Control circuit and DC / DC converter

Abstract

To provide a control circuit and a DC / DC converter capable of suppressing variation in output current when performing control of modifying an output voltage.SOLUTION: An error amplifier 522 generates a feedback signal VFB according to a difference between a detection voltage VR1 depending on a current ILED supplied from an output unit 4 to LEDs 21-2n, and a reference voltage VREF. A slope signal generation unit 523 generates a slope signal VSLP synchronized with a frequency of an oscillator 521. A comparator 524 compares the feedback signal VFB and the slope signal VSLP with each other and generates a comparison signal VCOMP. A switch control unit 525 outputs a drive signal VP having a duty depending on the comparison signal VCOMP. A feed-forward control unit 53 turns on a switch SW22 only for a constant time period to decrease the feedback signal VFB when turning on switches SW1 to SWn, and turns on a switch SW21 only for the constant time period to increase the feedback signal VFB when turning off the switches SW1 to SWn.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a control circuit and a DC / DC converter. [Background technology]

[0002] There are various lighting devices that use light-emitting elements such as LEDs as light sources and control the on / off of LEDs according to a predetermined blinking pattern. In these types of lighting devices, a drive circuit using a DC / DC converter is widely used as a circuit for driving the light-emitting elements. As a conventional example of a drive circuit, for example, Patent Document 1 discloses a light-emitting device that uses a step-up DC / DC converter to obtain a sufficient voltage for lighting multiple LEDs.

[0003] In recent years, so-called sequential lighting lamps, in which multiple LEDs are sequentially lit in a flowing manner, are becoming popular. As a driving circuit for realizing a sequential lighting lamp, for example, as disclosed in Patent Document 2, Patent Document 3, Non-Patent Document 1, etc., a circuit that generates a signal for sequential lighting and drives multiple LEDs has been proposed. In the driving method of Patent Document 3, it is necessary to operate multiple driving units in parallel to achieve sequential lighting, which increases costs. On the other hand, as in Non-Patent Document 1, a switch is provided in parallel with each of multiple LEDs connected in series, and sequential lighting is achieved by controlling the switches on and off, thereby making it possible to reduce costs.

[0004] However, as shown in FIG. 1 of Patent Document 1, when sequential lighting is realized by providing a switch in parallel with each of a number of series-connected LEDs and controlling the on / off of the switches, it has been found that the following problem occurs. When the switch connected in parallel to the LEDs is turned on, the output voltage of the DC / DC converter drops. Since the output voltage drops gradually, the voltage applied to each LED increases temporarily, and the output current supplied to the LEDs increases. At this time, the DC / DC converter performs control to lower the output current, but since it cannot be lowered immediately, the output current becomes excessive for a while, and there is a risk of damaging the LEDs.

[0005] Furthermore, when the switch connected in parallel to the LED is turned off, the output voltage of the DC / DC converter rises. Since the output voltage rises gradually, the voltage across each LED temporarily decreases, causing the output current to decrease. At this time, the DC / DC converter controls to increase the output current, but since it cannot increase the current immediately, there is a risk that the output current will be too low for a while. In other words, conventional DC / DC converters have the problem that the output current fluctuates greatly when the switch is turned on and off.

[0006] Also, a technique has been proposed for shortening the delay time until the output current stabilizes after returning to full illumination by holding the output voltage of the error amplifier at the output immediately before all the LEDs are turned off when all the LEDs are turned off (Patent Documents 4 and 5). However, although this technique is effective when all the LEDs are turned off, it cannot solve the above-mentioned problems. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6146984 [Patent Document 2] Japanese Patent Application Publication No. 51-36092 [Patent Document 3] JP 2017-74803 A [Patent Document 4] U.S. Patent No. 7,898,187 [Patent Document 5] U.S. Patent No. 8,975,831 [Non-patent literature]

[0008] [Non-Patent Document 1] Texas Instruments, TPS92661-Q1 Datasheet "High-Brightness LED Matrix Manager for Automotive Headlight Systems", [online], February 2016, [Retrieved November 12, 2020], Internet<http: / / www.tij.co.jp / jp / lit / gpn / TPS92661-Q1> Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a control circuit and a DC / DC converter that can suppress fluctuations in current flowing through a load when control is performed to change the output voltage. [Means for solving the problem]

