CN115224951A - Constant-voltage control system of primary-side feedback flyback converter - Google Patents

Constant-voltage control system of primary-side feedback flyback converter Download PDF

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CN115224951A
CN115224951A CN202211013951.3A CN202211013951A CN115224951A CN 115224951 A CN115224951 A CN 115224951A CN 202211013951 A CN202211013951 A CN 202211013951A CN 115224951 A CN115224951 A CN 115224951A
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voltage
switching tube
output
main
main switching
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王冲
桂桑
顾文华
孙大鹰
李现勤
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Wuxi Dekeli Optoelectronic Technology Co ltd
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Wuxi Dekeli Optoelectronic Technology Co ltd
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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
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
    • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
    • G05F1/10—Regulating voltage or current
    • G05F1/46—Regulating voltage or current wherein the variable actually regulated by the final control device is dc
    • G05F1/56—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices
    • 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
    • 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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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Automation & Control Theory (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention discloses a constant voltage control system of a primary side feedback flyback converter, which relates to the technical field of isolated converters and comprises the following components: the main topological circuit and a control circuit forming a closed loop with the main topological circuit; inputting feedback voltage output by an auxiliary winding voltage dividing end in the main topological circuit to a first input end of a control circuit, and obtaining transformer demagnetization time by combining a main switching tube driving signal; after voltage of a current sampling resistor between a main switching tube and an input ground in the main topological circuit is divided by a voltage dividing circuit, the voltage is input to a second input end of the control circuit, and a voltage value of the main switching tube at the moment of connection and disconnection is calculated by combining a driving signal of the main switching tube; the control circuit calculates to obtain output voltage based on the demagnetization time of the transformer and the voltage value of the main switching tube at the moment of switching on and switching off. The system obtains the output voltage through calculation of a simple closed-loop control circuit and realizes output constant voltage, and compared with the existing voltage sampling method, the system is lower in realization cost and simpler in control.

Description

Constant voltage control system of primary side feedback flyback converter
Technical Field
The invention relates to the technical field of isolated converters, in particular to a constant-voltage control system of a primary side feedback flyback converter.
Background
With the technical development, the switching power supply is widely applied to medium and small power occasions, the isolated switching power supply can realize the electrical isolation of input and output, and has the characteristics of safe isolation and high reliability, and the flyback converter has the characteristics of simple circuit, simple control, high reliability and the like, so that the isolated switching power supply is widely applied to medium and small power isolated switching power supplies, such as an adapter of portable equipment, a display power supply, an LED (light-emitting diode) lighting power supply and the like.
The flyback converter realizes the electrical isolation of input and output, so the reliability is higher, and because the main control circuit of the switching power supply is positioned at the input end, the voltage or current information of the output end needs to be transmitted to the input end control circuit, so the information interaction between the input end and the output must be realized. The output information is transmitted in an electro-optic-electro conversion mode through the optical coupler, so that the problems of nonlinearity, aging, temperature drift and complex supporting circuits of the optical coupler cannot be avoided, and the service life and the working temperature range of the converter are restricted; secondly, in constant voltage control, by means of a primary side main winding or a primary side auxiliary winding, output voltage information is obtained by sampling voltages of the primary side winding at different moments and processing the signals, wherein a common method is that the primary side auxiliary winding is added to a transformer, actual output voltage is indirectly obtained by sampling the voltage of the auxiliary winding at a certain moment, and as the voltage of the auxiliary winding is a changing waveform, sampling based on the voltage of the auxiliary winding needs a relatively complex processing circuit to judge sampling moment and perform sampling. The method can avoid the related problems of optical coupling feedback, but the complexity and difficulty of the design of the control circuit are increased by processing the variable waveform, if a digital control scheme is adopted, elements with higher circuit cost and complexity such as a digital-to-analog converter or an analog-to-digital converter and the like can be introduced, if an analog control scheme is adopted, a corresponding sampling point judgment circuit is needed to judge the sampling time, and the complexity is still higher.
Disclosure of Invention
The invention provides a constant voltage control system of a primary side feedback flyback converter aiming at the problems and the technical requirements, and the difficulty and the cost of sampling the output voltage of a primary side feedback control scheme are reduced.
The technical scheme of the invention is as follows:
a constant voltage control system of a primary side feedback flyback converter comprises a main topological circuit and a control circuit forming a closed loop with the main topological circuit;
inputting feedback voltage output by an auxiliary winding voltage division end in the main topological circuit to a first input end of a control circuit, and obtaining transformer demagnetization time by combining a main switching tube driving signal; after voltage of a current sampling resistor between a main switching tube and an input ground in the main topological circuit is divided by a voltage dividing circuit, the voltage is input to a second input end of the control circuit, and a voltage value of the main switching tube at the moment of connection and disconnection is calculated by combining a driving signal of the main switching tube; the control circuit calculates to obtain output voltage based on the demagnetization time of the transformer and the voltage value of the main switching tube at the on and off time.
