LED driving apparatus which controls based on LED state

An LED driving apparatus comprising: a power feed unit; a driving control unit; a current detection unit that detects load current flowing in an LED module; and an output control unit that determines whether the LED module is under conducting state or opening state, and outputs a signal in accordance with a result of the determination, wherein, when the LED module is under conducting state, the output control unit outputs a first signal to the driving control unit so that the load current is constant, wherein, when the LED module is under opening state, the output control unit outputs a second signal to the driving control unit so that a voltage becomes a predetermined constant-voltage value, and wherein the predetermined voltage value is a voltage or higher, at which the LED module starts conduction, and a voltage or lower corresponding to an upper limit of the LED.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2011-030175 filed on Feb. 15, 2011, the entire subject matter of which is incorporated herein by reference.

TECHNICAL FIELD

The invention relates to an Light Emitting Diode (LED) driving apparatus, and specifically, to an LED driving apparatus that appropriately performs control, based on whether an LED is under opening state or conducting state.

BACK GROUND

An LED module and an LED driving apparatus for driving the LED module are widely known, for example, in an illumination apparatus and the like. It is known that an LED module includes at least one or more LED arrays having at least one or more light emitting diodes (hereinafter, also referred to as ‘LED’). Here, in the LED module having two or more LED arrays, the respective LED arrays are connected in parallel with each other. Also, in the LED array having two or more LEDs, the respective LEDs are connected to each other in series.

JP-A-2010-161264 discloses an LED driving circuit driving a light source, in which LED strings having LEDs connected in series are arranged in parallel. The LED driving circuit drives the LEDs at constant-current, thereby making luminance of the LEDs uniform.

However, according to the above LED driving apparatus, when the LED module becomes under opening state, i.e., abnormal state, control of regulating an output voltage to the LED module may be performed. The control is performed with considering temperatures of the LED module, non-uniformity of forward voltages VFof the individual LEDs, and the like. A value of the output voltage is set to be larger than a predetermined voltage corresponding to an upper limit of load current that is supplied to the LED module.

When the opening state of the LED module is kept at a state in which the control of regulating the value of the output voltage is performed and the value of the output voltage is large, the charges are kept with being charged in a smoothing capacitor that is arranged at an output-side after power conversion. At this state, when the LED module becomes under conducting state, i.e., normal state, excessive inrush current instantaneously flows in the LED module. When the inrush current flows, the LEDs configuring the LED module may be damaged or burned out.

The above phenomenon may be occurred in a following case. That is, in case that the LED driving apparatus and the LED module are connected by using a connector and the like, the connection between the LED driving apparatus and the LED module may be inappropriate or unstable. As one example, in case that the LED module is connected to the LED driving apparatus being under conducting state, a user may connect the LED driving apparatus and the LED module in an erroneous connection direction (polarity and the like). As another example, a connector of the LED driving apparatus and a connector of the LED module may be imperfectly connected or an electrical contact of the LED driving apparatus and the LED module may disappear temporarily. In this case, when LED driving apparatus and the LED module are again connected correctly or the electrical contact thereof is recovered, the inrush current may flow in the LED module.

FIG. 5is a graph illustrating an example of a change in current that is supplied when an LED module is attached to and detached from a background LED driving apparatus.

InFIG. 5, the LED module is under conducting state at time T0. As shown inFIG. 5, a current value is zero (0) before time T0and the LED module is not under conducting state. Just after time T0, i.e., when the LED module is under conducting state, the current value abruptly increases from zero (0) and the inrush current IFpinstantaneously flows in the LED module. After the inrush current IFpflows, the current value decreases and constant forward current IFflows. A quality of the LED is considerably deteriorated due to the inrush current IFp.

For solving the above problem, a configuration has been known in which an inductor is connected to a power feed line after power conversion in series with the LED module.

FIG. 6is a circuit diagram illustrating an example of a configuration of a background LED driving apparatus.

