CN115149811A - Flyback converter and starting control method thereof - Google Patents

Flyback converter and starting control method thereof Download PDF

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Publication number
CN115149811A
CN115149811A CN202210221832.0A CN202210221832A CN115149811A CN 115149811 A CN115149811 A CN 115149811A CN 202210221832 A CN202210221832 A CN 202210221832A CN 115149811 A CN115149811 A CN 115149811A
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Prior art keywords
signal
output
control
flyback converter
control circuit
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CN202210221832.0A
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Chinese (zh)
Inventor
龚昌为
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Joulwatt Technology Co Ltd
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Joulwatt Technology Co Ltd
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Priority to CN202210221832.0A priority Critical patent/CN115149811A/en
Publication of CN115149811A publication Critical patent/CN115149811A/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
    • 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
    • H02M3/33507—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 with automatic control of the output voltage or current, e.g. flyback converters
    • H02M3/33523—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 with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop
    • 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
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • 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
    • H02M1/42—Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
    • 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
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention discloses a flyback converter and a starting control method thereof, wherein the flyback converter comprises the following components: a transformer; a power switch tube; a rectifier tube; the primary side control circuit generates a first control signal after the flyback converter is powered on so as to control the transmission of starting energy to the secondary side part of the flyback converter; and the secondary side control circuit transmits a stop signal and a second control signal to the primary side control circuit in sequence after being started. The invention can ensure that the primary side switching signal does not generate mutation in the starting process, realizes the smooth transition of the original secondary side control, can realize the smooth starting of the output voltage, and has the advantages of better output characteristic, simple control method, better compatibility and lower cost.

Description

Flyback converter and starting control method thereof
Technical Field
The invention relates to the technical field of converters, in particular to a flyback converter and a starting control method thereof.
Background
With the rapid development of power electronic technology application, people have increasingly high requirements on the small size, high efficiency and high reliability of the switching converter. The flyback converter has the characteristics of simple topology, few components, low cost and the like, and is widely applied to electronic industries such as a switching power supply and the like. Flyback converters are a type of isolated power converter commonly used for conversion between ac-to-dc and dc-to-dc current isolated from the current between an input and one or more outputs. More precisely, the flyback converter is a step-up/step-down converter with an inductor split, constituting a transformer, so that the voltage ratio is multiplied by the additional advantage of the insulation. In a conventional flyback converter, in order to improve efficiency, a synchronous rectifier is usually used to replace a diode rectifier in a secondary part, so that a secondary control circuit is correspondingly required to be arranged in the flyback converter to realize on-off control of the synchronous rectifier.
A typical configuration for a flyback converter includes a primary power switch coupled to a primary (or primary) transformer winding of a transformer, and a synchronous rectifier coupled to a secondary (or secondary) transformer winding of the transformer. The input voltage is provided by the primary winding and the primary power switch tube. The primary side driving voltage controls the conduction and the disconnection of the primary side power switch tube and conducts primary side current. Secondary switch and synchronous rectifier as a supplement in operation. The conduction periods of the power switch tube and the synchronous rectifier tube are not overlapped, one switch is switched on, and the other switch is switched off. The current flow in the secondary portion of the transformer is referred to as the secondary current, which charges the output capacitor and provides the output voltage.
In order to obtain higher system efficiency, the conventional flyback converter generally adopts a secondary control circuit to simultaneously realize on/off control of a primary power switching tube and a secondary synchronous rectifier tube. However, the secondary side control circuit cannot be directly started when the flyback converter is initially powered on, and the primary side control circuit needs to control the primary side power switching tube to work for a period of time first, so that energy is transferred to the secondary side through the transformer, the secondary side control circuit is started, and then the secondary side control circuit takes over control over the primary side power switching tube. However, the existing start-up scheme of the flyback converter has the following problems: 1. the start of the output voltage cannot be smoothly transited, and the problem of back hooking or overshoot exists. 2. The conventional primary side control system has high common risk of the primary side and the secondary side and low system efficiency.
Therefore, there is a need to provide an improved technical solution to overcome the above technical problems in the prior art.
Disclosure of Invention
In order to solve the technical problems, the invention provides a flyback converter and a starting control method thereof, which can prevent a primary side switching signal from sudden change in the starting process, realize the smooth transition of the primary side and the secondary side control, realize the smooth starting of output voltage, have better output characteristics, have simple control method, better compatibility and lower cost.
According to a first aspect of the present disclosure, there is provided a flyback converter including:
the transformer comprises a primary winding and a secondary winding;
the power switch tube is connected with the primary winding;
the rectifier tube is connected between the secondary winding and the output end of the flyback converter;
the primary side control circuit is started after the flyback converter is powered on, and generates a first control signal after the primary side control circuit is started so as to control the transmission of starting energy to a secondary side part of the flyback converter;
a secondary side control circuit which transmits a stop signal and a second control signal to the primary side control circuit in sequence after being started,
the first control signal and the second control signal are both used for triggering to realize on-off control of the power switch tube, and the stop signal is used for triggering the primary side control circuit to stop generating the first control signal or triggering to shield the on-off control of the first control signal on the power switch tube.
Optionally, the secondary control circuit is configured to deliver the stop signal to the primary control circuit at a first time after the start, and deliver the second control signal to the primary control circuit after a first time delay from the first time.
Optionally, the first time is a time when an output feedback signal reaches a first reference voltage, where the output feedback signal represents an output power of the flyback converter.
Optionally, the first time is a time when the first time is within a preset time period after the power switching tube starts to be turned on and the output feedback signal is greater than or equal to a first reference voltage, where the output feedback signal represents the output power of the flyback converter.
Optionally, the secondary side control circuit includes an output unit configured to receive the output feedback signal and generate the stop signal at the first time, and the output unit includes:
a first comparison unit, a non-inverting input terminal of which receives the output feedback signal and an inverting input terminal of which receives the first reference voltage, the first comparison unit being configured to output a first trigger signal if the output feedback signal is greater than or equal to the first reference voltage;
a stop signal generating unit, an input end of which is connected with an output end of the first comparing unit, the stop signal generating unit being configured to generate the stop signal when receiving the first trigger signal.
Optionally, the secondary side control circuit includes an output unit configured to receive the output feedback signal and generate the stop signal at the first time, and the output unit includes:
a second comparison unit having a non-inverting input terminal receiving the output feedback signal and an inverting input terminal receiving the first reference voltage, the second comparison unit configured to output a first comparison signal if the output feedback signal is greater than the first reference voltage;
a third comparison unit, wherein the positive phase input end receives a second reference voltage, the negative phase input end receives the voltage difference of two power ends of the rectifier tube, and the output end outputs a second comparison signal;
a rising edge pulse generating unit, an input end of which receives the second comparison signal and generates a pulse at the rising edge of the second comparison signal to output a first pulse signal;
a first combinational logic circuit receiving the first comparison signal and the first pulse signal, the first combinational logic circuit configured to output a first trigger signal when it is detected for a first time that the first comparison signal and the first pulse signal are simultaneously in an active state;
a stop signal generation unit having an input connected to the output of the first combinational logic circuit, the stop signal generation unit configured to generate the stop signal upon receiving the first trigger signal.
