JP5383380B2 - Lighting circuit and lighting fixture - Google Patents

Description

  The present invention relates to a lighting circuit for lighting an LED.

  In recent years, lighting fixtures using LEDs have become widespread.

JP 2009-105016 A

In a lighting fixture using an LED, the light output of the LED may become unstable, for example, a flash phenomenon in which the LED temporarily becomes brighter than usual immediately after the power is turned on.
The present invention has been made, for example, in order to solve the above-described problems, and an object thereof is to light an LED with a stable light output.

The lighting circuit according to the present invention includes:
In a lighting circuit for lighting a light emitting diode by applying a DC load voltage to a load circuit having the light emitting diode,
A DC power supply circuit for generating a DC power supply voltage;
An inverter circuit that generates a rectangular wave voltage from the DC power supply voltage generated by the DC power supply circuit;
A resonance circuit that has a coil and a capacitor, and generates an alternating voltage from a rectangular wave voltage generated by the inverter circuit by resonance between the coil and the capacitor;
A rectifier circuit that rectifies the AC voltage generated by the resonant circuit to generate a DC load voltage;
In the inverter circuit, the frequency of the rectangular wave voltage generated in at least one of a lighting start period for switching the light emitting diode from a lighting state to a lighting state and a lighting end period for switching the light emitting diode from a lighting state to a lighting state is The frequency is farther from the resonance frequency of the resonance circuit than the frequency of the rectangular wave voltage generated in the continuous lighting period in which the light emitting diode is continuously lit.

  According to the lighting apparatus according to the present invention, since the LED is lit after the DC power supply voltage generated by the DC power supply circuit is stabilized, the occurrence of a flash phenomenon or the like can be prevented.

FIG. 3 is an electric circuit diagram illustrating a circuit configuration of the lighting fixture 800 in the first embodiment. FIG. 5 is a flowchart showing a flow of lighting processing S510 in the first embodiment. FIG. 5 is a flowchart showing a flow of a turn-off process S520 in the first embodiment. FIG. 6 is a graph showing voltages and the like of respective parts of the lighting fixture 800 in the first embodiment. FIG. 6 is a graph showing voltages and the like of respective parts of the lighting fixture 800 in the first embodiment. FIG. 6 is a graph showing voltages and the like of respective parts of the lighting fixture 800 in the first embodiment. And the frequency f of the rectangular wave voltage inverter circuit 130 to generate in the first embodiment, characteristic graph showing the relationship between the peak-to-peak value v _C of the voltage generated across the resonance capacitor C42. FIG. 6 is a characteristic graph showing the relationship between the frequency f of the rectangular wave voltage generated by the inverter circuit 130 in Embodiment 1 and the current flowing through the load circuit 810. FIG. 3 is a graph showing a relationship between a parameter of a resonance circuit 140 and a lighting frequency f2 in the _first embodiment. FIG. 6 is a graph showing the relationship between the parameters of the resonance circuit 140 and the ratio of the period 732 in the first embodiment. The flowchart figure which shows the flow of the lighting process S510 in Embodiment 2. FIG. The flowchart figure which shows the flow of the light extinction process S520 in Embodiment 2. FIG. FIG. 10 is a graph showing voltages and the like at various parts of the lighting fixture 800 in the second embodiment. FIG. 6 is an electric circuit diagram illustrating a circuit configuration of a lighting fixture 800 according to Embodiment 3.

Embodiment 1 FIG.
The first embodiment will be described with reference to FIGS.

FIG. 1 is an electric circuit diagram showing a circuit configuration of a lighting fixture 800 according to this embodiment.
The lighting fixture 800 turns on an LED (light emitting diode) with electric power supplied from an AC power source AC such as a commercial power source. The lighting fixture 800 includes a lighting circuit 100 and a load circuit 810.
The lighting circuit 100 generates a DC load voltage to be applied to the load circuit 810. The lighting circuit 100 includes a rectifier circuit 110, a DC power supply circuit 120, an inverter circuit 130, a resonance circuit 140, a rectifier circuit 150, and an inverter control circuit 170.
The load circuit 810 has, for example, a plurality of LEDs electrically connected in series. The load circuit 810 lights the LED with the DC load voltage generated by the lighting circuit 100.

