JP4630930B2 - LED driving circuit and LED lighting device using the same - Google Patents

Description

  The present invention relates to a driving circuit for a lighting device (LED lighting device) using a light emitting diode (hereinafter referred to as LED), and more specifically, it is used by supplying alternating current (AC) 100V as a commercial power source. The present invention relates to an LED drive circuit that can be used, and an LED lighting device using the LED drive circuit.

  The LED illumination device is an illumination device using an “LED array” configured by connecting a plurality of LED elements in series, parallel connection, or series-parallel connection as a light source, and has various structures. For example, there is an LED lighting device configured as a light bulb-type lighting fixture, which is also referred to as an “LED lamp”. In general, LED illumination devices such as LED lamps have features such as small size, light weight, long life, and low power consumption as compared with conventional fluorescent lamps.

  By the way, a bulb-type LED lamp using a high-output power LED can be easily replaced with an incandescent bulb or a bulb-type fluorescent lamp that has been generally used for a long time. In order to achieve this, it must be possible to directly supply and turn on (that is, drive) commercial power source pressure (AC 100 V). In order to realize this, a small voltage conversion circuit for generating a drive current for the power LED and a heat radiator with high heat dissipation efficiency for dissipating heat generated from the power LED into the atmosphere are required.

  If the heat dissipation efficiency of the radiator is not sufficient, the current supplied to the power LED must be reduced to suppress heat generation, but this cannot achieve the desired brightness. In order to realize an LED lamp with a desired brightness, it is necessary to increase the heat dissipation efficiency of the heat dissipator as much as possible by using a material with high thermal conductivity and expanding the heat dissipating area, etc., and at the same time make the voltage conversion circuit as small as possible. There is.

  The heat dissipation efficiency of the heat dissipator can be increased by, for example, forming an aluminum heat dissipator having a large number of radial fins, but it is not always easy to downsize the voltage conversion circuit. In order to drive the power LED, conventionally, the following two driving methods have been adopted.

  As shown in FIG. 6, the first driving method uses a step-down transformer 101 to reduce the commercial AC power source pressure supplied to the pair of input terminals 107 to a predetermined voltage value, and then performs full-wave bridge rectification. Full-wave rectification is performed by the circuit 102, and ripples included in the obtained full-wave rectified voltage are removed (smoothed) using the electrolytic capacitor 105, and then a plurality of power LEDs 103 (LED arrays) connected in series are connected to each other. To supply. A current limiting resistor 104 is connected to the power LED 103 in series.

  As shown in FIG. 7, the second driving method uses an AC-DC converter 106 to convert the commercial AC power source pressure supplied to the input terminal 107 into a direct current (DC) voltage, and the obtained direct current voltage. Is removed (smoothed) using an electrolytic capacitor 105 and then supplied to a plurality of power LEDs 103 connected in series with each other.

  The first driving method has a drawback that a very large step-down transformer is required for voltage conversion. On the other hand, in the second driving method, the step-down transformer built in the AC-DC converter 106 can be reduced in size, so that the difficulty of the first method can be alleviated. However, even in the second driving method, the step-down transformer itself cannot be eliminated.

  Further, in any of these two driving methods, the power factor is not high. In order to increase the power factor, it is necessary to incorporate a power factor correction circuit separately.

  In recent years, in addition to these two driving methods, a third driving method has been developed and proposed. This driving method uses an inverter (PWM switching type inverter) that converts a DC voltage into an AC voltage using pulse width modulation (hereinafter referred to as PWM), and is an ON time ( By changing the ratio (duty ratio) of the lighting time, the LED blinks (switches) at high speed, and the apparent brightness is controlled. In general, the brightness of an LED changes greatly due to a slight change in forward current. However, according to this driving method, a change in forward current can be avoided by a change in duty ratio to achieve a constant brightness. . An example of such a third driving method is disclosed in Japanese Patent Application Laid-Open No. 2006-511078.

  Patent Document 1 discloses a power supply assembly that supplies power to an LED lighting module (that supplies a constant current). According to this power supply assembly, it is possible to omit means for switching on and off power supply to the LED array while performing low-frequency pulse modulation on the LED array.

