JP2012004054A - Lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress power loss in a lighting device.SOLUTION: There is provided a lighting device in which: a voltage from a power supply terminal is stepped down by driving of a first switching converter; the voltage from the power supply terminal is stepped down by driving of a second switching converter; the first switching converter and a first light source are connected in series; the second switching converter and a second light source are connected in series; the first switching converter and the second switching converter are connected in parallel with the power supply terminal; a signal detecting unit measures power, voltage, or a summation of current ripple supplied to the first switching converter and the second switching converter; a switching signal generating unit generates a switching signal based on a measurement result of the signal detecting unit such that the ripple becomes smaller; and the first switching converter and the second switching converter are driven by an output of the switching signal from the switching signal generating unit.

Description

  The present invention relates to a lighting device.

  In general, a lighting device is required to have no flicker, be bright, and have high efficiency (ratio of light emission to input power). In order to realize this, the illumination device is composed of a light source and a power supply circuit (or drive circuit). Examples of the light source include LED (light emitting diode) and OLED (organic LED). LEDs, OLEDs, and the like have features such as high efficiency, small size, light weight, and long life. In order to cause the LED to emit light, a power supply that satisfies a forward voltage of about 3 volts (in the case of a white LED) is required. The light emission characteristics (luminance, chromaticity, etc.) of the LED greatly depend on the current value. Therefore, PWM (pulse width modulation) is widely used for the LED, which is driven with a pulse waveform that periodically turns on and off while keeping the current at the time of on constant. In this method, the luminance can be controlled by an on / off ratio (duty).

  By the way, the commercial power supply uses an alternating current of 100 volts (in the case of Japan). Therefore, in order to drive an LED using a commercial AC power supply, a rectifier that converts AC to DC and a step-down voltage that converts voltage are indispensable. Further, as the DC power source, there are a DC power generator such as a rectifier of an AC power source, a secondary battery and a solar battery. When each voltage is different, a voltage down converter is required. If the input is alternating current, a transformer can be considered as a step-down converter. Moreover, there are a series regulator, a switching regulator, and the like as a device that actively transforms using a semiconductor element. Furthermore, switching regulators include a method using a capacitor and a method using an inductor. In the method using an inductor, a voltage is converted by turning on and off the switching circuit at a sufficiently high frequency using a circuit combining a switching circuit (such as a MOS FET) and an inductor (coil). Patent Document 1 and Patent Document 2 show the configuration of a switching regulator when the load connected to the output side is an LED.

  Each of the PWM circuit and the switching converter includes a switching circuit that repeatedly turns on and off the voltage or current supplied from the power supply. A configuration that simultaneously realizes voltage conversion and brightness control by integrating a PWM circuit and a switching converter using this switching circuit is also used. A lighting system is configured by connecting a power supply system that supplies power to the input end of the switching converter and connecting a load to the output end. Since the switching converter includes a switching circuit that turns on and off the power supply, the ripple is generated in principle.

  Ripple causes noise that affects other devices. The noise due to ripples is transmitted to other devices, resulting in power loss. In order to reduce the influence of noise on other devices, a method of removing noise using a noise filter, a method of increasing a switching frequency, a method of randomly changing a switching frequency, and the like are known.

  As a method for suppressing the occurrence of ripple (noise) itself, Non-Patent Document 1 discloses a configuration of a switching converter using a multiphase switching signal. Non-Patent Document 1 discloses a technique for reducing the total ripple at the output end by connecting a plurality of step-down converters in parallel and shifting the phase of each switching signal. In particular, Non-Patent Document 1 discloses that when the polyphase switching signals are arranged without gaps in the time direction, the total ripple on the output side is reduced. In Non-Patent Document 1, a state where a plurality of signals are out of phase is called a polyphase. Polyphase and multiphase are synonyms for polyphase. Ripple is a term meaning minute vibration of a signal. In the following description, ripples and noise may be mixed without notice.

JP 2009-200053 A Special table 2008-537459 gazette

Linear Technology, Application Note, AN77, “High Efficiency, High Density, PolyPhase Converters for High Current Applications”

  As a driving circuit of the lighting device, there are a switching converter that performs voltage conversion of a power supply system and a PWM circuit that controls brightness, and any of them generates ripple (noise) by turning on and off the power supply.

  If such a drive circuit is viewed from the power supply system, it is a cause of noise generated by repeatedly turning on and off the power supply. Noise propagates in the air via the power supply system or as electromagnetic waves, and adversely affects other devices. Also, power loss increases due to generation and transmission of unnecessary noise.

