JP5924568B2 - LED lighting device and lighting device using the same - Google Patents

Description

  The present invention relates to an LED lighting device and an illumination device using the LED lighting device.

  FIG. 5 shows a circuit configuration diagram of a conventional LED lighting device. The LED lighting device shown in the figure includes a rectifier circuit 2 that rectifies an AC power supply 1, a switching power supply circuit 3 that converts the output of the rectifier circuit 2 into a direct current and applies a DC voltage to the LED 7, and a current flowing through the LED 7 is constant at a target value. A feedback circuit 4 that controls the switching power supply circuit 3 is provided (see, for example, Patent Document 1).

  The feedback circuit 4 is supplied with control power from the smoothing capacitor 34 by a constant voltage circuit including a resistor 40 and a Zener diode 41. The feedback circuit 4 includes an operational amplifier 42 that is an error amplifier. The detected value of the LED current detected by the current detection resistor 50 is input to the inverting input of the operational amplifier 42, and the divided value by the resistors 43 and 44 of the constant voltage circuit output is input as the target current value to the non-inverting input. Is done. The operational amplifier 42 operates so that the detected current value matches the target current value, and a current corresponding to the error (potential difference between the inverting input and the non-inverting input) flows to the photodiode 45 a of the photocoupler 45. In the photocoupler 45, the output light amount increases or decreases according to the current flowing through the photodiode 45a, and the collector current of the phototransistor 45b of the photocoupler 45 also increases or decreases according to the light amount.

  The control circuit 30 performs PWM control on the transistor 31 in accordance with increase / decrease in the collector current of the phototransistor 45b. That is, when the error between the inverting input and the non-inverting input of the operational amplifier 42 increases, the light amount of the photodiode 45a increases and the collector current of the phototransistor 45b increases, and the control circuit 30 changes the on-duty ratio of the transistor 31 accordingly. Increase the output of the flyback converter 3.

  The smoothing capacitor 34 prevents the pulsating output of the rectifier circuit 2 from riding on the LED current. When this smoothing capacitor is not provided, the LED is turned off at every valley of the pulsating current of the LED current (for example, when the AC power source is 50 Hz, with a cycle of 100 Hz), which gives a flickering feeling to the human eye. Moreover, even when the LED does not turn off at every valley of the pulsating current of the LED current, the increase or decrease in the light output of the LED may give a flickering feeling. Therefore, a capacitor having a relatively large capacitance of several μF to several hundred μF is used as the smoothing capacitor 34 so that ripples caused by the AC power supply voltage can be sufficiently smoothed. Here, the ripple of the LED output can be eliminated by a configuration in which a smoothing capacitor is connected immediately after the rectifier circuit 2 (that is, the primary side of the transformer 32), but this configuration is a so-called capacitor input. In the capacitor input, since the input current flows only during the period when the capacitor is charged, it is not preferable because the input power factor is low and the power supply harmonic current becomes large. Therefore, a configuration in which a smoothing capacitor is connected to the secondary side of the transformer 32 is common.

JP 2011-34728 A

  In general, an LED does not emit current and does not emit light unless a voltage higher than the forward voltage of the LED is applied. In the case of a white LED often used for illumination, the forward voltage is about 3.5 V. When LEDs are connected in series, a voltage equal to or greater than the number of LEDs × the forward voltage is required as the output voltage of the flyback converter 3. . In the LED lighting device of FIG. 5, when the AC power supply 1 is turned off from the lighting state, the flyback converter 3 is stopped, no voltage is supplied to the LED 7, and the LED 7 is turned off. At that time, the LED 7 is not gradually turned off, but is turned off when the output voltage of the flyback converter 3 becomes equal to or lower than the total forward voltage of the LED 7 after the output of the flyback converter 3 is cut off. Therefore, the smoothing capacitor 34 remains charged when the LED 7 is turned off (total forward voltage minus several volts), and the voltage increases as the number of connected LEDs 7 increases. As described above, the smoothing capacitor 34 has a relatively large capacity of several μF to several hundred μF (although it is discharged with a slow time constant through the resistors 40, 43 and 44), the smoothing capacitor 34 It takes time for the charged voltage to drop.

