TWI666969B - Power supply device and lighting device provided with the same - Google Patents

Abstract

The present invention can make the step-down chopper circuit operate stably while enabling the disassembly detection function of the load to be effective. A step-down chopper circuit is a series circuit that connects an inductor and a capacitor between the output terminal of the switching element and the ground. The two ends of the capacitor are set as power supply terminals for the load. An input voltage is converted into an output voltage corresponding to the load, and is supplied to the load connected to the power supply terminal. The short circuit is connected in parallel with the capacitor, and the potential of the connection point between the inductor and the capacitor is pulled to the potential of the ground line during operation. The control circuit causes the short-circuit circuit to operate before starting the switching control of the switching element, and on the condition that the load is connected to the power supply terminal.

Description

Power supply device and lighting device provided with the same

Embodiments of the present invention relate to a power supply device and a lighting device including the power supply device.

A power supply device is known in which a voltage supplied from the outside is boosted and then stepped down to obtain the required power. Boost is used to improve the power factor. In the power supply device, a power factor improvement circuit is used. Step-down is to adjust the voltage to control the constant current. In the power supply device, a step-down chopper circuit is used.

The step-down chopper circuit generally uses a field-effect transistor (FET) as a switching element for performing chopper. A field-effect transistor uses a potential difference between a gate serving as a control terminal and a source serving as an output terminal to turn on or off the conduction between a drain serving as an input terminal and a source.

In a step-down chopper circuit using the field effect transistor as a switching element, a bootstrap method is widely used as a method of supplying a driving power to the switching element. In the case of a step-down chopper circuit, in order to generate a regenerative current when the switching element is turned off, a diode is connected between a source terminal of the switching element and a ground. The diode is connected in a direction that prevents the current flowing from the source terminal to the ground. Therefore, when the step-down chopper circuit is not operating, the potential of the source terminal of the switching element is not fixed. In order to activate the switching element, it is necessary to supply a voltage of a fixed value or more based on the potential of the source terminal to the control terminal. However, if the potential of the source terminal is not fixed, the driving power of the switching element cannot be sufficiently ensured by the bootstrap circuit, and the startup becomes unstable, so that the step-down chopper circuit may not start stably.

For this reason, there has been a prior art in which the switching element is stably started by short-circuiting the source terminal of the switching element and the ground line to set the potential of the source terminal to the ground potential.

In addition, when introducing such a technology, if a chip integrated circuit and a circuit that controls the switching of the switching element are used together to constitute a circuit that short-circuits the source terminal of the switching element and the ground wire, it can be realized with the circuit. It is considered that miniaturization, cost reduction, and the like resulting from a reduction in the number are preferred.

On the other hand, in a circuit that short-circuits the source terminal of the switching element and the ground, a current flows from the step-down chopper circuit side during a short circuit. Therefore, it is necessary to use a circuit element having a withstand current characteristic capable of withstanding the current. However, the use of high-performance circuit elements with excellent current resistance characteristics to form a general-purpose integrated circuit is not satisfactory in terms of cost.

On the other hand, in such a power supply device, a technique for detecting a load to be supplied, for example, a technique for detecting attachment and detachment of a light source unit is known. Specifically, a series resistor circuit having a plurality of resistors connected in series is connected between the output terminals of the power supply device, a predetermined voltage is applied to both ends of the series resistor circuit, and a voltage divided by the resistor is monitored. The voltage will change according to the presence or absence of the load, so the power supply device can detect the disassembly of the load.

However, when the source terminal of the switching element and the ground are short-circuited during startup, and the potential of the source terminal is set to the ground potential, the source terminal is connected to the output terminal. There is a problem in that the voltage applied to the series resistance circuit connected between the output terminals drops, and it is impossible to detect and disassemble the load.

Further, in such a power supply device, a technique is known in which, when an overvoltage of a DC voltage output to a load through conversion by a step-down chopper circuit is detected, the switching of the switching element is stopped to suppress the overvoltage. For example, when a load mounted on a power supply device is removed, the output voltage may rise and become overvoltage. In this case, the protection function works, so that the circuit can be prevented from being damaged by an overvoltage.

However, even if the switching of the switching element is stopped, the output voltage does not drop immediately. The output voltage gradually decreases according to the attenuation characteristics of the output capacitor. Therefore, if the load is reinstalled within a period in which the output voltage has not fallen, a rush current flows into the load. For example, when the load is a light-emitting load using a light-emitting diode, the light-emitting diode may malfunction due to the inrush current. In order to deal with such a problem, it is necessary to further add circuit components, which hinders miniaturization and cost reduction of the power supply device.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent No. 3775240

The problem to be solved by the embodiments of the present invention is to provide a power supply device with high reliability and a lighting device including the power supply device, which can enable the step-down chopper circuit to operate stably while enabling the load disassembly detection function to be effective .

In addition, the present invention provides a power supply device capable of realizing stable operation of a step-down chopper circuit and protection against overvoltage without causing obstacles to miniaturization and cost reduction, and a lighting device having the same with high reliability .

In addition, a power supply device capable of constituting a circuit for short-circuiting a source terminal of a switching element and a ground line by using a high-performance circuit element having excellent current resistance characteristics as required, and an illuminating device including the power supply device are provided. Device.

In one embodiment, the power supply device includes a step-down chopper circuit, a short circuit, and a control circuit. The step-down chopper circuit is a series circuit in which an inductor and a capacitor are connected between the output terminal of the first switching element and the ground. The two ends of the capacitor are used as power supply terminals for the load. The switch of the first switching element converts an input voltage into an output voltage corresponding to the load, and supplies the input voltage to the load connected to the power supply terminal. The short circuit is connected in parallel with the capacitor, and the potential of the connection point between the inductor and the capacitor is pulled to the potential of the ground wire during operation. The control circuit operates the short-circuit circuit on the condition that the load is connected to the power supply terminal before switching control of the first switching element is started.

In one embodiment, the lighting device includes the power supply device and a light-emitting load connected to the power supply terminal of the power supply device to control lighting.

In one embodiment, the power supply device further includes a monitoring circuit. The monitoring circuit monitors the output voltage and causes the short circuit to operate when an abnormality in the output voltage is detected.

Furthermore, in one embodiment, the power supply device uses an integrated circuit to configure the control circuit and the short-circuit circuit. Furthermore, an external terminal is included, and the external terminal is used to output a signal output from the control circuit to the short circuit in order to operate the short circuit to the outside of the integrated circuit.

According to one embodiment, it is possible to provide a power supply device capable of enabling the step-down chopper circuit to operate stably while enabling the load disassembly detection function to be effective, and having high reliability.

In addition, it is possible to provide a power supply device capable of realizing stable operation of the step-down chopper circuit and protection against overvoltage without causing obstacles to miniaturization and cost reduction, thereby providing a highly reliable power supply device.

