JP2013110059A - Led driving device, illuminating device and illumination apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED driving device, an illuminating device and an illumination apparatus configured including a boosting circuit and a step-down circuit, capable of reducing over current stress to an LED light source with a low cost.SOLUTION: An LED driving device A1 includes: a boosting chopper circuit A11 that outputs a step-up voltage V2 which is a boosted DC voltage V1 from a DC power supply E1; a step-down chopper circuit A12 that outputs an output voltage V3, which is a stepped-down step-up voltage V2, to an LED unit 3; and a control circuit A13 that controls a step-up operation of the boosting chopper circuit A11 and a step-down operation of the step-down chopper circuit A12. When the input voltage V1 is supplied, the control circuit A13 causes the step-down chopper circuit A12 to start the step-down operation and causes the boosting chopper circuit A11 to start the step-up operation in this order.

Description

  The present invention relates to an LED driving device, a lighting device, and a lighting fixture.

  In the lighting field, LED (Light Emitting Diode) elements are actively used and their uses are diversified. In vehicle lighting, white LED elements are used in the passenger compartment, and are also used for headlights, daytime running lamps, and the like due to higher brightness.

  LED elements have a longer life and faster response than incandescent bulbs, and can be mounted compactly in structure. Moreover, various colors can be easily realized, and lighting control by dimming is easy. And lighting fixtures, such as a lamp, can be reduced in thickness, and since it can be mounted in three dimensions, there is an advantage that a free design that does not limit the shape such as a car design is possible.

  The lighting fixture mentioned above is comprised by the fixture main body holding the LED element and the LED drive device which makes an LED element light. The LED driving device turns on the plurality of LED elements with uniform brightness by supplying a constant current to a light source formed by connecting the plurality of LED elements in series.

  In the LED driving device, DC / DC converters having various configurations are used in order to control the output voltage within a certain range even when the input voltage varies.

  For example, a configuration has been proposed in which the output chopper method is switched to a step-down chopper or a step-up chopper according to the value of the input voltage (see, for example, Patent Document 1). Furthermore, a configuration has also been proposed in which the output voltage is held constant even when switching between step-up / step-down when the step-down chopper and the step-up chopper are selectively operated according to the input voltage (for example, Patent Documents). 2). There has also been proposed a configuration in which a step-up chopper circuit and a step-down chopper circuit are provided independently, and a step-down chopper circuit is arranged at the subsequent stage of the step-up chopper circuit (see, for example, Patent Document 3).

  FIG. 14 shows a conventional LED driving device B1. The DC voltage of the DC power supply E101 is set as the input voltage V101 of the LED driving device B1, and the DC voltage obtained by boosting, stepping down or stepping up the input voltage V101 is set as the output voltage V102 of the LED driving device B1. The output voltage V102 is applied between both ends of an LED unit 103 (LED light source) in which a plurality of LED elements Z101 are connected in series, and an LED current I101 flows through the LED unit 103 to light it.

  When the LED drive device B1 is mounted on a vehicle and used as a vehicle-mounted LED drive device, the DC power supply E101 is constituted by a vehicle-mounted battery. In consideration of the fluctuation of the DC voltage (usually 12V) of the vehicle-mounted battery, 9 to 16V is assumed as the range of the input voltage V101. Considering the transient voltage fluctuation, the range of the input voltage V101 may be assumed to be 6 to 20V.

  The LED element Z101 used in the LED unit 103 is improved in forward voltage by improving luminous efficiency so that a necessary light beam can be obtained while reducing the number of LED elements used. Since the luminous flux of the LED element Z101 changes in proportion to the LED current I101, when using a plurality of LED elements Z101, the LED elements are connected in series and the same LED current is allowed to flow. The method of making it emit light is common.

  When an LED element is used in a vehicle-mounted passing headlamp, the number of LED elements Z101 to be used is often composed of about 4 to 12 due to the improvement of luminous efficiency. The forward voltage of one LED element Z101 varies depending on current capacity, element configuration and material, operating temperature, operating current, etc. If the forward current is several hundred mA, the forward voltage is 3 to 3. It is about 5V. In the case of the LED unit 103 in which four LED elements Z101 are connected in series, the voltage between both ends thereof is 12 to 14V. In the case of the LED unit 103 in which five LED elements Z101 are connected in series, the voltage between both ends is 15 to 17.5V. Become.

  FIG. 15 is a graph showing the relationship between the input voltage V101 and the output voltage V102. Then, with the straight line X101 where V101 = V102 as a boundary, the area below the straight line X101 is a region (step-down region) where V101> V102, and the region above the straight line X101 is a region (step-up region) where V101 <V102.

