WO2020017163A1 - Switching power supply - Google Patents

Switching power supply Download PDF

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Publication number
WO2020017163A1
WO2020017163A1 PCT/JP2019/021130 JP2019021130W WO2020017163A1 WO 2020017163 A1 WO2020017163 A1 WO 2020017163A1 JP 2019021130 W JP2019021130 W JP 2019021130W WO 2020017163 A1 WO2020017163 A1 WO 2020017163A1
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Prior art keywords
switching
time
control
burst
frequency
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PCT/JP2019/021130
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French (fr)
Japanese (ja)
Inventor
卓郎 秋山
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ソニー株式会社
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Application filed by ソニー株式会社 filed Critical ソニー株式会社
Priority to JP2020530919A priority Critical patent/JP7322881B2/en
Priority to CN201980046221.3A priority patent/CN112400273B/en
Publication of WO2020017163A1 publication Critical patent/WO2020017163A1/en

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Definitions

  • This technology relates to an LLC type switching power supply.
  • an LLC type switching power supply (DC-DC converter) using two Ls and one C is known.
  • Such a switching power supply is of a soft switching type, has characteristics of high efficiency and low noise, and is widely used. On the other hand, it has a characteristic that the regulation range is narrower than other methods, and therefore, it is not suitable for applications having a wide output voltage variable range or applications having a large input voltage fluctuation.
  • Patent Literature 1 discloses setting a normal mode in which the power supply is controlled by operating the oscillator continuously and a burst mode in which the power supply is controlled by operating the oscillator intermittently. Has been described. When the burst mode is set, the power supply control is intermittently stopped by detecting the output voltage on the secondary side, so that power consumption during standby can be reduced.
  • Patent Document 2 discloses that the power consumption of a switching power supply is further reduced. In Patent Document 2, attention is paid to the fact that switching control of the switch element is not required during the switching stop period, and the supply of control power to the control means is stopped to reduce power consumption.
  • Patent Document 1 or Patent Document 2 it is possible to widen the regulation range of the light load region of the LLC type switching power supply by using the burst mode (intermittent oscillation mode) at light load.
  • the technology described in Patent Literature 1 or Patent Literature 2 is a burst control technique for suppressing power consumption during standby, and a burst frequency of several tens Hz to several hundreds Hz is generally used.
  • an object of the present technology is to provide a switching power supply that can reduce a ripple current (or a ripple voltage) during a burst operation.
  • the present technology is an LLC type switching power supply, A feedback value indicating a load condition is supplied, the control unit forming a drive signal for the switching element, The control unit is In the first region where the load is heavy, frequency control for changing the switching frequency by the feedback value is performed, In the second region where the load is lighter than in the first region, burst control is performed in which the switching frequency is fixed to provide a switching ON section and a switching OFF section, In the burst control, the switching power supply is configured such that the ON time ratio is continuously varied according to load conditions by controlling both the number of times of switching and the OFF time.
  • the ON time ratio of the burst period can be continuously changed, and the minimum OFF time can be always controlled while the required minimum OFF time during the burst is secured.
  • the ripple current (or ripple voltage) during the burst operation can be minimized.
  • FIG. 1 is a connection diagram of an LLC type switching power supply.
  • FIG. 2 is a block diagram showing a configuration of the constant voltage control.
  • FIG. 3 is a block diagram showing a configuration of the constant current control.
  • FIG. 4 is a block diagram showing a configuration for performing both constant voltage control and constant current control.
  • FIG. 5 is a connection diagram showing a configuration of constant voltage control.
  • FIG. 6 is a connection diagram showing a configuration of constant current control.
  • FIG. 7 is a waveform diagram showing the waveform of the drive signal of the LLC type switching power supply.
  • FIG. 8 is a waveform diagram showing a waveform of a drive signal in a burst mode of the LLC switching power supply.
  • FIG. 1 is a connection diagram of an LLC type switching power supply.
  • FIG. 2 is a block diagram showing a configuration of the constant voltage control.
  • FIG. 3 is a block diagram showing a configuration of the constant current control.
  • FIG. 4 is a block diagram showing a configuration for
  • FIG. 9 is a waveform diagram showing a relationship between the length of the OFF section and the magnitude of the ripple.
  • FIG. 10 is a waveform diagram showing the length of the OFF section.
  • FIG. 11 is a waveform diagram showing the relationship between the switching frequency and the magnitude of the ripple.
  • FIG. 12 is a timing chart showing the relationship between the load and the ON time ratio.
  • FIG. 13 is a timing chart showing the relationship between the load and the ON time ratio.
  • FIG. 14 is a timing chart for explaining a change in the ON time ratio when changing from the non-burst mode to the burst mode.
  • FIG. 15 is a timing chart used for explaining the burst mode according to the present technology.
  • FIG. 16 is a timing chart for explaining control when the ON time ratio is high.
  • FIG. 17 is a timing chart for explaining control when the ON time ratio is low.
  • FIG. 18 is a timing chart for explaining control when the ON time ratio is high.
  • FIG. 19 is a timing chart for explaining control when the ON time ratio is low.
  • FIG. 20 is a flowchart for explaining control in the normal mode.
  • FIG. 21 is a flowchart for explaining control in the case of the burst mode (the number of switching times n ⁇ 2).
  • FIG. 23 is a flowchart for explaining the control of the burst mode when a table is used.
  • FIG. 24 is a diagram illustrating an example of a table for controlling the burst mode.
  • FIG. 24 is a diagram illustrating an example of a table for controlling the burst mode.
  • FIG. 25 is a diagram illustrating an example of a table for controlling the burst mode.
  • FIG. 26 is a graph showing the relationship between the ON time ratio and the burst frequency.
  • FIG. 27 is a graph showing the relationship between the ON time ratio and the OFF time.
  • FIG. 28 is a graph showing the relationship between the ON time ratio and the number of ON times.
  • FIG. 29 is a timing chart for explaining soft start and soft end.
  • FIG. 30 is a timing chart for explaining soft start and soft end.
  • FIG. 31 is a timing chart used to explain control when soft start and soft end are not used.
  • FIG. 32 is a timing chart for explaining a modification of the burst mode according to the present technology.
  • FIG. 1 shows an exemplary configuration of an LLC switching power supply to which the present invention is applied.
  • the configuration of FIG. 1 clearly shows the parasitic elements.
  • Vin is an input power supply
  • Q1 is a high-side MOSFET
  • Q2 is a low-side MOSFET.
  • a diode D1 and a capacitor C1 exist in parallel as a parasitic element between the drain and the source of the MOSFET Q1.
  • a diode D2 and a capacitor C2 exist in parallel as a parasitic element between the drain and the source of the MOSFET Q2.
  • a drive signal is supplied from the control unit to the respective gates of the MOSFETs Q1 and Q2, and the MOSFETs Q1 and Q2 perform a switching operation.
  • the inductance L0, the primary coil L1 of the transformer TR, and the capacitance C3 are connected in series between the connection point between the source of the MOSFET Q1 and the drain of the MOSFET Q2 and the source of the MOSFET Q2.
  • the secondary coil of the transformer TR is divided into two inductances L2a and L2b, one end of the secondary coil is connected to the output terminal t1 via the diode D3a, and the other end of the secondary coil is connected to the output terminal t1 via the diode D3b.
  • Connected to The connection middle point of the secondary coil is taken out as the output terminal t2, and the capacitor C4 is connected between the output terminals t1 and t2.
  • An output voltage Vout is extracted from the output terminals t1 and t2.
  • the switching power supply of the LLC system normally outputs a constant voltage, and the output voltage is controlled to a constant value by feedback control.
  • This is generally called constant voltage control or CV control.
  • the configuration of the feedback is as shown in FIG.
  • the output voltage (or its divided value) and the reference voltage are input to the error amplifier 11, and a feedback signal (denoted as FB in the figure) is formed at the output of the error amplifier 11.
  • This feedback signal is supplied to the control unit 12.
  • a feedback signal is supplied to the control unit 12 through an insulating element 13 such as a photocoupler.
  • a drive signal output to the switching elements MOSFETs Q1 and Q2
  • the output voltage is controlled by the drive signal output.
  • the control method includes burst control, frequency control, dead time control, and the like.
  • the output current is usually converted into a voltage value by an IV conversion amplifier 24 and input to an error amplifier 21 as shown in FIG.
  • an error amplifier 21 a comparison is made with a reference voltage corresponding to the control current value.
  • the output of the error amplifier is supplied to the control unit 12.
  • negative feedback negative feedback
  • the output current is controlled to a constant value by feedback control. This is generally called constant current control or CC control.
  • the operation itself of the control unit 12 is the same as that of the control unit 12 in the constant voltage (CV) control.
  • constant current and constant voltage charging is performed, so that constant current (CC) control and constant voltage (CV) control are used in combination.
  • CC constant current
  • CV constant voltage
  • the output of the error amplifier 11 and the output of the error amplifier 21 are added via diodes 22 and 23 to form a feedback signal.
  • the control unit 12 is controlled by the feedback signal.
  • FIG. 5 shows a more specific configuration of an LLC switching power supply that performs constant voltage control.
  • the configuration in FIG. 5 clearly shows the parasitic element.
  • Vin is an input power supply
  • Q1 is a high-side MOSFET
  • Q2 is a low-side MOSFET.
  • a diode D1 and a capacitor C1 exist in parallel as a parasitic element between the drain and the source of the MOSFET Q1.
  • a diode D2 and a capacitor C2 exist in parallel as a parasitic element between the drain and the source of the MOSFET Q2.
  • the drive signals H-DRV and L-DRV are supplied to the respective gates of the MOSFETs Q1 and Q2, and the MOSFETs Q1 and Q2 perform a switching operation.
  • the inductance L0, the primary coil L1 of the transformer TR, and the capacitance C3 are connected in series between the connection point between the source of the MOSFET Q1 and the drain of the MOSFET Q2 and the source of the MOSFET Q2.
  • the secondary coil of the transformer TR is divided into two inductances L2a and L2b, one end of the secondary coil is connected to the output terminal t1 via the diode D3a, and the other end of the secondary coil is connected to the output terminal t1 via the diode D3b.
  • Connected to The connection middle point of the secondary coil is taken out as the output terminal t2, and the capacitor C4 is connected between the output terminals t1 and t2.
  • An output voltage for the load 10 (for example, a lithium ion secondary battery) is extracted from the output terminals t1 and t2.
  • drive signals H-DRV and L-DRV having opposite phases are supplied to the gates of the MOSFETs Q1 and Q2, and these MOSFETs Q1 and Q2 perform a switching operation differentially.
  • the output voltage is divided by the resistors R1 and R2, the divided voltage is input to the error amplifier 11, compared with the reference voltage, and negative feedback (negative feedback) is applied so that these values become equal.
  • the feedback signal from the error amplifier 11 is supplied to the control unit 12 through the photo coupler 13.
  • the output unit 15 is connected to the control unit 12, and the output unit 15 outputs drive signals H-DRV and L-DRV for the MOSFETs Q1 and Q2.
  • FIG. 6 shows a specific configuration of an LLC switching power supply that performs constant current control.
  • the configuration of the switching power supply is the same as in the case of constant voltage control.
  • the output current is detected by the detection resistor R0 and supplied to the error amplifier 21 via the current amplifier 16.
  • the error amplifier 21 compares the control current value with the control current value, and performs negative feedback (negative feedback) so that these values become equal.
  • a feedback signal from the error amplifier 21 is supplied to the control unit 12 through the photocoupler 13.
  • the output unit 15 is connected to the control unit 12, and the output unit 15 outputs drive signals H-DRV and L-DRV for the MOSFETs Q1 and Q2.
  • FIG. 7 shows drive signals H-DRV and L-DRV in an LLC switching power supply. These drive signals are pulses of opposite phases.
  • the MOSFET is turned on during the high level period of the drive signal.
  • One cycle of the drive signals H-DRV and L-DRV is called a switching cycle. Also, one switching cycle is defined as one switching.
  • the switching frequency is the reciprocal of the switching cycle. In the case of the LLC method, constant voltage control or constant current control is possible by changing the switching frequency by feedback control.
  • the burst mode is a mode having a switching ON section and a switching OFF section as shown in FIG.
  • the switching ON section and the switching OFF section are collectively called a burst period, and the reciprocal thereof is the burst frequency.
  • constant current control or constant voltage control is performed based on the time ratio between the switching ON section and the switching OFF section.
  • the ripple current can be reduced as the switching OFF section is shorter. Comparing the waveform of the upper drive signal and the waveform of the lower drive signal in FIG. 9, the lower waveform has a shorter OFF section. As a result, the output ripple current (or ripple voltage) can be smaller when the OFF section is shorter.
  • the switching OFF section has a required minimum OFF time. This is because there is a period in which a current flows through the body diodes (diodes D1 and D2) of the MOSFET even if the switching is turned off. This causes a through current to flow, which is not preferable.