In addition, it is possible to provide a power supply device capable of forming a circuit for short-circuiting a source terminal of a switching element and a ground line using a high-performance circuit element having excellent current resistance characteristics as required, and having excellent practicability.

Furthermore, according to an embodiment, it is possible to provide a highly reliable lighting device capable of stably operating the step-down chopper circuit of the power supply device while enabling the disassembly detection function of the light emitting load of the power supply device to be effective.

1‧‧‧light source unit

2‧‧‧ Power Unit

10‧‧‧ Rectifier circuit

20‧‧‧Power factor improvement circuit

30‧‧‧Buck chopper circuit

40‧‧‧Control circuit

41‧‧‧PFC control circuit

42‧‧‧lighting control circuit

43‧‧‧Protection circuit

44‧‧‧ Power Circuit

45‧‧‧ Operational Amplifier

46‧‧‧Monitoring Circuit

47‧‧‧Judgment Circuit

48‧‧‧Start circuit

50‧‧‧Install detection circuit

100‧‧‧lighting device

200‧‧‧ external power supply

C1 ~ C5, C31‧‧‧ capacitor

C21‧‧‧electrolytic capacitor

D1, D21, D31, D51‧‧‧ diodes

D11‧‧‧light-emitting diode

GND‧‧‧Reference potential / ground of the control circuit

L21‧‧‧ primary coil

L22‧‧‧ secondary coil

L31‧‧‧Inductor

Q21‧‧‧Switch element

Q31‧‧‧Switching element (first switching element)

Q48‧‧‧ Switching element (second switching element)

R1 ~ R9, R11, R21, R22, R31, R32, R51 ~ R54, R101, R102‧‧‧ resistors

ST1 ~ ST5, ST11 ~ ST13 ‧‧‧ steps

MULT, GD, ZCD, CS, Vcc, VS, HO, VB, VFB, VDC, OCP, VC2, LGND, Vref, OP +, OP-, ABN, Lamp, DISin, DIS, T11 ~ T13

T21, T22‧‧‧‧Powered terminals

T31 ~ T33‧‧‧Power supply terminal

Tr21‧‧‧Transformer

FIG. 1 is a schematic electrical circuit configuration diagram of a lighting device including a power supply device according to this embodiment.

FIG. 2 is a block diagram showing a configuration of a main part of the control circuit in FIG. 1. FIG.

FIG. 3 is a flowchart showing an operation sequence when the power of the control circuit in FIG. 1 is turned on.

FIG. 4 is a flowchart showing an operation procedure when the control circuit in FIG. 1 detects an abnormality.

Hereinafter, embodiments will be described using drawings.

FIG. 1 is an electrical circuit configuration diagram of a lighting device 100 including a power supply device 2 of the present embodiment. In addition, FIG. 1 shows a schematic circuit configuration, and illustration of a part of various elements included in an actual circuit configuration has been omitted.

The lighting device 100 includes a light source unit 1 and a power supply device 2. The light source unit 1 controls the lighting load of the lighting by the power supply device 2, and is detachable from the power supply device 2. The power supply device 2 is fixedly mounted on the body of the lighting device 100.

The light source unit 1 includes a plurality of light emitting diodes (LEDs) D11 and a resistor R11. A plurality of light emitting diodes D11 are connected in series. In addition, although not shown, in the light source unit 1, a resistance element is also connected in parallel with the light emitting diode D11. The resistor R11 is connected to a current output terminal in a series circuit of the light emitting diode D11. The light source unit 1 has a current input terminal and a current output terminal in a series circuit of the light-emitting diode D11, and an end of the resistor R11 that is not connected to the light-emitting diode D11, and is respectively provided for freely attaching to a power source The terminal T11, the terminal T12, and the terminal T13 of the device 2.

The number of light-emitting diodes D11 is arbitrary. The light source unit 1 may also be provided with only one light emitting diode D11. In addition, multiple The series circuit of the photodiode D11 is connected in parallel. In addition, the light source unit 1 may be provided with other types of light emitting devices such as organic electroluminescence (EL) as a light source, instead of the light emitting diode D11.

The power source device 2 receives power from an external power source 200 such as a commercial power source, and generates DC power for emitting light from the light emitting diode D11 of the light source unit 1 connected as a load. Then, the power supply device 2 supplies the generated DC power to the light source unit 1 mounted on the power supply terminal T31, the power supply terminal T32, and the power supply terminal T33 to control lighting.

The power supply device 2 includes a rectifier circuit 10, a power factor improvement circuit 20, a step-down chopper circuit 30, a control circuit 40, and a mounting detection circuit 50. The power supply device 2 includes a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a capacitor C5, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7, and a resistor. Resistor R8, resistor R9, resistor R101, resistor R102, and diode D1 various circuit elements.

A pair of input terminals of the rectifier circuit 10 are connected to two power-supply terminals T21 and T22, respectively. The two power-supply terminals T21 and T22 are respectively connected with two power supply lines connected to an external power supply 200 such as a commercial power supply. Through this connection, AC power is supplied from the external power source 200 to a pair of input terminals of the rectifier circuit 10. The rectifier circuit 10 rectifies AC power and outputs DC power. The DC power output between the rectifier circuit 10 and the pair of output terminals is smoothed by the capacitor C1 and then supplied to the power factor improvement circuit 20. Capacitor C1 connects one end to one output end of the rectifier circuit 10 and the other end to the base of the main circuit Quasi-potential is the ground. Furthermore, since the capacitance of the capacitor C1 is in the order of a few microFarads (μF), the voltage across the two ends becomes a pulse current voltage that performs full-wave rectification of a sine wave.

The power factor improving circuit 20 boosts the DC power smoothed by the capacitor C1 to improve the power factor. The power factor improvement circuit 20 is also referred to as a power factor correction (PFC) circuit. The power factor improving circuit 20 includes a transformer Tr21, a switching element Q21, an electrolytic capacitor C21, a diode D21, a resistor R21, and a resistor R22.

The transformer Tr21 includes a primary-side coil L21 and a secondary-side coil L22. The transformer Tr21 connects the input end of the primary-side coil L21 to one end of the capacitor C1, and the output end to the anode of the diode D21. The transformer Tr21 connects the input terminal of the coil L22 on the secondary side to the ground, and connects the output terminal to one terminal of the resistor R22. The resistor R22 has one end connected to the output end of the coil L22 and the other end connected to the ZCD terminal of the control circuit 40.

The switching element Q21 is an N-channel field effect transistor (FET). The switching element Q21 connects the drain terminal to the connection point between the output terminal of the coil L21 and the anode of the diode D21, the source terminal to one end of the resistor R21 and the CS terminal of the control circuit 40, and the gate terminal to GD terminal of the control circuit 40. Resistor R21 connects one end to the source terminal of switching element Q21 and the other end to ground. The diode D21 connects the anode to the connection point between the other end of the coil L21 and the drain terminal of the switching element Q21, and connects the cathode to one end of the electrolytic capacitor C21. Electrolytic capacitor C21 connects one end to the cathode of diode D21 and the other end to ground. Both terminals of electrolytic capacitor C21 become a power factor improvement circuit 20 Output terminal.

