Power supply and lighting device

Abstract

Power supply device (1, 1a-g) which supplies a current to a solid-state luminous element (2), wherein the power supply device (1, 1a-g) comprises the following: a direct current-to-direct current converter, DC-DC converter (7, 10, 10c-e, 40); and an output detector (13, 13a, 13b) that detects an output from the DC-DC converter (7, 10, 10c-e, 40), wherein the DC-DC converter (7, 10, 10c-e, 40) includes the following: a switching element (16, 42); a control device (11, 11c-e) that switches the switching element (16, 42) on and off to generate the output; and a current detector (12) that detects a current flowing through the switching element (16, 42), and wherein, If the current value detected by the current detector (12) is below a predetermined threshold, the control unit (11, 11c-e) controls the switching element (16, 42) according to a duty cycle determined on the basis of an output value detected by the output detector (13, 13a, 13b), and if the current value is above the predetermined threshold, the control unit (11, 11c-e) controls the switching element (16, 42) according to a duty cycle below the duty cycle determined on the basis of the output value. characterized by the fact that: the control device (11, 11c-e) contains the following: a control circuit (52) that controls the switching element (16, 42); and a transistor (115, 314, 317, 321) connected to the control circuit (52), and If the current value exceeds the predetermined threshold, the control device (11, 11c-e) switches off the switching element (16, 42) by switching on the transistor (115, 314, 317, 321).

Description

[Invention area]

[0001] The present invention relates to a current supply device and a lighting device, and in particular to a current supply device which supplies a current to a solid-state luminous element, and to a lighting device which includes the current supply device. [General state of the art]

[0002] Various current supply devices have been proposed to supply current to solid-state luminous elements such as light-emitting diodes (LEDs) (see, for example, JP 2007 - 189 004 A).

[0003] From JP 2007-189004A, a current-converting device is known that includes a direct current-to-direct current (DC-DC) converter, which is a SEPIC (Single Ended Primary Inductance Converter). A SEPIC DC-DC converter performs a buck-boost operation. Furthermore, according to the SEPIC DC-DC converter, an inductor is connected to a commercial alternating current (AC) power source, and current flows through switching of a storage element throughout the entire cycle of the commercial AC power supply, thereby improving the power factor of the input current.

[0004] US 8,193,725 B2 discloses: A backlight module control system comprises several backlight submodules, a control signal output unit, a voltage converter, and several current regulators. The control signal output unit provides a voltage control signal, a current control signal, and several PWM signals. The voltage converter is connected to the control signal output unit and the backlight submodules and outputs a voltage to the submodules according to the voltage control signal. The current regulators are each connected to the backlight submodules and determine the current of the associated submodule based on the current control signal. Additionally, each current regulator uses the associated PWM signal to determine whether the associated submodule is activated.

[0005] DE 10 2010 037 684 A1 describes an open-loop dimming LED driver comprising: a full-wave rectifier circuit configured to receive an input voltage and provide a rectified voltage, wherein the input voltage is a phase-angle modulated AC voltage and is based on modulating a mains AC voltage, which has a normal operating range between a minimum voltage level and a maximum voltage level; a converter that converts the rectified voltage into an output voltage and an output current, wherein the output current has a magnitude that varies proportionally to a second power of the square mean of the input voltage; an oscillator circuit that controls switching of the converter at a frequency and with a duty cycle;and a maximum current control circuit that measures the output current and provides a current control signal indicating the output current; wherein the oscillator circuit includes a pulse-width modulation control circuit that receives the current control signal and controls either the frequency or the duty cycle to prevent the output current from exceeding the predetermined maximum current level; and the pulse-width modulation control circuit controls either the frequency or the duty cycle so that the predetermined maximum current level of the output current is maintained while the input voltage is at a level within the normal operating range of the mains AC voltage;wherein, if the input voltage for the dimming function is cut off and is below the minimum voltage level of the normal operating range, the dimming function with open control dominates, and if the input voltage reaches or exceeds the minimum voltage level, the output current remains constant at its predetermined maximum level, according to a current operation with closed control. [Brief description of the invention][Technical problem]

[0006] The switching control of a switching element contained in a DC-DC converter offers the advantage of simplifying a control circuit by switching on the switching element for each fixed period.

[0007] However, a current-energizing device disclosed in the aforementioned JP 2007-189004A has a problem in that a sudden change in the supply voltage of a commercial AC power supply leads to unstable operation if a switching element is turned on for each fixed period. In other words, if the supply voltage of a commercial AC power supply changes suddenly, an LC resonance occurs due to an inductor and a capacitor contained in a DC-DC converter, resulting in current oscillations. This slowly increases the current flowing through the switching element and damages it.

[0008] The present invention was conceived to solve such a problem and provides a power supply device which includes a DC-DC converter and prevents excessive current from flowing through a switching element contained in the DC-DC converter even when a voltage input to the DC-DC converter suddenly changes, and a lighting device which includes the power supply device.

[0009] Furthermore, the present invention provides a power supply device that includes a DC-DC converter which in turn switches on a switching element for each fixed period and operates stably even if an input AC power supply voltage suddenly changes, and a lighting device. [Solution to the problem]

[0010] To solve the above problem, the present invention relates to a power supply device according to claim 1 and a lighting device according to claim 7. Claims 2 to 6 describe particularly advantageous implementations of the power supply device according to claim 1. A power supply device according to one aspect of the present invention is a power supply device that supplies a current to a solid-state luminescent element, wherein the power supply device comprises: a direct current-to-direct current converter (DC-DC converter); and an output detector that detects an output from the DC-DC converter. The DC-DC converter comprises: a switching element; a control device that switches the switching element on and off to generate the output; and a current detector that detects a current flowing through the switching element.If the current detected by the current detector is below a predetermined threshold, the control unit operates the switching element according to a duty cycle determined based on an output value detected by the output detector. If the current value is above the predetermined threshold, the control unit operates the switching element according to a duty cycle below the one determined based on the output value.

[0011] Furthermore, a lighting device according to one aspect of the present invention includes the current supply device and a solid-state luminous element that receives a current supply from the current supply device. [Advantageous effects of the invention]

[0012] The present invention provides a power supply device that includes a DC-DC converter and prevents excessive current from flowing through a switching element contained in the DC-DC converter even when a voltage input into the DC-DC converter suddenly changes, and a lighting device that includes the power supply device. [Brief description of the drawings] Fig. 1 is a circuit diagram illustrating a configuration of a power supply device according to embodiment 1; Fig. Figure 2 is a circuit diagram illustrating a configuration of a feedback circuit according to embodiment 1; Fig. Figure 3 is a timing diagram that schematically illustrates the operation of the power supply device according to embodiment 1; Fig. Figure 4 is a circuit diagram illustrating a configuration of a power supply device according to a comparative example; Fig. Figure 5 is a timing diagram that schematically illustrates the operation of the power supply device according to the comparative example; Fig. Figure 6 is a circuit diagram illustrating a configuration of an overcurrent prevention circuit according to variant 1 of embodiment 1; Fig. Figure 7 is a circuit diagram illustrating a configuration of an overcurrent prevention circuit according to variant 2 of embodiment 1; Fig. Figure 8 is a circuit diagram illustrating a configuration of a power supply device according to variant 3 of embodiment 1; Fig. Figure 9 is a circuit diagram illustrating a configuration of a constant current circuit according to variant 3 of embodiment 1; Fig. Figure 10 is a circuit diagram illustrating a configuration of a power supply device according to variant 4 of embodiment 1; Fig. 11 is a circuit diagram illustrating a configuration of a power supply device according to embodiment 2; Fig. 12 is a circuit diagram illustrating a configuration of a feedback circuit according to embodiment 2; Fig. 13 is a circuit diagram illustrating a configuration of a power supply device according to embodiment 3; Fig. 14 is a circuit diagram illustrating a configuration of a feedback circuit according to embodiment 3; Fig. 15 is a timing diagram that schematically illustrates the operation of the power supply device according to embodiment 3; Fig. 16 is a circuit diagram illustrating a configuration of a power supply device according to embodiment 4; Fig. Figure 17 is a circuit diagram illustrating a configuration of an overcurrent prevention circuit according to embodiment 4; Fig. 18 is a timing diagram that schematically illustrates the operation of the power supply device according to embodiment 4; Fig. 19 is a circuit diagram illustrating a power supply device according to embodiment 5; Fig. Figure 20 is a timing diagram illustrating the stable operation of the power supply device according to embodiment 5; Fig. Figure 21 illustrates an example of a waveform of a current input into the current supply device according to embodiment 5; Fig. Figure 22 is a timing diagram illustrating the operation of a conventional power supply device. Fig. 23 is a timing diagram illustrating the operation of the power supply device according to embodiment 5; Fig. Figure 24 illustrates waveforms of currents and voltages at different sections of a circuit of the current supply device according to embodiment 5; Fig. Figure 25 is a timing diagram illustrating a power supply device according to variant 1 of embodiment 5; Fig. Figure 26 is a timing diagram illustrating the operation of the power supply device according to variant 1 of embodiment 5; Fig. Figure 27 is a timing diagram illustrating the operation of a power supply device according to variant 2 of embodiment 5; Fig. Figure 28 illustrates a waveform of a current flowing through a diode in variant 2 of embodiment 5; Fig. 29 is an external view of a lighting device according to embodiment 6; Fig. Figure 30 is an exterior view of a lighting device according to embodiment 6; and Fig. Figure 31 is an external view of a lighting device according to embodiment 6. [Description of the embodiments]

[0013] The following describes embodiments of the present invention with reference to the drawings. Each of the embodiments described below shows a specific example. The numerical values, shapes, materials, elements, the arrangement and connection of the elements, and other features shown in the following embodiments are merely examples and are therefore not intended to limit the present invention. Therefore, among the elements in the following embodiments, those elements not included in any of the independent claims that define the most generic part of the present invention are described as arbitrary.

[0014] Note that the drawings are schematic diagrams and do not necessarily provide a strictly accurate representation. Furthermore, essentially the same configurations in the drawings have been assigned the same numbers, and any overlapping descriptions have been omitted or simplified. [Execution form 1][1-1. Configuration]

[0015] First, a configuration of a power supply device according to embodiment 1 is described with reference to the drawings.

[0016] Fig. Figure 1 is a circuit diagram illustrating a configuration of the power supply device 1 according to the present embodiment. Note that Fig. Figure 1 illustrates an AC power supply 3, a filter circuit 4, a diode bridge 31 and a light-emitting diode (LED) 2 together with the power supply device 1.

[0017] AC power supply 3 outputs an alternating voltage. AC power supply 3 is not particularly limited as long as it outputs an alternating voltage. AC power supply 3 is a system power supply, such as a commercial power supply.

[0018] The filter circuit 4 is a filter to block high-frequency noise generated by a switching operation of the power supply device 1 from reaching the AC power supply 3. In the present embodiment, the filter circuit 4 includes a capacitor 430 connected between the output terminals of the AC power supply 3 and inductors 410 and 420 connected to the output terminals of the AC power supply 3.

[0019] The diode bridge 31 is a circuit that converts an input AC voltage into a DC voltage and outputs the DC voltage. In the present embodiment, the diode bridge 31 converts an AC voltage input from the AC power supply 3 into a DC voltage via the filter circuit 4 and outputs the DC voltage to the power supply unit 1. In the present embodiment, the diode bridge 31 does contain a diode bridge, but the diode bridge 31 is not particularly limited as long as the diode bridge is a circuit that converts an AC voltage into a DC voltage.

[0020] The current supply device 1 outputs a current to a solid-state light source. In the present embodiment, the LED 2 is used as a solid-state light source. As in Fig. As shown in Figure 1, the power supply unit 1 includes a DC-DC converter 10 and an output detector 13. The following describes elements of the power supply unit 1.

[0021] The output detector 13 detects an output from the DC-DC converter 10. In the present embodiment, the output detector 13 includes a resistor 131 and detects an output current from the DC-DC converter 10. The output detector 13 inputs a voltage applied across the resistor 131 into the control circuit 11 of the DC-DC converter 10. An output current from the DC-DC converter 10 flows through the resistor 131, and thus a voltage applied across the resistor 131 can be used as a signal corresponding to an output value from the DC-DC converter 10 (i.e., a current value output by it). Accordingly, the resistor 131 is used as a sensing resistor to detect an output current from the DC-DC converter 10.

