JP7409176B2 - Lighting devices and luminaires - Google Patents

Description

The present disclosure relates to lighting devices and lighting fixtures.

Patent Document 1 discloses a discharge lamp lighting device. This discharge lamp lighting device includes a DC power supply, a power conversion means that converts the DC power of the DC power supply into power and supplies it to the discharge lamp, and a control means that controls the power conversion means to supply substantially constant power to the discharge lamp. Equipped with. Further, the discharge lamp lighting device is provided with input power detection means for detecting input power from a DC power source and output power detection means for detecting output power supplied to the discharge lamp. The control means reduces the substantially constant power in accordance with the circuit loss when the circuit loss determined from the input power and the output power exceeds a predetermined value.

Patent No. 4524924

In a light source lighting device such as Patent Document 1, for example, when the input voltage to the power conversion means decreases, it is possible to reduce the power supplied to the discharge lamp by adjusting the ON width of a switching element included in the power conversion means. Conceivable. Here, when the input voltage decreases significantly, even if the power supplied to the discharge lamp is reduced, the on-width of the switching element may become wider than before the input voltage decreases. At this time, when the input voltage is restored, there is a possibility that the current increases compared to the steady state. Therefore, an overcurrent exceeding the rating may occur in the power conversion means, and circuit components may break down.

The present disclosure has been made 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 the occurrence of overcurrent.

A lighting device according to the present disclosure includes a lighting circuit that includes a switching element, is supplied with power from an external power source, and supplies an output current to a light source by turning on and off the switching element, and an on-width of the switching element is determined in advance. a control unit that controls the on-width so that the output current of the lighting circuit matches the target value within a range that is equal to or less than the upper limit value; When the specified voltage is higher than or equal to the specified voltage, the upper limit is set to a first upper limit, and when the power supply voltage is lower than the specified voltage, the upper limit is set to a second upper limit, which is smaller than the first upper limit. However, the second upper limit value is the ON width immediately before the power supply voltage drops below the specified voltage .

In the lighting device according to the present disclosure, when the power supply voltage becomes lower than the specified voltage, the upper limit value of the on width is lowered. Therefore, the occurrence of overcurrent can be suppressed.

1 is a circuit block diagram of a lighting fixture according to Embodiment 1. FIG. FIG. 7 is a diagram showing current and voltage waveforms of a lighting fixture according to a first comparative example. 3 is a diagram showing current and voltage waveforms of the lighting fixture according to Embodiment 1. FIG. It is a figure which shows the current voltage waveform of the lighting fixture based on a 2nd comparative example. 7 is a diagram showing current and voltage waveforms of a lighting fixture according to Embodiment 2. FIG.

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 1, an LED module 27, and a dimmer 4. The lighting device 1 is connected to an AC power source 7, which is an external power source, and AC voltage is input thereto. The lighting device 1 converts input AC voltage into DC power. The LED module 27 is supplied with an output current from the lighting device 1 and lights up.

The lighting device 1 includes a lighting circuit and a control circuit 40. The lighting circuit includes a rectifier circuit 8, a step-up chopper circuit 2, and a step-down chopper circuit 3. The lighting circuit is supplied with power from the AC power supply 7 and supplies an output current to the LED module 27 by turning the switching element 18 on and off.

The LED module 27 includes a plurality of LEDs 26 that are light sources. The plurality of LEDs 26 are a load of the lighting device 1. In FIG. 1, a plurality of LEDs 26 are connected in series. The plurality of LEDs 26 may be connected in parallel, or may be connected in series and in parallel. Further, as the light source of the lighting device 1, a light source such as an organic EL (Electro Luminescence) may be used.

An input terminal of the rectifier circuit 8 is connected to the AC power supply 7. The rectifier circuit 8 rectifies the power supply voltage of the AC power supply 7 and supplies it to the boost chopper circuit 2 .

The boost chopper circuit 2 is supplied with power from an external power supply via the rectifier circuit 8 . The boost chopper circuit 2 includes a capacitor 9, resistors 31 and 32, an inductor 10, a switching element 11, a diode 14, a capacitor 17, and resistors 15 and 16. Inductor 10 is also called a choke coil.