An example of a configuration of an background LED driving apparatus, in which an inductor is provided, is described with reference toFIG. 6. An LED driving apparatus801has an output control unit802, a power conversion unit807, a driving control unit808and a current detection unit810. The power conversion unit807has an interference suppression unit807athat performs a noise measure, a rectification unit807bthat rectifies alternating current, a power factor improvement unit807cand a power conversion circuit807dthat is a DC/DC converter. The LED driving apparatus801converts alternating current power from an alternating current power supply VACinto direct current power in the power conversion unit807and feeds the direct current power to the LED module500. An inductor L1is connected to a power feed line from the power conversion unit807to the LED module500in series with the LED module500.

The output control unit802has a constant-current control unit803and a constant-voltage control unit804. When the LED module500is under conducting state (normal state), a constant-current control of making current IFflowing in the LED module500constant is performed. When the LED module500is under opening state (abnormal state), an operation of the constant-voltage control unit804of the output control unit802is enabled based on a detection value of the current detection unit810. At this time, the constant-voltage control unit804outputs a feedback signal for driving voltage setting to the driving control unit808, based on a detection value of a voltage VAsupplied to the LED module and a reference voltage value VTH3. The feedback signal is a signal for outputting a voltage, which is higher than a voltage corresponding to an upper limit of load current to be supplied to the LED module500, for example a voltage value V04shown inFIG. 3, to the power conversion unit807. The reason is as follows. In order to securely conduct the LED module500when the LED module500is attached and detached during the operation of the LED driving apparatus801, a voltage is necessary which is higher than the maximum voltage to be applied to the LED module500under conducting state (normal state), with considering the non-uniformity of properties such as temperature characteristics and forward voltages VFof the respective LEDs, the environment change and the like. By performing the above control, even when addition values of the forward voltages VFof the LEDs of the respective LED arrays are increased due to the non-uniformity of properties of the individual LEDs, the environment change and the like, it is possible to turn on the LEDs instantaneously and securely.

Here, when the charges of a capacitor C1are charged by the high voltage at the time of opening state, the excessive current (inrush current) flows toward the LED module500in attaching and detaching the LED module500, so that the qualities of the individual LEDs and the LED module are considerably deteriorated. On the other hand, according to the LED driving apparatus801, the high inrush current does not flow to the LED module by the function of the inductor even for the above case, so that it is possible to protect the LED module.

However, according to the configuration of connecting the inductor as described above, an inductor having a high inductance value is required. Accordingly, it is difficult to make the LED driving apparatus small and the manufacturing cost of the LED driving apparatus is increased.

Additionally, JP-A-2010-161264 does not disclose an effective solution for the above problems.

SUMMARY OF THE INVENTION

With considering the above, this disclosure provides an LED driving apparatus, which may be miniaturized, may have a low manufacturing cost and may suppress an LED from being out of order due to inrush current.

A Light Emitting Diode driving apparatus of this disclosure that drives an LED module having at least one LED, comprises: a power feed unit that feeds direct current power to the LED module; a driving control unit that performs driving control of the power feed unit; a current detection unit that detects load current flowing in the LED module; and an output control unit that determines whether the LED module is under conducting state or opening state in accordance with a detection result of the current detection unit, outputs a signal to the driving control unit in accordance with a result of the determination, and thus controls an output from the power feed unit, wherein, when the LED module is under conducting state, the output control unit outputs a first signal to the driving control unit so that the load current is constant when a voltage is applied to the LED module by the power feed unit, wherein, when the LED module is under opening state, the output control unit outputs a second signal to the driving control unit so that a voltage, which is applied to the LED module by the power feed unit, becomes a predetermined constant-voltage value, and wherein the predetermined voltage value is a voltage or higher, at which the LED module starts conduction, and a voltage or lower corresponding to an upper limit of the load current when the LED module is under conducting state.

In the above-described LED driving apparatus, the output control unit may have a constant-current control unit that performs constant-current control and a constant-voltage control unit that performs constant-voltage control, wherein, when the LED module is under conducting state, by using: a voltage corresponding to the load current detected by the current detection unit; and a first reference value that is a reference voltage for generating the first signal, as inputs, the constant-current control unit performs the constant-current-control based on a comparison result of the inputs, and wherein, when the LED module is under opening state, by using: a voltage corresponding to the load current detected by the current detection unit; a voltage based on an output voltage of the power feed unit; a second reference value that is a voltage for generating the second signal; and an opening state detecting signal from the constant-current control unit, as inputs, the constant-voltage control unit generates a third reference value, based on the second reference value and the opening state detecting signal, and outputs the second signal based on a comparison result of the voltage based on the output voltage of the power feed unit and the third reference value, and thus the constant-voltage control perfumes unit performs the constant-voltage control on the output voltage of the power feed unit.