[0022] The DC-DC converter 10 is a circuit that converts a DC voltage input by the diode bridge 31 and outputs the resulting voltage. The DC-DC converter 10 includes a switching element 16, a control device 11, and a current detector 12. In the present embodiment, the DC-DC converter 10 further includes capacitors 14 and 17, inductors 15 and 18, a diode 19, and an electrolytic capacitor 20. The DC-DC converter 10 is a SEPIC converter, which is a type of buck-boost converter that increases or decreases an input voltage based on the characteristic curve of the LED 2, which is a load of the power supply 1. The capacitor 14 is connected between two output terminals of the diode bridge 31. The inductor 15 has one terminal connected to a high potential output terminal of the diode bridge 31 and another terminal connected to the drain electrode of the switching element 16.Capacitor 17 has one terminal connected to the drain electrode of switching element 16 and another terminal connected to a terminal of inductor 18. Inductor 18 has one terminal connected to the other terminal of capacitor 17 and another grounded terminal. Diode 19 has an anode connected to one terminal of inductor 18 and a cathode connected to a high-potential output terminal of power supply 1. Electrolytic capacitor 20 has a positive electrode connected to the high-potential output terminal of power supply 1 and a grounded negative electrode.

[0023] The switching element 16 switches on and off based on signals output by the control device 11 (i.e., repeatedly). In the present embodiment, the switching element 16 includes an n-channel metal-oxide-semiconductor field-effect transistor (MOSFET).

[0024] The control unit 11 switches the switching element 16 on and off. The control unit 11 controls the switching element 16 according to a duty cycle (OnDuty) determined based on an output value detected by the output detector 13 if a current value detected by the current detector 12 is below a predetermined threshold Ith. If the current value is above the threshold Ith, the control unit 11 controls the switching element 16 according to a duty cycle that is lower than the duty cycle based on the output value. The threshold Ith can be less than or equal to an absolute maximum rated current of the switching element 16. This prevents a current exceeding the absolute maximum rated current from flowing through the switching element 16.Furthermore, the threshold value Ith can be greater than or equal to a peak value of a current flowing through the switching element 16 if a nominal voltage of the power supply unit 1 is stably applied to the power supply unit 1. In this way, the control unit 11 controls the switching element 16 at a fixed frequency and for a fixed on-time during stable operation, thereby achieving a greater effect of improving the power factor of the power supply unit 1. The control unit 11 switches the switching element 16 on and off by outputting control signals to the gate electrode of the switching element 16. In the following embodiment, the control unit 11 includes a feedback circuit 110, an overcurrent protection circuit 111, and a drive circuit 112.

[0025] The control circuit 112 controls the switching element 16. The control circuit 112 has an input terminal connected to the terminals of resistors 113 and 114 and the collector electrode of transistor 115, and an output terminal connected to the gate electrode of switching element 16. The control circuit 112 amplifies an input signal and outputs the resulting signal as a control signal to the gate electrode of switching element 16. In this way, the control circuit 112 controls the switching element 16.

[0026] The feedback circuit 110 regulates an output current from the DC-DC converter 10 (i.e., a current output by the power supply 1) to a predetermined value. In the present embodiment, the feedback circuit 110 has a terminal FB, into which a signal from the output detector 13 is input, and a terminal OUT, through which signals for switching the switching element 16 on and off are output. The feedback circuit 110 outputs signals for switching the switching element 16 on and off from the terminal OUT to the control circuit 112, thereby switching the switching element 16 on and off according to a duty cycle determined on the basis of an output value detected by the output detector 13. The following describes a configuration of the feedback circuit 110 with reference to Fig. 2.

[0027] Fig. Figure 2 is a circuit diagram illustrating a configuration of the feedback circuit 110 according to the present embodiment.

[0028] As in Fig. As shown in Figure 2, the feedback circuit 110 contains a triangle wave generator circuit 211, an error amplifier 212, a capacitor 213 and a comparator 214.

[0029] The triangle wave generator circuit 211 is a circuit that outputs triangle waveform signals (i.e., a circuit that repeatedly outputs a ramp signal in a predetermined cycle). One cycle of such triangle waveform signals corresponds to one switching period of the switching element 16. An output signal from the triangle wave generator circuit 211 is fed into the inverting input terminal of the comparator 214.

[0030] The error amplifier 212 is a circuit that amplifies the error between a reference voltage Vref and the voltage of a signal input to terminal FB from the output detector 13 and outputs the amplified error. A signal from the output detector 13, input to terminal FB, is fed into the inverting input terminal of the error amplifier 212, and the reference voltage Vref is fed into the non-inverting input terminal of the error amplifier 212. The reference voltage Vref corresponds to a target value of an output current from the DC-DC converter 10 (i.e., an output current from the power supply 1). The error amplifier 212 amplifies the error between the reference voltage Vref and the voltage of a signal from the output detector 13 corresponding to an output current from the DC-DC converter 10 and outputs the amplified error to the non-inverting input terminal of the comparator 214.The error amplifier 212 increases an output voltage if the voltage of a signal input from terminal FB is below the reference voltage Vref, whereas if the voltage of a signal input from terminal FB is above the reference voltage Vref, the error amplifier 212 decreases an output voltage.

[0031] Capacitor 213 is used to smooth the output voltage of error amplifier 212. In the present embodiment, capacitor 213 has one terminal connected to the output terminal of error amplifier 212 and the non-inverting input terminal of comparator 214, and another grounded terminal. Capacitor 213 reduces, for example, noise components in an output signal from error amplifier 212 and also compensates for phase in a control loop of feedback circuit 110. Note that an impedance circuit, which is a combination of a capacitor and a resistor, can be used instead of capacitor 213, for example.

[0032] The comparator 214 is a circuit that compares an output signal from the triangle wave generator circuit 211 with an output signal from the error amplifier 212 and outputs a pulse width modulation (PWM) signal. An output signal from the triangle wave generator circuit 211 is input to the inverting input terminal of the comparator 214, and an output signal from the error amplifier 212 is input to the non-inverting input terminal of the comparator 214. An output signal from the comparator 214 is output to the OUT terminal of the feedback circuit 110.

[0033] Note that the feedback circuit 110, which has the configuration described above, may include an integrated circuit (IC).

[0034] The overcurrent prevention circuit 111 is a circuit that prevents excessive current from flowing through the switching element 16. As shown in Fig. As shown in Figure 1, the overcurrent prevention circuit contains 111 resistors 113, 114, 117 and 118, a transistor 115 and a capacitor 116.

[0035] Resistors 117 and 118 and capacitor 116 are components of an RC filter circuit. A signal from current detector 12 is fed into the base electrode of transistor 115 via the RC filter circuit.

[0036] Resistor 113 is a component used to prevent excessive current from flowing from the OUT terminal of feedback circuit 110. Resistor 113 has one terminal connected to the OUT terminal of feedback circuit 110 and another terminal connected to the input terminal of drive circuit 112 and to a terminal of resistor 114. When transistor 115 is switched on, the OUT terminal of feedback circuit 110 is grounded via resistor 113 instead of being directly grounded. This prevents excessive current from flowing from the OUT terminal of feedback circuit 110, which would otherwise occur if the OUT terminal were directly grounded.

[0037] Resistor 114, together with resistor 113, divides the voltage of an output signal from the OUT terminal of the feedback circuit 110. Resistor 114 has one terminal connected to the other terminal of resistor 113 and the input terminal of the control circuit 112, and another terminal that is grounded. Resistors 113 and 114 divide the voltage of an output signal from the OUT terminal and can thus input a desired voltage into the control circuit 112.

[0038] Transistor 115 is connected to the control circuit 112 and is controlled based on a signal from the current detector 12. In the present embodiment, transistor 115 is an npn bipolar transistor (negative-positive-negative). A signal from the current detector 12 is applied to the base electrode of transistor 115, the collector electrode of transistor 115 is connected to the input terminal of the control circuit 112, and the emitter electrode of transistor 115 is grounded. Transistor 115 is switched on if a current flowing through the switching element 16 exceeds a predetermined threshold value Ith, or in other words, if the voltage of a signal from the current detector 12 exceeds a voltage corresponding to the threshold value Ith.Since the input terminal of the control circuit 112 is grounded in this case, the voltage of an input signal from the control circuit 112 is reduced to zero, and the voltage of an output signal from the control circuit 112 is also reduced to zero. Accordingly, the voltage applied to the gate electrode of the switching element 16 is reduced to zero, and thus the switching element 16 is switched off. As a result, any current flowing through the switching element 16 also becomes zero. [1-2. Operation]

[0039] The following describes the operation of the power supply device 1 according to the present embodiment with reference to the drawings.

[0040] Fig. 3 is a timing diagram that schematically illustrates the operation of the power supply device 1 according to the present embodiment. The short (a) in Fig. Figure 3 illustrates a waveform of a voltage VC1 applied to a capacitor 14 of the power supply unit 1. The curve (b) in Fig. Figure 3 illustrates a waveform of the output signal (OUT) from the OUT terminal of the feedback circuit 110. The curve (c) in Fig. Figure 3 illustrates a waveform of a current ISW flowing through the switching element 16. The curve (d) in Fig. Figure 3 illustrates a waveform showing the state of transistor 115. The curve (e) in Fig. Figure 3 illustrates a waveform showing the state of switching element 16.

[0041] As in curve (a) in Fig. As shown in Figure 3, abnormal operation can occur in the power supply unit 1 instead of stable operation. During stable operation, the AC power supply 3 operates normally and the voltage VC1 is essentially constant (see the waveform up to time t14 in Figure 3). Fig. 3) In contrast, the voltage VC1 shows an abnormal increase (see the waveform after time t15 in Fig. 3) during abnormal operation, for example due to an anomaly in the AC power supply.

[0042] Abnormal operation occurs when an input voltage to the power supply unit 1 is unstable, for example, due to a sudden change in the output voltage of the AC power supply 3, an on / off switching operation of a power switch in the power supply unit 1, or a poor contact of the power switch. If an input voltage to the power supply unit 1 is unstable, resonance in an LC circuit in the power supply unit 1 generates a voltage higher than the input voltage in the DC-DC converter 10. When diode 19 conducts, the resonance occurs in an LC circuit containing inductor 15 and capacitors 14, 17, and 20; when diode 19 does not conduct, the resonance occurs in an LC circuit containing inductors 15 and 18 and capacitors 14 and 17.If, in particular, a voltage higher than the input voltage is generated in capacitor 14, the waveform of the current ISW flowing through the switching element 16 exhibits a steep rise, and thus a current greater than that flowing during stable operation flows through the switching element 16. This current, greater than that flowing during stable operation, flows through inductors 15 and 18, potentially saturating their cores and thus potentially resulting in an even higher current. The switching element 16 is subjected to stress from the aforementioned excessive current flowing through it. Furthermore, the switching element 16 can be damaged if the value of such an excessive current exceeds its absolute maximum rating.

[0043] In stable operation, a signal with a cycle determined by the triangle wave generator circuit 211 of the feedback circuit 110 and a duty cycle determined by the feedback circuit 110 based on an output value detected by the output detector 13 is output from the OUT terminal of the feedback circuit 110 (see curve (b) in Fig. 3).

[0044] A signal output from the OUT terminal of the feedback circuit 110 is amplified by the control circuit 112, and the amplified signal is fed into the gate electrode of the switching element 16. The switching element 16 is held in the on state for one period during which an output signal from the OUT terminal is at a high level (see curve (e) in Fig. 3) In the Fig. In the example shown, the switching period T of switching element 16 is one period from time t11 to time t13, for example. Furthermore, one tone period of switching element 16 is one period from time t11 to time t12, for example. Accordingly, the duty cycle of switching element 16 during stable operation is expressed as tone / T.

[0045] A current flowing through the switching element 16 when the switching element is held in the on state for time t is expressed by the following expression 1, where L1 denotes an inductance of the inductor 15. ISW=VC1×t / L1

[0046] According to expression 1 shown above, a peak value ISW_p of a current flowing through switching element 16 is expressed by VC1 × Ton / L1, where Ton denotes the on-period of switching element 16. During stable operation, the voltage VC1 applied to capacitor 14, or in other words, the voltage input to the power supply 1, is less than or equal to the rated voltage of the power supply 1, and thus ISW_p, which is the peak value, does not exceed the threshold value Ith. Accordingly, transistor 115 of overcurrent protection circuit 111 is held in the off state (see curve (d) in Fig. 3).

[0047] In the abnormal operating state, the voltage VC1 rises abnormally, as shown in curve (a) in Fig. 3 shown, Accordingly, as shown in curve (c) in Fig. Figure 3 shows the current ISW flowing through switching element 16 during the on-period of switching element 16 (time t15 to t16 and time t17 to t18 in Fig. 3) a steeper rise than the rise during stable operation. Accordingly, a peak value ISW_p of the current ISW is also greater than the peak value ISW_p during stable operation. If, furthermore, the voltage VC1 is above the nominal voltage of the power supply device 1, the current ISW may exceed the threshold value Ith. In the curve (c) in Fig. In the example shown, the current ISW exceeds the threshold value Ith at time t18. This switches on transistor 115 of the overcurrent protection circuit 111 (see curve (d) in Fig. 3), and thus the input terminal of the control circuit 112 is grounded and the voltage of an output signal from the control circuit 112 reaches zero. Accordingly, the switching element 16 is switched off (see curve (e) in Fig. 3) As a result, the current flowing through switching element 16 reaches zero. In other words, the on-period of switching element 16 is shortened from the one-period Tone during stable operation to the one-period Ton' between time t17 and time t18. Accordingly, the duty cycle of switching element 16 is expressed as Ton' / T, which is lower than the duty cycle during stable operation. The current-control device 1 can prevent an excessive current from flowing through switching element 16 by means of the above operation. [1-3. Comparative example]

[0048] The following describes the configuration and operation of a current-sensing device that does not include the current detector 12 and the overcurrent prevention circuit 111 according to the present embodiment, with reference to the drawings, in order to facilitate the understanding of advantageous effects achieved by the current-sensing device 1 according to the present embodiment.

