JP2012079602A - Lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lighting device capable of avoiding an adverse effect on an infrared remote controller by keeping a switching frequency of a step-down circuit at 40 kHz or higher even when a rectification voltage lowers.SOLUTION: A lighting device comprises: a rectification circuit 101 which converts a voltage of an AC power supply 100 into a DC voltage; a step-down circuit 102 which steps down the rectification voltage output from the rectification circuit and feeds power to a LED load 103; a driving circuit 105 which drives a switching element provided in the step-down circuit; a voltage drop detection circuit 106 which detects a rectification voltage drop; and at least one bypass means 104 which is operated according to an output from the voltage drop detection circuit. The LED load is provided with at least one of the LED series bodies to which a plurality of LEDs are connected in series. The bypass means is connected in parallel to some LEDs provided in the LED series body. The voltage drop detection circuit outputs a bypass command signal to the bypass means when the rectification voltage is lower than a set value.

Description

  The present invention relates to a lighting device driven by an AC power source, and more particularly, to a lighting device for a light emitting diode (hereinafter referred to as LED).

  LEDs are attracting attention as light sources with excellent environmental properties, and are used in a wide range of products such as spot lighting, interior lighting of automobiles, headlights, traffic lights, and backlights of liquid crystal displays. In general lighting for homes and offices, replacement of conventional light sources such as fluorescent lamps with LEDs has begun.

  As an example of the LED lighting device, there is a configuration in which a DC voltage (hereinafter referred to as a rectified voltage) is generated from an AC power source through a rectifier circuit, and the rectified voltage is stepped down by a step-down circuit to supply power to the LED. Although this device can supply power to the LED only under a condition where the rectified voltage is higher than the voltage of the LED load (hereinafter referred to as output voltage), there is an advantage that the configuration of the device is simple and the efficiency of power conversion is high. .

  As such an LED lighting device, there is a device described in Patent Document 1, for example. This device is configured to supply power to an LED from a DC power source via a step-down chopper so that the peak value of the current flowing through the switching element of the step-down chopper becomes constant and the step-down chopper operates in a current critical mode. Includes a self-excited drive circuit for turning on and off the switching element. In addition to the above advantages, this device can control the current flowing through the LED load (hereinafter referred to as the LED current) to be constant, and further, since the turn-on loss of the switching element hardly occurs, the efficiency of power conversion is improved. It can be even higher.

JP-A-2005-294063

  Regarding the above rectifier circuit, consider a configuration in which a smoothing capacitor is provided on the DC output side to smooth the rectified voltage. At this time, considering the reduction of power supply harmonics, the capacitance of the capacitor cannot be increased sufficiently, and the rectified voltage pulsates at the frequency of the AC power supply. The lower the rectified voltage and the smaller the difference between the rectified voltage and the output voltage, the lower the switching frequency of the switching element in the step-down circuit. When the switching frequency is lower than 40 kHz, the infrared remote control device may malfunction, so the step-down circuit should be designed so that the switching frequency is always 40 kHz or higher. However, depending on the configuration of the LED load, a situation may occur in which the difference between the rectified voltage and the output voltage becomes extremely small. In this case, the switching frequency cannot be maintained at 40 kHz or higher by adjusting the circuit constant. If the period during which the switching frequency cannot be maintained above 40 kHz is long, a method not using a step-down circuit should be considered. However, when the synchronization period is short, particularly when the synchronization period occurs only when the voltage of the AC power supply decreases, the above problem may be solved by some means from the viewpoint of miniaturization and high efficiency of the LED lighting device. It is desirable to solve and use a step-down circuit.

  The objective of this invention is providing the lighting device which avoided the bad influence (malfunction etc.) to the apparatus which communicates with a predetermined frequency.

