JP7273356B2 - Lighting device and lighting device - Google Patents

Description

The embodiments of the present invention relate to a lighting device having a conversion circuit that converts input power by switching a switching element that is switched by a PWM signal and supplies the input power to a load, and a lighting device that includes the same.

Conventionally, a lighting device used in a lighting device such as a downlight includes an AC/DC conversion circuit such as a power factor correction circuit (PFC) that converts an AC input voltage into a DC constant voltage, and a switching drive of a switching element by a PWM signal. and a DC/DC conversion circuit such as a step-down chopper circuit for outputting a DC constant voltage obtained by stepping down the voltage from the AC/DC conversion circuit to the light source. The output current of the DC/DC circuit is controlled by peak current control (current limit control) using, for example, a comparator that compares a peak current value with a reference threshold current value. In this configuration, the minimum duty ratio of the PWM signal is determined by the delay of the comparator and the turn-off delay of the switching element.

Japanese Patent No. 4901104

A problem to be solved by the present invention is to provide a lighting device capable of stably controlling the lighting of a light source regardless of the degree of dimming, and a lighting device including the same.

In the lighting device of the embodiment, the output current is changed to a constant current by switching the switching element based on the ON signal of the PWM signal transmitted at a constant cycle and the OFF signal of the PWM signal transmitted according to the comparison result. It is a lighting device that The lighting device includes a conversion circuit, a comparator, and a control section. The conversion circuit includes a switching element. The conversion circuit converts the input power by switching the switching element and supplies the converted power to the light source. A comparator compares the output current of the conversion circuit with a predetermined threshold current. The control unit includes first setting control and second setting control. The first setting control sets the off timing of the PWM signal according to the comparison result of the comparator. The second setting control directly sets the off timing of the PWM signal. The control unit performs the second setting control in a region where the degree of light control of the light source is equal to or less than a predetermined degree of light control.

According to the present invention, stable lighting control of the light source can be expected regardless of the degree of dimming.

1 is a circuit diagram of a lighting device including a lighting device according to an embodiment; FIG. 4 is a timing chart showing the output current of the conversion circuit of the same lighting device, the output of the comparator, the PWM signal, and the ON/OFF timing of the switching element.

An embodiment will be described below with reference to the drawings.

In FIG. 1, 10 is a lighting device. A downlight or the like is used as the lighting device 10, for example. The lighting device 10 includes a lighting device 12 that is a power supply device, a light source module 14 that includes a light source 13 such as an LED as a lighting load, and a dimmer 15 that sets the dimming degree of the light source 13 .

In the lighting device 12, a pair of input terminals of a rectifier circuit 21 are connected via a filter circuit (not shown) to a commercial AC power supply e, which is an external power supply for supplying AC input power of 100 V or the like. The rectifier circuit 21 rectifies the commercial AC power supply e into a DC power supply and outputs the DC power supply. A first conversion circuit 22 is connected to a pair of output terminals of the rectification circuit 21 . The first conversion circuit 22 is a known power factor correction circuit for power factor correction, and in this embodiment is a boost chopper circuit. The first conversion circuit 22 converts the input voltage into a predetermined first voltage, for example, a first DC constant voltage higher than 160V, and outputs it.

A second conversion circuit 23 is connected to the output side of the first conversion circuit 22 . In the present embodiment, the second conversion circuit 23 converts the first DC constant voltage input from the first conversion circuit 22 into a predetermined second voltage lower than the first voltage, for example, a second DC constant voltage higher than 42V. It is a step-down chopper circuit that converts and outputs. The first conversion circuit 22 and the second conversion circuit 23 constitute a conversion circuit 24 that converts the input power and supplies it to the light source 13 . One end of the second conversion circuit 23 is connected to a connection point between a series circuit of the switching element Q1 and the feedback diode D connected between the output terminals of the first conversion circuit 22 and the cathode of the switching element Q1 and the feedback diode D. and an inductor L. The switching element Q1 is made of _a semiconductor other than a silicon semiconductor, such as gallium nitride (GaN), silicon carbide (SiC), or gallium oxide ( _Ga2O3 ). Therefore, the switching element Q1 has less loss during a switching transition period than a switching element made of silicon semiconductor. A control terminal of the switching element Q1 is connected via a driver circuit DRV to a microcomputer 25 which is a control unit, and the switching element Q1 is driven by a PWM signal S1 output from the microcomputer 25 for switching. The switching element Q1 is switched by the PWM signal S1 at a predetermined operating frequency, for example, an operating frequency of 100 kHz or more. (Fig. 2). In this manner, the second conversion circuit 23 can reduce the ripple of the current IL, which is the output current, by switching-driving the switching element Q1 at an operating frequency of 100 kHz or higher.

