JP6187024B2 - LED power supply device and LED lighting device - Google Patents

Description

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

  Patent Document 1 discloses an LED driving device that determines the connection state of an LED light source from the detection result of the output current and adjusts the output to the LED. The LED driving device includes a converter that outputs a DC voltage to the LED light source and a current detection unit that detects a current flowing through the LED light source. If the detected current exceeds the threshold value, the LED light source is connected and the converter output voltage is adjusted so that the LED current becomes the set value. If the detected current is less than the threshold value, the LED light source is connected. As a result, the output voltage is gradually reduced. Thereby, the output of the LED driving device is set to a standby state or a stopped state.

Japanese Patent No. 4169008

  However, according to the configuration of Patent Document 1, since the output voltage is gradually reduced after no load is detected, it takes a long time to reach a predetermined low voltage state. Therefore, during this period of reduction of the output voltage, a high voltage is generated at the output terminal of the LED driving device, so that the desired protection function is not exhibited. Therefore, it is desirable to immediately reduce the output voltage to a low output voltage after detecting no load.

  By the way, when the input power supply is an AC power supply, a voltage of about 140 V (at 100 VAC) to 280 V (at 200 VAC) is applied to the primary side of the converter circuit. Such a configuration that directly generates a control voltage of about 5 to 15 V from a high primary voltage via a resistor has a large loss, and a configuration that directly generates the control voltage by a voltage regulator is expensive. Therefore, generally, when the input power supply is an AC power supply, the power generated on the secondary side of the converter circuit is used to generate the control power supply. Here, according to the configuration of Patent Document 1, the output voltage continues to decrease even after reaching a predetermined low output voltage. Therefore, when the output voltage is reduced in a configuration in which the input power supply is an AC power supply and the control power supply is generated according to the secondary output of the converter circuit, the control power supply is secured when the output voltage becomes very low. May not be maintained and the protection state may not be maintained. Similarly, when the output voltage is stopped, the protection state is not maintained.

  Accordingly, the present invention provides an LED power supply device configured to generate a control voltage in response to driving of a switching power supply circuit, and immediately lowers the output voltage of the LED power supply device to a low output voltage and maintains the low output voltage when there is no load. It is an object of the present invention to provide a configuration to perform.

  The LED power supply device of the present invention includes a switching power supply circuit that supplies a DC output current to an LED, an auxiliary power supply circuit that generates a control voltage in accordance with driving of the switching power supply circuit, and an output of the switching power supply circuit that is supplied with the control voltage. A control circuit having a constant voltage control unit for constant voltage control, and a switching power supply circuit configured to reduce the output voltage of the switching power supply circuit to a low output voltage when it is detected that the switching power supply circuit is in a no-load state. A voltage switching circuit for operating the voltage control unit is provided. The low output voltage is less than the safety extra low voltage, and the control voltage is secured when the switching power supply circuit is driven to output the low output voltage. Set to In one embodiment, the safety extra low voltage is 45V as defined in the Electrical Appliance and Material Safety Law.

  In this way, the voltage switching circuit operates the constant voltage control unit so as to lower the power supply output voltage to a low output voltage when it is detected that the switching power supply circuit is in a no-load state, and the safety extra low voltage or less. In addition, the low output voltage is set so that the control voltage is equal to or higher than the voltage at which the control voltage is ensured. Therefore, in the LED power supply apparatus configured to generate a control voltage according to the output of the switching power supply circuit, it is possible to immediately reduce the output voltage to a safe low output voltage and maintain the low output voltage when there is no load. .

  Here, the constant voltage control unit detects the output voltage and generates a voltage detection value, a second resistance circuit that generates a voltage reference value corresponding to the target value of the output voltage, and a voltage An error amplifier for operating the switching power supply circuit so that the detected value matches the voltage reference value, and the voltage switching circuit detects a no-load state and generates a no-load detection signal; A thyristor and a pre-stage switch circuit that conducts the thyristor when a no-load detection signal is input, and is configured to switch a combined resistance value of the first resistor circuit or the second resistor circuit when the thyristor is conducted; After the no-load signal is released, the conduction state of the thyristor is held by energization from the control voltage. According to this, the low output state of the switching power supply circuit is maintained even in the no-load state, and the continuation of the protective operation is reliably realized.