The rectifier circuit 110 includes, for example, a diode bridge DB1 in which rectifier elements are bridge-connected. The rectifier circuit 110 generates a pulsating voltage by full-wave rectifying the AC voltage input from the AC power supply AC.
The DC power supply circuit 120 (active filter circuit) is a step-up chopper circuit including, for example, a choke coil L21, a switching element Q22, a rectifying element D23, a smoothing capacitor C24, and a PFC 125. A DC voltage (hereinafter referred to as “DC power supply voltage”) having a target voltage value V ₀ (for example, 415 V) is generated.
The inverter circuit 130 includes, for example, two switching elements Q31 and Q32 that are electrically connected in series. The inverter circuit 130 receives an inverter control signal, and alternately turns on and off the two switching elements Q31 and Q32 in accordance with the input inverter control signal, thereby generating a rectangular wave voltage from the DC power supply voltage generated by the DC power supply circuit 120. Is generated.
The resonance circuit 140 includes, for example, a choke coil L41 (inductor), a resonance capacitor C42, and a coupling capacitor C43. The resonance circuit 140 generates an AC voltage from the rectangular wave voltage generated by the inverter circuit 130 due to resonance between the choke coil L41 and the resonance capacitor C42.
The rectifier circuit 150 includes, for example, a diode bridge DB2 and a smoothing capacitor C51. The rectifier circuit 150 generates a DC voltage (DC load voltage) from the AC voltage generated by the resonance circuit 140.

The inverter control circuit 170 generates an inverter control signal that controls the inverter circuit 130. The inverter control circuit 170 includes a frequency setting unit 171 and a control signal generation unit 172.
The frequency setting unit 171 sets the frequency f of the inverter control signal. Since the inverter circuit 130 turns on and off the two switching elements Q31 and Q32 in accordance with the inverter control signal, the frequency f of the inverter control signal is the frequency of the rectangular wave voltage generated by the inverter circuit 130.
The control signal generation unit 172 generates an inverter control signal according to the frequency f set by the frequency setting unit 171.
The inverter control circuit 170 is configured by a microcomputer, for example. The microcomputer includes a storage device such as a nonvolatile memory such as a ROM that stores programs and data, and a volatile memory such as a RAM that temporarily stores data, and a processing device that executes the programs and processes data. The frequency setting unit 171 and the control signal generation unit 172 described above are realized by a microcomputer processing device executing a program.
Note that the inverter control circuit 170 may be configured by a logic circuit, an analog circuit, or the like instead of a microcomputer.

FIG. 2 is a flowchart showing the flow of the lighting process S510 in this embodiment.
The lighting process S510 is a process executed during a lighting start period in which the LED is in an extinguished state and the LED is started to be lit to be in the lit state. The lighting process S510 includes a startup frequency setting step S511, a timer initialization step S513, an elapsed time determination step S514, and a lighting frequency setting step S515.

In starting frequency setting step S511, the frequency setting unit 171 sets the frequency f of the inverter control signal to the driving start frequency _{f 1.} The control signal generation unit 172 generates an inverter control signal whose frequency f is the starting frequency f ₁ according to the frequency set by the frequency setting unit 171. As a result, the inverter circuit 130 generates a rectangular wave voltage whose frequency f is the starting frequency f ₁ .

In the timer initialization step S513, the frequency setting unit 171 initializes a timer in order to monitor the elapsed time.
In the elapsed time judging step S514, the frequency setting unit 171 compares the elapsed time t and the predetermined time T ₁ of the timer in the timer initialization step S513 is initialized. If the elapsed time t is less than the time _{T 1,} the frequency setting unit 171 repeats the elapsed time determining step S514. If the elapsed time t is time above _{T 1,} the frequency setting unit 171 proceeds to the lighting frequency setting step S515.

  For example, in the timer initialization step S513, the frequency setting unit 171 stores a predetermined integer in a register used as a timer. In the elapsed time determination step S514, the frequency setting unit 171 decreases the value of the register used as a timer by one. When the value of the register is larger than 0, the frequency setting unit 171 repeats the elapsed time determination step S514. When the value of the register becomes 0, the frequency setting unit 171 proceeds to the lighting frequency setting step S515.

In the lighting frequency setting step S515, the frequency setting unit 171 sets the frequency f of the inverter control signal to the lighting frequency _{f 2.} The control signal generation unit 172 generates an inverter control signal whose frequency f is the lighting frequency f ₂ according to the frequency set by the frequency setting unit 171. Thus, the inverter circuit 130 generates a square wave voltage frequency f is the operating frequency f _2.

例えば、チョークコイルＬ４１のインダクタンスＬが１．１ｍＨ、共振コンデンサＣ４２の静電容量Ｃ_１が６８００ｐＦであれば、共振周波数ｆ_０は、約５８ｋＨｚである。 Here, the start-up frequency f ₁ is a frequency higher than the resonance frequency f ₀ determined by the choke coil L41 and the resonance capacitor C42 of the resonance circuit 140. When the inductance of the choke coil L41 L, the capacitance of the resonance capacitor C42 is C, the resonance frequency f ₀ is determined by the following equation.

