CN114006538B - Flyback converter control circuit and control method and flyback converter - Google Patents
Flyback converter control circuit and control method and flyback converter Download PDFInfo
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- CN114006538B CN114006538B CN202111364180.8A CN202111364180A CN114006538B CN 114006538 B CN114006538 B CN 114006538B CN 202111364180 A CN202111364180 A CN 202111364180A CN 114006538 B CN114006538 B CN 114006538B
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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
- H02M3/325—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 using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—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 using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
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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
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
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- 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
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- Power Engineering (AREA)
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Abstract
The invention discloses a control circuit and a control method of a flyback converter and the flyback converter. The feedback voltage acquisition circuit is used for acquiring feedback voltage representing the output voltage; the working mode control unit is coupled with the feedback voltage acquisition circuit and is used for controlling the working mode of the flyback converter according to the feedback voltage; the working mode control unit controls the flyback converter to enter a current continuous working mode when the flyback converter is in a low-voltage full-load state; and the working mode control unit controls the flyback converter to enter a quasi-resonance working mode when the flyback converter is in a high-voltage full-load state. The control circuit and the control method of the flyback converter and the flyback converter provided by the invention can ensure the stable operation of the circuit and effectively ensure the efficiency of the circuit.
Description
Technical Field
The invention belongs to the technical field of microelectronics, relates to a frequency control circuit, and particularly relates to a control circuit and a control method of a flyback converter and the flyback converter.
Background
The working frequency is kept unchanged when the flyback converter control system outputs short circuit, the power externally provided by the system is overlarge, and the risk of overheat failure of the system is caused
The primary side feedback PSR system adopts a quasi-resonance working mode (QR working mode for short) or a current continuous working mode (CCM working mode for short), and the current continuous working mode system has the advantage of strong carrying capacity, but has the defect of low efficiency. The quasi-resonant operating mode system has the advantages of high efficiency, but weak carrying capacity, and particularly has larger output ripple under low-voltage full load. According to the scheme provided by the invention, the CCM working mode is entered under the condition of low-pressure full load to work, the QR working mode is entered under the condition of high-pressure full load to work, the problem of large output ripple of the QR working mode during the low-pressure full load working is avoided, the efficiency of the system is ensured when the high-pressure full load is operated in the QR working mode, and the system automatically adjusts the working mode according to the input voltage, the output voltage and the load.
When the CV loop works, the system works from the CCM working mode to the QR working mode along with the reduction of load, and the sampling value of FB is slightly fluctuated due to noise generated during the chip work and is amplified by the error amplifier EA to cause the fluctuation of an error signal Vea, so that the system can be switched back and forth between the QR working mode and the CCM working mode in a certain load interval, and the system working frequency is unstable.
In view of this, there is an urgent need to design a control circuit of a new flyback converter in order to overcome at least some of the above-mentioned drawbacks of the control circuits of the existing flyback converters.
Disclosure of Invention
The invention provides a control circuit and a control method of a flyback converter and the flyback converter, which can ensure the stable operation of the circuit and effectively ensure the efficiency of the circuit.
In order to solve the technical problems, according to one aspect of the present invention, the following technical scheme is adopted:
a control circuit for a flyback converter, the control circuit comprising:
the feedback voltage acquisition circuit is used for acquiring feedback voltage representing the output voltage; and
the working mode control unit is coupled with the feedback voltage acquisition circuit and used for controlling the working mode of the flyback converter according to the feedback voltage; the working mode control unit controls the flyback converter to enter a current continuous working mode when the flyback converter is in a low-voltage full-load state; and the working mode control unit controls the flyback converter to enter a quasi-resonance working mode when the flyback converter is in a high-voltage full-load state.