Also, the feedback diode D is made of a semiconductor other than a silicon semiconductor, such as silicon carbide (SiC). Therefore, the feedback diode D has a smaller temperature change in the reverse recovery time than the silicon semiconductor. A switch circuit 26 having a switching element Q2 connected in parallel with the output end of the second conversion circuit 23 is connected to the output end of the second conversion circuit 23, and the input end of the light source module 14 is connected. A microcomputer 25 is connected to the control terminal of the switching element Q2, and the switching element Q2 is driven by a PWM signal S2 output from the microcomputer 25 according to the dimming degree set by the dimmer 15. FIG. Switching element Q2 is switched at a lower operating frequency than switching element Q1. Also, the switch circuit 26 generates a PWM signal for controlling the light source 13 by short-circuiting and opening the output terminals of the second conversion circuit 23 by switching the switching element Q2. That is, the load current I, which is the average current flowing through the light source 13 of the light source module 14, and the current IL, which is the output current of the conversion circuit 24 (second conversion circuit 23), are controlled to be constant currents by switching the switching element Q2. Further, in the second conversion circuit 23, a resistor R for detecting the current IL is connected between the anode of the feedback diode D and the switching element Q2 which is one output terminal. A detection circuit 27 for detecting the output voltage of the second conversion circuit 23, that is, the output voltage of the conversion circuit 24 is connected to the output terminal of the second conversion circuit 23. FIG.

Further, an inverting input terminal of a comparator 28 is connected between the resistor R of the second conversion circuit 23 and the light source 13, and a predetermined reference voltage is applied to the non-inverting input terminal of the comparator 28 from a reference voltage source 29. is entered. Therefore, the comparator 28 compares the magnitude of the current IL and the predetermined threshold current Ith based on the corresponding voltages. The output terminal of the comparator 28 is connected to the microcomputer 25, and the comparison result of the comparator 28 is input to the microcomputer 25 as a signal (voltage signal) S.

The microcomputer 25 performs first setting control, which is feedback control for setting the duty ratio of the PWM signal S1 according to the comparison result of the comparator 28, that is, based on the signal (voltage signal) S input from the comparator 28. , and a second setting control that directly sets the duty ratio of the PWM signal S1. The microcomputer 25 is set so as to perform the second setting control at least when the light source 13 is deeply dimmed below a predetermined dimming level, that is, when the load current I is below a predetermined level.

In addition, the microcomputer 25 monitors the output voltage of the conversion circuit 24 (second conversion circuit 23) by means of the detection circuit 27, and reduces or stops the output of the conversion circuit 24 (second conversion circuit 23) according to the output voltage. Perform protective action to prevent

Next, the operation of one embodiment will be described.

When power is supplied from the commercial AC power supply e to the lighting device 12, in the conversion circuit 24, the first conversion circuit 22 operates to boost the AC input voltage to the first DC constant voltage, and the second conversion circuit 23 It operates to step down the first DC constant voltage to the second DC constant voltage. At this time, in the second conversion circuit 23, the PWM signal S1 is output from the microcomputer 25 to the control terminal of the switching element Q1, and the switching element Q1 is switched according to the PWM signal S1. In the switch circuit 26, the PWM signal S2 is output from the microcomputer 25 to the control terminal of the switching element Q2, the switching element Q2 is switched according to the PWM signal S2, and the output terminals of the second conversion circuit 23 are short-circuited and opened. As a result, a load current I flows through the light source 13 according to the dimming degree set by the dimmer 15, and the light source 13 is lit at the set dimming degree.

In the second conversion circuit 23, when the switching element Q1 is in the ON state, the current IL1 is output from the second conversion circuit 23 via the inductor L from the switching element Q1, and energy is stored in the inductor L. Further, when the switching element Q2 is in the OFF state, the energy stored by the current IL1 is released to the inductor L, and the second conversion circuit 23 outputs the current IL2 from the feedback diode D through the inductor L. In this embodiment, the switching element Q1 is switching-driven at an operating frequency of 100 kHz or higher, and a current IL (IL=IL1+IL2) continuously flows through the inductor L as shown in FIG. The microcomputer 25 monitors the peak value of the current IL via the comparator 28, and sets the duty ratio of the PWM signal S1, which is the OFF timing in this embodiment, so that the current IL becomes a constant current.

When the dimming degree of the light source 13 is relatively high, the duty ratio of the PWM signal S2 that drives the switching element Q2 is set relatively small, and the load current I becomes relatively large. As indicated by the solid line in FIG. 2, the valley is deeper, and as the dimming level decreases, the load current I becomes relatively smaller. Therefore, the current IL reaches the peak value at an earlier timing as the dimming degree of the light source 13 is smaller. Therefore, in the comparator 28, the smaller the dimming degree of the light source 13, the earlier the peak value is detected. Become.

