Power-Source Device and LED Driving Device

Abstract

 [Summary]
[Object] To provide a non-isolated power-source device and an LED driving device, which can reduce power supplied to a load circuit without complicating their configurations even when either of both ends of the load circuit causes a ground fault.
[Means for Settlement] A non-isolated power-source device A1 that converts input power from a DC power-source E1, a negative electrode of which is grounded to a ground line G1 into desired DC power, and supplies the converted DC power to a load circuit Y1 includes a capacitor C1 electrically connected between one end of the load circuit Y1 and the negative electrode of the DC power-source E1, and a capacitor C2 electrically connected between the other end of load circuit Y1 and the positive electrode of the DC power-source E1.

Description

[Field of the Invention]

[0001] The present invention relates to a power-source device and an LED driving device.

[Background Art]

[0002] A power-source device supplying DC power to a DC load has been conventionally used in various fields (Refer to, for example, Patent Literature 1).

[0003] For example, in the illumination field, an LED (Light Emitting Diode) element has been actively used, and its use has diversified. In illumination for vehicles, a white LED element has been used in a vehicle interior and further, with higher luminance, used in a headlight, a day-time running lamp and so on.

[0004] The LED element has a longer life and a higher responsivity than an incandescent bulb, and can be mounted with a compact configuration. The LED element can also exhibit various colors easily, and achieve easy lighting control by means of dimming. As a result, an illumination fixture such as a lighting tool can be made thinner and mounted in three dimensions, thereby advantageously enabling free design of vehicles without restricting the shape of the vehicles.

[0005] The above-mentioned illumination fixture includes LED elements and a power-source device lighting the LED elements, and supplies a constant current to a light supply formed by serially connecting the plurality of LED elements, thereby lighting the plurality of LED elements at constant brightness.

[0006] As the power-source device, a step-up chopper circuit is used when an output voltage (for example, a voltage between both ends of the serially connected LED elements) is higher than an input voltage, and a step-down chopper circuit is used when the output voltage is lower than the input voltage. A step-up/down chopper circuit is used when the power-source device operates in both of a step-up mode and a step-down mode depending on surroundings of the power-source and a load state.

[0007] Fig. 13 shows a configuration of a CUK circuit as an example of the conventionally used step-up/down chopper circuit.

[0008] The CUK circuit is a non-isolated power-source device, and uses a DC power-source E101 as an input power-source to supply DC power to an LED unit X101 formed by serially connecting a plurality of LED elements. A negative electrode of the DC power-source E101 is grounded to a ground line G101.

[0009] A series circuit of an inductor L101 and a switching element S101 is connected between a positive electrode and the negative electrode of the DC power-source E101. A series circuit of a capacitor C101 and a diode D101 is connected between both ends of the switching element S101, and a series circuit of an inductor L102 and a capacitor C102 is connected between both ends of the diode D101. The LED unit X101 is connected between both ends of the capacitor C102, and a DC current is supplied to the LED unit X101.

[0010] With such configuration, a series circuit formed by serially connecting the inductor L101, the capacitor C101, the inductor L102, and the LED unit X101 in this order is provided in a path extending from the positive electrode to the negative electrode of the DC power-source E101. A path from the negative electrode of the DC power-source E101 and one end of the LED unit X101 (anode side of the LED element) is configured of a common line W101, and the one end of the LED unit X101 is at the same (or almost same) potential as the ground line G101. An anode of the diode D101 is connected to a connection point of the capacitor C101 and the inductor L102, and a cathode of the diode D101 is connected to the common line W101.

[0011] A control circuit not shown turns on/off the switching element S101, thereby supplies the DC power to the LED unit X101 to light each of the LED elements of the LED unit X101.

[Conventional Technique Document]

[Patent Literature]

[0012] [Patent Literature 1] JPA 2005-224049

[Disclosure of the Invention]

[Problems to be solved by the Invention]

[0013] In Fig. 13, when the LED unit X101 causes a ground fault (the LED unit X101 is in contact with the ground line G101), a following phenomenon occurs.

[0014] First, when an electric circuit Wa101 on the other end side causes a ground fault, a ground-fault current flows in a closed circuit passing the positive electrode of the DC power-source E101, the inductor L101, the capacitor C101, the inductor L102, the electric circuit Wa101, the ground line G101, and the negative electrode of the DC power-source E101. However, since the power-source side (DC power-source E101) and the load side (LED unit X101) are separated from each other in a DC manner by the capacitor C101, the ground-fault current is limited by the capacitor C101. Then, since the both ends of the LED unit X101 are substantially short-circuited by the ground line G101, the LED unit X101 is not lighted. The user can recognize the occurrence of abnormality through lighting-off of the LED unit X101.

[0015] When an electric circuit Wb101 on one end side causes a ground fault, since the electric circuit Wb101 is a part of the common line W101, the LED unit X101 continues to be lighted. In the case of the vehicle illumination fixture, the fact that the LED unit X101 continues to be lighted even when abnormality occurs can be regarded as a safe operation in operations of vehicles. However, since the user cannot recognize it as abnormality, when the power-source device is continuously used in the state where the abnormality occurs, a problem may be generated.

