JP2010097880A - Light-emitting diode lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-emitting diode lighting device capable of further reducing a power loss of an impedance means serially connected with a switching element of a step-down chopper and excellent in temperature characteristics and having little variations in an output current. <P>SOLUTION: The light-emitting diode lighting device is provided with a step-down chopper DC equipped with a first circuit A serially including a switching element Q1, an impedance means Z1 and a first inductor L1, a second circuit B serially including the first inductor and a diode D1, a self-excitation type driving signal generation circuit DSG equipped with a second inductor L2 magnetically coupled with the first inductor and impressing an induced voltage on a controlling terminal of the switching element to maintain the switching element in an On state, and a turn-off circuit TOF provided with a comparing means which, after detecting a voltage of the impedance means, outputs when the detected voltage exceeds a reference value, and a switching element which is turned on by the output of the comparing means and turns off the switching element by short-circuiting an output terminal of the self-excitation driving signal generation circuit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light emitting diode lighting device provided with a step-down chopper.

  A light-emitting diode lighting device including a step-down chopper is known (see, for example, Patent Document 1). In the light-emitting diode lighting device including the step-down chopper described in FIG. 2 of Patent Document 1, a resistance element 61 having a small resistance value is connected between the FET 5 serving as the first switching element and the first inductor 7. The resistor element 61 is connected between the base and emitter of the bipolar transistor 21 which is the second switching element. The collector of the transistor 21 is connected to the gate terminal of the FET 5.

  When the FET 5 is turned on, a current flows through the resistance element 61 and the first inductor 7 and this current gradually increases. When the voltage across the resistance element 61 reaches a bias for operating the transistor 21, the transistor 21 The FET 5 is turned on, whereby the FET 5 is turned off. The voltage across the resistor element 61 is used as the base bias of the transistor 21. When this voltage reaches a predetermined voltage, the transistor 21 is turned on to turn off the FET 5, so that the turn-off timing is set to the second inductor. 12 can always be accurately taken without being influenced by the voltage value induced in the circuit 12. That is, the FET 5 can always be switched accurately.

  In addition, the base bias for turning on the transistor 21 is as low as 0.5 V in the case of a silicon transistor. Therefore, there is almost no power consumption in the resistance element 61, and wasteful power consumption can be prevented as much as possible.

Japanese Patent No. 4123886

  However, there is a demand for further reducing the power loss of the resistance element connected in series with the first switching element in the light-emitting diode lighting device of Patent Document 1. In addition, the temperature characteristic is determined by the temperature characteristic of the transistor 21, and there is a problem that it is difficult to provide a desired temperature characteristic.

  An object of the present invention is to provide a light-emitting diode lighting device that can further reduce power loss of impedance means connected in series with a switching element of a step-down chopper, has good temperature characteristics, and has little variation in output current.

  Another object of the present invention is to provide a light emitting diode lighting device having an overvoltage protection function against an abnormal condition of the light emitting diode of the load in addition to the above.

  The light-emitting diode lighting device of the present invention includes a DC power supply; an input terminal connected to the DC power supply, an output terminal connecting a load, a switching element, impedance means, and a first inductor in series, and between the input terminal and the output terminal. A step-down chopper including a first circuit connected, and a second circuit including a first inductor and a diode in series and connected to an output end; a light-emitting diode connected as a load to the output end of the step-down chopper; and a step-down chopper The voltage of the impedance means is detected and is turned on at the output of the comparison means and the output of the comparison means that are output when the detected voltage exceeds the reference value, and the output terminal of the self-excited drive signal generation circuit is short-circuited. And a turn-off circuit including a switch element for turning off the switching element.

  The present invention allows the following aspects.

  The DC power supply supplies power for rectifying an AC power supply, for example, a commercial AC power supply voltage to light the light emitting diode, in a DC mode to a step-down chopper described later. The mode of rectification is not particularly limited, but full wave rectification is preferable. However, not only a rectified DC power supply but also a DC power supply including a battery or the like may be used.

  Further, when the DC power supply is a rectified DC power supply, a smoothing capacitor can be connected between the output terminals to smooth the DC output voltage.

