JP6411076B2 - LED lighting device - Google Patents

Description

  The present invention relates to an LED lighting device including a digital control circuit that corrects the light quantity of an LED (light emitting diode).

  In recent years, LEDs have attracted attention as lighting fixtures. The characteristics of the LED are that it has a longer life and less power consumption than a fluorescent lamp. Further, an LED control circuit composed of a DC-DC converter using a digital control circuit such as a microprocessor or a DSP as an LED control has attracted attention. This LED control circuit sets a predetermined value according to the dimming level, and controls the current / voltage applied to the LED to perform control to keep the light quantity constant.

  FIG. 9 shows the characteristics of the light amount reduction at the dimming level and the LED operating time. The output to the LED is kept constant by the predetermined value, and the dimming level that determines the predetermined value is changed by external control using communication or the like.

  LED is a solid element and does not light up due to filament disconnection like conventional light sources, but even if the light control level is kept constant, the amount of light gradually decreases over the lighting time due to material deterioration etc. To do. The lifetime of the LED is defined by the amount of decrease in the luminous flux maintenance factor. If the amount of decrease is within a specified value, it is considered normal, but there is a problem that the amount of light decreases compared to the initial stage.

  FIG. 10 shows an example in which a new dimming level is generated by adding a correction level to the original dimming level in accordance with a decrease in the light amount of the LED. By increasing the dimming level according to the light amount of the LED that has decreased due to the accumulation of operating time, it is possible to correct the light amount to a constant value.

  When automatically increasing the dimming level in accordance with the amount of decrease in the LED light amount, it is necessary to detect the current LED light amount. For this purpose, a method is known in which an illuminance sensor is installed and the current light quantity detected by the illuminance sensor is input to a digital control circuit.

  FIG. 11 shows a configuration of a conventional LED lighting device. This LED illumination device includes an LED control circuit 10C composed of an insulation type DC-DC converter that performs constant current control and light amount correction of an LED, an LED circuit 20A controlled by the LED control circuit 10C, and detection of the LED circuit 20A. A feedback circuit 40 that feeds back the amount of light to the LED control circuit 10C.

  The LED control circuit 10C includes a digital control circuit 11C that controls the whole, a switching circuit 12 that includes a drive circuit 121 that is driven by the digital control circuit 11C, and a transistor 122 that is switched by the drive circuit 121, and the switching circuit 12 Voltage detection circuit 13 that detects the output voltage of the switching circuit 12 and feeds back to the digital control circuit 11C. The current detection circuit 14 detects the output current of the switching circuit 12 and feeds back to the digital control circuit 11C. It has an insulating transformer 15 having a secondary winding 152, a rectifying diode 16 and a smoothing capacitor 17 constituting a rectifying and smoothing circuit.

  The LED circuit 20A includes a plurality of LEDs 21 connected in series, and an illuminance sensor 22 that detects the amount of light when the LEDs 21 are lit.

  The feedback circuit 40 includes a digital control circuit 41 that processes the output signal of the illuminance sensor 22 and an insulating circuit 42 that includes an insulating transformer, a photocoupler, and the like.

  FIG. 12A shows a flowchart of the update process on the primary side performed in the digital control circuit 11C. The digital control circuit 11C acquires an input voltage signal (step S31), acquires a current signal detected by the current detection circuit 14 (step S32), and acquires a voltage signal detected by the voltage detection circuit 13 (step S33). Perform the process. Moreover, the process of acquisition of the light control level set internally (S34) and acquisition of the correction level input from the insulation circuit 42 (step S35) is performed, and the default value of the secondary output is calculated (step S36). Then, the on / off time of the transistor 122 is calculated according to the input value acquired in steps S31 to S33 and the default value acquired in step S36 (step S37), and output to the drive circuit 121 (step S38). The above process is repeated.

  FIG. 12B shows a flowchart of the update process on the secondary side performed by the digital control circuit 40. The digital control circuit 32 acquires the illuminance signal detected by the illuminance sensor 22 (step S41), calculates a correction level corresponding to the illuminance signal (step S42), and outputs the calculation result to the insulation circuit 42. (Step S43) is repeated.

