CN102801300B - Primary-side feedback controlled switching power line loss compensating system and method - Google Patents

Abstract

The invention discloses a primary-side feedback controlled switching power line loss compensating system and method. The system comprises a sampling and holding circuit, a constant voltage loop error amplifier, a compensating network, an adjustable low-pass filter and a voltage-current converter, wherein the sampling and holding circuit, the constant voltage loop error amplifier, the adjustable low-pass filter and the voltage-current converter are connected in sequence; the output of the voltage-current converter is connected with the sampling and holding circuit; and the compensating network is connected with the input and the output of the constant voltage loop error amplifier respectively. The primary-side feedback controlled switching power line loss compensating system and method provided by the invention can be applied to the line loss compensation which does not need external compensation of capacitor or resistor in the field of primary-side feedback, and is capable of compensating the line loss pressure drop of an output wire so as to realize constant output voltage.

Description

The Switching Power Supply line loss compensation system and method for former limit FEEDBACK CONTROL

Technical field

The invention belongs to technical field of integrated circuits, relate to the Switching Power Supply of a kind of former limit FEEDBACK CONTROL, particularly relate to the Switching Power Supply line loss compensation system of a kind of former limit FEEDBACK CONTROL; Meanwhile, the invention still further relates to the Switching Power Supply line loss compensation method of a kind of former limit FEEDBACK CONTROL.

Background technology

Supply convertor is requisite assembly in electronic system.As everyone knows, power conversion rises and comprises linear transformations device and switching power converters two kinds of main Types, and conversion regime can be divided into again isolated and non-isolated two types.Switching power converters can realize high conversion efficiency, thus in be widely used to large-power occasions, and in the small-power occasion particularly system of less than several watts, based on linear quantizer.In recent years, in current small-power occasion, switching power converters also starts progressively to replace linear quantizer, and the cost that one of them key factor is exactly switching power converters to start progressively close to linear quantizer in system cost.Save energy and reduce the cost at present and become today of trend, substitute linear quantizer with high efficiency switch supply convertor and become trend of the times.In Switching Power Supply occasion, what be extensively suitable for is isolated converter, because isolation type switching power supply converter can protect load from the impacting with high pressure of inlet highway and damage, possesses and apply widely in telecommunication wireless network, automobile and Medical Devices.In the various topology of isolated converter, because anti exciting converter (flyback converter) topology is without the need to output inductor, circuit structure is simple, output is isolated, cost is low, very high ratio is occupied in the application of terminal equipment, Fig. 1 shows traditional isolated anti exciting converter application drawing that can be applied in charger occasion, and Fig. 2 is this system power voltage curve of output.

As can be seen from Figure 1, the sampled signal employing opto-coupled feedback of usual isolation type switching power supply converter output voltage realizes exporting constant voltage, and (CV, Constant Voltage0, comprises TL431 and isolation feedback compensation network thereof, also has secondary constant-current (CC, Constant Current) control circuit.As can be seen from Figure 1, adopt the anti exciting converter complex circuit designs that can be applied in charger occasion of isolation feedback, application cost is higher, is not suitable for being applied to small-power occasion.In recent years in flyback converter topology, occurred former limit modulation (PSR, PrimarySide Regulation) technology, former limit modulation technique is without the need to secondary optocoupler, and Tl431, and the secondary control circuit such as secondary constant-current, so system cost greatly declines.Because in low power charger occasion, small size and low cost are the factors that direct requirement is considered, such as 3, the charger for mobile phone of 5W, the cost of resistance is all very important, lets alone size and other some factors of PCB.

Be proposed a lot of IC adopting former limit modulation technique in the market, these IC based on system works at discontinuous mode (DCM, Discontinuous Conduction Mode), have employed different constant current constant voltages (CC/CV) to control, there is at present the different implementation of a lot of China and foreign countries' patent and the document description delivered, such as patent CN200810093354.X, CN200610057268.4, etc., will not enumerate at this.Its main thought is as follows:

Assuming that system is at discontinuous (DCM) MODE of operation, its power delivery equation is:

$P=\frac{\mathrm{\η}}{2}\×L_m\×I_{\mathrm{pk}}^2\×f_S=V_o\×I_o---\left(1\right)$

In above-mentioned equation, P is power output, Vo and Io is respectively system output voltage and electric current, η is system conversion efficiency, and Lm is transformer inductance, and fs is system frequency, Ipk is the peak value of system inductance electric current in each switch periods, and in above formula, we are assumed to the peak value of former limit inductive current.In dcm mode, in a switch periods, signal waveforms is as shown in Figure 3.

