JP2013027200A - Power-supply device and lighting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power-supply device and a lighting apparatus capable of implementing stable dimming control.SOLUTION: A power-supply device 10 comprises a DC-DC converter 20 including an inductor 22 connected to a semiconductor light-emitting element 6, and a switching element 21 turning on/off according to the logic level of a control signal CS. A current detecting part 25 detects a current flowing through the switching element 21. A control circuit 40 receives a reference signal VR corresponding to the setting value of a light output of the semiconductor light-emitting element 6 and a current detection signal from the current detecting part 25. After switching the logic level of the control signal CS from a first logic level placing the switching element 21 into an off-state to a second logic level placing the switching element 21 into an on-state, the control circuit 40 switches the logic level of the control signal from the second logic level to the first logic level when the current detection signal exceeds the reference signal VR by a current flowing through the inductor 22 gradually increasing.

Description

  The present invention relates to a power supply device having a dimming function used for driving a semiconductor light emitting element such as a light emitting diode, and a lighting fixture including the power supply device.

  In recent years, light emitting diodes (LEDs) have attracted attention as new light sources for illumination that replace light bulbs and fluorescent lamps. Light emitting diodes are expected to be widely used in the future because they have characteristics of longer life and relatively lower power consumption than conventional light sources.

  In order to continuously dim the light emitting diode, a method similar to the method conventionally used in incandescent lamps can be used. For example, Japanese Patent Application Laid-Open No. 2003-157986 (Patent Document 1) describes a method for controlling an applied voltage to a light emitting diode, and a method for combining control of the applied voltage and switching dimming by a switch element. (See paragraphs 0014 and 0015 of the same document).

  When only switching dimming by the switch element is performed, the frequency of the pulse signal for driving the switch element needs to be set high so that the light from the light emitting diode does not flicker. However, since the on-time of the pulse signal becomes extremely short during deep light control, it is difficult to control the on-time with high accuracy. For this reason, in the method described in the above document, switching dimming is performed until the on-time of the pulse signal can be controlled with high accuracy, and in deeper dimming, the pulse width is constant and the applied voltage of the light emitting diode is It is controlled.

JP 2003-157986 A

  By the way, since the current-voltage characteristic of the light emitting diode exhibits a substantially constant voltage characteristic, constant current control is generally used when the light emitting diode is driven using a switching power supply. In this case, a current is detected by a resistor inserted in series with the light emitting diode, and the output of the switching power supply is controlled based on a comparison between the current detection signal and a current reference value.

  However, when dimming is performed by constant current control, the current detection signal and the current reference value become minute in a deep dimming region. As a result, there are problems that high accuracy is required for the current detection circuit and the comparator, and that stable operation becomes difficult because of being easily affected by noise.

  On the other hand, in the method using constant voltage control, relatively stable light control can be realized even in a deep light control region. However, in the case of constant voltage control, the current flowing through the light emitting diode tends to vary due to variations in characteristics of the light emitting diode and heat generation. As a result, the light output of the light emitting diode varies.

  Accordingly, an object of the present invention is to provide a power supply device and a lighting fixture that can realize stable light control.

  In one aspect, the present invention is a power supply device for driving a semiconductor light emitting element, and includes a DC-DC converter, a current detection unit, and a control circuit. The DC-DC converter includes an inductor connected to the semiconductor light emitting element and a switching element connected to the inductor and turned on / off according to the logic level of the control signal. The current flowing through the inductor increases or decreases according to the on / off state of the switching element. The current detection unit detects a current flowing through the switching element, and outputs a current detection signal having a magnitude proportional to the detected current value. The control circuit generates the control signal. The control circuit receives a reference signal and a current detection signal corresponding to the set value of the light output of the semiconductor light emitting element. The control circuit switches the logic level of the control signal from the first logic level that turns off the switching element to the second logic level that turns on the switching element, and then the current flowing through the inductor gradually increases. Thus, when the magnitude of the current detection signal exceeds the magnitude of the reference signal, the logic level of the control signal is switched from the second logic level to the first logic level.

  Preferably, the power supply device further includes a time constant circuit including a capacitor. The capacitor is charged to a predetermined voltage by the control signal of the second logic level, and is discharged with a predetermined time constant when the logic level of the control signal is switched from the second logic level to the first logic level. The time constant circuit outputs a signal proportional to the voltage of the capacitor to the control circuit. The control circuit switches the logic level of the control signal from the second logic level to the first logic level, and then when the magnitude of the output signal of the time constant circuit falls below a predetermined reference value, The logic level is switched from the first logic level to the second logic level.

  Alternatively, the DC-DC converter further includes an auxiliary inductor that is magnetically coupled to the inductor. The control circuit switches the logic level of the control signal from the second logic level to the first logic level and then changes the logic level of the control signal when the induced voltage of the auxiliary inductor drops below a predetermined reference value. Switch from one logic level to a second logic level.