[0016] For example, even when a harness for a wiring connecting an output of the power-source device to the LED unit X101 gets caught in any structure and thus, the electric circuit Wb101 comes in contact with the ground line G101 and causes a ground fault, abnormality cannot be detected. When the device is continuously used in the abnormal state, the overheating of the harness and similar problems can occur. Further, the interference with a ground line of a near electrical component can occur.

[0017] Then, a method of detecting a ground fault by connecting a detection resistance or the like to the common line W101 is proposed, but problems of the detection accuracy and complicated control contribute to an increase in the number of parts due to complexity of a configuration of ground fault detection means, and an increase in costs.

[0018] The present invention is made in consideration of the above-mentioned situation, and its object is to provide a non-isolated power-source device and an LED driving device, which can reduce power supplied to a load circuit without complicating the configuration even when either of both ends of the load circuit causes a ground fault.

[Means Adapted to Solve the Problems]

[0019]  A power-source device of the present invention is a non-isolated power-source device that converts input power from a DC power-source, one electrode of which is grounded, into desired DC power, and supplies the converted DC power to a load circuit, the power-source device including a first capacitor electrically connected between one end of the load circuit and the one electrode of the DC power-source, and a second capacitor electrically connected between the other end of the load circuit and the other electrode of the DC power-source.

[0020] According to the present invention, it is preferred that the power-source device further includes a switching element electrically connected to the first and second capacitors, the switching element switching between charge and discharge of the first and second capacitors, a step-up part that raises a voltage of the DC power-source by turning on/off the switching element, and a step-down part that lowers the voltage raised by the step-up part by turning on/off the switching element, and applies the lowered voltage to the load circuit.

[0021] According to the present invention, it is preferred that a series circuit formed by connecting a first inductor, the second capacitor, a second inductor, the load circuit, and the first capacitor in this order is provided in a path extending from the other electrode of the DC power-source to the one electrode, the switching element is connected between a connection point of the first inductor and the second capacitor and the one electrode of the DC power-source, and a diode is connected between a connection point of the second capacitor and the second inductor and a connection point of the load circuit and the first capacitor.

[0022] According to the present invention, it is preferred that a series circuit formed by connecting a switching element, the second capacitor, a first inductor, the load circuit, and the first capacitor in this order is provided in a path extending from the other electrode of the DC power-source to the one electrode, a second inductor is connected between a connection point of the switching element and the second capacitor and the one electrode of the DC power-source, and a diode is connected between a connection point of the second capacitor and the first inductor and a connection point of the load circuit and the first capacitor.

[0023] According to the present invention, it is preferred that a series circuit formed by connecting a first inductor, the second capacitor, a diode, the load circuit, and the first capacitor in this order is provided in a path extending from the other electrode of the DC power-source to the one electrode, a switching element is connected between a connection point of the first inductor and the second capacitor and the one electrode of the DC power-source, and a second inductor is connected between a connection point of the second capacitor and the diode and a connection point of the load circuit and the first capacitor.

[0024] According to the present invention, it is preferred that the load circuit includes a load formed of an LED element, an incandescent lamp, or a resistance element.

[0025] According to the present invention, it is preferred that the load circuit includes a third capacitor connected to the load in parallel.

[0026] According to the present invention, it is preferred that the load circuit includes a third inductor connected to one end of the load, a fourth inductor connected to the other end of the load, and a third capacitor connected to a series circuit of the load and the third and fourth inductors.

[0027] According to the present invention, it is preferred that a resistor is connected to the first capacitor in parallel.

[0028] According to the present invention, it is preferred that a plurality of the load circuits are provided.

[0029] An LED driving device of the present invention is a non-isolated LED driving device that converts input power from a DC power-source, one electrode of which is grounded, into desired DC power, and supplies the converted DC power to a load circuit formed of one or plurality of LED element, the LED driving device including a first capacitor electrically connected between one end of the load circuit and the one electrode of the DC power-source, and a second capacitor electrically connected between the other end of the load circuit and the other electrode of the DC power-source.

[Effect of the Invention]

[0030] As has been described, according to the present invention, the non-isolated power-source device and the LED driving device can effectively reduce power supplied to the load circuit without complicating their configurations even when either of the both ends of the load circuit causes a ground fault.

[Brief Description of the Drawings]

[0031] 

[Fig. 1] Fig. 1 is a block diagram schematically showing a system in a first embodiment.

[Fig. 2] Figs. 2(a) to 2(c) are circuit diagrams showing an example of a load circuit.

[Fig. 3] Fig. 3 is a circuit diagram showing a configuration of a system in a second embodiment.

[Fig. 4] Fig. 4 is a circuit diagram showing another configuration of the load circuit in the second embodiment.

[Fig. 5] Fig. 5 is a circuit diagram showing another configuration around a first capacitor in the second embodiment.

[Fig. 6] Fig. 6 is a circuit diagram showing a configuration of another system in the second embodiment.

[Fig. 7] Fig. 7 is a circuit diagram showing a configuration of a system in a third embodiment.

[Fig. 8] Fig. 8 is a circuit diagram showing another configuration of a load circuit in the third embodiment.

[Fig. 9] Fig. 9 is a circuit diagram showing a configuration of another system in the third embodiment.

[Fig. 10] Fig. 10 is a circuit diagram showing a configuration of a system in a fourth embodiment.

[Fig. 11] Fig. 11 is a circuit diagram showing another configuration of a load circuit in the fourth embodiment.

[Fig. 12] Fig. 12 is a circuit diagram showing a configuration of another system in the fourth embodiment.

