Switching power supply device

Abstract

To provide a switching power supply device having improved response against dynamic load fluctuations.SOLUTION: A switching power supply device 1, for converting AC input power AC to desired DC output power and supplying it to an LED load 2, includes: a switching element Q1 which is a switching element to be on-off controlled; a ripple current reduction circuit 5, connected to the LED load 2 in series, for reducing current ripple flowing the LED load 2 by variably controlling impedance, and a control circuit 4 for performing on-off control of the switching element Q1 based on a feedback voltage VFB2 at a connection point B of the LED load 2 and the ripple current reduction circuit 5. The control circuit 4 raises the output voltage Vout to an initial voltage by making the response to a light control signal insensitive for a predetermined period, and performs average value control of the feedback voltage VFB2 with a target average voltage set according to the magnitude of the voltage ripple of the feedback voltage VFB2, after elapsing the predetermined period.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a switching power supply device that converts AC input power into a desired DC output power and supplies it to an LED load.

Background Art

[0002] The applicant of the present application has provided a switching power supply device that reduces the current ripple of the current flowing through an LED load with a simple power supply configuration according to Patent Document 1 shown below. In Patent Document 1, a feedback type constant current control circuit including a variable impedance element composed of a MOSFET or the like is used as a ripple current reduction circuit connected in series to the LED load. With this configuration, the voltage across the LED load is made constant, and the current ripple of the current flowing through the LED load is controlled to be reduced.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the prior art, the DC output power is controlled to a predetermined value by on / off controlling a switching element so that the average voltage of the feedback voltage V at the connection point between the LED load and the ripple current reduction circuit becomes a preset target average voltage V. This feedback voltage V has the same voltage ripple (voltage fluctuation) as the output voltage V as shown in FIG. 7. FB ref FB OUT ​​​​​​​​​​​​​includes. And the voltage ripple of the feedback voltage V FB becomes larger as the load increases, as shown in FIGS. 7(a) and (b), and becomes larger as the output capacitor deteriorates, as shown in FIGS. 7(c) and (d). When the feedback voltage V falls below the voltage at which the variable impedance element cannot operate in constant current mode due to the voltage ripple, the voltage across the LED load

[0005] cannot maintain the required voltage, and as a result, the current value flowing through the LED load periodically decreases FB and becomes visible as flicker. Therefore, the minimum voltage at which the variable impedance element can perform constant current control, various variations (such as the target average voltage V ref etc.), and the operation margin voltage V FB M M FB ref

[0006] ref FB is set considering the undershoot of the feedback voltage V

[0006] ref during transient operation. And the target average voltage V is set in anticipation of a certain degree of deterioration of the output capacitor and a large voltage ripple at maximum load. Therefore, when the output capacitor is not deteriorated, or when the voltage ripple is small during light load or medium load FB FB the feedback voltage V will transition at a voltage much higher than the operation margin In addition, in a switching power supply device having a dimming function, for example, from deep dimming such as a few percent of dimming When the brightness is variable from 80% or 100% dimming to 10%, it is accompanied by a rapid load fluctuation Therefore, the response of the feedback control of the switching power supply device cannot catch up, and the above-mentioned operation margin V M is interrupted, resulting in a problem of flickering of the brightness.

[0007] The present invention has been made in view of the above problems, solves the problems, further improves the power efficiency, and eliminates the flickering caused by the influence of dynamic load fluctuations accompanying dimming and provides a switching power supply device capable of doing so.

Means for Solving the Problems

[0008] 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 includes a switching element that is on-off controlled and a ripple current reduction circuit that is connected in series to the LED load and reduces the current ripple flowing through the LED load by variably controlling the impedance, and a control circuit that on-off controls the switching element based on the feedback voltage at the connection point between the LED load and the ripple current reduction circuit. The control circuit includes a dimming arithmetic unit that dims the illuminance of the LED load by variably controlling the current flowing through the LED load based on a dimming signal, and at a target average voltage set according to the magnitude of the voltage ripple of the feedback voltage, the feedback voltage is averaged, detects an increase in the dimming target value from the dimming arithmetic unit, and provides a dead time for the dimming target value. During the dead time, the LED load and the ripple current reduction circuit are Raise the voltage to a predetermined target voltage and perform control based on the dimming target value after the dead time has elapsed. It is characterized by performing such control.