  There is a noise filter as a conventional technique for reducing noise. However, when a noise filter is used, power is lost because a frequency component that causes noise is consumed by an internal resistor such as a capacitor. Further, increasing the switching frequency or changing it at random has the effect of changing the frequency component of noise, but does not have the effect of suppressing noise generation itself. In addition, since the gate capacitance of a MOSFET widely used as a switching circuit is large, when the switching frequency is increased, the power for driving the gate increases and the power consumption increases.

  The polyphase switching technology for suppressing noise generation disclosed in Non-Patent Document 1 focuses only on the output side, and does not consider noise transmitted to the power supply system on the input side. In addition, it is difficult to arrange a multiphase switching signal at the output terminal as a stabilized power source without a gap in the time direction for the following reason.

  First, according to the principle of the switching converter, the output voltage is determined by the component constant (inductance) of the inductor and the duty of the switching signal. On the other hand, arranging multi-phase switching signals without gaps means that the total duty of each switching signal is adjusted to 1 (100%). Setting the duty of the switching signal so that the above is compatible means fixing the output voltage determined by the inductance and the duty. However, there are many fluctuation factors, variations, nonlinear characteristics, etc. in the components of the power supply circuit. Therefore, even if adjustment is performed in the initial state, the output voltage may vary depending on characteristics such as temperature and life. Furthermore, the characteristics of the power supply system connected to the input terminal are often unknown in advance. The output voltage (or current) changes due to these characteristic fluctuations. In order to stabilize the power supply, it is necessary to control the duty of the switching signal based on the feedback signal. In this case, the duty is deviated from the initial setting. Furthermore, the response of the switching circuit may not be fast enough. After all, it is difficult to achieve both stabilization of the voltage (current) at the output end and arrangement of the multiphase switching signals without gaps in the time direction.

  As described above, the driving circuit for the light source including the switching circuit generates noise and causes power loss. Since the lighting device may perform continuous operation for a long period of time, even a slight power loss increases as it accumulates. From the viewpoint of improving the efficiency of the lighting device, noise reduction is an important issue.

  An object of the present invention is to suppress power loss in a lighting device.

  In order to solve the above problems, the present invention is as follows.

  (1) a first switching converter and a second switching converter; a first light source connected to an output terminal of the first switching converter and driven by a drive signal from the first switching converter; A second light source connected to an output terminal of the second switching converter and driven by a drive signal from the second switching converter; an input terminal of the first switching converter; and an input terminal of the second switching converter A connected power supply terminal; an input end of the first switching converter; a signal detection unit disposed between the input end of the second switching converter and the power supply terminal; and a switching connected to the signal detection unit A signal generator, and driving the first switching converter The voltage from the source terminal is stepped down, the voltage from the power supply terminal is stepped down by driving the second switching converter, the first switching converter and the first light source are connected in series, and the second switching converter The switching converter and the second light source are connected in series, the first switching converter and the second switching converter are connected in parallel to the power supply terminal, and the signal detection unit is the first switching converter and the Measuring the ripple of power, voltage or current supplied to the second switching converter, the switching signal generating unit generates a switching signal based on the measurement result of the signal detecting unit so as to reduce the ripple, According to the output of the switching signal from the switching signal generator. Lighting apparatus wherein the first switching converter and the second switching converter characterized in that it is driven.

  (2) In the above (1), the first step-down circuit includes a first switching unit, the second step-down circuit includes a second switching unit, and the switching signal generation unit includes: A lighting device that controls the phase and duty of the first switching unit and the second switching unit.

  (3) In the above (1), the signal detection unit measures ripples using dispersion.

  (4) In the above (1), the lighting device includes a storage unit, and the storage unit temporarily stores a measurement result obtained by the signal detection unit.

  (5) In the above (1), the signal detector measures the ripple based on a program procedure by a microprocessor.

  (6) In the above (1), a third switching converter is disposed between the signal detection unit and the first switching converter and the second switching converter, and the power supply terminal is driven by the third switching converter. The lighting device is characterized in that the voltage from is reduced.

  (7) In the above (1), the first switching converter includes a first switching unit, a first inductor, and a first diode. When the first switching unit is on, the first switching converter When the current passing through the inductor gradually increases and the first switching unit is off, the current passing through the first inductor gradually increases, and the second switching converter includes the second switching unit, A second inductor and a second diode; when the second switching unit is on, a current passing through the second inductor gradually increases; and when the second switching unit is off, the second switching unit A lighting device characterized in that a current passing through the second inductor gradually increases.