[0049] Fig. Figure 4 is a circuit diagram illustrating the configuration of a power supply unit 500 according to a comparative example.

[0050] As in Fig. As shown in Figure 4, the power supply unit 500 according to the comparative example includes a DC-DC converter 90 and the output detector 13. The DC-DC converter 90 includes a control unit 91. The power supply unit 500 differs from the power supply unit 1 according to the present embodiment in that the DC-DC converter 90 does not include the current detector 12 and the overcurrent prevention circuit 111, and is otherwise the same as the power supply unit 1. Thus, in the power supply unit 500, the switching element 16 is controlled at all times according to a switching period and a duty cycle determined by the feedback circuit 110.

[0051] The following describes the operation of the power supply unit 500 with reference to Fig. 5.

[0052] Fig. Figure 5 is a timing diagram that schematically illustrates the operation of the power supply unit 500 according to the comparative example. The curve (a) in Fig. Figure 5 illustrates a waveform of the voltage VC1 applied to the capacitor 14 of the power supply unit 500. The curve (b) in Fig. Figure 5 illustrates a waveform of an output signal (OUT) from the OUT terminal of the feedback circuit 110. The curve (c) in Fig. Figure 5 illustrates a waveform of the current ISW flowing through the switching element 16. The curve (d) in Fig. Figure 5 illustrates a waveform of the current ID flowing through diode 19.

[0053] As shown in curves (a) and (b) in Fig. As shown in Figure 5, the waveforms of the voltage VC1 and a signal from terminal OUT are the same as those of the present embodiment, according to the comparative example. However, the waveform of the current ISW differs from that of the current ISW in the present embodiment. The current supply device 500 does not include the overcurrent prevention circuit 111, and thus, during abnormal operation, the current ISW increases with the voltage VC1 and is not limited, as shown in curves (a) and (c) in Figure 5. Fig. 5 shown. In addition, the in Fig. In the example shown, current ID is also associated with current ISW and does not reach zero during the off-period of switching element 16 after time t24. Specifically, after time t24, the power supply device 500 operates in continuous current mode (CCM). Accordingly, current ISW is not zero when the on-period of switching element 16 begins (for example, at times t25, t27, and t29). Fig. 5), and thus the peak value of the current ISW continues to increase. As described above, the current-energizing device 500 according to the comparative example does not include the current detector 12 and the overcurrent prevention circuit 111, and thus an excessive current can flow through the switching element 16 during abnormal operation. In contrast, the current-energizing device 1 according to the present embodiment includes the current detector 12 and the overcurrent prevention circuit 111 and thus prevents an excessive current from flowing through the switching element 16, as in Fig. 3 shown. [1-4. Beneficial Effects and Others]

[0054] The power supply unit 1 according to the present embodiment comprises the DC-DC converter 10 and the output detector 13, which detects an output from the DC-DC converter 10, as described above. The DC-DC converter 10 comprises the switching element 16, the control unit 11, which switches the switching element 16 on and off to generate the output, and the current detector 12, which detects a current flowing through the switching element 16. If the current value of a current detected by the current detector 12 is below a predetermined threshold, the control unit 11 controls the switching element 16 according to a duty cycle determined based on an output value detected by the output detector 13. If a current value is above the threshold, the control unit 11 controls the switching element 16 according to a duty cycle that is lower than the duty cycle determined based on the output value.

[0055] Even if a voltage input into the DC-DC converter 10 of the power supply unit 1 suddenly changes, the power supply unit 1 can accordingly prevent an excessive current from flowing through the switching element 16 contained in the DC-DC converter 10.

[0056] Furthermore, in the current supply device 1 according to the present embodiment, the DC-DC converter 10 increases or decreases an input voltage based on the characteristic curve of the LED 2 and outputs the increased or decreased input voltage.

[0057] Accordingly, the current-generating device 1 can increase and decrease a voltage, thereby extending the dynamic range of an output voltage. This allows the current-generating device 1 to operate LEDs 2 with a wide range of forward voltages. Furthermore, the power factor of the current-generating device 1 can be improved.

[0058] In the power supply device 1 according to the present embodiment, the DC-DC converter 10 can be a SEPIC converter.

[0059] In the current supply device 1 according to the present embodiment, a threshold value is less than or equal to the absolute maximum rated current of the switching element 16 and is greater than or equal to a current flowing through the switching element 16 when a rated voltage of the current supply device 1 is stably applied to the current supply device 1.

[0060] This prevents a current exceeding the absolute maximum rated current from flowing through the switching element 16. Accordingly, damage to the switching element due to excessive current is prevented. Furthermore, the switching element 16 is controlled at a fixed frequency and for a fixed on-time during stable operation, thereby achieving improved power factor effects of the power supply device 1.

[0061] If, according to the present embodiment, a current value in the power supply device 1 exceeds the threshold value, the control device 11 can make the on-period of the switching element 16 shorter than the on-period for when a current value is below the threshold value.

[0062] Furthermore, in the current supply device 1 according to the present embodiment, the control device 11 can switch off the switching element 16 if a current value is greater than the threshold value.

[0063] Furthermore, in the current supply device 1 according to the present embodiment, the control device 11 can include the control circuit 112, which controls the switching element 16, and the transistor 115 connected to the control circuit 112, and if the current value is greater than the predetermined threshold value, the control device 11 can switch off the switching element 16 by switching on the transistor 115. [Variant 1 of embodiment 1]

[0064] The following describes a current-sensing device according to variant 1 of the embodiment 1 described above. In the current-sensing device 1 according to the embodiment 1 described above, the switching element 16 can be switched off immediately if a current ISW flowing through the switching element 16 exceeds the threshold value Ith, in order to prevent damage to the switching element 16 due to an excessive current flow. Accordingly, in the overcurrent prevention circuit 111 of the current-sensing device 1 according to the embodiment 1 described above, an RC filter containing the capacitor 116 and the resistors 117 and 118 can have a small time constant. If the time constant of the RC filter is comparatively small, the current ISW exceeds the threshold value Ith and the switching element 16 is switched off, and thereafter a voltage applied to the base electrode of the transistor 115 drops for a comparatively short time.Transistor 115 is switched off again due to a drop in the voltage applied to its base electrode. When transistor 115 is switched off, if a high-level signal is output from the OUT terminal of the feedback circuit 110, the switching element 16 is switched on again. In this way, the switching element 16 can be repeatedly switched on and off while a high-level signal is output from the OUT terminal during the period specified. This variant describes a current-sensing device that includes an overcurrent protection circuit which prevents the occurrence of the above phenomenon by keeping the switching element 16 in the off state for a fixed period of time.Note that the power supply device according to this variant differs from the power supply device 1 according to the embodiment 1 described above in the configuration of the overcurrent prevention circuit, but is otherwise the same as power supply device 1. Therefore, the description given here focuses on the overcurrent prevention circuit of the power supply device according to this variant.

[0065] Fig. Figure 6 is a circuit diagram illustrating a configuration of the overcurrent prevention circuit 111a according to this variant. Fig. Figure 6 illustrates not only the overcurrent prevention circuit 111a but also peripheral elements such as the switching element 16.

[0066] As in Fig. As shown in Figure 6, the overcurrent prevention circuit 111a differs from the overcurrent prevention circuit 111 according to the embodiment 1 described above by the configuration of the RC filter and is otherwise the same as the overcurrent prevention circuit 111. In particular, the RC filter in the overcurrent prevention circuit 111a according to this variant includes the capacitor 116, the resistors 117, 118a and 118b and the diode 119.

[0067] The RC filter of the overcurrent protection circuit 111a has the configuration described above. Therefore, if the current ISW flowing through the switching element 16 exceeds the threshold value Ith, the anode electrode of diode 119 has a potential higher than that of the cathode electrode, thus bringing diode 119 into a conducting state. In this case, an electrical charge is accumulated in capacitor 116 via the junction between switching element 16 and resistor 121 through resistors 118a and 118b, which are connected in parallel. Then, transistor 115 is switched on if the potential of a high-potential terminal of capacitor 116, or in other words, the potential of the base electrode of transistor 115, exceeds a predetermined potential.

[0068] If switching element 16 is switched off by switching on transistor 115, the current flowing through resistor 121 becomes zero, and the potential at the junction between switching element 16 and resistor 121—or, in other words, the potential of the anode electrode of diode 119—reaches zero. In this case, the potential of the cathode electrode of diode 119 decreases over a time constant determined by capacitor 116. The potential of the anode electrode of diode 119 becomes lower than the potential of the cathode electrode, thus bringing diode 119 into the non-conducting state. Here, resistor 121 has a small resistance value, which can be ignored compared to the resistance value of resistor 118a. Therefore, the electrical charge accumulated in capacitor 116 can be considered to flow to ground via resistor 118a and resistor 117, which are connected in parallel.Here, the resistance value of resistor 117 is increased above the resistance value of resistor 118b, thereby increasing the combined resistance value of the parallel-connected resistors 118a and 117 above the combined resistance value of resistors 118a and 118b. Accordingly, the time constant of the RC filter for when an electrical charge is discharged from capacitor 116 can be increased above the time constant of the RC filter for when an electrical charge is accumulated in capacitor 116. This achieves an overcurrent prevention circuit 111a, with which the time from when the current ISW is less than the threshold value Ith until transistor 115 is switched off is longer than the time from when the current ISW exceeds the threshold value Ith until transistor 115 is switched on.As described above, in the overcurrent prevention circuit 111a, according to this variant, the switching element 16 can be kept in the off state for a fixed time period after the current ISW exceeds the threshold Ith. [Variant 2 of embodiment 1]

[0069] The following describes a current-energizing device according to variant 2 of embodiment 1. According to the current-energizing device 1 of embodiment 1 described above, the threshold value Ith of the current ISW flowing through the switching element 16 is a value corresponding to the base voltage at which transistor 115 is switched on, yet the threshold value Ith may not be a value corresponding to the base voltage. This variant describes a current-energizing device according to which the threshold value Ith is a given value independent of the characteristic curve of transistor 115. Note that the current-energizing device according to this variant differs from the current-energizing device 1 of embodiment 1 described above in the configuration of the overcurrent prevention circuit and is otherwise the same as current-energizing device 1.Therefore, the following description focuses on an overcurrent prevention circuit for the power supply device according to this variant.

[0070] Fig. Figure 7 is a circuit diagram illustrating a configuration of the overcurrent prevention circuit 111b according to this variant. Fig. Figure 7 illustrates not only the overcurrent prevention circuit 111b but also peripheral elements such as the switching element 16.

[0071] As in Fig. As shown in Figure 7, the overcurrent protection circuit 111b differs from the overcurrent protection circuit 111 according to embodiment 1 described above in that it includes a comparator 120, and is otherwise identical to the overcurrent protection circuit 111. In the overcurrent protection circuit 111b, a high-potential terminal of the capacitor 116 is connected to the non-inverting input terminal of the comparator 120. The comparator 120 compares a voltage at the high-potential terminal of the capacitor 116 with the reference voltage Vref1 applied to the inverting input terminal of the comparator 120, and the output from the comparator 120 is applied to the base electrode of the transistor 115.

[0072] According to the configuration above, the overcurrent protection circuit 111b switches off the switching element 16 by switching on the transistor 115 when a voltage corresponding to a current flowing through the switching element 16 exceeds the reference voltage Vref1. In other words, the threshold Ith in the overcurrent protection circuit 111b can be set to a value corresponding to the reference voltage Vref1, which is independent of the characteristic curve of the transistor 115. Furthermore, the above configuration of the overcurrent protection circuit 111b reduces variations in the threshold Ith due to temperature dependence and individual differences in the characteristic curve of the transistor 115.

[0073] Note that although this variant has described a configuration using a comparator as an example of a configuration where a value other than the base voltage at which transistor 115 is turned on is used as a threshold, the configuration of the overcurrent prevention circuit is not limited to this. For example, a MOSFET threshold voltage can be used as a threshold instead of transistor 115. [Variant 3 of embodiment 1]

[0074] The following describes a current supply device according to variant 3 of embodiment 1. This variant describes a current supply device that further stabilizes an output current from the DC-DC converter 10 by including a constant current circuit downstream of the DC-DC converter 10 of the current supply device 1 according to embodiment 1 described above.