[Fig. 13] Fig. 13 is a circuit diagram showing a configuration of a conventional system.

[Best Mode for Carrying out the Invention]

[0032] Embodiments of the present invention will be described below referring to figures.

(First embodiment)

[0033] Fig. 1 shows a schematic configuration of a power-source device A1 in the present embodiment, and the power-source device A1 includes a converter part A11 including capacitors C1, C2 to constitute a non-isolated power-source device, and uses a DC power-source E1 as an input power-source to supply DC power to a load circuit Y1.

[0034] A negative electrode of the DC power-source E1 is grounded to a ground line G1, the capacitor C1 (first capacitor) is serially connected between a negative electrode of the DC power-source E1 and one end of the load circuit Y1, and the capacitor C2 (second capacitor) is serially connected between a positive electrode of the DC power-source E1 and the other end of the load circuit Y1.

[0035] One end of the load circuit Y1 is connected to the capacitor C1 via an electric circuit W11, and the other end of the load circuit Y1 is connected to the capacitor C2 via an electric circuit W12. That is, the electric circuits W11, W12 at the both ends of the load circuit Y1 are electrically connected to both electrodes of the DC power-source E1 via the capacitor C1 and the capacitor C2, respectively, and the electric circuit W11 is connected to the ground line G1 via the capacitor C1.

[0036] Thus, the electric circuit W12 includes the load circuit Y1 and the capacitor C1 between the electric circuit W12 and the ground line G1, and the electric circuit W11 includes the capacitor C1 between the electric circuit W11 and the ground line G1. Accordingly, both the electric circuits W11, W12 as the electric circuit at both ends of the load circuit Y1 have a potential that is different from a potential of the ground line G1.

[0037] Then, the converter part A11 uses the DC power-source E1 as an input power-source, and supplies DC power to the load circuit Y1 via the capacitors C1, C2 and the electric circuits W11, W12.

[0038] In the power-source device A1 having such configuration, when the electric circuit W12 causes a ground fault (comes in contact with the ground line G1), a ground-fault current flows in a closed path passing the positive electrode, the capacitor C2 of the DC power-source E1, the electric circuit W12, the ground line G1, and the negative electrode of the DC power-source E1. Accordingly, since the path is different from a current path at a normal circuit operation, supplying of power to the load circuit Y1 is suppressed, and the user can recognize that abnormality occurs in the power-source device A1 on the basis of stopping of the operation of the load circuit Y1.

[0039] In the power-source device A1, when the electric circuit W11 causes a ground fault (comes in contact with the ground line G1), a ground-fault current flows in a closed circuit passing the positive electrode of the DC power-source E1, the capacitor C2, the electric circuit W12, the load circuit Y1, the electric circuit W11, the negative electrode of the ground line G1, and the DC power-source E1. Accordingly, since the path is different from a current path at a normal circuit operation, supplying of power to the load circuit Y1 is suppressed, and the user can recognize that abnormality occurs in the power-source device A1 on the basis of the stop of the operation of the load circuit Y1.

[0040] Even when either of the electric circuits W11, W12 causes a ground fault, since the power-source side (DC power-source E1) and the load side (load circuit Y1) are separated from each other in a DC manner by the capacitor C2, thereby protecting the circuit.

[0041] When the electric circuit W12 causes a ground fault, a closed circuit passing the ground line G1, the electric circuit W12, the load circuit Y1, the electric circuit W11, the capacitor C1 and the ground line G1 is formed. When the electric circuit W11 causes a ground fault, a closed circuit passing the ground line G1, the electric circuit W11, the capacitor C1 and the ground line G11 is formed. That is, even when either of the electric circuits W11, W12 causes a ground fault, one end and the other end of the capacitor C1 are substantially separated from each other, thereby protecting the circuit.

[0042] When either of the electric circuit W11, W12 causes a ground fault in this manner, since the main circuit of the power-source device A1 is put into the above-mentioned state, it is no need to provide control means detecting and determining a ground fault, thereby simplifying the circuit configuration and reducing costs. That is, even when either of the electric circuits W11, W12 causes a ground fault, by using the capacitors C1, C2 of the converter part A11 as capacitors to counter the ground fault, power supplied to the load circuit Y1 can be reduced without complicating the configuration.

[0043] The capacitor C2 is a capacitor used to perform the normal power supplying operation of the converter part A11, and is also used to separate the power-source side from the load side at the occurrence of a ground fault. Accordingly, the capacitor C1 only needs to be added as a circuit component to counter the ground fault.

[0044] Figs. 2(a) to 2(c) are examples of a configuration of the load circuit Y1, and the load circuit Y1 is formed of one or plurality of LED elements (Fig. 2(a)), a filament bulb (Fig. 2(b)), a resistance load (Fig. 2(c)) or the like. In the case of the load circuit Y1 formed of the filament bulb, a converter making an applied voltage constant is used. Since the LED element and the filament bulb are light source loads, when the electric circuits W11, W12 cause a ground fault, the LED element and the filament bulb are lighted off (or dimmed) and thus, the user can recognize the occurrence of abnormality in the power-source device A1. In the case of the load circuit Y1 formed of a driving load such as the resistance load, at occurrence of a ground fault of the electric circuits W11, W12, the user can recognize the occurrence of abnormality in the power-source device A1 on the basis of the stop of the operation of the load circuit Y1.

