Switching power supply device

Abstract

To provide a switching power supply device capable of further improving power supply efficiency.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 DC output voltage to a predetermined target voltage at start up, 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 by operating the ripple current reduction circuit 5 after the DC output voltage reaches the target voltage.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 reduced by control.

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 FB ref FB This feedback voltage V OUT has the same voltage ripple (voltage variation includes (dynamic). And the voltage ripple of the feedback voltage V FB becomes larger as the load increases, as shown in FIGS. 10(a) and (b), and becomes larger as the output capacitor deteriorates, as shown in FIGS. 10(c) and (d). As shown in FIGS. 10(c) and (d), as the load increases, the voltage ripple becomes larger, and as the output capacitor deteriorates, the voltage ripple becomes larger. As shown in FIGS. 10(c) and (d), as the load increases, the voltage ripple becomes larger, and as the output capacitor deteriorates, the voltage ripple becomes larger.

[0005] And, as shown in FIG. 10(d), when the feedback voltage V FB drops below the voltage at which the variable impedance element cannot operate in constant current due to the voltage ripple, the voltage across the LED load cannot maintain the required voltage, and as a result, the current value flowing through the LED load periodically drops 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 etc.), and the operation margin voltage V set in consideration of the undershoot of the feedback voltage V ref during transient operation are set, and this operation margin voltage V is set so that the feedback voltage V FB does not fall below it, and the target average voltage V is set. M is set so that the feedback voltage V M does not fall below it, and the target average voltage V FB is set so that the feedback voltage V does not fall below it, and the target average voltage V ref is set.

[0006] 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 large voltage ripple at the maximum load. Therefore, when the output capacitor is not deteriorated, or when the voltage ripple is small during light load or medium load, as shown in FIGS. 10(a) and (b), the feedback voltage V when the output capacitor is not deteriorated, or when the voltage ripple is small during light load or medium load, as shown in FIGS. 10(a) and (b), the feedback voltage V when the output capacitor is not deteriorated, or when the voltage ripple is small during light load or medium load, as shown in FIGS. 10(a) and (b), the feedback voltage V FB will transition at a voltage that is considerably higher than the operation margin and the surplus will result in power loss, which is a problem. and the surplus will result in power loss, which is a problem. In addition, as a problem other than power loss, during startup when power is applied, the variable impedance element starts to operate, causing a problem of flickering where the LED load emits light momentarily. This is because when the LED load lights up from a state where the voltage applied to it is insufficient, the current rapidly increases along the I-V characteristics of the LED load, resulting in malfunctioning lighting. This problem is likely to occur when the feedback voltage V is near the operating margin, and is also likely to occur under conditions of deep dimming such as 1% dimming. As a countermeasure, a measure to slow down the response of the variable impedance element during startup can be considered, but this causes a problem of increasing the startup time and impairing the product value. FB This invention has been made in view of the above problems, aims to solve those problems, further improve power efficiency, and provide a switching power supply device capable of shortening the startup time.

[0007]

[0008] The above-mentioned

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, 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 raises the voltage to a preset target voltage during startup, The above-mentioned operates the ripple current reduction circuit after reaching the target voltage, and controls the feedback voltage at an average value at a target average voltage set according to the magnitude of the voltage ripple of the feedback voltage. together with, as the LED current flowing through the LED load becomes smaller by the dimming signal, set to the lower target average voltage This is the feature.

Effects of the Invention

[0009] 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 efficiency can be improved. This has the effect of

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following embodiments, Configurations showing 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 the present embodiment is a switching power supply device that converts AC input power into DC output power and supplies it to an LED load. A flyback type constant current control circuit including a variable impedance element composed of a MOSFET or the like is provided as a ripple current reduction circuit connected in series with the LED load. Using the flyback type constant current control circuit, the output voltage Vout of the LED load and the ripple current reduction circuit connected in series is increased to a target voltage preset 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. FB FB

[0013] (First Embodiment) The switching power supply device 1 of the first embodiment is a flyback converter that drives an LED load 2 composed of n serially connected LED elements (LED21 to 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 end of the switching element Q1. 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) and an IGBT (Insulated Gate Bipolar Transistor). In this embodiment, the switching element Q1 will be described as a MOSFET . . 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.

[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 . . . itors 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 . .