[0075] Fig. Figure 8 is a circuit diagram illustrating a configuration of the power supply device 1a according to this variant.

[0076] Fig. Figure 9 is a circuit diagram illustrating a configuration of the constant current circuit 6 according to this variant.

[0077] As in Fig. As shown in Figure 8, the current-energizing device 1a according to this variant contains an output detector 13a, which includes a constant current circuit 6, instead of the output detector 13, which includes the resistor 131 of the current-energizing device 1 according to the embodiment 1 described above. Accordingly, a potential difference between the terminals of the constant current circuit 6 is input into the terminal FB of the feedback circuit 110. As shown in Fig. As shown in Figure 9, the constant current circuit 6 comprises the comparator 61, resistors 62 and 64, the switching element 63, and the capacitor 65. A reference voltage Vref2 is applied to the non-inverting input terminal of the comparator 61, while a voltage applied across resistor 64 is applied to the inverting input terminal of the comparator 61. Here, resistor 64 is a sensing resistor for detecting an output current from the DC-DC converter 10. The output terminal of the comparator 61 is connected to the gate electrode of the switching element 63, which contains a MOSFET. Furthermore, the output terminal and the inverting input terminal of the comparator 61 are connected via resistor 62.Capacitor 65 is connected between the input and output terminals of the constant current circuit 6, thereby smoothing the voltage applied to the constant current circuit 6, or in other words, the current flowing through resistor 64. The above configuration of the constant current circuit 6 allows the switching element 63 to be controlled such that the voltage applied to resistor 64 is equal to the reference voltage Vref2. Accordingly, the constant current circuit 6 further stabilizes an output current from the DC-DC converter 10, or in other words, an output current from the power supply 1. In particular, the constant current circuit 6 reduces the ripple contained in a DC voltage input to the power supply 1, which has a frequency twice that of the AC power supply 3. [Variant 4 of embodiment 1]

[0078] The following describes a current supply device according to variant 4 of embodiment 1. This variant describes a current supply device that further stabilizes an output current from the DC-DC converter 10 by further including another DC-DC converter downstream of the DC-DC converter 10 of the current supply device 1 according to embodiment 1 described above.

[0079] Fig. Figure 10 is a circuit diagram illustrating a configuration of the power supply device 1b according to this variant.

[0080] As in Fig. As shown in Figure 10, a further DC-DC converter 7 is connected downstream of the DC-DC converter 10 in the power supply unit 1b according to this variant. In addition, an output detector 13b in the power supply unit 1b detects an input voltage into the DC-DC converter 7, or in other words, an output voltage from the DC-DC converter 10, in order to stabilize an input voltage into the DC-DC converter 7.

[0081] The output detector 13b contains resistors 132 and 133, and the resistors 132 and 133 divide an output voltage from the DC-DC converter 10. The output detector 13b outputs the divided voltage as a detected value to the terminal FB of the feedback circuit 110.

[0082] The DC-DC converter 7 is a circuit into which an output voltage from the DC-DC converter 10 is input, and which outputs a current to a solid-state light source. Any of a variety of DC-DC converter types can be used as a suitable DC-DC converter 7. For example, a reverse converter can be used.

[0083] As described above, in this variant of the power supply unit 1b, another DC-DC converter 7 is connected downstream of the DC-DC converter 10. Accordingly, the downstream DC-DC converter 7 prevents a drop in the output current to a solid-state light source, even if the output voltage from the DC-DC converter 10 temporarily decreases, for example, due to a brief power outage. Therefore, the power supply unit 1b can further stabilize the output current to a solid-state light source.

[0084] Furthermore, any of a variety of DC-DC converter types can be used as DC-DC converter 7 in the power supply unit 1b, and DC-DC converters 7 and 10 can be controlled individually. This increases the flexibility of the control of the power supply unit 1b. [Version 2]

[0085] The following describes a current-sensing device according to embodiment 2. The current-sensing device 1 according to embodiment 1 described above has a configuration in which, if an excessive current flows through the switching element 16, the overcurrent prevention circuit 111 prevents a signal output from the OUT terminal of the feedback circuit 110 from being input into the control circuit 112. In the present embodiment, instead of such a configuration, a configuration is used in which a signal output from the OUT terminal of the feedback circuit 110 is dropped if an excessive current flows through the switching element 16. In particular, the configuration used is intended to shorten the on-period of the switching element 16 determined by the feedback circuit 110 if an excessive current flows through the switching element 16.The power supply device according to the present embodiment differs from the power supply device according to embodiment 1 described above in the configurations of the overcurrent prevention circuit and the feedback circuit, and is otherwise the same as the power supply device 1 according to embodiment 1 described above. Thus, the following mainly describes the overcurrent prevention circuit and the feedback circuit of the power supply device according to the present embodiment. [2-1. Configuration]

[0086] First, a configuration of the power supply device according to the present embodiment is described with reference to the drawings.

[0087] Fig. Figure 11 is a circuit diagram illustrating a configuration of a power supply device 1c according to the present embodiment.

[0088] Fig. Figure 12 is a circuit diagram illustrating a configuration of a feedback circuit 110c according to the present embodiment.

[0089] As in Fig. As shown in Figure 11, the DC-DC converter 10c according to the present embodiment includes the feedback circuit 110c in the control unit 11c. As shown in Fig. As shown in Figure 12, the feedback circuit 110c in the present embodiment includes an overcurrent prevention circuit 111c.

[0090] The feedback circuit 110c has a CS terminal in addition to the FB and OUT terminals. A voltage corresponding to the current ISW flowing through the switching element 16 and detected by the current detector 12 is applied to the CS terminal. The voltage applied to the CS terminal is then applied to the overcurrent protection circuit 111c.

[0091] As in Fig. As shown in Figure 12, the overcurrent prevention circuit 111c contains resistors 117, 118 and 215, capacitor 116 and transistor 115.

[0092] The resistor 215 is a component to prevent excessive current from flowing from the output terminal of the error amplifier 212 when the transistor 115 is switched on. [2-2. Operation]

[0093] The above configuration of the power supply device 1c allows an electrical charge accumulated in capacitor 213 to flow to ground via a path through resistor 215 and transistor 115 when the current ISW flowing through switching element 16 exceeds the threshold value Ith. Accordingly, an output voltage from the error amplifier 212, or in other words, an input voltage to the non-inverting input terminal of comparator 214, temporarily drops. This shortens one period during which a signal output from terminal OUT of feedback circuit 110 has a high voltage, thereby shortening one period of the switching element 16's tone. In this way, if the current ISW exceeds the threshold value Ith, the one-period tone of switching element 16 is shortened. Thus, the peak value ISW_p of the current ISW does not rise excessively, and damage to switching element 16 is avoided. [2-3. Beneficial Effects and Others]

[0094] If, as described above, a current value in the current supply device 1c according to the present embodiment is above the threshold value, the control device 11c makes the on-period of the switching element 16 shorter than the on-period for when a current value is less than the threshold value.

[0095] In this way, even if a voltage input into the DC-DC converter 10c of the power supply unit 1c suddenly changes, an excessive current is prevented from flowing through the switching element 16 contained in the DC-DC converter 10c. [Version 3]

[0096] The following describes a current-energizing device according to embodiment 3. In the embodiments above, the one-period tone of the switching element 16 is shortened when the current ISW flowing through the switching element 16 exceeds the threshold Ith, whereas in the present embodiment, a switching period is lengthened (i.e., the switching frequency is reduced) without changing the one-period tone. A current-energizing device according to the present embodiment differs from the current-energizing device 1c according to embodiment 2 described above in the configuration of the feedback circuit and is otherwise the same as current-energizing device 1c; thus, the following mainly describes the configuration and operation of the feedback circuit of the current-energizing device according to the present embodiment. [3-1. Configuration]

[0097] First, the configuration of the power supply device according to the present embodiment is described with reference to the drawings.

[0098] Fig. Figure 13 is a circuit diagram illustrating a configuration of the power supply device 1d according to the present embodiment.

[0099] Fig. Figure 14 is a circuit diagram illustrating a configuration of the feedback circuit 110d according to the present embodiment.

[0100] As in Fig. As shown in Figure 13, the DC-DC converter 10d according to the present embodiment includes the feedback circuit 110d in the control unit 11d.

[0101] The feedback circuit 110d does not include an overcurrent prevention circuit, as described in Fig. Figure 14 shows the feedback circuit 110d containing a triangle wave generator circuit 211d, and a signal input from terminal CS is fed into the triangle wave generator circuit 211d.

[0102] The triangle wave generator circuit 211d detects that the current ISW flowing through the switching element 16 exceeds the threshold Ith, according to a signal input from terminal CS. In this case, the triangle wave generator circuit 211d extends the switching period of the switching element 16 by lengthening one cycle of an output signal. Furthermore, the triangle wave generator circuit 211d adjusts the rise time of an output signal so that one period of tone from the switching element 16 when the current ISW does not exceed the threshold Ith is essentially the same as one period of tone when the current ISW does exceed the threshold Ith. The above configuration of the triangle wave generator circuit 211d allows the feedback circuit 110c to reduce the duty cycle of the switching element 16 below the duty cycle when the current ISW is below the threshold Ith.This prevents excessive current from flowing through the switching element 16. [3-2. Operation]

[0103] The following describes the operation of the power supply device 1d according to the present embodiment with reference to the drawings.

[0104] Fig. Figure 15 is a timing diagram that schematically illustrates the operation of the power supply device 1d according to the present embodiment. The curve (a) in Fig. Figure 15 illustrates a waveform of the voltage VC1 applied to the capacitor 14 of the power supply unit 1d. The curve (b) in Fig. Figure 15 illustrates a waveform of an output signal (OUT) from the OUT terminal of the feedback circuit 110d. The curve (c) in Fig. Figure 15 illustrates a waveform of the current ISW flowing through the switching element 16. The curve (d) in Fig. Figure 15 illustrates a waveform of a current ID flowing through diode 19. The curve (e) in Fig. Figure 15 illustrates a waveform that indicates the state of the switching element 16.

[0105] As in curve (a) in Fig. As shown in Figure 15, the occurrence of abnormal operation in the power supply unit 1d abnormally increases the voltage VC1 and consequently the current ISW flowing through the switching element 16 can exceed the threshold value Ith (see time t36 in Figure 15). Fig. 15), as in embodiment 1 described above. In this case, a voltage corresponding to the current ISW is applied to terminal CS of the feedback circuit 110d. The voltage applied to terminal CS is applied to the triangular wave generator circuit 211d. If the triangular wave generator circuit 211d detects, based on the applied voltage, that the current ISW is too high, the voltage is then applied to the feedback circuit 110d. Fig. At time t36, as shown in Figure 15, when the threshold Ith has been exceeded, the triangle wave generator circuit 211d is configured to extend one cycle of an output signal by a predetermined period, thus extending one switching period of the switching element 16. Furthermore, the triangle wave generator circuit 211d is configured to adjust the rise of an output signal such that the one-period tone of the switching element 16, when the current ISW does not exceed the threshold Ith, is essentially the same as the one-period tone when the current ISW does exceed the threshold Ith. As shown in curve (e) in Fig. As shown in Figure 15, this does not change the one-period tone of the switching element 16 when the current ISW exceeds the threshold Ith, but rather lengthens a switching period (i.e., reduces a switching frequency). Accordingly, when the current ISW exceeds the threshold Ith, a duty cycle is reduced below the duty cycle when the current ISW does not exceed the threshold Ith, thereby achieving a current-limiting device 1d that can prevent an excessive current from flowing through the switching element 16 (see curve (c) in Figure 15). Fig. 15) Note that a period during which the triangular wave generator circuit 211d continues to output a signal in an extended cycle can be determined according to the characteristic curve of the current-energizing device 1d, the cycle, and other factors deemed appropriate. For example, the period may be essentially equivalent to several cycles during which the triangular wave generator circuit 211d outputs signals. [3-3. Advantageous Effects and Others]

[0106] If, as described above, a current value is greater than the threshold value, the control device 11d in the current supply device 1d according to the present embodiment reduces a switching frequency of the switching element 16 below a switching frequency for when a current value is below the threshold value.

[0107] In this way, even if a voltage input into the DC-DC converter 10d of the power supply device 1d suddenly changes, it can be prevented that an excessive current flows through the switching element 16 contained in the DC-DC converter 10d. [Version 4]

[0108] The following describes a current-energizing device 1e according to embodiment 4. In the present embodiment, if the current ISW flowing through the switching element 16 exceeds the threshold value Ith, the duty cycle of the switching element 16 is reduced compared to the duty cycle used when the current ISW does not exceed the threshold value Ith, as in the embodiments above. The present embodiment uses a configuration in which the switching element 16 is not switched on during the subsequent on-period of the switching element 16 if the current ISW exceeds the threshold value Ith. The current-energizing device according to the present embodiment differs from the current-energizing device 1 according to embodiment 1 described above in the configuration of the overcurrent prevention circuit and is otherwise identical to current-energizing device 1.Thus, the following mainly describes the configuration and operation of the overcurrent prevention circuit of the power supply device according to the present embodiment. [4-1. Configuration]

[0109] First, the configuration of the power supply device according to the present embodiment is described with reference to the drawings.

