JP2015043273A - Lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To smoothly change the amount of light down to a low dimming level.SOLUTION: A control part 2 includes an on-timing control part 20 for controlling on-timing of outputting a driving signal by a driver part 10, and an off-timing control part 21 for controlling off-timing for halting output of the driving signal by the driver part 10. The control part 2 also includes a burst control part 22 for switching an operation period Ton which allows timing control of the on-timing control part 20 and a halt period Toff for prohibiting the timing control, and increasing/decreasing the operation period Ton according to a dimming level. The control part 2 furthermore includes an adjustment part 23 for adjusting the off-timing controlled by the off-timing control part 21 according to the dimming level. Therefore, the adjustment part 23 adjusts an off-timing of a switching element Q1 according to the dimming level, and the amount of light can be changed smoothly down to a low dimming level.

Description

  The present invention relates to a lighting device for lighting a light source, and more particularly to a lighting device for a light source including a solid light emitting element such as a light emitting diode.

  In recent years, solid light-emitting elements such as light-emitting diodes and organic electroluminescence (EL) elements have become widespread as illumination light sources in place of incandescent lamps and fluorescent lamps. For example, Patent Document 1 discloses a lighting device (solid-state light source) that adjusts (light-controls) the amount of LED light according to a dimming signal provided from a dimmer as a lighting device that lights a light source composed of a light-emitting diode (LED). Lighting device) is disclosed.

  By the way, the dimming method of the LED includes a dimming method (hereinafter referred to as a DC dimming method) that changes the magnitude of a current that continuously flows through the LED, and an LED that is periodically turned on and off. In addition, there is a method of changing the ratio of the energization period (on-duty ratio) (hereinafter referred to as a burst dimming method). Further, as in the conventional example described in Patent Document 1, there are cases where the DC dimming method and the burst dimming method are combined.

JP 2012-204026 A

  By the way, a switching power supply circuit is usually used as a lighting circuit for lighting an LED. In the burst dimming method, the energization period in which the switching power supply circuit performs the switching operation is shortened (the number of times of performing the switching operation is decreased) as the dimming level is lowered. That is, the light output of the LED changes only stepwise (discretely) with respect to the change in the dimming level. The range of the dimming level (the dimming level resolution) that provides the same light output is limited by the ratio between the switching period and the burst period (the sum of the energization period and the non-energization period) of the switching power supply circuit. When the energization period is relatively long, that is, when the brightness indicated by the dimming level is relatively high, even if the light amount varies stepwise according to the dimming level, it will not be recognized by a person , Almost no problem.

  However, when the energization period is relatively short, that is, when the brightness indicated by the dimming level is relatively low, a step change in the amount of light is easily recognized by a person.

  The present invention has been made in view of the above problems, and an object thereof is to smoothly change the amount of light to a low dimming level.

  The lighting device of the present invention uses a light source unit having a solid light-emitting element as a light source as a load, converts power to DC power required for the light source unit, and converts the power conversion unit at predetermined burst periods. Control means for operating for an operation period not longer than the burst period, and for expanding and contracting a ratio of the operation period to the burst period according to a dimming level indicated by a dimming signal, And a switching power supply circuit comprising: an inductor connected in series with the light source unit; a switching element connected in series to the inductor; and a drive unit that outputs a drive signal to turn on the switching element; An on-timing control unit that controls an on-timing at which the driving unit outputs the driving signal, and the driving unit stops output of the driving signal. An off-timing control unit that controls the off-timing to be switched, an operation period that allows timing control of the on-timing control unit, and a stop period that prohibits the timing control, and the operation period is increased or decreased according to the dimming level A burst control unit that controls the off timing controlled by the off timing control unit according to the dimming level.

  In this lighting device, the off-timing control unit outputs the drive signal to the drive unit when the current flowing through the inductor reaches a predetermined threshold after the drive unit outputs the drive signal. It is configured to stop, and the adjustment unit preferably changes the off timing in the operation period by increasing or decreasing the threshold according to the dimming level.

