JP5810306B2 - LED lighting device and lighting apparatus using the same - Google Patents

Description

  The present invention relates to an LED lighting device that controls lighting of an LED (Light Emitting Diode) and a lighting fixture using the same.

  Conventionally, LED lighting devices that perform feedback control of LED lighting output are known (see, for example, Patent Documents 1 and 2). The conventional LED lighting device includes a current detection resistor connected in series with the LED, and can measure the current flowing through the LED by measuring the voltage across the current detection resistor.

JP-T-2004-527138 JP-T-2006-511082

  However, in the conventional LED lighting device, a power loss proportional to the resistance value of the current detection resistor and the square of the current flowing through the current detection resistor is caused by the current detection resistor provided to detect the current flowing through the LED. There are concerns such as temperature rise. In order to suppress such power loss and temperature rise of components, it is necessary to make the resistance value of the current detection resistor as small as possible.

  However, if the resistance value of the current detection resistor is decreased, the detection voltage and the reference voltage to be compared with the detection voltage are decreased. Therefore, when noise is superimposed on at least one of the detection voltage and the reference voltage, the influence of noise is reduced. There is a risk of receiving.

  In particular, when the light is turned off and when dimming at a low dimming level, the detection voltage and the reference voltage are lower than when all lights are on. For this reason, when noise is superimposed on at least one of the detection voltage and the reference voltage, there is a concern that malfunctions such as minute light emission or flickering at the lower limit of dimming may occur even when the light is extinguished.

  This invention is made in view of said point, and the objective of this invention is providing the LED lighting device which can improve noise tolerance, and a lighting fixture using the same.

The LED lighting device of the present invention is an LED lighting device that is used by being connected to an LED and an external power supply, and controls a power supply unit that supplies power to the LED and power supplied from the power supply unit to the LED. A lighting control unit, and when the light is turned off , the lighting control unit biases a DC voltage obtained from a path different from the power supply unit with respect to a voltage indicating a current flowing through the LED. And a reference voltage indicating a dimming level according to a control signal input from the outside, and when detected, the detection obtained by biasing the DC voltage with respect to a voltage indicating a current flowing through the LED The voltage and the reference voltage at the time of lighting are compared with the reference voltage at the time of lighting, which is obtained by DC biasing the same voltage as the DC voltage to the reference voltage at the time of lighting off. The The LED is characterized in that the feedback control of the power supply unit such that the dimming level.

  In this LED lighting device, the lighting control unit has a current detection resistor connected in series with the LED in a path of a current flowing through the LED, and detects a voltage across the resistor as a current flowing through the LED. Is preferred.

  In this LED lighting device, the lighting control unit includes a series circuit including a plurality of DC bias resistors connected in series to the current detection resistor, and at least one ends of the plurality of DC bias resistors in the series circuit. The voltage is preferably the DC voltage obtained from a different path from the power supply unit.

  In this LED lighting device, it is preferable that the lighting control unit receives a PWM signal as the control signal and sets the dimming level according to a duty ratio of the PWM signal.

  The lighting fixture of this invention is equipped with the said LED lighting device and LED which lights with the electric power supplied from the said LED lighting device, It is characterized by the above-mentioned.

  In the lighting control unit in which the detection voltage and the reference voltage tend to be low, the present invention generates a detection voltage by biasing a DC voltage obtained from a different path from the power supply unit that supplies power to the LED. Thereby, since the detection voltage compared with a reference voltage can be made high, even if a noise is superimposed on a detection voltage, it becomes difficult to influence a comparison result, and noise tolerance can be improved. This is particularly effective when the detection voltage is low, such as when the light is turned off and when dimming at a low dimming level.

It is a circuit diagram which shows the structure of the lighting fixture which concerns on embodiment. It is explanatory drawing of operation | movement of the electric power supply part which concerns on the same as the above. It is explanatory drawing about the DC bias at the time of light extinction and lighting of the LED lighting device which concerns on the same as the above.

  In the following embodiments, an LED lighting device that controls lighting of an LED (Light Emitting Diode) and a lighting fixture using the LED lighting device will be described.

  The lighting fixture 1 which concerns on this embodiment is provided with the LED lighting device 2 and the LED unit 3 which lights with the electric power supplied from the LED lighting device 2, as shown in FIG.

  The LED unit 3 includes a plurality of LEDs 31 and 31. The plurality of LEDs 31 are connected in series.