[0010] In order to achieve the above object, a control circuit and a DC / DC converter according to the present invention comprise the following features [1] to [ 9 ] is one of its features. [1] A control circuit for controlling on / off of a first switching element constituting an output section that converts an input voltage and outputs a constant current, the first switching element performing on / off operation to supply a current to a load, An oscillator; an error amplifier that generates an error signal corresponding to a difference between a first detection voltage corresponding to a current supplied from the output section to a load and a reference voltage; a slope signal generating unit that generates a slope signal synchronized with a frequency of the oscillator; a comparator that compares the error signal with the slope signal to generate a comparison signal; a first switch control unit that outputs a drive signal for the first switching element having a duty corresponding to the comparison signal; a feedforward control unit that changes the voltage of the error signal in advance or increases a voltage change rate for a certain period of time before changing the output voltage when performing control to change the output voltage of the output unit; 、 a second switch control unit that controls on / off of a second switching element connected in parallel to the load, The feedforward control unit, when the second switch control unit performs on-control on the second switching element, reduces a voltage of the error signal in advance or increases a voltage drop rate for a certain period of time before performing on-control, and when the second switch control unit performs off-control on the second switching element, increases a voltage of the error signal in advance or increases a voltage rise rate for a certain period of time before performing off-control, The second switch control unit, when controlling the second switching element to be on, controls the first switching element to be off for a certain period of time. It is a control circuit. [2] A control circuit for controlling on / off of a first switching element constituting an output section that converts an input voltage and outputs a constant current, the first switching element performing on / off operation to supply a current to a load, An oscillator; an error amplifier that generates an error signal corresponding to a difference between a first detection voltage corresponding to a current supplied from the output section to a load and a reference voltage; a slope signal generating unit that generates a slope signal synchronized with a frequency of the oscillator; a comparator that compares the error signal with the slope signal to generate a comparison signal; a first switch control unit that outputs a drive signal for the first switching element having a duty corresponding to the comparison signal; a feedforward control unit that changes a voltage of the error signal in advance or increases a voltage change rate for a certain period of time before changing the output voltage when performing control to change the output voltage of the output unit; a second switch control unit that controls on / off of second switching elements that are connected in parallel to the plurality of loads that are connected in series with each other, The feedforward control unit changes the voltage of the error signal in advance or increases a voltage change rate for a certain period of time before turning on and off the second switching element by a magnitude corresponding to the number of the second switching elements that the second switch control unit turns on and off simultaneously. It is a control circuit. [3] A control circuit for controlling on / off of a first switching element constituting an output section that converts an input voltage and outputs a constant current, the first switching element performing on / off operation to supply a current to a load, An oscillator; an error amplifier that generates an error signal corresponding to a difference between a first detection voltage corresponding to a current supplied from the output section to a load and a reference voltage; a slope signal generating unit that generates a slope signal synchronized with a frequency of the oscillator; a comparator that compares the error signal with the slope signal to generate a comparison signal; a first switch control unit that outputs a drive signal for the first switching element having a duty corresponding to the comparison signal; a feedforward control unit that changes a voltage of the error signal in advance or increases a voltage change rate for a certain period of time before changing the output voltage when performing control to change the output voltage of the output unit; When performing control to change the output voltage of the output section, a feedforward control is performed to increase a voltage change rate for a certain period of time, and then the output of the error amplifier is set to a high impedance for a certain period of time. It is a control circuit. [4] [ 3

[0023] A control circuit according to the present invention, a second switch control unit that controls on / off of a second switching element connected in parallel to the load, The feedforward control unit, when the second switch control unit performs on-control on the second switching element, reduces the voltage of the error signal in advance or increases a voltage drop rate for a certain period of time before performing on-control, and when the second switch control unit performs off-control on the second switching element, increases the voltage of the error signal in advance or increases a voltage rise rate for a certain period of time before performing off-control. Control circuit To be 。 [5] [ 3