  • the required minimum OFF time varies slightly depending on the exciting current of the circuit and the load condition, but as shown in FIG. 10, the switching time is about one switching cycle according to the result of the experiment.
  • the higher the switching frequency the shorter the switching OFF time.
  • the lower waveform has a higher switching frequency than the upper waveform in FIG. The higher the switching frequency, the shorter the switching OFF time, so that the output ripple current (output ripple voltage) can be reduced.
  • the OFF time has a required minimum OFF time to be ensured, which is about one switching cycle (see FIG. 10).
  • increasing the OFF time increases the ripple current. Therefore, in order to suppress the ripple current, it is better to shorten the OFF time as much as possible while securing the necessary OFF period. .
  • the ON time ratio during the burst is changed as continuously as possible in accordance with the load, a stable regulation characteristic cannot be obtained. Since the ON time at the time of the burst is a discrete value according to the number of switching times, if the burst frequency is fixed at a high frequency burst, the ON time ratio greatly varies due to the change of the number of times of the ON step. In addition, fine control of the ON time ratio due to load fluctuation cannot be performed, and stable operation cannot be obtained.
  • Example of a simple high-frequency burst (burst frequency fixed) (see FIG. 13)
  • OFF one cycle of switching (the ON time ratio in this case is 0.75)
  • ⁇ one step down when the load becomes lighter
  • OFF two cycles of switching (in this case, ON time ratio is 0.5)
  • the ON time ratio fluctuates greatly at the boundary where the burst operation starts from the non-burst operation, and the stable operation is performed under the load condition corresponding to this boundary. You can't do that.
  • Example of a simple high-frequency burst (burst frequency fixed) (see FIG. 14)
  • the ON time ratio jumps greatly when the burst enters with the minimum OFF time and when the burst operation is not performed, and stable operation is not performed under the load condition corresponding to this boundary.
  • burst control method using this technology In the present technology, in the burst control of the LLC system, the number of times of switching ON and the OFF time of the burst period are controlled so that the ON time ratio of the burst period can be continuously varied according to the load condition. By controlling the OFF time continuously (eg, in steps smaller than one switching cycle or steplessly) by this control method, the ON time ratio during the burst operation can be continuously changed, and the burst time can be changed. It is possible to optimally control the OFF time.
  • the burst mode according to the present technology will be described. It should be noted that “continuous” is expressed as continuous, including a variable in a relatively small step that does not greatly jump or a variable in a stepless manner.
  • the LLC method is a frequency control method.
  • the control is such that the switching frequency increases as the load becomes lighter.
  • An upper limit set value (fmax1) is provided for this switching frequency, and for a light load region beyond that, fixed at the upper limit switching frequency (fmax1), burst control is performed, and control is performed according to the ratio of switching ON time. .
  • FIG. 15 shows the burst control according to the present technology, and illustrates control from a heavy load to an extremely light load.
  • an upper limit value fmax1 of the switching frequency to be frequency-controlled is set. Up to the upper limit value fmax1, the switching frequency fsw is controlled according to the feedback value (expressed as FB value) indicating the weight of the load. That is, when the load is reduced, the switching frequency fsw is increased.
  • FB value feedback value
  • This control is in the range of non-burst control.
  • fmax1 is set to less than 150 kHz. This frequency is lower than the regulation band of the noise terminal voltage, and the cost of the AC filter can be reduced.
  • the switching frequency fsw is fixed at the upper limit set value fmax1, and the number of switching times and the OFF time are controlled by the FB value.
  • the number of ON times is reduced as the load becomes lighter.
  • the ON time ratio is adjusted by controlling the number of switching times and the OFF time by feedback. I do.
  • the number of ON times is reduced as the load becomes lighter.
  • ON time switching cycle ⁇ number of switching times. Note that the OFF time in FIGS. 16 and 17 indicates an optimal value of one switching cycle or more and less than two switching cycles.
  • the OFF time is controlled as shown in FIGS.
  • the OFF time is extended as the load becomes lighter.
  • the ON time ratio is close to 0.5, the number of times of switching is reduced. Note that the OFF time in FIG. 18 indicates an optimum value of one switching cycle or more and less than two switching cycles.
  • points when the number of switching times ⁇ 2 are as follows. Control is performed such that the higher the ON time ratio (closer to 1), the greater the number of times of switching during the burst period.
  • the control is performed such that the lower the ON time ratio (closer to 0.5), the smaller the number of switching operations during the burst period.
  • the ON time the switching cycle ⁇ the number of times of switching, and takes a discrete value.
  • the ON time becomes longer.
  • the ratio can be finely adjusted continuously.
  • the points when the number of times of switching is 1 are as follows.
  • the ON time ratio can be continuously finely adjusted.
  • Step S1 Determine whether the value (FB value) of the feedback signal is high.
  • a high FB value means that the output is insufficient.
  • Step S2 If it is determined that the FB value is high, it is determined whether the switching frequency is higher than a lower limit value.
  • Step S3 If it is determined in step S2 that the switching frequency is higher than the lower limit, the switching frequency is decreased. Then, the process returns to the determination processing of step S1.
  • Step S4 If it is determined in step S2 that the switching frequency is equal to or lower than the lower limit, the switching frequency is operated at the lower limit. Then, the process returns to the determination processing of step S1.
  • Step S5 If it is determined in step S1 that the FB value is not high, that is, the output is excessive, it is determined whether the switching frequency is less than the upper limit.
  • Step S6 If it is determined in step S5 that the switching frequency is not less than the upper limit, the mode is set to the burst mode.
  • Step S7 If it is determined in step S5 that the switching frequency is lower than the upper limit value, the switching frequency is increased, and the process returns to the determination processing in step S1.
  • Step S11 Determine whether the FB value is high.
  • a high FB value means that the output is insufficient.
  • Step S14 If it is determined in step S13 that the number of times of switching is not the upper limit value, the number of times of switching is increased. Then, the process returns to the determination processing of step S1.
  • Step S15 If it is determined in step S13 that the number of times of switching is the upper limit value, the process shifts to frequency control (continuous mode).
  • Step S16 If it is determined in step S12 that the OFF time is not at the lower limit, the OFF time is reduced to a value equal to or more than the lower limit. Then, the control returns to the FB value determination (step S11).
  • Step S17 If it is determined in the FB value determination in step S11 that the FB value is not high (excessive output), it is determined whether the OFF time is the upper limit value. That is, it is determined whether or not the OFF time is ( ⁇ (T ⁇ n) / (n ⁇ 1)).
  • T indicates a switching cycle
  • n indicates the number of times of switching in one burst cycle.
  • Step S18 If it is determined in step S17 that the OFF time is not the upper limit value, the OFF time is increased below the upper limit. Then, the control returns to the FB value determination (step S11).
  • Step S31 Determine whether the FB value is high.
  • a high FB value means that the output is insufficient.
  • Step S34 If it is determined in step S32 that the OFF time is at the lower limit, the number of switching times is set to 2 and control is shifted to (n ⁇ 2).
  • Step S35 If it is determined in step S31 that the FB value is not high (that is, the output is excessive), the OFF time is increased, and the process returns to the FB value determination process.
  • the switching frequency is fixed at the upper limit, and the OFF time is T or more.
  • T is a switching cycle.
  • a table of the number of switching times and the OFF time is prepared according to the ON time ratio, and the ON time ratio is set according to the FB value, as described later. Change.
  • Step S41 Determine whether the FB value is high.
  • a high FB value means that the output is insufficient.
  • Step S42 If it is determined that the FB value is high, it is determined whether the ON time ratio of the table is less than the upper limit.
  • Step S43 If the ON time ratio is determined to be less than the upper limit, the ON time ratio is increased. Then, the process returns to the determination processing of step S41.
  • Step S44 If it is determined in step S42 that the ON time ratio is not less than the upper limit, the mode shifts to the frequency control mode (continuous operation).
  • Step S45 If it is determined in step S41 that the FB value is not high, the ON time ratio is reduced.
  • FIGS. 24 and 25 show examples of variable ON time ratios, ON times, and OFF times of bursts in the form of tables. These two tables are a series of tables following the table of FIG. 24 to the table of FIG. 25, and assume that the load becomes lighter from the top to the bottom of the table. That is, the top row in FIG. 24 is the value when the load is the heaviest, and the bottom row in FIG. 25 is the value when the load is the lightest. As can be seen from the examples of FIGS. 24 and 25, the number of ONs is reduced as the load becomes lighter. By adjusting the OFF time in steps smaller than one switching cycle to some extent, or steplessly, the ON time ratio does not jump, and stable regulation characteristics can be realized. In addition, the OFF time is described in increments of 0.1 for convenience, but may not actually be in increments of 0.1 or may be stepless.
  • This table controls the number of times of switching and the OFF time during one burst period, and controls the OFF time in steps smaller than one switching period to change the ON time ratio during the burst period without jumping. It is a representation of what can be done.
  • the maximum value of the OFF time is determined. If the output becomes excessive unless the OFF time is made longer than this maximum value, it means that the number of switching times should be reduced by one.
  • the OFF time T is feedback controlled so that the OFF time X is as follows.
  • a logic circuit When such control is implemented in actual hardware, a logic circuit may be configured and hardware may be constructed from the above relational expression, or a table as described above may be created, The control may be performed based on the table.
  • FIG. 26 shows the relationship between the ON time ratio and the burst frequency when the above control is performed
  • FIG. 27 shows the relationship between the ON time ratio and the OFF time
  • FIG. 28 shows the relationship between the ON time ratio and the number of ON times.
  • burst control sound may actually occur, and a burst frequency of 20 kHz or more, which is higher than the audible band, or a low frequency that is hard to be heard is often selected.
  • the burst frequency fluctuates depending on the load condition, there are cases where the burst frequency falls within the audible band of 20 kHz or less.
  • the switching frequency starts to oscillate from a high place, and then gradually lowers the frequency. It is effective to use a so-called soft OFF (or soft end).
  • the following control is also effective from the viewpoint of minimizing ripple current. That is, in the case where the number of switching times is 1, and the soft start is not used, the following method is effective as a device for reducing the ripple current.
  • the upper limit switching frequency fmax2 is set higher than fmax1, and feedback control is performed between fmax1 and fmax2. 3.
  • the load reaches fmax2 and the output becomes unregulated (that is, excessive output) at a further light load, the fmax2 is fixed and the process shifts to the OFF time control.
  • An LLC type switching power supply A feedback value indicating a load condition is supplied, the control unit forming a drive signal for the switching element, The control unit is In the first region where the load is heavy, frequency control for changing the switching frequency by the feedback value is performed, In the second region where the load is lighter than in the first region, burst control is performed in which the switching frequency is fixed to provide a switching ON section and a switching OFF section, A switching power supply in which in the burst control, the ON time ratio is continuously varied according to load conditions by controlling both the number of times of switching and the OFF time.
  • Q1, Q2 MOSFET
  • TR Transformer
  • t1, t2 Output terminal, 11, 21 ... error amplifier, 12 ... control unit

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Abstract

Provided is an LLC-type switching power supply including a control unit to which feedback values for indicating load conditions are supplied, and which forms a drive signal for a switching element, wherein: the control unit performs a frequency control for varying a switching frequency by means of the feedback value in a first region in which the load is heavy, and performing a burst control for fixing the switching frequency and setting a switching ON period and a switching OFF period in a second region in which the load is lighter than that in the first region; and, in the burst control, both of the number of switching ON times and an OFF time are controlled during one burst period so that an ON time ratio consecutively varies according to the load conditions.

Description

スイッチング電源Switching power supply
　本技術は、ＬＬＣ方式のスイッチング電源に関する。 技術 This technology relates to an LLC type switching power supply.
　従来、２つのＬと一つのＣを使用するＬＬＣ方式のスイッチング電源（ＤＣ－ＤＣコンバータ）が知られている。かかるスイッチング電源は、ソフトスイッチング方式で、効率が良く、低ノイズという特長があり、広く使われている。一方で、他の方式に比較してレギュレーション範囲が狭いという特性があるため、出力電圧可変範囲が広い用途や、入力電圧変動が大きい用途には適さなかった。 Conventionally, an LLC type switching power supply (DC-DC converter) using two Ls and one C is known. Such a switching power supply is of a soft switching type, has characteristics of high efficiency and low noise, and is widely used. On the other hand, it has a characteristic that the regulation range is narrower than other methods, and therefore, it is not suitable for applications having a wide output voltage variable range or applications having a large input voltage fluctuation.
