CN115224950A - Large-leakage-inductance constant-current control system of primary-side feedback flyback converter - Google Patents
Large-leakage-inductance constant-current control system of primary-side feedback flyback converter Download PDFInfo
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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
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- 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
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
Abstract
The invention discloses a constant current control system of a large leakage inductance primary side feedback flyback converter, which relates to the technical field of switching power supplies and comprises a main topological circuit and a control circuit forming a closed loop with the main topological circuit, wherein a clamping circuit structure is adjusted in the main topological circuit, the current sampling resistor voltage on the input side in the main topological circuit is used as a first input signal of the control circuit, the peak current and the average current of a primary side winding and the conduction time of a clamping diode are obtained by combining the calculation of a voltage signal, the voltage division value of an auxiliary winding is used as a second input signal of the control circuit, the demagnetization time of a transformer is obtained by combining the demagnetization time of the transformer, and the average current of the diode in an output circuit is calculated by combining the parameters obtained by the calculation and the switching period. The system considers the energy loss brought by the primary side leakage inductance to the charging stage of the clamping circuit, so that high-precision constant output current can be realized in the flyback converter with large leakage inductance.
Description
Technical Field
The invention relates to the technical field of switching power supplies, in particular to a constant-current control system of a large-leakage-inductance primary-side feedback flyback converter.
Background
With the development of the technology, the switch power supply is widely applied to medium and small power occasions, and the isolated switch power supply can realize the electrical isolation of input and output and has the characteristics of safe isolation and high reliability. The flyback converter has the advantages of simple structure, high reliability, low cost and the like, and is widely applied to medium and small power consumer electronics. Compared with the traditional flyback converter based on the secondary feedback technology, the flyback converter based on the primary feedback technology is simpler in circuit structure, does not need to use nonlinear devices such as an optocoupler and the like, and can further improve the reliability, the service life, the integration level and the like.
The method for realizing the constant current output of the current primary side feedback flyback converter mainly controls the current of an output diode to be constant, and the main thought is as follows: calculating to obtain the average current of the primary winding of the transformer in the conduction stage by a correlation method, and obtaining the average current of the output winding in the demagnetization stage according to the principle that the ratio of the current of the primary winding of the transformer to the current of the output winding is equal to the turn ratio of the primary winding to the secondary winding; and finally, obtaining the average current of the output diode based on the average current of the demagnetization stage, the time length of the demagnetization stage and the switching period, and keeping the average current constant to realize the constant load current. At present, the method can be used in an interrupted current mode and a continuous current mode, and can obtain better output voltage precision.
However, the current primary side feedback constant current control method ignores the influence of the leakage inductance of the transformer on the accuracy of the output current, when the leakage inductance is significant, the ratio of the average current of the primary side winding to the average current of the output winding is lower than the turn ratio of the primary side winding to the secondary side winding of the transformer, and if the current primary side feedback constant current control method is adopted, the actual output current is lower than the target reference current. In order to solve the problem, a special winding method is usually adopted at present to reduce the leakage inductance of the transformer and increase the clamping resistance value to increase the voltage of the clamping capacitor, but the special winding method can increase the winding difficulty and cost of the transformer, the clamping voltage of the clamping circuit is higher, the voltage of the drain end of the switching tube is increased, and the breakdown risk is also increased.
Disclosure of Invention
The invention provides a constant-current control system of a large-leakage-inductance primary-side feedback flyback converter aiming at the problems and the technical requirements, so that the circuit control is simplified, and the output current precision is improved.