(Second embodiment)

[0045] Fig. 3 shows a specific circuit configuration of the power-source device A1, which is a step-up/down chopper circuit basically as the CUK circuit. Hereinafter, a reference numeral Ala is assigned to the power-source device in Fig. 3. The same constituents as those in the first embodiment are given the same reference numerals.

[0046] The power-source device Ala basically as the CUK circuit is a non-isolated power-source device, and constitutes an LED driving device that uses the DC power-source E1 as the input power-source and supplies DC power to an LED unit X1 formed by serially connecting a plurality of LED elements. A negative electrode of the DC power-source E1 is grounded to the ground line G1.

[0047]  A series circuit formed by serially connecting an inductor L1 (first inductor), the capacitor C2 (second capacitor), an inductor L2 (second inductor), the load circuit Y1, and the capacitor C1 (first capacitor) in this order is arranged in a path extending from the positive electrode of the DC power-source E1 to the negative electrode of the DC power-source E1. A switching element S1 is connected between a connection point of the inductor L1 and the capacitor C2 and the negative electrode of the DC power-source E1. An anode of a diode D1 is connected to a connection point of the capacitor C2 and the inductor L2, and a cathode of the diode D1 is connected to a connection point of the load circuit Y1 and the capacitor C1.

[0048] The load circuit Y1 is formed of a parallel circuit including the LED unit X1 formed by serially connecting the plurality of LED elements and a capacitor C3 (third capacitor), and a DC current is supplied from the power-source device Ala to the parallel circuit of the LED unit X1 and the capacitor C3. Anodes of the LED elements of the LED unit X1 are connected to the electric circuit W11, and cathodes of the LED elements are connected to the electric circuit W12.

[0049] Such power-source device Ala is formed of a converter part A11 (step-up part) having a step-up function using the DC power-source E1 as a power-source and a converter part A12 (step-down part) having a step-down function using the capacitors C1, C2 as power sources. The converter part A11 is configured of the inductor L1, the switching element S1, the capacitors C1, C2, and the diode D1. The converter part A12 is configured of the switching element S1, the capacitors C1, C2, the diode D1, and the inductor L2.

[0050] A control circuit not shown turns on/off the switching element S1, thereby supplying DC power to the load circuit Y1 to light each LED element of the LED unit X1.

[0051] Operations of this circuit will be described below.

[0052] First, describing operations of the converter part A11 having the step-up function, when the switching element S1 is turned on, a current flows in a closed circuit passing the DC power-source E1, the inductor L1, the switching element S1, and the DC power-source E1, and the inductor L1 stores magnetic energy. Then, when the switching element S1 is turned off, the magnetic energy in the inductor L1 is discharged in a closed circuit passing the inductor L1, the capacitor C2, the diode D1, the capacitor C1-DC power-source E1, and the inductor L1, and electric charges are stored in the capacitors C1, C2. According to the turning-on/off operation of the switching element S1, a voltage between both ends of the capacitors C1, C2 is raised to a voltage that is higher than the voltage at the DC power-source E1.

[0053] Next, describing operations of the converter part A12 having the step-down function, when the switching element S1 is turned on, the voltage between both ends of the capacitors C1, C2 thus stored serves as the power-source, and electric charges stored in the capacitors C1, C2 are discharged. Specifically, the electric charges stored in the capacitors C1, C2 are discharged in a closed circuit passing the capacitor C2-switching element S1, the capacitor C1, the load circuit Y1 (LED unit X1, capacitor C3), the inductor L2, and the capacitor C2. At this time, magnetic energy is stored in the inductor L2.

[0054] When the switching element S1 is turned off, a counter-electromotive force occurs in the inductor L2, and a current flows in a closed circuit passing the inductor L2, the diode D1, the load circuit Y1 (LED unit X1, capacitor C3), and the inductor L2 so as to maintain the current direction at turning-on of the switching element S1. According to the turning-on/off direction of the switching element S1, a voltage that is lower than the voltage between both ends of each of the capacitors C1, C2 is applied to the load circuit Y1. Whether the voltage applied to the load circuit Y1 is higher or lower than the voltage of the DC power-source E1 can be set according to operations (on-duty, frequency and so on) of the switching element S1 and a circuit constant.

[0055] As described above, according to the turning-on/off operation of the switching element S1, the power-source device operates with respect to the DC power-source E1 in the step-up mode, and with respect to the voltage between both ends of each of the capacitors C1, C2 in the step-down mode. The current of the inductors L1, L2 has a waveform such as a triangular waveform, while the current of the LED unit X1 is a DC current smoothed by the capacitor C3.

[0056] In the power-source device Ala basically as the CUK circuit, one end of the capacitor C1 is at the same (or almost same) potential as the ground line G1. Further, the electric circuit W11 connects the capacitor C1 to the load circuit Y1, and the electric circuit W12 connects the load circuit Y1 to the inductor L2. In Fig. 3, the electric circuit W11 is configured of an electric circuit between the capacitor C1 and the LED unit X1 and an electric circuit between the capacitor C1 and the capacitor C3. The electric circuit W12 is configured of an electric circuit between the LED unit X1 and the inductor L2 and an electric circuit between the capacitor C3 and the inductor L2.