  As a preferred mode when using the rectified DC power supply of the present invention, a configuration in which the capacity of the smoothing capacitor is set to 12 to 20 μF and the output voltage of the step-down chopper is set to 35 to 48 V during lighting of the light emitting diode at an AC power supply voltage of 100 V Can be adopted. According to this aspect, the light-emitting diode lighting device satisfies the harmonic standard (JIS C61000-3-2 Class C) of the input current of 25 W or less, and the light-emitting diode can be used even for a reduction in the capacity of the smoothing capacitor during its lifetime. Since the current can be continuously supplied, the circuit life can be extended.

The step-down chopper is composed of first and second circuits, and a known chopper circuit in which a switching element and a first inductor are connected in series to an input end, and a first inductor and a diode are connected in series to an output end. It is. If the ON time of the switching element is T _ON , the OFF time is T _OFF , the DC power supply voltage is _VIN and the output voltage is _VOUT , the output voltage is V _OUT = V _IN · T _ON / (T _ON + T _OFF ) And lower than the input voltage.

  In the present invention, the impedance means is connected in series with the switching element of the step-down chopper, and when the current flowing through the impedance means reaches a predetermined value, a turn-off circuit described later is operated to turn off the switching element.

  The light emitting diode is connected to the output terminal of the step-down chopper as a load and is lit by being energized by the output current of the step-down chopper. The light emitting diodes connected to the output terminal of the step-down chopper may be a series circuit in which a plurality of light emitting diodes are connected in series, or may be a single one. A plurality of these may be connected in parallel to constitute a load circuit.

  In addition, since the light emitting diode is not particularly limited in its light emission characteristics, package mode, and the like, various known light emission characteristics, package modes, ratings, and the like can be appropriately selected and used.

  The self-excited drive signal generation circuit includes a second inductor magnetically coupled to the first inductor of the step-down chopper, and applies a voltage induced in the second inductor as a drive signal to the control terminal of the switching element. The switching element is kept on. If desired, an impedance element such as a series circuit of a capacitor and a resistor can be interposed between the second inductor and the control terminal.

  The turn-off circuit includes comparison means and a switch element, detects the voltage of the impedance means of the step-down chopper, and turns on the switch element with the output of the comparison means generated when the detected voltage exceeds a reference value. The switch element short-circuits the output end of the self-excited drive signal generation circuit. The switching element of the step-down chopper is turned off by this short circuit.

  The comparison means can set the input voltage to a voltage that is clearly lower than the base-emitter voltage when the switch element is turned on, for example, 0.3 V or less, by configuring the turn-off circuit with a switch element such as a transistor. it can. Thereby, the impedance of the impedance means can be reduced to a small value that can reduce the power loss generated there.

  Further, by interposing the comparison means between the impedance means and the switch element so that the switch element is turned on by the output voltage of the comparison means, the temperature characteristic of the step-down chopper turn-off is accompanied by the presence of the comparison means. Unaffected. As a result, the temperature characteristics of the light emitting diode lighting device are improved. That is, the comparison means compares the input voltage with a reference voltage set inside, and amplifies the input voltage to a high voltage and outputs it when the input voltage exceeds the reference voltage. The reference voltage is generally set using a Zener diode. Since the temperature characteristic of the comparison means is substantially determined by the temperature characteristic of the Zener diode that sets the reference voltage, selecting a Zener diode having a slightly negative characteristic or a flat temperature characteristic that is suitable as the temperature characteristic of the turn-off circuit is not possible. Easy.

  Furthermore, since the turn-off control of the switching element of the step-down chopper is performed by the operation of the comparison means, the variation management of the output current of the step-down chopper is easy and the variation is reduced.

  In the present invention, the turn-off circuit including the comparison means and the switch element can be configured mainly by a voltage comparator using an operational amplifier, that is, a comparator. In this case, either the first mode in which the turn-off circuit is configured by the comparator and the switch element that is turned on by the output voltage, or the second mode in which the turn-off circuit is configured by only the comparator having a relatively large sink current capacity. It may be. In the second mode, since the comparator itself has a relatively large sink current capacity, it exhibits the function of a switch element, so that a separate switch element is unnecessary.

  In the present invention, a preferred third aspect is the light emitting diode lighting device described above, further comprising a third inductor magnetically coupled to the first inductor of the step-down chopper, and the induced voltage of the third inductor exceeds a predetermined value. An overvoltage protection circuit for turning off the switching element of the step-down chopper.