In the above-described LED driving apparatus, when the LED module is under conducting state, the constant-current control unit may output the first signal to the driving control unit, based on a comparison result of the voltage corresponding to the load current and the first reference value, and when the LED module is under opening state, the constant-current control unit may stop the output of the first signal, and wherein, when the LED module is under opening state, the constant-voltage control unit may output the second signal to the driving control unit, based on a comparison result of the voltage based on the output voltage and the second reference value, and when the LED module is under conducting state, the constant-voltage control unit may stop the output of the second signal.

According to this disclosure, when the LED module is under opening state, the output voltage to the LED module is controlled to be lower than a voltage corresponding to the upper limit of the load current. Therefore, it is possible to provide the LED driving apparatus, which may be miniaturized, may have a low manufacturing cost and may suppress an LED from being out of order due to inrush current.

DETAILED DESCRIPTION

Hereinafter, an LED driving apparatus according to an illustrative embodiment of this disclosure will be described with reference to the drawings.

An LED driving apparatus feeds direct current power to an LED module having one or more LEDs and thus drives the LED module. The LED module is used for an illumination apparatus, for example. In this illustrative embodiment, the LED driving apparatus converts alternating current power into direct current power and feeds the converted direct current power to the LED module. The LED driving apparatus is configured to prevent inrush current from flowing in the LED module when connecting the LED module, for example.

Illustrative Embodiment

First, a circuit configuration of an LED driving apparatus1according to an illustrative embodiment of this disclosure is described.

FIG. 1is a circuit diagram illustrating a configuration of the LED driving apparatus1according to an illustrative embodiment of this disclosure.

As shown inFIG. 1, the LED driving apparatus1has an output control unit102, a power conversion unit107(which is an example of a power feed unit), a driving control unit108and a current detection unit110. The output control unit102has a constant-current control unit103and a constant-voltage control unit104. The power conversion unit107is connected to an alternating current power supply VAC. The power conversion unit107converts alternating current power from the alternating current power supply VACinto direct current power and outputs. As the direct current power is fed from the power conversion unit107to an LED module500, the LED module500is driven.

The LED module500has a plurality of LED arrays501. Each of the LED arrays501is connected to the power conversion unit107and is connected in parallel with the other LED arrays501. Each LED array501has a plurality of LEDs511. In each LED array501, each of the LEDs511is connected in series with the other LEDs511. Like this, the LED module500is configured by the LEDs511of m rows and n columns (m, n: 2 or larger).

The constant-current control unit103outputs a signal to the driving control unit108, based on an output of the current detection unit110and a first reference value VR1. The first reference value VR1is a voltage that is a basis of the constant-current-control. In the meantime, the first reference value VR1is a reference value of the constant-current control and an operating value for dimming control of the LED module500.

The constant-voltage control unit104has an open detection circuit105and an open-voltage setting circuit106. The open detection circuit105outputs a signal to the open-voltage setting circuit106, based on an output of the current detection unit110, an output of the constant-current control unit103and a second reference value (voltage) VTH1for generating a reference value of constant-voltage control. The open-voltage setting circuit106outputs a signal to the driving control unit108, based on a voltage of a high-voltage side of power feed lines to the LED module, i.e., an applied voltage to the LED module500, the signal from the open detection circuit105and a third reference value VTH2that is generated from the second reference value VTH1, and performs constant-voltage controlling of the voltage of the high-voltage side of the power feed lines to the LED module, i.e., the applied voltage to the LED module500. Meanwhile, in this illustrative embodiment, a value of the applied voltage to the LED module500is the substantially same as an output voltage V0of the power conversion unit107.