  According to the present invention, power loss in the light source illumination device can be suppressed. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

The figure which shows the structure of the illuminating device of one Example of this invention. The figure which shows the example of a connection of a light source. The figure which shows the structural example of a switching converter. The figure which shows the structure of one Example of this invention. The figure which shows operation | movement of one Example of this invention. The figure which shows operation | movement of one Example of this invention. The figure which shows operation | movement of one Example of this invention. The figure which shows the characteristic of a ripple value. The figure which shows the effect of one Example of this invention. The figure which shows the effect of one Example of this invention. The figure which shows the structure of one Example of this invention. The figure which shows the structure of the wide area illumination of one Example of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following examples show specific examples of the contents of the present invention, and the present invention is not limited to these examples, but by those skilled in the art within the scope of the technical idea disclosed in this specification. Various changes and modifications are possible. Further, in all the drawings for explaining the embodiments, the same reference numerals are given to those having the same function, and repeated explanation thereof is omitted.

  FIG. 1 shows a basic configuration example of a lighting device. Here, the lighting device 10 includes a power supply terminal 100, a switching converter 101, and a light source 103. As the light source 103, an LED (light emitting diode), an OLED (organic LED), or the like can be used. The switching converter 101 outputs a pulse obtained by turning on and off the power supply system as a drive signal 102 to drive the light source 103. Here, the electric power system refers to equipment such as an incoming line from the outside, an indoor power supply wiring, a distribution board, or an outlet. The input terminal of the switching converter 101 is connected to the power supply terminal 100, and the power supply terminal 100 is connected to the power supply system. A 100 volt AC or 48 volt direct current called a commercial power source is used as the power supply system. If the power supply system is alternating current, it is used after being converted to direct current using a rectifier, and if it is direct current, it is used as it is.

  The brightness of light emitted from the light source 103 is determined by the voltage, current, waveform, etc. of the drive signal 102. Since the voltage and current are in a non-linear dependency, the brightness is determined by the duty (ratio between the period and the on time) with the drive signal 102 as an on / off binary signal.

  The lighting device 10 is required to have sufficient brightness so that no flicker is felt. It is known that the temporal change in brightness that can be perceived as human visual characteristics is about 100 Hz. Therefore, flickering can be prevented by stabilizing the frequency component up to 1000 Hz as the lighting device 10. For example, if the switching frequency of the switching converter 101 is 100 kHz and the PWM period is 1 kHz, 100 (= 100 kHz / 1 kHz) switching frequencies are included in the PWM period. By turning on and off in synchronism with the 100 switching frequencies, pulses from a minimum of 0 to a maximum of 100 can be output. If the light source 103 is driven with this output, the brightness can be changed from 0 to 100.

  The efficiency of the illumination device 10 is calculated by the ratio (for example, lum / W) between the power consumption (for example, watt W) and the light emission luminance (for example, the total luminous flux lum). The efficiency of the lighting device 10 is determined by a combination of the light emission efficiency of the light source 103 and the conversion efficiency of the switching converter 101. When the switching converter 101 is used as a step-down circuit, ripple (noise) is generated by switching of the switching converter 101 and is transmitted to the input side of the switching converter 101 and the output side of the switching converter 101. In general, when the switching converter 101 is used as a stabilized power supply, output stability is important, and therefore a filter circuit is used to remove ripples (noise).

  In contrast, in this embodiment, the light source 103 is connected to the output terminal of the switching converter 101. If the frequency of the switching converter 101 is not visually detected, it is not necessary to remove the ripple, so that the average brightness is reflected on the light source 103 at the output end of the switching converter 101.

  In this way, by allowing ripples at the output end of the switching converter 101, a filter circuit becomes unnecessary, and the degree of freedom in circuit configuration increases. In this embodiment, the circuit is configured to suppress the occurrence of ripple at the input end of the switching converter 101.

  FIG. 2 illustrates a circuit configuration using an LED as the light source 103. Since an LED has a non-linear characteristic relationship between voltage and current as in a general diode, it is used in combination with the switching converter 101. In order to emit white light as an illumination device, a red LED, a blue LED, and a green LED are used as LEDs, and a YAG phosphor is used as a blue LED. In order to obtain a specific color, the LEDs described above may be used individually as the light source 103. In the case of a white LED, the forward voltage at which current begins to flow is approximately 3 volts to 4 volts. When the amount of light is insufficient with one LED as the illumination device 10, a plurality of LEDs are combined in series or in parallel to ensure brightness. The power supply method varies depending on the combination of LEDs. For example, if 30 white LEDs are connected in series, the total forward voltage is close to 100 volts, so there is no need to convert the voltage by simply rectifying the commercial power supply. In this method, since the circuit is formed so as to satisfy the relationship of power supply voltage = forward voltage × number of LEDs, the number of LEDs is limited. Therefore, it becomes difficult to adjust the required brightness by the number of LEDs. In addition, one failure may interrupt the entire operation, and a high voltage may be applied to the failure location.