Advantages of the Invention

[0009] According to the present invention, even when there is a large change in the dimming signal, stable dimming can be performed without flickering by ensuring the operating voltage of the LED load and the ripple current reduction circuit. Further, in an operating environment with a small voltage ripple of the feedback voltage V the target average voltage can be set to a low value FB2 and the power supply efficiency can be improved.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that in the following embodiments ​In the following description, components having the same functions are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

[0012] The switching power supply device of this embodiment is a switching power supply device that converts AC input power into DC output power and supplies it to an LED load. It is a flyback type constant current control circuit that is connected in series with the LED load and includes a variable impedance element composed of a MOSFET or the like as a ripple current reduction circuit. Using this circuit, the output voltage Vout of the LED load and the ripple current reduction circuit connected in series is raised to a preset target voltage at startup, and after reaching the target voltage, the average voltage of the feedback voltage V at the connection point between the LED load and the ripple current reduction circuit is changed according to the magnitude of the voltage ripple of the feedback voltage V . FB2 of the FB2 feedback voltage V is changed according to the magnitude of the voltage ripple of the feedback voltage V.

[0013] (Embodiment) The switching power supply device 1 of the embodiment is a flyback converter that drives an LED load 2 composed of n serially connected LED elements (LED2 1~LED2n). Referring to FIG. 1, it includes a rectifier circuit DB, a transformer TR, a switching element Q1, a rectifying and smoothing circuit 3, a control circuit 4, a ripple current reduction circuit 5, and an auxiliary power supply 6.

[0014] The rectifier circuit DB is a well-known diode bridge circuit, which is connected to an AC input power supply AC, rectifies the AC input power into a unidirectional pulsating current, and outputs it to the transformer TR.

[0015] 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 It is connected to the secondary. A rectifying and 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.

[0016] The switching element Q1 is driven by a drive signal (PWM signal) generated by the control circuit 4 and is composed of elements such as a FET (Field Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor). 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 and smoothing circuit 3 is composed of a diode D1 and a capacitor C1. The connection point A between the cathode of the diode D1 and one end of the capacitor C1 is connected to the anode of the LED21 that constitutes the LED load 2, and the other end of the capacitor C1 is grounded. Note that the capacitor C1 is an output capacitor. In this embodiment, it is composed of an electrolytic capacitor, but other capacitors may also be used. Regarding the life and capacitance of the electrolytic capacitor, generally, the phenomenon of the electrolyte evaporating to the outside through the sealing part is dominant, resulting in a decrease in capacitance and an increase in the tangent of the loss angle. The ripple current reduction circuit 5 functions as a feedback type constant current control circuit that variably controls impedance and includes a variable impedance element Q2 and a detection resistor Rs. The variable impedance element Q2 is composed of elements such as a FET, an IGBT, or a BiTr. In this embodiment, the variable impedance element Q2 will be described as a MOSFET.

[0017] The rectifying and smoothing circuit 3 is composed of a diode D1 and a capacitor C1. The connection point A between the cathode of the diode D1 and one end of the capacitor C1 is connected to the anode of the LED21 that constitutes the LED load 2, and the other end of the capacitor C1 is grounded. Note that the capacitor C1 is an output capacitor. In this embodiment, it is composed of an electrolytic capacitor, but other capacitors may also be used. And regarding the life and capacitance of the electrolytic capacitor, generally, the phenomenon of the electrolyte evaporating to the outside through the sealing part is dominant, resulting in a decrease in capacitance and an increase in the tangent of the loss angle. The connection point A between the cathode of the diode D1 and one end of the capacitor C1 is connected to the anode of the LED21 that constitutes the LED load 2, and the other end of the capacitor C1 is grounded. Note that the capacitor C1 is an output capacitor. In this embodiment, it is composed of an electrolytic capacitor, but other capacitors may also be used. And regarding the life and capacitance of the electrolytic capacitor, generally, the phenomenon of the electrolyte evaporating to the outside through the sealing part is dominant, resulting in a decrease in capacitance and an increase in the tangent of the loss angle. appears. The ripple current reduction circuit 5 functions as a feedback type constant current control circuit that variably controls impedance and includes a variable impedance element Q2 and a detection resistor Rs. The variable impedance element Q2 is composed of elements such as a FET, an IGBT, or a BiTr. In this embodiment, the variable impedance element Q2 will be described as a MOSFET. The ripple current reduction circuit 5 functions as a feedback type constant current control circuit that variably controls impedance and includes a variable impedance element Q2 and a detection resistor Rs. The variable impedance element Q2 is composed of elements such as a FET, an IGBT, or a BiTr. In this embodiment, the variable impedance element Q2 will be described as a MOSFET. appears. appears.