  Preferably, the power supply device described above includes a rectifier circuit that rectifies an input AC voltage, a force that converts a pulsating voltage output from the rectifier circuit into a constant voltage, and outputs the converted constant voltage to a DC-DC converter. And a rate improvement circuit.

  In the case where the drive voltage for driving the control circuit is input to the power input terminal provided in the control circuit, the power supply device is preferably provided between the output node on the high voltage side of the power factor correction circuit and the power input terminal. And a power switch connected to the. The power switch is turned off when the voltage of the output node on the high voltage side of the power factor correction circuit is less than a predetermined first reference value, and the voltage of the output node on the high voltage side of the power factor improvement circuit is the first voltage. Turns on when the reference value is exceeded.

  Preferably, the power supply device further includes a resistance portion that is connected in series with the power switch and has a variable resistance value between the output node on the high voltage side of the power factor correction circuit and the power supply input terminal. The resistance unit has a first resistance value when the voltage at the power input terminal is less than a predetermined second reference value, and has a value greater than the first resistance value when the voltage at the power input terminal is greater than or equal to the second reference value. It has a large second resistance value.

  This invention is a lighting fixture in another situation, Comprising: Said power supply device and the semiconductor light-emitting element driven by a power supply device are provided.

  According to the present invention, based on a comparison between the current detection signal proportional to the current value flowing through the switching element in the on state and the reference signal corresponding to the set value of the optical output of the semiconductor light emitting element, the switching element is turned on from off. Since the switching timing is controlled, stable dimming control can be realized.

It is a circuit diagram which shows the structure of the power supply device 10 by Embodiment 1 of this invention. FIG. 2 is a circuit diagram illustrating an example of a configuration of a PFC circuit 70 in FIG. 1. It is a circuit diagram which shows the example which comprised the control circuit 40 of FIG. 1 by control IC50 for commercially available PFC. FIG. 7 is a circuit diagram showing a configuration of a power supply device 10A as a modification of the power supply device 10 of FIG. It is a circuit diagram which shows the structure of 10 C of power supply devices by Embodiment 2 of this invention. FIG. 6 is a circuit diagram showing a configuration of a power supply device 10D as a first modification of the power supply device 10C of FIG. 5. FIG. 6 is a circuit diagram showing a configuration of a power supply device 10E as a second modification of the power supply device 10C of FIG. 5.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

<Embodiment 1>
[Configuration of power supply unit]
FIG. 1 is a circuit diagram showing a configuration of a power supply device 10 according to Embodiment 1 of the present invention. Referring to FIG. 1, power supply device 10 is a switching power supply having a dimming function, converts an AC voltage input from AC power supply 5 between input nodes N1 and N2 into a DC voltage, and converts the converted DC voltage. Is output to the light source unit 6 including a plurality of light emitting diodes connected between the output nodes N7 and N8. The amount of current flowing through the light source unit 6 is controlled by a dimming signal. In addition to the light source unit 6 and the power supply device 10, the luminaire 1 includes a light distribution control unit (not shown) that guides light from the light source unit 6 in an appropriate direction and a housing unit (not shown) that holds each unit. Consists of.

  The power supply device 10 includes a full-wave rectifier circuit 11, a power factor control (PFC) circuit 70, a DC-DC converter 20, a reference signal generator 12, a resistance element 25 as a current detector, A time constant circuit 30 and a control circuit 40 are included. Hereinafter, the configuration of each unit will be described.

(Full-wave rectifier circuit)
The full-wave rectification circuit 11 performs full-wave rectification on the AC voltage received from the AC power supply 5. The pulsating voltage output from the full wave rectifier circuit 11 is input to the PFC circuit 70.

(PFC circuit)
The PFC circuit 70 converts the pulsating voltage output from the full-wave rectifier circuit 11 into a constant voltage, and shapes the input current waveform so that the current waveform input to the power supply device 10 becomes a waveform close to a sine wave. The PFC circuit 70 can be configured using, for example, a boost converter. In the following description, output node N5 on the high voltage side of PFC circuit 70 is also referred to as power supply node VCC, and output node N6 on the low voltage side is also referred to as ground node VEE. A specific configuration example of the PFC circuit 70 will be described with reference to FIG.

(DC-DC converter)
The DC-DC converter 20 converts the DC voltage output from the PFC circuit 70 into DC voltages having different magnitudes and outputs the converted DC voltage to the light source unit 6. In the case of the first embodiment shown in FIG. 1, the DC-DC converter 20 is constituted by a step-down converter, more specifically, a step-down chopper. Hereinafter, the DC-DC converter 20 is also referred to as a step-down chopper 20.