  The power supply assembly of Patent Document 1 includes a DC power source, a switch mode converter, and a controller that controls switching of the switch of the switch mode converter, and the controller transmits the dual pulse width modulation switching signal at two frequencies. These two frequencies are a high frequency pulse width modulation switching signal component that controls the magnitude of the LED current and a low frequency pulse width modulation switching signal component that controls the duration of the LED current. It is characterized by having. The switch mode converter includes a transformer (see claims 1, 2, FIGS. 5 to 12, paragraphs (0008) to (0012), (0014)).

  Patent Document 1 does not mention the power factor.

  Examples of the power factor correction circuit include those described in Patent Document 2 (Japanese Patent Laid-Open No. 2005-267999) and Patent Document 3 (Japanese Patent Laid-Open No. 11-162234).

  Patent Document 2 discloses an LED illumination device used in a studio or a theater using an LED as a light source unit, and performs LED lighting control using a PWM method. This LED type illumination device includes a power factor correction circuit to improve the power factor of the power source so that the input voltage and the input current are in phase and to improve the loss of power supplied to the LED. (See FIG. 1, paragraphs (0016) and (0018)). Patent Document 2 does not disclose details about the lighting control circuit using the PWM method.

  Patent Document 3 discloses a light source using an LED suitable for illumination or display, and a power factor correction circuit is provided in a drive circuit for driving the LED. Patent Document 3 lists chopper circuits such as a step-down type, a step-up type, and a polarity inversion type as examples of the power factor correction circuit. “This type of chopper circuit includes an inductor, a switching element, and a switching element. Therefore, when the AC power supply is connected, the input current is increased at a high frequency because the output of the rectifier circuit is supplied to the inductor at a high frequency by turning on and off the switching element at a high frequency. The input power factor is increased because the input current distortion can be prevented by increasing the input current and the envelope of the input current can be made proportional to the input voltage. ”(FIG. 7, paragraph (0009) ), (0011), (0027)).

JP 2006-511078 gazette JP 2005-267999 A JP-A-11-162234

  In the power supply assembly of Patent Document 1 described above, since the switch mode converter includes a transformer (transformer), it is difficult to reduce the size of the light bulb type LED lamp to such an extent that it can be realized. There is no mention of power factor improvements.

  The above-described lighting control circuit using the PWM method of Patent Document 2 considers improvement of the power factor, but does not consider miniaturization.

  As for the light source using the LED of Patent Document 3 described above, as with the lighting control circuit of Patent Document 2 described above, improvement of the power factor is considered, but miniaturization is not considered.

  The present invention has been made in consideration of such circumstances, and the purpose of the present invention is to realize power factor improvement and prevention of inrush current at the time of lighting with a smaller number of parts than conventional, An object of the present invention is to provide an LED drive circuit that can easily reduce the size of the LED lamp to a realizable level, and an LED lighting device using the LED drive circuit.

  Another object of the present invention is to provide an LED driving circuit capable of easily realizing a small and bright light bulb-type lighting fixture (for example, an LED lamp), and an LED lighting device using the LED driving circuit.

  Other objects of the present invention which are not specified here will be apparent from the following description and the accompanying drawings.

(1) An LED drive circuit according to a first aspect of the present invention is
A pair of input terminals;
A rectifier circuit that rectifies an alternating voltage input via the pair of input terminals to generate a rectified output voltage;
A resistive circuit element having one end connected to one of the pair of input terminals and the other end connected to one input terminal of the rectifier circuit;
A capacitive circuit element connected between a pair of output terminals of the rectifier circuit;
A transformerless controller for controlling the rectified output voltage by a PWM switching method to generate a drive voltage for LED driving ,
The time constant determined by the resistance value of the resistive circuit element and the capacitance value of the capacitive circuit element is such that the charging period of the capacitive circuit element is longer than when the resistive circuit element is not connected. It is characterized by being set .