In figure 3, chip internal needs generation erase signal DEM, records transformer inductance erasing time Tdem in each switch periods, utilizes this information to control to be CC/CV.

Assuming that system enters CC pattern, at this time have:

$I_o=\frac{\mathrm{\η}\×L_m\×I_{\mathrm{pk}}^2\×f_S}{2V_o}---\left(2\right)$

Under CC pattern, need to make Io be steady state value, and this value needs and Vo, Lm, input line voltage is all irrelevant.As everyone knows, in dcm mode, the relation of transformer erasing time Tdem and output voltage Vo, Lm is as follows:

$\frac{V_o}{L_m}\×T_{\mathrm{dem}}=\frac{N_S}{N_P}\×I_{\mathrm{pk}}---\left(3\right)$

In above formula, Np and Ns is respectively transformer primary side and the secondary number of turn.In conjunction with (2) (3) formula, have

$I_o=\frac{\mathrm{\η}}{2}\×I_{\mathrm{pk}}\×\frac{N_P}{N_S}\×f_S\×T_{\mathrm{dem}}---\left(4\right)$

Known by (4) formula, realizing CC has two kinds of methods, and a kind of method is PFM(Pulse FrequencyModulation) control, be implemented as: make Ipk be fixed value, make the product of fs and Tdem be constant in addition.Such Io is constant, with output voltage Vo, and transformer sensibility reciprocal Lm, and input line voltage is all irrelevant.The method that the second realizes CC is PWM(Pulse Width Modulation), be implemented as, make fs be fixed value, make the product of Tdem and Ipk be constant in addition, the Tdem modulates information duty ratio namely by detecting.No matter be PFM, or PWM, be all by overcurrent protection OCP(Over currentprotection) realize, difference is exactly: in PFM, the compare threshold of this overcurrent protector is fixed value; In PWM controls, this overcurrent protection compare threshold is changing value, modulates by Tdem.In these two kinds of implementation methods, all need accurately to detect transformer inductance electric current, otherwise CC deleterious (according to 4 formulas) can be caused.

After CC realizes, CV can be realized, as long as sample (" platform sampling " as shown in Figure 3) to the land regions of auxiliary winding Naux output voltage before Tdem terminates, in specific implementation, the voltage (winding voltage in FIG before rectifier diode D1) of auxiliary winding Naux in electric resistance partial pressure sample graph 1 can be utilized, this voltage GATE close have no progeny until demagnetization terminate before the value of land regions and output voltage proportional, proportionality coefficient is auxiliary winding and secondary winding turns ratio, i.e. Naux/Ns.The information of voltage sampled is utilized to carry out CV control.

In sum, in isolated former limit modulation constant-current constant-voltage controller, need sampling transformer inductance demagnetization information to obtain demagnetization pulsewidth in power controller.Utilize this demagnetization pulse width information to carry out CC/CV process, method can have PFM or PWM, both needs accurately to detect transformer inductance electric current to obtain accurate CC value.

But the former limit adopting such scheme and version thereof and design controls constant-current constant-voltage system individual significant deficiency: in the ordinary course of things, voltage stabilizing adjustment regulates for load variable.But in the fields such as practical application especially charger for mobile phone, along with the specification of power takeoff leads is different, length is different, the resistance Rcable of output lead can be very large, and it also can cause the instability of output voltage.As shown below:

When exporting cable resistance Rcable and existing, the feedback detection pin FB of chip U1 closes at Q1 auxiliary winding Naux actual platform voltage (see Fig. 3 and Fig. 4) detected of having no progeny and is:

$V_{\mathrm{FB}}=\frac{R3}{R2+R3}\×\frac{N_{\mathrm{aux}}}{N_S}\×(\mathrm{Vout}+\mathrm{Vd}+\mathrm{Iout}*\mathrm{Rcable})$

In above formula, Iout is output current, and Vd is the pressure drop exporting rectifier diode D1, and Naux is auxiliary umber of turn, and Ns is secondary winding turns, R2 and R3 is auxiliary winding divider resistance, sees Fig. 4.So Vout virtual voltage is:

$\mathrm{Vout}=\frac{R2+R3}{R2}*\frac{N_S}{N_{\mathrm{aux}}}-\mathrm{Vd}-\mathrm{Iout}*\mathrm{Rcable}$

From above formula, after output lead is selected, its conductor resistance Rcable is a fixing value, but output current Iout is an amount along with load variations, and control loop only carries out voltage stabilizing adjustment to Vout variable, voltage stabilizing adjustment is not carried out to Iout, so control loop loses, the voltage stabilizing exported is controlled.