　二次電池を充電する充電器の場合、出力電圧変動範囲が広いので、従来、ＰＷＭ制御方式のスイッチング電源が使われてきた。最近では、大容量化（数百Ｗ以上）の要求が多くなってきており、従来のＰＷＭ制御方式のスイッチング電源を使用すると、効率が悪く、サイズ及びコストの面で不利である。そこで、ＬＬＣ方式のスイッチング電源によって充電器を実現することができれば、低コスト、高効率な充電器が実現することができる。しかしながら、上述したように、ＬＬＣ方式のスイッチング電源のレギュレーション範囲が狭いという特性から、充電器においては、軽負荷（低電圧かつ小電流）領域での挙動に課題があった。 (4) In the case of a charger for charging a secondary battery, a switching power supply of a PWM control method has been conventionally used because the output voltage fluctuation range is wide. Recently, demands for large capacity (several hundred W or more) have been increasing, and using a switching power supply of the conventional PWM control method is inefficient and disadvantageous in size and cost. Therefore, if a charger can be realized by an LLC type switching power supply, a low-cost, high-efficiency charger can be realized. However, as described above, the charger has a problem in behavior in a light load (low voltage and small current) region due to the characteristic that the regulation range of the LLC switching power supply is narrow.
　ＬＬＣ方式のスイッチング電源では、負荷が小さくなると、二次側で出力する電流に対する励磁電流の割合が大きくなり、効率が低下する。このため、電子機器のスタンバイ時の消費電力が大きくなるという問題が生じてくる。すなわち、二次側に伝えるエネルギーとなる電流の他に、共振により一次側だけを流れている励磁電流が流れる。この共振による励磁電流は、負荷で消費される電流に係わらず流れ続ける。したがって、軽負荷のときには、共振による励磁電流による効率の低下が相対的に大きくなる。 In the switching power supply of the LLC system, when the load is reduced, the ratio of the exciting current to the current output on the secondary side is increased, and the efficiency is reduced. For this reason, a problem arises in that the power consumption of the electronic device during standby increases. That is, in addition to the current serving as the energy transmitted to the secondary side, the exciting current flowing only on the primary side flows due to resonance. The exciting current due to this resonance continues to flow regardless of the current consumed by the load. Therefore, when the load is light, the reduction in efficiency due to the exciting current due to resonance becomes relatively large.
　特許文献１には、かかる問題を解決するために、発振器を連続的に動作させて電源制御を行う通常モードと、発振器を間欠的に動作させて電源制御を行うバーストモードとを設定することが記載されている。バーストモードが設定されると、二次側の出力電圧を検出することで、電源制御を間欠的に停止させているので、スタンバイ時の消費電力を低減することができる。 In order to solve such a problem, Patent Literature 1 discloses setting a normal mode in which the power supply is controlled by operating the oscillator continuously and a burst mode in which the power supply is controlled by operating the oscillator intermittently. Has been described. When the burst mode is set, the power supply control is intermittently stopped by detecting the output voltage on the secondary side, so that power consumption during standby can be reduced.
　また、特許文献２では、スイッチング電源の消費電力をより一層低減することが記載されている。特許文献２では、スイッチング停止期間では、スイッチ素子のスイッチング制御が不要であることに着目し、制御手段への制御電力の供給を停止して消費電力の低減を図るようにしている。 Patent Document 2 discloses that the power consumption of a switching power supply is further reduced. In Patent Document 2, attention is paid to the fact that switching control of the switch element is not required during the switching stop period, and the supply of control power to the control means is stopped to reduce power consumption.
特開２００９－１８９１０８号公報JP 2009-189108 A 特開２０１３－０３８８５７号公報JP 2013-038857 A
　特許文献１又は特許文献２に記載のように、軽負荷時にバーストモード（間欠発振モード）を使うことで、ＬＬＣ方式のスイッチング電源の軽負荷領域のレギュレーション範囲を広げることは可能である。特許文献１又は特許文献２に記載のものは、待機時の消費電力を抑えるためのバースト制御技術であり、通常、数十Ｈｚ～数百Ｈｚ程度のバースト周波数が使われる。 (4) As described in Patent Document 1 or Patent Document 2, it is possible to widen the regulation range of the light load region of the LLC type switching power supply by using the burst mode (intermittent oscillation mode) at light load. The technology described in Patent Literature 1 or Patent Literature 2 is a burst control technique for suppressing power consumption during standby, and a burst frequency of several tens Hz to several hundreds Hz is generally used.
　しかしながら、数十Ｈｚ～数百Ｈｚという低いバースト周波数の場合、スイッチングが停止している時間が長くなるため、出力のリップル電流、またはリップル電圧が大きくなる。充電器の場合、軽負荷時にも、充電するリップル電流を抑えたいという要求があり、低いバースト周波数では、リップル電流が大きいため、バッテリーの要求仕様を満たせない場合がある。バースト周波数を数十ｋＨｚと高くすれば、リップル電流は小さくできるが、単純に高いバースト周波数にしただけでは、バースト期間中のＯＮ時間比率の微調整が困難になり、安定して動かすのが難しくなるという問題がある。 However, in the case of a low burst frequency of several tens of Hz to several hundreds of Hz, the time during which switching is stopped is long, so that the ripple current or ripple voltage of the output increases. In the case of a charger, there is a demand to suppress the ripple current to be charged even at a light load, and the required current of the battery may not be satisfied at a low burst frequency because the ripple current is large. If the burst frequency is increased to several tens of kHz, the ripple current can be reduced, but if the burst frequency is simply increased, fine adjustment of the ON time ratio during the burst period becomes difficult, and it is difficult to operate stably. Problem.
　したがって、本技術の目的は、バースト動作時のリップル電流（またはリップル電圧）を低減できるスイッチング電源を提供することにある。 Therefore, an object of the present technology is to provide a switching power supply that can reduce a ripple current (or a ripple voltage) during a burst operation.
　本技術は、ＬＬＣ方式のスイッチング電源であって、
　負荷条件を示すフィードバック値が供給され、スイッチング素子に対するドライブ信号を形成する制御部を有し、
　制御部は、
　負荷が重い第１の領域において、フィードバック値によってスイッチング周波数を可変する周波数制御を行い、
　第１の領域に比して負荷が軽い第２の領域において、スイッチング周波数を固定してスイッチングＯＮ区間とスイッチングＯＦＦ区間を設けるバースト制御を行い、
　バースト制御において、スイッチングＯＮ回数とＯＦＦ時間の両方を制御することによって、ＯＮ時間比率を負荷条件によって連続的に可変するようにしたスイッチング電源である。 The present technology is an LLC type switching power supply,
A feedback value indicating a load condition is supplied, the control unit forming a drive signal for the switching element,
The control unit is
In the first region where the load is heavy, frequency control for changing the switching frequency by the feedback value is performed,
In the second region where the load is lighter than in the first region, burst control is performed in which the switching frequency is fixed to provide a switching ON section and a switching OFF section,
In the burst control, the switching power supply is configured such that the ON time ratio is continuously varied according to load conditions by controlling both the number of times of switching and the OFF time.
　少なくとも一つの実施形態によれば、バースト期間のＯＮ時間比率を、連続的に変化させることができ、且つ、バースト時の必要最小ＯＦＦ時間を確保しながら、常にＯＦＦ時間を最小制御することも可能となり、バースト動作時のリップル電流（またはリップル電圧）を最小にすることができる。なお、ここに記載された効果は必ずしも限定されるものではなく、本技術中に記載されたいずれかの効果又はそれらと異質な効果であっても良い。 According to at least one embodiment, the ON time ratio of the burst period can be continuously changed, and the minimum OFF time can be always controlled while the required minimum OFF time during the burst is secured. Thus, the ripple current (or ripple voltage) during the burst operation can be minimized. Note that the effects described here are not necessarily limited, and may be any of the effects described in the present technology or an effect different from them.
図１は、ＬＬＣ方式のスイッチング電源の接続図である。FIG. 1 is a connection diagram of an LLC type switching power supply. 図２は、定電圧制御の構成を示すブロック図である。FIG. 2 is a block diagram showing a configuration of the constant voltage control. 図３は、定電流制御の構成を示すブロック図である。FIG. 3 is a block diagram showing a configuration of the constant current control. 図４は、定電圧制御及び定電流制御の両方を行う構成を示すブロック図である。FIG. 4 is a block diagram showing a configuration for performing both constant voltage control and constant current control. 図５は、定電圧制御の構成を示す接続図である。FIG. 5 is a connection diagram showing a configuration of constant voltage control. 図６は、定電流制御の構成を示す接続図である。FIG. 6 is a connection diagram showing a configuration of constant current control. 図７は、ＬＬＣ方式のスイッチング電源のドライブ信号の波形を示す波形図である。FIG. 7 is a waveform diagram showing the waveform of the drive signal of the LLC type switching power supply. 図８は、ＬＬＣ方式のスイッチング電源のバーストモードにおけるドライブ信号の波形を示す波形図である。FIG. 8 is a waveform diagram showing a waveform of a drive signal in a burst mode of the LLC switching power supply. 図９は、ＯＦＦ区間の長さとリップルの大きさの関係を示す波形図である。FIG. 9 is a waveform diagram showing a relationship between the length of the OFF section and the magnitude of the ripple. 図１０は、ＯＦＦ区間の長さを示す波形図である。FIG. 10 is a waveform diagram showing the length of the OFF section. 図１１は、スイッチング周波数とリップルの大きさの関係を示す波形図である。FIG. 11 is a waveform diagram showing the relationship between the switching frequency and the magnitude of the ripple. 図１２は、負荷とＯＮ時間比率の関係を示すタイミングチャートである。FIG. 12 is a timing chart showing the relationship between the load and the ON time ratio. 図１３は、負荷とＯＮ時間比率の関係を示すタイミングチャートである。FIG. 13 is a timing chart showing the relationship between the load and the ON time ratio. 図１４は、非バーストモードからバーストモードへ変化する場合のＯＮ時間比率の変化を説明するためのタイミングチャートである。FIG. 14 is a timing chart for explaining a change in the ON time ratio when changing from the non-burst mode to the burst mode. 図１５は、本技術によるバーストモードの説明に用いるタイミングチャートである。FIG. 15 is a timing chart used for explaining the burst mode according to the present technology. 図１６は、ＯＮ時間比率が高いときの制御を説明するためのタイミングチャートである。FIG. 16 is a timing chart for explaining control when the ON time ratio is high. 図１７は、ＯＮ時間比率が低いときの制御を説明するためのタイミングチャートである。FIG. 17 is a timing chart for explaining control when the ON time ratio is low. 図１８は、ＯＮ時間比率が高いときの制御を説明するためのタイミングチャートである。FIG. 18 is a timing chart for explaining control when the ON time ratio is high. 図１９は、ＯＮ時間比率が低いときの制御を説明するためのタイミングチャートである。FIG. 19 is a timing chart for explaining control when the ON time ratio is low. 図２０は、通常モードの制御を説明するためのフローチャートである。FIG. 20 is a flowchart for explaining control in the normal mode. 図２１は、バーストモード（スイッチング回数ｎ≧２）の場合の制御を説明するためのフローチャートである。FIG. 21 is a flowchart for explaining control in the case of the burst mode (the number of switching times n ≧ 2). 図２２は、バーストモード（スイッチング回数ｎ＝１）の場合の制御を説明するためのフローチャートである。FIG. 22 is a flowchart for explaining control in the case of the burst mode (the number of switching times n = 1). 図２３は、テーブルを用いる場合のバーストモードの制御を説明するためのフローチャートである。FIG. 23 is a flowchart for explaining the control of the burst mode when a table is used. 図２４は、バーストモードの制御のためのテーブルの一例を示す図である。FIG. 24 is a diagram illustrating an example of a table for controlling the burst mode. 図２５は、バーストモードの制御のためのテーブルの一例を示す図である。FIG. 25 is a diagram illustrating an example of a table for controlling the burst mode. 図２６は、ＯＮ時間比率とバースト周波数の関係を示すグラフである。FIG. 26 is a graph showing the relationship between the ON time ratio and the burst frequency. 図２７は、ＯＮ時間比率とＯＦＦ時間の関係を示すグラフである。FIG. 27 is a graph showing the relationship between the ON time ratio and the OFF time. 図２８は、ＯＮ時間比率とＯＮ回数の関係を示すグラフである。FIG. 28 is a graph showing the relationship between the ON time ratio and the number of ON times. 図２９は、ソフトスタート及びソフトエンドを説明するためのタイミングチャートである。FIG. 29 is a timing chart for explaining soft start and soft end. 図３０は、ソフトスタート及びソフトエンドを説明するためのタイミングチャートである。FIG. 30 is a timing chart for explaining soft start and soft end. 図３１は、ソフトスタート及びソフトエンドを使用しない場合の制御の説明に使用するタイミングチャートである。FIG. 31 is a timing chart used to explain control when soft start and soft end are not used. 図３２は、本技術によるバーストモードの変形例を説明するためのタイミングチャートである。FIG. 32 is a timing chart for explaining a modification of the burst mode according to the present technology.
　以下、本技術の実施形態等について図面を参照しながら説明する。
　以下に説明する実施の形態等は本技術の好適な具体例であり、本技術の内容がこれらの実施形態等に限定されるものではない。 Hereinafter, embodiments of the present technology will be described with reference to the drawings.
The embodiments and the like described below are preferred specific examples of the present technology, and the contents of the present technology are not limited to these embodiments and the like.