  The present invention is characterized in that the bypass means is connected in parallel with some of the LEDs included in the LED series body, and the voltage drop detection circuit outputs a bypass command signal to the bypass means when the rectified voltage is lower than a set value. And

  In the present invention, when the rectified voltage rectified from the AC power supply becomes close to the voltage applied to the light emitter (for example, the LED series body), the rectified voltage does not become closer to the voltage applied to the light emitter. The voltage applied to the light emitter is lowered.

  The present invention detects auxiliary rectification devices (for example, MOSFETs) connected in parallel to some of the LEDs included in the LED group, detects a rectified voltage, compares the rectified voltage with a set value (Vdc set value), and rectifies A circuit (voltage drop detection circuit) that turns off the auxiliary switching element when the voltage is larger than the set value and turns on the auxiliary switching element when the rectified voltage is smaller than the set value is provided. The voltage set value is applied to the LED group. It is characterized by being higher than the voltage.

  According to the present invention, the bypass means is connected in parallel with some of the LEDs included in the LED series body, and the voltage drop detection circuit outputs a bypass command signal to the bypass means when the rectified voltage is lower than the set value. Thus, even when the rectified voltage is lowered, the switching frequency of the step-down circuit can be maintained at a predetermined frequency or more, and adverse effects (such as malfunction) on devices that communicate at the predetermined frequency can be avoided. For example, if the switching frequency can be maintained at 40 kHz or higher, adverse effects (such as malfunctions) on the infrared communication device can be avoided.

  Alternatively, according to the present invention, when the rectified voltage rectified from the AC power supply becomes close to the voltage applied to the light emitter, the light emitter is prevented from becoming any closer to the voltage applied to the light emitter. By reducing the voltage applied to, the switching frequency of the step-down circuit can be maintained at a predetermined frequency or higher even when the rectified voltage is reduced, and adverse effects (such as malfunctions) on devices communicating at the predetermined frequency can be avoided.

  Alternatively, according to the present invention, the auxiliary switching element connected in parallel to some of the LEDs included in the LED group and the rectified voltage are detected, the rectified voltage is compared with the set value, and the rectified voltage is greater than the set value. When the auxiliary switching element is turned off and the auxiliary switching element is turned on when the rectified voltage is smaller than the set value, the voltage set value is higher than the voltage applied to the LED group, thereby reducing the rectified voltage. Even at times, the switching frequency of the switching element in the step-down circuit can be maintained at a predetermined frequency or higher, and adverse effects (such as malfunctions) on devices communicating at the predetermined frequency can be avoided.

It is a block diagram of the LED lighting device in 1st Embodiment of this invention. It is a LED lighting device in a 1st embodiment of the present invention. It is an operation | movement waveform of the conventional LED lighting device. It is an operation | movement waveform of the conventional LED lighting device. It is an operation | movement waveform of the LED lighting device in 1st Embodiment of this invention. It is an operation | movement waveform of the LED lighting device in 1st Embodiment of this invention. It is the LED load and bypass means in 1st Embodiment of this invention. It is the LED load and bypass means in 1st Embodiment of this invention. It is the LED load and bypass means in 2nd Embodiment of this invention. It is an LED lighting device in 2nd Embodiment of this invention. It is an operation | movement waveform of the LED lighting device in 2nd Embodiment of this invention. It is the mounting form of the bypass means in this invention. It is the mounting form of the bypass means in this invention.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram of an LED lighting device according to the first embodiment of the present invention. The LED lighting device of FIG. 1 includes an AC power source 100, a rectifier circuit 101 that converts the voltage of the AC power source 100 into a DC voltage (rectified voltage), and a step-down circuit that steps down the rectified voltage and supplies power to an LED (light emitting diode) load 103. 102, LED load 103 is provided. The step-down circuit 102 includes a switching element. The LED load 103 includes at least one LED series body in which a plurality of LEDs are connected in series. The LED lighting device includes bypass means 104 connected in parallel to some of the LEDs included in the LED series body. The LED load 103 may include a series of LED series connected in parallel, and this case will be described later. The drive circuit 105 detects the current flowing through the step-down circuit 102 or the current flowing through the LED load 103, and drives the switching element of the step-down circuit 102 based on the detected current. The voltage drop detection circuit 106 detects the rectified voltage that is the output of the rectifier circuit 101, and outputs a bypass command signal to the bypass means 104 and a current setting value to the drive circuit 105 according to the rectified voltage. The voltage drop detection circuit 106 may generate a signal corresponding to the current set value and output the signal to the drive circuit 105. Alternatively, the drive circuit 105 may generate a signal corresponding to the current set value, and the voltage drop detection circuit 106 May output a signal instructing the drive circuit 105 to set the current set value.

