JP2013110060A - 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 simplifying the circuit configuration.SOLUTION: An LED driving device A1 includes: a boosting chopper circuit A11 that turns on/off a switching element S1 to output a step-up voltage V2 which is a stepped up input voltage V1 from a DC power supply E1; a step-down chopper circuit A12 that turns on/off a switching element S2 to output an output voltage V3, which is a stepped down step-up voltage V2, to an LED unit 3; and a control circuit A13 that drives the switching elements S1 and S2 to turn on/off to control the step-up operation of the boosting chopper circuit A11 and the step-down operation of the step-down chopper circuit A12. One end of each of the switching elements S1 and S2 is connected to the negative electrode of the DC power supply E1.

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. 10 shows an example of a conventional LED driving device B1, which is configured by providing a step-down chopper circuit B12 subsequent to the step-up chopper circuit B11.

  In the boost chopper circuit B11, one end of the switching element S101 is connected to the low voltage side (low side) of the input voltage V101 supplied from the DC power supply E101. The switching element S101 is turned on / off to generate a boosted voltage V102 obtained by boosting the input voltage V101. In the step-down chopper circuit B12, the switching element S102 is inserted on the high voltage side (high side) of the boosted voltage V102, and the output voltage V103 obtained by stepping down the boosted voltage V102 by driving the switching element S102 on and off. Is output. The output voltage V103 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.

JP-A-62-18970 JP 2010-268590 A JP 2010-205778 A

  In the conventional LED driving device B1 shown in FIG. 10, the switching element S102 of the step-down chopper circuit B12 is interposed on the high voltage side of the step-up voltage V102. Therefore, when an FET (Field Effect Transistor) or the like is used as the switching element S102, it is necessary to generate a driving voltage for on / off driving by a charge pump circuit or the like, which complicates the circuit configuration and causes a component. This was a factor that increased the score and increased costs.

  The present invention has been made in view of the above-described reasons, and an object thereof is to provide an LED driving device, a lighting device, and a lighting fixture that are configured by a booster circuit and a step-down circuit and that can simplify the circuit configuration. is there.

  The LED drive device of the present invention is an LED drive device that supplies direct current power to an LED light source composed of one or more LED elements, and has a first switching element, and the first switching element is turned on. A step-up circuit that outputs a second DC voltage obtained by stepping up the first DC voltage of the DC power supply by turning off and a second switching element; and turning on / off the second switching element. By turning on and off the step-down circuit that outputs a third DC voltage obtained by stepping down the second DC voltage to the LED light source, the first switching element, and the second switching element, A control circuit for controlling the step-up operation of the step-up circuit and the step-down operation of the step-down circuit, wherein the first switching element and the second switching element are: One end of Les is characterized by connecting the negative electrode of the DC power source.

  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. Preferably, the first switching element is turned on / off, and the second switching element is turned on / off based on a detected value of a current flowing through the LED light source.

  In the present invention, the control circuit preferably drives each of the first and second switching elements on and off at the same frequency.

  In the present invention, the control circuit preferably drives each of the first and second switching elements on and off at different frequencies.

  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 circuit configuration can be simplified.

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. 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 circuit diagram which shows the structure of the switch drive circuit of a boost control circuit same as the above. It is a circuit diagram which shows the structure of the switch drive circuit of a pressure | voltage fall control circuit same as the above. FIG. 5 is a block diagram illustrating a configuration of a control circuit according to a second embodiment. (A)-(c) It is a wave form diagram which shows the waveform of each part same as the above. It is a block diagram which shows schematic structure of the conventional LED drive device.

  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 step-up chopper circuit A11 includes a switching element S1 (first switching element). By turning on / off the switching element S1, the input voltage V1 (first DC voltage) is increased to the step-up voltage V2 (second switching element). DC voltage). The step-down chopper circuit A12 includes a switching element S2 (second switching element), and steps down the boosted voltage V2 to the output voltage V3 (third DC voltage) by turning on and off the switching element S2. The control circuit A13 controls the step-up operation of the step-up chopper circuit A11 by driving the switching element S1 on and off, and controls the step-down operation of the step-down chopper circuit A12 by driving the switching element S2 on and off.

