JP2017142970A - Electric power unit for led and led lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power unit for LED that precisely detect power supply voltage variation by a circuit standardized for a wide range of source voltages, and suppresses an overshoot of an output current in power supply recovery.SOLUTION: An electric power unit 100 for LED includes: a rectifying circuit 200 which rectifies a source voltage; a DC/DC converter 300 which supplies an output current from a rectification output voltage to an LED 50; a driver circuit 600 which increases the output current as a predetermined terminal voltage rises; a feedback circuit 700 which determines the predetermined terminal voltage so that the output current reaches a target value; and a terminal voltage pull-out circuit 800 having a reference value acquiring circuit Rf which acquires, as a reference value, a voltage division value of the rectification output voltage at a relatively low voltage division ratio with a large time constant, a detection value acquiring circuit Dt which acquires, as a detection value, a voltage division value of the rectification output voltage at a high voltage division ratio with a small time constant, a comparing circuit which outputs predetermined logic when the detection value is less than the reference value, and a discharging circuit Ds which lowers the predetermined terminal voltage according to the predetermined logic.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an LED power supply device and an LED lighting device using the same.

  The power supply device of Patent Literature 1 includes an overload state of a conversion unit that converts alternating current to direct current, a switching element that switches direct current supplied from the conversion unit to the transformer primary side, and a load provided on the transformer secondary side. An overload detection unit to detect, and an overload protection unit that stops the operation of the switching element and maintains the stopped state when an overload state is detected by the overload detection unit. The power supply device also includes a voltage detection unit that detects a voltage output from the conversion unit, and a control unit that stops the operation of the switching element when the voltage detected by the voltage detection unit is lower than a threshold value. Thereby, the operation of the switching element is stopped by the control unit in the case of an instantaneous power failure or instantaneous voltage drop of the commercial power supply. When the commercial power supply returns to normal, the control unit resumes the operation of the switching element. The voltage detection unit includes a series circuit of a diode and a capacitor connected to the output terminal of the smoothing circuit unit, a series circuit of a resistor that divides the voltage at the connection point of the diode and the capacitor, and a Zener at the voltage dividing point. A diode and an NPN transistor having a base terminal connected via the diode are provided. The emitter terminal of the NPN transistor functions as a control terminal for the overload protection circuit unit.

Japanese Patent No. 5435912

  In the LED power supply device, as will be described in detail later, an LED current overshoot caused by a transient operation of the control circuit becomes a problem when the power supply is restored after the power supply voltage is lowered. In order to suppress this overshoot, it is necessary to accurately detect a decrease and recovery of the power supply voltage (that is, power supply voltage fluctuation). In recent years, it has become common to standardize circuits by adapting one type of LED power supply device to a wide range of power supply voltages (for example, both AC100V and AC200V). It is desired that the detection circuit also supports a wide range of power supply voltages.

  Here, the voltage detection unit disclosed in Patent Document 1 has a problem of detection accuracy of power supply voltage fluctuations and a problem of dealing with a wide range of power supply voltages, as will be described in detail later. As a general rule, in the above voltage detector, the detection accuracy depends on the operation threshold value of the transistor, but since the transistor operation threshold value generally has a large individual variation, it is highly accurate to detect the power supply voltage fluctuation using this operation threshold value. difficult. Further, since the voltage detection unit is configured to compare the detection value proportional to the power supply voltage with one threshold value, the circuit cannot be standardized by corresponding the detection operation to a plurality of power supply voltages.

  Therefore, the present invention can accurately detect power supply voltage fluctuations with a circuit configuration standardized over a wide range of power supply voltages, and suppress overshoot of the LED current when power is restored after the power supply voltage drops. An object is to provide an LED power supply device and an LED lighting device using the same.

  The LED power supply device according to the first aspect of the present invention includes a rectifier circuit that rectifies an AC power supply voltage and outputs a rectified output voltage, generates a DC output current from the rectified output voltage, and supplies the output current to the LED. A DC / DC converter that has a predetermined terminal, a driver circuit that drives the DC / DC converter to increase the output current in response to an increase in voltage at the predetermined terminal, and the output current matches a target value A feedback circuit for determining a voltage at a predetermined terminal and a terminal voltage extracting circuit are provided, and the terminal voltage extracting circuit acquires a divided value of the rectified output voltage as a reference value with a first voltage dividing ratio and a first time constant. A reference value acquisition circuit and a detection value acquisition for acquiring a divided value of the rectified output voltage as a detection value with a second voltage division ratio higher than the first voltage division ratio and a second time constant smaller than the first time constant. Circuit and reference value A comparison circuit that outputs a predetermined logic when the detection value is compared to a reference value by comparing the detection value, and a discharge circuit that reduces the voltage at the predetermined terminal regardless of the operation of the feedback circuit according to the output of the predetermined logic. .

  According to the above configuration, the reference value is acquired with a relatively low partial pressure ratio and a large time constant, and the detected value is acquired with a relatively high partial pressure ratio and a small time constant. As a result, regardless of the power supply voltage value, the detected value exceeds the reference value when the power supply voltage is steady, and when the power supply voltage drops, the detected value responds to the power supply voltage drop faster than the reference value. Falls below the reference value, and the voltage at the predetermined terminal is pulled out in accordance with the reversal of the magnitude relationship between the reference value and the detected value. Accordingly, it is possible to detect the power supply voltage fluctuation with high accuracy with a circuit configuration standardized for a wide range of power supply voltages. When the power supply voltage is restored, the driving of the DC / DC converter is started in a state where the voltage at the predetermined terminal is pulled out, so that an overshoot of the output current, that is, the LED current when the power supply is restored after the power supply voltage is lowered is suppressed. It becomes possible.

  Further, it is preferable that the capacitance of the detection-side capacitor that smoothes the divided voltage value of the detection value acquisition circuit is smaller than the capacitance of the reference-side capacitor that smoothes the divided value of the reference value acquisition circuit. As a result, the resistance component of the detection value acquisition circuit and the resistance component of the reference value acquisition circuit can be made close to each other, so that the second time constant can be significantly higher than the first time constant. The design of the reference value acquisition circuit becomes easy. In addition, since it is possible to reduce the capacitance of the detection-side capacitor, it is possible to detect power supply voltage fluctuations at a high response speed.

  The DC / DC converter is a flyback converter, and the capacity of the input capacitor for smoothing the rectified output voltage is smaller than the capacity of the output capacitor connected to the output side of the flyback converter. Thus, this embodiment is suitably applied to a power factor improving type flyback converter having a small-capacity input capacitor.