  The voltage drop detection circuit 106 may vary the current setting value, and as an example, may switch between a first current setting value having a small value and a second current setting value having a large value. Note that there may be three or more current set values. The drive circuit 105 may generate a plurality of current set values, and the voltage drop detection circuit 106 may output a signal instructing the drive circuit 105 to switch the current set values. In a state where the rectified voltage is equal to or higher than the voltage set value, the voltage drop detection circuit 106 does not output a bypass command signal to the bypass means 104 and outputs a first current set value to the drive circuit 105. The drive circuit 105 controls the step-down circuit 102 based on the first current setting value. As an example of a method for controlling the step-down circuit 102, there is a method for controlling on / off of the switching element so that the peak value of the current flowing through the switching element of the step-down circuit 102 matches the first current set value. On the other hand, the voltage drop detection circuit 106 outputs a bypass command signal to the bypass means 104 and outputs a second current set value to the drive circuit 105 when the rectified voltage becomes smaller than the voltage set value stored in advance. To do. The bypass means 104 bypasses some of the LEDs in the LED series body, and as a result, only some of the LEDs in the LED series body are not lit, and only the remaining LEDs are lit. The drive circuit 105 controls the step-down circuit 102 based on the second current setting value. The specific control method is the same as that when the first current set value is used.

  FIG. 2 shows the LED lighting device according to the first embodiment of the present invention, and specifically shows the main circuit portion of FIG. A diode bridge 107 is connected to the AC power supply 100. A smoothing capacitor 108 is connected to the DC output side of the diode bridge 107. A series body of a power MOSFET 109, a current detection means 113, and a diode 110 is connected in parallel with the smoothing capacitor. A series body of a choke coil 111 and a capacitor 112 is connected in parallel with the diode 110. An LED load 103 is connected in parallel with the capacitor 112. The voltage detection input terminal of the voltage drop detection circuit 106 is connected to the positive side of the direct current output of the diode bridge 107, the current setting output terminal is connected to the drive circuit 105, and the bypass command output terminal is the MOSFET 114. Connected to the gate. The input terminal for current detection of the drive circuit 105 is connected to the current detection means 113, and the output terminal of the drive signal is connected to the gate of the power MOSFET 109. In FIG. 2, a full-wave rectifier circuit including a diode bridge 107 and a smoothing capacitor 108 corresponds to the rectifier circuit 101 of FIG. Further, the step-down chopper constituted by the power MOSFET 109, the diode 110, the choke coil 111, the capacitor 112, and the current detection means 113, which are switching elements, corresponds to the step-down circuit 102 in FIG. Instead of the power MOSFET 109, other types of switching elements such as bipolar transistors may be used. A MOSFET 114 as an auxiliary switching element is connected in parallel to a part of the LED load 103, and this MOSFET 114 corresponds to the bypass means 104 in FIG. As shown in FIG. 2, a portion of the LED load 103 that is bypassed by the MOSFET 114 is defined as an LED group 116, and a portion that is not bypassed is defined as an LED group 117. The voltage of the AC power supply 100 is defined as Vin, the rectified voltage is defined as Vdc, and the output voltage after the rectified voltage is stepped down by the step-down circuit 102 is defined as Vout. Vout is a voltage applied to the LED load 103. The voltage drop detection circuit 106 outputs a drive signal for the MOSFET 114 as a signal corresponding to the bypass command signal in FIG. By not driving (turning off) the MOSFET 114, the LED group 116 and the LED group 117 are all lit (all lit). By driving (turning on) the MOSFET 114, the LED group 116 is bypassed and only the LED group 117 is lit (partial lighting). For example, if the total number of LEDs included in the LED series body is eight, the number of LEDs included in the bypassed LED group 116 may be four or two.

