JP2012084489A - Led lighting device and led illuminating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED lighting device which allows improvement of power factor and enables reduction in device size.SOLUTION: An LED lighting device comprises: a power factor correction (PFC) circuit to which a coil 13 and a switch 14 are connected in series, and whose both ends are connected to output terminals of a rectifier circuit 33; a power storage circuit to which a capacitor 15 and a diode 16 are connected in series, whose both ends are connected to the switch, and which charges, via the diode, the capacitor with a total voltage of electromotive force generated in the coil and a voltage from the rectifier circuit when the switch is in an open state, and supplies an electrical charge accumulated in the capacitor to an LED 40 via the switch 14 when the switch is in a short-circuited state; and a smoothing circuit to which a smoothing coil 17 and a smoothing capacitor 18 are connected in series, whose both ends are connected to the diode, and which smooths current output from the power storage circuit and supplies a both-end voltage of the smoothing capacitor to the LED.

Description

  The present invention relates to an LED lighting device and an LED lighting device.

  FIG. 1 of Patent Document 1 discloses an LED lighting device including a power factor correction circuit. In this LED lighting device, AC power from an AC power source is converted to DC power and supplied to the LED, and the current waveform output from the rectifier circuit is controlled to resemble the voltage waveform, thereby improving the power factor is doing.

JP 2004-327152 A

  In the technique described in Patent Document 1, the output voltage is controlled so that the current flowing through the LED becomes constant. For this reason, there is a problem that it is easily affected by ripples. Specifically, when 40 LEDs having a forward drop voltage (Vf) of 2.7 V and an internal resistance R of 5Ω are connected in series and lighted through a current of 100 mA, the forward drop voltage of the 40 LEDs is reduced. Is 108V, and the total internal resistance is 200Ω. At this time, in order to pass a current of 100 mA, it is necessary to apply a voltage of 128 V (= 108 V + 100 mA × 200Ω). Here, when a ripple of ± 5% (121.6 to 134.4 V) exists in the applied voltage, the current flowing through the LED is 68 mA (= (121.6 V−108 V) / 200Ω) to 132 mA (= (134. 4V-108V) / 200Ω), which results in a ripple of ± 32%. For this reason, in order to prevent such a ripple, it is necessary to use an electrolytic capacitor having a large capacity as a smoothing capacitor, and there is a problem that the size of the circuit increases. In particular, in recent years, the internal resistance of LEDs tends to decrease, and those having an internal resistance of less than 0.1Ω have been developed. In the case of such an LED, since the current fluctuation with respect to the voltage fluctuation is further increased, there is a problem that an electrolytic capacitor having a larger capacity is required.

  An object of the present invention is to provide an LED lighting device and an LED lighting device capable of improving the power factor and miniaturizing the device.

The present invention for solving the above-mentioned problems is directed to an LED lighting device for lighting one or a plurality of LEDs with pulsating power obtained by rectifying AC power with a rectifier circuit, wherein a coil and a switch are connected in series, and the rectification is performed. A PFC circuit whose both ends are connected to the output terminal of the circuit; a capacitor and a diode are connected in series; both ends are connected to the switch; and the electromotive force generated in the coil when the switch is in an open state; A power storage circuit that charges the capacitor via the diode by a total voltage from a rectifier circuit, and supplies the charge accumulated in the capacitor to the LED via the switch when the switch is short-circuited; A smoothing coil and a smoothing capacitor are connected in series, and both ends thereof are connected to the diode. It smoothes the current al output, and having a smoothing circuit for supplying the LED voltage across the smoothing capacitor.
According to such a configuration, it is possible to provide an LED lighting device capable of improving the power factor and reducing the size of the device.

In addition to the above invention, another invention is characterized in that an on-time of the switch is controlled in accordance with a current flowing through the LED.
According to such a configuration, it is possible to arbitrarily control the current flowing through the LED.

In addition to the above-mentioned invention, another invention is characterized in that the switch is turned on or off based on PWM control or FM control corresponding to a current flowing through the LED.
According to such a configuration, it is possible to accurately control the current flowing through the LED.