  The LED lighting device 2 includes a power supply unit 4, a dimming control circuit 5, and an output feedback circuit 6, and is used by being connected to an LED unit 3 and an AC power source (external power source) 7.

  The power supply unit 4 includes an input filter circuit unit 41, a rectification unit 42, an inrush prevention circuit 43, a boost chopper circuit 44, a flyback circuit 45, and a control power supply 46, and supplies power to the LED unit 3. The plurality of LEDs 31, 31 are turned on.

  The input filter circuit unit 41 reduces normal mode noise, common mode noise, or the like, and suppresses noise from flowing to the AC power supply 7 side. The rectifying unit 42 is a diode bridge (DB) composed of four diodes, and rectifies the AC power input from the input filter circuit unit 41 and outputs it to the boost chopper circuit 44. The inrush prevention circuit 43 prevents an inrush current from flowing when the power is turned on.

  The step-up chopper circuit 44 includes a capacitor 441, a chopper choke 442, a first switching element 443, a diode 444, an electrolytic capacitor 445, and a step-up chopper control circuit 446.

  One end of the chopper choke 442 is connected to the inrush prevention circuit 43 and the capacitor 441, and the other end is connected to the anode of the diode 444.

  The first switching element 443 is an N-channel MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), the gate is connected to the boost chopper control circuit 446, the drain is connected to the chopper choke 442, and the source is ground. It is connected to the. The first switching element 443 performs a switching operation for switching on and off by the boost chopper control of the boost chopper control circuit 446.

  In the step-up chopper circuit 44, the chopper choke 442 accumulates energy during the period when the first switching element 443 is on. When the first switching element 443 is turned off, the energy of the chopper choke 442 charges the electrolytic capacitor 445 through the diode 444. As a result, the step-up chopper circuit 44 generates a DC smoothed voltage boosted from the peak value of the AC voltage of the AC power supply 7.

  The flyback circuit 45 is connected to the subsequent stage of the step-up chopper circuit 44, and includes a flyback transformer 451, a second switching element 452, a diode 453, an electrolytic capacitor 454, and a flyback control circuit 455.

  The flyback transformer 451 has one end on the primary side connected to the cathode of the diode 444 and the other end connected to the drain of the second switching element 452. One end of the secondary side is connected to the positive electrode of the electrolytic capacitor 454 and the anode of the LED 31 of the LED unit 3 via the diode 453, and the other end is connected to a current detection resistor 61 and a secondary side ground described later.

  The second switching element 452 is an N-channel MOSFET, the gate is connected to the flyback control circuit 455, the drain is connected to the primary side of the flyback transformer 451, and the source is connected to the primary side ground. .

  In the flyback circuit 45, the flyback transformer 451 stores energy during the period in which the second switching element 452 is on. When the second switching element 452 is turned off, the energy of the flyback transformer 451 charges the electrolytic capacitor 454 through the secondary-side diode 453. As a result, the smoothed output voltage is output from the flyback circuit 45 to the LED unit 3.

  The control power supply 46 supplies a control voltage to the boost chopper control circuit 446 and the flyback control circuit 455.

  Next, operation | movement of the flyback circuit 45 of the LED lighting device 2 which concerns on this embodiment is demonstrated using FIG.

  As shown in FIG. 2, when the output voltage Vout of the flyback control circuit 455 changes from the low (L) level to the high (H) level at time T1, the second switching element 452 of the flyback circuit 45 is turned on. . Thereafter, the drain current Id of the second switching element 452 increases. When the drain current Id of the second switching element 452 reaches the threshold value at time T2, the output voltage Vout of the flyback control circuit 455 changes from the high (H) level to the low (L) level, and the second switching element 452 turns off. At time T3, the secondary current of the flyback transformer 451 becomes zero and the drain-source voltage Vds of the second switching element 452 starts to decrease, but there is a delay time due to the oscillation frequency of the drain-source voltage Vds. For this reason, at time T4, the output voltage Vout of the flyback control circuit 455 changes from the low (L) level to the high (H) level, and the second switching element 452 is turned on.

  Next, the dimming control circuit 5 and the output feedback circuit 6 will be described with reference to FIG. The dimming control circuit 5 and the output feedback circuit 6 have a function as a lighting control unit that controls power supply from the power supply unit 4 to the LED unit 3.

  The dimming control circuit 5 sets the dimming level (including full lighting and extinguishing) of the LED unit 3 in accordance with a control signal input from an external device (not shown). In the present embodiment, the control signal is a PWM (Pulse Width Modulation) signal, and the dimming control circuit 5 sets the dimming level of the LED unit 3 according to the duty ratio of the PWM signal. The dimming control circuit 5 is connected to the output feedback circuit 6 and outputs a reference voltage indicating the set dimming level to the output feedback circuit 6.