[0110] Fig. Figure 16 is a circuit diagram illustrating a configuration of the power supply device 1e according to the present embodiment.

[0111] Fig. Figure 17 is a circuit diagram illustrating a configuration of an overcurrent prevention circuit 111e according to the present embodiment.

[0112] As in Fig. As shown in Figure 16, the DC-DC converter 10e according to the present embodiment includes the overcurrent prevention circuit 111e in the control unit 11e.

[0113] As in Fig. As shown in Figure 17, the overcurrent prevention circuit 111e contains the terminals PIN, POUT, CS and GND, the resistors 311, 313, 315, 316, 318, 319, 322 and 323, the capacitors 312 and 320 and the transistors 314, 317 and 321.

[0114] The PIN connection is a connection into which a signal for switching the switching element 16 on and off is input from the OUT connection of the feedback circuit 110.

[0115] The POUT terminal is a terminal that outputs a signal generated by the overcurrent protection circuit 111e to the control circuit 112. The signal generated by the overcurrent protection circuit 111e is a signal for controlling the switching element 16 to prevent excessive current from flowing through it.

[0116] The CS terminal is a terminal into which a signal with a voltage corresponding to the current ISW flowing through the switching element 16 is input.

[0117] The GND connection is a grounded connection.

[0118] Resistors 311 and 313 and capacitor 312 are components of an RC filter. A signal from current detector 12 is fed through the RC filter to the base electrode of transistor 314.

[0119] Transistor 314 is a control element based on an output signal from current detector 12. In the present embodiment, transistor 314 is an npn-type bipolar transistor. Transistor 314 has a base electrode connected to terminal CS via the RC filter, a collector electrode connected to the base electrode of transistor 317, and a grounded emitter electrode. Transistor 314 is switched on when a current ISW flowing through switching element 16 exceeds the threshold value Ith.

[0120] Resistors 315 and 316 are used to divide the voltage V0. Note that the voltage V0 is a constant voltage used to apply a voltage, for example, to the gate electrode of transistor 321. Resistor 315 has one terminal to which the voltage V0 is applied, and another terminal connected to one terminal of resistor 316 and the collector electrode of transistor 314. The other terminal of resistor 316 is grounded. The junction between resistors 315 and 316 is connected to the base electrode of transistor 317. When transistor 314 is in the off state, a voltage obtained by resistors 315 and 316 dividing the voltage V0 is applied to the base electrode of transistor 317.

[0121] Transistor 317 is a device that switches on and off according to the state of transistor 314. In the present embodiment, transistor 317 is an npn-type bipolar transistor. Transistor 317 has a base electrode connected to the collector electrode of transistor 314 and the junction between resistors 315 and 316, a collector electrode connected to the base electrode of transistor 321, and a grounded emitter electrode. Transistor 317 is switched on when transistor 314 is in the off state, or in other words, when the current ISW flowing through switching element 16 does not exceed the threshold value Ith, and is switched off when the current ISW exceeds the threshold value Ith.

[0122] Resistors 318 and 319 are used to divide the voltage V0. Resistor 318 has one terminal to which the voltage V0 is applied, and another terminal connected to one terminal of resistor 319 and the collector of transistor 317. The other terminal of resistor 319 is grounded. The junction between resistors 318 and 319 is connected to one terminal of capacitor 320 and the base of transistor 321. Therefore, a voltage obtained by resistors 315 and 316 dividing the voltage V0 is applied to the base of transistor 317 when transistor 314 is off.

[0123] Capacitor 320 is a component included in an RC filter along with resistors 318 and 319. Capacitor 320 has one terminal connected to the junction between resistors 318 and 319, and another terminal that is grounded.

[0124] Transistor 321 is a device that switches on and off according to the state of transistor 317. In the present embodiment, transistor 321 is an npn-type bipolar transistor. Transistor 321 has a base electrode connected to the collector electrode of transistor 317, the junction between resistors 318 and 319, and a terminal of capacitor 320; a collector electrode connected to terminal POUT; and an emitter electrode that is grounded. Transistor 321 is switched on when transistor 317 is in the off state, or in other words, when the current ISW flowing through switching element 16 exceeds the threshold value Ith, and is switched off when the current ISW does not exceed the threshold value Ith.

[0125] Resistors 322 and 323 divide a voltage input at the PIN terminal and output the divided voltage to the POUT terminal. Resistor 322 has one terminal connected to the PIN terminal and another connected to one terminal of resistor 323. The other terminal of resistor 323 is grounded. The junction between resistors 322 and 323 is connected to the collector of transistor 321 and to the POUT terminal. Resistor 322 also acts as a limiter to prevent excessive current from flowing from the OUT terminal of feedback circuit 110 when transistor 321 is switched on. [4-2. Operation]

[0126] The following describes the operation of the power supply device 1e according to the present embodiment with reference to the drawings.

[0127] Fig. Figure 18 is a timing diagram that schematically illustrates the operation of the power supply device 1e according to the present embodiment. The curve (a) in Fig. Figure 18 illustrates a waveform of the voltage VC1 applied to the capacitor 14 of the power supply unit 1e. The curve (b) in Fig. Figure 18 illustrates a waveform of an output signal (OUT) from the OUT terminal of the feedback circuit 110. The curve (c) in Fig. Figure 18 illustrates a waveform of the current ISW flowing through the switching element 16. The curve (d) in Fig. Figure 18 illustrates a waveform of a current ID flowing through diode 19. The curve (e) in Fig. Figure 18 illustrates a waveform indicating the state of transistor 321. The curve (f) in Fig. Figure 18 illustrates a waveform that indicates the state of the switching element 16.

[0128] As in curve (a) in Fig. As shown in Figure 18, there are cases where the power supply unit 1e is in a stable operating state and cases where the power supply unit 1e is in an abnormal operating state and the voltage VC1 rises abnormally (see time t43 in Figure 18). Fig. 18 and thereafter), as in embodiment 1 described above.

[0129] In any case, a voltage corresponding to the current ISW is applied to terminal CS of the overcurrent protection circuit 111e. The voltage applied to terminal CS is fed into transistor 314 via the RC filter, which contains resistors 311 and 313 and capacitor 312.

[0130] In stable operation, the current ISW does not exceed the threshold value Ith, transistors 314 and 321 are kept in the off state, and transistor 317 is kept in the on state. Accordingly, the voltage of a signal output from the PIN terminal is split by resistors 322 and 323 and output to POUT. Thus, switching element 16 is controlled based on a signal output from the OUT terminal of the feedback circuit 110.

[0131] If an abnormal operating condition occurs and the current ISW exceeds the threshold Ith, transistor 314 is switched on after a time corresponding to the time constant of the RC filter. Consequently, the base electrode of transistor 317 is grounded, thus switching transistor 317 off. In this way, a voltage obtained through resistors 318 and 319, which divide the voltage V0, is applied to the base electrode of transistor 321. The resulting divided voltage is adjusted to a voltage greater than or equal to a threshold voltage to switch transistor 321 on. Accordingly, transistor 321 is switched on after a time corresponding to the time constant of the RC filter, which, for example, contains capacitor 320. Consequently, the POUT terminal is grounded, and thus the input voltage to the drive circuit 112 becomes zero. In this way, switching element 16 is switched off.

[0132] Switching element 16 is switched off, and consequently, the voltage of a signal input to terminal CS drops to zero. In contrast to the case where the current ISW exceeds the threshold Ith, transistor 314 is switched off, and transistor 317 is switched on after one period according to the time constant of the RC filter, which in this case includes, for example, capacitor 312. Transistor 321 is switched off after one period according to the time constant of the RC filter, which includes, for example, capacitor 320, because transistor 317 is switched on. Accordingly, switching element 16 is maintained for a predetermined period according to the time constants of the RC filters included in the overcurrent prevention circuit 111e, starting from when switching element 16 is switched off due to the current ISW exceeding the threshold Ith.In the present embodiment, RC filters are used where the predetermined time period is greater than or equal to a switching period. Thus, in the current-energizing device 1e according to the present embodiment, the switching element 16 is not switched on for at least one switching period of the switching element 16 if the current ISW exceeds the threshold value Ith. If the current ISW exceeds the threshold value Ith, the switching element 16 is correspondingly not switched on in the subsequent on-period. Accordingly, the duty cycle of the switching element 16 is reduced, and thus an excessive current flowing through the switching element 16 is prevented. [4-3. Advantageous Effects and Others]

[0133] As described above, the control device 11e in the current supply device 1e according to the present embodiment does not switch on the switching element 16 during the switching period of the switching element 16 if a current value exceeds the threshold value.

[0134] Even if a voltage input into the DC-DC converter 10e of the power supply unit 1e suddenly changes, an excessive current is prevented from flowing through the switching element 16 contained in the DC-DC converter 10e. [Version 5]

[0135] Fig. Figure 19 is a circuit diagram illustrating the power supply device 1f according to embodiment 5. The power supply device 1f is a constant current circuit connected to the AC power supply 3 and supplies current to the solid-state luminescent element 2. The power supply device 1f includes a rectifier circuit 30, a DC-DC converter 40, the periodic signal generator circuit 51, the drive circuit 52, the single-signal generator circuit 53, the zero-crossing detector circuit 54, and the current detector circuit 55.

[0136] The AC power supply 3 is a power supply that delivers AC power to the power supply device 1f, and is a commercial AC power supply, as an example.

[0137] The solid-state luminescent element 2 is an element that emits light in response to a current supplied by the current-supplying device 1f and is, for example, a light-emitting diode (LED) or an organic electroluminescent element (EL element).

[0138] The rectifier circuit 30 rectifies AC power from the AC power supply 3 and in the present embodiment includes a diode bridge 31 for rectification and a capacitor 32 for smoothing.

[0139] The DC-DC converter 40 is a circuit that increases or decreases a DC voltage from the rectifier circuit 30 and converts the resulting voltage into a DC voltage applied to the solid-state luminescent element 2. In the present embodiment, the DC-DC converter 40 is a SEPIC DC-DC converter and includes inductors 41 and 44, the switching element 42, capacitors 43 and 46, and the diode 45. The inductors 41 and 44 form a primary winding and a secondary winding of a transformer, respectively. The capacitor 43 is a coupling capacitor that connects the two inductors 41 and 44 in series. The switching element 42 chops a DC current from the rectifier circuit 30 by repeatedly switching it on and off and, in the present embodiment, is an N-channel metal-oxide-semiconductor field-effect transistor (N-MOSFET). The diode 45 is a rectifier element that rectifies AC into a direct current as a result of the chopping by the switching element 42.Capacitor 46 is a smoothing capacitor that smooths a pulsating current (and a ripple voltage) resulting from rectification by diode 45 into a direct current (and a direct voltage) for application to the solid-state luminescent element 2. A basic operation of the DC-DC converter 40 with such a configuration consists of chopping a direct current from the rectifier circuit 30 by repeatedly switching the switching element 42 on and off, and then rectifying the resulting current in the diode 45.

[0140] The periodic signal generator circuit 51 generates a periodic signal indicating the arrival of a fixed period and outputs the periodic signal to a single-signal generator circuit 53. For example, the periodic signal generator circuit 51 includes a clock generator and a frequency divider and outputs a pulse that rises as a periodic signal at each fixed period. Here, a fixed period is a predetermined period (switching period) to ensure that a current flowing through the diode 45 reliably reaches zero within one cyclic period when a power supply voltage is stable (a change in the AC voltage supplied by the AC power supply 3 is within a certain range).In other words, a fixed period is determined such that the DC-DC converter 40 operates in discontinuous current mode (DCM) or boundary current mode (BCM) when a power supply voltage is stable.

[0141] The zero-crossing detector circuit 54 detects that a current flowing through the diode 45 has reached zero (zero crossing) during the off-period of the switching element 42 and outputs a signal (zero-crossing signal) to the on-signal generator circuit 53, indicating the time at which a value has crossed zero. In the present embodiment, the zero-crossing detector circuit 54 includes, for example, a comparator that detects a voltage across the inductor 44 (detects, for example, that a voltage at the junction between the inductor 44 and the diode 45 has changed from a positive voltage to zero).

[0142] The current detector circuit 55 detects an output current from the current supply device 1f, or in other words, a current flowing through the solid-state luminescent element 2, and outputs the detected current as a feedback signal (FB) to the single-signal generator circuit 53. In the present embodiment, the current detector circuit 55 includes a resistor connected in series with the solid-state luminescent element 2.