The control circuit is positioned at the input side and comprises a primary side current measuring and calculating module, a demagnetization time detection module, an output voltage calculation module, a PID calculation module and a PWM driving module; the input end of the primary side current measuring and calculating module is used as the second input end of the control circuit to receive the divided voltage of the current sampling resistor, the output end of the primary side current detecting module is connected with the input end of the output voltage calculating module, and the primary side current detecting module is used for calculating the maximum voltage value and the minimum voltage value of the main switching tube at the conduction stage based on the divided voltage expression; the input end of the demagnetization time detection module is used as a first input end of the control circuit to receive the feedback voltage, the output end of the demagnetization time detection module is connected with the input end of the output voltage calculation module, and the demagnetization time detection module is used for acquiring the demagnetization time of the transformer in the current mode based on the comparison result of the feedback voltage and zero and the driving signal of the main switching tube; the output voltage calculation module is connected with the PWM driving module through the PID calculation module, the output voltage calculation module is used for calculating the output voltage of the n switching period demagnetization stage, and the PWM driving module outputs a main switching tube driving signal as an output signal of the control circuit and is connected with the grid end of the main switching tube.
In the primary side current measuring and calculating module, during the conduction period of the main switching tube, the relation between the divided voltage and the primary side current flowing through the main switching tube is as follows:
Figure BDA0003811924510000021
wherein v is p A divided voltage i output from the voltage dividing circuit p Primary side current, R, flowing through the main switch tube when the main switch tube is conducted p Resistance value of a current sampling resistor, R 3 、R 4 A voltage dividing resistor of the voltage dividing circuit;
acquiring primary side current I of main switching tube at conduction time pm Primary side current at turn-off time I pp Calculating the maximum voltage value V of the main switch tube in the conduction stage based on the expression pp And a minimum voltage value V pm The expressions are respectively:
Figure BDA0003811924510000022
Figure BDA0003811924510000023
wherein the minimum voltage value V pm Voltage value corresponding to the conduction time of the main switch tube, maximum voltage value V pp And the voltage value corresponds to the turn-off time of the main switching tube.
The demagnetization time detection module comprises a comparator and a time calculation unit, wherein the non-inverting input end of the comparator is used as the input end of the demagnetization time detection module to receive feedback voltage and is recorded as v FB The inverting input of the comparator is set to zero when v is FB When the voltage is higher than 0, the comparator outputs high level, otherwise, the comparator outputs low level;the output end of the comparator and the driving signal of the main switching tube are connected with the input end of the time calculation unit, and the output end of the time calculation unit is used as the output end of the demagnetization time detection module to output the demagnetization time of the transformer in the current mode;
in a time calculation unit, defining a state variable of a transformer in a switching period based on an output result of a comparator and a driving signal of a main switching tube, and determining a working mode of the transformer according to the change condition of the state variable, wherein the state variable comprises a low level state, a first level state, a second level state and a third level state from low to high; when in the continuous current mode, acquiring the time length of the first level state as the demagnetization time in the mode, and when in the discontinuous current mode, respectively acquiring the time length T of the first level state r_temp And a time length t of the second level state valley Based on [ T r_temp -(t valley /2)]As the demagnetization time in this mode.
In the output voltage calculation module, the input signals are the maximum voltage value and the minimum voltage value of the main switching tube in the conduction stage and the demagnetization time of the transformer in the current mode; the output signal is the output voltage V of the n switching period demagnetization stage o (n) defining the starting time of the switching period as the time when the driving signal of the main switching tube rises from low level to high level, and defining the ending time of the switching period as the time when the driving signal of the next main switching tube rises from low level to high level, and outputting the voltage V o (n) the expression is:
Figure BDA0003811924510000031
Figure BDA0003811924510000032
wherein, V pp (n) is the maximum voltage value of the conduction stage of the main switching tube in the nth switching period, V pm (n + 1) is the minimum voltage value of the conduction stage of the main switching tube in the (n + 1) th switching period,T r (n) is the demagnetization time of the nth switching cycle transformer in the current mode; n is ps Is the ratio of the number of turns of the primary winding to the number of turns of the secondary winding, R, of the transformer p Resistance value of a current sampling resistor, V f Is the conduction voltage of the output diode in the main topology circuit, and R p 、n ps And V f Are all constant; l is a radical of an alcohol m Is the excitation inductance of the primary winding of the transformer, L eq Is an equivalent main winding excitation inductance based on the voltage division ratio of the current voltage division circuit, R 3 、R 4 Is a voltage dividing resistor of the voltage dividing circuit.
