CN114389454B - Secondary side control method and secondary side control system for isolated power supply - Google Patents
Secondary side control method and secondary side control system for isolated power supply Download PDFInfo
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- CN114389454B CN114389454B CN202011131735.XA CN202011131735A CN114389454B CN 114389454 B CN114389454 B CN 114389454B CN 202011131735 A CN202011131735 A CN 202011131735A CN 114389454 B CN114389454 B CN 114389454B
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
- H02M3/33523—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
- H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
- H02H7/1213—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for DC-DC converters
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Dc-Dc Converters (AREA)
Abstract
A secondary side control method and a secondary side control system of an isolated power supply adopt secondary side peak current mode control to realize accurate control of a secondary side on current parameters; detecting voltages at two ends of a secondary inductor of a transformer during the turn-on period of a primary power tube, acquiring primary inductor current information of an isolation power supply, judging whether the primary inductor current of the isolation power supply reaches a peak value according to the primary inductor current information of the isolation power supply, and turning off the primary power tube when the peak value is reached; in addition, the output load current of the isolation power supply is calculated according to the duty ratio of the secondary side freewheel time to one switching period and the secondary side peak current obtained by the voltages at the two ends of the secondary side winding of the transformer, so that the starting control of the primary side power tube and the control of the peak current of the primary side power tube are realized. Compared with a primary side peak current mode control mode, the invention naturally counteracts non-ideal factors of voltage transformation and improves control precision; meanwhile, a sampling resistor is not required to be arranged, the problem of resistance loss of the traditional control scheme is solved, and the system efficiency is improved.
Description
Technical Field
The invention belongs to the technical field of switching power supplies, and relates to a secondary side control method and a secondary side control system of an isolated power supply.
Background
For the topology structure of the switching power supply, current information of an inductor or a transformer, particularly a control method of a peak current mode, is often required to be monitored, and the peak current is required to be sampled to control the turn-off of the main MOS. The isolated power supply, as shown in fig. 1, generally includes a transformer I101, a secondary diode I102 and a primary power tube I108, and in order to obtain better current accuracy, the conventional architecture generally needs to use a primary sampling resistor RCS2, i.e. I110, to obtain peak current information of the primary inductance of the transformer. Meanwhile, as the primary side sampling resistor controls the current of the inductor in the primary side of the transformer, but the transmission ratio of the primary side current to the secondary side is influenced by the parameters such as the turn ratio and leakage inductance of the transformer, the production process cannot accurately control the equivalent turn ratio of the transformer, so that the secondary side output current cannot be accurately controlled through the primary side sampling resistor, and the influence of non-ideal factors of the transformer on the accuracy of primary side control output current cannot be eliminated.
For the secondary side control architecture, since the secondary side control part is difficult to accurately obtain the inductor current information of the primary side, the secondary side accurate control of the peak inductor current cannot be realized. Taking the flyback type isolation switch power supply shown in fig. 1 as an example, a secondary side control architecture is used, and the isolation power supply system comprises a transformer I101, a secondary side diode I102, two voltage dividing resistors I103 and I104, a secondary side control unit I105, a primary side secondary side signal transmission unit I106, a primary side control unit I107 and a primary side power tube I108, and in order to obtain primary side information and secondary side signals, a primary side sampling resistor R CS2 and a secondary side sampling resistor R CS1 are usually respectively arranged on the primary side and the secondary side. The two voltage dividing resistors I103 and I104 are used for sampling the output voltage of the power supply system to obtain the divided voltage of the output voltage as a feedback signal FB and outputting the feedback signal FB to the secondary side control unit I105; the secondary side sampling resistor R CS1 is used for sampling output current, the product of the output current and the self resistance of the secondary side sampling resistor R CS1 is converted into a SENSE1 voltage, and the SENSE1 voltage outputs current information represented by the SENSE1 voltage to the secondary side control unit I105 to be compared with output voltage information contained in the feedback signal FB. The secondary side control unit I105 controls the working mode of the whole power supply chip according to the input secondary side current and voltage information, and transmits the secondary side information to the primary side control unit I107 through the primary side secondary side signal transmission unit I106. The primary side control unit I107 is controlled by the secondary side control unit I105, and the signal of the secondary side control unit I105 controls the primary side control unit I107 to start the primary side power tube I108 and control the peak current of the primary side power tube I108 through the primary side secondary side signal transmission unit I106; but because it is controlled by the peak current mode, the primary side control unit I107 also samples the peak current of the primary side inductance of the transformer through the primary side sampling resistor I110, i.e., R CS2, and is used to control the turn-off of the primary side power transistor I108.
It can be seen that in the conventional secondary control architecture, two sampling resistors R CS1 and R CS2 are generally required, the secondary sampling resistor R CS1 samples output load information of the secondary side of the transformer, the primary sampling resistor R CS2 samples peak current information of the primary inductance of the transformer, and control of the primary and secondary sides is implemented according to the collected information, and in this way, the primary and secondary sides must be provided with current sampling resistors, but there is power consumption due to current flowing through the resistors, which may cause a decrease in system efficiency.