  In the LED lighting device of FIG. 2, the capacitance of the smoothing capacitor 108 can be set large only within a range satisfying the reduction of power supply harmonics. That is, the capacitance of the capacitor 108 is small. Therefore, the rectified voltage is not completely smoothed, but fluctuates at the same frequency as the frequency of the AC power supply 100 as shown in FIG. In FIG. 3, the solid line Vdc is the rectified voltage, the broken line Vout is the output voltage, and the dotted line Vin is the voltage of the AC power supply 100. As shown in FIG. 3, depending on the number of LEDs included in the LED load 103, a situation may occur where the difference between Vdc and Vout becomes extremely small when Vdc is low. For example, Vdc is sufficiently larger than Vout at the point (a) in FIG. 3, but the difference between Vdc and Vout is extremely small at the point (b).

  Here, the thing without the bypass means 104 and the voltage drop detection circuit 106, ie, the conventional LED lighting device, is considered. 4A shows an operation waveform of the step-down chopper when Vdc is sufficiently higher than Vout (Vdc >> Vout), and FIG. 4B shows that the difference between Vdc and Vout is extremely small (Vdc≈Vout). ) Is an operation waveform of the step-down chopper. As a vertical axis item in FIG. 4, SW is an on / off state of the power MOSFET 109, IQ is a current of the power MOSFET 109, IL is a current of the choke coil 111, and ILED is a current of the LED load 103. It is assumed that the step-down chopper is controlled by controlling the peak value of the current flowing through the power MOSFET 109 and operating in the current critical mode. However, the control method is not particularly limited as long as the current peak value of the power MOSFET 109 is controlled. Further, it is assumed that the capacitance of the capacitor 112 is sufficiently large and that the ILED becomes a direct current component of IL.

  When the power MOSFET 109 is on, a current flows through the step-down chopper through the path of the power MOSFET 109, current detection means 113, choke coil 111, LED load 103 and capacitor 112 in parallel, and IQ and IL are as shown in FIG. Increase with time. Since the voltage (Vdc−Vout) of the difference between Vdc and Vout is applied to the choke coil 111, IL and IQ increase with a constant slope during a period in which Vdc−Vout can be regarded as constant. Increasing slopes of IL and IQ are proportional to Vdc−Vout and inversely proportional to the self-inductance of the choke coil 111. In the method of controlling the peak value of current, the power MOSFET 109 is turned off when IQ reaches the current set value. Although details are omitted, after the power MOSFET 109 is turned off, IQ stops flowing and IL decreases. The slope of decrease in IL depends on Vout and the self-inductance of the choke coil 111. The greater the Vout, the greater the slope at which IL decreases, and the smaller the Vout, the smaller the slope at which IL decreases. As an example of the timing at which the power MOSFET 109 is turned on again, there are a system in which the power MOSFET 109 is turned on when a desired time has elapsed since the power MOSFET 109 is turned off, and a system in which the power MOSFET 109 is turned on when it is detected that IL has decreased to zero.