　図１は、本発明が適用されるＬＬＣ方式のスイッチング電源の一例の構成を示す。図１の構成は、寄生素子を明記したものである。Ｖｉｎが入力電源であり、Ｑ１がハイサイド側のＭＯＳＦＥＴであり、Ｑ２がローサイド側のＭＯＳＦＥＴである。ＭＯＳＦＥＴＱ１のドレイン及びソース間に寄生素子としてダイオードＤ１及び容量Ｃ１が並列に存在する。ＭＯＳＦＥＴＱ２のドレイン及びソース間に寄生素子としてダイオードＤ２及び容量Ｃ２が並列に存在する。ＭＯＳＦＥＴＱ１及びＭＯＳＦＥＴＱ２のそれぞれのゲートに対して制御部からドライブ信号が供給され、ＭＯＳＦＥＴＱ１及びＭＯＳＦＥＴＱ２がスイッチング動作を行う。 FIG. 1 shows an exemplary configuration of an LLC switching power supply to which the present invention is applied. The configuration of FIG. 1 clearly shows the parasitic elements. Vin is an input power supply, Q1 is a high-side MOSFET, and Q2 is a low-side MOSFET. A diode D1 and a capacitor C1 exist in parallel as a parasitic element between the drain and the source of the MOSFET Q1. A diode D2 and a capacitor C2 exist in parallel as a parasitic element between the drain and the source of the MOSFET Q2. A drive signal is supplied from the control unit to the respective gates of the MOSFETs Q1 and Q2, and the MOSFETs Q1 and Q2 perform a switching operation.
　ＭＯＳＦＥＴＱ１のソース及びＭＯＳＦＥＴＱ２のドレインの接続点とＭＯＳＦＥＴＱ２のソースの間にインダクタンスＬ０、トランスＴＲの１次コイルＬ１及び容量Ｃ３が直列に接続される。トランスＴＲの二次コイルが二つのインダクタンスＬ２ａ及びＬ２ｂに分割され、二次コイルの一端がダイオードＤ３ａを介して出力端子ｔ１と接続され、二次コイルの他端がダイオードＤ３ｂを介して出力端子ｔ１と接続される。二次コイルの接続中点が出力端子ｔ２として取り出され、出力端子ｔ１及びｔ２間に容量Ｃ４が接続される。出力端子ｔ１及びｔ２から出力電圧Ｖｏｕｔが取り出される。 (4) The inductance L0, the primary coil L1 of the transformer TR, and the capacitance C3 are connected in series between the connection point between the source of the MOSFET Q1 and the drain of the MOSFET Q2 and the source of the MOSFET Q2. The secondary coil of the transformer TR is divided into two inductances L2a and L2b, one end of the secondary coil is connected to the output terminal t1 via the diode D3a, and the other end of the secondary coil is connected to the output terminal t1 via the diode D3b. Connected to The connection middle point of the secondary coil is taken out as the output terminal t2, and the capacitor C4 is connected between the output terminals t1 and t2. An output voltage Vout is extracted from the output terminals t1 and t2.
　上述したＬＬＣ方式のスイッチング電源では、ＭＯＳＦＥＴＱ１とＭＯＳＦＥＴＱ２のゲートに対して逆位相のドライブ信号が供給され、これらのＭＯＳＦＥＴＱ１とＱ２が差動でスイッチング動作を行う。 (4) In the LLC switching power supply described above, drive signals having opposite phases are supplied to the gates of the MOSFETs Q1 and Q2, and the MOSFETs Q1 and Q2 perform switching operations in a differential manner.
　ＬＬＣ方式のスイッチング電源は、通常、定電圧出力し、出力電圧はフィードバック制御によって一定値に制御するようになされる。これを一般的に定電圧制御、又はＣＶ制御と呼ぶ。フィードバックの構成は、図２に示すものとなる。出力電圧（又はその分圧値）と基準電圧がエラーアンプ１１に入力され、エラーアンプ１１の出力にフィードバック（図ではＦＢと表記する）信号が形成される。このフィードバック信号が制御部１２に供給される。出力と制御部１２が絶縁されている場合は、フィードバック信号がフォトカプラなどの絶縁素子１３を通じて制御部１２に供給される。制御部１２からスイッチング素子（ＭＯＳＦＥＴＱ１及びＱ２）に対するドライブ信号出力が得られる。出力電圧がドライブ信号出力によって制御される。エラーアンプでは、二つの入力（出力電圧またはその分圧値と基準電圧）が等しい値になるように負帰還（ネガティブフィードバック）がかけられるので、その結果として、出力電圧を一定に制御することができる。制御方式としては、バースト制御、周波数制御、デッドタイムコントロールなどがある。 The switching power supply of the LLC system normally outputs a constant voltage, and the output voltage is controlled to a constant value by feedback control. This is generally called constant voltage control or CV control. The configuration of the feedback is as shown in FIG. The output voltage (or its divided value) and the reference voltage are input to the error amplifier 11, and a feedback signal (denoted as FB in the figure) is formed at the output of the error amplifier 11. This feedback signal is supplied to the control unit 12. When the output and the control unit 12 are insulated, a feedback signal is supplied to the control unit 12 through an insulating element 13 such as a photocoupler. A drive signal output to the switching elements (MOSFETs Q1 and Q2) is obtained from the control unit 12. The output voltage is controlled by the drive signal output. In the error amplifier, negative feedback (negative feedback) is applied so that two inputs (the output voltage or its divided value and the reference voltage) become equal. As a result, the output voltage can be controlled to be constant. it can. The control method includes burst control, frequency control, dead time control, and the like.
　ＬＬＣ方式のスイッチング電源を充電器に使用する場合、図３に示すように、通常は、出力電流をＩ－Ｖ変換増幅器２４によって電圧値へ変換してエラーアンプ２１に入力する。エラーアンプ２１では、制御電流値に対応する基準電圧と比較される。制御部１２にエラーアンプの出力が供給される。エラーアンプは、二つ入力が等しくなるように負帰還（ネガティブフィードバック）がかけられるので、出力電流は、フィードバック制御によって一定値に制御される。これを一般的に定電流制御、又はＣＣ制御と呼ぶ。制御部１２の動作自体は、定電圧（ＣＶ）制御における制御部１２と同様である。 When an LLC type switching power supply is used for a charger, the output current is usually converted into a voltage value by an IV conversion amplifier 24 and input to an error amplifier 21 as shown in FIG. In the error amplifier 21, a comparison is made with a reference voltage corresponding to the control current value. The output of the error amplifier is supplied to the control unit 12. In the error amplifier, negative feedback (negative feedback) is applied so that two inputs are equal. Therefore, the output current is controlled to a constant value by feedback control. This is generally called constant current control or CC control. The operation itself of the control unit 12 is the same as that of the control unit 12 in the constant voltage (CV) control.
　例えばリチウムイオン二次電池の場合は、定電流定電圧充電を行うので、定電流（ＣＣ）制御と定電圧（ＣＶ）制御を組み合わせて使うようになされる。図４に示すように、エラーアンプ１１の出力と、エラーアンプ２１の出力がダイオード２２及び２３を介して加算されてフィードバック信号が形成される。このフィードバック信号によって制御部１２が制御される。 For example, in the case of a lithium ion secondary battery, constant current and constant voltage charging is performed, so that constant current (CC) control and constant voltage (CV) control are used in combination. As shown in FIG. 4, the output of the error amplifier 11 and the output of the error amplifier 21 are added via diodes 22 and 23 to form a feedback signal. The control unit 12 is controlled by the feedback signal.
　図５は、定電圧制御を行うＬＬＣ方式のスイッチング電源のより具体的構成を示す。図５の構成は、寄生素子を明記したものである。Ｖｉｎが入力電源であり、Ｑ１がハイサイド側のＭＯＳＦＥＴであり、Ｑ２がローサイド側のＭＯＳＦＥＴである。ＭＯＳＦＥＴＱ１のドレイン及びソース間に寄生素子としてダイオードＤ１及び容量Ｃ１が並列に存在する。ＭＯＳＦＥＴＱ２のドレイン及びソース間に寄生素子としてダイオードＤ２及び容量Ｃ２が並列に存在する。ＭＯＳＦＥＴＱ１及びＭＯＳＦＥＴＱ２のそれぞれのゲートに対してドライブ信号Ｈ－ＤＲＶ及びＬ－ＤＲＶが供給され、ＭＯＳＦＥＴＱ１及びＭＯＳＦＥＴＱ２がスイッチング動作を行う。 FIG. 5 shows a more specific configuration of an LLC switching power supply that performs constant voltage control. The configuration in FIG. 5 clearly shows the parasitic element. Vin is an input power supply, Q1 is a high-side MOSFET, and Q2 is a low-side MOSFET. A diode D1 and a capacitor C1 exist in parallel as a parasitic element between the drain and the source of the MOSFET Q1. A diode D2 and a capacitor C2 exist in parallel as a parasitic element between the drain and the source of the MOSFET Q2. The drive signals H-DRV and L-DRV are supplied to the respective gates of the MOSFETs Q1 and Q2, and the MOSFETs Q1 and Q2 perform a switching operation.
　ＭＯＳＦＥＴＱ１のソース及びＭＯＳＦＥＴＱ２のドレインの接続点とＭＯＳＦＥＴＱ２のソースの間にインダクタンスＬ０、トランスＴＲの１次コイルＬ１及び容量Ｃ３が直列に接続される。トランスＴＲの二次コイルが二つのインダクタンスＬ２ａ及びＬ２ｂに分割され、二次コイルの一端がダイオードＤ３ａを介して出力端子ｔ１と接続され、二次コイルの他端がダイオードＤ３ｂを介して出力端子ｔ１と接続される。二次コイルの接続中点が出力端子ｔ２として取り出され、出力端子ｔ１及びｔ２間に容量Ｃ４が接続される。出力端子ｔ１及びｔ２から負荷１０（例えばリチウムイオン二次電池）に対する出力電圧が取り出される。上述したＬＬＣ方式のスイッチング電源では、ＭＯＳＦＥＴＱ１とＭＯＳＦＥＴＱ２のゲートに対して逆位相のドライブ信号Ｈ－ＤＲＶ及びＬ－ＤＲＶが供給され、これらのＭＯＳＦＥＴＱ１とＱ２が差動でスイッチング動作を行う。 (4) The inductance L0, the primary coil L1 of the transformer TR, and the capacitance C3 are connected in series between the connection point between the source of the MOSFET Q1 and the drain of the MOSFET Q2 and the source of the MOSFET Q2. The secondary coil of the transformer TR is divided into two inductances L2a and L2b, one end of the secondary coil is connected to the output terminal t1 via the diode D3a, and the other end of the secondary coil is connected to the output terminal t1 via the diode D3b. Connected to The connection middle point of the secondary coil is taken out as the output terminal t2, and the capacitor C4 is connected between the output terminals t1 and t2. An output voltage for the load 10 (for example, a lithium ion secondary battery) is extracted from the output terminals t1 and t2. In the switching power supply of the LLC system described above, drive signals H-DRV and L-DRV having opposite phases are supplied to the gates of the MOSFETs Q1 and Q2, and these MOSFETs Q1 and Q2 perform a switching operation differentially.
　出力電圧が抵抗Ｒ１及びＲ２によって分圧され、分圧電圧がエラーアンプ１１に入力され、基準電圧と比較され、これらが等しい値になるよう負帰還（ネガティブフィードバック）がかけられる。エラーアンプ１１からのフィードバック信号がフォトカプラ１３を通じて制御部１２に供給される。制御部１２に対して出力部１５が接続されており、出力部１５からＭＯＳＦＥＴＱ１及びＱ２に対するドライブ信号Ｈ－ＤＲＶ及びＬ－ＤＲＶが出力される。 (4) The output voltage is divided by the resistors R1 and R2, the divided voltage is input to the error amplifier 11, compared with the reference voltage, and negative feedback (negative feedback) is applied so that these values become equal. The feedback signal from the error amplifier 11 is supplied to the control unit 12 through the photo coupler 13. The output unit 15 is connected to the control unit 12, and the output unit 15 outputs drive signals H-DRV and L-DRV for the MOSFETs Q1 and Q2.
　定電流制御を行うＬＬＣ方式のスイッチング電源の具体的構成を図６に示す。スイッチング電源の構成は、定電圧制御の場合と同様である。出力電流が検出抵抗Ｒ０によって検出され、電流アンプ１６を介してエラーアンプ２１に供給される。エラーアンプ２１にて制御電流値と比較され、これらが等しい値になるよう負帰還（ネガティブフィードバック）がかけられる。エラーアンプ２１からのフィードバック信号がフォトカプラ１３を通じて制御部１２に供給される。制御部１２に対して出力部１５が接続されており、出力部１５からＭＯＳＦＥＴＱ１及びＱ２に対するドライブ信号Ｈ－ＤＲＶ及びＬ－ＤＲＶが出力される。 FIG. 6 shows a specific configuration of an LLC switching power supply that performs constant current control. The configuration of the switching power supply is the same as in the case of constant voltage control. The output current is detected by the detection resistor R0 and supplied to the error amplifier 21 via the current amplifier 16. The error amplifier 21 compares the control current value with the control current value, and performs negative feedback (negative feedback) so that these values become equal. A feedback signal from the error amplifier 21 is supplied to the control unit 12 through the photocoupler 13. The output unit 15 is connected to the control unit 12, and the output unit 15 outputs drive signals H-DRV and L-DRV for the MOSFETs Q1 and Q2.