The power conversion unit107has an interference suppression unit107a, a rectification unit107b, a power factor improvement unit107c, a power conversion circuit107dand a capacitor C1. The interference suppression unit107ais a filter circuit that is provided to the power feed lines from the alternating current power supply VACto the rectification unit107b, and the filter circuit suppresses a noise from being leaked or introduced through a wiring. The rectification unit107brectifies the alternating current that is supplied from the alternating current power supply VAC. The power factor improvement unit107cis a Power Factor Correction (PFC) circuit that improves a power factor of the output of the rectification unit107b. The power conversion circuit107dis a DC/DC converter. The power conversion circuit107dconverts and outputs direct current power to be fed to the LED module500, in accordance with the control of the driving control unit108. The power conversion circuit107dand the LED module500are connected to each other by two power feed lines of a low-voltage side line and a high-voltage side line. The low-voltage side line is connected to a ground potential, for example.

The capacitor C1is a smoothing capacitor and is connected to the feed lines of the direct current power from the power conversion circuit107dto the LED module500, in line with the LED module500. That is, one end of the capacitor C1is connected to the high-voltage side line of the power feed lines to the LED module500and the other end is connected to the low-voltage side line that is a ground potential.

In the meantime, the power conversion unit107is not limited to the above configuration. For example, the interference suppression unit107a, the rectification unit107band the power factor improvement unit107cmay be appropriately provided depending on the circuit configuration of the power conversion unit107. Also, the power conversion unit107may include a circuit other than the above configuration.

The driving control unit108controls the power conversion circuit107din accordance with the signals output from the constant-current control unit103and the open-voltage setting circuit106. The driving control unit108controls the power conversion circuit107dto feed the direct current power from the power conversion unit107to the LED module500, thereby driving the LED module500.

The current detection unit110is arranged at the low-voltage side line that connects the power conversion unit107dand the LED module500. The current detection unit110is connected between an end of a cathode of the LED module500and the ground potential. The current detection unit110detects load current IFflowing in the LED module500. The current detection unit110outputs a voltage, as a detection value, corresponding to the load current IFto the output control unit102, for example. Also, the constant-current control unit103outputs an open detection signal to the open detection circuit105, based on a detection result of the current detection unit110. Thereby, the output control unit102determines whether the LED module500is under conducting state (normal state) or opening state (abnormal state), and performs the constant-current control when the LED module is under conducting state (normal state) and the constant-voltage control when the LED module is under opening state (abnormal state).

FIG. 2is a circuit diagram illustrating a detailed configuration of the LED driving apparatus1.

As shown inFIG. 2, the power conversion circuit107dhas a transformer T1and a transistor Q5that is connected to a primary side of the transformer T1. The transistor Q5is a MOS-type field effect transistor, for example. However, this disclosure is not limited thereto.

The driving control unit108has a control IC108a, a photo coupler PC that is connected to the control IC108a, a resistance R6and the like. An output terminal of the control IC108ais connected to a gate terminal of the transistor Q5. One terminal of output terminals of the photo coupler PC is connected to the ground potential and the other terminal is connected to the control IC108a. One of input terminals, which is different from the one of input terminal connecting the transistors Q2and Q3, of the photo coupler PC is connected to a predetermined voltage (for example, second reference voltage VTH1. However, this disclosure is not limited thereto) via the resistance R6and the other end is connected to collectors of transistors Q2, Q3that will be described later. The control IC108aturns on or off the transistor Q5in accordance with a signal of the photo coupler PC. The transformer T1is energized as the transistor Q5becomes on or off.

The current detection unit110has a resistance R0. The resistance R0is arranged at the low-voltage side line that connects the power conversion circuit107dand the LED module500, in series with the LED module500. The load current IF(refer to IrinFIG. 2) flown in the LED module500flows in the resistance R0.

The output control unit102is connected to an end of the resistance R0at a side of the LED module500. A voltage Vaof the end of the resistance R0at the LED module500side corresponds to the load current IF. The output control unit102can detect whether the LED module500is under conducting state or opening state, based on the voltage Vaof the end of the resistance R0at the side of the LED module500. Also, the output control unit102is connected to the high-voltage side line of the power feed lines to the LED module500.

The constant-current control unit103has a comparator X1and a transistor Q3. The first reference value VR1is input to a negative input terminal of the comparator X1via a resistance, for example. The voltage Vafrom the current detection unit110is input to a positive input terminal of the comparator X1via a resistance, for example. An output terminal of the comparator X1is connected to a base of the transistor Q3via a resistance R10, for example. An emitter of the transistor Q3is grounded and a collector of the transistor Q3is connected to the one of the input terminals of the photo coupler PC.