  In addition, the range W101 [9 to 16 V] of the input voltage V101 takes into account fluctuations in the DC voltage (usually 12 V) of the in-vehicle battery. The range W102 [6 to 20 V] of the input voltage V101 also considers transient voltage fluctuations of the DC voltage of the in-vehicle battery.

  A region G101 in FIG. 15 is surrounded by a range W102 of the input voltage V101 and a range W103 [15 to 17.5 V] of both-ends voltage that can be taken by the LED unit 103 in which the five LED elements Z101 are connected in series. Area. A region G102 in FIG. 15 is a region surrounded by a range W102 of the input voltage V101 and a range W104 [12 to 14V] of both-end voltage that can be taken by the LED unit 103 in which the four LED elements Z101 are connected in series. . The LED driving device B1 operates assuming the region G101 or the region G102.

JP-A-62-18970 JP 2010-268590 A JP 2011-1000062 A1

  As shown in FIG. 16, in the LED element Z101, when the forward voltage Vf exceeds the threshold voltage, the fluctuation of the forward voltage Vf becomes smaller than the fluctuation of the forward current If, and the forward voltage Vf is It becomes a substantially constant value. As an example, in the normal use range (about several hundred mA) of the forward current If, the forward voltage Vf is about 3 to 4 V, and shows almost constant voltage characteristics (even if the forward current If changes, The forward voltage Vf does not vary much).

  And in LED drive device B1 which uses battery power supplies, such as a vehicle-mounted use, the input voltage V101 fluctuates with use environments, on / off of other loads, etc. In the LED driving device B1, constant voltage control is performed so that the output voltage V102 is constant with respect to the fluctuation of the input voltage V101. On the other hand, also in the LED unit 103, since the LED element itself has a constant voltage characteristic as described above, a substantially constant both-end voltage is maintained in a region where the LED current I101 is large to some extent.

  However, when the LED driving device B1 is composed of a booster circuit and a step-down circuit, the step-up circuit is stopped when the input voltage V101 is turned on and when the input voltage V101 is turned off, depending on the operation start timing of the booster circuit and the step-down circuit. Only may work. In such a case, in the LED driving device B1, the high boosted voltage by the booster circuit is output as the output voltage V102 without being stepped down, and the energy change of the output voltage V102 appears as the change of the LED current I101. That is, the LED current I101 increases instantaneously and an overcurrent flows through the LED unit 103. For example, in the region where the forward voltage Vf of FIG. 16 shows a substantially constant voltage characteristic, the increase ΔIf of the forward current If is relatively larger than the minute increase ΔVf of the forward voltage Vf. Overcurrent flows.

  Therefore, the LED unit 103 is subjected to stress due to overcurrent, which may cause a problem and impair the reliability of the device.

  Further, as a method for suppressing the overcurrent stress of the LED unit 103, a method of connecting a current limiting element in series to the LED unit 103 has been proposed. Furthermore, a method of providing an overcurrent protection circuit in which a switch is connected in series to the LED unit 103 and the switch is turned off when the LED current I101 exceeds a predetermined current has been proposed. However, the addition of a current limiting element and an overcurrent protection circuit has been a cause of cost increase.

  The present invention has been made in view of the above reasons, and an object of the present invention is to provide an LED driving device and an illumination that are configured by a booster circuit and a step-down circuit and can suppress overcurrent stress on the LED light source at low cost. It is in providing an apparatus and a lighting fixture.

  The LED driving device of the present invention is an LED driving device that supplies DC power to an LED light source composed of one or a plurality of LED elements, and a second DC voltage obtained by boosting the first DC voltage of a DC power source. A step-up circuit for outputting; a step-down circuit for outputting a third DC voltage obtained by stepping down the second DC voltage to the LED light source; a control circuit for controlling the step-up operation of the step-up circuit and the step-down operation of the step-down circuit; The control circuit starts the step-down operation of the step-down circuit and the step-up operation of the step-up circuit when the first DC voltage is input.

  In the present invention, it is preferable that the control circuit stops the step-up operation of the step-up circuit and the step-down operation of the step-down circuit in this order when the first DC voltage is cut off.

  In the present invention, a voltage detection unit that detects the second DC voltage and a current detection unit that detects a current flowing through the LED light source, and the control circuit is based on a detection value of the second DC voltage. Controlling the step-up operation of the step-up circuit, controlling the step-down operation of the step-down circuit based on the detected value of the current flowing through the LED light source, and when the first DC voltage is applied, The first time from the start of the step-down operation to the start of the step-up operation of the step-up circuit is the same as the step-down circuit after the step-up operation of the step-up circuit is stopped when the first DC voltage is cut off. It is preferable that the time is longer than the second time until the step-down operation is stopped.