Current PSR chip product on the market mainly realizes line loss compensation by non-essential resistance or electric capacity, the OB2520 of AP3706/3708/3768/3770 and the Ang Bao company of such as BCD company, etc.But outside line loss compensating device can increase system cost, therefore compensate the change of the output voltage that Iout causes in the urgent need to a kind of built-in line loss compensation circuit., thus realize exporting voltage regulation result accurately.

Summary of the invention

Technical problem to be solved by this invention is: the Switching Power Supply line loss compensation system providing a kind of former limit FEEDBACK CONTROL, can be applicable to feedback field, former limit, without the need to the line loss compensation of external compensation electric capacity or resistance, it can compensate the line loss pressure drop of output lead, thus realizes the constant of output voltage.

In addition, the present invention also provides the Switching Power Supply line loss compensation method of a kind of former limit FEEDBACK CONTROL, can be applicable to feedback field, former limit, without the need to the line loss compensation of external compensation electric capacity or resistance, it can compensate the line loss pressure drop of output lead, thus realizes the constant of output voltage.

For solving the problems of the technologies described above, the present invention adopts following technical scheme:

A Switching Power Supply line loss compensation system for former limit FEEDBACK CONTROL, described system comprises: sampling hold circuit, constant voltage loop error amplifier, compensating network, tunable low pass filter, voltage current adapter;

Described sampling hold circuit, constant voltage loop error amplifier, tunable low pass filter, voltage current adapter connect successively, the output access sampling hold circuit of voltage current adapter, described compensating network connects input and the output of constant voltage loop error amplifier respectively;

Described sampling hold circuit carries out platform sampling to auxiliary winding, and output voltage is designated as voltage V_SH;

Voltage V SH carries out application condition amplification by constant voltage loop error amplifier and reference voltage Vref, and output voltage Vcomp is to tunable low pass filter;

The control signal of described tunable low pass filter is the PWM output signal of chip, and the output of tunable low pass filter is voltage V_Lpf;

Voltage V_Lpf exports line loss offset current Icable through voltage current adapter; Line loss compensation electric current I cable compensates the pressure drop exporting cable Rcable.

As a preferred embodiment of the present invention, described constant voltage loop error amplifier is trsanscondutance amplifier Gm;

Described compensating network comprises building-out capacitor Cc and the compensating resistance Rc of series connection, carries out series compensation to constant voltage loop error amplifier;

One end ground connection of described building-out capacitor Cc, the other end connects one end of compensating resistance Rc, and the other end of compensating resistance Rc connects the output of trsanscondutance amplifier Gm.

As a preferred embodiment of the present invention, described constant voltage loop error amplifier is fixed gain amplifier;

Described compensating network comprises the first resistance Rc1, the second resistance Rc2; One end of first resistance Rc1 connects reference voltage Vref, and the other end is connected and fixed the negative pole of gain amplifier; One end of second resistance Rc2 is connected and fixed the negative pole of gain amplifier, and the other end is connected and fixed the output of gain amplifier; Voltage V_SH accesses the positive pole of fixed gain amplifier.

As a preferred embodiment of the present invention, described tunable low pass filter comprises inverter INV1, the first switch S 1, second switch S1b, the first electric capacity C1, the second electric capacity C2;

The Frequency point of described tunable low pass filter is controlled by pwm signal; The output voltage Vcomp of constant voltage loop error amplifier is connected with one end of the first switch S 1, and the other end of the first switch S 1 is connected with second switch S1b;

First switch S 1 connects the first electric capacity C1, and second switch S1b connects the second electric capacity C2; The control signal of the first switch S 1, second switch S1b is reverse, is controlled by inverter INV1; First switch S 1 is connected with one end of inverter INV1, and second switch S1b is connected with the other end of inverter INV1.