For example, if the inductance L of the choke coil L41 is 1.1MH, capacitance _{C 1} of the resonant capacitor C42 6800pF, the resonance frequency _{f 0} is approximately 58 kHz.

The lighting frequency f ₂ is a frequency lower than the starting frequency f _1, than starting frequency f ₁ is a frequency close to the resonance frequency f _0. Incidentally, the lighting frequency f ₂ may be at a frequency higher than the resonance frequency f _0, may be at a frequency lower than the resonance frequency f _0. For example, if the resonance frequency f ₀ is 58 kHz, the startup frequency f ₁ is 90 kHz, and the lighting frequency f ₂ is 45 kHz, the difference | f ₁ −f ₀ | between the startup frequency f ₁ and the resonance frequency f ₀ is 32 kHz. On the other hand, since the difference | f ₂ −f ₀ | between the lighting frequency f ₂ and the resonance frequency f ₀ is 13 kHz, the lighting frequency f ₂ is closer to the resonance frequency f ₀ than the starting frequency f ₁ .

When the total forward voltage drop (for example, 170 V) of the LEDs electrically connected in series constituting the load circuit 810 is V _f (hereinafter referred to as “lighting voltage”), the DC load voltage generated by the rectifier circuit 150 is LED lights if the voltage value _{v D} lighting voltage _{V f} above, LED is not lit when the voltage value _{v D} less than the operating voltage _{V f.}
Voltage value v _D of the DC load voltage of the rectifier circuit 150 generates the maximum value of the AC voltage resonance circuit 140 generates (0 peak) approximately equal. The maximum value of the AC voltage generated by the resonance circuit 140 is about half of the peak-peak value of the voltage generated at both ends of the resonance capacitor C42.
When the voltage value of the DC power supply voltage generated by the DC power supply circuit 120 is constant, the peak-peak value of the voltage across the resonance capacitor C42 depends on the frequency f of the rectangular wave voltage generated by the inverter circuit 130. In a state where the LED is not lit, peak-to-peak value of the voltage across the resonant capacitor C42 increases as the frequency f is close to the resonance frequency f _0.

Therefore, starting frequency f ₁ includes a DC power supply circuit 120 generates DC power voltage DC load voltage voltage value v _D is the lighting voltage V _f of the voltage value rectifier circuit 150 is generated when a target voltage value V ₀ which Set to a frequency that is less than Therefore, the LED is not lit. In particular, it is desirable to look at the margin of the order of 10-20%, is set to a frequency voltage _{v D} of the DC load voltage is less than 80-90% of the operating voltage _{V f.} This is because immediately after the power is turned on, the voltage value of the DC power supply voltage generated by the DC power supply circuit 120 is not stable and may cause overshoot. If the voltage value of the DC power supply voltage is the target voltage value V ₀ and the voltage value v _D of the DC load voltage is set to be less than 80 to 90% of the lighting voltage V _f , a temporary overload will occur. chute, even when the voltage value of the DC power supply voltage becomes 10 to 20% higher than the target voltage value V _0, the voltage value v _D of the DC load voltage falls below the ignition voltage V _f.

On the other hand, the lighting frequency f ₂ is determined by the voltage value v _D of the DC load voltage generated by the rectifier circuit 150 when the voltage value of the DC power supply voltage generated by the DC power supply circuit 120 is the target voltage value V _0. Set to a frequency that is less than _Vf . Thereby, the LED is turned on.

Waiting time T ₁ of the frequency f of the rectangular wave voltage from the starting frequency f ₁ to switch the lighting frequency f ₂ to the inverter circuit 130 is generated from the power-on, the voltage value of the DC power supply voltage DC power supply circuit 120 is generated set longer than the time it takes to stabilize at the target voltage value V _0. Thus, since the LED is lit after the DC power supply voltage is stabilized, a phenomenon (flash phenomenon) in which the LED temporarily becomes brighter than usual due to overshoot of the DC power supply circuit 120 can be prevented.

FIG. 3 is a flowchart showing the flow of the extinguishing process S520 in this embodiment.
The extinguishing process S520 is a process executed during a lighting end period in which the LED is in a lighting state, the LED is turned off, and the LED is turned off. The extinguishing process S520 includes an extinguishing frequency setting step S521, a timer initialization step S523, an elapsed time determination step S524, and a power supply circuit off step S525.

In off frequency setting step S521, the frequency setting unit 171 sets the frequency f of the inverter control signal to turn off the frequency _{f 3.} The control signal generation unit 172 generates an inverter control signal whose frequency f is the extinguishing frequency f ₃ according to the frequency set by the frequency setting unit 171. Thus, the inverter circuit 130 generates a square wave voltage frequency f is off frequency f _3.

