CN111880598B - Voltage compensation circuit of self-adaptive load cable - Google Patents

Voltage compensation circuit of self-adaptive load cable Download PDF

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CN111880598B
CN111880598B CN202010861438.4A CN202010861438A CN111880598B CN 111880598 B CN111880598 B CN 111880598B CN 202010861438 A CN202010861438 A CN 202010861438A CN 111880598 B CN111880598 B CN 111880598B
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voltage
resistor
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flyback converter
primary side
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CN111880598A (en
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周泽坤
肖志平
王祖傲
王卓
张波
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University of Electronic Science and Technology of China
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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
    • G05F1/561—Voltage to current converters

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Abstract

A voltage compensation circuit of a self-adaptive load cable comprises the steps that firstly, an operation module is utilized to convert output voltage of an error amplifier containing peak current limit information of a primary side feedback flyback converter into first intermediate voltage related to output current of the primary side feedback flyback converter, then level shift conversion is carried out on the first intermediate voltage to obtain second intermediate voltage capable of adapting to a common mode input range of a voltage-current conversion module, then ripple elimination conversion is carried out on the second intermediate voltage to obtain third intermediate voltage, the third intermediate voltage is subjected to corresponding current obtaining through the voltage-current conversion module, voltage drop is generated on a fifth resistor to obtain compensation voltage which is in direct proportion to the output current, the compensation voltage is superposed to reference voltage adjusted by a system loop to obtain new reference voltage compensated by the load cable for loop adjustment of the system, and the output voltage of the primary side feedback flyback converter can be adaptively changed along with the load current, and the stability of the actual charging voltage is ensured.

Description

Voltage compensation circuit of self-adaptive load cable
Technical Field
The invention belongs to the technical field of analog integrated circuits, and relates to a voltage compensation circuit of a self-adaptive load cable, which can be applied to a primary side feedback flyback converter controlled by a constant voltage, so that the actual charging voltage provided to a load by the output voltage of the primary side feedback flyback converter after passing through the load cable is constant.
Background
The wide use and increasing development of portable electronic products make the market of power supply industry to develop and grow larger, and meanwhile, the market also has more and more stringent requirements on power supply products. The lithium battery can provide 3-4 times of electricity quantity of the lead storage battery with the same volume due to the fact that the charge quantity (namely specific capacity) released by the unit mass of the lithium battery is as high as 3861 mAh/g. In the application of portable electronic products, the lithium battery has the remarkable advantages of high energy density, long cycle life, good safety performance, no heavy metal, low environmental pollution and the like, thereby being widely applied. The use of lithium batteries has relatively strict requirements and limitations, which cannot be overcharged or overdischarged, and the charging Current cannot be too large, which would otherwise cause overheating, swelling or even explosion of the battery, so the charge control chip for the lithium battery generally requires a hybrid control mode having Constant Current (CC) and Constant Voltage (CV) outputs.
In a current common topological structure, a flyback switching power supply realizes the electrical isolation of input and output by using transformer coupling, and simultaneously can realize different outputs by adding a new secondary winding; in addition, the flyback converter has few peripheral components, a compact and simple structure and low cost, and is widely applied to a power adapter with medium and small power below 150W and an isolated lithium battery charger. For a primary side feedback flyback converter in a constant voltage control mode, it is necessary to acquire voltage information of an output node of a chip for loop regulation, as shown in fig. 2, in the existing primary side feedback flyback converter in the constant voltage control mode, an error amplifier EA is used to amplify a difference between an output sampling voltage VS and a reference voltage VREF to obtain an output voltage VC of the error amplifier EA, the output voltage VC of the error amplifier EA is used to generate a cycle-by-cycle peak current limit, so as to adjust the on-off time of a power tube in the primary side feedback flyback converter, when the output of the primary side feedback flyback converter is increased, VC is reduced to control the on-off time of the power tube to be reduced, when the output of the primary side feedback flyback converter is reduced, VC is increased to control the on-off time of the power tube to be increased, and the whole control loop.