  An LED power supply device according to a second embodiment of the present invention includes a first rectifier circuit that rectifies an AC power supply voltage and outputs a first rectified output voltage, and generates a DC output current from the first rectified output voltage. A DC / DC converter that supplies this output current to the LED, a driver circuit that has a predetermined terminal and drives the DC / DC converter so as to increase the output current with respect to an increase in voltage at the predetermined terminal, and an output A feedback circuit that determines a voltage at a predetermined terminal so that the current matches a target value, a second rectifier circuit that rectifies an AC power supply voltage and outputs a second rectified output voltage, and a terminal voltage extraction circuit are provided. The terminal voltage extraction circuit includes a reference value acquisition circuit that acquires a divided value of the first rectified output voltage as a reference value using a first voltage division ratio and a first time constant, and a divided voltage of the second rectified output voltage. Value higher than the first partial pressure ratio A detection value acquisition circuit that acquires a detection value with a partial pressure ratio of 2 and a second time constant smaller than the first time constant, and a predetermined value when the detection value is less than the reference value by comparing the reference value with the detection value A comparator circuit that outputs logic and a discharge circuit that lowers the voltage at a predetermined terminal regardless of the operation of the feedback circuit according to the output of the predetermined logic.

  According to the above configuration, as in the first embodiment, the power supply voltage fluctuation is accurately detected with a circuit configuration standardized over a wide range of power supply voltages, and the output current at the time of power recovery after the power supply voltage drops, that is, the LED current It is possible to suppress the overshoot. In addition, the responsiveness of the detected value with respect to the power supply voltage fluctuation is ensured regardless of the capacitance component of the rectified output of the first rectifier circuit, and the terminal voltage drawing operation can be performed in a timely manner.

  Here, the DC / DC converter is a flyback converter, and the capacity of the input capacitor for smoothing the first rectified output voltage is larger than the capacity of the output capacitor connected to the output side of the flyback converter. Thus, this embodiment is also suitably applied to a non-power factor improving flyback converter having a large-capacity input capacitor.

  In the first and second embodiments, the comparison circuit includes a comparator, a reference value is input to one input terminal of the comparator, a detection value is input to the other input terminal of the comparator, and a predetermined logic is output by the comparator. Configured to be. As a result, the discharge circuit can be operated based on a highly accurate comparison between the reference value and the detected value.

  In the first and second embodiments, the reference value acquisition circuit includes a resistance voltage dividing circuit having a first voltage dividing ratio, a reference side capacitor for smoothing a voltage at a voltage dividing point of the resistance voltage dividing circuit, and a resistor. The diode is inserted in the current path from the voltage dividing point of the voltage dividing circuit to the reference side capacitor, the anode is connected to the voltage dividing point, and the cathode is connected to the reference side capacitor, and the cathode voltage is used as the reference value. You may comprise so that it may be acquired. Thereby, the discharge from the reference side capacitor to the resistance voltage dividing circuit during the period when the power supply voltage is reduced is suppressed by the diode, and the reference value obtained before the power supply voltage is reduced is maintained for a longer time. Therefore, the terminal voltage extracting operation is reliably maintained even when the power supply voltage is lowered for a longer period.

  The LED lighting device of the present invention includes any one of the above-described LED power supply devices and LEDs. Since the LED lighting device of this configuration includes the LED power supply device that can suppress the overshoot of the output current as described above, the LED brightness overshoot at the time of power recovery after the power supply voltage is reduced is suppressed. Lighting is realized.

It is a figure which shows the power supply device and LED illumination device for LED by 1st Embodiment. It is a figure explaining the driver circuit of the power supply device for LED of FIG. It is a figure explaining operation | movement of the power supply device for LED by 1st Embodiment. It is a figure which shows the power supply device and LED illumination device for LED by 2nd Embodiment. It is a figure which shows the terminal voltage drawing circuit of the power supply device for LED by 3rd Embodiment. It is a figure which shows the terminal voltage drawing circuit by a modification. It is a figure which shows the terminal voltage drawing circuit by a modification. It is a figure which shows the terminal voltage drawing circuit by a modification. It is a figure which shows the terminal voltage drawing circuit by a comparative example.

<First Embodiment>
FIG. 1 shows an LED power supply device 100 and an LED lighting device 150 according to the first embodiment. The LED lighting device 150 includes an LED power supply circuit 100 and an LED 50 (LED unit). The LED power supply device 100 is supplied with an input power supply voltage from an AC power supply AC (for example, commercial power supply) via the input terminals T1 and T2, and a DC output current generated by the LED power supply device 100 is output to the output terminal T3. And T4, wires W1 and W2, and terminals T5 and T6. The LED 50 is an array of a plurality of LED elements connected in series or in series and parallel. The LED power supply device 100 includes a rectifier circuit 200, a DC / DC converter 300, a detection circuit 400, an auxiliary power supply circuit 500, a driver circuit 600, a feedback circuit 700, and a terminal voltage extraction circuit 800. In the present disclosure, the input power supply voltage from the AC power supply AC is referred to as “power supply voltage”.

  The rectifier circuit 200 includes current fuses 1 and 2, a diode bridge 3, an input capacitor 4, and a noise filter as necessary. An AC voltage from the AC power supply AC is input to the rectifier circuit 200, and a full-wave rectified output from the diode bridge 3 is slightly smoothed by the input capacitor 4 (for example, a film capacitor) and output to the DC / DC converter 300.

  The DC / DC converter 300 is an isolated flyback converter in the present embodiment, and constitutes a so-called one-converter type flyback circuit having a power factor improving function. The DC / DC converter 300 includes a switching element 5, a transformer 6, a current detection resistor 7, a diode 8, and an output capacitor 9. In the present embodiment, since the switching element 5 is composed of a MOSFET, the switching element 5 is hereinafter also referred to as an FET 5. The reference potential on the primary winding side of the transformer 6 (that is, the low potential electrode side node of the input capacitor 4) is referred to as the primary side ground G1, and the reference potential on the secondary winding side (that is, the low potential of the output capacitor 9). The electrode side node) is referred to as a secondary side ground G2. Since the DC / DC converter 300 of the present embodiment is a power factor improving type, the output capacitor 9 (for example, an electrolytic capacitor) has a smoothing function of low frequency ripple (ripple based on the input power supply frequency). Therefore, the capacitance of the input capacitor 4 << the capacitance of the output capacitor 9.

  In PWM control of the DC / DC converter 300, energy is accumulated in the primary winding of the transformer 6 during the ON period of the FET 5, and the energy is output from the secondary winding side of the transformer 6 via the diode 8 during the OFF period of the FET 5. The capacitor 9 is charged. The output of the DC / DC converter 300 is determined by the ON duty (ON width) of the FET 5, the turn ratio of the secondary winding to the primary winding of the transformer 6, and the like. The FET 5 is driven by a PWM gate signal output from the control IC 20. In the following description, the output current of the DC / DC converter 300 is referred to as “output current”, and the output voltage of the DC / DC converter 300 is referred to as “output voltage”. In the present disclosure, the LED current is substantially equal to the output current.