  In this aspect, when the output voltage becomes an overvoltage due to the load abnormality, the voltage induced in the third inductor rises proportionally. As a result, the overvoltage protection circuit operates and the switching element of the step-down chopper is turned off to protect the circuit.

  The overvoltage protection circuit is preferably configured to output a negative voltage when the induced voltage of the third inductor becomes abnormally high using a comparator. Then, the negative output voltage is applied to the control terminal of the switching element of the step-down chopper. As a result, the switching element is turned off, the step-down chopper operation is stopped, and the protection operation is performed.

  According to a fourth preferred embodiment of the present invention, in the above configuration, a photocoupler is connected in parallel to the reference voltage source of the comparator of the turn-off circuit, and the photocoupler is driven in accordance with the PWM dimming signal. is doing. When the dimming signal is not a PWM system, the photocoupler may be driven after obtaining the PWM signal using a conversion circuit that converts the dimming signal into a PWM signal.

  According to this aspect, a light emitting diode lighting device having a dimming function can be obtained.

  According to the present invention, the turn-off circuit that turns off the switching element of the step-down chopper is connected in series with the switching element that short-circuits the output terminal of the self-excited drive signal generation circuit that supplies a driving signal to the switching element, and the switching element of the step-down chopper Impedance means and comparison means interposed between the switching elements, the impedance of the impedance means can be further reduced to further reduce the power loss of the impedance means, and the temperature characteristics are good, A light-emitting diode lighting device with little variation in output current can be provided.

  In addition, by including a third inductor that is magnetically coupled to the first inductor of the step-down chopper, and having an overvoltage protection circuit that turns off the switching element of the step-down chopper when the induced voltage exceeds a predetermined value, Since the protective operation is performed when the output voltage becomes an overvoltage due to a load abnormality, the light emitting diode of the load can be turned off before being damaged.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram showing a first embodiment for implementing the light-emitting diode lighting device of the present invention. In this embodiment, the light emitting diode lighting device includes a direct current power source DC, a step-down chopper SDC, a light emitting diode LED, a self-excited drive signal generation circuit DSG, and a turn-off circuit TOF. In addition to the above components, a starter circuit ST is attached.

  The DC power source DC includes a full-wave rectifier circuit DB and a capacitor C1 whose input ends are connected to the AC power source AC. The smoothing capacitor C1 is connected between the output terminals of the full-wave rectifier circuit DB. Note that a noise prevention capacitor C2 is connected between the input terminals of the full-wave rectifier circuit DB.

  The step-down chopper SDC includes input terminals t1 and t2 connected to a DC power source DC, output terminals t3 and t4 connecting a load, a switching element Q1, impedance means Z1, and a first inductor L1 in series. The circuit includes a first circuit A connected between the terminals t3, and a second circuit B including a first inductor L1 and a diode D1 connected in series and connected between the output terminals t3 and t4. A smoothing capacitor C3 is connected between the output terminals t3 and t4.

  In this embodiment, the switching element Q1 of the step-down chopper SDC is composed of an FET (field effect transistor), and its drain and source are connected to the first circuit A. Then, the first circuit A forms a charging circuit for the first inductor L1 via the capacitor C3 and / or a load circuit LC described later, and the second circuit B includes the first inductor L1 and the diode D1 as the capacitor C3. And / or the discharge circuit of the 1st inductor L1 is formed via the load circuit LC mentioned later. In this embodiment, the impedance means Z1 is a resistor, but an inductor or a capacitor having an appropriate resistance component can be used if desired.

  The desired number of the light emitting diodes LED forms the load circuit LC, and is connected between the output terminals t3 and t4 of the step-down chopper SDC, and is energized to light up.

  The self-excited drive signal generation circuit DSG includes a second inductor L2 magnetically coupled to the first inductor L1 of the step-down chopper SDC. Then, the voltage induced in the second inductor L2 is applied as a drive signal between the control terminal (gate) and the drain of the switching element Q1, and the switching element Q1 is maintained in the ON state. Note that the other end of the second inductor L2 is connected to the source of the switching element Q1 via the impedance means Z1.

  In this embodiment, the self-excited drive signal generation circuit DSG includes a series circuit of a capacitor C4 and a resistor R1 between the one end of the second inductor L2 and the control terminal (gate) of the switching element Q1 in addition to the above configuration. In series. Further, a zener diode ZD1 is connected between the output ends of the self-excited drive signal generating circuit DSG, and an overvoltage is applied between the control terminal (gate) and the drain of the switching element Q1 so that the switching element Q1 is not destroyed. A protection circuit is formed.