The input signal of the PID calculation module is calculated output voltage, the output signal is a switch control parameter corresponding to the voltage and serves as the input signal of the PWM driving module, and the PWM driving module gives a main switching tube driving signal based on the switch control parameter;
in the PID calculation module, the target value of the output voltage is subtracted from the calculated output voltage to obtain an output voltage error, and proportional-integral-derivative compensation operation is carried out on the basis of the output voltage error to obtain a corresponding switch control parameter, wherein the switch control parameter comprises the duty ratio and the switching period of a main switching tube.
The voltage division ratio of the current sampling resistor is adjusted by adjusting the resistance value of the variable resistor, and the voltage division ratio is used for compensating excitation inductance disturbance of a main winding of a transformer and realizing the constancy of equivalent main winding excitation inductance.
The further technical scheme is that a state variable of the transformer under a switching period is defined based on an output result of the comparator and a driving signal of the main switching tube, and a working mode of the transformer is determined according to a change condition of the state variable, and the method comprises the following steps:
when the driving signal of the main switching tube is in a high level, the state variable is in a low level state;
when the driving signal of the main switching tube is at a low level, if the output result of the comparator is changed from low to high level, the state variable is switched to a first level state; if the state variable is in the first level state and the output result of the comparator is changed from high level to low level, the state variable is switched to the second level state; if the state variable is in the second level state and the output result of the comparator changes from low to high level, the state variable is switched to a third level state;
when the state variable is switched only between the low level state and the first level state, the transformer operates in a continuous current mode; the transformer operates in discontinuous current mode when the state variable switches between four level states.
The further technical scheme is that the main topological circuit comprises a main winding and an auxiliary winding of the transformer, a main switching tube, an auxiliary winding, a clamping circuit and an output circuit; the primary winding is positioned on the input side, the different name end of the primary winding is connected with the rectified direct-current voltage positive end, the same name end of the primary winding is connected with the drain end of the main switching tube, the source end of the main switching tube is connected with the ground end of the input side through a current sampling resistor, and a voltage division circuit is connected between the drain end and the ground end of the input side; the clamping circuit is connected between the main winding and the direct-current voltage positive end; the secondary winding is positioned on the output side and connected with the output circuit; the auxiliary winding is positioned at the input side, two ends of the auxiliary winding are connected with the divider resistor in series, and the synonym end of the auxiliary winding is connected with the ground end of the input side.
The beneficial technical effects of the invention are as follows:
(1) The sampling of output voltage is realized based on the indirect calculation mode of the control circuit, compared with the traditional primary side feedback control mode, the sampling of the voltage of an auxiliary winding or a primary side main winding at a specific moment is not needed, the sampling complexity is reduced, fewer components are needed, and the structure is simpler.
(2) According to the method, the output voltage is obtained through indirect calculation by obtaining the maximum voltage and the minimum voltage of the main switching tube in the conduction stage and the demagnetization time; and based on the voltage division adjustment of the primary current sampling resistor voltage, the equivalent excitation inductance of the control loop can be modulated, the equivalent excitation inductance is realized in different systems, and the interference of difference brought by the transformer excitation inductance in production is eliminated.
(3) The demagnetization time detection module only needs a simple comparator and a time calculation module to process the result of the comparator, and the implementation complexity of the demagnetization time detection module is far lower than that of a method for processing the feedback voltage of the auxiliary winding in the existing scheme.
(4) The switching mode of the main switching tube is controlled based on the output voltage obtained through calculation, and the output voltage is constant.
(5) The method and the device are applicable to isolated or non-isolated switch power supply circuit structures, and have universality, reusability and transportability.
Drawings
Fig. 1 is a schematic diagram of a constant voltage control system of a primary side feedback flyback converter proposed in the present application.
Fig. 2 is a schematic diagram and a waveform diagram of a primary side current measurement module in a discontinuous current mode and a continuous current mode. Wherein: FIG. 2 (a) is R 4 A voltage divider circuit which is a variable resistor; FIG. 2 (b) is R 3 A voltage divider circuit which is a variable resistor; FIG. 2 (c) shows the driving signal duty and the switching current i of the main switch tube in the discontinuous current mode p Exciting current i m And current sampling resistor voltage division v p The waveform of (a); FIG. 2 (d) shows the main switch tube driving signal duty and the switch current i in the continuous current mode p Exciting current i m And current sampling resistor voltage division v p The waveform of (2).
Fig. 3 is a waveform of a demagnetization time detection module according to the present application. Wherein: FIG. 3 (a) is a waveform associated with the discontinuous current mode; fig. 3 (b) shows the waveform in the continuous current mode.
FIG. 4 shows a main switch tube driving signal duty and a switch current i in the output voltage calculating module of the present application p Exciting current i m Schematic diagram of waveforms. FIG. 4 (a) is a waveform associated with discontinuous current mode; fig. 4 (b) shows the waveform in the continuous current mode.
