JP2022030035A - Switching power supply device - Google Patents

Abstract

To provide a switching power supply device in which the power supply efficiency can be further improved.SOLUTION: A switching power supply device 1 converts alternating current input power AC to desired direct current output power, and supplies the direct current output power to an LED load 2. The switching power supply device includes a switching element Q1 the on/off of which is controlled, a ripple current reducing circuit 5 that is connected in series with the LED load 2, and reduces a current ripple flowing through the LED load 2 by variably controlling the impedance, and a control circuit 4 that controls the on/off of the switching element Q1 on the basis of a feedback voltage VFB at a connection point B between the LED load 2 and the ripple current reducing circuit 5. The control circuit 4 performs mean value control on the feedback voltage VFB in accordance with a target mean voltage that is set according to the magnitude of the voltage ripple of the feedback voltage VFB.SELECTED DRAWING: Figure 1

Description

The present invention relates to a switching power supply that converts AC input power into desired DC output power and supplies it to an LED load.

According to Patent Document 1 shown below, the applicant has provided a switching power supply device that reduces the current ripple of the current flowing through the LED load with a simple power supply configuration. Patent Document 1 uses a feedback type constant current control circuit provided with a variable impedance element composed of a MOSFET or the like as a ripple current reduction circuit connected in series with an LED load. With this configuration, the voltage across the LED load is kept constant, and the current ripple of the current flowing through the LED load is controlled to be reduced.

Japanese Unexamined Patent Publication No. 2012-164633

In the prior art, the DC output power is determined by controlling the switching element on and off so that the average voltage of the feedback voltage _VFB at the connection point between the LED load and the ripple current reduction circuit becomes a preset target average voltage _Vref . It is controlled by the value. As shown in FIG. 8, this feedback voltage V _FB includes a voltage ripple (voltage fluctuation) similar to the output voltage V _OUT . Then, the voltage ripple of the feedback voltage _VFB becomes larger as the load becomes larger as shown in FIGS. 8 (a) and 8 (b), and the deterioration of the output capacitor is increased as shown in FIGS. 8 (c) and 8 (d). It gets bigger with.

Then, as shown in FIG. 8D, when the feedback voltage _VFB drops below a voltage at which the variable impedance element cannot operate at a constant current due to voltage ripple, the voltage across the LED load cannot maintain the required voltage, and as a result, the LED The value of the current flowing through the load decreases periodically and becomes visible as flickering. Therefore, the operation set in consideration of the minimum voltage at which the variable impedance element can perform constant current control, various variations (target average voltage V _ref , etc.), and the undershoot of the feedback voltage V _FB during transient operation. The margin voltage VM is set, and the target average voltage _{V ref is} set so that the feedback voltage V _FB does not fall below this operating margin voltage _VM .

However, the target average voltage V _ref set in this way is set in anticipation of a certain degree of deterioration of the output capacitor and a state in which the voltage ripple at the maximum load is large. Therefore, when the output capacitor is not deteriorated, or when the voltage ripple at light load or medium load is small, the feedback voltage _VFB is larger than the operating margin as shown in FIGS. 8A and 8B. There was a problem that the voltage would change at a high voltage with a considerable margin, and that margin would result in power loss.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a switching power supply device capable of solving the problems and further improving the power supply efficiency.

The switching power supply device of the present invention is a switching power supply device that converts AC input power into a desired DC output power and supplies it to an LED load, and is connected to a switching element controlled on / off in series with the LED load. A ripple current reduction circuit that reduces the current ripple flowing through the LED load by variably controlling the impedance, and a control circuit that controls the switching element on and off based on the feedback voltage at the connection point between the LED load and the ripple current reduction circuit. The control circuit is characterized in that the feedback voltage is controlled by an average value with a target average voltage set according to the magnitude of the voltage ripple of the feedback voltage.

According to the present invention, in an operating environment where the voltage ripple of the feedback voltage V _FB is small, the target average voltage V _ref can be set to a low value, and the power supply efficiency can be improved.

