JP5624390B2 - LED lighting device - Google Patents

Description

  The present invention relates to an LED lighting device using a visible light emitting diode (hereinafter referred to as “LED”).

  A circuit configuration example of a conventional LED lighting device is shown in FIG. 6 (see Patent Document 1).

  A conventional LED lighting device 90 shown in FIG. 6 includes a bridge diode 3, an LED module 6, a resistor 31, and a constant current circuit 40 each including a plurality of LED elements. The constant current circuit 40 includes an NPN transistor 41, a resistor 42, and a Zener diode 43. Reference numeral 2 denotes an AC voltage source.

  A commercial AC 100V AC voltage source 2 is connected to the input side of the bridge diode 3. In addition, the LED module 6, the NPN transistor 41, and the resistor 42 are connected in series from the positive output terminal to the output side of the bridge diode 3.

  One end of the resistor 31 is connected to the connection point between the bridge diode 3 and the LED module 6, and the other end of the resistor 31 is connected to the base of the NPN transistor 41 and the cathode of the Zener diode 43. The NPN transistor 41 has a collector connected to the LED module 6 and an emitter connected to one end of the resistor 42. The other end of the resistor 42 is connected to the anode of the Zener diode 43 and the negative output terminal of the bridge diode 3.

  According to such a configuration, as a result of full-wave rectification of the AC voltage output from the AC voltage source 2 of commercial AC 100V by the bridge diode 2, a pulsating voltage having a peak value of about 141V is obtained.

In the constant current circuit 40, the base potential of the NPN transistor 41 exhibits a constant value is clamped by the Zener voltage V _z of the Zener diode 43. Therefore, when the base-emitter voltage of the NPN transistor 41 is V _be41 , the voltage across the resistor 42 is (V _z −V _be41 ). At this time, assuming that the resistance value of the resistor 42 is R ₄₂ , the current flowing through the resistor 42 is (V _z −V _be41 ) / R ₄₂ , which is a constant value.

Since a current substantially the same as the current value flowing through the resistor 42 flows into the NPN transistor 41 via the LED module 6 as a collector current, the current value flowing through the LED module 6 is also substantially (V _z −V _be41 ) / R _42. It can be expressed. Therefore, the current flowing through the LED module 6 can be a constant value. As shown in FIG. 7, since the luminous intensity of the LED element depends on the amount of current flowing through the LED element, in order to cause the LED element to emit light at a constant luminous intensity, it is necessary to maintain the current flowing through the element at a constant value.

In practice, the absolute value of the voltage outputted from the bridge diode 3, while below the Zener voltage V _Z, the zener diode 43 is non-conductive, the LED module 6 voltage does not flow. That is, at least at the moment when the instantaneous value of the AC voltage source 2 indicates 0 V, the LED module 6 does not emit light. The absolute value of the voltage output from the bridge diode 3 exceeds the Zener voltage V _z by raising the instantaneous value of the AC voltage source 2 in either positive or negative direction, and the base potential of the NPN transistor 41 becomes the Zener voltage V. _Clamped with _z . As a result, the current of (V _z −V _be41 ) / R ₄₂ flows to the LED module 6. FIG. 8 is a graph for explaining such an operation.

FIG. 8A is a graph showing changes in the output voltage V ₂ of the AC voltage source 2 at time t. FIG. 4B is a graph showing a change in the output voltage V ₃ of the bridge diode 3 at time t. FIG. 4C is a graph showing a change in the current I ₆ flowing through the LED module 6 at time t. From FIG. 8, below the output voltage V ₃ is predetermined value shown in (b) (a value substantially equal to the Zener voltage V _z), the current I ₆ flowing through the LED module 6 is zero. At other timings, the current I ₆ shows a constant value. The light intensity adjustment of the LED module 6 is performed by changing the duty ratio in the graph of (c).