The output voltage of the primary side feedback flyback converter provides charging voltage for a load through a load cable, and the actual charging voltage under different load conditions is different due to the existence of the load cable, so that the sampling precision of the output node of the primary side feedback flyback converter chip is not high. Under the condition of light load, the output current is small, so that the cable impedance loss generated by the cable impedance after passing through the load cable is small; under the condition of heavy load, the output current is large, so that the loss generated after the output current passes through a load cable is large, and the actual charging voltage cannot be truly stable. In order to maintain accurate control of the output voltage, compensation needs to be made for the load cable so that the actual charging voltage can be kept stable under different loads.
The most common compensation method is to inject or extract a strand of cable compensation current related to the output current at the sampling feedback VS pin. Both schemes affect the value of the output voltage by generating an additional compensation voltage on the VS pin, the former subtracting the compensation voltage and the latter superimposing the compensation voltage, ensuring that the final charging voltage does not change with load changes through internal loop regulation. Both methods have certain disadvantages, one of which is that the sampling and control of the loop are directly influenced, the stability of the loop is influenced, and a system control error is caused; another disadvantage is that the compensation voltage cannot be generated adaptively, and the output voltage is unstable when the CC (constant current) mode is switched to the CV (constant voltage) mode, which may cause a charging hidden trouble.
Disclosure of Invention
Aiming at the defects of direct influence on the sampling and control of a loop and incapability of generating compensation voltage in a self-adaptive manner in the compensation scheme, the invention provides a voltage compensation circuit of a self-adaptive load cable, which generates the compensation voltage V of the self-adaptive load cable by utilizing the output voltage VC of an error amplifier containing peak current limit information of a primary side feedback flyback converterCABLEAnd will compensate the voltage VCABLEThe reference voltage VREFC after compensation is obtained by superposing the reference voltage VREF adjusted by the internal loop of the primary side feedback flyback converter, so that the voltage of an output node of the primary side feedback flyback converter can be increased along with the increase of the load current, the consumed voltage of a load cable is offset, the loss of the load cable is compensated under different load currents, and the actual charging voltage of the output node of the primary side feedback flyback converter reaching the load through the load cable is controlled to be constant under different loads; and because the scheme of the invention does not directly participate in and influence sampling, the sampling and the stability of a loop are not influenced while the system control precision is improved, and the invention can be better applied to a primary side feedback flyback converter with CC (constant current)/CV (constant voltage) control.
The technical scheme of the invention is as follows:
a voltage compensation circuit of a self-adaptive load cable is suitable for a primary side feedback flyback converter controlled by constant voltage output, wherein the primary side feedback flyback converter utilizes an error amplifier to carry out error amplification on a sampling voltage of the output voltage of the primary side feedback flyback converter and a reference voltage and then controls a power tube of the primary side feedback flyback converter to be switched on and off;
the voltage compensation circuit comprises an operation module, a level shift module, a ripple wave elimination sampling module, a voltage-current conversion module and a buffer,
the operation module is used for generating a first intermediate voltage which is in direct proportion to the output current of the primary side feedback flyback converter according to the output voltage of the error amplifier;
the level shift module is used for raising a direct current level of the first intermediate voltage to obtain a second intermediate voltage, so that the second intermediate voltage meets a common-mode input range of the voltage-current conversion module;
the ripple eliminating and sampling module comprises a first resistor, a first transmission gate, a second transmission gate, a first capacitor and a second capacitor, wherein one end of the first resistor is connected with the second intermediate voltage, and the other end of the first resistor is connected with one end of the first transmission gate; one end of the second transmission gate is connected with the other end of the first transmission gate and is grounded after passing through the first capacitor, and the other end of the second transmission gate generates third intermediate voltage and is grounded after passing through the second capacitor; the first transmission gate and the second transmission gate are only switched on for a first sampling time at the turn-on time and the turn-off time of the secondary side of the primary side feedback flyback converter;