For the above reasons, when Vdc decreases, Vdc−Vout decreases, so that the slopes of IL and IQ decrease. At this time, since the time until IQ reaches the IQ set value, that is, the on-time of the power MOSFET 109 becomes longer, the switching frequency of the power MOSFET 109 becomes lower. In particular, when Vdc≈Vout and the operation waveform is as shown in FIG. 4B, the switching frequency is extremely lower than in the case of FIG. In this case, it is difficult to maintain the switching frequency at 40 kHz or higher simply by adjusting the self-inductance of the choke coil 111. When the switching frequency is lower than 40 kHz, the infrared remote control device is adversely affected (malfunction) as described above. Even if the switching frequency is designed to be 40 kHz or more in the state of Vdc≈Vout in FIG. 4B, the switching frequency becomes extremely high when Vdc >> Vout in FIG. The power MOSFET 109 may be damaged due to an abnormal increase in the current.
The infrared carrier frequency used for the remote control is 38 kHz or 40 kHz, but actually varies from 30 kHz to 40 kHz.

  In the present invention, the above problem is solved by using the MOSFET 114 of the auxiliary switching element and the voltage drop detection circuit 106. The voltage drop detection circuit 106 has a Vdc setting value with respect to Vdc, and turns on the MOSFET 114 when detecting that Vdc has become lower than the Vdc setting value. As a result, both ends of the LED group 116 in the LED load 103 are short-circuited. This is equivalent to a reduction in the number of LEDs connected in series in the LED load 103 by the amount of the LED group 116, and Vout also decreases by the amount of the LED group 116. Since the ILED is bypassed by the MOSFET 114 and flows, no current flows through the LED group 116, and the LED group 116 is temporarily turned off. The Vdc set value is higher than Vout applied to the LED group 116 and the LED group 117 with the MOSFET 114 turned off. Of course, the Vdc set value is higher than Vout when the MOSFET 114 is turned on and decreased by the amount of the LED group 116, and is lower than the peak value of Vdc. For example, when Vin is 100 Vac, the peak value of Vdc is about 141 V. Vout applied to the LED load 103 when the MOSFET 114 is off depends on the number of LEDs connected in series in the LED load 103, but is about 75V, for example. At this time, the Vdc set value is about 80 to 85 V, which is 5 to 10 V higher than Vout applied to the LED load 103.

  The operation waveform of the step-down chopper of the present invention is shown in FIG. 5 corresponds to FIG. 3, and the time axis of FIG. 6 corresponds to FIG. As the vertical axis items in FIGS. 5 and 6, SW2 is the on / off state of the MOSFET 114, and other items are the same as those in FIG. 3 or FIG. FIG. 6A shows an operation waveform when Vdc is higher than the Vdc set value and the MOSFET 114 is OFF (all lighting), and FIG. 6B shows a case where Vdc is lower than the Vdc set value and the MOSFET 114 is ON. It is an operation waveform of (partial lighting).

  As shown in FIG. 5, the voltage drop detection circuit 106 detects Vdc, which is a rectified voltage, and compares Vdc with a Vdc set value. When the voltage drop detection circuit 106 determines that Vdc is lower than the Vdc set value, it outputs a drive signal to the MOSFET 114 to turn on the MOSFET 114 and bypass the LED group 116. As a result, Vout is lowered. When the voltage drop detection circuit 106 determines that Vdc is lower than the Vdc set value, the voltage drop detection circuit 106 outputs a second IQ set value larger than the first IQ set value to the drive circuit 105. Since the IQ set value increases, the ILED also increases. The reason why the IQ setting value is increased in this way will be described later. However, the control operation for outputting the second IQ set value of the voltage drop detection circuit 106 is not an essential configuration. That is, the voltage drop detection circuit 106 may output the first IQ setting value even when it is determined that Vdc is lower than the Vdc setting value. On the other hand, when it is determined that Vdc is higher than the Vdc set value, the voltage drop detection circuit 106 does not output a drive signal to the MOSFET 114, turns off the MOSFET 114, and does not bypass the LED group 116. As a result, Vout increases. When the voltage drop detection circuit 106 determines that Vdc is higher than the Vdc set value, the voltage drop detection circuit 106 outputs a first IQ set value smaller than the second IQ set value to the drive circuit 105. Note that the operation in which the drive circuit 105 controls the on / off of the power MOSFET 109 based on the IQ set value is the same as in the case of FIG. 4 already described.