Optionally, the output unit further includes:
a delay unit, an input end of which receives the first trigger signal, the delay unit being configured to start timing when receiving the first trigger signal and output a second trigger signal after the first time;
a first and logic circuit, a first input terminal of which receives the second control signal, a second input terminal of which is connected to the output terminal of the delay unit, the first and logic circuit being configured to output the received second control signal after receiving the second trigger signal;
an or logic circuit, a first input terminal of the or logic circuit being connected to an output terminal of the first and logic circuit, a second input terminal of the or logic circuit being connected to an output terminal of the stop signal generating unit, the or logic circuit being configured to implement time-sharing output of the stop signal and the second control signal.
Optionally, the secondary side control circuit further includes:
an output feedback signal generation circuit configured to generate the output feedback signal according to an output voltage of the flyback converter;
a second control signal generation unit configured to generate the second control signal according to the output feedback signal.
Optionally, the difference between the frequency and the pulse width parameter of the second control signal in at least the initial pulse period and the frequency and the pulse width parameter of the first control signal are both smaller than a preset threshold.
Optionally, the primary side control circuit comprises:
the first control signal generation unit is configured to start generating the first control signal after the flyback converter is powered on, and stop generating the first control signal according to the trigger of the stop signal;
and the driving unit is configured to transmit a first driving control signal to the control end of the power switch tube when receiving the first control signal or the second control signal so as to realize on-off control of the power switch tube.
According to a second aspect of the present disclosure, there is provided a start-up control method of a flyback converter, which is applicable to the flyback converter as described above, the start-up control method including:
after the flyback converter is powered on, a primary side control circuit is used for generating a first control signal to control the transmission of starting energy to a secondary side part of the flyback converter;
after the secondary side control circuit is started, the secondary side control circuit is utilized to transmit a stop signal and a second control signal to the primary side control circuit in sequence,
the first control signal and the second control signal are both used for triggering to realize on-off control of the power switch tube, and the stop signal is used for triggering the primary side control circuit to stop generating the first control signal or triggering to shield the on-off control of the first control signal on the power switch tube.
Optionally, successively transmitting the stop signal and the second control signal to the primary side control circuit by using the secondary side control circuit includes:
and transmitting the stop signal to the primary side control circuit at a first time after the secondary side control circuit is started, and transmitting the second control signal to the primary side control circuit after delaying for a first time from the first time.
Optionally, the first time is a time when the output feedback signal of the flyback converter reaches a first reference voltage.
Optionally, the first time is a time when the first time is within a preset time period after the power switching tube starts to be turned on and the output feedback signal is greater than or equal to a first reference voltage, where the output feedback signal represents the output power of the flyback converter.
Optionally, the difference between the frequency and the pulse width parameter of the second control signal in at least the initial pulse period and the frequency and the pulse width parameter of the first control signal is smaller than a preset threshold.
Optionally, a difference between the first time and the period of the first control signal is smaller than a preset threshold.
The beneficial effects of the invention at least comprise:
according to the embodiment of the invention, the primary side control circuit is set to be powered on and started after the flyback converter is powered on, and then the first control signal is output to carry out on-off control on the power switch tube so as to control the supply of the starting energy to the output of the secondary side control circuit and the flyback converter, and after the secondary side control circuit is started after the secondary side control circuit obtains the starting energy, the secondary side control circuit is set to firstly trigger the primary side control circuit to stop generating the first control signal, and then the second control signal is transmitted to the primary side control circuit to replace the first control signal to continue carrying out on-off control on the power switch tube, so that the switching from the primary side control to the secondary side control can be smoothly realized. Meanwhile, under the condition that the difference values of the frequency and the pulse width parameter of the second control signal in the initial pulse period and the frequency and the pulse width parameter of the first control signal are smaller than the preset threshold value (namely the second control signal has the frequency and the pulse width which are basically the same as those of the first control signal in the initial pulse period), the driving signal of the primary side power switch tube can not be suddenly changed in the starting process, the smooth transition of the primary side and secondary side control and the smooth starting of the output voltage are realized, and the output quality of the flyback converter is improved.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
Drawings
Fig. 1 is a schematic diagram illustrating a structure of a flyback converter according to an embodiment of the present invention;
fig. 2 is a schematic diagram illustrating a primary side control circuit according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a secondary control circuit according to an embodiment of the present invention;
fig. 4 shows a schematic structural diagram of an output unit provided according to a first embodiment of the present invention;
fig. 5 shows a schematic structural diagram of an output unit provided according to a second embodiment of the present invention;
fig. 6 illustrates timing waveforms according to the start-up control of the flyback converter provided in fig. 4;
fig. 7 is a timing waveform diagram illustrating start-up control of the flyback converter according to the embodiment of the present invention;
fig. 8 is a timing waveform diagram illustrating another timing waveform of the start-up control of the flyback converter according to the embodiment of the present invention;
fig. 9 illustrates a timing waveform diagram according to the start-up control of the flyback converter provided in fig. 5;
fig. 10 illustrates another timing waveform diagram according to the start-up control of the flyback converter provided in fig. 5;
fig. 11 is a flowchart illustrating a start-up control method of a flyback converter according to an embodiment of the present invention.
Detailed Description
To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Referring to fig. 1, a flyback converter disclosed in the embodiment of the present invention includes: comprising a primary winding N P And secondary winding N S Is connected to the primary winding N P Voltage input circuit of (2) connected to the secondary winding N S Voltage output circuit of, and powerThe circuit comprises a switching tube Q1, a primary side control circuit 5, a rectifying tube Q2, a secondary side control circuit 8, an isolation device 6 and an output feedback signal generating circuit 9.
The voltage input circuit is connected between the input end of the flyback converter and the primary winding Np, and comprises a rectifying circuit 3 and an input capacitor C1. The rectifying circuit 3 can be connected with a power supply through the first connecting port 1, so that the power supply can provide electric energy to the flyback converter conveniently. The power source may include, but is not limited to, a power grid, a generator, a transformer, a battery, solar panels, wind turbines, a regenerative braking system, a hydraulic or wind generator, or any other form of device capable of providing electrical power to a flyback converter. The voltage input circuit may further include a filter circuit 2 connected between the rectifier circuit 3 and the first connection port 1 and a power factor correction circuit 4 connected between the rectifier circuit 3 and the input capacitor C1.