  In this lighting device, it is preferable that the on-timing control unit causes the driving unit to output the driving signal when current stops flowing through the inductor after the driving unit stops outputting the driving signal. .

  In the lighting device of the present invention, the adjustment unit adjusts the OFF timing of the switching element in accordance with the dimming level, so that the amount of light can be smoothly changed to a low dimming level.

It is a circuit block diagram which shows embodiment of the lighting device which concerns on this invention. (a)-(d) is a waveform diagram of an on-trigger signal and inductor current in the same as above. It is explanatory drawing for demonstrating the relationship between the frequency | count of operation | movement and a light control level in the same as the above. It is explanatory drawing for demonstrating the relationship between the frequency | count of operation | movement and the light control level in a prior art example. It is a circuit block diagram which shows another structure same as the above. It is a circuit block diagram which shows another structure same as the above.

  Hereinafter, an embodiment in which the technical idea of the present invention is applied to a lighting device using a light emitting diode as a light source will be described in detail with reference to the drawings. However, the solid light-emitting element that can be lit by the lighting device according to the present invention is not limited to a light-emitting diode, and may be another solid-state light-emitting element such as an organic EL element.

  As shown in FIG. 1, the lighting device of this embodiment includes a power conversion unit 1 that converts (for example, step-down) an input voltage Vin input from a DC power source 5 into a voltage Vo that can be applied to the light source unit 3, and power conversion. The control part 2 which controls the part 1 is provided. Note that the DC power supply 5 is configured by, for example, a power conversion circuit (AC / DC converter) that converts AC power supplied from a commercial power system into DC power.

  The light source unit 3 is configured by connecting a series circuit of a plurality of light emitting diodes (not shown) or a series circuit of a plurality of light emitting diodes in parallel. The rated voltage of the light source unit 3 is a voltage obtained by multiplying the forward voltage of the light emitting diode by the number of light emitting diodes connected in series.

  The power conversion unit 1 is configured by a conventionally known non-insulated buck converter, and includes a switching element Q1 made of a field effect transistor, an inductor L1, a diode D1, a smoothing capacitor C1, a detection resistor R1, a driving unit 10, and the like. .

  The drain of the switching element Q1 is connected to the positive electrode of the DC power supply 5, and the cathode of the diode D1 and one end of the inductor L1 are connected to the source of the switching element Q1. The other end of the inductor L1 is connected to one end on the high potential side of the smoothing capacitor C1 and one end of the light source unit 3 (the anode of the light emitting diode). Further, the anode of the diode D1 is connected to the negative electrode of the DC power source 5, and is connected to one end on the low potential side of the smoothing capacitor C1 and the other end of the light source unit 3 (the cathode of the light emitting diode) via the detection resistor R1. ing. The drive unit 10 is controlled by the control unit 2 to output a drive signal composed of a rectangular wave signal and apply it to the gate of the switching element Q1. The switching element Q1 is turned on when the drive signal is output (becomes high level), and is turned off when the drive signal is stopped (becomes low level). However, the circuit configuration of the power conversion unit 1 is an example, and any other circuit configuration may be used as long as it is a switching power supply circuit capable of converting (stepping down or boosting) the input voltage Vin to the rated voltage of the light source unit 3. I do not care.

  The control unit 2 includes an on timing control unit 20, an off timing control unit 21, a burst control unit 22, an adjustment unit 23, a dimming signal input unit 24, and the like.

  The on-timing control unit 20 outputs an on-trigger signal composed of a rectangular wave signal having a constant cycle (switching cycle) T1 to the drive unit 10 (see FIGS. 2A to 2D). The drive unit 10 outputs a drive signal when the on trigger signal falls from a high level to a low level. The switching element Q1 is turned on when a drive signal is applied to the gate. When the switching element Q1 is turned on, a current (inductor current) flows through the path of the DC power source 5 → the switching element Q1 → the inductor L1 → the smoothing capacitor C1 and the light source unit 3 → the DC power source 5. The inductor current increases linearly from the time point when the switching element Q1 is turned on as shown in FIGS.