Capacitor 9 is connected in parallel to the output terminal of rectifier circuit 8 . A voltage dividing circuit in which resistors 31 and 32 are connected in series is connected in parallel to capacitor 9. The voltage across capacitor 9 is divided using resistors 31 and 32 and input to control circuit 40 . The voltage dividing circuit formed by the resistors 31 and 32 is a first voltage detection circuit that detects the output voltage of the rectifier circuit 8. Furthermore, one end of the inductor 10 is connected to the high potential side of the output terminal of the rectifier circuit 8 .

In this embodiment, the switching element 11 is a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). The switching element 11 includes a first terminal, a second terminal, and a control terminal for switching between the first and second terminals. In this embodiment, the first terminal is the drain, the second terminal is the source, and the control terminal is the gate. A first terminal is connected to the other end of the inductor 10. An anode of the diode 14 is connected to a connection point between the first terminal of the switching element 11 and the other end of the inductor 10 . Further, the control terminal is connected to the drive circuit 41 of the control circuit 40. A second terminal of the switching element 11 is connected to the output of the rectifier circuit 8 on the low potential side.

The capacitor 17 has a positive electrode connected to the cathode of the diode 14 and a negative electrode connected to the output of the rectifier circuit 8 on the low potential side. The capacitor 17 is, for example, an electrolytic capacitor. A voltage dividing circuit in which resistors 15 and 16 are connected in series is connected in parallel to a capacitor 17. The voltage across capacitor 17 is divided using resistors 15 and 16 and input to control circuit 40 . The voltage dividing circuit formed by the resistors 15 and 16 is a second voltage detection circuit that detects the voltage supplied from the step-up chopper circuit 2 to the step-down chopper circuit 3. The control circuit 40 turns the switching element 11 on and off so that the voltage across the capacitor 17 is constant, that is, the voltage across the resistor 16 is constant.

Inductor 10, switching element 11 and diode 14 form a power factor correction circuit. The power factor improvement circuit is connected to the output of the rectifier circuit 8 and improves the power factor by turning on and off the switching element 11.

The step-down chopper circuit 3 includes a switching element 18 , a diode 21 , an inductor 22 , a capacitor 23 , and a detection resistor 24 . A series circuit consisting of the switching element 18 and the diode 21 is connected in parallel with the capacitor 17 of the boost chopper circuit 2. The switching element 18 is a MOSFET in this embodiment. The switching element 18 includes a first terminal, a second terminal, and a control terminal for switching between the first and second terminals. In this embodiment, the first terminal is the drain, the second terminal is the source, and the control terminal is the gate. The first terminal is connected to the positive electrode of the capacitor 17. A cathode of the diode 21 is connected to the second terminal. The anode of the diode 21 is connected to the negative electrode of the capacitor 17.

Inductor 22, capacitor 23, and detection resistor 24 are connected in this order to form a series circuit. This series circuit is connected in parallel to diode 21. The inductor 22 is also called a choke coil.

A voltage corresponding to the LED current flowing through the LED module 27 is generated in the detection resistor 24 . Therefore, the detection resistor 24 detects the LED current as a detection voltage. A connection point between the detection resistor 24 and the capacitor 23 is connected to one end of the resistor 19. The other end of resistor 19 is connected to control circuit 40 . The other end of the resistor 19 is connected to a ground terminal via a capacitor 23. The detected voltage from the detection resistor 24 is smoothed by a resistor 19 and a capacitor 20 and input to the control circuit 40 .

The control circuit 40 turns on and off the switching element 18 based on the smoothed detection voltage so that the current flowing through the LED module 27 becomes a constant current. In this way, the step-down chopper circuit 3 is supplied with voltage from the step-up chopper circuit 2 and supplies an output current to the light source 26 by turning the switching element 18 on and off.

Various types of microcomputers provided as digital power supply control devices are already known. Therefore, these known microcomputers can be used in the control circuit 40 as appropriate. The control circuit 40 may be formed by one control device such as a microcomputer, or may be formed by a plurality of control devices. An example of the control circuit 40 is shown in FIG. The control circuit 40 includes drive circuits 41 and 42, a storage section 43, an A/D conversion circuit 44, and a processing device 45, which are connected to each other via an internal bus.