As a preferred embodiment of the present invention, described voltage current adapter comprises operational amplifier A 2, the 3rd resistance R1, NMOS tube M1, and the current mirror of PMOS M2, PMOS M3 composition;

The output of the grid concatenation operation amplifier A2 of NMOS tube M1; The source electrode of NMOS tube M1 connects one end of the 3rd resistance R1, an input of same one end concatenation operation amplifier A2 of the 3rd resistance R1;

The drain electrode of NMOS tube M1 connects drain electrode, the grid of PMOS M2 and the grid of PMOS M3.

A compensation process for the Switching Power Supply line loss compensation system of above-mentioned former limit FEEDBACK CONTROL, described method comprises the steps:

Step S1, sampling hold circuit carry out platform sampling to auxiliary winding, and output voltage is designated as voltage V_SH;

Step S2, voltage V_SH carry out application condition amplification by constant voltage loop error amplifier and reference voltage Vref, and output voltage Vcomp is to tunable low pass filter;

The control signal of step S3, tunable low pass filter is the PWM output signal of chip, and the output of tunable low pass filter is voltage V_Lpf;

Step S4, voltage V_Lpf export line loss offset current Icable through voltage current adapter; Line loss compensation electric current I cable compensates the pressure drop exporting cable Rcable.

As a preferred embodiment of the present invention, described constant voltage loop error amplifier is trsanscondutance amplifier Gm;

Described compensating network comprises building-out capacitor Cc and the compensating resistance Rc of series connection, carries out series compensation to constant voltage loop error amplifier;

One end ground connection of described building-out capacitor Cc, the other end connects one end of compensating resistance Rc, and the other end of compensating resistance Rc connects the output of trsanscondutance amplifier Gm.

As a preferred embodiment of the present invention, described constant voltage loop error amplifier is fixed gain amplifier;

Described compensating network comprises the first resistance Rc1, the second resistance Rc2; One end of first resistance Rc1 connects reference voltage Vref, and the other end is connected and fixed the negative pole of gain amplifier; One end of second resistance Rc2 is connected and fixed the negative pole of gain amplifier, and the other end is connected and fixed the output of gain amplifier; Voltage V_SH accesses the positive pole of fixed gain amplifier.

As a preferred embodiment of the present invention, described tunable low pass filter comprises inverter INV1, the first switch S 1, second switch S1b, the first electric capacity C1, the second electric capacity C2;

The Frequency point of described tunable low pass filter is controlled by pwm signal; The output voltage Vcomp of constant voltage loop error amplifier is connected with one end of the first switch S 1, and the other end of the first switch S 1 is connected with second switch S1b;

First switch S 1 connects the first electric capacity C1, and second switch S1b connects the second electric capacity C2; The control signal of the first switch S 1, second switch S1b is reverse, is controlled by inverter INV1; First switch S 1 is connected with one end of inverter INV1, and second switch S1b is connected with the other end of inverter INV1.

As a preferred embodiment of the present invention, described voltage current adapter comprises operational amplifier A 2, the 3rd resistance R1, NMOS tube M1, and the current mirror of PMOS M2, PMOS M3 composition;

The output of the grid concatenation operation amplifier A2 of NMOS tube M1; The source electrode of NMOS tube M1 connects one end of the 3rd resistance R1, an input of same one end concatenation operation amplifier A2 of the 3rd resistance R1;

The drain electrode of NMOS tube M1 connects drain electrode, the grid of PMOS M2 and the grid of PMOS M3.

Beneficial effect of the present invention is: the Switching Power Supply line loss compensation system and method for the former limit FEEDBACK CONTROL that the present invention proposes, can be applicable to feedback field, former limit, without the need to the line loss compensation of external compensation electric capacity or resistance, the line loss pressure drop of output lead can be compensated, thus realize the constant of output voltage.

Accompanying drawing explanation

Fig. 1 is traditional isolated anti exciting converter application drawing that can be applied in charger occasion.

Fig. 2 is this system power voltage output curve diagram.

Fig. 3 is signal waveforms in a switch periods in dcm mode.

Fig. 4 is the composition schematic diagram that existing former limit controls constant-current constant-voltage system.

Fig. 5 is the composition schematic diagram of line loss compensation system of the present invention.

Fig. 6 is the composition schematic diagram of CV loop error amplifier and compensating network thereof.

Fig. 7 is another composition schematic diagram of CV loop error amplifier and compensating network thereof.

Fig. 8 is the composition schematic diagram of tunable low pass filter.