「ＬＬＣ方式のスイッチング電源におけるドライブ信号」
　ＬＬＣ方式のスイッチング電源において、ドライブ信号Ｈ－ＤＲＶおよびＬ－ＤＲＶを図７に示す。これらのドライブ信号は、逆位相のパルスである。ドライブ信号のハイレベル期間でＭＯＳＦＥＴがＯＮする。ドライブ信号Ｈ－ＤＲＶおよびＬ－ＤＲＶの１周期をスイッチング周期と称する。また、スイッチング周期の１周期をスイッチング回数の１回とする。スイッチング周期の逆数がスイッチング周波数であり、ＬＬＣ方式の場合は、フィードバック制御によってスイッチング周波数を変えることで、定電圧制御又は定電流制御が可能である。 "Drive signal in LLC switching power supply"
FIG. 7 shows drive signals H-DRV and L-DRV in an LLC switching power supply. These drive signals are pulses of opposite phases. The MOSFET is turned on during the high level period of the drive signal. One cycle of the drive signals H-DRV and L-DRV is called a switching cycle. Also, one switching cycle is defined as one switching. The switching frequency is the reciprocal of the switching cycle. In the case of the LLC method, constant voltage control or constant current control is possible by changing the switching frequency by feedback control.
　バーストモード（間欠発振モード）とは、図８に示すように、スイッチングＯＮ区間とスイッチングＯＦＦの区間があるモードである。スイッチングＯＮ区間とスイッチングＯＦＦ区間を合わせてバースト周期と呼び、その逆数がバースト周波数となる。バーストモードにおいては、スイッチングＯＮ区間とスイッチングＯＦＦ区間の時間比率でもって定電流制御又は定電圧制御を行う。 The burst mode (intermittent oscillation mode) is a mode having a switching ON section and a switching OFF section as shown in FIG. The switching ON section and the switching OFF section are collectively called a burst period, and the reciprocal thereof is the burst frequency. In the burst mode, constant current control or constant voltage control is performed based on the time ratio between the switching ON section and the switching OFF section.
　リップル電流（リップル電圧）は、スイッチングＯＦＦの区間が短いほど小さくすることができる。図９の上側のドライブ信号による波形と下側のドライブ信号による波形を比較すると、下側の波形の方がＯＦＦ区間が短い。その結果、出力リップル電流（又はリップル電圧）がＯＦＦ区間が短い方が小とすることができる。 The ripple current (ripple voltage) can be reduced as the switching OFF section is shorter. Comparing the waveform of the upper drive signal and the waveform of the lower drive signal in FIG. 9, the lower waveform has a shorter OFF section. As a result, the output ripple current (or ripple voltage) can be smaller when the OFF section is shorter.
　リップル電流（又はリップル電圧）を最小にするという観点では、スイッチングＯＦＦの区間が短いほど良い。しかしながら、ＬＬＣ方式では、スイッチングＯＦＦ区間は、必要最低ＯＦＦ時間がある。これは、スイッチングＯＦＦしても、ＭＯＳＦＥＴのボディダイオード（ダイオードＤ１及びＤ２）を通って電流が流れる期間があるためで、この期間にスイッチングを開始すると、ボディダイオードの逆回復期間中に、ハーフブリッジに貫通電流が流れることになり、好ましくない。必要最低ＯＦＦ時間は、回路の励磁電流や負荷条件によって多少の違いがあるが、図１０に示すように、実験の結果より、およそ１スイッチング周期となる。 From the viewpoint of minimizing the ripple current (or ripple voltage), the shorter the switching OFF section, the better. However, in the LLC method, the switching OFF section has a required minimum OFF time. This is because there is a period in which a current flows through the body diodes (diodes D1 and D2) of the MOSFET even if the switching is turned off. This causes a through current to flow, which is not preferable. The required minimum OFF time varies slightly depending on the exciting current of the circuit and the load condition, but as shown in FIG. 10, the switching time is about one switching cycle according to the result of the experiment.
　さらに、同じスイッチング回数１回の場合、スイッチング周波数が高い方がスイッチングＯＦＦ時間は短くできる。図１１の上側の波形に対して下側の波形の方がスイッチング周波数が高い。スイッチング周波数が高い方がスイッチングＯＦＦ時間を短くできるので、出力リップル電流（出力リップル電圧）を小さいものとできる。 Furthermore, in the case of the same number of times of switching, the higher the switching frequency, the shorter the switching OFF time. The lower waveform has a higher switching frequency than the upper waveform in FIG. The higher the switching frequency, the shorter the switching OFF time, so that the output ripple current (output ripple voltage) can be reduced.
「既存のバースト制御の方法」
　かかるＬＬＣ方式のスイッチング電源における既存のバースト制御の方法について図１２を参照して説明する。バーストの基本的な制御方法は、バースト時のスイッチングＯＮ時間比率を調整して制御する。負荷が軽くなると、スイッチングＯＮ時間の比率を低くする。ＬＬＣ方式のスイッチング電源の場合では、１回のスイッチングで、「ハイサイドのＭＯＳＦＥＴＱ１のＯＮ、ローサイドのＭＯＳＦＥＴＱ２のＯＦＦ」→「ハイサイドのＭＯＳＦＥＴＱ１のＯＦＦ、ローサイドのＭＯＳＦＥＴＱ２のＯＮ」となる。ＯＮ時間は、そのスイッチング回数で調整するため、スイッチング回数によって、ＯＮ時間は、「スイッチング周期×ＯＮ回数」となり、離散的な値を取る（図７参照）。 "Existing Burst Control Methods"
An existing burst control method in the LLC type switching power supply will be described with reference to FIG. The basic control method of the burst is controlled by adjusting the switching ON time ratio at the time of the burst. When the load is reduced, the ratio of the switching ON time is reduced. In the case of the LLC switching power supply, one switching operation changes “the high-side MOSFET Q1 is turned on, the low-side MOSFET Q2 is turned off” → “the high-side MOSFET Q1 is turned off, and the low-side MOSFET Q2 is turned on”. Since the ON time is adjusted by the number of times of switching, the ON time becomes “switching cycle × number of times of ON” and takes a discrete value according to the number of times of switching (see FIG. 7).
　一方、ＯＦＦ時間は、確保すべき必要な最小ＯＦＦ時間があり、それは、およそスイッチング１周期分である（図１０参照）。図９を参照して説明したように、ＯＦＦ時間を長くすると、リップル電流が大きくなるので、リップル電流を抑えるためには、必要なＯＦＦ期間を確保しながら、できるだけＯＦＦ時間を短くした方がよい。 On the other hand, the OFF time has a required minimum OFF time to be ensured, which is about one switching cycle (see FIG. 10). As described with reference to FIG. 9, increasing the OFF time increases the ripple current. Therefore, in order to suppress the ripple current, it is better to shorten the OFF time as much as possible while securing the necessary OFF period. .
　また、バースト時のＯＮ時間比率は、負荷に応じて、できるだけ連続的に変化させないと、安定的なレギュレーション特性を得られない。バースト時のＯＮ時間は、スイッチング回数に応じて離散的な値となるので、もし、高周波バーストで、バースト周波数固定とした場合は、ＯＮ回数の１ステップの変化で、ＯＮ時間比率が大きく変動し、負荷変動による、細かいＯＮ時間比率の制御ができず、安定動作を得られない。 Further, unless the ON time ratio during the burst is changed as continuously as possible in accordance with the load, a stable regulation characteristic cannot be obtained. Since the ON time at the time of the burst is a discrete value according to the number of switching times, if the burst frequency is fixed at a high frequency burst, the ON time ratio greatly varies due to the change of the number of times of the ON step. In addition, fine control of the ON time ratio due to load fluctuation cannot be performed, and stable operation cannot be obtained.
　仮に、単純な高周波バースト（バースト周波数固定）とした場合の例（図１３参照）
　例えば、スイッチング回数３回、ＯＦＦ＝スイッチング１周期（この場合のＯＮ時間比率が０．７５）→（負荷が軽くなると、１ステップダウン）→スイッチング回数２回、ＯＦＦ＝スイッチング２周期（この場合のＯＮ時間比率が０．５）
　高周波バーストで、バースト周波数を固定とすると、１ステップの調整で、ＯＮ時間が大きく変化してしまい、安定動作せず、リップルが大きくなってしまう問題が発生する。 Example of a simple high-frequency burst (burst frequency fixed) (see FIG. 13)
For example, three times of switching, OFF = one cycle of switching (the ON time ratio in this case is 0.75) → (one step down when the load becomes lighter) → two times of switching, OFF = two cycles of switching (in this case, ON time ratio is 0.5)
If the burst frequency is fixed in the high-frequency burst, the ON time greatly changes by one-step adjustment, causing a problem that the operation is not stable and the ripple becomes large.
　また、もし、高周波バーストで、バースト周波数固定とした場合は、非バースト動作から、バースト動作に入る境界のところで、ＯＮ時間比率が大きく変動し、この境界に相当する負荷条件の時に、安定動作をすることができなくなる。 If the burst frequency is fixed at a high frequency burst, the ON time ratio fluctuates greatly at the boundary where the burst operation starts from the non-burst operation, and the stable operation is performed under the load condition corresponding to this boundary. You can't do that.
　仮に、単純な高周波バースト（バースト周波数固定）とした場合の例（図１４参照）
　例えば、バースト周期＝スイッチング周期の４倍の場合（非バースト動作の場合のＯＮ時間比率が１．０）→（負荷が軽くなると）→スイッチング回数３回、ＯＦＦ＝スイッチング１周期（この場合のＯＮ時間比率が０．７５）
　高周波バーストで、バースト周波数固定の場合は、最小ＯＦＦ時間でバーストに入った状態と、非バースト動作の時のＯＮ時間比率の飛躍が大きく、この境界に相当する負荷条件の時に安定動作しない。 Example of a simple high-frequency burst (burst frequency fixed) (see FIG. 14)
For example, when the burst cycle = four times the switching cycle (the ON time ratio in the case of non-burst operation is 1.0) → (when the load becomes lighter) → 3 times of switching, OFF = one cycle of switching (ON in this case) (Time ratio is 0.75)
When the burst frequency is fixed and the burst frequency is fixed, the ON time ratio jumps greatly when the burst enters with the minimum OFF time and when the burst operation is not performed, and stable operation is not performed under the load condition corresponding to this boundary.
「本技術によるバースト制御の方法」
　本技術では、ＬＬＣ方式のバースト制御において、バースト期間のＯＮ時間比率が、負荷条件によって、連続的に可変できるよう、バースト期間のスイッチングＯＮ回数とＯＦＦ時間を制御する。この制御方法によりＯＦＦ時間を連続的（スイッチング１周期よりもある程度細かいステップあるいは無段階等）に制御することで、バースト動作時のＯＮ時間比率を、連続的に変化させることができ、且つ、バーストＯＦＦの時間を最適制御することが可能となる。以下、本技術によるバーストモードについて説明する。なお、「連続的」とは、大きく飛躍することのない比較的小さいステップでの可変、或いは無段階での可変を含めて、連続的と表現している。 "Burst control method using this technology"
In the present technology, in the burst control of the LLC system, the number of times of switching ON and the OFF time of the burst period are controlled so that the ON time ratio of the burst period can be continuously varied according to the load condition. By controlling the OFF time continuously (eg, in steps smaller than one switching cycle or steplessly) by this control method, the ON time ratio during the burst operation can be continuously changed, and the burst time can be changed. It is possible to optimally control the OFF time. Hereinafter, the burst mode according to the present technology will be described. It should be noted that “continuous” is expressed as continuous, including a variable in a relatively small step that does not greatly jump or a variable in a stepless manner.
　ＬＬＣ方式は、周波数制御の方式である。軽負荷になるほど、スイッチング周波数が上がる制御になる。このスイッチング周波数に上限設定値（ｆｍａｘ１）を設け、それ以上の軽負荷領域については、上限スイッチング周波数（ｆｍａｘ１）で固定して、バースト制御に入れ、スイッチングＯＮ時間の比率により、制御させる方法を取る。 The LLC method is a frequency control method. The control is such that the switching frequency increases as the load becomes lighter. An upper limit set value (fmax1) is provided for this switching frequency, and for a light load region beyond that, fixed at the upper limit switching frequency (fmax1), burst control is performed, and control is performed according to the ratio of switching ON time. .