The technical scheme of the invention is as follows:
a constant current control system of a large leakage inductance primary side feedback flyback converter comprises a main topological circuit and a control circuit forming a closed loop with the main topological circuit;
the main topological circuit comprises a primary winding and a secondary winding of the transformer, a switching tube, an auxiliary winding, a clamping circuit and an output circuit; the primary winding is positioned on the input side, the dotted terminal of the primary winding is connected with the positive end of direct-current voltage, the unlike terminal of the primary winding is connected with the drain terminal of the switching tube, and the source terminal of the switching tube is connected with the ground terminal of the input side through the current sampling resistor; the clamping circuit comprises a clamping diode, a clamping capacitor and a clamping resistor, wherein the clamping capacitor and the clamping resistor are connected in parallel; the secondary winding is positioned on the output side and connected with an output circuit; the auxiliary winding is positioned on the input side, two ends of the auxiliary winding are connected with a voltage dividing resistor in series, and the same name end of the auxiliary winding is connected with the ground end of the input side;
the voltage of the current sampling resistor is used as a first input signal of the control circuit, the peak current, the average current and the conduction time of the clamping diode of the primary winding are calculated by combining a voltage signal, the voltage division value of the auxiliary winding is used as a second input signal of the control circuit, so that the demagnetization time of the transformer is obtained, and the average current of the diode in the output circuit is calculated by combining the peak current, the average current, the conduction time of the clamping diode, the demagnetization time of the transformer and the switching period of the primary winding.
The control circuit is positioned at the input side and comprises a primary side current detection module, a demagnetization time detection module, an output current calculation module, a PID calculation module and a PWM drive module; the primary side current detection module is used for calculating the peak current and the average current of a primary side winding and the conduction time of a clamping diode based on the comparison result of the voltage and the voltage signal of a current sampling resistor and a switching tube driving signal; the input end of the demagnetization time detection module receives a second input signal, the output end of the demagnetization time detection module is connected with the input end of the output current calculation module, and the demagnetization time detection module is used for acquiring demagnetization time of the transformer in the current mode based on a comparison result of the partial pressure value of the auxiliary winding and zero and a switching tube driving signal; the output current calculation module is connected with the PWM driving module through the PID calculation module, the output current calculation module is used for calculating the average current of a diode in the output circuit, and the PWM driving module outputs a driving signal of the switching tube as an output signal of the control circuit and is connected with the grid end of the switching tube.
The primary side current detection module comprises a first comparator, a second comparator and a primary side current calculation unit, wherein the non-inverting input ends of the first comparator and the second comparator are used as the non-inverting input end of the primary side current detection module to receive a first input signal v p The inverting input end of the first comparator is used as the inverting input end of the primary current detection module to receive the first voltage signal V pp The inverting input end of the second comparator is used as the inverting input end of the primary side current detection module to receive the second voltage signal V pm And V is pm ＝k*V pp Wherein 0 is<k<1; when v is p ＞V pp If so, the first comparator outputs a high level, otherwise, the first comparator outputs a low level; when v is p ＞V pm If so, the second comparator outputs a high level, otherwise, a low level is output; the output ends of the first comparator and the second comparator and the driving signal of the switching tube are connected with the input end of the primary side current computing unit, and the output end of the primary side current computing unit is used as the output end of the primary side current detection module to output the computed primary side windingPeak current of (I) p max Average current I pav And the conduction time T of the clamping diode c ；
When the driving signal of the switching tube is in a high level, acquiring the time length t that the output results of the first comparator and the second comparator are in a low level 1 Acquiring the time length t of the output result of the first comparator being low level and the output result of the second comparator being high level 2 (ii) a When the driving signal of the switching tube is in a low level, acquiring the time length t that the output results of the first comparator and the second comparator are in a high level 3 Acquiring the time length t when the output result of the first comparator is low level and the output result of the second comparator is high level 4 Substituting into corresponding calculation formula to obtain I p max 、I pav And T c The expression is respectively:
wherein R is p The resistance value of the current sampling resistor.
The demagnetization time detection module comprises a third comparator and a demagnetization time calculation unit, wherein the non-inverting input end of the third comparator is used as the input end of the demagnetization time detection module to receive a second input signal v FB The inverting input terminal of the third comparator is set to zero when v is FB When the voltage is higher than 0, the third comparator outputs high level, otherwise, the third comparator outputs low level; the output end of the third comparator and the input end of the switch tube driving signal connection demagnetization time calculation unit, the output end of the demagnetization time calculation unit is used as the output end of the demagnetization time detection module to output the output end of the transformer in the current modeDemagnetizing time;
in the demagnetization time calculation unit, defining a state variable of the transformer in a switching period based on an output result of the third comparator and a driving signal of a 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.