[0023] A control circuit according to the present invention, The feedforward control unit includes a current source that supplies a constant current to an output of the error amplifier or flows a constant current from the output of the error amplifier, a switch that cuts off the constant current of the current source, and a third switch control unit that controls on / off of the switch. It is a control circuit. [6] The control circuit according to any one of [1] to [5], the slope signal generating unit generates the slope signal by superimposing a slope compensation signal on a second detection voltage obtained by detecting a current flowing through the first switching element or a coil constituting the output unit. It is a control circuit. [7] an output section that converts an input voltage and outputs a constant current; a control circuit that configures the output unit and controls on / off of a first switching element that supplies a current to a load by performing an on / off operation, The control circuit comprises: an oscillator; an error amplifier that generates an error signal corresponding to a difference between a first detection voltage corresponding to a current supplied from the output section to a load and a reference voltage; a slope signal generating unit that generates a slope signal synchronized with a frequency of the oscillator; a comparator that compares the error signal with the slope signal to generate a comparison signal; a first switch control unit that outputs a drive signal for the first switching element having a duty corresponding to the comparison signal; a feedforward control unit that changes a voltage of the error signal in advance or increases a voltage change rate for a certain period of time before changing the output voltage when performing control to change the output voltage of the output unit; a second switch control unit that controls on / off of a second switching element connected in parallel to the load, The feedforward control unit, when the second switch control unit performs on-control on the second switching element, reduces a voltage of the error signal in advance or increases a voltage drop rate for a certain period of time before performing on-control, and when the second switch control unit performs off-control on the second switching element, increases a voltage of the error signal in advance or increases a voltage rise rate for a certain period of time before performing off-control, The second switch control unit, when controlling the second switching element to be on, controls the first switching element to be off for a certain period of time. DC / DC Converter To be 。 [8] an output section that converts an input voltage and outputs a constant current; a control circuit that configures the output unit and controls on / off of a first switching element that supplies a current to a load by performing an on / off operation, The control circuit comprises: an oscillator; an error amplifier that generates an error signal corresponding to a difference between a first detection voltage corresponding to a current supplied from the output section to a load and a reference voltage; a slope signal generating unit that generates a slope signal synchronized with a frequency of the oscillator; a comparator that compares the error signal with the slope signal to generate a comparison signal; a first switch control unit that outputs a drive signal for the first switching element having a duty corresponding to the comparison signal; a feedforward control unit that changes the voltage of the error signal in advance or increases a voltage change rate for a certain period of time before changing the output voltage when performing control to change the output voltage of the output unit; 、 a second switch control unit that controls on / off of second switching elements that are connected in parallel to the plurality of loads that are connected in series with each other, The feedforward control unit changes the voltage of the error signal in advance or increases a voltage change rate for a certain period of time before turning on and off the second switching element by a magnitude corresponding to the number of the second switching elements that the second switch control unit turns on and off simultaneously. It is a DC / DC converter. [9] an output section that converts an input voltage and outputs a constant current; a control circuit that configures the output unit and controls on / off of a first switching element that supplies a current to a load by performing an on / off operation, The control circuit comprises: an oscillator; an error amplifier that generates an error signal corresponding to a difference between a first detection voltage corresponding to a current supplied from the output section to a load and a reference voltage; a slope signal generating unit that generates a slope signal synchronized with a frequency of the oscillator; a comparator that compares the error signal with the slope signal to generate a comparison signal; a first switch control unit that outputs a drive signal for the first switching element having a duty corresponding to the comparison signal; a feedforward control unit that changes the voltage of the error signal in advance or increases a voltage change rate for a certain period of time before changing the output voltage when performing control to change the output voltage of the output unit; When performing control to change the output voltage of the output section, a feedforward control is performed to increase a voltage change rate for a certain period of time, and then the output of the error amplifier is set to a high impedance for a certain period of time. It is a DC / DC converter. Effect of the Invention

[0011] According to the present invention, it is possible to provide a control circuit and a DC / DC converter that can suppress fluctuations in output current when control is performed to change the output voltage.

[0012] The present invention has been briefly described above. Furthermore, the details of the present invention will be further clarified by reading the following description of the preferred embodiment of the present invention (hereinafter, referred to as "embodiment") with reference to the accompanying drawings. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 shows an LED light emitting device incorporating a control circuit and a DC / DC converter according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a time chart of the switches SW1 to SWn, the output voltage VOUT, the feedback voltage VFB, the current ILED, and the switches shown in FIG. [Diagram 3]FIG. 3 shows an LED light emitting device incorporating a control circuit and a DC / DC converter according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] (First embodiment) Specific embodiments of the present invention will be described below with reference to the accompanying drawings.

[0015] The LED light emitting device 1 as a load driving device includes a plurality of LEDs 21-2n (loads) and a DC / DC converter 3 that boosts an input voltage VIN and supplies current to the plurality of LEDs 21-2n. The plurality of LEDs 21-2n are connected in series with each other. The plurality of LEDs 21-2n are also arranged in a line in the order in which they are connected in series.

[0016] The DC / DC converter 3 includes an output section 4 that boosts a DC input voltage VIN and converts it into a DC output voltage VOUT by turning a switching transistor M1 (first switching element) on and off, current detection resistors R1 and R2, a control IC5 (control circuit) that controls the on and off of the switching transistor M1 that constitutes the output section 4, and a phase compensation circuit 6.