  The adjustment unit 23 includes an integrator including an operational amplifier 230, an input resistor R2, a feedback resistor R3, and a capacitor C2, and a bias power supply VR. An input resistor R2 is connected to the inverting input terminal of the operational amplifier 230, and a parallel circuit of a feedback resistor R3 and a capacitor C2 is connected between the inverting input terminal and the output terminal of the operational amplifier 230. The bias power supply VR applies a bias voltage to the non-inverting input terminal of the operational amplifier 230. Thus, the operational amplifier 230 changes the output voltage so that the value (voltage value) obtained by integrating the inductor current over time from the time when the switching element Q1 is turned on matches the voltage value (bias voltage value) of the bias power supply VR. .

  The off-timing control unit 21 measures the inductor current from the voltage across the detection resistor R1, and outputs the off-trigger signal composed of a rectangular wave signal to the drive unit 10 when the measured value of the inductor current reaches a predetermined threshold value If. . However, the threshold value If changes according to the output of the adjusting unit 23 (the output voltage of the operational amplifier 230).

  When the off trigger signal is input from the off timing control unit 21, the driving unit 10 stops the driving signal and turns off the switching element Q1. When the switching element Q1 is turned off, until the energy stored in the inductor L1 is completely discharged, the regenerative current is in the path of the inductor L1 → the smoothing capacitor C1 and the light source unit 3 → the detection resistor R1 → the diode D1 → the inductor L1. (Inductor current) continues to flow. Note that the regenerative current (inductor current) decreases linearly from the time point when the switching element Q1 is turned off, as shown in FIGS.

  The dimming signal input unit 24 receives a dimming signal from an external dimmer (not shown), reads the dimming level from the input dimming signal, and sends the read dimming level to the burst control unit 22. hand over. The dimming signal is a rectangular wave signal having a constant frequency (for example, 1 kHz), and the dimming level is represented by the on-duty ratio. For example, the on-duty ratio of the dimming signal is 0% at the rated lighting, and the on-duty ratio of the dimming signal is 90% at the dimming lower limit. That is, the dimming signal input unit 24 reads the dimming level by measuring the on-duty ratio of the dimming signal.

  The burst control unit 22 sets a burst period T (= Ton + Toff), which is a combination of the operation period Ton and the stop period Toff, to a time obtained by multiplying the switching period T1 by N (N is an integer of 2 or more). For example, FIG. 2 illustrates a case where N = 8. Then, the burst control unit 22 controls the on-timing control unit 20 to output an on-trigger signal at the switching period T1 during the operation period Ton and to stop outputting the on-trigger signal during the stop period Toff (see FIG. 2). .

  The burst control unit 22 measures the on-duty ratio X (0 ≦ X ≦ 90) of the dimming signal, and the on-duty ratio is a value (90 / N) obtained by dividing the dimming range (0% to 90%) into N equal parts. A value M (= N−X ÷ (90 / N)) obtained by subtracting a quotient obtained by dividing X (an integer quotient) from N is calculated.

  For example, when N = 8, the on-duty ratio X is 7 in the range of 7 × (90/8) ≦ X <8 × (90/8), and the on-duty ratio X is 6 × (90/8). In the range of ≦ X <7 × (90/8), M = 2. In the range where the on-duty ratio X is 5 × (90/8) ≦ X <6 × (90/8), M = 3, and the on-duty ratio X is 4 × (90/8) ≦ X <5 × ( In the range of 90/8), M = 4. Further, when the on-duty ratio X is in the range of 3 × (90/8) ≦ X <4 × (90/8), M = 5, and the on-duty ratio X is 2 × (90/8) ≦ X <3 × ( In the range of 90/8), M = 6. When the on-duty ratio X is in the range of 90/8 ≦ X <2 × (90/8), M = 7, and when the on-duty ratio X is in the range of 0 ≦ X <90/8, M = 8.