  However, according to FIG. 8C, it can be seen that the LED module 6 repeats blinking at a frequency twice the output voltage of the AC voltage source 2. If the flicker frequency is sufficiently high, this flicker cannot be visually recognized. However, if the flicker frequency is about twice that of the commercial frequency, the flicker may be visually recognized. there were.

  In response to this, FIG. 9 shows an example of a configuration in which the flicker frequency is intentionally set to a high frequency so that flicker cannot be detected by humans.

  9 includes an AC voltage source 2, a bridge diode 3, an electrolytic capacitor 51, an oscillation circuit 52, a MOS-FET 54, a primary side circuit including primary windings of a transformer 53, a diode 61, Electrolytic capacitor 62, resistor 63, resistor 64, resistor 65, error amplifier 71, reference voltage 73, error amplifier 72, reference voltage 74, LED module 6, photocoupler 55, and secondary side including secondary winding of transformer 53 Circuit.

  The commercial voltage output from the AC voltage source 2 is full-wave rectified by the bridge diode 3, smoothed by the electrolytic capacitor 51, and converted into a DC voltage. The DC voltage is converted into an AC voltage by a switching circuit including the oscillation circuit 52, the primary winding of the transformer 53, and the MOS-FET 54, and is sent to the secondary winding of the transformer 53.

  The AC voltage induced in the secondary winding of the transformer 53 is converted back to a DC voltage by a rectifier circuit including a diode 61 and an electrolytic capacitor 62. Thereby, a DC voltage is applied between both ends of the series circuit including the resistors 64 and 65 and between both ends of the LED module 6.

  The voltage of the intermediate node N1 of the voltage dividing circuit composed of the resistors 64 and 65 is compared with the reference voltage 74 by the error amplifier 72. When the former becomes equal to or higher than the latter voltage value, the voltage is output from the error amplifier 72 and the photocoupler A current is supplied to the LED 55 to stop the oscillation circuit 52. Thereby, the voltage induced in the secondary side circuit is reduced. On the other hand, when the former is less than the latter voltage value, the oscillation of the oscillation circuit 52 is continued and the induced voltage of the secondary circuit is increased.

  Further, since the amount of current flowing through the LED module 6 varies depending on the value of the secondary side voltage, in order to keep the luminous intensity of the LED module 6 constant, it is necessary to keep the value of the secondary side voltage constant. Since the voltage across the resistor 63 changes depending on the secondary side voltage, the light intensity can be kept constant by controlling the oscillation circuit 52 based on the magnitude of the voltage across the resistor 63. Specifically, the voltage between both ends of the resistor 63 is compared with the reference voltage 73 in the error amplifier 71, and when the former becomes equal to or higher than the latter voltage value, a voltage is output from the error amplifier 71 to supply a current to the LED of the photocoupler 55. The oscillation circuit 52 is stopped. On the other hand, when the former is less than the latter voltage value, the oscillation of the oscillation circuit 52 is continued and the induced voltage of the secondary circuit is increased.

  In such a configuration, the voltage across the LED module 6 is kept constant. Further, by setting the oscillation frequency of the oscillation circuit 52 sufficiently higher than the commercial frequency, the problem of flickering like the configuration described in Patent Document 1 can be solved.

JP 2000-260578 A

  Since the forward voltage of an LED element changes due to temperature and aging deterioration, even if constant voltage driving is performed, the current changes depending on the element state, and in some cases an overcurrent may flow and destroy the element. is there. Moreover, as shown in FIG. 7, the luminous intensity of the LED element has a relationship depending on the current. Therefore, the LED module 6 is required to be current driven. In the configurations of FIGS. 6 and 8, current driving is also performed.

  However, according to the configuration of FIG. 8, the number of driving elements is greatly increased as compared with FIG. Furthermore, the configuration of FIG. 8 includes smoothing electrolytic capacitors 51 and 62 for smoothing the rectified DC voltage. However, since the electrolytic capacitors are vulnerable to heat, a mechanism for heat dissipation is required. From this point of view, it is not suitable for downsizing.