the voltage-current conversion module comprises a first operational amplifier, a first NMOS (N-channel metal oxide semiconductor) tube, a second resistor, a third resistor, a fourth resistor and a fifth resistor, wherein the positive input end of the first operational amplifier is connected with the third intermediate voltage, the negative input end of the first operational amplifier is connected with one end of the second resistor and one end of the third resistor, and the output end of the first operational amplifier is connected with the grid electrode of the first NMOS tube; one end of the fourth resistor is connected with the other end of the second resistor and the source electrode of the first NMOS tube, and the other end of the fourth resistor is connected with the other end of the third resistor and grounded; the reference voltage is connected with one end of a fifth resistor after passing through the buffer, and the other end of the fifth resistor is connected with the drain electrode of the first NMOS tube and used as the output end of the voltage compensation circuit to output the compensated reference voltage;
the error amplifier amplifies the error between the sampling voltage of the output voltage of the primary side feedback flyback converter and the compensated reference voltage output by the output end of the voltage compensation circuit, and controls the power tube of the primary side feedback flyback converter to be switched on and off according to the output voltage of the error amplifier, so that the voltage of the output voltage of the primary side feedback flyback converter after passing through the load cable is kept constant.
Specifically, the operation module comprises a third transmission gate, a sixth resistor, a seventh resistor, a second NMOS transistor, a third capacitor and a fourth capacitor, wherein one end of the third transmission gate is used as the input end of the operation module, and the other end of the third transmission gate is connected with the drain electrode of the second NMOS transistor and one end of the sixth resistor; one end of the seventh resistor is connected with the other end of the sixth resistor and is grounded after passing through the third capacitor, and the other end of the seventh resistor is used as the output end of the operation module and is grounded after passing through the fourth capacitor; the source electrode of the second NMOS tube is grounded; and when the primary side feedback flyback converter is in the secondary side conduction period, controlling the third transmission gate to be opened and the second NMOS tube to be closed, otherwise controlling the third transmission gate to be closed and the second NMOS tube to be opened.
Specifically, the buffer comprises a second operational amplifier, wherein a positive input end of the second operational amplifier is used as an input end of the buffer, and a negative input end and an output end of the second operational amplifier are connected with each other and used as an output end of the buffer.
The invention has the beneficial effects that: according to the invention, the voltage signal containing the peak current limit information of the primary side feedback flyback converter is subjected to operation processing, level displacement conversion and ripple wave elimination processing, so that the compensation voltage in direct proportion to the output current of the primary side feedback flyback converter is obtained, the consumed voltage of a load cable can be offset by using the compensation voltage, the loss of the load cable can be compensated under different load currents, and the stability of the actual charging voltage is ensured; meanwhile, the compensation voltage is superposed to the reference voltage adjusted by the internal loop of the primary side feedback flyback converter, so that the loss compensation of the load cable can be completed without directly participating in and influencing the sampling of the output node of the primary side feedback flyback converter, the loop stability is not influenced, and the system control error is not brought.
Drawings
Fig. 1 is an output characteristic curve of a primary side feedback flyback converter when compensation is not performed, an output characteristic curve of the primary side feedback flyback converter after the voltage compensation circuit of the adaptive load cable provided by the invention is applied, and an ideal output characteristic curve of the primary side feedback flyback converter.
Fig. 2 is a schematic diagram of a voltage compensation circuit of an adaptive load cable according to the present invention applied to a primary side feedback flyback converter.
Fig. 3 is a block diagram of an implementation of a voltage compensation circuit of an adaptive load cable according to the present invention.
Fig. 4 is a circuit implementation diagram of an operation module in the voltage compensation circuit of the adaptive load cable according to the present invention.