Further, the voltage input circuit further includes a primary winding N on the transformer TR P A resistor R1, a capacitor C2 and a diode D1 are arranged between the homonymous terminal and the heteronymous terminal. Wherein, the resistor R1 and the capacitor C2 are connected in parallel and then connected to the primary winding N P Between the different name terminal of (1) and the cathode of the diode D1, the anode of the diode D1 and the primary winding N P The resistor R1, the capacitor C2 and the diode D1 can absorb the primary winding N P The leakage inductance current, and further the performance of the transformer is improved.
The voltage output circuit is connected with the secondary winding N S And the output end of the flyback converter, an output capacitor Co is included, and the output capacitor Co can be connected with a load through a second connection port 7, and the load receives the electric energy (such as voltage and current) converted by the flyback converter. In some examples, the power converted by the flyback converter also passes through a filter before reaching the load. In some examples, the filter is a subcomponent of the flyback converter, an external component of the flyback converter, and/or a subcomponent of the load. In any case, the load may perform a function using filtered or unfiltered power from the flyback converter. Alternatively, the load may include, but is not limited to, a computing device and associated components, such as a microprocessor, electrical components, circuitry, laptopA tablet computer, a desktop computer, a tablet computer, a mobile phone, a battery, a speaker, a lighting unit, a related component of an automobile/watercraft/aviation/train, a motor, a transformer, or any other type of electrical device and/or circuit that receives a voltage or current from a flyback converter.
Power switch tube Q1 and primary winding N P And (4) connecting. In one possible embodiment, the power switch Q1 is a field effect transistor using NMOS.
The primary side control circuit 5 is configured to provide a first driving signal Vgs1 to the control terminal of the power switch Q1 to control on/off of the power switch Q1. In this embodiment, the primary control circuit 5 is configured to start after the flyback converter is powered on, and to generate a first control signal Vgs1_ P after the start to control the transfer of start energy to the secondary part of the flyback converter. The primary side control circuit 5 further comprises a first input SYNC, a first output DRV and a ground GND. A first input end SYNC of the primary side control circuit 5 is connected with the isolation device 6 to receive a signal transmitted by the secondary side control circuit 8; a first output end DRV of the primary side control circuit 5 is connected with a control end of the power switch tube Q1 to output a first driving signal Vgs1 to the control end of the power switch tube Q1; the ground terminal GND of the primary side control circuit 5 is connected to a reference ground.
Illustratively, the flyback converter disclosed in the present invention may operate in a secondary-side control manner to obtain higher system efficiency, that is, after the secondary-side control circuit 8 is started, the control signal for turning on/off the primary-side power switch Q1 is provided by the secondary-side control circuit 8. At this time, the primary side control circuit 5 can only serve as a driver in the normal operation process of the flyback converter to convert the second control signal transmitted by the secondary side control circuit and then drive the power switch tube Q1, so that the complexity and the system cost of the primary side control circuit 5 can be greatly reduced. Further in one possible embodiment, as shown in fig. 2, the primary side control circuit 5 includes: a first control signal generation unit 51 and a drive unit 52.
Wherein, the first control signal generating unit 51 is configured to start generating the first control signal Vgs _ P after the flyback converter is powered on, and to stop generating the first control signal Vgs _ P according to the trigger of the stop signal. The driving unit 52 is configured to transmit a first driving signal Vgs1 to the control terminal of the power switch Q1 when receiving the first control signal Vgs _ P or the second control signal PWM1, so as to implement on-off control of the power switch Q1.
It can be understood that the power supply of the flyback converter is located in the primary side portion, so after the flyback converter is powered on, the primary side control circuit 5 on the primary side of the flyback converter is powered on first, and the secondary side control circuit 8 on the secondary side of the flyback converter needs the primary side portion to transmit starting energy before being started. The first control signal generating unit 51 disposed in the primary side control circuit 5 is to generate a first control signal Vgs _ P before the secondary side control circuit 8 of the flyback converter is started to perform on-off control on the power switch Q1 to implement transmission of primary side energy to the secondary side portion, so as to implement starting of the secondary side control circuit 8. Further, the first control signal Vgs _ P is, for example, an open-loop pulse signal with a fixed frequency and a fixed pulse width (refer to fig. 6 to 10, note that the frequency of the first control signal Vgs _ P is 1/Ts _ P), so that the initial energy transmission process of the flyback converter is stable and control management is facilitated. And a driving unit 52 for implementing the driving function of the primary side control circuit 5.
It should be noted that the first control signal generating unit 51 receives the stop signal from the first input end SYNC of the primary side control circuit 5, the driving unit 52 transmits the first driving signal Vgs1 from the first output end DRV of the primary side control circuit 5 to the control end of the power switch Q1, and receives the second control signal PWM1 from the first input end SYNC of the primary side control circuit 5. In fig. 4, the dotted line with an arrow and the solid line with an arrow are only used to indicate that the stop signal and the second control signal PWM1 received by the primary side control circuit 5 are received in a time-sharing manner from the first input terminal SYNC thereof. The first control signal Vgs1_ P and the second control signal PWM1 are both used for triggering to realize on-off control of the power switch Q1, and the stop signal is used for triggering the primary side control circuit 5 to stop generating the first control signal Vgs1_ P, or the stop signal is used for triggering to shield the on-off control of the first control signal Vgs1_ P on the power switch Q1.
Optionally, the isolation device 6 may be any one of an isolation transformer, an optical coupler, an isolation capacitor, and an isolation chip. Through the isolation device 6, signal transmission between the primary side and the secondary side of the flyback converter can be realized.
The rectifier Q2 is connected between the secondary winding Ns and the voltage output circuit. Optionally, a rectifier tube Q2 may be connected to the secondary winding N S Between the first end of the secondary winding and the low-order output end of the flyback converter, namely the reference ground, and can also be connected with the secondary winding N S Between the second terminal and the high-side output terminal of the flyback converter, which is not limited in the present invention.
Optionally, the rectifier Q2 is a freewheeling diode or a synchronous rectifier, for example. When the rectifier Q2 is a synchronous rectifier, the synchronous rectifier Q2 may be an NMOS field effect transistor, and further, the flyback converter further includes a resistor R2 and a capacitor C3 connected in series between the drain and the source of the synchronous rectifier Q2. The resistor R2 and the capacitor C3 can absorb the stress of the MOS tube and protect the synchronous rectifier tube Q2. It should be noted that, in the drawings and the description of the present application, the technical solution of the present invention is only exemplified by using a synchronous rectifier tube, and for the solution using a freewheeling diode, it can be directly or unambiguously obtained based on the content of this document, and it should also be within the protection scope of the present invention.
The secondary side control circuit 8 is started according to the starting energy, and transmits a stop signal and a second control signal PWM1 to the primary side control circuit 5 in sequence after the starting. Further, the secondary control circuit 8 is configured to deliver a stop signal to the primary control circuit 5 at a first time after its start, and to deliver a second control signal PWM1 to the primary control circuit 5 after a delay of a first time (denoted as Td) from the first time.