  By performing the control as described above, the switching of the transistor 122 of the switching circuit 12 is controlled so that the amount of light detected by the illuminance sensor 22 becomes a predetermined value, and the current flowing through the LED 21 is controlled. It is possible to compensate for variations in the amount of light. For example, Patent Document 1 discloses a technique for detecting the amount of light of an LED using a detection element such as a photodiode and controlling the amount of light of the LED constant according to the detected value.

JP 2003-163090 A

  However, when the illuminance sensor 22 is arranged, the digital control circuit 41 for obtaining the correction level from the adjustment of the arrangement position of the illuminance sensor 22 and the detection signal of the illuminance sensor 22 and the primary side and the secondary side are insulated. The insulation circuit 42 is necessary, and there are problems such as not only an increase in cost but also an increase in equipment size due to an increase in the mounting area of the instrument.

  An object of the present invention is to provide an LED lighting device that solves the above-described problems by allowing the light quantity of an LED to be controlled to be constant without using an illuminance sensor.

In order to achieve the above object, an LED lighting device according to a first aspect of the present invention generates a voltage on the secondary side of the transformer by switching an input voltage on the primary side of the transformer with a digital control circuit. An LED control circuit composed of a DC-DC converter that outputs a DC voltage by rectifying and smoothing a voltage appearing on the secondary side and at least one LED to which the DC voltage output from the LED control circuit is applied are connected In the LED lighting apparatus including the LED circuit, the digital control circuit includes the input voltage on the primary side of the transformer, a voltage signal and a current signal on the primary side of the transformer, a dimming level set internally, and takes in the correction level corresponding to the LED uptime, calculates the default value of the secondary side output of the transformer for controlling the LED circuit And wherein the door.

  According to a second aspect of the present invention, in the LED lighting device according to the first aspect, the digital control circuit obtains the operating time of the LED by a timer and calculates the correction level.

  According to a third aspect of the present invention, in the LED lighting device according to the first or second aspect, the digital control circuit calculates the input voltage, the current flowing through the primary side of the transformer, and the voltage at the primary side of the transformer. The switching level is acquired and controlled so that the predetermined value is maintained, and the correction level for determining the predetermined value is updated every time the operating time is updated. To do.

  According to a fourth aspect of the present invention, in the LED lighting device according to the first, second, or third aspect, the communication device includes a communication module that communicates with the outside, and the digital control circuit acquires the dimming level from the communication module. Then, it is set internally, and a correction coefficient for calculating the correction level according to the operating time is taken in, or a table value for determining the correction level according to the operating time is taken in.

According to a fifth aspect of the present invention, in the LED lighting device according to the first, second, third, or fourth aspect, a temperature sensor that detects a temperature of the LED lighting device is provided, and the digital control circuit is detected by the temperature sensor. The correction level is corrected in accordance with the set temperature.

  According to the present invention, since the correction level is calculated according to the operating time of the LED, an illuminance sensor and a feedback circuit are not necessary, and a simple circuit configuration can be realized. Further, the operation time can be measured by using a timer function in the digital control circuit, and the burden on internal processing is small, so that a low-cost DSP can be used.

It is a circuit diagram of the LED lighting apparatus of the 1st Example of this invention. It is a flowchart of the primary side update process and primary side timer process of the digital processing circuit of the LED lighting apparatus of FIG. It is a circuit diagram of the LED lighting apparatus of the 2nd Example of this invention. It is a flowchart of the communication process of the digital processing circuit of the LED lighting apparatus of FIG. It is a characteristic view of the light quantity fall of individual LED. It is a circuit diagram of the LED lighting apparatus of the 3rd Example of this invention. It is a flowchart of the primary side timer process of the digital processing circuit of the LED lighting apparatus of FIG. It is a characteristic view of the light quantity fluctuation | variation of LED by a temperature change, and the light control level which should be controlled. It is a characteristic figure of the light quantity of LED, and the conventional light control level. It is a characteristic view of the light quantity of LED and the conventional light control level adjustment. It is a circuit diagram of the conventional LED lighting apparatus. It is a flowchart of the primary side update process and secondary side update process of the digital processing circuit of the LED lighting apparatus of FIG.