  As shown in FIG. 1, the step-down chopper 20 includes an NMOS (Negative-channel Metal Oxide Semiconductor) transistor 21 as a switching element, an inductor 22, a diode 23, a capacitor 24, and a resistance element 26. Hereinafter, the connection relationship of these components will be described.

  The diode 23, the NMOS transistor 21, and the resistance element 25 as a current detection unit are connected in series between the output nodes N5 and N6 of the PFC circuit 70 in this order. At this time, the cathode of the diode 23 is connected to the output node N5 of the PFC circuit 70. The output node N5 of the PFC circuit 70 is directly connected to the output node N7 on the high voltage side of the power supply device 10. Inductor 22 is connected between a connection node N9 of diode 23 and NMOS transistor 21 and output node N8 on the low voltage side of power supply device 10. Capacitor 24 is connected between output nodes N8 and N9. One end of the resistance element 26 is connected to the gate of the NMOS transistor 21 and the other end (node N20) is supplied with a control signal CS from the control circuit 40.

(Reference signal generator)
The reference signal generation unit 12 receives a dimming signal corresponding to the light output level of the light source unit 6 and generates a reference signal VR whose voltage level changes according to the dimming signal. The voltage level of the reference signal VR increases as the set value of the light output of the light source unit 6 increases. The dimming signal is, for example, a dimming command value input by the user of the lighting fixture 1. The generated reference signal VR is input to the control circuit 40.

(Current detector)
In order to detect a current flowing through the NMOS transistor 21, a resistance element 25 as a current detection unit is provided. The voltage applied to the resistance element 25 (the voltage at the node N10) is input to the control circuit 40.

(Time constant circuit)
Time constant circuit 30 is provided between one end (node N20) of gate resistor 26 of NMOS transistor 21 and ground node VEE. In the case of FIG. 1, the time constant circuit 30 includes a diode 31, a capacitor 32, and resistance elements 33 and 34. Diode 31 and resistance elements 33 and 34 are connected in series between node N20 and ground node VEE in this order so that the anode of diode 31 is on node N20 side. The capacitor 32 is connected in parallel with the resistance element 34.

  When the control signal CS output from the control circuit 40 is at a high (H) level, that is, when the NMOS transistor 21 is on, the capacitor 32 is charged. At this time, the voltage of the capacitor 32 becomes equal to the voltage obtained by dividing the control signal CS at the H level by the resistance elements 33 and 34.

  When the control signal CS is at a low (L) level, that is, when the NMOS transistor 21 is in an off state, the charge accumulated in the capacitor 32 is discharged through the resistance element 34. As a result, the voltage of the capacitor 32 gradually decreases with a time constant determined by the resistance value of the resistance element 34 and the capacitance of the capacitor 32. The voltage applied to the capacitor 32 (the voltage at the node N11) is input to the control circuit 40.

(Control circuit)
The control circuit 40 generates a control signal CS and outputs it to the gate of the NMOS transistor 21. As shown in FIG. 1, the control circuit 40 includes comparators 41 and 42, a reset priority RS flip-flop 43, and a buffer amplifier 44.

  The comparator 41 receives the reference signal VR output from the reference signal generation unit 12 and the detection voltage by the resistance element 25. The comparator 41 outputs an H level signal when the detection voltage from the resistance element 25 exceeds the voltage level of the reference signal VR.

  The comparator 42 receives the output voltage of the time constant circuit 30 and a predetermined reference voltage 45. The comparator 42 outputs an H level signal when the output voltage of the time constant circuit 30 becomes smaller than the reference voltage 45.

  The RS flip-flop 43 receives the output of the comparator 42 at the set terminal (S) and the output of the comparator 41 at the reset terminal (R). The RS flip-flop 43 outputs an H level signal from the output terminal Q when the output of the comparator 42 is H level, and outputs an L level signal from the output terminal Q when the output of the comparator 41 is H level. Since the RS flip-flop 43 has priority for resetting, an L level signal is output from the output terminal Q when the outputs of the comparators 41 and 42 are both at the H level. The output of the RS flip-flop 43 is amplified by the buffer amplifier 44 and input to the gate of the NMOS transistor 21 as the control signal CS.

[Power supply operation]
Hereinafter, the operation of the power supply apparatus 10 will be described with reference to FIG. Note that the capacitor 24 is provided in order to suppress the ripple of the output current and has a relatively small capacity, and is therefore ignored in the following description.

  First, when the NMOS transistor 21 is turned on by switching the control signal CS from the L level to the H level, the output voltage of the PFC circuit 70 is applied to the light source unit 6 and the inductor 22. As a result, the current flowing through the inductor 22 gradually increases, and the current flowing through the NMOS transistor 21 increases. Along with this, the voltage of the resistance element (current detection unit) 25 that detects the current flowing through the NMOS transistor 21 increases. As a result, when the voltage of the resistance element 25 becomes higher than the voltage level of the reference signal VR, the output of the comparator 41 (that is, the input of the reset terminal (R) of the RS flip-flop 43) is switched to the H level. As a result, the control signal CS is switched from the H level to the L level, so that the NMOS transistor 21 is switched to the OFF state.

