JP6928878B2 - Lighting device - Google Patents

Description

The present invention relates to a lighting device that lights a light source.

Patent Document 1 includes a detection unit that detects a decrease in the DC voltage output from the power supply circuit unit in a lighting device having a power supply circuit unit (boost chopper circuit), thereby suppressing an excessive power supply to the load. The technology to be used is disclosed. Specifically, in Patent Document 1, a switching element that operates under the control of a boost chopper control circuit is provided in the power supply circuit unit, and the power supply circuit unit boosts the voltage by controlling the switching element by pulse width modulation (PWM). The DC voltage is output.

Japanese Unexamined Patent Publication No. 2012-243458

However, in the prior art as in Patent Document 1, when the power supply voltage increases, the power proportional to the power supply voltage is supplied to the load circuit section, so that an excessive power may be supplied to the load circuit section. There is a problem.

Therefore, an object of the present invention is to provide a lighting device in which fluctuations in power supply capacity are suppressed even when the power supply voltage fluctuates.

In order to solve the above problems, the lighting device for lighting the light source according to the embodiment of the present invention is a lighting device that lights the light source based on the power supplied from the power supply, and the inductor and the inductor are used. A step-up chopper circuit having a switching element for controlling the flowing current, a control circuit for controlling the output voltage or output power of the step-up chopper circuit by controlling the switching element on and off, and an output voltage of the step-up chopper circuit. The control circuit includes a step-down circuit that steps down the voltage and supplies the light source to the light source, and a voltage correction circuit that outputs a correction signal that changes according to the voltage fluctuation of the power supply. The control circuit responds to the current flowing through the switching element. The switching element is on / off controlled based on a control signal generated by superimposing the correction signal on the current detection signal.

According to the present invention, it is possible to suppress fluctuations in the current supply capacity when the power supply voltage fluctuates.

Circuit block diagram showing a configuration example of a lighting device The figure which shows an example of the input signal waveform of IS terminal The figure which shows an example of the input signal waveform of IS terminal The figure which shows an example of the input signal waveform of IS terminal The figure which shows the relationship between the power supply voltage and the power supply of a lighting device The figure which shows the relationship between the power supply voltage and the power supply of a lighting device The figure which shows the relationship between the voltage division ratio of a voltage correction circuit, and the power supply of a lighting device.

Hereinafter, each embodiment of the present invention will be described in detail with reference to the drawings. The following description of each embodiment is merely an example and is not intended to limit the present invention, its application or its use.

-Structure of lighting device-
FIG. 1 is a configuration diagram showing the configuration of the lighting device 1 according to the embodiment. As shown in FIG. 1, the lighting device 1 includes a rectifier circuit 2, a step-up chopper circuit 3, a control circuit 4, a voltage correction circuit 5, and a step-down circuit 6.

The rectifier circuit 2 is a circuit that rectifies and outputs the power supply voltage Vin received from the power supply E, and is, for example, a bridge circuit of a diode (not shown) that performs full-wave rectification. Specifically, the rectifier circuit 2 has a pair of input terminals 21 and 22 and a pair of output terminals 23 and 24. Then, the rectifier circuit 2 receives the power supply voltage Vin at the input terminals 21 and 22, rectifies it, and outputs it from the output terminals 23 and 24.

The step-up chopper circuit 3 boosts the voltage received from the output terminals 23 and 24 of the rectifier circuit 2 and outputs the voltage to the step-down circuit 6. The step-down circuit 6 turns on the light source 7 by lowering the output voltage of the step-up chopper circuit 24 and outputting it to the light source 7. The control circuit 4 can be realized by, for example, an IC (Integrated Circuit), and includes a comparator 41 for on / off control of the switching element TR1 of the step-up chopper circuit 3. The voltage correction circuit 5 outputs a correction signal Va that changes according to the voltage fluctuation of the power supply voltage Vin.

The technique according to the present disclosure is characterized by a boost chopper circuit 3, a control circuit 4, and a voltage correction circuit 5, and will be specifically described below. Since the step-down circuit 6 can adopt the circuit according to the conventional configuration, detailed description thereof will be omitted here.

The boost chopper circuit 3 has a positive electrode input terminal 31 and a negative electrode input terminal 32, and a positive electrode output terminal 33 and a negative electrode output terminal 34. The positive electrode input terminal 31 and the negative electrode input terminal 32 are electrically connected to the output terminals 23 and 24 of the rectifier circuit 2. The term "electrically connected" is a concept including a case where a passive element (not shown) such as a resistor or a transistor is connected between the two in addition to the case where the two are directly connected. In the following description, even if it is simply described as connecting, it shall refer to this electrical connection.