  On the other hand, consider a configuration in which LEDs are connected in parallel (series and parallel may be mixed). First, a single LED circuit in which one or a plurality of LEDs are connected in series is made. Then, the LED circuits are connected in parallel to form the light source 103. In this case, the brightness can be easily adjusted by the number of LEDs. In addition, even if one of the LEDs fails, another LED circuit that does not include the failed LED can continue to emit light. However, the supplied voltage must be converted according to the number of LEDs. For example, assuming that 30 LEDs are used to ensure brightness, if three LED circuits connecting 10 LEDs in series are arranged in parallel, the total forward voltage is about 30 volts. In this case, if a commercial power supply (100 volts) is used, the switching converter 101 that performs voltage conversion is required. In order to stabilize the current flowing through the LED circuit, it is better not to provide one switching converter 101 for the entire light source 103 but to provide the switching converter 101 in series with each LED circuit.

  When the LED circuits are connected in parallel, the luminance control controls the luminance by combining a plurality of LEDs. When the individual switching frequency is 100 kHz and the PWM frequency is 1 kHz, the number of luminance steps is 100. The number of brightness stages of the entire light source 103 is determined by the combination of the brightness of each LED circuit.

  In the present embodiment, it is desirable to connect the light source 103 (LED circuit in the above example) in parallel as the lighting device 10 from the viewpoint of brightness adjustment and countermeasures against failure. Thus, when LED circuits are connected in parallel, the switching converter 101 is provided in each LED circuit in order to stabilize the voltage and current of each LED circuit. From the viewpoint of the power supply terminal 100 on the input side of the switching converter 101, this means that a plurality of switching converters 101 are connected to the light source 103 as loads. Therefore, it is desirable that the ripple (noise) generated in the switching converter 101 is low.

  FIG. 3 is a diagram illustrating a basic configuration of a switching converter 101 using a switching regulator system. The switching converter 101 includes a switching signal generation unit 104, a switching unit 106, an inductor 107, and a return diode 108. Driving the switching unit 106 using the switching signal 105 reduces the voltage from the power supply terminal 100. When the switching converter 101 is synchronized with the switching signal 105, a change in current (current ripple) occurs.

  When the switching unit 106 is on, the input current from the power supply terminal 100 flows through the inductor 107. At this time, since a voltage is applied to the diode 108 in the reverse direction, no current flows.

  Next, when the switching unit 106 is off, there is no input current from the power supply terminal 100, but the magnetic field in the inductor 107 gradually decreases, and current tends to flow. At this time, the diode 108 becomes a path for current generated in the inductor 107.

  That is, when the switching unit 106 is on, the input current from the power supply terminal 100 becomes the output current, and when the switching unit 106 is off, the current generated by the inductor 107 becomes the output current, and the current is output without interruption. The An increase amount ΔIon and a decrease amount ΔIoff of the current within the switching period appearing in the drive signal 102 on the output side of the switching converter 101 are expressed by the following equations. Here, Vi is an input voltage, Vo is an output voltage, Ton is an on time, Toff is an off time, and L is an inductance. In a steady state, the output voltage Vo is determined by an on time and an off time (duty). The frequency component of the ripple depends on the frequency and duty of the switching signal 105. When the load on the output side of the switching converter 101 is the light source 103, if the switching frequency is sufficiently high, a change in brightness due to ripple is hardly visually detected. On the other hand, a ripple synchronized with the switching frequency of the switching converter is transmitted to the power supply terminal 100 on the input side of the switching converter 101.

  Since the circuit constant (inductance, etc.) of the switching converter 101 is determined by the components used, the operation is controlled by the switching signal 105. In the steady state, the amount of increase in current ripple and the amount of decrease in current ripple have the same value, and the output current is stabilized based on the duty of the switching signal 105. For example, in a stable state with a duty of 50%, the amount of increase in current ripple and the amount of decrease in current ripple are the same value, and the output voltage is half the input voltage. On the other hand, in the unsteady state from the initial state to the steady state, the increase amount of the current ripple is different from the decrease amount of the current ripple.

  If the output current is Ia in the initial state, the increase amount of the current ripple becomes larger than the decrease amount of the current ripple, the output current is gradually accumulated every switching cycle, and the output voltage increases. If the output current further increases, the output voltage increases, and the amount of decrease in current ripple is greater than the amount of increase in current ripple. By repeating the above, the output current is stabilized at Ib by gradually shifting from the initial state to the steady state.

  When the switching signal 105 is turned on / off at intervals of a plurality of switching cycles, the transition from the initial state to the steady state and the transition from the steady state to the stop state are repeated. Here, the stop means that no operation is performed. This repetitive transition applies to, for example, the above-described PWM cycle on / off operation. Therefore, the waveform of the output signal obtained by combining the switching converter 101 and the PWM becomes a binary level pulse series subjected to amplitude modulation. The amplitude of the output signal varies with the transition time setting. The average output can be controlled not only by the PWM duty but also by the PWM cycle (on / off time).