Disclosure of Invention
Aiming at the problems that the system efficiency is reduced and the secondary side output current cannot be accurately controlled through a primary side sampling resistor due to the power consumption caused by the arrangement of the sampling resistor of an isolation power supply of a traditional secondary side control architecture, the invention provides a secondary side control method and a secondary side control system without the sampling resistor, which are applicable to a switching power supply with a transformer and comprise ACDC, DCDC and other isolation power supply control systems; according to the secondary side control system provided by the invention, the primary side inductance current is accurately detected by acquiring the secondary side voltage, and the primary side power tube is controlled according to the detection result, so that the influence of non-ideal factors of a transformer on the primary side control output current precision when the primary side sampling resistor is used for controlling the secondary side output current is solved, high precision can be realized, and no power consumption generated by current flowing through the resistor is avoided because the sampling resistor is not required to be arranged, and therefore, the problem of low efficiency existing in the traditional secondary side control architecture due to the adoption of the sampling resistor is solved, and the system efficiency is improved.
The technical scheme of the secondary side control method of the isolated power supply provided by the invention is as follows:
the secondary side control method of the isolation power supply comprises a transformer and a primary side power tube, wherein the transformer comprises a primary side inductor and a secondary side inductor, and the primary side power tube is connected with the primary side inductor of the transformer in series; the secondary side control method of the isolated power supply comprises the steps of controlling the on-off of the primary side power tube, wherein the method for controlling the turn-off of the primary side power tube comprises the following steps:
A1, detecting the voltages at two ends of a secondary side inductor of the transformer in the turn-on period of the primary side power tube, wherein the ratio of the input voltage of the isolation power supply to the voltages at two ends of the secondary side inductor of the transformer is the turns ratio of the primary side winding and the secondary side winding of the transformer, the primary side inductor current of the isolation power supply is positively correlated with the input voltage of the isolation power supply, and the primary side inductor current information of the isolation power supply can be obtained by processing the detected voltages at two ends of the secondary side inductor of the transformer;
A2, judging whether the primary side inductance current of the isolation power supply reaches a peak value according to the primary side inductance current information of the isolation power supply obtained in the step A1, and switching off the primary side power tube when the peak value is reached;
The method for controlling the opening of the primary side power tube comprises the following steps:
b1, detecting voltages at two ends of a secondary inductor of the transformer and acquiring a duty ratio D of the secondary follow current time to one switching period;
B2, obtaining the peak voltage of the voltages at the two ends of the secondary inductor of the transformer and converting the peak voltage into secondary peak current L S_PK, wherein the output load current of the isolated power supply is
And B3, sampling the output voltage of the isolation power supply to obtain feedback voltage, processing the output load current of the isolation power supply to obtain a voltage signal containing the output load current information of the isolation power supply, comparing the voltage signal with the feedback voltage, and controlling the switching state of the primary side switching tube according to a comparison result.
Specifically, in the step A1, the detected voltages at two ends of the secondary inductor of the transformer are converted into current signals, then the first capacitor is charged, the voltage on the first capacitor is compared with a set threshold voltage, and when the voltage on the first capacitor is greater than the threshold voltage, the primary inductor current of the isolation power supply reaches a peak value, so that a signal for turning off the primary power tube is generated.
Specifically, the peak values of the primary inductor current corresponding to different output loads of the isolated power supply are also different, and the following three methods are used for adapting to different peak values of the primary inductor current:
The first method comprises the steps of adjusting the capacitance value of the first capacitor;
the second method is that the voltage value of the threshold voltage is regulated;
and thirdly, regulating the ratio coefficient of the voltage at two ends of the secondary inductor of the transformer to be converted into a current signal.
Specifically, the primary side inductance current of the isolated power supply is controlled according to the output load current of the isolated power supply obtained in the step B2, so that the output load current of the isolated power supply is kept constant; and comparing the output load current of the isolated power supply with a set overload protection threshold current, and controlling the primary side switching tube to keep off when the overload protection threshold current is exceeded so as to realize output overload protection.
In order to realize the secondary side control method, the invention also provides a specific structure of the secondary side control system of the isolated power supply, and the technical scheme is as follows:
The secondary side control system of the isolation power supply comprises a transformer, a primary side power tube and a secondary side diode, wherein one end of a primary side winding of the transformer is connected with the input voltage of the isolation power supply, and the other end of the primary side winding of the transformer is grounded after passing through the primary side power tube; one end of a secondary winding of the transformer is connected with the anode of the secondary diode, and the other end of the secondary winding of the transformer is grounded; the cathode of the secondary diode outputs the output voltage of the isolation power supply, and the output voltage of the isolation power supply is sampled to obtain feedback voltage;
The secondary side control system of the isolated power supply is used for controlling the on and off of the primary side power tube and comprises a primary side current detection module, an information processing unit and a control module,
The input end of the primary side current detection module is connected with the voltage at two ends of the secondary side inductor of the transformer and is used for generating an output signal containing primary side inductor current information of the isolated power supply; the information processing unit is used for judging whether the primary side inductance current of the isolation power supply reaches a peak value according to the output signal of the primary side current detection module, and controlling the control module to turn off the primary side power tube when the peak value is reached;
The information processing unit is further configured to calculate a duty ratio D of a secondary freewheeling time to one switching period according to the voltages at two ends of the secondary inductor of the transformer detected by the primary current detection module, and calculate a secondary peak current L S_PK according to the peak voltages of the voltages at two ends of the secondary inductor of the transformer detected by the primary current detection module, so as to obtain an output load current of the isolated power supply as a duty ratio And generating a voltage signal containing output load current information of the isolated power supply and outputting the voltage signal to the control module; and the control module compares the voltage signal containing the output load current information of the isolated power supply with the feedback voltage and controls the switching state of the primary side power tube according to a comparison result.