[0018] The ripple current reduction circuit 5 functions as a feedback type constant current control circuit that variably controls impedance and includes a variable impedance element Q2 and a detection resistor Rs. The variable impedance element Q2 is composed of elements such as a FET, an IGBT, or a BiTr. In this embodiment, the variable impedance element Q2 will be described as a MOSFET. The variable impedance element Q2 is composed of elements such as a FET, an IGBT, or a BiTr. In this embodiment, the variable impedance element Q2 will be described as a MOSFET. In this embodiment, the variable impedance element Q2 will be described as a MOSFET.

[0019] The drain terminal of the variable impedance element Q2 is connected to the cathode of the LED2n that constitutes 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 via the ZR terminal of the control circuit 4.

[0020] 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 via the cc terminal of the control circuit 4. The detection resistor Rs converts the LED current I flowing through the LED load 2 into a voltage signal and outputs it to the error amplifier AMP1. LED

[0021] The dimming arithmetic unit 47 generates a digitized dimming target value according to the dimming signal input from the DIM terminal, and the DAC48 converts the digitized dimming target value generated by the dimming arithmetic unit 47 into an analog signal and inputs it to the non-inverting input terminal of the error amplifier AMP1.

[0022] The non-inverting input terminal of the error amplifier AMP1 inputs the signal (reference voltage value V ) of the dimming target value converted from the analog signal from the DAC48. IR

[0023] 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 flowing through the LED load 2 and the reference value (reference LED voltage value V IR ) 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 (reference voltage value V IR ), and the drain of the variable impedance element Q2 ​ Reduce the resistance value between sources. Also, the error amplifier AMP1 decreases the voltage level of the error signal as the LED current ILED becomes larger than the reference value (reference voltage value V IR ) and operates so as to increase the resistance value between the drain and source of the variable impedance element Q2. That is, the variable impedance element Q2 of the ripple current reduction circuit 5 functions as a variable impedance element that continuously changes the resistance value between the drain and source in response to the output of the error amplifier AMP 1. Thereby, the current ripple included in the LED current I

[0024] 1 can be reduced. Note that the response speed of the ripple current reduction circuit 5 is set higher than the response speed of the control circuit 4, and preferably LED is set higher than the frequency of the AC input power supply AC. IR ). The control circuit 4 includes a start section 41, an internal power supply section 42, an ADC (analog-to-digital converter) 43, an arithmetic unit 44, a PWM generation section 45, a driver 46, a dimming arithmetic unit 47, and a DAC (digital-to-analog converter) 48. Note that 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, or it may be entirely an analog control circuit. The start section 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 also connected to the diode D2 and the capacitor via the Vcc terminal. LED

[0025] The control circuit 4 includes a start section 41, an internal power supply section 42, an ADC (analog-to-digital converter) 43, an arithmetic unit 44, a PWM generation section 45, a driver 46, a dimming arithmetic unit 47, and a DAC (digital-to-analog converter) 48. Note that 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, or it may be entirely an analog control circuit.

[0026] The start section 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 also connected to the diode D2 and the capacitor via the Vcc terminal. It is connected to the auxiliary power supply 6 composed of the capacitor C2. The start-up section 41 charges the capacitor C2 of the auxiliary power supply 6 and, after start-up, supplies the power from the auxiliary power supply 6 to the internal power supply circuit (REG) 42 that generates the internal power supply within the control circuit 4.

[0027] The ADC 431 is connected to the connection point of the resistors R3 and R4 that constitute the voltage detection circuit 7 for detecting the voltage of the rectifying and smoothing circuit 3 via the CV1 terminal, and the voltage at the connection point is input as the feedback voltage V FB1 . The ADC 432 is connected to the connection point B of the LED load 2 and the ripple reduction circuit 5 (the drain terminal of the variable impedance element Q2) via the CV2 terminal, and the voltage at the connection point B is input as the feedback voltage V FB2 . Then, the ADCs 431 and 432 sample the feedback voltages V FB1 , V FB2 at intervals (for example, 20 μs) that are sufficiently shorter than the period of the voltage ripple including the feedback voltages V FB1 , V FB2 , convert them into digitized voltages, and output them to the arithmetic unit 44.

[0028] As shown in FIG. 2, the arithmetic unit 44 functions as an initial voltage setting section 440, an average voltage calculation section 441, an average value control section 442, an operation amount calculation section 443, a bottom voltage detection section 444, a bottom voltage comparison section 445, a target value correction section 446, and a target value setting section 447.