In the timer initialization step S523, the frequency setting unit 171 initializes a timer in order to monitor the elapsed time.
In the elapsed time judging step S524, the frequency setting unit 171 compares the elapsed time t and the predetermined time T ₂ of the timer in the timer initialization step S523 is initialized. If the elapsed time t is less than the time _{T 2,} the frequency setting unit 171 repeats the elapsed time determining step S524. If the elapsed time t is the time _{T 2} or more, the frequency setting unit 171 proceeds to the power supply circuit off process S525.

  In the power supply circuit off step S525, the DC power supply circuit 120 stops generating the DC power supply voltage.

The turn-off frequency f ₃ is the voltage value v _D of the DC load voltage generated by the rectifier circuit 150 when the voltage value of the DC power supply voltage generated by the DC power supply circuit 120 is the target voltage value V ₀ , similar to the start-up frequency f _1. Is set to a frequency at which becomes less than the lighting voltage _Vf . Off frequency f ₃ may be the same frequency as the starting frequency f _1, or at different frequencies. Thereby, the LED is turned off.
Further, after switching the frequency f of the rectangular wave voltage inverter circuit 130 to generate the off frequency f ₃ from the operating frequency f _2, waiting time T ₂ of the until turning off the DC power supply circuit 120, LED turns off reliably Set a time longer than the previous time. As a result, even after the DC power supply circuit 120 is turned off, even if the DC power supply voltage becomes temporarily unstable, the LED is turned off, so that an abnormal phenomenon such as a flash phenomenon can be prevented.

FIG. 4 is a graph showing the voltage of each part of the lighting fixture 800 in this embodiment.
The horizontal axis indicates time. The vertical axis represents voltage, frequency, current, and the like. A solid line 701 indicates the voltage value of the DC power supply voltage generated by the DC power supply circuit 120. A solid line 702 indicates the frequency f of the rectangular wave voltage generated by the inverter circuit 130. A solid line 703 indicates the voltage value of the DC load voltage generated by the rectifier circuit 150. A solid line 704 indicates an average value of the current flowing through the load circuit 810.

At time _{t 1,} and the like turning on the power, the lighting circuit 100 starts the lighting process S510. The voltage value of the DC power supply voltage DC power supply circuit 120 is generated while repeatedly overshoot or undershoot, the until time t ₂ stably, converges to the target voltage value V _0.

A period from time t ₁ to time t ₂ is a lighting start period 721.
In the lighting start period 721, the inverter control circuit 170, the frequency f of the inverter control signal and starting frequency f _1, the inverter circuit 130, the frequency f to produce a square wave voltage driving start frequency f _1.
Thereby, the voltage value of the DC load voltage generated by the rectifier circuit 150 is lower than the lighting voltage _Vf regardless of the voltage value of the DC power supply voltage. Therefore, no current flows through the load circuit 810, and the LED is not lit.

A period after time t ₂ is a continuous lighting period 722.
In time _{t 2, the} inverter control circuit 170, the frequency f of the inverter control signal and the lighting frequency _{f 2,} the inverter circuit 130, the frequency f to produce a square wave voltage of the lighting frequency _{f 2.}
Thereby, at time t ₃ , the voltage value of the DC load voltage generated by the rectifier circuit 150 reaches the lighting voltage V _f , and at time t ₄ , the current value of the current flowing through the load circuit 810 becomes the desired current value I. _D is reached. Thereby, the LED is stably lit at a desired brightness.

At time _{t 5,} due to a switch of the operation, the lighting circuit 100 starts off process S520. After time _{t 5} of the period is a lighting end of the period 723. Inverter control circuit 170, the frequency f of the inverter control signal and turned off frequency f _3. In this example, the turn-off frequency f ₃ is the same as the activation frequency f ₁ . The inverter circuit 130, the frequency f to produce a square wave voltage off frequency f _3.
Thus, at time t _6, the voltage value of the DC load voltage rectifier circuit 150 is generated below the ignition voltage V _f, the current flowing through the load circuit 810 becomes 0, LED is turned off.

At time _{t 7,} the DC power supply circuit 120 stops operating. The voltage value of the DC power supply circuit 120 is a DC power supply voltage to be generated is by time t ₈ becomes zero.

FIG. 5 is a graph showing the voltage of each part of the lighting fixture 800 in this embodiment.
The horizontal axis indicates time on a time scale shorter than that in FIG. The vertical axis represents voltage, current, and the like. A broken line 705 indicates the voltage value of the rectangular wave voltage generated by the inverter circuit 130. A solid line 706 indicates a voltage generated at both ends of the resonance capacitor C42. A solid line 707 indicates a current flowing through the choke coil L41.

