JP6900840B2 - Lighting device and lighting device - Google Patents

Description

The present invention relates to a lighting device and a lighting device.

Patent Document 1 discloses an LED lighting device. This LED lighting device includes a DC conversion device that lights an LED by an output current. The DC converter includes a switching element. When the input voltage to the DC converter fluctuates, the on-duty of the drive signal of the switching element is narrowed to suppress the peak value of the output current.

Japanese Patent No. 5472691

When controlling the lighting of a semiconductor light source included in a luminaire, a switching power supply that is generally controlled by a constant current is often used. Here, while the switching power supply is in steady operation, the power supply may fluctuate for some reason. Generally, the switching power supply is feedback controlled. Therefore, when the power supply fluctuates, the feedback circuit operates so as to compensate for the fluctuation. However, the current flowing through the semiconductor light source fluctuates even for a short time until the current flowing through the semiconductor light source is recovered by the feedback control. Therefore, the light emitted by the semiconductor light source fluctuates.

Here, with the practical application of DC power supply such as a solar cell or a battery, DC power supply may be applied to a lighting fixture. In the case of DC power supply, for example, when the photovoltaic power generation is switched to the battery, the DC power supply voltage fluctuates, that is, a so-called sag state is likely to occur. For this reason, flicker that fluctuates the light of the lighting equipment is likely to occur, and the user may feel inconvenience.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain a lighting device and a lighting device capable of suppressing fluctuations in the current flowing through a light source with respect to fluctuations in the power supply voltage.

The lighting device according to the present invention detects a converter that is supplied with power from a DC power source and turns on the light source by turning on / off the switching element, detects the output current of the converter, and cancels the difference between the output current and the target value. The on-time control unit that controls the on-time of the switching element and the on-time control unit that detects the output current and turns off the switching element when the output current reaches a first threshold value equal to or higher than the target value. The current suppression unit that turns off the switching element earlier than the timing, and the on-time control unit that detects the output current and turns off the switching element when the output current is smaller than the second threshold value below the target value. It is provided with a current maintenance unit that keeps the switching element on even after the lapse of the timing.

In the lighting device according to the present invention, the switching element is turned off when the output current of the converter reaches the first threshold value. Further, when the output current of the converter is smaller than the second threshold value, the switching element is kept on. Therefore, it is possible to suppress fluctuations in the current flowing through the light source with respect to fluctuations in the power supply voltage.

This is a circuit block portion of the lighting device according to the first embodiment. It is a circuit block part of the constant current control part which concerns on Embodiment 1. It is a figure explaining the operation of the lighting apparatus when a DC voltage rises. It is a figure explaining the operation of the lighting apparatus when a DC voltage drops.

The lighting device and the lighting device according to the embodiment of the present invention will be described with reference to the drawings. The same or corresponding components may be designated by the same reference numerals and the description may be omitted.

Embodiment 1.
FIG. 1 is a circuit block portion of the lighting device 100 according to the first embodiment. The lighting device 100 includes a lighting device 10 and an LED light source unit 50. The lighting device 10 is supplied with a DC voltage from the DC power supply DC to light the light source 51 included in the LED light source unit 50. The DC power supply DC is, for example, a solar cell, a battery or a DC power supply system.

The LED light source unit 50 includes a plurality of light sources 51 connected in series. The light source 51 is a semiconductor light source. In this embodiment, the light source 51 is an LED. The number of light sources 51 included in the LED light source unit 50 may be one or more. Further, in the LED light source unit 50, the plurality of light sources 51 may be connected in parallel or series-parallel.

The lighting device 10 includes a converter 20 and a constant current control unit 30. The converter 20 includes a switching element Q1. The switching element Q1 is, for example, a MOSFET (Metal-Oxide-Semiconductor Field-Effective Transistor). The drain of the switching element Q1 is connected to the positive electrode of the DC power supply DC. The cathode of the diode D1 and one end of the inductor L1 are connected to the source of the switching element Q1. The Vg terminal of the constant current control unit 30 is connected to the gate of the switching element Q1.

A positive electrode of the capacitor C1 is connected to the other end of the inductor L1. The LED light source unit 50 is connected in parallel with the capacitor C1. The anode side of the light source 51 is connected to the positive electrode of the capacitor C1, and the cathode side is connected to the negative electrode of the capacitor C1. One end of the resistor R1 is connected to the negative electrode of the capacitor C1 and the cathode side of the LED light source unit 50. The other end of the resistor R1 is connected to the grounding terminal.