[0057] Thus, the electric circuit W11 includes the capacitor C1 between the electric circuit W11 and the ground line G1, and the electric circuit W12 includes the load circuit Y1 and the capacitor C1 between the electric circuit W12 and the ground line G1. Accordingly, both the electric circuits W11, W12 as the electric circuits at both ends of the load circuit Y1, and the ground line G1 are at different potentials.

[0058] In such power-source device Ala basically as the CUK circuit, even when either of the electric circuits W11, W12 causes a ground fault (comes in contact with the ground line G1), a ground-fault current flows in a closed circuit passing the positive electrode of the DC power-source E1, the inductor L1, the capacitor C2, and the inductor L2. At this time, the capacitor C2 in the closed circuit as well as the capacitor C1 is charged with a current supplied from the electric circuit W11. Accordingly, even when either of the electric circuit W11, W12 causes a ground fault, the power-source side (DC power-source E1) and the load side (load circuit Y1) are separated from each other in a DC manner by the capacitors C1, C2, thereby protecting the circuit.

[0059] The capacitor C2 is a capacitor used to perform the normal power supplying operation of the CUK circuit, and is also used to separate the power-source side from the load side at the occurrence of a ground fault. Accordingly, the capacitor C1 only needs to be added as a circuit component to counter the ground fault.

[0060] For example, the LED unit X1 may be arranged away from the power-source device Ala, and a harness of a wiring connecting an output of the power-source device A1a to the LED unit X1 may get caught by any structure. In this case, the electric circuits W11, W12 can come in contact with the ground line G1, causing a ground fault.

[0061] When the electric circuit W12 causes a ground fault, a ground-fault current flows in a closed circuit passing the positive electrode of the DC power-source E1, the inductor L1, the capacitor C2, the inductor L2-electric circuit W12, the ground line G1, and the negative electrode of the DC power-source E1. Since the path is different from a current path at a normal circuit operation, supplying of power to the load circuit Y1 is suppressed. The user can recognize the occurrence of abnormality in the power-source device A1a on the basis of lighting-off (or dimming) of the LED unit X1.

[0062] When the electric circuit W11 causes a ground fault, a ground-fault current flows in a closed circuit passing the positive electrode of the DC power-source E1, the inductor L1, the capacitor C2, the inductor L2-electric circuit W12, the load circuit Y1 (LED unit X1, capacitor C3), the electric circuit W11, the ground line G1-the negative electrode of the DC power-source E1. Since the path is different from a current path at a normal circuit operation, supplying of power to the load circuit Y1 is suppressed. The user can recognize the occurrence of abnormality in the power-source device A1a on the basis of lighting-off (or dimming) of the LED unit X1.

[0063] When either of the electric circuits W11, W12 causes a ground fault, since the ground-fault current passes the inductors L1, L2, no sharp ground-fault current flows, and the ground-fault current has a moderate waveform, thereby a stress on the circuit components is reduced. Then, by detecting lighting-off (or dimming) of the LED unit X1, turning-on/off of the switching element S1 may be stopped.

[0064] Fig. 4 shows another type of the load circuit Y1. In the converter part A12, a mode of the current supplied to the load circuit Y1 becomes a continuous mode, a discontinuous mode, or a critical mode, depending on the value of the inductor L2, and a double value of the current flowing through the LED unit X1 largely varies depending on the current waveform. In Fig. 4, inductors L31, L32 (third and fourth inductors) are serially connected to both ends of the LED unit X1, respectively, and the series circuit is connected to the capacitor C3 (third capacitor) in parallel, and has a filtering function of reducing the ripple current. The ripple current is determined depending on values of the capacitor C3 and the inductors L31, L32, and the current mode.

[0065] As shown in Fig. 5, a resistor R1 may be serially connected to the capacitor C1. Also in this case, similarly, when the electric circuits W11, W12 cause a ground fault, the above-mentioned actions and effects can be obtained.

[0066] Fig. 6 shows a power-source device A1b provided with a plurality of load circuits Y1, the inductor L2 is serially connected to each of the load circuits Y1. In this case, on the basis of the ground fault of either of the connected electric circuits of the load circuit Y1, as described above, the LED unit X1 of one or more load circuits Y1 is lighted off (or dimmed) and thus, the user can recognize the occurrence of abnormality in the power-source device A1b.

(Third embodiment)

[0067] Fig. 7 shows a specific circuit configuration of the power-source device A1, which is a step-up/down chopper circuit basically as a ZETASEPIC (zeta sepic) circuit. Hereinafter, a reference numeral A1c is assigned to the power-source device in Fig. 7. The same constituents as those in the first embodiment are given the same reference numerals.

[0068] The power-source device A1c basically as the ZETASEPIC circuit is a non-isolated power-source device, and constitutes an LED driving device that uses the DC power-source E1 as the input power-source, and supplies DC power to an LED unit X11 formed by serially connecting a plurality of LED elements. The negative electrode of the DC power-source E1 is grounded to the ground line G1.

[0069] A series circuit formed by connecting the switching element S11, the capacitor C2 (second capacitor), the inductor L11 (first inductor), the load circuit Y1, and the capacitor C1 (first capacitor) in this order is arranged in a path extending from the positive electrode of the DC power-source E1 to the negative electrode of the DC power-source E1. The inductor L12 (second inductor) is connected between a connection point of the switching element S11 and the capacitor C2 and the negative electrode of the DC power-source E1. An anode of a diode D11 is connected to a connection point of the load circuit Y1 and the capacitor C1, and a cathode of the diode D11 is connected to a connection point of the capacitor C2 and the inductor L11.