  In the present invention, the booster circuit includes a first switching element, and the second DC voltage is generated by turning on / off the first switching element. The switching circuit has a switching element, and the second switching element is turned on / off to generate the third DC voltage. The control circuit causes each of the first and second switching elements to have the same frequency. It is preferable to drive on / off.

  In the present invention, when the boosting operation of the booster circuit is stopped, the second DC voltage is substantially equal to the first DC voltage, and the control circuit is configured such that the first DC voltage is the second DC voltage. When the voltage is lower than the DC voltage, it is preferable that the boosting operation of the boosting circuit is executed, and when the first DC voltage is higher than the second DC voltage, the boosting operation of the boosting circuit is stopped.

  The illuminating device of this invention is equipped with the LED drive device of this invention, and the LED light source comprised by the 1 thru | or several LED element driven by the said LED drive device, It is characterized by the above-mentioned.

  The lighting fixture of this invention is equipped with the lighting device of this invention, and the fixture main body holding the said lighting device, It is characterized by the above-mentioned.

  As described above, the present invention includes the booster circuit and the step-down circuit, and has an effect that the overcurrent stress on the LED light source can be suppressed at a low cost.

It is a block diagram which shows schematic structure of the LED drive device of Embodiment 1. It is a circuit diagram which shows a structure same as the above. (A)-(c) It is explanatory drawing which shows operation | movement same as the above. (A)-(c) It is explanatory drawing which shows another operation | movement same as the above. It is a circuit diagram which shows a detailed structure same as the above. It is a block diagram which shows the structure of a pressure | voltage rise control circuit same as the above. It is a block diagram which shows the structure of a pressure | voltage fall control circuit same as the above. It is a block diagram which shows the structure of the main control circuit same as the above. (A)-(c) It is explanatory drawing which shows operation | movement of the main control circuit same as the above. FIG. 5 is a block diagram illustrating a configuration of a control circuit according to a second embodiment. FIG. 6 is a circuit diagram illustrating a configuration of a step-down chopper circuit according to a third embodiment. It is a circuit diagram which shows the structure of the detection means of LED current same as the above. (A)-(c) It is a wave form diagram which shows the detection waveform of LED current same as the above. It is a block diagram which shows schematic structure of the conventional LED drive device. It is a graph which shows the relationship of the input voltage-output voltage of a LED drive device. It is a graph which shows the characteristic of an LED element.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 shows an LED driving device A1 of the present embodiment. The LED driving device A1 inputs the DC voltage of the DC power source E1 as the input voltage V1, and connects the LED unit 3 (LED light source) in which a plurality of LED elements Z1 are connected in series to the output. The output voltage V3 of the LED driving device A1 is applied to both ends of the LED unit 3, and the LED unit 3 is turned on when the LED current I1 flows. The LED driving device A1 and the LED unit 3 constitute the lighting device of the present invention.

  The LED driving device A1 includes a step-up chopper circuit A11 (step-up circuit), a step-down chopper circuit A12 (step-down circuit), and a control circuit A13. The step-down chopper circuit A12 is connected to the subsequent stage of the step-up chopper circuit A11. ing.

  The boost chopper circuit A11 boosts the input voltage V1 (first DC voltage) to the boost voltage V2 (second DC voltage). The step-down chopper circuit A12 steps down the boosted voltage V2 to the output voltage V3 (third DC voltage). The control circuit A13 controls the step-up operation of the step-up chopper circuit A11 and the step-down operation of the step-down chopper circuit A12.

  When the input voltage V1 is input from the DC power supply E1 (when the LED driving device A1 is started), the control circuit A13 starts the step-down operation of the step-down chopper circuit A12 and the step-up operation of the step-up chopper circuit A11. In addition, when the input voltage V1 is cut off (when the LED driving device A1 is stopped), the control circuit A13 may stop the boosting operation of the boosting chopper circuit A11 and the bucking operation of the step-down chopper circuit A12 in this order. The input voltage V1 is turned on / off by switching means (not shown) provided in the LED driving device A1, switching means (not shown) provided in the circuit between the DC power supply E1 and the LED driving device A1, and turning on / off the DC power supply E1. This is done by operation.

  FIG. 2 shows an example of the LED driving device A1.

  The step-up chopper circuit A11 includes a series circuit of an inductor L1 and a switching element S1 (first switching element) connected between both ends of the DC power supply E1, and a series circuit of a diode D1 and a capacitor C1 connected in parallel to the switching element S1. With. Then, the control circuit A13 drives the switching element S1 on and off at a high frequency to generate a boosted voltage V2 obtained by boosting the input voltage V1 between both ends of the capacitor C1.

