JP6102020B2 - Light emitting diode lighting device and lighting fixture using the light emitting diode lighting device - Google Patents

Description

  The present invention relates to a light emitting diode lighting device and a lighting fixture using the light emitting diode lighting device.

  Conventionally, a light emitting diode lighting device is provided in which a buck converter (also referred to as a step-down converter or a step-down chopper circuit) is connected after a boost converter (also referred to as a step-up converter or a step-up chopper circuit) (for example, a patent) Reference 1).

  The boost converter, for example, receives DC power (pulsating power) obtained by full-wave rectification of AC power by a diode bridge and outputs predetermined DC power, and is provided for the purpose of power factor improvement.

JP 2011-249174 A

  Here, FIG. 8 shows an example of the relationship between the voltage Vf across the light emitting diode and the temperature when a constant current is input to the light emitting diode. In the example of FIG. 8, when the temperature is 40 ° C., the voltage Vf necessary for flowing the constant current is about 10% lower than when the temperature is −40 ° C. In this way, the electric power required to allow a constant current to flow through the light emitting diode (that is, to light the light emitting diode at a constant brightness) is lower at a low temperature (that is, immediately after the start of lighting) than at a high temperature (that is, in a steady state). Also gets higher. Furthermore, the buck converter cannot output power that is higher than the output power of the boost converter.

  Therefore, when trying to secure the luminous flux of the light emitting diode immediately after the start of lighting, the output of the boost converter is the maximum power necessary for lighting the light emitting diode, that is, the power required at low temperatures (that is, immediately after starting lighting). There was a need to do.

  However, in a state where a certain amount of time has elapsed from the start of lighting and the temperature of the light emitting diode is stable, the above power is uselessly high. That is, in the configuration in which the output of the boost converter is constant, wasteful power consumption is large.

  The present invention has been made in view of the above-described reasons, and an object of the present invention is to provide a light-emitting diode lighting device capable of securing a luminous flux of the light-emitting diode immediately after the start of lighting and suppressing unnecessary power consumption, and lighting of the light-emitting diode. It is providing the lighting fixture using an apparatus.

A light emitting diode lighting device of the present invention includes a boost converter that outputs DC power, a buck converter that steps down the output voltage of the boost converter and outputs the boosted voltage to the light emitting diode, and a current detection circuit . The boost converter includes a series circuit of an inductor and a switching element connected between input terminals to which DC power is input, a series circuit of a diode and a capacitor connected in parallel to the switching element, and the switching A drive circuit that drives the element on and off, and the current detection circuit inputs a higher detection voltage to the drive circuit as the current value of the current flowing through the switching element is higher. When the predetermined threshold is reached, the switching element is turned off, and the inductor The switching element is turned on when an end voltage falls below a predetermined value, and the current detection circuit sets a ratio of the detection voltage to the current value in a steady period to the current value in an output increase period. higher than the ratio of the detected voltage, the boost converter, the output power at the output increasing period from said lighting of the light emitting diode is started until after the predetermined switching time, after elapse of the output increasing period characterized by higher than the output power at a said constant period.

In addition, another light emitting diode lighting device of the present invention includes a boost converter that outputs DC power, a buck converter that steps down the output voltage of the boost converter and outputs it to the light emitting diode, and a current. The boost converter includes a series circuit of an inductor and a switching element connected between input terminals to which DC power is input, and a series circuit of a diode and a capacitor connected in parallel to the switching element. And a drive circuit that drives the switching element on and off, and the current detection circuit inputs a higher detection voltage to the drive circuit as the current value of the current flowing through the switching element is higher. When the detection voltage reaches a predetermined threshold, the switching element is turned off, and the The switching element is turned on when a voltage across the ductor falls below a predetermined value, and the current detection circuit determines a ratio of the detection voltage to the current value in a steady period, and the current value in an output increase period. higher than the ratio of the detected voltage for the boost converter, the output power at the output rise time temperature is below a predetermined switching temperature of the light emitting diode, the temperature of the light emitting diode is at the switching temperature or higher characterized by higher than the output power at the constant period.

  Further, any one of the light emitting diode lighting devices includes a load abnormality determining circuit that determines whether or not the light emitting diode is abnormal, and the boost converter is in a period in which it is determined that there is an abnormality by the load abnormality determining circuit. It is desirable that the output power be lower than the output power during a period when it is determined that there is no abnormality by the load abnormality determination circuit.