The further technical scheme is that the input signal of the output current calculation module also comprises a switching period provided by the PID calculation module, the output signal of the output current calculation module is the average current of a diode in the output circuit in the current period, and the expression is as follows:
wherein n is ps Is the ratio of the number of turns of the primary winding to the secondary winding, I p max Is the peak current of the primary winding, I pav Is the average current of the primary winding, T c For clamping the conduction time of the diode, T r For the demagnetization time in the current mode of the transformer, T s Is the current switching cycle.
The input signal of the PID calculation module is the average current of a diode in an output circuit, the output signal of the PID calculation module is a first voltage signal, a second voltage signal and a switching period which are obtained by error calculation and PID compensation algorithm calculation, and the output current is constant by controlling the average current of the diode in the output circuit to be equal to the target reference current required to be realized; the first voltage signal and the second voltage signal are transmitted to the inverting input end of the primary side current detection module, and the switching period is transmitted to the PWM driving module.
The further technical scheme is that the input signal of the PWM driving module comprises a switching period provided by the PID calculation module, and a comparison result of a current sampling resistor voltage provided by the primary side current detection module and a first voltage signal, and the output signal of the PWM driving module is a driving signal of a switching tube, and the expression is as follows: and setting the driving signal to be at a high level and switching on the switching tube every the time length of the switching period, and setting the driving signal to be at a low level and switching off the switching tube when the comparison result is changed from low to high.
The further technical scheme is that a state variable of the transformer in a switching period is defined based on an output result of the third comparator and a driving signal of the 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 switching tube is at a high level, the state variable is at a low level state;
when the driving signal of the switching tube is at a low level, if the output result of the third 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 the first level state and the output result of the third 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 third comparator changes from low to high level, the state variable is switched to the 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 beneficial technical effects of the invention are as follows:
the system reduces the circuit complexity by adjusting the clamping circuit structure of the primary side feedback flyback converter, and the current flowing into the clamping circuit is obtained by the low-voltage current sampling resistor voltage, so that the high-voltage current or voltage sampling of the traditional clamping circuit is not needed, and the current sampling difficulty of the clamping circuit is greatly reduced; the voltage of a primary sampling resistor is judged to obtain the peak current and the average current of a primary winding and the conduction time of a clamping diode, the voltage of a partial voltage value of an auxiliary winding is judged to obtain the demagnetization time of the auxiliary winding, and the accurate value of the average current of an output diode is obtained through comprehensive calculation, namely, the constant current control can well eliminate the calculation error caused by large leakage inductance based on a simple peripheral circuit and a simple calculation method, and better output current precision can still be obtained under the condition of large leakage inductance; the system can be suitable for isolated or non-isolated switch power supply circuit structures, and has the advantages of universality, reusability, transportability and the like.
Drawings
Fig. 1 is a schematic structural diagram of a constant current control system of a large-leakage-inductance primary-side feedback flyback converter provided by the present application.
Fig. 2 is a schematic diagram of an operating waveform of a primary side current detection module provided in the present application.
FIG. 3 is a schematic diagram of waveforms of relevant variables of a demagnetization time detection module provided by the present application; graph (a) is a waveform of a relevant variable in the discontinuous current mode, and graph (b) is a waveform of a relevant variable in the continuous current mode.
FIG. 4 is a schematic diagram related to a method for calculating an average current of a diode of an output circuit by an output current calculation module provided in the present application; fig. (a) is a schematic view of a calculation method in the discontinuous current mode, and fig. (b) is a schematic view of a calculation method in the continuous current mode.
FIG. 5 is a diagram of a method for calculating an average current of an output diode of a conventional primary side feedback flyback converter; fig. (a) is a schematic view of a calculation method in the discontinuous current mode, and fig. (b) is a schematic view of a calculation method in the continuous current mode.
Detailed Description
The following further describes the embodiments of the present invention with reference to the drawings.
Compared with the traditional primary feedback flyback converter, the constant-current control system of the large-leakage-inductance primary feedback flyback converter has the advantages that the auxiliary winding is additionally arranged on the input side, the structure of the clamping circuit on the input side is adjusted, and the accuracy of the average current of the output diode is improved by combining a certain calculation mode on the basis of simplifying circuit control. The specific structure of the constant current control system of the large-leakage-inductance primary-side feedback flyback converter will be described in detail below.
