JP2022182331A - Switching power supply device - Google Patents

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

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

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

JP 2012-164633 A

In the prior art, the DC output power is set to a predetermined level by controlling the on/off of the switching element so that the average voltage of the feedback voltage _VFB at the connection point between the LED load and the ripple current reduction circuit becomes a preset target average voltage _Vref . value is controlled. This feedback voltage V _FB includes voltage ripples (voltage fluctuations) similar to the output voltage V _OUT , as shown in FIG. The voltage ripple of the feedback voltage _VFB increases as the load increases, as shown in FIGS. 7(a) and 7(b). grows with the

Then, as shown in FIG. 7(d), when the feedback voltage _VFB falls below the voltage at which the variable impedance element cannot operate at a constant current due to the voltage ripple, the voltage across the LED load cannot be maintained at the required voltage, resulting in the LED The current value flowing through the load periodically drops, which is visible as flickering. Therefore, the operation is set in consideration of the minimum voltage at which the variable impedance element can perform constant current control, various variations (target average voltage _Vref, etc.), and the undershoot of the feedback voltage _VFB during transient operation. A margin voltage _VM is set, and a target average voltage _Vref is set so that the feedback voltage _VFB does not fall below the operating margin voltage _VM .

However, the target average voltage V _ref set in this manner 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 has not deteriorated, or when the voltage ripple is small at light load or medium load, as shown in _FIGS . There is a problem that the voltage changes at a high voltage with a considerable margin, and the margin becomes a power loss.
In addition, in a switching power supply with a dimming function, when the brightness is varied from deep dimming such as dimming to 80% or from 100% dimming to 10%, for example, abrupt load fluctuations are involved. The feedback control response of the power supply cannot catch up, interrupting the above-mentioned operating margin _VM , resulting in a problem of brightness flickering.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a switching power supply device that solves the problems, further improves power supply efficiency, and eliminates flickering due to the effects of dynamic load fluctuations associated with dimming. to provide.

The switching power supply device of the present invention converts AC input power into desired DC output power and converts it into LE.
A switching power supply device for supplying a D load, which is connected in series to a switching element that is ON/OFF controlled and the LED load, and variably controls the impedance to control the LED
a ripple current reduction circuit that reduces current ripple flowing through a load; and a control circuit that turns on and off the switching element based on a feedback voltage at a connection point between the LED load and the ripple current reduction circuit, wherein the control circuit is 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, and a target average set according to the magnitude of the voltage ripple of the feedback voltage voltage to control the average value of the feedback voltage, detect an increase in the dimming target value from the dimming calculator, provide a dead time for the dimming target value, and control the LED load and the ripple during the dead time zone. The voltage of the current reduction circuit is increased to a predetermined target voltage, and control is performed based on the dimming target value after the dead time has elapsed.

According to the present invention, stable dimming can be performed without flickering by securing the operating voltages of the LED load and the ripple current reduction circuit even when there is a large change in the dimming signal. again,
In an operating environment in which the voltage ripple of the feedback voltage _VFB2 is small, the target average voltage can be set to a low value, and the power supply efficiency can be improved.

1 is a circuit diagram showing the configuration of an embodiment of a switching power supply device according to the present invention; FIG. 2 is a block diagram showing the configuration of a calculator shown in FIG. 1; FIG. 2 shows waveforms at various parts under conditions of a drastic change in the dimming signal DIM in the switching power supply device shown in FIG. 1. FIG. 1 is a circuit diagram showing an example in which an embodiment of a switching power supply device according to the present invention is configured with a buck-boost converter; FIG. 5 is a block diagram showing the configuration of a control IC shown in FIG. 4; FIG. 2 is a waveform diagram of an output voltage and a feedback voltage in the switching power supply device shown in FIG. 1; FIG. FIG. 4 is a waveform diagram of output voltage and feedback voltage in a conventional switching power supply;

Embodiments of the present invention will be described in detail below with reference to the drawings. It should be noted that, in the following embodiments, the same reference numerals are given to the structures showing the same functions, and the description thereof will be omitted as appropriate.