Specifically, the primary side current detection module comprises a primary side current unit for monitoring secondary side voltage, and the information processing unit comprises a peak inductance current comparator;
the input end of the secondary side voltage monitoring primary side current unit is connected with two ends of a secondary side winding of the transformer and is used for acquiring voltages of two ends of a secondary side inductor of the transformer and charging a first capacitor after the voltages are converted into corresponding currents;
And when the voltage of the first input end of the peak inductive current comparator is larger than the voltage of the second input end of the peak inductive current comparator, the peak inductive current comparator generates a turn-off control signal and turns off the primary side power tube through the control module.
Specifically, the primary side current detection module further includes a current programming modulation unit, where the current programming modulation unit is configured to adjust a capacitance value of the first capacitor to adjust a rising slope of the voltage of the first input end of the peak inductor current comparator.
Specifically, the primary side current detection module further includes a current programming modulation unit, where the current programming modulation unit is configured to adjust a voltage value of the peak inductor current threshold voltage.
Specifically, the primary side current detection module further includes a current programming modulation unit, where the current programming modulation unit is configured to adjust a ratio coefficient of voltage at two ends of the secondary side inductor of the transformer to a corresponding current, so as to adjust a rising slope of the voltage at the first input end of the peak inductor current comparator.
Specifically, the information processing unit further comprises a constant current control circuit and an output overload protection circuit, wherein the constant current control circuit controls the primary side inductance current of the isolation power supply according to the output load current of the isolation power supply, so that the output load current of the isolation power supply is kept constant; and the output overload protection circuit compares the output load current of the isolated power supply with a set overload protection threshold current, and controls the primary side switching tube to keep off through the control module when the output load current exceeds the overload protection threshold current so as to realize output overload protection.
The beneficial effects of the invention are as follows: compared with the primary side peak current mode control, the secondary side peak current mode control is adopted, so that the maximum value of the output current load can be controlled more accurately, the non-ideal factors of the transformation are naturally offset, and the accurate control of the secondary side on the current parameters is realized; the primary inductance current peak value information is extracted through sampling the voltages at two ends of the secondary winding of the transformer, the turn-off control of the primary power tube is realized, and the accurate sampling of the primary current of the transformer is realized without a primary sampling resistor; the method comprises the steps of calculating and outputting load current information by acquiring secondary side peak current information and secondary side conduction time duty ratio, realizing starting control of a primary side power tube and control of the peak current of the primary side power tube, and realizing accurate sampling of the output current of a transformer without a secondary side sampling resistor; the problem of resistance loss caused by setting a sampling resistor in the traditional control scheme is solved, and the system efficiency is improved; and the invention is easy to realize in the monolithic integrated circuit, and does not need to add extra chip external components and chip pins.
Drawings
The following drawings, which schematically illustrate the principal features of some embodiments of the invention, assist in better understanding the following description of various embodiments of the invention. The figures and embodiments provide some embodiments of the invention in a non-limiting, non-exhaustive manner.
Fig. 1 is a block diagram of a conventional isolated flyback switch control system, which uses resistor sampling to implement control.
Fig. 2 is a schematic diagram of a secondary side control method and a secondary side control system for isolating a power supply according to a first embodiment of the present invention.
Fig. 3 is a schematic diagram showing a secondary side control method and a secondary side control system for an isolated power supply according to the present invention, in which the rising slope of V CS is modulated by capacitive programming.
Fig. 4 is a schematic diagram showing a specific implementation form of a secondary side control method and a secondary side control system for an isolated power supply according to the present invention in the third embodiment, and the voltage value of V SET is modulated by resistance programming.
Fig. 5 is a schematic diagram showing a specific implementation form of a secondary side control method and a secondary side control system for an isolated power supply according to the present invention in the third embodiment, where the rising slope of V CS is modulated by resistance programming.
Detailed Description
The technical scheme of the invention is described in detail below with reference to the accompanying drawings and specific embodiments.
The following specific details of the embodiments are set forth in order to provide a better understanding of the embodiments of the present invention, and are not intended to limit the scope of the present invention. Those skilled in the art will appreciate that embodiments of the invention may be practiced without some of the details, steps, or with other methods, connections, etc. The invention is suitable for an isolated power supply with a transformer, comprises an ACDC (alternating current direct current) and DCDC (direct current) and other isolated power supply control systems, and is a secondary side control system. The secondary side mentioned in the invention refers to the isolated two ends of the isolated transformer relative to the primary side of the transformer, and the primary side and the secondary side of the transformer are sometimes called as primary side and secondary side, etc.