In the LED driving circuit according to the first aspect of the present invention, the time constant determined by the resistance value of the resistive circuit element and the capacitance value of the capacitive circuit element is more than that when the resistive circuit element is not connected. Since the charging period for the capacitive circuit element is set to be long , the power factor is improved as compared with the case where the resistive circuit element is not connected.

  Further, since the resistive circuit element is provided between the pair of input terminals and the rectifier circuit, by setting the resistance value according to the magnitude of the input current, the inrush current during lighting can be reduced. Can be prevented.

  Although the power loss is generated by the resistive circuit element, the input current flowing through the resistive circuit element is reduced due to the improvement of the power factor. Therefore, the power loss (increase) by the resistive circuit element is suppressed to be sufficiently small. Can do.

Further, the controller generates the drive voltage for LED driving by controlling the rectified output voltage by a PWM switching method, and is a transformer-less, in other words, a transformer (for example, a voltage conversion transformer or Since it does not include an oscillation transformer, it can be easily downsized by forming an integrated circuit (IC).

  Therefore, the LED driving circuit according to the first aspect of the present invention can achieve power factor improvement and prevention of inrush current at the time of lighting with a smaller number of parts than conventional ones, and is small enough to realize an LED lamp. It is easy to make. As a result, by adopting an efficient heat dissipation structure, a small and bright bulb-type lighting fixture (for example, an LED lamp) can be easily realized.

  Note that a conventionally known power factor correction circuit is usually provided between the rectifier circuit and the capacitive circuit element, and is configured by combining a plurality of circuit elements. On the other hand, in the LED drive circuit according to the first aspect of the present invention, it is sufficient to provide the resistive circuit element between one of the pair of input terminals and one input terminal of the rectifier circuit. Therefore, the power factor can be improved with a minimum number of parts.

  (2) In a preferred example of the LED drive circuit according to the first aspect of the present invention, the resistive circuit element is a resistor. This example is suitable when the input current is small (for example, 0.1 A or less).

In this example, the resistance value of the resistor can be increased to such an extent that the power loss does not become excessive. Therefore, the power loss is suppressed by a simple circuit configuration of only the resistor in the range of the input current as described above. However, there is an advantage that power factor improvement and inrush current prevention can be realized at the same time.
(3) In another preferred example of the LED drive circuit according to the first aspect of the present invention, the resistive circuit element is composed of a resistor and a thermistor connected in series with each other. This example is suitable when the input current is slightly larger than the case (2) (for example, in a range of 0.1 A to 0.3 A).

  In this example, the power factor can be improved to the same extent by using a resistor having a smaller resistance value than in the case of (2). However, such a small resistance value may not provide a desired inrush current preventing action. If the resistance value is increased so as to obtain a desired inrush current prevention action, power loss due to the resistor increases. Therefore, by adding a thermistor connected in series to the resistor, the resistance of the thermistor is added, thereby realizing an inrush current preventing action during lighting without increasing the resistance value of the resistor. After lighting (after the temperature rises), the resistance of the thermistor decreases, so power loss does not become excessive due to the addition of the thermistor. Thus, in the range of the input current as described above, by combining the thermistor with the resistor, there is an advantage that power factor improvement and inrush current prevention can be realized simultaneously while suppressing power loss.

  (4) In still another preferred example of the LED drive circuit according to the first aspect of the present invention, the resistive circuit element is a thermistor. This example is suitable when the input current is larger than (3) above (for example, exceeding 0.3 A).

  In this case, at the time of lighting, a desired inrush current preventing action can be obtained by the initial resistance of the thermistor. After the lighting (after the temperature rise), a desired power factor improving action can be obtained while preventing the power loss from becoming excessive due to the reduced resistance of the thermistor. Thus, within the range of the input current as described above, there is an advantage that power factor improvement and inrush current prevention can be realized at the same time while suppressing power loss with a simple circuit configuration of only the thermistor.

  (5) In still another preferred example of the LED drive circuit according to the first aspect of the present invention, the capacitive circuit element is a capacitor.