  While the control signal CS is at the H level, the capacitor 32 of the time constant circuit 30 holds the voltage obtained by dividing the H level voltage of the control signal CS by the resistance elements 33 and 34.

  Next, when the NMOS transistor 21 is turned off by switching the control signal CS from the H level to the L level, the step-down chopper 20 is electrically disconnected from the PFC circuit 70, so that the inductor 22, the diode 23, and the light source A current circulating through the section 6 flows. This current gradually decreases.

  Furthermore, since the diode 31 is turned off when the control signal CS becomes L level, the voltage of the capacitor 32 (the voltage of the node N11) gradually increases with a time constant determined by the capacitance of the capacitor 32 and the resistance value of the resistance element 34. Decrease. Eventually, when the voltage of the capacitor 32 (the voltage of the node N11) becomes smaller than the reference voltage 45, the output of the comparator 42 (that is, the input of the set terminal (S) of the RS flip-flop 43) is switched to the H level. As a result, the control signal CS is switched from the L level to the H level. Thus, the off time of the NMOS transistor 21 is a constant value determined by the time constant of the time constant circuit 30.

  Here, when the dimming is changed in a deeper direction, that is, when the set value of the light output of the light source unit 6 is decreased, the magnitude of the reference signal VR is also decreased. For a while after the reference signal VR decreases, the current flowing through the inductor 22 exceeds the current value corresponding to the reference signal VR. Therefore, even if the NMOS transistor 21 is switched on, the current is immediately switched off. Change. That is, the on-time of the NMOS transistor 21 is almost zero. As a result, the current flowing through the inductor 22 decreases rapidly. Eventually, when the current flowing through the inductor 22 decreases to a level equal to or lower than the current value corresponding to the reference signal VR, the on-time of the NMOS transistor 21 starts to increase. Finally, the current flowing through the inductor 22 is set to a value corresponding to the current reference signal VR. Since the current flowing through the light source unit 6 is substantially equal to the average value of the current flowing through the inductor 22 (the ripple is removed by the capacitor 24), the light emission output of the light source unit 6 decreases as the reference signal VR decreases. become.

  On the contrary, when the dimming is changed in the direction of decreasing light, that is, when the set value of the light output of the light source unit 6 is increased, the magnitude of the reference signal VR is also increased. In this case, since the magnitude of the current flowing through the inductor 22 is smaller than the current value corresponding to the reference signal VR, the current flowing through the inductor 22 corresponds to the reference signal VR after the NMOS transistor 21 is switched on. The NMOS transistor 21 remains on until the current value is reached. Finally, the current flowing through the inductor 22 is set to a value corresponding to the current reference signal VR. As a result, the light emission output of the light source unit 6 increases as the reference signal VR increases.

  As described above, according to the power supply device 10 according to the first embodiment, the detection signal proportional to the current value flowing through the NMOS transistor 21 in the ON state and the reference signal VR corresponding to the set value of the light output of the light source unit 6 are obtained. Based on the comparison, the switching timing of the switching element from on to off is controlled. As long as the reference signal VR is not 0, the power supply device 10 operates stably. As a result, stable light control can be realized.

  The circuit system for controlling the off time of the NMOS transistor 21 to be constant is not limited to the method using the time constant circuit 30 shown in FIG. For example, a one-shot multivibrator (monostable multivibrator) may be provided instead of the RS flip-flop 43, the comparator 42, and the time constant circuit 30 in FIG. The one-shot multivibrator receives the output of the comparator 41 and outputs an L level signal for a predetermined time (corresponding to the off time of the NMOS transistor 21) when the output of the comparator 41 changes to the H level. Thereafter, an H level signal is output. The output signal of the one-shot multivibrator is given to the gate of the NMOS transistor 21 through the buffer amplifier 44 and the gate resistor 26.

[PFC circuit configuration example]
FIG. 2 is a circuit diagram showing an example of the configuration of the PFC circuit 70 of FIG. Since the configuration of the PFC circuit 70 is publicly known, it will be briefly described below with reference to FIG.

  The PFC circuit 70 includes a boost chopper 60, a control IC (Integrated Circuit) 50, and voltage dividing circuits 71 and 74 (resistance elements 72, 73, 75, and 76).

  The step-up chopper 60 converts the voltage input between the input nodes into a constant voltage corresponding to the energization rate of the NMOS transistor 62, and outputs it. As shown in FIG. 2, the step-up chopper 60 includes inductors 61 and 66, an NMOS transistor 62, a diode 63, a large capacity electrolytic capacitor 64, resistance elements 65, 68 and 69, and a capacitor 67.