According to another aspect of the invention, in addition to the above-described invention, the switch turns off the switch when the current flowing through the LED increases and reaches a predetermined current value, and the current flowing through the smoothing coil decreases. It is controlled by current critical mode control for turning on the switch when it becomes substantially zero.
According to such a configuration, it is possible to accurately control the current flowing through the LED.

In addition to the above-described invention, another invention may be configured such that the reference voltage of the PWM control or FM control or the predetermined current value of the current critical mode control is a dimming target value as a dimming target value of the LED. It is set according to.
According to such a configuration, it is possible to adjust the light emission intensity of the LED by adjusting the dimming target value.

In addition to the above-mentioned invention, another invention is characterized in that the switch is controlled to be in an ON state at a timing when the current flowing through the smoothing coil becomes substantially zero.
According to such a configuration, it becomes possible to use a diode with a slow recovery time, so that the manufacturing cost of the device can be reduced.

Further, the present invention is characterized in that the LED lighting device described above and the LED are accommodated in a housing.
According to such a configuration, it is possible to provide an LED lighting device capable of improving the power factor and reducing the size of the device.

It is a block diagram which shows the LED lighting device which concerns on 1st Embodiment of this invention. It is a figure which shows the electric current which flows into an LED lighting device, when the transistor 14 of FIG. 1 is ON. It is a figure which shows the electric current which flows into an LED lighting device, when the transistor 14 of FIG. 1 is OFF. It is a figure which shows the time change of the electric current which flows into the coil 17 of FIG. It is a figure which compares the electric current which flows into 1st Embodiment of this invention, and the electric current which flows into the conventional circuit. It is a block diagram which shows the LED lighting device which concerns on 2nd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(A) Description of Configuration of First Embodiment FIG. 1 is a block diagram illustrating a configuration example of an LED (Light Emitting Diode) lighting device according to the first embodiment of the present invention. As shown in this figure, the LED lighting device 10 includes a capacitor 11, a diode 12, a coil 13, a transistor 14, a capacitor 15, a diode 16, a coil 17, a capacitor 18, a resistor 19, and a PWM (Pulse Width Modulation) control circuit. 20 is a main component. The LED lighting device 10 lights the LED 40 based on the pulsating power supplied from the AC power supply 30 and rectified by the diode bridge 33. In the following, the case where the LED lighting device 10 supplies a current of 100 mA to the LED 40 will be described as an example. Of course, other values may be used.

  Capacitor 11 is 0. It is composed of a ceramic capacitor or a film capacitor having a capacity of about several μF (for example, about 0.1 to 0.47 μF), and attenuates high frequency components included in pulsating power output from the diode bridge 33. The switching noise flowing out to the AC power supply 30 is attenuated.

  The diode 12 is a rectifying diode and is a diode for preventing a backflow from the capacitor 15. The coil 13 (corresponding to “Coil” in the claims) is a choke coil for PFC (Power Factor Correction), and in this example, is constituted by a coil having an element value of about 0.5 mH, for example.

  The transistor 14 (corresponding to “switch” in the claims) is configured by, for example, a MOS-FET (Metal-Oxide Semiconductor Field Effect Transistor) or the like, and is turned on or off under the control of the PWM control circuit 20. In the example of FIG. 1, an N-channel MOS-FET is used as the transistor 14, but other semiconductor switches (for example, bipolar transistors, IGBTs, etc.) can also be used.

  The capacitor 15 (corresponding to “capacitor” in the claims) is charged by the sum of the pulsating voltage and the electromotive force generated in the coil 13 when the transistor 14 is off. Further, when the transistor 14 is on, the accumulated charge is discharged to the LED 40. The capacitor 15 has a capacity of, for example, about several tens of μF to several tens of μF. In the first embodiment, the capacitor 15 is configured by an electrolytic capacitor having a capacity of 22 μF.

  The diode 16 (corresponding to “diode” in the claims) is a free wheel diode (commutation diode). When the transistor 14 is on, the diode 15 is reverse-biased and discharged from the capacitor 15. When the current is cut off and the transistor 14 is off, the charging current from the coil 13 to the capacitor 15 is passed through the forward bias state.