It is a circuit diagram which shows the structure of 1st Embodiment of the switching power supply device which concerns on this invention. It is a block diagram which shows the structure of the arithmetic unit shown in FIG. It is a circuit diagram which shows the example which configured the 1st Embodiment of the switching power supply device which concerns on this invention with a back boost converter. It is a block diagram which shows the structure of the control IC shown in FIG. It is a waveform diagram of the output voltage and the feedback voltage in the switching power supply device shown in FIG. 1. It is a circuit diagram which shows the structure of the 3rd Embodiment of the switching power supply device which concerns on this invention. It is a block diagram which shows the structure of the arithmetic unit shown in FIG. It is a waveform diagram of the output voltage and the feedback voltage in the conventional switching power supply device.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following embodiments, the same reference numerals are given to the configurations showing the same functions, and the description thereof will be omitted as appropriate.

The switching power supply device of the present embodiment is a switching power supply device that converts AC input power into DC output power and supplies it to the LED load, and is connected in series with the LED load and is configured as a ripple current reduction circuit, such as a MOSFET. Using a feedback type constant current control circuit equipped with a variable impedance element, the average voltage of the feedback voltage V _FB at the connection point between the LED load and the ripple current reduction circuit is adjusted according to the magnitude of the voltage ripple of the feedback voltage V _FB . To change.

(First Embodiment)
The switching power supply device 1 of the first embodiment is a flyback type converter for driving an LED load 2 composed of n LED elements (LED21 to LED2n) connected in series, and is a rectifier circuit with reference to FIG. 1. It includes a DB, a transformer TR, a switching element Q1, a rectifying smoothing circuit 3, a control circuit 4, a ripple current reduction circuit 5, and an auxiliary power supply 6.

The rectifier circuit DB is a well-known diode bridge circuit, which is connected to an AC input power supply AC, rectifies AC input power into a unidirectional pulsating current, and outputs it to a transformer TR.

The transformer TR includes a primary winding W1, a secondary winding W2, and a tertiary winding W3. One end of the primary winding W1 is connected to the rectifier circuit DB, and the other end is connected to the drain terminal of the switching element Q1. A rectifying smoothing circuit 3 is connected between both ends of the secondary winding W2, and an auxiliary power supply 6 is connected between both ends of the tertiary winding W3.

The switching element Q1 is composed of elements such as a FET (Field Effect Transistor) and an IGBT (Insulated Gate Bipolar Transistor) driven by a drive signal (PWM signal) generated by the control circuit 4. In this embodiment, the switching element Q1 will be described as a MOSFET. The source terminal of the switching element Q1 is grounded, and the gate terminal is connected to the VG terminal of the control circuit 4.

The rectifying smoothing circuit 3 is composed of a diode D1 and a capacitor C1, a connection point A between the cathode of the diode D1 and one end of the capacitor C1 is connected to the anode of the LED 21 constituting the LED load 2, and the other end of the capacitor C1 is grounded. Has been done. The capacitor C1 is an output capacitor, and in this embodiment, it is composed of an electrolytic capacitor, but other capacitors may be used. As for the life and capacity of the electrolytic capacitor, the phenomenon that the electrolytic solution evaporates to the outside through the sealing portion is generally dominant, and it appears as a decrease in capacitance and an increase in tangent of the loss angle.

The ripple current reduction circuit 5 functions as a feedback type constant current control circuit that variably controls the impedance, and includes a variable impedance element Q2, a detection resistor Rs, and an error amplifier AMP1. The variable impedance element Q2 is composed of elements such as FET, IGBT, and BiTr. In this embodiment, the variable impedance element Q2 will be described as a MOSFET.

The drain terminal of the variable impedance element Q2 is connected to the cathode of the LED 2n constituting the LED load 2, the source terminal is grounded via the detection resistor Rs, and the gate terminal is connected to the output terminal of the error amplifier AMP1.