[0017] The output section 4 includes a coil L1, a rectifying diode D1, a switching transistor M1, and an output capacitor C1. One end of the coil L1 is connected to an input voltage supply section, and the other end is connected to the anode of the diode D1. The cathode of the diode D1 is connected to the output. The switching transistor M1 is composed of an N-channel MOSFET. The switching transistor M1 is connected between the connection point of the coil L1 and the diode D1 and one end of a current detection resistor R2, and the other end of the current detection resistor R2 is connected to ground. The output capacitor C1 is connected between the cathode of the diode D1 and ground.

[0018] According to the above-described output unit 4, when the switching transistor M1 is on, energy is stored in the coil L1. On the other hand, when the switching transistor M1 is off, the energy stored in the coil L1 is sent to the output capacitor C1, and the output voltage VOUT is output.

[0019] The current detection resistor R1 is connected between the LEDs 21-2n and the ground, is a resistor for detecting the current ILED flowing through the LEDs 21-2n, and outputs a detection voltage VR1 (first detection voltage) corresponding to the current ILED. The current detection resistor R2 is connected between the switching transistor M1 and the ground, is a resistor for detecting the current flowing through the switching transistor M1, and outputs a detection voltage VR2 (second detection voltage) corresponding to the current flowing through the switching transistor M1.

[0020] The control IC 5 has an LED control unit 51 that controls the on / off of the LEDs 21 to 2n, a power supply control unit 52 that controls the on / off of the switching transistor M1 so that the current ILED becomes a constant current at a target value, and a feedforward control unit 53. The LED control unit 51 has switches SW1 to SWn (second switching elements) connected in parallel to the LEDs 21 to 2n, respectively, and a switch control unit 511 (second switch control unit, third switch control unit) that controls the on / off of the switches SW1 to SWn. The switches SW1 to SWn are, for example, composed of N-channel MOSFETs, and their gates are connected to the switch control unit 511. The switch control unit 511 is configured as a block that performs switch control in response to commands from outside or inside.

[0021] When the switch control unit 511 receives a signal to instruct the LEDs 21 to 2n to be turned off, it outputs an H-level on signal to the gates of the switches SW1 to SWn, turning on the switches SW1 to SWn and turning off all the LEDs 21 to 2n. When the switch control unit 511 receives a signal to instruct the LEDs 21 to 2n to be turned on, it outputs an L-level off signal or an H-level on signal to the switches SW1 to SWn in sequence, and repeats this process. This allows sequential lighting in which the LEDs 21 to 2n are turned on or off in the order in which they are lined up.

[0022] The power supply control unit 52 includes an oscillator 521, an error amplifier 522, a slope signal generating unit 523, a comparator 524, and a switch control unit 525 (first switch control unit). The oscillator 521 outputs a clock signal Vclk. A detection voltage VR1 and a reference voltage VREF are input to the error amplifier 522. The reference voltage VREF is set to the same value as the detection voltage VR1 generated in the current detection resistor R1 when a current ILED of a predetermined target value flows. In this embodiment, the error amplifier 522 is a transconductor amplifier, and the error between the detection voltage VR1 and the reference voltage VREF is amplified and output to the inverting input of the comparator 524 as a feedback voltage VFB by flowing an output current of the error amplifier to a phase compensation circuit 6 described later.

[0023] The slope signal generating unit 523 generates a slope signal VSLP for current mode control. In this embodiment, a detection voltage VR2 corresponding to the current flowing through the switching transistor M1 is input to the slope signal generating unit 523. The slope signal generating unit 523 generates a slope signal VSLP synchronized with the clock signal Vclk by superimposing a slope compensation signal on the detection voltage VR2, and supplies the slope signal VSLP to the non-inverting input of the comparator 524.

[0024] The comparator 524 compares the feedback signal VFB (error signal) with the slope signal VSLP, and outputs a comparison signal VCOMP to the R terminal of the flip-flop 525A. The switch control unit 525 outputs a drive signal VP for the switching transistor M1, the duty of which corresponds to the comparison signal VCOMP. In this embodiment, the switch control unit 525 has a flip-flop 525A and a gate driver 525B.

[0025] The flip-flop 525A receives the clock signal Vclk at its S terminal. The output of the flip-flop 525A is input to a gate driver 525B, and the output of the gate driver 525B is connected to the gate of the switching transistor M1. The phase compensation circuit 6 is composed of a capacitor CFB and a resistor RFB. In order to operate stably at the expected output voltage and output current, the phase compensation circuit 6 has an appropriate time constant set by the capacitor CFB and the resistor RFB.