  The coil 17 (corresponding to the “smoothing coil” in the claims) functions as a smoothing coil and also functions as a so-called Buck coil constituting a Buck type switching regulator. The coil 17 stores the electric charge discharged from the capacitor 15 as magnetic energy when the transistor 14 is on, and supplies the stored magnetic energy to the LED 40 when the transistor 14 is off. In this example, the coil 17 is a coil having an element value of about 2.5 mH, for example.

  The capacitor 18 (corresponding to the “smoothing capacitor” in the claims) is a smoothing capacitor, and is constituted by an electrolytic capacitor having a capacity of several μF to several tens μF (for example, about 4.7 μF to 22 μF), and a coil. The output of 17 is smoothed and output. The resistor 19 is a detection resistor for detecting a current flowing through the LED 40.

  The PWM control circuit 20 controls the transistor 14 to be on or off at a constant cycle (switching frequency) based on the PWM control. That is, the PWM control circuit 20 receives the detection voltage Vr from the resistor 19, compares the detection voltage Vr with a predetermined reference voltage Vref, and turns the transistor 14 on or off based on these comparison results. It controls so that the electric current which flows into LED40 may become a predetermined target value (for example, 100 mA). Specifically, when the current flowing through the LED 40 is less than the target value, control is performed so as to increase the on-time, and when the current flowing through the LED 40 is greater than the target value, control is performed so as to shorten the on-time. I do. As an example, the PWM control circuit 20 obtains a PWM signal as an output signal by obtaining a difference between the detection voltage Vr and the reference voltage Vref as an error and comparing the obtained error with a triangular wave and a comparator. Note that the PWM control circuit 20 switches the transistor 14 at a frequency of about several tens of kHz to several MHz, for example. In the first embodiment, the switching frequency of the PWM control circuit 20 is set to 60 kHz, for example. Of course, other frequencies may be used.

  The AC power supply 30 is a commercial power supply having a voltage of 100 V, for example, and has a frequency of about 50 Hz or 60 Hz. Of course, other voltages (for example, 200 V) and frequencies may be used. Note that AC power from the AC power supply 30 is supplied to the diode bridge 33 via the terminals 31 and 32. The diode bridge 33 includes four diodes 33a to 33d, generates a pulsating power by full-wave rectifying the AC power from the AC power supply 30, and supplies the pulsating power to a subsequent circuit.

  The LED 40 is configured by connecting a plurality (for example, 20) of the same type of LEDs having a forward voltage drop of, for example, 3.2 V and an internal resistance of, for example, 0.1Ω. In addition, the number connected in series can be selected according to a power supply voltage or a use purpose, for example.

(B) Description of Operation of First Embodiment FIGS. 2 and 3 are diagrams for explaining the operation of the first embodiment shown in FIG. 1, and FIG. 2 flows through the circuit when the transistor 14 is on. FIG. 3 shows the current flowing through the circuit when transistor 14 is off. 2 and 3, for the sake of simplicity, the PWM control circuit 20 is omitted and the transistor 14 is shown as a switch.

(When transistor 14 is on)
When the transistor 14 is controlled to be in the ON state by the PWM control circuit 20, the diode bridge 33 from the diode 12, the coil 13, and the closed circuit formed by the transistor 14 is controlled as shown in FIG. A current I1 (current indicated by a broken line) passes. As a result, magnetic energy is accumulated in the coil 13.

  Further, the charge having the polarity shown in FIG. 2 is accumulated in the capacitor 15 by the previous operation. When the transistor 14 is turned on, the diode 16 is reverse-biased and cut off. As a result, a closed circuit is formed by the capacitor 15, the transistor 14, the resistor 19, the LED 40, and the coil 17, and the electric charge accumulated in the capacitor 15 is passed to the closed circuit as a current I2 (current indicated by a broken line). As a result, the LED 40 is lit through the current I2 and magnetic energy is accumulated in the coil 17.

(When transistor 14 is off)
Next, when the transistor 14 is controlled to be in an off state, the current from the diode bridge 33 to the coil 13 is cut off, so that an electromotive force in the same direction as the current I3 is generated in the coil 13 by self-induction. At this time, since the diode 16 is in a forward bias state, a closed circuit is formed by the diode 12, the coil 13, the capacitor 15, and the diode 16. As a result, since the output voltage from the diode bridge 33 and the voltage of the electromotive force generated by the coil 13 are applied to the capacitor 15, the current I3 passes through the closed circuit, and the capacitor 15 is applied. Charged by voltage.