  The inductor 66 is provided to detect the zero current of the inductor 61 by being magnetically coupled to the inductor 61. The capacitor 67 is provided in order to remove the ripple current included in the current flowing through the inductor 61 and prevent the ripple current from flowing out to the power system on the input side.

  The control IC 50 is a simplified configuration of a commercially available dedicated IC used for current critical mode PFC. The control IC 50 includes an FB terminal, a MULT terminal, a CS terminal, a ZCS terminal, a GATE terminal, a GND terminal, a VIN terminal, and a COMP terminal as input / output terminals.

  The voltage between the output nodes N5 and N6 is divided by the voltage dividing circuit 74 and input to the FB terminal. The voltage between the input nodes N3 and N4 is divided by the voltage dividing circuit 71 and input to the MULT terminal. A current flowing through the NMOS transistor 62 is detected by the resistance element 65 and input to the CS terminal. The induced voltage of the inductor 66 is input to the ZCS terminal. A gate drive signal for the NMOS transistor 62 is output from the GATE terminal. The GND terminal is an input terminal for ground voltage, and the VIN terminal is an input terminal for drive voltage, but is not shown in FIG. A capacitor 77 is connected to the COMP terminal in order to remove a high frequency component of the output voltage of the differential amplifier 54.

  The control IC 50 further includes a differential amplifier 54, a multiplier 51, comparators 52 and 53, an RS flip-flop 55, and an amplifier 56 as components of the internal circuit.

  The differential amplifier 54 amplifies and outputs the difference between the input voltage at the FB terminal (the output voltage of the voltage dividing circuit 74) and the reference voltage 58. A value obtained by multiplying the reference voltage 58 by the reciprocal of the voltage dividing ratio of the voltage dividing circuit 74 becomes a target value of the output voltage of the boosting chopper 60.

  The multiplier 51 multiplies the pulsation voltage, which is the input voltage of the MULT terminal (the output voltage of the voltage dividing circuit 71), and the output voltage of the differential amplifier 54. The output voltage of the multiplier 51 becomes the target value of the current flowing through the inductor 61.

  The comparator 52 compares the input voltage of the CS terminal (the voltage of the resistance element 65) with the output voltage of the multiplier 51. The comparison result is input to the reset terminal (R) of the RS flip-flop 55. When the current flowing through the NMOS transistor 62 (current of the inductor 61) exceeds the target value corresponding to the output voltage of the multiplier 51, the RS flip-flop 55 is reset, so that the NMOS transistor 62 is turned off. .

  The comparator 53 compares the input voltage at the ZCS terminal (induced voltage of the inductor 66) with the reference voltage 57. The comparison result is input to the set terminal (S) of the RS flip-flop 55. When the current flowing through the inductor 61 becomes 0, the RS flip-flop 55 is set, so that the NMOS transistor 62 is turned on.

  The amplifier 56 amplifies the output voltage of the RS flip-flop 55, and the amplified voltage is output from the GATE terminal and input to the gate of the NMOS transistor 62.

  Due to the functions of the comparators 52 and 53, the current flowing through the inductor 61 has a triangular waveform, and the shape of the envelope connecting the peaks of each pulse becomes a sine wave (full-wave rectified waveform). The ripple included in the inductor current is removed by the capacitor 67.

[Configuration Example of Control Circuit 40 Using Control IC for PFC Circuit]
The control circuit 40 in FIG. 1 can be easily configured by a commercially available control IC 50 used in the PFC shown in FIG. This will be specifically described below.

  FIG. 3 is a circuit diagram showing an example in which the control circuit 40 of FIG. 1 is configured by a commercially available control IC 50 for PFC. 1 and 3, comparators 41 and 42 in FIG. 1 correspond to comparators 52 and 53 in FIG. 3, respectively, and RS flip-flop 43 in FIG. 1 corresponds to RS flip-flop 55 in FIG. The amplifier (buffer amplifier) 44 in FIG. 1 corresponds to the amplifier 56 in FIG. Since the functions of the differential amplifier 54 and the multiplier 51 in FIG. 3 are not necessary, constant voltages 82 and 81 are input to the COMP terminal and the FB terminal. Therefore, the multiplier 51 multiplies the input voltage at the MULT terminal by a proportional constant and outputs the result.

[Modification]
FIG. 4 is a circuit diagram showing a configuration of a power supply device 10A as a modification of the power supply device 10 of FIG. The power supply device 10A is different from the power supply device 10 of FIG. 1 in that it includes an auxiliary inductor 27 that is magnetically coupled to the inductor 22 of the step-down chopper 20, instead of the time constant circuit 30. The auxiliary inductor 27 is connected to the inverting input terminal of the comparator 42 through the resistance element 28.