The connection point between the detection resistor Rs and the source terminal of the variable impedance element Q2 is connected to the inverting input terminal of the error amplifier AMP1. The detection resistance Rs converts the LED current I _LED flowing through the LED load 2 into a voltage signal and outputs it to the error amplifier AMP1.

The cathode of the Zener diode ZD1 is connected to the rectifying smoothing circuit 3 (connection point A) via the resistor R1, and the anode is grounded.

The non-inverting input terminal of the error amplifier AMP1 is connected to the connection point between the resistor R1 and the cathode of the Zener diode ZD1, that is, the reference voltage generated by the Zener diode ZD1.

The output terminal of the error amplifier AMP1 is connected to the gate terminal of the variable impedance element Q2. The error amplifier AMP1 outputs an error signal based on the LED current I _LED flowing through the LED load 2 and the reference value (reference voltage) to the variable impedance element Q2. Specifically, the error amplifier AMP1 increases the voltage level of the error signal as the LED current I _LED becomes smaller than the reference value, and lowers the resistance value between the drain and the source of the variable impedance element Q2. Further, the error amplifier AMP1 operates so as to reduce the voltage level of the error signal and increase the resistance value between the drain and the source of the variable impedance element Q2 as the LED current ILED becomes larger than the reference value.

That is, the variable impedance element Q2 of the ripple current reduction circuit 5 continuously sets the resistance value between the drain and the source so that the LED current I _LED becomes the reference value (reference voltage) according to the output of the error amplifier AMP1. It functions as a variable impedance element that changes. Thereby, the current ripple contained in the LED current I _LED can be reduced. The response speed of the ripple current reduction circuit 5 is set higher than the response speed of the control circuit 4, preferably higher than the frequency of the AC input power supply AC.

The control circuit 4 includes a start unit 41, an internal power supply unit 42, an ADC (analog digital converter) 43, an arithmetic unit 44, a PWM generation unit 45, and a driver 46. The control circuit 4 may be entirely a digital control circuit (including a circuit operated by software), or a part of its components may be a digital control circuit, and all of the control circuits 4 may be analog control circuits. May be.

The start portion 41 is connected to the connection point between the rectifier circuit DB and the primary winding W1 of the transformer TR via the ST terminal and the resistor R2, and is composed of the diode D2 and the capacitor C2 via the Vcc terminal. It is connected to the auxiliary power supply 6. The start unit 41 charges the capacitor C2 of the auxiliary power supply 6 at the time of startup, and supplies the power from the auxiliary power supply 6 to the internal power supply unit 42 that generates the internal power supply in the control circuit 4 after the start-up.

The ADC 43 is connected to the connection point B of the LED load 2 and the ripple reduction circuit 5 (drain terminal of the variable impedance element Q2) via the CV terminal, and the voltage of the connection point B is input as the feedback voltage _VFB . Then, the ADC 43 samples the feedback voltage V _FB at intervals sufficiently shorter than the period of the voltage ripple included in the feedback voltage V FB (for example, 20 μs), converts the feedback voltage V _FB into a digitized voltage, and outputs the sample to the arithmetic unit 44. ..

With reference to FIG. 2, the arithmetic unit 44 has an average voltage calculation unit 441, an average value control unit 442, an operation amount calculation unit 443, a bottom voltage detection unit 444, a bottom voltage comparison unit 445, and a target value correction unit. Functions as 446.

The average voltage calculation unit 441 calculates, for example, the average voltage V _Ave of the feedback voltage V _FB for each cycle of the AC input power supply AC based on the feedback voltage V _FB input from the ADC 43, and calculates the average voltage V _Ave. It is output to the average value control unit 442.

The average value control unit 442 calculates the error between the target average voltage V _ref and the average voltage V _Ave by comparing the target average voltage V _ref with the average voltage V _Ave calculated by the average voltage calculation unit 441. , The calculated error is output to the operation amount calculation unit 443 as an error signal.