  Further, when the transistor 14 changes from the on state to the off state, the current I2 (see FIG. 2) flowing through the coil 17 is cut off, so that an electromotive force in the same direction as the current I2 is generated in the coil 17. The electromotive force generated in the coil 17 in this way generates a current I4 that leads to a closed circuit constituted by the diode 16, the resistor 19, and the LED 40. As a result, current flows through the LDE 40 and the LED 40 is turned on.

  The above operation is repeated at a predetermined cycle (for example, several tens of kHz to several MHz). FIG. 4 is a diagram showing a temporal change in the current flowing through the coil 17. In the first embodiment shown in FIG. 1, the current flowing through the coil 17 is a continuous current type in which current is continuous as shown in FIG. 4B and a current interruption in which current is intermittent as shown in FIG. It operates as a current critical type shown in FIG. More specifically, since the transistor 14 is controlled to be in an ON state at the timing of time t1 in FIG. 4A, the electric charge accumulated in the capacitor 15 is discharged through the coil 17, so that As time passes, the current flowing through the coil 17 increases. At time t2, the transistor 14 is controlled to be off. As a result, since the magnetic energy accumulated in the coil 17 is gradually released, the current flowing through the coil 17 decreases with time. Then, at time t3 when the current flowing through the coil 17 becomes 0, the transistor 14 is again controlled to be turned on, and the charge accumulated in the capacitor 15 is discharged through the coil 17 as in the case of time t1. The In this way, by controlling the transistor 14 to be in an ON state at a timing when the current flowing through the coil 17 becomes 0, the diode 16 is changed to a reverse bias state when no current is flowing. Since a diode (inexpensive diode) having a slow time (reverse recovery time) can be used, the manufacturing cost of the device can be reduced.

ここで、Ｖ_Ｌはコイル１７の端子電圧を示し、τはΔＩの変化に要する時間を示し、Ｌはコイル１７のインダクタンス値を示す。ここで、ΔＩとＶ_Ｌが略一定とすると、スイッチングの周期に関する値であるτを小さくすると（スイッチング周波数を高くすると）、Ｌを小さくすることができる。つまり、サイズが小さいコイル１７を使用することができる。また、スイッチング周波数が一定の場合には、電流臨界型に設定してΔＩの値を大きくすることで、Ｌの値を小さくすることができる。例えば、リップル値が±１５％の電流連続型（図４（Ｂ）参照）に比較して、電流臨界型（図４（Ａ）参照）では、コイル１７の値を１／７程度（≒０．１５）に小さくすることができることから、コイル１７のサイズを小型化することができる。 Incidentally, the current change ΔI shown in FIG. 4A can be expressed by the following equation (1).

Here, V _L indicates the terminal voltage of the coil 17, τ indicates the time required for the change of ΔI, and L indicates the inductance value of the coil 17. Here, if ΔI and V _L are substantially constant, L can be reduced by decreasing τ, which is a value related to the switching period (increasing the switching frequency). That is, the coil 17 having a small size can be used. Further, when the switching frequency is constant, the value of L can be reduced by setting the current critical type and increasing the value of ΔI. For example, the value of the coil 17 is about 1/7 (≈0) in the current critical type (see FIG. 4A) compared to the current continuous type (see FIG. 4B) with a ripple value of ± 15%. .15), the size of the coil 17 can be reduced.

  As described above, in the first embodiment, the current flowing through the LED 40 is detected by the resistor 19 and the output current is controlled by the PWM control. Therefore, compared to the case where the output voltage is controlled, it is caused by the ripple. Current fluctuation can be suppressed. Thereby, even when the LED 40 having a low internal resistance is used (for example, when the LED 40 having an internal resistance almost close to 0) is used, the capacitor 18 is not so large in capacity. Therefore, the apparatus can be miniaturized.