[0029] The initial voltage setting section 440 compares the initial voltage set at start-up with the feedback voltage V input from the ADC 431, thereby comparing the initial voltage with the feedback voltage V FB1 F B1 Calculate the error with [it], and output the calculated error as an error signal V st to the operation amount calculation unit 443 . Here, the initial voltage is set to be equal to or higher than the lowest voltage at which the LED load 2 and the ripple reduction circuit 5 can perform constant current control .

[0030] The average voltage calculation unit 441 is based on the feedback voltage V FB2 input from the ADC 432. For example, for each cycle of the AC input power supply AC, the average voltage of the feedback voltage V FB2 is calculated, and the calculated average voltage V V Ave is output to the average value control unit 442 Ave .

[0031] When the output voltage at point A rises to near the initial voltage at startup, the operation amount calculation unit 443 switches from the error signal of the initial voltage setting unit 440 to the error signal of the average value control unit 442. To smooth the output voltage fluctuation during this switching transition and prevent malfunction such as flickering of the LED load , the error signal from the average value control unit 442 is set to a preset upper limit value . . This is because first, at startup, feedback control by the initial voltage setting unit 440 is performed and the output voltage V at the connection point A of the rectifying smoothing circuit 7 rises toward the initial voltage. Before the output voltage V out reaches the initial voltage, the error signal from the average value control unit 442 reaches the preset out upper limit value. Here, the operation amount calculation unit 443 switches from the feedback control by the initial voltage setting unit 440 to the feedback control by the average value control unit 442. Next, the error signal of the average value control unit 442 is based on the error signal between the target average voltage V and the average voltage V and the average voltage V ref and Ave and Gradually decrease from the peak value until reaching a preset lower limit value. When the lower limit value is reached, the target average voltage V ref is shifted to be corrected by the correction value from the target value correction unit 446.

[0032] The operation amount calculation unit 443 first calculates, based on the error signal input from the initial voltage setting unit 440 at startup, the operation amount Δ for increasing or decreasing the on-time of the PWM (pulse width modulation) signal for on / off control of the switching element Q1, and outputs the calculated operation amount Δ to the PWM generation unit 45. When the calculated operation amount Δ falls within a predetermined range that is approximately zero, the error signal input from the initial voltage setting unit 440 is disconnected, and based on the error signal input from the average value control unit 442, the operation amount Δ for increasing or decreasing the on-time of the PWM (pulse width modulation) signal for on / off control of the switching element Q1 is calculated, and the calculated operation amount Δ is output to the PWM generation unit 45.

[0033] The bottom voltage detection unit 444 detects the bottom voltage V FB2 of the feedback voltage V B input from the ADC43. The bottom voltage detection unit 444 detects, for example, the bottom voltage V when the voltage value of the feedback voltage V FB2 input from the ADC43 is lower than both the voltage value one sampling before and the voltage value one sampling after. B

[0034] The bottom voltage comparison unit 445 compares the preset reference bottom voltage V Bref 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 4 46. Note that the reference bottom voltage VB ref is due to variations in various elements and during transient operations ​​​​Feedback voltage V in FB2 Even considering the undershoot of The variable impedance element Q2, which is a variable impedance element, can perform constant current control at a voltage set to a value exceeding the minimum voltage.

[0035] The target value correction unit 446 corrects the target average voltage V B when the bottom voltage V Bref is lower than the reference bottom voltage V upward so that the average value control unit 442 compares it with the average voltage V Ave and the target average voltage V ref When the bottom voltage V is higher than the reference bottom voltage V B the average value control Bref unit 442 corrects the target average voltage V downward so that it compares with the average voltage V Ave and the target average voltage V ref Note that the correction width of the target average voltage V ref may be a preset correction value or a correction value calculated based on the difference between the bottom voltage V B and the reference bottom voltage V Bref

[0036] .

[0036] The target value setting unit 447 has a conversion table or conversion formula that converts the reference voltage value generated by the dimming calculator 47 into the target average voltage V ref and sets the target average voltage V converted according to the dimming voltage value generated by the dimming calculator 47 to the average value control unit 442. Also ref The target value setting unit 447 is corrected by a correction value based on the difference between the bottom voltage V B and the reference bottom voltage V Bref through the bottom voltage detection unit 444, the bottom voltage comparison unit 445, and the target value correction unit 446. The target value setting unit 447 is such that the dimming voltage value generated by the dimming calculator 47 is Lower the LED current I LED The lower it becomes, the lower the target average voltage V ref is converted and set to . That is, in the switching power supply device 1, the average voltage of the feedback voltage V FB2 is controlled so that it becomes higher as the magnitude of the voltage ripple that changes according to the dimming signal becomes larger, and lower as the voltage ripple becomes smaller. V Ave is controlled so that it becomes higher as the magnitude of the voltage ripple that changes according to the dimming signal becomes larger, and lower as the voltage ripple becomes smaller. is controlled so that it becomes higher as the magnitude of the voltage ripple that changes according to the dimming signal becomes larger, and lower as the voltage ripple becomes smaller.