  Here, since the operating power supply of the feedback circuit 4 is generated by a series circuit of a resistor 40 and a Zener diode 41 connected in parallel with the smoothing capacitor 34, the voltage of the smoothing capacitor 34 is maintained even when the AC power supply 1 is turned off. If the voltage does not drop below the voltage of the Zener diode 41, the feedback circuit 4 continues to operate. Specifically, since the LED 7 is turned off, no current flows through the current detection resistor 50 (that is, the input to the non-inverting input of the operational amplifier 42 becomes 0 V), and the non-inverting input is performed by the feedback operation of the operational amplifier 42. And a current corresponding to the voltage difference between the inverting input flows through the photodiode 45a and the phototransistor 45b. That is, the feedback circuit 4 continues to output a signal for increasing the LED current to the stopped control circuit 30.

When the AC power source 1 is turned on in this state, the feedback circuit 4 outputs a signal output for increasing the LED current to the control circuit 30, so that the flyback converter 3 starts to flow current at the same time as starting. It will be. For this reason, as shown in FIG. 6, immediately after the LED 7 is turned on (t _ON ), more current than necessary flows from the flyback converter 3 to the LED 7, which may cause damage to the LED 7. In particular, when a mechanical contact such as a relay or a switch is used to turn on / off the AC power source 1, chattering (repetition of interruption due to mechanical vibration) may occur, and there is further concern about damage to the LED 7.

  Therefore, in the LED lighting device in which the smoothing capacitor is connected to the output stage of the switching power supply circuit such as a flyback converter, the present invention prevents overcurrent from flowing from the switching power supply circuit to the LED at the time of relighting after the LED is turned off. Accordingly, it is an object to suppress damage to the LED caused by AC power on / off.

  The LED lighting device of the present invention has a transformer and a smoothing capacitor connected to the secondary side of the transformer, a switching power supply circuit that applies a DC voltage to the LED, operates by receiving voltage supply from the smoothing capacitor, When detecting the presence or absence of the primary voltage or secondary voltage of the feedback circuit that controls the switching power supply circuit so that the detected current value becomes the target current value and the presence of the primary voltage or secondary voltage of the transformer, and no primary voltage or secondary voltage is generated Includes a feedback invalidation circuit for invalidating the operation of the feedback circuit.

  Here, when the feedback invalidation circuit detects the primary voltage or the secondary voltage and the detection unit detects that the primary voltage or the secondary voltage is generated, the feedback invalidation circuit is in a closed state. A switch that is opened when the detection unit detects that no secondary voltage is generated is provided, and in the opened state, the switch is configured to cut off power supply from the smoothing capacitor to the feedback circuit.

  The feedback invalidation circuit is closed when the detection unit detects the primary voltage or the secondary voltage and the detection unit detects that the primary voltage or the secondary voltage is generated. A switch that is opened when the detection unit detects that the next voltage is not generated may be provided, and the switch may set the target current value to zero in the opened state.

  The feedback invalidation circuit may include a photocoupler, the detection unit may include a photodiode of a photocoupler, and the switch may include a phototransistor of the photocoupler.

  Further, the feedback invalidation circuit may include a delay circuit that validates the operation of the feedback circuit after a predetermined period has elapsed after the generation of the primary voltage or the secondary voltage.

  The illuminating device of this invention is equipped with LED connected to the output terminal of said LED lighting device and LED lighting device.

It is a circuit block diagram which shows the LED lighting device by the Example of this invention. 1 is a detailed circuit configuration diagram illustrating an LED lighting device according to an embodiment of the present invention. It is a circuit block diagram explaining the LED lighting device by the modification of this invention. It is a circuit block diagram explaining the LED lighting device by the modification of this invention. It is a circuit block diagram which shows the conventional LED lighting device. It is a figure explaining the conventional LED lighting device.

Example.
FIG. 1 shows a circuit configuration diagram of an LED lighting device according to an embodiment of the present invention. The LED lighting device includes a rectifier circuit 2 that rectifies an AC power source 1, a switching power source circuit 3 that receives an output of the rectifier circuit 2 and applies a DC voltage to the LED 7, detects a current flowing through the LED 7, and a detected current value is a target current value A feedback circuit 4 for controlling the switching power supply circuit 3 so as to become, and a feedback invalidation circuit for detecting the presence or absence of the primary voltage to the switching power supply circuit 3 and invalidating the operation of the feedback circuit 4 when there is no primary voltage 6 is provided. The lighting device is configured by connecting the LED 7 to the output end of the LED lighting device. If a DC power supply is connected instead of the AC power supply 1, the rectifier circuit 2 may not be provided.