  And each one end of switching element S1, S2 is connected to the negative electrode of DC power supply E1, and is connected to the low voltage side (low side) of the input voltage V1. Therefore, when the FET (Field Effect Transistor) or the like is used for the switching elements S1 and S2, the control circuit A13 has a simple circuit configuration without using a charge pump circuit or the like for driving voltage for on / off driving. Can be generated. That is, the number of parts can be reduced and the cost can be reduced. Note that the low voltage sides of the input voltage V1 and the boosted voltage V2 are common potentials.

  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 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. Here, one end of the inductor L1 is connected to the positive electrode of the DC power supply E1, and one end of the switching element S1 is connected to the negative electrode of the DC power supply E1. The boosting control circuit 11 of the control circuit A13 generates a boosted voltage V2 obtained by boosting the input voltage V1 between both ends of the capacitor C1 by driving the switching element S1 on and off at a high frequency.

  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 having one end connected to the negative electrode of the capacitor C1, and between the other ends of the inductor L2 and the switching element S2, an LED is connected. Unit 3 is connected. Further, a regenerative diode D2 is connected in parallel to the series circuit of the inductor L2 and the LED unit 3. Then, the step-down control circuit 12 of the control circuit A13 applies the output voltage V3 obtained by stepping down the boosted voltage V2 between both ends of the LED unit 3 by driving the switching element S2 on and off at a high frequency to generate the LED current I1. Control to 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.

  Next, a specific circuit of the LED driving device A1 is shown in FIG. 3, 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.

  First, the main control circuit 10 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 to control the operation of each part.

  As shown in FIG. 4, the boost control circuit 11 includes an error amplifier 11a, a PWM control unit 11b, and a switch drive circuit 11e. The PWM control unit 11b includes an error amplifier 11c and a reference voltage generation circuit 11d. Is done. The error amplifier 11a amplifies and outputs an error between the voltage at the connection point P1 (detected value of the boosted voltage V2) and a preset reference voltage Vref1. The reference voltage generation circuit 11d generates a sawtooth voltage. The error amplifier 11c compares the output of the error amplifier 11a with the sawtooth voltage generated by the reference voltage generation circuit 11d, and outputs a PWM signal that alternately repeats the H level and the L level according to the comparison result. . The PWM signal is a signal that determines the on-duty of the switching element S1, and the switch drive circuit 11e 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. 5, the step-down control circuit 12 includes an error amplifier 12a, a PWM control unit 12b, and a switch drive circuit 12e. The PWM control unit 12b includes an error amplifier 12c and a reference voltage generation circuit 12d. . The error amplifier 12a amplifies and outputs an error between the voltage at the connection point P2 (the detected value of the LED current I1) and a preset reference voltage Vref2. The reference voltage generation circuit 12d generates a sawtooth voltage. The error amplifier 12c compares the output of the error amplifier 12a with the sawtooth voltage generated by the reference voltage generation circuit 12d, and outputs a PWM signal that alternately repeats the H level and the L level according to the comparison result. . The PWM signal is a signal that determines the on-duty of the switching element S2, and the switch drive circuit 12e 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.

  The drive frequency of the switching element S1 is determined by the oscillation frequency of the reference voltage generation circuit 11d, and the drive frequency of the switching element S2 is determined by the oscillation frequency of the reference voltage generation circuit 12d. Therefore, by setting the oscillation frequencies of the reference voltage generation circuits 11d and 12d to different frequencies, the switching elements S1 and S2 can be driven at different frequencies, and the power supplied to the LED unit 3 can be set in a wide range. Can be adjusted.

  Next, FIG. 6 shows a circuit configuration of the switch drive circuit 11e. The switch drive circuit 11e includes a series circuit of a PNP transistor Q11 and an NPN transistor Q12, and the collectors of the transistors Q11 and Q12 are connected to each other. The emitter of the transistor Q11 is connected to the control voltage Vc, and the emitter of the transistor Q12 is grounded. Further, the bases of the transistors Q11 and Q12 are connected to the output of the error amplifier 11c via a resistor R11. The switching element S1 is composed of an N-channel MOSFET, and the connection point between the transistors Q11 and Q12 is connected to the gate of the switching element S1 via the resistor R12.