(6) In still another preferred example of the LED drive circuit according to the first aspect of the present invention, the resistance value of the resistive circuit element flows through the resistive circuit element in order to prevent an inrush current during lighting. It is set according to the magnitude of the current .

(7) The LED lighting device according to the second aspect of the present invention includes:
The LED driving circuit according to the first aspect of the present invention described above;
It comprises at least one LED driven by the drive voltage generated by the LED drive circuit.

  The LED lighting device according to the second aspect of the present invention includes the LED driving circuit according to the first aspect of the present invention, and the LED driving circuit drives the LED, so that the same effect as the LED driving circuit is obtained. It is clear that

  According to the LED driving circuit according to the first aspect of the present invention and the LED lighting device according to the second aspect of the present invention, (a) power factor improvement and prevention of inrush current during lighting are realized with a smaller number of parts than in the past. (B) It is easy to reduce the size of the LED lamp to the extent that it can be realized, (c) It is possible to easily realize a small and bright light bulb-type lighting fixture (for example, an LED lamp). An effect is obtained.

It is a circuit diagram which shows the structure of the LED lighting apparatus (LED drive circuit) which concerns on 1st Embodiment of this invention. It is a circuit diagram which shows the structure of the LED lighting apparatus (LED drive circuit) which concerns on 2nd Embodiment of this invention. It is a circuit diagram which shows the structure of the LED lighting apparatus (LED drive circuit) which concerns on 3rd Embodiment of this invention. It is a circuit diagram which shows the structure of the PWM switching system inverter used for the LED lighting apparatus (LED drive circuit) which concerns on 1st Embodiment of this invention. It is a wave form diagram which shows the operation principle of the LED lighting apparatus (LED drive circuit) which concerns on 1st Embodiment of this invention. It is a conceptual diagram which shows an example of the conventional LED drive method in an LED lighting apparatus. It is a conceptual diagram which shows the other example of the conventional LED drive method in an LED lighting apparatus.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings.
(Configuration of the first embodiment)
FIG. 1 is a circuit diagram showing a configuration of an LED lighting device 1 according to the first embodiment of the present invention. As shown in FIG. 1, the LED lighting device 1 includes a pair of input terminals 50, a power factor improving resistor 11, a full-wave bridge rectifier circuit 12, an electrolytic capacitor 13, and a PWM switching inverter 40. And a plurality of high output power LEDs 19 (power LED arrays).

  A circuit obtained by removing the plurality of high output power LEDs 19 from the LED lighting device 1 constitutes an LED drive circuit according to the first embodiment of the present invention. Therefore, the LED lighting device 1 corresponds to a combination of the LED drive circuit and the power LED 19 (power LED array).

  The first embodiment is suitable when the input current is small (for example, 0.1 A or less).

  Commercial AC power source pressure (AC 100 V) is directly applied to the pair of input terminals 50 of the LED lighting device 1 (LED drive circuit).

  The full-wave bridge rectifier circuit 12 is formed by interconnecting four diodes in a bridge shape, its two input terminals are respectively connected to a pair of input terminals 50, and its two output terminals are two inverters 40. Each input terminal is connected.

  An electrolytic capacitor 13 is connected between two input terminals of the inverter 40 (that is, two output terminals of the full-wave bridge rectifier circuit 12). That is, the full-wave bridge rectifier circuit 12 is a capacitor input type. This electrolytic capacitor 13 acts to remove and smooth the ripple contained in the rectified output voltage (that is, full-wave rectified voltage) of the full-wave bridge rectifier circuit 12 as much as possible. In this way, pulsation is almost removed from the waveform of the rectified output voltage, and the voltage (rectified output voltage) at both ends of the electrolytic capacitor 13 becomes a waveform close to a direct current having a substantially constant amplitude, as shown in FIG. The smoothed rectified output voltage is input to the inverter 40.

  A resistor 11 as a resistive circuit element is connected between one of the pair of input terminals 50 and one of the two input terminals of the full-wave bridge rectifier circuit 12. This resistor 11 is provided for power factor improvement and prevention of inrush current during lighting.