In the first embodiment, the invention is applied to a flyback isolated switching power supply as an example, but the invention is also applicable to other switching power supply systems which use transformers to realize isolation. As shown in fig. 2, the isolated power supply comprises a transformer I101, a primary power tube I108 and a secondary diode I102, the transformer I101 comprises a primary winding and a secondary winding, one end of the primary winding of the transformer I101 is connected with an input voltage VIN of the isolated power supply, and the other end is grounded after passing through the primary power tube I108; one end of a secondary winding of the transformer I101 is connected with the anode of the secondary diode I102, and the other end of the secondary winding is grounded; the cathode output of the secondary side diode I102 isolates the output voltage VOUT of the power supply.
In order to perform accurate control, output load current information of an isolated power supply and primary side inductance peak current information of a transformer are required to be sampled, according to the background technology, real-time turn-off of a primary side power tube is realized by controlling primary side peak current through a secondary side in a traditional secondary side control framework, primary side sampling resistor R CS2 is required to sample the primary side inductance peak current information of the transformer, secondary side sampling resistor R CS1 is required to sample the output load current information, and therefore two sampling resistors are required, and additional power consumption is increased by the sampling resistors, so that the overall efficiency of a system is reduced. In order to solve the technical problem, the invention provides a novel secondary side control architecture, which can acquire output load current information and primary side inductance peak current information of a transformer without setting a sampling resistor, and control the on and off of a primary side switching tube I108 according to the acquired information.
Firstly, describing the process of obtaining the primary inductance peak current information of the transformer to control the primary switching tube I108 to be turned off, as shown in FIG. 2, the secondary control system provided by the invention comprises a primary current detection module, an information processing unit I114 and a control module, wherein the primary current detection module is used for generating an output signal containing the primary inductance current information of an isolated power supply and comprises a secondary voltage detection primary current unit I112 and a current programming modulation unit I113; the information processing unit I114 processes the output signal of the primary side current detection module to generate a corresponding control signal; the control module controls the primary side power tube I108 according to a control signal output by the information processing unit I114, and comprises a secondary side control unit I105, a primary side secondary side signal transmission unit I106 and a primary side control unit I107.
The input end of the secondary side voltage detection primary side current unit I112 is connected with two ends of a secondary side winding of the transformer, and is used for acquiring voltage V 1-2 at two ends of a secondary side inductance of the transformer during the turn-on period of the primary side power tube and charging the first capacitor after converting the voltage V 1-2 into corresponding current, an output signal of the primary side current detection module is voltage V CS on the first capacitor, and voltage V CS on the first capacitor contains primary side inductance current information of an isolated power supply, and the specific analysis is as follows.
According to the working principle of the isolated power supply, the relationship between the primary inductor current Ip in the time domain and the input voltage VIN and primary inductor value Lp of the isolated power supply is as follows:
lp is a constant, the value of Ip (t) is related only to time t and input voltage VIN. In addition, because the voltage difference V 1-2 between the two ends of the secondary winding of the transformer is sampled at the opening time of the primary switching tube I108, V 1-2 =VIN/N can be obtained, wherein N is the turn ratio of the transformer, namely the turn ratio of the primary winding and the secondary winding of the transformer. Therefore, the detected voltage V 1-2 at two ends of the secondary inductor of the transformer can be processed to obtain the information of the primary inductor current Ip of the isolated power supply.
The following describes the substitution of the primary sampling resistor R CS2 in combination with the working process of using the primary sampling resistor R CS2 to sample the peak current information of the primary inductance of the transformer in the conventional secondary control architecture.
For conventional peak current control, current sampling is performed by using a primary sampling resistor R CS2 and converted into a corresponding voltage signal V SENSE2, and the peak current information that can be obtained is represented by the voltage as follows:
In this formula, lp and R CS2 are constant, and the value of V SENSE2 is only related to time t and input voltage VIN, so if information of input voltage VIN is available on the secondary side, we can generate a time domain waveform as that of V SENSE2 on the secondary side, and the method of detecting primary side current of the transformer on the secondary side is realized.
The invention processes the voltage V 1-2 at two ends of the secondary inductor of the transformer obtained by detection, converts the voltage V 1-2 into corresponding current and then charges a first capacitor to obtain a ramp waveform with rising slope in direct proportion to V 1-2, namely the voltage V CS on the first capacitor:
the peak value of primary side inductance current corresponding to different output loads of the isolation power supply is also different, and the K value can be adjusted to be suitable for different situations. According to the inductance current peak value to be set, a reasonable K value can be calculated according to different systems, so that the following relation is established:
Under the relationship established by the above formula, we can derive: I.e. if we set/>, relative to the conventional primary sampling resistor R CS2 The setting of the K value is equal to the setting of R CS2 in the conventional manner, and can be set according to the maximum load requirement of practical application, so that different peak current control of different K pairs is realized. And as shown in the above formula, once the system requirement is determined, K is a constant, so that the K value in the invention replaces the function of R CS2 in the traditional secondary side control architecture.