  FIG. 4 shows a configuration example of the illumination device 10 of the present embodiment. The lighting device 10 is based on the switching converter 101, the light source 103 connected to the output terminal of the switching converter 101, the signal detection unit 200 placed between the power supply terminal 100 and the switching converter 101, and the detection signal of the signal detection unit 200. The switching signal generation unit 104 that generates the switching signal 105 of the switching unit 106 is provided. The switching signal generation unit 104 is connected to the signal detection unit 200. A plurality of switching converters 101 are connected in parallel to the power supply terminal 100. The signal detection unit 200 measures power, voltage, current, and the like supplied from the power supply terminal 100 to the plurality of switching converters 101. The switching signal generation unit 104 generates the switching signal 105 based on the detection result of the signal detection unit 200.

  Here, it is assumed that two switching converters 101 are connected in parallel, and the phase of each switching signal 105 is shifted by 180 degrees. Each switching converter 101 performs voltage conversion in synchronization with the switching signal 105 and drives the light source 103 connected to the output terminal of each switching converter 101. On the other hand, the input terminals of the respective switching converters 101 are commonly connected to the power supply terminal 100 and are supplied with power from the power supply terminal 100.

  At the output end of each switching converter 101, the ripple generated by the switching operation is converted into the brightness of each light source 103. On the other hand, both ripples are added at the input ends of the respective switching converters 101. If the ripple at the input end has the same waveform as the switching signal 105, the duty of the switching signal 105 may be set so that the ripple at the input end is minimized (smaller) (smaller). In principle, if the phase of one switching signal 105 is shifted by 180 degrees with respect to the phase of one switching signal 105 and each switching signal 105 is set to 50% duty, the power supply in each switching converter 101 is turned on / off. Since the timing complements, the ripple should be cancelled. However, in an actual circuit configuration, the ripple is not a binary signal but an analog-distorted waveform, so that the two switching signals 105 with a 50% duty that are 180 degrees out of phase cannot always minimize the ripple. .

  Therefore, a signal detection unit 200 that detects ripples is arranged at a connection point between the power supply terminal 100 at the input end of the switching converter 101 and the switching converter 101. Signals detected by the signal detection unit 200 are power, voltage, current, and the like. And the magnitude | size of a ripple is calculated from the detection signal which the signal detection part 200 detected, and it outputs to each switching signal generation part 104 as a ripple value. Based on the signal detection result, the switching signal generation unit 104 generates the switching signal 105 so that the ripple at the input end is minimized.

  The switching signal generation unit 104 controls the frequency, phase, and duty of each switching converter 101. However, since frequency control is not always necessary, the following description will be made on the assumption of phase and duty control.

  There are several methods for quantifying signal fluctuations. In this embodiment, variance or the sum of absolute values is used as a quantification method for ripples. The variance is obtained by accumulating the square of (signal value−average value) for sample points within a certain period. By adjusting the parameters (horizontal axis) so that the variance (vertical axis) becomes a concave curve, a parameter that minimizes ripple can be found.

  Further, in order to accumulate the amplitude value of the signal, the sum of the absolute values of the signal may be used. The sum is obtained by Σ | signal value−average value | for the sample points within a certain period. The symbol || is an operator for calculating an absolute value. Even when the sum of absolute values is used, a parameter that minimizes ripple can be found. The dispersion requires a circuit for squaring (for example, a multiplication circuit), but has characteristics suitable for theoretical analysis. The absolute value is not suitable for theoretical analysis because it does not use four arithmetic operations, but it is simple because the absolute value can be obtained simply by changing the sign by the arithmetic circuit.

  In this embodiment, the variance of the signal detected at the input end of the switching converter 101 is calculated using the duty as a parameter. Then, the duty is calculated so as to minimize the variance (that is, ripple). Although the minimum ripple value is calculated based on a mathematical principle, this embodiment allows a practical resolution error. By setting the range of the above-mentioned fixed period for calculating the variance of the signal that changes with time as the switching period or a multiple of the switching period, it is possible to repeatedly detect a change in ripple.

  The ripple operation at the input end of the switching converter 101 will be described with reference to FIG. In the case of a single circuit configuration as shown in FIG. 5A, a switching signal 105 that is periodically turned on / off is prepared, and a current supplied from a power source is turned on / off by the switching unit 106. As a result, the current passing through the inductor 107 gradually increases when the switch is on, and gradually decreases when the switch is off. That is, it becomes a triangular wave in which the current input from the power supply system (current flowing through the inductor 107 when turned on) gradually increases. However, since the actual circuit operates in an analog manner, the current input from the power supply system has a distorted waveform. And the repetition of the current waveform synchronized with the switching cycle becomes a ripple.

