JP2016006761A - Led driver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED driver capable of meeting a request with respect to flickering, and fitting harmonic regulation.SOLUTION: An LED driver comprises: a rectification circuit 11 for rectifying AC voltage to output ripple voltage; an LED series circuit 20 that is composed of a plurality of LEDs 21 to 24 connected in series and emits light when LED current depending on the ripple voltage from the rectification circuit 11 flows; a plurality of switching elements 31 to 33 connected to connection points between LEDs adjacent to each other of the LEDs composing the LED series circuit; and a capacitor C to be charged with charging current depending on ripple voltage supplied from the rectification circuit through a diode D depending on states of the switching elements. The LED driver performs control so that the sum of the charging current to the capacitor and the LED current to the LED series circuit becomes a current value corresponding to the ripple voltage from the rectification circuit; makes the capacitor discharge when the ripple voltage is lower than a predetermined threshold; and makes current flow in part of the LEDs composing the LED series circuit to make the part emit light.

Description

  The present invention relates to an LED drive device that drives a light emitting diode (LED), and more particularly to an LED drive device that is required to suppress flicker.

  There is known an AC direct drive type LED drive device that detects a commercial voltage or an LED current and controls on / off of a switching element based on the detection result to switch the number of LEDs connected in series to light them ( Patent Document 1).

  FIG. 7A is a diagram showing the configuration of this type of LED driving device. In this LED driving device, an AC voltage supplied from the outside is full-wave rectified by a rectifier circuit 11, and a pulsating voltage obtained by this full-wave rectification is supplied to an LED series circuit in which a plurality of LEDs 21 to 24 are connected in series. The

  The plurality of LEDs 21 to 24 are turned on or off when a current based on the constant current control circuits 41 to 44 flows through switching elements 31 to 33 that are turned on / off by a control signal from a control circuit (not shown). At this time, in the phase range in which the pulsating voltage from the rectifier circuit 11 changes from a low value to a high value, the LEDs 21 to 24 increase the number of LEDs in series corresponding to the change, and the pulsating voltage changes from a high value to a low value. In the changing phase range, lighting control is performed so that the number of LEDs in series decreases corresponding to the change.

  In such lighting control, the input voltage and input current to the LEDs 21 to 24 change as shown in FIG. This LED drive device has a non-switching constant current control circuit using a dropper method, and the number of LEDs in series is changed according to the input voltage, so a wide conduction angle can be realized while suppressing loss, enabling efficient lighting become. In addition, since a large power conversion element such as a reactor or a capacitor is not used because of the dropper method, a significant reduction in size can be realized, and low back mounting is facilitated.

JP 2006-147933 A

However, when the LED lighting device is configured by the LED driving device described above, it is not possible to meet the demand for flicker defined in the JIS standard. In other words, the JIS standard stipulates that “light output should not cause flickering by humans”, but in order to satisfy this rule,
(1) The output has no missing part (part of 5% or less of the peak value of the light output) and the repetition frequency is 100 Hz or more, or
(2) It is necessary to satisfy the condition that the repetition frequency of the light output is 500 Hz or more.

  FIG. 8 is a diagram showing the waveform of the light output of the LED driving device, which is obtained by receiving the light output with a sensor and observing it with an oscilloscope. In this LED drive device, constant current control is performed in stages, so that the waveform of the light output is stepped.

  The AC direct drive method employed in this LED drive device only lights the LED with a pulsating voltage obtained by full-wave rectification of the AC input, and as shown in the Z part of FIG. 8 when the AC voltage becomes zero. In addition, the light output becomes zero and a non-lighting period occurs.

  As a result, there is a problem that the request for flicker cannot be met. In addition, although a circuit for reducing flicker has been developed, since the input current is greatly distorted, there remains a problem that it is difficult to comply with harmonic regulation (JIS C 61000-3-2) class C (25 W or more). Has been.

  Although a circuit for reducing flicker that can cope with harmonic regulation is also considered, since it is synchronized with the current switching timing, there is a momentary non-lighting period, and it is not possible to meet the demand for flicker.

  The subject of this invention is providing the LED drive device which can respond to the request | requirement with respect to flicker, and can adapt a harmonic regulation.