Drive circuits 41 and 42 are connected to control terminals of switching elements 11 and 18, respectively. The drive circuits 41 and 42 output PWM (Pulse Width Modulation) signals for switching the switching elements 11 and 18, respectively.

The storage unit 43 includes, for example, a nonvolatile memory. The storage unit 43 stores calculation programs to be executed by the processing device 45 and various data used in the calculations. Data is written to and read from the storage unit 43 from the outside. For example, the storage unit 43 stores the on-width of the switching elements 11 and 18, the upper limit value of the on-width, and the target value of the output current of the lighting circuit, which will be described later.

A voltage divided by the resistors 15 and 16, a voltage divided by the resistors 31 and 32, and a voltage corresponding to the LED current detected by the detection resistor 24 are input to the control circuit 40. The A/D conversion circuit 44 converts these voltage values into digital values. Arithmetic processing is performed by the processing device 45 using this digital value.

The processing device 45 adjusts the ON width of the switching element 11 based on the voltage detected by the resistors 15 and 16 so that the output voltage of the boost chopper circuit 2 matches a preset target voltage. Thereby, the boost chopper circuit 2 is subjected to constant voltage control.

Further, the dimmer 4 is connected to the dimmer circuit 46 . The dimmer circuit 46 transmits a PWM signal to the processing device 45 based on the signal from the dimmer 4. The processing device 45 determines the target value based on the on period or off period of the PWM signal. The processing device 45 adjusts the ON width of the switching element 18 so that the LED current detected by the detection resistor 24 matches the target value. As a result, the step-down chopper circuit 3 is controlled to have a constant current.

Here, the on width of the switching elements 11 and 18 indicates a period during which the switching elements 11 and 18 continue to be in the on state. On-width is also called on-time. Further, the off width may be adjusted instead of the on width. The larger the ON width of the switching element 11, the larger the output voltage of the boost chopper circuit 2 becomes. Further, the larger the ON width of the switching element 18, the larger the output current of the step-down chopper circuit 3 becomes.

FIG. 2 is a diagram showing current and voltage waveforms of the lighting fixture according to the first comparative example. With reference to FIG. 2, an operation in which an overcurrent occurs when the power supply voltage drops below a normal value and then returns to normal in the lighting fixture according to the comparative example will be described.

In step S101, the lighting device 1 is in a steady state. At this time, the power supply voltage of the AC power supply 7 is at a normal value. Further, the output voltage of the boost chopper circuit 2 is the first voltage. The control circuit 40 controls the ON width of the switching element 18 so that the output current of the step-down chopper circuit 3 matches a predetermined target value. The output current of the step-down chopper circuit 3 corresponds to the LED current. Note that in FIGS. 2 to 5, enlarged views of the waveform at each step are shown below the waveform of the switching element 18.

Further, a predetermined upper limit value is set for the ON width of the switching element 18. The control circuit 40 controls the on-width so that the output current of the lighting circuit matches the target value within a range where the on-width of the switching element 18 is equal to or less than the upper limit value. The upper limit value of the on-width is set to a value larger than the on-width when the power supply voltage is at a normal value, taking into consideration circuit design variations. When the power supply voltage of the AC power supply 7 is a normal value, the switching element 18 is controlled within a range in which the ON width does not exceed the upper limit value.

In step S102, the power supply voltage drops below the normal value. Accordingly, the output voltage of the boost chopper circuit 2 decreases. Furthermore, the LED current also decreases.

In step S103, the output voltage of the boost chopper circuit 2 is a second voltage lower than the first voltage. The boost chopper circuit 2 is controlled with a constant voltage. Therefore, when the output voltage of the boost chopper circuit 2 decreases, the control circuit 40 increases the ON width of the switching element 11 so that the output voltage matches the first voltage. Here, an upper limit value is also set in advance for the ON width of the switching element 11. The ON width of the switching element 11 does not become larger than the upper limit value. Therefore, if the amount of decrease in the power supply voltage is large, the output voltage of the boost chopper circuit 2 may not return to the first voltage due to the ON width control. Further, the output voltage of the boost chopper circuit 2 may not increase.