  Specifically, in the step-up chopper circuit A11, when the switching element S1 is turned on, a current flows through the path of the DC power supply E1-inductor L1-switching element S1-DC power supply E1, and magnetic energy is accumulated in the inductor L1. When the switching element S1 is turned off, the magnetic energy stored in the inductor L1 is released, and a current flows through the path of the inductor L1-diode D1-capacitor C1-DC power supply E1-inductor L1. As the switching element S1 is repeatedly turned on and off, a boosted voltage V2 higher than the input voltage V1 is generated at both ends of the capacitor C1. The control circuit A13 performs PWM (Pulse Width Modulation) control of the on-duty of the switching element S1 so that the detected value of the boosted voltage V2 matches a predetermined target voltage.

  The step-down chopper circuit A12 includes an inductor L2 having one end connected to the positive electrode of the capacitor C1, and a switching element S2 (second switching element) having one end connected to the negative electrode of the capacitor C1, and includes each of the inductor L2 and the switching element S2. The LED unit 3 is connected between the other ends. Further, a regenerative diode D2 is connected in parallel to the series circuit of the inductor L2 and the LED unit 3. Then, the control circuit A13 drives the switching element S2 on and off at a high frequency, thereby applying the output voltage V3 obtained by stepping down the boosted voltage V2 across the LED unit 3, and controlling the LED current I1 to the target current. .

  Specifically, in the step-down chopper circuit A12, when the switching element S2 is turned on, a current flows through a path of the capacitor C1-inductor L2-LED unit 3-switching element S2-capacitor C1. When the switching element S2 is turned off, the magnetic energy accumulated in the inductor L2 is released, and a current flows through the path of the inductor L2-LED unit 3-diode D2-inductor L2. As the switching element S2 is repeatedly turned on and off, the LED current I1 continuously flows through the LED unit 3, and the LED element Z1 emits light according to the LED current I1. The control circuit A13 performs PWM control on the on-duty of the switching element S2 so that the detected value of the LED current I1 matches a predetermined target current.

  3A to 3C show an example of operation timings of the switching elements S1 and S2 of the LED driving device A1.

  The control circuit A13 internally generates a control power supply from the input voltage V1, and operates with this control power supply. Then, the control circuit A13, which has been supplied with the input voltage V1 and started generating the control power supply, starts on / off driving of the switching element S2 of the step-down chopper circuit A12 (timing t0). Next, the control circuit A13 does not drive the switching element S1 of the step-up chopper circuit A11 on / off until the time T1 (first time) elapses from the timing t0 (maintains the off state), and the step-down chopper circuit A12. Only the switching element S2 is turned on / off. Therefore, in the period from time t0 until time T1 elapses, the boosted voltage V2 becomes a voltage equal to the input voltage V1 (or a voltage substantially equal to the input voltage V1), and the LED current I1 gradually increases.

  Next, the control circuit A13 starts on / off driving of the switching element S1 of the step-up chopper circuit A11 when the time T1 has elapsed from the timing t0 (timing t1). That is, when the input voltage V1 is input from the DC power source E1, the control circuit A13 starts the step-down operation of the step-down chopper circuit A12 and the step-up operation of the step-up chopper circuit A11. Therefore, after timing t1, the boosted voltage V2 becomes a voltage obtained by boosting the input voltage V1, and the LED current I1 rises rapidly.

  For example, when the input voltage V1 is turned on, it is assumed that the step-up operation of the step-up chopper circuit A11 and the step-down operation of the step-down chopper circuit A12 are started in the order opposite to the operation of FIG. In this case, immediately after the step-down chopper circuit A12 starts operation, the step-down operation tends to become unstable, and the output voltage V3 equal to the step-up voltage V2 may be instantaneously output without stepping down the step-up voltage V2. There is. Thus, overcurrent flows through the LED unit 3, and the LED unit 3 is subjected to overcurrent stress.

  On the other hand, the LED driving device A1 that performs the operation of FIG. 3 starts the step-down operation of the step-down chopper circuit A12 and the step-up operation of the step-up chopper circuit A11 when the input voltage V1 is turned on. The step-down operation of the step-down chopper circuit A12 is stable. That is, even when the input voltage V1 is turned on, the boosted voltage V2 is surely stepped down. Therefore, even when the input voltage V1 is turned on, the output voltage V3 obtained by stepping down the boosted voltage V2 is output, and no overcurrent flows through the LED unit 3. Therefore, the overcurrent stress of the LED unit 3 can be suppressed. Further, since it is not necessary to separately provide a current limiting element or an overcurrent protection circuit, the cost can be reduced.