  The LED lighting device of the present invention includes the above-described LED power supply device and an LED module having LEDs fed from the LED power supply device. Thereby, the LED lighting device with improved safety such as removal, attachment, and replacement of the LED module is realized.

It is a circuit block diagram of the LED power supply device which concerns on embodiment of this invention, and an LED lighting apparatus using the same. It is a circuit block diagram of the voltage switching circuit shown in FIG. It is a figure explaining operation | movement of embodiment of this invention. FIG. 7 is a diagram showing a modification of the auxiliary power circuit in FIG. 1. FIG. 5 is a diagram illustrating a modification of the voltage switching circuit of FIG. 2. FIG. 10 is a diagram showing another modification of the voltage switching circuit of FIG. 2.

  In FIG. 1, the circuit block diagram of the LED power supply device 1 which concerns on embodiment of this invention, and the LED lighting apparatus 3 using the same is shown. The LED lighting device 3 includes an LED power supply device 1 and an LED module 2. An input voltage from the AC power supply AC is input to the input terminals T1 and T2 of the LED power supply device 1, and a DC output from the output terminals T3 and T4 of the LED power supply device 1 is supplied to the terminals T5 and T6 of the LED module 2. The LED module 2 includes a plurality of LEDs 20 connected in series between the terminal T5 and the terminal T6.

  The LED power supply device 1 includes an input circuit 100, a switching power supply circuit 200, an auxiliary power supply circuit 300, a control circuit 400, and a voltage switching circuit 500. In the description of the present specification, it is convenient for each circuit or component to belong to which block, and the present invention is not bound thereto.

  The input circuit 100 includes a full wave rectifier 101 and a capacitor 102. In the input circuit 100, the full-wave rectifier 101 is formed of a diode bridge, the input voltage from the AC power supply AC is full-wave rectified by the full-wave rectifier 101, and the full-wave rectified output is input to the switching power supply circuit 200. When the input power source is a DC power source, the input circuit 100 is not necessary.

  The switching power supply circuit 200 includes a switching element 201, a transformer 202, a diode 203 and a smoothing capacitor 204. The switching power supply circuit 200 is formed of an insulating flyback converter and constitutes a so-called one-converter type flyback step-down circuit having a power factor improving function.

  In the switching power supply circuit 200, energy is accumulated by the primary winding N1 of the transformer 202 during the ON period of the switching element 201, and the energy is transmitted from the secondary winding N2 side of the transformer 202 via the diode 203 during the OFF period of the switching element 201. Thus, the smoothing capacitor 204 is charged. The step-down ratio is determined by the turn ratio of the secondary winding N2 to the primary winding N1, and the output current is determined by the ON duty (ON period width) in the PWM control of the switching element 201. In the following description, the output current of the switching power supply circuit 200 (the LED current when the LED module 2 is connected) is referred to as the power supply output current, and the output voltage of the switching power supply circuit 200 (the LED module 2 is connected). LED voltage (Vf) in the case of being present is referred to as power supply output voltage.

  The auxiliary power supply circuit 300 generates a control power supply (also referred to as a control voltage) to the control circuit 400 and the voltage switching circuit 500 from the voltage generated in the auxiliary windings N3 and N4 of the transformer 202 of the switching power supply circuit 200. The auxiliary power supply circuit 300 includes a first auxiliary power supply unit 310 on the auxiliary winding N3 side and a second auxiliary power supply unit 320 on the auxiliary winding N4 side.

  The auxiliary power supply unit 310 includes a diode 311 and a capacitor 312 for rectifying and smoothing a voltage generated in the auxiliary winding N3, and a resistor 313 and a constant voltage diode 314 for generating a constant voltage from the voltage of the capacitor 312. The voltage determined by the constant voltage diode 314 becomes the constant current control unit 410 and the constant voltage control unit 420 of the control circuit 400 and the control power source Vcc of the voltage switching circuit 500. A voltage regulator may be used instead of the constant voltage diode 314.

  The auxiliary power supply unit 320 includes a diode 321 and a capacitor 322 that rectify and smooth the voltage generated in the auxiliary winding N4, and a starting resistor 323 that draws a primary voltage of the switching power supply circuit 200. The PWM control circuit 434 of the control circuit 400 Generate the control power. The PWM control circuit 434 (driver IC) is supplied with power through the starting resistor 323 at the time of startup, and operates by power supply from the auxiliary winding N4 after startup.