The anode of the diode D1 and the negative electrode of the DC power supply DC are also connected to the grounding terminal. Therefore, a back converter circuit composed of a switching element Q1, a diode D1 and an inductor L1 is connected between the DC power supply DC and the LED light source unit 50.

The constant current control unit 30 is a control IC that controls the converter 20. The constant current control unit 30 includes a Vg terminal and a Vcc terminal. A control power supply Vcc1 for operating the control IC is supplied to the Vcc terminal. Further, one end of the resistor R1 is connected to the current detection terminal 31 via the resistor R2. Further, the inductor L1 has a secondary winding. The secondary winding of the inductor L1 is connected to the zcd terminal of the constant current control unit 30 via the resistor R3. The current flowing through the secondary winding is limited by the resistor R3 and input to the zcd terminal.

The operation of constant current control of the output current of the converter 20, that is, the current flowing through the LED light source unit 50 will be described below. When the switching element Q1 is turned on, a high-frequency current is supplied from the DC power supply DC to the capacitors C1 and the LED light source unit 50 connected in parallel to each other via the inductor L1. The capacitor C1 smoothes the high-frequency current obtained from the inductor L1 and supplies it to the LED light source unit 50. As a result, electric power is supplied to the light source 51 and the light source 51 is turned on.

When the switching element Q1 is off, the energy of the inductor L1 stored when the switching element Q1 is on is released to the capacitor C1 and the LED light source unit 50 via the diode D1. That is, the converter 20 turns on the light source 51 by supplying the energy stored in the inductor L1 to the light source 51.

In this way, the converter 20 is supplied with electric power from the DC power supply DC, and the light source 51 is turned on by turning on / off the switching element Q1. When the switching element Q1 is switched, the current flowing through the capacitor C1 and the LED light source unit 50 flows through the resistor R1. The current flowing through the capacitor C1 and the LED light source unit 50 is the coil current flowing through the inductor L1. That is, the voltage applied across the resistor R1 corresponds to the coil current. The average value of the coil current is equal to the current flowing through the LED light source unit 50.

The voltage generated in the resistor R1 is detected by the current detection terminal 31 via the resistor R2. FIG. 2 is a circuit block unit of the constant current control unit 30 according to the first embodiment. The constant current control unit 30 includes an on-time control unit 32, a current suppression unit 33, and a current maintenance unit 34. In FIG. 2, parts other than the on-time control unit 32, the current suppression unit 33, and the current maintenance unit 34 of the constant current control unit 30 are omitted.

The on-time control unit 32 includes a first comparator OP1. A current detection terminal 31 is connected to the − terminal of the first comparator OP1 via a resistor R4. The voltage Vref0 is input to the + terminal of the first comparator OP1. The voltage Vref0 is a voltage corresponding to a target value of the output current of the converter 20. A capacitor C2 is connected between the output of the first comparator OP1 and the − terminal. Further, an on-width control circuit 35 is connected to the output of the first comparator OP1.

The voltage of the resistor R1 detected by the current detection terminal 31 is input to the − terminal of the first comparator OP1 and compared with the voltage Vref0. That is, the first comparator OP1 compares the voltage corresponding to the output current of the converter 20 with the voltage corresponding to the target value. The first comparator OP1 changes the output voltage so that the voltage input to the − terminal matches the voltage Vref0. Therefore, the first comparator OP1 changes the output voltage so that the on-time is shortened when the output current is larger than the target value and the on-time is lengthened when the output current is smaller than the target value.

The comparison result of the first comparator OP1 is detected by the on-width control circuit 35. The on-width control circuit 35 controls the on-time of the switching element Q1 according to the output voltage of the first comparator OP1. The output of the on-width control circuit 35 is connected to the Vg terminal via a drive circuit (not shown) or the like. The drive circuit outputs a drive signal to the switching element Q1. Therefore, the switching element Q1 switches according to the on-time instruction output by the on-width control circuit 35.

From the above, the on-time control unit 32 detects the output current of the converter 20 and controls the on-time of the switching element Q1 so as to cancel the difference between the output current and the target value. That is, the on-time control unit 32 controls the on-time of the switching element Q1 so that the output current of the converter 20 matches the target value. The on-time control unit 32 shortens the on-time when the output current of the converter 20 is larger than the target value, and lengthens the on-time when the output current of the converter 20 is smaller than the target value. Therefore, the on-time control unit 32 can perform constant current control to keep the current flowing through the LED light source unit 50 constant.