As an embodiment of the present invention, the operation mode control unit includes a frequency control unit for controlling the frequency of the flyback converter; the frequency control unit includes:
the upper clamp frequency control unit is used for controlling the upper clamp frequency signal according to the feedback voltage, and controlling the upper clamp frequency signal to be reduced when the feedback voltage is reduced and is lower than a set threshold value; and
the lower clamp frequency control unit is used for controlling the lower clamp frequency signal according to the feedback voltage, and controlling the lower clamp frequency signal to be reduced when the feedback voltage is reduced and is lower than a set threshold value; and when the feedback voltage is higher than a set threshold value, the lower clamp frequency control unit controls the lower clamp frequency signal to be a set fixed value.
As an embodiment of the present invention, the frequency control unit further includes a second and gate; the output end of the upper clamp frequency control unit is coupled with the first input end of the second AND gate, the output end of the lower clamp frequency control unit is coupled with the second input end of the second AND gate, and the output end of the second AND gate outputs a control signal for controlling the frequency in a current continuous working mode.
As one embodiment of the present invention, the lower clamp frequency control unit includes:
the first oscillator has a first input end coupled to the feedback voltage and a second input end coupled to an error signal of the feedback voltage and the first reference voltage;
the second oscillator is an oscillator with fixed frequency;
the input end of the oscillator selection unit is respectively coupled with the first oscillator and the second oscillator; the first oscillator is selected when the feedback voltage is lower than a set threshold value, and the second oscillator is selected when the feedback voltage is higher than the set threshold value.
As an embodiment of the present invention, the lower clamp frequency control unit controls the lower clamp frequency signal to remain unchanged while the flyback converter is in the constant voltage mode section.
As an embodiment of the present invention, the operation mode control unit includes:
the input end of the degaussing detection circuit is coupled with the feedback voltage and is used for generating a valley conduction signal;
the first input end of the error amplifier is coupled with the first reference voltage, and the second input end of the error amplifier is coupled with the feedback voltage; generating an error signal based on the feedback voltage and the first reference voltage;
a first input end of the first comparator is coupled with the output end of the error amplifier, and a second input end of the first comparator is coupled with a second reference voltage; the first comparison signal is obtained according to the error signal and the second reference voltage;
the input end of the first AND gate is respectively coupled with the output end of the degaussing detection circuit, the output end of the first comparator and the upper clamp frequency control signal;
the first input end of the second AND gate is coupled with the clamp frequency control signal, and the second input end of the second AND gate is coupled with the lower clamp frequency control signal;
the first input end of the OR gate is coupled with the output end of the first AND gate, and the second input end of the OR gate is coupled with the output end of the second AND gate;
and the first input end of the trigger is coupled with the output end of the OR gate, and the output end of the trigger outputs a switch control signal.
As an embodiment of the present invention, the operation mode control unit further includes:
the input end of the low-pass filter is coupled with the output end of the error amplifier and is used for carrying out low-pass filtering on an error signal;
the input end of the amplitude modulation circuit is coupled with the output end of the low-pass filter and used for carrying out amplitude modulation on the information output by the low-pass filter;
a first input end of the second comparator is coupled with the current feedback voltage, and a second input end of the second comparator is coupled with an output end of the amplitude modulation circuit; the second input end of the trigger is coupled with the output end of the second comparator.
According to another aspect of the invention, the following technical scheme is adopted: a flyback converter comprises the control circuit of the flyback converter.
According to a further aspect of the invention, the following technical scheme is adopted: a control method of a flyback converter, the control method comprising:
a feedback voltage obtaining step of obtaining a feedback voltage representing the output voltage; and
a working mode control step of controlling the working mode of the flyback converter according to the feedback voltage; controlling the flyback converter to enter a current continuous working mode when the flyback converter is in a low-voltage full-load state; and controlling the flyback converter to enter a quasi-resonance working mode under the condition that the flyback converter is in a high-voltage full-load state.
As an embodiment of the present invention, the operation mode control step includes a frequency control step of controlling a frequency of the flyback converter; the frequency control step includes:
an upper clamp frequency control step; controlling the upper clamp frequency signal to be reduced when the feedback voltage is reduced and is lower than a set threshold value according to the feedback voltage; and
a lower clamp frequency control step; controlling the lower clamp frequency signal according to the feedback voltage, and controlling the lower clamp frequency signal to be reduced when the feedback voltage is reduced and is lower than a set threshold value; and when the feedback voltage is higher than the set threshold value, controlling the clamp frequency signal to be a set fixed value.