Fig. 5 is a circuit diagram of a ripple cancellation sampling module in a voltage compensation circuit of an adaptive load cable according to the present invention.
Detailed Description
The invention is further illustrated with reference to the figures and the specific examples.
Fig. 1 is a graph showing a comparison of an output characteristic curve of a primary feedback flyback converter without compensation, an output characteristic curve of a voltage compensation applied with the present invention, and an ideal output characteristic curve. The constant voltage output controlled primary side feedback flyback converter utilizes an error amplifier EA to carry out error amplification on a sampling voltage VS of an output voltage of the primary side feedback flyback converter and a reference voltage VREF, then a power tube of the primary side feedback flyback converter is controlled to be switched on and switched off, an output characteristic voltage curve of the primary side feedback flyback converter is an ideal output characteristic voltage curve of a curve 1, at the moment, no load cable exists, the voltage of an output node of the primary side feedback flyback converter is firstly in a CC (constant current) mode, and the output current is in a constant current IOCCCharging is performed, and the output voltage gradually rises to reach the output voltage V of CV (constant voltage) controlOCV_IThereafter in CV mode with the output voltage held at VOCV_IDoes not change, but the output current gradually decreases. With no load cable repair in the presence of a load cableFor compensation, the charging voltage characteristic of the battery terminal (taking the load as the battery for example) is curve 2, and it can be seen that in the CV mode, the actual charging voltage of the load will be changed from the ideal output voltage value VOCV_IThe losses on the load cable are subtracted and the loss voltage increases with increasing current. In order to maintain the battery charging voltage constant, it is necessary to maintain the desired output voltage VOCV_IOn the basis of which a current I is superposed with the output currentOThe invention compensates the reference voltage VREF to output the current IOAssociated compensation voltage VCABLESuperposing the reference voltage VREF to obtain a compensated reference voltage VREFC, and performing error amplification on the compensated reference voltage VREFC and VS by using an error amplifier EA to control a power tube so that the voltage of the output voltage of the primary-side feedback flyback converter after passing through a load cable is kept constant; as shown in curve 3, the output voltage of the compensated primary feedback flyback converter provided by the present invention is added to the output voltage curve of the primary feedback flyback converter, and at this time, the output voltage of the chip can counteract the loss of the load cable, so that the battery charging voltage is consistent with the ideal voltage curve (i.e., curve 1), and the effect of load cable compensation is achieved.
In order to realize the output characteristic curve of the curve 3, the invention utilizes the VC voltage containing the peak current limit information in the primary side feedback flyback converter to generate the compensation voltage V of the self-adaptive load cable after passing through the voltage compensation circuit of the self-adaptive load cable provided by the inventionCABLESuperimposed on the reference voltage of the inner loop, as shown in fig. 2, so that by loop regulation, the compensation voltage V isCABLEThe output voltage of the primary side feedback flyback converter is superposed to show the characteristic of curve 3 in figure 1, so that the output voltage of the primary side feedback flyback converter is realized along with the output current IOThe self-adaptive change compensates the voltage of the load cable which is increased along with the increase of the load current, so that the actual charging voltage is kept stable, and the current and the voltage of a VS end of a system sampling end are not influenced, namely the sampling and the stability of a loop are not influenced.