[0026] According to the above-mentioned power supply control unit 52, when the clock signal Vclk rises, the flip-flop 525A is set and an H-level signal is output from the Q terminal of the flip-flop 525A. This H-level signal is input to the gate of the switching transistor M1 as the drive signal VP via the gate driver 525B, and the switching transistor M1 is turned on. After that, when the slope signal VSLP exceeds the feedback signal VFB, the comparator 524 outputs an H-level comparison signal VCOMP to reset the flip-flop 525A.

[0027] As a result, an L-level signal is output from the Q terminal of the flip-flop 525A. The L-level signal is input to the gate of the switching transistor M1 as a drive signal VP via the gate driver 525B, and the switching transistor M1 is turned off. The larger the feedback signal VFB is, the later the timing of resetting the flip-flop 525A becomes, and the longer the ON time of the switching transistor M1 becomes. In this way, feedback is applied so that the detection voltage VR1 and the reference voltage VREF match, and the LEDs 21 to 2n are driven with a constant current so that ILED=VREF / R1 holds.

[0028] The feedforward control unit 53 includes a current source I1 that supplies a constant current to the output of the error amplifier 522, a constant current source I2 that flows a constant current from the output of the error amplifier 522, a switch SW21 that cuts off the constant current of the current source I1, a switch S22 that cuts off the constant current of the constant current I2, and a switch control unit 511. One end of the current source I1 is connected to a high potential power supply, and the other end is connected to the switch SW21. One end of the current source I2 is connected to a low potential power supply (ground), and the other end is connected to the switch SW22. The switches SW21 and SW22 are connected in series, and the connection point of the switches SW21 and SW22 is connected to the output of the error amplifier 522. The on / off of the switches SW21 and SW22 is controlled by the switch control unit 511.

[0029] According to the above-described feedforward control unit 53, when the switch SW21 is turned on and the switch SW22 is turned off, a constant current supplied from the constant current source I1 flows in the phase compensation circuit 6 in addition to the output current (source current) from the error amplifier 522. As a result, the feedback voltage VFB is forcibly increased by the constant current. On the other hand, when the switch SW21 is turned off and the switch SW22 is turned on, a current added by the constant current source I2 flows in addition to the output current (sink current) from the error amplifier 522 in the phase compensation circuit 6. As a result, the feedback voltage VFB is forcibly decreased by the constant current.

[0030] Next, the operation of the LED light emitting device 1 configured as described above will be described with reference to Fig. 2. In Fig. 2, the solid lines indicate the output voltage VOUT, feedback voltage VFB, and current ILED of the LED light emitting device 1 of this embodiment provided with the feedforward control unit 53. In Fig. 2, the dotted lines indicate the output voltage VOUT, feedback voltage VFB, and current ILED of a conventional LED light emitting device not provided with the feedforward control unit 53.

[0031] For example, when the switch SW1 is turned on, the output voltage VOUT of the DC / DC converter 3 appropriate for the target current ILED drops sharply by the amount of the reduction in the total forward voltage of the lit LEDs 22 to 2n. At this time, the charge in the output capacitor C1 is drawn out in a short time, causing the current ILED to rise sharply. After that, the error amplifier 522 of the conventional circuit lowers the feedback signal VFB when the detection voltage VR1 becomes larger than the reference voltage VREF as the current ILED increases.

[0032] When the feedback signal VFB decreases, the duty of the switching transistor M1 decreases, and the current ILED decreases. However, as shown by the dotted line in Fig. 2, the transconductance and output current capacity of the error amplifier 522 have an upper limit, so the feedback signal VFB does not decrease easily. For this reason, the current ILED becomes excessive for a while, and there is a risk of damaging LED21 to LED2n.

[0033] Also, for example, when the switch SW1 is turned off, the DC / DC converter 3 increases the output voltage VOUT to keep the current ILED constant. In the case of a conventional circuit, the output voltage VOUT does not rise immediately after the switch SW1 is turned off, but starts to rise after the current ILED decreases due to a temporary decrease in the voltage applied to the LEDs 22 to 2n, as shown by the dotted line in Figure 2.

[0034] In the case of the conventional circuit, when the detection voltage VR1 becomes smaller than the reference voltage VREF as the current ILED decreases, the error amplifier 522 increases the feedback signal VFB. When the feedback signal VFB increases, the duty of the switching transistor M1 increases, increasing the output voltage VOUT and increasing the current ILED. However, as shown by the dotted line in Figure 2, the transconductance and output current capacity of the error amplifier 522 have an upper limit, so the feedback signal VFB does not increase easily. As a result, the current ILED remains too small for a while.