[0143] The single-signal generator circuit 53 generates a single signal indicating a single period of the switching element 42 and outputs the generated single signal to the control circuit 52. The single-signal generator circuit 53 includes, for example, non-volatile memory in which a program is stored, a processor that executes the program to perform the functions described herein, volatile memory, and an analog-to-digital converter. The single-signal generator circuit 53 generates a single signal that essentially causes a single period to start and continue for one period, in the fixed period indicated by a periodic signal output by the periodic signal generator circuit 51, during which the average of a current detected by the current detector circuit 55 reaches a target current value.Here, an average current value is, for example, the average value of a current over a predetermined number of cycles, indicated by a periodic signal output from the periodic signal generator circuit 51. A target current value is a predetermined current value, such as an output current from the current supply device 1f or a current value determined by an externally provided dimming indicator.

[0144] The single-signal generator circuit 53 performs the following control as a distinctive control during the off-period of the switching element 42. In other words, if the zero-crossing detector circuit 54 has not detected a zero crossing at a time when the periodic signal from the periodic signal generator circuit 51 indicates the arrival of a fixed period, the single-signal generator circuit 53 waits at least until a zero crossing is detected and then generates an on signal. This is intended to prevent the switching element 42 from being switched on before the zero crossing is detected if a power supply voltage from the AC power supply 3 changes suddenly. In other words, this is intended to prevent the DC-DC converter 40 from operating in continuous current mode (CCM) if a power supply voltage from the AC power supply 3 changes suddenly.

[0145] More precisely, in the present embodiment, the one-signal generator circuit 53 performs the following control during the off-period of the switching element 42. In other words, if the zero-crossing detector circuit 54 has not detected a zero crossing at a time when a periodic signal indicates the arrival of a fixed period, the one-signal generator circuit 53 generates an on-signal at least after a zero crossing has been detected and at a time when a periodic signal indicates the arrival of a fixed period. In short, the one-signal generator circuit 53 skips generating an on-signal until the zero crossing is detected.

[0146] The control circuit 52 generates a control signal to switch on the switching element 42 (i.e., a control signal) according to the time indicated by the input signal generated by the input-signal generator circuit 53 and outputs the control signal to the switching element 42. The control circuit 52 is, for example, a buffer amplifier.

[0147] The following describes the operation of the power supply device 1f according to the present embodiment with the configuration as described above. Here, the operation when the power supply is stable (a state where any change in the AC voltage supplied by the AC power supply 3 is within a fixed range) and when the power supply voltage changes suddenly (when any change in the AC voltage supplied by the AC power supply 3 is outside the fixed range) are described separately. (1) If the power supply voltage is stable

[0148] When the power supply voltage is stable, the current-energizing device 1f operates stably. In other words, the single-signal generator circuit 53 performs control based on an FB signal from the current detector circuit 55, so that the on-time of the switching element 42 is essentially the same regardless of the phase of an AC voltage from the AC power supply 3. Consequently, the duty cycle of the switching element 42 is essentially the same.

[0149] Fig. Figure 20 is a timing diagram illustrating the stable operation of the power supply unit 1f. Fig. Figure 20 illustrates (a) a waveform of the current i_Q1 flowing through the switching element 42 and a waveform of the current i_D1 flowing through the diode 45, and (b) illustrates a waveform of a current i_L1 flowing through the inductor 41 and a waveform of the current i_L2 flowing through the inductor 44. The following describes the stable operation of the current-energizing device 1f when a supply voltage is stable, for each of the three in Fig. 20 periods shown (i.e., TQ1_on, TD1_on, Toff). (1-1) One-period of switching element 42 (TQ1_on)

[0150] When the switching element 42 is switched on, a current flows through the inductor 41, and a current flowing from the inductor 44 through the capacitor 43 flows into the switching element 42. At this time, the diode 45 is reverse-biased and switched off. In the present embodiment, the DC-DC converter 40 is a SEPIC DC-DC converter. According to the SEPIC DC-DC converter, a voltage across capacitor 32 during stable operation and a voltage across capacitor 43 are each substantially the same as an input voltage (i.e., an output voltage from the rectifier circuit 30), as a characteristic of the circuit operation. In other words, capacitor 32, capacitor 43, inductor 41, and inductor 44 are in an equivalent state to the state when capacitor 32, capacitor 43, inductor 41, and inductor 44 are all connected in parallel.

[0151] A current flowing through switching element 42 is the sum of a current flowing through inductor 41 and a current flowing through inductor 44. Accordingly, a rate of change ΔiQ1on of a current flowing through switching element 42 is the sum of the rate of change ΔiL1_Q1on of a current flowing through inductor 41 and the rate of change ΔiL2_Q1 of a current flowing through inductor 44, as shown by expression 2 below. ΔiL1_Q1on=Vac / L1, ΔiL2_Q1on=Vac / L2 ΔiQ1on=Vac / L,L=(L1×L2)(L1+L2)

[0152] Here, Vac denotes an alternating voltage from the AC power supply 3, L1 denotes an inductance of inductor 41, L2 denotes an inductance of inductor 44, and L is a synthetic inductance of inductors 41 and 44.

[0153] Accordingly, the peak current ipeak_Q1 of the switching element 42 after the one-period TQ1_on has elapsed is a value shown by expression 3 below. ipeak_Q1=Vac / LxTQ1_on (1-2) One-period of diode 45 (TD1_on)

[0154] When the switching element 42 is off, the diode 45 is forward-biased and switched on, and a current flowing through the inductor 41 and a current flowing through the inductor 44 pass through the diode 45 and flow into the capacitor 46 and the solid-state luminescent element 2. Since a voltage across the capacitor 32 during stable operation and a voltage across the capacitor 43 are essentially the same as an input voltage, a voltage that is essentially the same as the output voltage Vout is applied to the inductors 41 and 44 in the opposite direction to that in the direction when the switching element 42 is switched on.

[0155] The rate of change ΔiD1on of a current flowing through diode 45 is a total sum of the rate of change ΔiL1_D1on of a current flowing through inductor 41 and a rate of change ΔiL2_D1on of a current flowing through inductor 44, as shown by expression 4 below. ΔiL1_D1on=Vout / L1, ΔiL2_D1on=Vout / L2 ΔiD1on=Vout / L

[0156] Here, the peak value ipeak_D1 of a current flowing through diode 45 is shown by expression 5 below and is equal to the peak value ipeak_Q1 of a current flowing through switching element 42. ipeak_D1=Vout / L×TD1_on=ipeak_Q1

[0157] Accordingly, a one-period (TD1_on) of diode 45 has a value shown by expression 6 based on expressions 3 and 5 shown above. TD1_on=TQ1_on×Vac / Vout (1-3) Off period of diode 45 (Toff)

[0158] The energy stored in inductor 41 and inductor 44 show no change during period Toff until the switching element 42 is next switched on after the current flowing through diode 45 (i.e., the sum of the currents flowing through inductor 41 and inductor 44) has reached zero. Thus, inductors 41 and 44 continue to conduct a current that flows at a time when diode 45 is switched off (the current flowing through diode 45 has reached zero).

[0159] The input current I_in to the current supply device 1f is a current obtained by the capacitor 32 smoothing the current i_L1 flowing through the inductor 41, and is equal to an average value of the current i_L1 in each switching period, as shown by expression 7. I_in=TQ1_on / 2L×OnDuty×Vac Vac=√2×Vac_rms×Sin(2πfT) OnDuty=Vout(Vout+√2Vac_rms)

[0160] Here, Vac_rms denotes an RMS value of the alternating voltage Vac of the AC power supply 3, and f denotes a frequency of the alternating current Vac.

[0161] Note that an output current from the current supply device 1f is a current obtained by the capacitor 46 smoothing the current i_D1, which flows through the diode 45 during the period TD1_on when the diode 45 is switched on, and is equal to an average value of the current i_D1.

[0162] An output current is supplied to the solid-state luminescent element 2 using energy released by inductors 41 and 44 during the one-period TD1_on of diode 45. Similarly, energy accumulated in inductors 41 and 44 during the one-period TQ1_on of switching element 42 is energy drawn from the AC power supply 3. In particular, the input current I_in can be viewed as a change in the current in inductors 41 and 44 during the one-period TQ1_on of switching element 42, or in other words, an average current flowing through switching element 42.

[0163] As shown above by expression 7, the input current I_in to the current-energizing device 1f exhibits the same sinusoidal waveform as the input AC voltage, as with a typical boost converter. Fig. Figure 21 illustrates an example of a waveform of the input current I_in into the power supply unit 1f. As described above, the power supply unit 1f according to the present embodiment includes the SEPIC DC-DC converter 40 and achieves a high power factor and a reduction in high-frequency distortion independent of a difference between an input voltage and an output voltage.

[0164] Note that with respect to one cycle of switching on the switching element 42 (switching period), the periodic signal generator circuit 51 is designed such that the DC-DC converter 40 operates in BCM or DCM during stable operation. Typical operating modes for a current in the DC-DC converter include continuous operation (CCM), discontinuous operation (DCM), and limiting current mode (BCM). Continuous operation (CCM) is an operating mode for switching on the switching element 42 before the current flowing through the diode 45 reaches zero. Discontinuous operation (DCM) is an operating mode for switching on the switching element 42 after the current flowing through the diode 45 reaches zero. Limiting current mode (BCM) is an operating mode for switching on the switching element 42 at a time when the current flowing through the diode 45 has essentially reached zero.

[0165] If the DC-DC converter operates in discontinuous conduction mode (DCM), the input current I_in increases and a sinusoidal waveform is not obtained. Accordingly, the DC-DC converter 40 circuit is designed such that it operates in discontinuous conduction mode (DCM) or continuous conduction mode (CCM) at the peak of an input voltage from the AC power supply 3. In particular, the fixed period Tper, indicated by a periodic signal generated by the periodic signal generator circuit 51, is determined such that the conditions specified by expression 8 below are satisfied. Tper≥4×(Pout×L / η) / (OnDuty×√2×Vac_rms)2

[0166] Here, Pout denotes the output power of the power supply device 1f, and η denotes the circuit efficiency of the power supply device 1f.

[0167] In the present embodiment, the switching element 42 is switched on at each fixed period Tper, thereby achieving a high power factor and a reduction in high frequency distortion regardless of a difference between an input voltage and an output voltage.

[0168] As described above, the switching element 42 is switched on at each fixed period during stable operation according to a fixed duty cycle. The switching element 42 is switched on after the current flowing through diode 45 reaches zero, or in other words, when the current flowing through diode 45 is essentially zero. Thus, after the switching element 42 is switched on, the current flowing through it increases from zero. (2) If a power supply voltage suddenly changes

[0169] If a power supply voltage changes suddenly, LC resonance can occur in the inductors and capacitors included in the current-driving device 1f, and a strong current oscillation can occur in diode 45. For example, if an input filter is provided to eliminate noise at an input stage of the current-driving device, and if an inductor is used in the input filter, the output voltage from the rectifier circuit can rise to a voltage approximately twice the AC voltage from the AC power supply.

[0170] At this time, after a switching element is turned on, a current greater than the current flowing during stable operation flows into the conventional power supply device, and more energy is stored in inductors (corresponding to inductors 41 and 44 in the present embodiment). Even if a certain period of time elapses after the switching element is turned off, a current flowing through a diode (corresponding to diode 45 in the present embodiment) does not cease to flow. Consequently, a current flowing through the diode next flows into the switching element when the switching element is turned on. At this time, the inductors are saturated, causing an even stronger current to flow within the power supply device.

[0171] Fig. Figure 22 is a timing diagram illustrating the operation of a conventional power supply device. Here it is illustrated. Fig. 22 waveforms of a reverse bias voltage (v_D1) applied to a diode contained in the conventional current-energizing device, and a current (i_L2) flowing through an inductor contained in the conventional current-energizing device. In Fig. Figure 22 shows (a) a waveform when a power supply voltage is stable (i.e. during stable operation), and (b) shows a waveform when a power supply voltage changes suddenly.

[0172] As from (b) in Fig. As shown in Figure 22, in a conventional power supply device, when a power supply voltage changes suddenly, a switching element is turned on at each fixed interval before the current flowing through a diode drops to zero, and the DC-DC converter operates in continuous conduction mode (CCM). As a result, the current flowing through the diode flows sequentially into the switching element, and the current flowing into the switching element increases. Consequently, a large stress is placed on the switching element, and it can be damaged.

[0173] In light of this, the single-signal generator circuit 53 in the power supply unit 1f, according to the present embodiment, performs the following control during the off-period of the switching element 42. In other words, if a zero-crossing detector circuit 54 has not detected the zero crossing at a time when a periodic signal from the periodic signal generator circuit 51 indicates the arrival of a fixed period, the single-signal generator circuit 53 waits at least until a zero crossing is detected and then generates an on signal. This prevents the switching element 42 from being switched on before the zero crossing is detected, even if the supply voltage of the AC power supply 3 changes suddenly. In other words, if the supply voltage of the AC power supply 3 changes suddenly, the DC-DC converter 40 is prevented from operating in continuous conduction mode (CCM).