Through the connection, a series circuit of the diode D21 and the electrolytic capacitor C21 is formed between the drain terminal and the source terminal of the switching element Q21. On the other hand, the switching element Q21 is turned on after the gate signal applied to the gate terminal is turned on to form a closed circuit including a capacitor C1, a coil L21, and a resistor R21. In addition, the switching element Q21 is turned on after the gate signal applied to the gate terminal is turned off to cut off the closed circuit. As a result, the electrolytic capacitor C21 is charged by the voltage charged to the capacitor C1 when the switching element Q21 is in the off state, and is discharged when the switching element Q21 is in the on state. In this way, the power factor improving circuit 20 boosts the DC voltage rectified by the rectifying circuit 10 by the switching operation of the switching element Q21, obtains a predetermined DC voltage, and outputs it to the step-down chopper circuit 30.

The step-down chopper circuit 30 includes a switching element (first switching element) Q31, an inductor L31 for power storage, a capacitor C31 for output, a diode D31 for regeneration, a resistor R31, and a resistor R32. The switching element Q31 is an N-channel field effect transistor (FET). The switching element Q31 is connected to the drain terminal of one end of the electrolytic capacitor C21 which is an output terminal of the power factor improvement circuit 20, and the source terminal is connected to the connection point between the input terminal of the inductor L31 and the cathode of the diode D31. The gate terminal is connected to the HO terminal of the control circuit 40. The inductor L31 connects the input terminal to the source terminal of the switching element Q31, and connects the output terminal to one end of the capacitor C31. Capacitor C31 has one end connected to the output end of inductor L31 and the other end connected to one end of resistor R31. The resistor R31 connects one end to the other end of the capacitor C31 and the other end to the anode of the diode D31. Diode D31 connects the cathode to the The connection point between the source terminal of the off element Q31 and the inductor connects the anode to the ground.

The step-down chopper circuit 30 connects both ends of the capacitor C31 to the power supply terminal T31, the power supply terminal T32, and the power supply terminal T33 of the power supply device 2. Specifically, the step-down chopper circuit 30 connects the side of the capacitor C31 connected to the output terminal of the inductor L31 to the power supply terminal T31, and connects the side of the capacitor C31 connected to the resistor R31 to the power supply terminal T33. The side of the capacitor C31 connected to the resistor R31 is connected to the power supply terminal T32 via a resistor R32.

Therefore, when the light source unit 1 as a load is connected to the power supply device 2, the terminal T11 of the light source unit 1 is connected to the power supply terminal T31, the terminal T12 of the light source unit 1 is connected to the power supply terminal T32, and the power supply terminal T33 is connected. Connect the terminal T13 of the light source unit 1. The terminal T11 is a current input terminal of the light source unit 1. The terminal T12 is a current output terminal of the light source unit 1.

Through the connection, the switching element Q31 is turned on after the gate signal applied to the gate terminal is turned on, and the output current of the power factor improvement circuit 20 is guided to the inductor L31. The switching element Q31 is turned on after the gate signal applied to the gate terminal is turned off, and cuts off the output current of the power factor improvement circuit 20. The inductor L31 accumulates the DC power when the switching element Q31 is turned on and a DC voltage is applied. If the switching element Q31 is turned off and a DC voltage cannot be applied, the stored DC power is released. The DC power released from the inductor L31 is smoothed by the capacitor C31, and is supplied to a load connected to the power supply terminal T31, the power supply terminal T32, and the power supply terminal T33, for example, the light source unit 1.

The mounting detection circuit 50 includes a diode D51 and a resistor R51, Resistor R52, resistor R53, and resistor R54. The mounting detection circuit 50 connects one end of the resistor R54 to the VC2 terminal of the control circuit 40, the other end to the anode of the diode D51, and the cathode of the diode D51 to the power supply terminal T31 of the power supply device 2. In addition, the mounting detection circuit 50 uses a resistor R51 and a resistor R52 to form a series resistance circuit R51-R52. One end of the series resistance circuit R51-R52 is connected to the anode of the diode D51, and the other end is connected to the ground. Therefore, the series resistance circuits R51-R52 are connected in parallel with the capacitor C31 of the step-down chopper circuit 30.

The mounting detection circuit 50 connects one end of the resistor R53 to the midpoint of the series resistance circuits R51-R52, and connects the other end of the resistor R53 to the Lamp terminal of the control circuit 40. Here, the mounting detection circuit 50 is a circuit that can determine whether it is at the power supply terminal T31, the power supply terminal of the power supply device 2 by the change in the voltage divided by the resistance ratio of the series resistance circuits R51-R52. A load is connected to T32 and power supply terminal T33.

The control circuit 40 is composed of an analog integrated circuit (IC). The control circuit 40 includes MULT terminals, GD terminals, ZCD terminals, CS terminals, Vcc terminals, VS terminals, HO terminals, VB terminals, VFB terminals, VDC terminals, OCP terminals, and VC2 as external terminals for connection with the outside. Terminal, LGND terminal, Vref terminal, OP + terminal, OP- terminal, ABN terminal, Lamp terminal, DISin terminal, and DIS terminal. It is needless to say that the external terminals included in the control circuit 40 are not limited to these terminals.

The MULT terminal is connected to the midpoint of a series resistance circuit R1-R2 formed by a resistor R1 and a resistor R2. Series resistor circuits R1-R2 are connected to capacitor C1 Between the two terminals. With this connection, the potential of the MULT terminal depends on the voltage obtained by dividing the output voltage of the capacitor C1 by the resistance ratio of the series resistance circuits R1-R2. The control circuit 40 detects the input voltage to the power factor improvement circuit 20 using the potential of the MULT terminal.

The GD terminal is connected to the gate terminal of the switching element Q21. The control circuit 40 generates a gate signal of the switching element Q21. Then, the control circuit 40 outputs a gate signal of a gate-on or a gate-off from the GD terminal to the gate terminal of the switching element Q21.

The ZCD terminal is connected to the output terminal of the coil L22 via a resistor R22. The coil L22 supplies a potential corresponding to a change amount of the current flowing into the coil L21 to the ZCD terminal. The control circuit 40 detects the timing when the current flowing in the coil L21 on the primary side of the transformer Tr21 becomes zero by using the potential of the ZCD terminal, and generates a trigger signal for turning on the switching element Q21.

The CS terminal is connected to the source terminal of the switching element Q21. The potential of the CS terminal depends on the current flowing between the drain and source of the switching element Q21. The control circuit 40 uses a potential of the CS terminal to detect a current flowing in the switching element Q21, which is a so-called switching current.