[0037] The PWM generation unit 45 generates a PWM signal with the on-time increased or decreased based on the operation amount Δ from the operation amount calculation unit 443, and controls the switching element Q1 to be turned on and off via the driver 46 by the generated PWM signal. Note that, as in this embodiment, when calculating the operation amount Δ of the on-time based on the error between the average voltage V calculated for each cycle of the AC input power supply AC and the target average voltage V , the on-time of the PWM signal is constant over one cycle of the AC input power supply AC. 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 operation amount Δ is calculated based on the error between them. When calculating the operation amount Δ of the on-time based on the error between the average voltage V calculated for each cycle of the AC input power supply AC and the target average voltage V , the on-time of the PWM signal is constant over one cycle of the AC input power supply AC.

[0038] The dimming calculator 47 integrates the externally PWM-modulated dimming signal DIM and outputs it as a dimming target value to the target value setting unit 447, and at the same time outputs it as a reference voltage value V to the error amplifier AMP1 that constitutes the ripple current reduction circuit 5 via the DAC 48. ZREF Here, the dimming calculator 47 integrates the dimming signal DIM to generate a dimming target value. However, when the change (increase or decrease) of the dimming signal DIM becomes larger than a predetermined value, the dimming calculator 47 sends an instruction for initial voltage setting to the initial voltage setting unit 440 and starts controlling to raise the B connection point (V Here, the dimming calculator 47 integrates the dimming signal DIM to generate a dimming target value. However, when the change (increase or decrease) of the dimming signal DIM becomes larger than a predetermined value, the dimming calculator 47 sends an instruction for initial voltage setting to the initial voltage setting unit 440 and starts controlling to raise the B connection point (V Here, the dimming calculator 47 integrates the dimming signal DIM to generate a dimming target value. However, when the change (increase or decrease) of the dimming signal DIM becomes larger than a predetermined value, the dimming calculator 47 sends an instruction for initial voltage setting to the initial voltage setting unit 440 and starts controlling to raise the B connection point (V Here, the dimming calculator 47 integrates the dimming signal DIM to generate a dimming target value. However, when the change (increase or decrease) of the dimming signal DIM becomes larger than a predetermined value, the dimming calculator 47 sends an instruction for initial voltage setting to the initial voltage setting unit 440 and starts controlling to raise the B connection point (V out ) to the initial voltage. At the same time, the dimming calculator 47 sets the B connection point (V ou t ) has a dead time (for example, 100 ms) corresponding to the time until it rises to the initial voltage and, after the dead time has elapsed, outputs a dimming target value and a reference voltage value V ZREF . Alternatively, the above operation is performed only when the increase in the dimming signal DIM becomes larger than a predetermined value, and when the decrease in the dimming signal DIM becomes larger than a predetermined value , during the dead time zone, the control to raise the B connection point (V out ) to the initial voltage may be omitted . Also, by configuring the dimming calculator 47 with a microcomputer or the like, after the dead time has elapsed, the dimming target value and the reference voltage value V ZREF are output. At this time, the dimming target value and the reference voltage value V ZREF are preferably gradually changed through a filter or the like to reach the target value or the voltage value . Thereby, when the change (increase / decrease) in the dimming signal DIM becomes large, the operating voltage of the ripple current reduction circuit 5 does not interrupt the lower limit value, preventing flicker of the LED load .