On the other hand, the step-down chopper circuit 3 is subjected to constant current control. Therefore, when the LED current decreases from the target value, the control circuit 40 increases the ON width of the switching element 18. At this time, the ON width of the switching element 18 increases, for example, near the upper limit value or up to the upper limit value. Therefore, the LED current increases and matches the target value.

In step S104, the power supply voltage returns to its normal value. As a result, the output voltage of the boost chopper circuit 2 and the LED current also rise.

In step S105, the output voltage of the boost chopper circuit 2 reaches the first voltage. At this time, in the step-down chopper circuit 3, the ON width of the switching element 18 increases near the upper limit value or reaches the upper limit value. Therefore, as the output voltage of the boost chopper circuit 2 returns, an overcurrent exceeding the rating may occur. This may cause failure of circuit components.

Also, consider a case where the target value of the LED current is reduced when the voltage input from the step-up chopper circuit 2 to the step-down chopper circuit 3 decreases. In this case, even if the target value of the LED current is made small, if the amount of decrease in the output voltage of the boost chopper circuit 2 is large, the ON width of the switching element 18 will change before the output voltage of the boost chopper circuit 2 decreases from the first voltage. may be larger than the on-width. At this time, when the power supply voltage returns to a normal value and the output voltage of the boost chopper circuit 2 increases, an overcurrent exceeding the rating may occur. In this way, even if the target value of the LED current is made small, there is a possibility that overcurrent cannot be suppressed.

FIG. 3 is a diagram showing current and voltage waveforms of the lighting fixture 100 according to the first embodiment. The operation of the lighting device 1 according to the present embodiment when the power supply voltage temporarily decreases will be explained using FIG. 3. The behavior of the power supply voltage of the AC power supply 7 and the output voltage of the boost chopper circuit 2 is the same as that described in FIG. 2.

The waveform of the switching element 18 in step S201 is the same as that in step S101. At this time, the LED current matches the target value. Further, in step S201, the upper limit value of the ON width of the switching element 18 is set to the first upper limit value.

In step S202, the power supply voltage of the AC power supply 7 decreases from a normal value. As a result, the output voltage of the boost chopper circuit 2 decreases from the first voltage. Moreover, the LED current also decreases from the target value.

The control circuit 40 of the present embodiment sets the upper limit value of the ON width of the switching element 18 to a second upper limit value smaller than the first upper limit value when the power supply voltage of the AC power supply 7 is lower than a predetermined specified voltage. Set. The second upper limit value is the ON width immediately before the power supply voltage drops below the specified voltage. Here, the specified voltage is, for example, a normal value of the power supply voltage.

Further, the control circuit 40 detects the output voltage of the boost chopper circuit 2 using a second voltage detection circuit formed from the resistors 15 and 16. The control circuit 40 detects the power supply voltage of the AC power supply 7 from the voltage supplied from the step-up chopper circuit 2 to the step-down chopper circuit 3 using the second voltage detection circuit. The control circuit 40 sets the upper limit value of the ON width of the switching element 18 to the second upper limit value when the detected voltage of the second voltage detection circuit becomes lower than the voltage corresponding to the specified voltage.

In step S203, the output voltage of the boost chopper circuit 2 is the second voltage. On the other hand, even if the LED current falls below the target value, the ON width of the switching element 18 is controlled so as not to exceed the upper limit value. In the present embodiment, the ON width of the switching element 18 does not become larger than the second upper limit, which is the ON width immediately before the power supply voltage drops below the specified voltage. Therefore, the LED current does not vary.

In step S204, the power supply voltage of the AC power supply 7 returns to its normal value. As a result, the output voltage of the boost chopper circuit 2 increases. Along with this, the LED current also increases.

In step S205, the output voltage of the boost chopper circuit 2 reaches the first voltage. The on-width of the switching element 18 is controlled so as not to exceed the on-width before the power supply voltage drops. Therefore, when the output voltage of the boost chopper circuit 2 returns to the first voltage, the occurrence of overcurrent can be suppressed. Specifically, when the output voltage of the boost chopper circuit 2 returns to the first voltage, the LED current returns to the target value. This can prevent failure of circuit components.