[0174] Fig. Figure 23 is a timing diagram illustrating the operation of the power supply device 1f according to the present embodiment. Here it shows Fig. 23 waveforms of the current i_Q1 flowing through the switching element 42, the current i_D1 flowing through the diode 45, an on-signal output from the on-signal generator circuit 53, a voltage across the inductor 44, and a zero-crossing signal output from the zero-crossing detector circuit 54. Note that, strictly speaking, a voltage across the inductor 44 is a potential at the junction between the inductor 44 and the diode 45 relative to a reference potential of a DC voltage output by the rectifier circuit 30.

[0175] The solid lines in Fig. Figures 23 show the operation of the power supply device 1f according to the present embodiment, and the dashed lines show the operation of the above-mentioned conventional power supply device (power supply device not including a distinctive single-signal generator circuit 53 according to the present embodiment) when a power supply voltage suddenly changes.

[0176] If a power supply voltage is stable (one period, until the second zero-crossing signal (pulse) from the beginning in Fig. 23), the single-signal generator circuit 53 generates a single-signal at each fixed period Tper according to a periodic signal from the periodic-signal generator circuit 51. The single-signal is input to the control circuit 52 and supplied to the control terminal of the switching element 42 as a control signal, and the switching element 42 is switched on. Furthermore, the single-period tone of a single-signal is controlled by a single-signal generator circuit 53 such that an average value of a current detected by the current detector circuit 55 reaches a target current value. However, if a power supply voltage is stable, the AC voltage Vac is essentially constant, and thus the single-period tone is essentially the same.Accordingly, a peak value of the current i_D1 flowing through the diode 45 is essentially the same and the zero-crossing detector circuit 54 detects a zero crossing (see “zero-crossing signal”) before an on signal is generated next in each switching period.

[0177] As a result, the current i_D1 flowing through diode 45 has already reached essentially zero by the time switching element 42 is turned on (for example, at time T0). If a power supply voltage is stable, the DC-DC converter 40 operates in limiting current mode (BCM) or in discontinuous current mode (DCM).

[0178] If a power supply voltage suddenly changes (one period after the second zero-crossing signal (pulse) in Fig. 23 is generated), an output voltage of the rectifier circuit 30 increases. Along with this increase, the peak value of the current i_Q1 flowing through the switching element 42 and the peak value of the current i_D1 flowing through the diode 45 increase, as shown in Fig. 23 shown.

[0179] In such a state, a conventional current-generating device produces an on-signal at each fixed time period Tper (time T1), as shown by the dashed lines in Fig. Figure 23 shows that the DC-DC converter operates in continuous conduction mode (CCM). In other words, the current i_Q1 begins to flow into the switching element before the current i_D1 flowing through a diode reaches zero. Consequently, whenever an on signal is generated, the peak values ​​of the current i_Q1 flowing through the switching element 42 and the current i_D1 flowing through the diode 45 continuously increase, which can damage the switching element.

[0180] In contrast, according to the current-energizing device 1f of the present embodiment, if no zero crossing is detected by the zero-crossing detector circuit 54 at a time when a periodic signal from the periodic signal generator circuit 51 indicates the arrival of a fixed period, no on-signal is generated (time T1). In the present embodiment, the on-signal generator circuit 53 skips the generation of an on-signal for one period. In other words, the on-signal generator circuit 53 generates an on-signal after a zero crossing is detected (after the third zero-crossing signal is generated) and at a time when a periodic signal from the periodic signal generator circuit 51 indicates the arrival of a fixed period (time T2).

[0181] Accordingly, as can be seen from the waveforms (solid lines) of the current i_Q1 flowing through the switching element 42 and the current i_D1 flowing through the diode 45 in Fig. The flow of current 23, as is clear, prevents the switching element 42 from being switched on before the zero crossing is detected, even if a power supply voltage changes suddenly. In other words, even if a power supply voltage changes suddenly, the DC-DC converter 40 is prevented from operating in continuous conduction mode (CCM), and thus damage to the switching element 42 is prevented.

[0182] As described above, the power supply device 1f according to the present embodiment is a device connected to the AC power supply 3 and supplies a current to the solid-state luminescent element 2. The power supply device 1f includes the rectifier circuit 30, the DC-DC converter 40, the periodic signal generator circuit 51, the zero-crossing detector circuit 54, the on-signal generator circuit 53, and the drive circuit 52. The rectifier circuit 30 rectifies AC power from the AC power supply 3. The DC-DC converter 40 includes the switching element 42 and the diode 45 and chops a DC current from the rectifier circuit 30 by repeatedly switching the switching element 42 on and off. Subsequently, the diode 45 rectifies a current obtained by chopping the DC current. The periodic signal generator circuit 51 generates a periodic signal indicating the arrival of a fixed period.The zero-crossing detector circuit 54 detects that a current flowing through diode 45 has reached zero during the off-period of switching element 42. If the zero-crossing detector circuit 54 detects that a current has reached zero at a time when a periodic signal indicates the arrival of a fixed period in the off-period of switching element 42, the on-signal generator circuit 53 generates an on-signal indicating a time to turn on switching element 42. The control circuit 52 turns on switching element 42 according to the time indicated by an on-signal generated by the on-signal generator circuit 53. At this time, the on-signal generator circuit 53 performs the following control during the off-period of switching element 42.In other words, if the zero-crossing detector circuit 54 has not detected that a current has reached zero at a time when a periodic signal indicates the arrival of a fixed period, the one-signal generator circuit 53 waits at least until the zero crossing is detected and generates an one-signal.

[0183] If the zero-crossing detector circuit 54 has not detected a zero crossing at a time when a fixed period arrives in the off-period of the switching element 42, the on-signal generator circuit 53 accordingly generates an on-signal after at least one zero crossing has been detected. This prevents the switching element 42 from being switched on before the zero crossing is detected, or in other words, prevents the DC-DC converter 40 from operating in continuous conduction mode (CCM). Even if a supply voltage to be input from the AC power supply 3 changes suddenly, this prevents the switching element 42 from being damaged by a gradual increase in the current flowing through it, and ensures the stable operation of the power supply device 1f.

[0184] Furthermore, in the present embodiment, the single-signal generator circuit 53 performs the following control if the zero-crossing detector circuit 54 has not detected that a current in the off-period of the switching element 42 has reached zero at a time when a periodic signal indicates the arrival of a fixed period. In other words, the single-signal generator circuit 53 generates an on-signal at least after the zero-crossing detector circuit 54 has detected that a current has reached zero, and at a time when a periodic signal indicates the arrival of a fixed period.

[0185] If the zero-crossing detector circuit 54 has not detected a zero crossing at a time when a fixed period arrives in the off-period of the switching element 42, a corresponding periodic signal is skipped and the on-signal generator circuit 53 generates an on-signal, at least after the zero-crossing detector circuit 54 has detected a zero crossing. Thus, the DC-DC converter 40 is reliably prevented from operating in continuous mode, and the stable operation of the power supply device 1f is ensured.

[0186] Note that in the present embodiment, the zero-crossing detector circuit 54 detects that a current flowing through the diode 45 has reached zero (zero crossing) during the off-period of the switching element 42 by detecting a voltage across the inductor 44; however, the present embodiment is not limited to this. In the current-energizing device 1f, a voltage or current can be detected at another section where a zero crossing can be detected. Fig. Figure 24 illustrates waveforms of voltages and currents at different sections of a circuit of the power supply device 1f according to the present embodiment. Here, the following is illustrated: Fig. 24 the current i_D1-anode that flows through the diode 45 ((a) in Fig. 24), the current i_Q1-D flowing through the switching element 42 ((b) in Fig. 24), the voltage v_C2 across capacitor 43 ((c) in Fig. 24), the voltage v_C1 across capacitor 32 ((d) in Fig. 24), the voltage v_L2 at the inductor 44 ((e) in Fig. 24), the voltage v_Q1-D at the source and drain of the switching element 42 ((f) in Fig. 24), the voltage v_L1 at inductor 41 ((g) in Fig. 24) and the voltage v_D1 (reverse bias) across diode 45 ((h) in Fig. 24).

[0187] As from Fig. 24, they possess a current and voltages, which are shown in (a) and (e) to (h) in Fig. Figure 24 shows waveforms that depict zero-crossing timing controls and can therefore be used to detect a zero crossing. Note that a current sensor must be connected in series in a target section to detect a current, but this can lead to an increase in power consumption. Accordingly, from the perspective of power consumption, the zero crossing can be detected by detecting a voltage. To detect a voltage at inductor 41 or 44, a secondary winding can also be added to the inductor, and a voltage generated in the secondary winding can be detected. [Variant 1 of embodiment 5]

[0188] In the embodiment 5 described above, the single-signal generator circuit 53 skips a periodic signal when a power supply voltage changes suddenly and generates a single-signal after a zero crossing is detected. However, a method for delaying the generation of a single-signal is not limited to this. For example, the single-signal generator circuit 53 can delay the generation of a single-signal until the zero-crossing detector circuit 54 detects a zero crossing and output a single-signal at the time a zero crossing is detected. It can also be caused the periodic signal generator circuit 51 to generate a periodic signal whose starting point is the time.

[0189] Fig. Figure 25 is a circuit diagram of a current supply device 1g according to variant 1 of the embodiment 5 described above, which outputs an on signal at a time when a zero crossing is detected, and causes the periodic signal generator circuit 51 to generate a periodic signal whose starting point is the time as described above. Fig. In 25, the same elements are provided with the same reference symbols as the reference symbols in embodiment 5 described above, and a description of them is omitted. The power supply device 1g according to variant 1 differs from the power supply device 1f according to embodiment 5 described above by the function of a single-signal generator circuit 53a and by the fact that the single-signal generator circuit 53a outputs a reset signal to the periodic signal generator circuit 51.

[0190] The one-signal generator circuit 53a performs the following control during the off-period of the switching element 42. In other words, if the zero-crossing detector circuit 54 has not detected that the current has reached zero at a time when a periodic signal indicates the arrival of a fixed period, the one-signal generator circuit 53a outputs an on-signal and sends a reset signal to the periodic signal generator circuit 51 at a time when a zero crossing is detected.

[0191] The periodic signal generator circuit 51, which has received the reset signal, generates a periodic signal whose starting point is the time when the reset signal is received, in each fixed period Tper.

[0192] Fig. Figure 26 is a timing diagram illustrating the operation of the power supply unit 1g according to variant 1. Here it shows Fig. 26 waveforms of the current i_Q1 flowing through the switching element 42, the current i_D1 flowing through the diode 45, an on-signal, a voltage across the inductor 44 and a zero-crossing signal, as in Fig. 23 in the embodiment described above 5. As can be seen from a comparison between Fig. 26 and Fig. As can be seen from 23, an on-signal is not generated (time T1) if no zero crossing is detected at a given time, if a periodic signal indicates the arrival of a fixed period, if a power supply voltage is stable, and if a power supply voltage suddenly changes, which is the same as in the embodiments above.

[0193] However, if a zero crossing is detected in variant 1 (time T2), an on signal is output, and subsequently, an on signal is generated at each fixed period Tper. This is because the on-signal generator circuit 53a performs the following control during the off period of the switching element 42. In other words, if no zero crossing is detected at a time when a periodic signal indicates the arrival of a fixed period, the generation of an on signal is delayed until a zero crossing is detected, and an on signal is then output. The periodic signal generator circuit 51 is reset at the time a zero crossing is detected.

[0194] Note that this is in Fig. The example shown in Figure 26 demonstrates that a sudden change in the power supply voltage ceases within one period Tper. Furthermore, the single-signal generator circuit 53a may first send a reset signal to the periodic signal generator circuit 51 at time T2 before generating a single-signal, and then generate a single-signal according to a periodic signal sent by the periodic signal generator circuit 51.

[0195] Accordingly, the single-signal generator circuit 53a in the current-energizing device 1g of variant 1 performs the following distinctive control during the off-period of the switching element 42. In other words, if the zero-crossing detector circuit 54 has not detected that a current has reached zero at a time when a periodic signal indicates the arrival of a fixed period, the single-signal generator circuit 53a outputs an on-signal and resets the periodic signal generator circuit 51 to a time when a zero crossing is detected.

[0196] If a zero crossing is not detected at a time when a fixed period in the off-period of the switching element 42 is detected, an on signal is generated accordingly, at least after the detection of a zero crossing, by delaying the generation of an on signal until a zero crossing is detected. This reliably prevents the DC-DC converter 40 from operating in continuous mode and ensures stable operation of the power supply unit 1g. [Variant 2 of embodiment 5]

[0197] A method for delaying an on-signal when a power supply voltage suddenly changes is not limited to the methods according to embodiment 5 and variant 1 described above. The generation of an on-signal can be delayed such that the average value of a current flowing through the solid-state luminescent element 2 in each of the on-off periods (switching periods) of the switching element 42 does not deviate from a past value.