  The present invention includes a rectifier circuit that rectifies an alternating voltage and outputs a pulsating voltage, and an LED series circuit that emits light when an LED current corresponding to the pulsating voltage from the rectifier circuit flows, in which a plurality of LEDs are connected in series. A plurality of switching elements connected to connection points of adjacent LEDs among the plurality of LEDs constituting the LED series circuit, and depending on the state of the plurality of switching elements, from the rectifier circuit via a diode A capacitor charged with a charging current corresponding to the supplied pulsating voltage, and the sum of the charging current to the capacitor and the LED current to the LED series circuit becomes a current corresponding to the pulsating voltage from the rectifier circuit. A control circuit that controls the power supply, and a circuit that discharges the capacitor when the pulsation voltage becomes smaller than a predetermined threshold value, and constitutes the LED series circuit. Characterized in that it comprises an auxiliary lighting circuit to partially emit light by applying a current of the LED.

  According to the present invention, the total of the charging current to the capacitor and the LED current to the LED series circuit is controlled to be a current corresponding to the pulsating voltage from the rectifier circuit, and the pulsating voltage is smaller than a predetermined threshold value. In this case, the capacitor is discharged, and a current is passed through a part of the plurality of LEDs to emit light. Therefore, it is possible to provide an LED driving device that can meet the demand for flickering and can also meet harmonic regulations.

It is a figure which shows the structure of the LED drive device which concerns on Example 1 of this invention. It is a timing chart which shows operation | movement of the LED drive device which concerns on Example 1 of this invention. It is a figure which shows the detailed structure of the LED drive device which concerns on Example 1 of this invention. It is a figure which shows the structure of the LED drive device which concerns on Example 2 of this invention. It is a figure which shows the relationship between the light control rate which showed the phase angle in percentage when the input voltage of the LED drive device which concerns on Example 2 of this invention was phase-controlled, and the total electric current value of each LED row | line | column. It is a figure which shows the relationship between the light control rate of the LED drive device which concerns on Example 2 of this invention, and the electric current value ratio of each LED row | line | column. It is a figure for demonstrating the LED drive device using the conventional LED drive device. It is a figure which shows the waveform of the optical output of the LED drive device shown in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol as the code | symbol used by the prior art is attached | subjected to the same structure as the conventional LED drive device, and the description is abbreviate | omitted.

  FIG. 1 is a diagram illustrating a configuration of an LED driving device according to Embodiment 1 of the present invention. This LED driving device includes a rectifier circuit 11, LEDs 21 to 24 constituting an LED series circuit, switching elements 31 to 33, constant current control circuits 41 to 44, a diode D1, a capacitor C, an AC voltage detection unit 51, a discharge switching element SW. And a constant current control circuit 52. The switching elements 31 to 33 and the constant current control circuits 41 to 44 are included in one integrated circuit (IC) 30. The AC voltage detector 51, the discharge switching element SW, and the constant current control circuit 52 constitute an auxiliary lighting circuit of the present invention.

  The rectifier circuit 11 performs full-wave rectification on an AC voltage supplied from the outside. The pulsating voltage obtained by full wave rectification is applied to the LED series circuit 20 and the AC voltage detection unit 51 in which a plurality of LEDs 21 to 24 are connected in series.

  Both ends of the LED series circuit 20 having the LEDs 21 to 24 are connected to both ends of the rectifier circuit 11 via a constant current control circuit 44. The anode of the LED 21 is connected to the positive electrode of the rectifier circuit 11, and the cathode of the LED 21 is connected to the anode of the LED 22. The cathode of the LED 22 is connected to the anode of the LED 23, the cathode of the LED 23 is connected to the anode of the LED 24, and the cathode of the LED 24 is connected to the negative electrode of the rectifier circuit 11 via the constant current control circuit 44.

  When the pulsating voltage from the rectifier circuit 11 is applied to the LED series circuit 20, the LED current flows through the LEDs 21 to 24 to emit light.

  The switching element 31 is composed of, for example, a MOSFET, the drain is connected to the connection point between the LED 21 and the LED 22, the source is connected to the negative electrode of the rectifier circuit 11 via the constant current control circuit 41, and the gate is connected to a control circuit (not shown). It is connected. The switching element 31 is turned on / off when a control signal from the control circuit is supplied to the gate.

  The switching element 32 is composed of, for example, a MOSFET, the drain is connected to the connection point between the LED 22 and the LED 23, the source is connected to the negative electrode of the rectifier circuit 11 via the constant current control circuit 42, and the gate is connected to a control circuit (not shown). It is connected. The switching element 32 is turned on / off when a control signal from the control circuit is supplied to the gate.

  The switching element 33 is composed of, for example, a MOSFET, the drain is connected to the connection point between the LED 23 and the LED 24, the source is connected to the negative electrode of the rectifier circuit 11 via the constant current control circuit 43, and the gate is connected to a control circuit (not shown). It is connected. The switching element 33 is turned on / off when a control signal from the control circuit is supplied to the gate.