The control circuit 40 sets the upper limit value of the ON width of the switching element 18 to the first upper limit value when the power supply voltage of the AC power supply 7 changes from a state lower than the specified voltage to a specified voltage or higher. The control circuit 40 sets the upper limit value of the ON width of the switching element 18 to the first upper limit value when the detected voltage of the second voltage detection circuit becomes equal to or higher than the voltage corresponding to the specified voltage. In this way, the lighting device 1 can be returned to normal operation by returning the upper limit value of the ON width to the first upper limit value before the decrease in the power supply voltage.

In this way, the control circuit 40 according to the present embodiment sets the upper limit value of the ON width of the switching element 18 to the first upper limit value when the power supply voltage of the external power supply is equal to or higher than a predetermined voltage. Further, when the power supply voltage is lower than the specified voltage, the control circuit 40 sets the upper limit value of the ON width of the switching element 18 to the second upper limit value.

Here, the second upper limit value is not limited to the ON width immediately before the power supply voltage drops below the specified voltage, but may be any value smaller than the first upper limit value. Thereby, it is possible to suppress the power supply voltage from being restored in a state where the ON width is larger than expected. Therefore, the occurrence of overcurrent can be suppressed. For example, the second upper limit value may be a value equal to or less than the on-width immediately before the power supply voltage drops below the specified voltage. Further, the control circuit 40 may set the upper limit value of the on-width of the switching element 18 to the current on-width of the switching element 18 when the power supply voltage of the external power supply falls below a specified voltage.

Further, the specified voltage is not limited to the normal value of the power supply voltage of the AC power supply 7, but may be a voltage lower than the normal value of the power supply voltage.

Further, the voltage supplied from the step-up chopper circuit 2 to the step-down chopper circuit 3 changes from the first voltage to the second voltage when the power supply voltage drops below the specified voltage, and changes to the second voltage when the power supply voltage rises above the specified voltage. to the first voltage. In this way, the output voltage of the boost chopper circuit 2 is linked to the power supply voltage.

Therefore, the control circuit 40 can detect the power supply voltage of the AC power supply 7 from the detection voltage of the second voltage detection circuit. The present invention is not limited to this, and the control circuit 40 may detect the power supply voltage from the output voltage of the rectifier circuit 8. In other words, the control circuit 40 may detect the power supply voltage of the AC power supply 7 from the detection voltage of the first voltage detection circuit. The control circuit 40 according to the present embodiment may switch the control method for the step-down chopper circuit 3 when a voltage drop is detected by the first voltage detection circuit or the second voltage detection circuit.

Further, the configuration of the lighting circuit shown in FIG. 1 is an example. The lighting circuit may be any circuit that is supplied with power from an external power source and supplies an output current to the light source by turning on and off a switching element.

These modifications can be applied as appropriate to the lighting devices and lighting fixtures according to the following embodiments. Note that the lighting device and lighting fixture according to the following embodiments have many features in common with Embodiment 1, so the description will focus on the differences from Embodiment 1.

Embodiment 2.
FIG. 4 is a diagram showing current and voltage waveforms of a lighting fixture according to a second comparative example. As a second comparative example, an operation in which an overcurrent occurs when the power supply voltage of the AC power supply 7 returns from a state where it has decreased below a normal value will be described using FIG. 4.

In step S301, the lighting device 1 is in a steady state. At this time, the power supply voltage of the AC power supply 7 is at a normal value. Further, the output voltage of the boost chopper circuit 2 is the first voltage. The control circuit 40 controls the ON width of the switching element 18 so that the output current of the step-down chopper circuit 3 matches a predetermined target value. Further, as in the first embodiment, a predetermined upper limit value is set for the ON width of the switching element 18.

In step S302, the power supply voltage drops below the normal value. Accordingly, the output voltage of the boost chopper circuit 2 decreases. Furthermore, the LED current also decreases.