  In FIG. 3, when the input voltage V1 is cut off, the step-up operation of the step-up chopper circuit A11 and the step-down operation of the step-down chopper circuit A12 are stopped simultaneously (timing t2). However, in this stop operation, the boosted voltage V2 remains in the capacitor C1, and there is a risk of electric shock. When the input power supply V1 is turned on next time, the rise of the LED current I1 becomes steep due to the residual voltage of the capacitor C1.

  Therefore, as shown in FIGS. 4A to 4C, when the input voltage V1 is interrupted, the control circuit A13 stops the step-up operation of the step-up chopper circuit A11 and the step-down operation of the step-down chopper circuit A12 in this order. Also good.

  First, the control circuit A13, which has started operating when the input voltage V1 is input, starts ON / OFF driving of the switching element S2 of the step-down chopper circuit A12 (timing t10). Next, the control circuit A13 does not drive the switching element S1 of the step-up chopper circuit A11 on / off (maintains the off state) until the time T11 (first time) elapses from the timing t10, and the step-down chopper circuit A12. Only the switching element S2 is turned on / off. Therefore, in the period from the timing t10 until the time T11 elapses, the boosted voltage V2 becomes a voltage equal to the input voltage V1 (or a voltage substantially equal to the input voltage V1), and the LED current I1 gradually increases.

  Next, the control circuit A13 starts on / off driving of the switching element S1 of the step-up chopper circuit A11 when the time T11 (first time) elapses from the timing t10 (timing t11).

  When the input voltage V1 is cut off, the control circuit A13 first stops the on / off drive of the switching element S1 of the boost chopper circuit A11 until the control power supply is lowered and becomes inoperable (timing t12). . Next, the control circuit A13 stops the on / off driving of the switching element S2 of the step-down chopper circuit A12 when the time T12 (second time) elapses from the timing t12 (timing t13).

  As described above, the LED driving device A1 stops the step-up operation of the step-up chopper circuit A11 and the step-down operation of the step-down chopper circuit A12 when the input voltage V1 is cut off. Therefore, even after the boosting operation of the step-up chopper circuit A11 is stopped, the switching element S2 of the step-down chopper circuit A12 continues the on / off operation for the time T12, so that the residual voltage of the capacitor C1 causes the switching element S2 to It is discharged through. Thus, when the input voltage V1 is cut off, the boosted voltage V2 does not remain in the capacitor C1, and an electric shock or the like can be prevented. Further, when the input power supply V1 is turned on next time, the rising slope of the LED current I1 is suppressed.

  Also, when the input voltage V1 is cut off, it is assumed that the step-down operation of the step-down chopper circuit A12 and the step-up operation of the step-up chopper circuit A11 are stopped in this order, contrary to the operation of FIG. In this case, when the step-down chopper circuit A12 stops its operation, the step-down operation tends to become unstable. Therefore, the boosted voltage V2 obtained by boosting the DC voltage V1 is not stepped down, and the high output voltage V3 is instantaneously output. There is a risk of being. Thus, overcurrent flows through the LED unit 3, and the LED unit 3 is subjected to overcurrent stress.

  On the other hand, the LED driving device A1 that performs the operation of FIG. 4 stops the step-up operation of the step-up chopper circuit A11 and the step-down operation of the step-down chopper circuit A12 when the input voltage V1 is cut off. That is, when the step-down chopper circuit A12 stops operating, the operation of the step-up chopper circuit A11 has already stopped, and the step-up voltage V2 becomes a relatively low voltage. Therefore, when the input voltage V1 is cut off, there is no possibility that the high output voltage V3 is instantaneously output, and no overcurrent flows through the LED unit 3, so that overcurrent stress of the LED unit 3 can be suppressed.

  Next, the operation of the LED driving device A1 based on the magnitude relationship between the input voltage V1 and the boosted voltage V2 will be described. Here, the control circuit A13 determines the magnitude relationship between the input voltage V1 and the boosted voltage V2 by comparing the detected value of the input voltage V1 with the detected value of the boosted voltage V2. The detection means for the input voltage V1 and the boosted voltage V2 has a well-known configuration using a voltage dividing resistor or the like, and the description thereof is omitted.

  For example, it is assumed that the input voltage V1 = 12V, the boost voltage V2 = 18V, the output voltage V3 = 16V, and the input voltage V1 <the boost voltage V2. In this case, the control circuit A13 drives the switching element S1 on and off to control the boosted voltage V2 by the boost chopper circuit A11 to 18V that is the target voltage. Then, the control circuit A13 steps down the boosted voltage V2 = 18V to the output voltage V3 = 16V, and drives the switching element S2 on and off so that the LED current I1 matches the target current.