The switching power supply device of the present embodiment converts AC input power into DC output power to convert LE
A switching power supply that supplies a D load, and uses a feedback type constant current control circuit equipped with a variable impedance element composed of a MOSFET or the like as a ripple current reduction circuit connected in series with the LED load. The output voltage Vout of the ripple current reduction circuit connected to is increased to a preset target voltage at startup, and after reaching the target voltage, the average voltage of the feedback voltage V _FB2 at the connection point between the LED load and the ripple current reduction circuit is changed according to the magnitude of the voltage ripple in the feedback voltage _VFB2 .

(Embodiment)
The switching power supply device 1 of the embodiment includes n LED elements (LED2
1 to LED2n), the flyback converter drives an LED load 2. Referring to FIG. A ripple current reduction circuit 5 and an auxiliary power supply 6 are provided.

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

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

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

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

The ripple current reduction circuit 5 functions as a feedback 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 an element such as FET, IGBT, BiTr. In this embodiment, the variable impedance element Q2 will be described as a MOSFET.

The drain terminal of the variable impedance element Q2 is connected to the cathode of the LED2n forming the LED load 2, the source terminal is grounded via the detection resistor Rs, and the gate terminal is connected to the error amplifier AMP1 via the ZR terminal of the control circuit 4. Connected to the output terminal.

A connection point between the detection resistor Rs and the source terminal of the variable impedance element Q2 is connected via the cc terminal of the control circuit 4 to the inverting input terminal of the error amplifier AMP1. The detection resistor Rs converts the LED current _ILED flowing through the LED load 2 into a voltage signal and outputs the voltage signal to the error amplifier AMP1.

The dimming calculator 47 generates a digitized dimming target value according to the dimming signal input from the DIM terminal, and the DAC 48 converts the digitized dimming target value generated by the dimming calculator 47 The value is converted into an analog signal and input to the non-inverting input terminal of the error amplifier AMP1.

The non-inverting input terminal of the error amplifier AMP1 receives the dimming target value signal (reference voltage value V _IR ) converted from the DAC 48 into an analog signal.

The output terminal of error amplifier AMP1 is connected to the gate terminal of variable impedance element Q2. The error amplifier AMP1 outputs an error signal based on the LED current I _LED flowing through the LED load 2 and the reference value (reference voltage value V _IR ) to the variable impedance element Q2. More 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 ).
Lower the resistance between the sources.
Further, the error amplifier AMP1 reduces the voltage level of the error signal as the LED current ILED becomes larger than the reference value (reference voltage value V _IR ), and increases the resistance value between the drain and source of the variable impedance element Q2. Operate.

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

The control circuit 4 includes a start unit 41, an internal power supply unit 42, an ADC (analog-to-digital converter) 43, a calculator 44, a PWM generator 45, a driver 46, and a dimming calculator 47.
, and a DAC (digital-to-analog converter) 48 . In addition, the control circuit 4
All of them may be digital control circuits (including circuits operated by software), some of the components may be digital control circuits, and all of them may be analog control circuits.

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 composed of a diode D2 and a capacitor C2 via the Vcc terminal. It is connected to the auxiliary power supply 6 . The start unit 41 charges the capacitor C2 of the auxiliary power supply 6 at startup, and supplies power from the auxiliary power supply 6 after startup to an internal power supply circuit (REG) 42 that generates an internal power supply within the control circuit 4 .

The ADC 431 is connected via a CV1 terminal to a connection point between resistors R3 and R4 that constitute a voltage detection circuit 7 that detects the voltage of the rectifying/smoothing circuit 3, and the voltage at this connection point is input as a feedback voltage _VFB1 . .
The ADC 432 is connected to a connection point B between 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 _VFB2 .
Then, the ADC 431 and ADC 432 apply feedback voltage V at sufficiently shorter intervals (for example, 20 μs) than the cycle of the voltage ripple included in the feedback voltages V _FB1 and V _FB2 .
_FB1 and _VFB2 are sampled, converted to digitized voltages, and output to the calculator 44. FIG.

Referring to FIG. 2, the computing unit 44 includes an initial voltage setting unit 440, an average voltage calculating unit 441,
It functions as an average value control unit 442 , an operation amount calculation unit 443 , a bottom voltage detection unit 444 , a bottom voltage comparison unit 445 , a target value correction unit 446 and a target value setting unit 447 .