  The switching power supply circuit 3 includes an insulating flyback converter (hereinafter referred to as “flyback converter 3”), and includes a control circuit 30, a transistor 31, a transformer 32, a diode 33, and a smoothing capacitor. The primary side input of the transformer 32 is PWM-controlled by the control circuit 30 and the transistor 31, and the secondary side output is rectified and smoothed by the diode 33 and the smoothing capacitor 34. Thus, since the smoothing capacitor 34 is connected to the secondary side (output side), a high power factor and a suppressed power supply harmonic current are realized. Further, the LED 7 is insulated from the AC power source 1 by the transformer 32, and safety on the secondary side (LED side) is ensured. The switching power supply circuit 3 may be a circuit having another configuration such as a forward converter as long as it is an insulating switching converter.

  The feedback circuit 4 operates by receiving control power from the smoothing capacitor 34 by a constant voltage circuit including a resistor 40 and a Zener diode 41. The detected value of the LED current detected by the current detection resistor 50 is input to the inverting input of the operational amplifier 42, and the divided value by the resistors 43 and 44 of the constant voltage circuit output is input as the target current value to the non-inverting input. Is done. A photodiode 45 a of the photocoupler 45 is connected to the output of the operational amplifier 42. The operational amplifier 42 operates so that the detected current value matches the target current value, and a current corresponding to the error (potential difference between the inverting input and the non-inverting input) flows to the photodiode 45a. In the photocoupler 45, the output light amount increases or decreases according to the current flowing through the photodiode 45a, and the collector current of the phototransistor 45b increases or decreases according to the light amount. For clarity of illustration, the photodiode 45a and the phototransistor 45b are shown separately, but in actuality, both are included in one IC package to constitute the photocoupler 45.

  The control circuit 30 performs PWM control on the transistor 31 in accordance with increase / decrease in the collector current of the phototransistor 45b. That is, when the error between the inverting input and the non-inverting input of the operational amplifier 42 increases, the amount of light of the photodiode 45a increases, the collector current of the phototransistor 45b increases accordingly, and the control circuit 30 increases the on-duty ratio of the transistor 31. The output of the flyback converter 3 is increased. On the other hand, when the error between the inverting input and the non-inverting input of the operational amplifier 42 is small (or both are substantially equal), the collector current of the phototransistor 45b decreases (or approaches zero), and the flyback converter 3 is stably feedback controlled. It will be in the state.

  The feedback invalidation circuit 6 includes a detection unit 6a and a switch 6b. The detector 6a detects the presence or absence of a primary voltage (or input voltage from the AC power supply 1) to the transformer 32 of the flyback converter 3. The switch 6b is in the closed state when the detection unit 6a detects that the primary voltage is generated, and is in the open state when it is detected that the primary voltage is not generated. When the switch 6b is opened, power supply from the smoothing capacitor 34 to the feedback circuit 4 is interrupted. In this example, the detection unit 6a only needs to be able to detect on / off of the AC power supply 1, and therefore may be provided in the front stage of the rectifier circuit 2.

  When the AC power source 1 is turned off while the LED 7 is lit, power supply to the control circuit 30 is stopped, and the flyback converter 3 stops operating. Then, when the voltage of the smoothing capacitor 34 becomes equal to or less than the total forward voltage value of the LED 7, the LED 7 is turned off. In the feedback invalidation circuit 6, the detection unit 6a detects that the AC power source 1 is turned off, and opens the switch 6b. As a result, the power supply to the photodiode 45a is cut off (and the operation of the operational amplifier 42 is also stopped), and the collector current of the phototransistor 45b does not flow. Therefore, when the AC power supply 1 is turned off, the operation of the feedback circuit 4 is invalidated even if a voltage remains in the smoothing capacitor 34 that is the operation power supply of the feedback circuit 4.

  Thereafter, when the AC power source 1 is turned on, the flyback converter 3 starts operating, while the detection unit 6a closes the switch 6b. Therefore, the flyback converter 3 starts operating in a state where no collector current flows through the phototransistor 45b. That is, since the output of the flyback converter 3 is smaller than when the collector current is flowing through the phototransistor 45b, an excessive current as shown in FIG.