  On the other hand, the configuration of FIG. 6 has a flickering problem as described above. In addition, in the configuration of FIG. 6, it is necessary to set the breakdown voltage of the NPN transistor 41 in the constant current circuit 40 to be equal to or higher than the peak voltage of the pulsating voltage that is full-wave rectified by the bridge diode 3. As described above, in the case of the configuration shown in FIG. 6, since the peak voltage indicates about 141 V, it is necessary to dispose a transistor having a higher breakdown voltage. However, in order to increase the breakdown voltage of the transistor, it is necessary to increase the transistor area, which is a bottleneck from the viewpoint of miniaturization.

  In view of the above problems, an object of the present invention is to realize an LED lighting device capable of both preventing flickering and reducing the size of the device.

The LED lighting device of the present invention is
A bridge diode that rectifies an AC voltage, an LED module in which LED elements are connected in series, a constant current circuit, and a switching circuit;
Both ends of a series circuit formed by the LED module, the constant current circuit, and the switching circuit are connected to both positive and negative output ends of the bridge diode,
The constant current circuit includes a normally-on type GaN-FET, one end is electrically connected to the gate and source of the GaN-FET, and the other end is connected to the drain.
Said switching circuit includes an oscillation circuit for outputting a high-frequency oscillation signal than before Symbol AC voltage, and a switching MOS-FET in which the oscillation signal is supplied to the gate, one end of the MOS-FET for the switching The drain is configured with the other end connected to the source of the switching MOS-FET,
The oscillation circuit has two input terminals electrically connected to a source and a drain of the switching MOS-FET, and the oscillation circuit is based on a voltage between the one end and the other end of the switching circuit. Output signal,
The switching MOS-FET is controlled to be turned on / off by the oscillation signal, whereby conduction / non-conduction control of the LED module is performed.

  In the above configuration, it is preferable that the frequency of the oscillation signal is higher than the upper limit of the frequency at which the blinking can be visually recognized when the LED element blinks.

  In the above configuration, the GaN-FET has another feature in that a gate and a source are directly connected.

  Moreover, it is another feature that the constant current circuit has a resistance between the one end and the source of the GaN-FET instead of the above configuration.

  At this time, it is also preferable to provide a PTC thermistor instead of the resistor or together with the resistor.

  In the above configuration, the switching circuit further includes a rectifier circuit that rectifies current from the one end of the constant current circuit and supplies the rectified current to the oscillation circuit.

  Further, in the above configuration, the switching circuit includes a Zener diode having one end connected to the source of the switching MOS-FET and the other end connected to the drain of the switching MOS-FET. .

  According to the LED lighting device of the present invention, the switching circuit for controlling the conduction of the LED module is provided, and this switching circuit performs on / off control of the switching MOS-FET based on the oscillation signal output from the oscillation circuit. In this configuration, the conduction is controlled. Therefore, by setting the frequency of the oscillation signal to a value sufficiently higher than the frequency of the AC voltage, blinking of the LED module cannot be visually recognized, and as a result, flicker can be prevented.

  In addition, since the constant current circuit is realized by the normally-on type GaN-FET, the number of elements constituting the constant current circuit can be greatly reduced, and downsizing can be realized. In particular, GaN-FETs can easily increase the withstand voltage compared to MOS-FETs or junction FETs, and therefore can be supplied to a series circuit including an LED module without reducing the pulsating voltage from the bridge diode. It becomes possible. As a result, the number of elements can be greatly reduced compared to the conventional LED lighting device that is configured to step down the pulsating voltage using a transformer and a rectifier circuit, and downsizing can be realized.

  Furthermore, since no transformer is required, a rectifying electrolytic capacitor is also unnecessary. Therefore, it is not necessary to provide a heat dissipation mechanism considering the heat resistance of the electrolytic capacitor. From this point, downsizing can be realized and the life can be extended.