  The turn-off circuit TOF includes a comparator CP1, a switch element Q2, and first and second control circuit power supplies ES1 and ES2. The terminal P1 of the comparator CP1 is derived from the base potential side of the internal reference voltage circuit and is connected to the connection point between the impedance means Z1 and the first inductor L1. The reference voltage circuit is provided in the comparator CP1, generates a reference voltage by receiving power from a second control circuit power supply ES2 (described later) at a terminal P4, and operates as a non-operational amplifier in the comparator CP1. A reference voltage is applied to the inverting input terminal. Similarly, the terminal P2 is an input terminal of the comparator CP1, and is connected to a connection point between the first switching element Q1 and the impedance means Z1, and applies an input voltage to the inverting input terminal of the operational amplifier. A terminal P3 is an output terminal of the comparator CP1, and is connected to a base of a second switching element Q2 described later to apply an output voltage to the second switching element Q2. Further, the terminal P5 is connected to a first control circuit power supply ES1 described later, and supplies control power to the comparator CP1.

  The switch element Q2 is formed of a transistor, and has a collector connected to the control terminal of the first switching element Q1, and an emitter connected to a connection point between the impedance element Z1 and the first inductor L1. Therefore, when the switching element Q2 is turned on, the output terminal of the self-excited drive signal generation circuit DSG is short-circuited. Thus, the switching element Q1 is turned off. A resistor R2 is connected between the base and emitter of the switch element Q2.

  The first control circuit power supply ES1 is configured by connecting a series circuit of a diode D2 and a capacitor C5 to both ends of the second inductor L2, and the second inductor L2 is charged when the first inductor L1 is charged. The capacitor C5 is charged via the diode D2 with the induced voltage generated in the circuit, and a positive potential is output from the connection point between the diode D2 and the capacitor C5, and the control voltage is applied to the output terminal of the comparator CP1. Yes.

  The second control circuit power source ES2 is configured by connecting a series circuit of a diode D3 and a capacitor C6 to both ends of a third inductor L3 that is magnetically coupled to the first inductor L1, and the first inductor L1 is discharged. When the capacitor C6 is charged via the diode D3 with the induced voltage generated in the third inductor L3, a positive voltage is output from the connection point of the diode D3 and the capacitor C6, and the control voltage is applied to the reference voltage circuit. Thus, the reference voltage is generated.

  The starting circuit ST is a series circuit of a resistor R3 connected between the drain and gate of the first switching element Q1, and a resistor R10 connected in parallel to the resistor R1 and the capacitor C4 of the self-excited drive signal generating circuit DSG. , A second inductor L2, and a series circuit composed of the capacitor C3 of the second circuit B of the step-down chopper SDC and / or the light emitting diode LED of the load circuit LC, and the resistor R3 mainly when the DC power source DC is turned on. A positive starting voltage determined by the resistance value ratio of R10 is applied to the gate of the first switching element Q1, and the step-down chopper SDC is started.

  Next, circuit operation will be described.

  When the direct current power source DC is turned on and the step-down chopper SDC is activated by the activation circuit ST, the switching element Q1 is turned on, and the smoothing capacitor C3 and / or the light emitting diode LED of the load circuit LC is passed through the first circuit A from the direct current power source DC. An increasing current that increases linearly begins to flow. Due to this increased current, a positive voltage is induced in the second inductor L2 of the self-excited drive signal generation circuit DSG on the capacitor C4 side, and this induced voltage is applied to the switching element Q1 via the capacitor C4 and the resistor R1. Since a positive voltage is applied to the control terminal (gate), the switching element Q1 is maintained in the ON state and the increased current continues to flow. At the same time, a voltage drop occurs in the impedance means Z1 due to the increased current, and the drop voltage is applied as an input voltage to the terminal P2 of the comparator CP1 of the turn-off circuit TOF.

  When the input voltage of the comparator CP1 increases with the increase current and exceeds the reference voltage, the comparator CP1 operates and a positive output voltage is generated at the terminal P3. As a result, the switch element Q2 of the turn-off circuit TOF is turned on to short-circuit the output terminal of the self-excited drive signal generation circuit DSG, so that the switching element Q1 of the step-down chopper SDC is turned off and the increased current is cut off.