[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, and 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 of the control circuit 4 via the cc terminal. 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 non-inverting input terminal of the error amplifier AMP1 of the control circuit 4 is connected to the reference voltage (PWM signal) generated at the reference voltage 49 via the DAC (digital-to-analog converter) 48. In other words, the reference voltage generated by the PWM signal generated at the reference voltage 49 is replaced with an analog signal by the DAC 48 and input to the non-inverting input terminal of the error amplifier AMP1 .

[0022] The output terminal of the error amplifier AMP1 is connected to the gate terminal of the variable impedance element Q2 via the ZR terminal of the control circuit 4. 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 voltage) to the variable impedance LED element Q2. Specifically, the error amplifier AMP1 increases the voltage level of the error signal as the LED current I becomes smaller than the reference value, and decreases the resistance value between the drain and LED source of the variable impedance element Q2. Also, the error amplifier AMP1 decreases the voltage level of the error signal as the LED current ILED becomes larger than the reference value, and operates 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 so that the LED current I becomes the reference value (reference voltage). As a result, the current ripple included in the LED current I

[0023] 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 higher than the frequency of the commercial power supply AC. LED The control circuit 4 includes a start section 41, an internal power supply section 42, ADCs (analog-to-digital converters) 431 and 432, an arithmetic unit 44, a PWM generation section 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, or it may be entirely an analog control circuit. LED 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 auxiliary power supply 6 composed of the diode D2 and the capacitor C2 via the Vcc terminal. The start section 41 charges the capacitor C2 of the auxiliary power supply 6 at startup, and after startup, supplies the power from the auxiliary power supply 6 to the inside of the control circuit 4.

[0024]

[0025] ​​​​​​​​​​The internal power supply circuit (REG) 42 generates the internal power supply.

[0026] The ADC431 is a voltage detection circuit that detects the voltage of the rectifier / smoothing circuit 3 via the CV1 terminal. 7, the voltage at the connection point between resistors R3 and R4 is the feedback voltage. V FB1 is entered as The ADC432 is connected to the LED load 2 and the ripple reduction circuit 5 (variable impedance The voltage at node B is fed back to the feedback loop. Clock voltage V FB2 is entered as And ADC431 and ADC432 are feedback voltage V FB1 , V FB2 Contains The feedback voltage V FB1 , V FB2 is sampled, converted into a digital voltage, and output to the calculator 44. do.

[0027] Referring to FIG. 2, the calculator 44 includes an initial voltage setting unit 440, an average voltage calculation unit 441, and , an average value control unit 442, an operation amount calculation unit 443, a bottom voltage detection unit 444, and a bottom voltage It functions as a pressure comparison unit 445 and a target value correction unit 446 .

[0028] The initial voltage setting unit 440 receives the initial voltage that is initially set at the time of startup and the The feedback voltage V FB1 By comparing the initial voltage and the feedback voltage V F B1 The error between is calculated and the calculated error is expressed as an error signal V st to the operation amount calculation unit 443. do. Here, the initial voltage is set to be equal to or higher than the minimum voltage at which the LED load 2 and the ripple reduction circuit 5 can perform constant current control.

[0029] The average voltage calculation unit 441 calculates, based on the feedback voltage V input from the ADC 432, for example, the average voltage FB2 of the feedback voltage V for each cycle of the AC input power supply AC, and outputs the calculated average voltage V to the average value control unit 442. FB2 V Ave Ave

[0030] The average value control unit 442 calculates the difference between the target average voltage V ref and the average voltage V calculated by the average voltage calculation unit 441, and outputs the calculated difference as an error signal to the operation amount calculation unit 443. Ave ref Ave

[0031] When the output voltage at point A rises to 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 gently reduce 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. First, at startup, feedback control is performed by the initial voltage setting unit 440, and the output voltage V at the connection point A of the rectifying smoothing circuit 7 rises toward the initial voltage. When the output voltage V out reaches the initial voltage, the error signal from the average value control unit 442 has already reached the preset upper limit value. Here, the operation amount calculation unit 443 switches from the initial voltage setting unit 440 to out Switch from feedback control by [device name] to feedback control by the average value control unit 442 As a result, the average value control unit 442 can gently perform feedback control from the upper limit value to the lower limit value of the error signal. Next, the error signal of the average value control unit 442 is gradually decreased from the upper limit value based on the error signal between the target average voltage V ref and the average voltage V Ave to reach a preset lower limit value. When the lower limit value is reached, the target average voltage V is corrected with the correction value from the target value correction unit 446. ref

[0032] Based on the error signal input from the initial voltage setting unit 440 at startup, the operation amount calculation unit 443 first calculates an 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 is within a predetermined range close to 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, an 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 input from the ADC43. For example, when the voltage value of the feedback voltage V B input from the ADC43 is lower than both the voltage value one sampling before and the voltage value one sampling after, that voltage value is set as the bottom voltage V FB2 B ​​​​​​​​​​Detect as.