  In this way, the configuration in which the control power is generated from the auxiliary winding of the transformer 202 is sufficient with less loss than the configuration in which the control power is generated by using a voltage drop due to resistance from the high-potential side wiring on the transformer primary side, for example. It is preferable because a large amount of energy can be obtained. In general, an operational amplifier IC such as the error amplifiers 415 and 425 and a control power supply necessary for the operation in the periphery thereof and a control power supply necessary for the operation of the driver IC constituting the PWM control circuit 434 differ in voltage and current capacity. . In the present embodiment, the first and second auxiliary power supply units are provided to supply control power to circuits having different reference potentials. As an accompanying advantage, different voltages or currents are used for the respective circuits. The auxiliary power supply unit can be configured. For example, the amount of power supplied to the auxiliary power supply units 310 and 320 can be set by the number of turns of the auxiliary windings N3 and N4, respectively.

  The control circuit 400 includes a constant current control unit 410, a constant voltage control unit 420, and a drive control unit 430. In general, the constant current control unit 410 operates to perform constant current control on the output of the switching power supply circuit 200, the constant voltage control unit 420 operates to perform constant voltage control on the output of the switching power supply circuit 200, and generates a drive signal. The unit 430 selects one of the operations and performs PWM control of the switching element 201. That is, the switching element 201 is PWM-controlled by the control circuit 400 so as to perform either constant current control or constant voltage control.

  The constant current control unit 410 includes a current detection resistor 411, resistors 412 and 413 for determining a voltage (hereinafter referred to as “current reference value”) corresponding to a target value of a power supply output current (ie, LED current), and an error amplifier 415. Including. The current detection resistor 411 includes a low resistance element inserted between the reference potential side node of the smoothing capacitor 204 of the switching power supply circuit 200 and the output terminal T4. A voltage proportional to the power supply output current (hereinafter referred to as “current detection value”) is generated in the current detection resistor 411 and input to the negative input terminal of the error amplifier 415. The resistors 412 and 413 are connected between the control power supply Vcc and the ground, and the divided voltage value is input to the positive input terminal of the error amplifier 415 as a current reference value. Note that a feedback element (not shown) (a resistor, a capacitor, or a series circuit or a parallel circuit thereof) is connected between the negative input terminal and the output terminal of the error amplifier 415. The error amplifier 415 operates by receiving power from the control power supply Vcc, and amplifies and outputs an error between the current detection value input to the negative input terminal and the current reference value input to the positive input terminal. In other words, when the constant current control is selected in the drive signal generation unit 430, the constant current control unit 410 operates the switching power supply circuit 200 so that the detected current value matches the current reference value.

  The constant voltage control unit 420 includes resistors 421 and 422 (first resistance circuit) for voltage detection, and resistors 423 and 424 that determine a voltage corresponding to a target value of the power supply output voltage (hereinafter referred to as “voltage reference value”). (Second resistor circuit) and an error amplifier 425 are included. The resistors 421 and 422 are voltage dividing resistor circuits connected in parallel to the smoothing capacitor 204 of the switching power supply circuit 200. A voltage proportional to the power supply output voltage (hereinafter referred to as “voltage detection value”) is generated in the resistor 422 and input to the negative input terminal of the error amplifier 425. The resistors 423 and 424 are connected between the control power supply Vcc and the ground, and the divided voltage value is input to the positive input terminal of the error amplifier 425 as a voltage reference value. Note that, similarly to the error amplifier 415, a feedback element (not shown) (a resistor, a capacitor, or a series circuit or a parallel circuit thereof) is connected between the negative input terminal and the output terminal of the error amplifier 425. The error amplifier 425 operates by receiving power from the control power supply Vcc, and amplifies and outputs an error between the voltage detection value (VSNS) input to the negative input terminal and the voltage reference value input to the positive input terminal. In other words, when constant voltage control is selected in the drive signal generation unit 430, the constant voltage control unit 420 operates the switching power supply circuit 200 so that the detected voltage value matches the voltage reference value. Note that the error amplifiers 415 and 425 can be composed of operational amplifiers built in the same IC.