Further, an inductor L1 and a diode D1 are provided in series on the positive electrode side node Np that connects the positive electrode input terminal 31 and the positive electrode output terminal 33 of the boost chopper circuit 3. Further, between the intermediate node N31 between the inductor L1 and the diode D1 and the negative electrode side node Nm connecting the negative electrode input terminal 32 and the negative electrode output terminal 34, a switching element TR1 and a switching element TR1 are provided. A detection resistor R1 used to output a current detection signal Vis corresponding to the flowing current is provided in series. The switching element TR1 is, for example, a semiconductor switching element such as a field effect transistor (FET). Further, a capacitor C1 is provided between the cathode of the diode D1 and the node Nm on the negative electrode side. The boost chopper circuit 3 configured in this way generates an output voltage higher than the voltage input between both input terminals 31 and 32 between both ends of the capacitor C1 by the switching operation of the switching element TR1.

As described above, the control circuit 4 includes a comparator 41 for on / off control of the switching element TR1 of the step-up chopper circuit 24.

A predetermined detection threshold value Vth is given to one input terminal of the comparator 41. The detection threshold value Vth is, for example, a voltage (for example, about 0.5V to 0.7V) preset inside the control circuit 4, and is generated by a regulator or the like (not shown).

A control signal for on / off control of the switching element TR1 is given to the other input terminal (hereinafter referred to as IS terminal) of the comparator 41. That is, the comparator 41 turns on the switching element TR1 when the control signal is equal to or less than the detection threshold value Vth, while turns off the switching element TR1 when the control signal exceeds the detection threshold value Vth. The IS terminal of the comparator 41 is connected to the intermediate node N32 between the switching element TR1 and the detection resistor R1 via the voltage dividing resistor R2. With this configuration, a signal (current-voltage converted voltage signal) that changes according to the current flowing through the switching element TR1 is given to the IS terminal via a detection resistor and a voltage dividing resistor. In the following description, among the control signals given to the IS terminals, a signal component that changes according to the current flowing through the switching element is referred to as a current detection signal and is described as Vis. Further, the same code Vis is used for the voltage value of the current detection signal Vis.

Further, the output terminal 53 of the voltage correction circuit 5 is connected to the IS terminal of the comparator 41.

The voltage correction circuit 5 has a pair of input terminals 51 and 52 and an output terminal 53. The input terminals 51 and 52 of the voltage correction circuit 5 are connected to the power supply E. The voltage correction circuit 5 includes diodes D2 and D3 connected to the input terminals 51 and 52, respectively, and a voltage dividing resistor R3 connected between the cathode of the diodes D2 and D3 and the output terminal 53. Further, a smoothing capacitor 54 is connected between the cathodes of the diodes D2 and D3 and the voltage dividing resistor R3. With this configuration, the voltage correction circuit 5 rectifies the power supply voltage Vin received from the power supply E to the input terminals 51 and 52, and outputs the power supply voltage Vin from the output terminal 53 via the voltage dividing resistor R3.

In the following description, among the control signals given to the IS terminals, the signal component output from the voltage correction circuit 5 is referred to as a correction signal and is described as Va. Further, the same reference numeral Va is used for the voltage value of the correction signal.

Since the voltage dividing resistor R2 and the detection resistor R1 are connected in series between the output terminal 53 of the voltage correction circuit 5 and the negative side node Nm of the boost chopper circuit, the correction signal (voltage value) Va can be set. , Expressed by the following equation (1).

Va = Vin x β
= Vin × (R1 + R2) / (R1 + R2 + R3) ・ ・ (1)

Here, β is a voltage division ratio generated at the IS terminal, and is a value on the horizontal axis in FIG. 5, which will be described later. As shown in the above equation (1), the value of the voltage dividing ratio β can be adjusted by changing the resistance values of the detection resistors R1 and the voltage dividing resistors R2 and R3, and the supply power varies, which will be described later. It is preferable that the value is set to the minimum value.

Summarizing the above, a control signal in which the correction signal Va is superimposed on the current detection signal Vis is given to the IS terminal of the comparator 41.

2 to 4 show an example of a change in the control signal given to the IS terminal. In each figure, the lower waveform is an enlargement of a part of the upper waveform.