  Here, the value of the integer M corresponds to the number of operations of the switching element Q1 in the operation period Ton of the burst period T (the number of times the on trigger signal is output). That is, when the rated lighting is on, M = N, the stop period Toff becomes zero (see FIG. 2A), and the number of operations (number of outputs) as the dimming level decreases (the on-duty ratio X increases). The value of M decreases in steps (see FIG. 2). For example, when the on-duty ratio X of the dimming signal is 50%, since 90/8 = 11.25, 50 ÷ 11.25 = 4 remainder 5 and M = 8−4 = 4.

  Thus, the burst control unit 22 causes the on-timing control unit 20 to output the on-trigger signal a number of times equal to the number of operations M during the operation period Ton, and turns on to maintain the on-trigger signal at a high level during the stop period Toff. The timing control unit 20 is controlled.

  Here, as described above, the light output of the light source unit 3 is changed stepwise (discretely) as shown in FIG. 4 simply by increasing or decreasing the number of operations M corresponding to the dimming level (on-duty ratio X). Only so-called step dimming can be realized.

  Therefore, the burst control unit 22 increases or decreases the bias voltage of the bias power supply VR of the adjustment unit 23 according to the remainder (residue) when the on-duty ratio X is divided by a value obtained by dividing the dimming range into N equal parts. . When the bias voltage increases or decreases, the threshold value of the off-timing control unit 21 increases or decreases, and the off-timing of the switching element Q1 becomes late or early. If the off timing of the switching element Q1 is delayed, the average value Im of the load current (current flowing through the light source unit 3) in one cycle of the burst cycle T increases. On the other hand, if the switching element Q1 is turned off earlier, the average value Im of the load current in one period of the burst period T decreases. That is, even if the number of operations M (operation period Ton) for each burst cycle T is the same, the average value Im of the load current can be made variable by adjusting the OFF timing of the switching element Q1, and the light output of the light source unit 3 can be changed. Fine adjustment can be made (see FIG. 3).

  Therefore, in the present embodiment, so-called continuous dimming in which the light output of the light source unit 3 is changed substantially linearly (continuously) with respect to the dimming level as indicated by a solid line α in FIG. 3 can be realized. In addition, the rectangle in FIG. 3 has shown the range of the light control level which can be adjusted by the OFF timing adjustment of the switching element Q1 for every frequency | count M of each operation | movement.

  As described above, the lighting device according to the present embodiment includes the power conversion unit (power conversion unit) 1 that converts the input power into the DC power necessary for the light source unit 3 with the light source unit 3 having a solid light emitting element as a light source as a load. Prepare. Further, the lighting device operates the power conversion unit 1 for each predetermined burst period T for an operation period Ton that is not longer than the burst period T, and for the burst period T according to the dimming level indicated by the dimming signal. And a control means (control unit) 2 that expands and contracts the ratio of the operation period Ton. The power conversion means 1 includes a inductor L1 connected in series with the light source unit 3, a switching element Q1 connected in series with the inductor L1, and a drive unit 10 that outputs a drive signal and turns on the switching element Q1. It consists of a power circuit. The control unit 2 includes an on-timing control unit 20 that controls an on-timing when the driving unit 10 outputs a driving signal, and an off-timing control unit 21 that controls an off-timing at which the driving unit 10 stops outputting the driving signal. . Further, the control means 2 switches the operation period Ton for permitting the timing control of the on-timing control unit 20 and the stop period Toff for prohibiting the timing control, and increases or decreases the operation period Ton according to the dimming level. Have Furthermore, the control means 2 includes an adjusting unit 23 that adjusts the off timing controlled by the off timing control unit 22 in accordance with the dimming level.

  Thus, according to the present embodiment, since the OFF timing of the switching element Q1 is adjusted according to the dimming level, the amount of light can be changed smoothly to a low dimming level. That is, in the conventional example, the dimming lower limit is when the number of operations M per burst period T is one, but in this embodiment, the switching element Q1 is turned off when the number of operations M is one. The deeper dimming becomes possible by accelerating.

