JP2013065487A - Led lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED lighting device that has such an overheat protection function of reducing the power of the LED lighting device when an ambient temperature is high to avoid shortening the life of the LED lighting device as is generally applicable to a wide range of main circuit types and as changes the power reduction in accordance with whether a dimmer is connected to balance short life avoidance and light output retention.SOLUTION: The LED lighting device having a rectification circuit for converting an AC supply voltage to a DC voltage and a DC-DC conversion circuit for converting the DC voltage to feed an LED load includes a voltage detection circuit for detecting the DC voltage and outputting a voltage detection signal, and a temperature-sensitive circuit connected to the voltage detection circuit. The temperature-sensitive circuit includes a temperature-sensitive element, outputs a current setting value for the DC-DC conversion circuit and reduces the current setting value when an ambient temperature is high.

Description

  The present invention relates to a lighting device for a light emitting diode (hereinafter referred to as LED).

  LED attracts attention as a light source excellent in environmental performance, and has come to be used as general lighting in houses and offices as LED lighting. Among LED lighting, there is a bulb-type LED lighting that has a base similar to an incandescent light bulb and is attached to an incandescent light fixture. In addition, products corresponding to phase control type dimmers that have been used as dimming means for incandescent bulbs are also seen.

  The light output of the LED is determined by the current flowing through the LED (hereinafter referred to as LED current). The LED lighting device controls the light output of the LED by controlling the LED current.

  The LED generates heat during light emission. Further, in many cases, the LED lighting device is disposed in a sealed space such as the inside of the housing near the LED. Therefore, when the LED lighting device controls the LED current to be constant regardless of the ambient temperature, the temperature of the LED and the LED lighting device (hereinafter referred to as the LED lighting device including the LED) is considerably high when the ambient temperature is high. The increase in the service life becomes a problem. The ambient temperature is the temperature of the outside air that touches the LED lighting. When the LED lighting is sealed by an appliance or wall surface to which the LED lighting is attached, the temperature of the sealed space is the ambient temperature.

  In order to solve the above problem, an LED lighting device having an overheat protection function that reduces the LED current when the ambient temperature is high and suppresses the temperature rise of the LED lighting device is desirable. As an LED lighting device having an overheat protection function, for example, there is a device described in Patent Document 1. In the device described in Patent Document 1, a linear constant current circuit is cited as the main circuit for supplying power to the LED, and the thermistor, which is a temperature sensitive element, is configured to supply power to the LED from the power source via the constant current circuit. The current of the constant current circuit is controlled by the peripheral circuit provided. When the ambient temperature is high, the resistance value of the thermistor changes and the LED current decreases.

JP 2010-62349 A

  However, the method of the constant current circuit is not limited to the linear method described in Patent Document 1, and a more efficient switching method circuit is also conceivable. Therefore, a versatile overheat protection function capable of supporting a wide range of main circuit systems is required.

  In the present invention, the case of using a phase control type dimmer is also considered. When the dimmer is connected, an inrush current flows into the LED lighting device immediately after the semiconductor element in the dimmer is turned on. Due to this inrush current, heat generation of components such as an inrush current preventing resistor, an input filter choke coil, and an input smoothing capacitor is increased, and shortening of their life becomes a problem. Therefore, in order to prevent the life of the LED lighting device from being shortened even when the dimmer is connected, it is necessary to increase the decrease in the LED current more than when the dimmer is not connected. Of course, if the decrease of the LED current is increased, the light output of the LED also decreases.

  Here, even if it corresponds to the dimmer, it may be used without being connected to the dimmer. In addition, there may be a demand to make the configuration of the LED lighting device and the parts to be used as common as possible between products that correspond to the dimmer and those that do not. When the dimmer is connected and it is desired to achieve both short life and secure light output, the LED current is less when the dimmer is connected than when not connected. It is desirable to realize a function with a larger decrease.