Fig. 5 is a waveform for verifying the output correlation of the closed-loop constant voltage by using the constant voltage control system.
Detailed Description
The following further describes the embodiments of the present invention with reference to the drawings.
The application provides a primary side feedback flyback converter constant voltage control system, and its topological structure is more simple, and the reliability is higher than traditional flyback converter based on opto-coupler feedback. Because the primary side feedback control method cannot directly sample the output voltage, the auxiliary winding voltage at a specific moment needs to be sampled, so that the sampling complexity is increased.
As shown in fig. 1, the constant voltage control system includes a main topology circuit and a control circuit forming a closed loop therewith. The main topology circuit adopts a primary side feedback flyback converter structure and comprises a transformer main winding W p And a secondary winding W s Main switch tube M 1 Auxiliary winding W a A clamp circuit and an output circuit. Main winding W p On the input side, the different name end is connected with the rectified DC voltage positive end V in (the input alternating current is converted into direct current voltage after passing through a rectifier), and the dotted terminal is connected with a main switching tube M 1 The drain terminal of the main switch tube M 1 Source end of the resistor passes through a current sampling resistor R with small resistance value p Ground terminal G of ground input side ND1 Drain and input side ground terminals G ND1 Is connected with two resistors R 3 、R 4 The voltage divider circuit is formed. The clamping circuit is connected with the main winding W p And a positive terminal of a direct current voltage in The positive electrode of a clamping diode Dc in the clamping circuit is connected with a main switching tube M 1 The negative pole of the clamping diode Dc is respectively connected with one end of a clamping resistor Rc and one end of a clamping capacitor Cc, and the other end of the clamping resistor Rc and the other end of the clamping capacitor Cc is connected with a direct-current voltage positive end V in . Secondary winding W s On the output side, the secondary winding W s Connecting output circuit, output diode D in output circuit 1 Negative pole of the capacitor is connected with an output capacitor C l Positive electrode of (2), output capacitor C l Negative pole is connected with output ground terminal G ND2 . Auxiliary winding W a On the input side, an auxiliary winding W a Both ends of the voltage dividing resistor R are connected in series 1 、R 2 And the different name end of the auxiliary winding is connected with the ground end of the input sideG ND1 。
Voltage dividing end (R) of auxiliary winding in main topological circuit 1 、R 2 In between) the output of the feedback voltage v FB The output voltage is input to a first input end of the control circuit, and the demagnetization time of the transformer is obtained by combining the driving signal duty of the main switching tube. A current sampling resistor R between a main switching tube and an input ground in a main topological circuit p After the voltage is divided by the voltage dividing circuit, the divided voltage is input to a second input end of the control circuit, and the voltage value of the main switching tube at the moment of switching on and switching off is calculated by combining the drive signal duty of the main switching tube. The control circuit calculates to obtain output voltage based on the demagnetization time of the transformer and the voltage value of the main switching tube at the on and off time.
The control circuit is positioned on the input side and comprises a primary side current measuring and calculating module, a demagnetization time detection module, an output voltage calculating module, a PID calculating module and a PWM driving module. The input end of the primary side current measuring and calculating module is used as the second input end of the control circuit to receive the divided voltage v of the current sampling resistor p The output end of the primary side current detection module is connected with the input end of the output voltage calculation module, and the primary side current detection module is used for calculating the maximum voltage value V of the main switching tube in the conduction stage based on the partial voltage expression pp And a minimum voltage value V pm . The input end of the demagnetization time detection module is used as the first input end of the control circuit to receive the feedback voltage v FB The output end of the demagnetization time detection module is connected with the input end of the output voltage calculation module, and the demagnetization time detection module is used for detecting the demagnetization time based on the feedback voltage v FB Obtaining the demagnetization time T of the transformer in the current mode according to the comparison result with zero and the drive signal duty of the main switching tube r . The output voltage calculation module is connected with the PWM driving module through the PID calculation module and used for calculating the output voltage V of the n switching period demagnetization stage o (n), the PWM driving module outputs a main switching tube driving signal duty as an output signal of the control circuit, and is connected with the main switching tube M 1 The gate terminal of (1).
The sampling of output voltage is realized based on the indirect calculation mode of the control circuit, compared with the traditional primary side feedback control mode, the sampling of the voltage of an auxiliary winding or a primary side main winding at a specific moment is not needed, the sampling complexity is reduced, fewer components are needed, and the structure is simpler. The most fundamental reason for the advantage is the innovation of the invention in principle and thought, and the specific structure and principle of each module will be described in detail below.