The secondary control circuit 8 receives a first voltage (denoted as V1, the first voltage V1 is used for representing a potential difference between a first node a and a second node b in the flyback converter, and the first voltage V1 is in a direct proportional relationship with the output voltage Vo of the flyback converter, i.e. V1 × k = Vo, k is a positive number), a second voltage (denoted as V1), and a third voltage SW The second voltage V SW The control circuit is used for representing the potential difference between a third node c and a second node b in the flyback converter, at least one of the third node c and the second node b is connected with the rectifier tube Q2), outputting a stop signal and a second control signal PWM1 to the isolation device 6 to be transmitted to the primary side control circuit 5 through the isolation device 6, and outputting a third control signal (marked as PWM 2) to the control end of the synchronous rectifier tube Q2 to control the on/off of the synchronous rectifier tube Q2. It is understood that the second node b is used to characterize the reference zero potential point of the secondary side control circuit 8, for example, in some possible embodiments of the present invention, the second node b, i.e. the reference zero potential point of the secondary side control circuit 8, is the same as the reference ground potential point of the secondary side portion of the flyback converter, and is connected to the low-order output terminal of the flyback converter; in other possible embodiments of the present invention, the reference zero point of the second node b, i.e. the secondary side control circuit 8, is different from the reference ground point of the secondary side portion of the flyback converter.
The secondary control circuit 8 further includes: a power supply terminal Vcc _ s, a first input terminal SW, a second input terminal V1, a third input terminal SCS, a fourth input terminal COMP, a first output terminal GT, a second output terminal SYNC, and a ground terminal GND. A power supply terminal Vcc _ s of the secondary control circuit 8 is connected to the second node b via the first capacitor Ci, and is configured to provide a power supply voltage for the secondary control circuit 8 according to the start energy transmitted by the primary side of the flyback converter; the first input terminal SW of the secondary control circuit 8 is connected to the third node c for receiving the second voltage V SW (ii) a A second input terminal V1 of the secondary side control circuit 8 is connected to the first node a to receive the first voltage V1; the third input SCS of the secondary control circuit 8 is connected to a predetermined proportional resistor (denoted as R in this embodiment) CS_S ) Is connected to the second node b to receive a proportional voltage (denoted as V) SCS ) And further according to the proportional voltage V SCS Obtaining a voltage signal representing excitation current information of the flyback converter; a fourth input end COMP of the secondary side control circuit 8 is connected with a high-order output end of the output feedback signal generation circuit 9 to receive the output feedback signal Vcomp; a first output terminal GT of the secondary control circuit 8 is connected to the control terminal of the synchronous rectifier Q2 to output a third control signal PWM2 to the control terminal of the synchronous rectifier Q2; secondary side controlThe second output end SYNC of the circuit 8 is connected to the isolation device 6, so as to implement signal transmission with the primary side control circuit 5 of the flyback converter through the isolation device 6, for example, the stop signal and the second control signal PWM1 are transmitted to the primary side control circuit 5 through the isolation device 6; the ground GND of the secondary control circuit 8 is connected to the second node b.
Referring to fig. 3, the secondary-side control circuit 8 further includes: a start unit 81, a second control signal generation unit 82, an output unit 83, a drive interlock unit 84, and a third control signal generation unit 85.
Wherein the starting unit 81 is configured to receive starting energy and to generate a supply voltage required by the secondary side control circuit 8 across the first capacitor Ci in dependence on the received starting energy. For example, the starting unit 81 may adopt two power supply units to provide a required power supply voltage to the secondary side control circuit 8 by matching with a corresponding linear regulator (LDO) based on the first voltage V1 and the second voltage Vsw, so that the secondary side control circuit 8 can have a suitable power supply voltage value to support a corresponding application scenario of the flyback converter under different voltage states of the output voltage Vo of the flyback converter, which is beneficial to improving the working efficiency and compatibility of the flyback converter.
Optionally, in some possible embodiments of the present invention, the synchronous rectifier Q2 is connected to the low-side output terminal of the flyback converter, where the first voltage V1 is a voltage of the first terminal of the secondary winding Ns, that is, the output voltage Vo of the flyback converter, and the second voltage V is a voltage of the second terminal of the secondary winding Ns SW I.e. the voltage at the second end of the secondary winding Ns connected to the synchronous rectifier tube 2. In other possible embodiments of the present invention, the synchronous rectifying tube Q2 is connected to the low-side output terminal of the flyback converter, and at this time, the first voltage V1 is a potential difference between the high-side output terminal of the flyback converter and the second node b, that is, the output voltage Vo of the flyback converter, and the second voltage V SW I.e. the potential difference between the first end of the secondary winding Ns and the second node b, wherein the second node b has the same potential value as the reference ground point of the secondary part of the flyback converter. In some further possible embodiments of the invention, the transformer TR further comprises an auxiliaryOne end of the auxiliary winding is connected with a second node b, meanwhile, the synchronous rectifier tube Q2 is connected with a high-order output end of the flyback converter, at the moment, the first voltage V1 is the voltage difference between two ends of the auxiliary winding, and the second voltage V SW Namely, the potential difference between the high-order output end of the flyback converter and the second node b, where the second node b is the common connection node between the secondary winding Ns and the synchronous rectifier Q2.
In the present embodiment, the output feedback signal generation circuit 9 is configured to generate the output feedback signal Vcomp according to the output voltage Vo of the flyback converter to characterize the output power of the flyback converter. It is understood that the circuit structure of the output feedback signal generating circuit 9 may adopt the existing conventional circuit structure, such as the combination structure of the error amplifier and the compensation, to obtain the output feedback signal Vcomp, which is not limited by the present invention.
With continued reference to fig. 5, the second control signal generation unit 82 is configured to generate the second control signal according to the output feedback signal Vcomp and according to the proportional voltage V SCS And obtaining a voltage signal representing the excitation current information of the flyback converter to generate a second control signal PWM1. Here, the specific operation principle and the circuit structure of the second control signal generating unit 82 have little relevance to the technical problem to be solved by the present application, and can be understood by referring to the prior art, and therefore, detailed description is not given.
The third control signal generating unit 85 is configured to generate a third control signal PWM2 according to the voltage Vsw of the two-power-end of the synchronous rectifier Q2, where the third control signal PWM2 is used for implementing on-off control of the synchronous rectifier Q2. Here, the specific operation principle and the circuit structure of the third control signal generating unit 85 have little relevance to the technical problem to be solved by the present application, and can be understood by referring to the prior art, and therefore, will not be described in detail.