　図１５は、本技術のバースト制御を示すものであり、重負荷から超軽負荷までの間の制御を表している。本技術では、周波数制御するスイッチング周波数の上限値ｆｍａｘ１を設定する。上限値ｆｍａｘ１までは、スイッチング周波数（ｆｓｗと表記する）を負荷の重さを示すフィードバック値（ＦＢ値と表記する）に応じてスイッチング周波数ｆｓｗを制御する。すなわち、負荷が軽くなるとスイッチング周波数ｆｓｗを高くする。この制御は、非バースト制御の範囲である。一例として、ｆｍａｘ１を１５０ｋＨｚ未満に設定する。この周波数は、雑音端子電圧の規制帯域以下となり、ＡＣフィルタのコストダウンが可能となる。 FIG. 15 shows the burst control according to the present technology, and illustrates control from a heavy load to an extremely light load. In the present technology, an upper limit value fmax1 of the switching frequency to be frequency-controlled is set. Up to the upper limit value fmax1, the switching frequency fsw is controlled according to the feedback value (expressed as FB value) indicating the weight of the load. That is, when the load is reduced, the switching frequency fsw is increased. This control is in the range of non-burst control. As an example, fmax1 is set to less than 150 kHz. This frequency is lower than the regulation band of the noise terminal voltage, and the cost of the AC filter can be reduced.
　スイッチング周波数ｆｓｗが上限設定値ｆｍａｘ１に達すると、バースト制御に移行する。スイッチング周波数ｆｓｗが上限設定値ｆｍａｘ１に固定され、ＦＢ値によりスイッチング回数とＯＦＦ時間を制御する。軽負荷となるほどＯＮ回数を減少させる。さらに、本技術によるバースト制御は、バースト期間中の（スイッチング回数≧２）の場合と、（スイッチング回数＝１）の場合に分けられる。 (4) When the switching frequency fsw reaches the upper limit set value fmax1, the flow shifts to burst control. The switching frequency fsw is fixed at the upper limit set value fmax1, and the number of switching times and the OFF time are controlled by the FB value. The number of ON times is reduced as the load becomes lighter. Furthermore, the burst control according to the present technology is divided into a case where (the number of switching times ≧ 2) during a burst period and a case where (the number of switching times = 1).
　（スイッチング回数≧２）の場合（ＯＮ時間比率≧０．５の場合）は、図１６及び図１７に示すように、フィードバックにより、スイッチング回数とＯＦＦ時間を制御することで、ＯＮ時間比率を調整する。軽負荷となるほど、ＯＮ回数を減少させる。ＯＮ時間＝スイッチング周期×スイッチング回数と表される。なお、図１６及び図１７におけるＯＦＦ時間は、１スイッチング周期以上、２スイッチング周期未満の最適値を示している。 In the case of (the number of switching times ≧ 2) (when the ON time ratio ≧ 0.5), as shown in FIGS. 16 and 17, the ON time ratio is adjusted by controlling the number of switching times and the OFF time by feedback. I do. The number of ON times is reduced as the load becomes lighter. ON time = switching cycle × number of switching times. Note that the OFF time in FIGS. 16 and 17 indicates an optimal value of one switching cycle or more and less than two switching cycles.
　（スイッチング回数＝１）の場合では、図１８及び図１９に示すように、ＯＦＦ時間を制御する。軽負荷となるほどＯＦＦ時間を伸ばす。図１８に示すように、ＯＮ時間比率が０．５に近い時なので、スイッチング回数が少なくなる。なお、図１８におけるＯＦＦ時間は、１スイッチング周期以上、２スイッチング周期未満の最適値を示している。 In the case of (number of switching = 1), the OFF time is controlled as shown in FIGS. The OFF time is extended as the load becomes lighter. As shown in FIG. 18, since the ON time ratio is close to 0.5, the number of times of switching is reduced. Note that the OFF time in FIG. 18 indicates an optimum value of one switching cycle or more and less than two switching cycles.
　上述した本技術におけるバースト制御において、スイッチング回数≧２の場合のポイントは、次のようになる。
　ＯＮ時間比率が高い（１に近い）ほど、バースト期間中のスイッチング回数を多くするように制御する。ＯＦＦ時間は、例えば、必要最小ＯＦＦ時間（＝約１スイッチング周期）以上、２スイッチング周期未満の最適値に制御する。結果として、バースト周波数は、低くなる。 In the above-described burst control according to the present technology, points when the number of switching times ≧ 2 are as follows.
Control is performed such that the higher the ON time ratio (closer to 1), the greater the number of times of switching during the burst period. The OFF time is controlled, for example, to an optimum value which is equal to or longer than the required minimum OFF time (= about one switching cycle) and shorter than two switching cycles. As a result, the burst frequency will be lower.
　ＯＮ時間比率が低い（０．５に近い）ほど、バースト期間中のスイッチング回数を減らすように制御する。ＯＦＦ時間は、例えば、必要最小ＯＦＦ時間（＝約１スイッチング周期）以上、２スイッチング周期未満の最適値に制御する。結果として、バースト周波数は、高くなる。軽負荷になるほど、バースト期間中のスイッチング回数を減らし、ＯＮ時間比率０．５のところで、スイッチング回数＝１、ＯＦＦ時間＝スイッチング１周期（＝最小ＯＦＦ時間）となる。 (4) The control is performed such that the lower the ON time ratio (closer to 0.5), the smaller the number of switching operations during the burst period. The OFF time is controlled, for example, to an optimum value which is equal to or longer than the required minimum OFF time (= about one switching cycle) and shorter than two switching cycles. As a result, the burst frequency will be higher. As the load becomes lighter, the number of times of switching during the burst period is reduced, and at the ON time ratio of 0.5, the number of times of switching = 1, and the OFF time = one cycle of switching (= minimum OFF time).
　上述したように、ＯＮ時間＝スイッチング周期×スイッチング回数となり、離散的な値を取るが、ＯＦＦ時間を、連続的（１スイッチング周期よりもある程度細かいステップ或いは無段階）に制御することによって、ＯＮ時間比率を、連続的に微調整することが可能となる。 As described above, the ON time = the switching cycle × the number of times of switching, and takes a discrete value. By controlling the OFF time continuously (steps smaller than one switching cycle or steplessly), the ON time becomes longer. The ratio can be finely adjusted continuously.
　上述した本技術におけるバースト制御において、スイッチング回数＝１の場合は、スイッチング回数＝１で固定とし、ＯＦＦ時間を必要最小ＯＦＦ時間（＝約スイッチング１周期）以上で制御することで、ＯＮ時間比率を調整する。 In the above-described burst control in the present technology, when the number of times of switching = 1, the number of times of switching = 1 is fixed, and the ON time ratio is controlled by controlling the OFF time to be equal to or more than the required minimum OFF time (= about one switching cycle). adjust.
　スイッチング回数＝１の場合（ＯＮ時間比率＜０．５）でＯＮ時間比率が高い時（ＯＮ時間比率が０．５に近い時）は、図１８に示すように、ＯＦＦ時間が最小ＯＦＦ時間に近いものとなる。 When the number of times of switching = 1 (ON time ratio <0.5) and the ON time ratio is high (when the ON time ratio is close to 0.5), as shown in FIG. 18, the OFF time becomes the minimum OFF time. It will be close.
　スイッチング回数＝１の場合でＯＮ時間比率が低い時（ＯＮ時間比率が０に近い時）は、図１９に示すように、ＯＦＦ時間が１スイッチング周期以上の最適値となる。 {Circle around (1)} When the ON time ratio is low (when the ON time ratio is close to 0) in the case where the number of switching times is 1, as shown in FIG.
　上述した本技術におけるバースト制御において、スイッチング回数＝１の場合のポイントは、次のようになる。
　スイッチング回数は１回固定として、ＯＦＦ時間は、必要最小ＯＦＦ時間（＝約１スイッチング周期）以上の最適値に制御する。 In the burst control according to the present technology described above, the points when the number of times of switching is 1 are as follows.
The number of times of switching is fixed to one, and the OFF time is controlled to an optimum value equal to or longer than a necessary minimum OFF time (= about one switching cycle).
　ＯＮ時間比率が高い（０．５に近い）時は、ＯＦＦ時間が、必要最小ＯＦＦ時間（＝約１スイッチング周期）に近いので、結果として、バースト周波数が高い。 When the ON time ratio is high (close to 0.5), the OFF time is close to the required minimum OFF time (= about one switching cycle), and as a result, the burst frequency is high.
　ＯＮ時間比率が低い（０に近い）時は、ＯＦＦ時間が長くなるので、結果として、バースト周波数が低くなる。 When the ON time ratio is low (close to 0), the OFF time is long, and as a result, the burst frequency is low.
　ＯＦＦ時間を、連続的（１スイッチング周期よりもある程度細かいステップ或いは無段階等）に制御することで、ＯＮ時間比率を、連続的に微調整することが可能となる。 By controlling the OFF time continuously (eg, in steps smaller than one switching cycle or steplessly), the ON time ratio can be continuously finely adjusted.
　リップル電流を最小化するという観点では、スイッチング回数＝１の場合でも、ＯＦＦ時間は短い方がよい。スイッチング回数＝１で、ＯＦＦ時間を短くする方法については、後述する。 (4) From the viewpoint of minimizing the ripple current, it is preferable that the OFF time is short even when the number of times of switching = 1. A method for shortening the OFF time when the number of times of switching = 1 will be described later.
「通常モード（周波数制御）のフィードバック制御の説明」
　制御部１２の制御動作について説明する。図２０を参照して通常モードのフィードバック制御について、その一例を説明する。この例では、スイッチング周波数ｆｓｗについて、上限値、下限値を設定しているものとする。 "Description of feedback control in normal mode (frequency control)"
The control operation of the control unit 12 will be described. An example of the feedback control in the normal mode will be described with reference to FIG. In this example, it is assumed that an upper limit value and a lower limit value are set for the switching frequency fsw.
　ステップＳ１：フィードバック信号の値（ＦＢ値）が高いかどうかを判定する。ここでは、ＦＢ値が高いことは、出力が不足していることを意味する。
　ステップＳ２：ＦＢ値が高いと判定されると、スイッチング周波数が下限値より高いかどうか判定される。
　ステップＳ３：ステップＳ２においてスイッチング周波数が下限値より高いと判定されると、スイッチング周波数が下げられる。そして、ステップＳ１の判定処理に戻る。
　ステップＳ４：ステップＳ２においてスイッチング周波数が下限値以下と判定されると、スイッチング周波数が下限値で動作される。そして、ステップＳ１の判定処理に戻る。 Step S1: Determine whether the value (FB value) of the feedback signal is high. Here, a high FB value means that the output is insufficient.
Step S2: If it is determined that the FB value is high, it is determined whether the switching frequency is higher than a lower limit value.
Step S3: If it is determined in step S2 that the switching frequency is higher than the lower limit, the switching frequency is decreased. Then, the process returns to the determination processing of step S1.
Step S4: If it is determined in step S2 that the switching frequency is equal to or lower than the lower limit, the switching frequency is operated at the lower limit. Then, the process returns to the determination processing of step S1.
　ステップＳ５：ステップＳ１において、ＦＢ値が高くない、すなわち、出力が過多と判定されると、スイッチング周波数が上限値未満かどうかが判定される。
　ステップＳ６：ステップＳ５において、スイッチング周波数が上限値未満でないと判定されると、バーストモードとする。
　ステップＳ７：ステップＳ５において、スイッチング周波数が上限値未満と判定されると、スイッチング周波数が上げられて、ステップＳ１の判定処理に戻る。 Step S5: If it is determined in step S1 that the FB value is not high, that is, the output is excessive, it is determined whether the switching frequency is less than the upper limit.
Step S6: If it is determined in step S5 that the switching frequency is not less than the upper limit, the mode is set to the burst mode.
Step S7: If it is determined in step S5 that the switching frequency is lower than the upper limit value, the switching frequency is increased, and the process returns to the determination processing in step S1.
「バーストモード（スイッチング回数ｎ≧２）の説明」
　次に、図２１を参照してバーストモード（スイッチング回数ｎ≧２）のフィードバック制御について、その一例を説明する。なお、この例では、バースト１周期中のスイッチング回数については、上限値を設定することとする。
　ステップＳ１１：ＦＢ値が高いかどうかを判定する。ここでは、ＦＢ値が高いことは、出力が不足していることを意味する。
　ステップＳ１２：ＦＢ値が高いと判定されると、ＯＦＦ時間が下限値かどうかが判定される。
　ステップＳ１３：ＯＦＦ時間が下限値と判定されると、スイッチング回数が上限値かどうかが判定される。
　ステップＳ１４：ステップＳ１３で、スイッチング回数が上限値でないと判定されると、スイッチング回数が増やされる。そして、ステップＳ１の判定処理に戻る。
　ステップＳ１５：ステップＳ１３で、スイッチング回数が上限値と判定されると、周波数制御（連続モード）へ移行する。 "Explanation of burst mode (switching frequency n ≧ 2)"
Next, an example of feedback control in the burst mode (the number of switching times n ≧ 2) will be described with reference to FIG. In this example, an upper limit value is set for the number of times of switching during one burst period.
Step S11: Determine whether the FB value is high. Here, a high FB value means that the output is insufficient.