The initial voltage setting unit 440 compares the initial voltage, which is initially set at startup, with the feedback voltage _VFB1 input from the ADC 431, thereby determining the initial voltage and the feedback voltage _VF.
The error from _B1 is calculated, and the calculated error is output to the manipulated variable calculation unit 443 as the error signal _Vst .
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.

The average voltage calculation unit 441 calculates the average voltage V _Ave of the feedback voltage V _FB2 for each cycle of the AC input power supply AC based on the feedback voltage V _FB2 input from the ADC 432, and calculates the calculated average voltage V _Ave. Output to the average value control unit 442 .

The manipulated variable calculator 443 switches from the error signal of the initial voltage setting unit 440 to the error signal of the average value controller 442 when the output voltage at point A rises to near the initial voltage at startup. The error signal from the average value control unit 442 is set to a preset upper limit value in order to moderate the output voltage fluctuation at the switching transition and prevent malfunction such as flickering of the LED load.
First, feedback control is performed by the initial voltage setting unit 440 at the time of start-up, and the output voltage _Vout at the connection point A of the rectifying/smoothing circuit 7 rises toward the initial voltage. Output voltage V
By the time _out reaches the initial voltage, the error signal from the average value control unit 442 reaches a preset upper limit value. Here, the manipulated variable calculation unit 443 switches from feedback control by the initial voltage setting unit 440 to feedback control by the average value control unit 442 . Next, the error signal of the average value control section 442 is gradually decreased from the upper limit value based on the error signal between the target average voltage _Vref and the average voltage V _Ave , and reaches the preset lower limit value. When the lower limit value is reached, the target average voltage V _ref is shifted to be corrected with the correction value from the target value corrector 446 .

Based on the error signal input from the initial voltage setting unit 440 at startup, the operation amount calculation unit 443 first calculates the operation amount Δ for increasing or decreasing the ON time of the PWM (pulse width modulation) signal that controls the ON/OFF of the switching element Q1. It calculates and outputs the calculated manipulated variable Δ to the PWM generator 45 .
When the calculated manipulated variable Δ falls within a predetermined range of approximately zero, the error signal input from the initial voltage setting section 440 is separated, and based on the error signal input from the average value control section 442,
A manipulated variable Δ for increasing or decreasing the ON time of a PWM (Pulse Width Modulation) signal for ON/OFF-controlling the switching element Q 1 is calculated, and the calculated manipulated variable Δ is output to the PWM generator 45 .

The bottom voltage detector 444 detects the bottom voltage _VB of the feedback voltage _VFB2 input from the ADC 43 . For example, when the voltage value of the feedback voltage _VFB2 input from the ADC 43 is lower than the voltage value before one sampling and the voltage value after one sampling, the bottom voltage detection unit 444 detects the voltage value as the bottom voltage. Detect as _VB .

The bottom voltage comparator 445 compares the preset reference bottom voltage V _Bref with the bottom voltage V _B detected by the bottom voltage detector 444 , and outputs the comparison result to the target value corrector 4 .
46. Note that the reference bottom voltage VB _ref is the lowest voltage at which the variable impedance element Q2, which is a variable impedance element, can perform constant current control even in consideration of variations in various elements and undershoot of the feedback voltage _VFB2 during transient operation. is set to a value that exceeds the maximum voltage.

When the bottom voltage _VB is lower than the reference bottom voltage VBref, the target value correction unit 446 corrects the target average voltage _Vref to be compared with the average _{voltage VAve} by the average value control unit 442 so as to increase the bottom voltage. When _VB exceeds the reference bottom voltage V _Bref , the average value control unit 442 corrects the target average voltage V _ref to be compared with the average voltage V _Ave to be lower. The correction width of the target average voltage _Vref may be a preset correction value, or may be a correction value calculated based on the difference between the bottom voltage _VB and the reference bottom voltage _VBref .