When the frequency f of the rectangular wave voltage generated by the inverter circuit 130 is the starting frequency f ₁ , the period T of the rectangular wave voltage is the reciprocal of the starting frequency f ₁ . For example, if the activation frequency f ₁ is 90 kHz, the period T is about 11 microseconds.
At this time, the peak-to-peak value v _C of the voltage generated at both ends of the resonance capacitor C42 is less than twice the lighting voltage V _f , so the LED of the load circuit 810 is not lit.

FIG. 6 is a graph showing the voltage of each part of the lighting fixture 800 in this embodiment.
The horizontal axis indicates the time on the same time scale as in FIG. The vertical axis represents voltage, current, and the like. Portions common to FIG. 5 are denoted by the same reference numerals. A broken line 708 indicates a current flowing through the load circuit 810.

If the frequency f of the rectangular wave voltage inverter circuit 130 is generated by an operating frequency f _2, the period T of the rectangular wave voltage is the inverse of the operating frequency f _2. For example, if the lighting frequency _{f 2} is a 45 kHz, the period T is approximately 22 microseconds.
At this time, the peak-to-peak value v _C of the voltage generated at both ends of the resonance capacitor C42 exceeds twice the lighting voltage V _f , a current flows through the load circuit 810, and the LED is lit.

Here, the circuit operation of the lighting circuit 100 is divided into three periods 731, 732, and 733, and this is repeated every half cycle of the rectangular wave voltage generated by the inverter circuit 130. The period 731 is a period from when the instantaneous value of the rectangular wave voltage generated by the inverter circuit 130 is switched to when the polarity of the current flowing through the choke coil L41 is switched. Since the polarity of the current flowing through the choke coil L41 is switched, the rectifying element of the diode bridge DB2 that has been turned on is turned off. The period 732 is a period until the rectifier having the reverse polarity of the diode bridge DB2 is turned on thereafter. The period 733 is a period until the instantaneous value of the rectangular wave voltage generated by the inverter circuit 130 is switched thereafter.
During the periods 731 and 733, most of the current flowing through the choke coil L41 flows through the load circuit 810 or indirectly through the load circuit 810 by charging the smoothing capacitor C51. On the other hand, the current flowing through the choke coil L41 in the period 732 charges or discharges the resonance capacitor C42, and returns to the inverter circuit 130 through the choke coil L41 in the period 732 after a half cycle. That is, the current flowing through the choke coil L41 during the period 732 does not contribute to the lighting of the LED.
Considering that there is a power loss due to the copper loss of the choke coil L41 and the switching of the switching elements Q31 and Q32, the current that does not contribute to the lighting of the LED should be as small as possible. Therefore, the period 732 is preferably as short as possible, and the ratio of the period 732 to the period T is desirably 1/9 (40 degrees in angle) or less.

FIG. 7 is a characteristic graph showing the relationship between the frequency f of the rectangular wave voltage generated by the inverter circuit 130 in this embodiment and the peak-to-peak value v _C of the voltage generated at both ends of the resonance capacitor C42.
The horizontal axis represents the frequency f of the rectangular wave voltage generated by the inverter circuit 130. The vertical axis represents the peak-to-peak value v _C of the voltage generated at both ends of the resonance capacitor C42. A solid line 712 indicates a case where the load circuit 810 is present, and a dotted line 713 indicates a case where the load circuit 810 is not present. Threshold frequency f _T represents the frequency at which the peak-to-peak value v _C of the voltage generated across the resonance capacitor C42 is equal to two times the operating voltage V _f.

Higher than the frequency f is the threshold frequency f _T of the rectangular wave voltage inverter circuit 130 is generated, if the peak-to-peak value v _C of the voltage generated across the resonance capacitor C42 is less than twice the operating voltage V _f is the load circuit It is the same whether or not there is 810, and the peak peak value v _C describes a mountain shape having a peak at the resonance frequency f ₀ of the choke coil L41 and the resonance capacitor C42.