[0070] The load circuit Y1 is configured of a parallel circuit of the LED unit X11 formed by serially connecting a plurality of LED elements and the capacitor C13 (third capacitor), and a DC current is supplied from the power-source device A1c to the parallel circuit of the LED unit X11 and the capacitor C13. Anodes of the LED elements of the LED unit X11 are connected to the electric circuit W12, and cathodes of the LED elements of the LED unit X11 are connected to the electric circuit W11.

[0071] A control circuit not shown turns on/off the switching element S11, thereby supplying DC power to the load circuit Y1 to light each LED element of the LED unit X11. Operations of the ZETASEPIC circuit are publicly known and thus, description thereof is omitted.

[0072] In the power-source device A1c basically as the ZETASEPIC circuit, one end of the capacitor C1 is at the same (or almost same) potential as the ground line G1. Further, the electric circuit W11 connects the capacitor C1 to the load circuit Y1, and the electric circuit W12 connects the load circuit Y1 to the inductor L11. In Fig. 7, the electric circuit W11 is configured of an electric circuit between the capacitor C1 and the LED unit X11 and an electric circuit between the capacitor C1 and the capacitor C13. The electric circuit W12 is configured of an electric circuit between the LED unit X11 and the inductor L11 and an electric circuit between the capacitor C13 and the inductor L11.

[0073] Thus, the electric circuit W11 includes the capacitor C1 between the electric circuit W11 and the ground line G1, and the electric circuit W12 includes the load circuit Y1 and the capacitor C1 between the electric circuit W12 and the ground line G1. Accordingly, both the electric circuits W11, W12 as the electric circuits at both ends of the load circuit Y1, and the ground line G1 are at different potentials.

[0074] In such power-source device A1c basically as the ZETASEPIC circuit, even when either of the electric circuits W11, W12 causes a ground fault (comes in contact with the ground line G1), a ground-fault current flows in a closed circuit passing the positive electrode of the DC power-source E1, the switching element S11, the capacitor C2, and the inductor L11. At this time, the capacitor C2 in the closed circuit as well as the capacitor C1 is charged with a current supplied from the electric circuit W11. Accordingly, even when either of the electric circuits W11, W12 causes a ground fault, the power-source side (DC power-source E1) and the load side (load circuit Y1) are separated from each other in a DC manner by the capacitors C1, C2, thereby protecting the circuit.

[0075] The capacitor C2 is a capacitor used to perform the normal power supplying operation of the ZETASEPIC circuit, and is also used to separate the power-source side from the load side at the occurrence of a ground fault. Accordingly, the capacitor C1 only needs to be added as a circuit component to counter the ground fault.

[0076] For example, the LED unit X11 may be arranged away from the power-source device A1c, and a harness of a wiring connecting an output of the power-source device A1c to the LED unit X11 may get caught by any structure. In this case, the electric circuits W11, W12 can come in contact with the ground line G1, causing a ground fault.

[0077] When the electric circuit W12 causes a ground fault, a ground-fault current flows in a closed circuit passing the positive electrode of the DC power-source E1-switching element S11, the capacitor C2, the inductor L11-electric circuit W12, the ground line G1, and the negative electrode of the DC power-source E1. Since the path is different from a current path at a normal circuit operation, supplying of power to the load circuit Y1 is suppressed. The user can recognize the occurrence of abnormality in the power-source device A1c on the basis of lighting-off (or dimming) of the LED unit X11.

[0078] When the electric circuit W11 causes a ground fault, a ground-fault current flows in a closed circuit passing the positive electrode of the DC power-source E1, the switching element S11, the capacitor C2, the inductor L11, the electric circuit W12, the load circuit Y1 (LED unit X11, capacitor C13), the electric circuit W11, the ground line G1, and the negative electrode of the DC power-source E1. Since the path is different from a current path at a normal circuit operation, supplying of power to the load circuit Y1 is suppressed. The user can recognize the occurrence of abnormality in the power-source device A1c on the basis of lighting-off (or dimming) of the LED unit X11.

[0079] Even when either of the electric circuits W11, W12 causes a ground fault, since the ground-fault current passes the inductor L11, no sharp ground-fault current flows, and the ground-fault current has a moderate waveform, thereby reducing a stress on the circuit components. Then, by detecting lighting-off (or dimming) of the LED unit X11, turning-on/off of the switching element S11 may be stopped.

[0080] Fig. 8 shows another type of the load circuit Y1. In the power-source device A1c, the mode of the current supplied to the load circuit Y1 becomes the continuous mode, the discontinuous mode, or the critical mode, depending on the value of the inductor L2, and a ripple value of the current flowing through the LED unit X11 largely varies depending on the current waveform. In Fig. 8, inductors L41, L42 (third and fourth inductors) are serially connected to both ends of the LED unit X11, respectively, and the series circuit is connected to a capacitor C13 (third capacitor) in parallel, and has a filtering function of reducing the ripple current. The ripple current is determined depending on values of the capacitor C13 and the inductors L41, L42, and the current mode.

[0081] As shown in Fig. 5, the resistor R1 may be serially connected to the capacitor C1. Also in this case, similarly, when either of the electric circuits W11, W12 causes a ground fault, the above-mentioned actions and effects can be achieved.