The target value setting unit 447 has a conversion table and a conversion formula for converting the reference voltage value generated by the dimming calculator 47 into the target average voltage _Vref , and converts the dimming voltage value generated by the dimming calculator 47 into a target average voltage Vref. The target average voltage V _ref converted according to is set in the average value control unit 442 . Also, the target value setting unit 447 is corrected with a correction value based on the difference between the bottom voltage _VB and the reference bottom voltage _VBref via 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 converts and sets a lower target average voltage V _ref as the dimming voltage value generated by the dimming calculator 47 becomes lower and the LED current I _LED becomes lower. That is, in the switching power supply device 1, the average voltage V _Ave of the feedback voltage V _FB2 is controlled to be higher as the voltage ripple increases and lower as the voltage ripple decreases, depending on the magnitude of the voltage ripple that changes according to the dimming signal. be done.

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

The dimming calculator 47 integrates the PWM-modulated dimming signal DIM from the outside and outputs it as a dimming target value to the target value setting unit 447. It is output to the amplifier AMP1 as a reference voltage value V-- _ZREF .
Here, the dimming calculator 47 integrates the dimming signal DIM to generate the dimming target value. The dimming calculator 47 sends an initial voltage setting instruction to the initial voltage setting unit 440, and the B connection point (V _out )
to the initial voltage. At the same time, the dimming calculator 47 controls the B connection point (V _ou
A dead time (for example, 100 ms) corresponding to the time until t 2 ) rises to the initial voltage is provided, _and after the dead time has elapsed, the dimming target value and the reference voltage value V _ZREF are output.
Alternatively, the above operation is performed only when the increase in the dimming signal DIM exceeds a predetermined value, and when the decrease in the dimming signal DIM exceeds a predetermined value, the operation is performed during the dead time period. , the control to raise the B connection point (V _out ) to the initial voltage may be omitted.
Further, by constructing the dimming calculator 47 with a microcomputer or the like, it outputs the dimming target value and the reference voltage value _VZREF after the dead time has elapsed. At this time, it is preferable that the dimming target value and the reference voltage value _VZREF are gradually changed through a filter or the like to reach the target value or voltage value.
As a result, when the change (increase/decrease) of the dimming signal DIM becomes large, the operating voltage of the ripple current reduction circuit 5 can be prevented from falling below the lower limit value and causing the LED load to flicker.

FIG. 3 shows a sequence diagram of the output voltage V _OUT in the switching power supply device 1 shown in FIG. 1 from the start of a large change in the dimming signal DIM (time t0) to steady operation (time t3). As shown in FIG. 3, from time t0 to t1, the output voltage V _OUT is controlled with the initial voltage as a target, and after reaching the initial voltage at time t1, the control shifts to average value control. The output voltage V _OUT is controlled to gradually decrease toward the lower limit of the preset target value of the average value control, and reaches the lower limit of the target value at time t2. Here, at time t2 when the lower limit 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 the reference bottom voltage V _Br from the bottom voltage detector 444.
Average value control is performed so as to obtain a reference bottom voltage based on the _ef signal.
As described above, when there is a large change in the dimming signal DIM, the flickering of the LED load can be prevented by switching the target value of the output voltage _VOUT from the initial voltage to the average value control to the average value control of the reference bottom voltage. can do. In particular, switching from the average value control to the average value control of the reference bottom voltage does not increase the difference between the target value voltage and the feedback voltage VFB. this is,
The average value control can gradually lower the target average value by performing control so that the target average value is updated for each switching cycle. That is, in the average value control of the reference bottom voltage,
This is because the target average value is updated with a commercial frequency cycle of 8 to 10 ms for the AC input power, and it is difficult to gradually lower the target average value from the initial voltage. .
As a result, the Vcc voltage of the control circuit 4 shown in FIG. 1 changes in the same manner as the output voltage _VOUT , so there is the 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, but the present invention may be applied to a buck converter, a boost converter, and a buck-boost converter. 1 shows a switching power supply device 1a composed of In addition, in the switching power supply device 1a, the same reference numerals are given to the configurations showing the same functions as the switching power supply device 1, and the description thereof will be omitted as appropriate.

The switching power supply 1a includes a synchronous rectifying element Q3 that functions as a diode D1, and the control circuit 4a includes a PWM generator 45 that generates a PWM signal that drives the synchronous rectifying element Q3.
a and a driver 46a.