As one embodiment of the present invention, the frequency control step includes: and in the constant-voltage mode interval of the flyback converter, the clamp frequency signal is controlled to be unchanged.
As an embodiment of the present invention, the frequency control step further includes:
a frequency modulation step; realizing a frequency modulation function according to the acquired upper clamp frequency control signal and lower clamp frequency control signal;
the frequency of the flyback converter when working in the quasi-resonant working mode is controlled by the upper clamp frequency control signal, and the frequency of the flyback converter when working in the current continuous working mode is controlled by the upper clamp frequency control signal and the lower clamp frequency control signal.
As an embodiment of the present invention, the operation mode control step includes an amplitude modulation step of modulating a current amplitude of the flyback converter.
The invention has the beneficial effects that: the control circuit and the control method of the flyback converter and the flyback converter provided by the invention can ensure the stable operation of the circuit and effectively ensure the efficiency of the circuit. The clamp frequency f_low_clamp is kept unchanged in a CV (constant voltage) interval, so that the stability of the frequency is improved.
Drawings
Fig. 1 is a circuit diagram of a conventional flyback voltage conversion system.
FIG. 2 is a diagram of waveforms for a conventional QR operation mode system.
Fig. 3 is a diagram of an operation waveform of a system in a conventional CCM operation mode.
Fig. 4 is a schematic diagram of an amplitude-frequency control curve of a conventional flyback voltage conversion system.
Fig. 5 is a schematic diagram of an amplitude-frequency control curve of a control circuit of a flyback converter according to an embodiment of the invention.
Fig. 6 is a circuit diagram of an operation mode control unit according to an embodiment of the invention.
Fig. 7 is a schematic circuit diagram of a portion of a frequency control unit according to an embodiment of the invention.
Fig. 8 is a schematic diagram illustrating a control circuit of a flyback converter according to an embodiment of the present invention.
Fig. 9 is a schematic diagram illustrating a control circuit of a flyback converter according to an embodiment of the present invention.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
For a further understanding of the present invention, preferred embodiments of the invention are described below in conjunction with the examples, but it should be understood that these descriptions are merely intended to illustrate further features and advantages of the invention, and are not limiting of the claims of the invention.
The description of this section is intended to be illustrative of only a few exemplary embodiments and the invention is not to be limited in scope by the description of the embodiments. It is also within the scope of the description and claims of the invention to interchange some of the technical features of the embodiments with other technical features of the same or similar prior art.
The description of the steps in the various embodiments in the specification is merely for convenience of description, and the implementation of the present application is not limited by the order in which the steps are implemented.
"coupled" or "connected" in the specification includes both direct and indirect connections, such as through some active, passive, or electrically conductive medium; connections through other active or passive devices, such as through switches, follower circuits, etc. circuits or components, may be included as known to those skilled in the art, on the basis of achieving the same or similar functional objectives.
The invention discloses a control circuit of a flyback converter, and FIG. 8 is a schematic diagram of the control circuit of the flyback converter in an embodiment of the invention; referring to fig. 8, the frequency control circuit includes: a feedback voltage acquisition circuit 1 and an operation mode control unit 2. The feedback voltage acquisition circuit 1 is used for acquiring a feedback voltage representing an output voltage. The working mode control unit 2 is coupled to the feedback voltage acquisition circuit 1, and controls the working mode of the flyback converter according to the feedback voltage. The specific control parameter of the operation mode of the flyback converter may be the frequency of the flyback converter (i.e. the switching frequency of the main switching tube) or the current amplitude (e.g. the amplitude of the current flowing through the main switching tube). In a specific embodiment, the operation mode control unit 2 is configured to control the frequency of the flyback converter according to the feedback voltage. Further, the operation modes of the flyback converter may include a current continuous operation mode (CCM operation mode for short) and a quasi-resonant operation mode (QR operation mode). The working mode control unit 2 controls the flyback converter to enter a current continuous working mode when the flyback converter is in a low-voltage full-load state; the operation mode control unit 2 controls the flyback converter to enter a quasi-resonant operation mode in a state in which the flyback converter is at a high-voltage full load.