  When the switching element Q1 is turned off, the increased current flows through the first inductor L1, so that the electromagnetic energy stored therein is released, and the inside of the second circuit B including the first inductor L1 and the diode D1. Through the capacitor C3 and / or the light emitting diode LED of the load circuit LC. Due to this reduced current, a negative voltage is induced in the second inductor L2 of the self-excited drive signal generating circuit DSG on the capacitor C4 side, and this induced voltage causes a negative potential to be applied to the capacitor C4 via the Zener diode ZD1. In addition, since a zero potential is applied to the control terminal (gate) of the switching element Q1, the switching element Q1 is maintained in the off state and the reduced current continues to flow.

  When the emission of electromagnetic energy accumulated in the first inductor L1 ends and the reduced current becomes zero, a back electromotive force is generated in the first inductor L1, and the voltage induced in the second inductor L2 Is reversed, and the capacitor C4 side is again turned positive. When this induced voltage is applied to the gate of the switching element Q1 via the capacitor C4 and the resistor R1, the switching element Q1 is again turned on. Then, the increased current starts flowing again.

  Thereafter, the circuit operation similar to the above is repeated, and the increase current and the decrease current are combined and a triangular load current flows, whereby the light emitting diode LED of the load circuit LC is turned on.

  In the above circuit operation, the operation of the turn-off circuit TOF is performed by the two-stage operation of the comparator CP1 and the switch element Q2, and the comparator CP1 operates stably and accurately even when the input voltage is 0.3V or less. For this reason, since the resistance value of the impedance means Z1 can be reduced, even if the input voltage in the prior art is 0.5V, according to the present invention, the power loss of the impedance means Z1 is 40% more than in the prior art. % Or more can be reduced.

  Further, the temperature characteristic of the turn-off circuit TOF is determined on the comparator CP1 side, and a desired good temperature characteristic can be given to the comparator CP1, so that the problem caused by the temperature characteristic of the switch element Q2 as in the prior art is Disappear. The temperature characteristics of the comparator CP1 can be easily selected, for example, as a Zener diode used in the reference voltage circuit, whose temperature characteristics are slightly negative or flat. It can contribute as a temperature characteristic. Thereby, the light emitting diode lighting device with favorable temperature characteristics can be obtained.

  Further, by providing the comparator CP1 in the turn-off circuit TOF, the switch element Q2 can be operated stably and accurately, so that variations in the output of the light emitting diode lighting device are reduced.

  FIG. 2 is a circuit diagram showing a second mode for carrying out the light-emitting diode lighting device of the present invention. In the figure, the same parts as those in FIG. This embodiment is mainly different from the first embodiment in that an overvoltage protection circuit OVP is added.

  The overvoltage protection circuit OVP is mainly composed of the second control circuit power supply ES2 and the comparator CP2.

  The second control circuit power supply ES2 is the same as that in the first embodiment shown in FIG. Furthermore, one end of a series circuit of the resistor R4 and the resistor R5 and one end of a series circuit of the resistor R6 and the Zener diode ZD2 are connected in parallel to the connection point of the diode D3 and the capacitor C6.

  The comparator CP2 has an inverting input terminal P6 connected to the connection point of the resistor R4 and the resistor R5, and a series circuit of the resistor R4 and the resistor R5 connected in parallel to the capacitor C6 of the second control circuit power supply ES2. Yes. The resistors R4 and R5 constitute a voltage dividing circuit, and the divided terminal voltage of the resistor R5 is applied to the inverting input terminal P6.

  Further, the non-inverting input terminal P7 is connected to the reference voltage circuit of the comparator CP1, and thus to the input terminal P2 of the comparator CP1. The reference voltage circuit of the comparator CP1 includes a constant voltage unit and a reference voltage output unit. The constant voltage unit is composed of a series circuit of a resistor R6 and a Zener diode ZD2, and is connected in parallel to the capacitor C6 of the second control circuit power supply ES2. The reference voltage output unit of the reference voltage circuit is constituted by a voltage dividing circuit of resistors R7 and R8 connected in parallel to the Zener diode ZD2, and the divided terminal voltage of the resistor R8 is output as a reference voltage. This reference voltage is applied to the inverting input terminal P6 of the operational amplifier of the comparator CP1 and the non-inverting input terminal P7 of the comparator CP2. The terminal P1 in FIG. 1 is a connection point between the resistor R8 and the anode of the Zener diode ZD2.