Further, an error amplifier AMP1 that constitutes the ripple current reduction circuit 5 is built in the control circuit 4a.

6 shows the output voltage Vout at connection point A and the feedback voltage V at connection point B shown in FIG.
The waveform of _FB2 is shown. In FIG. 6, (a) is at medium load with little deterioration of capacitor C1, (b) is at rated load with little deterioration of capacitor C1, and (c) is with large deterioration of capacitor C1. (d) shows the waveforms of the output voltage Vout and the feedback voltage _VFB at the rated load when the deterioration of the capacitor C1 is greater.

In this embodiment, as shown in FIGS. 6A to 6D, regardless of the magnitude of the voltage ripple,
Average value control of the feedback voltage _VFB is performed so that the bottom voltage _VB becomes the reference bottom voltage _VBref . Therefore, the average voltage V _Ave of the feedback voltage V _FB2 is controlled according to the magnitude of the voltage ripple, which varies depending on the operating environment, such that the larger the voltage ripple, the higher the voltage ripple, and the smaller the voltage ripple, the lower the average voltage V Ave .

As a result, when the deterioration of the capacitor C1 is small and the voltage ripple is small, the power supply efficiency can be improved in all regions regardless of the magnitude of the load. For example, FIG. 7(a), (
The average voltage V _Ave of the feedback voltage V _FB in the conventional average value control shown in b) is
The average voltage V _Ave of the feedback voltage V _FB2 in the average value control of the present embodiment is 1.0 V, and 1.2 V at the rated load shown in FIG. 6(b). In other words, the power loss can be reduced by Δ0.5 V×LED current I _LED under medium load, and the power loss can be reduced by Δ0.3 V×LED current I _LED under rated load.

In addition, in the method of fixing the average voltage V _Ave of the feedback voltage V _FB as in the conventional method, even if the end of life or the variation in the capacity of the output capacitor occurs as shown in FIGS. It was necessary to anticipate and design so that a sufficient operating margin would be secured in the end. On the other hand, in the present embodiment, the bottom voltage _VB of the feedback voltage _VFB2 remains the reference bottom voltage V as shown in FIGS. Since _{the Bref} is controlled to the lower limit, it is stable and there is little variation due to mass production of the feedback voltage _VFB2 . That is, in this embodiment, simplification of power supply design can be expected.

Furthermore, in the method of fixing the _average voltage V _Ave of the feedback voltage V _FB as in the conventional method, the deterioration of the output capacitor becomes large, and as shown in FIGS. If the voltage falls below _VM , the rated current may not be obtained or flickering may occur. In contrast, in the present embodiment, even if the deterioration of the output capacitor becomes large, the bottom voltage _VB of the feedback voltage _VFB2 is lower than the reference bottom voltage _VBref as shown in FIGS. 6(c) and 6(d). Since the value is controlled, the feedback voltage V
_{L _ _}
The ED load 2 can be driven without problems, and the life of the power supply can be extended as an emergency evacuation.

Also, when the load is light, the voltage ripple of the feedback voltage _VFB2 becomes small, and it may become difficult to detect the voltage ripple. Therefore, the feedback voltage V such as the input of the Deming signal
Under environmental conditions where the voltage ripple of _FB2 is small, stability may be enhanced by switching to other control such as conventional average value control in which the target average voltage _Vref is fixed.

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 section 442 . In this case, the smaller (lower) the input voltage, the larger the voltage ripple. Therefore, the larger (higher) the input voltage is, the lower the target average voltage _Vref is set. As a result, the average voltage V _Ave of the feedback voltage V _FB2 is controlled according to the magnitude of the voltage ripple, which varies with the input voltage, so as to increase as the voltage ripple increases and decrease as the voltage ripple decreases.

As described above, the present embodiment is a switching power supply device 1 that converts alternating current input power AC into desired direct current output power and supplies it to an LED load 2, and is a switching element that is ON/OFF controlled. Q1, a ripple current reduction circuit 5 that is connected in series with the LED load 2 and that reduces the current ripple flowing through the LED load 2 by variably controlling the impedance, and a connection point B between the LED load 2 and the ripple current reduction circuit 5. and a control circuit 4 that controls on/off of the switching element Q1 based on the feedback voltage _VFB at the target average voltage _Vref set according to the magnitude of the voltage ripple of the feedback voltage _VFB2 . It controls the average value of the feedback voltage _VFB .
With this configuration, the target average voltage V _ref can be set to a low value in an operating environment in which the voltage ripple of the feedback voltage V _FB2 is small, and the power supply efficiency can be improved.