  The constant current control circuit 41 causes a constant current to flow through the switching element 31 when the switching element 31 is on. The constant current control circuit 42 supplies a constant current to the switching element 32 when the switching element 32 is on. The constant current control circuit 43 supplies a constant current to the switching element 33 when the switching element 33 is turned on. The constant current control circuit 44 causes a constant current to flow through the path from the LED 24 to the negative electrode of the rectifier circuit 11 when all of the switching elements 31 to 33 are off.

  A charging circuit in which a diode D1 and a capacitor C are connected in series is connected in parallel to a series circuit composed of an LED 22, an LED 23, and an LED 24. The anode of the diode D1 is connected to the connection between the LED 21 and the LED 22, and the cathode is connected to one end of the capacitor C. The other end of the capacitor C is connected to the cathode of the LED 24. The capacitor C is charged by the charging current Icc flowing through the path of the rectifier circuit 11 → LED 21 → diode D1.

  When the AC voltage detection unit 51 detects that the pulsation voltage output from the rectifier circuit 11 is equal to or lower than a predetermined threshold (AC detection threshold), the AC voltage detection unit 51 outputs an H level discharge start signal.

  The discharge switching element SW is composed of, for example, a MOSFET, and controls the discharge of the capacitor C. The drain of the discharge switching element SW is connected to the connection point of the diode D1 and the capacitor C, the source is connected to the connection point of the LED 22 and the LED 23 via the constant current control circuit 52, and the gate is connected to the AC voltage detection unit 51. ing.

  The discharge switching element SW is turned on when an H level discharge start signal is sent from the AC voltage detector 51. As a result, the electric charge charged in the capacitor C is discharged through the path of the capacitor C → the discharge switching element SW → the constant current control circuit 52 → the LED 23 → the LED 24 → the capacitor C, and the discharge current Icd flows.

  Next, the operation of the LED driving device configured as described above will be described with reference to the timing chart shown in FIG.

  First, when an AC voltage is applied from the outside, the rectifier circuit 11 performs full-wave rectification on the applied AC voltage and generates an input voltage Vin having a pulsating waveform. The input voltage Vin generated by the rectifier circuit 11 is applied to the LED series circuit 20 including the LEDs 21 to 24 and the AC voltage detector 51.

  On the other hand, the switching elements 31 to 33 are turned on / off according to a control signal from a control circuit (not shown), and constant current control is performed in stages. As a result, an input current Iin having a stepped waveform corresponding to the input voltage Vin flows between the output terminals of the rectifier circuit 11.

  That is, when the switching element 31 is turned on by a control signal from the control circuit, a current flows through the path of the rectifier circuit 11 → the LED 21 → the switching element 31 → the constant current control circuit 41 → the rectifier circuit 11, and only the LED 21 is lit. FIG. 2 shows a state where the light output changes.

  Further, when the switching element 31 is turned off and the switching element 32 is turned on by a control signal from the control circuit, the path of the rectifier circuit 11 → LED 21 → LED 22 → switching element 32 → constant current control circuit 42 → rectifier circuit 11 Current flows, and the LEDs 21 and 22 are lit.

  When the switching elements 31 and 32 are turned off and the switching element 33 is turned on by a control signal from the control circuit, the rectifier circuit 11 → LED21 → LED22 → LED23 → switching element 33 → constant current control circuit 43 → rectifier circuit. The current flows through the path 11, and the LED 21, LED 22, and LED 23 are lit.

  Further, if none of the switching elements 31 to 33 is turned on by a control signal from the control circuit, a current flows through the path of the rectifier circuit 11 → LED 21 → LED 22 → LED 23 → LED 24 → constant current control circuit 44 → rectifier circuit 11 and the LED 21 , LED22, LED23 and LED24 are all lit.

  Next, the operation in each period T1 to T5 will be described.

  First, during the period T1, the discharge switching element SW is off, the capacitor voltage Vc is equal to or lower than the first voltage V1, and the diode D1 is not turned on while the input voltage Vin is low, so the charging current Icc does not flow. .

  However, when the input voltage Vin becomes higher than the first voltage V1 in the period T2, the charging current Icc flows through the path of the rectifier circuit 11 → the LED 21 → the diode D1 → the capacitor C, and charging of the capacitor C is started. As a result, the capacitor voltage Vc increases as shown in the period T2, and the capacitor voltage Vc maintains the second voltage V2 even when the charging current Icc disappears as shown in the period T3.

  In this state, when the AC voltage detection unit 51 detects that the input voltage Vin is smaller than the AC detection threshold, an H level control signal is applied to the gate of the discharge switching element SW.