  The present invention is a versatile overheat protection function that can be applied to a wide range of main circuit methods among overheat protection functions that avoid shortening the life of the LED lighting device. An object of the present invention is to provide an LED lighting device that realizes an overheat protection function that achieves both avoidance of shortening of the life and ensuring of light output by changing the amount of decrease.

  In order to solve the above problems, the present invention is an LED lighting device including a rectifier circuit that converts an AC power supply voltage into a DC voltage, and a DC-DC conversion circuit that converts the DC voltage and supplies power to an LED load. A voltage detection circuit for detecting the DC voltage and outputting a voltage detection signal; and a temperature sensing circuit connected to the voltage detection circuit, the temperature sensing circuit comprising a temperature sensing element, and the DC An LED lighting device is characterized in that the current set value of the DC conversion circuit is output and the current set value is decreased when the ambient temperature is high.

  According to the LED lighting device of the present invention, it can be applied to a wide range of main circuit methods in the overheat protection function that reduces the power of the LED lighting device when the ambient temperature is high and avoids shortening the life of the LED lighting device. It is a highly versatile overheat protection function, and by changing the amount of power reduction depending on whether a dimmer is connected, it is possible to realize an overheat protection function that avoids shortening the life and ensures light output. .

It is a block diagram of the LED lighting device in this invention. It is a block diagram (dimmer connection) of the LED lighting device in this invention. It is an example of a voltage detection signal. It is the LED lighting device (specific example of a temperature sensitive circuit) in this invention. It is a temperature characteristic of the LED lighting device in this invention. It is an operation | movement waveform (light control device connection) of the LED lighting device in this invention. It is an operation | movement waveform (without dimmer) of the LED lighting device in this invention. It is an example of a voltage detection signal. It is the LED lighting device (specific examples, such as a DC-DC conversion circuit) in this invention. It is the LED lighting device (specific examples, such as a DC-DC conversion circuit) in this invention. It is another example of a temperature sensing circuit. It is another example of a temperature sensing circuit. It is another example of a temperature sensing circuit. It is another example of a temperature sensing circuit. It is another example of a temperature sensing circuit. It is another example of a temperature sensing circuit.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram of an LED lighting device according to the present invention. In FIG. 1, the right side from the rectifier circuit 101 is the LED lighting device of the present invention. The LED lighting device according to the present invention includes a rectifier circuit 101, a DC-DC conversion circuit 102, an LED load 103, a voltage detection circuit 104, and a temperature sensing circuit 105. The AC power supply 100 and the rectifier circuit 101 are connected, and the AC power supply voltage supplied from the AC power supply 100 is converted into a DC voltage by the rectifier circuit 101. The direct current voltage converted by the rectifier circuit 101 is converted by the DC-DC converter circuit 102 connected to the rectifier circuit 101 and supplied to the LED load 103 connected to the DC-DC converter circuit 102. The DC voltage output from the rectifier circuit is hereinafter referred to as a rectified voltage. The LED load 103 is not limited in the number of LEDs and the connection form, and may include an LED module incorporating a protective element or the like.

  FIG. 2 shows a dimmer 106 connected between the AC power source 100 and the rectifier circuit 101 in the LED lighting device of FIG. Also in FIG. 2, the right side from the rectifier circuit 101 is the LED lighting device of the present invention. In FIG. 2, the output voltage of the dimmer 106 becomes an AC power supply voltage and is supplied to the LED lighting device. The dimmer 106 is called a phase control type dimmer, and controls conduction / non-conduction between the AC power supply 100 and the rectifier circuit 101 by on / off control of a semiconductor element.

  The voltage detection circuit 104 is connected to the DC output side of the rectifier circuit 101, detects the rectified voltage generated by the rectifier circuit 101, and outputs a voltage detection signal. A plurality of voltage detection signals can be considered as specific operations of the voltage detection circuit 104 and voltage detection signals determined thereby. For example, a configuration is conceivable in which a signal that is H level during a period in which the rectified voltage is higher than the threshold value that is substantially zero and that is L level in a period in which the rectified voltage is lower than the threshold value that is substantially zero is output as the voltage detection signal.