As shown in FIG. 2 upper, current detection signal Vis, depending on the period T _E of the power supply voltage Vin, the peak value has changed. Further, as shown in the lower part of FIG. 2, Vis rises when the switching element TR1 is turned on, and the switching element TR1 is set to OFF when a predetermined ON width is reached. Then, since Vis = 0, the control signal of the IS terminal drops to Va. This "predetermined on-width" is set based on the required power supply. That is, in the lighting device 1, when the required power supply becomes large, the on-width of the switching element TR1 is lengthened to increase the amplitude of the current detection signal Vis.

FIG. 3 shows a state in which the power supply of the boost chopper circuit 3 is increased from the state of FIG. 2, and the sum of the correction signal Va and the maximum value of the current detection signal Vis reaches Vth. In other words, it shows an example of the change of the control signal given to the IS terminal when the power supply of the boost chopper reaches near the maximum.

In this way, when the control signal exceeds the detection threshold value Vth, that is,
Vth <Vis + Va ... (2)
When the relationship is satisfied, the switching element is turned off and the control signal drops to Va. Then, after a while, the switching element TR1 is turned on again and the control signal rises, and when the control signal exceeds the detection threshold value Vth, the switching element TR1 is turned off and controlled repeatedly.

By performing the above operation, the supply power Wpfc of the following equation (3) is supplied from the step-up chopper circuit 3 to the step-down circuit 6. In the following equation (3), Ipfc is the output current of the step-up chopper circuit 3. Further, α is a ratio of the supply current Ipfc of the step-up chopper circuit 3 to the peak current value of the triangular wave flowing through the detection resistor R1, and is treated as a constant here.

Wpfc = Vin x Ipfc
= Vin × (Vth-Vin × β) / R1 × α
= -Αβ / R1 × (Vin-Vth / 2β) ^ 2
+ Vth ^ 2 / R1 × α / 4β ・ ・ (3)

From the above equation (3), Wpfc has a quadratic function relationship having a maximum point of the maximum value Vth ^ 2 / R1 × α / 4β when Vin = Vth / 2β. The solid line in FIG. 3 shows the change in the supplied power when the power supply voltage is changed.

As shown in the above equation (1), the value of the voltage dividing ratio β can be adjusted by changing the resistance values of the detection resistors R1 and the voltage dividing resistors R2 and R3. Therefore, as shown in FIG. 3, by setting the maximum value of the supply power Wpfc within the range of the predetermined rated voltage (for example, 100V ± 10V), the variation in the supply power is made as compared with the conventional technique. It can be made smaller.

Note that FIG. 4 shows an example in which the power supply of the step-up chopper circuit 3 is further increased from the state of FIG. The operation of the lighting device 1 in FIG. 4 is basically the same as that in FIG. 3, and detailed description thereof will be omitted. In FIG. 4, the range in which the equation (2) “Vth <Vis + Va” is satisfied is increased from the state of FIG.

-Comparative example-
In FIG. 5, when the voltage correction circuit 5 is not provided, the change in the supplied power when the power supply voltage Vin is changed is shown by a broken line. As shown in FIG. 5, when the voltage correction circuit 5 is not provided, the control signal given to the IS terminal of the comparator 41 of the control circuit 4 increases in proportion to the power supply voltage Vin. That is, the power supplied from the step-up chopper circuit 3 to the step-down circuit 6 increases in proportion to the power supply voltage Vin. Then, the variation in the power supply becomes large, but this is not the case in the configuration according to the present embodiment.

As shown in Examples 2 and 3 of FIG. 6, tentatively, in the present embodiment, the position of the maximum value of the supply power Wpfc represented by the equation (3) is slightly up and down from the predetermined rated voltage range. Even if it deviates, the variation in the supplied power Wpfc can be reduced as compared with the conventional technique. In FIG. 6, Example 1 corresponds to the waveform of FIG. 5, in Example 2 the voltage dividing ratio β2 is larger than the voltage dividing ratio β1 of Example 1, and in Example 3, the voltage dividing ratio β3 is Example 1. An example is shown in which the voltage division ratio of β1 is smaller than that of β1.

In the above embodiment, the superiority of the technique according to the present disclosure with respect to the fluctuation of the power supply voltage Vin has been described. On the other hand, the technique according to the present disclosure is characterized in that not only the fluctuation of the power supply voltage Vin but also the variation of the detection threshold value Vth of the control circuit 4 (for example, the control IC) can be taken into consideration.