  In this embodiment, as shown in FIG. 5 (2) or FIG. 5 (3), the plurality of switching converters 101 are operated with the phases shifted. At this time, the output waveform and the current waveform input from the power supply system are overlapped with a phase shift. In principle, in the case of two circuits, if a binary signal with a duty of 50% in which the phases of the two switching converters 101 are shifted by 180 degrees, the binary signal input or output by each circuit has a time gap. Ripple is suppressed because it is smaller and overlapped. Further, in the case of three circuits, if the binary signals having a duty of 33.3% in which the phases of the three switching converters 101 are shifted by 120 degrees are used, the binary signals input or output by each circuit have a small temporal gap. Ripple is suppressed by overlapping. However, since the actual circuit creates the distortion as described above, it is not possible to know the conditions for suppressing or starting the ripple in advance. Therefore, an input current waveform (ripple) obtained by summing the current waveforms of the plurality of switching converters 101 is measured at a connection point between the power supply and the plurality of switching converters 101.

  FIG. 6 shows the relationship between ripple and duty. Here, for simplicity, the duty values of the plurality of switching converters 101 are made common. Accordingly, it is not necessary to prepare a large number of setting circuits as compared with the case where the respective duty values are set independently, and the circuit can be made small and simple. Further, the duty of the plurality of switching converters 101 may be set separately. When the component constants of the plurality of switching converters 101 are different and the relationship between the duty and the ripple waveform is not constant, it is effective to set the duties of the plurality of switching converters 101 separately.

  If the ripple is calculated as variance and placed on the vertical axis and the duty is taken on the horizontal axis, the relationship between the two is represented by a concave curve having a minimum value. That is, when the duty of two sets of binary signals whose phases are shifted by 180 degrees is shifted from 0 to 100%, the ripple (dispersion) is maximum when the duty is 0% and 100%, and is minimum when the duty is 50%. (0 in this example). Regardless of whether the duty is moved from the minimum ripple point to the larger or smaller duty, the ripple increases. At the initial stage, the duty at which the ripple is minimized is unknown. Therefore, from the change in the magnitude of the ripple when the duty of the switching signal 105 is minutely changed, the minimum point of the ripple is obtained by using a search type procedure (corresponding to the iterative search method used in the field of mathematics). Can be found. Since the method for calculating the ripple value and how to find the minimum point of the ripple are not unique, switching may be performed as appropriate during the procedure. The present embodiment includes a procedure for finding the minimum point of ripple, and transmits the duty to the switching signal generation unit 104 so as to minimize the ripple value, thereby driving the switching unit 106. In this way, the ripple reduction effect can be stably obtained even if there are characteristic changes due to variations, variations, nonlinear characteristics, temperature, life, etc. of the component parts. In addition, noise transmitted to other devices via the power supply system can be reduced.

  As is well known, an error is included in the result obtained by numerical calculation. For example, in order to keep the error small by numerical calculation such as Newton-Raphson method, a method of reducing the step width of the variable of the iteration operation or increasing the number of iterations is adopted. On the other hand, these methods increase calculation load (in other words, calculation time). Therefore, as a practical usage of numerical calculation, an appropriate condition such as the number of repetitions is set, and the calculation is often interrupted when the condition is satisfied. The result of the search for the minimum ripple point described above also has an error due to numerical calculation. Further, in digital signal processing, there are quantization errors and errors due to temporal discretization. The minimum in the present embodiment allows a range of numerical values due to an error.

  Shifting the phases of the plurality of switching converters 101 to operate cyclically means that the switching signal 105 is generated cyclically. There is one round of waiting time before the ripple detection result is reflected in the generation of the switching signal 105. For example, when the two switching converters 101 are operated alternately to reduce ripple, the switching signal 105 is generated alternately. That is, one switching converter 101 waits for the operation of the other switching converter 101. When three switching converters 101 are combined, the operation of the two switching converters 101 is awaited before returning to their own order. The waiting time of the switching converter 101 increases as the number of the switching converters 101 increases.

  Therefore, in this embodiment, a storage unit (memory or register) that temporarily stores a ripple detection result during a period from when a ripple is detected to when the switching signal 105 is generated is provided. The procedures such as ripple detection, temporary storage of detection results, reading, and generation of the switching signal 105 are executed based on some clock. In addition, in order to calculate the moving average of the ripple detection signal, a circuit for storing a signal for a certain period for calculating the moving average value may be provided. A moving average is obtained by moving the time window of a certain period and outputting an average value of signals included in the period. Thereby, the noise which generate | occur | produces with a ripple detection signal can be suppressed.