Circuit configuration example of LED lighting device of the present invention Graph showing current-voltage characteristics of normally-on GaN-FET The graph which shows the electric current change and voltage change for demonstrating operation | movement of a LED lighting apparatus. Another circuit configuration example of the LED lighting device of the present invention Another circuit configuration example of the LED lighting device of the present invention Circuit configuration example of conventional LED lighting device The graph which shows the relationship between the electric current which flows through an LED element, and luminous intensity The graph which shows the electric current change and voltage change for demonstrating operation | movement of a LED lighting apparatus. Another circuit configuration example of the conventional LED lighting device

  FIG. 1 shows a circuit example of the LED lighting device of the present invention. The LED lighting device 1 includes a bridge diode 3, a switching circuit 4, a constant current circuit 5, and an LED module 6. Reference numeral 2 denotes an AC voltage source. The same reference numerals are given to the same elements as those in the past.

  A commercial AC 100V AC voltage source 2 is connected to the input side of the bridge diode 3. The anode side of the LED module 6 is connected to the positive output terminal of the bridge diode 3. One end of a constant current circuit 5 is connected to the cathode side of the LED module 6. One end of the switching circuit 4 is connected to the other end of the constant current circuit 5. An output terminal on the negative side of the bridge diode 3 is connected to the other end of the switching circuit 4.

  The LED module 6 is configured by connecting a plurality of LED elements in series.

The constant current circuit 5 is composed of a normally-on type GaN-FET 21 in which a gate and a source are connected. As shown in FIG. 2, a constant current circuit can be realized by utilizing the constant current characteristics in the saturation region between the drain and source of the GaN-FET. In FIG. 2, the horizontal axis represents the drain-source voltage V _{d — s} , and the vertical axis represents the current I _d — s flowing between the drain and source, and V V when the gate-source voltage V _{g — s} is varied. The relationship between _{d_s} and I _{d_s} is illustrated.

  The switching circuit 4 includes an oscillation circuit 11, a capacitor 12, a diode 13, a Zener diode 14, and a switching MOS-FET 15 (abbreviated as “MOS-FET 15” as appropriate).

  One end of the switching circuit 4 is connected to the drain terminal of the MOS-FET 15, the cathode terminal of the Zener diode 14, and the anode terminal of the diode 13. The cathode terminal of the diode 13 is connected to one electrode of the capacitor 12 and the positive power supply terminal of the oscillation circuit 11. The other end of the switching circuit 4 is connected to the source terminal of the MOS-FET 15, the anode terminal of the Zener diode 14, the other electrode of the capacitor 12, and the negative power supply terminal of the oscillation circuit 11. The gate terminal of the MOS-FET 15 is connected to the output terminal of the oscillation circuit 11.

  In the configuration of FIG. 1 as well, the commercial AC 100V output from the constant voltage source 1 as shown in FIG. 3A is full-wave rectified by the bridge diode 2 as in the configuration of FIG. The pulsating voltage as shown in FIG. 6 is obtained (the peak voltage is about 141 V). The pulsating voltage is supplied to a series circuit including the LED module 6, the constant current circuit 5, and the switching circuit 4.

As described above, the GaN-FET 21 provided in the constant current circuit 5 has current-voltage characteristics as shown in FIG. 2, and therefore, as long as a voltage of a predetermined value or higher is applied between the drain and the source, the drain-source current. I _{d — s} indicates a constant value. Note that the GaN-FET is superior to the junction FET and depletion type MOS-FET having the same constant current characteristics, and operates at a high current. Therefore, the GaN-FET operates like a LED lighting device 91 in FIG. It is not necessary to reduce the applied voltage using the pressure resistors 64 and 65.