The driving interlock unit 84 is configured to generate a secondary-side turn-off signal according to the second control signal PWM1, where the secondary-side turn-off signal is used to trigger and implement turn-off control on the synchronous rectifier Q2. In this embodiment, the driving interlock unit 84 can realize driving interlock of the primary side and the secondary side of the flyback converter, and prevent the primary side power switch Q1 and the secondary side synchronous rectifier Q2 from being turned on simultaneously. Meanwhile, because the control signal of the power switch tube Q1 is also generated by the secondary side control circuit 8, an additional isolation device is not required to be arranged to receive the feedback signal of the primary side.
The output unit 83 receives the output feedback signal Vcomp and the second control signal PWM1, and the output unit 83 is configured to determine a first time according to the output feedback signal Vcomp, generate a stop signal at the first time, and output the second control signal PWM1 after delaying the first time Td from the first time.
As shown in fig. 4 and 5, the output unit 83 further includes: a first trigger signal generation unit, a stop signal generation unit 833, a delay unit 834, a first and logic circuit 835, and an or logic circuit 836. The first trigger signal generation unit is configured to determine a first time instant from the output feedback signal Vcomp and generate a first trigger signal at the first time instant. The stop signal generating unit 833 is configured to generate a stop signal when receiving the first trigger signal, and in this embodiment, the stop signal is a single pulse signal, as shown in fig. 6 to 10. An input of the delay unit 834 receives the first trigger signal, and the delay unit 834 is configured to start timing when receiving the first trigger signal and output the second trigger signal after the first time Td. A first input terminal of the first and logic circuit 835 receives the second control signal PWM1, a second input terminal of the first and logic circuit 835 is connected to an output terminal of the delay unit 834, and the first and logic circuit 835 is configured to output the received second control signal PWM1 after receiving the second trigger signal. A first input terminal of the or logic circuit 836 is connected to an output terminal of the first and logic circuit 835, and a second input terminal of the or logic circuit 836 is connected to an output terminal of the stop signal generating unit 833, and the or logic circuit 836 is configured to implement time-sharing output of the stop signal and the second control signal PWM1.
In the first embodiment of the present invention, the first time is a time when the output feedback signal Vcomp reaches the first reference voltage Vref 1. In this embodiment, referring to fig. 4, the first trigger signal generating unit includes a first comparing unit 831. Wherein a non-inverting input terminal of the first comparing unit 831 receives the output feedback signal Vcomp, an inverting input terminal of the first comparing unit 831 receives the first reference voltage Vref1, and the first comparing unit 831 is configured to output the first trigger signal if the output feedback signal Vcomp is greater than or equal to the first reference voltage Vref 1.
The following describes the starting process of the flyback converter in the first embodiment of the present invention in detail with reference to fig. 6:
at time t0, the primary control circuit 5 of the flyback converter starts to generate the first control signal Vgs1_ P, and the first control signal Vgs1_ P starts to control the transfer of the start energy to the secondary part of the flyback converter, i.e. the start unit 81 in the secondary control circuit 8 starts to obtain the start energy through the first input SW and the second input Vo of the secondary control circuit 8 and starts to boost the voltage of the supply terminal in the secondary control circuit 8.
At time t1, the secondary control circuit 8 is enabled and starts soft start, i.e. the output voltage Vo of the flyback converter and the output feedback signal Vcomp representing the output voltage Vo start to rise smoothly.
In the time period from t1 to t2, the secondary side control circuit 8 gradually starts softly, that is, the output voltage Vo of the flyback converter and the output feedback signal Vcomp representing the output voltage Vo gradually rise steadily, so that the smooth start of the output voltage Vo is realized.
At time t2, the output feedback signal Vcomp reaches the first reference voltage Vref1, i.e. the first time mentioned above. At this time, the stop signal generation unit 833 in the secondary control circuit 8 starts to transmit the stop signal to the primary control circuit 5, the first control signal generation unit 51 in the primary control circuit 5 stops generating the first control signal Vgs1_ P under the trigger of the stop signal, and the delay unit 834 starts timing. Wherein the stop signal is represented by a dashed line during the time period from t2 to t 3. In one embodiment, the first control signal generating unit 51 in the primary side control circuit 5 may be configured to stop generating the first control signal Vgs1_ P upon receiving the stop signal.
After the time delay unit 834 times the first time Td, that is, at time t3, the secondary control circuit 8 starts to normally transmit a second control signal PWM1 to the primary control circuit 5, and the second control signal PWM1 starts to take over the first control signal Vgs1_ P to trigger the driving unit 52 to generate a first driving signal Vgs1, so as to continue to perform on-off control on the power switching tube Q1, thereby realizing energy transmission between the primary side and the secondary side of the flyback converter. That is, from time t3, the flyback converter enters the secondary side control mode.
In a second embodiment of the present invention, the first time is a time when the first time is satisfied within a preset time period after the power switch Q1 starts to be turned on, and the output feedback signal Vcomp is greater than or equal to the first reference voltage Vref 1. Preferably, the time length of the preset time period is less than the pulse period T of the first control signal Vgs1_ P S_P And is at least greater than one high-level period of validity of the first control signal Vgs1_ P and one high-level period of validity of the first pulse signal Von 2.
Optionally, in a possible implementation of this embodiment, the first time is commonly determined by the voltage difference Vds2 between the two power terminals of the rectifier Q2 and the output feedback signal Vcomp. Referring to fig. 5, the first trigger signal generating unit includes a second comparing unit 837, a rising edge pulse generating unit 838, a third comparing unit 839, and a first combinational logic circuit. Wherein a non-inverting input terminal of the second comparing unit 837 receives the output feedback signal Vcomp, an inverting input terminal of the second comparing unit 837 receives the first reference voltage Vref1, the second comparing unit is configured to output the first comparing signal if the output feedback signal Vcomp is greater than the first reference voltage Vref 1. A non-inverting input terminal of the third comparing unit 839 receives the second reference voltage Vref2, an inverting input terminal of the third comparing unit 839 receives the voltage difference Vds2 between the two power terminals of the rectifier Q2, and an output terminal of the third comparing unit 839 outputs a second comparison signal. The input terminal of the rising edge pulse generating unit 838 receives the second comparison signal, and generates a pulse at the rising edge of the second comparison signal to output the first pulse signal Von2, as shown in fig. 9 and 10. The first combinational logic circuit receives the first comparison signal and the first pulse signal Von2 and is configured to output a first trigger signal when the first comparison signal and the first pulse signal Von2 are detected to be in an active state at the same time for the first time.
Illustratively, the first combinational logic circuit further includes a second and logic circuit 8311, a not logic circuit 8310, and an RS flip-flop 8312. A first input terminal of the second and logic circuit 8311 is connected to the output terminal of the rising edge pulse generating unit 838, a second input terminal of the second and logic circuit 8311 is connected to the output terminal of the third comparing unit 839, and an output terminal of the second and logic circuit 8311 is connected to the set terminal of the RS flip-flop 8312. An input end of the not logic circuit 8310 is connected to an output end of the third comparing unit 839, and an output end of the not logic circuit 8310 is connected to a reset end of the RS flip-flop 8312. An output terminal of the RS flip-flop 8312 is connected to an input terminal of the stop signal generation unit 833 to transmit the first trigger signal to the stop signal generation unit 833 at the first timing. It should be understood that in other embodiments of the present invention, the first combinational logic circuit may also adopt other conventional combinational logic circuit configurations as long as the corresponding functions described above can be achieved.