The theory above essentially considers that the primary inductor peak current is controlled by controlling the on time of the primary power tube I108, and for accurate control, the inductor current needs to be 0 in each switching period, and the waveform rising process of each V CS needs to start from 0 voltage, so the invention is suitable for the isolated power supply of discontinuous current mode (DCM mode).
The magnitude of the K value is controlled by the current programming modulation unit I113, and three specific embodiments are given below to implement the adjustment of the K value, but the adjustment manner of the K value is not limited to the following three embodiments.
In the embodiment, the adjustment of the K value is achieved by adjusting the capacitance value of the first capacitor, as shown in fig. 3, which is a schematic diagram of a control architecture of the present embodiment, where the primary-side secondary-side signal transmission unit I106 and the primary-side control unit I107 of the control module are not shown in fig. 3, and can be seen in fig. 2.
During the on period of the primary power tube I108, the voltage sampling interval control logic circuit I207 controls the voltage V 1-2 at two ends of the secondary winding of the transformer at the corresponding sampling time, and converts the sampled voltage into current through the voltage-to-current conversion circuit I208 to charge the first capacitor, in the embodiment, the first capacitor can be a programmable capacitor I206 or a series of programmable capacitor arrays, the capacitance value of the first capacitor is controlled by the programming modulation unit I113, the rising slope of the V CS during inductor current monitoring is determined, and the peak inductor current comparator I201 is utilized to compare the V CS with the peak inductor current threshold voltage V CSPK set by the system to control the turn-off of the primary power tube I108. Since V CS and V CSPK determine the on-time of the primary inductor by comparing them, the inductance value of the first capacitor actually determines the on-time of the corresponding primary power transistor, that is, indirectly determines the peak current of the primary inductor. The peak current of the transformer can be controlled by reasonably setting the inductance value of the first capacitor, and compared with the traditional control mode with the sampling resistor, the function of the first capacitor is equivalent to that of the primary sampling resistor R CS2.
The peak inductor current comparator I201 functions to compare the current monitoring information V CS at the input to the peak current target value V CSPK of the system control, thereby controlling the peak inductor current of the transformer. When the primary power tube is opened, the voltage V CS on the first capacitor is increased from 0 to up, when the voltage V CS is equal to the system control target value V CSPK, the peak inductor current comparator I201 turns over the output signal, which indicates that the primary inductor current reaches the peak value set by the system, and then the primary power tube turn-off signal is fed back to the primary control unit I107 through the primary secondary signal transmission unit I106 by the secondary control unit I105 in the control module, so that the primary power tube I108 is turned off, and the secondary control of the primary inductor current is realized. In some embodiments, a capacitance reset control I209 is further configured to perform a reset control on the first capacitance.
In the third embodiment, the adjustment of the K value is achieved by adjusting the voltage value of the threshold voltage compared with V CS, as shown in fig. 4, which is a schematic diagram of the control architecture of the present embodiment, compared with fig. 3 in the second embodiment, the current programming modulation unit I113 adopts the programming resistor I212 to achieve the control of the peak current threshold, the function of which is similar to the capacitor programming in the second embodiment, the system sets a peak current target value V CSPK, the voltage dividing resistance V SET obtained by dividing the voltage by the resistors I211 and I212 is compared with V CS, and the I212 is a programming resistor, and the resistance value of the current programming modulation unit I113 can be adjusted, thereby changing the resistance value of V SET. Under the condition that the rising slope of V CS is unchanged, different ratio coefficients of V SET and V CSPK are changed by adjusting different resistance values of the programming resistor I212, so that peak inductive current detection is realized. Essentially, the peak current of the transformer is controlled by controlling the on time of the primary side power tube, and in a closed loop system, the peak currents corresponding to different output loads are different, so that the peak current target value V CSPK determined by the system is related to the output load, and the loop can be adjusted in real time.
In the fourth embodiment, the adjustment of the K value is achieved by adjusting the proportionality coefficient of the voltage V 1-2 at the two ends of the secondary inductor of the transformer to be converted into the current signal, as shown in fig. 5, which is a schematic diagram of the control architecture of the present embodiment, and the difference between the second embodiment and the third embodiment is that the current programming modulation unit I113 in the present embodiment adjusts the resistance value of the resistor I213 through resistance programming, and the resistor I213 is used for controlling the proportionality coefficient of the voltage to the current in the voltage to current conversion circuit I208, so as to control the rising slope of V CS, so as to achieve the expected primary power tube on time control.