  As shown in FIG. 5 or FIG. 6, by turning on the MOSFET 114, Vdc≈Vout is not satisfied even in a situation where Vdc is low, and Vdc >> Vout can be maintained. Therefore, as shown in FIG. 6B, the switching frequency when Vdc is low is lower than that when Vdc is high in FIG. 6A, but extremely low as shown in FIG. 4B. Never become. As a result, the switching frequency can be maintained at 40 kHz or higher even when Vdc is reduced by adjusting the self-inductance of the choke coil 111.

  When the current peak value is controlled to be constant, that is, the ILED is controlled to be constant, if Vout is decreased when Vdc is low as described above, the output power and thus the light output of the LED load 103 is decreased. Therefore, when Vdc is lower than the Vdc setting value (partial lighting), as shown in FIG. 5 and FIG. 6B, the MOSFET 114 is turned on, and at the same time, the IQ according to the number of LEDs in the LED group 116 that is temporarily turned off. It is preferable to increase the set value. Thereby, even if Vout decreases, the ILED increases, so that the output power and the light output can be maintained. For example, when the total number of LEDs of the LED load 103 is 25 and the number of LEDs in the LED group 116 that is temporarily turned off is 5, the second IQ setting value is 5/4 times the first IQ setting value. Then, output power and optical output can be maintained. However, since the period during which Vdc is higher than the Vdc set value is sufficiently longer than the period during which Vdc is lower than the Vdc set value, the period during which the LED load 103 is partially lit (the period during which the LED group 116 is temporarily turned off) It is shorter than the period when the LED load 103 is fully lit. Therefore, even if the ILED is not raised when the LED load 103 is partially lit, the light output of the LED load 103 is not significantly affected. Therefore, it is not necessary to increase the IQ set value when the LED load 103 is partially lit, and even if it is increased, it is not necessary to increase the light output of the LED group 116 that is extinguished completely.

  Another example regarding the configuration of the LED load and the connection mode of the bypass means will be described. First, as shown in FIG. 7, the place where the bypass means is connected to the LED series body is not limited. As shown in FIG. 2, the end part of the LED series body may be sufficient, and the intermediate part of an LED series body may be sufficient as shown in FIG. Next, when two or more LED series bodies are connected in parallel like the LED load 115 of FIG. 8, the bypass means 104 and the bypass means 118 may be connected to each LED series body. When LEDs are connected in parallel, a circuit for balancing the LED current is generally inserted, but is omitted in FIG.

  As another example of the bypass means 104, other types of auxiliary switching elements such as transistors may be used in addition to MOSFETs. Further, a mechanical auxiliary switch such as a relay may be used.

  The implementation of the bypass means 104 will be described. The LED lighting device described above is an electronic circuit, and each component of the LED lighting device is mounted on a circuit board. However, the LED load 103 is mounted on a board (hereinafter referred to as an LED board) different from the circuit board, and the circuit board and the LED board are electrically connected by a cable or the like. The bypass means 104 is generally mounted on a circuit board, but may be mounted on an LED board as shown in FIG. In FIG. 12, surface-mounted LED modules 301 to 304 and surface-mounted auxiliary switching elements 305 that are bypass means 104 are mounted on the LED substrate 300. The LED substrate 300 has three electrodes 306 to 308, the electrode 306 has a positive output side of the step-down circuit, the electrode 307 has a negative output side of the output of the step-down circuit, and the electrode 308 has an auxiliary switching signal that is a bypass command signal. A driving signal for the element 305 is input. The inside of the dotted line is the wiring pattern of the LED substrate 300. In FIG. 12, among the LED modules 301 to 304 connected in series, the LED module 304 is bypassed by the auxiliary switching element. In addition, as an internal structure of an LED module, it does not ask | require about the number and connection form of LED.