In one embodiment of the invention, the low and high voltages refer to input ac voltages; in ACDC systems, 110Vac is generally referred to as low pressure below and 230Vac is referred to as high pressure above. This is a generic trade designation and there is no specific voltage determination threshold. Low-voltage full load refers to an input ac voltage below 100Vac and a load current approaching the OCP (over-current protection threshold) of the system; high voltage full load means that the input ac voltage is higher than 230Vac and the load current is close to the OCP (over-current protection threshold) of the system.
FIG. 9 is a schematic diagram illustrating a control circuit of a flyback converter according to an embodiment of the present invention; referring to fig. 9, in an embodiment of the present invention, the operation mode control unit 2 includes a frequency control unit for controlling the frequency of the flyback converter; the frequency control unit includes an upper clamp frequency control unit 211 and a lower clamp frequency control unit 212.
The upper clamp frequency control unit 211 is configured to control an upper clamp frequency signal; the upper clamp frequency control unit controls the upper clamp frequency signal according to the feedback voltage FB, and controls the upper clamp frequency signal to be reduced when the feedback voltage FB is reduced and is lower than a set threshold value.
The lower clamp frequency control unit 212 is configured to control a lower clamp frequency signal; the lower clamp frequency control unit controls the lower clamp frequency signal according to the feedback voltage FB, and controls the lower clamp frequency signal to be reduced when the feedback voltage FB is reduced and is lower than a set threshold value; and when the feedback voltage FB is higher than a set threshold value, the lower clamp frequency control unit controls the lower clamp frequency signal to be a set fixed value. In a specific embodiment, as shown in fig. 5, the lower clamp control unit controls the lower clamp signal to be a set fixed value when the feedback voltage is higher than 1V (i.e., the set threshold). In this embodiment, it is understood that there are two values of different phases of setting the fixed value, the lower clamp signal being a value other than zero in the first phase, the lower clamp signal being zero in the second phase or the lower clamp being inactive in the second phase. In an embodiment, the lower clamp frequency control unit controls the lower clamp frequency signal to remain unchanged during a constant voltage mode (abbreviated as CV mode) interval of the flyback converter.
In an embodiment of the invention, the frequency control unit further comprises a second and gate; the output end of the upper clamp frequency control unit is coupled with the first input end of the second AND gate, the output end of the lower clamp frequency control unit is coupled with the second input end of the second AND gate, and the output end of the first AND gate outputs a control signal for controlling the frequency in a current continuous working mode.
Furthermore, the operation mode control unit 2 may further comprise an amplitude modulation unit 22, the amplitude modulation unit 22 being arranged to modulate the current amplitude of the flyback converter. In a specific embodiment, the amplitude modulation unit 22 is configured to modulate the amplitude of the current flowing through the main switching tube.
FIG. 5 is a schematic diagram of an amplitude-frequency control curve of a control circuit of a flyback converter according to an embodiment of the present invention, and FIG. 6 is a schematic diagram of a circuit of an operation mode control unit according to an embodiment of the present invention; referring to fig. 5 and 6, in an embodiment of the present invention, the operation mode control unit 2 includes: a degaussing detection circuit 201, an error amplifier 202, a first comparator 203, a first and gate 204, a low pass filter 205, an amplitude modulation circuit 206, a second comparator 207, a second and gate 208, an or gate 209, and a flip-flop 210.
The input end of the degaussing detection circuit 201 is coupled to a feedback voltage FB of the output voltage Vout, and the feedback voltage FB is proportional to the output voltage Vout; the degaussing detection circuit 201 is configured to generate a valley conduction signal.