  The detection circuit 400 includes a current detection circuit including the current detection resistor 10 and a voltage detection circuit including resistors 11, 12 and 13, and uses the secondary side ground G2 as a reference potential. The current detection resistor 10 is a low resistance element inserted between the secondary side ground G2 and the cathode end of the LED 50, and a voltage proportional to the output current is generated in the current detection resistor 10. The voltage detection circuit (resistors 11, 12 and 13) is a voltage dividing resistor circuit connected in parallel to the output capacitor 9, and a voltage proportional to the output voltage is generated in the resistor 13.

  The auxiliary power supply circuit 500 includes a primary-side power supply circuit that uses the primary-side ground G1 as a reference potential, and a secondary-side power supply circuit (not shown) that uses the secondary-side ground G2 as a reference potential. The primary power supply circuit includes an auxiliary winding 6s of the transformer 6, resistors 14 and 15, a diode 16, a capacitor 17, and a Zener diode 18 as necessary. The primary power supply circuit generates the control power supply Vcc1 for the driver circuit 600 based on the input voltage of the DC / DC converter 300 and the switching operation of the FET 5. Specifically, the input voltage is dropped through the resistors 14 and 15, and the voltage generated in the auxiliary winding 6s is rectified and smoothed by the diode 16 and the capacitor 17, and is constant by the Zener diode 18 as necessary. As a result, the control power supply Vcc1 is generated. In the secondary power supply circuit (not shown), the voltage generated in the other auxiliary winding (not shown) of the transformer 6 or the output capacitor 9 is converted to a constant voltage by a constant voltage circuit (not shown). Vcc2 is generated. The constant voltage circuit may be a three-terminal regulator, a series regulator, a shunt regulator, or the like.

  The driver circuit 600 includes a control IC 20 and a capacitor 19, and receives the supply of the control power source Vcc1 and operates using the primary side ground G1 as a reference potential. The capacitor 19 is connected between a feedback terminal (FB terminal) described later and the primary side ground G1. The driver circuit 600 PWM-drives the FET 5 of the DC / DC converter 300 according to the input from the feedback circuit 700 to the FB terminal. Note that peripheral circuit components and wiring (not shown) can be appropriately connected to terminals other than the FB terminal of the control IC 20.

  The control IC 20 may be a general-purpose switching control IC for driving the flyback converter, and at least a control power supply terminal (VCC terminal), a ground terminal (GND terminal), a gate output terminal (OUT terminal), and a current sense terminal. (ISNS terminal) and a feedback terminal (FB terminal). Further, the control IC 20 has a zero cross detection terminal (ZCD terminal), a multiplier input terminal (MUL terminal), and a compensation terminal (COMP terminal) (not shown).

  The control IC 20 receives operation power from the VCC terminal connected to the control power supply Vcc1, and operates using the GND terminal connected to the primary side ground G1 as a reference potential. Note that the control IC 20 operates with power supplied via the resistors 14 and 15 when starting or stopping, that is, when there is no power supplied from the auxiliary winding 6s. The OUT terminal is connected to the gate terminal of the FET 5 (via a gate resistor (not shown) if necessary), and its internal circuit outputs the PWM gate signal of the FET 5. The ISNS terminal is connected to a connection point between the current detection resistor 7 and the source terminal of the FET 5 and receives a voltage input corresponding to the FET current generated in the current detection resistor 7. The switching operation of the FET 5 is optimized by the inputs of the MUL terminal (not shown) and the ISNS terminal. The FB terminal is connected to the collector terminal of the phototransistor 30 t and the capacitor 19.

  As shown in FIG. 2, in the control IC 20, for example, the FB terminal is connected to an internal reference voltage source 20a (for example, a 5V constant voltage source) via a resistor 20b, and the OUT terminal is connected to a gate circuit 20c. The In the gate circuit 20c, the pulse width (ON width) of the PWM gate signal is determined according to the input voltage at the FB terminal. Specifically, the control IC 20 is configured so that the on-width of the PWM gate signal increases with an increase in the FB terminal voltage, whereby the output current increases with an increase in the FB terminal voltage. . Further, the control IC 20 stops outputting the PWM gate signal from the OUT terminal when the FB terminal voltage is equal to or lower than the lower limit threshold (for example, about 0.5 V). This stop state is canceled when the FB terminal voltage becomes higher than the lower limit threshold. The control IC 20 having each terminal described above is available on the market (for example, MM3460 manufactured by Mitsumi Electric Co., Ltd.), and the functions of other terminals are well known to those skilled in the art. The detailed explanation is omitted.

  The feedback circuit 700 includes operational amplifiers 21 and 22, voltage sources 23, 24 and 27, diodes 25 and 26, resistors 28 and 29, and a photocoupler 30 (photodiode 30d and phototransistor 30t), and constitutes a secondary side control circuit. To do. The feedback circuit 700 receives the supply of the control power Vcc2 and operates using the secondary side ground G2 as a reference potential. In general, the operational amplifier 21 is a constant current control operational amplifier that has a function of making the output current constant, and the operational amplifier 22 is a constant voltage control operational amplifier that has a function of making the output voltage constant. Then, according to the output state of the DC / DC converter 300, one of constant current control and constant voltage control is selected by the diode OR circuit composed of the diodes 25 and 26, and the input state of the photodiode 30d is determined. Note that an input signal or an output signal of the photocoupler 30 is referred to as a feedback signal.

  The detection current value detected by the detection circuit 400 (current detection resistor 10) is input to the inverting input terminal (−) of the operational amplifier 21 for constant current control, and the target value of the output current is input to the non-inverting input terminal (+). A voltage corresponding to (target current value) is input from the voltage source 23. Note that a feedback element (not shown) (a resistor, a capacitor, or a series or parallel circuit thereof) is connected between the inverting input terminal and the output terminal of the operational amplifier 21. The operational amplifier 21 amplifies and outputs an error between the detected current value input to the inverting input terminal and the target current value input to the non-inverting input terminal. In other words, when the diode 25 is turned on and constant current control is selected, the operational amplifier 21 generates a feedback signal so that the detected current value matches the target current value. The voltage value of the voltage source 23 may be a divided value of the control power supply Vcc2.

  The detection voltage value detected by the detection circuit 400 (resistors 11, 12 and 13) is input to the inverting input terminal (−) of the operational amplifier 22 for constant voltage control, and the output voltage is input to the non-inverting input terminal (+). A voltage corresponding to the target voltage value (upper limit voltage value) is input from the voltage source 24. A feedback element (not shown) is also connected between the inverting input terminal and the output terminal of the operational amplifier 22. The operational amplifier 22 amplifies and outputs an error between the detection voltage value input to the inverting input terminal and the upper limit voltage value input to the non-inverting input terminal. In other words, when the diode 26 is turned on and constant voltage control is selected, the operational amplifier 22 generates a feedback signal so that the detected voltage value matches the upper limit voltage value. The voltage value of the voltage source 24 may be a divided value of the control power supply Vcc2.