1) A primary side current measuring and calculating module, the input signal of which is the voltage division value v of the current sampling resistor voltage p The output signal is the main switch tube M 1 Maximum voltage value V of conducting stage pp And a minimum voltage value V pm . During the conduction period of the main switch tube, when the current flows through the main switch tube M 1 Has a current of i p When the voltage flowing through the current sampling resistor is current i p And the resistance value R of the sampling resistor p Product of (a), large resistance R 3 、R 4 Voltage division on the sampling resistor, R 3 One end of the main switch tube is connected with a source end of the main switch tube, R 3 、R 4 In series, R 4 The other end of the input ground terminal G ND1 ，R 3 、R 4 Between the divided voltage v output from the divided voltage terminal p And flows through the main switching tube M 1 Primary side current i of p The relationship between them is shown in formula (1):
Figure BDA0003811924510000071
wherein R is 3 、R 4 The voltage dividing resistor is a voltage dividing resistor of a voltage dividing circuit, the voltage dividing resistor is a variable resistor, and the voltage dividing ratio of the current sampling resistor is adjusted by adjusting the resistance value of the variable resistor, as shown in fig. 2 (a) and 2 (b), the voltage dividing resistor is used for compensating excitation inductance disturbance of a main winding of a transformer, and the excitation inductance of an equivalent main winding is constant.
FIGS. 2 (c) and 2 (d) show the main switch tube driving signal duty and the switch current i in the discontinuous current mode and the continuous current mode, respectively p Exciting inductive current i of transformer m And current sampling resistor voltage division v p The waveform of (1), wherein: v pm For dividing voltage v at the conduction time of the main switch tube p Voltage value (i.e. minimum voltage value), V pp For dividing voltage v at turn-off time of switching tube p Voltage value (i.e. maximum voltage value), I pm Primary side current i at the moment of conducting main switch tube p Value of (A), I pp Primary side current i at the moment of switching off a main switching tube p The value of (c). When duty is set high, i.e. the switching tube is on m Is equal to i p Both from I pm Is raised to I pp When duty is low, i p The current is zero, the exciting current is in the demagnetizing time T r Internal slave I pp Down to I pm . Obtaining I pm And I pp Calculating the maximum voltage value V of the main switching tube in the conduction stage based on the expression (1) pp And a minimum voltage value V pm The expressions are respectively shown in formulas (2) and (3):
Figure BDA0003811924510000072
Figure BDA0003811924510000073
wherein, in discontinuous current mode, I pm Is equal to zero, thus V pm Is equal to zero; in continuous current mode, I pm Greater than zero, thus V pm Greater than zero.
2) The input signal of the demagnetization time detection module comprises an auxiliary winding partial pressure feedback value v FB 0V and a main switching tube driving signal duty; the output signal is the demagnetization time T of the transformer in the current mode r 。
The module comprises a comparator and a time calculation unit, wherein the non-inverting input end of the comparator is used as the input end of the demagnetization time detection module to receive feedback voltage which is recorded as v FB The inverting input of the comparator is set to zero when v is FB When the voltage is higher than 0, the comparator outputs high level, otherwise, the comparator outputs low level. The output end of the comparator and the duty of the driving signal of the main switching tube are connected with the input end of the time calculation unit, and the output end of the time calculation unit is used as the output end of the demagnetization time detection module to output the demagnetization time of the transformer in the current modeT r 。
In the time calculation unit, a state variable state of the transformer in one switching period is defined based on an output result Scomp _ zvs of the comparator and the main switching tube driving signal duty, and an operation mode of the transformer is determined according to a change condition of the state variable state, wherein the state variable state comprises a low level state from low to high, a first level state "1", a second level state "2" and a third level state "3". As shown in fig. 3 (a) and (b), when the main switching tube driving signal duty is at a high level, the state variable state is at a low state "0". When the duty of the switching tube driving signal is low level, if the output result Scomp _ zvs of the comparator changes from low to high level, the state variable state is switched to the first level state "1"; if the state variable state is in the first level state "1" and the output result Scomp _ zvs of the comparator changes from high to low, the state variable state is switched to the second level state "2"; if the state variable state is in the second level state "2" and the output result Scomp _ zvs of the comparator changes from low to high, the state variable state is switched to the third level state "3".
When the state variable state is switched between four level states, the transformer operates in discontinuous current mode DCM, as shown in fig. 3 (a); in this mode, the time lengths T of the first level states "1" are respectively obtained r_temp And a time length t of a second level state "2 valley Due to the excitation current i m After decreasing to zero, v FB Resonates around zero voltage, thus t valley Representing half the length of the resonance period, based on [ T r_temp -(t valley /2)]As a demagnetization time T in this mode r . When the state of the state variable is switched only between the low level state "0" and the first level state "1", the transformer operates in the continuous current mode CCM, as shown in fig. 3 (b); in this mode, the time length of the first level state "1" is acquired as the demagnetization time in this mode, i.e., T r ＝T r_temp 。
3) The output voltage calculation module takes the input signal as the maximum voltage value V of the conduction stage of the main switching tube pp And most preferablySmall voltage value V pm And demagnetization time T of the current mode of the transformer r . The output signal is the output voltage V of the n-th switching period demagnetization stage o And (n), defining the starting time of the switching period as the time when the driving signal of the main switching tube rises from the low level to the high level, and defining the ending time of the switching period as the time when the driving signal of the next main switching tube rises from the low level to the high level.