  The lighting fixture of this invention is equipped with one of the said light emitting diode lighting devices.

  According to the present invention, since the output power of the boost converter is higher than the steady period in the output increase period, the output increase immediately after the start of lighting of the light-emitting diode is compared with the case where the output power of the boost converter is constant. While securing the luminous flux in the period, wasteful power consumption in the steady period can be suppressed.

It is a circuit block diagram showing an embodiment of the present invention. It is explanatory drawing which shows an example of the time change of the output power of the boost converter same as the above. (A) shows the example of the time change of the input voltage Vd to the drive circuit in the output rise period same as the above, and (b) shows the example of the time change of the input voltage Vd to the drive circuit in the steady period same as the above. (A) (b) is explanatory drawing which shows another example of the time change of the output electric power of a boost converter same as the above, respectively, (a) (b) shows a mutually different example. It is a circuit block diagram which shows the example of a change same as the above. It is a circuit block diagram which shows another example of a change same as the above. It is a circuit block diagram which shows another example of a change same as the above. It is explanatory drawing which shows an example of the relationship between the both-ends voltage of this light emitting diode, and temperature, when a fixed electric current is input into a light emitting diode.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  In the present embodiment, as shown in FIG. 1, a boost converter 1 that outputs DC power, and a buck converter 2 that turns on the light emitting diode 3 by stepping down the output voltage of the boost converter 1 and outputting it to the light emitting diode 3. Is provided.

  Furthermore, the present embodiment includes a diode bridge DB that full-wave rectifies AC power input from an external AC power supply AC, and a capacitor C0 connected between the output terminals of the diode bridge DB. The output terminal on the low voltage side of the diode bridge DB is connected to the ground.

  The boost converter 1 boosts the DC power obtained by smoothing the DC output of the diode bridge DB by the capacitor C0.

  More specifically, the boost converter 1 includes an inductor L1 having one end connected to the output terminal on the high voltage side of the diode bridge DB, and a diode D1 having an anode connected to the other end of the inductor L1. The boost converter 1 also includes a capacitor C1 (hereinafter referred to as “output capacitor”) having one end connected to the cathode of the diode D1 and the other end connected to the output terminal on the low voltage side of the diode bridge DB. Both ends of the output capacitor C1 are output ends. Further, the boost converter 1 includes a switching element Q1 having one end connected to a connection point between the inductor L1 and the diode D1. The other end of the switching element Q1 is connected to the output terminal on the low voltage side of the diode bridge DB via a current detection resistor (hereinafter referred to as “detection resistor”) R1. The switching element Q1 is made of, for example, an N-channel field effect transistor (FET), and has a drain connected to the inductor L1 and a source connected to the detection resistor R1.

  That is, energy is stored in the inductor L1 during the period when the switching element Q1 is on, and the output capacitor C1 is generated by the voltage obtained by superimposing the voltage across the inductor L1 on the input voltage during the period when the switching element Q1 is off. Charged.

  Further, boost converter 1 includes a drive circuit 10 that drives switching element Q1 on and off.

  The drive circuit 10 turns on the switching element Q1 when the voltage across the secondary winding N1 provided in the inductor L1 falls below a predetermined value (that is, when the voltage across the inductor L1 falls below a predetermined value). The drive circuit 10 has a control terminal, and when the voltage Vd input to the control terminal reaches a predetermined threshold value (hereinafter referred to as “off voltage”) Vth (see FIG. 3A). The switching element Q1 is turned off. A higher voltage (that is, a higher voltage as the current value of the current flowing through the switching element Q1 is higher, hereinafter referred to as “detection voltage”) Vd is input to the control terminal. Is done.

  Next, the buck converter 2 will be described. Buck converter 2 includes a series circuit of a capacitor (hereinafter referred to as “output capacitor”) C2, inductor L2, switching element Q2, and resistor R2 connected between the output terminals of boost converter 1. Then, both ends of the output capacitor C2 are connected to the light emitting diode 3 as output terminals of the buck converter 2. The switching element Q2 is composed of, for example, an N-channel field effect transistor (FET), and has a drain connected to the inductor L2 and a source connected to the ground via the resistor R2. Further, the buck converter 2 includes a diode D2 having an anode connected to a connection point between the inductor L2 and the switching element Q2 via the ferrite bead FB1, and a cathode connected to a connection point between the boost converter 1 and the output capacitor C2. . Further, a series circuit of a ferrite bead FB2 and a capacitor C21 is connected between both ends of the switching element Q2. A discharging resistor R21 is connected between both ends of the output capacitor C2. In the figure, the discharging resistor R21 is constituted by a series circuit composed of three elements.