  Since the rectified output voltage (full wave rectified voltage) of the full wave bridge rectifier circuit 12 is applied to the electrolytic capacitor 13, the electrolytic capacitor 13 is charged because the rectified output voltage corresponds to the vicinity of the peak value of the sine wave. It is only a period to do. This short charging period is the cause of the low power factor. Therefore, the resistor 11 is connected by appropriately setting the resistance value R of the resistor 11 and the capacitance value C of the electrolytic capacitor 13 as the capacitive circuit element, and increasing the RC time constant determined by them. Compared with the case where it does not, the charging period in each of the current pulses flowing through the electrolytic capacitor 13 can be lengthened. (As shown in FIG. 5, each current pulse is composed of a charging period and a discharging period.) Therefore, by connecting the resistor 11, the resistor can be connected without incorporating the power factor correction circuit of the conventional configuration. The power factor is improved as compared with the case where 11 is not connected.

  For example, when the power factor improving resistor 11 is omitted in the configuration of the LED drive circuit of the first embodiment, the power factor is 0.5 to 0.6. On the other hand, in the LED drive circuit of the first embodiment provided with the power factor improving resistor 11, the power factor is improved to 0.7 to 0.9.

  In addition, since the resistor 11 is provided between the pair of input terminals 50 and the full-wave bridge rectifier circuit 12, the resistance value of the resistor 11 is set according to the magnitude of the input current flowing therethrough. Inrush current can be easily prevented.

  Note that power loss occurs due to the resistor 11. However, since the input current flowing through the resistor 11 (which is usually 0.1 A or less) decreases due to the improvement of the power factor, the power loss caused by the resistor 11 can be kept sufficiently small. For example, when the resistor 11 is not connected and the input voltage is AC100V, the power consumption (active power) is 5W, and the power factor is 0.5, the apparent power is 10VA and the input current is 0.1A. .

  On the other hand, by connecting a 100Ω resistor as the resistor 11 between one of the pair of input terminals 50 and one of the input terminals of the full-wave bridge rectifier circuit 12, the power factor is improved to 0.8. Assuming that the power consumption (power loss) = 0.46 W by the resistor 11 is added, the power consumption (active power) is 5 W + 0.46 W = 5.46 W. However, since the power factor is improved from 0.5 to 0.8, the apparent power is 6.82 A, the input current is 0.0682 A, and it can be seen that the insertion of the resistor 11 reduces the input current.

  A conventionally known power factor correction circuit is usually provided between the full-wave bridge rectifier circuit 12 and the electrolytic capacitor 13, and is configured by combining a plurality of circuit elements. On the other hand, in the LED drive circuit of the first embodiment, there is no need to provide a power factor correction circuit having a conventional configuration between the full-wave bridge rectifier circuit 12 and the electrolytic capacitor 13, and one of the pair of input terminals 50 and the full-wave. It is only necessary to provide the resistor 11 between one input terminal of the bridge rectifier circuit 12. Therefore, the power factor can be improved with a minimum number of parts.

  The inverter 40 as a controller for generating a drive voltage for driving the LED controls the on / off control (switching) of the input rectified output voltage (which has a substantially DC waveform as shown in FIG. 5) by the PWM switching method. And a rectangular pulse AC voltage (PWM output voltage) with a variable duty ratio is generated. The PWM output voltage thus generated is output from the two output terminals of the inverter 40 as an LED drive voltage. The on / off control is performed using the PWM output voltage fed back to the inverter 40 so that the brightness of the light emitted from the power LED 19 is constant.

  Since the main part of the inverter 40 is integrated as a driver IC 30 and does not include a transformer (transformer-less), it can be manufactured as a small component capable of realizing an LED lamp. The detailed configuration of the inverter 40 will be described later with reference to FIG.

The plurality of high output power LEDs 19 are connected to each other in series to form an LED array. A PWM output voltage (LED drive voltage) output from the inverter 40 is applied to both ends of the LED array. As a result, a forward current having a constant amplitude flows in each of the power LEDs 19 in a pulse shape, and each of the power LEDs 19 emits light. Light corresponding to the light emission of all the power LEDs 19 is emitted to the outside of the LED lighting device 1.

