JP5393744B2 - LED lighting device - Google Patents

Description

  The present invention relates to an LED lighting device.

  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 incandescent bulbs and fluorescent lamps with LEDs has begun.

  The light output of the LED is determined by the current flowing through the LED load (hereinafter referred to as LED current). Therefore, the LED lighting device desirably has a function of controlling the light output of the LED substantially constant by controlling the LED current substantially constant.

  As an LED lighting device having such a function, for example, there is a device described in Patent Document 1. The apparatus 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 is 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. Thereby, the LED current is controlled to be constant, and furthermore, since the turn-on loss of the switching element hardly occurs, high efficiency can be realized in power conversion.

  In many cases, an LED lighting device that uses an AC power source such as a commercial power source includes a rectifier circuit for generating a DC voltage from the AC voltage. In many cases, a capacitor is connected to the DC output side of the rectifier circuit to smooth the DC voltage. Hereinafter, such a capacitor is described as an input smoothing capacitor. The DC voltage generated on the DC output side of the rectifier circuit is referred to as the rectified voltage. As an input smoothing capacitor, an electrolytic capacitor (hereinafter referred to as an electrolytic capacitor) is generally used because of the advantage that the capacitance per volume (hereinafter referred to as a capacitance) is large. For example, aluminum electrolytic capacitors and tantalum electrolytic capacitors correspond to this. However, electrolytic capacitors have the disadvantage of having a short lifetime at high temperatures. The LED generates heat when emitting light. In many cases, the LED lighting device is arranged in a closed space such as the inside of the housing near the LED, so that the surroundings of the LED lighting device become high temperature. In particular, in a small and high-power LED lighting device, since the temperature rises seriously, it is desirable not to use an electrolytic capacitor as an input smoothing capacitor, but to replace it with a non-electrolytic capacitor (hereinafter referred to as a non-electrolytic capacitor). For example, ceramic capacitors and film capacitors correspond to this.

JP-A-2005-294063

  However, non-electrolytic capacitors have a smaller capacity per volume than electrolytic capacitors. Therefore, it is difficult to secure an equivalent capacity when there is a restriction on the size of the device. As a result, the rectified voltage cannot be sufficiently smoothed, and the pulsation amplitude of the rectified voltage may increase. In other words, the minimum value of the rectified voltage may be reduced.

  In the device described in Patent Document 1, when the rectified voltage becomes lower than the voltage of the LED load (hereinafter referred to as LED voltage), the step-down chopper becomes inoperable and the LED current rapidly decreases. Since this phenomenon occurs every half cycle of the AC power supply, if the frequency of the AC power supply is fac, the LED current may pulsate at a frequency of (2fac). This pulsation can cause flicker, or flicker. As a countermeasure against this problem, it is conceivable to use a step-up / step-down circuit such as a step-up / step-down chopper or a flyback converter instead of the step-down chopper. The step-up / step-down circuit can stably supply power to the LED even when the rectified voltage is lower than the LED voltage.

  However, if the control for operating in the current critical mode is applied to the step-up / step-down circuit with the peak value of the current flowing through the switching element being constant, the LED current pulsates according to the pulsation of the rectified voltage. When the non-electrolytic capacitor is used as the input smoothing capacitor, the pulsation of the rectified voltage is large and the pulsation of the LED current is also large, which may cause flicker, that is, flicker.

  In solving the above-described problems, a rectifier circuit that generates a DC voltage (hereinafter referred to as a rectified voltage) by AC-DC conversion of an AC power supply voltage, a capacitor connected to a DC output side of the rectifier circuit, and the rectifier An LED lighting device comprising a step-up / step-down circuit for DC-DC conversion of a voltage to feed a light-emitting diode (hereinafter referred to as LED) load, and a control circuit for driving a switching element included in the step-up / step-down circuit, The capacitor is a non-electrolytic capacitor (hereinafter referred to as an non-electrolytic capacitor), and the control circuit is configured so that the step-up / step-down circuit operates in a current intermittent mode and the switching frequency of the switching element is The LED lighting device is characterized in that the switching element is driven so that the product of the current setting value of the buck-boost circuit is substantially constant. That.