  That is, in the buck converter 2, energy is stored in the inductor L2 during the period when the switching element Q2 is on, and the output capacitor via the diode D2 using the inductor L2 as a power source during the period when the switching element Q2 is off. C2 is charged.

  The inductor L2 is provided with a secondary winding N2. The buck converter 2 turns on the switching element Q2 when the voltage across the secondary winding N2 of the inductor L2 falls below a predetermined value, and turns off the switching element Q2 when the voltage across the resistor R2 reaches a predetermined threshold. The drive circuit 20 is provided. This achieves feedback control that maintains the output current of the buck converter 2 substantially constant.

  Hereafter, the characteristic part of this embodiment is demonstrated.

  In the present embodiment, as shown in FIG. 2, the period P1 during which the temperature of the light emitting diode 3 is estimated to be low (hereinafter referred to as “output increase period”) P1 is the other period (hereinafter referred to as “steady period”). It is characterized in that the output power of the boost converter 1 is increased compared to P2. In other words, the output power of the boost converter 1 is reduced after the elapse of the output increase period P1.

  In the output increase period P1, for example, an elapsed time (hereinafter referred to as “operation time”) after the lighting of the light emitting diode 3 is started (that is, after the boost converter 1 starts operation) is referred to as a predetermined time. (Hereinafter referred to as “switching time”). The above switching time is the time from the start of lighting of the light emitting diode 3 under the assumed use conditions until the temperature of the light emitting diode 3 is stabilized.

  Specifically, the boost converter 1 controls the drive circuit 10 using the timer circuit 11 that measures the above-described operation time, and the voltage corresponding to the both-end voltage of the detection resistor R1 and the output of the timer circuit 11 as the detection voltage Vd. And a voltage conversion circuit 12 input to the terminal. The timer circuit 11 sets the output to the H level until the operation time reaches the switching time (that is, during the output rising period P1), and after the operation time reaches the switching time (that is, during the steady period P2), the output is set to the L level. To do. The voltage conversion circuit 12 inputs the voltage across the detection resistor R1 as it is to the drive circuit 10 as the detection voltage Vd during the period when the output of the timer circuit 11 is at the H level (that is, the output increase period P1). During a period in which the output is at the L level (that is, the steady period P2), a voltage obtained by adding a constant voltage Vu to the voltage across the detection resistor R1 is input to the drive circuit 10 as the detection voltage Vd. That is, in the steady period P2, the ratio of the detected voltage Vd to the current value of the current flowing through the switching element Q1 (that is, the value obtained by dividing the detected voltage Vd by the above current value, hereinafter referred to as “detection ratio”). It becomes higher than the detection ratio (resistance value of the detection resistor R1) in the output increase period P1. That is, the detection resistor R1 and the voltage conversion circuit 12 constitute a current detection circuit. Since the timer circuit 11 and the voltage conversion circuit 12 as described above can be realized by a well-known technique, detailed illustration and description are omitted.

  An example of the time change of the detection voltage Vd is shown in FIG. 3A for the output increase period P1 and shown in FIG. 3B for the steady period P2. By converting the detection voltage Vd as described above in the steady period P2, the on-duty of the switching element Q1 is made smaller than that in the output increase period P1, that is, the output power of the boost converter 1 is reduced.

  According to the above configuration, as compared with the case where the output power of the boost converter 1 is constant, wasteful power in the steady period P2 is ensured while securing the light flux in the output increase period P1 immediately after the light emitting diode 3 starts to light. Consumption is suppressed.

  Note that the output power of the boost converter 1 during the output increase period P1 is constant until the output power during the steady period P1 as shown in FIGS. 4 (a) and 4 (b), instead of being constant as shown in FIG. It may be gradually reduced. In such an operation, for example, the voltage conversion circuit 12 drives a voltage obtained by adding a voltage (hereinafter referred to as “addition voltage”) to the voltage across the detection resistor R1 from the output rise period P1 as the detection voltage Vd. This can be realized by inputting to the circuit 10 and gradually increasing the above added voltage to the value Vu during the steady period P2. In this case, the detection ratio in the output increase period P1 is gradually increased to the detection ratio in the steady period P2.