The operation amount calculation unit 443 calculates and calculates the operation amount Δ that increases or decreases the on-time of the PWM (pulse width modulation) signal that controls the on / off of the switching element Q1 based on the error signal input from the average value control unit 442. The operation amount Δ is output to the PWM generation unit 45.

The bottom voltage detection unit 444 detects the bottom voltage V _B of the feedback voltage V _FB input from the ADC 43. For example, when the feedback voltage _VFB voltage value input from the ADC 43 falls below both the voltage value before one sampling and the voltage value after one sampling, the bottom voltage detection unit 444 sets the voltage value as the bottom voltage. Detected as V _B.

The bottom voltage comparison unit 445 compares the preset reference bottom voltage V _Blef with the bottom voltage V _B detected by the bottom voltage detection unit 444, and outputs the comparison result to the target value correction unit 446. The reference bottom voltage VB _ref is the lowest that the variable impedance element Q2, which is a variable impedance element, can perform constant current control even if the variation of various elements and the undershoot of the feedback voltage _VFB during transient operation are taken into consideration. It is set to a value that exceeds the limit voltage.

When the bottom voltage V _B is lower than the reference bottom voltage V _Bref , the target value correction unit 446 corrects the average value control unit 442 in the direction of increasing the target average voltage V _ref to be compared with the average voltage V _Ave , and the bottom voltage. When V _B exceeds the reference bottom voltage V _Bref , the average value control unit 442 corrects in the direction of lowering the target average voltage V _ref to be compared with the average voltage V _Ave. The correction width of the target average voltage V _ref may be a preset correction value, or may be a correction value calculated based on the difference between the bottom voltage V _B and the reference bottom voltage V _Ref .

The PWM generation unit 45 generates a PWM signal whose on-time is increased or decreased based on the operation amount Δ from the operation amount calculation unit 443, and controls the switching element Q1 on and off via the driver 46 by the generated PWM signal. As in the present embodiment, when the on-time operation amount Δ is calculated based on the error between the average voltage V _Ave calculated for each cycle of the AC input power supply AC and the target average voltage V _ref . The on-time of the PWM signal is constant in one cycle of the AC input power supply AC.

In the switching power supply unit 1 shown in FIG. 1, an example of a flyback type converter has been described, but the present invention may be applied to a back converter, a boost converter, and a back boost converter, and the back boost converter is shown in FIGS. 3 and 4. The switching power supply device 1a configured by is shown. In the switching power supply device 1a, the same reference numerals are given to the configurations showing the same functions as the switching power supply device 1, and the description thereof will be omitted as appropriate.

The switching power supply device 1a includes a synchronous rectifying element Q3 that functions as a diode D1, and the control circuit 4a includes a PWM generating unit 45a and a driver 46a that generate a PWM signal for driving the synchronous rectifying element Q3.

Further, the control circuit 4a includes an error amplifier AMP1 constituting the ripple current reduction circuit 5, and includes a dimming calculator 47 and a DAC (digital-to-analog converter) 48. The dimming calculator 47 generates a digitized reference voltage value according to the dimming signal input from the DIM terminal, and the DAC 48 generates the digitized reference voltage value generated by the dimming calculator 47. It is converted into an analog signal and input to the non-inverting input terminal of the error amplifier AMP1. This makes it possible to control the LED current I _LED supplied to the LED load 2 according to the dimming signal.

FIG. 5 shows waveforms of the output voltage Vout of the connection point A and the feedback voltage _VFB of the connection point B shown in FIG. In FIG. 5, (a) is a medium load with a small deterioration of the capacitor C1, (b) is a rated load with a small deterioration of the capacitor C1, and (c) is a state with a large deterioration of the capacitor C1. (D) is the waveform of each output voltage Vout and feedback voltage _VFB at the rated load in the state where the deterioration of the capacitor C1 is further large.

