current supply lines, receives power from the DC power supply via the pair of current supply lines, and a boost chopper circuit that lights up a light source by turning on and off a first switching element;
a current limiting element provided on the high potential side of the pair of current supply lines;
a first terminal electrically connected to one end of the current limiting element, a second terminal electrically connected to the other end of the current limiting element, and a connection between the first terminal and the second terminal. a second switching element having a control terminal for switching to a conduction state or a cutoff state;
a voltage adjustment circuit that supplies a control terminal voltage to the control terminal;
Equipped with
When the output voltage of the step-up chopper circuit is higher than the power supply voltage of the DC power supply, the voltage adjustment circuit receives current from the coil when the first switching element is in an OFF state, and adjusts the voltage to the second switching element. generates the control terminal voltage that brings the converter into the conductive state, and generates the control terminal voltage that brings the second switching element into the cutoff state when the output voltage of the boost chopper circuit is equal to or lower than the power supply voltage;
The voltage adjustment circuit includes a second capacitor electrically connected between a terminal on the coil side of the first terminal and the second terminal and the control terminal. Device. When the output voltage of the step-up chopper circuit is higher than the power supply voltage, the supply of current from the coil to the voltage adjustment circuit is cut off while the first switching element is in the on state, and the voltage adjustment circuit 5. The lighting device according to claim 1, wherein the control terminal voltage is maintained at or above a threshold value of the second switching element. 6. The lighting device according to claim 1 , wherein the second switching element is a MOSFET. The lighting device according to any one of claims 1 to 6 ,
the light source;
A lighting fixture comprising:

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