  The comparator 42 compares the induced voltage of the auxiliary inductor 27 with the reference voltage 45, and when the induced voltage of the auxiliary inductor 27 is lower than the reference voltage 45, the comparator 42 is at the H level at the set terminal (S) of the RS flip-flop 43. The signal is output. As a result, when the current flowing through the inductor 22 becomes almost zero, the RS flip-flop 43 is set and the NMOS transistor 21 is turned on. While the step-down chopper 20 in FIG. 1 is operating in the continuous current mode, the step-down chopper 20 in the power supply device 10A in FIG. 4 operates in the current critical mode.

  Since the other points of FIG. 4 are the same as those of FIG. 1, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  Although the step-down chopper is shown as an example of the DC-DC converter 20 in the first embodiment, it is not necessarily limited to this circuit system. For example, the DC-DC converter 20 may be configured by a step-up / down chopper, a flyback converter, or the like.

  The configuration of the time constant circuit 30 shown in FIG. 1 is an example. Any circuit configuration may be used as long as the capacitor charged by the control signal CS at the H level is discharged with a predetermined time constant when the control signal CS is at the L level.

<Embodiment 2>
In the case of a two-converter system such as the power supply device 10 of the first embodiment, the power supply voltage used in the control IC (control circuit) 40 for the downstream step-down converter is supplied from the output node of the upstream PFC circuit 70. It is normal. In this case, in order to reduce the number of components, the output voltage of the PFC circuit 70 is preferably reduced and supplied to the control IC 40 by resistance voltage division. However, in this method, the control IC 40 for the subsequent step-down converter may start to operate before the front-stage PFC circuit 70 completely rises. In this case, the light source unit 6 blinks because the power supply voltage is insufficient. Sometimes

  In order to prevent such an abnormal operation from occurring, it is necessary that the control IC 40 for the step-down converter in the subsequent stage starts its operation after the PFC circuit 70 in the previous stage is completely started up. In the power supply device 10C according to the second embodiment, the output voltage of the PFC circuit 70 in the previous stage is detected, and the power supply voltage is supplied to the control IC 40 when the voltage value exceeds a predetermined reference value. As a result, it is possible to prevent the flickering of illumination from occurring due to a shortage of the drive voltage supplied to the control IC 40. Hereinafter, a specific description will be given with reference to FIGS.

[Configuration of Power Supply Device 10C]
FIG. 5 is a circuit diagram showing a configuration of a power supply device 10C according to the second embodiment of the present invention. Referring to FIG. 5, power supply device 10 </ b> C further includes a voltage detection unit 90, a PNP-type bipolar transistor 121 as a power switch, a Zener diode 122, a capacitor 123, and a resistance element 120. Different from 10. In FIG. 5, the time constant circuit 30 and the gate resistor 26 are not shown.

  The voltage detector 90 is a circuit that detects a voltage obtained by dividing the voltage between the output nodes N5 and N6 of the PFC circuit 70 and switches on / off of the bipolar transistor 121 according to the detected divided voltage. The voltage detection unit 90 includes resistance elements 91 to 95, an NPN bipolar transistor 96, and a Zener diode 97.

  Hereinafter, the connection between the components of the voltage detection unit 90 will be described. The resistance elements 91 and 92 include an output node N5 (power supply node VCC) on the high voltage side and an output node N6 (ground node) on the low voltage side of the PFC circuit 70. VEE) are connected in series in this order. Connection node N14 of resistance elements 91 and 92 is connected to the base terminal of bipolar transistor 96 through resistance element 93. Zener diode 97 is connected between the emitter terminal of bipolar transistor 96 and ground node VEE so that the anode is on the ground node VEE side. Resistance element 94 is connected between the collector terminal of bipolar transistor 96 and the base terminal of bipolar transistor 121. The resistance element 95 is connected between the emitter terminal and the base terminal of the PNP-type bipolar transistor 121.

  Resistance element 120 is connected between output node N5 (power supply node VCC) on the high voltage side of PFC circuit 70 and the emitter terminal (node N16) of bipolar transistor 121. The collector terminal of the bipolar transistor 121 is connected to a VIN terminal which is a power input terminal of the control IC 40. Therefore, the resistance element 120 and the bipolar transistor 121 are connected in series between the output node N5 on the high voltage side of the PFC circuit 70 and the VIN terminal of the control IC 40. A GND terminal which is a terminal for ground voltage input of the control IC 40 is connected to the output node N6 (ground node VEE) on the low voltage side of the PFC circuit 70. The zener diode 122 and the capacitor 123 are connected in parallel with each other between the VIN terminal and the GND terminal of the control IC 40.