In the present embodiment, as shown in FIGS. 5A to 5D, the average value of the feedback voltage V _FB is set so that the bottom voltage V _B becomes the reference bottom voltage V _Blef regardless of the magnitude of the voltage ripple. Control is done. Therefore, the average voltage V _Ave of the feedback voltage V _FB is controlled so as to be higher as the voltage ripple is larger and lower as the voltage ripple is smaller, according to the magnitude of the voltage ripple that changes depending on the operating environment.

As a result, when the deterioration of the capacitor C1 is small and the voltage ripple is small, the power supply efficiency can be improved in all regions regardless of the magnitude of the load. For example, the average voltage V _Ave of the feedback voltage _VFB in the conventional average value control shown in FIGS. 8 (a) and 8 (b) is 1.5 V at both the medium load and the rated load, whereas this is the present. The average voltage V _Ave of the feedback voltage _VFB in the average value control of the embodiment is 1.0 V at the medium load shown in FIG. 5 (a) and 1.2 V at the rated load shown in FIG. 5 (b). become. That is, at the time of medium load, the power loss can be reduced only by Δ0.5V × LED current I _LED , and at the rated load, the power loss can be reduced by only Δ0.3V × LED current I _LED .

Further, in the conventional method of fixing the average voltage V _Ave of the feedback voltage V _FB , it is appropriate even if the end of life or the capacity variation of the output capacitor occurs as shown in FIGS. 8 (c) and 8 (d). It was necessary to design in anticipation of ensuring a sufficient operating margin in the end. On the other hand, in the present embodiment, the bottom voltage V _B of the feedback voltage V _FB is the reference bottom voltage V as shown in FIGS. 5 (c) and 5 (d) even if the capacitor C1 varies or the life of the capacitor C1 ends. It is stable because the lower limit is controlled by _Blef , and there is little variation due to mass production of the feedback voltage _VFB . That is, in this embodiment, simplification of the power supply design can be expected.

Further, in the conventional method of fixing the average voltage V _Ave of the feedback voltage V _FB , the deterioration of the output voltage becomes large, and as shown in FIGS. 8 (c) and 8 (d), the feedback voltage V _FB has an operating margin. If the voltage is lower than _VM , the rated current may not be obtained or flicker may occur. On the other hand, in the present embodiment, even if the deterioration of the output capacitor becomes large, the bottom voltage V _B of the feedback voltage V _FB is the lower limit of the reference bottom voltage V _Blef as shown in FIGS. 5 (c) and 5 (d). Since the value is controlled, the LED load 2 can be driven without any problem without the bottom voltage V _B of the feedback voltage V _FB greatly exceeding the reference bottom voltage V _Blef , and the power supply life is extended as an emergency evacuation. Can be made to.

As shown in FIG. 5D, if the average voltage V _Ave of the feedback voltage V _FB becomes too high, it may become inoperable depending on the design of other power supply parts, or it may adversely affect other power supply elements. There is a risk of exerting it. Therefore, in the arithmetic unit 44, the average voltage V _Ave of the feedback voltage V _FB is compared with the preset operation stop threshold value, and when the average voltage V _Ave and the preset operation stop threshold value are exceeded, the LED load is applied. It is preferable to configure it so as to stop the drive of 2.

Further, when the load is light, the voltage ripple of the feedback voltage _VFB becomes small, and it may be difficult to detect the voltage ripple. Therefore, even if the stability is improved by switching to other control such as the conventional mean value control in which the target mean voltage V _ref is fixed in the environmental condition where the voltage ripple of the feedback voltage V _FB such as the input of the deming signal becomes small. good.

(Second embodiment)
In the switching power supply device 1b of the second embodiment, referring to FIGS. 6 and 7, a dimming calculator 47 and a DAC (digital-to-analog converter) 48 are added to the control circuit 4 of the switching power supply device 1. It is configured.