  The drive signal generation unit 430 includes a selection circuit 431, a photocoupler 432, a resistor 433, and a PWM control circuit 434. The selection circuit 431 includes, for example, a diode OR circuit, and validates either the output terminal voltage of the error amplifier 415 of the constant current control unit 410 or the output terminal voltage of the error amplifier 425 of the constant voltage control unit 420. The anode of the photodiode of the photocoupler 432 is connected to the control power supply Vcc via the resistor 433. The resistor 433 may be inserted on the cathode side of the photodiode. An output current corresponding to a current (light emission) flowing through the photodiode flows through the phototransistor of the photocoupler 432. The PWM control circuit 434 generates a PWM drive signal having a pulse width corresponding to the output state of the phototransistor of the photocoupler 432, and outputs it as the gate voltage of the switching element 201.

  In the operation when the LED power supply device 1 and the LED module 2 are normal (hereinafter referred to as “normal lighting operation”), basically, the operation of the error amplifier 415 is selected by the selection circuit 431 and the power output current is reduced. Constant current control by feedback is performed. Here, even when the constant current control is performed during the normal lighting operation, the power supply output voltage may exceed the set value if the voltage drop Vf of the LED 20 is large. In such a case, the operation of the error amplifier 425 is selected by the selection circuit 431, and constant voltage control is performed. Therefore, during the normal lighting operation, the target value of the power supply output voltage (that is, the limiter voltage) is set higher than the total voltage drop Vf when the LED 20 is normally lit, and the voltage reference value also corresponds to this. Is set.

  In addition, in the operation when the LED module 2 is removed or one of the LEDs 20 of the LED module 2 is disconnected and the LED power supply device 1 is in a no-load state (hereinafter referred to as “no-load operation”), it is selected. The operation of the error amplifier 425 is selected by the circuit 431. Thus, constant voltage control is performed so that the power supply output voltage becomes the limiter voltage. As will be described in detail later, in the present invention, the limiter voltage at the time of no-load operation is set lower than the limiter voltage at the time of normal lighting operation, specifically, the Electrical Appliance and Material Safety Law (J60598-1 (H14 )), The safety extra low voltage (SELV) is set to 45V or less.

  The voltage switching circuit 500 includes a no-load detection circuit 510, a front-stage switch circuit 520, a thyristor circuit 530, and a rear-stage switch circuit 540. Note that the resistance value, Zener voltage, and transistor characteristics of each circuit are set as appropriate so that the operations described below can be performed. Although each transistor is described as a bipolar transistor, each transistor can be replaced with an FET such as a MOSFET by appropriately selecting each resistance value. In this case, the base terminal, the collector terminal, and the emitter terminal in the following description will be read as the gate terminal, the drain terminal, and the source terminal, respectively.

  The no-load detection circuit 510 includes a resistor 511, a resistor 512, a constant voltage diode 513, and a resistor 514, detects a no-load state, and generates a no-load detection signal. Specifically, the resistors 511 and 512 are connected between the secondary high potential line (Vout) of the switching power supply circuit 200 and the ground, and divide the power supply output voltage. The voltage dividing point is connected to the cathode of the constant voltage diode 513. Thus, when the divided voltage value exceeds the set value for detecting no load, the constant voltage diode 513 is turned on, and a no load detection signal is output from the anode side of the constant voltage diode 513.

  The pre-stage switch circuit 520 includes a resistor 521, a capacitor 522, a transistor 523, a transistor 524, a resistor 525, and a resistor 526. When a no-load detection signal is input, the thyristor 531 is turned on. Specifically, the capacitor 522 is charged from the control power supply Vcc via the resistor 521, and the charging voltage is input to the emitter terminal of the transistor 523. When the transistor 524 is turned on by a no-load detection signal input to the base terminal of the transistor 524, the base terminal of the transistor 523 is connected to the ground, and the transistor 523 is turned on. When the transistor 523 is turned on, the charging voltage of the capacitor 522 is applied to the resistors 525 and 526, and the potential at the connection point between the resistor 525 and the resistor 526 increases.