The Vcc terminal is connected to the anode of the diode D1. The cathode of the diode D1 is connected to the VB terminal, and is connected to one end of the capacitor C2 for bootstrapping. The other end of the capacitor C2 is connected to the VS terminal, and is connected to the source terminal of the switching element Q31. The control circuit 40 applies a predetermined circuit operating voltage Vcc to the Vcc terminal. When the potential of the circuit operating voltage Vcc is higher than the potential of the source terminal of the switching element Q31, the capacitor C2 is charged. The control circuit 40 detects the voltage of the capacitor C2 from the VB terminal. The potential at one end side (the side connected to the cathode of the diode D1) is the potential at the other end side (the side connected to the source terminal of the switching element Q31) of the capacitor C2 from the VS terminal.

The HO terminal is connected to the gate terminal of the switching element Q31. The control circuit 40 generates a gate signal of the switching element Q31 based on a potential difference between both ends of the capacitor C2. Then, the control circuit 40 outputs a gate signal of a gate-on or a gate-off from the HO terminal to the gate terminal of the switching element Q31.

The VFB terminal is connected to the midpoint of a series resistance circuit R3-R4 formed by a resistor R3 and a resistor R4. The series resistance circuit R3-R4 is connected between two terminals of the capacitor C21. With this connection, the potential of the VFB terminal depends on the voltage obtained by dividing the output voltage of the capacitor C21 by the resistance ratio of the series resistance circuits R3-R4. The control circuit 40 detects, from the VFB terminal, the amount of change in the DC voltage output from the power factor improvement circuit 20 to the step-down chopper circuit 30 every fixed time.

The VDC terminal is connected to the connection point between the cathode of the diode D21 in the power factor improvement circuit 20 and the drain terminal of the switching element Q31 in the step-down chopper circuit 30. With this connection, a high voltage output from the power factor improvement circuit 20 is applied to the VDC terminal. The control circuit 40 generates a circuit operation voltage Vcc and the like in a step-down manner based on the high voltage applied to the VDC terminal.

The OCP terminal is connected to a connection point between the capacitor C31 and the resistor R31 of the step-down chopper circuit 30 via a resistor R5. The potential of the OCP terminal depends on the current flowing in the resistor R31. The current flowing in the resistor R31 is a current flowing in the step-down chopper circuit 30. The control circuit 40 uses the potential of the OCP terminal to detect Current flowing in the step-down chopper circuit 30.

The VC2 terminal is connected to the ground through the capacitor C3. The VC2 terminal is connected to a power supply terminal T31 of the power supply device 2 via a resistor R54 and a diode D51. Through this connection, a voltage obtained by dividing the potential of the VC2 terminal, that is, the potential equivalent to the charging voltage of the capacitor C3, is applied between the power supply terminal T31 and the power supply terminal T33 of the power supply device 2.

The LGND terminal is connected to the ground.

The Vref terminal is connected to the ground via a parallel circuit of a series resistance circuit R101-R102 and a capacitor C4, which is formed by a resistor R101 and a resistor R102. The OP + terminal is connected to the midpoint of the series resistor circuits R101-R102. The OP + terminal is also connected to the ground through the capacitor C5. With these connections, the potential of the OP + terminal becomes the potential of the reference voltage determined by the resistance division of the resistors R101 and R102.

The OP-terminal is connected to a power supply terminal T32 of the power supply device 2 via a resistor R9. The potential of the OP-terminal depends on the current flowing in the combined resistance of the resistors R11, R31, and R32. The current flowing in the combined resistance of the resistor R11, the resistor R31, and the resistor R32 is the current flowing in the power supply terminal T31, that is, when the light source unit 1 as a load is mounted on the power source device 2, Current flowing in the light emitting diode D11. The control circuit 40 detects a current flowing in the light emitting diode D11 of the light source unit 1, which is a so-called load current, using the potential of the OP- terminal.

The ABN terminal is connected to a series formed by a resistor R7 and a resistor R8 The midpoint of the resistor circuits R7-R8. The series resistance circuits R7-R8 are connected between the connection point of the inductor L31 and the capacitor C31 of the step-down chopper circuit 30 and the ground. That is, the series resistance circuits R7 to R8 are connected in parallel to the capacitor C31. With this connection, the potential of the ABN terminal depends on the potential obtained by dividing the DC voltage supplied from the step-down chopper circuit 30 to the load by the resistance ratio of the series resistor circuits R7-R8. The control circuit 40 detects the voltage supplied from the step-down chopper circuit 30 to the light source unit 1 based on the potential of the ABN terminal.

The lamp terminal is connected to the midpoint of the series resistance circuits R51-R52 via a resistor R53. The series resistance circuits R51-R52 are connected between the power supply terminal T31 and the power supply terminal T33 of the power supply device 2 via a diode D51 for backflow prevention. With this connection, the potential of the Lamp terminal depends on the voltage obtained by dividing the voltage corresponding to the potential difference between the power supply terminal T31 and the power supply terminal T33 of the power supply device 2 by the resistance ratio of the series resistance circuit R51-R52. . If a load including a resistive element is connected between the power supply terminal T31 and the power supply terminal T33, a current flows into the load and the voltage between the power supply terminal T31 and the power supply terminal T33 decreases. If no load is connected, the voltage will not drop. The control circuit 40 detects the voltage drop between the power supply terminal T31 and the power supply terminal T33 by using the potential of the Lamp terminal.

The DISin terminal is open. The DISin terminal is used, for example, when a semiconductor element is connected to the outside of the control circuit 40.

The DIS terminal is connected to a connection point between the inductor L31 and the capacitor C31 of the step-down chopper circuit 30 via a resistor R6. A switch is built in between the DIS terminal and the GND of the control circuit 40, and the control circuit 40 controls the switch to be on or off. When the switch between the DIS terminal and GND is turned on, the voltage of the capacitor C31 is discharged through the resistor R6, so that the potential at the connection point between the inductor L31 and the capacitor C31 drops to approximately GND potential.

Although the resistor R6 can be omitted, in order to suppress the discharge current of the capacitor C31, it is connected to alleviate the stress on the switch built in between the DIS terminal and GND. In addition, GND is a reference potential of the control circuit 40, and is connected to a ground line which is a reference potential of the main circuit via the LGND terminal.

FIG. 2 is a block diagram showing a configuration of a main part of the control circuit 40.

The control circuit 40 includes a PFC control circuit 41, a lighting control circuit 42, a protection circuit 43, a power supply circuit 44, an operational amplifier 45, a monitoring circuit 46, a determination circuit 47, and a startup circuit 48. The control circuit 40 uses analog circuits to configure each of the circuits 41 to 48. In addition, the control circuit 40 uses digital circuits to configure at least a part of each of the circuits 41 to 48, and implements at least a part of the processing performed in each of the circuits 41 to 48 by software processing using a computer.