The open detection circuit105has a transistor Q1and a comparator X2. A base of the transistor Q1is connected to the output terminal of the comparator X1and is input with an output voltage Vbof the comparator X1. An emitter of the transistor Q1is grounded. A collector of the transistor Q1and a positive input terminal of the comparator X2are connected to the second reference value VTH1via a resistance. The voltage Vafrom the current detection unit110is input to a negative input terminal of the comparator X2via a resistance. An output terminal of the comparator X2is connected to the open-voltage setting circuit106.

The open-voltage setting circuit106has transistors Q2, Q4, a comparator X3, resistances R1, R2, R3and the like. A base of the transistor Q4is connected to the output terminal of the comparator X2and an emitter of the transistor Q4is grounded. A negative input terminal of the comparator X3is connected to a collector of the transistor Q4via the resistance R1, is connected to the ground potential via the resistance R2and is connected to the second reference value VTH1via the resistance R3. A positive input terminal of the comparator X3is connected to the high-voltage side line of the power feed lines to the LED module500via a resistance, for example. The voltage V0(output voltage V0) of the high-voltage side line is input to the positive input terminal of the comparator X3via a resistance, for example. An output terminal of the comparator X3is connected to a base of the transistor Q2via a resistance. An emitter of the transistor Q2is grounded and a collector of the transistor Q2is connected to one of the input terminals of the photo coupler PC.

[Operations of LED Driving Apparatus1]

Below, the operations of the LED driving apparatus11are described. In this illustrative embodiment, when the alternating current power is input from the alternating current power supply VACto the LED driving apparatus1, i.e., when the LED driving apparatus1can output the direct current power, the output control unit102determines whether the LED module500is under conducting state or opening state in accordance with the detection result of the current detection unit110. The output control unit102outputs a signal to the driving control unit108in accordance with a result of the determination and controls the output from the power conversion circuit107dto the LED module500. As described below, the output control unit102determines whether the LED module500is under conducting state or opening state in accordance with a value of the load current IF.

FIG. 3is a graph illustrating a relation between the load current IFflowing in the LED module500and the output voltage V0from the power conversion unit107.

When the LED module500is under conducting state, the constant-current control unit103of the output control unit102outputs a first signal (feedback signal for current setting) to the driving control unit108so that the load current IFflowing in the LED module500is constant. The first signal is output, based on the first reference value VR1. The load current IFof the LED module500is regulated depending on the first reference value VR1. In other words, the first reference value VR1is a dimming signal and the LED module500is dimmed depending on the dimming signal.

That is, when the LED module500is under conducting state, as shown inFIG. 3, the output voltage V0monotonically increases as the load current IFincreases. As the constant-current control unit103is controlled depending on the first reference value VR1, the load current IFis regulated and takes a value within a dimming range from the upper limit IF1to the lower limit IF2. The upper limit IF1of the load current IFcorresponds to the upper limit V01of the output voltage V0. Also, the lower limit IF2of the load current corresponds to the lower limit V01of the output voltage V0.

In the meantime, when the LED module500is under conducting state, the constant-current control unit103performs the constant-current-control, so that additional values of the forward voltages VFof the LEDs511may be increased accompanied by the non-uniformity of the properties of the individual LEDs511, the environment change of the LED module500and the like. In this case, the output voltage V0may exceed the upper limit V01within the dimming range.

In the meantime, when the LED module500is under opening state, the constant-voltage control unit104of the output control unit102controls so that the output voltage V0becomes a constant-voltage value. The control is performed by outputting a second signal (feedback signal for voltage setting) to the driving control unit108. At this time, the output voltage V0is controlled so that it becomes a voltage value V03(which is an example of a predetermined voltage value), which is a voltage or a higher, at which the LED module500starts conduction, and is a voltage or lower that corresponds to the upper limit IF1of the load current IFflowing in the LED module500.