  FIG. 3A shows the waveforms of the rectified voltage and the voltage detection signal when the dimmer 106 is connected as shown in FIG. As shown in FIG. 3A, the voltage detection signal is a rectangular wave signal that becomes H level during the ON period of the dimmer 106. If such a voltage detection signal is appropriately smoothed to obtain the current setting value of the DC-DC conversion circuit 102, the LED current can be controlled according to the ON period of the dimmer 106, that is, dimming can be performed. .

  FIG. 3B shows waveforms of the rectified voltage and the voltage detection signal when the dimmer is not connected as shown in FIG. As described above, when the threshold value is set to substantially zero, the voltage detection signal is always at the H level. In particular, if a smoothing element is formed by inserting a capacitor on the input side of the DC-DC conversion circuit 102, the voltage detection signal is always at the H level. Further, a capacitor may be inserted in the input portion of the voltage detection circuit 104 to have a function of slightly smoothing.

  Another example of the voltage detection circuit 104 will be described. First, the threshold value does not necessarily have to be substantially zero, and may be a desired voltage value. Such a voltage detection circuit 104 can be easily realized using a comparator, but the detailed circuit configuration is not limited. There are other possible operations of the voltage detection circuit. For example, a circuit that clamps the rectified voltage at a desired voltage value as shown in FIG. 8 or a circuit that divides the rectified voltage may be used. Further, it may be a circuit combining comparison with a threshold raised so far, clamping, partial pressure, and the like.

  The temperature sensing circuit 105 includes a temperature sensing element and is connected to the voltage detection circuit 104. The temperature sensing circuit 105 outputs the current setting value of the DC-DC conversion circuit 102. Examples of the temperature sensing element include a temperature sensing resistor such as a PTC thermistor and an NTC thermistor, and a capacitor whose capacitance changes with temperature (hereinafter referred to as a temperature sensing capacitor). When the ambient temperature is high, the temperature sensing circuit decreases the current set value of the DC-DC conversion circuit 102, whereby the LED current and thus the power of the LED lighting device is reduced, and the effect of overheating protection is generated.

  FIG. 4 specifically shows the temperature sensing circuit 105 in the block diagram shown in FIG. In the temperature sensing circuit 105, the presence or absence of the smoothing circuit 107 is arbitrary. With the smoothing circuit 107 that smoothes the current setting value, the current setting value becomes substantially constant over one cycle of the AC power supply, and the pulsation of the LED current that causes flickering can be suppressed. In addition to the smoothing circuit, it is optional to connect a voltage dividing circuit and an amplifier circuit for adjusting the voltage value. Further, the AC power supply 100 may be directly connected to the rectifier circuit 101 as shown in FIG. Hereinafter, both the case where the dimmer 106 is connected and the case where it is not connected will be described. A plurality of operations of the voltage detection circuit 104 can be considered as described above. In the following description, the operation is shown in FIG.

  The temperature sensing circuit 105 in FIG. 4 will be described. A series body of a diode 109, a resistor 110, and a resistor 111 is connected between the output terminal of the voltage detection circuit 104 and the ground (GND) in this order, and a contact point between the resistor 110 and the resistor 111 is connected to the smoothing circuit 107. Connected to. At this time, the diode 109 is connected so that the cathode of the diode 109 faces the voltage detection circuit 104 side. A PTC thermistor 108 which is a temperature sensitive element is connected in parallel with the series body of the diode 109 and the resistor 110. A capacitor 112 is connected in parallel with the resistor 111. When the smoothing circuit 107 is not provided, a contact point between the resistor 110 and the resistor 111 becomes an output of the temperature sensing circuit 105.