  FIG. 2 shows a specific circuit configuration diagram of the LED lighting device according to this embodiment. In the LED lighting device shown in the figure, the feedback invalidation circuit 6 smoothes the voltage applied to the photocoupler 60 including the photodiode 60a and the phototransistor 60b, the resistors 61-63 constituting the voltage dividing circuit, and the photodiode 60a. A capacitor 64 is provided. In the relationship with FIG. 1, the photodiode 60a, the resistors 61-63, and the capacitor 64 correspond to the detection unit 6a, and the phototransistor 60b corresponds to the switch 6b. For the sake of clarity, the photodiode 60a and the phototransistor 60b are shown separately, but in actuality, both are included in one IC package to constitute the photocoupler 60.

  When the AC power source 1 is turned off while the LED 7 is lit, the flyback converter 3 stops operating with the smoothing capacitor 34 charged as described above. On the other hand, since no voltage is applied to the photodiode 60a, the phototransistor 60b is opened. Thereby, the operation of the feedback circuit 4 is invalidated.

  When the AC power source 1 is turned on again, the flyback converter 3 starts operating, while the divided voltage value of the AC power source is applied to the photodiode 60a, and the phototransistor 60b is closed. Thereby, the operation of the feedback circuit 4 is validated after the flyback converter 3 is started.

Here, the operation of the feedback circuit 4 may be validated after a lapse of a predetermined period after the start of the flyback converter 3. For example, it is also possible to select the capacitance of the capacitor 64 so that the collector current flows through the phototransistor 60b with a delay after starting the flyback converter 3 a predetermined time constant only. In this case, the capacitor 64 also functions as a delay circuit. Thereby, the invalidation of the operation of the feedback circuit 4 can be reliably maintained at the time when the flyback converter 3 is activated. It should be noted that the timing of disabling the operation of the feedback circuit 4 when the LED is turned off is not a problem even after the flyback converter 3 stops operating, so that the capacity of the capacitor 64 can be set sufficiently large.

  As another example of the delay circuit, a capacitor (not shown) different from the capacitor 64 is connected in parallel to the Zener diode 41 so that the operational amplifier 42 is activated after a predetermined period has elapsed since the activation of the flyback converter 3. Also good. Further, a capacitor (not shown) different from the capacitor 64 may be connected in parallel to the resistor 44 so that the target current value gradually increases after the operational amplifier 42 is started.

  In the present embodiment, the detection unit 6a and the switch 6b are configured by the photocoupler 60, but the detection unit 6a and the switch 6b may be configured by a relay switch.

  As described above, in the LED lighting device in which the smoothing capacitor is connected to the output stage of the flyback converter 3, it is possible to prevent an overcurrent from flowing from the flyback converter 3 to the LED 7 when the LED is turned on again after the LED is turned off. LED damage due to on / off is suppressed.

Modification 1
FIG. 3 shows a circuit configuration diagram of an LED lighting device according to a modification of the present invention. The difference from the LED lighting device of FIG. 1 is the connection position of the detection unit 6 a of the feedback invalidation circuit 6. In this example, the detection unit 6 a is connected to the secondary winding side of the transformer 32. The configuration of this example is effective when the control circuit 30 is controlled by the remote controller with the AC power source 1 turned on, and the operation of the flyback converter is turned on / off.

  When the detection unit 6a detects that the AC power source 1 or the control circuit 30 is turned off and the flyback converter 3 is stopped, the switch 6b is opened. Thereafter, when the AC power source 1 or the control circuit 30 is turned on again, the flyback converter 3 starts operating, and the switch 6b is closed. That is, according to the configuration of this example, the feedback circuit 4 can be validated after the flyback converter 3 is started without providing a delay circuit having a large time constant. However, unlike the embodiment of FIG. 1, since the detection unit 6a and the switch 6b are in the feedback system, it is necessary to design so that these operations do not interfere with the feedback operation.

  Also in this example, the configuration of FIG. 2 can be adopted as a specific configuration of the feedback invalidation circuit 6. That is, the photodiode 60a, the resistors 61-63 and the capacitor 64 in FIG. 2 may be connected to the position of the detection unit 6a in FIG. 3, and the phototransistor 60b may be connected to the position of the switch 6b in FIG.