FIG. 3 is a block diagram of a voltage compensation circuit according to the present invention, which is suitable for constant voltage outputFirstly, an operation module is utilized to convert output voltage VC of an error amplifier EA containing peak current limit information of the primary side feedback flyback converter into output current I of the primary side feedback flyback converterOThe first intermediate voltage VA, the peak current limit voltage in the primary feedback flyback converter, generally refers to a voltage signal used to set the peak current in the system. Obtaining the output current I of the primary side feedback flyback converterOThe first intermediate voltage VA is then passed through a level shift module to generate a second intermediate voltage VB that is adapted to the common-mode input range of the first operational amplifier OP1 in the voltage-current conversion module. Since the harmonic component on the second intermediate voltage VB affects the accuracy, the ripple eliminating and sampling module is designed to perform the ripple eliminating and converting on the second intermediate voltage VB to obtain the third intermediate voltage Vsampled. The third intermediate voltage Vsampled passes through the voltage-current conversion module to obtain a corresponding current and the corresponding current flows through the fifth resistor RVREFCThe compensation voltage VCABLE is obtained by generating voltage drop, the compensation voltage VCABLE is added to a reference end of the system loop adjustment of the primary side feedback flyback converter and is superposed with a reference voltage VREF, and the reference voltage VREFC compensated by the load cable is obtained and used for loop adjustment of the system, so that the output voltage of the primary side feedback flyback converter can be changed along with the load current in a self-adaptive manner, the actual charging voltage provided for the load can be ensured to be constant, and the stable and accurate self-adaptive load cable compensation function is realized.
The working principle and the implementation structure of each module are explained in detail below.
The operation module is used for processing the output voltage VC of the error amplifier EA containing the peak current limit information (namely containing the output current information) to obtain the output current I of the primary side feedback flyback converterOThe proportional first intermediate voltage VA, as shown in fig. 4, shows an implementation form of the operation module, which includes a third transmission gate TG3, a sixth resistor RC1A seventh resistor RC2A second NMOS transistor MN1, a third capacitor CC1And a fourth capacitance CC2One end of the third transmission gate TG3 is used as the input end of the operation module, and the other end is connected with the drain electrode of the second NMOS tube MN1And a sixth resistor RC1One end of (a); a seventh resistor RC2Is connected with a sixth resistor RC1And the other end of the third capacitor CC1The other end of the rear grounding is used as the output end of the operation module and passes through a fourth capacitor CC2Then grounding; the source electrode of the second NMOS transistor MN1 is grounded; when the primary side feedback flyback converter is in the secondary side conduction period, the third transmission gate TG3 is controlled to be opened, the second NMOS transistor MN1 is controlled to be closed, otherwise, the third transmission gate TG3 is controlled to be closed, and the second NMOS transistor MN1 is controlled to be opened.
A second switching signal S2 may be used to control the on/off of the third transmission gate TG3 and the second NMOS transistor MN1, the second switching signal S2 is connected to the gate of the NMOS transistor in the third transmission gate TG3, the inverse signal of the second switching signal S2 is connected to the gate of the PMOS transistor in the third transmission gate TG3 and the gate of the second NMOS transistor MN1, and during the secondary conduction period of the primary feedback flyback converter (i.e., the demagnetization time T of the primary feedback flyback converter)demagnetizationIn), the second switching signal S2 is at a high level, and at this time, the third transmission gate TG3 is turned on, the second NMOS transistor MN1 is turned off, and passes through the sixth resistor R under the action of the output voltage VC of the error amplifier EAC1A seventh resistor RC2A third capacitor CC1And a fourth capacitance CC2The second-order low-pass filter charges the output end of the operation module, namely the point A, at the moment, the voltage at the point A is the first intermediate voltage VA and the output current I of the primary side feedback flyback converterOIs in direct proportion; in other periods, the second switching signal S2 is low, which controls the third transmission gate TG3 to turn off, the second NMOS transistor MN1 to turn on, and discharge the point a, where the point a voltage, i.e. the first intermediate voltage VA, is zero, which is similar to the operation process of the output stage of the BUCK converter, and therefore, the point a dc voltage can be approximately expressed as:
Figure BDA0002648280820000061
in the above formula TSIs the switching period of the primary-side feedback flyback converter, d2Is the secondary side conduction duty ratio of the primary side feedback flyback converterOIs the output of a primary side feedback flyback converterOut of load current, NPSThe primary side feedback flyback converter has the turn ratio of a primary side inductance coil to a secondary side inductance coil.