  The output feedback circuit 6 includes a current detection resistor 61, a comparator 62, and a transistor 63. Further, the output feedback circuit 6 includes a first DC bias resistor 64 and a second DC bias resistor 65.

  The current detection resistor 61 is connected in series with the LED unit 3 in a path through which the forward current of the LED unit 3 flows. Thereby, the output feedback circuit 6 detects the voltage across the current detection resistor 61 as a voltage indicating the current flowing through the LED unit 3.

  The first DC bias resistor 64, the second DC bias resistor 65, and the current detection resistor 61 are connected in series. A connection point between the first DC bias resistor 64 and the second DC bias resistor 65 is connected to a non-inverting input terminal of the comparator 62. First DC bias resistor 64, second DC bias resistor 65, and current detection resistor 61 divide DC voltage Vcc output from control power supply 46.

  The comparison unit 62 is composed of an operational amplifier. The non-inverting input terminal (plus terminal) of the operational amplifier is connected between the LED unit 3 and the current detection resistor 61 via the second DC bias resistor 65. The input of the non-inverting input terminal of the operational amplifier is a detection voltage, and the input of the inverting input terminal (minus terminal) is a reference voltage.

  The output terminal of the comparator 62 is connected to the base of the transistor 63. The transistor 63 is connected between the feedback terminal (not shown) of the control IC of the flyback control circuit 455 and the ground.

  In the output feedback circuit 6, the comparator 62 divides the voltage across the current detection resistor 61 by the first DC bias resistor 64, the second DC bias resistor 65, and the current detection resistor 61. The detection voltage obtained by biasing the voltage (DC voltage) is compared with the reference voltage. The transistor 63 is turned on / off according to the comparison result that is the output of the comparator 62. The power supply to the LED unit 3 by the flyback circuit 45 is controlled according to the operation of the transistor 63. When the detection voltage is higher than the reference voltage, the transistor 63 is turned on, and the flyback control circuit 455 stops the on / off switching of the second switching element 452, whereby the flyback circuit 45 to the LED unit 3 is turned off. The power supply stops. On the other hand, when the detection voltage is lower than the reference voltage, the transistor 63 is turned off, and the flyback control circuit 455 controls the on / off switching of the second switching element 452, so that the LED unit 3 is controlled from the flyback circuit 45. Is supplied with power. In this way, the output feedback circuit 6 performs feedback control of the power supply unit 4 so that the LED unit 3 has a desired dimming level.

  Next, the operation of the LED lighting device 2 according to this embodiment will be described. Here, as an example, the resistance value of the first DC bias resistor 64 is 4.9 kΩ, the resistance value of the second DC bias resistor 65 is 100Ω, and the resistance value of the current detection resistor 61 is 1.8Ω. The control voltage Vcc applied to the series circuit of the first DC bias resistor 64, the second DC bias resistor 65, and the current detection resistor 61 is 5V.

  The LED lighting device 2 controls the lighting and extinguishing of the LED unit 3 and the dimming level of the LED unit 3 according to the control signal. At the time of lighting, the light output of the LED unit 3 can be adjusted in a range of about 5% to 100%, and the forward current (LED drive current Io) flowing through the LED unit 3 is in a range of 0.015A to 0.300A. Be controlled.

  First, a case where a turn-off operation is performed by a control signal will be described. In this case, the output feedback circuit 6 controls the output current flowing through the LED 31 to 0 A by setting the reference voltage to approximately 0V. The output feedback circuit 6 biases a DC voltage of 0.1 V obtained by dividing the control voltage Vcc by the first DC bias resistor 64 and the second DC bias resistor 65 to the voltage across the current detection resistor 61. Obtain the detection voltage. As a result, the detection voltage can be increased by 0.1 V from the reference voltage (approximately 0 V), so that it is possible to increase noise resistance when the light is turned off. Note that the current detection resistor 61 is very small compared to the first DC bias resistor 64 and the second DC bias resistor 65, and therefore can be ignored when calculating the divided voltage.

  On the other hand, when the voltage across the current detection resistor 61 has no DC voltage bias, both the detection voltage and the reference voltage are 0V. For this reason, when the reference voltage is affected by noise, the power supply unit 4 operates so as to pass a current through the LED unit 3, and there is a high possibility of causing problems such as minute light emission.