Here, the microcomputer 25 performs the first setting control when the dimming degree of the light source 13 is greater than a predetermined dimming degree (shallow dimming). In the first setting control, the off timing of the PWM signal S1 output from the microcomputer 25 corresponds to the current IL as a result of comparing the voltage corresponding to the current IL with the reference voltage corresponding to the threshold current Ith by the comparator 28. is set when the voltage applied is greater than the reference voltage, that is, when the current IL exceeds the threshold current Ith.

Further, when the dimming degree of the light source 13 becomes less than the predetermined dimming degree (deep dimming), the effects of the delay T1 of the comparator 28 and the turn-on delay T2 of the switching element Q1 cannot be ignored, and the duty ratio of the PWM signal S1 becomes , it becomes difficult to narrow down the duty ratio to a predetermined minimum duty ratio or less determined according to the delay T1 of the comparator 28 and the turn-on delay T2 of the switching element Q1. In the drawings, the delays T1 and T2 are exaggerated for clarity of explanation.

Therefore, the microcomputer 25 performs the second setting control when the dimming degree of the light source 13 is equal to or less than a predetermined dimming degree. In the second setting control, the off timing of the PWM signal S1 output from the microcomputer 25 is directly set by the microcomputer 25. FIG. The microcomputer 25 directly sets the off timing of the PWM signal S1 based on the dimming degree set by the dimmer 15. FIG.

When the degree of dimming is equal to or less than a predetermined degree of dimming, the microcomputer 25 may perform only the second setting control, or may operate the first setting control and the second setting control in parallel. The PWM signal S1 may be set to the smaller duty ratio, that is, the earlier off timing.

Further, the microcomputer 25 performs protection operation when the output voltage detected by the detection circuit 27 exceeds a predetermined voltage threshold.

According to the embodiment described above, the microcomputer 25 has the first setting control for setting the duty ratio of the PWM signal S1 according to the comparison result by the comparator 28, and the second setting control for directly setting the duty ratio of the PWM signal S1. Setting control is set, and the second setting control is performed in a region where at least the dimming degree of the light source 13 is equal to or lower than the predetermined dimming degree. It is possible to set an appropriate duty ratio even in a deep dimming range regardless of the stop-down limit of . Therefore, the lighting control of the light source 13 can be stably performed regardless of the degree of dimming.

When the microcomputer 25 switches between the first setting control and the second setting control depending on whether the degree of dimming of the light source 13 is greater than the predetermined degree of dimming, either the first setting control or the second setting control is selected. It suffices to selectively implement either, and the control can be simplified.

Further, the microcomputer 25 performs the first setting control in a region where the dimming degree of the light source 13 is greater than the predetermined dimming degree, and the first setting control and the second setting control in a region where the dimming degree of the light source 13 is less than the predetermined dimming degree. are performed in parallel to set the duty ratio of the PWM signal S1 to the smaller one among these controls, the lighting control of the light source 13 can be smoothly performed when switching between the first setting control and the second setting control. .

In the above embodiment, the conversion circuit 24 is composed of the first conversion circuit 22, which is a boost chopper circuit, and the second conversion circuit 23, which is a step-down chopper circuit. However, it is not limited to this. Alternatively, a configuration including a plurality of voltage step-up or voltage step-down circuits that convert electric power by switching switching elements may be used.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.

10 lighting equipment
12 lighting device
13 light source
24 conversion circuit
25 Microcomputer as control unit
28 Comparator
Q1 switching element
S1 PWM signal

Claims (4)

A lighting device in which a switching element is switched by an on-signal of a PWM signal transmitted at a constant cycle and an off-signal of the PWM signal transmitted according to a comparison result, thereby making an output current constant. ,
a conversion circuit comprising the switching element, wherein input power is converted by switching of the switching element and supplied to a light source;
a comparator that compares the output current of the conversion circuit with a predetermined threshold current;
a first setting control for setting the off timing of the PWM signal according to the comparison result of the comparator; and a second setting control for directly setting the off timing of the PWM signal, wherein the dimming degree of the light source is a control unit that performs the second setting control in a region below a predetermined dimming level;
A lighting device comprising: The lighting device according to claim 1, wherein the control unit switches between the first setting control and the second setting control depending on whether the degree of dimming of the light source is greater than the predetermined degree of dimming. . The control unit performs the first setting control in a region where the light source dimming degree is greater than the predetermined dimming degree, and performs the first setting control and the 2. The lighting device according to claim 1, wherein the off timing of the PWM signal is set earlier in the second setting control. a light source;
A lighting device according to any one of claims 1 to 3;
A lighting device comprising:

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