  The thyristor circuit 530 includes a thyristor 531 and a resistor 532. The thyristor 531 is turned on by increasing the potential at the connection point between the resistor 525 and the resistor 526 and is energized from the control power supply Vcc via the resistor 532.

  The post-stage switch circuit 540 includes a diode 541, a resistor 542, a resistor 543, a transistor 544, a resistor 545, a resistor 546, a transistor 547, and a resistor 548. The switch circuit 540 reduces the combined resistance value between the positive input terminal of the error amplifier 425 and the ground by connecting the resistor 548 in parallel with the resistor 424 in accordance with the conduction of the thyristor 531.

  When the thyristor 531 is off, the diode 541 is on. Therefore, a divided voltage of the control power source Vcc by the resistor 543 and the parallel resistance of the resistors 532 and 542 is applied to the base terminal of the transistor 544, and the transistor 544 is turned on. That is, since the base terminal of the transistor 547 is at the ground potential, the transistor 547 is turned off. That is, only the resistor 424 is connected between the positive input terminal of the error amplifier 425 and the ground.

  On the other hand, when the thyristor 531 is in the on state, the anode of the diode 541 is at the ground potential, and the diode 541 is in the off state. Therefore, a divided voltage of the control power source Vcc by the resistor 542 and the resistor 543 (a voltage lower than the voltage divided by the parallel resistor of the resistors 532 and 542 and the resistor 543) is applied to the base terminal of the transistor 544, and the transistor 544 Turns off. Accordingly, a divided voltage of the control power supply Vcc by the resistor 542 and the resistor 543 is applied to the base terminal of the transistor 547, and the transistor 547 is turned on. That is, a parallel circuit of resistors 424 and 548 is connected to the positive input terminal of the error amplifier 425. Thus, according to the voltage switching circuit 500, when the no-load detection circuit 510 outputs a no-load detection signal, the resistor 548 is connected in parallel to the resistor 424, and the voltage reference value is lowered.

  An operation after the voltage switching circuit 500 once operates will be described. It is important that the load current (that is, the LED current) continues to flow even after the voltage switching circuit 500 is activated. When the low output voltage and current are generated by the primary winding N1 and the secondary winding N2 of the transformer 202, the voltage and current are also generated in the auxiliary windings N3 and N4. The control power supply Vcc is secured by the energy generated in the auxiliary windings N3 and N4, and the control power supply of the PWM control circuit 434 is secured. The oscillation operation of the switching power supply circuit 200 and the control operation of the control circuit 400 and the voltage switching circuit 500 are secured. Is maintained. Thus, when the switching power supply circuit 200 is driven to output this low output voltage, the low output voltage is set so that the first and second control power supplies are secured. The low output voltage is set to a higher value than the control power supply (5V to 15V).

  When the power supply output voltage decreases, the no-load detection signal from the no-load detection circuit 510 is canceled. However, since a current flows from the control power supply Vcc through the resistor 532 to the thyristor 531, this becomes a holding current and becomes a thyristor. The ON state of 531 is maintained. Thereby, the switching power supply circuit 200 can continue the output of the low output voltage.

  Here, as described above, the low output voltage is set to 45 V or less which is a safety extra low voltage. Therefore, when there is no load, the voltage between the output terminals T3 and T4 of the LED power supply device 1 is maintained at 45V or less. Thereby, the handling (maintenance, cleaning, etc.) of the LED power supply device 1 in which the AC power supply is turned on but the LED module 2 is not attached, the attachment of the LED module 2 to the LED power supply device 1, or the LED module The safety of the user in the exchange of 2 is improved.

  FIG. 3 shows a timing chart of the above protection operation. It is assumed that the normal lighting operation has been performed until time t1. It is assumed that at time t1, the LED module 2 is removed from the LED power supply device 1 or one of the LEDs 20 is disconnected, and the LED power supply device 1 is in a no-load state. The power supply output voltage rises due to the occurrence of a no-load condition.