[0034] The bottom voltage comparison unit 445 compares a 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 V Bref is set to a value higher than the minimum voltage at which the variable impedance element Q2, which is a variable impedance element, can perform constant current control, considering variations in various elements and undershoot of the feedback voltage V during transient operation. FB2

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

[0036] The PWM generation unit 45 generates a PWM signal with the on-time increased or decreased based on the operation amount △ from the operation amount calculation unit 443, and switches via the driver 46 with the generated PWM signal The element Q1 is turned on and off. Note that, as in the present embodiment, for each cycle of the AC input power supply AC the calculated average voltage V Ave and the target average voltage V ref based on the error therebetween, the operation amount Δ of the on-time is calculated. When this is the case, the on-time of the PWM signal becomes constant in one cycle of the AC input power supply AC is.

[0037] Fig. 3 shows a sequence diagram of the output voltage V from the start of startup (time t0) to the steady operation (time OUT t4) of the switching power supply device 1 shown in Fig. 1. As shown in Fig. 3, from time t0 to t1, the output voltage V OUT is controlled with the initial voltage as the target. After reaching the initial voltage at time t1, the control shifts to average value control. The output voltage V OUT performs control to gradually decrease it toward the lower limit value of the preset target value of the average value control. When current starts to flow through the LED load 2 at time t2, it reaches the lower limit value of the target value at time t3. Here, at time t3 when the lower limit value of the target value is reached, the average value control unit 442 causes the target average voltage V ref to be corrected with the correction value from the target value correction unit 446. The output voltage V OUT at the connection point A is subjected to average value control so as to become the reference bottom voltage based on the reference bottom voltage signal from the bottom voltage detection unit 44 4. Bref is performed.

[0038] As described above, by switching the target value of the output voltage V OUT at startup from the initial voltage to the average value control to the reference bottom voltage average value control, it is possible to achieve both shortening of the startup time and prevention of flickering of the LED load. In particular, the switching to the average value control to the reference bottom voltage average value control ​​​By doing this, the difference between the target 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 has a commercial frequency period of 8 to 10 ms of the AC input power, and it is difficult to gradually decrease the target average value from the initial voltage. Therefore, it can be stably transferred once 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 way as the output voltage V OUT and there is an advantage that a stable power supply voltage can be ensured.

[0039] Next, referring to FIGS. 2 and 3, the operation of the ripple current reduction circuit 5 at startup is as follows: when the output voltage V out reaches the initial voltage at time t1, the reference voltage signal (PWM signal ) from the reference voltage 49 is output as an analog signal from the ZR terminal to the gate signal V of the variable impedance element Q2 via the DAC (digital-to-analog converter) 48. ZR

[0040] Here, the reference voltage signal (PWM signal) from the reference voltage 49 during the period from time t1 to t2 is a prescribed on-width in order to raise it to near the gate voltage threshold of the variable impedance element Q2. Therefore, an on-pulse signal longer than the prescribed on-width is sent. As a result, at time t2, the gate signal V of the variable impedance element Q2 ZR rises to near the gate voltage threshold.

[0041] Next, during the period from time t2 to t4, the on-width of the reference voltage signal (PWM signal) from the reference voltage 49 is gradually increased from a state where the on-width is suddenly narrowed to the prescribed reference voltage. As a result, The gate signal V of the variable impedance element Q2 ZR gradually rises from near the gate voltage threshold, so that the current I of the LED load also increases smoothly from time t2. LED This can be achieved.

[0042] As described above, by controlling the reference voltage signals (PWM signals) at times t1 to t2 and t2 to t4, the start-up time of the current I of the LED load can be shortened, and it can be started stably. LED

[0043] (Second Embodiment) Referring to FIGS. 4 and 5, the switching power supply device 1a of the second embodiment is configured by adding a dimming arithmetic unit 47 to the control circuit 4a of the switching power supply device 1 instead of the reference voltage 49.