[0198] A current supply device according to variant 2 of the embodiment 5 described above, which performs such a function, has the same configuration as the configuration of the current supply device 1g according to the embodiment 5 described above and in Fig. Variant 1, shown in Figure 25, is as follows: Note that in Variant 2, if the zero-crossing detector circuit 54 has not detected that the current reaches zero at a time when a periodic signal indicates the arrival of a fixed period during the off-period of the switching element 42, the one-signal generator circuit 53a performs the following control action. In other words, the one-signal generator circuit 53a extends the off-period of the switching element 42 such that the average value of the current flowing through the solid-state luminescent element 2 during a switching period that includes the time is substantially the same as the value at least one period in the past, and then generates an on-signal. At this time, the one-signal generator circuit 53a simultaneously sends a reset signal to the periodic signal generator circuit 51 along with the output of an on-signal.

[0199] The periodic signal generator circuit 51, which has received the reset signal, generates a periodic signal whose starting point is a time when the reset signal is received for each fixed period Tper, as in variant 1 described above.

[0200] Fig. Figure 27 is a timing diagram illustrating the operation of the power supply unit according to variant 2. Here it shows Fig. 27 Waveforms of the current i_Q1 flowing through the switching element 42, the current i_D1 flowing through the diode 45, an on-signal, a voltage across the inductor 44 and a zero-crossing signal, as in Fig. 23 in the embodiment described above 5. If, as can be seen from a comparison between Fig. 27 and Fig. 23 and Fig. 26 shows that no zero crossing is detected at a time when a periodic signal indicates the arrival of a fixed period, the one-signal generator circuit 53a does not generate a one-signal (time T1) when a power supply voltage suddenly changes, as in the embodiment 5 and variant 1 described above.

[0201] In variant 2, however, the single-signal generator circuit 53a generates a single signal at a time (time T2) when the average current flowing through the solid-state luminescent element 2 in each switching period when the power supply voltage is stable is the same as the average current flowing through the solid-state luminescent element 2 in each switching period when the power supply voltage changes suddenly. Specifically, the single-signal generator circuit 53a calculates a delay time Tper2 according to expression 9 below if no zero crossing is detected at a time when a periodic signal from a periodic signal generator circuit 51 indicates the arrival of a fixed period (Tper1). Tper2=(T_Don2)2 / (T_Don1)2×Tper1

[0202] Here, T_Don2 is a time period when a current flows through diode 45 if no zero crossing is detected at the time when a periodic signal from the periodic signal generator circuit 51 indicates the arrival of a fixed period (Tper1). In other words, T_Don2 is a time period from when the output of a preceding on-signal ends (i.e., the preceding on-signal goes low) until a zero crossing is detected when a power supply voltage changes abruptly. T_Don1 is a time period when a current flows through diode 45 in one period (when a power supply voltage is stable) immediately before a power supply voltage changes abruptly.

[0203] Then the single-signal generator circuit 53a generates a single-signal at a time (time T2) after the currently calculated delay time Tper2 has elapsed since a single-signal is generated, immediately before a power supply voltage suddenly changes.

[0204] Here, expression 9 shown above is derived from expression 10 below. (T_Don1)2 / Tper1=(T_Don2)2 / Tper2

[0205] Here, the voltage across the solid-state luminescent element 2 is essentially the same during T_Don1 and T_Don2, and thus T_Don1 and T_Don2 are proportional to peak values ​​of a current flowing through diode 45. Therefore, expression 10 given above shows that the mean current flowing through diode 45 during one period Tper1 and the mean current flowing through diode 45 during one period Tper2 are the same as in Fig. Figure 28 shows that the above control by the single-signal generator circuit 53a essentially achieves the same average values ​​of a current flowing through the diode 45 (i.e., a current flowing through the solid-state luminescent element 2) when a supply voltage is stable (periodic Tper1) and when a supply voltage changes suddenly (periodic Tper2).

[0206] As described above, according to variant 2, if no zero crossing is detected at a time when a fixed period arrives in the off-period of the switching element 42, the generation of an on-signal is delayed so that the average value of the current flowing through the solid-state luminaire 2 is fixed. Accordingly, a constant current mode is maintained, and the DC-DC converter 40 is reliably prevented from operating in continuous mode. Thus, stable operation of the power supply device 1f is ensured. Furthermore, according to variant 2, the average value of the current flowing through the solid-state luminaire 2 is fixed in each period, and therefore a change in the optical output of the solid-state luminaire 2 is blocked if the power supply voltage changes suddenly.

[0207] Note that in the above example of a controller, the single-signal generator circuit 53a uses a time T_Don1 during which a current flowed through diode 45 in a previous period (Tper1) when a power supply voltage suddenly changes; however, the single-signal generator circuit 53a can use such a time in two or more periods. For example, the delay time Tper2 described above can be calculated using the times T_Don0 and T_Don1 during which a current flowed in periods Tper0 and Tper1. Fig. 27 flowed through diode 45. [Version 6]

[0208] Next, embodiment 6 describes lighting devices that include the power supply devices according to the embodiments above, with reference to the Fig. 29 to 31.

[0209] The Fig. Figures 29 to 31 illustrate external views of lighting devices according to the present embodiment. Examples of such a lighting device include a downlight 100a ( Fig. 29) and Spots 100b ( Fig. 30) and 100c ( Fig. 31). The downlight 100a and the spots 100b and 100c contain junction boxes 101a, 101b and 101c, respectively. The junction boxes 101a, 101b and 101c are housings in which at least one circuit of the power supply devices according to the embodiments described above is contained. The downlight 100a and the spots 100b and 100c contain lamps 102a, 102b and 102c, respectively. The lamps 102a, 102b and 102c each contain an LED 2. The downlight 100a and the spot 100b contain conductors 103a and 103b, respectively, which electrically connect the junction boxes 101a and 101b to the LED 2 of each of the lamps 102a and 102b.

[0210] The present embodiment also achieves equivalent effects to those of the embodiments above. [Variants and other]

[0211] The above has described the current supply devices according to the present invention based on the above embodiments, but the present invention is not limited to these embodiments.

[0212] For example, while the circuit diagrams illustrate one LED 2, the number of LEDs 2 is not limited to one. For instance, a configuration in which several LED chips are connected in series in parallel, a configuration in which several LED elements are modularized, or a configuration in which several modules are combined can be used.

[0213] Furthermore, although an LED is used as a solid-state luminescent element in the above embodiments, the solid-state luminescent element that is a load of the power supply is not limited to an LED. For example, another solid-state luminescent element, such as an organic EL element, can be used as a load of the power supply.

[0214] A feedback circuit can contain an integrated circuit (IC). Furthermore, a feedback circuit can have a digital control configuration using a microcomputer, for example.

[0215] Furthermore, in the above embodiments, the current detector directly detects a current flowing through the switching element 16, but can indirectly detect a current flowing through the switching element 16 by detecting a current flowing through another element.

[0216] Furthermore, in the embodiment 1 described above, the overcurrent prevention circuit 111 is included on the input side of the control circuit 112, but it can also be included on the output side.

[0217] In the above embodiments, the current detector 12 and the output detector 13 detect a current or voltage using a resistor, but, for example, an element other than a resistor can be used to detect a current or voltage.

[0218] Furthermore, the inductor 18 used in the above embodiments can have a transformer structure comprising a primary winding and a secondary winding. If the inductor 18 has a transformer structure, its windings are connected to other elements as follows. In particular, in the current-energizing devices according to the above embodiments, one terminal of the primary winding is connected to an output terminal of the capacitor 17, and the other terminal of the primary winding is grounded. Additionally, one terminal of the secondary winding is connected to the anode electrode of the diode 19, and the other terminal of the secondary winding is grounded. Furthermore, the capacitor 17 and the diode 19 are separated by the inductor 18, which has a transformer structure.In this case, the output detector of the power supply devices can define output currents from the power supply devices as outputs, or a detection resistor can be connected on the primary winding side and the output detector can detect a current flowing through the primary winding as an output.

[0219] For example, although single-signal generator circuits 53 and 53a in embodiment 5 and the variants above each contain, for example, a processor and a program, the configurations of the single-signal generator circuits 53 and 53a are not limited to such a configuration and may include logic circuits such as an AND gate and an analog circuit such as an A / D converter, for example.

[0220] In embodiment 5 and the variants above, the power supply devices 1f and 1g each contain a SEPIC DC-DC converter, but the type of DC-DC converter is not limited to this. The power supply devices 1f and 1g can each contain a DC-DC converter that switches on a switching element at each fixed period. As long as a power supply device contains the distinctive single-signal generator circuit according to the present invention, the DC-DC converter is even prevented from operating in continuous conduction mode (CCM) when a power supply voltage changes suddenly.

[0221] The scope of protection of the present invention may also include embodiments resulting from the addition of various modifications to the embodiments that can be devised by a person skilled in the art, and embodiments obtained by combining elements and functions in the embodiments in any way possible, as long as the combinations do not deviate from the concept of the present invention.

[0222] For example, a combination of embodiments 1 and 2 described above achieves an improved advantageous effect in preventing excessive current, since the switching element 16 can be switched off immediately, and the subsequent on-time can also be shortened if the current ISW exceeds the threshold Ith.

[0223] Although the present invention has been described and illustrated in detail, it is clearly understood that this is only exemplary and not to be regarded as a limitation, the scope of protection of the present invention being limited only by the expressions of the attached claims. [List of reference symbols] 1, 1a, 1b, 1c, 1d, 1e, 1f, 1g power supply device 2 LEDs (solid-state light element) 3 AC power supply 7, 10, 10c, 10d, 10e, 40 DC-DC converters 11, 11c, 11d, 11e Control unit 12 Current detector 13, 13a, 13b Output detector 16, 42 Switching element 30 Rectifier circuit 41, 44 Inductor 51 Periodic Signal Generator Circuit 52 Control circuit 53, 53a Single-signal generator circuit 54 Zero-crossing detector circuit 112 Control circuit 115, 314, 317, 321 Transistor

Claims

[1] Current supply device (1, 1a-g) which supplies a current to a solid-state luminous element (2), wherein the current supply device (1, 1a-g) comprises: a direct current-to-direct current converter, DC-DC converter (7, 10, 10c-e, 40); and an output detector (13, 13a, 13b) that detects an output from the DC-DC converter (7, 10, 10c-e, 40), wherein the DC-DC converter (7, 10, 10c-e, 40) includes the following: a switching element (16, 42); a control device (11, 11c-e) that switches the switching element (16, 42) on and off to generate the output; and a current detector (12) that detects a current flowing through the switching element (16, 42), and wherein, If the current value detected by the current detector (12) is below a predetermined threshold, the control unit (11, 11c-e) controls the switching element (16, 42) according to a duty cycle determined on the basis of an output value detected by the output detector (13, 13a, 13b), and if the current value is above the predetermined threshold, the control unit (11, 11c-e) controls the switching element (16, 42) according to a duty cycle below the duty cycle determined on the basis of the output value. characterized by , that: the control device (11, 11c-e) contains the following: a control circuit (52) that controls the switching element (16, 42); and a transistor (115, 314, 317, 321) connected to the control circuit (52), and If the current value exceeds the predetermined threshold, the control device (11, 11c-e) switches off the switching element (16, 42) by switching on the transistor (115, 314, 317, 321). [2] Current supply device (1, 1a-g) according to claim 1, wherein the DC-DC converter (7, 10, 10c-e, 40) increases or decreases an input voltage based on characteristics of the solid-state luminescent element and outputs the increased or decreased input voltage. [3] Power supply device (1, 1a-g) according to claim 1 or 2, wherein the DC-DC converter (7, 10, 10c-e, 40) is a SEPIC, Single Ended Primary Inductance Converter. [4] Current supply device (1, 1a-g) according to one of claims 1 to 3, wherein the predetermined threshold is less than or equal to an absolute maximum rated current of the switching element (16, 42). [5] Current supply device (1, 1a-g) according to one of claims 1 to 4, wherein the predetermined threshold is greater than or equal to a current value of a current flowing through the switching element (16, 42) when a nominal voltage of the current supply device (1, 1a-g) is stably applied to the current supply device (1, 1a-g). [6] Current supply device (1, 1a-g) according to one of claims 1 to 5, wherein if the current value is above the predetermined threshold value, the control device (11, 11c-e) keeps the switching element (16, 42) switched off during a switching period of the switching element (16, 42). [7] Lighting device comprising: the current supply device (1, 1a-g) according to one of claims 1 to 6; and a solid-state luminescent element that receives a current supply from the current supply device (1, 1a-g).

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