  As shown in FIG. 13, the LED module may incorporate a bypass unit together with a plurality of LEDs. In FIG. 13, LEDs 309 to 312 and bypass means 313 are built in the LED module 315. A bypass command signal is input to the electrode 314. A dotted line is a wiring in the LED module 315. In FIG. 13, among the LEDs 309 to 312 connected in series, the LEDs 311 and 312 are bypassed by the auxiliary switching element 305. The implementation of the bypass means described above is applicable to all embodiments of the present invention.

  According to the first embodiment, when Vdc pulsates and Vdc becomes close to Vout, for example, the number of LEDs to be lit is reduced to lower Vout so that Vdc does not approach Vout any more and IQ becomes IQ By preventing the time to reach the set value from becoming longer, the switching frequency of the step-down circuit can be maintained at a predetermined frequency or higher even when Vdc decreases, and adverse effects (such as malfunctions) on devices that communicate at the predetermined frequency Can be avoided. For example, if the switching frequency can be maintained at 40 kHz or higher, adverse effects (such as malfunctions) on the infrared communication device can be avoided.

  The LED lighting device of the present invention can be applied to a backlight of a lighting fixture or a liquid crystal display device. The LED lighting device of the present invention can also be applied to light emitters other than LEDs, such as EL elements.

  The second embodiment of the present invention will be described below, but the description of the same points as in the first embodiment will be omitted.

  In the second embodiment of the present invention, as shown in FIG. 9, a plurality of bypass means (104, 204, 205) are connected to one LED series body. There may be an LED that is not bypassed by the bypass means, that is, an LED in which the LED current always flows regardless of the bypass command signal. FIG. 10 shows an LED lighting device according to the second embodiment of the present invention. Two auxiliary switching elements MOSFET 114 and MOSFET 214 are connected to a part of the LED load 103, and these correspond to the bypass means of FIG. As shown in FIG. 10, the portion of the LED load 103 that is bypassed by the MOSFET 114 or the MOSFET 214 is defined as an LED group 116 or an LED group 216, respectively.

  FIG. 11 shows operation waveforms in the second embodiment of the present invention, and the time axis corresponds to FIG. 3 and FIG. For the vertical axis items in FIG. 11, SW3 is the on / off state of the MOSFET 214, and the other items are the same as in FIG. As shown in FIG. 11, the voltage drop detection circuit 106 turns on the MOSFET 114 and the MOSFET 214 in turn each time it detects that Vdc is lower than the Vdc set value. Even if either MOSFET is turned on first, Vout decreases. Therefore, even if Vdc decreases, the relationship of Vdc >> Vout can be maintained, and the same effect as in the first embodiment can be obtained.

  In the first embodiment of FIG. 2, only the LED group 116 is turned off each time Vdc decreases, and LEDs that are not included in the LED group 116 are always lit regardless of Vdc. Therefore, the lifetime of LEDs included in the LED group 116 in the LED load is shorter than other LEDs. In the second embodiment, the frequency at which each LED is turned off becomes more uniform, and therefore, the LED life is less likely to vary in the LED load.

100 AC power supply 101 Rectifier circuit 102 Step-down circuit 103, 115 LED load 104, 118, 204, 205, 313 Bypass means 105 Drive circuit 106 Voltage drop detection circuit 107 Diode bridge 108, 112 Capacitor 109 Power MOSFET
110 Diode 111 Choke coil 113 Current detection means 114, 214 MOSFET
116, 117, 216 LED group 300 LED boards 301, 302 to 304, 315 LED module 305 Auxiliary switching elements 306, 307, 308, 314 Electrodes 309, 310 to 312 LEDs

Claims (14)