At demagnetization time T r Phase, exciting current i m In the excitation phase of the nth switching cycle, from I pp (n) linearly decreasing to I pm (n + 1) wherein I pp (n) is the peak current of the switching tube in the nth switching cycle, I pm And (n + 1) is the current of the switching tube when the switching tube is conducted in the (n + 1) th switching period.
FIGS. 4 (a) and 4 (b) show the main switch tube driving signal duty and the switch current i in the discontinuous current mode and the continuous current mode, respectively p And an excitation current i m The waveform of (2). In the demagnetization phase of the nth switching cycle, the excitation current i m The rate of decrease of (d) is related to the output voltage and the transformer excitation inductance, as shown in equation (4).
Figure BDA0003811924510000091
Based on the formulas (2) and (3), I pp (n)、I pm V for (n + 1) pp (n) and V pm (n + 1) to obtain an output voltage V o The expression of (n) is shown in formulas (5) and (6):
Figure BDA0003811924510000092
Figure BDA0003811924510000093
wherein, V pp (n) is the maximum voltage value of the conduction stage of the main switching tube in the nth switching period, V pm (n + 1) is the conduction stage of the main switching tube in the (n + 1) th switching periodMinimum voltage value, T r (n) is the demagnetization time of the nth switching cycle transformer in the current mode; n is ps Is the ratio of the number of turns of the primary winding to the number of turns of the secondary winding, R, of the transformer p Resistance value of current sampling resistor, V f The conduction voltage of an output diode in the main topological circuit; l is a radical of an alcohol m Is the excitation inductance of the primary winding of the transformer, L eq Is an equivalent main winding excitation inductance based on the voltage division ratio of the current voltage division circuit, R 3 、R 4 Is a voltage dividing resistor of a voltage dividing circuit. Considering the excitation inductance L of the transformer in actual production m The small change of the winding mode and the difference of the air gap of the magnetic core can generate fluctuation along with the difference of the transformer framework and the magnetic core, and the scheme only needs to adjust the variable resistor R 3 Or R 4 Can realize L by the resistance value of eq The constant state is ensured, and the calculated output voltage is accurate. Based on equation (5), consider L eq 、R p 、n ps And V f Are all regarded as constant, and V pp 、V pm And T r All can be accurately detected, so that accurate output voltage can be calculated.
4) PID calculation module, the input signal of which is the calculated output voltage V o And (n), the output signal is a switch control parameter corresponding to the voltage and serves as an input signal of the PWM driving module, and the PWM driving module gives a main switching tube driving signal duty based on the switch control parameter so as to realize the control of the switching tube of the switching power supply.
In the PID calculation module, the target value of the output voltage is subtracted from the calculated output voltage to obtain an output voltage error, and a proportional-integral-derivative compensation operation is performed based on the output voltage error to obtain corresponding switching control parameters, such as a duty ratio D and a switching period Ts of the main switching tube, or a peak current voltage Vpeak and the switching period Ts.
FIG. 5 is a simulation example of the closed-loop constant voltage output using the proposed constant voltage control system, with the simulation parameters of transformer magnetizing inductance L m 2.5mH, the turn ratio n of the main winding, the auxiliary winding and the auxiliary winding ps 16The circuit obtains a partial pressure v of one fourth of the circuit FB Fed back to the control circuit, the circuit works at 20kHz frequency, and the primary side current sampling resistor R p Is 2 ohm, R p The voltage is divided by one half to obtain a voltage v p And the voltage is fed back to a control circuit, and the output voltage is required to be constant at 5V. The figure shows the relevant waveforms of 90V alternating current input voltage and 10 ohm load resistance, which are primary side current i p Feedback voltage v FB State of state, demagnetization time T r The calculated waveform, the output voltage Vo _ sample calculated by adopting the proposed scheme and the closed-loop output voltage Vo realized based on the sampled voltage can be seen that based on the proposed system, the output voltage Vo _ sample calculated by the control circuit is extremely consistent with the actual output voltage Vo, and the output stability can be realized based on the sampled voltage.
In the embodiment, the output voltage is obtained through indirect calculation by obtaining the maximum voltage and the minimum voltage of the main switching tube in the conduction stage and the demagnetization time; and based on the voltage division adjustment of the primary current sampling resistor voltage, the equivalent excitation inductance of the control loop can be modulated, the equivalent excitation inductance is realized in different systems, and the interference of difference brought by the transformer excitation inductance in production is eliminated.