Since the voltage amplitude of the first intermediate voltage VA is biased to the ground potential, in order to adapt to the common-mode input range of the voltage-current conversion module, the dc level of the first intermediate voltage VA needs to be raised by the level shifting module to obtain the second intermediate voltage VB. The level shift module may adopt the existing upward shift type level shift circuits with various structures, which are not described herein again.
Because the voltage at the point a has ripples and the voltage at the point B also has certain ripples, that is, after passing through the operation module and the level shift module, the output end of the level shift module, that is, the second intermediate voltage VB output by the point B, carries a certain ripple component, in order to prevent the ac ripple component from affecting the precision of the subsequent V-to-I circuit and causing compensation errors, the ripple elimination operation is usually performed on the ac ripple component to obtain and output current IOThe proportional dc level voltage, i.e. the third intermediate voltage Vsampled. Fig. 5 is a specific structural diagram of the ripple cancellation sampling module according to the present invention, which includes a first resistor RSH1A first transmission gate TG1, a second transmission gate TG2, a first capacitor CSH1And a second capacitor CSH2First resistance RSH1One end of the first transmission gate TG1 is connected with the second intermediate voltage VB, and the other end of the first transmission gate TG1 is connected with the first intermediate voltage VB; one end of the second transmission gate TG2 is connected with the other end of the first transmission gate TG1 and passes through the first capacitor CSH1Back ground, the other end of which generates a third intermediate voltage Vsampled via a second capacitor CSH2And then grounded.
When the time constant of the low-pass filter is large enough, ripples can be filtered, but the resistance capacitor of the filter in the circuit is an on-chip integrated element, and particularly, the capacitor is limited by the area and cannot be too large, so that the time constant is limited, and the sizes of the ripples cannot be ignored. The ripple sampling cancellation module shown in fig. 5 of the present invention utilizes the first switch signal S1 to control the first transmission gate TG1 and the second transmission gate TG2, and the first switch signal S1 is triggered to generate a pulse width t at the time of the secondary turn-on and the time of the secondary turn-off (i.e. the time of the "knee point")S1Thus the first transmission gate TG1 andthe second transmission gate TG2 is turned on for two times only at the turn-on time of the secondary side and the turn-off time of the primary side feedback flyback converter, and the first sampling time is determined by the pulse width t of the first switch signal S1S1And (6) determining. At the moment of conducting the secondary side, the output voltage VC of the error amplifier EA just charges the point A, and the voltage of the point A is minimum at the moment; at the time of "knee point", discharge starts at point a, and the voltage at point a is maximum. The two sampling operations make the voltage value of the third intermediate voltage Vsampled an average value of the voltage value of the second intermediate voltage VB, so that the voltage ripple of the third intermediate voltage Vsampled is negligible. The resistance of the ripple eliminating and sampling module is R when the first transmission gate TG1 and the second transmission gate TG2 are openedSH1When the first transmission gate TG1 and the second transmission gate TG2 are turned off, the resistance of the ripple cancellation sampling module is infinite, which is equivalent to amplifying the resistance value of the ripple cancellation sampling module by TS/tS1Is multiplied so that the first resistance RSH1A first capacitor CSH1And a second capacitor CSH2The time constant of the low-pass filter is further increased. From a quantitative point of view, this problem can be derived from the first order response:
Figure BDA0002648280820000071
the conversion to the z-domain function is:
Figure BDA0002648280820000072
obtaining a transfer function of the system as
Figure BDA0002648280820000073
The discrete transmission system z domain is converted into the continuous time system s domain, and the obtained system transmission function is as follows:
Figure BDA0002648280820000074
from the above formula, the time constant of the low-pass filter is represented by RSH1CSH1Increase in
Figure BDA0002648280820000075
A good ripple cancellation effect can be achieved, so that the third intermediate voltage Vsampled only contains a dc component in the first intermediate voltage VA.