The calculator 44a includes a bottom voltage detection unit 444, a bottom voltage comparison unit 445, and a target value setting unit 447 instead of the target value correction unit 446. The target value setting unit 447 has a conversion table and a conversion formula for converting the reference voltage value generated by the dimming calculator 47 into the target average voltage V _ref , and converts the reference voltage value generated by the dimming calculator 47 to the reference voltage value. The target average voltage V _ref converted accordingly is set in the average value control unit 442. The target value setting unit 447 converts the reference voltage value generated by the dimming calculator 47 into a lower target average voltage V _ref as the LED current I _LED becomes lower. That is, in the switching power supply device 1b of the second embodiment, the average voltage _VAve of the feedback voltage _VFB increases as the voltage ripple increases according to the magnitude of the voltage ripple that changes depending on the dimming signal, and the voltage ripple. Is controlled to be lower as the value becomes smaller.

The target average voltage V _ref that detects the input voltage and is converted according to the input voltage may be set in the average value control unit 442. In this case, the smaller (lower) the input voltage, the larger the voltage ripple. Therefore, the larger (higher) the input voltage is, the lower the target average voltage V _ref is converted and set. As a result, the average voltage V _Ave of the feedback voltage V _FB is controlled so as to be higher as the voltage ripple is larger and lower as the voltage ripple is smaller, according to the magnitude of the voltage ripple that changes depending on the input voltage.

Further, the total operating time may be recorded in the control circuit 4b, and the target average voltage V _ref converted according to the total operating time may be set in the average value control unit 442. In this case, the longer the total operating time, the more the capacitor C1 deteriorates and the larger the voltage ripple becomes. Therefore, the longer the total operating time is, the higher the target average voltage V _ref is converted and set. As a result, the average voltage V _Ave of the feedback voltage V _FB is controlled so that the period during which the voltage ripple is small is low and the elapsed time during which the voltage ripple is large increases, depending on the magnitude of the voltage ripple that changes depending on the total operating time. Will be done.

Furthermore, by using a temperature sensor, the total operating time including the environmental temperature is recorded in the control circuit 4b, and the target average voltage V _ref converted according to the total operating time including the environmental temperature is set as the mean value control unit. It may be set to 442. In this case, the higher the environmental temperature, the faster the deterioration of the capacitor C1 and the larger the voltage ripple. Therefore, the longer the total operating time at a high environmental temperature, the higher the target average voltage V _ref is converted and set. As a result, the average voltage V _Ave of the feedback voltage V _FB is low during the period when the voltage ripple is small and increases as the voltage ripple is large, depending on the magnitude of the voltage ripple that changes depending on the total operating time including the environmental temperature. Is controlled by.

As described above, the present embodiment is a switching power supply device 1 that converts an AC input power AC into a desired DC output power and supplies it to the LED load 2, and is a switching element that is on / off controlled. A ripple current reduction circuit 5 connected in series with Q1 and reducing the current ripple flowing through the LED load 2 by variably controlling the impedance, and a connection point B between the LED load 2 and the ripple current reduction circuit 5. A control circuit 4 that controls on / off of the switching element Q1 based on the feedback voltage V _FB in the above is provided, and the control circuit 4 has a target average voltage V _ref set according to the magnitude of the voltage ripple of the feedback voltage V _FB . The feedback voltage _VFB is controlled by the average value.
With this configuration, in an operating environment where the voltage ripple of the feedback voltage V _FB is small, the target average voltage V _ref can be set to a low value, and the power supply efficiency can be improved.

Further, in the present embodiment, the control circuit 4 detects the bottom voltage V _B of the feedback voltage V _FB , and sets the target average voltage so that the detected bottom voltage V _B becomes the preset reference bottom voltage V _Blef . to correct.
With this configuration, when the deterioration of the capacitor C1 is small and the voltage ripple is small, the target average voltage V _ref can be corrected to a low value, so that the power supply efficiency is improved in all regions regardless of the load size. be able to. In addition, even if the capacitor C1 varies or the end of the life of the capacitor C1 is reached, the bottom voltage V _B of the feedback voltage V _FB is stable because the lower limit is controlled to the reference bottom voltage V _Blef , which simplifies the power supply design. You can expect it. Further, even if the deterioration of the output capacitor becomes large, the LED load 2 can be driven without any problem without the bottom voltage V _B of the feedback voltage V _FB greatly exceeding the reference bottom voltage V _Bref , which is an emergency evacuation. The power life can be extended.