  When the output of the error amplifier 11c is at L level, the transistor Q11 is turned on, the transistor Q12 is turned off, the control voltage Vc is applied to the gate of the switching element S1, and the switching element S1 is turned on. On the other hand, when the output of the error amplifier 11c is at the H level, the transistor Q11 is turned off, the transistor Q12 is turned on, the gate of the switching element S1 is grounded, and the switching element S1 is turned off.

  FIG. 7 shows a circuit configuration of the switch drive circuit 12e. The switch drive circuit 12e includes a series circuit of a PNP transistor Q21 and an NPN transistor Q22, and the collectors of the transistors Q21 and Q22 are connected to each other. The emitter of the transistor Q21 is connected to the control voltage Vc, and the emitter of the transistor Q22 is grounded. Further, the bases of the transistors Q21 and Q22 are connected to the output of the error amplifier 12c via a resistor R21. The switching element S2 is composed of an N-channel MOSFET, and the connection point between the transistors Q21 and Q22 is connected to the gate of the switching element S2 via the resistor R22.

  When the output of the error amplifier 12c is L level, the transistor Q21 is turned on, the transistor Q22 is turned off, the control voltage Vc is applied to the gate of the switching element S2, and the switching element S2 is turned on. On the other hand, when the output of the error amplifier 12c is H level, the transistor Q21 is turned off, the transistor Q22 is turned on, the gate of the switching element S2 is grounded, and the switching element S2 is turned off.

  As described above, the switch drive circuits 11e and 12e can be configured with a simple circuit without using a charge pump circuit or the like by connecting the switching elements S1 and S2 to the low voltage side, thereby reducing the number of components and reducing the cost. Can be realized. The resistor R3 has a low resistance of about several tens of mΩ, and one end (source) of the switching elements S1 and S2 can be regarded as being connected to a common potential.

  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. First, the main control circuit 10 can detect the boosted voltage V <b> 2 by detecting the voltage at the connection point P <b> 1 via the boost control circuit 11. Further, the main control circuit 10 receives the input voltage V1, and can detect the input voltage V1. The main control circuit 10 determines the magnitude relationship between the input voltage V1 and the boost voltage V2, and controls the operation of the boost control circuit 11 based on the determination result.

  Normally, the relationship is input voltage V1 <output voltage V3 <boosted voltage V2, and the main control circuit 10 drives the switching element S1 on and off by the boost control circuit 11 if the input voltage V1 <boosted voltage V2. Thus, the boosting operation of the boosting chopper circuit A11 is executed. However, when the input voltage V1 rises and the relationship of input voltage V1 ≧ boosted voltage V2 is established, the main control circuit 10 maintains the switching element S1 in the OFF state by the boosting control circuit 11, and performs the boosting operation of the boosting chopper circuit A11. Stop. The boosted voltage V2 output from the boost chopper circuit A11 that has stopped the boosting operation is equal to the input voltage V1 (or approximately equal to the input voltage V1).

  As described above, the input voltage V1 input to the boost chopper circuit A11 may become equal to or higher 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 equal to or higher than the boost 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 equal to or higher than the boost voltage V2 (target voltage), an unnecessary boost operation is not performed. Therefore, the LED unit 3 can be controlled while suppressing the withstand voltage performance required for each component. Such overcurrent stress can be suppressed.

(Embodiment 2)
The LED drive device of this embodiment uses a control circuit A13a shown in FIG. 8 in place of the control circuit A13 of Embodiment 1, and the same components as those in Embodiment 1 are denoted by the same reference numerals and described. Is omitted.

  The control circuit A13a includes error amplifiers 13 and 14, a PWM control circuit 15, and switch drive circuits 16 and 17. The PWM control circuit 15 includes error amplifiers 15a and 15b and a reference voltage generation circuit 15c.