[0039] In the switching power supply device 1 shown in FIG. 1 in FIG. 3, the output voltage V from the start (time t0) of a significant change in the dimming signal DIM to the steady operation (time t3) OUT sequence diagram is shown. As shown in FIG. 3, the output voltage V OUT is controlled with the initial voltage as the target from time t0 to t1, and after reaching the initial voltage at time t1, it shifts to average value control. The output voltage V OUT is controlled to gradually decrease toward the lower limit value of the preset target value of the average value control, and reaches the lower limit value of the target value at time t2. Here, at time t2 when the lower limit value is reached, the average value control unit 442 is the target average voltage V​ref It is shifted so as to be corrected by the correction value from the target value correction unit 446. The output voltage V of the connection point A OUT becomes the reference bottom voltage based on the reference bottom voltage V signal from the bottom voltage detection unit 444. Br ef Average value control is performed so that it becomes a reference bottom voltage based on the signal. As described above, when there is a large change in the dimming signal DIM, the target value of the output voltage V OUT is switched from the initial voltage to the average value control to the average value control of the reference bottom voltage, thereby preventing the LED load from flickering. In particular, by switching to the average value control of the reference bottom voltage, the difference between the target value voltage and the feedback voltage VFB does not increase. This is because the average value control is performed so that the target average value is updated every switching period, and the target average value can be gradually decreased. That is, in the average value control of the reference bottom voltage, the update of the target average value becomes the commercial frequency period of the AC input power of 8 to 10 ms, and it is difficult to gradually decrease the target average value from the initial voltage. Therefore, it can be stably shifted through the average value control once. By doing so, the Vcc voltage of the control circuit 4 shown in FIG. 1 also changes in the same manner as the output voltage V, and there is an advantage that a stable power supply voltage can be ensured. In the switching power supply device 1 shown in FIG. 1, an example of a flyback converter has been described. However, the present invention may be applied to a buck converter, a boost converter, and a buck-boost converter. FIGS. 4 and 5 show a switching power supply device 1a configured by a buck-boost converter. In the switching power supply device 1a, the same reference numerals are given to the configurations showing the same functions as those of the switching power supply device 1, and the description thereof will be omitted as appropriate. This is because the average value control is performed so that the target average value is updated every switching period, and the target average value can be gradually decreased. That is, in the average value control of the reference bottom voltage, the update of the target average value becomes the commercial frequency period of the AC input power of 8 to 10 ms, and it is difficult to gradually decrease the target average value from the initial voltage. Therefore, it can be stably shifted through the average value control once. The average value control is performed so that the target average value is updated every switching period, and the target average value can be gradually decreased. That is, in the average value control of the reference bottom voltage, the update of the target average value becomes the commercial frequency period of the AC input power of 8 to 10 ms, and it is difficult to gradually decrease the target average value from the initial voltage. Therefore, it can be stably shifted through the average value control once. That is, in the average value control of the reference bottom voltage, the update of the target average value becomes the commercial frequency period of the AC input power of 8 to 10 ms, and it is difficult to gradually decrease the target average value from the initial voltage. Therefore, it can be stably shifted through the average value control once. The update of the target average value becomes the commercial frequency period of the AC input power of 8 to 10 ms, and it is difficult to gradually decrease the target average value from the initial voltage. Therefore, it can be stably shifted through the average value control once. Once, it can be stably shifted through the average value control. Once, it can be stably shifted through the average value control. As a result, the Vcc voltage of the control circuit 4 shown in FIG. 1 also changes in the same manner as the output voltage V, and there is an advantage that a stable power supply voltage can be ensured. OUT in the same manner, and there is an advantage that a stable power supply voltage can be ensured. in the same manner, and there is an advantage that a stable power supply voltage can be ensured.

[0040] In the switching power supply device 1 shown in FIG. 1, an example of a flyback converter has been described. However, the present invention may be applied to a buck converter, a boost converter, and a buck-boost converter. FIGS. 4 and 5 show a switching power supply device 1a configured by a buck-boost converter. In the switching power supply device 1a, the same reference numerals are given to the configurations showing the same functions as those of the switching power supply device 1, and the description thereof will be omitted as appropriate. In the switching power supply device 1a, the same reference numerals are given to the configurations showing the same functions as those of the switching power supply device 1, and the description thereof will be omitted as appropriate.

[0041] The switching power supply device 1a includes a synchronous rectifier element Q3 that functions as a diode D1. The control circuit 4a includes a PWM generation unit 45 that generates a PWM signal for driving the synchronous rectifier element Q3 and a driver 46a.

[0042] The control circuit 4a also incorporates an error amplifier AMP1 that constitutes a ripple current reduction circuit 5. It is built in.

[0043] FIG. 6 shows the waveforms of the output voltage Vout at the connection point A and the feedback voltage V FB2 shown in FIG. 1. In FIG. 6, (a) is for medium load when the deterioration of the capacitor C1 is small, (b) is for rated load when the deterioration of the capacitor C1 is small, (c) is for rated load when the deterioration of the capacitor C1 is large, and (d) is for rated load when the deterioration of the capacitor C1 is even larger. The respective waveforms of the output voltage Vout and the feedback voltage V are shown. V FB in FIG. 6 are shown.