The three embodiments provide the scheme that the current programming modulation unit I113 is programmed to control the K value in different modes, so long as the K value is reasonably set to meet the following theoryThe primary side sampling resistor R CS2 in the traditional secondary side control architecture can be completely replaced, so that the real-time monitoring control of primary side inductance current is realized through the voltage of the secondary side V 1-2, and the accurate control of the turn-off of the primary side power tube I108 is realized. The processing of the turn ratio of the transformer possibly has certain batch errors, and in the ideal case, the turn ratio N of the transformer is unchanged, the peak current of the primary inductor is controlled by the invention, and is also equivalent to the peak current of the secondary inductor of flyback, N in actual batch application has certain errors due to individual differences of processing technology, and the ratio of V 1-2 to VIN, so that the current information controlled by V 1-2 of the invention corresponds to the peak current of the primary side with certain errors, but if only the peak current of the secondary flyback is considered, the influence of N is exactly counteracted. The secondary side sampling information has a certain error on primary side inductance current information sampling, but when the secondary side inductance current information is converted into secondary side peak current through turn ratio, the influence of the turn ratio can be counteracted on the secondary side peak current, so that the influence of turn ratio micro-variation on the maximum output current capacity of the system can be ignored, the control is considered to be similar to primary side peak inductance current control, and the influence of N deviation on the control system can be ignored. Compared with the accurate control of the primary side peak current, the control of the secondary side peak current is more accurate, the control of the output full load capacity is more effective and accurate, and the control method has the advantages of being more accurate and more advantageous in the aspect of overload point control.
The process of acquiring output load current information to control the primary side switching tube I108 to be turned on is described next, and because the control of DCM is realized based on an intermittent current mode, the secondary side can easily obtain the secondary side inductance freewheel time through V 1-2, so that the duty ratio D of the secondary side freewheel time to the whole period can be obtained easily. When the primary inductor current reaches the peak value set by the system, the output load current calculation module I202 in the information processing unit I114 obtains a secondary inductor current peak value according to the primary inductor current peak value, and obtains a secondary peak current by sampling the peak value of V CS in each period, and theoretically obtains the secondary peak current according to the previous relational expression:
LS_PK＝VCS_PK×K′
where V CS_PK is the peak value of V CS in the switching cycle, K' is the corresponding coefficient of voltage to secondary peak current conversion, which is related to K and Lp and is also a constant. The output load current can be derived:
therefore, the invention can easily know the output load current of the isolated power supply without the secondary side sampling resistor R CS1 of the traditional secondary side control architecture, thereby realizing the function of replacing the secondary side sampling resistor R CS1.
In the traditional secondary side control architecture, a secondary side sampling resistor R CS1 is used for sampling output current and converting the product of the output current and the self resistance of R CS1 into a SENSE1 voltage, and current information contained in the SENSE1 voltage is compared with output voltage information contained in a feedback signal FB to control the opening of a primary side power tube I108 and control the peak current of the primary side power tube I108. The feedback voltage FB is obtained by sampling the output voltage of the isolated power supply, and as shown in fig. 2, a resistor sampling mode may be adopted, and two voltage dividing resistors I103 and I104 are connected in series between the output voltage of the isolated power supply and ground, and the series point thereof outputs the feedback voltage FB.
The invention obtains the secondary side inductance current peak value information and the secondary side conduction time duty ratio through the processing of the information processing unit I114, and can calculate the output load current information, so that the more accurate the secondary side peak value current control is, the more accurate the maximum output load capacity Io is controlled, and the improvement of the overall performance parameters of the system is facilitated. The output load current information is then used to generate a corresponding signal through calculation processing to replace the SENSE1 voltage in the conventional secondary control architecture to be compared with the feedback signal FB for system control, and several specific ways of using the output load current information to perform system control are given below. Firstly, constant current effect (namely CC function) can be realized by using the monitored load current information, and the CC function unit I204 controls the primary side inductance current under the effect of the secondary side control unit I105 according to the monitored load current information, and closed loop control ensures that the load current is constant. In addition, output overload protection can be realized by using the monitored peak value information of the primary inductor current, when the monitored load current exceeds the threshold current set by the output overload protection circuit I203, the output overload protection circuit I203 outputs a system error signal, the system can enter a protection state, and the primary power tube is kept to be turned off by controlling the primary power tube, so that the primary power tube is not allowed to be turned on, and the abnormal state of the system is protected. In addition, other current-related functions, such as internal line voltage compensation and output line compensation, can be completed by using the monitored load current information, and the functions related to the current are common in a switching power supply, and are not described one by one.
As described above, in the existing control system, it is generally required to sample the peak current information of the primary inductance of the transformer and the output load information of the secondary, the secondary control system realizes closed-loop control on the whole power system by controlling the turn-on of the primary power tube and the peak current of the power tube, the primary secondary signal transmission unit I106 in the control module is used for transmitting the signal of the secondary control unit I105 to the primary control unit I107, so as to realize the communication control of the primary and secondary information, and the primary secondary signal transmission unit I106 can be generally realized in various manners such as optocoupler, capacitive coupling and isolation transmission, or transformer magnetic coupling and isolation transmission.
In summary, on the one hand, in the invention, during the on period of the primary side power tube I108, the secondary side voltage monitoring primary side current unit I112 is used for sampling the voltage V 1-2 at two ends of the secondary side winding of the transformer, and the external programming control programming function is added to realize the method for sampling and monitoring the inductance current of the transformer, so that the monitoring information of the peak inductance current of the transformer can be obtained and processed under the condition that the current sampling resistor is not needed; on the other hand, output load current information can be calculated through secondary side peak current information and secondary side on-time duty ratio, and the fact that primary side inductance current information and output load current information are obtained without setting a sampling resistor and used for peak current mode loop control is achieved, and accurate control of secondary side on current is achieved. Compared with the traditional control mode, the invention can save the current sampling resistor and realize higher system efficiency.