  According to the above configuration, when the divided voltage between the output nodes N5 and N6 of the PFC circuit 70 (that is, the voltage at the connection node N14) is less than the threshold voltage of the bipolar transistor 96, the base voltage of the bipolar transistor 121 is It becomes equal to the voltage of power supply node VCC. Therefore, the bipolar transistor 121 is in an off state. When the voltage at the connection node N14 becomes equal to or higher than the threshold voltage of the bipolar transistor 96, the bipolar transistor 96 is turned on. As a result, the bipolar transistor 121 is turned on. As a result, charging of the capacitor 123 is started by the voltage of the power supply node VCC. Eventually, the input voltage at the VIN terminal becomes equal to the Zener voltage of the Zener diode 122.

[Modification 1]
FIG. 6 is a circuit diagram showing a configuration of a power supply device 10D as a first modification of the power supply device 10C of FIG. Referring to FIG. 6, power supply device 10 </ b> D further includes voltage detection unit 90 </ b> A, NPN bipolar transistor 124 as a power switch, Zener diode 122, capacitor 123, and resistance element 120. Different from 10.

  The voltage detector 90A is a circuit that detects a voltage obtained by dividing the voltage between the output nodes N5 and N6 of the PFC circuit 70, and switches the bipolar transistor 124 on and off according to the detected divided voltage. Voltage detection unit 90A includes resistance elements 91, 92, and 98. Resistive elements 91 and 92 are connected in series in this order between output node N5 (power supply node VCC) on the high voltage side and output node N6 (ground node VEE) on the low voltage side of PFC circuit 70. Connection node N14 of resistance elements 91 and 92 is connected to the base terminal of bipolar transistor 124 via resistance element 98.

  Resistance element 120 is connected between output node N5 (power supply node VCC) on the high voltage side of PFC circuit 70 and the collector terminal (node N15) of bipolar transistor 124. The emitter terminal of the bipolar transistor 124 is connected to a VIN terminal which is a power input terminal of the control IC 40. Therefore, the resistance element 120 and the bipolar transistor 124 are connected in series between the output node N5 on the high voltage side of the PFC circuit 70 and the VIN terminal of the control IC 40. A GND terminal which is a terminal for ground voltage input of the control IC 40 is connected to the output node N6 (ground node VEE) on the low voltage side of the PFC circuit 70. The zener diode 122 and the capacitor 123 are connected in parallel with each other between the VIN terminal and the GND terminal of the control IC 40. Zener diode 122 and capacitor 123 are connected in parallel to each other between connection node N15 of resistance element 120 and bipolar transistor 124 and ground node VEE.

  According to the above configuration, when the divided voltage between the output nodes N5 and N6 of the PFC circuit 70 (that is, the voltage at the connection node N14) exceeds the threshold voltage of the bipolar transistor 124, the bipolar transistor 124 is turned on. Supply of the power supply voltage from the output node N5 on the high voltage side of the PFC circuit 70 to the control IC 40 is started.

[Modification 2]
FIG. 7 is a circuit diagram showing a configuration of a power supply device 10E as a second modification of the power supply device 10C of FIG. The power supply device 10E of FIG. 7 differs from the power supply device 10C of FIG. 5 in that a resistance unit 100 is provided instead of the resistance element 120 of FIG.

  The resistance unit 100 includes resistance elements 101 and 102 and an NMOS transistor 103. Resistance element 101 is connected between output node N5 on the high voltage side of PFC circuit 70 and the emitter terminal (node N16) of bipolar transistor 121. NMOS transistor 103 and resistance element 102 are connected in series with each other between output node N5 and node N16 and in parallel with resistance element 101. The resistance value of the resistance element 101 is larger than the resistance value of the resistance element 102. Therefore, the resistance value of the resistance unit 100 is switched in two stages according to the on / off state of the NMOS transistor 103.

  The switching control unit 110 includes an NPN bipolar transistor 111 and resistance elements 112 and 113. Resistance element 112 and bipolar transistor 111 are connected in series in this order between output node N5 on the high voltage side of PFC circuit 70 and output node N6 on the low voltage side. A connection node N17 between the resistance element 112 and the bipolar transistor 111 is connected to the gate of the NMOS transistor 103. The resistance element 113 is connected between the base terminal of the bipolar transistor 111 and the VIN terminal of the control IC 40.

  According to the above configuration, when input from AC power supply 5 is first started, capacitor 123 is not charged because bipolar transistor 121 is off. When the output voltage of the PFC circuit 70 reaches a predetermined voltage, the bipolar transistor 121 is turned on, and charging of the capacitor 123 is started. For a while after the bipolar transistor 121 is turned on, the bipolar transistor 111 is in an off state and the NMOS transistor 103 is in an on state. Therefore, the charging current for the capacitor 123 is supplied via both the resistance elements 101 and 102. Thereafter, when the voltage of the capacitor 123 (that is, the voltage at the VIN terminal) exceeds the threshold voltage of the bipolar transistor 111, the bipolar transistor 111 is turned on and the NMOS transistor 103 is turned off. As a result, the charging current for the capacitor 123 is supplied only through the resistance element 101.