[0035] Therefore, in this embodiment, a feedforward control unit 53 is provided. For example, the switch control unit 511 turns on the switch SW22 for a certain period of time just before turning on the switch SW1. As a result, a current that is the sum of the output current of the error amplifier 522 and the constant current of the constant current source I2 flows through the phase compensation circuit 6. Therefore, as shown by the solid line in FIG. 2, the feedback voltage VFB immediately drops by a certain amount according to the constant current. Therefore, the duty of the drive signal VP quickly approaches a value according to the output voltage VOUT that has dropped sharply after the switch SW1 is turned on, and the current ILED can be suppressed and the time until the current ILED returns to a constant value can be shortened.

[0036] Also, the switch control section 511 temporarily turns on the switch SW21, for example, immediately before or simultaneously with turning off the switch SW1. As a result, a current obtained by adding the constant current of the constant current source I1 to the output current of the error amplifier 522 flows through the phase compensation circuit 6. Therefore, as shown by the solid line in Fig. 2, the feedback voltage VFB immediately rises by a constant amount according to the constant current, and the time until the current ILED returns to a constant value can be shortened.

[0037] According to the above-described embodiment, when the feedforward control unit 53 is provided to control the output voltage by turning on and off the switches SW1 to SWn, the feedback voltage VFB is changed in advance for a certain period of time before the load changes, or the voltage change rate is increased for a certain period of time. This makes it possible to quickly change the duty of the drive signal VP to a value that makes the current ILED a constant value, and suppresses the fluctuation of the current ILED.

[0038] Second embodiment Next, a second embodiment will be described with reference to Fig. 3. The first embodiment and the second embodiment differ in that a stop circuit 54 is provided that forcibly turns off the switching transistor M1 and decreases the output voltage VOUT. The stop circuit 54 turns off the switching transistor M1 and decreases the output voltage VOUT, for example, by setting the output of the Q terminal of the switch control unit 525A to an L level. The stop circuit 54 is controlled by the switch control unit 511.

[0039] Next, the operation of the LED light emitting device 1 of the second embodiment will be described. As in the first embodiment, the switch control unit 511 turns on the switch SW22 for a certain period of time when the switch SW1 is on. Therefore, the feedback voltage VFB drops immediately. In addition, the switch control unit 511 stops the switching transistor M1 for a certain period of time by the stop circuit 54 when the switch SW1 is on. This makes it possible to further suppress the rise in the current ILED.

[0040] The fixed time for turning on the switch SW22 and the fixed time for turning off the switching transistor M1 may be the same or different. These fixed times are set so as to minimize the fluctuation of the current ILED.

[0041] In addition, after the aforementioned switch SW22 is turned on for a certain period of time, the feedback voltage VFB may generate ringing. This ringing occurs due to fluctuations in the output current of the error amplifier 522, so at this timing, the switch control unit 511 stops the error amplifier 522 for a certain period of time and sets the output to high impedance. This makes it possible to further stabilize the feedback voltage VFB and to make the current ILED reach the target current value more smoothly. Note that in this embodiment, the error amplifier 522 is configured as a transconductor amplifier, but even in the case of an error amplifier that similarly outputs a voltage, the current ILED can be made to reach the target current value more smoothly by setting the output to high impedance.

[0042] Third embodiment Next, a third embodiment will be described. In the above-mentioned first embodiment, an example in which the switches SW1 to SWn are turned on and off one by one has been described, but the present invention is not limited to this. For example, when the switches SW1 to SWn are turned on and off two by two at a time at the same time, the output voltage VOUT for achieving the target current ILED changes significantly compared to when the switches are turned on and off one by one. Therefore, it is considered to employ current sources I1 and I2 that supply constant currents according to the number of the switches SW1 to SWn that are turned on and off simultaneously. This allows the feedforward control unit 53 to increase the change speed of the feedback signal VFB by an amount according to the number of the switches SW1 to SWn that are turned on and off simultaneously.

[0043] In addition, in the case where the number of switches SW1 to SWn that are simultaneously controlled on and off varies, the current sources I1 and I2 may be made variable, and the feedforward control unit 53 may adjust the current to a constant value according to the number of switches SW1 to SWn that are simultaneously controlled on and off.

[0044] The present invention is not limited to the above-described embodiment, and can be appropriately modified, improved, etc. In addition, the material, shape, size, number, arrangement location, etc. of each component in the above-described embodiment are arbitrary as long as the present invention can be achieved, and are not limited.