  Of the temperature sensing circuit 105, a circuit connected upstream of the smoothing circuit 107 has two functions of an RC filter and a partial pressure. First, an RC filter is configured by the PTC thermistor 108, the diode 109, the resistor 110, and the capacitor 112. Due to the presence of the diode 109, the time constant of this RC filter differs between the rising edge and the falling edge of the voltage detection signal. At the rise of the voltage detection signal, the time constant is determined by the PTC thermistor 108 and the capacitor 112. On the other hand, at the fall of the voltage detection signal, the time constant is determined by the PTC thermistor 108, the resistor 110, and the capacitor 112. Next, a resistance voltage dividing circuit is constituted by the PTC thermistor 108 and the resistor 111, and the voltage detection signal is divided.

  The resistance value of the PTC thermistor 108 changes as shown in FIG. 5 with respect to the temperature. In FIG. 5, the relationship between the power of the LED lighting device and the temperature of the PTC thermistor 108 is indicated by a broken line, which will be described later. Generally, in a PTC thermistor, the resistance value is substantially constant regardless of the temperature at a temperature lower than a certain temperature (Tc in FIG. 5), but at a temperature higher than a certain temperature (Tc in FIG. 5), the resistance value increases with increasing temperature. Increases rapidly. In the following description, the ambient temperature when the temperature of the PTC thermistor 108 becomes Tc is defined as the reference temperature. When the ambient temperature is lower than the reference temperature (hereinafter simply referred to as low temperature) or high (hereinafter simply referred to as high temperature), the temperature of the PTC thermistor 108 is, for example, the temperature Ta or Tb shown in FIG. How many times the reference temperature is set depends on the specifications (particularly power and structure) of the LED lighting product, and a PTC thermistor having optimum temperature characteristics is selected according to this specification. For example, Ta = 80 ° C., Tb = 120 ° C., Tc = 100 ° C., and the like can be considered. Even in this case, ± 20 ° C. may vary depending on power consumption, heat dissipation structure, circuit component arrangement, and the like.

  A voltage detection signal when the phase control dimmer is connected and the ambient temperature is low or high, and the temperature of the PTC thermistor 108 is, for example, Ta or Tb in FIG. 5, the input signal of the smoothing circuit 107, DC The current setting values of the DC conversion circuit are as shown in FIG. From the above, the input signal of the smoothing circuit 107 is the voltage of the resistor 111, and this average value becomes the current set value. In FIG. 6, with respect to the input signal and current setting value of the smoothing circuit 107, the voltage detection signal is shown by being overlapped with a broken line. As shown in FIG. 6, the input signal of the smoothing circuit 107 has a waveform in which the voltage detection signal is divided and the rise and fall are delayed according to the time constant of the RC filter. When the resistance value of the PTC thermistor 108 increases from a low temperature to a high temperature, the voltage division ratio between the PTC thermistor 108 and the resistor 111 changes, and the average value of the input signal of the smoothing circuit 107, that is, the current set value decreases. In addition, at the rising edge of the voltage detection signal, the current set value is further reduced by increasing the time constant of the RC filter. That is, the current set value decreases due to two effects of a change in the voltage division ratio and an increase in the RC filter time constant.

  FIG. 7 shows the voltage detection signal, the input signal of the smoothing circuit 107, and the current setting value when the dimmer is not connected. At this time, as shown in FIG. 3, since the voltage detection signal is always at the H level, the effect as an RC filter does not appear, and the current set value is only determined by the effect of changing the voltage dividing ratio by the PTC thermistor 108 and the resistor 111. Decrease. Therefore, as shown in FIG. 6, compared with the case where the dimmer is connected, the current set value and thus the power decrease is reduced. As described above, it is possible to realize an overheat protection function in which the amount of decrease in electric power changes depending on whether or not the dimmer is connected, and it is possible to achieve both avoidance of shortening the life and ensuring optical output.