When the LED module500is under opening state, the constant-voltage control unit104outputs a second signal to the driving control unit108, based on the output voltage V0and the third reference value VTH2that is switched by the open detection circuit105on the basis of the second reference value VTH1, as described below. As shown inFIG. 3, the output voltage V0is controlled so that it becomes a predetermined voltage value V03within a range between a voltage VOFFat which the LED module500starts conduction and the upper limit V01of the output voltage V0. The second signal is output from the open-voltage setting circuit106to the driving control unit108, as described below, and the driving control unit108controls the output voltage V0in accordance with the second signal, as described above.

In the below, the operations of the LED driving apparatus1will be described in the respective cases that the LED module500is under conduction-state and under opening state with reference toFIG. 2.

When the LED module500is under conducting state, the load current IF(refer to IrinFIG. 2) flows in the resistance R0. Accordingly, the detected voltage Vabecomes a voltage corresponding to the load current IF.

At this time, the constant-current control unit103uses inputs of the voltage Vabased on the load current IFdetected by the current detection unit110and the first reference value VR1that is a reference voltage for generating the first signal and performs the constant-current-control, based on a comparison result of the inputs. Based on the comparison result of the voltage based on the load current IFand the first reference value VR1, the first signal is output to the driving control unit108.

That is, in the constant-current control unit103, when the detected voltage Vaand the first reference value VR1are input to the comparator X1, the output voltage Vbis obtained from the comparator X1. The transistor Q3becomes on-state in accordance with the output voltage Vb. When the transistor Q3becomes on-state, predetermined current depending on base current of the transistor Q3and a current amplification factor flows to the photo coupler PC. That is, the first signal is output from the constant-current control unit103to the driving control unit108.

Meanwhile, at this time, in the constant-voltage control unit104, the transistor Q1of the open detection circuit105becomes on-state in accordance with the output voltage Vbfrom the comparator X1. When the transistor Q1becomes on-state, the positive input terminal of the comparator X2is connected to the ground potential and thus becomes ‘L (low).’ Thereby, the comparator X2compares the potential of the positive input terminal and the detected voltage Vainput to the negative input terminal and outputs ‘L.’

As the output of the comparator X2becomes ‘L’, the transistor Q4of the open-voltage setting circuit106becomes off-state. Therefore, the negative input terminal of the comparator X3becomes relatively ‘H (high)’ to the positive input terminal. Thereby, the output of the comparator X3becomes ‘L.’

As the output of the comparator X3becomes ‘L’, the transistor Q2becomes off-state. Therefore, the second signal is not output from the constant-voltage control unit104and the constant-voltage control is thus not performed.

[Operation When LED Module500is Under Opening State (Abnormal State)]

When the LED module500is under opening state, the load current IFdoes not flow in the resistance R0. Accordingly, the detected voltage Vabecomes ‘L’, i.e., zero.

At this time, in the constant-current control unit103, the detected voltage Vaof ‘L’ and the first reference value VR1are input to the comparator X1. The output voltage Vbof the comparator X1becomes ‘L.’ Since the output voltage Vbis ‘L’, the transistor Q3becomes off-state. Accordingly, the output of the first signal from the constant-current control unit103is stopped and the constant-current control is not thus performed.

On the other hand, at this time, the operation of the constant-voltage control unit104becomes effective by the output voltage Vbbased on the detected voltage Va. In the constant-voltage control unit104, as the operation of the open detection circuit105is switched, the third reference value VTH2is internally generated from the second reference value VTH1in accordance with the detected voltage Va. The third reference value VTH2becomes a reference value of the open-voltage setting circuit106. The constant-voltage control unit104performs the constant-voltage control on the output voltage V0, based on the third reference value VTH2.

That is, in the constant-voltage control unit104, since the output voltage Vbof the comparator X1is ‘L’, the output voltage Vbis input, as an opening state detecting signal, to the transistor Q1of the open detection circuit105and the transistor Q1of the open detection circuit105becomes off-state. Therefore, the positive input of the comparator X2connected to the collector of the transistor Q1becomes effective. The positive input terminal of the comparator X2is connected to the voltage based on the second reference value VTH1and becomes relatively ‘H’ with respect to the negative input terminal connected to the detected voltage Vaof ‘L.’ Therefore, the output of the comparator X2becomes ‘H’ and the transistor Q4of the open-voltage setting circuit106becomes on-state.