  According to the LED lighting device of the present invention, flickerlessness can be realized by reducing the pulsation of the LED current even when the high temperature resistance is enhanced by using a non-electrolytic capacitor.

It is a block diagram of the LED lighting device in this invention. It is a structure of the LED lighting device in 1st and 2nd embodiment of this invention. It is an operation | movement waveform of the LED lighting device in 1st Embodiment of this invention. It is a structure of the LED lighting device in 1st and 2nd embodiment of this invention. It is an operation | movement waveform of the LED lighting device in 2nd Embodiment of this invention. It is a structure of the LED lighting device in 3rd and 4th embodiment of this invention. It is an operation | movement waveform of the LED lighting device in 3rd Embodiment of this invention. It is a structural example of the setting signal generation circuit in 3rd Embodiment of this invention. It is a structural example of the setting signal generation circuit in 3rd Embodiment of this invention. It is an operation | movement waveform of the LED lighting device in 4th Embodiment of this invention. It is an operation | movement waveform of the LED lighting device in 5th Embodiment of this invention. It is a structure of the LED lighting device in 5th Embodiment of this invention. It is another structure of the LED lighting device in 1st and 2nd embodiment of 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 present invention. The LED lighting device includes a rectifier circuit 101 for obtaining a DC rectified voltage from an AC voltage of the AC power supply 100, a non-electrolytic capacitor 102 connected to the DC output side of the rectifier circuit 101, and a rectified voltage. A step-up / down circuit 103 that performs DC-DC conversion and supplies power to the LED load 104 and a control circuit 105 that drives a switching element included in the step-up / down circuit 103 are configured. The LED load 104 is not limited in the number and connection form of LEDs, and may include an LED module incorporating a protection element or the like.

  In the control circuit 105, the frequency variable circuit 107 turns on the drive circuit 106 so as to vary the switching frequency (fs) of the switching element in the step-up / down circuit 103 based on the frequency setting signal output from the setting signal generation circuit 109. Output a signal. Here, the magnitude of the frequency setting signal does not necessarily determine the switching frequency. For example, it may be considered that the frequency setting signal is a periodic signal, and the period corresponds to the switching period, and hence the switching frequency. Since the frequency variable circuit 107 also changes the off time of the switching element as a result, it can also be said to be an off time variable circuit. However, this is an expression problem, and the operation of the obtained LED lighting device is the same. Therefore, in the following description, it is unified as a frequency variable circuit.

  The on-time variable circuit 108 outputs a turn-off signal to the drive circuit 106 so as to vary the on-time of the switching element based on the detected current of the step-up / down circuit 103 and the current setting signal output from the setting signal generation circuit 109. To do. Specifically, a turn-off signal is output to the drive circuit 106 when the detected current of the step-up / down circuit 103 reaches a value determined by the current setting signal (hereinafter, this value is referred to as a current setting value Ip). Here, the magnitude of the current setting signal does not necessarily determine the current setting value. For example, it may be considered that the frequency setting signal is a pulse signal having a constant amplitude and the pulse density corresponds to the current setting value.

  The drive circuit 106 outputs a drive signal so as to turn on or off the switching element of the step-up / down circuit 103 according to the turn-on signal output from the frequency variable circuit 107 and the turn-off signal output from the on-time variable circuit 108.

  The setting signal generation circuit 109 determines the frequency setting signal and the current setting signal so that (Ip × fs) is substantially constant. Here, the reason why it is described as being substantially constant is that it is difficult to make (Ip × fs) a completely constant value in consideration of component variations and control delay time, and a slight variation is expected. is there. Actually, if (Ip × fs) is in the range of ± 10%, it can be considered that it fluctuates. In the present invention, such a fluctuation is considered to be allowed. In some embodiments, the detected value of the rectified voltage is fed back to the setting signal generation circuit 109 as shown in FIG. 1, and the frequency setting signal and the current setting signal are determined based on this feedback.