The PFC control circuit 41 generates a gate signal for turning on / off the switching element Q21 based on the respective potentials of the MULT terminal, the ZCD terminal, the CS terminal, and the VFB terminal. Then, the PFC control circuit 41 controls the operation of the power factor improvement circuit 20 by outputting the gate signal from the GD terminal to the gate terminal of the switching element Q21 to turn the switching element Q21 on / off. In addition, the control of the power factor improvement circuit 20 by the PFC control circuit 41 and the operation of the power factor improvement circuit 20 by the control are well known, so descriptions are omitted here.

The lighting control circuit 42 is based on the respective power of the VS terminal and the VB terminal. This bit generates a gate signal for turning on / off the switching element Q31. The lighting control circuit 42 determines the frequency and the duty ratio of the gate signal based on the voltage signal output from the operational amplifier 45. Then, the lighting control circuit 42 outputs the gate signal to the gate terminal of the switching element Q31 from the HO terminal to turn on / off the switching element Q31 to control the operation of the step-down chopper circuit 30. In addition, the control of the step-down chopper circuit 30 by the lighting control circuit 42 and the operation of the step-down chopper circuit 30 by the control are well known, so the description is omitted here.

The protection circuit 43 usually connects a VDC terminal to the power supply circuit 44. The protection circuit 43 monitors the current flowing in the step-down chopper circuit 30 using the potential of the OCP terminal. When a current abnormality such as an overcurrent is detected, the protection circuit 43 stops the operations of the PFC control circuit 41 and the lighting control circuit 42 and cuts off the connection between the VDC terminal and the power supply circuit 44. The protection circuit 43 may receive an abnormal signal from the monitoring circuit 46. Then, when an abnormal signal is received, the protection circuit 43 also stops the operations of the PFC control circuit 41 and the lighting control circuit 42 and cuts off the connection between the VDC terminal and the power supply circuit 44.

Before the control circuit 40 is started, the power supply circuit 44 generates a circuit operating voltage Vcc and the like in a step-down manner using a high-voltage full-wave rectified voltage captured through a VDC terminal. Then, the power supply circuit 44 applies a circuit operating voltage Vcc to the Vcc terminal. In addition, the power supply circuit 44 appropriately applies a step-down voltage including the circuit operating voltage Vcc to other circuits.

The operational amplifier 45 connects the positive terminal (+) to the OP + terminal, the negative terminal (-) to the OP- terminal, and the output terminal to the lighting control circuit 42. And monitoring circuit 46. The operational amplifier 45 outputs a voltage signal having a magnitude corresponding to a difference between the potential of the OP- terminal and the potential of the OP + terminal to the lighting control circuit 42 and the monitoring circuit 46. As described above, the lighting control circuit 42 adjusts the switching frequency and the duty ratio of the switching element Q31 based on the voltage signal from the operational amplifier 45. The adjustment is to perform feedback control on the output current of the step-down chopper circuit 30 such that the load current corresponding to the potential of the OP- terminal and the target current corresponding to the potential of the OP + terminal are consistent. Here, the operational amplifier 45 functions as an error amplifier. In addition, since the light emitting diode has a constant voltage characteristic, the output voltage is increased or decreased by controlling the output current.

The monitoring circuit 46 monitors whether the load current is normal based on a voltage signal output from the operational amplifier 45. The monitoring circuit 46 monitors whether the output voltage of the step-down chopper circuit 30 is normal by using the potential of the ABN terminal. Then, when an abnormality in the load current or the output voltage is detected, the monitoring circuit 46 outputs an abnormality signal to the protection circuit 43 and the startup circuit 48.

The determination circuit 47 monitors the potential of the Lamp terminal, that is, the midpoint potential of the series resistance circuits R51 to R52. When no load is installed on the power supply device 2, the voltage applied from the VC2 terminal and the variable frequency of the resistor R7, resistor R8, resistor R51, resistor R52, resistor R54, and diode D51 (Variable frequency (VF)) is applied to the Lamp terminal. When a load is mounted on the power supply device 2, a resistor connected in parallel with the light-emitting diode D11 of the light source unit 1 as a load is connected in parallel with the series resistance circuits R7-R8. Voltage when the load is installed. Detecting the voltage difference, The determination circuit 47 determines that a load is mounted on the power supply device 2. When it is determined that a load is mounted on the power supply device 2, the determination circuit 47 outputs a start signal to the start circuit 48.

The startup circuit 48 includes a switching element (second switching element) Q48. The switching element Q48 is an N-channel field effect transistor (FET). The switching element Q48 connects the drain terminal to the DIS terminal and the source terminal to the ground (GND). The switching element Q48 connects the gate terminal to the output terminal of the start signal output from the self-determination circuit 47 and the output terminal of the abnormal signal output from the self-monitoring circuit 46, respectively. The switching element Q48 is turned on after a start signal or an abnormal signal is input to the gate terminal, and the potential of the DIS terminal is pulled down to the ground potential. Here, the switching element Q48 constitutes a short circuit that pulls the potential at the connection point of the inductor L31 and the capacitor C31 to the potential of the ground.

In addition, the determination circuit 47 determines that a load is mounted on the power supply device 2, and then outputs an activation signal to the PFC control circuit 41, the lighting control circuit 42, the protection circuit 43, and the monitoring circuit 46. Based on the activation signal, the PFC control circuit 41, the lighting control circuit 42, the protection circuit 43 and the monitoring circuit 46 are reset.

The start-up circuit 48 short-circuits the gate terminal of the switching element Q48 and the DISin terminal of the control circuit 40. By the short circuit, a signal supplied to the gate terminal of the switching element Q48, that is, a start signal or an abnormal signal is output from the DISin terminal. Therefore, when a base terminal of, for example, an N-channel field effect transistor (FET) is connected to the DISin terminal, the field effect transistor operates in the same manner as the switching element Q48.

In addition, the circuit operating voltage is applied to the PFC control circuit 41, the lighting control circuit 42, the protection circuit 43, and the monitoring circuit 46 from the power supply circuit 44, but not to the determination circuit 47 and the startup circuit 48. The determination circuit 47 and the start-up circuit 48 connect a power line to a VC2 terminal, and set a voltage generated at the VC2 terminal as a circuit operating voltage. Therefore, the determination circuit 47 and the startup circuit 48 can be operated before the power supply circuit 44 uses the high-voltage full-wave rectified voltage generation circuit operating voltage Vcc and the like, which are extracted through the VDC terminal.

Next, the main operation procedures of the control circuit 40 will be described using FIG. 3 and FIG. 4.

FIG. 3 is a flowchart showing an operation procedure of the control circuit 40 when the power is turned on. When the external power supply 200 is turned on by turning on a power switch (not shown), the control circuit 40 starts a sequence of operations shown in the flowchart of FIG. 3.