The following describes the starting process of the flyback converter in this implementation of the present embodiment in detail with reference to fig. 9 and fig. 10:
at time t0, the primary control circuit 5 of the flyback converter starts to generate the first control signal Vgs1_ P, and the first control signal Vgs1_ P starts to control the transfer of the start energy to the secondary part of the flyback converter, i.e. the start unit 81 in the secondary control circuit 8 starts to obtain the start energy through the first input SW and the second input Vo in the secondary control circuit 8 and starts to boost the voltage of the supply terminal in the secondary control circuit 8.
At time t1, the secondary control circuit 8 is enabled and starts soft-start, i.e. the output voltage Vo of the flyback converter and the output feedback signal Vcomp representing the output voltage Vo start to rise smoothly.
In the time period from t1 to t2, the secondary side control circuit 8 gradually starts softly, that is, the output voltage Vo of the flyback converter and the output feedback signal Vcomp representing the output voltage Vo gradually rise steadily, so that the smooth start of the output voltage Vo is realized.
At the time t2, the output feedback signal Vcomp is in a state greater than or equal to the first reference voltage Vref1, and the first pulse signal Von2 is also in an active high state, that is, the first time is reached. At this time, the stop signal generation unit 833 in the secondary control circuit 8 starts to transmit the stop signal to the primary control circuit 5, the first control signal generation unit 51 in the primary control circuit 5 stops generating the first control signal Vgs1_ P under the trigger of the stop signal, and the delay unit 834 starts timing. Wherein the stop signal is represented by a dashed line during the time period from t2 to t 3. In one embodiment, the first control signal generating unit 51 in the primary side control circuit 5 may be configured to stop generating the first control signal Vgs1_ P upon receiving the stop signal.
After the time delay unit 834 times the first time Td, that is, at time t3, the secondary control circuit 8 starts to normally transmit a second control signal PWM1 to the primary control circuit 5, and the second control signal PWM1 starts to take over the first control signal Vgs1_ P to trigger the driving unit 52 to generate a first driving signal Vgs1, so as to continue to perform on-off control on the power switching tube Q1, thereby realizing energy transmission between the primary side and the secondary side of the flyback converter. That is, from time t3, the flyback converter enters the secondary side control mode.
It should be noted that, if the output feedback signal Vcomp reaches the first reference voltage Vref1 in the low level state of the first pulse signal Von2, the time t2 is the time when the first pulse signal Von2 starts to change to the high level state for the first time since the output feedback signal Vcomp reaches the first reference voltage Vref1, as shown in fig. 9; if the output feedback signal Vcomp reaches the first reference voltage Vref1 in the high level state of the first pulse signal Von2, the time t2 is the time when the output feedback signal Vcomp reaches the first reference voltage Vref1, as shown in fig. 10.
In another possible implementation of this embodiment (the foregoing second embodiment), the first time is commonly confirmed by the conducting state of the power switch Q1 and the output feedback signal Vcomp. It is understood that, at this time, the output unit 83 in this implementation may adopt substantially the same circuit structure as that in the first implementation of the foregoing second embodiment, and only the circuit generating the first pulse signal Von2 in fig. 5 needs to be replaced by a corresponding circuit structure detecting the on state of the power switch Q1. Illustratively, the conducting state of the power switch tube Q1 may be obtained by comparing the voltage difference between the two power ends of the rectifier tube Q2 with a corresponding reference voltage, or by providing an additional isolation device in the flyback converter to detect at least one of parameters, such as a control signal of the power switch tube Q1, the voltage difference between the two power ends of the power switch tube Q1, and a current flowing through the power switch tube Q1, and the specific circuit structure may be understood with reference to the prior art, and will not be described in detail herein.
The following describes in detail the starting process of the flyback converter in this implementation of the present embodiment with reference to fig. 7 and 8:
at time t0, the primary control circuit 5 of the flyback converter starts to generate the first control signal Vgs1_ P, and the first control signal Vgs1_ P starts to control the transfer of the start energy to the secondary part of the flyback converter, i.e. the start unit 81 in the secondary control circuit 8 starts to obtain the start energy through the first input SW and the second input Vo of the secondary control circuit 8 and starts to boost the voltage of the supply terminal in the secondary control circuit 8.
At time t1, the secondary control circuit 8 is enabled and starts soft-start, i.e. the output voltage Vo of the flyback converter and the output feedback signal Vcomp representing the output voltage Vo start to rise smoothly.
In the time period from t1 to t2, the secondary side control circuit 8 gradually starts softly, that is, the output voltage Vo of the flyback converter and the output feedback signal Vcomp representing the output voltage Vo gradually rise steadily, so that the smooth start of the output voltage Vo is realized.
At time t2, the output feedback signal Vcomp is in a state greater than or equal to the first reference voltage Vref1, and the first control signal vgs1_ P is also in an active high state, that is, at the first time. At this time, the stop signal generating unit 833 in the secondary control circuit 8 starts to transmit the stop signal to the primary control circuit 5, the first control signal generating unit 51 in the primary control circuit 5 stops generating the first control signal Vgs1_ P under the trigger of the stop signal, and the delay unit 834 starts to count time. Wherein the stop signal is represented by a dashed line during the time period from t2 to t 3. In order to ensure the stability and continuity of the flyback converter during the switching of the primary and secondary control modes, optionally, if the time t2 occurs in a state where the first control signal Vgs1_ P is at a low level, that is, if the first control signal generating unit 51 in the primary control circuit 5 receives the stop signal in a state where the first control signal Vgs1_ P is at a low level, it may be configured to stop generating the first control signal Vgs1_ P when receiving the stop signal; if the time t2 is in a state where the first control signal Vgs1_ P is at a high level, that is, the first control signal generating unit 51 in the primary side control circuit 5 receives the stop signal when the first control signal Vgs1_ P is at a high level, it may be configured to stop generating the first control signal Vgs1_ P after the first control signal Vgs1_ P changes to a low level.
After the time delay unit 834 times the first time Td, that is, at time t3, the secondary control circuit 8 starts to normally transmit a second control signal PWM1 to the primary control circuit 5, and the second control signal PWM1 starts to take over the first control signal Vgs1_ P to trigger the driving unit 52 to generate a first driving signal Vgs1, so as to continue to perform on-off control on the power switching tube Q1, thereby realizing energy transmission between the primary side and the secondary side of the flyback converter. That is, from time t3, the flyback converter enters the secondary side control mode.