  Next, when the input voltage V1 increases to 20V due to the use environment or other load on / off, etc., and the relation of the input voltage V1 ≧ the boosted voltage V2 is established, the control circuit A13 turns on / off the switching element S1. Stop off driving. That is, the switching element S1 is maintained in the OFF state, and the boosting operation of the boosting chopper circuit A11 is stopped. At this time, the boost voltage V2 output from the boost chopper circuit A11 is 20V equal to the input voltage V1 (or about 20V approximately equal to the input voltage V1). Then, the step-down chopper circuit A12 controls the LED current I1 to the target current by reducing the on-duty of the switching element S2 compared to when the input voltage V1 = 12V (when the boost voltage V2 = 18V).

  As described above, the input voltage V1 input to the boost chopper circuit A11 may be larger than the boost voltage V2 (target voltage) depending on the use environment, on / off of other loads, and the like. Therefore, when the input voltage V1 becomes higher than the boosted voltage V2 (target voltage), the operation of the boost chopper circuit A11 at the previous stage is stopped, and only the step-down chopper circuit A12 at the subsequent stage is operated, thereby obtaining the LED current I1. Control to target current. Thus, when the input voltage V1 becomes larger than the boosted voltage V2 (target voltage), unnecessary boosting operation is not performed, so that the LED unit 3 can be controlled while suppressing the withstand voltage performance required for each component. Such overcurrent stress can be suppressed.

  Next, a specific circuit of the LED driving device A1 is shown in FIG. 5, and driving control of the switching elements S1 and S2 will be described.

  First, in the step-up chopper circuit A11, a series circuit of resistors R1 and R2 is connected between both ends of the capacitor C1 to form a voltage detection unit, and the voltage at the connection point P1 of the resistors R1 and R2 is set as the detected value of the boost voltage V2. Output as.

  In the step-down chopper circuit A12, a resistor R3 is connected between the switching element S2 and the negative electrode of the DC power supply E1 to constitute a current detection unit. Then, the voltage at the connection point P2 between the switching element S2 and the resistor R3 is output as the detected value of the LED current I1 when the switching element S2 is on.

  The control circuit A13 includes a main control circuit 10, a boost control circuit 11, and a step-down control circuit 12.

  As shown in FIG. 6, the boost control circuit 11 includes a PWM control unit 11a and a switch drive circuit 11d. The PWM control unit 11a includes an error amplifier 11b and a reference voltage generation circuit 11c. The reference voltage generation circuit 11c generates a sawtooth voltage. The error amplifier 11b compares the voltage at the connection point P1 (the detected value of the boosted voltage V2) with the sawtooth voltage generated by the reference voltage generation circuit 11c, and compares the H level and the L level according to the comparison result. A PWM signal that repeats alternately is output. The PWM signal is a signal that determines the on-duty of the switching element S1, and the switch drive circuit 11d drives the switching element S1 on and off based on the PWM signal. For example, when the boost voltage V2 increases, the boost control circuit 11 performs control so as to reduce the on-duty of the switching element S1.

  As shown in FIG. 7, the step-down control circuit 12 includes a PWM control unit 12a and a switch drive circuit 12d. The PWM control unit 12a includes an error amplifier 12b and a reference voltage generation circuit 12c. The reference voltage generation circuit 12c generates a sawtooth voltage. The error amplifier 12b compares the voltage at the connection point P2 (the detected value of the LED current I1) with the sawtooth voltage generated by the reference voltage generation circuit 12c, and compares the H level and the L level according to the comparison result. A PWM signal that repeats alternately is output. The PWM signal is a signal that determines the on-duty of the switching element S2, and the switch drive circuit 12d drives the switching element S2 on and off based on the PWM signal. For example, when the LED current I1 increases, the step-down control circuit 12 performs control so as to reduce the on-duty of the switching element S2.

  As shown in FIG. 8, the main control circuit 10 includes a control power supply circuit 10a, a delay circuit 10b, and switch elements 10c and 10d. The control power supply circuit 10a generates a control power supply from the input voltage V1, and uses this control power supply as an operation power supply for each part of the control circuit A13. The switch element 10c conducts / cuts off the control power supplied from the control power supply circuit 10a to the boost control circuit 11, and the switch element 10d conducts / cuts off the control power supplied from the control power supply circuit 10a to the step-down control circuit 12. To do. The delay circuit 10b determines the start timing and stop timing of each operation of the step-up control circuit 11 and step-down control circuit 12 by controlling the conduction / cutoff of the switch elements 10c and 10d.

  Then, when the input voltage V1 is input and the control power supply is generated, the delay circuit 10b conducts the switch element 10d and the switch element 10c in this order, thereby causing the control power supply in the order of the step-down control circuit 12 and the step-up control circuit 11. Supply. That is, when the input voltage V1 is turned on, the step-down operation of the step-down chopper circuit A12 and the step-up operation of the step-up chopper circuit A11 are started in this order.