The switching circuit 4 is in an off state when the supply of the output voltage from the AC voltage source 2 is started. When the oscillation circuit 11 is operated by the voltage rectified by the rectification circuit constituted by the diode 13 and the capacitor 12, the MOS-FET 15 is switched according to the output voltage of the oscillation circuit 11. Thereby, the current flowing through the switching circuit 4 can be varied at a frequency higher than that of the commercial power source. Since the switching circuit 4, the constant current circuit 5, and the LED module 6 constitute a series circuit, the current flowing through the switching circuit 4 becomes the current I ₆ flowing through the LED module 6 as it is (see FIG. 3C). That is, since the current value I ₆ flowing through the LED module 6 can be varied at a high frequency, no flicker occurs unlike the configuration of FIG.

As shown in FIG. 3C, when the current I ₆ flowing through the LED module 6 varies, the voltage supplied to the anode terminal of the diode 13 also varies. This voltage is, by being rectified by configured the diode rectifier 13 and a capacitor 12, a stable voltage V ₁₁ that is supplied to the oscillation circuit 11 (see FIG. 3 (d)).

  The Zener diode 14 is provided to generate a constant voltage from a constant current and limit an increase in voltage applied to the oscillation circuit 11. A similar function may be realized by a resistor instead of the Zener diode 14.

  In summary, the LED lighting device 1 shown in FIG. 1 has the following characteristics.

  (1) The switching frequency of the MOS-FET in the switching circuit is switched by the output voltage of the oscillation circuit that vibrates at a frequency higher than that of the commercial power supply, so that the fluctuation frequency of the current flowing through the LED module is sufficiently higher than that of the commercial power supply. It can be. As a result, flickering of the LED module can be prevented without being detected by humans.

  (2) Since the constant current circuit is realized by a normally-on type FET, the number of elements constituting the constant current circuit can be greatly reduced, and downsizing can be realized. In particular, since the FET can be realized by a GaN-FET, the withstand voltage can be increased, so that the pulsating voltage from the bridge diode can be supplied to a series circuit including the LED module without being stepped down. As a result, the number of elements can be significantly reduced as compared with the conventional LED lighting device 91 shown in FIG.

  In the case of a GaN-FET, a normally-on type FET is formed by a general manufacturing method, and therefore there is an advantage that an additional process for making the normally-on type is not required.

  (3) Further, since the pulsating voltage from the bridge diode can be directly supplied to the series circuit, unlike the LED lighting device 91 of FIG. 9, the transformer 53 is unnecessary, and accordingly, the electrolytic capacitors 51 and 62 are also unnecessary. Become. Therefore, it is not necessary to provide a heat dissipating mechanism in consideration of the heat resistance of the electrolytic capacitors 51 and 62. From this point, downsizing can be realized, leading to a long life.

  Another embodiment will be described below.

<1> The constant current circuit 5 may include the GaN-FET 21 and the resistor 22 by providing the resistor 22 between the source of the GaN-FET 21 and the switching circuit side terminal of the constant current circuit 5 (FIG. 4). With the configuration of the LED lighting device 1 a shown in FIG. 4, the voltage value corresponding to (current I ₅ flowing through the constant current circuit ₅ ) × (resistance value R ₂₂ of the resistor ₂₂ ) is the gate-source of the GaN-FET 21. The voltage at the gate terminal is biased to the negative side compared to the source terminal. At this time, when the current I ₅ flowing through the constant current circuit 5 shows a large value, the bias component toward the negative side becomes large, and the GaN-FET 21 is turned off.

Therefore, since the upper limit value of the current I ₅ flowing through the constant current circuit 5 can be set, an overcurrent protection function for the LED module 6 can be realized. Moreover, since it is only necessary to provide the resistor 22 between the gate and the source as compared with the LED lighting device 1 of FIG. 1, it is possible to realize a sufficiently small size when compared with the conventional configuration.