The rectifier circuit that converts the voltage of the AC power source into a DC voltage, the step-down circuit that steps down the rectified voltage that is the output of the rectifier circuit and supplies power to a light emitting diode load (hereinafter referred to as LED load), and the step-down circuit A lighting device comprising: a drive circuit for driving a switching element; a voltage drop detection circuit for detecting a drop in the rectified voltage; and at least one bypass means operated by an output of the voltage drop detection circuit,
The LED load includes at least one LED series body in which a plurality of LEDs are connected in series,
The bypass means is connected in parallel with some of the LEDs included in the LED series body,
The voltage drop detection circuit outputs a bypass command signal to the bypass means when the rectified voltage is lower than a set value. The lighting device according to claim 1,
The bypass means includes an auxiliary switching element connected in parallel with some of the LEDs included in the LED series body,
The voltage drop detection circuit outputs a drive signal for the auxiliary switching element as the bypass command signal when the rectified voltage is lower than a set value. The lighting device according to claim 1,
Two or more said bypass means are connected per said LED serial body, The lighting device characterized by the above-mentioned. The lighting device according to claim 3,
The lighting device according to claim 1, wherein the voltage drop detection circuit sequentially outputs a bypass command signal to the two or more bypass means each time it detects that the rectified voltage is lower than a set value. The lighting device according to any one of claims 1 to 4,
The drive circuit detects the current flowing through the step-down circuit and drives the switching element to control the current according to a current setting value;
The voltage drop detection circuit increases the current set value when the rectified voltage is lower than a set value. The lighting device according to claim 5,
The driving device is configured to turn off the switching element when the current flowing through the step-down circuit reaches a current set value when the switching element is on. The lighting device according to any one of claims 1 to 6,
The rectifier circuit includes a diode bridge and a smoothing capacitor,
The step-down circuit includes a diode, a power MOSFET corresponding to the switching element, a choke coil, a capacitor, and current detection means.
The driving circuit detects a current flowing through the power MOSFET, and turns off the power MOSFET when the current flowing through the power MOSFET reaches a current setting value when the power MOSFET is on. Lighting device. The lighting device according to any one of claims 1 to 7,
The bypass device is mounted on a substrate on which the LED is mounted. The lighting device according to any one of claims 1 to 8,
The bypass unit is built in an LED module including a plurality of LEDs. The lighting device according to any one of claims 1 to 9,
The switching device has a switching frequency of 40 kHz or more. In the lighting device for controlling the current supplied to the light emitter while rectifying and stepping down the AC power supply and supplying the light emitter,
When the rectified voltage rectified from the AC power source becomes close to the voltage applied to the light emitter, the rectified voltage is applied to the light emitter so that it does not become closer to the voltage applied to the light emitter. The lighting device characterized by lowering the voltage. The lighting device according to claim 11,
A lighting device, wherein a voltage applied to the light emitter is lowered by bypassing a part of the light emitter. The lighting device according to claim 11,
The lighting device, wherein the rectified voltage is close to a voltage applied to the light emitter when the rectified voltage is smaller than a voltage set value set higher than a voltage applied to the light emitter. AC power supply, a diode bridge connected to the AC power supply, a first capacitor connected in parallel to the diode bridge, a first switching element connected in parallel to the first capacitor, and current detection means And a series body of diodes, a series body of a choke coil and a second capacitor connected in parallel to the diode, an LED group connected in parallel to the second capacitor, and a current of the first switching element Or a lighting device comprising: a drive circuit that detects the current of the coil and drives the first switching element by comparing the current of the first switching element or the current of the coil with a current setting value;
A second switching element connected in parallel to some of the LEDs included in the LED group; and detecting a voltage of the first capacitor; comparing the voltage of the first capacitor with a voltage setting value; When the voltage of the first capacitor is larger than the voltage setting value, the second switching element is turned off, and when the voltage of the first capacitor is smaller than the voltage setting value, the second switching element is turned on. With a circuit,
The voltage setting value is higher than the voltage applied to the LED group.

Images