What has been described above is only a preferred embodiment of the present application, and the present invention is not limited to the above embodiment. It is to be understood that the invention described herein is susceptible to numerous modifications and that the voltage sampling and constant voltage control system may be employed in other switching power supplies and that other modifications and variations directly derivable or suggested to a person skilled in the art without departing from the spirit and the scope of the present invention are deemed to be within the scope of the present invention.

Claims (9)

1. A constant voltage control system of a primary side feedback flyback converter is characterized by comprising a main topological circuit and a control circuit which forms a closed loop with the main topological circuit;
inputting the feedback voltage output by the auxiliary winding voltage dividing end in the main topological circuit to a first input end of the control circuit, and obtaining the demagnetization time of the transformer by combining a main switching tube driving signal; after voltage of a current sampling resistor between a main switching tube and an input ground in the main topology circuit is divided by a voltage dividing circuit, the voltage is input to a second input end of the control circuit, and a voltage value of the main switching tube at the moment of connection and disconnection is calculated by combining a driving signal of the main switching tube; and the control circuit calculates to obtain output voltage based on the demagnetization time of the transformer and the voltage value of the main switching tube at the on and off moments.
2. The constant voltage control system of the primary feedback flyback converter of claim 1, wherein the control circuit is located at an input side and comprises a primary current measuring module, a demagnetization time detection module, an output voltage calculation module, a PID calculation module and a PWM driving module; the input end of the primary side current measuring and calculating module is used as a second input end of the control circuit to receive the divided voltage of the current sampling resistor, the output end of the primary side current detecting module is connected with the input end of the output voltage calculating module, and the primary side current detecting module is used for calculating the maximum voltage value and the minimum voltage value of the main switching tube at the conduction stage based on the divided voltage expression; the input end of the demagnetization time detection module is used as the first input end of the control circuit to receive the feedback voltage, the output end of the demagnetization time detection module is connected with the input end of the output voltage calculation module, and the demagnetization time detection module is used for acquiring demagnetization time of the transformer in the current mode based on the comparison result of the feedback voltage and zero and a main switching tube driving signal; the output voltage calculation module is connected with the PWM driving module through the PID calculation module, the output voltage calculation module is used for calculating the output voltage of the n-th switching period demagnetization stage, and the PWM driving module outputs the main switching tube driving signal as the output signal of the control circuit and is connected with the gate end of the main switching tube.
3. The constant voltage control system of the primary feedback flyback converter of claim 2, wherein in the primary current measurement module, during a period when the main switching tube is turned on, a relationship between the divided voltage and a primary current flowing through the main switching tube is:
Figure FDA0003811924500000011
wherein v is p A divided voltage i outputted from the voltage dividing circuit p Is primary side current R flowing through the main switch tube when the main switch tube is conducted p Resistance value of a current sampling resistor, R 3 、R 4 A voltage dividing resistor of the voltage dividing circuit;
acquiring primary side current I of main switching tube at conduction time pm Primary side current at turn-off time I pp Calculating the maximum voltage value V of the main switch tube in the conduction stage based on the expression pp And a minimum voltage value V pm The expressions are respectively:
Figure FDA0003811924500000021
Figure FDA0003811924500000022
wherein the minimum voltage value V pm The maximum voltage value V corresponds to the voltage value of the main switching tube at the conduction time pp And the voltage value corresponds to the turn-off moment of the main switching tube.
4. The constant voltage control system of the primary feedback flyback converter of claim 2, wherein the demagnetization time detection module comprises a comparator and a time calculation unit, and a non-inverting input terminal of the comparator is used as an input terminal of the demagnetization time detection module to receive the feedback voltage, which is denoted as v FB The inverting input terminal of the comparator is set to zero potential when v FB When the voltage is higher than 0, the comparator outputs high level, otherwise, the comparator outputs low level; the output end of the comparator and the main switching tube are connected with a driving signalThe output end of the time calculation unit is used as the output end of the demagnetization time detection module to output demagnetization time of the transformer in the current mode;
in the time calculation unit, defining a state variable of the transformer in a switching period based on an output result of the comparator and a driving signal of a main switching tube, and determining a working mode of the transformer according to a change condition of the state variable, wherein the state variable comprises a low level state, a first level state, a second level state and a third level state from low to high; when in the continuous current mode, acquiring the time length of a first level state as the demagnetization time in the mode, and when in the discontinuous current mode, respectively acquiring the time length T of the first level state r_temp And a time length t of said second level state valley Based on [ T r_temp -(t valley /2)]As the demagnetization time in this mode.