<First Embodiment>
FIG. 2 shows an LED lighting device according to the first embodiment of the present invention. In FIG. 2, the full-wave rectifier circuit using the diode bridge 110 corresponds to the rectifier circuit 101 of FIG. Further, the step-up / step-down chopper configured by the choke coil 112, the power MOSFET 113 which is a switching element, the diode 114, the capacitor 115, and the current detection means 116 corresponds to the step-up / down circuit 103 in FIG.

  In FIG. 2, instead of the power MOSFET 113, other types of switching elements such as bipolar transistors and IGBTs may be used. The switching element may be built in the IC. Instead of the full-wave rectifier circuit, another type of rectifier circuit such as a voltage doubler rectifier circuit may be used. Instead of the step-up / step-down chopper, another type of step-up / step-down circuit such as a flyback converter may be used. Circuit protection parts such as fuses and capacitors and choke coils may be added as noise countermeasure parts. These alternatives and additional items are applicable to all embodiments of the present invention.

  FIG. 3 is an operation waveform of the LED lighting device according to the first embodiment of the present invention. On the upper side of FIG. 3, the rectified voltage (Vdc) in one cycle (Tac) of the AC power supply 101 is shown by a solid line. For reference, a full-wave rectified waveform when Vdc is not smoothed at all is indicated by a dotted line. When a non-electrolytic capacitor is used as the input smoothing capacitor, it is difficult to ensure a sufficient capacity for smoothing. As a result, Vdc pulsates at a cycle (Tac / 2), that is, at a frequency twice that of the AC power supply, as shown on the upper side of FIG. The smaller the capacity or the larger the power of the LED load, the larger the amplitude of the Vdc pulsation and the closer to the dotted full-wave rectified waveform. In other words, the minimum value of Vdc is reduced.

  The lower part of FIG. 3 shows waveforms in which the time axis range is expanded for (a) when Vdc is high and (b) when Vdc is lowest. In the lower diagram, in addition to Vdc, the power MOSFET 113 on / off state (SW), power MOSFET 113 current (IQ), choke coil 112 current (IL), diode 114 current (ID), LED current (ILED ) Waveform is also shown. Regarding the polarity of these voltages and currents, the direction of the arrow shown in FIG. 2 is positive. Note that the capacitor 115 removes the pulsation of the switching frequency, and it is considered that a sufficient capacity can be secured even if a non-electrolytic capacitor is used. For this reason, it was assumed that the ILED is completely smoothed and becomes the DC component of the ID, that is, the average value.

  The operation of the step-up / step-down chopper and the control circuit 105 will be described with reference to FIG. First, the operation of the buck-boost chopper will be described. When the power MOSFET 113 is on, a current flows through the step-up / down chopper through the path of the choke coil 112, the power MOSFET 113, and the current detection means 116 using the rectified voltage of the non-electrolytic capacitor 102 as a voltage source. At this time, substantially the same voltage as Vdc is applied to the choke coil 112. Further, as shown in the lower side of FIG. 3, Vdc hardly changes in the switching period of the power MOSFET 113. Therefore, like the IQ and IL waveforms in FIG. 3, this current increases linearly with time. The on-time variable circuit 108 turns off the power MOSFET 113 when this current reaches the current set value (Ip). In other words, the on-time of the power MOSFET 113 is varied so that the peak value of the current flowing through the power MOSFET 113 serving as a switching element matches Ip. If the on-time of the power MOSFET 113 is defined as Ton, Ton can be written as (Equation 1).