  Next, a detailed configuration of the inverter 40 will be described with reference to FIGS. 1 and 4.

  As shown in FIG. 1, the inverter 40 includes a driver IC 30, a capacitor 14 provided on the input side outside the driver IC 30, and a field effect metal-oxidation provided on the output side outside the driver IC 30. A metal-oxide-semiconductor field effect transistor (MOSFET) 15, a resistor 16, an inductor 17, and a diode 18 are provided. The MOSFET 15 is a switching element that performs on / off control by a PWM switching method based on an input rectified output voltage.

  A detailed configuration of the inverter 40 and the driver IC 30 is shown in FIG. As apparent from FIG. 4, in addition to the driver IC 30, the inverter 40 includes a diode 18 for protecting the power LED 19 from an overcurrent generated at the time of switching off, an inductor 17 for smoothing a current flowing through the power LED 19, and an input. MOSFET 15 for switching control of the PWM output voltage (LED drive voltage) based on the rectified output voltage, the oscillation adjustment resistor 42 of the oscillation circuit 37 (which is inside the driver IC 30), and the current flowing through the MOSFET 15 And a resistor 41 for supplying a predetermined reference voltage to the comparator 33 (which is inside the driver IC 30).

  The driver IC 30 includes a switching regulator 31, comparators (voltage comparison circuits) 32 and 33, an OR circuit 34, a reset set flip-flop (hereinafter referred to as an R-S flip-flop) 35, An AND circuit 36 and an oscillation circuit 37 are formed. (The driver IC 30 includes elements and circuits other than these, but they are omitted because they are not related to the present invention.)

  When the logic state of the signal voltage output from the oscillation circuit 37 and input to the set terminal (S) of the RS flip-flop 35 becomes, for example, a high level (H), the RS flip-flop 35 is set. The logic state of the output terminal (Q) becomes H. Then, since the logic state of the gate voltage of the MOSFET 15 becomes H, the MOSFET 15 is turned on (conductive state), and as a result, the current flowing through the MOSFET 15 (that is, the inductor 17) increases rapidly. Along with this, the voltage across the resistor 16 increases. This voltage is applied to one input terminal of each of the comparators 32 and 33.

  Since the DC reference voltage generated by the switching regulator 37 is applied to the other input terminal of the comparator 33 via the resistor 41, the resistor 16 is increased with an increase in the current flowing through the MOSFET 15 (inductor 17). Since the logical state of the output voltage of the OR circuit 34 applied to the reset terminal (R) of the RS flip-flop 35 becomes H when the voltage at both ends of the signal increases and becomes equal to the DC reference voltage, RS The flip-flop 35 is reset. That is, the RS flip-flop 35 is reset, and the logic state of the output terminal (Q) becomes a low level (L). Then, the logic state of the gate voltage of the MOSFET 15 becomes L, and the MOSFET 15 is turned off (cut-off state). As a result, the current flowing through the MOSFET 15, that is, the inductor 17 rapidly decreases. As a result, the voltage across the resistor 16 decreases.

  Next, when the logic state of the output voltage of the oscillation circuit 37 becomes H level again, the RS flip-flop 35 is set, the MOSFET 15 is turned on, and the current flowing through the inductor 17 increases rapidly. Thereafter, the same operation as described above is repeated in the same manner. Thus, a pulse current flows through the power LED 19.

  Since the current flowing through the power LED 19 is determined by the resistance value of the resistor 16, it is a constant current. The LED drive voltage is determined by the inductor 17.

  The output voltage of the comparator 32 is applied to the other input terminal of the OR circuit 34 and controls the reset operation of the RS flip-flop 35.

  The switching regulator 31 generates a DC reference voltage without using a transformer. For this reason, the driver IC 30 can be sufficiently downsized.

As described above, in the LED driving circuit according to a first embodiment of the present invention, RC time constant determined by them with the resistance value R of the resistor 11 and the capacitance value C of the electrolytic capacitor 13 is appropriately set By enlarging, the charging period to the electrolytic capacitor 13 can be lengthened as compared with the case where the resistor 11 is not connected. For this reason, a power factor is improved compared with the case where the resistor 11 is not connected.