It should be noted that, if the output feedback signal Vcomp reaches the first reference voltage Vref1 in the low level state of the first control signal vgs1_ P, the time t2 is the time when the first control signal vgs1_ P changes to the high level state for the first time since the output feedback signal Vcomp reaches the first reference voltage Vref1, as shown in fig. 7; if the output feedback signal Vcomp reaches the first reference voltage Vref1 in the high level state of the first control signal vgs1_ P, the time t2 is the time when the output feedback signal Vcomp reaches the first reference voltage Vref1, as shown in fig. 8.
As can be seen from the above description, the output unit 83 according to the first embodiment of the present invention has a simple circuit structure and is manufactured at a low cost. The output unit 83 disclosed in the second embodiment of the present invention can prevent the primary power switch Q1 from being controlled by the flyback converter during the switching of the primary and secondary control modes, i.e., the first driving signal Vgs1 does not have a pulse missing condition, which is beneficial to improving the stability and continuity of the control switching of the primary power switch Q1.
Further, in the embodiment of the present invention, a difference between the first time Td and the period of the first control signal Vgs1_ P is also set to be smaller than a preset threshold, so as to further improve the stability and continuity of the flyback converter during the switching of the primary and secondary control modes.
Furthermore, the invention also sets the frequency (i.e. 1/Ts _ s) and the pulse width parameter of the second control signal PWM1 at least in the initial pulse period (corresponding to the time period from t3 to t 4) to be substantially consistent with the frequency (i.e. 1/Ts _ P) and the pulse width parameter of the first control signal Vgs1_ P, that is, sets the difference between the frequency and the pulse width parameter of the second control signal PWM1 at least in the initial pulse period (corresponding to the time period from t3 to t 4) and the frequency and the pulse width parameter of the first control signal Vgs1_ P to be smaller than the preset threshold, so that the driving signal of the primary side power switching tube does not generate sudden change in the starting process, thereby realizing the smooth transition of the primary side control and the smooth start of the output voltage, and further improving the output quality of the converter.
It should be further noted that, in the first embodiment of the present invention, although there is a missing situation of one pulse in the first driving signal Vgs1 output by the primary side control circuit 5 to the gate of the power switch Q1 during the primary side control switching process, that is, during the period that the stop signal triggers the first control signal generating unit 51 to stop generating the first control signal Vgs1_ P, since the output end of the flyback converter is provided with the output capacitor Co and the frequency of the first driving signal Vgs1 is very high, the smoothness and the continuity of the output voltage Vo of the flyback converter are not affected.
Furthermore, the flyback converter disclosed by the invention also comprises a current limiting resistor R connected in series in a primary power loop of the flyback converter CS_P . And further the primary control circuit 5 comprises a fifth input PCS. The fifth input PCS of the primary side control circuit 5 is used for receiving the current limiting resistor R CS_P The voltage across the terminals. WhereinAnd the primary side control circuit is used for switching off the power switch tube Q1 when the voltage at the two ends of the current-limiting resistor is greater than a preset voltage threshold value.
In this embodiment, the primary side control circuit 5 collects the current limiting resistor R CS_P The voltage at both ends is compared with a preset voltage threshold value and is measured at the current limiting resistor R CS_P And when the voltage at the two ends is greater than a preset voltage threshold value, the power switch tube Q1 is switched off. In this way, the present embodiment can effectively suppress the current in the power loop when the excitation inductance of the transformer is abnormal, prevent the current in the power loop from being abnormally increased, and contribute to improving the system stability and reliability. It should be noted that, in this embodiment, the preset voltage threshold is a fixed value and is only used for determining whether the current in the power loop is abnormal, and the current limiting resistor R is used for limiting the current of the power loop CS_P Has a smaller resistance value, for example, smaller than a predetermined threshold value, and has a lower power, i.e., the current limiting resistor R CS_P The resistance value of the sampling resistor is far smaller than that of a sampling resistor connected in series in a primary power loop of a traditional flyback converter, peak current control of the flyback converter cannot be achieved, too much integrated circuit area cannot be occupied, specification and quantity of resistors in the system can be reduced, and influences on efficiency and cost of the flyback converter system can be ignored.
Further, the invention also discloses a starting control method of the flyback converter, which can be applied to the flyback converter described in fig. 1 to 10. Referring to fig. 11, the start control method specifically includes the following steps:
in step S1, after the flyback converter is powered on, a primary control circuit is used to generate a first control signal to control the transfer of start-up energy to a secondary part of the flyback converter. In this embodiment, the specific operation method of step S1 can be understood by referring to the foregoing description of the primary side control circuit 5 and the first control signal generating unit 51, and is not described herein again.
In step S2, after the secondary control circuit is started, the secondary control circuit is used to transmit the stop signal and the second control signal to the primary control circuit in sequence. The first control signal and the second control signal are both used for triggering to realize on-off control of the power switch tube, the stop signal is used for triggering the primary side control circuit to stop generating the first control signal Vgs1_ P, or the stop signal is used for triggering to shield the on-off control of the first control signal Vgs1_ P on the power switch tube Q1. Meanwhile, the difference values of the frequency and the pulse width parameters of the second control signal in at least the initial pulse period and the frequency and the pulse width parameters of the first control signal are smaller than a preset threshold value.
In this embodiment, step S2 further includes: the method comprises the steps of transmitting a stop signal to a primary side control circuit at a first moment after a secondary side control circuit is started, and transmitting a second control signal to the primary side control circuit after delaying a first time from the first moment. The first moment is the moment when the output feedback signal of the flyback converter reaches a first reference voltage; or the first time and the second time are simultaneously within a preset time period after the power switch tube starts to be conducted, and the output feedback signal is greater than or equal to the first reference voltage. Further, the specific operation method of step S2 can be understood by referring to the foregoing description of the output unit 83, and is not described herein again.
In summary, in the embodiment of the present invention, the primary side control circuit is set to be powered on and started after the flyback converter is powered on, and then outputs the first control signal to perform on-off control on the power switching tube to control the supply of the starting energy to the outputs of the secondary side control circuit and the flyback converter, and after the secondary side control circuit is started after obtaining the starting energy, the secondary side control circuit is set to first trigger the primary side control circuit to stop generating the first control signal, and then transmits the second control signal to the primary side control circuit to take over the first control signal to continue the on-off control on the power switching tube, so that the switching from the primary side control to the secondary side control can be smoothly achieved. Meanwhile, under the condition that the difference values of the frequency and the pulse width parameter of the second control signal in the initial pulse period and the frequency and the pulse width parameter of the first control signal are smaller than the preset threshold value (namely the second control signal has the frequency and the pulse width which are basically the same as those of the first control signal in the initial pulse period), the driving signal of the primary side power switch tube can not be suddenly changed in the starting process, the smooth transition of the primary side and secondary side control and the smooth starting of the output voltage are realized, and the output quality of the flyback converter is improved.