When the transistor Q4becomes on-state, the third reference value VTH2, which is set by the second reference value VTH1and the resistances R1, R2, R3, is input the negative input terminal of the comparator X3. That is, the third reference value VTH2is generated as the transistor Q4becomes on-state and thus the resistance R1becomes effective, based on the opening state detecting signal from the comparator X1. Also, the voltage based on the output voltage V0to the LED module500is input to the positive input terminal of the comparator X3via the resistance R4and the positive input terminal of the comparator X3is grounded via the resistance R5. Here, the third reference value VTH2is set so that the output voltage V0to the LED module500becomes the predetermined constant-voltage value V03, which is the voltage VOFFor higher corresponding to the lower limit I0of the load current IFand the voltage V0lor lower corresponding to the upper limit IF1of the load current IFBased on a comparison result of the input values of the positive and negative sides of the comparator X3, a predetermined voltage is output from the comparator X3. Based on the output of the comparator X3, the transistor Q2becomes on-state. When the transistor Q2becomes on-state, predetermined current depending on the base current of the transistor Q2and a current amplification factor flows to the photo coupler PC. That is, the second signal is output from the constant-voltage control unit104to the driving control unit108so that the output voltage becomes the predetermined voltage value V03.

Effects of Illustrative Embodiment

As described above, when the LED module500is under opening state, the LED driving apparatus1controls so that the output voltage to the LED module500becomes lower than the voltage V01corresponding to the upper limit IF1of the load current IF. As a result, when the LED module500is attached to and detached from the LED driving apparatus1while the LED driving apparatus1operates, the current flowing in the LED module500starts to flow from a current value smaller than the upper limit IF1of the load current IF, and the current gradually increases and reaches the upper limit IF1. When the LED module500is under opening state, the output voltage to the LED module500is set to any value smaller than the voltage V0lcorresponding to the upper limit IF1of the load current IF, so that it is possible to suppress a value of peak current flowing in the LED module500. Therefore, the breakdown (burnout and the like) of the LEDs511due to the inrush current is suppressed.

FIG. 4is a graph illustrating an example of a change in current that is supplied when the LED module500is attached to and detached from the LED driving apparatus1according to the illustrative embodiment.

InFIG. 4, time before time T0indicates a period in which the LED module500is under opening state and time after time T0indicates a period in which the LED module500is under conducting state. As shown inFIG. 4, in the LED driving apparatus1, when the LED module500shifts from the opening state to the conducting state (around time T0), the load current IFsmoothly increases from the IF3, so that the inrush current shown inFIG. 5does not flow in the LED module500. Thereby, it is possible to suppress the LEDs511configuring the LED module500from being damaged.

The LED driving apparatus1has the simple circuit in which the relatively simple circuit devices such as comparator, transistor and the like are used while the large circuit device such as inductor is not used. Accordingly, it is possible to realize the LED driving circuit1that can be miniaturized and has a high product quality and a low manufacturing cost.

The LED driving circuit may not have the dimming function.

The power conversion circuit and the peripheral circuits may not have an insulating type configuration. Also, the LED driving circuit may be a circuit that converts the direct current power input from the direct current power supply by the power conversion circuit and feeds the same to the LED module.

Instead of the transistor connected to the input terminal of the comparator of the open detection circuit and the transistor connected to the input terminal of the comparator of the open-voltage setting circuit, the other type-switch device such as field effect transistor may be used.

The photo couplers may be individually connected to the respective collectors of the transistor Q3of the constant-current control unit103and the transistor Q2of the constant-voltage control unit104and the signals may be output to the control IC108a.

In the meantime, the LED module that is driven by the LED driving apparatus is not limited to the above module having the plurality of LED arrays. The LED module may have one LED array. Also, the LED array is not limited to the LED array having the plurality of LEDs. The LED array may have only one LED. That is, the LED module may have only one LED. For example, the LED module may have one LED array in which two LEDs are arranged in series. Also, the LED module may have a configuration in which two LEDs are arranged in parallel.

The illustrative embodiments are just illustrative example and is not limited to limit this disclosure. The scope of this disclosure is indicated by the claims and includes all modifications and equivalents.