  On the other hand, the operational amplifier of the comparator CP1 has a non-inverting input terminal connected to the terminal P2 in FIG. 1, an output terminal connected to the terminal P3, and also connected to the terminal P5 via the resistor R9.

  Thus, in this embodiment, when the light emitting diode LED of the load circuit LC becomes abnormal for some reason during lighting, and the output of the step-down chopper SDC becomes an overvoltage, the first inductor L1 is magnetically coupled and the first Since the voltage induced when the inductor L1 is the voltage at the time of discharging is output to the third inductor L3, which is proportional to the output voltage of the step-down chopper SDC, the terminal voltage of the capacitor C6 of the second control circuit power supply ES2 is also Increase proportionally. As a result, the terminal voltage of the capacitor C6 is divided by the resistors R4 and R5, and the voltage input to the inverting input terminal P6 of the comparator CP2 exceeds the reference voltage, so that a negative output voltage is output from the terminal P9. For this reason, the potential of the control terminal (gate) of the first switching element Q1 becomes negative, the first switching element Q1 is turned off, and the light emitting diode LED is turned off to be protected. After that, it is configured so that it cannot be restarted by setting the resistance values of the resistors R3 and R10 of the starting circuit ST. Other circuit operations are the same as those in the first embodiment shown in FIG.

  FIG. 3 is a circuit diagram showing a third mode for carrying out the light-emitting diode lighting device of the present invention. In the figure, the same parts as those in FIG. 1 and FIG. This embodiment is mainly different from the first embodiment in that a dimming control circuit DIM is added.

  The dimming control circuit DIM is configured by connecting the phototransistor on the photoreceiver side of the photocoupler PC in parallel to the resistor R8 of the reference voltage circuit, and connecting the not shown light emitter side to the output terminal of the dimming signal generation circuit. Has been.

  Thus, when the PWM dimming signal is emitted on the light emitter side of the photocoupler PC, the phototransistor on the light receiver side receives this light and turns it on / off. During the period when the phototransistor is on, the output of the reference voltage circuit is short-circuited and becomes almost zero, the switch element Q2 is turned on and the switching element Q1 is turned off, so that almost no current flows through the load circuit LC. In the dimming signal, the on-duty of the photocoupler PC increases as the dimming degree progresses.

  Therefore, the light emitting diode of the load circuit LC can be dimmed by changing the on-duty of the photocoupler PC by the dimming signal.

  4 to 6 are graphs for explaining a fourth embodiment for implementing the light-emitting diode lighting device of the present invention. The present embodiment is a light-emitting diode lighting device provided with means for satisfying a harmonic standard with a harmonic distortion of 25 W or less and having practical circuit efficiency. The above standard is JIS C61000-3-2 Class C, and the phase θ of the input current peak is 65 ° or less, the third harmonic is 86% or less, and the fifth harmonic is 61% or less. It stipulates that it must not be.

  FIG. 4 is a graph showing the relationship between the capacity of the smoothing capacitor of the DC power supply, the phase of the input current peak, and the harmonic component. In the figure, the horizontal axis indicates the capacitance Cin [μF] of the smoothing capacitor C1 (FIGS. 1 to 3), the vertical axis indicates the phase θ of the input current peak on the left side, and the harmonic [%] indicating the harmonic component on the right side. Each is shown. Further, “θ” attached to the curve in the figure indicates the phase of the input current peak, “3rd order” indicates the third harmonic component ratio, and “5th order” indicates the fifth harmonic component ratio. .

  As can be understood from the figure, when the capacity of the smoothing capacitor is practically 8 to 25 μF, the phase θ of the input current peak satisfies 65 ° or less, so there is no problem. The third harmonic component ratio “third order” is not a problem as long as the capacitance of the smoothing capacitor is about 22 μF or less. The fifth harmonic component ratio “fifth order” is not a problem as long as the capacitance of the smoothing capacitor is about 20 μF or less.

  Therefore, in the present invention, the capacity of the smoothing capacitor of the DC power supply is optimally 15 μF, and satisfies the above standard if it is in the range of 10 to 20 μF in consideration of component variations. The range is preferably 12 to 18 μF.