  As a result, the discharge switching element SW is turned on as shown in the period T4. As a result, a discharge current Icd (current opposite to the charging current Icc) flows through the path of the capacitor C → the discharge switching element SW → the constant current control circuit 52 → the LED 23 → the LED 24 → the capacitor C. Since the AC voltage detection unit 51 is independent, the period T4 can be made longer than the period in which the input current Iin is zero.

  As a result, even if the input current Iin is zero, the current Icd flows through the LED 23 and the LED 24. Therefore, as shown in the period T4, the light output is raised, and a non-lighting period in which all the LEDs 21 to 24 are turned off occurs. do not do. As a result, the request | requirement with respect to the flicker in LED21-24 can be met.

  The IC 30 operates in cooperation with the auxiliary lighting circuit, and calculates the total of the charging current Icc to the capacitor C constituting the charging circuit and the LED current to the LEDs 21 to LED 24 constituting the LED series circuit 20 as the pulsating voltage from the rectifier circuit 11. Therefore, the input current is not distorted by a sine wave and can be adapted to the JIS standard harmonic regulation class C (25 W or more). In addition, the peak value of the light output is reduced and the light output frequency is increased.

  Furthermore, since high-frequency switching is not performed, conduction noise and radiation noise are reduced, and a margin of 10 dB or more can be obtained with respect to CISPR15 which is a noise standard for illumination even though there is no noise filter.

  FIG. 3 is a circuit diagram illustrating a detailed configuration of the LED drive device according to the first embodiment. In this circuit diagram, each of the LEDs 21 to 24 shows an example of 12 or 9 single LEDs.

  Since each of the LEDs 21 to 24 has a different lighting period, FIG. 3 shows an image in which the arrangement order of the single LEDs is adjusted in order to smooth the light output.

  Moreover, when the board | substrate of the LED drive device which concerns on Example 1 shown in FIG. 3 is incorporated in a straight tube fluorescent lamp type LED lighting, for example, a control circuit is arrange | positioned in a nozzle | cap | die or the periphery of LED, and influence on a light emission area | region Is mounted on the same substrate as the LED while avoiding as much as possible. In addition, AC input terminals are provided at both ends in order to facilitate lengthening. Moreover, by applying to crime prevention lights and facility lights, it is possible to reduce the size and weight of the lamp.

  As described above, according to the first embodiment of the present invention, it is possible to avoid the non-lighting period in which the light output becomes zero, and thus it is possible to meet the demand for flicker. Moreover, there exists an advantage that it can respond to harmonic regulation class C (25W or more).

  Moreover, the result of having evaluated the flicker of the LED drive device which concerns on Example 1 is as follows. That is, the minimum value of the light output is 28.1% of the peak value, and the frequency of the light output is about 200 Hz. Therefore, a result conforming to the JIS standard was obtained.

  Further, in the case of a fluorescent lamp, the minimum value of the light output is 41.9% of the peak value, but the frequency of the light output is about 100 Hz, which is half that of the first embodiment, so that the flicker is easily visually recognized. On the other hand, in the LED drive device according to the first embodiment, there is an effect that it is difficult to visually recognize flicker even when compared with a fluorescent lamp.

  As mentioned above, although this invention was described by embodiment, it should not be understood that the description and drawing which form a part of this indication limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art. That is, it goes without saying that the present invention includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description. For example, the number of LEDs constituting the LED series circuit 20 in series and the number of single LEDs constituting each LED can be any number. Further, the path through which the discharge current Icd flows can be any path of the LED series circuit 20.

  FIG. 4 is a diagram showing a configuration of an LED driving device according to Embodiment 2 of the present invention. FIG. 4 shows the configuration of only the main part of the LED driving device. The LED driving device includes LEDs 1 to 4 constituting the LED series circuit, diodes D1 and D2, a capacitor C, and a discharge switching element SW. The discharge switching element SW also has a function of a constant current control circuit. The LEDs 1 and 2 are configured by connecting 12 single LEDs in series. The LEDs 3 and 4 are configured by connecting nine single LEDs in series.

  In the LED drive device according to the second embodiment, the color temperature of the LED 2 that emits light by the auxiliary lighting circuit having the discharge switching element SW is set to be different from the color temperatures of the other LEDs 1, 3, and 4. The color temperature of the LED 2 that emits light by the auxiliary lighting circuit is set lower than the color temperature of the LEDs 1, 3, and 4 other than the LED 2.