  FIGS. 7A and 7B show an example in which the ripple reduction effect is calculated by a semiconductor simulator (SPICE). FIG. 7A shows the waveform of the input current when two switching converters 101 are connected in parallel and operated in common with the power supply terminal 100 on the input side, based on this embodiment. FIG. 7B shows a waveform of the input current when the single switching converter 101 is operated so that the equivalent input current flows. The vertical axis represents current (mA), and the horizontal axis represents time (ms).

  In FIG. 7 (1) and FIG. 7 (2), three waveforms are plotted for three types of duty (50%, 60%, 72%). The unit% indicates the ratio of the time during which the input current flows in the periodic period. 0% means an off state, and 100% means an on state. The waveform in the figure shows a state of transition from the initial state at time 0 to the stable state by repeating the switching operation. It can be seen that the waveform in the figure changes with the duty of the switching signal 105 and the amplitude of the ripple changes.

  As can be seen from FIGS. 7 (1) and 7 (2), the ripple amplitude in FIG. 7 (1) is about half of the ripple amplitude in FIG. 7 (2). However, it is difficult to determine in advance the conditions for reducing the ripple amplitude at the design stage. This is because the waveform shape of a practical circuit changes due to variations in duty setting values and component characteristics.

  FIG. 8 (1) and FIG. 8 (2) show frequency components of input current waveforms of two configurations simulated under the same conditions as described above. The horizontal axis represents the frequency (Hz), the vertical axis represents the magnitude of the frequency component (decibel dB), and the lower the plot, the smaller the frequency component.

  FIG. 8 (1) shows a case where the two switching converters 101 are operated. FIG. 8B shows the case where the operation is performed by one switching converter 101. When the magnitude of the frequency component that becomes noise is 1000 Hz, FIG. 8A is plotted below FIG. 8B. That is, noise can be reduced in FIG. 8 (1) compared to FIG. 8 (2).

  Other embodiments will be described in detail. In order to detect the voltage using the signal detection unit 200, the potential difference between the ground and the detection point is measured. In order to detect the current using the signal detection unit 200, the voltage across the resistor in the signal circuit is measured, and the voltage value is divided by the resistance value. In order to detect electric power using the signal detection unit 200, calculation is performed by multiplying the results of the voltage and current measurements described above.

  These signals can be converted into digital data using an AD converter and used for calculating ripples. When calculating ripple as variance, measurement data over a time range such as a switching cycle is used. This operation can be made with a hardware circuit. Further, the above calculation can be executed by a procedure described by software using a microprocessor.

  A microprocessor incorporating an AD converter can easily measure voltage or current. Further, the switching signal 105 using the ripple detection result may be generated by the microprocessor software. By describing the procedure in software and operating it digitally, analog fluctuation factors can be eliminated. In addition, operation characteristics can be corrected and updated only by rewriting the software, so that the maintenance and management of the mounted circuit becomes easy.

  In addition, since the AD converter can be easily connected to various sensors, for example, the brightness of the external environment and the amount of light emitted from the external converter are measured in combination with the luminance sensor, and the switching converter 101 is based on the result. You can also decide the action.

  Other embodiments will be described in detail. FIG. 9 shows a configuration example in which the switching converters 101 are connected hierarchically. The input to the switching converter 101 is a commercial power supply of AC 100 volts.

  First, it is converted into direct current by a rectifier circuit. However, since the input voltage is high, the load is driven after stepping down in the first stage and the second stage. In other words, the switching converter 101 is connected in a branched manner (two branches in the example in FIG. 8). In this case, another switching converter (a third switching converter 203 and a second switching converter 203) is connected between the two switching converters connected in parallel (the first switching converter 201 and the second switching converter 202) and the signal detection unit 200. Connected). The voltage from the power supply terminal 100 is stepped down by driving the third switching converter 203.

  Only the first stage by the third switching converter 203 handles the same voltage as the power supply system, and the withstand voltage of the second stage components by the first switching converter 201 and the second switching converter 202 may be low. For example, when the switching unit 106 is formed of an FET transistor, the breakdown voltage decreases, so that the selection range of the component characteristics of the FET transistor can be expanded and the cost can be reduced. Similarly, since the service life of components can be expected to increase due to a decrease in breakdown voltage, maintenance management costs can be reduced.

  FIG. 10 shows a configuration example in which a large number of lighting devices are wired. When the brightness and irradiation area of the single lighting device 303 are insufficient, a large number of lighting devices 303 are combined to form a wide-area lighting area 301 to ensure brightness. Here, when connecting the power supply terminal 100 and a large number of lighting devices 303, there are several methods for combining a switching converter, a light source and wiring as follows.