[0044] In this embodiment, as shown in FIGS. 6(a) to 6(d), regardless of the magnitude of the voltage ripple, the bottom voltage V B becomes the reference bottom voltage V Bref so that the average value control of the feedback voltage V FB is performed. Therefore, the average voltage V of the feedback voltage V FB2 is controlled to be higher as the voltage ripple increases and lower as the voltage ripple decreases, according to the magnitude of the voltage ripple that varies depending on the operating Ave environment. Thus, when the deterioration of the capacitor C1 is small and the voltage ripple is small, the load is large and when the deterioration of the capacitor C1 is large and the voltage ripple is large, the load is small.

[0045] Accordingly, when the deterioration of the capacitor C1 is small and the voltage ripple is small, the load is large Power efficiency can be improved in all regions regardless of the load. For example, in the conventional average value control shown in FIGS. 7(a) and (b), the average voltage V FB of the feedback voltage V Ave is 1.5V both in medium load and rated load, while the average voltage V of the feedback voltage V FB2 in the average value control of this embodiment is Ave 1.0V at medium load shown in FIG. 6(a) and 1.2V at rated load shown in FIG. 6(b). That is , at medium load, the power loss can be reduced by Δ0.5V × LED current I LED , and at rated load , the power loss can be reduced by Δ0.3V × LED current I LED .

[0046] Also, in the method of fixing the average voltage V FB of the feedback voltage V Ave as in the conventional case , even when variations such as the end of life or variations in the capacitance of the output capacitor occur as shown in FIGS. 7(c) and (d) , it was necessary to design with a view to finally ensuring an appropriate operation margin. In contrast, in this embodiment, even with variations in the capacitor C1 or at the end of life of the capacitor C1 , as shown in FIGS. 6(c) and (d), the bottom voltage V FB2 of the feedback voltage V B is stable because it is controlled to have a lower limit value with respect to the reference bottom voltage V Bref , and there are few variations due to mass production of the feedback voltage V FB2 . That is, in this embodiment, simplification of the power supply design can be expected.

[0047]

[0047] Furthermore, as in the conventional case, the average voltage V FB of the feedback voltage V Avein a fixed manner the deterioration of the output capacitor becomes large, and as shown in FIGS. 7(c) and 7(d), the feedbac k voltage V FB falls below the operating margin voltage V M , there is a risk that the rated current cannot be obtained or flicker occurs. In contrast, in the present embodiment, even if the deterioration of the output capacitor becomes large, as shown in FIGS. 6(c) and 6(d), the bottom of the feedback voltage V FB2 voltage V is controlled to the reference bottom voltage V B so that the bottom voltage V Bref of the feedback voltage V FB2 does not greatly exceed or fall below the reference bottom voltage V B , and the LED load 2 can be driven without problems, and the power supply life can be extended emergently Bref .

[0048] Also, during light load operation, the voltage ripple of the feedback voltage V FB2 becomes small, and it may become difficult to detect the voltage ripple . Therefore, in an environmental condition where the voltage ripple of the feedback voltage V FB2 such as the input of a dithering signal becomes small, the stability may be improved by switching to another control such as the conventional ref average value control in which the target average voltage V is fixed.

[0049] Note that the input voltage may be detected, and the target average voltage V ref converted according to the input voltage may be set in the average value control unit 442. In this case, the voltage ripple becomes larger as the input voltage is smaller (lower). Therefore, the higher the input voltage, the lower the target average voltage V is converted and set. Thereby, the average voltage V ref of the feedback voltage V FB2 ​​​​Ave varies according to the magnitude of the voltage ripple that changes with the input voltage and is controlled so that the higher the voltage ripple, the higher it becomes, and the lower the voltage ripple, the lower it becomes.

[0050] As described above, this embodiment is a switching power supply device 1 that converts AC input power AC into a desired DC output power and supplies it to the LED load 2, and includes a switching element Q1 that is an on-off controlled switching element, a ripple current reduction circuit 5 that is connected in series with the LED load 2 and reduces the 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 based on the feedback voltage V at the connection point B between the LED load 2 and the ripple current reduction circuit 5. The control circuit 4 sets a target average voltage V based on the magnitude of the voltage ripple of the feedback voltage V and performs average value control on the feedback voltage V . FB With this configuration, in an operating environment where the voltage ripple of the feedback voltage V is small, the target average voltage V FB2 can be set to a low value, and the power supply efficiency can be improved. ref FB Furthermore, in this embodiment, the control circuit 4 detects the bottom voltage V FB2 of the feedback voltage V and corrects the target average voltage so that the detected bottom voltage V ref becomes equal to a preset reference bottom voltage V

[0051] FB2 B B Bref With this configuration, when the deterioration of the capacitor C1 is small and the voltage ripple is small, the target average voltage V refSince it can be corrected to a low value, the power efficiency can be improved in all regions regardless of the magnitude of the load.