  In the first embodiment, a current is supplied to the LED 40 in both the period during which the transistor 14 is on and the period during which the transistor 14 is off. Specifically, as shown in FIG. 5A, in the first embodiment, the period in which the transistor 14 is on (t1 to t2, t3 to t4) and the period in which the transistor 14 is off (t2 .., T3, t4 to t5), the current flows through the LED 40. For example, in the conventional one converter power supply (for example, the power supply of Patent Document 1), the transistor is on (t1 to t2, t3). ~ T4), no current flows through the LED, and current flows through the LED during the period when the transistor is off (t2-t3, t4-t5). As described above, in the first embodiment, since the current flows through the LED 40 in both the period in which the transistor 14 is on and the period in which the transistor 14 is off, the lighting efficiency of the LED 40 can be increased. Moreover, since the capacitor | condenser whose capacity | capacitance is not so large can be used as the capacitor | condenser 18 for smoothing, the size of an apparatus can be reduced in size.

  In the first embodiment described above, since the transistor 14 is controlled to be turned on / off at a constant switching frequency, the peak current waveform (envelope waveform) leading to the coil 13 is the full wave supplied from the diode bridge 33. The waveform is similar to the rectified waveform. Therefore, by performing smoothing by the capacitor 11, the input current waveform from the AC power supply 30 is similar to the input voltage waveform, so that the power factor can be set to approximately 100%.

  In the first embodiment described above, since the power factor correction circuit and the step-down converter (buck converter) are configured by one transistor 14, the number of transistors is reduced and the circuit is simplified. The control circuit can be simplified.

(C) Description of Configuration of Second Embodiment FIG. 6 is a block diagram illustrating a configuration example of the second embodiment. In this figure, portions corresponding to those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. In the second embodiment, compared with the first embodiment of FIG. 1, the PWM control circuit 20 is replaced with a PWM control circuit 20A, and a dimming input circuit 21 is newly added. Other configurations are the same as those in FIG.

  Here, the dimming input circuit 21 receives an external dimming signal D (for example, a digital signal of several bits), and generates and outputs a control voltage Vc corresponding to the dimming signal D. For example, when the dimming signal D is 4 bits, the dimming input circuit 21 inputs a dimming signal in the range of 0 to 15, so that the current flowing through the LED 40 is 0 to the maximum current Imax (for example, 100 mA). A control voltage Vc (for example, a voltage changing in the range of Vc1 to Vc2) is generated and output.

  The PWM control circuit 20A uses the control voltage Vc supplied from the dimming input circuit 21 as a reference voltage, compares it with the detection voltage Vr detected by the resistor 19, and based on these comparison results, the transistor 14 is subjected to PWM control. Drive based on.

(D) Description of Operation of Second Embodiment In the second embodiment, the basic operation is the same as that of the first embodiment of FIG. 1, but the LED 40 is controlled by the control voltage Vc from the dimming input circuit 21. The difference is that the current flowing through That is, in the second embodiment, the dimming input circuit 21 outputs the control voltage Vc corresponding to the dimming signal D, and the PWM control circuit 20A uses the control voltage Vc as a reference voltage, and the LED 40 according to the reference voltage. Control the flowing current. Thereby, by changing the light control signal D, the electric current which flows into LED40 can be changed and the emitted light intensity of LED40 can be changed.

  As described above, according to the second embodiment, in addition to the effects of the first embodiment described above, the light emission intensity of the LED 40 can be arbitrarily adjusted.

(E) Modified Embodiment The above-described embodiment is an example, and it goes without saying that there are various modified embodiments. For example, the diode 12 in each of the above embodiments may be excluded. That is, according to an experiment, it has been confirmed that the circuit operates even if the diode 12 is excluded depending on the state of the circuit.

  The element values of the elements constituting the circuit described above are merely examples, and are not limited to such cases. For example, the internal resistance of the LED 40, the switching frequency, and the voltage of the AC power supply 30 are not limited. It can be arbitrarily set according to the above.

  Moreover, in each embodiment shown above, although only the circuit structure was shown, it is also possible to comprise as LED lighting apparatus which accommodated the diode bridge 33, LED lighting device 10, and LED40 in the housing | casing, for example. Specifically, the LED bridge 33, the LED lighting device 10, and the LED 40 can be accommodated in a housing having a bulb shape or a fluorescent lamp shape to form an LED lighting device. Note that the dimming input circuit 21 shown in FIG. 6 may be housed in the same housing or in another housing.