  At time t2, the detection value of the power supply output voltage in the no-load detection circuit 510 exceeds the set value Vn, and the no-load detection signal is output. Accordingly, the transistor 524 is turned on, the thyristor 531 is turned on, the voltage reference value is lowered due to the conduction of the thyristor 531, and the power supply output voltage is lowered. At this time, although the power supply output voltage lowering speed depends on the response speed of the constant voltage control or the like, a substantially instantaneous output lowering is performed. Accordingly, the on state of the transistor 524 is temporary, but the on state of the thyristor 531 is latched as described above. Thereafter, the power supply output voltage is maintained at the low output voltage Vs that is equal to or lower than the safety extra low voltage (45 V) by the constant voltage control using the reduced voltage reference value in the constant voltage control unit 420. The dotted line in the power supply output voltage graph indicates the power supply output voltage when the voltage switching circuit 500 is not provided.

  As described above, according to the voltage switching circuit 500 of the present embodiment, when the switching power supply circuit 200 is detected to be in a no-load state, the constant voltage control unit 420 is configured to reduce the power supply output voltage to a low output voltage. To work. The low output voltage is set so that the control voltage is secured when the switching power supply circuit 200 is driven to output a low output voltage that is equal to or lower than the safety extra low voltage (45 V). Therefore, in the LED power supply device 1 configured to generate a control voltage according to the output of the switching power supply circuit 200, the power supply output voltage is immediately reduced to a safe low output voltage when no load is applied, and the low output voltage is maintained. Is possible.

  The voltage switching circuit 500 is configured such that when a no-load detection signal is output from the no-load detection circuit 510, the thyristor 531 is turned on, and a resistor 548 is connected in parallel to the resistor 424 so that the voltage reference value decreases. The And after cancellation | release of a no-load detection signal, the conduction | electrical_connection state of the thyristor 531 is hold | maintained by electricity supply from a control voltage. Accordingly, the low output state of the switching power supply circuit 200 is maintained even in the no-load state, and the continuation of the protection operation is reliably realized.

  And by using the LED power supply device 1 as described above, in the LED lighting device 3, it is possible to improve safety in removing, attaching, replacing, etc. the LED module 2.

<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.

-Modification of Circuit Configuration of Switching Power Supply Circuit 200 In the above embodiment, the switching power supply circuit 200 is a so-called one-converter type isolated flyback converter, but the switching power supply circuit 200 is a step-down converter of another type. May be. For example, the switching power supply circuit 200 may be a circuit including a power factor correction circuit and a flyback converter circuit. In this case, the auxiliary windings N3 and N4 of the auxiliary power supply circuit 300 may be auxiliary windings provided in a transformer constituting the flyback converter circuit or a coil constituting the power factor correction circuit. The switching power supply circuit 200 may be a circuit including a power factor correction circuit and a non-insulated step-down chopper circuit. In this case, the auxiliary windings N3 and N4 of the auxiliary power supply circuit 300 may be auxiliary windings provided in the choke coil constituting the step-down chopper circuit. Alternatively, in the case of such a non-insulated converter, the control circuit 400 and the voltage switching circuit 500 all have the same reference potential (ground), so that all control is performed from one auxiliary winding provided in the choke coil. A configuration in which a power supply is generated may be employed.

Modification of Auxiliary Power Supply Circuit 300 In the embodiment and the modification described above, a control power supply is generated from an auxiliary winding of an inductor element such as the transformer 202 as a configuration for generating a control voltage according to driving of the switching power supply circuit 200. Although the configuration is shown, the configuration of the auxiliary power supply circuit 300 is not limited to this. For example, as shown in FIG. 4, the control power source on the drive signal generation unit 430 side may be generated from a snubber circuit 250 connected in parallel to the switching element 201. The snubber circuit 250 includes a capacitor 251 and a diode 252 connected in series. The capacitor 251 is connected to the drain terminal of the switching element 201, and the anode of the diode 252 is connected to the source terminal (reference potential). A connection point between the capacitor 251 and the diode 252 is connected to the anode of the diode 321 of the auxiliary power supply unit 320. Thereby, the pulsed voltage that can be generated in the capacitor 251 during the operation of the switching power supply circuit 200 can be used for generating the power supply voltage.

-Modification of voltage switching circuit 500 (1)
In the above embodiment, the configuration in which the post-stage switch circuit 540 is provided between the thyristor 531 and the positive input terminal of the error amplifier 425 is shown. However, the thyristor circuit 531 and the positive input terminal of the error amplifier 425 are directly connected. Also good. For example, as shown in FIG. 5, the thyristor circuit 530 may be configured by a thyristor 531 and a resistor 535, and the thyristor 531 may be connected between the resistor 535 and the ground. However, in this case, in order to obtain the same effect as in the above embodiment, it is necessary to secure a holding current of the thyristor 531 by a current flowing from the control power supply Vcc to the thyristor 531 through the resistor 423 and the resistor 535.