Fig. 9 is the amplitude-frequency response figure of tunable low pass filter.

Figure 10 is the composition schematic diagram of voltage current adapter.

Embodiment

The preferred embodiments of the present invention are described in detail below in conjunction with accompanying drawing.

Embodiment one

Refer to Fig. 5, present invention is disclosed the Switching Power Supply line loss compensation system of a kind of former limit FEEDBACK CONTROL, described system comprises: sampling hold circuit 10, constant voltage loop error amplifier 20, compensating network 30, tunable low pass filter 40, voltage current adapter 50.Described sampling hold circuit 10, constant voltage loop error amplifier 20, tunable low pass filter 40, voltage current adapter 50 connect successively, the output access sampling hold circuit 10 of voltage current adapter 50; Described compensating network 30 connects input and the output of constant voltage loop error amplifier 20 respectively.

Sampling hold circuit 10 carries out platform sampling by FB pin to auxiliary winding, and as shown in Figure 3, output voltage is V_SH.Voltage V_SH carries out application condition amplification by constant voltage loop error amplifier 20 and reference voltage Vref, exports Vcomp to tunable low pass filter 40.The control signal of tunable low pass filter 40 is the PWM output signal of chip, namely the GATE output signal of Fig. 4, and the output of tunable low pass filter 40 is VLpf.V_Lpf exports line loss offset current Icable through voltage current adapter.Line loss compensation electric current I cable is compensated the pressure drop exporting cable Rcable by R2 and R3 in Fig. 4.

Refer to Fig. 6, in the present embodiment, described constant voltage loop error amplifier 20 is trsanscondutance amplifier Gm; Described compensating network comprises building-out capacitor Cc and the compensating resistance Rc of series connection, carries out series compensation to constant voltage loop error amplifier 20, exports as PI compensates (compensating resistance Rc and building-out capacitor Cc series compensation); One end ground connection of described building-out capacitor Cc, the other end connects one end of compensating resistance Rc, and the other end of compensating resistance Rc connects the output of trsanscondutance amplifier Gm.

Refer to Fig. 8, described tunable low pass filter 40 comprises inverter INV1, the first switch S 1, second switch S1b, the first electric capacity C1, the second electric capacity C2.-3dB the Frequency point of described tunable low pass filter is controlled by pwm signal, F_PWM as shown in Figure 8.First switch S 1, second switch S1b and the first electric capacity C1, the second electric capacity C2 constitute switching capacity low pass filter, export as V_Lpf.

The output voltage Vcomp of constant voltage loop error amplifier 20 is connected with one end of the first switch S 1, and the other end of the first switch S 1 is connected with second switch S1b.First switch S 1 connects the first electric capacity C1, and second switch S1b connects the second electric capacity C2; The control signal of the first switch S 1, second switch S1b is reverse, is controlled by inverter INV1; First switch S 1 is connected with one end of inverter INV1, and second switch S1b is connected with the other end of inverter INV1.

It is the amplitude-frequency response of tunable low pass filter in Fig. 9.Therefrom can find out, F_PWM frequency is higher, and-3dB the dot frequency of filter is higher.F_PWM frequency is lower, and-3dB the dot frequency of filter is lower.

Refer to Figure 10, described voltage current adapter 50 comprises operational amplifier A 2, the 3rd resistance R1, NMOS tube M1, and the current mirror of PMOS M2, PMOS M3 composition; Voltage current adapter 50 realizes Voltage to current transducer, changes output current into Icable, outputs to chip FB pin, thus realizes line loss compensation control.

The output of the grid concatenation operation amplifier A2 of NMOS tube M1; The source electrode of NMOS tube M1 connects one end of the 3rd resistance R1, an input of same one end concatenation operation amplifier A2 of the 3rd resistance R1.The drain electrode of NMOS tube M1 connects drain electrode, the grid of PMOS M2 and the grid of PMOS M3.

Be described above the composition of the Switching Power Supply line loss compensation system of the present invention former limit FEEDBACK CONTROL, the present invention is while announcement said system, also disclose the compensation process of the Switching Power Supply line loss compensation system of a kind of above-mentioned former limit FEEDBACK CONTROL, described method comprises the steps:

[step S1] sampling hold circuit carries out platform sampling to auxiliary winding, and output voltage is designated as voltage V_SH;

[step S2] voltage V_SH carries out application condition amplification by constant voltage loop error amplifier and reference voltage Vref, and output voltage Vcomp is to tunable low pass filter;

The control signal of [step S3] tunable low pass filter is the PWM output signal of chip, and the output of tunable low pass filter is voltage V_Lpf;

[step S4] voltage V_Lpf exports line loss offset current Icable through voltage current adapter; Line loss compensation electric current I cable compensates the pressure drop exporting cable Rcable.