<First embodiment>
FIG. 1 shows a circuit of an LED lighting apparatus according to the first embodiment of the present invention. The LED lighting device includes an LED control circuit 10 including an insulated DC-DC converter that performs constant current control and light amount correction of an LED, and an LED circuit 20 that is controlled by the LED control circuit 10.

  The LED control circuit 10 includes a digital control circuit 11 that controls the whole, a drive circuit 121 that is driven by the digital control circuit 11, and a switching circuit 12 that is turned on / off by the drive circuit 121, A voltage detection circuit 13 for detecting the output voltage of the switching circuit 12 and feeding it back to the digital control circuit 11, a current detection circuit 14 for detecting the output current of the switching circuit 12 and feeding it back to the digital control circuit 11, and a primary side It has an insulating transformer 15 having a winding 151 and a secondary winding 152, a rectifying diode 16 and a smoothing capacitor 17 constituting a rectifying and smoothing circuit. The LED circuit 20 has a plurality of LEDs 21 connected in series.

  FIG. 2A shows a flowchart of the update process on the primary side performed by the digital control circuit 11. The digital control circuit 11 acquires an input voltage signal (step S1), acquires a current signal detected by the current detection circuit 14 (step S2), and acquires a voltage signal detected by the voltage detection circuit 13 (step S3). Perform the process. Acquisition at this time is performed by converting the signal into a digital signal by an A / D converter. Further, the process of obtaining the internally set dimming level (S4) and obtaining the correction level by the timer count (step S5) is performed, and the default value of the secondary side output is calculated (step S6). Then, the on / off time of the transistor 122 is calculated according to the input value acquired in steps S1 to S3 and the default value acquired in step S6 (step S7), and is output to the drive circuit 121 (step S8). The above process is repeated.

  FIG. 2B shows a flowchart of the primary timer processing by the digital control circuit 11. For each process, the count value of the internal timer of the digital control circuit 11 is updated by +1 (step S11), the operating time of the LED 21 is updated (step S12), and the correction level is calculated according to the operating time. (Step S13). This calculation is performed by calculating a reduction amount of the light amount of the LED 21 per count of the timer in advance and setting a correction coefficient. Note that a correction level may be determined by preparing a table in advance and reading the table according to the operating time.

  As a result, according to the present embodiment, the correction level can be increased as the operating time increases, and the default value can be determined by a new dimming level obtained by adding the correction bell and the original dimming level. The on / off time is calculated based on the predetermined value and the input value obtained in steps S1 to S3 described above, and the transistor 122 is controlled based on the on / off time. The decrease can be compensated.

  At this time, the illuminance sensor 22 described with reference to FIG. 11 is not required, and the feedback circuit 40 is not required, so that not only the cost can be reduced, but also the device size can be reduced by reducing the mounting area of the device.

<Second embodiment>
FIG. 3 shows a circuit of the LED lighting device according to the second embodiment of the present invention. In this embodiment, a digital control circuit 11A having an external input terminal is used for the LED control circuit 10A, and the communication module 30 is connected to the digital control circuit 11A. Thereby, in addition to the function described in the first embodiment, a control signal from a control device such as a personal computer can be transmitted to the digital control circuit 11A via the communication module 30. For this reason, the internal setting data of the digital control circuit 11A can be changed.

  FIG. 4 shows a flowchart of communication processing of the digital control circuit 11A. When the communication module 30 communicates with the outside, the dimming level received from the communication module 30 is acquired (step S21), and the dimming level to be internally set is updated (step S22). Further, a correction coefficient corresponding to the secular change of the LED 21 is acquired (step S23), and based on this, the calculated value of the correction level acquired in the timer process of FIG. 2B is updated (step S24).

  In this embodiment, since not only the dimming level but also the correction coefficient can be acquired from the outside, as shown in FIG. 5, when using, for example, LED_1, LED_2, LED_3 having different coefficients of aging as the LED 21, the relevant LED_1 , LED_2, and LED_3, a correction coefficient corresponding to the LED to be used can be acquired. Thereby, an appropriate correction level according to the LED to be used can be calculated. Note that a table for changing the correction level in place of the correction coefficient may be fetched.