5. The constant voltage control system of the primary side feedback flyback converter according to claim 2, wherein in the output voltage calculation module, input signals of the output voltage calculation module are a maximum voltage value and a minimum voltage value of a main switching tube at a conduction stage, and demagnetization time of a transformer in a current mode; the output signal is the output voltage V of the n switching period demagnetization stage o (n), the starting time of the switching period is defined as the time when the driving signal of the main switching tube rises from low level to high level, the ending time of the switching period is the time when the driving signal of the next main switching tube rises from low level to high level, and the output voltage V is defined o (n) the expression is:
Figure FDA0003811924500000023
Figure FDA0003811924500000024
wherein, the first and the second end of the pipe are connected with each other,V pp (n) is the maximum voltage value of the conduction stage of the main switching tube in the nth switching period, V pm (n + 1) is the minimum voltage value of the conduction stage of the main switching tube in the (n + 1) th switching period, T r (n) is the demagnetization time of the nth switching cycle transformer in the current mode; n is a radical of an alkyl radical ps Is the ratio of the number of turns of the primary winding to the number of turns of the secondary winding, R, of the transformer p Resistance value of a current sampling resistor, V f Is the turn-on voltage of the output diode in the main topology circuit, and R p 、n ps And V f Are all constant; l is a radical of an alcohol m Is the excitation inductance of the primary winding of the transformer, L eq Is an equivalent main winding excitation inductance based on the voltage division ratio of the current voltage division circuit, R 3 、R 4 Is a voltage dividing resistor of the voltage dividing circuit.
6. The constant voltage control system of the primary feedback flyback converter according to claim 2, wherein an input signal of the PID calculation module is a calculated output voltage, an output signal is a switch control parameter corresponding to the voltage and is used as an input signal of the PWM driving module, and the PWM driving module provides a main switching tube driving signal based on the switch control parameter;
in the PID calculation module, the target value of the output voltage is subtracted from the calculated output voltage to obtain an output voltage error, and proportional-integral-derivative compensation operation is carried out on the basis of the output voltage error to obtain a corresponding switch control parameter, wherein the switch control parameter comprises the duty ratio and the switching period of a main switching tube.
7. The constant voltage control system of the primary feedback flyback converter according to claim 3, wherein the voltage dividing resistor of the voltage dividing circuit is a variable resistor, and the voltage dividing ratio of the current sampling resistor is adjusted by adjusting the resistance value of the variable resistor, so as to compensate for excitation inductance disturbance of the primary winding of the transformer and achieve the constancy of the excitation inductance of the equivalent primary winding.
8. The constant voltage control system of the primary feedback flyback converter of claim 4, wherein the step of defining a state variable of the transformer in a switching period based on the output result of the comparator and the main switching tube driving signal, and the step of determining the operation mode of the transformer according to the variation of the state variable comprises:
when the driving signal of the main switching tube is in a high level state, the state variable is in a low level state;
when the driving signal of the main switching tube is at a low level, if the output result of the comparator changes from a low level to a high level, the state variable is switched to a first level state; if the state variable is in a first level state and the output result of the comparator is changed from high level to low level, the state variable is switched to a second level state; if the state variable is in a second level state and the output result of the comparator changes from low to high level, the state variable is switched to a third level state;
when the state variable is switched only between a low level state and a first level state, the transformer operates in a continuous current mode; when the state variable is switched between four level states, the transformer operates in discontinuous current mode.
9. The constant voltage control system of the primary feedback flyback converter of any of claims 1-8, wherein the main topology circuit comprises a primary and secondary winding of the transformer, a main switching tube, an auxiliary winding, a clamping circuit and an output circuit; the main winding is positioned on the input side, the different-name end of the main winding is connected with the rectified direct-current voltage positive end, the same-name end of the main winding is connected with the drain end of the main switching tube, the source end of the main switching tube is connected with the ground end of the input side through a current sampling resistor, and a voltage division circuit is connected between the drain end and the ground end of the input side; the clamping circuit is connected between the primary winding and a direct current voltage positive terminal; the secondary winding is positioned on the output side and connected with the output circuit; the auxiliary winding is positioned on the input side, two ends of the auxiliary winding are connected with the divider resistor in series, and the synonym end of the auxiliary winding is connected with the ground end of the input side.
CN202211013951.3A 2022-08-23 2022-08-23 Constant-voltage control system of primary-side feedback flyback converter Pending CN115224951A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116360540A (en) * 2023-05-19 2023-06-30 四川奥库科技有限公司 Voltage regulating system and voltage regulating method for chip test
TWI836980B (en) * 2023-03-14 2024-03-21 大陸商昂寶電子（上海）有限公司 Asymmetric half-bridge flyback converter power supply and its control chip and control method

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TWI836980B (en) * 2023-03-14 2024-03-21 大陸商昂寶電子（上海）有限公司 Asymmetric half-bridge flyback converter power supply and its control chip and control method
CN116360540A (en) * 2023-05-19 2023-06-30 四川奥库科技有限公司 Voltage regulating system and voltage regulating method for chip test
CN116360540B (en) * 2023-05-19 2023-09-29 四川奥库科技有限公司 Voltage regulating system and voltage regulating method for chip test

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