Finally, it should be noted that: it should be understood that the above examples are only for clearly illustrating the present invention and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. This need not be, nor should it be exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the scope of the invention.

Claims (16)

1. A flyback converter, comprising:
the transformer comprises a primary winding and a secondary winding;
the power switch tube is connected with the primary winding;
the rectifier tube is connected between the secondary winding and the output end of the flyback converter;
the primary side control circuit is started after the flyback converter is powered on, and generates a first control signal after the primary side control circuit is started so as to control the transmission of starting energy to a secondary side part of the flyback converter;
a secondary side control circuit which transmits a stop signal and a second control signal to the primary side control circuit in sequence after being started,
the first control signal and the second control signal are both used for triggering to realize on-off control of the power switch tube, and the stop signal is used for triggering the primary side control circuit to stop generating the first control signal or triggering to shield the on-off control of the first control signal on the power switch tube.
2. The flyback converter of claim 1, wherein the secondary control circuit is configured to deliver the stop signal to the primary control circuit at a first time after startup and to deliver the second control signal to the primary control circuit after a first time delay from the first time.
3. The flyback converter of claim 2, wherein the first time is a time at which an output feedback signal, which is indicative of the output power of the flyback converter, reaches a first reference voltage.
4. The flyback converter of claim 2, wherein the first time is a time when the first time is within a preset time period after the power switch tube starts to be turned on and the output feedback signal is greater than or equal to a first reference voltage, wherein the output feedback signal represents the output power of the flyback converter.
5. The flyback converter of claim 3, wherein the secondary-side control circuit includes an output unit configured to receive the output feedback signal and generate the stop signal at the first time, the output unit including:
a first comparing unit, a non-inverting input terminal of which receives the output feedback signal and an inverting input terminal of which receives the first reference voltage, the first comparing unit being configured to output a first trigger signal if the output feedback signal is greater than or equal to the first reference voltage;
a stop signal generating unit, an input end of which is connected with an output end of the first comparing unit, the stop signal generating unit being configured to generate the stop signal when receiving the first trigger signal.
6. The flyback converter of claim 4, wherein the secondary-side control circuit includes an output unit configured to receive the output feedback signal and generate the stop signal at the first time, the output unit including:
a second comparing unit having a non-inverting input terminal receiving the output feedback signal and an inverting input terminal receiving the first reference voltage, the second comparing unit being configured to output a first comparing signal if the output feedback signal is greater than the first reference voltage;
a third comparison unit, wherein the positive phase input end receives a second reference voltage, the negative phase input end receives the voltage difference of two power ends of the rectifier tube, and the output end outputs a second comparison signal;
a rising edge pulse generating unit, an input end of which receives the second comparison signal and generates a pulse at the rising edge of the second comparison signal to output a first pulse signal;
a first combinational logic circuit receiving the first comparison signal and the first pulse signal, the first combinational logic circuit configured to output a first trigger signal when it is detected for a first time that the first comparison signal and the first pulse signal are simultaneously in an active state;
a stop signal generation unit having an input connected to the output of the first combinational logic circuit, the stop signal generation unit configured to generate the stop signal upon receiving the first trigger signal.
7. The flyback converter of claim 5 or 6, wherein the output unit further comprises:
a delay unit, an input end of which receives the first trigger signal, the delay unit being configured to start timing when receiving the first trigger signal and output a second trigger signal after the first time;
a first and logic circuit, a first input terminal of which receives the second control signal, a second input terminal of which is connected to the output terminal of the delay unit, the first and logic circuit being configured to output the received second control signal after receiving the second trigger signal;
an or logic circuit, a first input terminal of the or logic circuit being connected to an output terminal of the first and logic circuit, a second input terminal of the or logic circuit being connected to an output terminal of the stop signal generating unit, the or logic circuit being configured to implement time-sharing output of the stop signal and the second control signal.
8. The flyback converter of claim 3 or 4, wherein the secondary side control circuit further comprises:
an output feedback signal generation circuit configured to generate the output feedback signal according to an output voltage of the flyback converter;
a second control signal generation unit configured to generate the second control signal according to the output feedback signal.
9. The flyback converter of claim 1, wherein the frequency and pulse width parameters of the second control signal at least during an initial pulse period are both less than a preset threshold value different from the frequency and pulse width parameters of the first control signal.
10. The flyback converter of claim 1, wherein the primary control circuit comprises:
a first control signal generation unit configured to start generating the first control signal after the flyback converter is powered on, and to stop generating the first control signal according to the stop signal trigger;
and the driving unit is configured to transmit a first driving control signal to the control end of the power switch tube when receiving the first control signal or the second control signal so as to realize on-off control of the power switch tube.
11. A start-up control method of a flyback converter, applied to the flyback converter as claimed in any one of claims 1 to 10, wherein the start-up control method comprises:
after the flyback converter is powered on, a primary side control circuit is utilized to generate a first control signal so as to control the transmission of starting energy to a secondary side part of the flyback converter;
after the secondary side control circuit is started, the secondary side control circuit is utilized to transmit a stop signal and a second control signal to the primary side control circuit in sequence,
the first control signal and the second control signal are both used for triggering to realize on-off control of the power switch tube, and the stop signal is used for triggering the primary side control circuit to stop generating the first control signal or triggering to shield the on-off control of the first control signal on the power switch tube.
12. The startup control method according to claim 11, wherein successively transferring the stop signal and the second control signal to the primary side control circuit using the secondary side control circuit comprises:
and transmitting the stop signal to the primary side control circuit at a first time after the secondary side control circuit is started, and transmitting the second control signal to the primary side control circuit after delaying for a first time from the first time.
13. The start-up control method of claim 12, wherein the first time is a time when the output feedback signal of the flyback converter reaches a first reference voltage.
14. The start-up control method according to claim 12, wherein the first time is a time when a first time is satisfied within a preset time period after the power switching tube starts to be turned on and an output feedback signal is greater than or equal to a first reference voltage, wherein the output feedback signal represents the output power of the flyback converter.
15. The startup control method according to claim 11, and the difference values of the frequency and the pulse width parameter of the second control signal in at least the initial pulse period and the frequency and the pulse width parameter of the first control signal are both smaller than a preset threshold value.
16. The activation control method of claim 12, wherein a difference between said first time and a period of said first control signal is less than a preset threshold.
CN202210221832.0A 2022-03-09 2022-03-09 Flyback converter and starting control method thereof Pending CN115149811A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116526856A (en) * 2023-04-28 2023-08-01 上海晶丰明源半导体股份有限公司 Controller, isolated power converter and control method

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116526856A (en) * 2023-04-28 2023-08-01 上海晶丰明源半导体股份有限公司 Controller, isolated power converter and control method

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