-Modification of voltage switching circuit 500 (2)
In the above embodiment, the configuration in which the combined resistance value between the positive input terminal of the error amplifier 425 and the ground is reduced to reduce the voltage reference value when there is no load is shown. The combined resistance value may be increased to increase the voltage detection value. For example, as shown in FIG. 6, in the subsequent switch circuit 540 of the voltage switching circuit 500, a series circuit of a resistor 549 and a transistor 544 may be connected between the negative input terminal of the error amplifier 425 and the ground. In this case, the resistor 549 is connected in parallel to the resistor 422 during normal lighting (when the thyristor 531 is off and the transistor 544 is on), and no load is detected (when the thyristor 531 is on and the transistor 544 is off). In the case), the resistor 549 is disconnected.

-Modification of voltage switching circuit 500 (3)
In the above embodiment, the configuration in which the combined resistance value between the positive input terminal of the error amplifier 425 and the ground is decreased as the configuration for reducing the voltage reference value. However, the positive input terminal of the error amplifier 425 and the control power supply Vcc are shown. It is good also as a structure which increases the synthetic | combination resistance value between.

-Modification of the no-load detection circuit 510 In the said embodiment, although the voltage dividing circuit which detects the voltage-divided value of a power supply output voltage was shown as a no-load detection circuit, a no-load detection part is not restricted to this. For example, when an illuminance sensor is arranged in the vicinity of the LED 20 or the LED module 2 and no increase in illuminance is detected even though the switching power supply circuit 200 is driven, it is detected that there is no load. May be.

-Example of safety extra low voltage In the said embodiment, although the safety extra low voltage was set to DC45V prescribed | regulated to the electrical appliance safety law (J60598-1 (H14)), it is good also as a voltage based on another law. The definition of the safety extra low voltage may be 60V DC defined in IEC 60950 (J60950), 42V defined in IEC 60335-1 (J60335-1) (no-load voltage is 50V), or the like.

1 LED power supply device 2 LED module 3 LED lighting device 20 LED
200 switching power supply circuit 300 auxiliary power supply circuit 400 control circuit 420 constant voltage control unit 421, 422 resistance (first resistance circuit)
423, 424 resistor (second resistor circuit)
425 Error amplifier 500 Voltage switching circuit 510 No-load detection circuit 520 Pre-stage switch circuit 531 Thyristor

Claims (3)

An LED power supply,
A switching power supply circuit for supplying a DC output current to the LED;
An auxiliary power supply circuit that generates a control voltage according to driving of the switching power supply circuit;
A control circuit having a constant-voltage control unit for the output voltage to the constant voltage control of the previous SL switching power supply circuit and a control circuit the control voltage is supplied,
A voltage switching circuit that operates the constant voltage control unit so as to lower the output voltage of the switching power supply circuit to a low output voltage when it is detected that the switching power supply circuit is in a no-load state; The output voltage is set to ensure the control voltage when the switching power supply circuit is driven to output the low output voltage, which is equal to or lower than the safety extra low voltage ,
The constant voltage control unit detects the output voltage and generates a voltage detection value; a second resistance circuit that generates a voltage reference value corresponding to a target value of the output voltage; An error amplifier for operating the switching power supply circuit so that a voltage detection value matches the voltage reference value;
The voltage switching circuit detects a no-load condition and generates a no-load detection signal, a thyristor, and a pre-stage switch circuit that turns on the thyristor when the no-load detection signal is input. And when the thyristor is turned on, a combined resistance value of the first resistor circuit or the second resistor circuit is switched. After the no-load detection signal is released, the conduction state of the thyristor is changed from the control voltage. An LED power supply device configured to be held by energizing the LED.   2. The LED power supply device according to claim 1, wherein the safety extra low voltage is 45V defined in the Electrical Appliance and Material Safety Law. An LED lighting device comprising: the LED power supply device according to claim 1 or 2 ; and an LED module having the LED fed from the LED power supply device.

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