Ton = (L × Ip) / Vdc (Formula 1)
In (Expression 1), L is the self-inductance of the choke coil 112. From (Equation 1) and FIG. 3, Ton depends on Vdc, and Ton becomes shorter as Vdc becomes higher. When the power MOSFET 113 is turned off, the step-up / step-down chopper is disconnected from the voltage source, but the path of the parallel body of the choke coil 112, the diode 114, the LED load 104, and the capacitor 115 by the energy stored in the choke coil 112. A reflux current flows through At this time, substantially the same voltage as the LED voltage (VLED) is applied to the choke coil 112 in the direction opposite to the ON period. Therefore, like the IL and ID waveforms in FIG. 3, the circulating current decreases linearly with time. As described above, the frequency variable circuit 107 turns on the power MOSFET 113 so that the switching frequency (fs) of the power MOSFET 113 becomes a value according to the frequency setting signal. That is, when the switching period (Ts = 1 / fs) determined as the reciprocal of fs has elapsed since the power MOSFET 113 was previously turned on, the power MOSFET 113 is turned on again. Here, in the first embodiment, as shown in FIG. 3, the step-up / step-down chopper is operated in the current intermittent mode regardless of Vdc. That is, the power MOSFET 113 is turned on when a further time elapses after the circulating current decreases to zero. Here, the off time of the power MOSFET 113 is defined as Toff, and the time until the circulating current becomes zero in Toff is defined as the circulating time (Toff1), and the remaining time is defined as the intermittent time (Toff2). Toff1 and Toff2 can be written as (Equation 2) and (Equation 3), respectively.

Toff1 = (L × Ip) / VLED (Formula 2)
Toff2 = Ts− (Ton + Toff1) (Formula 3)
Toff1 does not depend on Vdc. VLED is a constant determined by the number of LEDs connected in series in the LED load, and Toff1 may be treated as a constant. The mode in which Toff2 becomes substantially zero, that is, the mode in which the power MOSFET 113 is turned on when the circulating current is reduced to substantially zero is called a current critical mode. In the present invention, the current critical mode is considered to be included in the current intermittent mode. However, only when the current critical mode is intentionally used, it is described as the current critical mode.

  Next, an equation for determining the ILED in the buck-boost chopper and the operation of the control circuit 105 in the first embodiment will be described. As already described, since ILED is a DC component (average value) of ID, it can be written as (Equation 4) using Ip.

ILED = (Ip / 2) × (Toff1 / Ts)
= (Ip × fs × Toff1) / 2 (Formula 4)
(Equation 4) shows that ILED is proportional to (Ip × fs) in the buck-boost chopper. In the present invention, since (Ip × fs) is controlled to be substantially constant regardless of Vdc, the ILED can also be controlled to be substantially constant regardless of Vdc, and flickerless can be realized. Particularly in the first embodiment, as the simplest method among them, fs and Ip are set to be substantially constant regardless of Vdc. This method does not require detection of Vdc, and has the advantage that the configuration of the apparatus is simple. Specifically, an IC for LED (hereinafter simply referred to as IC) capable of setting Ip and fs is commercially available, and each element of the control circuit 105 can be configured by the IC and its peripheral circuits. As an IC having such a function, for example, there is HV9910B manufactured by SuperTex.

  FIG. 4 shows more specifically the control circuit 105 in the LED lighting device of FIG. 2, and uses HV9910B of SuperTex as an IC. The IC 117 shown as a block in FIG. 4 is the HV9910B. In FIG. 4, a resistance voltage dividing circuit including resistors 118 and 119 is generated, and the voltage input to the LD pin of the IC 117 corresponds to the current setting value. Since the VDD pin is a constant voltage source, Ip has a substantially constant value determined by the voltage division ratio. Note that Ip increases as the voltage input to the LD pin increases. The switching frequency is determined by the value of the resistor 120 connected to the RT pin of the IC 117. Therefore, it can be said that the resistor 120 generates a frequency setting signal for obtaining a substantially constant fs. Note that the larger the value of the resistor 120, the smaller fs becomes (Ts becomes larger).