[0044] The arithmetic unit 44a is provided with an added target value setting unit 447. The target value setting unit 4 47 has a conversion table or conversion formula for converting the reference voltage value generated by the dimming arithmetic unit 47 into the target average voltage V ref and sets the converted target average voltage V to the average value control unit 442 according to the reference voltage value generated by the dimming arithmetic unit 47. Further, the target value setting unit 4 47 is corrected by a correction value based on the difference between the bottom voltage V ref and the reference bottom voltage V 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 sets a lower target average voltage V as the reference voltage value generated by the dimming arithmetic unit 47 becomes lower and the LED current I B becomes lower. That is, in the second Bref LED ref In the switching power supply device 1b of the embodiment, the feedback voltage V FB2 average voltage V Ave is controlled so that it becomes higher as the voltage ripple, which changes according to the dimming signal, becomes larger, and lower as the voltage ripple becomes smaller.

[0045] Next, referring to FIG. 6, the operation of the ripple current reduction circuit 5 at startup is as follows: when the output voltage Vout reaches the initial voltage at time t1, a reference voltage signal (PWM signal) is output from the dimming arithmetic unit 47 as an analog signal from the ZR terminal via the DAC (digital-to-analog converter) 48 to the gate signal V of the variable impedance element Q2. ZR Here, the reference voltage signal (PWM signal) from the dimming arithmetic unit 47 during the period from time t1 to t2 is a pulse signal with an on-width longer than the specified on-width in order to raise it to near the gate voltage threshold of the variable impedance element Q2. As a result, at time t2, the gate signal V of the variable impedance element Q2 rises to near the gate voltage threshold. ZR During the period from time t2 to t4, the on-width of the reference voltage signal (PWM signal) from the dimming arithmetic unit 47 is gradually increased from the state where the on-width is suddenly narrowed to the value of the original dimming signal. As a result, the gate signal V of the variable impedance element Q2 gradually rises from near the gate voltage threshold, so that the current I ZR of the LED load also increases smoothly from time t2. LED As described above, by controlling the reference voltage signal (P WM signal) from the dimming arithmetic unit 47 during the periods from time t1 to t2 and from time t2 to t4, the startup time of the current I LED of the LED load is shortened, and ​​​​​​It becomes possible to start stably.

[0046] In addition, the input voltage is detected, and the target average voltage V converted according to the input voltage ref may be set in the averaging control unit 442. In this case, the smaller (lower) the input voltage, the larger the voltage ripple becomes. Therefore, the higher the input voltage, the lower the target average voltage V is converted and set. As a result, the average voltage V of the feedback voltage V ref is controlled so that it becomes higher as the voltage ripple, which changes according to the input voltage , becomes larger, and lower as the voltage ripple becomes smaller. FB2 of the average voltage V Ave is, according to the magnitude of the voltage ripple that changes depending on the input voltage , higher as the voltage ripple becomes larger, and lower as the voltage ripple becomes smaller.

[0047] Also, the control circuit 4a records the cumulative operation time, and the target average voltage V converted according to the cumulative operation time may be set in the averaging control unit 442. In this case, the longer the cumulative operation time ref , the more the capacitor C1 deteriorates and the larger the voltage ripple becomes. Therefore, the longer the cumulative operation time , the higher the target average voltage V is converted and set. As a result, the average voltage V of the feedback voltage V ref is controlled so that it is low during a period when the voltage ripple is small, and higher as the elapsed time when the voltage ripple becomes larger becomes. FB2 of the average voltage V Ave is, according to the magnitude of the voltage ripple that changes depending on the cumulative operation time , higher as the elapsed time when the voltage ripple becomes larger, and lower during a period when the voltage ripple is small.

[0048] Furthermore, by using a temperature sensor, the control circuit 4a records the cumulative operation time taking into account the ambient temperature, and the target average voltage V converted according to the cumulative operation time taking into account the ambient temperature may be set in the averaging control unit 442. In this case, when operating in a high ambient temperature state re f ​ The deterioration of the capacitor C1 becomes faster and the voltage ripple becomes larger. Therefore, at a high ambient temperature The longer the total operating time of, the higher the target average voltage V ref is converted and set. This Accordingly, the average voltage V of the feedback voltage V FB2 is the total considering the ambient temperature Ave The average voltage V is controlled to be low during a period with a small voltage ripple and high as the voltage ripple increases, according to the magnitude of the voltage ripple that changes depending on the total operating time.

[0049] In the switching power supply device 1a shown in FIG. 4, an example of a flyback converter was described However, the present invention may be applied to a buck converter, a boost converter, or a buck-boost converter. FIGS. 7 and 8 show a switching power supply device 1a configured with a buck-boost converter. In the switching power supply device 1a, components having the same functions as those of the switching power supply device 1 are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

[0050] (Application Example of the Second Embodiment) The switching power supply device 1b includes a synchronous rectifying element Q3 that functions as a diode D1 , and the control circuit 4b includes a PWM generation unit 45 a that generates a PWM signal for driving the synchronous rectifying element Q3 and a driver 46a.