  FIG. 5 shows the relationship between the dimming rate indicating the phase angle as a percentage when the input voltage of the LED drive device according to the second embodiment of the present invention is phase controlled and the total current value (brightness) of each LED array. FIG. The total current value is a current value obtained by multiplying the current value of each LED array by the number of LEDs. In this case, the LED that emits light by the auxiliary lighting circuit is LED2. As can be seen from FIG. 5, when the dimming rate is 20%, the current is almost zero except for the LED 2, while the current flows in the LED 2.

  FIG. 6 is a diagram illustrating the relationship between the dimming rate of the LED drive device according to Example 2 of the present invention and the current value ratio (brightness ratio) of each LED array. The current value ratio is the ratio of the current value of each LED array to the total LED current value at each dimming rate. In FIG. 6, the current value ratio of the LED 2 to the other LEDs 1, 3, 4 when the dimming rate is 100% is about 30%. However, when the dimming rate is 20%, the current value ratio is as large as about 70%. For this reason, by setting the color temperature of the LED 2 to be different from the color temperatures of the other LEDs 1, 3, and 4, it is possible to perform toning that changes the color temperature according to the dimming rate during phase control dimming.

  In addition, by setting the color temperature of the LED 2 that emits light by the auxiliary lighting circuit to be lower than the color temperature of the LEDs 1, 3, and 4 other than the LED 2, the overall color temperature is lowered during dimming, and the incandescent light bulb is dimmed Just like time, natural color changes can be achieved. Of course, it is also possible to achieve toning that increases the overall color temperature during dimming.

  Even if there is no auxiliary lighting circuit, the LED string that is lit at the lowest voltage (LED1 in this example) is lit to the end, and a similar color temperature change can be realized, but an auxiliary lighting circuit is provided. Therefore, there are the following advantages. That is, it can conform to the JIS flicker standard when 100% is lit. Further, color adjustment with a high degree of freedom is possible by adjusting the auxiliary lighting circuit.

11 Rectifier circuit 20 LED series circuit 1-4, 21-24 LED
30 Integrated Circuit (IC)
31-33 Switching elements 41-44, 52 Constant current control circuit 51 AC voltage detector D1, Diode C Capacitor SW Discharge switching element Vin AC voltage Iin Input current Icc Charging current Icd Discharging current Vc Capacitor voltage

Claims (6)

A rectifier circuit that rectifies an alternating voltage and outputs a pulsating voltage;
A plurality of LEDs connected in series, and an LED series circuit that emits light when an LED current corresponding to a pulsating voltage from the rectifier circuit flows;
A plurality of switching elements connected to connection points of adjacent LEDs among the plurality of LEDs constituting the LED series circuit;
According to the state of the plurality of switching elements, a capacitor charged by a charging current according to a pulsation voltage supplied from the rectifier circuit via a diode;
A control circuit for controlling the sum of the charging current to the capacitor and the LED current to the LED series circuit to be a current corresponding to the pulsating voltage from the rectifier circuit;
An auxiliary lighting circuit that discharges the capacitor when the pulsation voltage becomes smaller than a predetermined threshold, and causes a current to flow through a part of the plurality of LEDs that constitute the LED series circuit;
An LED driving device comprising: The auxiliary lighting circuit is provided in parallel with a part of the LEDs constituting the LED series circuit, and a discharge switching element connected in series to the capacitor, and a constant current control circuit for flowing a discharge current when the discharge switching element is turned on A discharge circuit having
2. The LED driving device according to claim 1, wherein the capacitor is discharged through a discharge switching element of the discharge circuit, thereby causing a discharge current to flow through a part of the LEDs constituting the LED series circuit to emit light. The auxiliary lighting circuit includes an AC voltage detection unit that detects whether the pulsation voltage output from the rectifier circuit is equal to or lower than a predetermined threshold value independently of the control circuit.
When the AC voltage detection unit detects that the pulsation voltage has become a predetermined threshold value or less, it turns on the discharge switching element to discharge the capacitor, and forms a part of the LED constituting the LED series circuit. The LED driving device according to claim 2, wherein the LED driving device emits light by flowing a discharge current.   4. The LED driving device according to claim 2, wherein a color temperature of the LED that emits light by the auxiliary lighting circuit is different from a color temperature of an LED other than the LED that emits light by the auxiliary lighting circuit. 5.   The LED driving device according to claim 4, wherein the color temperature of the LED that emits light by the auxiliary lighting circuit is set lower than the color temperature of the LED other than the LED that emits light by the auxiliary lighting circuit. The LED driving device according to claim 4, wherein the color temperature of the LED that emits light by the auxiliary lighting circuit is set higher than the color temperature of the LED other than the LED that emits light by the auxiliary lighting circuit.

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