  Method 1: The input AC high voltage power supply is rectified and stepped down, and then wired to each lighting device 303 to drive the light source 103.

  Method 2: Input AC high-voltage power supply is wired to each lighting device 303, and rectification and step-down are performed in each lighting device 303 to drive the light source 103.

  Method 3: The input AC high-voltage power supply is rectified and stepped down (first step-down), then wired to each lighting device 303, and stepped down (second step-down) in each lighting device 303. To drive.

  In method 3, an intermediate voltage different from the voltage from the power supply system and the driving voltage of the light source 103 is generated, and then wiring to the plurality of lighting devices 303 is performed. For example, 100 volt alternating current of the power supply system is input to the first switching converter 302 and converted into an intermediate voltage of 48 volt direct current by rectification and first step-down. Next, this intermediate voltage is wired to a plurality of lighting devices 303, and in each lighting device 303, the 48 volt direct current is converted into a voltage suitable for LED lighting by the second step-down to cause the LEDs to emit light. Each of the plurality of lighting devices 303 includes a second switching converter 304 and a light source 103. Each lighting device 303 operates so as to suppress the ripple of the intermediate voltage wiring.

  In the configuration of method 3, safety is enhanced by wiring with a low-voltage DC instead of a high-voltage power supply, and generation of electromagnetic noise can be suppressed. In addition, since the input voltage to the switching converter 304 disposed in each lighting device is low, a circuit may be configured with components with low withstand voltage, and generated noise can be suppressed low.

  By the way, if these lighting devices are regarded as a group of devices connected by power supply wiring, it is desirable that the operation of each lighting device can be controlled. A signal line for transmitting a control signal may be wired to control the lighting device. However, as another solution, there is a method of superimposing a certain control signal on the power supply wiring system. Since the power supply system ripple (noise) can be suppressed by the configuration of the present invention, the error rate of the control signal to be superimposed can be reduced. In the above example, by suppressing the ripple of the intermediate voltage wiring system, it is possible to easily superimpose control signals transmitted to a plurality of lighting devices.

DESCRIPTION OF SYMBOLS 10,303 Lighting apparatus 100 Power supply terminal 101 Switching converter 102 Drive signal 103 Light source 104 Switching signal generation part 105 Switching signal 106 Switching part 107 Inductor 108 Diode 200 Signal detection part 201,302 1st switching converter 202,304 2nd switching Converter 203 Third switching converter 301 Wide area lighting area

Claims (7)

A first switching converter and a second switching converter;
A first light source connected to the output terminal of the first switching converter and driven by a drive signal from the first switching converter;
A second light source connected to the output terminal of the second switching converter and driven by a drive signal from the second switching converter;
A power supply terminal connected to the input end of the first switching converter and the input end of the second switching converter;
A signal detector disposed between an input end of the first switching converter and an input end of the second switching converter and a power supply terminal;
A switching signal generation unit connected to the signal detection unit,
The voltage from the power supply terminal is stepped down by driving the first switching converter,
The voltage from the power supply terminal is stepped down by driving the second switching converter,
The first switching converter and the first light source are connected in series;
The second switching converter and the second light source are connected in series;
The first switching converter and the second switching converter are connected in parallel to the power supply terminal,
The signal detector measures a ripple of power, voltage or current supplied to the first switching converter and the second switching converter;
The switching signal generator generates a switching signal so that the ripple is reduced based on the measurement result of the signal detector,
The lighting device, wherein the first switching converter and the second switching converter are driven by the output of the switching signal from the switching signal generator. In claim 1,
The first step-down circuit includes a first switching unit,
The second step-down circuit includes a second switching unit,
The lighting device according to claim 1, wherein the switching signal generator controls the phase and duty of the first switching unit and the second switching unit. In claim 1,
The illumination device according to claim 1, wherein the signal detection unit measures ripple using dispersion. In claim 1,
The lighting device has a storage unit,
The said storage part memorize | stores the measurement result by the said signal detection part temporarily, The illuminating device characterized by the above-mentioned. In claim 1,
The lighting device according to claim 1, wherein the signal detector measures the ripple based on a program procedure by a microprocessor. In claim 1,
A third switching converter is disposed between the signal detector and the first switching converter and the second switching converter;
The lighting device, wherein the voltage from the power supply terminal is stepped down by driving the third switching converter. In claim 1,
The first switching converter has a first switching unit, a first inductor, a first diode,
When the first switching unit is on, the current passing through the first inductor gradually increases,
When the first switching unit is off, the current passing through the first inductor gradually increases,
The second switching converter includes a second switching unit, a second inductor, and a second diode,
When the second switching unit is on, the current passing through the second inductor gradually increases,
The lighting device, wherein the current passing through the second inductor gradually increases when the second switching unit is off.

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