  Further, when the input voltage V1 is cut off, the delay circuit 10b cuts off the switch element 10c and the switch element 10d in that order until the control power supply is lowered and becomes inoperable, thereby increasing the step-up control circuit 11 and the step-down control. The control power supply is shut off in the order of the circuit 12. That is, when the input voltage V1 is cut off, the step-up operation of the step-up chopper circuit A11 and the step-down operation of the step-down chopper circuit A12 are stopped in this order.

  9A to 9C show an example of the operation of the delay circuit 10b. When the input voltage V1 is input and the control power supply is generated, the delay circuit 10b first turns on the switch element 10d. The delay circuit 10b turns on the switch element 10c when the time T1 has elapsed after turning on the switch element 10d. That is, when the input voltage V1 is turned on, the step-up chopper circuit A11 starts operation after a time T1 from the start of the step-down chopper circuit A12.

(Embodiment 2)
The LED drive device according to the present embodiment uses a control circuit A13a shown in FIG. 10 instead of the control circuit A13 according to the first embodiment. The same components as those in the first embodiment are denoted by the same reference numerals and described. Is omitted.

  The control circuit A 13 a includes a PWM control circuit 13, switch drive circuits 14 and 15, a switch element 16, and a main control circuit 17. The PWM control circuit 13 includes error amplifiers 13a and 13b and a reference voltage generation circuit 13c.

  The reference voltage generation circuit 13c generates a sawtooth voltage. Then, the error amplifier 13a compares the voltage at the connection point P1 (detected value of the boosted voltage V2) with the sawtooth voltage generated by the reference voltage generation circuit 13c, and H level and L level according to the comparison result. A PWM signal that alternately repeats is output. The PWM signal is a signal that determines the on-duty of the switching element S1, and the switch drive circuit 14 drives the switching element S1 on and off based on the PWM signal.

  The error amplifier 13b compares the voltage at the connection point P2 (the detected value of the LED current I1) with the sawtooth voltage generated by the reference voltage generation circuit 13c, and compares the H level and the L level according to the comparison result. A PWM signal that repeats alternately is output. The PWM signal is a signal that determines the on-duty of the switching element S2, and the switch drive circuit 15 drives the switching element S2 on and off based on the PWM signal.

  A switch element 16 is inserted in a path through which the drive circuit 14 outputs a drive signal for the switching element S <b> 1, and the switch element 16 is controlled to be turned on and off by the main control circuit 17.

  When the input voltage V1 is input, the main control circuit 17 generates a control power supply and uses this control power supply as an operation power supply for each part of the control circuit A13a. When the input voltage V1 is turned on, the switching element 16 is maintained in the cut-off state, and the switching element S1 is not driven on / off (the off state is maintained), and only the switching element S2 is driven on / off. The main control circuit 17 turns on the switch element 16 and starts on / off driving of the switching element S1 when a predetermined time has elapsed since the generation of the control power supply is started. That is, when the input voltage V1 is turned on, the step-down operation of the step-down chopper circuit A12 and the step-up operation of the step-up chopper circuit A11 are started in this order.

  Further, when the input voltage V1 is interrupted, the main control circuit 17 stops the on / off driving of the switching element S1 by interrupting the switch element 16 until the control power supply is lowered and becomes inoperable. Thereafter, the control power supply further decreases, and the on / off driving of the switching element S2 is also stopped. That is, when the input voltage V1 is cut off, the step-up operation of the step-up chopper circuit A11 and the step-down operation of the step-down chopper circuit A12 are stopped in this order.

  Since the control circuit A13a of the present embodiment generates the PWM signal of the switching elements S1 and S2 using one reference voltage generation circuit 13c, the switching elements S1 and S2 are driven on and off at the same frequency. Therefore, the circuit configuration of the control circuit A13a can be simplified.

(Embodiment 3)
The LED drive device of this embodiment uses a step-down chopper circuit A12a shown in FIG. 11 in place of the step-down chopper circuit A12 of Embodiment 1, and the same reference numerals are given to the same configurations as those of Embodiment 1. Description is omitted.

  The step-down chopper circuit A12a includes a series circuit of a switching element S2a (second switching element) connected to the positive electrode of the capacitor C1 of the step-up chopper circuit A11 and an inductor L2a. The LED unit 3 is connected. Further, a regenerative diode D2a is connected in parallel to the series circuit of the inductor L2a and the LED unit 3. Then, the control circuit A13 drives the switching element S2a on and off to apply the output voltage V3 obtained by stepping down the boosted voltage V2 across the LED unit 3, thereby controlling the LED current I1 to the target current.