  In each of the above embodiments, the current critical type shown in FIG. 4A is operated. However, the current continuous type shown in FIG. 4B is operated, or the current shown in FIG. It may be operated as an intermittent type.

  Further, in each of the embodiments described above, the current flowing through the LED 40 is controlled by PWM control. However, a switching operation may be performed in which the off-duty is constant and the on-duty is changed by feedback control.

  In each of the above embodiments, the transistor 14 is switched based on the PWM control. However, for example, based on FM (Frequency Modulation) control in which the off time of the transistor 14 is constant and only the on time is varied. You may make it switch. When FM control is applied to the first embodiment, the detection voltage Vr and the reference voltage are compared, and the on-time of the transistor 14 may be controlled based on the comparison result. In the case of the second embodiment, the control voltage Vc is used as a reference voltage and compared with the detection voltage Vr, and the on-time of the transistor 14 may be controlled based on these comparison results. Needless to say, even in the case of FM control, control can be performed as the above-described continuous current type, intermittent current type, and critical current type.

  Alternatively, instead of PWM control, when the current value flowing through the LED 40 reaches a predetermined current value (peak current value) specified in advance, the transistor 14 is turned off, and the current flowing through the coil 17 is reduced to substantially zero. In this case, the transistor 14 may be switched on based on current critical mode control. When current critical mode control is applied to the first embodiment, the detection voltage Vr and the reference voltage are compared, and the peak current value may be controlled based on the comparison result. In the case of the second embodiment, the control voltage Vc supplied from the dimming input circuit 21 is used as a reference voltage, compared with the detection voltage Vr detected by the resistor 19, and the peak current is determined based on these comparison results. The value may be controlled.

  In the above embodiment, the commercial power supply is used after full-wave rectification, but may be used after half-wave rectification.

DESCRIPTION OF SYMBOLS 10 LED lighting device 11 Capacitor 12 Diode 13 Coil 14 Transistor 15 Capacitor 16 Diode 17 Coil 18 Capacitor 19 Resistor 20 PWM control circuit 21 Dimming input circuit 30 AC power supply 31, 32 Terminal 33 Diode bridge

Claims (7)

In an LED lighting device that lights one or a plurality of LEDs with pulsating power obtained by rectifying AC power with a rectifier circuit,
A PFC circuit in which a coil and a switch are connected in series, and both ends of which are connected to the output terminal of the rectifier circuit;
A capacitor and a diode are connected in series, and both ends thereof are connected to the switch. When the switch is opened, the capacitor is passed through the diode by the total voltage of the electromotive force generated in the coil and the voltage from the rectifier circuit. A storage circuit that charges the LED via the switch when the switch is short-circuited, and the charge stored in the capacitor via the switch;
A smoothing circuit in which a smoothing coil and a smoothing capacitor are connected in series, both ends of which are connected to the diode, smooth the current output from the power storage circuit, and supply the voltage across the smoothing capacitor to the LED; ,
The LED lighting device characterized by having.   The LED lighting device according to claim 1, wherein an ON time of the switch is controlled in accordance with a current flowing through the LED.   The LED lighting device according to claim 2, wherein the switch is turned on or off based on PWM control or FM control corresponding to a current flowing through the LED.   The switch is configured to turn off the switch when the current flowing through the LED increases and reaches a predetermined current value, and turns on the switch when the current flowing through the smoothing coil decreases to approximately zero. The LED lighting device according to claim 1, wherein the LED lighting device is controlled by control.   The reference voltage of the PWM control or FM control or the predetermined current value of the current critical mode control is set according to a dimming target value as a dimming target value of the LED. The LED lighting device according to 3 or 4.   4. The LED lighting device according to claim 1, wherein the switch is controlled to be in an ON state at a timing when a current flowing through the smoothing coil becomes substantially zero.   The LED lighting device according to any one of claims 1 to 6, and an LED lighting device in which the LED is housed in a housing.

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