As shown in fig. 1, the system includes a main topology circuit and a control circuit forming a closed loop therewith. The main topological circuit comprises a primary winding and a secondary winding of the transformer and a switching tube M p Auxiliary winding W a A clamp circuit and an output circuit. Primary winding W p Is located at the input side, and the dotted terminal of the input side is connected with a direct-current voltage positive terminal V in The negative end of the direct current voltage is grounded, and the primary winding W p Different name end connecting switch tube M p Drain terminal of, switching tube M p The source end of the resistor passes through a current sampling resistor R with small resistance value p And is connected with the input side ground terminal. The clamping circuit comprises a clamping diode D c A clamp capacitor C c And a clamp resistor R c Clamping diode D c Positive pole of the switch tube M p Drain terminal of, clamping diode D c Negative electrode of the clamping capacitor C c Positive electrode of (2), clamping capacitor C c Negative pole of (3) is connected with a switch tube M p Source terminal of, clamping capacitor C c And a clamp resistor R c Are connected in parallel. Secondary winding W s On the output side, the output circuit includes an output diode D 1 And a parallel output capacitor C L And a load R L Secondary winding W s The different name end of the output diode D is connected with the output diode D 1 Anode of (2), output diode D 1 Negative pole of the capacitor is connected with an output capacitor C L Positive electrode of (2), output capacitor C L Negative pole and secondary winding W of s The homonymous terminals of the two terminals are all connected with the ground terminal of the output side. 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 And R 2 And its homonym is connected to the input side ground. Wherein the current is sampled by the voltage v of the resistor p As a first input signal to the control circuit, the auxiliary winding W a Partial pressure value V of FB A second input signal as a control circuit is connected to the control circuit for calculating the output diode D 1 Average current of (2).
In this embodiment, by adjusting the clamp circuit structure, not only is the circuit complexity reduced, but also the current flowing into the clamp circuit is obtained by the low-voltage end current sampling resistor voltage which is easy to obtain, and the current or voltage sampling of the high-voltage end of the traditional clamp circuit is not needed, so that the current sampling difficulty of the clamp circuit is greatly reduced.
The control circuit is positioned on the input side and comprises a primary side current detection module, a demagnetization time detection module, an output current calculation module, a PID calculation module and a PWM driving module. The non-inverting input end of the primary side current detection module receives a first input signal, the inverting input end of the primary side current detection module receives a voltage signal provided by the PID calculation module, the output end of the primary side current detection module is connected with the input end of the output current calculation module, and the primary side current detection module is used for sampling a resistor voltage v based on current p And calculating the peak current and the average current of the primary winding and the conduction time of the clamping diode according to the comparison result of the voltage signal and the driving signal of the switching tube. The input end of the demagnetization time detection module receives a second input signal, the output end of the demagnetization time detection module is connected with the input end of the output current calculation module, and the demagnetization time detection module is used for calculating the voltage division value V based on the auxiliary winding FB And obtaining the demagnetization time of the transformer in the current mode according to the comparison result with zero and the switching tube driving signal. The output current calculation module is connected with the PWM driving module through the PID calculation module and used for calculating an output diode D 1 The PWM driving module outputs a driving signal of the switching tube as an output signal of the control circuit and is connected with a gate end of the switching tube of the main topology circuit.
The system can well eliminate the calculation error caused by large leakage inductance based on a simple peripheral circuit and a calculation method, can still obtain better output current precision in a flyback converter with large leakage inductance, and overcomes the problem of lower actual output current in the traditional scheme, so the system has the advantages of low cost, simple control, high precision and the like; the combined innovation of the structural adjustment and the simplified control is the most fundamental reason for bringing this advantage, and the specific structure and principle of each module will be described below.
1) Primary side current detection module, input signal thereofComprising a primary current sampling signal v p Voltage signal V pp And V pm And a switching tube drive signal duty; the output signal comprising the comparison result S comp1 ，S comp1 The peak current is transmitted to the PWM driving module to realize peak current control, and the peak current I of the primary winding is also included p max Average current I pav And clamping diode conduction time T c And the three signals are transmitted to an output current calculation module for calculating accurate output current.