  FIG. 9 specifically shows the configuration of the rectifier circuit 101 and the DC-DC conversion circuit 102 in the LED lighting device shown in FIG. 9, the full-wave rectifier circuit including the diode bridge 115 corresponds to the rectifier circuit 101 in FIG. 4. The diode 116, the capacitor 117, the current control circuit 118, the diode 119, the MOSFET 120 serving as a switching element, the choke coil 121, and the capacitor A step-down chopper circuit composed of 122 and a resistor 123 corresponds to the DC-DC conversion circuit 102 of FIG. In FIG. 4, an inrush current preventing resistor 113 and an input filter choke coil 114 are shown as omitted elements. In addition, a fuse, a filter capacitor, or the like may be added. Depending on the voltage of the LED load 103, not a step-down chopper circuit, but a chopper circuit in general such as a step-up / step-down chopper circuit or a step-up chopper circuit, or another circuit such as a flyback converter may be used if insulation is necessary. The switching element is not limited to the MOSFET, and other types of elements such as bipolar transistors and IGBTs may be used.

  In FIG. 9, the current control circuit 118 drives the MOSFET 120 so as to control the current of the MOSFET 120 detected from the resistor 123 according to the current setting value output from the smoothing circuit 107. Specifically, it is conceivable to control the MOSFET 120 until the current of the MOSFET 120 reaches the current set value. Such a current control circuit 118 can be easily configured using a commercially available LED control IC. Of course, the control IC may not be used and a discrete component such as a comparator may be combined.

  The present invention can be applied not only to the above-described switching type DC-DC conversion circuit but also to a linear type DC-DC conversion circuit. FIG. 10 is a diagram in the case of using a linear constant current circuit including a MOSFET 120, a resistor 123, and an operational amplifier 124. Thus, the overheat protection function of the present invention is highly versatile and can be applied to a wide range of DC-DC conversion circuits. However, the above-mentioned chopper circuit is considered advantageous in terms of circuit efficiency.

  Here, another example of a circuit connected to the preceding stage of the smoothing circuit 107 in the temperature sensing circuit 105 is shown. First, as shown in FIG. 11, a circuit in which a resistor 125 is inserted in series with the PTC thermistor 108 with respect to the circuit of FIG. Although not shown, a resistor may be connected in parallel with the PTC thermistor 108. Adding a resistor in this way is effective in that the resistance value can be adjusted, although it is disadvantageous in terms of the number of parts. Of course, not only the PTC thermistor 108 but also the resistor 110 and the resistor 111 may be connected in series or in parallel with a resistor for adjusting the resistance value. Note that resistors can be connected in the same manner for all circuits described below. Further, as shown in FIG. 14, a circuit in which a diode 126 is added to the circuit of FIG. 4 may be used.

  Next, as shown in FIG. 12, a circuit in which the resistor 111 is removed from the circuit of FIG. By eliminating the resistor 111, the circuit of FIG. 12 does not have a function of reducing the power by changing the resistance voltage division ratio as in the circuit of FIG. Therefore, when the dimmer is not connected and the voltage detection signal is always at the H level, the effect of overheat protection does not appear. This is effective when it is desired to reduce the power only when a dimmer is connected and an inrush current flows through the LED lighting device. Further, the number of parts can be reduced as compared with the circuit of FIG.

  Next, as shown in FIG. 13, a circuit in which the diode 109, the resistor 110, and the capacitor 112 are eliminated from the circuit of FIG. The circuit of FIG. 13 does not have a function of reducing the power by changing the time constant of the RC filter as in the circuit of FIG. 4, and the power is reduced only by changing the resistance voltage dividing ratio. Therefore, it is effective when it is desired to realize the same level of power reduction regardless of the presence or absence of the dimmer. In addition, the number of parts can be reduced as compared with the circuits of FIGS.

  In the temperature sensing circuit described above, a PTC thermistor is used as the temperature sensing element, but an NTC thermistor may be used. The NTC thermistor is a temperature sensitive element having a characteristic that the resistance value decreases with increasing temperature. In the circuit of FIG. 15, an NTC thermistor is used instead of the PTC thermistor. When the temperature is changed from a low temperature to a high temperature, the time constant of the RC filter decreases at the fall of the voltage detection signal, and the current set value decreases. Also in the circuit of FIG. 16, an NTC thermistor is used, and when the temperature is changed from a low temperature to a high temperature, the voltage dividing ratio by the resistor 110 and the NTC thermistor 128 changes, and the current set value decreases.