[0082] Fig. 9 shows a power-source device A1d provided with a plurality of load circuits Y1, the inductor L11 is serially connected to each of the load circuits Y1. In this case, on the basis of the ground fault of either of the connected electric circuits of the load circuit Y1, as described above, the LED unit X1 of one or more load circuits Y1 is lighted off (or dimmed) and thus, the user can recognize the occurrence of abnormality in the power-source device A1d.

(Fourth embodiment)

[0083] Fig. 10 shows a specific circuit configuration of the power-source device A1, which is a step-up/down chopper circuit basically as a SEPIC (sepic) circuit. Hereinafter, a reference numeral Ale is assigned to the power-source device in Fig. 10. The same constituents as those in the first embodiment are given the same reference numerals.

[0084] The power-source device Ale basically as the SEPIC circuit is a non-isolated power-source device, and constitutes an LED driving device that uses the DC power-source E1 as the input power-source, and supplies DC power to an LED unit X21 formed by serially connecting the plurality of LED elements. The negative electrode of the DC power-source E1 is grounded to the ground line G1.

[0085] A series circuit formed by serially connecting the inductor L21 (first inductor), the capacitor C2 (second capacitor), a diode D21, the load circuit Y1, and the capacitor C1 (first capacitor) in this order is arranged in a path extending from the positive electrode of the DC power-source E1 to the negative electrode of the DC power-source E1. A switching element S21 is connected between a connection point of the inductor L21 and the capacitor C2 and the negative electrode of the DC power-source E1. An inductor L22 (second inductor) is connected between a connection point of the capacitor C2 and the diode D21 and a connection point of the load circuit Y1 and the capacitor C1. An anode of the diode D21 is connected to the capacitor C2, and a cathode of the diode D21 is connected to the load circuit Y1.

[0086] The load circuit Y1 is formed of a parallel circuit of the LED unit X21 formed by serially connecting a plurality of LED elements and the capacitor C23 (third capacitor), and a DC current is supplied from the power-source device Ale to the parallel circuit of the LED unit X21 and the capacitor C23.

[0087] A control circuit not shown turns on/off the switching element S21, thereby supplying DC power to the load circuit Y1 to light each LED element of the LED unit X21. Operations of the SEPIC circuit are publicly known and thus, description thereof is omitted.

[0088] In the power-source device Ale basically as the SEPIC circuit, one end of the capacitor C1 is at the same (or almost sate) potential as the ground line G1. Further, the electric circuit W11 connects the capacitor C1 to the load circuit Y1, and the electric circuit W12 connects the load circuit Y1 to the diode D21. In Fig. 10, the electric circuit W11 is configured of an electric circuit between the capacitor C1 and the LED unit X21 and an electric circuit between the capacitor C1 and the capacitor C23. The electric circuit W12 is configured of an electric circuit between the LED unit X21 and the diode D21 and an electric circuit between the capacitor C23 and the diode D21.

[0089] Thus, the electric circuit W11 includes the capacitor C1 between the electric circuit W11 and the ground line G1, and the electric circuit W12 includes the load circuit Y1 and the capacitor C1 between the electric circuit W12 and the ground line G1. Accordingly, both the electric circuits W11, W12 as the electric circuits at both ends of the load circuit Y1, and the ground line G1 are at different potentials.

[0090] In such power-source device Ale basically as the SEPIC circuit, even when either of the electric circuits W11, W12 causes a ground fault (comes in contact with the ground line G1), a ground-fault current flows in a closed circuit passing the positive electrode of the DC power-source E1, the inductor L21, the capacitor C2, and the diode D21. At this time, the capacitor C2 in the closed circuit as well as the capacitor C1 is charged with the current supplied from the electric circuit W11. Accordingly, even when either of the electric circuits W11, W12 causes a ground fault, the power-source side (DC power-source E1) and the load side (load circuit Y1) are separated from each other in a DC manner by the capacitors C1, C2, thereby protecting the circuit.

[0091] The capacitor C2 is a capacitor used to perform the normal power supplying operation of the SEPIC circuit, and is also used to separate the power-source side from the load side at the occurrence of a ground fault. Accordingly, the capacitor C1 only needs to be added as a circuit component to counter the ground fault.

[0092] For example, the LED unit X21 may be arranged away from the power-source device Ale, and a harness of a wiring connecting an output of the power-source device Ale to the LED unit X21 may get caught by any structure. In this case, the electric circuits W11, W12 can come in contact with the ground line G1, causing a ground fault.

[0093] When the electric circuit W12 causes a ground fault, a ground-fault current flows in a closed circuit passing the positive electrode of the DC power-source E1, the inductor L21, the capacitor C2, the diode D21, the electric circuit W12, the ground line G1, and the negative electrode of the DC power-source E1. Since the path is different from a current path at a normal circuit operation, supplying of power to the load circuit Y1 is suppressed. The user can recognize the occurrence of abnormality in the power-source device Ale on the basis of lighting-off (or dimming) of the LED unit X21.