  Moreover, since the resistor 11 is provided between the pair of input terminals 50 and the full-wave bridge rectifier circuit 12, by setting the resistance value according to the magnitude of the input current flowing through the resistor 11, Inrush current can be prevented.

  Although a power loss occurs due to the resistor 11, the input current flowing through the resistor 11 is reduced due to the improvement of the power factor, so that the power loss can be kept sufficiently small.

  Further, the inverter 40 (controller) generates the drive voltage for driving the LED by controlling the rectified output voltage of the full-wave bridge rectifier circuit 12 by the PWM switching method, and does not include a transformer. By making it (IC), it can be easily downsized.

  Therefore, the LED drive circuit according to the first embodiment of the present invention can achieve power factor improvement and prevention of inrush current at the time of lighting with a smaller number of parts than conventional ones, and is downsized to such an extent that an LED lamp can be realized. Easy to do. As a result, a small and bright bulb-type lighting fixture (for example, an LED lamp) can be easily realized.

  A conventionally known power factor correction circuit is usually provided between the full-wave bridge rectifier circuit 12 and the electrolytic capacitor 13, and is configured by combining a plurality of circuit elements, so that the circuit configuration is complicated. . On the other hand, in the LED drive circuit of the first embodiment, it is only necessary to provide the resistor 11 between one of the pair of input terminals 50 and one input terminal of the full-wave bridge rectifier circuit 12. Therefore, the power factor can be improved with a minimum number of parts.

  The LED lighting device 1 according to the first embodiment of the present invention includes the LED drive circuit according to the first embodiment having the above-described configuration, and the power LED 19 is driven by the LED drive circuit. A high power factor is obtained. As a result, by adopting an efficient heat dissipation structure, a small and bright bulb-type lighting fixture (for example, an LED lamp) can be easily realized.

  As a matter of course, it is not necessary to provide a power factor correction circuit having a conventional configuration between the full-wave bridge rectifier circuit 12 and the electrolytic capacitor 13.

(Second Embodiment)
FIG. 2 shows a configuration of an LED illumination device 1A according to the second embodiment of the present invention.

As shown in FIG. 2, the configuration of the LED lighting apparatus 1A of the second embodiment is the same as that of the first embodiment described above except that a thermistor 20 is added in addition to the resistor 11 as a circuit element for power factor improvement. This is the same as the LED lighting device 1 of FIG. Therefore, about the part with the same structure, the same code | symbol as used in the LED lighting apparatus 1 of the said 1st Embodiment is attached | subjected, and the description is abbreviate | omitted.

  In the second embodiment, the resistive circuit element includes the resistor 11 and the thermistor 20 connected in series with each other. This form is suitable when the input current is slightly larger than the first embodiment (for example, in the range of 0.1 A to 0.3 A).

  Even if the resistor 11 having a smaller resistance value than that of the first embodiment is used, the same power factor improvement can be performed. However, such a small resistance value may not provide a desired inrush current preventing action. If the resistance value is increased so as to obtain a desired inrush current preventing action, the power loss caused by the resistor 11 increases. Therefore, by adding a thermistor 20 connected in series to the resistor 11, the resistance of the thermistor 20 is added, thereby realizing an inrush current preventing action during lighting without increasing the resistance value of the resistor 11. .

  After the lighting (after the temperature rises), the resistance of the thermistor 20 decreases, so that the power loss does not become excessive due to the addition of the thermistor 20. Thus, by combining the thermistor 20 with the resistor 11 in the input current range as in the first embodiment, power factor improvement and inrush current prevention can be realized simultaneously while suppressing power loss.

(Third embodiment)
FIG. 3 shows a configuration of an LED lighting device 1B according to the third embodiment of the present invention.