  The diode OR circuit composed of the diodes 25 and 26 is turned on with respect to the lower one of the output terminal voltage of the operational amplifier 21 and the output terminal voltage of the operational amplifier 22. The common anode of the diode OR circuit is connected to the cathode side of the photodiode 30d. The anode of the photodiode 30d is connected to the voltage source 27 via a resistor 28, and the resistor 29 is connected in parallel to the photodiode 30d. The voltage value of the voltage source 27 may be the control power supply Vcc2 or the like. An output current corresponding to the current (light emission) flowing through the photodiode 30d flows through the phototransistor 30t. In this way, in the feedback circuit 700, a feedback signal is generated based on the error between the detected current value (or detected voltage value) and the target current value (or upper limit voltage value), and the primary signal is output from the feedback circuit 700 via the photocoupler 30. Is transmitted to the driver circuit 600 on the side.

  Therefore, for example, in the constant current control, when the detected current value is higher than the target current value, the current of the photodiode 30d and the phototransistor 30t increases due to the error amplification effect of the operational amplifier 21. As a result, the FB terminal voltage of the control IC 20 is lowered, the ON width in the PWM drive of the FET 5 is narrowed, and the output current is reduced. On the contrary, at the time when the detected current value is lower than the target current value, the current of the photodiode 30d and the phototransistor 30t decreases due to the error amplification function of the operational amplifier 21. As a result, the FB terminal voltage of the control IC 20 increases, the ON width in the PWM drive of the FET 5 increases, and the output current increases.

  Here, a circuit operation in the case where a drop in the power supply voltage occurs in the LED power supply device 100 when the terminal voltage extracting circuit 800 is not provided will be described. When there is no terminal voltage drawing circuit 800, an overshoot of the output current occurs when the power supply voltage is restored. This overshoot of the output current may cause failure of the LED 50, the FET 5, etc. or a shortened life.

  Specifically, when the amount of decrease in power supply voltage is relatively large (for example, when the power supply voltage is about 30% or less of the rated value), the control power supplies Vcc1 and Vcc2 obtained from the auxiliary power supply circuit 500 are reduced. Then, the operation of the driver circuit 600 and the feedback circuit 700 is also stopped. Therefore, in this state, the DC / DC converter 300 stops operating and the LED 50 is turned off. Here, in a short period from when the power supply voltage starts to decrease until the control power supplies Vcc1 and Vcc2 can no longer be generated, the FB terminal voltage rises due to the action of constant current control of the feedback circuit 700 against the power supply voltage drop. Therefore, when the driver circuit 600, the feedback circuit 700, and the DC / DC converter 300 stop operating, the capacitor 19 connected to the FB terminal is charged with the increased FB terminal voltage. In this state, when the power supply voltage is subsequently restored and the driver circuit 600 starts operating, the driver circuit 600 starts driving the FET 5 of the DC / DC converter 300 based on the increased FB terminal voltage. For this reason, until the response of the feedback circuit 700 is stabilized after the power supply voltage is restored, an output current exceeding the target value is output, which results in an overshoot of the output current and an overshoot in the illuminance of the LED 50.

  Further, when the power supply voltage decrease amount is relatively small (for example, when the power supply voltage is about 30 to 70% of the rated value), the driver circuit 600, the feedback circuit 700, and the DC / DC converter 300 continue to operate. The LED 50 continues to be lit. In the state where the power supply voltage is lowered, the FB terminal voltage rises due to the action of constant current control of the feedback circuit 700 against the power supply voltage drop. When the power supply voltage is restored, the driver circuit 600 drives the FET 5 of the DC / DC converter 300 based on the increased FB terminal voltage. For this reason, until the response of the feedback circuit 700 is stabilized after the power supply voltage is restored, an output current exceeding the target value is output, which results in an overshoot of the output current and an overshoot in the illuminance of the LED 50. Note that when the amount of decrease in the power supply voltage is small (for example, when the power supply voltage is about 70% or more of the rated value), the overshoot in the output current and the illuminance is small, which is not a problem.

  Therefore, when the power supply voltage decreases by a predetermined amount or more, it is necessary to draw out the FB terminal voltage (that is, the voltage of the capacitor 19) of the control IC 20 and operate the driver circuit 600 from a sufficiently low state when the power supply voltage is restored. There is. Here, as a premise of the configuration in which the FB terminal voltage is pulled out when the power supply voltage is lowered, it is necessary to accurately detect fluctuations in the power supply voltage.

  FIG. 8 shows a terminal voltage extracting circuit X of a comparative example. As shown in FIG. 8, the terminal voltage extraction circuit X includes a resistance voltage dividing circuit including resistors 61, 62, and 63, a smoothing capacitor 64, an FET 65, a resistor 66, and a transistor 67. A resistance voltage dividing circuit (61-63) is connected between the high potential side output terminal of the diode bridge 3 and the primary side ground G1, and the voltage dividing point is connected to the gate terminal of the FET 65. Since the input capacitor 4 has a small capacity, the rectified output voltage of the diode bridge 3 has a pulsating waveform, and therefore a smoothing capacitor 64 having a relatively large capacity for smoothing the divided voltage value is connected in parallel to the resistor 63. The drain terminal of the FET 65 and the base terminal of the transistor 67 are supplied with power from the control power supply Vcc1 through the resistor 66, and the source terminal of the FET 65 and the emitter terminal of the transistor 67 are connected to the primary side ground G1. The collector terminal of the transistor 67 is connected to the FB terminal of the control IC 20.

  In the terminal voltage drawing circuit X, the following operations are intended. When the power supply voltage is in the normal range, the voltage dividing values of the resistance voltage dividing circuits 61 to 63 are equal to or higher than the operation threshold value of the FET 65, the FET 65 is turned on, the transistor 67 is turned off, and the FB terminal voltage is the terminal voltage extracting circuit. Unaffected by X. On the other hand, when the power supply voltage falls below a predetermined value, the divided voltage values of the resistance voltage dividing circuits 61 to 63 become less than the operation threshold value of the FET 65, the FET 65 is turned off, the transistor 67 is turned on, and the FB terminal voltage is pulled out to zero. Become.