Modification 2
FIG. 4 shows a circuit configuration diagram of an LED lighting device according to another modification of the present invention. The difference from the LED lighting device of FIG. 1 is the insertion position of the switch 6 b of the feedback invalidation circuit 6. In this example, the switch 6 b is inserted at a position where the resistor 43 is disconnected from the non-inverting input of the operational amplifier 42. When the detection unit 6a detects that the AC power source 1 is turned off and opens the switch 6b, the target current value that is the non-inverting input of the operational amplifier 42 becomes zero. That is, since the detected current value and the target current value are both zero when the LED is turned off, no current flows through the photodiode 45a and no light is emitted. Therefore, the collector current of the phototransistor 45b does not flow, and the operation of the feedback circuit 4 is substantially invalidated.

  Also in this example, the specific configuration of the feedback invalidation circuit 6 can employ the configuration of FIG. That is, the photodiode 60a, the resistors 61-63 and the capacitor 64 in FIG. 2 may be connected to the position of the detection unit 6a in FIG. 4, and the phototransistor 60b may be connected to the position of the switch 6b in FIG. As the delay circuit, the capacity of the capacitor 64 may be set as appropriate, or a separate capacitor (not shown) may be connected in parallel to the resistor 44.

  In combination with the first and second modifications, the detector 6a is arranged on the secondary winding side of the transformer 32 as shown in FIG. 3, the switch 6b is shown as a resistor 43 as shown in FIG. Each may be connected to a position to be disconnected from the input.

  According to the configurations of the above-described embodiments and modifications, in the LED lighting device in which the smoothing capacitor is connected to the subsequent stage of the switching power supply circuit, damage to the LED caused by AC power on / off is suppressed, and the reliability of the LED lighting device is improved. Can be improved.

2. 2. Rectifier circuit Switching power supply circuit (flyback converter)
4). Feedback circuit 6. Feedback invalidation circuit 6a. Detection unit 6b. Switch 7. LED
30. Control circuit 31. Transistor 32. Transformer 33. Diode 34. Smoothing capacitors 40, 43, 44, 46, 47, 49, 50, 51. Resistance 41. Zener diode 42. Operational amplifier 45. Photocoupler 45a. Photodiode 45b. Phototransistor 48. Capacitor 60. Photocoupler 60a. Photodiode 60b. Phototransistors 61, 62, 63. Resistor 64. Capacitor

Claims (6)

An LED lighting device,
Has a connection to a smoothing capacitor via a diode to the transformer and the transformer secondary winding, a switching power supply circuit for applying a DC voltage to the LED,
Operates by receiving a voltage supply from the smoothing capacitor, a feedback circuit detecting the current value by detecting a current flowing through the LED to control the switching power supply circuit so that the target current value, and the transformer primary voltage or The presence or absence of a secondary voltage generated in the secondary winding is detected, and when the primary voltage or the secondary voltage is not generated and when the voltage remains in the smoothing capacitor, the voltage of the smoothing capacitor LED lighting device provided with a feedback disabling circuit for disabling the operation of the feedback circuit by the input path before Symbol target current value in the open state of also feeding path to a feedback circuit from the voltage of the smoothing capacitor. The LED lighting device according to claim 1,
The feedback invalidation circuit is
A detection unit that detects the primary voltage or the secondary voltage, and is connected to a power supply path from the smoothing capacitor to the feedback circuit, and the detection unit detects that the primary voltage or the secondary voltage is generated. So that the power supply from the smoothing capacitor to the feedback circuit is cut off when the detection unit detects that the primary voltage or the secondary voltage is not generated. An LED lighting device comprising a configured switch. The LED lighting device according to claim 1,
The feedback invalidation circuit is
The detection unit that detects the primary voltage or the secondary voltage, and is connected between the power feeding unit to the feedback circuit and the input unit of the target current value, and the primary voltage or the secondary voltage is generated. The target current value is set to zero by being closed when detected by the detection unit and being opened when the detection unit detects that the primary voltage or the secondary voltage is not generated. An LED lighting device comprising a switch configured as described above.   4. The LED lighting device according to claim 2, wherein the feedback invalidation circuit includes a photocoupler, the detection unit includes a photodiode of the photocoupler, and the switch includes a phototransistor of the photocoupler. apparatus.   5. The LED lighting device according to claim 1, wherein the feedback invalidation circuit activates the operation of the feedback circuit after a predetermined period after the primary voltage or secondary voltage is generated. LED lighting device with a circuit.   An LED lighting device comprising: the LED lighting device according to any one of claims 1 to 5; and an LED connected to an output terminal of the LED lighting device.

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