[0051] The control circuit 4b also incorporates an error amplifier AMP1 that constitutes a ripple current reduction circuit 5 , and includes a dimming arithmetic unit 47 and a DAC (digital-to-analog converter) 48. The dimming arithmetic unit 47 generates a digitized reference voltage value according to a dimming signal input from the DIM terminal, and the DAC 48 converts the digitized reference generated by the dimming arithmetic unit 47 ​​​The voltage value 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. This becomes possible.

[0052] FIG. 9 shows the waveforms of the output voltage Vout at the connection point A and the feedback voltage V FB2 at the connection point B shown in FIG. 1. In FIG. 9, (a) shows the medium load condition when the deterioration of the capacitor C1 is small, (b) shows the rated load condition when the deterioration of the capacitor C1 is small, (c) shows the rated load condition when the deterioration of the capacitor C1 is large, and (d) shows the respective output voltages Vout and feedback voltages V at the rated load condition when the deterioration of the capacitor C1 is even larger. These are the waveforms of the feedback voltage V and the feedback voltage V FB2 at the rated load condition when the deterioration of the capacitor C1 is even larger.

[0053] In this embodiment, as shown in FIGS. 9(a) to 9(d), regardless of the magnitude of the voltage ripple, the average value control of the feedback voltage V B is performed so that the bottom voltage V Bref becomes the reference bottom voltage V FB2 . Therefore, the average voltage V FB2 of the feedback voltage V Ave 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 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 load size. For example, in the conventional average value control shown in FIGS. 9(a) and (b), the average voltage V

[0054] of the feedback voltage V is such that regardless of the load size, the power supply efficiency can be improved in all regions. For example, in the conventional average value control shown in FIGS. 9(a), ( b), the average voltage V FB2 of the feedback voltage V Ave is is 1.5V both under medium load and rated load, whereas the average value of the feedback voltage V in the control of this embodiment FB2 of the average voltage V Ave becomes 1.0V under medium load shown in Fig. 9(a), and becomes 1.2V under rated load shown in Fig. 9(b). That is, under medium load, the power loss can be reduced by Δ0.5V × LED current I , and under rated load, the power loss can be reduced by Δ0.3V × LED current I LED . . LED

[0055] Also, in the method of fixing the average voltage V FB of the feedback voltage V Ave as in the prior art, even if variations such as the end-of-life or the capacitance variation of the output capacitor occur as shown in Figs. 9(c) and (d), it is necessary to design with foresight so as to finally ensure an appropriate operation margin. In contrast, in this embodiment, even with the variation of the capacitor C1 or at the end-of-life of the capacitor C1, as shown in Figs. 9(c) and (d), the bottom voltage V FB2 of the feedback voltage V B is controlled to have a lower limit value with respect to the reference bottom voltage V Bref , so it is stable, and the variation due to mass production of the feedback voltage V FB2 is small. That is, in this embodiment, simplification of the power supply design can be expected.

[0056] Furthermore, in the method of fixing the average voltage V FB of the feedback voltage V Ave as in the prior art, the deterioration of the output capacitor becomes large, and as shown in Figs. 9(c) and (d), the feedback voltage V FB is the operation margin voltage V M ​​​If it falls below this, the rated current may not be available or flickering may occur. In contrast, in the present embodiment, the deterioration of the output capacitor is prevented. Even if the feedback voltage V FB2 Bottom Voltage V B is the reference bottom voltage V Bref Since the feedback voltage V FB2 Bottom voltage V B is the reference bottom voltage V Bref Without significantly exceeding or falling below L It is possible to drive ED load 2 without any problems, and it is possible to extend the life of the power supply in an emergency. can.

[0057] As shown in Fig. 9(d), the feedback voltage V FB2 The average voltage V Ave High If it becomes too large, it may become inoperable or other power supply elements may be damaged depending on the design of the other power supply parts. Therefore, in the calculator 44, the feedback voltage Pressure V FB2 The average voltage V Ave and the preset operation stop threshold, and the average voltage V A ve If the preset operation stop threshold is exceeded, the driving of the LED load 2 is stopped. It is preferable to configure it as above.