A first input terminal (e.g., a forward input terminal) of the error amplifier 202 is coupled to the first reference voltage Vref, and a second input terminal (e.g., an inverse input terminal) of the error amplifier 202 is coupled to the feedback voltage FB; the error amplifier 202 is configured to amplify a difference between the feedback voltage FB and the first reference voltage Vref, and the amplified error signal represents an error between the actual output voltage and the ideal output voltage, and reflects the current load depth.
A first input terminal (e.g., may be an inverting input terminal) of the first comparator 203 is coupled to the output terminal of the error amplifier 202, and a second input terminal (e.g., may be a non-inverting input terminal) of the first comparator 203 is coupled to a second reference voltage; the first comparator 203 is configured to obtain a first comparison signal according to the output terminal of the error amplifier and a second reference voltage. In one embodiment, the second reference voltage is a ramp signal Vramp.
The input end of the first and gate 204 is coupled to the output end of the degaussing detection circuit 201, the output end of the first comparator 203, and the up clamp signal f_up_clamp, respectively. The input end of the low-pass filter 205 is coupled to the output end of the error amplifier 202, so as to perform low-pass filtering on the information output by the error amplifier 202. An input terminal of the amplitude modulation circuit 206 is coupled to an output terminal of the low-pass filter, so as to amplitude modulate the information output by the low-pass filter.
A first input terminal of the second comparator 207 is coupled to the current feedback voltage, and a second input terminal of the second comparator 207 is coupled to the output terminal of the amplitude modulation circuit 206. The first input of the second AND gate 208 is coupled to the clamp signal f_up_clamp, and the second input of the second AND gate 208 is coupled to the lower clamp signal f_low_clamp.
A first input of the or gate 209 is coupled to an output of the first and gate 204, and a second input of the or gate 209 is coupled to an output of the second and gate 208. A first input terminal of the flip-flop 210 is coupled to the output terminal of the or gate 209, a second input terminal of the flip-flop 210 is coupled to the output terminal of the second comparator, and the output terminal of the flip-flop 210 outputs the frequency signal PWM.
The first and gate 204 is used to control the flyback converter to operate in a quasi-resonant mode of operation and the second and gate 208 is used to control the flyback converter to operate in a current continuous mode of operation. The output end of the first and gate 204 and the output end of the second and gate 208 serve as two input ends of the or gate 209; the output of the or gate 209 is high as long as one of the signals output from the first and second and gates 204, 208 is high. If the output signal of the first AND gate 204 is high, the flyback converter is controlled to operate in a quasi-resonant operation mode; if the output signal of the second AND gate 208 is high, the flyback converter is controlled to operate in the current continuous operation mode. The control mode can be adjusted according to the selection and load conditions of the peripheral elements.
The feedback voltage FB is sampled to obtain a feedback signal of the output voltage Vout, and the feedback voltage FB is proportional to Vout, so that the information of the output voltage is obtained by sampling the signal of the feedback voltage FB. The degaussing detection circuit 201 is used to generate a valley conduction signal, and the conduction of the system in the valley can reduce the switching loss so as to improve the working efficiency.
The sampled feedback voltage FB signal and the internal reference voltage are input to two ends of the error amplifier to amplify the difference between the feedback voltage FB signal and the internal reference voltage, the amplification ratio is R2/R1, and the amplified error signal Vea represents the error between the actual output voltage and the ideal output voltage and also reflects the current load depth.
The error signal Vea is compared with an internal ramp signal Vramp to obtain the cv_ct signal. When the system works in the QR working mode, the pwm signal can be set to 1 only when the three types of cv_ct, QR and f_up_clamp are simultaneously 1, namely, the pwm_set_QR is generated. When the system is operated in CCM operation mode, when f_up_clamp and f_low_clamp are simultaneously 1, the pwm signal can be set to 1, i.e. pwm_set_ccm is generated.
The system generates a PWM set 1 signal according to the generation time of the pwm_set_ccm and the pwm_set_QR, and the PWM set 0 signal is controlled by the Vcs_ref_cv, so that the working frequency of the system is indirectly controlled. When the voltage of CS rises to Vcs_ref_cv, the pwm signal is set to 0.