  Further, as means for switching the output power of the boost converter 1, instead of providing the voltage conversion circuit 12 as described above, a current detection resistor R1 is a series circuit of two resistors R11 and R12 as shown in FIG. The switching element Q11 may be connected in parallel to one resistor R12, and the switching element Q11 may be turned on / off by the output of the timer circuit 11. In FIG. 5, the switching element Q11 comprises an NPN transistor, and the base is connected to the timer circuit 11 via a resistor and is connected to the ground via a parallel circuit of a resistor and a capacitor. As the detection voltage Vd input to the drive circuit 10, the voltage across the series circuit of the resistors R11 and R12 is used as it is. That is, the switching element Q11 is turned on during the output rise period P1, and the switching element Q11 is turned off during the steady period P2, so that the detection voltage Vd for a constant current is higher than the steady period P2 in the output rise period P1. Lower. That is, the detection ratio (resistance value of one resistor R11) in the output increase period P1 is lower than the detection ratio (sum of resistance values of the two resistors R11 and R12) in the steady period P2. As a result, the output power of the boost converter 1 as a result of the operation based on the detection voltage Vd becomes higher in the output increase period P1 than in the steady period P2. In the example of FIG. 5, the switching element Q11 and the resistors R11 and R12 form a current detection circuit.

  Further, a period in which the temperature of the light emitting diode 3 is less than a predetermined value (hereinafter referred to as “switching temperature”, for example, 40 ° C.) may be set as the output increase period P1. For example, as shown in FIG. 6, a temperature detection circuit that outputs an H level when the temperature of the light emitting diode 3 is lower than the switching temperature and outputs an L level when the temperature of the light emitting diode 3 is equal to or higher than the switching temperature. 13 is provided. Such a temperature detection circuit 13 can be realized by a well-known technique using a well-known temperature-sensitive element (for example, a thermistor) disposed close to the light-emitting diode 3, and thus detailed illustration and description thereof are omitted. That is, in the example of FIG. 6, not only the period from the start of lighting of the light emitting diode 3 until the switching time elapses but also the period in which the temperature of the light emitting diode 3 is lower than the switching temperature is included in the output increase period P1. In the example of FIG. 6, the timer circuit 11 may be omitted. In this case, only the period in which the temperature of the light emitting diode 3 is lower than the switching temperature is the output increase period P1. Furthermore, using the temperature detection circuit 13 in which the output voltage continuously changes according to the temperature of the light emitting diode 3, the output power of the boost converter 1 continuously changes according to the temperature detected by the temperature detection circuit 13. You may make it do.

  Furthermore, a load abnormality determination circuit (not shown) for determining whether or not the light emitting diode 3 is abnormal is provided, and when the load abnormality determination circuit determines that the light emitting diode 3 is abnormal, the output power of the boost converter 1 is increased. It may be reduced. Specifically, the load abnormality determination circuit detects at least one of the output voltage and the output current of the buck converter 2, and any of the detected output voltage and output current is within a predetermined normal range. Sometimes it is determined that there is no abnormality in the light emitting diode 3, and it is determined that there is an abnormality in the light emitting diode 3 when the output voltage or output current of the buck converter 2 is outside the normal range. Specifically, when the output voltage of the buck converter 2 is higher than the upper limit value of the normal range, or when the output current of the buck converter 2 is lower than the lower limit value of the normal range, an abnormal no-load state occurs. Can be determined. Further, when the output voltage of the buck converter 2 is lower than the lower limit value of the normal range, or when the output current of the buck converter 2 is higher than the upper limit value of the normal range, it can be determined that an abnormal short circuit has occurred. Since the load abnormality determination circuit as described above can be realized by a known technique, illustration and detailed description thereof are omitted. Drive circuit 10 operates to reduce the output power of boost converter 1 when it is determined by the load abnormality determination circuit that there is an abnormality. As a specific operation of the drive circuit 10 when reducing the output power of the boost converter 1, the off-voltage Vth may be lowered, or the driving of the switching element Q1 may be stopped.