Step S12: If it is determined that the FB value is high, it is determined whether or not the OFF time is the lower limit value.
Step S13: If the OFF time is determined to be the lower limit, it is determined whether the number of switching times is the upper limit.
Step S14: If it is determined in step S13 that the number of times of switching is not the upper limit value, the number of times of switching is increased. Then, the process returns to the determination processing of step S1.
Step S15: If it is determined in step S13 that the number of times of switching is the upper limit value, the process shifts to frequency control (continuous mode).
　ステップＳ１６：ステップＳ１２において、ＯＦＦ時間が下限値でないと判定されると、下限値以上でＯＦＦ時間を減らすようになされる。そして、ＦＢ値判定（ステップＳ１１）に制御が戻る。
　ステップＳ１７：ステップＳ１１のＦＢ値判定において、ＦＢ値が高くない（出力過多）と判定されると、ＯＦＦ時間が上限値か、どうかが判定される。すなわち、ＯＦＦ時間が（＜（Ｔ・ｎ）／（ｎ－１））か、どうかが判定される。ここで、Ｔはスイッチング周期、ｎは１バースト周期中のスイッチング回数を示す。
　ステップＳ１８：ステップＳ１７において、ＯＦＦ時間が上限値でないと判定されると、ＯＦＦ時間が上限以下で増やされる。そして、ＦＢ値判定（ステップＳ１１）に制御が戻る。 Step S16: If it is determined in step S12 that the OFF time is not at the lower limit, the OFF time is reduced to a value equal to or more than the lower limit. Then, the control returns to the FB value determination (step S11).
Step S17: If it is determined in the FB value determination in step S11 that the FB value is not high (excessive output), it is determined whether the OFF time is the upper limit value. That is, it is determined whether or not the OFF time is (<(T · n) / (n−1)). Here, T indicates a switching cycle, and n indicates the number of times of switching in one burst cycle.
Step S18: If it is determined in step S17 that the OFF time is not the upper limit value, the OFF time is increased below the upper limit. Then, the control returns to the FB value determination (step S11).
　ステップＳ１９：ステップＳ１７において、ＯＦＦ時間が上限値と判定されると、スイッチング回数が２より多いかどうか判定される。
　ステップＳ２０：ステップＳ１９において、スイッチング回数が２より多いと判定されると、スイッチング回数が減らされる。そして、ＦＢ値判定（ステップＳ１１）に制御が戻る。
　ステップＳ２１：ステップＳ１９において、スイッチング回数が２以下と判定されると、スイッチング回数＝１のモードへ制御が移る。 Step S19: If it is determined in step S17 that the OFF time is the upper limit value, it is determined whether the number of switching times is greater than two.
Step S20: If it is determined in step S19 that the number of times of switching is greater than 2, the number of times of switching is reduced. Then, the control returns to the FB value determination (step S11).
Step S21: If it is determined in step S19 that the number of times of switching is 2 or less, the control is shifted to a mode in which the number of times of switching = 1.
「バーストモード（スイッチング回数ｎ＝１）の説明」
　次に、図２２を参照してバーストモード（スイッチング回数ｎ＝１）のフィードバック制御について説明する。
　ステップＳ３１：ＦＢ値が高いかどうかを判定する。ここでは、ＦＢ値が高いことは、出力が不足していることを意味する。
　ステップＳ３２：ＦＢ値が高いと判定されると、ＯＦＦ時間が下限値か、どうかが判定される。
　ステップＳ３３：ＯＦＦ時間が下限値でないと判定されると、下限値以下でＯＦＦ時間が減らされる。そして、ステップＳ３１のＦＢ値の判定処理に戻る。
　ステップＳ３４：ステップＳ３２において、ＯＦＦ時間が下限値であると判定されると、スイッチング回数を２にして（ｎ≧２）の制御に移る。
　ステップＳ３５：ステップＳ３１において、ＦＢ値が高くない（すなわち、出力が過多）と判定されると、ＯＦＦ時間か増やされ、ＦＢ値の判定処理に戻る。 "Explanation of burst mode (switching frequency n = 1)"
Next, the feedback control in the burst mode (the number of switching times n = 1) will be described with reference to FIG.
Step S31: Determine whether the FB value is high. Here, a high FB value means that the output is insufficient.
Step S32: When it is determined that the FB value is high, it is determined whether or not the OFF time is the lower limit value.
Step S33: If it is determined that the OFF time is not at the lower limit, the OFF time is reduced below the lower limit. Then, the process returns to the FB value determination process in step S31.
Step S34: If it is determined in step S32 that the OFF time is at the lower limit, the number of switching times is set to 2 and control is shifted to (n ≧ 2).
Step S35: If it is determined in step S31 that the FB value is not high (that is, the output is excessive), the OFF time is increased, and the process returns to the FB value determination process.
「テーブルを用いるバーストモード」
　スイッチング周波数は、上限値で固定し、ＯＦＦ時間はＴ以上。但し、Ｔはスイッチング周期である。
　図２３のフローチャートに示すように、テーブルを用いる場合では、後述するように、ＯＮ時間比率に応じた、スイッチング回数とＯＦＦ時間のテーブルを用意しておいて、ＦＢ値に応じてＯＮ時間比率を変える。 "Burst mode using a table"
The switching frequency is fixed at the upper limit, and the OFF time is T or more. Here, T is a switching cycle.
As shown in the flowchart of FIG. 23, in the case of using the table, a table of the number of switching times and the OFF time is prepared according to the ON time ratio, and the ON time ratio is set according to the FB value, as described later. Change.
　ステップＳ４１：ＦＢ値が高いかどうかを判定する。ここでは、ＦＢ値が高いことは、出力が不足していることを意味する。
　ステップＳ４２：ＦＢ値が高いと判定されると、テーブルのＯＮ時間比率が上限未満か、どうかが判定される。
　ステップＳ４３：ＯＮ時間比率が上限未満と判定されると、ＯＮ時間比率が高くされる。そして、ステップＳ４１の判定処理に戻る。
　ステップＳ４４：ステップＳ４２で、ＯＮ時間比率が上限未満でないと判定されると、周波数制御モード（連続動作）に移行する。
　ステップＳ４５：ステップＳ４１において、ＦＢ値が高くないと判定されると、ＯＮ時間比率が低くされる。 Step S41: Determine whether the FB value is high. Here, a high FB value means that the output is insufficient.
Step S42: If it is determined that the FB value is high, it is determined whether the ON time ratio of the table is less than the upper limit.
Step S43: If the ON time ratio is determined to be less than the upper limit, the ON time ratio is increased. Then, the process returns to the determination processing of step S41.
Step S44: If it is determined in step S42 that the ON time ratio is not less than the upper limit, the mode shifts to the frequency control mode (continuous operation).
Step S45: If it is determined in step S41 that the FB value is not high, the ON time ratio is reduced.
「テーブルの一例」
　バーストのＯＮ時間比率とＯＮ回数、ＯＦＦ時間の可変の一例をテーブルの形式で図２４および図２５に示す。これらの二つの表は、一連の表であって、図２４の表から図２５の表に続くもので、表の上から下に向かうほど負荷が軽くなるものとしている。すなわち、図２４の最上段の行が最も負荷が重い時の値であり、図２５の最下段の行が最も負荷が軽い時の値である。図２４および図２５の例から分かるように、軽負荷になるほど、ＯＮ数を減らす。ＯＦＦ時間は、１スイッチング周期よりある程度細かいステップか、あるいは無段階等で調整することで、ＯＮ時間比率の飛躍が無くなり、安定したレギュレーション特性を実現できる。なお、ＯＦＦ時間は、便宜上０．１刻みで表記しているが、実際には、０．１刻みでなくてもよいし、無段階でもよい。 "Example of table"
FIGS. 24 and 25 show examples of variable ON time ratios, ON times, and OFF times of bursts in the form of tables. These two tables are a series of tables following the table of FIG. 24 to the table of FIG. 25, and assume that the load becomes lighter from the top to the bottom of the table. That is, the top row in FIG. 24 is the value when the load is the heaviest, and the bottom row in FIG. 25 is the value when the load is the lightest. As can be seen from the examples of FIGS. 24 and 25, the number of ONs is reduced as the load becomes lighter. By adjusting the OFF time in steps smaller than one switching cycle to some extent, or steplessly, the ON time ratio does not jump, and stable regulation characteristics can be realized. In addition, the OFF time is described in increments of 0.1 for convenience, but may not actually be in increments of 0.1 or may be stepless.
　さらに、図２４および図２５に示すテーブルのポイントについて説明する。
　このテーブルは、１バースト周期中のスイッチング回数とＯＦＦ時間を制御し、ＯＦＦ時 間を１スイッチング周期よりある程度小さいステップで制御することで、バースト期間中のＯＮ時間比率を飛躍することなく変化させることができることを、表したものである。 Further, points of the tables shown in FIGS. 24 and 25 will be described.
This table controls the number of times of switching and the OFF time during one burst period, and controls the OFF time in steps smaller than one switching period to change the ON time ratio during the burst period without jumping. It is a representation of what can be done.
　ＯＮ時間比率を調整する際、スイッチング回数とＯＦＦ時間を組み合わせて制御することで、ＯＦＦ時間を単に長くするよりも、スイッチング回数を減らすという制御を示している。ＯＦＦ時間を最適制御することで、リップル電流（又はリップル電圧）を最小限に抑えることができる。これは、リップル電流（又はリップル電圧）を最小にするという目的で、ＯＦＦ時間を最適制御する一例である。 (4) When the ON time ratio is adjusted, control is performed by reducing the number of switching times by simply controlling the number of switching times and the OFF time, rather than simply increasing the OFF time. By optimally controlling the OFF time, the ripple current (or ripple voltage) can be minimized. This is an example of optimally controlling the OFF time for the purpose of minimizing the ripple current (or ripple voltage).
　このテーブルに示したスイッチング回数ｎとそのスイッチング回数における最大ＯＦＦ時間の関係を式で表すと、次のようになる。スイッチング回数ｎ≧２の場合において、ＯＦＦ時間の最大値を×とし、スイッチング周期をＴとすると、ＯＮ時間比率の関係から、以下の式が成り立つ（ただし、ｎは２以上の整数）。 関係 The relationship between the number of switchings n shown in this table and the maximum OFF time at the number of switchings is expressed by the following equation. If the maximum value of the OFF time is x and the switching period is T in the case where the number of times of switching n ≧ 2, then the following formula is established from the relation of the ON time ratio (where n is an integer of 2 or more).
　｛Ｔ・（ｎ－１）｝／｛Ｔ・（ｎ－１）＋Ｔ｝＜Ｔ・ｎ　／｛Ｔ・ｎ＋×｝ {T. (n-1)} / {T. (n-1) + T} <T.n} / {T.n + ×}
　この式を、×（ＯＦＦ時間の最大値）について解くと、下記の式が得られる。 解 When this equation is solved for × (maximum value of OFF time), the following equation is obtained.
　Ｘ　＜　Ｔ・ｎ／（ｎ－１） X <Tn / (n-1)
　したがって、スイッチング回数ｎと、スイッチング周期Ｔが決まれば、ＯＦＦ時間の最大値は決まる。ＯＦＦ時間を、この最大値より伸ばさないと出力過多になる場合、スイッチング回数を１回減らせばよいということになる。この式のように、スイッチング回数とＯＦＦ時間を制御すれば、ＯＦＦ時間を最適に制御することができ、この制御式の場合、リップル電流（又はリップル電圧）を最小化できる。スイッチング回数＝１の場合を含めてまとめると、次のようになる。 Therefore, if the number of switching times n and the switching period T are determined, the maximum value of the OFF time is determined. If the output becomes excessive unless the OFF time is made longer than this maximum value, it means that the number of switching times should be reduced by one. By controlling the number of times of switching and the OFF time as in this equation, the OFF time can be optimally controlled. In the case of this control equation, the ripple current (or ripple voltage) can be minimized. The following is a summary including the case where the number of switching times = 1.
　スイッチング回数ｎ≧２の場合
　ＯＦＦ時間Ｘが、下記となるようにスイッチング回数ｎとＯＦＦ時間×をフィードバック制御する。 When the Number of Switchings n ≧ 2 The number of switchings n and the OFF time × are feedback-controlled so that the OFF time X is as follows.
　Ｔ＜Ｘ＜Ｔ・ｎ／（ｎ－１）　　（Ｔ：スイッチング周期、　ｎ：スッチング回数） {T <X <Tn / (n-1)} (T: switching cycle, Δn: number of times of switching)
　出力が不足な場合、ｎ→（ｎ＋１）
　出力が出し過ぎになる場合、ｎ→（ｎ－１）
　ｎ＝１になった場合は、ｎ＝１の制御に移行 If the output is insufficient, n → (n + 1)
If the output is too high, n → (n-1)
When n = 1, shift to control of n = 1
　スイッチング回数ｎ＝１の場合
　ＯＦＦ時間Ｘが、下記となるようにＯＦＦ時間Ｔをフィードバック制御 When the number of switching times n = 1, the OFF time T is feedback controlled so that the OFF time X is as follows.