Specifically, the module comprises a first comparator, a second comparator and a primary current calculation unit, wherein the non-inverting input ends of the first comparator and the second comparator are used as the non-inverting input end of the primary current detection module to receive a first input signal v p The inverting input end of the first comparator is used as the inverting input end of the primary current detection module to receive the first voltage signal V pp The inverting input end of the second comparator is used as the inverting input end of the primary current detection module to receive the second voltage signal V pm And V is pm ＝k*V pp Wherein, 0<k<1; when v is p ＞V pp If so, the first comparator outputs a high level, otherwise, the first comparator outputs a low level; when v is p ＞V pm When the voltage is higher than the first voltage, the second comparator outputs a high level, otherwise, the second comparator outputs a low level. The output ends of the first comparator and the second comparator and the duty of the driving signal of the switching tube are connected with the input end of the primary side current computing unit, and the output end of the primary side current computing unit is used as the output end of the primary side current detection module to output the calculated peak current I of the primary side winding p max Average current I pav And the conduction time T of the clamping diode c 。
FIG. 2 is a waveform of operation of a primary side current sense module in Continuous Current Mode (CCM) including switching tube drive signals duty, v p 、V pp 、V pm And the comparison result S comp1 、S comp2 The waveform of (2). After duty set to "1", a turn-on delay t d After that, the switch tube is turned on, v p From V pmin Linearly rising to its peak value V pmax . The method for calculating the relevant time variable is as follows: when the switch tube drives the letterWhen the signal is high level '1', the time length that the output results of the first comparator and the second comparator are the same as the low level is obtained and recorded as t 1 (ii) a The length of time during which the output result of the first comparator is at a low level and the output result of the second comparator is at a high level, i.e., v p From V pm Is raised to V pp The time length of (1), is recorded as t 2 . When the driving signal of the switching tube is low level '0', the time length that the output results of the first comparator and the second comparator are both high level is obtained and recorded as t 3 I.e. the turn-off delay t of the switching tube d (ii) a The length of time during which the output result of the first comparator is at a low level and the output result of the second comparator is at a high level, i.e., v p From V pp Down to V pm The time length of (1), is recorded as t 4 。
Assuming that the turn-on delay and turn-off delay of the switching tube are equal, v p From V pmin Linearly up to V pm Has a time length of t 1 -t d I.e. is t 1 -t 3 . Considering v p Rising slope k p Constant, therefore k is estimated p 、V pmin 、V pmax The value of (A) is shown by the following formula:
based on V pmax And V pmin Further calculating to obtain the peak current I of the primary side current of the conduction stage of the switching tube p max And the average current I pav (i.e. the primary side current corresponding to the midpoint time of the conduction phase of the switching tube) is shown as follows. Optionally, V pm Is generally taken fromV pmax And V pmin Values in between, commonly taken as V mentioned above pm ＝k*V pp Or V pm Can also take V pmax And V pmin Average value of (d), etc. Since the current calculation of Discontinuous Current Mode (DCM) is the same as CCM, it is not described herein.
Considering v p The slope of the fall is constant, based on V pmax And V pp Calculating to obtain the conduction time T of the clamping diode c As shown in equation (6), consider the actual t in equation (2) 3 <<t 2 (t 3 For the turn-off delay of the switching tube, generally small), and therefore V pp And V pmax (V pmax ＝I pmax *R p ) Approximately equal, equation (6) is further simplified to equation (7).
2) The input signal of the demagnetization time detection module comprises an auxiliary winding partial pressure value v FB 0V and a switching tube driving signal duty; the output signal is the demagnetization time T of the transformer in the current mode r Represents the output diode D 1 On-time of, i.e. output diode current i d A length of time greater than zero.