Finally, the third intermediate voltage Vsampled is converted into a strand of current I and the output current I by using the voltage-current conversion moduleOA proportional current flows through the fifth resistor RVREFCTo obtain a compensation voltage VCABLEAnd the reference voltage VREF is superposed to the reference voltage VREF regulated by the loop, and the reference voltage VREF is isolated from the compensation voltage V by the bufferCABLEThe compensated reference voltage VREFC obtained by subtraction participates in loop adjustment to realize compensation voltage VCABLEAnd the voltage is converted into the output voltage of the primary side feedback flyback converter, so that the compensation effect of the load cable is achieved. As shown in fig. 3, the voltage-current conversion module provided by the present invention comprises a first operational amplifier OP1, a first NMOS transistor MN0, and a second resistor RS1A third resistor RS2A fourth resistor RS3And a fifth resistor RVREFCThe positive input terminal of the first operational amplifier OP1 is connected to the third intermediate voltage Vsampled, and the negative input terminal thereof is connected to the second resistor RS1And a third resistor RS2The output end of the first NMOS transistor MN0 is connected with the grid electrode of the first NMOS transistor MN 0; a fourth resistor RS3One end of the resistor is connected with a second resistor RS1The other end of the first NMOS transistor MN0, and the other end of the first NMOS transistor MN0 is connected with a third resistor RS2The other end of the first and second electrodes is grounded. In some embodiments, the buffer is implemented by using an OP-amp, as shown in fig. 3, the buffer includes a second operational amplifier OP2, a positive input terminal of the second operational amplifier OP2 is used as an input terminal of the buffer, a negative input terminal and an output terminal of the second operational amplifier OP2 are connected with each other and used as an output terminal of the buffer, and a buffer circuit formed by the second operational amplifier OP2 has a blocking function, so that the sampling and stability of the loop are not affected by the superposition operation.
The VX voltage (i.e. the second resistor R) in FIG. 3 is generated by the operational amplifier clamping and level shifting of the first operational amplifier OP1S1And a third resistor RS2Voltage at the junction) is equal to the first intermediate voltage VA, and the VX voltage is converted into a current through the second resistor R using a negative feedback regulation circuit composed of voltage-current conversion modulesS1And a third resistor RS2The current of (2). According to the principle of the voltage-current conversion circuit, the fifth resistor RVREFCThe flowing current is equal to the current flowing through the first NMOS transistor MN 0. Namely:
Figure BDA0002648280820000081
then the compensation voltage VCABLEExpressed as:
Figure BDA0002648280820000082
visible compensation voltage VCABLEFor one and primary side feedback flyback converter output current IOThe proportional voltage is superposed to the VREF reference end, so that the voltage at the output end of the primary side feedback flyback converter chip is superposed with IOThe voltage is in direct proportion, and the voltage drop loss on the load cable is counteracted by the voltage, so that the charging voltage at the output end of the load cable can be kept constant under the condition of load change, and the compensation effect of the load cable is realized.
In summary, the compensation voltage V is obtained by operating, level-shifting, and eliminating ripples on the output voltage VC of the error amplifier containing the peak current voltage limit information of the primary-side feedback flyback converterCABLECompensating voltage VCABLEOutput load current I along with primary side feedback flyback converterOThe voltage drop compensation circuit can be used for compensating the voltage drop consumed on the impedance of a load cable output by the primary feedback flyback converter, so that the actual charging voltage passing through the load cable can be kept constant, and the self-adaptive negative voltage under the condition of not influencing the sampling control precision and the stability of a loop is realizedAnd (4) carrying cable compensation.
Although the invention is applied to the primary side feedback flyback converter controlled by constant voltage, the design concept based on the invention can also be applied to other systems controlled by constant voltage to realize load cable compensation, thereby improving the accuracy of the output voltage of the system. Those skilled in the art, having the benefit of this disclosure, may effect numerous modifications thereto and changes may be made without departing from the scope of the invention in its broader aspects.