Further, in the present embodiment, the control circuit 4b is set to a lower target average voltage V _ref as the LED current I _LED flowing through the LED load 2 due to the dimming signal becomes smaller.
With this configuration, the target average voltage V _ref can be set to a low value in a region where the load with a small voltage ripple is small, and the power supply efficiency can be improved.

Further, in the present embodiment, the control circuit 4b is set to a lower target average voltage V _ref as the input voltage is larger.
With this configuration, the target average voltage V _ref can be set to a low value at a large input voltage with a small voltage ripple, and the power supply efficiency can be improved.

Further, in the present embodiment, the control circuit 4b is set to a higher target average voltage V _ref as the total operating time is longer.
With this configuration, in an operating environment where the total operating time is short and the voltage ripple is small, the target average voltage V _ref can be set to a low value, and the power supply efficiency can be improved.

Further, in the present embodiment, the control circuit 4 is set to a higher target average voltage V _ref as the total operating time in a state where the environmental temperature is high is longer.
With this configuration, the reference bottom voltage _VBref can be set in consideration of the operating time at the environmental temperature.

The present invention has been described above based on the embodiments. This embodiment is an example, and it is understood by those skilled in the art that various modifications are possible in the combination of each of these components, and that such modifications are also within the scope of the present invention.

1, 1a, 1b Switching power supply 2 LED load 3 Rectifier smoothing circuit 4, 4a, 4b Control circuit 5 Ripple current reduction circuit 6 Auxiliary power supply 21 to 2n LED
41 Start section 42 Internal power supply section 43 ADC
44, 44a Arithmetic unit 45, 45a PWM generator 46, 46a Driver 47 Dimming calculator 48 DAC
441 Average voltage calculation unit 442 Average value control unit 443 Operation amount calculation unit 444 Bottom voltage detection unit 445 Bottom voltage comparison unit 446 Target value correction unit 447 Target value setting unit AC AC input power supply AMP1 Error amplifier C1, C2 Condenser D1 Diode DB Rectifier Circuit Q1 Switching element Q2 Variable impedance element Q3 Synchronous rectifier element R1 Resistance Rs Detection resistance TR Transformer W1 Primary winding W2 Secondary winding W3 Tertiary winding ZD1 Zener diode

Claims (6)

A switching power supply that converts AC input power into desired DC output power and supplies it to the LED load.
Switching elements that are controlled on and off, and
A ripple current reduction circuit that is connected in series with the LED load and reduces the current ripple that flows through the LED load by variably controlling the impedance.
A control circuit that controls on / off of the switching element based on a feedback voltage at a connection point between the LED load and the ripple current reduction circuit is provided.
The control circuit is a switching power supply device characterized in that the feedback voltage is controlled by an average value with a target average voltage set according to the magnitude of the voltage ripple of the feedback voltage. The switching power supply according to claim 1, wherein the control circuit detects the bottom voltage of the feedback voltage and corrects the target average voltage so that the detected bottom voltage becomes a preset reference bottom voltage. Device. The switching power supply device according to claim 1, wherein the control circuit is set to a lower target average voltage as the LED current flowing through the LED load becomes smaller due to a dimming signal. The switching power supply device according to claim 1, wherein the control circuit is set to the target average voltage, which is lower as the input voltage is larger. The switching power supply device according to claim 1, wherein the control circuit is set to a higher target average voltage as the total operating time is longer. The switching power supply device according to claim 5, wherein the control circuit is set to a higher target average voltage as the total operating time in a high environmental temperature is longer.

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