In order to obtain peak current information of primary inductor of the transformer and control the primary switch tube I108 to turn off, so as to control the peak current of the transformer and realize coarse control on the output load current of the system, in the embodiment, the voltage V 1-2 at two ends of the secondary winding of the transformer is converted into corresponding current and then charges the first capacitor, the voltage V CS on the first capacitor represents the primary inductor current information of the isolated power supply, and simultaneously, the current programming modulation unit I113 is utilized to adjust the K value in combination with reasonable configuration of the secondary voltage monitoring primary current unit I112, so that the peak value setting of various primary inductor currents can be adapted. Then the V CS information is output to the information processing unit I114 for processing, and after the information processing unit I114 receives the V CS signal, the peak current mode control mode of the system can be realized according to the peak value of V CS without the need of a primary side sampling resistor R CS2. When the current information represented by V CS rises to the preset peak current of the closed loop control of the system, the information processing unit I114 outputs a corresponding signal to turn off the primary power tube I108 through the secondary side control unit I105, and controls the primary power tube I108 to turn off. When (when)When the primary side power tube switching-on time controlled by the V CS generated by the invention is equivalent to the switching-on time controlled by the primary side sampling resistor R CS2 in the traditional mode, so that the secondary side can effectively obtain the information of the primary side inductance current under the condition of not needing R CS2, the real-time switching-off control of the primary side power tube I108 is realized, and the accurate control of the peak inductance current of the transformer is realized.
In order to obtain the information of the output load current, control the primary side switch tube I108 to open and control the peak current of the primary side power tube I108, the invention provides that the secondary side inductance follow current time is obtained according to the voltage V 1-2 at the two ends of the secondary side winding of the transformer, so as to obtain the duty ratio D, when the primary side inductance current reaches the peak value set by the system, the secondary side inductance current peak value L S_PK is obtained according to the primary side inductance current peak value, and the output load current is calculated by combining D and L S_PK The output load current information and the output voltage information are compared to control the opening of the primary side power tube I108 and the peak current of the primary side power tube I108, and the output load current information and the output voltage information can be used for realizing the functions of output overload protection, constant current, line voltage compensation and the like.
Although the embodiment uses flyback power as an example, the scope of the invention is not limited, and the invention is applicable to isolated power supplies including transformers; in the further embodiments, the manner in which the K value is adjusted and the application of the output load current are described by way of example only, but it will be understood by those skilled in the art that other structures and methods may be applied to the present invention for achieving the respective possible functions, that variations and modifications are possible for the disclosed embodiments, that alternative embodiments and equivalent variations of the elements of the embodiments may be understood by those skilled in the art, and that insubstantial changes or modifications of the elements of the embodiments may be made without departing from the spirit of the invention, and that it is intended to be within the scope of the claims of the invention.
Claims (10)
1. The secondary side control method of the isolation power supply comprises a transformer and a primary side power tube, wherein the transformer comprises a primary side inductor and a secondary side inductor, and the primary side power tube is connected with the primary side inductor of the transformer in series; the secondary side control method of the isolated power supply is characterized by comprising the steps of controlling the on-off of the primary side power tube, wherein the method for controlling the on-off of the primary side power tube comprises the following steps:
A1, detecting the voltages at two ends of a secondary side inductor of the transformer in the turn-on period of the primary side power tube, wherein the ratio of the input voltage of the isolation power supply to the voltages at two ends of the secondary side inductor of the transformer is the turns ratio of the primary side winding and the secondary side winding of the transformer, the primary side inductor current of the isolation power supply is positively correlated with the input voltage of the isolation power supply, and the primary side inductor current information of the isolation power supply can be obtained by processing the detected voltages at two ends of the secondary side inductor of the transformer;
A2, judging whether the primary side inductance current of the isolation power supply reaches a peak value according to the primary side inductance current information of the isolation power supply obtained in the step A1, and switching off the primary side power tube when the peak value is reached;
The method for controlling the opening of the primary side power tube comprises the following steps:
b1, detecting voltages at two ends of a secondary inductor of the transformer and acquiring a duty ratio D of the secondary follow current time to one switching period;
B2, obtaining the peak voltage of the voltages at the two ends of the secondary inductor of the transformer and converting the peak voltage into secondary peak current L S_PK, wherein the output load current of the isolated power supply is ；
And B3, sampling the output voltage of the isolation power supply to obtain feedback voltage, processing the output load current of the isolation power supply to obtain a voltage signal containing the output load current information of the isolation power supply, comparing the voltage signal with the feedback voltage, and controlling the switching state of the primary side power tube according to a comparison result.