  However, the terminal voltage extraction circuit X has problems with respect to detection accuracy, corresponding power supply voltage range, and responsiveness. Regarding the detection accuracy, in the terminal voltage extraction circuit X, the detection accuracy of the drop in the power supply voltage depends exclusively on the accuracy of the operation threshold value of the FET 65. In general, the operation threshold value of the FET varies within a range of about 1.5 to 3 V. Considering that the range of the control power supply Vcc1 is about 15 to 20 V, the detection accuracy is improved by the variation of the operation threshold value. It becomes difficult. With respect to the corresponding power supply voltage range, the configuration in which the divided value by the single resistance voltage dividing circuit is compared with the operation threshold value of the FET can deal with only a single power supply voltage. For example, since the divided voltage value is twice different between the case where the power supply voltage is AC100V and the case where the power supply voltage is AC200V (the detected value at the normal time when the power supply voltage is AC100V is 50% of the case where the power supply voltage is AC200V). Therefore, it is impossible to detect and compare both power supply voltage drops in the same circuit. Regarding the responsiveness, since the smoothing capacitor 64 having a relatively large capacity is required because of the configuration that requires the detection value to be constant voltage, the responsiveness of the detection with respect to the fluctuation of the power supply voltage, that is, the responsiveness of the terminal voltage extracting circuit X is as follows. Low. For this reason, there is a possibility that the terminal voltage extracting operation is not performed in a timely manner.

  The terminal voltage extraction circuit 800 of the present embodiment can solve the problems of the detection accuracy, the corresponding power supply voltage range, and the responsiveness, and can appropriately suppress the overshoot of the output current when the power supply voltage is restored. . Returning to FIG. 1, the terminal voltage extraction circuit 800 includes a reference value acquisition circuit Rf, a detection value acquisition circuit Dt, a comparison circuit Cp, and a discharge circuit Ds.

  The reference value acquisition circuit Rf includes a resistance voltage dividing circuit including resistors 31, 32 and 33 and a reference side capacitor 34, and is connected between the high potential side output terminal of the diode bridge 3 and the primary side ground G1. The divided voltage value (voltage of the resistor 33) by the resistance voltage dividing circuit is smoothed by the reference side capacitor 34 and becomes the reference value.

  The detection value acquisition circuit Dt includes a resistance voltage dividing circuit including resistors 35, 36 and 37 and a detection side capacitor 38, and is connected between the high potential side output terminal of the diode bridge 3 and the primary side ground G1. A divided value (voltage of the resistor 37) obtained by the resistance voltage dividing circuit is slightly smoothed by the detection-side capacitor 38 to become a detected value.

  The voltage dividing ratio of the resistors 35 to 37 is slightly higher than the voltage dividing ratio of the resistors 31 to 33. That is, when there is no fluctuation in the power supply voltage, each resistance value is set so that the detected value (voltage of the resistor 37) is slightly higher than the reference value (voltage of the resistor 33). The total resistance value of the resistors 31 to 33 and the total resistance value of the resistors 35 to 37 are approximately approximated (in the same order) within a range that ensures a slight difference in the voltage dividing ratio. This is because the loss increases when the total resistance value is too low, and noise resistance decreases when the total resistance value is too high.

  The time constant of the detection value acquisition circuit Dt is smaller than the time constant of the reference value acquisition circuit Rf. As described above, the total resistance value of the resistors 31 to 33 and the total resistance value of the resistors 35 to 37 are approximated, so that the capacitance of the detection-side capacitor 38 is sufficiently smaller than the capacitance of the reference-side capacitor 34. Each capacity is set. As a result, the time constant of the reference value acquisition circuit Rf can be made significantly higher than the time constant of the detection value acquisition circuit Dt. In addition, since the capacitance of the detection-side capacitor 38 can be reduced, high responsiveness in detection of power supply voltage fluctuation can be obtained.

  The comparison circuit Cp includes resistors 39 and 40 and a comparator 41. The comparator 41 receives power from the control power supply Vcc1 (power supply line is not shown) and operates using the primary side ground G1 as a reference potential. The reference value is input to the inverting input terminal (−) of the comparator 41 via the resistor 39, and the detection value is input to the non-inverting input terminal (+) via the resistor 40. The output of the comparator 41 is logic high (for example, open) when the detected value is equal to or higher than the reference value, and is logic low (the potential of the primary side ground G1) when the detected value is less than the reference value. Since the comparison circuit Cp includes the comparator 41, the discharge circuit Ds can be operated based on a highly accurate comparison between the reference value and the detected value.

  The discharge circuit Ds includes a resistor 42, an FET 43, a resistor 44, and a transistor 45. The output terminal of the comparator 41 is connected to the gate terminal of the FET 43, and the gate terminal of the FET 43 is supplied with power from the control power supply Vcc1 via the resistor. When the output of the comparator 41 is logic high, the resistor 42 may not be provided if the output terminal of the comparator 41 can be output instead of being opened. The drain terminal of the FET 43 and the base terminal of the transistor 45 are supplied with power from the control power supply Vcc1 through the resistor 44, and the source terminal of the FET 43 and the emitter terminal of the transistor 45 are connected to the primary side ground G1. The collector terminal of the transistor 45 is connected to the FB terminal of the control IC 20. When the output of the comparator 41 is high, the FET 43 is turned on and the transistor 45 is turned off. Therefore, the FB terminal voltage is not affected by the terminal voltage extraction circuit 800. On the other hand, when the output of the comparator 41 is low, the FET 43 is turned off, the transistor 45 is turned on, and the FB terminal voltage is reduced to zero. For each switch element, a transistor may be used instead of the FET 43, or an FET may be used instead of the transistor 45.

  FIG. 3 shows the waveforms of each part when the power supply voltage of the LED power supply device 100 having the terminal voltage extraction circuit 800 is lowered. FIG. 3 shows, from the bottom, the power supply voltage of the AC power supply AC, the input voltage of the comparator 41, the output state of the comparator 41, the FB terminal voltage, and the output current, and the horizontal axis is time. Note that the figures are not exactly the same.

  Until time t1, the power supply voltage is in a steady state (normal state). In this case, the detected value is higher than the reference value, and the output of the comparator 41 is high. Here, since the capacitance of the detection side capacitor 38 is smaller than the capacitance of the reference side capacitor 34, the ripple of the detection value is larger than the ripple of the reference value. The difference between the waveform of the detected value and the waveform of the reference value is small, but the ripple of the detected value and the ripple of the reference value are in phase. The magnitude relationship between the value and the reference value is not reversed. Since the output of the comparator 41 is high, the FET 43 / transistor 45 are in the on state / off state, respectively, and the FB terminal voltage becomes the voltage Va determined by the feedback signal from the feedback circuit 700. As a result, the output current becomes a value Ia corresponding to the FB terminal voltage Va (current value corresponding to the target current value).