First, the control circuit 40 confirms whether or not the light source unit 1 is mounted on the power supply device 2 as step ST1. That is, the voltage generated on the VC2 terminal of the control circuit 40 is applied between the power supply terminal T31 and the power supply terminal T33 of the power supply device 2 through the resistor R54 by turning on the external power supply 200. Therefore, in the control circuit 40, The determination circuit 47 monitors the potential of the Lamp terminal. When the terminals T11, T12, and T13 of the light source unit 1 are mounted on the power supply terminal T31, power supply terminal T32, and power supply terminal T33 of the power supply device 2, a current flows into a resistance element (not shown) connected in parallel with the light emitting diode D11. , The voltage between the power supply terminal T31 and the power supply terminal T33 drops. As a result of the voltage drop, the potential at the midpoint of the series resistance circuits R51 to R52 connected between the power supply terminal T31 and the power supply terminal T33 changes. Lamp terminal The potential depends on the midpoint potential of the series resistor circuits R51-R52. Therefore, the determination circuit 47 monitors the potential of the Lamp terminal, and the control circuit 40 can confirm whether or not the light source unit 1 is mounted on the power supply device 2.

The voltage applied between the power supply terminal T31 and the power supply terminal T33 via the resistor R54, that is, the voltage generated at the VC2 terminal of the control circuit 40 is equal to or lower than the forward voltage of the light emitting diode D11. With this arrangement, it is possible to prevent the lighting diode D11 from being turned on as long as the light source unit 1 is mounted to the power supply device 2.

When the light source unit 1 is not mounted on the power supply device 2 (NO in step ST1), the control circuit 40 continues the monitoring operation of step ST1.

When the light source unit 1 is mounted on the power supply device 2, or when it is confirmed that the light source unit 1 is mounted (YES in step ST1), the control circuit 40 turns on the start-up circuit 48 as step ST2. That is, in the control circuit 40, when the determination circuit 47 confirms that the light source unit 1 is mounted, the determination circuit 47 outputs a start signal to the start circuit 48. By the start signal, the switching element Q48 is turned on in the start circuit 48. Therefore, when the determination circuit 47 outputs a start signal to the start circuit 48, the control circuit 40 can turn on the start circuit 48.

When the switching element Q48 of the startup circuit 48 is turned on, the potential of the DIS terminal of the control circuit 40 becomes the ground potential. When the potential of the DIS terminal becomes the ground potential, the potential at the connection point between the inductor L31 and the capacitor C31 of the step-down chopper circuit 30 is pulled up to the ground potential. The result is equivalent to the case where the source terminal of the switching element Q31 is short-circuited to the ground.

Therefore, the control circuit 40 starts the switching operation of the switching element Q21 of the power factor improvement circuit 20 as step ST3, and then starts the switching of the switching element Q31 of the step-down chopper circuit 30 as step ST4. That is, in the control circuit 40, if the determination circuit 47 determines that a load is mounted on the power supply device 2, the start circuit 48 outputs an activation signal to the PFC control circuit 41, the lighting control circuit 42, the protection circuit 43, and the monitoring circuit 46 . Based on the activation signal, the PFC control circuit 41 generates a gate signal for the switching element Q21, and outputs the generated gate signal from the GD terminal to the switching element Q21 of the power factor improvement circuit 20. As a result, the switching element Q21 starts switching operation. Therefore, when the control operation is started by the PFC control circuit 41, the control circuit 40 can start the switching operation of the switching element Q21.

Similarly, the lighting control circuit 42 generates a gate signal for the switching element Q31 by the start signal, and outputs the generated gate signal from the HO terminal to the switching element Q31 of the step-down chopper circuit 30. As a result, the switching element Q31 starts switching operation. Therefore, by starting the control operation of the lighting control circuit 42, the control circuit 40 can start the switching operation of the switching element Q31.

Here, before the control circuit 40 turns on the startup circuit 48, the source potential of the switching element Q31 is not fixed. However, at step ST4 when the lighting control circuit 42 starts to operate, the startup circuit 48 is turned on in step ST2 until the source potential of the switching element Q31 is pulled down to the ground potential. Therefore, the bootstrap circuit can be used to sufficiently ensure the driving. power supply. Therefore, the switching element Q31 can be stably activated by the control of the lighting control circuit 42. That is, the step-down chopper circuit 30 can be operated stably. In addition, the switching element Q48 of the startup circuit 48 is activated immediately before the step-down chopper circuit 30 is activated. Run.

Thereafter, the control circuit 40 performs constant current control as step ST5. That is, in the control circuit 40, based on the voltage signal of the operational amplifier 45, the lighting control circuit 42 adjusts the switching frequency and the duty ratio of the switching element Q31 so that the load current input to the OP- terminal becomes the input to the OP + terminal Target current. By repeating the adjustment, the load current is close to the target constant current. Therefore, by performing the feedback control using the operational amplifier 45 as an error amplifier, the control circuit 40 can perform constant current control.

Next, the operation sequence when the control circuit 40 detects an abnormality during the period when the constant current control is performed will be described using the flowchart of FIG. 4.

First, during the period when the constant current control is performed, the control circuit 40 determines the presence or absence of an abnormality as step ST11. That is, the monitoring circuit 46 activated by the start signal from the start circuit 48 uses the voltage signal output from the operational amplifier 45 to monitor whether the load current is normal. Then, for example, when the load current exceeds a predetermined upper limit threshold value or a lower limit threshold value, the monitoring circuit 46 determines that there is an abnormality. Therefore, the monitoring circuit 46 monitors the load current, and the control circuit 40 can determine the presence or absence of an abnormality. When there is no abnormality (NO in step ST11), the control circuit 40 continues to determine whether there is an abnormality.

When there is an abnormality (YES in step ST11), the control circuit 40 operates the protection circuit 43 as step ST12. That is, in the control circuit 40, if the monitoring circuit 46 determines that there is an abnormality, the monitoring circuit 46 also outputs an abnormality signal to the protection circuit 43. When an abnormal signal is received, the protection circuit 43 disconnects the VDC terminal The connection to the power supply circuit 44 is cut off. The protection circuit 43 stops the operations of the PFC control circuit 41 and the lighting control circuit 42. That is, the switching of the switching elements Q21 and Q31 is stopped. Therefore, by monitoring the circuit 46 to output an abnormal signal to the protection circuit 43, the control circuit 40 can cause the protection circuit 43 to operate.

The control circuit 40 turns on the start-up circuit 48 as step ST13. That is, in the control circuit 40, if the monitoring circuit 46 determines that there is an abnormality, the monitoring circuit 46 also outputs an abnormality signal to the startup circuit 48. After the operation of the lighting control circuit 42 is stopped by the abnormal signal, that is, after the switching of the switching element Q31 is stopped, the switching element Q48 of the startup circuit 48 is turned on. Therefore, by outputting an abnormal signal to the start-up circuit 48 by the monitoring circuit 46, the control circuit 40 can turn on the start-up circuit 48, that is, the short-circuit circuit (switching element Q48) is operated. Furthermore, when the start-up circuit 48 turns on the switching element Q48, the connection between the VDC terminal and the power circuit 44 is cut off, and the virtual channel connection (VCC) supply is lost, so the monitoring circuit 46 stops the operation. . However, although not shown, the startup circuit 48 has a function of holding the signal of the monitoring circuit 46. Therefore, even if the monitoring circuit 46 has stopped the operation, the startup circuit 48 can control the switching element Q48 to be turned on or off.