Vcs_ref_cv is a signal obtained by low-pass filtering by Vea, and vcs_ref_cv represents an amplitude modulation function of CS; the frequency modulation function is realized through the upper clamp signal f_up_clamp and the lower clamp signal f_low_clamp. Therefore, the whole loop realizes the function of controlling the output voltage by frequency modulation and amplitude modulation.
FIG. 7 is a schematic diagram of a portion of a frequency control unit according to an embodiment of the invention; referring to fig. 7, fig. 7 discloses a specific implementation of the upper and lower clamp signals.
Vea and FB control the charging current through the first transconductance amplifier circuit OTA1 and the second transconductance amplifier circuit OTA2, respectively, and the charging current ichar=i0-gm1 (3-Vea) -gm2 (1.6-FB), ichar=t=1.6v×c0, to obtain t=1.6v×c0/Ichar, i.e. the period of the component 1 is T.
In one embodiment, the up clamp signal f_up_clamp is obtained by counting 11 cycles, i.e., f_up_clamp=1/(11T); the lower clamp frequency signal f_low_clamp is synthesized through two signals, V4 is selected when FB is more than or equal to 1V, and W4 is selected when FB is less than 1V; v4 is obtained by dividing a signal of a fixed frequency, and W4 is obtained by dividing T.
In an embodiment of the present invention, the lower clamp frequency control unit includes: the first oscillator, the second oscillator and the oscillator selection unit. The first input end of the first oscillator is coupled with the feedback voltage FB, and the second input end of the first oscillator is coupled with the error signal Vea of the feedback voltage FB and the first reference voltage; the second oscillator is an oscillator with fixed frequency; the input end of the oscillator selection unit is coupled to the first oscillator and the second oscillator respectively, and is used for selecting the first oscillator when the feedback voltage FB is lower than a set threshold value and selecting the second oscillator when the feedback voltage FB is higher than the set threshold value.
The upper clamp frequency signal is set to lower the working frequency when the load is reduced so as to reduce the energy output; the manner of reducing the energy output may be achieved by reducing the frequency of the output energy or reducing the energy of a single output. The error voltage Vea output by the error amplifier EA represents the load depth, the higher the error voltage Vea represents the heavier the load, the lower the frequency or Vcs amplitude as the load decreases to achieve the input energy and output energy balance to stabilize the output voltage, and the upper clamp frequency signal is used to control the operating frequency.
Setting a lower clamp frequency signal for limiting the working condition of the CCM working mode, wherein the upper clamp frequency can only control the frequency of working in the QR working mode, and the lower clamp frequency can control the working frequency of the CCM working mode. Because the working frequency is lower under the condition of full load under the low pressure, the lower clamp frequency control of the CCM working mode is adopted, the working frequency is forcedly increased to the CCM working mode, the QR working mode is separated, the working frequency is higher under the high pressure, but the working frequency is clamped by the upper clamp frequency, so the working frequency can be just the upper clamp frequency. The high-voltage working at the upper clamp frequency is mainly because the frequency is too fast, if some signal processing is not enough, the risk of losing lock of a control loop is easily caused, and the low-voltage working mode is separated from the QR working mode to enter the CCM working mode mainly for separating from the problem that the input ripple of the primary side is large in the low-voltage QR working mode, so that the output ripple is also enlarged.
The invention also discloses a flyback converter, which comprises the control circuit of the flyback converter.
The invention further discloses a control method of the flyback converter, which comprises the following steps:
a working state detection step of detecting the working state of the flyback converter; and
a working mode control step of controlling the working mode of the flyback converter according to the working state of the flyback converter detected in the working state detection step; controlling the flyback converter to enter a current continuous working mode when the flyback converter is in a low-voltage full-load state; and controlling the flyback converter to enter a quasi-resonance working mode under the condition that the flyback converter is in a high-voltage full-load state.