  <2> The PTC thermistor 23 may be provided instead of the resistor 22 of the alternative embodiment <1> so that the constant current circuit 5 includes the GaN-FET 21 and the PTC thermistor 23 (see FIG. 5). With the configuration of the LED lighting device 1b shown in FIG. 5, when the ambient temperature of the constant current circuit 5 reaches the operating temperature of the PTC thermistor 23 or higher, the PTC thermistor 23 has a high resistance value. For the same reason, the GaN-FET 21 is turned off. Thereby, since the allowable upper limit temperature of the constant current circuit 5 can be set, an overheat protection function can be realized.

  Of course, it is also possible to connect a resistor in series to the PTC thermistor 23 or use the resistance component of the PTC thermistor 23 to have both an overheat protection function and an overcurrent protection function.

  <3> In FIG. 1, a series circuit in which the LED module 6, the constant current circuit 5, and the switching circuit 4 are connected in order from the positive electrode side is formed between the positive electrode side output terminal and the negative electrode side output terminal of the bridge diode 3. The case is shown. However, the connection order of the LED module 6, the constant current circuit 5, and the switching circuit 4 constituting this series circuit is not limited to the order shown in FIG.

1, 1a, 1b: Circuit configuration example of LED lighting device of the present invention 2: AC voltage source 3: Bridge diode 4: Switching circuit 5: Constant current circuit 6: LED module 11: Oscillation circuit 12: Capacitor 13: Diode 14: Zener diode 15: Switching MOS-FET
21: Normally-on GaN-FET
22: Resistance 23: PTC thermistor 31: Resistance 40: Constant current circuit 41: NPN transistor 42: Resistance 43: Zener diode 51: Electrolytic capacitor 52: Oscillation circuit 53: Transformer 54: MOS-FET
55: Photocoupler 61: Diode 62: Electrolytic capacitor 63, 64, 65: Resistor 71: Error amplifier 72: Reference voltage 73: Error amplifier 74: Reference voltage 90, 91: Conventional LED lighting device N1: Intermediate node

Claims (7)

A bridge diode that rectifies an AC voltage, an LED module in which LED elements are connected in series, a constant current circuit, and a switching circuit;
Both ends of a series circuit formed by the LED module, the constant current circuit, and the switching circuit are connected to both positive and negative output ends of the bridge diode,
The constant current circuit includes a normally-on type GaN-FET, one end is electrically connected to the gate and source of the GaN-FET, and the other end is connected to the drain.
Said switching circuit includes an oscillation circuit for outputting a high-frequency oscillation signal than before Symbol AC voltage, and a switching MOS-FET in which the oscillation signal is supplied to the gate, one end of the MOS-FET for the switching The drain is configured with the other end connected to the source of the switching MOS-FET,
The oscillation circuit has two input terminals electrically connected to a source and a drain of the switching MOS-FET, and the oscillation circuit is based on a voltage between the one end and the other end of the switching circuit. Output signal,
The LED illumination device according to claim 1, wherein the switching MOS-FET is controlled to be turned on and off by the oscillation signal, whereby conduction / non-conduction control of the LED module is performed.
  2. The LED lighting device according to claim 1, wherein the frequency of the oscillation signal is higher than an upper limit of a frequency at which the blinking can be visually recognized when the LED element blinks.   The LED lighting device according to claim 1, wherein the GaN-FET directly connects a gate and a source.   The LED lighting device according to claim 1, wherein the constant current circuit has a resistance between the one end and a source of the GaN-FET.   The LED lighting device according to claim 1, wherein the constant current circuit includes a PTC thermistor between the one end and a source of the GaN-FET.   6. The LED lighting device according to claim 1, wherein the switching circuit includes a rectifier circuit that rectifies a current from the one end of the constant current circuit and supplies the rectified current to the oscillation circuit. .   The LED lighting according to claim 6, wherein the switching circuit includes a Zener diode having one end connected to the source of the switching MOS-FET and the other end connected to the drain of the switching MOS-FET. apparatus.

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