Similarly to the first embodiment, the control circuit 40 uses a second voltage detection circuit formed by the resistors 15 and 16 to detect that the output voltage of the boost chopper circuit 2 has fallen below a predetermined value. As a result, the control circuit 40 sets the upper limit value of the ON width of the switching element 18 to the second upper limit value, similarly to the first embodiment. The second upper limit value is the ON width immediately before the power supply voltage drops below the specified voltage.

Further, the boost chopper circuit 2 is controlled at a constant voltage. Therefore, when the output voltage of the boost chopper circuit 2 falls below the first voltage corresponding to the normal value of the power supply voltage, the control circuit 40 controls the ON width of the switching element 11 to increase the output voltage of the boost chopper circuit 2. Make it bigger. Further, the control circuit 40 controls the on-width of the switching element 11 within a range that is equal to or less than a preset upper limit value. As a result, if the voltage drop in the AC power supply 7 is small, the output voltage of the boost chopper circuit 2 may increase as shown in step S303.

That is, the voltage supplied from the step-up chopper circuit 2 to the step-down chopper circuit 3 changes from the first voltage to the second voltage when the power supply voltage drops below the specified voltage. Further, the voltage supplied from the step-up chopper circuit 2 to the step-down chopper circuit 3 changes from the second voltage to the first voltage after the power supply voltage falls below the specified voltage but before it rises above the specified voltage.

On the other hand, as in the first embodiment, even when the LED current is lower than the target value, the ON width of the switching element 18 is controlled so as not to exceed the second upper limit value. The LED current increases as the output voltage of the boost chopper circuit 2 increases. When the output voltage of the boost chopper circuit 2 reaches the first voltage, the LED current reaches the target value.

In step S304, the power supply voltage returns to its normal value. At this time, the ON width of the switching element 11 of the boost chopper circuit 2 is larger than before the power supply voltage drops. The on-width of the switching element 11 may extend to an upper limit value, for example. When the power supply voltage reaches a normal value in this state, the output voltage of the boost chopper circuit 2 rises above the first voltage. Along with this, the LED current also increases.

Since the output voltage of the boost chopper circuit 2 has become higher than the first voltage, control is performed to reduce the ON width of the switching element 11. Therefore, as shown in step S305, the output voltage of the boost chopper circuit 2 decreases. Along with this, the LED current decreases.

In this way, even if the upper limit value of the ON width of the switching element 18 is set to the second upper limit value as the power supply voltage decreases, there is a possibility that an overcurrent will occur due to an increase in the output voltage of the boost chopper circuit 2. There is.

FIG. 5 is a diagram showing current and voltage waveforms of the lighting fixture 100 according to the second embodiment. The operation of the lighting device 1 according to the present embodiment when the power supply voltage temporarily decreases will be explained using FIG. 5. The behavior of the power supply voltage of the AC power supply 7 and the output voltage of the boost chopper circuit 2 is the same as that explained in FIG. 4.

The waveform of the switching element 18 in step S401 is the same as in step S301. Further, the LED current matches the target value. Further, the upper limit value of the ON width of the switching element 18 at this time is set to the first upper limit value.

In step S402, the voltage of the AC power supply 7 drops below the normal value. As a result, the output voltage of the boost chopper circuit 2 decreases. Furthermore, the LED current also decreases.

The control circuit 40 of the present embodiment sets the upper limit value of the ON width of the switching element 18 to a second upper limit value smaller than the first upper limit value when the power supply voltage of the AC power supply 7 is lower than a predetermined specified voltage. Set. The second upper limit value is the ON width immediately before the power supply voltage drops below the specified voltage. Here, the specified voltage is, for example, a normal value of the power supply voltage.

Further, the control circuit 40 of the present embodiment sets the target value of the output current of the step-down chopper circuit 3 to the first target value when the power supply voltage of the AC power supply 7 is equal to or higher than the specified voltage. Further, when the power supply voltage is lower than the specified voltage, the control circuit 40 sets the target value of the output current of the step-down chopper circuit 3 to a second target value smaller than the first target value.