Further, in the present embodiment, the control circuit 4 detects the bottom voltage _VB of the feedback voltage _VFB2 , and adjusts the target average voltage so that the detected bottom voltage _VB becomes a preset reference bottom voltage _VBref . to correct.
With this configuration, when the deterioration of the capacitor C1 is small and the voltage ripple is small, the target average voltage _Vref can be corrected to a low value, so the power supply efficiency is improved in all regions regardless of the load size. be able to.

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.
A dead time for the dimming target value is provided by detecting an increase in the dimming target value from the dimming calculator, and the voltage of the LED load and the ripple current reduction circuit is increased to the initial voltage during the dead time zone, and the dead time is reached. Since control is performed based on the dimming target value after the elapse of time, stable control can be performed without flickering of the illuminance of the LED load in response to a sudden change in the dimming signal.

The present invention has been described above based on the embodiments. It should be understood by those skilled in the art that this embodiment is an example, and that various modifications can be made to the combination of each component, etc., and that such modifications are also within the scope of the present invention.

1, 1a switching power supply device 2 LED load 3 rectification smoothing circuit 4, 4a control circuit 5 ripple current reduction circuit 6 auxiliary power supply 7 voltage detection circuit 21 to 2n LED
41 start section 42 internal power supply section 431, 432 ADC
44, 44a calculators 45, 45a PWM generators 46, 46a driver 47 dimming calculator 48 DAC
440 Initial voltage setting unit 441 Average voltage calculation unit 442 Average value control unit 443 Manipulated 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 amplifiers C1 and C2 Capacitor D1 Diode DB Rectifying circuit Q1 Switching element Q2 Variable impedance element Q3 Synchronous rectifying elements R1 to R4 Resistor Rs Detection resistor TR Transformer W1 Primary winding W2 Secondary winding W3 Tertiary winding

Claims (6)

A switching power supply that converts AC input power into desired DC output power and supplies it to an LED load,
a switching element that is on/off controlled;
a ripple current reduction circuit that is connected in series with the LED load and that reduces current ripple flowing through the LED load by variably controlling impedance;
a control circuit that controls on/off of the switching element based on a feedback voltage at a connection point between the LED load and the ripple current reduction circuit;
The control circuit includes a dimming calculator that dims the illuminance of the LED load by variably controlling the current flowing through the LED load based on a dimming signal;
The feedback voltage is average-value controlled with a target average voltage set according to the magnitude of the voltage ripple of the feedback voltage, and an increase in the dimming target value from the dimming calculator is detected to detect the dimming target value. is provided, the voltage of the LED load and the ripple current reduction circuit is increased to a predetermined target voltage during the dead time period, and control is performed based on the dimming target value after the dead time has passed. and switching power supplies. The control circuit detects a decrease in the dimming target value from the dimming calculator, provides a dead time for the calculation signal, and reduces the voltage of the LED load and the ripple current reduction circuit to a predetermined target value during the dead time period. 2. The switching power supply device according to claim 1, wherein the voltage is increased to a voltage, and control is performed based on the dimming target value after the dead time has elapsed. 3. The switching power supply device according to claim 1, wherein said control circuit gradually changes the dimming target value from said dimming calculator to reach the target value while performing control. The control circuit detects a bottom voltage of the feedback voltage after transferring the feedback voltage to the average value control at the target average voltage, and controls the target voltage so that the detected bottom voltage becomes a preset reference bottom voltage. 4. The switching power supply device according to claim 1, wherein the average voltage is corrected. 4. The switching power supply device according to claim 1, wherein the control circuit sets the target average voltage lower as the LED current flowing through the LED load decreases according to the dimming signal. 4. The switching power supply device according to claim 1, wherein the control circuit sets the target average voltage lower as the input voltage increases.

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