Further, the voltage generated in the secondary winding of the inductor L1 is detected at the zcd terminal. When the constant current control unit 30 detects that the switching element Q1 is turned off from the zcd terminal and energy is released from the inductor L1, the constant current control unit 30 performs a critical operation of turning on the switching element Q1 again. The voltage generated in the resistor R1 is integrated by the capacitor C2.

The current suppression unit 33 includes a second comparator CP1. A current detection terminal 31 is connected to the − terminal of the second comparator CP1. The voltage Vref1 is input to the + terminal of the second comparator CP1. The output terminal of the second comparator CP1 is connected to the off control circuit 36. The second comparator CP1 compares the voltage corresponding to the output current of the converter 20 with the voltage Vref1 corresponding to the first threshold value.

The second comparator CP1 changes the output voltage so that the switching element Q1 is turned off when the output current reaches the first threshold value. The first threshold value is a value equal to or higher than the target value of the output current. The comparison result of the second comparator CP1 is detected by the off control circuit 36. The off control circuit 36 turns off the switching element Q1 according to the output voltage of the second comparator CP1.

The current maintenance unit 34 includes a third comparator CP2. A current detection terminal 31 is connected to the + terminal of the third comparator CP2. The voltage Vref2 is input to the-terminal of the third comparator CP2. The output terminal of the third comparator CP2 is connected to the on control circuit 37. The third comparator CP2 compares the voltage corresponding to the output current of the converter 20 with the voltage Vref2 corresponding to the second threshold value.

The third comparator CP2 maintains a state in which the switching element Q1 is turned on when the output current is smaller than the second threshold value. The second threshold value is a value equal to or less than the target value of the output current. The comparison result of the third comparator CP2 is detected by the on control circuit 37. The on control circuit 37 maintains a state in which the switching element Q1 is turned on according to the output voltage of the third comparator CP2.

Here, it is assumed that the DC voltage of the DC power supply DC rises for some reason. FIG. 3 is a diagram illustrating the operation of the lighting device 100 when the DC voltage rises. First, as a comparative example, the operation when the current suppression unit 33 is not provided will be described. At time t1, the DC voltage of the DC power supply DC rises. Immediately after the increase in the DC voltage of the DC power supply DC, the on-time of the switching element Q1 is the same as before the increase in the DC voltage. Therefore, as shown by the broken line 160, the peak value of the coil current increases.

After that, the feedback control of the constant current control unit 30 gradually lowers the peak value of the coil current and returns to the constant current control state. Therefore, a period in which the peak value of the coil current is higher than that in the steady lighting occurs before returning to the constant current control state by the feedback control.

Here, when the current suppression unit 33 is not provided, the peak value of the coil current rises to a value determined by the DC voltage of the DC power supply DC, the on-time, and the inductance value of the inductor L1. Therefore, the larger the DC voltage, the larger the peak value of the coil current. As a result, as shown by the broken line 161 there is a possibility that the LED current flowing through the light source 51 changes significantly, and the fluctuation of the light emitted by the light source 51 becomes large.

Next, the operation of the lighting device 100 when the DC voltage rises will be described. At time t1, the DC voltage of the DC power supply DC rises. At this time, the on-time of the switching element Q1 is the same as before the increase in the DC voltage. Therefore, as shown by the solid line 60, the peak value of the coil current flowing through the inductor L1 becomes higher than the target value at the time of steady lighting.

At time t2, the coil current reaches the first threshold. When the coil current reaches the first threshold value, the current suppression unit 33 turns off the switching element Q1. The current suppression unit 33 turns off the switching element Q1 regardless of the output signal of the on-time control unit 32. Therefore, when the output current of the converter 20 reaches the first threshold value, the switching element Q1 is turned off earlier than the timing when the on-time control unit 32 turns off the switching element Q1.

Here, the first threshold value ≈ Vref1 / R1. The first threshold value may be a fixed value. Further, the first threshold value may be set by calculation or the like from the output current of the converter 20 at the time of steady lighting. Further, the first threshold value may be set based on the peak value of the coil current when the switching element Q1 was switched last time. In this case, for example, the first threshold value is set to 1.1 times the peak value of the coil current when the switching element Q1 was switched last time.