The control circuit 40 detects the output voltage of the rectifier circuit 8 using a first voltage detection circuit formed from resistors 31 and 32. The control circuit 40 detects the power supply voltage of the AC power supply 7 from the output voltage of the rectifier circuit 8 . The control circuit 40 sets the upper limit value of the ON width of the switching element 18 to the second upper limit value when the detected voltage of the first voltage detection circuit becomes lower than the voltage corresponding to the specified voltage. Further, the control circuit 40 sets the target value of the output current of the step-down chopper circuit 3 to the second target value when the detected voltage of the first voltage detection circuit becomes lower than the voltage corresponding to the specified voltage.

In step S403, the output voltage of the boost chopper circuit 2 increases similarly to step S303. In this way, the voltage supplied from the boost chopper circuit 2 to the buck chopper circuit 3 changes from the second voltage to the first voltage after the power supply voltage drops below the specified voltage but before it rises above the specified voltage. .

On the other hand, even when the LED current is lower than the target value, the on-width of the switching element 18 is controlled so as not to exceed the second upper limit, as in the first embodiment. The LED current increases with the output voltage of the boost chopper circuit 2. At this time, the target value of the LED current is set to a second target value smaller than the first target value. Therefore, when the output voltage of the boost chopper circuit 2 returns to the first voltage, the ON width of the switching element 18 becomes narrower than before the power supply voltage of the AC power supply 7 decreases. When the output voltage of the boost chopper circuit 2 reaches the first voltage, the LED current reaches the second target value.

In step S404, the power supply voltage returns to its normal value. At this time, as explained in step S304, the ON width of the switching element 11 of the boost chopper circuit 2 is larger than before the power supply voltage drops. Therefore, the output voltage of the boost chopper circuit 2 increases. Along with this, the LED current also increases.

Here, the target value of the LED current is set smaller than before the power supply voltage drops. Therefore, the ON width of the switching element 18 is narrower than in the state before the power supply voltage drops. Therefore, as shown in step S405, even if the output voltage of the boost chopper circuit 2 rises above the first voltage, the rise in the LED current can be suppressed compared to the case of FIG. 4. Therefore, it is possible to reduce the occurrence of overcurrent and prevent failure of circuit components.

Further, when the power supply voltage of the AC power supply 7 increases from a state lower than the specified voltage to a specified voltage or higher, the control circuit 40 sets the upper limit value of the ON width of the switching element 18 to the first upper limit value, and controls the step-down chopper circuit 3. A target value of the output current is set to a first target value. Thereby, the lighting device 1 can be returned to normal operation.

In this embodiment, the output voltage of the boost chopper circuit 2 increases before the power supply voltage is restored. Therefore, the second voltage detection circuit cannot accurately detect the power supply voltage. The control circuit 40 can accurately detect the power supply voltage of the AC power supply 7 based on the detection voltage of the first voltage detection circuit that is linked to the power supply voltage.

Embodiment 3.
In the first and second embodiments, when the power supply voltage of the external power supply is equal to or higher than the specified voltage, the upper limit value of the ON width of the switching element 18 is set to the first upper limit value, and when the power supply voltage is lower than the specified voltage, the upper limit value is set to the first upper limit value. was set to a second upper limit value that is smaller than the first upper limit value. In this embodiment, when the power supply voltage drops below the specified voltage, the upper limit value of the on-width of the switching element 18 is set to zero time. In other words, the second upper limit is zero.

Thereby, when the power supply voltage drops below the specified voltage, the LED module 27 is turned off. Therefore, even when the power supply voltage of the AC power supply 7 is restored and the output voltage of the boost chopper circuit 2 increases, no overcurrent occurs. Therefore, failure of circuit components can be prevented.

The control circuit 40 controls the switching element 18 when the first voltage detection circuit detects a drop in the voltage of the AC power supply 7 or when the second voltage detection circuit detects a drop in the voltage input to the step-down chopper circuit 3. Set the upper limit of the on width to zero. Further, when the first voltage detection circuit detects a drop in the voltage of the AC power supply 7 and the second voltage detection circuit detects a drop in the voltage input to the step-down chopper circuit 3, the control circuit 40 controls the switching element. The upper limit value of the 18 ON widths may be set to zero.