　Ｔ＜Ｘ T <X
　出力が出し過ぎになる場合、×を長くする
　出力が不足な場合、Ｔ＜の範囲で×を短くする
　Ｘ＝Ｔで、出力が不足な場合、ｎ＝２にして、スイッチング回数ｎ≧２の制御に移行 If the output is excessive, lengthen x. If the output is insufficient, shorten x within the range of T <. If X = T, and if the output is insufficient, set n = 2 and set the switching frequency n ≧ 2. Transfer to control
　このような制御を実際のハードウエアに実装する場合は、上述の関係式から、論理回路を構成し、ハードウエアを構築してもよいし、又は、先に示したようなテーブルを作成し、そのテーブルを元に制御してもよい。 When such control is implemented in actual hardware, a logic circuit may be configured and hardware may be constructed from the above relational expression, or a table as described above may be created, The control may be performed based on the table.
　上述した制御をした場合のＯＮ時間比率とバースト周波数の関係を図２６に示し、ＯＮ時間比率とＯＦＦ時間の関係を図２７に示し、ＯＮ時間比率とＯＮ回数の関係を図２８に示す。 FIG. 26 shows the relationship between the ON time ratio and the burst frequency when the above control is performed, FIG. 27 shows the relationship between the ON time ratio and the OFF time, and FIG. 28 shows the relationship between the ON time ratio and the number of ON times.
　バースト制御の際には、実際には、音鳴きが発生することがあり、バースト周波数として、可聴帯域以上の２０ｋＨｚ以上にするか、あるいは、耳に付きにくい低い周波数が選ばれることが多い。しかし、本制御では、バースト周波数は、負荷条件により変動してしまうため、２０ｋＨｚ以下の可聴帯域に入るケースも発生する。その場合は、図２９に示すように、バースト開始時に、スイッチング周波数を高いところから発振し始め、少しずつ周波数を下げていく、いわゆるソフトスタートと、バースト終了時にスイッチング周波数を少しずつ上げてからＯＦＦにする、いわゆるソフトＯＦＦ（又はソフトエンド）を使うことが有効である。 (4) In the case of burst control, sound may actually occur, and a burst frequency of 20 kHz or more, which is higher than the audible band, or a low frequency that is hard to be heard is often selected. However, in this control, since the burst frequency fluctuates depending on the load condition, there are cases where the burst frequency falls within the audible band of 20 kHz or less. In this case, as shown in FIG. 29, at the start of the burst, the switching frequency starts to oscillate from a high place, and then gradually lowers the frequency. It is effective to use a so-called soft OFF (or soft end).
　なお、ソフトスタートを使うと、副次的なメリットも発生する。軽負荷になっていくと、バースト時のスイッチングのＯＮ回数が減っていくので、最終的には、ソフトスタート部分のみが残り、最終的に、スイッチング回数＝１回となる場合、ソフトスタートの作用で、自動的にスイッチング周波数が高くなる（図３０参照）。 By using soft start, there are some additional benefits. When the load becomes lighter, the number of times of switching ON at the time of the burst decreases, so that only the soft start part is finally left. Then, the switching frequency automatically increases (see FIG. 30).
　同じスイッチング回数が１回の場合は、スイッチング周波数を高めた方が、ゲインが下がり、同負荷条件だとＯＦＦ時間が短くなるため、ソフトスタートの副次的作用として、リップル電流を低減することが可能となる。 When the same number of switching times is one, increasing the switching frequency lowers the gain and shortens the OFF time under the same load condition. Therefore, as a secondary effect of the soft start, the ripple current can be reduced. It becomes possible.
　また、この考え方から、ソフトスタートやソフトＯＦＦを使わない場合、次のような制御も、リップル電流を最小化する観点で有効である。すなわち、スイッチング回数＝１の場合で、ソフトスタートを用いない場合、リップル電流を減らす工夫として、以下の方法が有効である。 か ら Also, based on this concept, if soft start or soft OFF is not used, the following control is also effective from the viewpoint of minimizing ripple current. That is, in the case where the number of switching times is 1, and the soft start is not used, the following method is effective as a device for reducing the ripple current.
　上述した図１５に示すバースト動作での制御は、スイッチング回数≧２の場合と、スイッチング回数＝１の場合の２つのモードに分けたが、スイッチング回数＝１の場合を、さらに２つのモードに分ける（図３１及び図３２参照）。 The above-described control in the burst operation shown in FIG. 15 is divided into two modes, that is, the case where the number of switching times ≧ 2 and the case where the number of switching times = 1, and the case where the number of switching = 1 is further divided into two modes. (See FIGS. 31 and 32).
　１．スイッチング回数が１回になると、スイッチング回数＝１回固定とし、ＯＦＦ時間を最小ＯＦＦ時間で固定。
　２．このモードでの上限スイッチング周波数ｆｍａｘ２をｆｍａｘ１より高く設定しておいて、フィードバックによりｆｍａｘ１からｆｍａｘ２の間で制御。
　３．さらなる軽負荷時に、ｆｍａｘ２に到達し、アンレギュレーション（つまり出力過多）になった場合、ｆｍａｘ２を固定として、ＯＦＦ時間制御に移行。 1. When the number of times of switching becomes one, the number of times of switching is fixed at one time, and the OFF time is fixed at the minimum OFF time.
2. In this mode, the upper limit switching frequency fmax2 is set higher than fmax1, and feedback control is performed between fmax1 and fmax2.
3. When the load reaches fmax2 and the output becomes unregulated (that is, excessive output) at a further light load, the fmax2 is fixed and the process shifts to the OFF time control.
＜４．変形例＞
　以上、本技術の一実施の形態について具体的に説明したが、本技術は、上述の一実施の形態に限定されるものではなく、本技術の技術的思想に基づく各種の変形が可能である。また、上述の実施形態において挙げた構成、方法、工程、形状、材料及び数値などはあくまでも例に過ぎず、必要に応じてこれと異なる構成、方法、工程、形状、材料及び数値などを用いてもよい。 <4. Modification>
As described above, one embodiment of the present technology has been specifically described. However, the present technology is not limited to the above-described embodiment, and various modifications based on the technical idea of the present technology are possible. . In addition, the configurations, methods, steps, shapes, materials, numerical values, and the like described in the above embodiments are merely examples, and if necessary, different configurations, methods, processes, shapes, materials, numerical values, and the like may be used. Is also good.
　なお、本技術は、以下のような構成も取ることができる。
（１）
　ＬＬＣ方式のスイッチング電源であって、
　負荷条件を示すフィードバック値が供給され、スイッチング素子に対するドライブ信号を形成する制御部を有し、
　制御部は、
　負荷が重い第１の領域において、前記フィードバック値によってスイッチング周波数を可変する周波数制御を行い、
　前記第１の領域に比して負荷が軽い第２の領域において、スイッチング周波数を固定してスイッチングＯＮ区間とスイッチングＯＦＦ区間を設けるバースト制御を行い、
　前記バースト制御において、スイッチングＯＮ回数とＯＦＦ時間の両方を制御することによって、ＯＮ時間比率を負荷条件によって連続的に可変するようにしたスイッチング電源。
（２）
　前記ＯＮ時間比率を下げる場合に、前記ＯＦＦ時間を最適値に制御すると共に，負荷が軽くなるほど１バースト周期中のスイッチング回数を減らすようにした（１）に記載のスイッチング電源。
（３）
　前記スイッチング回数が１回になると、負荷が軽くなるほどＯＦＦ時間を伸ばすように制御する（２）に記載のスイッチング電源。
（４）
　前記バースト制御において、ソフトスタート及びソフトエンドを組み合わせるようにした（１）から（３）のいずれかに記載のスイッチング電源。
（５）
　前記バースト制御において、前記スイッチング回数が１回になると、スイッチング回数及びＯＦＦ時間を固定し、再度、周波数制御を行うようにした（１）から（３）のいずれかに記載のスイッチング電源。
（６）
　前記周波数制御において、出力過多で安定化ができなくなったときに、周波数を固定してＯＦＦ時間を制御するようにした（５）に記載のスイッチング電源。
（７）
　前記負荷が二次電池である（１）に記載のスイッチング電源。 Note that the present technology may also have the following configurations.
(1)
An LLC type switching power supply,
A feedback value indicating a load condition is supplied, the control unit forming a drive signal for the switching element,
The control unit is
In the first region where the load is heavy, frequency control for changing the switching frequency by the feedback value is performed,
In the second region where the load is lighter than in the first region, burst control is performed in which the switching frequency is fixed to provide a switching ON section and a switching OFF section,
A switching power supply in which in the burst control, the ON time ratio is continuously varied according to load conditions by controlling both the number of times of switching and the OFF time.
(2)
The switching power supply according to (1), wherein when the ON time ratio is reduced, the OFF time is controlled to an optimum value, and the number of times of switching in one burst cycle is reduced as the load becomes lighter.
(3)
The switching power supply according to (2), wherein when the number of times of switching is one, the OFF time is controlled to be extended as the load becomes lighter.
(4)
The switching power supply according to any one of (1) to (3), wherein a soft start and a soft end are combined in the burst control.
(5)
The switching power supply according to any one of (1) to (3), wherein in the burst control, when the number of times of switching becomes one, the number of times of switching and the OFF time are fixed, and the frequency control is performed again.
(6)
The switching power supply according to (5), wherein in the frequency control, when stabilization cannot be performed due to excessive output, the OFF time is controlled by fixing the frequency.
(7)
The switching power supply according to (1), wherein the load is a secondary battery.
Ｑ１，Ｑ２・・・ＭＯＳＦＥＴ、ＴＲ・・・トランス、ｔ１，ｔ２・・・出力端子、
１１，２１・・・エラーアンプ、１２・・・制御部 Q1, Q2: MOSFET, TR: Transformer, t1, t2: Output terminal,
11, 21 ... error amplifier, 12 ... control unit

Claims (7)

  1. 　ＬＬＣ方式のスイッチング電源であって、
    　負荷条件を示すフィードバック値が供給され、スイッチング素子に対するドライブ信号を形成する制御部を有し、
    　制御部は、
    　負荷が重い第１の領域において、前記フィードバック値によってスイッチング周波数を可変する周波数制御を行い、
    　前記第１の領域に比して負荷が軽い第２の領域において、スイッチング周波数を固定してスイッチングＯＮ区間とスイッチングＯＦＦ区間を設けるバースト制御を行い、
    　前記バースト制御において、スイッチングＯＮ回数とＯＦＦ時間の両方を制御することによって、ＯＮ時間比率を負荷条件によって連続的に可変するようにしたスイッチング電源。     An LLC type switching power supply,
    A feedback value indicating a load condition is supplied, the control unit forming a drive signal for the switching element,
    The control unit is
    In the first region where the load is heavy, frequency control for changing the switching frequency by the feedback value is performed,
    In the second region where the load is lighter than in the first region, burst control is performed in which the switching frequency is fixed to provide a switching ON section and a switching OFF section,
    A switching power supply in which in the burst control, the ON time ratio is continuously varied according to load conditions by controlling both the number of times of switching and the OFF time.
  2. 　前記ＯＮ時間比率を下げる場合に、前記ＯＦＦ時間を最適値に制御すると共に，負荷が軽くなるほど１バースト周期中のスイッチング回数を減らすようにした請求項１に記載のスイッチング電源。 4. The switching power supply according to claim 1, wherein when the ON time ratio is reduced, the OFF time is controlled to an optimum value, and the number of times of switching in one burst cycle is reduced as the load becomes lighter.
  3. 　前記スイッチング回数が１回になると、負荷が軽くなるほどＯＦＦ時間を伸ばすように制御する請求項２に記載のスイッチング電源。 3. The switching power supply according to claim 2, wherein when the number of times of switching is one, control is performed such that the OFF time is extended as the load becomes lighter.
  4. 　前記バースト制御において、ソフトスタート及びソフトエンドを組み合わせるようにした請求項１に記載のスイッチング電源。 The switching power supply according to claim 1, wherein soft start and soft end are combined in the burst control.
  5. 　前記バースト制御において、前記スイッチング回数が１回になると、スイッチング回数及びＯＦＦ時間を固定し、再度、周波数制御を行うようにした請求項１に記載のスイッチング電源。 4. The switching power supply according to claim 1, wherein in the burst control, when the number of times of switching is one, the number of times of switching and the OFF time are fixed, and the frequency control is performed again.
  6. 　前記周波数制御において、出力過多で安定化ができなくなったときに、周波数を固定してＯＦＦ時間を制御するようにした請求項５に記載のスイッチング電源。 6. The switching power supply according to claim 5, wherein in the frequency control, when stabilization cannot be performed due to excessive output, the OFF time is controlled by fixing the frequency.
  7. 　前記負荷が二次電池である請求項１に記載のスイッチング電源。 The switching power supply according to claim 1, wherein the load is a secondary battery.
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