Frequency f of the rectangular wave voltage inverter circuit 130 to generate is lower than the threshold frequency f _T, if the peak-to-peak value v _C of the voltage generated across the resonance capacitor C42 is greater than twice the operating voltage V _f, the load circuit 810 Therefore, the resonance frequency f ₀ ′ is determined by the equivalent capacitor obtained by combining the resonance capacitor C42 and the coupling capacitor C43 electrically connected in parallel, and the choke coil L41. Since the combined capacitance of the capacitor which is electrically connected in parallel is the sum of the capacitance of each capacitor, the capacitance of the equivalent capacitor becomes larger than the electrostatic capacitance of the resonance capacitor C42, the resonance frequency f _{0 'is} resonant It is lower than the frequency _{f 0.}

FIG. 8 is a characteristic graph showing the relationship between the frequency f of the rectangular wave voltage generated by the inverter circuit 130 in this embodiment and the current flowing through the load circuit 810.
The horizontal axis represents the frequency f of the rectangular wave voltage generated by the inverter circuit 130. The vertical axis represents the average value of the current flowing through the load circuit 810. A solid line 714 shows the relationship between the frequency f and the average value of the current flowing through the LED.

If the frequency f of the rectangular wave voltage inverter circuit 130 to generate is higher than the threshold frequency f _T, the current flowing through the load circuit 810 is zero.
If the frequency f of the rectangular wave voltage inverter circuit 130 to generate is lower than the threshold frequency f _T, the average value of the current flowing through the load circuit 810 draws a mountain type with a peak resonant frequency f _{0 '.}
Therefore, by setting the lighting frequency f ₂ so that the average value of the current flowing through the load circuit 810 becomes a desired current value _ID , the LED can be lit with a desired brightness.

Incidentally, the operation of the user, may be configured to be changed the lighting frequency f _2. Thereby, since the brightness of LED can be adjusted, the lighting fixture 800 can be provided with the light control function.

FIG. 9 is a graph showing the relationship between the parameters of the resonance circuit 140 and the lighting frequency f ₂ in this embodiment.
The horizontal axis shows the capacitance of the resonant capacitor C42. The vertical axis shows the operating frequency _{f 2.} The solid line 741-743, when changing the inductance and capacitance of the resonant capacitor C42 of the choke coil L41, shows the operating frequency _{f 2} at which the current flowing through the load circuit 810 becomes a predetermined current value, a solid line 741 choke coil When the inductance of L41 is small, a solid line 742 indicates a case where the inductance of the choke coil L41 is intermediate, and a solid line 743 indicates a case where the inductance of the choke coil L41 is large.

The larger the inductance of the choke coil L41, the more the current flowing through the choke coil L41 is limited. Therefore, in order to keep the current flowing through the load circuit 810 to a predetermined current value, it is necessary to reduce the operating frequency f _2.

FIG. 10 is a graph showing the relationship between the parameters of the resonance circuit 140 and the ratio of the period 732 in this embodiment.
The horizontal axis shows the capacitance of the resonant capacitor C42. The vertical axis represents the ratio of the period 732 to the period T. Solid lines 751 to 753 indicate the angle of the period 732 when the inductance of the choke coil L41 and the capacitance of the resonance capacitor C42 are changed. When the inductance is intermediate, a solid line 753 indicates a case where the inductance of the choke coil L41 is large.

Thus, the ratio of the period 732 decreases as the inductance of the choke coil L41 increases. This is because the operating frequency f ₂ higher inductance of the choke coil L41 is large is low, because the period T becomes longer.
Further, the smaller the capacitance of the resonant capacitor C42, the smaller the ratio of the period 732 is. This is because the smaller the capacitance of the resonant capacitor C42, the shorter the time taken to charge / discharge the resonant capacitor C42.

As described above, since the ratio of the period 732 is desirably 1/9 or less, the inductance of the choke coil L41 and the capacitance of the resonance capacitor C42 are set so that the ratio of the period 732 is 1/9 or less. Set.
Thereby, the power loss due to the copper loss of the choke coil L41 and the switching of the switching elements Q31 and Q32 can be reduced, and the power efficiency of the lighting circuit 100 can be increased.

Embodiment 2. FIG.
The second embodiment will be described with reference to FIGS.
In addition, about the part which is common in the lighting fixture 800 demonstrated in Embodiment 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

FIG. 11 is a flowchart showing the flow of the lighting process S510 in this embodiment.
The lighting process S510 includes a startup frequency setting step S511, a timer initialization step S513, an elapsed time determination step S514, and a frequency change step S516.

In the frequency changing step S516, the frequency setting unit 171 changes the frequency f of the inverter control signal set, than before the change brought close to the operating frequency f _2. The control signal generation unit 172 generates an inverter control signal according to the frequency changed by the frequency setting unit 171. Thereby, the inverter circuit 130 generates a rectangular wave voltage having the changed frequency changed by the frequency setting unit 171.
If the frequency f after the change is higher than the operating frequency _{f 2,} the frequency setting unit 171 repeats the frequency changing step S516.
If the frequency f after the change is equal to the operating frequency _{f 2,} the frequency setting unit 171 terminates the lighting process S510.