  In addition, the off timing adjustment (threshold value adjustment) can be controlled by an analog value, and the load current can be controlled in accordance with the resolution of the bias voltage of the bias power supply VR. For example, when the burst control unit 22 is configured by a microcomputer, the light output of the light source unit 3 can be changed (dimmed) almost continuously on the order of N ≧ 1000 using the PWM output of the microcomputer. .

  Further, as in this embodiment, the off-timing control unit 22 outputs a drive signal to the drive unit 10 when the current If flowing in the inductor L1 reaches a predetermined threshold after the drive unit 10 outputs the drive signal. The output is preferably stopped. Furthermore, it is preferable that the adjusting unit 23 changes the off timing in the operation period Ton by increasing or decreasing the threshold value according to the dimming level.

  In this embodiment, burst dimming is performed over the entire dimming range. However, in the dimming range from rated lighting to a predetermined dimming level, only dimming by off-timing adjustment is performed, and predetermined dimming is performed. You may make it perform burst light control in the range from a level to the light control minimum.

  Further, in the power conversion unit 1 in the present embodiment, the switching element Q1 is connected to the high potential side (high side) with respect to the DC power supply 5, but the switching element Q1 is connected to the DC power supply 5 as shown in FIG. The circuit configuration may be such that Q1 is connected to the low potential side (low side).

  In the meantime, in the embodiment shown in FIGS. 1 and 5, so-called discontinuous control is performed in which the on-timing controller 20 switches the switching element Q1 at a constant period T1. However, the on-timing control unit 20 performs so-called critical control that causes the drive unit 10 to output a drive signal at the time when the current stops flowing to the inductor L1 (zero cross) after the drive unit 10 stops outputting the drive signal. You can go.

  FIG. 6 shows a circuit configuration when the on-timing control unit 20 performs critical control. Compared to the circuit configuration shown in FIG. 1, a detection winding is provided in the power conversion unit 1 in order to detect a zero crossing of the inductor current. Line L2 is provided. The detection winding L2 is magnetically coupled to the inductor L1, one end is connected to the negative electrode of the DC power supply 5, and the other end is connected to the on-timing control unit 20 via the diode D2. The on-timing control unit 20 detects the zero cross by reversing the direction of the voltage induced in the detection winding L2 by the inductor current, and outputs an on-trigger signal when the zero cross is detected.

  Thus, even when the on-timing control unit 20 performs critical control, as in the case of discontinuous control, the adjusting unit 23 increases or decreases the threshold according to the dimming level, and the off-timing in the operation period Ton. Can be changed smoothly to a low dimming level.

1 Power converter (power conversion means)
2 Control unit (control means)
3 Light source
10 Drive unit
20 On-timing controller
21 Off-timing controller
22 Burst controller
23 Adjustment section
L1 inductor
Q1 Switching element

Claims (3)

Power conversion means for converting input power into direct-current power required for the light source section using a light source section having a solid light-emitting element as a light source, and the power conversion means not longer than the burst period every predetermined burst period Control means for operating only during the operation period and extending or contracting the ratio of the operation period to the burst period according to the dimming level indicated by the dimming signal;
The power conversion means includes an inductor connected in series with the light source unit, a switching element connected in series with the inductor, and a drive unit that outputs a drive signal and turns on the switching element. Become
The control means includes an on-timing control unit that controls on-timing at which the driving unit outputs the driving signal, an off-timing control unit that controls off-timing at which the driving unit stops outputting the driving signal, and A burst control unit that switches between an operation period that permits timing control of the on-timing control unit and a stop period that prohibits the timing control, and that increases or decreases the operation period according to the dimming level, and according to the dimming level A lighting device comprising: an adjustment unit that adjusts the off timing controlled by the off timing control unit.   The off-timing control unit is configured to cause the driving unit to stop outputting the driving signal when the current flowing through the inductor reaches a predetermined threshold after the driving unit outputs the driving signal. The lighting device according to claim 1, wherein the adjustment unit changes the off timing in the operation period by increasing or decreasing the threshold value according to the dimming level.   2. The on-timing control unit causes the driving unit to output the driving signal when current stops flowing through the inductor after the driving unit stops outputting the driving signal. Or the lighting device of 2.

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