In addition, when the control circuit 40 detects that the power supply voltage has changed from a state lower than the specified voltage to a specified voltage or more by the first voltage detection circuit and the second voltage detection circuit, the control circuit 40 detects the upper limit of the ON width of the switching element 18. Returns to the value before the power supply voltage drop. Thereby, the lighting device 1 can be returned to normal operation.

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

1 lighting device, 2 step-up chopper circuit, 3 step-down chopper circuit, 4 dimmer, 7 AC power supply, 8 rectifier circuit, 9 capacitor, 10 inductor, 11 switching element, 14 diode, 15, 16 resistor, 17 capacitor, 18 switching element, 19 resistor, 20 capacitor, 21 diode, 22 inductor, 23 capacitor, 24 detection resistor, 26 light source, 27 LED module, 31, 32 resistor, 40 control circuit, 41 drive circuit, 43 storage section, 44 A/D conversion circuit, 45 processing device, 46 dimmer circuit, 100 lighting equipment

Claims (10)

a lighting circuit that has a switching element, is supplied with power from an external power source, and supplies an output current to a light source by turning on and off the switching element;
a control unit that controls the on-width so that the output current of the lighting circuit matches a target value within a range where the on-width of the switching element is equal to or less than a predetermined upper limit;
Equipped with
The control unit sets the upper limit to a first upper limit when the power supply voltage of the external power supply is equal to or higher than a predetermined voltage, and sets the upper limit to a first upper limit when the power supply voltage is lower than the specified voltage. setting a second upper limit value smaller than the first upper limit value ;
The lighting device , wherein the second upper limit value is the on-width immediately before the power supply voltage drops below the specified voltage . The lighting circuit includes a step-up circuit that is supplied with power from the external power source, and a step-down circuit that is supplied with voltage from the step-up circuit and supplies the output current to the light source by turning on and off the switching element,
The voltage supplied from the step-up circuit to the step-down circuit changes from a first voltage to a second voltage lower than the first voltage when the power supply voltage falls below the specified voltage, and when the power supply voltage falls below the specified voltage. The lighting device according to claim 1, wherein the second voltage changes to the first voltage when the voltage increases above the voltage. 3. The lighting device according to claim 2 , wherein the control unit detects the power supply voltage from the voltage supplied from the booster circuit to the step-down circuit. The lighting circuit includes a rectifier circuit that rectifies the power supply voltage and supplies it to the booster circuit,
The lighting device according to claim 2 , wherein the control section detects the power supply voltage from the output voltage of the rectifier circuit. Any one of claims 1 to 4 , wherein the control unit sets the upper limit value to the first upper limit value when the power supply voltage increases from a state lower than the specified voltage to the specified voltage or more. The lighting device described in section. The control unit sets the target value to a first target value when the power supply voltage is equal to or higher than the specified voltage, and sets the target value to be lower than the first target value when the power supply voltage is lower than the specified voltage. 2. The lighting device according to claim 1, wherein the second target value is set to a smaller value. The lighting circuit includes a step-up circuit that is supplied with power from the external power source, and a step-down circuit that is supplied with voltage from the step-up circuit and supplies the output current to the light source by turning on and off the switching element,
The voltage supplied from the step-up circuit to the step-down circuit changes from a first voltage to a second voltage lower than the first voltage when the power supply voltage falls below the specified voltage, and when the power supply voltage falls below the specified voltage. 7. The lighting device according to claim 6 , wherein the second voltage changes to the first voltage after the voltage drops below the specified voltage and before the voltage rises above the specified voltage. The lighting circuit includes a rectifier circuit that rectifies the power supply voltage and supplies it to the booster circuit,
The lighting device according to claim 7 , wherein the control section detects the power supply voltage from the output voltage of the rectifier circuit. 9. The control unit sets the target value to the first target value when the power source voltage becomes equal to or higher than the specified voltage from a state lower than the specified voltage . The lighting device described in section . The lighting device according to any one of claims 1 to 9 ,
the light source that is lit by being supplied with the output current from the lighting device;
A lighting fixture comprising:

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