Specifically, the module comprises a third comparator and a demagnetization time calculation unit, wherein the non-inverting input end of the third comparator is used as the input of the demagnetization time detection moduleTerminal receiving a second input signal v FB The inverting input terminal of the third comparator is set to zero when v is FB And when the voltage is higher than 0, the third comparator outputs high level, otherwise, the third comparator outputs low level. The output end of the third comparator and the duty of the switching tube driving signal are connected with the input end of the demagnetization time calculation unit, and the output end of the demagnetization time calculation unit is used as the output end of the demagnetization time detection module to output the demagnetization time T in the current mode of the transformer r 。
In the demagnetization time calculation unit, based on the output result S of the third comparator comp3 And the switching tube driving signal duty defines a state variable enable of the transformer in a switching period, and determines the working mode of the transformer according to the change condition of the state variable enable, wherein the state variable enable 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'. FIG. 3 is a graph of the demagnetization time detection module based on duty, v FB Calculating the demagnetization time T r The waveform of (1) shows duty and v FB 、i d 、S comp3 And an enable waveform. As shown in fig. 3 (a) and (b), when the duty of the switching tube driving signal is high, the state variable is in a low state "0". When the duty of the switch tube driving signal is low, if the output result S of the third comparator is high comp3 When the low level is changed into the high level, the state variable is switched into a first level state 1; if the state variable is the first level state "1", and the output result S of the third comparator is obtained comp3 When the high level is changed into the low level, the state variable is switched into a second level state of 2; if the state variable is the second level state "2", and the output result S of the third comparator is obtained comp3 When the state variable changes from low to high, the state variable is switched to the third level state "3", and the state switching conditions are shown in table 1.
TABLE 1 State variable switching conditions
When state variable enable when switching between four level states, the transformer operates in 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 Based on [ T r_temp -(t valley /2)]As a demagnetization time T in this mode r . When the state variable enable is switched only between the low level state "0" and the first level state "1", the transformer operates in 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 input signal of the output current calculation module comprises the peak current I of the primary winding p max Average current I pav On-time T of clamp diode c And a demagnetization time T in the current mode r And the switching period T provided by the PID calculation module s (ii) a The output signal is the average current I of the diode in the output circuit in the current period d1 。
FIG. 4 shows the average current I of the output diode after obtaining the above parameters d1 Is shown in the figure, which shows the primary winding current i p Exciting current i m And output diode current i d Waveform i of p Shown as a solid line, in the conduction stage i of the switch tube p Increase linearly when i m And i p Coincidence, i d Is equal to zero; at i d Greater than zero, i m Greater than i p 。i d Is proportional to i m And i p The difference, the expression is: i.e. i d ＝n ps (i m -i p ) Wherein n is ps The ratio of the number of turns of the primary winding to the secondary winding.
FIG. 4 (a) is a related diagram under DCM, output diode D 1 Can be described as i d Average value integrated over time, denoted as I d1 And I is d1 Proportional to the area of the shaded portion of the graph. Which may be formed from m And i p At T r Average value after integration of phase and timeCalculate to obtain i m The integral over time can be represented by I pav 、T r And T s To obtain i p The integral over time can be represented by I pmax 、T c And T s Thus obtaining the product. FIG. 4 (b) is a schematic diagram of the calculation method in CCM, and the output diode D 1 The derived formula for the average current of (d) is consistent with DCM and is expressed as:
fig. 5 (a) and (b) are design ideas of constant current control of the conventional primary side feedback flyback converter under two modes, and primary side winding current i is shown in the drawings p Exciting current i m And output diode current i d The current of the primary winding of the transformer is transferred to the output winding immediately after the switch tube is turned off, namely the charging period T of the clamping circuit is not considered by the leakage inductance of the primary side c With consequent loss of energy, i.e. T c =0. The average current of the output diode at this time is denoted as I d2 And I is d2 In proportion to the area of the shaded portion in the figure, the calculation formula is shown in formula (9). As can be seen from comparison with equation (8), I calculated by the conventional scheme d2 Than actual value I d1 Large leakage inductance, and therefore, large T c When the current is more significant, the actual output current is more than I d2 And when the scheme provided by the application is adopted, the deviation of the output current introduced by the large leakage inductance can be corrected.
4) PID calculation module with input signal of average current I of diode in output circuit d1 The output signal is a first voltage signal V obtained by error calculation and PID compensation algorithm calculation pp A second voltage signal V pm And a switching period T s By controlling the average current I of the diodes in the output circuit d1 Equal to the target reference current I to be achieved REF Realizing constant output currentAnd (4) determining. Wherein the first voltage signal V pp A second voltage signal V pm Transmitted to the reverse input end of the primary current detection module and has a switching period T s And transmitting the data to the PWM driving module.