  It is assumed that the power supply voltage drops sharply at time t1. Here, due to the relatively large capacity of the reference-side capacitor 34 (relatively large time constant of the reference value acquisition circuit Rf), the reference value gradually decreases with respect to the decrease of the power supply voltage. On the other hand, due to the relatively small capacitance of the detection-side capacitor 38 (relatively small time constant of the detection value acquisition circuit Dt), the detection value decreases sharply with respect to the decrease of the power supply voltage. That is, the decrease in the detected value is faster than the decrease in the reference value. The increase in the FB terminal voltage immediately after time t1 is due to the constant current control action of the feedback circuit 700.

  At time t2 immediately after time t1, the detected value falls below the reference value. As a result, the output of the comparator 41 becomes low, the FET 43 / transistor 45 is turned off / on, and the FB terminal voltage is pulled out by the transistor 45 and becomes zero. Thereby, the switching of the FET is stopped, and the output current becomes zero. After the time t2, the power supply from the auxiliary winding 6s is stopped by the switching of the FET 5 being stopped, but the control power supply Vcc1 for operating the comparator 41 and the transistor 45 is secured by the power supply from the resistors 14 and 15. .

  It is assumed that the power supply voltage recovers and rises sharply at time t3. Here, due to the relatively large capacity (relatively large time constant) of the reference-side capacitor 34, the reference value increases slowly with respect to the increase of the power supply voltage. On the other hand, due to the relatively small capacitance (relatively small time constant) of the detection-side capacitor 38, the detected value rises sharply as the power supply voltage increases. That is, the detection value rises faster than the reference value rises.

  At time t4 immediately after time t3, the detected value exceeds the reference value. As a result, the output of the comparator 41 becomes high, the FET 43 / transistor 45 are turned on / off, and the FB terminal voltage becomes the voltage Va determined by the feedback circuit 700. As a result, the output current Ia corresponding to the FB terminal voltage is obtained as before time t1.

  As described above, in the terminal voltage extracting circuit 800, the detected value is relatively high with respect to the reference value when the power supply voltage is steady, and the detected value is compared with the change rate of the reference value when the power supply voltage is varied. The terminal voltage extraction operation is controlled by utilizing the large change speed. As described above, by reducing the difference between the reference value and the detected value and increasing the difference between the change speeds of the reference value and the detected value, the fluctuation of the power supply voltage is detected with higher accuracy with respect to a wide range of power supply voltages. It becomes possible. Furthermore, the terminal voltage extraction circuit 800 having the same circuit constant is provided for various power supply voltages such as AC100V, AC110V, AC115V, AC120V, AC127V, AC200V, AC220V, AC230V, AC242V, AC256V, etc. (each nominal value) in Japan and other countries. The standardization of the circuit can be promoted. In addition, since the capacitance of the detection-side capacitor 38 can be reduced, the responsiveness of the terminal voltage extraction operation with respect to the power supply voltage fluctuation is also ensured.

  As described above, the LED power supply device 100 according to the present embodiment rectifies the power supply voltage of the AC power supply AC and outputs a rectified output voltage, and generates a DC output current from the rectified output voltage. A DC / DC converter 300 that supplies output current to the LED 50, a driver circuit 600 that drives the DC / DC converter 300 to increase the output current in response to an increase in the FB terminal voltage, and the output current matches the target current value Thus, a feedback circuit 700 for determining the FB terminal voltage and a terminal voltage extraction circuit 800 are provided. The terminal voltage extraction circuit 800 includes a reference value acquisition circuit Rf, a detection value acquisition circuit Dt, a comparison circuit Cp, and a discharge circuit Ds. . In the reference value acquisition circuit Rf, the divided value of the rectified output voltage is acquired as a reference value with a relatively low voltage dividing ratio and a relatively large time constant. In the detected value acquisition circuit Dt, the divided value of the rectified output voltage is The detection value is obtained with a relatively high partial pressure ratio and a relatively small time constant. In the comparison circuit Cp, the reference value and the detected value are compared, and when the detected value is less than the reference value, a predetermined logic (logic low in this example) is output. The discharge circuit Ds is configured to decrease the FB terminal voltage in accordance with the output of the predetermined logic regardless of the operation of the feedback circuit 700.

  Thus, the reference value is acquired with a relatively low voltage division ratio and a large time constant, and the detected value is acquired with a relatively high voltage division ratio and a small time constant. As a result, regardless of the power supply voltage value, the detected value exceeds the reference value when the power supply voltage is steady, and when the power supply voltage drops, the detected value responds to the power supply voltage drop faster than the reference value. Falls below the reference value, and the voltage at the predetermined terminal is pulled out in accordance with the reversal of the magnitude relationship between the reference value and the detected value. Therefore, it is possible to detect a drop in power supply voltage with high accuracy with a circuit configuration standardized with respect to a wide range of power supply voltages (for example, AC 100 V to AC 256 V). Since the driving of the FET 5 is started with the FB terminal voltage pulled out when the power supply voltage is restored, it is possible to suppress overshoot of the output current when the power supply voltage is restored. By suppressing the overshoot of the output current, shortening of the lifetime of the LED 50, the FET 5, etc. is avoided, and the reliability is improved. Further, since the LED lighting device 150 includes the LED power supply device 100 capable of suppressing the overshoot of the output current as described above, a comfortable illumination in which the overshoot of the brightness of the LED 50 at the time of power recovery is suppressed is realized. Is done.

<Second Embodiment>
In the first embodiment, the configuration using the power factor improving type flyback converter in which the capacity of the input capacitor is smaller than the capacity of the output capacitor is shown. However, in this embodiment, the capacity of the input capacitor is larger than the capacity of the output capacitor. A configuration using a large non-power factor flyback converter is also shown. Such a flyback converter that is not a power factor improving type may be applied to an LED power supply device for low wattage (input power is 30 W or less). Here, the same terminal voltage extraction circuit 800 as that of the first embodiment can be applied to the LED power supply apparatus using the non-power factor improved flyback converter. In this case, the rectified output of the rectifier circuit 200 is the input capacitor. Therefore, it is theoretically possible to eliminate the reference-side capacitor 34 (however, a small-capacitance reference-side capacitor 34 may be necessary for noise removal or the like). On the other hand, this embodiment shows a configuration in which the FB terminal voltage extracting circuit is operated before the power supply voltage fluctuation appears in the smoothed voltage of the input capacitor.

  FIG. 4 shows the LED power supply device 100 and the LED lighting device 150 according to the present embodiment. In the present embodiment, configurations that are substantially the same as or correspond to those in the first embodiment are denoted by the same reference numerals, and redundant description thereof is omitted.

  In the present embodiment, an input capacitor 54 (for example, an electrolytic capacitor) is connected to the output part of the rectifier circuit 200, and an output capacitor 59 (for example, a film capacitor) is connected to the output part of the DC / DC converter 300. The capacity of the input capacitor 54 is sufficiently larger than the capacity of the output capacitor 59. Therefore, the rectified output of the rectifier circuit 200 (diode bridge 3) is not a pulsating waveform but a constant voltage waveform substantially equal to the peak value of the power supply voltage.