Claims (3)

1. A voltage compensation circuit of a self-adaptive load cable is suitable for a primary side feedback flyback converter controlled by constant voltage output, wherein the primary side feedback flyback converter utilizes an error amplifier to carry out error amplification on a sampling voltage of the output voltage of the primary side feedback flyback converter and a reference voltage and then controls a power tube of the primary side feedback flyback converter to be switched on and off;
it is characterized in that the voltage compensation circuit comprises an operation module, a level shift module, a ripple wave elimination sampling module, a voltage-current conversion module and a buffer,
the operation module is used for generating a first intermediate voltage which is in direct proportion to the output current of the primary side feedback flyback converter according to the output voltage of the error amplifier;
the level shift module is used for raising a direct current level of the first intermediate voltage to obtain a second intermediate voltage, so that the second intermediate voltage meets a common-mode input range of the voltage-current conversion module;
the ripple eliminating and sampling module comprises a first resistor, a first transmission gate, a second transmission gate, a first capacitor and a second capacitor, wherein one end of the first resistor is connected with the second intermediate voltage, and the other end of the first resistor is connected with one end of the first transmission gate; one end of the second transmission gate is connected with the other end of the first transmission gate and is grounded after passing through the first capacitor, and the other end of the second transmission gate generates third intermediate voltage and is grounded after passing through the second capacitor; the first transmission gate and the second transmission gate are only switched on for a first sampling time at the turn-on time and the turn-off time of the secondary side of the primary side feedback flyback converter;
the voltage-current conversion module comprises a first operational amplifier, a first NMOS (N-channel metal oxide semiconductor) tube, a second resistor, a third resistor, a fourth resistor and a fifth resistor, wherein the positive input end of the first operational amplifier is connected with the third intermediate voltage, the negative input end of the first operational amplifier is connected with one end of the second resistor and one end of the third resistor, and the output end of the first operational amplifier is connected with the grid electrode of the first NMOS tube; one end of the fourth resistor is connected with the other end of the second resistor and the source electrode of the first NMOS tube, and the other end of the fourth resistor is connected with the other end of the third resistor and grounded; the reference voltage is connected with one end of a fifth resistor after passing through the buffer, and the other end of the fifth resistor is connected with the drain electrode of the first NMOS tube and used as the output end of the voltage compensation circuit to output the compensated reference voltage;
the error amplifier amplifies the error between the sampling voltage of the output voltage of the primary side feedback flyback converter and the compensated reference voltage output by the output end of the voltage compensation circuit, and controls the power tube of the primary side feedback flyback converter to be switched on and off according to the output voltage of the error amplifier, so that the voltage of the output voltage of the primary side feedback flyback converter after passing through the load cable is kept constant.
2. The voltage compensation circuit of the adaptive load cable according to claim 1, wherein the operation module comprises a third transmission gate, a sixth resistor, a seventh resistor, a second NMOS transistor, a third capacitor and a fourth capacitor, one end of the third transmission gate is used as the input end of the operation module, and the other end of the third transmission gate is connected to the drain of the second NMOS transistor and one end of the sixth resistor; one end of the seventh resistor is connected with the other end of the sixth resistor and is grounded after passing through the third capacitor, and the other end of the seventh resistor is used as the output end of the operation module and is grounded after passing through the fourth capacitor; the inverted signal end of the third transmission gate is connected with the grid electrode of the second NMOS tube; the source electrode of the second NMOS tube is grounded; and when the primary side feedback flyback converter is in the secondary side conduction period, controlling the third transmission gate to be opened and the second NMOS tube to be closed, otherwise controlling the third transmission gate to be closed and the second NMOS tube to be opened.
3. The adaptive-load cable voltage compensation circuit according to claim 1 or 2, wherein the buffer includes a second operational amplifier, a positive input terminal of the second operational amplifier is used as an input terminal of the buffer, and a negative input terminal and an output terminal thereof are connected to each other and used as an output terminal of the buffer.
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