Embodiment two

Refer to Fig. 7, the difference of the present embodiment and embodiment one is, in the present embodiment, described constant voltage loop error amplifier 20 is fixed gain amplifier.Described compensating network comprises the first resistance Rc1, the second resistance Rc2; One end of first resistance Rc1 connects reference voltage Vref, and the other end is connected and fixed the negative pole of gain amplifier; One end of second resistance Rc2 is connected and fixed the negative pole of gain amplifier, and the other end is connected and fixed the output of gain amplifier; Voltage V_SH accesses the positive pole of fixed gain amplifier.It is the function of Rc2/Rc1 that constant voltage loop error amplifier 20 completes amplification fixed gain.

In sum, the Switching Power Supply line loss compensation system and method for the former limit FEEDBACK CONTROL that the present invention proposes, can be applicable to feedback field, former limit, without the need to the line loss compensation of external compensation electric capacity or resistance, the line loss pressure drop of output lead can be compensated, thus realize the constant of output voltage.

The present invention is applied to supply convertor in an illustrative manner.But will be appreciated that, the present invention has more wide range of application.

Here description of the invention and application is illustrative, not wants by scope restriction of the present invention in the above-described embodiments.Distortion and the change of embodiment disclosed are here possible, are known for the replacement of embodiment those those of ordinary skill in the art and the various parts of equivalence.Those skilled in the art are noted that when not departing from spirit of the present invention or substantive characteristics, the present invention can in other forms, structure, layout, ratio, and to realize with other assembly, material and parts.When not departing from the scope of the invention and spirit, can other distortion be carried out here to disclosed embodiment and change.

Claims (10)

1. a Switching Power Supply line loss compensation system for former limit FEEDBACK CONTROL, it is characterized in that, described system comprises: sampling hold circuit, constant voltage loop error amplifier, compensating network, tunable low pass filter, voltage current adapter;

Described sampling hold circuit, constant voltage loop error amplifier, tunable low pass filter, voltage current adapter connect successively, the output access sampling hold circuit of voltage current adapter, described compensating network connects input and the output of constant voltage loop error amplifier respectively;

Described sampling hold circuit carries out platform sampling to auxiliary winding, and output voltage is designated as voltage VSH;

Voltage V_SH carries out application condition amplification by constant voltage loop error amplifier and reference voltage Vref, and output voltage Vcomp is to tunable low pass filter;

The control signal of described tunable low pass filter is the PWM output signal of chip, and the output of tunable low pass filter is voltage V_Lpf;

Voltage V_Lpf exports line loss offset current Icable through voltage current adapter; Line loss compensation electric current I cable compensates the pressure drop exporting cable Rcable.

2. the Switching Power Supply line loss compensation system of former limit according to claim 1 FEEDBACK CONTROL, is characterized in that:

Described constant voltage loop error amplifier is trsanscondutance amplifier Gm;

Described compensating network comprises building-out capacitor Cc and the compensating resistance Rc of series connection, carries out series compensation to constant voltage loop error amplifier;

One end ground connection of described building-out capacitor Cc, the other end connects one end of compensating resistance Rc, and the other end of compensating resistance Rc connects the output of trsanscondutance amplifier Gm.

3. the Switching Power Supply line loss compensation system of former limit according to claim 1 FEEDBACK CONTROL, is characterized in that:

Described constant voltage loop error amplifier is fixed gain amplifier;

Described compensating network comprises the first resistance Rc1, the second resistance Rc2; One end of first resistance Rc1 connects reference voltage Vref, and the other end is connected and fixed the negative pole of gain amplifier; One end of second resistance Rc2 is connected and fixed the negative pole of gain amplifier, and the other end is connected and fixed the output of gain amplifier; Voltage V_SH accesses the positive pole of fixed gain amplifier.