  In the present embodiment, a rectifier circuit 205 is provided separately from the rectifier circuit 200. The rectifier circuit 205 is formed of a diode bridge, and this diode bridge is connected in parallel with the diode bridge 3 when viewed from the AC power source AC. The detection value acquisition circuit Dt is connected between the high potential side output terminal of the rectifier circuit 205 and the primary side ground G1. As in the first embodiment, the reference value acquisition circuit Rf is connected between the high potential side output terminal of the rectifier circuit 200 (diode bridge 3) and the primary side ground G1.

  Here, the resistance values of the resistors 31 to 33 of the reference value acquisition circuit Rf and the capacitance of the reference side capacitor 34, the resistance values of the resistors 35 to 37 of the detection value acquisition circuit Dt, and the capacitance of the detection side capacitor 38 are obtained as a result. The waveform of the reference value and the detection value may be selected so as to be the same as that in the case of the first embodiment (reference value and detection value shown in FIG. 3). Alternatively, the reference value may be further smoothed than in the case of the first embodiment. Therefore, the operation of the LED power supply device 100 of this embodiment is substantially the same as that of the first embodiment shown in FIG.

  That is, the time constant determined by the reference value acquisition circuit Rf and the large-capacity input capacitor 54 of the present embodiment is the time constant determined by the reference value acquisition circuit Rf and the small-capacity input capacitor 4 of the first embodiment. (The capacity of the input capacitor 4 hardly affects). Therefore, the capacity of the reference side capacitor 34 in the present embodiment may be equal to or less than the capacity of the reference side capacitor 34 in the first embodiment. Further, the circuit constant of the detection value acquisition circuit Dt of the present embodiment may be the same as the circuit constant of the detection value acquisition circuit Dt of the first embodiment. As described above, the fluctuation of the reference value accompanying the fluctuation of the power supply voltage is affected by the input capacitor 54, while the fluctuation of the detection value is not affected by the input capacitor 54. Responsiveness of voltage extraction operation) is ensured.

  As described above, the LED power supply device 100 according to this embodiment generates rectified output current from the rectified output voltage by using the rectified circuits 200 and 205 that rectify the power supply voltage of the AC power supply AC and output the rectified output voltage. A DC / DC converter 300 for supplying the output current to the LED 50, a driver circuit 600 for driving the DC / DC converter 300 to increase the output current in response to an increase in the FB terminal voltage, and the output current is a target current value. A feedback circuit 700 that determines the FB terminal voltage so as to match the terminal voltage, and a terminal voltage extraction circuit 800. The terminal voltage extraction circuit 800 includes a reference value acquisition circuit Rf, a detection value acquisition circuit Dt, a comparison circuit Cp, and a discharge circuit Ds. Is provided. In the reference value acquisition circuit Rf, the divided value of the rectified output voltage of the rectifier circuit 200 is acquired as a reference value with a relatively low voltage division ratio and a relatively large time constant. In the detection value acquisition circuit Dt, the rectifier circuit 205 A divided value of the rectified output voltage is acquired as a detection value with a relatively high voltage dividing ratio and a relatively small time constant. In the comparison circuit Cp, the reference value and the detected value are compared, and when the detected value is less than the reference value, a predetermined logic (logic low in this example) is output. The discharge circuit Ds is configured to decrease the FB terminal voltage in accordance with the output of the predetermined logic regardless of the operation of the feedback circuit 700.

  In the present embodiment, the same effect as in the first embodiment can be obtained. That is, also in this embodiment, it is possible to accurately detect a power supply voltage drop with a circuit configuration standardized over a wide range of power supply voltages, and to suppress overshoot of the output current when the power supply voltage is restored. Further, in this embodiment, since the responsiveness of the detection value to the power supply voltage fluctuation is ensured regardless of the capacitance component of the rectified output of the rectifier circuit 200 (capacitance of the input capacitor 54), it is possible to perform the terminal voltage extraction operation in a timely manner. Become.

<Third Embodiment>
In the first and second embodiments, a power supply voltage drop is assumed to be relatively short (for example, within about 1 second) (for example, see IEC standard 61000-4-11). On the other hand, in the present embodiment, a configuration corresponding to a power supply voltage drop for a relatively long time is shown. FIG. 5 shows a terminal voltage extracting circuit 800 of this embodiment. In the present embodiment, the same reference numerals are given to substantially the same or corresponding configurations as those in the first or second embodiment, and the overlapping description will be omitted.

  As shown in FIG. 5, the reference value acquisition circuit Rf includes at least resistors 31 to 33, a reference side capacitor 34, and a diode 46. The detection value acquisition circuit Dt is connected to the high-potential side output terminal of the rectifier circuit 200 (see the first embodiment) or the rectifier circuit 205 (see the second embodiment). The diode 46 is inserted and connected to a current path from the voltage dividing point of the resistance voltage dividing circuit (31 to 33) toward the reference side capacitor 34. The anode of the diode 46 is connected to the voltage dividing point, the cathode is connected to the reference-side capacitor 34, and the cathode voltage of the diode 46 becomes the reference value. In order to slightly reduce the input impedance of the comparator 41, a resistor 47 having a resistance value sufficiently higher than that of the resistor 33 may be connected between the cathode of the diode 46 and the primary side ground G1.

  The circuit operation of this embodiment and the circuit operation of the first embodiment (see FIG. 3) are basically the same, but from time t1 when the power supply voltage starts to drop to time t3 when the power supply voltage returns. The reference value waveform in the period is different. Specifically, when the power supply voltage starts decreasing at time t1, the potential of the resistor 33 decreases, the diode 46 is turned off, and the discharge path of the reference-side capacitor 34 is only the resistor 47. Since the resistance value of the resistor 47 is sufficiently higher than the resistance value of the resistor 33, the decrease in the reference value at times t1 to t3 is smaller than when the diode 46 is not connected. Further, at times t1 to t3, the ripple corresponding to the full-wave rectified waveform of the power supply voltage does not appear in the reference value.

  As described above, according to the terminal voltage extracting circuit 800 of this embodiment, the discharge from the reference-side capacitor 34 to the resistance voltage dividing circuit (particularly the resistor 33) during the period when the power supply voltage is reduced is suppressed by the diode 46, and the power supply voltage The reference value obtained before the decrease is maintained for a longer time. Therefore, the terminal voltage extracting operation is reliably maintained even when the power supply voltage is lowered for a long time.

<Modification>
Although preferred embodiments of the present invention have been described above, the present invention can be modified into various modes as shown below, for example.