  Further, a circuit abnormality determination circuit for determining whether or not the buck converter 2 is abnormal is provided so that the output power of the boost converter 1 is reduced when the circuit abnormality determination circuit determines that the buck converter 2 is abnormal. Also good. As the circuit abnormality determination circuit, for example, as shown in FIG. 7, a voltage across the current detection resistor R2 of the buck converter 2 is input to the non-inverting input terminal, and a predetermined reference voltage is input to the inverting input terminal. A comparator CP can be used. The output of the comparator CP is input to the drive circuit 10 of the boost converter 1, for example. The reference voltage is generated, for example, by dividing the power supply voltage Vc of the drive circuit 20, and is higher (for example, 1.2 times) than the voltage at which the drive circuit 20 of the buck converter 2 turns off the switching element Q2. If there is no abnormality in the buck converter 2, the output of the comparator CP is maintained at the L level, that is, it is determined that there is no abnormality in the buck converter 2. In addition, when an abnormality occurs in either the switching element Q2 or the drive circuit 20 in the buck converter 2 and an excessive current flows through the switching element Q2, the output of the comparator CP becomes H level (that is, there is an abnormality in the buck converter 2). Is determined). When it is determined by the circuit abnormality determination circuit that there is an abnormality (that is, when the output of the comparator CP becomes H level), the drive circuit 10 operates to reduce the output power of the boost converter 1. As a specific operation of the drive circuit 10 when reducing the output power of the boost converter 1, the off-voltage Vth may be lowered, or the driving of the switching element Q1 may be stopped.

  Needless to say, the illustrated circuit can be replaced with an appropriate equivalent circuit. For example, the output capacitor C1 of the boost converter 1 may be configured by a parallel circuit of a plurality of capacitors.

The various light emitting diode lighting devices described above include, for example, lighting fixtures together with appropriately shaped fixture bodies (not shown) for holding and holding the circuit components of the buck converter 2 and the boost converter 1 and holding the light emitting diodes 3 respectively. Can be configured.

1 Boost Converter 2 Buck Converter 10 Drive Circuit 12 Voltage Conversion Circuit (Part of Current Detection Circuit)
C1 Output capacitor L1 Inductor P1 Output rise period P2 Steady period Q1 Switching element Q11 Switching element (part of current detection circuit)
R1 detection resistor (part of current detection circuit)
R11, R12 resistance (part of current detection circuit)

Claims (4)

A boost converter that outputs DC power;
A buck converter for lighting the light emitting diode by stepping down the output voltage of the boost converter and outputting it to the light emitting diode, and a current detection circuit ;
The boost converter includes a series circuit of an inductor and a switching element connected between input terminals to which DC power is input, a series circuit of a diode and a capacitor connected in parallel to the switching element, and the switching element. A drive circuit for on-off driving,
The current detection circuit inputs a higher detection voltage to the drive circuit as the current value of the current flowing through the switching element is higher,
The drive circuit turns off the switching element when the detection voltage reaches a predetermined threshold, and turns on the switching element when a voltage across the inductor falls below a predetermined value;
The current detection circuit has a ratio of the detection voltage to the current value in a steady period higher than a ratio of the detection voltage to the current value in an output increase period,
The boost converter, the output power at the output increasing period from said lighting of the light emitting diode is started until after the predetermined switching time, than the output power at the constant period is after the lapse of the output increasing period Increase
A light-emitting diode lighting device. A boost converter that outputs DC power;
A buck converter for lighting the light emitting diode by stepping down the output voltage of the boost converter and outputting it to the light emitting diode, and a current detection circuit ;
The boost converter includes a series circuit of an inductor and a switching element connected between input terminals to which DC power is input, a series circuit of a diode and a capacitor connected in parallel to the switching element, and the switching element. A drive circuit for on-off driving,
The current detection circuit inputs a higher detection voltage to the drive circuit as the current value of the current flowing through the switching element is higher,
The drive circuit turns off the switching element when the detection voltage reaches a predetermined threshold, and turns on the switching element when a voltage across the inductor falls below a predetermined value;
The current detection circuit has a ratio of the detection voltage to the current value in a steady period higher than a ratio of the detection voltage to the current value in an output increase period,
The boost converter, the output power at the output rise time temperature is below a predetermined switching temperature of the light emitting diode is higher than the output power at the constant period temperature is the switching temperature or more of said light emitting diode
A light-emitting diode lighting device. A load abnormality determination circuit for determining presence or absence of abnormality of the light emitting diode,
The boost converter makes output power in a period in which it is determined that there is an abnormality by the load abnormality determination circuit lower than output power in a period in which there is no abnormality by the load abnormality determination circuit
The light-emitting diode lighting device according to claim 1 or 2 .   The light-emitting diode lighting device according to claim 1.
  A lighting apparatus characterized by that.

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