  FIG. 5 is a graph for explaining the relationship between the output voltage of the step-down chopper and the circuit efficiency. In the figure, the horizontal axis represents the output voltage VL [V], and the vertical axis represents the circuit efficiency WL / Win [%].

  As can be seen from the figure, a practical circuit efficiency of 89% or more can be obtained in the range of about 36 to 86V.

  FIG. 6 is a graph showing the relationship between the capacity of the smoothing capacitor of the DC power supply and the voltage ripple minimum value of the DC power supply. In the figure, the horizontal axis represents the capacitance Cin [μF] of the smoothing capacitor C1 (FIGS. 1 to 3), and the vertical axis represents the voltage ripple minimum value VDC-min [V] of the DC power supply. The minimum voltage ripple value is the minimum voltage ripple value obtained when the smoothing capacitor has a reduced capacity at the end of its life.

  As can be seen from the figure, the electrolytic capacitor used for the smoothing capacitor has a capacity decreasing at the end of its life, and the voltage ripple minimum value tends to be lowered accordingly, and the voltage ripple minimum value when the capacity is about 10 μF. 53V. The output voltage of the step-down chopper is less than or equal to the input voltage with respect to the AC power supply voltage of 100 V. However, in order to continue operation even when the voltage ripple of the input voltage is the lowest value, the output voltage is less than or equal to the lowest voltage ripple value. There must be. In addition, in order to perform switching of the step-down chopper stably, a margin of 5 V or more is further required, so it is preferable to set the output voltage to 48 V or less.

  In summary, if the smoothing capacitor has a capacitance of 10 to 20 μF (preferably 12 to 18 μF) and the output voltage is set to a range of 35 to 48 V, the harmonic distortion satisfies the harmonic standard of 25 W or less. At the same time, a light emitting diode lighting device having practical circuit efficiency can be provided. Note that this embodiment is preferably applied to the first to third embodiments of the present invention shown in FIGS. 1 to 3, but does not include a turn-off circuit comparator. Circuit configurations other than those shown in FIGS. 1 to 3 may be used.

The circuit diagram which shows the 1st form for implementing the light emitting diode lighting device of this invention The circuit diagram which shows the 2nd form for implementing the light emitting diode lighting device of this invention The circuit diagram which shows the 3rd form for implementing the light emitting diode lighting device of this invention Graph showing the relationship between the capacity of the smoothing capacitor of the DC power supply, the phase of the input current peak, and the harmonic components Graph explaining the relationship between the output voltage of the step-down chopper and circuit efficiency Graph showing the relationship between the capacity of the smoothing capacitor of the DC power supply and the minimum voltage ripple of the DC power supply

Explanation of symbols

  DC: DC power supply, DB: full-wave rectifier circuit, C1: smoothing capacitor, SDC: step-down chopper, Q1: switching element, Z1: impedance means, L1: first inductor, A: first circuit, B: second Circuit, D1, D2, D3 ... diode, LED ... light emitting diode, LC ... load circuit, DSG ... self-excited drive signal generation circuit, TOF ... turn-off circuit, ST ... start-up circuit, CP1, CP2 ... comparator, Q2 ... switch Element, ES1 ... first control circuit power supply, ES2 ... second control circuit power supply

Claims (2)

DC power supply;
An input terminal connected to a DC power source, an output terminal connected to a load, a switching element, an impedance means and a first circuit including a first inductor connected in series and connected between the input terminal and the output terminal, and a first inductor and A step-down chopper having a second circuit including a diode in series and connected to an output end;
A light emitting diode connected as a load to the output end of the step-down chopper;
A second inductor magnetically coupled to the first inductor of the step-down chopper is provided. The voltage induced in the second inductor is applied as a drive signal to the control terminal of the switching element, and the switching element is maintained in the on state. An excitation drive signal generation circuit;
The voltage of the impedance means of the step-down chopper is detected, and when the detected voltage exceeds the reference value, it is turned on by the output of the comparison means and the comparison means, and the output terminal of the self-excited drive signal generation circuit is short-circuited A turn-off circuit comprising a switch element for turning off the switching element;
A light-emitting diode lighting device comprising:   2. An overvoltage protection circuit comprising a third inductor magnetically coupled to the first inductor of the step-down chopper, wherein the switching element is turned off when the induced voltage exceeds a predetermined value. The light emitting diode lighting device of description.

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