  Further, the communication module 30 not only receives the dimming level, correction coefficient, and table signal from the outside and transmits them to the digital control circuit 11A, but also receives the operation time counted by the timer processing by the digital control circuit 11A. You may make it transmit outside. Since the lifetime of the LED control circuit 10A can be calculated from this operating time, it can be transmitted to the outside that the LED control circuit 10A is nearing the end of life, and the replacement of the LED control circuit 10A can be urged.

  As described above, according to the present embodiment, by using the communication module 30, the dimming level is set from the outside, the correction coefficient is set from the outside according to the LED to be used, and the lifetime of the LED control circuit 10 is increased. Notification to the outside can be performed.

<Third embodiment>
FIG. 6 shows a circuit of an LED lighting device according to a third embodiment of the present invention. In the present embodiment, in addition to the functions described in the first and second embodiments, the LED control circuit 10B can acquire a temperature signal from the temperature sensor 18 installed in the LED control circuit 10B and perform control based thereon. A control circuit 11B is provided.

  In this embodiment, the ambient temperature signal detected by the temperature sensor 18 is input to the digital control circuit 10B, and the correction level can be changed. FIG. 7 shows a flowchart of the primary timer process in which the temperature detection process is added to the digital control circuit 10B.

  As shown in FIG. 8A, it is known that the amount of decrease in the amount of light according to the operating time varies depending on the temperature of the LED, and the amount of decrease is higher than that at room temperature as the temperature continues. Therefore, the digital control circuit 11B acquires the temperature signal from the temperature sensor 18 (step S12A) in addition to the update (step S12) of the operation time based on the count value (step S11) obtained by the internal timer. The correction level is calculated according to the temperature (step S13). As a result, the dimming level for each timer process is changed according to the temperature as shown in FIG. 8B, so that the decrease in the amount of light of the LED due to the temperature rise can be compensated.

  As described above, according to the present embodiment, by using the temperature sensor 18, it is possible to compensate for a light amount decrease due to temperature.

  The flowcharts described in FIGS. 2A, 2B, 4 and 7 described above are programs for causing a computer in the digital control circuits 11, 11A and 11B to execute the digital control circuit. 11, 11 </ b> A, and 11 </ b> B are stored in a memory (not shown).

10, 10A, 10B, 10C: LED control circuit, 11, 11A, 11B, 11C: digital control circuit, 12: switching circuit, 121: drive circuit, 122: transistor, 13: voltage detection circuit, 14: current detection circuit, 15: transformer, 151: primary winding, 152: secondary winding, 16: rectifier diode, 17: smoothing capacitor, 18: temperature sensor 20, 20A: LED circuit, 21: LED, 22: illuminance sensor 30 : Communication module 40: Feedback circuit, 41: Digital control circuit, 42: Insulation circuit

Claims (5)

A DC-DC converter that generates a voltage on the secondary side of the transformer by switching an input voltage on the primary side of the transformer by a digital control circuit, rectifies and smoothes the voltage appearing on the secondary side, and outputs a DC voltage In an LED lighting device comprising: an LED control circuit comprising: an LED circuit connected to at least one LED to which the DC voltage output from the LED control circuit is applied;
On the primary side of the transformer, the digital control circuit includes a correction level corresponding to the input voltage, a voltage signal and a current signal on the primary side of the transformer, a dimming level set internally, and an operating time of the LED. , And calculating a predetermined value of the secondary side output of the transformer to control the LED circuit.
The LED lighting device according to claim 1,
The digital control circuit obtains the operating time of the LED by a timer and calculates the correction level. The LED lighting device according to claim 1 or 2,
The digital control circuit obtains the input voltage, the current flowing in the primary side of the transformer, and the voltage on the primary side of the transformer, and sets the on / off period of the switching so that the predetermined value is maintained. The LED lighting device, wherein the correction level that controls and determines the predetermined value is updated every time the operating time is updated. In the LED lighting device according to claim 1, 2, or 3,
It has a communication module that communicates with the outside,
The digital control circuit acquires the dimming level from the communication module and internally sets it, incorporates a correction coefficient for calculating the correction level according to the operating time, or corrects the correction according to the operating time An LED lighting device, which takes in a table value for determining a level. In the LED lighting device according to claim 1, 2, 3, or 4,
A temperature sensor for detecting the temperature of the LED lighting device;
The LED control device, wherein the digital control circuit corrects the correction level according to a temperature detected by the temperature sensor.