4., according to the Switching Power Supply line loss compensation system of the former limit FEEDBACK CONTROL one of claims 1 to 3 Suo Shu, it is characterized in that:

Described tunable low pass filter comprises inverter INV1, the first switch S 1, second switch S1b, the first electric capacity C1, the second electric capacity C2;

The Frequency point of described tunable low pass filter is controlled by pwm signal; The output voltage Vcomp of constant voltage loop error amplifier is connected with one end of the first switch S 1, and the other end of the first switch S 1 is connected with second switch S1b;

First switch S 1 connects the first electric capacity C1, and second switch S1b connects the second electric capacity C2; The control signal of the first switch S 1, second switch S1b is reverse, is controlled by inverter INV1; First switch S 1 is connected with one end of inverter INV1, and second switch S1b is connected with the other end of inverter INV1.

5., according to the Switching Power Supply line loss compensation system of the former limit FEEDBACK CONTROL one of claims 1 to 3 Suo Shu, it is characterized in that:

Described voltage current adapter comprises operational amplifier A 2, the 3rd resistance R1, NMOS tube M1, and the current mirror of PMOS M2, PMOS M3 composition;

The output of the grid concatenation operation amplifier A2 of NMOS tube M1; The source electrode of NMOS tube M1 connects one end of the 3rd resistance R1, an input of same one end concatenation operation amplifier A2 of the 3rd resistance R1;

The drain electrode of NMOS tube M1 connects drain electrode, the grid of PMOS M2 and the grid of PMOS M3.

6. a compensation process for the Switching Power Supply line loss compensation system of former limit FEEDBACK CONTROL described in claim 1, it is characterized in that, described method comprises the steps:

Step S1, sampling hold circuit carry out platform sampling to auxiliary winding, and output voltage is designated as voltage V_SH;

Step S2, voltage V_SH carry out application condition amplification by constant voltage loop error amplifier and reference voltage Vref, and output voltage Vcomp is to tunable low pass filter;

The control signal of step S3, tunable low pass filter is the PWM output signal of chip, and the output of tunable low pass filter is voltage V_Lpf;

Step S4, voltage V_Lpf export line loss offset current Icable through voltage current adapter; Line loss compensation electric current I cable compensates the pressure drop exporting cable Rcable.

7. compensation process according to claim 6, is characterized in that:

Described constant voltage loop error amplifier is trsanscondutance amplifier Gm;

Described compensating network comprises building-out capacitor Cc and the compensating resistance Rc of series connection, carries out series compensation to constant voltage loop error amplifier;

One end ground connection of described building-out capacitor Cc, the other end connects one end of compensating resistance Rc, and the other end of compensating resistance Rc connects the output of trsanscondutance amplifier Gm.

8. compensation process according to claim 6, is characterized in that:

Described constant voltage loop error amplifier is fixed gain amplifier;

Described compensating network comprises the first resistance Rc1, the second resistance Rc2; One end of first resistance Rc1 connects reference voltage Vref, and the other end is connected and fixed the negative pole of gain amplifier; One end of second resistance Rc2 is connected and fixed the negative pole of gain amplifier, and the other end is connected and fixed the output of gain amplifier; Voltage V_SH accesses the positive pole of fixed gain amplifier.

9. the compensation process according to claim 7 or 8, is characterized in that:

Described tunable low pass filter comprises inverter INV1, the first switch S 1, second switch S1b, the first electric capacity C1, the second electric capacity C2;

The Frequency point of described tunable low pass filter is controlled by pwm signal; The output voltage Vcomp of constant voltage loop error amplifier is connected with one end of the first switch S 1, and the other end of the first switch S 1 is connected with second switch S1b;

First switch S 1 connects the first electric capacity C1, and second switch S1b connects the second electric capacity C2; The control signal of the first switch S 1, second switch S1b is reverse, is controlled by inverter INV1; First switch S 1 is connected with one end of inverter INV1, and second switch S1b is connected with the other end of inverter INV1.

10. the compensation process according to claim 7 or 8, is characterized in that:

Described voltage current adapter comprises operational amplifier A 2, the 3rd resistance R1, NMOS tube M1, and the current mirror of PMOS M2, PMOS M3 composition;

The output of the grid concatenation operation amplifier A2 of NMOS tube M1; The source electrode of NMOS tube M1 connects one end of the 3rd resistance R1, an input of same one end concatenation operation amplifier A2 of the 3rd resistance R1;

The drain electrode of NMOS tube M1 connects drain electrode, the grid of PMOS M2 and the grid of PMOS M3.