For example, 1/100 of the difference f ₁ −f ₂ between the starting frequency f ₁ and the lighting frequency f ₂ is set as the step frequency Δf, and in the frequency changing step S 516, the frequency setting unit 171 steps the frequency f of the inverter control signal. The frequency is changed to a frequency f−Δf which is lower by the frequency. For example, if the starting frequency f ₁ is 90 kHz and the lighting frequency is 45 kHz, the step frequency Δf is 450 Hz. The frequency setting unit 171 repeats this 100 times. Thereby, the frequency of the inverter control signal gradually decreases from 90 kHz which is the starting frequency f ₁ to 89.55 kHz, 89.1 kHz and 88.65 kHz, and reaches 45 kHz which is the lighting frequency f ₂ .

FIG. 12 is a flowchart showing the flow of the extinguishing process S520 in this embodiment.
The extinguishing process S520 includes a frequency changing step S522 and a power supply circuit off step S525.

In the frequency changing step S522, the frequency setting unit 171 changes the frequency f of the inverter control signal set, than before the change closer to off frequency f _3. The control signal generation unit 172 generates an inverter control signal according to the frequency changed by the frequency setting unit 171. Thereby, the inverter circuit 130 generates a rectangular wave voltage having the changed frequency changed by the frequency setting unit 171.
If the frequency f after the change is lower than the off frequency _{f 3,} the frequency setting unit 171 repeats the frequency changing step S522.
If the frequency f after the change is equal to the operating frequency _{f 2,} the frequency setting unit 171 proceeds to the power supply circuit off process S525.

  Thus, the lighting circuit 100 continuously changes the frequency f of the rectangular wave voltage generated by the inverter circuit 130 little by little in the lighting process S510 and the extinguishing process S520.

  FIG. 13 is a graph showing the voltage of each part of the lighting fixture 800 in this embodiment.

Lighting start period 721 is a period from the time _{t 1} to time _{t 4.}
In time t _2, the frequency setting unit 171 initiate a change of the frequency f of the inverter control signal, the frequency f of the rectangular wave voltage inverter circuit 130 to generate becomes lower gradually. Accordingly, the voltage value of the DC load voltage generated by the rectifier circuit 150 is gradually increased.
At time t _3, when the frequency f of the rectangular wave voltage inverter circuit 130 is generated reaches the threshold frequency f _T, the voltage value of the DC load voltage rectifier circuit 150 generates reaches the ignition voltage V _f, the load circuit 810 Current begins to flow.
Thereafter, as the frequency f of the rectangular wave voltage generated by the inverter circuit 130 decreases, the current flowing through the load circuit 810 gradually increases.
At time t _4, when the frequency f of the rectangular wave voltage inverter circuit 130 is generated reaches the operating frequency f _2, the current value of the current flowing through the load circuit 810 becomes a desired current value I _D.

Lighting end of the period 723 is a period from the time _{t 5} to time _{t 8.}
At time t _5, the frequency setting unit 171 initiate a change of the frequency f of the inverter control signal, the frequency f of the rectangular wave voltage inverter circuit 130 is generated, the higher little by little. Along with this, the current flowing through the load circuit 810 gradually decreases.
At time t _6, when the frequency f of the rectangular wave voltage inverter circuit 130 is generated reaches the threshold frequency f _T, the voltage value of the DC load voltage rectifier circuit 150 generates drops to lighting voltage V _f.
Thereafter, when the frequency f of the rectangular wave voltage generated by the inverter circuit 130 is further increased, the voltage value of the DC load voltage generated by the rectifier circuit 150 is lower than the lighting voltage _Vf , so that the current flowing through the load circuit 810 becomes zero. .
At time t ₇ , the frequency f of the rectangular wave voltage generated by the inverter circuit 130 reaches the extinguishing frequency f ₃ (= f ₁ ). The DC power supply circuit 120 stops generating the DC power supply voltage.

  As described above, by gradually changing the frequency f of the rectangular wave voltage generated by the inverter circuit 130, it is possible to suppress a transient phenomenon that may occur when the frequency f is suddenly changed. Moreover, when the LED is turned on, a fade-in illumination effect can be obtained in which the LED gradually becomes brighter and reaches a desired brightness. When the LED is turned off, a fade-out illumination effect is obtained in which the LED gradually becomes darker and extinguishes. be able to.

Embodiment 3 FIG.
Embodiment 3 will be described with reference to FIG.
In addition, about the part which is common in the lighting fixture 800 demonstrated in Embodiment 1 or Embodiment 2, the same code | symbol is attached | subjected and description is abbreviate | omitted.