[0058] In addition, at light loads, the feedback voltage V FB2 The voltage ripple of the Therefore, it may be difficult to detect the feedback voltage V FB2 Under environmental conditions where the voltage ripple is small, the target average voltage V ref Fixed Stability may be improved by switching to other control such as the conventional average value control.

[0059] As described above, the present embodiment is a power supply for converting AC input power AC into a desired DC output power. The switching power supply device 1 supplies a current to an LED load 2 through an on / off controlled switch. The switching element Q1 is connected in series with the LED load 2, and the impedance is By variably controlling the dance, the current ripple flowing through the LED load 2 is reduced. The feedback voltage at the connection point B between the LED load 2 and the ripple current reduction circuit 5 is Pressure V FB2 and a control circuit for controlling the on / off of the switching element Q1 based on the The control circuit controls the feedback voltage V FB2 The target voltage is set according to the magnitude of the voltage ripple. Standard mean voltage V ref And the feedback voltage V FB2 is average value controlled. This configuration allows the feedback voltage V FB2 In an operating environment with small voltage ripple, the target Average voltage V ref can be set to a lower value, improving power supply efficiency.

[0060] Furthermore, in this embodiment, the control circuit controls the feedback voltage V FB2 Bottom pressure V B Detects the bottom voltage V B is the preset reference bottom voltage V Bref Nina The target average voltage is corrected so as to With this configuration, when the deterioration of the capacitor C1 is small and the voltage ripple is small, Average voltage V ref can be corrected to a low value, so it is suitable for all loads regardless of their magnitude. Power efficiency can be improved in the region. Also, even with variations in capacitor C1 or at the end of the life of capacitor C1, the bottom voltage V of the feedback voltage V is controlled to the reference bottom voltage FB2 V B and is stable, enabling simplification of the power supply design. V Bref Furthermore, even when the deterioration of the output capacitor becomes large, the bottom voltage V of the feedback voltage V does not exceed or fall below the reference bottom voltage V FB by a large margin, and LED load 2 can be driven without problems, and the power supply life can be extended emergently. V B V Bref Moreover, in this embodiment, control circuits 4a and 4b set the target average voltage V to a lower value as the LED current I

[0061] flowing through LED load 2 becomes smaller according to the dimming signal. I LED V ref With this configuration, in the region with a small load and small voltage ripple, the target average voltage V V ref can be set to a low value, and power efficiency can be improved. Furthermore, in this embodiment, the control circuit sets the target average voltage V

[0062] to a lower value as the input voltage becomes larger. V ref With this configuration, at a large input voltage where the voltage ripple becomes small, the target average voltage V V ref can be set to a low value, and power efficiency can be improved.

[0063] Furthermore, in this embodiment, the control circuit sets the target average voltage V V ref to a higher value as the total operation time becomes longer. With this configuration, in an operating environment where the cumulative operation time is short and the voltage ripple is small, the target average electric voltage V ref can be set to a low value, and the power supply efficiency can be improved.

[0064] Furthermore, in this embodiment, the control circuit sets the target average voltage V to a higher value as the cumulative operation time in a state where the environmental temperature is high is ref longer. With this configuration, the reference bottom voltage V Bref can be set taking into account the operation time at the environmental temperature.

[0065] The present invention has been described based on the embodiment. This embodiment is an example, and it is understood by those skilled in the art that various modifications are possible in combinations of these components and the like, and such modifications are also within the scope of the present invention.

Explanation of Reference Numerals

[0066] 1, 1a, 1b Switching power supply device 2 LED load 3 Rectifier smoothing circuit 4, 4a, 4b 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 Arithmetic unit 45, 45a PWM generation section 46, 46a Driver 47 Dimming arithmetic unit 48 DAC 49 Reference voltage 440 Initial voltage setting section 441 Average voltage calculation section 442 Average value control section ​​​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 R2~R4 Resistors Rs Detection resistor TR Transformer W1 Primary winding W2 Secondary winding W3 Tertiary winding

Claims

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 a feedback voltage at a connection point between the LED load and the ripple current reduction circuit. The switching power supply device is characterized in that: The control circuit raises the voltage to a preset target voltage at startup, operates the ripple current reduction circuit after reaching the target voltage, and controls the feedback voltage at a target average voltage set according to the magnitude of the voltage ripple of the feedback voltage. At the same time, as the LED current flowing through the LED load decreases due to a dimming signal, the target average voltage is set to a lower value.

2. The switching power supply device according to claim 1, wherein after the control circuit shifts to average value control of the feedback voltage at the target average voltage, 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.

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