[0052] Furthermore, in this embodiment, the control circuit 4 includes a dimming calculator that dims the illuminance of the LED load by variably controlling the current flowing through the LED load based on the dimming signal. By detecting an increase in the dimming target value from the dimming calculator and providing a dead time for the dimming target value, and raising the voltages of the LED load and the ripple current reduction circuit to the initial voltage during this dead time, and performing control based on the dimming target value after the dead time has elapsed, stable control can be performed without causing flickering of the illuminance of the LED load due to sudden changes in the dimming signal. By detecting an increase in the dimming target value from the dimming calculator and providing a dead time for the dimming target value, and raising the voltages of the LED load and the ripple current reduction circuit to the initial voltage during this dead time, and performing control based on the dimming target value after the dead time has elapsed, stable control can be performed without causing flickering of the illuminance of the LED load due to sudden changes in the dimming signal. By detecting an increase in the dimming target value from the dimming calculator and providing a dead time for the dimming target value, and raising the voltages of the LED load and the ripple current reduction circuit to the initial voltage during this dead time, and performing control based on the dimming target value after the dead time has elapsed, stable control can be performed without causing flickering of the illuminance of the LED load due to sudden changes in the dimming signal. By detecting an increase in the dimming target value from the dimming calculator and providing a dead time for the dimming target value, and raising the voltages of the LED load and the ripple current reduction circuit to the initial voltage during this dead time, and performing control based on the dimming target value after the dead time has elapsed, stable control can be performed without causing flickering of the illuminance of the LED load due to sudden changes in the dimming signal. By detecting an increase in the dimming target value from the dimming calculator and providing a dead time for the dimming target value, and raising the voltages of the LED load and the ripple current reduction circuit to the initial voltage during this dead time, and performing control based on the dimming target value after the dead time has elapsed, stable control can be performed without causing flickering of the illuminance of the LED load due to sudden changes in the dimming signal.

[0053] The present invention has been described based on the embodiments. These embodiments are illustrative, and it is understood by those skilled in the art that various modifications are possible in combinations of their respective components and the like, and such modifications are also within the scope of the present invention. The present invention has been described based on the embodiments. These embodiments are illustrative, and it is understood by those skilled in the art that various modifications are possible in combinations of their respective components and the like, and such modifications are also within the scope of the present invention. The present invention has been described based on the embodiments. These embodiments are illustrative, and it is understood by those skilled in the art that various modifications are possible in combinations of their respective components and the like, and such modifications are also within the scope of the present invention.

Explanation of Reference Numerals

[0054] 1, 1a Switching Power Supply Device 2 LED Load 3 Rectifying and Smoothing Circuit 4, 4a Control Circuit 5 Ripple Current Reduction Circuit 6 Auxiliary Power Supply 7 Voltage Detection Circuit 21~2n LED 41 Start Section 42 Internal Power Supply Section 431, 432 ADC 44, 44a Calculator 45, 45a PWM Generation Section 46, 46a Driver 47 Dimming Calculator 48 DAC 440 Initial Voltage Setting Section 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 Capacitors D1 Diode DB Rectifier circuit Q1 Switching element Q2 Variable impedance element Q3 Synchronous rectifier element R1~R4 Resistors Rs Detection resistor TR Transformer W1 Primary winding W2 Secondary winding W3 Tertiary winding

Claims

Claim 1 A switching power supply device that converts AC input power into a desired DC output power and supplies it to an LED load, comprising: A switching element that is on-off controlled; A ripple current reduction circuit that is connected in series to the LED load and reduces the current ripple flowing through the LED load by variably controlling the impedance; A control circuit that on-off controls the switching element based on the feedback voltage at the connection point between the LED load and the ripple current reduction circuit; The control circuit includes a dimming arithmetic unit that dims the illuminance of the LED load by variably controlling the current flowing through the LED load based on a dimming signal; The switching power supply device is characterized in that the feedback voltage is subjected to average value control at a target average voltage set according to the magnitude of the voltage ripple of the feedback voltage, an increase in the dimming target value from the dimming arithmetic unit is detected to provide a dead time for the dimming target value, the voltages of the LED load and the ripple current reduction circuit are raised to a predetermined target voltage during the dead time, and control is performed based on the dimming target value after the dead time has elapsed.

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