  The error amplifier 13 amplifies and outputs an error between the voltage at the connection point P1 (detected value of the boosted voltage V2) and a preset reference voltage Vref3. The reference voltage generation circuit 15c generates a sawtooth voltage. Then, the error amplifier 15a compares the output of the error amplifier 13 with the sawtooth voltage generated by the reference voltage generation circuit 15c, and generates a PWM signal that alternately repeats the H level and the L level according to the comparison result. Output. The PWM signal is a signal that determines the on-duty of the switching element S1, and the switch drive circuit 16 drives the switching element S1 on and off based on the PWM signal.

  The error amplifier 14 amplifies and outputs an error between the voltage at the connection point P2 (detected value of the LED current I1) and a preset reference voltage Vref4. Then, the error amplifier 15b compares the output of the error amplifier 14 with the sawtooth voltage generated by the reference voltage generation circuit 15c, and generates a PWM signal that alternately repeats the H level and the L level according to the comparison result. Output. The PWM signal is a signal that determines the on-duty of the switching element S2, and the switch drive circuit 17 drives the switching element S2 on and off based on the PWM signal.

  Since the control circuit A13a of the present embodiment generates a PWM signal of the switching elements S1 and S2 using one reference voltage generation circuit 15c, 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. The oscillation frequency of the reference voltage generation circuit 15c is determined based on the specifications of the inductors L1 and L2, the capacitor C1, and the LED unit 3.

  Next, FIGS. 9A to 9C show waveforms of respective parts for driving the switching element S2 as the operation of the control circuit A13a.

  9A shows the output voltage Va of the error amplifier 14 and the sawtooth wave voltage Vb of the period T1 generated by the reference voltage generation circuit 15c. FIG. 9B shows the output voltage Vc (PWM of the error amplifier 15b. FIG. 9C shows the output voltage Vd of the switch drive circuit 17. Note that the switch drive circuit 17 has the same circuit configuration as the switch drive circuit 12e shown in FIG.

  The error amplifier 15b compares the output voltage Va of the error amplifier 14 with the sawtooth wave voltage Vb generated by the reference voltage generation circuit 15c, and is at the H level when Va> Vb and at the L level when Va <Vb. Output voltage Vc is output. The switch drive circuit 17 to which the output voltage Vc is input outputs an output voltage Vd obtained by inverting the output voltage Vc, and drives the switching element S2. Accordingly, the switching element S2 is turned on during the period Ton when the output voltage Va of the error amplifier 14 is lower than the sawtooth voltage Vb, and the switching element S2 during the period Toff when the output voltage Va of the error amplifier 14 is higher than the sawtooth voltage Vb. Turns off. That is, the higher the output voltage Va of the error amplifier 14, the shorter the on-time of the switching element S2, and the control is performed in the direction of reducing the LED current I1.

  If the same circuit configuration as the switch drive circuit 11e shown in FIG. 6 is used as the switch drive circuit 16, the waveforms of the respective parts for driving the switching element S1 are also shown in the same manner as described above.

  Moreover, the illuminating device of this invention can be comprised by hold | maintaining an illuminating device provided with LED drive device A1 and LED unit 3 of Embodiment 1, 2 to an instrument main body.

A1 LED drive device A11 Boost chopper circuit (Boost circuit)
A12 Step-down chopper circuit (Step-down circuit)
A13 Control circuit S1 Switching element (first switching element)
S2 switching element (second switching element)
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 boosting circuit that has a first switching element and outputs a second DC voltage obtained by boosting the first DC voltage of the DC power supply by turning on and off the first switching element;
A step-down circuit that has a second switching element and outputs a third DC voltage obtained by stepping down the second DC voltage to the LED light source by turning on and off the second switching element;
A control circuit that controls the step-up operation of the step-up circuit and the step-down operation of the step-down circuit by turning on and off the first switching element and the second switching element;
One end of each of the first switching element and the second switching element is connected to a negative electrode of the DC power supply. 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:
Driving the first switching element on / off based on the detected value of the second DC voltage, and driving the second switching element on / off based on the detected value of the current flowing through the LED light source; The LED driving device according to claim 1.   3. The LED driving device according to claim 1, wherein the control circuit drives the first and second switching elements on and off at the same frequency. 4.   3. The LED driving device according to claim 1, wherein the control circuit drives the first and second switching elements on and off at different frequencies. 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.

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