[0045] According to the above-described embodiment, the current sources I1 and I2 are provided, but the present invention is not limited to this. Only the current source I2 may be provided to simply lower the feedback signal VFB when the switches SW1 to SWn are controlled to be on. Also, only the current source I1 may be provided to simply raise the feedback signal VFB when the switches SW1 to SWn are controlled to be off. Also, although the embodiment has been described as a step-up switching regulator, the present invention can be similarly applied to a step-down switching regulator.

[0046] According to the embodiment described above, a transconductance that outputs an output current obtained by amplifying the difference between the input voltages is used as the error amplifier 522, and the change rate of the feedback voltage VFB is increased by the current sources I1 and I2, but this is not limited to the above. The error amplifier 522 may be one that outputs an output voltage obtained by amplifying the difference between the input voltages, and the change rate of the feedback voltage VFB may be increased by a voltage source. [Explanation of symbols]

[0047] 3 DC / DC Converter 4 Output section 5 Control IC (control circuit) 21~2n LED(load) 53 Feedforward control section 511 Switch control section (second switch control section, third switch control section) 521 Oscillator 522 Error Amplifier 523 Slope signal generator 525 Switch control section (first switch control section) I1, I2 current source ILED current M1 Switching transistor (first switching element) SW1 to SWn switches (second switching elements) SW21, SW22 Switches VCOMP comparison signal VFB Feedback voltage (error signal) VIN Input voltage VOUT Output voltage VP drive signal VR1 Detection voltage (first detection voltage) VR2 detection voltage (second detection voltage) VREF Reference voltage VSLP Slope signal

Claims

1. A control circuit for controlling on / off of a first switching element constituting an output section that converts an input voltage and outputs a constant current, the first switching element being operated on / off to supply a current to a load, An oscillator; an error amplifier that generates an error signal corresponding to a difference between a first detection voltage corresponding to a current supplied from the output section to a load and a reference voltage; a slope signal generating unit that generates a slope signal synchronized with a frequency of the oscillator; a comparator that compares the error signal with the slope signal to generate a comparison signal; a first switch control unit that outputs a drive signal for the first switching element having a duty corresponding to the comparison signal; a feedforward control unit that changes a voltage of the error signal in advance or increases a voltage change rate for a certain period of time before changing the output voltage when performing control to change the output voltage of the output unit; a second switch control unit that controls on / off of a second switching element connected in parallel to the load, The feedforward control unit, when the second switch control unit performs on-control on the second switching element, reduces a voltage of the error signal in advance or increases a voltage drop rate for a certain period of time before performing on-control, and when the second switch control unit performs off-control on the second switching element, increases a voltage of the error signal in advance or increases a voltage rise rate for a certain period of time before performing off-control, the second switch control unit, when controlling the second switching element to be on, controls the first switching element to be off for a certain period of time; Control circuit.

2. A first switching element constituting an output section that converts an input voltage and outputs a constant current, the first switching element being turned on and off to supply a current to a load, the first switching element being turned on and off by a control circuit, An oscillator; an error amplifier that generates an error signal corresponding to a difference between a first detection voltage corresponding to a current supplied from the output section to a load and a reference voltage; a slope signal generating unit that generates a slope signal synchronized with a frequency of the oscillator; a comparator that compares the error signal with the slope signal to generate a comparison signal; a first switch control unit that outputs a drive signal for the first switching element having a duty corresponding to the comparison signal; a feedforward control unit that changes a voltage of the error signal in advance or increases a voltage change rate for a certain period of time before changing the output voltage when performing control to change the output voltage of the output unit; a second switch control unit that controls on / off of second switching elements that are connected in parallel to the plurality of loads that are connected in series with each other, The feedforward control unit changes the voltage of the error signal in advance or increases a voltage change rate for a certain period of time before turning on and off the second switching element by a magnitude corresponding to the number of the second switching elements that the second switch control unit turns on and off simultaneously. Control circuit.

3. A first switching element constituting an output section that converts an input voltage and outputs a constant current, the first switching element being turned on and off to supply a current to a load, the first switching element being turned on and off by a control circuit, An oscillator; an error amplifier that generates an error signal corresponding to a difference between a first detection voltage corresponding to a current supplied from the output section to a load and a reference voltage; a slope signal generating unit that generates a slope signal synchronized with a frequency of the oscillator; a comparator that compares the error signal with the slope signal to generate a comparison signal; a first switch control unit that outputs a drive signal for the first switching element having a duty corresponding to the comparison signal; a feedforward control unit that changes a voltage of the error signal in advance or increases a voltage change rate for a certain period of time before changing the output voltage when performing control to change the output voltage of the output unit; When performing control to change the output voltage of the output section, a feedforward control is performed to increase a voltage change rate for a certain period of time, and then the output of the error amplifier is set to a high impedance for a certain period of time. Control circuit.