(1) Modification of Terminal Voltage Extraction Circuit 800 In each of the above embodiments, the discharge circuit Ds of the terminal voltage extraction circuit 800 is formed by two stages of switch elements (FET 43 and transistor 45). As shown in FIG. The logic of 41 may be inverted and it may be configured by a single-stage switch element (FET 43). If the current drawing capability of the comparator 41 is sufficient, as shown in FIG. 6B, the output terminal of the comparator 41 may be directly connected to the FB terminal without providing a switch element. In this case, the wiring between the output terminal of the comparator 41 and the FB terminal constitutes the discharge circuit Ds. In any case, in the discharge circuit Ds, the FET as the switch element and the transistor are interchangeable.

(2) Modification of Terminal Voltage Extraction Circuit 800 In each of the above embodiments, the output current is stopped when the FB terminal voltage is reduced to zero when the terminal voltage extraction circuit 800 is operated, and the LED 50 is turned off. . On the other hand, as shown in FIG. 7, a resistor 48 having an appropriate resistance value is connected between the FB terminal and the collector terminal of the transistor 45, so that the FB terminal voltage is lowered to a sufficiently low voltage when the terminal voltage extracting circuit 800 is operated. It is good also as a structure to be made. As a result, in a state where the power supply voltage is lowered, the output current is reduced while the operation of the driver circuit 600 and the like is continued, and the LED 50 is dimmed. However, the amount of decrease in the FB terminal voltage (that is, the resistance value of the resistor 48) needs to be determined to such an extent that the output current does not overshoot even when the phototransistor 30t of the photocoupler 30 is in the off state. Note that the configuration of this modification is also applicable to the circuits of FIGS. 6A and 6B.

(3) Modification of DC / DC Converter 300 In the above embodiments, the DC / DC converter 300 is a flyback converter. However, in the present invention, the DC / DC converter 300 includes a buck converter and a buck boost. The present invention is also applicable to a configuration that is a DC / DC converter of another form such as a converter. The present invention is also applicable to a configuration in which a power factor correction circuit (such as a boost chopper circuit) is connected to the previous stage of the DC / DC converter 300 (that is, the subsequent stage of the rectifier circuit 200).

(4) Modification Regarding Control IC 20 In each of the above embodiments, the case where the driver circuit 600 is configured by a specific control IC 20 has been described. However, the driver may be a driver using another control IC or analog circuit that realizes the function of each terminal described above. The present invention is also applicable when the circuit 600 is configured.

4, 54 Input capacitor 9, 59 Output capacitor 31-33, 35-37 Resistance (resistance voltage divider)
34 Reference-side capacitor 38 Detection-side capacitor 41 Comparator 46 Diode 50 LED
100 LED power supply device 150 LED lighting device 200, 205 rectifier circuit 300 DC / DC converter 600 driver circuit 700 feedback circuit 800 terminal voltage extraction circuit Rf reference value acquisition circuit Dt detection value acquisition circuit Cp comparison circuit Ds discharge circuit

Claims (8)

A power supply for LED,
A rectifier circuit that rectifies an AC power supply voltage and outputs a rectified output voltage;
A DC / DC converter that generates a DC output current from the rectified output voltage and supplies the output current to the LED;
A driver circuit having a predetermined terminal and driving the DC / DC converter so as to increase the output current with respect to an increase in voltage of the predetermined terminal;
A feedback circuit for determining a voltage of the predetermined terminal so that the output current matches a target value;
A reference value acquisition circuit that acquires a divided value of the rectified output voltage as a reference value using a first voltage division ratio and a first time constant, and a voltage value that is higher than the first voltage division ratio. A detection value acquisition circuit that acquires a detection value with a partial pressure ratio of 2 and a second time constant smaller than the first time constant, and the detection value is less than the reference value by comparing the reference value with the detection value A comparator circuit for outputting a predetermined logic in the case, and a terminal voltage extracting circuit having a discharge circuit for reducing the voltage of the predetermined terminal regardless of the operation of the feedback circuit according to the output of the predetermined logic. Power supply.   2. The LED power supply device according to claim 1, wherein a capacitance of a detection-side capacitor that smoothes the divided voltage value of the detection value acquisition circuit is a capacitance of a reference-side capacitor that smoothes the divided voltage value of the reference value acquisition circuit. LED power supply device smaller than   3. The LED power supply device according to claim 1, wherein the DC / DC converter is a flyback converter, and a capacity of an input capacitor for smoothing the rectified output voltage is connected to an output side of the flyback converter. LED power supply device smaller than the capacity of the output capacitor. A power supply for LED,
A first rectifier circuit that rectifies an AC power supply voltage and outputs a first rectified output voltage;
A DC / DC converter that generates a DC output current from the first rectified output voltage and supplies the output current to the LED;
A driver circuit having a predetermined terminal and driving the DC / DC converter so as to increase the output current with respect to an increase in voltage of the predetermined terminal;
A feedback circuit for determining a voltage of the predetermined terminal so that the output current matches a target value;
A second rectifier circuit that rectifies the AC power supply voltage and outputs a second rectified output voltage;
A reference value acquisition circuit that acquires a divided value of the first rectified output voltage as a reference value using a first voltage division ratio and a first time constant; and a divided value of the second rectified output voltage as the first value A detection value acquisition circuit for acquiring a detection value with a second voltage division ratio higher than the voltage division ratio and a second time constant smaller than the first time constant; and comparing the reference value with the detection value to detect the detection value A comparator circuit that outputs a predetermined logic when the voltage is less than the reference value, and a terminal voltage extraction circuit having a discharge circuit that reduces the voltage of the predetermined terminal regardless of the operation of the feedback circuit in accordance with the output of the predetermined logic LED power supply device comprising:   5. The LED power supply device according to claim 4, wherein the DC / DC converter is a flyback converter, and a capacity of an input capacitor for smoothing the first rectified output voltage is connected to an output side of the flyback converter. LED power supply that is larger than the output capacitor.   6. The LED power supply device according to claim 1, wherein the comparison circuit includes a comparator, the reference value is connected to one input terminal of the comparator, and the detection value is An LED power supply device configured to be input to the other input terminal and to output the predetermined logic by the comparator. In the LED power supply device according to any one of claims 1 to 6,
The reference value acquisition circuit includes a resistance voltage dividing circuit having the first voltage dividing ratio, a reference side capacitor for smoothing a voltage at a voltage dividing point of the resistance voltage dividing circuit, and a voltage dividing point of the resistance voltage dividing circuit. A diode inserted in a current path toward the reference side capacitor and having an anode connected to the voltage dividing point and a cathode connected to the reference side capacitor, and the cathode voltage is acquired as the reference value. The power supply device for LED comprised as follows. The LED illuminating device provided with the power supply device for LED as described in any one of Claim 1 to 7, and the said LED.

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