  As a configuration of the control circuit 105, an IC is not necessarily used. For example, the on-time variable circuit 108 can be configured by using a comparator. It is also conceivable that all or part of the functions of the control circuit 105 are realized by software using a microcomputer or a digital signal processor instead of the IC. As described above, a specific method for realizing the control circuit 105 does not matter.

The conditions for operating the buck-boost chopper in the current intermittent mode regardless of Vdc will be described.
As shown in FIG. 3, Ton is the longest when Vdc is the lowest. The minimum value of Vdc is defined as Vdc (min), and Ton at Vdc (min) is defined as Ton (max). Ton (max) can be written as (Equation 5).

Ton (max) = (L × Ip) / Vdc (min) (Formula 5)
Ip, fs, and other constants may be determined so that Ts = (1 / fs) is larger than the sum of Ton (max) and Toff1. Therefore, the conditional expression for operating in the current intermittent mode regardless of Vdc is (Expression 6).

Ts = (1 / fs)> Ton (max) + Toff1
= (L × Ip) {1 / Vdc (min) + 1 / VLED} (Formula 6)
In order to set a constant according to (Expression 6), it is necessary to grasp Vdc (min) in advance. Vdc (min) varies depending on the power supplied to the LED load 104 and the electrostatic capacity of the non-electrolytic capacitor 102, but can be measured by performing circuit simulation or actual machine experiment.

  As described above, it is possible to realize flickerlessness by reducing the pulsation of the LED current while enhancing the high temperature resistance by using the non-electrolytic capacitor.

Second Embodiment
In the second embodiment of the present invention, the configuration of the lighting device is the same as that of the first embodiment, but the setting method of Ip and fs in the control circuit 105 is different from that of the first embodiment. FIG. 5 is an operation waveform of the LED lighting device according to the second embodiment of the present invention. As shown in FIG. 5, in the second embodiment, Ip and fs are determined so as to operate in the current critical mode when Vdc is the lowest.
Other points are the same as in the first embodiment. As already described, in the current critical mode, the power MOSFET 113 is turned on when IL or IQ decreases to substantially zero after the power MOSFET 113 is turned off. As shown in FIG. 5, when Vdc is the lowest, Toff2 may be set to substantially zero, so the conditional expression for setting Ip, fs, etc. is (Expression 7).

(1 / fs) = Ton (max) + Toff1
= (L × Ip) {1 / Vdc (min) + 1 / VLED} (Expression 7) Here, in the setting based on (Expression 7), an error of about ± 10% is allowed to occur. This is because the setting uses nominal values for constants such as L and VLED, but the actual L and VLED do not completely match the nominal values. Considering that there are variations in L and VLED, it is considered reasonable to allow an error of ± 10%.

  Toff2 being substantially zero means that the ratio of the circulation period (Toff1) to the switching period (Ts) is maximized. Therefore, from (Equation 4), Ip for supplying the same ILED can be minimized. As a result, the peak value of the current flowing through the buck-boost chopper is reduced, and the lighting device can be made smaller and more efficient.

<Third Embodiment>
FIG. 6 shows an LED lighting device according to the third embodiment of the present invention. 2 is almost the same as in FIG. 2 relating to the first embodiment, but differs only in that Vdc is detected and fed back to the setting signal generation circuit 109 of the control circuit 105. That is, in the third embodiment, Ip and fs are changed according to Vdc in a range where (Ip × fs) is substantially constant. FIG. 7 is an operation waveform of the LED lighting device according to the third embodiment of the present invention. As shown in FIG. 7, in the third embodiment, Ip and Ts are decreased as Vdc increases. The reciprocal of Ts, fs, increases as Vdc increases.