2. The secondary side control method of the isolated power supply according to claim 1, wherein in the step A1, the detected voltages at both ends of the secondary side inductor of the transformer are converted into current signals, then the first capacitor is charged, the voltage on the first capacitor is compared with a set threshold voltage, and when the voltage on the first capacitor is greater than the threshold voltage, the peak value of the primary side inductor current of the isolated power supply is indicated, and a signal for turning off the primary side power tube is generated.
3. The secondary side control method of an isolated power supply according to claim 2, wherein the peak values of primary side inductor currents corresponding to different output loads of the isolated power supply are also different, and the method comprising one of the following three methods is used for adapting to different peak values of primary side inductor currents:
The first method comprises the steps of adjusting the capacitance value of the first capacitor;
the second method is that the voltage value of the threshold voltage is regulated;
and thirdly, regulating the ratio coefficient of the voltage at two ends of the secondary inductor of the transformer to be converted into a current signal.
4. A secondary side control method of an isolated power supply according to any one of claims 1 to 3, wherein the primary side inductor current of the isolated power supply is controlled according to the output load current of the isolated power supply obtained in step B2 so that the output load current of the isolated power supply is kept constant; and comparing the output load current of the isolated power supply with a set overload protection threshold current, and controlling the primary side power tube to keep off when the overload protection threshold current is exceeded so as to realize output overload protection.
5. The secondary side control system of the isolation power supply comprises a transformer, a primary side power tube and a secondary side diode, wherein one end of a primary side winding of the transformer is connected with the input voltage of the isolation power supply, and the other end of the primary side winding of the transformer is grounded after passing through the primary side power tube; one end of a secondary winding of the transformer is connected with the anode of the secondary diode, and the other end of the secondary winding of the transformer is grounded; the cathode of the secondary diode outputs the output voltage of the isolation power supply, and the output voltage of the isolation power supply is sampled to obtain feedback voltage;
it is characterized in that the secondary side control system of the isolated power supply is used for controlling the on and off of the primary side power tube and comprises a primary side current detection module, an information processing unit and a control module,
The input end of the primary side current detection module is connected with the voltage at two ends of the secondary side inductor of the transformer and is used for generating an output signal containing primary side inductor current information of the isolated power supply; the information processing unit is used for judging whether the primary side inductance current of the isolation power supply reaches a peak value according to the output signal of the primary side current detection module, and controlling the control module to turn off the primary side power tube when the peak value is reached;
The information processing unit is further configured to calculate a duty ratio D of a secondary freewheeling time to one switching period according to the voltages at two ends of the secondary inductor of the transformer detected by the primary current detection module, and calculate a secondary peak current L S_PK according to the peak voltages of the voltages at two ends of the secondary inductor of the transformer detected by the primary current detection module, so as to obtain an output load current of the isolated power supply as a duty ratio And generating a voltage signal containing output load current information of the isolated power supply and outputting the voltage signal to the control module; and the control module compares the voltage signal containing the output load current information of the isolated power supply with the feedback voltage and controls the switching state of the primary side power tube according to a comparison result.
6. The secondary side control system of claim 5, wherein the primary side current detection module comprises a secondary side voltage monitoring primary side current unit, and the information processing unit comprises a peak inductor current comparator;
the input end of the secondary side voltage monitoring primary side current unit is connected with two ends of a secondary side winding of the transformer and is used for acquiring voltages of two ends of a secondary side inductor of the transformer and charging a first capacitor after the voltages are converted into corresponding currents;
And when the voltage of the first input end of the peak inductive current comparator is larger than the voltage of the second input end of the peak inductive current comparator, the peak inductive current comparator generates a turn-off control signal and turns off the primary side power tube through the control module.
7. The isolated power supply secondary side control system of claim 6, wherein the primary side current detection module further comprises a current programming modulation unit for adjusting a capacitance value of the first capacitor to adjust a rising slope of the peak inductor current comparator first input voltage.
8. The secondary side control system of claim 6, wherein the primary side current detection module further comprises a current programming modulation unit for adjusting a voltage value of the peak inductor current threshold voltage.
9. The isolated power supply secondary side control system of claim 6, wherein the primary side current detection module further comprises a current programming modulation unit for adjusting a scaling factor of a voltage across the transformer secondary side inductor to a corresponding current to adjust a rising slope of the peak inductor current comparator first input voltage.
10. The secondary side control system of an isolated power supply according to any one of claims 5 to 9, wherein the information processing unit further comprises a constant current control circuit and an output overload protection circuit, the constant current control circuit controlling a primary side inductor current of the isolated power supply according to an output load current of the isolated power supply so that the output load current of the isolated power supply remains constant; and the output overload protection circuit compares the output load current of the isolated power supply with a set overload protection threshold current, and controls the primary side power tube to keep off to realize output overload protection through the control module when the output load current exceeds the overload protection threshold current.
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| CN115912936B (en) * | 2023-01-03 | 2023-06-06 | 成都智融微电子有限公司 | Flyback switching power supply circuit, flyback switching power supply control method and power supply equipment |
| CN118137856A (en) * | 2024-05-08 | 2024-06-04 | 茂睿芯（深圳）科技有限公司 | Control device for switching power supply and switching power supply |
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