In an embodiment of the present invention, the operation mode control step includes a frequency control step of controlling a frequency of the flyback converter; the frequency control step includes:
an upper clamp frequency control step; controlling the upper clamp frequency signal according to the feedback voltage FB, and controlling the upper clamp frequency signal to be reduced when the feedback voltage FB is reduced;
a lower clamp frequency control step; controlling the lower clamp frequency signal according to the feedback voltage FB, and controlling the lower clamp frequency signal to be reduced when the feedback voltage FB is reduced; and when the feedback voltage FB is higher than a set threshold value, the lower clamp frequency control unit controls the lower clamp frequency signal to be a set fixed value. In one embodiment, the clamp frequency signal is controlled to be unchanged when the flyback converter is in a constant voltage mode interval;
a frequency modulation step; and realizing the frequency modulation function according to the acquired upper clamp frequency signal and lower clamp frequency signal.
The frequency control step may further include: the frequency of the flyback converter when working in the quasi-resonant QR working mode is controlled through the upper clamp frequency signal, and the frequency of the flyback converter when working in the current continuous CCM working mode is controlled through the lower clamp frequency signal.
In addition, the operation mode control step may further include an amplitude modulation step of modulating the amplitude of the flyback converter.
In summary, the control circuit and the control method of the flyback converter and the flyback converter provided by the invention can ensure the stable operation of the circuit and effectively ensure the efficiency of the circuit.
In the use scene of the invention, the system enters the CCM working mode to work under low-pressure full load and works under high-pressure full load, so that the problem of large output ripple wave of the QR working mode during low-pressure full load working is avoided, and the efficiency of the system is ensured when the high-pressure full load working is in the QR working mode.
The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The description and applications of the present invention herein are illustrative and are not intended to limit the scope of the invention to the embodiments described above. Effects or advantages referred to in the embodiments may not be embodied in the embodiments due to interference of various factors, and description of the effects or advantages is not intended to limit the embodiments. Variations and modifications of the embodiments disclosed herein are possible, and alternatives and equivalents of the various components of the embodiments are known to those of ordinary skill in the art. It will be clear to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, and with other assemblies, materials, and components, without departing from the spirit or essential characteristics thereof. Other variations and modifications of the embodiments disclosed herein may be made without departing from the scope and spirit of the invention.
Claims (11)
1. A control circuit for a flyback converter, the control circuit comprising:
the feedback voltage acquisition circuit is used for acquiring feedback voltage representing the output voltage; and
the working mode control unit is coupled with the feedback voltage acquisition circuit and used for controlling the working mode of the flyback converter according to the feedback voltage; the working mode control unit controls the flyback converter to enter a current continuous working mode when the flyback converter is in a low-voltage full-load state; the working mode control unit controls the flyback converter to enter a quasi-resonance working mode when the flyback converter is in a high-voltage full-load state; the working mode control unit comprises a frequency control unit for controlling the frequency of the flyback converter; the frequency control unit includes:
the upper clamp frequency control unit is used for controlling the upper clamp frequency signal according to the feedback voltage, and controlling the upper clamp frequency signal to be reduced when the feedback voltage is reduced and is lower than a set threshold value; and
the lower clamp frequency control unit is used for controlling the lower clamp frequency signal according to the feedback voltage, and controlling the lower clamp frequency signal to be reduced when the feedback voltage is reduced and is lower than a set threshold value; and when the feedback voltage is higher than the set threshold value, the lower clamp frequency control unit controls the lower clamp frequency signal to be a set fixed value.
2. The flyback converter control circuit of claim 1, wherein:
the frequency control unit further comprises a second and gate; the output end of the upper clamp frequency control unit is coupled with the first input end of the second AND gate, the output end of the lower clamp frequency control unit is coupled with the second input end of the second AND gate, and the output end of the second AND gate outputs a control signal for controlling the frequency in a current continuous working mode.
3. The flyback converter control circuit of claim 1, wherein:
the lower clamp frequency control unit comprises:
the first oscillator has a first input end coupled to the feedback voltage and a second input end coupled to an error signal of the feedback voltage and the first reference voltage;
the second oscillator is an oscillator with fixed frequency; and
the input end of the oscillator selection unit is respectively coupled with the first oscillator and the second oscillator; the first oscillator is selected when the feedback voltage is lower than a set threshold value, and the second oscillator is selected when the feedback voltage is higher than the set threshold value.