  FIG. 8 is a configuration example of the setting signal generation circuit 109 in the third embodiment. In FIG. 8, preprocessing is applied to Vdc by the gain circuit 125 and the adder circuit 126. By this pretreatment, the amount of change in Ip and fs with respect to the change in Vdc can be adjusted. However, the presence or absence of this pre-processing is arbitrary and may be omitted. Further, there is no limitation on the detailed configuration of the preprocessing portion, such as providing another gain circuit after the adder circuit 126 or providing a buffer circuit in the middle. As shown in FIG. 8, the preprocessed Vdc is defined as Vdc ′. For Vdc ′, the proportional circuit 123 generates fs, and the inverse proportional circuit 124 generates Ip. As a result, Ip can be decreased and fs can be increased as Vdc increases while (Ip × fs) is substantially constant. Note that the proportional circuit 123, the inverse proportional circuit 124, the gain circuit 125, and the adder circuit 126 can all be realized by an analog electronic circuit using an operational amplifier or the like, but the specific implementation method is not limited. An IC incorporating these analog circuits may be used. It is also conceivable to use a microcomputer or a digital signal processor instead of the IC to make the function of the setting signal generation circuit 109 into software.

  Here, as long as (Ip × fs) is made substantially constant, the setting signal generation circuit 109 can be realized by an analog electronic circuit having a simpler configuration. That is, instead of the inverse proportional circuit 124, a circuit for generating Ip so that Vdc ′ and Ip are in a monotonically decreasing relationship is provided. FIG. 9 is a configuration example of the setting signal generation circuit 109 when it is assumed that the SuperTex HV9910B used in FIG. 4 is used. Transistors 127 and 128 are inserted into the peripheral circuit of the RT pin that determines fs and the peripheral circuit of the LD pin that determines Ip, respectively, and these are used as variable resistors, so that Ip decreases as Vdc increases, and fs Increased control can be realized. Note that another semiconductor element such as a MOSFET may be used instead of the transistor.

  The conditions for operating the buck-boost chopper in the current intermittent mode regardless of Vdc are the same as in the first embodiment, and Ip, fs and other constants in Vdc (min) may be determined according to (Equation 6).

  In the third embodiment, since the current peak value when Vdc is high can be further reduced as compared with the second embodiment, the lighting device can be reduced in size and efficiency.

<Fourth embodiment>
FIG. 10 shows operation waveforms of the LED lighting device according to the fourth embodiment of the present invention. In the fourth embodiment, on the basis of the third embodiment, Ip, fs, etc. are determined so as to operate in the current critical mode when Vdc is the lowest. Other points are the same as in the third embodiment. The conditions for operating the step-up / step-down chopper in the current intermittent mode regardless of Vdc and in the current critical mode only at Vdc (min) are as in the second embodiment (Formula 7). Here, as in the second embodiment, an error of about ± 10% is allowed in the setting of Ip and fs based on (Equation 7). The reason is omitted as it is described in the description of the second embodiment.

  In the fourth embodiment, since the current peak value can be further reduced as compared with the third embodiment, the lighting device can be reduced in size and efficiency.

<Fifth Embodiment>
FIG. 11 is an operation waveform of the LED lighting device according to the fifth embodiment of the present invention. As shown in FIG. 11, in the fifth embodiment, the current critical mode is always operated regardless of Vdc, and Ip is decreased as Vdc is higher. Assuming that the current critical mode is always operated regardless of Vdc under the condition that Ip is constant, Ts decreases as Vdc increases. On the other hand, Toff1 does not depend on Vdc. Therefore, from (Equation 4), ILED increases as Vdc increases, and flickerless cannot be realized. As a countermeasure, Ip is decreased as Vdc increases. In addition, since fs increases automatically as Vdc increases, (Ip × fs) becomes substantially constant.