As shown in FIG. 3, the configuration of the LED lighting device 1B of the third embodiment is the same as that of the first embodiment described above except that a thermistor 20 is used instead of the resistor 11 as a circuit element for power factor improvement. This is the same as the LED lighting device 1 of FIG. Therefore, about the part with the same structure, the same code | symbol as used in the LED lighting apparatus 1 of the said 1st Embodiment is attached | subjected, and the description is abbreviate | omitted.

In the third embodiment, the thermistor 20 is used as the resistive circuit element. This form is suitable when the input current is larger than that of the second embodiment (for example, exceeding 0.3 A).

  In the third embodiment, a desired inrush current preventing action is obtained by the initial resistance of the thermistor 20 during lighting. After the lighting (after the temperature rise), the power factor is improved while preventing the power loss from becoming excessive due to the reduced resistance of the thermistor 20. As described above, in the range of the input current as described above, the power factor improvement and the inrush current prevention can be realized at the same time while suppressing the power loss by the simple circuit configuration of the thermistor 20 alone.

(Modification)
The first to third embodiments described above show examples embodying the present invention. Accordingly, the present invention is not limited to these embodiments, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.

  For example, in the first to third embodiments described above, an LED array in which a plurality of power LEDs 19 are connected in series is used, but the present invention is not limited to such a configuration. An LED array in which a plurality of power LEDs 19 are connected in parallel to each other may be used, or an LED array in which a plurality of power LEDs 19 are connected in series to each other (parallel-connected LED array). Also good. A single LED may be used.

  In the first to third embodiments, a resistor or a thermistor or a combination of a resistor and a thermistor is used as the resistive circuit element. However, the present invention is not limited to such a configuration. Any other resistive circuit element can be used as long as the power factor improving effect and the inrush current preventing effect can be obtained.

  Further, in the first to third embodiments, a PWM switching type inverter having a built-in driver IC 30 is used as a controller that generates a driving voltage for LED driving by controlling the rectified output voltage by the PWM switching type. However, the present invention is not limited to this. An inverter having any other configuration can be used as long as the rectified output voltage can be controlled by the PWM switching method to generate a drive voltage for LED driving.

  Needless to say, the full-wave bridge rectifier circuit used in the first to third embodiments may be replaced with a rectifier circuit having another configuration (for example, a non-bridge type full-wave rectifier circuit).

1, 1A, 1B LED lighting device 11 Resistor 12 Full wave bridge rectifier circuit 13 Electrolytic capacitor 14 Capacitor 15 MOSFET
16 Resistor 17 Inductor 18 Diode 19 Power LED
20 Thermistor 30 Driver IC
31 Spring 32, 33 Comparator 34 OR (OR) circuit 35 Reset set flip-flop 36 AND circuit 37 Oscillation circuit 40 PWM switching inverter 41, 42 Resistor 50 Input terminal

Claims (7)

A pair of input terminals;
A rectifier circuit that rectifies an alternating voltage input via the pair of input terminals to generate a rectified output voltage;
A resistive circuit element having one end connected to one of the pair of input terminals and the other end connected to one input terminal of the rectifier circuit;
A capacitive circuit element connected between the output terminals of the rectifier circuit;
A transformerless controller for controlling the rectified output voltage by a PWM switching method to generate a drive voltage for LED driving ,
The time constant determined by the resistance value of the resistive circuit element and the capacitance value of the capacitive circuit element is such that the charging period of the capacitive circuit element is longer than when the resistive circuit element is not connected. An LED driving circuit that is set .   The LED driving circuit according to claim 1, wherein the resistive circuit element is a resistor.   The LED driving circuit according to claim 1, wherein the resistive circuit element includes a resistor and a thermistor connected in series with each other.   The LED driving circuit according to claim 1, wherein the resistive circuit element is a thermistor.   The LED drive circuit according to claim 1, wherein the capacitive circuit element is a capacitor. The resistance value of the resistive circuit element is set according to the magnitude of the current flowing through the resistive circuit element in order to prevent an inrush current at the time of lighting. The LED driving circuit described. The LED drive circuit according to any one of claims 1 to 6,
An LED lighting device comprising: at least one LED driven by the driving voltage generated by the LED driving circuit.

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