4. The flyback converter control circuit of claim 1, wherein:
and in the constant-voltage mode interval of the flyback converter, the lower clamp frequency control unit controls the lower clamp frequency signal to be unchanged.
5. The flyback converter control circuit of claim 1, wherein:
the operation mode control unit includes:
the input end of the degaussing detection circuit is coupled with the feedback voltage and is used for generating a valley conduction signal;
the first input end of the error amplifier is coupled with the first reference voltage, and the second input end of the error amplifier is coupled with the feedback voltage; generating an error signal based on the feedback voltage and the first reference voltage;
a first input end of the first comparator is coupled with the output end of the error amplifier, and a second input end of the first comparator is coupled with a second reference voltage; the first comparison signal is obtained according to the error signal and the second reference voltage;
the input end of the first AND gate is respectively coupled with the output end of the degaussing detection circuit, the output end of the first comparator and the upper clamp frequency control signal;
the first input end of the second AND gate is coupled with the clamp frequency control signal, and the second input end of the second AND gate is coupled with the lower clamp frequency control signal;
the first input end of the OR gate is coupled with the output end of the first AND gate, and the second input end of the OR gate is coupled with the output end of the second AND gate; and
and the first input end of the trigger is coupled with the output end of the OR gate, and the output end of the trigger outputs a switch control signal.
6. The flyback converter control circuit of claim 5 wherein:
the operation mode control unit further includes:
the input end of the low-pass filter is coupled with the output end of the error amplifier and is used for carrying out low-pass filtering on an error signal;
the input end of the amplitude modulation circuit is coupled with the output end of the low-pass filter and used for carrying out amplitude modulation on the information output by the low-pass filter; and
a first input end of the second comparator is coupled with the current feedback voltage, and a second input end of the second comparator is coupled with an output end of the amplitude modulation circuit; the second input end of the trigger is coupled with the output end of the second comparator.
7. A flyback converter, characterized by: control circuit comprising a flyback converter according to any of claims 1 to 6.
8. A method of controlling a flyback converter, the method comprising:
a feedback voltage obtaining step of obtaining a feedback voltage representing the output voltage; and
a working mode control step of controlling the working mode of the flyback converter according to the feedback voltage; controlling the flyback converter to enter a current continuous working mode when the flyback converter is in a low-voltage full-load state; controlling the flyback converter to enter a quasi-resonance working mode under the condition that the flyback converter is in a high-voltage full-load state; the working mode control step comprises a frequency control step, wherein the frequency of the flyback converter is controlled; the frequency control step includes:
an upper clamp frequency control step; controlling the upper clamp frequency signal to be reduced when the feedback voltage is reduced and is lower than a set threshold value according to the feedback voltage; and
a lower clamp frequency control step; controlling the lower clamp frequency signal according to the feedback voltage, and controlling the lower clamp frequency signal to be reduced when the feedback voltage is reduced and is lower than a set threshold value; and when the feedback voltage is higher than the set threshold value, controlling the clamp frequency signal to be a set fixed value.
9. The control method of a flyback converter according to claim 8, wherein:
the frequency control step includes: and in the constant-voltage mode interval of the flyback converter, the clamp frequency signal is controlled to be unchanged.
10. The control method of a flyback converter according to claim 8, wherein:
the frequency control step further includes:
a frequency modulation step; realizing a frequency modulation function according to the acquired upper clamp frequency control signal and lower clamp frequency control signal;
the frequency of the flyback converter when working in the quasi-resonant working mode is controlled by the upper clamp frequency control signal, and the frequency of the flyback converter when working in the current continuous working mode is controlled by the upper clamp frequency control signal and the lower clamp frequency control signal.
11. The control method of a flyback converter according to claim 8, wherein:
the operation mode control step includes an amplitude modulation step of modulating the current amplitude of the flyback converter.
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