FIG. 14 is an electric circuit diagram showing a circuit configuration of the lighting fixture 800 in this embodiment.
In the lighting fixture 800 in this embodiment, the configuration of the resonance circuit 140 is different from that in the first embodiment, and the coupling capacitor C43 is electrically connected in series with the resonance capacitor C42 instead of in parallel.

It is assumed that the capacitance of the coupling capacitor C43 is sufficiently larger than the capacitance of the resonance capacitor C42.
In a state where the LED is not lit, an equivalent capacitor by combining a resonance capacitor C42 and a coupling capacitor C43 connected in series may be considered. Since the reciprocal of the capacitance of the equivalent capacitor is the sum of the reciprocals of the capacitances of the capacitors connected in series, if the capacitance of the coupling capacitor C43 is sufficiently larger than the capacitance of the resonance capacitor C42. The capacitance of the equivalent capacitor is substantially equal to the capacitance of the resonance capacitor C42.
In a state where the LED is lit, the voltage across the resonant capacitor C42 is kept substantially constant by the lighting voltage V _f of the load circuit 810, the resonance frequency f _{0 'is} the inductance of the choke coil L41, binding It is determined by the capacitance of the capacitor C43.
Therefore, lighting circuit 100 operates in the same manner as lighting circuit 100 in the first embodiment.

  Thus, even if the configuration of the resonance circuit 140 is changed, the same effects as those described in the first embodiment and the second embodiment can be obtained.

  In addition, regarding the configuration of the rectifier circuit 110, the DC power supply circuit 120, etc., the configuration described so far is merely an example, and it is obvious that other configurations may be used.

  100 lighting circuit, 110, 150 rectifier circuit, 120 DC power supply circuit, 125 PFC, 130 inverter circuit, 140 resonance circuit, 170 inverter control circuit, 171 frequency setting unit, 172 control signal generation unit, 721 lighting start period, 722 continuous lighting Period, 723 lighting end period, 731 to 733 period, 800 lighting fixture, 810 load circuit, AC AC power supply, C24, C51 smoothing capacitor, C42 resonance capacitor, C43 coupling capacitor, D23 rectifier, DB1, DB2 diode bridge, L21, L41 Choke coil, Q22, Q31, Q32 switching element.

Claims (5)

In a lighting circuit for lighting a light emitting diode by applying a DC load voltage to a load circuit having the light emitting diode,
A DC power supply circuit for generating a DC power supply voltage;
An inverter circuit that generates a rectangular wave voltage from the DC power supply voltage generated by the DC power supply circuit;
A resonance circuit that includes a coil and a capacitor, and generates an AC voltage from a rectangular wave voltage generated by the inverter circuit by resonance between the coil and the capacitor;
A rectifier circuit that rectifies the AC voltage generated by the resonant circuit to generate a DC load voltage;
In the inverter circuit, the frequency of the rectangular wave voltage generated in at least one of a lighting start period for switching the light emitting diode from a lighting state to a lighting state and a lighting end period for switching the light emitting diode from a lighting state to a lighting state is The rectifier circuit has a frequency farther from the resonant frequency of the resonant circuit than the frequency of the rectangular wave voltage generated in the continuous lighting period in which the light emitting diode is continuously lit, and the lighting voltage at which the light emitting diode of the load circuit is lit A lighting circuit characterized by having a frequency at which the DC load voltage generated by is reduced . The inverter circuit generates a frequency of a rectangular wave voltage generated during a lighting start period of the light emitting diode from a frequency at which a DC load voltage generated by the rectifier circuit is lower than a lighting voltage at which the light emitting diode of the load circuit lights. The lighting circuit according to claim 1 , wherein the lighting circuit is changed to a frequency at which a DC load voltage generated by the rectifier circuit is higher than a lighting voltage at which a light emitting diode of the load circuit is lit. The inverter circuit generates a frequency of a rectangular wave voltage generated during a lighting end period of the light emitting diode from a frequency at which a DC load voltage generated by the rectifier circuit is higher than a lighting voltage at which the light emitting diode of the load circuit lights. The lighting circuit according to claim 1 or 2 , wherein the lighting circuit is changed from a lighting voltage at which a light emitting diode of the load circuit is lit to a frequency at which a DC load voltage generated by the rectifier circuit is lowered. 2. The resonance circuit according to claim 1, wherein a ratio of a period in which a current output to the rectifier circuit is 0 in a continuous lighting period in which the light emitting diode is continuously lit is 1/9 or less. The lighting circuit according to claim 3 . An illumination fixture comprising: a load circuit having a light emitting diode; and the lighting circuit according to any one of claims 1 to 4 .

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