  Specifically, in the step-down chopper circuit A12a, when the switching element S2a is turned on, a current flows through a path of the capacitor C1-switching element S2a-inductor L2a-LED unit 3-capacitor C1. When the switching element S2a is turned off, the magnetic energy accumulated in the inductor L2a is released, and a current flows through the path of the inductor L2a-LED unit 3-diode D2a-inductor L2a. By repeating ON / OFF of the switching element S2a, the LED current I1 continuously flows through the LED unit 3, and the LED element Z1 emits light according to the LED current I1. The control circuit A13 performs PWM (Pulse Width Modulation) control of the on-duty of the switching element S2a so that the detected value of the LED current I1 matches a predetermined target current.

  FIG. 12 shows a configuration of a current detection unit that detects the LED current I1, and any one of the resistors R11 to R13 is used. The resistor R11 is interposed between the connection point between the LED unit 3 and the diode D2a and the negative electrode of the capacitor C1, and detects the LED current I1 when the switching element S2a is turned on (FIG. 13A). The resistor R12 is connected in series to the diode D2a, and detects the LED current I1 when the switching element S2a is off (FIG. 13B). The resistor R13 is connected in series to the LED unit 3, and detects the LED current I1 when the switching element S2a is on and off (FIG. 13 (c)). Note that which of the resistors R11 to R13 is used may be selected depending on a load or a control method.

  In the step-down chopper circuit A12a of the present embodiment, the switching element S2a is provided on the high voltage side, and one end (cathode side) of the LED unit 3 is connected to the negative electrode of the DC power supply E1. Therefore, when the negative electrode of the DC power supply E1 is grounded to a heat radiation fin (not shown) provided for heat dissipation of the LED element Z1, there is no need to consider the insulation of the LED element Z1, and there is a merit in terms of structure.

  In the present embodiment, the same effect can be obtained even when the control circuit A13a of the second embodiment is used.

  Moreover, the illuminating device of Embodiment 1 can be comprised by hold | maintaining the illuminating device provided with LED drive device A1 and LED unit 3 of Embodiment 1-3 to the fixture main body.

A1 LED drive device A11 Boost chopper circuit (Boost circuit)
A12 Step-down chopper circuit (Step-down circuit)
A13 Control circuit E1 DC power supply 3 LED unit (LED light source)
Z1 LED element

Claims (7)

An LED driving device for supplying DC power to an LED light source composed of one or more LED elements,
A step-up circuit that outputs a second DC voltage obtained by stepping up a first DC voltage of a DC power supply; a step-down circuit that outputs a third DC voltage obtained by stepping down the second DC voltage to the LED light source; and the step-up circuit A control circuit for controlling the step-up operation of the circuit and the step-down operation of the step-down circuit,
The LED driving device, wherein when the first DC voltage is input, the control circuit starts a step-down operation of the step-down circuit and a step-up operation of the step-up circuit.   2. The LED driving device according to claim 1, wherein when the first DC voltage is interrupted, the control circuit stops the step-up operation of the step-up circuit and the step-down operation of the step-down circuit in order. A voltage detection unit that detects the second DC voltage; and a current detection unit that detects a current flowing through the LED light source;
The control circuit includes:
Controlling the step-up operation of the step-up circuit based on the detected value of the second DC voltage, controlling the step-down operation of the step-down circuit based on the detected value of the current flowing through the LED light source,
When the first DC voltage is applied, the first DC voltage is cut off for a first time from the start of the step-down operation of the step-down circuit to the start of the step-up operation of the step-up circuit. 3. The LED driving device according to claim 2, wherein the LED drive device is longer than a second time from when the step-up operation of the step-up circuit is stopped to when the step-down operation of the step-down circuit is stopped. The booster circuit includes a first switching element, and generates the second DC voltage by turning on and off the first switching element.
The step-down circuit has a second switching element, and generates the third DC voltage by turning on and off the second switching element.
4. The LED driving device according to claim 1, wherein the control circuit drives each of the first and second switching elements on and off at the same frequency. 5. When the boosting operation of the booster circuit is stopped, the second DC voltage is substantially equal to the first DC voltage,
The control circuit, when the first DC voltage is lower than the second DC voltage, causes the boost circuit to perform a boost operation, and when the first DC voltage is higher than the second DC voltage, The LED driving device according to claim 1, wherein the boosting operation of the boosting circuit is stopped. An LED driving device according to any one of claims 1 to 5,
An illumination device comprising: an LED light source composed of one or more LED elements driven by the LED driving device.   7. A lighting fixture comprising: the lighting device according to claim 6; and a fixture main body that holds the lighting device.

Images