After that, since the coil current becomes larger than that at the time of steady lighting, the on-time control unit 32 controls the on-time to be shorter at time t3. After time t3, the peak value of the coil current decreases with each switching due to the feedback control of the constant current control unit 30. At time t4, the coil current becomes the value at the time of steady lighting. Therefore, the LED light source unit 50 returns to the constant current control state even at the increased DC voltage. The peak value of the coil current during steady lighting is approximately Vref0 / R1 × 2.

In the present embodiment, the current suppression unit 33 detects the output current of the converter 20 and turns off the switching element Q1 earlier than the timing when the on-time control unit 32 turns off the switching element Q1. Further, the current suppression unit 33 turns off the switching element Q1 before the on-time control unit 32 shortens the on-time by feedback control. That is, the current suppression unit 33 turns off the switching element Q1 when the first threshold value is reached before the coil current reaches a value determined by the DC voltage, the on-time, and the inductance value of the inductor L1.

Therefore, as shown by the solid line 60, the peak value of the coil current becomes the first threshold value even when the DC voltage rises significantly. Therefore, as shown by the solid line 61, the fluctuation of the LED current with respect to the fluctuation of the power supply voltage can be suppressed as compared with the case where the current suppression unit 33 is not provided. Therefore, the flicker of the light source 51 can be suppressed.

Here, the capacitor C2 is connected to the first comparator OP1. Therefore, the output voltage of the first comparator OP1 is output later than the output voltage of the second comparator CP1. Therefore, when the DC voltage rises, the signal that shortens the on-time output by the on-time control unit 32 is output later than the signal that turns off the switching element Q1 output by the current suppression unit 33. As a result, it is possible to prevent the signal that the on-width control circuit 35 controls the switching element Q1 from competing with the signal that the off-control circuit 36 controls the switching element Q1.

Next, it is assumed that the DC voltage of the DC power supply DC drops for some reason. FIG. 4 is a diagram illustrating the operation of the lighting device 100 when the DC voltage drops. First, as a comparative example, the operation when the current maintenance unit 34 is not provided will be described. At time t1, the DC voltage of the DC power supply DC drops. Immediately after the decrease in the DC voltage of the DC power supply DC, the on-time of the switching element Q1 is the same as before the decrease in the DC voltage. Therefore, as shown by the broken line 162, the peak value of the coil current decreases.

After that, the feedback control of the constant current control unit 30 gradually raises the peak value of the coil current and returns to the constant current control state. Therefore, a period in which the peak value of the coil current is lower than that in the steady lighting occurs before returning to the constant current control state by the feedback control.

At this time, the peak value of the coil current drops to a value determined by the DC voltage of the DC power supply DC, the on-time, and the inductance value of the inductor L1. Therefore, the larger the DC voltage, the smaller the peak value of the coil current. As a result, as shown by the broken line 163, the LED current flowing through the light source 51 may change significantly, and the fluctuation of the light emitted by the light source 51 may increase.

Next, the operation of the lighting device 100 when the DC voltage drops will be described. At time t1, the DC voltage of the DC power supply DC drops. At this time, the on-time of the switching element Q1 is the same as before the decrease in the DC voltage. Therefore, as shown by the solid line 62, the peak value of the coil current flowing through the inductor L1 is lower than the target value at the time of steady lighting.

Here, when the output current of the converter 20 is smaller than the second threshold value, the current maintenance unit 34 maintains the switching element Q1 on even after the timing at which the on-time control unit 32 turns off the switching element Q1 has elapsed. .. Even if the on-time control unit 32 outputs a signal to turn off the switching element Q1 before the coil current reaches the second threshold value, the current maintenance unit 34 keeps the switching element Q1 on. Therefore, when the output current of the converter 20 is smaller than the second threshold value, the ON state of the switching element Q1 is maintained even after the lapse of the ON time set by the ON time control unit 32.

When the coil current reaches the second threshold value at time t2, the current maintenance unit 34 ends the maintenance of the switching element Q1 in the ON state. As a result, the switching element Q1 is turned off.

Here, the second threshold value ≈ Vref2 / R1. The second threshold value may be a fixed value. Further, the second threshold value may be set by calculation or the like from the output current of the converter 20 at the time of steady lighting. Further, the second threshold value may be set based on the peak value of the coil current when the switching element Q1 was switched last time. In this case, for example, the second threshold value is set to 0.9 times the peak value of the coil current when the switching element Q1 was switched last time.