  Next, a case where the LED unit 3 is turned on at a dimming level (brightness) of 100% will be described. In this case, the LED drive current Io flowing through the LED unit 3 is 0.300 A, and the voltage across the current detection resistor 61 is 0.54 V. If the 0.1V DC voltage obtained by dividing the control voltage Vcc by the first DC bias resistor 64 and the second DC bias resistor 65 is biased to the both-ends voltage, the detection voltage becomes 0.64V. The detection voltage after the bias is about 1.2 times as compared with the both-end voltage before the bias.

  On the other hand, when the LED unit 3 is lit at a dimming level of 5%, the LED drive current Io flowing through the LED unit 3 is 0.015 A, and the voltage across the current detection resistor 61 is 0.027V. When the same DC voltage of 0.1V as when the LED unit 3 is lit at a dimming level of 100% is biased to the both-ends voltage, the detection voltage becomes 0.127V.

  In the LED lighting device 2 of the present embodiment, as shown in FIG. 3A, when the LED is turned off (LED drive current Io = 0A), the detection voltage is 0 by applying a DC bias to the voltage across the current detection resistor 61. Therefore, the detection voltage is higher than the reference voltage by the DC bias. As a result, the output of the comparator 62 is always at the high (H) level, and the transistor 63 can be kept on unless noise equal to or greater than the DC bias is applied to at least one of the detection voltage and the reference voltage. As a result, the unlit state of the LED unit 3 can be held more reliably and stably than when the detection voltage is not DC biased.

  When the LED unit 3 is turned on (including the case of dimming), the dimming control circuit 5 increases the reference voltage by the amount corresponding to the DC bias, as shown in FIG. 3B. Therefore, noise resistance can be improved. That is, the detection voltage becomes larger than the reference voltage when the light is turned off, and the detection voltage and the reference voltage become equal when the light is turned on.

  As described above, according to the lighting fixture 1 of the present embodiment, in the output feedback circuit 6 in which the detection voltage and the reference voltage tend to be low, the DC voltage obtained from a different path from the power supply unit 4 that supplies power to the LED unit 3 is converted to DC. A detection voltage is generated by biasing. Thereby, noise tolerance can be improved by making detection voltage higher than a reference voltage at the time of light extinction.

  Moreover, according to the lighting fixture 1 of this embodiment, by detecting the current (LED drive current Io) flowing through the LED unit 3 with the voltage across the current detection resistor 61 connected in series to the LED unit 3, the LED The current flowing through the unit 3 can be easily detected.

DESCRIPTION OF SYMBOLS 1 Lighting fixture 2 LED lighting device 3 LED unit 4 Electric power supply part 5 Dimming control circuit (lighting control part)
6 Output feedback circuit (lighting controller)
61 Current detection resistor 64 First DC bias resistor 65 Second DC bias resistor

Claims (5)

An LED lighting device used by being connected to an LED and an external power source,
A power supply unit for supplying power to the LED;
A lighting control unit for controlling power supplied from the power supply unit to the LED,
The lighting control unit
At the time of extinguishing the light, the detected voltage obtained by biasing the DC voltage obtained from a path different from the power supply unit with respect to the voltage indicating the current flowing through the LED, and dimming according to the control signal input from the outside Compare with the reference voltage indicating the level,
At the time of lighting, the detection voltage obtained by biasing the DC voltage with respect to the voltage indicating the current flowing in the LED, and the voltage of the same magnitude as the DC voltage are biased to the reference voltage when the LED is turned off. Compare the obtained reference voltage when lighting,
The LED lighting device, wherein the power supply unit is feedback controlled so that the LED is at the dimming level using the comparison result both when the light is turned off and when the light is turned on.   The lighting control unit has a current detection resistor connected in series with the LED in a path of a current flowing through the LED, and detects a voltage across the resistor as a current flowing through the LED. The LED lighting device according to 1.   The lighting control unit includes a series circuit including a plurality of DC bias resistors connected in series to the current detection resistor, and the power supply supplies the voltage across at least one of the plurality of DC bias resistors in the series circuit. The LED lighting device according to claim 2, wherein the DC voltage is obtained from a path different from the unit.   4. The LED lighting according to claim 1, wherein the lighting control unit receives a PWM signal as the control signal, and sets the dimming level according to a duty ratio of the PWM signal. 5. apparatus. The LED lighting device according to any one of claims 1 to 4,
A lighting device comprising: an LED that is lit by electric power supplied from the LED lighting device.

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