[0094] When the electric circuit W11 causes a ground fault, a ground-fault current flows in a closed circuit passing the positive electrode of the DC power-source E1, the inductor L21, the capacitor C2, diode D21-electric circuit W12, the load circuit Y1 (LED unit X21, capacitor C23), the electric circuit W11, the ground line G1, and the negative electrode of the DC power-source E1. Since the path is different from a current path at a normal circuit operation, supplying of power to the load circuit Y1 is suppressed. The user can recognize the occurrence of abnormality in the power-source device Ale on the basis of lighting-off (or dimming) of the LED unit X21.

[0095] Even when either of the electric circuits W11, W12 causes a ground fault, since the ground-fault current passes the inductor L21, no sharp ground-fault current flows, and the ground-fault current has a moderate waveform, thereby reducing a stress on the circuit components. Then, by detecting lighting-off (or dimming) of the LED unit X21, turning-on/off of the switching element S1 may be stopped.

[0096] Fig. 11 shows another type of the load circuit Y1. In the power-source device Ale, the mode of the current supplied to the load circuit Y1 becomes the continuous mode, the discontinuous mode, or the critical mode, depending on the value of the inductor L2, and a ripple value of the current flowing through the LED unit X21 largely varies depending on the current waveform. In Fig. 11, inductors L51, L52 (third and fourth inductors) are serially connected to both ends of the LED unit X21, respectively, and the series circuit is connected to the capacitor C23 (third capacitor) in parallel, and has a filtering function of reducing the ripple current. The ripple current is determined depending on values of the capacitor C23 and the inductors L51, L52, and the current mode.

[0097] As shown in Fig. 5, the resistor R1 may be serially connected to the capacitor C1. Also in this case, similarly, when either of the electric circuits W11, W12 causes a ground fault, the above-mentioned actions and effects can be achieved.

[0098] Fig. 12 shows a power-source device A1f provided with a plurality of load circuits Y1, and the diode D21 is serially connected to each of the load circuits Y1. In this case, on the basis of the ground fault of either of the connected electric circuits of the load circuit Y1, as described above, the LED unit X21 of one or more load circuits Y1 is lighted off (or dimmed) and thus, the user can recognize the occurrence of abnormality in the power-source device A1d.

[Description of Reference Numerals]

[0099] 

A1

Power-source device

A11

Converter part

E1

DC power-source

C1

Capacitor (first capacitor)

C2

Capacitor (second capacitor)

Y1

Load circuit

G1

Ground line

Claims

1. A non-isolated power-source device that converts input power from a DC power-source, one electrode of which is grounded, into desired DC power, and supplies the converted DC power to a load circuit, the power-source device comprising:

a first capacitor electrically connected between one end of the load circuit and the one electrode of the DC power-source; and

a second capacitor electrically connected between the other end of the load circuit and the other electrode of the DC power-source.

2. The power-source device according to claim 1, further comprising:

a switching element electrically connected to the first and second capacitors, the switching element switching between charge and discharge of the first and second capacitors;

a step-up part that raises a voltage of the DC power-source by turning on/off the switching element; and

a step-down part that lowers the voltage raised by the step-up part by turning on/off the switching element, and applies the lowered voltage to the load circuit.

3. The power-source device according to claim 2, wherein
a series circuit formed by connecting a first inductor, the second capacitor, a second inductor, the load circuit, and the first capacitor in this order is provided in a path extending from the other electrode of the DC power-source to the one electrode,
the switching element is connected between a connection point of the first inductor and the second capacitor and the one electrode of the DC power-source, and
a diode is connected between a connection point of the second capacitor and the second inductor and a connection point of the load circuit and the first capacitor.

4. The power-source device according to claim 1, wherein
a series circuit formed by connecting a switching element, the second capacitor, a first inductor, the load circuit, and the first capacitor in this order is provided in a path extending from the other electrode of the DC power-source to the one electrode,
a second inductor is connected between a connection point of the switching element and the second capacitor and the one electrode of the DC power-source, and
a diode is connected between a connection point of the second capacitor and the first inductor and a connection point of the load circuit and the first capacitor.

5. The power-source device according to claim 1,
a series circuit formed by connecting a first inductor, the second capacitor, a diode, the load circuit, and the first capacitor in this order is provided in a path extending from the other electrode of the DC power-source to the one electrode,
a switching element is connected between a connection point of the first inductor and the second capacitor and the one electrode of the DC power-source, and
a second inductor is connected between a connection point of the second capacitor and the diode and a connection point of the load circuit and the first capacitor.

6. The power-source device according to any one of claims 1 to 5,
wherein the load circuit includes a load formed of an LED element, an incandescent lamp, or a resistance element.

7. The power-source device according to claim 6, wherein the load circuit includes a third capacitor connected to the load in parallel.

8. The power-source device according to claim 6, wherein the load circuit includes a third inductor connected to one end of the load, a fourth inductor connected to the other end of the load, and a third capacitor connected to a series circuit of the load and the third and fourth inductors.

9. The power-source device according to any one of claims 1 to 8,
wherein a resistor is connected to the first capacitor in parallel.

10. The power-source device according to any one of claims 1 to 9,
wherein a plurality of the load circuits is provided.

11. A non-isolated LED driving device that converts input power from a DC power-source, one electrode of which is grounded, into desired DC power, and supplies the converted DC power to a load circuit formed of one or plurality of LED element, the LED driving device comprising:

a first capacitor electrically connected between one end of the load circuit and the one electrode of the DC power-source; and

a second capacitor electrically connected between the other end of the load circuit and the other electrode of the DC power-source.

Drawing