After that, since the coil current became smaller than that at the time of steady lighting, the on-time control unit 32 controls the on-time for a long time at time t3. After that, the peak value of the coil current increases with each switching due to the feedback control of the constant current control unit 30. At time t4, the coil current becomes the value at the time of steady lighting. Therefore, the LED light source unit 50 returns to the constant current control state even when the DC voltage is lowered.

In the present embodiment, the current maintenance unit 34 detects the output current of the converter 20, and when the output current is smaller than the second threshold value, the switching element even after the timing at which the on-time control unit 32 turns off the switching element Q1 has elapsed. Keep Q1 on. Further, the current maintenance unit 34 keeps the switching element Q1 on before the on-time control unit 32 prolongs the on-time by feedback control. That is, the current maintenance unit 34 maintains the ON state of the switching element Q1 even after the coil current reaches a value determined by the DC voltage, the ON time, and the inductance value of the inductor L1.

As a result, the coil current reaches the second threshold. Therefore, even when the DC voltage drops significantly, the peak value of the coil current becomes the second threshold value as shown by the solid line 62. Therefore, as shown by the solid line 63, the fluctuation of the LED current with respect to the fluctuation of the power supply voltage can be suppressed as compared with the case where the current maintenance unit 34 is not provided. Therefore, the flicker of the light source 51 can be suppressed.

Here, the capacitor C2 is connected to the first comparator OP1. Therefore, the output voltage of the first comparator OP1 is output later than the output voltage of the third comparator CP2. When the DC voltage drops, the signal for lengthening the on-time output by the on-time control unit 32 is output later than the signal for maintaining the on state of the switching element Q1 output by the current maintenance unit 34. As a result, it is possible to prevent the signal that the on-width control circuit 35 controls the switching element Q1 from competing with the signal that the on-control circuit 37 controls the switching element Q1.

From the above, in the present embodiment, it is possible to suppress fluctuations in the current flowing through the light source 51 as the power supply voltage rises and falls. Therefore, it is possible to suppress the flicker of the light source 51 and provide a lighting device that is less inconvenient for the user.

In this embodiment, the converter 20 is operated critically. Not limited to this, the converter 20 may be duty-controlled with a fixed frequency. The present embodiment can be applied as long as the control is such that the on-time of the switching element Q1 becomes shorter as the voltage of the DC power supply DC becomes higher. The converter 20 shown in FIG. 1 is an example. Any circuit that supplies power from the DC power supply to the light source 51 via the inductor L1 when the switching element Q1 is on and supplies the energy stored in the inductor L1 to the light source 51 when the switching element Q1 is off can be adopted as the converter 20.

100 lighting device, 10 lighting device, 20 converter, 32 on-time control unit, 33 current suppression unit, 34 current maintenance unit, 50 LED light source unit, 51 light source, DC DC power supply, Q1 switching element, OP1 first comparator, CP1 2nd comparator, CP2 3rd comparator

Claims (4)

A converter that is supplied with power from a DC power supply and turns on the light source by turning the switching element on and off.
An on-time control unit that detects the output current of the converter and controls the on-time of the switching element so as to cancel the difference between the output current and the target value.
When the output current is detected and the output current reaches the first threshold value equal to or higher than the target value, the on-time control unit turns off the switching element earlier than the timing when the switching element is turned off.
When the output current is detected and the output current is smaller than the second threshold value equal to or less than the target value, the switching element is maintained in the on state even after the timing at which the on-time control unit turns off the switching element has elapsed. Current maintenance unit and
A lighting device characterized by being provided with. The on-time control unit shortens the on-time when the output current is larger than the target value, and lengthens the on-time when the output current is smaller than the target value.
Prior to the on-time control unit shortening the on-time, the current suppression unit turns off the switching element.
The lighting device according to claim 1, wherein the current maintenance unit maintains a state in which the switching element is turned on prior to the on-time control unit prolonging the on-time. The on-time control unit includes a first comparator that compares a voltage corresponding to the output current with a voltage corresponding to the target value.
The current suppression unit includes a second comparator that compares a voltage corresponding to the output current with a voltage corresponding to the first threshold value.
The current maintenance unit includes a third comparator that compares the voltage corresponding to the output current with the voltage corresponding to the second threshold value.
The lighting device according to claim 1 or 2, wherein the output voltage of the first comparator is output later than the output voltage of the second comparator and the third comparator. The lighting device according to any one of claims 1 to 3,
With the light source
A lighting device characterized by being provided with.

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