  In the above, another example of the temperature sensing circuit has been described. However, any specific circuit configuration may be used as long as the current setting value is reduced at a high temperature.

DESCRIPTION OF SYMBOLS 100 AC power supply 101 Rectification circuit 102 DC-DC conversion circuit 103 LED load 104 Voltage detection circuit 105 Temperature sensing circuit 106 Dimmer 107 Smoothing circuit 108 PTC thermistor 109 Diode (116, 119, 126 is also the same)
110 Resistance (same for 111, 113, 123, 125)
112 capacitor (same for 117 and 122)
114 choke coil (same for 121)
115 Diode Bridge 118 Current Control Circuit 120 MOSFET
124 operational amplifier 127 NTC thermistor (128 is also the same)

Claims (9)

An LED lighting device comprising: a rectifier circuit that converts an AC power supply voltage into a DC voltage; and a DC-DC conversion circuit that converts the DC voltage and supplies power to an LED load,
A voltage detection circuit that detects the DC voltage and outputs a voltage detection signal; and a temperature sensing circuit connected to the voltage detection circuit;
The temperature sensing circuit includes a temperature sensing element, outputs a current setting value of the DC-DC conversion circuit, and reduces the current setting value when the ambient temperature is high. The LED lighting device according to claim 1,
The temperature sensing circuit is configured to reduce the current set value when the ambient temperature is higher than the reference temperature and the ambient temperature is lower than the reference temperature when the ambient temperature is higher than the reference temperature. LED lighting device characterized. The LED lighting device according to claim 1,
The temperature sensing circuit makes the current setting value substantially constant when the ambient temperature is lower than the reference temperature, and decreases the current setting value as the ambient temperature is higher when the ambient temperature is higher than the reference temperature. The LED lighting device characterized by making it do. In the LED lighting device according to claim 1,
The temperature sensing circuit constitutes an RC filter including the temperature sensing element, and when the ambient temperature is high, the time constant of the RC filter at the rising edge of the voltage detection signal increases. apparatus. In the LED lighting device according to claim 1,
The temperature sensing circuit constitutes an RC filter including the temperature sensing element, and the time constant of the RC filter at the fall of the voltage detection signal decreases when the ambient temperature is high. Lighting device. In the LED lighting device according to claim 1,
The LED lighting device, wherein the temperature sensing circuit constitutes a voltage dividing circuit including the temperature sensing element, and a voltage dividing ratio of the voltage dividing circuit changes when the ambient temperature is high. In the LED lighting device according to claim 1,
The temperature sensing circuit is connected in parallel to a diode, a first resistor and a second resistor connected in series to the output terminal of the voltage detection circuit, and a diode and the first resistor connected in series. An LED lighting device comprising: a temperature sensitive resistor as the temperature sensitive element; and a capacitor connected in parallel with the second resistor. The LED lighting device according to claim 1,
The voltage detection circuit outputs the voltage detection signal that becomes H level when the DC voltage is higher than a desired threshold and L level when the DC voltage is lower than the threshold. Lighting device. In an LED lighting device including a rectifier circuit that converts an AC power supply voltage into a DC voltage, and a DC-DC conversion circuit that converts the DC voltage and supplies power to an LED load.
A voltage detection circuit that detects a DC voltage converted by the rectifier circuit and outputs a voltage detection signal to the DC-DC conversion circuit; and a temperature sensing circuit connected to the voltage detection circuit.
The temperature sensing circuit includes a temperature sensing element, a capacitor, and a resistor, and outputs a current setting value of the DC-DC conversion circuit.
The temperature sensing element and the resistor are connected between the output terminal of the voltage detection circuit and the ground,
An LED lighting device, wherein the capacitor is connected in parallel with the resistor.