As the control circuit in the fifth embodiment, it is desirable to apply a dedicated configuration for operating in the current critical mode. As an example of such a configuration, there is a choke coil provided with an auxiliary winding. FIG. 12 shows an example of a lighting device according to the fifth embodiment, in which the current critical mode is realized using the auxiliary winding 131 of the choke coil provided in the choke coil 112. The setting signal generation circuit 109 outputs Ip according to Vdc, and outputs a current setting signal to the on-time variable circuit 108 so that Ip decreases as Vdc increases. Further, the end point of the circulation period (Toff1) is detected based on the voltage generated in the auxiliary winding 131 of the choke coil, and the frequency setting signal is output to the frequency variable circuit 107 based on this.
Specifically, it is utilized that the polarity of the voltage generated in the auxiliary winding 131 of the choke coil is reversed at the end of Toff1. As a result, even if Vdc changes, and Ip changes accordingly, the switching frequency can be automatically changed so as to always maintain the operation in the current critical mode. There are other methods for detecting the end point of Toff1, for example, a detection method using the fact that the drain voltage of the power MOSFET 113, which is a switching element, is detected and this voltage drops below a certain value at the end point of Toff1. May be used.

  In the fifth embodiment, since the current peak value can be further reduced as compared with the fourth embodiment, the lighting device can be reduced in size and efficiency.

  As another configuration common to all the embodiments of the present invention, description will be given of replacing the buck-boost chopper with a flyback converter. For example, in the LED lighting device shown in FIG. 2, when the choke coil 112 is changed to a transformer and the buck-boost chopper is replaced with a flyback converter, FIG. 13 is obtained. The flyback converter is effective in an application for insulating between the LED load 104 and the AC power supply 100. Moreover, if the transformer transformation ratio is used, it is possible to cope with LED loads with a wide range of LED voltages. A detailed description of the operation when the flyback converter is used is omitted because it is similar to the step-up / step-down chopper.

DESCRIPTION OF SYMBOLS 100 AC power supply 101 Rectifier circuit 102 Non-electrolytic capacitor 103 Buck-boost circuit 104 LED load 105 Control circuit 106 Drive circuit 107 Frequency variable circuit 108 On-time variable circuit 109 Setting signal generation circuit 110 Diode bridge 112 Choke coil 113 Power MOSFET
114 Diode 115 Capacitor 116 Current detection means 117 IC (SuperTex, HV9910B)
118 resistor (119, 120, 121, 122, 129, 130 are the same)
123 Proportional circuit 124 Inverse proportional circuit 125 Gain circuit 126 Adder circuit 131 Auxiliary winding 135 of choke coil Primary winding 136 of transformer 136 Secondary winding of transformer

Claims (5)

A rectifier circuit that AC-DC converts an AC power supply voltage to generate a rectified voltage, a capacitor connected to a DC output side of the rectifier circuit, and a step-up / step-down converter that DC-DC converts the rectified voltage to supply an LED load An LED lighting device comprising a circuit and a control circuit for driving a switching element provided in the step-up / step-down circuit,
The capacitor is a non-electrolytic capacitor, and the control circuit is configured so that the step-up / step-down circuit operates in a current intermittent mode, and the switching frequency of the switching element and the current setting value of the step-up / down step circuit The LED lighting device is characterized in that the switching element is driven so that the product of is substantially constant. The LED lighting device according to claim 1,
The control circuit detects a setting signal generation circuit that generates a frequency setting signal and a current setting signal, a frequency variable circuit that varies a switching frequency of the switching element according to the frequency setting signal, and a current flowing through the switching element. And an on-time variable circuit that turns off the switching element when the current reaches a current set value determined by the current setting signal, and the setting signal generation circuit is configured to calculate a product of the switching frequency and the current set value. The LED lighting device is characterized in that the switching element is driven so that is substantially constant. The LED lighting device according to claim 1,
The LED lighting device, wherein the control circuit operates the step-up / step-down circuit in a current critical mode when the rectified voltage becomes the lowest. In the LED lighting device according to claim 1,
The LED lighting device, wherein the control circuit makes the switching frequency and the current set value substantially constant. In the LED lighting device according to claim 1,
The LED lighting device, wherein the control circuit detects the rectified voltage and decreases the current set value as the rectified voltage is higher.