5) PWM driving module, its input signal includes switching period T provided by PID calculation module s Comparison result S of voltage of current sampling resistor provided by primary side current detection module and first voltage signal comp1 The output signal is the driving signal duty of the switching tube, and the waveform is expressed as: time length T of every other switching period s Setting the driving signal to high level "1", turning on the switch tube, and comparing the result S comp1 When the voltage is changed from low to high level, the driving signal is set to be low level '0', the switching tube is switched off, and peak current control is achieved.
In the embodiment, the peak current and the average current of the primary winding and the conduction time of the clamping diode are obtained by judging the voltage of the primary sampling resistor, the demagnetization time is obtained by judging the voltage of the voltage division value of the auxiliary winding, and the accurate value of the average current of the output diode is obtained by comprehensive calculation. The system is suitable for isolated or non-isolated switch power supply circuit structures, and has the advantages of universality, reusability, transportability and the like.
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 other modifications and variations directly derivable or suggested by those skilled in the art without departing from the spirit and concept of the present invention are to be considered as included within the scope of the present invention.
Claims (8)
1. A constant-current control system of a large-leakage-inductance primary-side feedback flyback converter is characterized by comprising a main topological circuit and a control circuit forming a closed loop with the main topological circuit;
the main topological circuit comprises a primary winding and a secondary winding of the transformer, a switching tube, an auxiliary winding, a clamping circuit and an output circuit; the primary winding is positioned on the input side, the homonymous terminal of the primary winding is connected with the positive direct-current voltage terminal, the heteronymous terminal of the primary winding is connected with the drain terminal of the switching tube, and the source terminal of the switching tube is connected with the ground terminal of the input side through the current sampling resistor; the clamping circuit comprises a clamping diode, a clamping capacitor and a clamping resistor, wherein the clamping capacitor and the clamping resistor are connected in parallel; 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 a voltage dividing resistor in series, and the same name end of the auxiliary winding is connected with the ground end of the input side;
and calculating the average current of the diodes in the output circuit by combining the peak current, the average current, the conducting time of the clamping diodes, the demagnetizing time of the transformer and the switching period of the transformer.
2. The constant-current control system of the large-leakage-inductance primary-side feedback flyback converter according to claim 1, wherein the control circuit is positioned on an input side and comprises a primary-side current detection module, a demagnetization time detection module, an output current calculation module, a PID calculation module and a PWM driving module; the primary side current detection module is used for calculating peak current, average current and conduction time of a clamping diode of the primary side winding based on a comparison result of current sampling resistor voltage and a voltage signal and a switching tube driving signal; the input end of the demagnetization time detection module receives the second input signal, the output end of the demagnetization time detection module is connected with the input end of the output current calculation module, and the demagnetization time detection module is used for acquiring demagnetization time of the transformer in the current mode based on a comparison result of the partial pressure value of the auxiliary winding and zero and a switching tube driving signal; the output current calculation module is connected with the PWM drive module through the PID calculation module, the output current calculation module is used for calculating the average current of a diode in the output circuit, and the PWM drive module outputs a drive signal of the switch tube as an output signal of the control circuit and is connected with the grid end of the switch tube.
3. The constant-current control system of claim 2, wherein the primary current detection module comprises a first comparator, a second comparator and a primary current calculation unit, and non-inverting input terminals of the first comparator and the second comparator are used as non-inverting input terminals of the primary current detection module to receive the first input signal v p The inverting input end of the first comparator is used as the inverting input end of the primary side current detection module to receive the first voltage signal V pp The inverting input end of the second comparator is used as the inverting input end of the primary side current detection module to receive a second voltage signal V pm And V is pm ＝k*V pp Wherein, 0<k<1; when v is p ＞V pp If so, outputting a high level by the first comparator, otherwise, outputting a low level; when v is p ＞V pm If so, the second comparator outputs a high level, otherwise, a low level is output; the output ends of the first comparator and the second comparator and the driving signal of the switching tube are connected with the input end of the primary side current calculation unit, and the output end of the primary side current calculation unit is used as the output end of the primary side current detection module to output the calculated peak current I of the primary side winding p max Average current I pav And the conduction time T of the clamping diode c ；
When the switch tube driving signal is at a high level, acquiring the time length t that the output results of the first comparator and the second comparator are at a low level 1 Obtaining that the output result of the first comparator is low level and the second comparator is low levelTime length t of high level output result of comparator 2 (ii) a When the switch tube driving signal is at a low level, acquiring the time length t that the output results of the first comparator and the second comparator are at a high level 3 Acquiring the time length t that the output result of the first comparator is at low level and the output result of the second comparator is at high level 4 Substituting into corresponding calculation formula to obtain I p max 、I pav And T c The expression is respectively:
wherein R is p The resistance value of the current sampling resistor.