  As described above, the resistance value of the resistance unit 100 is relatively low resistance (parallel combined resistance of the resistance elements 101 and 102) when the voltage at the VIN terminal is lower than a predetermined voltage (that is, the threshold voltage of the bipolar transistor 111). Thus, when the voltage at the VIN terminal becomes equal to or higher than a predetermined voltage, the resistance becomes relatively high (resistance value of the resistance element 101). As a result, the capacitor 123 is rapidly charged at the initial stage of the rise of the control IC 40, so that the speed of rise can be increased, and power consumption can be suppressed after reaching the steady state.

  The embodiment disclosed this time must be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Lighting fixture, 5 AC power supply, 6 Light source part 10,10A, 10C, 10D, 10E Power supply device, 11 Full wave rectifier circuit, 12 Reference signal generation part, 20 DC-DC converter (step-down chopper), 21 NMOS transistor ( Switching element), 22 inductor, 23 diode, 24 capacitor, 25 resistor element (current detection unit), 27 auxiliary inductor, 30 time constant circuit, 40, 50 control circuit (control IC), 41, 42, 52, 53 comparator , 43,55 RS flip-flop, 44,56 buffer amplifier, 60 step-up chopper, 70 PFC circuit, 90 voltage detection unit, 121 bipolar transistor (power switch), 122 Zener diode, 120 resistance element, 100 resistance unit, 110 switching control Part, CS control signal, VR base Signal.

Claims (7)

A power supply device for driving a semiconductor light emitting element,
A DC-DC converter including an inductor connected to the semiconductor light emitting element and a switching element connected to the inductor and turned on / off according to a logic level of a control signal;
The current flowing through the inductor increases or decreases in accordance with on / off of the switching element,
The power supply device further includes:
A current detection unit that detects a current flowing through the switching element and outputs a current detection signal having a magnitude proportional to the detected current value;
A control circuit for generating the control signal,
The control circuit receives a reference signal corresponding to a set value of light output of the semiconductor light emitting element and the current detection signal,
The control circuit switches the logic level of the control signal from a first logic level that turns off the switching element to a second logic level that turns on the switching element. A power supply device that switches the logic level of the control signal from the second logic level to the first logic level when the magnitude of the current detection signal exceeds the magnitude of the reference signal by gradually increasing . The power supply device further includes a time constant circuit including a capacitor,
The capacitor is charged to a predetermined voltage by the control signal of the second logic level, and has a predetermined time constant when the logic level of the control signal is switched from the second logic level to the first logic level. Discharged,
The time constant circuit outputs a signal proportional to the voltage of the capacitor to the control circuit,
The control circuit switches the logic level of the control signal from the second logic level to the first logic level and then the magnitude of the output signal of the time constant circuit falls below a predetermined reference value The power supply device according to claim 1, wherein the logic level of the control signal is switched from the first logic level to the second logic level. The DC-DC converter further includes an auxiliary inductor that is magnetically coupled to the inductor;
The control circuit switches the logic level of the control signal from the second logic level to the first logic level, and then when the induced voltage of the auxiliary inductor drops below a predetermined reference value, The power supply device according to claim 1, wherein a logic level of a signal is switched from the first logic level to the second logic level. A rectifier circuit for rectifying the input AC voltage;
The power supply device according to claim 1, further comprising: a power factor correction circuit that converts the pulsating voltage output from the rectifier circuit into a constant voltage and outputs the converted constant voltage to the DC-DC converter. A driving voltage for driving the control circuit is input to a power input terminal provided in the control circuit,
The power supply device further includes a power switch connected between an output node on the high voltage side of the power factor correction circuit and the power input terminal,
The power switch is turned off when the voltage of the output node on the high voltage side of the power factor correction circuit is less than a predetermined first reference value, and the voltage of the output node on the high voltage side of the power factor improvement circuit is The power supply device according to claim 4, wherein the power supply device is turned on when the reference value is equal to or greater than the first reference value. The power supply device further includes a resistance unit that is connected in series with the power switch between the output node on the high voltage side of the power factor correction circuit and the power input terminal, and has a variable resistance value.
The resistor unit has a first resistance value when a voltage of the power input terminal is less than a predetermined second reference value, and the voltage of the power input terminal is equal to or higher than the second reference value. The power supply device according to claim 5, wherein the power supply device has a second resistance value larger than a resistance value of one. The power supply device according to any one of claims 1 to 6,
The lighting fixture provided with the semiconductor light-emitting device driven by the said power supply device.

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