In addition, when the switching element Q48 of the startup circuit 48 is turned on, as described above, the potential of the DIS terminal of the control circuit 40 becomes the ground potential, thereby setting the potential of the connection point between the inductor L31 and the capacitor C31 of the step-down chopper circuit 30. Pull to ground potential.

For example, if the light source unit 1 is removed from the power supply device when constant current control has been performed 2 is removed, the output terminal of the power supply device 2 becomes open, and the output voltage rises until the protection circuit 43 stops the operation of the lighting control circuit 42. With this, the voltage of the capacitor C31 also rises. Then, during the period until the charge of the capacitor C31 runs out, it takes time to decrease in accordance with the attenuation characteristics. Here, if the light source unit 1 is mounted again when the voltage has dropped, there is a possibility that an inrush current may flow to the light source unit 1 side and cause the light emitting diode D11 to malfunction.

In this embodiment, if the monitoring circuit 46 determines that there is an abnormality, the connection point between the inductor L31 and the capacitor C31 of the step-down chopper circuit 30 is short-circuited to the ground by the action of the startup circuit 48. Therefore, the electric charge charged into the capacitor C31 becomes zero instantaneously, so even if the light source unit 1 is mounted again, the inrush current does not flow to the light source unit 1 side. Therefore, the light-emitting diode D11 of the light source unit 1 is unlikely to malfunction due to the inrush current.

However, when the switching element Q48 included in the startup circuit 48 is turned on by an abnormal signal from the monitoring circuit 46, in order to extract the charge charged to the capacitor C31, it is necessary to have a charge that can withstand the charge when the extraction capacitor C31 is fully charged. Capability (current resistance characteristics). On the other hand, by combining the capacitance of the capacitor C31 to determine the capability of the switching element Q48 and incorporating it into the start-up circuit 48, it is possible to eliminate wasteful use of a switching element with a high capability (high price).

On the other hand, depending on the performance and the like of the light source unit 1 as a power supply target, there is a case where the capacitance of the capacitor C31 must be made larger than the current state. For example, when the light source unit 1 that controls the smoothness of the current flowing in the light emitting diode body to be higher than the current state and has a flat waveform is required to be controlled, the capacitance of the capacitor C31 must be increased. then, When the capacitance of the capacitor C31 is increased, the switching element Q48 also needs to be changed to a switching element with a high current resistance characteristic and a strong ability. However, since the switching element Q48 is incorporated in the IC-based control circuit 40, if a change occurs, the control circuit 40 itself must be re-produced.

In this regard, in the power supply device 2 of this embodiment, the gate terminal of the switching element Q48 and the DISin terminal that is an external terminal of the control circuit 40 are short-circuited. Therefore, the gate terminal of the switching element is connected to the DISin terminal with respect to the control circuit 40 having an external switching element suitable for the capacity of the capacitor C31. The drain terminal of the switching element is connected to the DIS terminal, and the source terminal is connected to the ground. As described above, it is possible to use a switching element having a high capacity as a switching element for short circuit without changing the current control circuit 40.

As described in detail above, the power supply device 2 according to the embodiment includes the step-down chopper circuit 30, a short circuit (switching element Q48), a determination circuit 47, and a control circuit 40. In addition, the short-circuit circuit is connected in parallel with the capacitor C31 of the step-down chopper circuit 30 and is configured to pull the potential at the connection point between the inductor L31 and the capacitor C31 of the step-down chopper circuit 30 to the potential of the ground line during operation. Further, the determination circuit 47 is configured to determine whether or not the light source unit 1 as a load is connected to the power supply terminal T31, the power supply terminal T32, and the power supply terminal T31 based on a midpoint potential of a series resistance circuit R51 to R52 connected in parallel with the capacitor C31. In addition, the control circuit 40 is configured to operate the short-circuit circuit on the condition that the light source unit 1 is connected to the determination circuit 47 before the switching control of the switching element Q31 of the step-down chopper circuit 30 is started.

Therefore, it is assumed that the short-circuit circuit (switching element Q48) is operated during operation. When the potential of the connection point between the inductor L31 and the capacitor C31 is pulled to the potential of the ground, the light source unit 1 is detached and detected by the determination circuit 47. Therefore, the power source device 2 can reliably perform the removal of the light source unit 1. Install detection. Then, on the condition that the light source unit 1 is confirmed to be installed, the power supply device 2 operates the short-circuit circuit and pulls the potential of the connection point between the inductor L31 and the capacitor C31 to the potential of the ground line, so that the step-down chopper circuit 30 can be stabilized. start. Therefore, the reliability of the power supply device 2 can be improved.

In the power supply device 2, the short-circuit circuit includes a switching element Q48 that connects the connection point of the inductor L31 and the capacitor C31 to the ground wire when the short circuit is turned on. Then, the control circuit 40 outputs a signal for turning on the switching element Q48 to the short-circuiting circuit through the determination circuit 47, thereby operating the short-circuiting circuit. Therefore, according to the power supply device 2, the determination circuit 47 can correspond to the detection of the installation of the light source unit 1, and turn on the switching element Q48 to pull the potential of the connection point between the inductor L31 and the capacitor C31 of the step-down chopper circuit 30 to ground. The potential of the line. That is, the connection point between the inductor L31 and the capacitor C31 will not be short-circuited to the ground line before the disassembly detection of the light source unit 1 is completed, so that erroneous operation can be prevented.

The power supply device 2 according to one embodiment further includes a monitoring circuit 46. The monitoring circuit 46 is configured to monitor the output voltage supplied from the step-down chopper circuit 30 to the light source unit 1 (load) using the potential of the ABN terminal, and to operate the short-circuit circuit when an abnormality in the output voltage such as an overvoltage is detected.

Therefore, according to the power supply device 2, the potential of the connection point between the inductor L31 and the capacitor C31 of the step-down chopper circuit 30 is pulled even when an abnormality such as an overvoltage occurs in the voltage input to the light source unit 11. Potential to ground. therefore, The capacitor 31 is immediately discharged to reduce the remaining capacitance. Therefore, even if the light source unit 1 temporarily removed is installed again, there is no danger that an inrush current flows into the light source unit 1.

As described above, according to the power supply device 2, a short circuit can be used to realize the stable operation of the step-down chopper circuit 30 and the protection function against overvoltage. Therefore, circuit components can be saved, and a power supply device 2 with high reliability without hindering miniaturization and cost reduction can be provided.