Specifically, in the technique according to the present disclosure, the output voltage of the voltage correction circuit 5 is superimposed on the IS terminal of the comparator 41 in order to suppress the variation in the supplied power Wpfc due to the fluctuation of the power supply voltage Vin. At this time, by considering Vth = Vth ± ΔVth as the detection threshold value including the variation, the influence of the detection threshold value variation can be determined.
ΔVth / Vis = ΔVth (Vth-Va) = ΔVth (Vth-Vin × β) ・ ・ (4)
It can be expressed as.

Therefore, when adjusting the value of the voltage division ratio β, optimization for variations in the detection threshold value Vth can be realized by considering the above equation (4). FIG. 7 shows the variation of the supplied power Wpfc with respect to the voltage division ratio β. As shown in FIG. 7, the minimum value of the variation in the supplied power can be optimized by considering the variation in the detection threshold value Vth in addition to the variation due to the power supply voltage Vin. In the example of FIG. 7, the minimum value of the variation of the supplied power can be reduced to about 22%, and the variation of the supplied power Wpfc is compared with the variation of the prior art (see the voltage division ratio β = 0 in FIG. 7). It has been able to be significantly reduced.

(Other embodiments)
As described above, embodiments have been described as an example of the techniques disclosed in this application. However, the technique in the present disclosure is not limited to this, and can be applied to embodiments in which changes, replacements, additions, omissions, etc. are made as appropriate. It is also possible to combine the components described in the above embodiment to form a new embodiment.

The above embodiment may have the following configuration.

For example, in the above embodiment, the voltage correction circuit 5 has described an example in which the correction signal Va generated by the resistance voltage division is superimposed on the current detection signal, but the present invention is not limited to this. For example, although not shown, a voltage correction circuit that changes the voltage division ratio β according to the power supply voltage Vin may be used under the control of a microcomputer. However, it is possible to make a cheaper and simpler configuration by adopting the configuration as in the above embodiment. Further, the program control by the microcomputer has a concern such as a control failure due to a program bug or the like, but the configuration according to the above embodiment does not have such a problem.

Further, in the above-described embodiment, a configuration example of each circuit is shown, but the configuration is not limited to that of the embodiment, and it is possible to replace the circuit with another circuit having the same function. For example, the smoothing capacitor 54 may be omitted from the voltage correction circuit 5. In this case, for example, another voltage dividing resistor (not shown) is provided between the voltage dividing resistors R2 and R3, and a capacitor grounded in parallel between the voltage dividing resistor and the voltage dividing resistor R3 of the voltage correction circuit 5 (not shown). It is advisable to connect (not shown).

The lighting device according to the present invention has an effect of being able to suppress fluctuations in the current supply capacity when the power supply voltage fluctuates, and is extremely useful as a lighting device for lighting a light source such as an LED, for example.

1 Lighting device 3 Booster chopper circuit 4 Control circuit 41 Comparator 5 Voltage correction circuit

Claims (5)

A lighting device that lights a light source based on the power supplied from the power supply.
A step-up chopper circuit having an inductor and a switching element for controlling the current flowing through the inductor.
A control circuit that controls the output voltage or output power of the step-up chopper circuit by controlling the switching element on and off, and
A step-down circuit that steps down the output voltage of the step-up chopper circuit and supplies it to the light source.
It is provided with a voltage correction circuit that outputs a correction signal that changes according to the voltage fluctuation of the power supply.
The control circuit is a lighting device that controls on / off of the switching element based on a control signal generated by superimposing the correction signal on a current detection signal corresponding to a current flowing through the switching element. The lighting device according to claim 1, wherein the voltage correction circuit includes a rectifying unit for rectifying the power supply voltage and a voltage dividing resistor for dividing the rectified power supply voltage. The control circuit turns on the switching element when the control signal is equal to or lower than a predetermined detection threshold value, and turns off the switching element when the control signal exceeds the detection threshold value. Has a comparator and
The lighting device according to claim 2, wherein the magnitude of the correction signal is 20% or more and less than 80% of the detection threshold value. The lighting device according to claim 3, wherein the magnitude of the correction signal is 50% of the detection threshold value. The control circuit turns on the switching element when the control signal is equal to or lower than a predetermined detection threshold value, and turns off the switching element when the control signal exceeds the detection threshold value. Has a comparator and
The DC output power of the step-up chopper circuit increases or decreases according to the voltage dividing ratio of the voltage dividing resistor for generating the correction signal, and has a maximum value at a predetermined voltage dividing ratio.
The lighting device according to claim 2, wherein the voltage division ratio is set so that the maximum value is within a predetermined rated voltage range.

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