4. 4. A control circuit according to claim 3, a second switch control unit that controls on / off of a second switching element connected in parallel to the load, The feedforward control unit, when the second switch control unit performs an on-control on the second switching element, reduces the voltage of the error signal in advance or increases a voltage drop rate for a certain period of time before performing the on-control, and, when the second switch control unit performs an off-control on the second switching element, increases the voltage of the error signal in advance or increases a voltage rise rate for a certain period of time before performing the off-control. Control circuit.

5. 4. A control circuit according to claim 3, The feedforward control unit includes a current source that supplies a constant current to an output of the error amplifier or flows a constant current from the output of the error amplifier, a switch that cuts off the constant current of the current source, and a third switch control unit that controls on / off of the switch. Control circuit.

6. A control circuit according to any one of claims 1 to 5, The slope signal generating unit generates the slope signal by superimposing a slope compensation signal on a second detection voltage obtained by detecting a current flowing through the first switching element or a coil constituting the output unit. Control circuit.

7. An output section that converts an input voltage and outputs a constant current; a control circuit that configures the output unit and controls on / off of a first switching element that supplies a current to a load by performing an on / off operation, The control circuit comprises: an oscillator; an error amplifier that generates an error signal corresponding to a difference between a first detection voltage corresponding to a current supplied from the output section to a load and a reference voltage; a slope signal generating unit that generates a slope signal synchronized with a frequency of the oscillator; a comparator that compares the error signal with the slope signal to generate a comparison signal; a first switch control unit that outputs a drive signal for the first switching element having a duty corresponding to the comparison signal; a feedforward control unit that changes a voltage of the error signal in advance or increases a voltage change rate for a certain period of time before changing the output voltage when performing control to change the output voltage of the output unit; a second switch control unit that controls on / off of a second switching element connected in parallel to the load, The feedforward control unit, when the second switch control unit performs on-control on the second switching element, reduces a voltage of the error signal in advance or increases a voltage drop rate for a certain period of time before performing on-control, and when the second switch control unit performs off-control on the second switching element, increases a voltage of the error signal in advance or increases a voltage rise rate for a certain period of time before performing off-control, the second switch control unit, when controlling the second switching element to be on, controls the first switching element to be off for a certain period of time; DC / DC converter.

8. an output section that converts an input voltage and outputs a constant current; a control circuit that configures the output unit and controls on / off of a first switching element that supplies a current to a load by performing an on / off operation, The control circuit comprises: an oscillator; an error amplifier that generates an error signal corresponding to a difference between a first detection voltage corresponding to a current supplied from the output section to a load and a reference voltage; a slope signal generating unit that generates a slope signal synchronized with a frequency of the oscillator; a comparator that compares the error signal with the slope signal to generate a comparison signal; a first switch control unit that outputs a drive signal for the first switching element having a duty corresponding to the comparison signal; a feedforward control unit that changes a voltage of the error signal in advance or increases a voltage change rate for a certain period of time before changing the output voltage when performing control to change the output voltage of the output unit; a second switch control unit that controls on / off of second switching elements that are connected in parallel to the plurality of loads that are connected in series with each other, The feedforward control unit changes the voltage of the error signal in advance or increases a voltage change rate for a certain period of time before turning on and off the second switching element by a magnitude corresponding to the number of the second switching elements that the second switch control unit turns on and off simultaneously. DC / DC converter.

9. An output section that converts an input voltage and outputs a constant current; a control circuit that configures the output unit and controls on / off of a first switching element that supplies a current to a load by performing an on / off operation, The control circuit comprises: an oscillator; an error amplifier that generates an error signal corresponding to a difference between a first detection voltage corresponding to a current supplied from the output section to a load and a reference voltage; a slope signal generating unit that generates a slope signal synchronized with a frequency of the oscillator; a comparator that compares the error signal with the slope signal to generate a comparison signal; a first switch control unit that outputs a drive signal for the first switching element having a duty corresponding to the comparison signal; a feedforward control unit that changes the voltage of the error signal in advance or increases a voltage change rate for a certain period of time before changing the output voltage when performing control to change the output voltage of the output unit; When performing control to change the output voltage of the output section, a feedforward control is performed to increase a voltage change rate for a certain period of time, and then the output of the error amplifier is set to a high impedance for a certain period of time. DC / DC converter.

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