4. The constant current control system of the large-leakage-inductance primary-side feedback flyback converter according to claim 2, wherein the demagnetization time detection module comprises a third comparator and a demagnetization time calculation unit, and a non-inverting input end of the third comparator is used as an input end of the demagnetization time detection module to receive a second input signal v FB The inverting input terminal of the third comparator is set to zero potential when v FB When the voltage is higher than 0, the third comparator outputs high level, otherwise, the third comparator outputs low level; the output end of the third comparator and a switch tube driving signal are connected with the input end of the demagnetization time calculation unit, and the output end of the demagnetization 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 demagnetization time calculation unit, based onThe output result of the third comparator and the driving signal of the switching tube define a state variable of the transformer in a switching period, and the working mode of the transformer is determined 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 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-current control system of the large-leakage-inductance primary-side feedback flyback converter, according to claim 2, wherein the input signal of the output current calculation module further includes a switching period provided by the PID calculation module, the output signal of the output current calculation module is an average current of a diode in the output circuit in a current period, and an expression is as follows:
wherein n is ps Is the ratio of the number of turns of the primary winding to the secondary winding, I p max Is the peak current of the primary winding, I pav Is the average current of the primary winding, T c For the conduction time, T, of said clamping diode r Is the demagnetization time, T, of the current mode of the transformer s Is the current switching cycle.
6. The constant-current control system of the large-leakage-inductance primary-side feedback flyback converter, according to claim 2, is characterized in that an input signal of the PID calculation module is an average current of a diode in the output circuit, an output signal of the PID calculation module is a first voltage signal, a second voltage signal and a switching period which are obtained through error calculation and PID compensation algorithm calculation, and the output current is constant by controlling the average current of the diode in the output circuit to be equal to a target reference current to be realized; the first voltage signal and the second voltage signal are transmitted to the inverting input end of the primary side current detection module, and the switching period is transmitted to the PWM driving module.
7. The constant-current control system of the large-leakage-inductance primary-side feedback flyback converter, according to claim 2, wherein the input signal of the PWM driving module includes a switching period provided by the PID calculation module, and a comparison result between a current sampling resistor voltage provided by the primary-side current detection module and a first voltage signal, and the output signal of the PWM driving module is a driving signal of the switching tube, and is expressed as: and setting the driving signal to be at a high level every the time length of a switching period, switching on the switching tube, and setting the driving signal to be at a low level and switching off the switching tube when the comparison result is changed from low to high.
8. The constant current control system of the large-leakage-inductance primary-side feedback flyback converter of claim 4, wherein the step of defining a state variable of the transformer in a switching period based on an output result of the third comparator and a driving signal of a switching tube and determining a working mode of the transformer according to a variation condition of the state variable comprises the steps of:
when the driving signal of the switching tube is at a high level, the state variable is at a low level state;
when the switch tube driving signal is at a low level, if the output result of the third comparator changes from low to 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 third 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 third 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.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115603283A (en) * | 2022-11-21 | 2023-01-13 | 珠海智融科技股份有限公司（Cn） | Flyback protection circuit |
| CN116915073A (en) * | 2023-09-06 | 2023-10-20 | 深圳莱福德科技股份有限公司 | Method for widening constant-current output voltage range |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115603283A (en) * | 2022-11-21 | 2023-01-13 | 珠海智融科技股份有限公司（Cn） | Flyback protection circuit |
| CN116915073A (en) * | 2023-09-06 | 2023-10-20 | 深圳莱福德科技股份有限公司 | Method for widening constant-current output voltage range |
| CN116915073B (en) * | 2023-09-06 | 2024-01-05 | 深圳莱福德科技股份有限公司 | Method for widening constant-current output voltage range |
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