In addition, the power supply device 2 includes a protection circuit 43 that switches the switching elements Q21 and Q31 of the power factor improvement circuit 20 and the step-down chopper circuit 30 when an abnormality is detected by the monitoring circuit 46. stop. Therefore, when an abnormality of the output voltage is detected, the power conversion function performed in the power factor improving circuit 20 and the step-down chopper circuit 30 is stopped, so the safety of the power supply device 2 can be further improved.

In addition, the power supply device 2 according to one embodiment uses a integrated circuit to form a control circuit 40 including a short circuit and the like. In addition, the power supply device 2 provides an external terminal, that is, a DISin terminal, to the integrated circuit, and the external terminal outputs a signal output from the control circuit 40 to the short-circuit circuit to operate the short-circuit circuit to the outside of the integrated circuit. Terminal.

Therefore, according to the power supply device 2, a circuit having the same configuration as the short circuit included in the control circuit 40 can be provided outside the integrated circuit via the DISin terminal. Therefore, if there is an obstacle to the current resistance characteristics of the circuit element (switching element Q48) constituting the short circuit, the new integrated short circuit can be easily installed without changing the integrated circuit. Outside of the integrated circuit, the new short-circuit circuit is composed of circuit elements with excellent current resistance and strong capabilities. For example, even if there is a design change in which the capacitance of the capacitor C31 of the step-down chopper circuit 30 must be increased, a switching element suitable for the capacitance of the capacitor C31 can be externally placed in the control circuit so as to have a function equivalent to the switching element Q48 40 on. As a result, it is possible to obtain excellent effects such as cost savings associated with design changes and shortening of design periods. Therefore, it is possible to provide the power supply device 2 excellent in practicality.

In addition, the power supply device 2 uses the switching element Q48 to constitute a short circuit, so that the determination circuit 47 or the monitoring circuit 46 of the control circuit 40 can operate the short circuit as long as it outputs a signal for turning on the switching element Q48. Therefore, even when the short-circuit circuit is configured outside the integrated circuit by using another switching element, the short-circuit circuit only needs to be configured such that the switching element is turned on by a signal from the DISin terminal, and thus the circuit configuration is simple.

On the other hand, the lighting device 100 formed by connecting the light source unit 1 to the power supply terminal T31, the power supply terminal T32, and the power supply terminal T33 of the power supply device 2 can make the disassembly and detection function of the light source unit 1 of the power supply device 2 effective. On the other hand, the step-down chopper circuit 30 of the power supply device 2 is operated stably. In addition, it is possible to stably operate the step-down chopper circuit 30 of the power supply device 2 while exerting a protection function against overvoltage without causing obstacles to miniaturization and cost reduction of the power supply device 2. Therefore, the reliability of the lighting device 100 can be improved.

In addition, the present invention is not directly limited to the above-mentioned embodiments, and the constituent elements can be modified and concreted without departing from the gist during the implementation phase. Into.

For example, in the embodiment described above, the switching element Q48 as a short-circuit circuit is constituted by a field effect transistor, but a switching element other than a field effect transistor may be applied.

In the above-mentioned embodiment, the start-up circuit 48 including the short-circuit circuit is provided in the control circuit 40, but the start-up circuit 48 including the short-circuit circuit may be provided outside the control circuit 40. Alternatively, a short circuit may be provided outside the control circuit 40, and a start-up circuit 48 other than the short circuit may be provided inside the control circuit 40.

Moreover, in the said embodiment, although the load was the light source unit 1, the power supply device 2 which supplies DC power to the load other than the light source unit 1 may be sufficient.

In the above-mentioned embodiment, the load (light source unit 1) is detachable from the power supply device 2, but the load may be fixedly mounted on the power supply device 2. In this case, the mounting detection circuit 50 of FIG. 1 may be omitted. When omitted, the control circuit 40 replaces the determination circuit 47 and operates the short-circuit circuit before the switching control of the switching element Q31 is started.

In addition, various inventions can be formed by an appropriate combination of a plurality of constituent elements disclosed in the embodiments. For example, several constituent elements may be deleted from all the constituent elements shown in the embodiment. In addition, it is also possible to combine constituent elements across different embodiments.

Claims (7)

A power supply device includes a step-down chopper circuit, a series circuit of an inductor and a capacitor connected between an output terminal of a first switching element and a ground line, and both ends of the capacitor are used as power supply terminals for a load, The input voltage is converted into an output voltage corresponding to the load by the switching of the first switching element, and is supplied to the load connected to the power supply terminal; a short circuit is connected in parallel with the capacitor, and During operation, the potential of the connection point of the inductor and the capacitor is pulled to the potential of the ground line; the control circuit is connected to the power supply terminal before starting the switching control of the first switching element. With the load as a condition, the short circuit is operated; and a monitoring circuit (46) monitors the output voltage, and causes the short circuit to operate when an abnormality in the output voltage is detected. The power supply device according to item 1 of the scope of patent application, further comprising: a determination circuit that determines whether the load is connected to the power supply terminal by a midpoint potential of a series resistance circuit connected in parallel with the capacitor. The power supply device according to item 1 of the scope of patent application, further comprising: a protection circuit that stops a switch of the first switching element (Q31) when an abnormality is detected by the monitoring circuit. The power supply device according to item 1 of the scope of patent application, wherein the control circuit and the short-circuit circuit are composed of integrated circuits, and the power supply device further includes: an external terminal for controlling the short-circuit circuit to operate. A signal output from the control circuit to the short circuit is output to the outside of the integrated circuit. The power supply device according to item 4 of the scope of patent application, wherein the monitoring circuit monitors the output voltage, and when an abnormality of the output voltage is detected, a signal that causes the short circuit to operate is output to the short circuit And the external terminal further outputs a signal output from the monitoring circuit to the short circuit to the outside of the integrated circuit. The power supply device according to item 1 of the scope of patent application, wherein the short-circuit circuit includes: a second switching element that connects a connection point of the inductor and the capacitor to the ground wire when conducting; and The control circuit operates the short circuit by outputting a signal for turning on the second switching element of the short circuit to the short circuit. A lighting device includes a power supply device including a step-down chopper circuit, a series circuit of an inductor and a capacitor connected between an output terminal of a switching element and a ground line, and two ends of the capacitor are set to a load The power supply terminal converts an input voltage into an output voltage corresponding to the load through the switching of the switching element, and supplies the output voltage to the load connected to the power supply terminal; a short circuit is connected in parallel with the capacitor, During operation, the potential of the connection point of the inductor and the capacitor is pulled to the potential of the ground line; the control circuit, before starting the switching control of the switching element, is connected to the power supply terminal The load is conditional to cause the short-circuit circuit to operate; and a monitoring circuit (46) to monitor the output voltage and operate the short-circuit circuit when an abnormality of the output voltage is detected; and a light-emitting load to communicate with the The power supply terminal of the power supply device is connected and controlled to be lit.