Primary side feedback switching power supply and line loss compensation circuit and control chip thereof

Abstract

The embodiment of the invention provides a primary side feedback switching power supply and a line loss compensation circuit and a control chip thereof, and relates to the technical field of switching power supplies, and the line loss compensation circuit comprises N first compensation modules and N second compensation modules, each first compensation module is used for generating a first current signal according to a first voltage signal which is linearly proportional to the switching frequency of the switching power supply in a constant voltage mode or a second voltage signal which is linearly proportional to the switching frequency of the switching power supply in the constant voltage mode, and a corresponding first resistor and a first current source; the second compensation module generates a second current signal based on the first voltage signal and the second resistor, and provides line compensation current to the feedback end of the switching power supply in a segmented manner based on the N first current signals and the N second current signals. According to the embodiment of the invention, the line loss compensation effect on the terminal voltage can be effectively improved, so that the constant voltage precision is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power supplies, and in particular to a primary-side feedback switching power supply and a line loss compensation circuit and a control chip thereof. Background Art

[0002] Primary Side Regulator (PSR) switching power supply control technology is widely used in fields such as mobile phone chargers. Figure 1 This is a common PSR switching power supply schematic, including the primary winding, secondary winding, and auxiliary winding located in the primary part. The battery and charger are generally connected by a certain length of wire, which will also result in the line voltage V transmitted to the battery end. o A certain voltage drop will be generated, which may cause charging failure. Summary of the Invention

[0003] The embodiments of the present invention provide a primary-side feedback switching power supply and a line loss compensation circuit and a control chip thereof, which can effectively improve the line loss compensation effect of the line-end voltage, thereby improving the constant voltage accuracy.

[0004] To solve the above problems, an embodiment of the present invention discloses a line loss compensation circuit, which is applied to a primary-side feedback switching power supply. The line loss compensation circuit includes: N first compensation modules, each first compensation module configured to generate a first current signal based on a first voltage signal linearly proportional to a switching frequency of the switching power supply in a constant voltage mode or a second voltage signal linearly proportional to the switching frequency of the switching power supply in the constant voltage mode, and a corresponding first resistor and a first current source; N ≥ 1; The second compensation module generates a second current signal based on the first voltage signal and the second resistor, and generates a line compensation current in segments based on the N first current signals and the second current signals to compensate the feedback end of the switching power supply.

[0005] According to some embodiments, the first voltage signal and the second voltage signal are equal in a steady state.

[0006] According to some embodiments, I1 (n)* R1 (n) >I1 (n-1)* R1 (n-1) ......>I1 (1)* R1 (1) , where I1 (n) represents the current value generated by the first current source corresponding to the nth first compensation module among the N first compensation modules, * represents the product, R1 (n)represents the resistance value of the first resistor corresponding to the nth first compensation module among the N first compensation modules, and the value range of n is 1≤n≤N.

[0007] According to some embodiments, N≥2.

[0008] According to some embodiments, the line compensation current flows from the line loss compensation circuit to the feedback terminal; Alternatively, the line compensation current flows from the feedback end to the line loss compensation circuit.

[0009] According to some embodiments, the second compensation module includes: a second current generating unit and a second current source; The second current generating unit is used to generate a second current signal Ifb2 according to the input first voltage signal, the second resistor and the current value generated by the second current source; wherein, I1 (1)* R1 (1) >I2*R2, I2 is the current value generated by the second current source, and R2 is the resistance value of the second resistor.

[0010] According to some embodiments, the first compensation module includes: a first current source and a first current generating unit, and the first current generating unit is connected to the first current source; wherein the first current generating unit is used to transmit the first current signal to a node for outputting the second current signal in the second compensation module based on the first voltage signal or the second voltage signal and the current value generated by its corresponding first resistor and the first current source.

[0011] According to some embodiments, the first current generating unit includes: a first operational amplifier, a first resistor, a first switch and a first current mirror; the first input terminal of the first operational amplifier is connected to the first voltage signal or the second voltage signal, and the second input terminal is grounded through the first resistor and connected to the first current source; the gate of the first switch is connected to the output terminal of the first operational amplifier, the source is connected to the second input terminal of the first operational amplifier, and the drain is connected to the input branch of the first current mirror; the output branch of the first current mirror is used to output the first current signal.

[0012] According to some embodiments, the second current generating unit includes: a second operational amplifier, a second resistor, a second switch and a second current mirror; the first input terminal of the second operational amplifier is connected to the first voltage signal, the second input terminal is grounded through the second resistor and connected to the second current source; the gate of the second switch is connected to the output terminal of the second operational amplifier, the source is connected to the second input terminal of the second operational amplifier, and the drain is connected to the input branch of the second current mirror; the output branch of the second current mirror is used to output the second current signal.

[0013] According to some embodiments, the second compensation module further includes: a line compensation current generating unit configured to generate the line compensation current in segments based on the N first current signals and the second current signals and the maximum value of the line compensation current.

[0014] According to some embodiments, the line compensation current generating unit includes: A third current source is used to generate a maximum value of the line compensation current; The third current mirror has an input branch for receiving a current generated based on the first current signal, the second current signal and the maximum value of the line compensation current, and an output branch for outputting the line compensation current.

[0015] According to some embodiments, the line loss compensation circuit further includes: a first conversion module, the first conversion module being configured to generate a first voltage signal according to a reference voltage, a switching frequency, and a full load frequency.

[0016] According to some embodiments, the first conversion module includes: a frequency-to-voltage unit, configured to output a third voltage signal according to a reference voltage, a switching frequency, and a full-load frequency; The filtering unit is configured to input the third voltage signal and output the first voltage signal under the control of the switching frequency.

[0017] According to some embodiments, the filtering unit includes a third switch, a fourth switch, an inverter, a first capacitor, and a second capacitor. The first end of the third switch is used to access a third voltage signal, the second end of the third switch is grounded via the first capacitor and connected to the first end of the fourth switch, and the control end of the third switch is used to access a switching frequency; the second end of the fourth switch is grounded via the second capacitor, and the control end of the fourth switch is used to access a signal after the switching frequency passes through the inverter; the voltage on the second capacitor is the first voltage signal.

[0018] Based on the same inventive concept, an embodiment of the present invention further discloses a control chip, comprising: a feedback end and the line loss compensation circuit as described in the embodiment of the present invention.

[0019] Based on the same inventive concept, an embodiment of the present invention further discloses a primary-side feedback switching power supply, which is characterized by comprising the control chip as described in the embodiment of the present invention.

[0020] The embodiments of the present invention include the following advantages: Embodiments of the present invention propose a line loss compensation circuit for a primary-side feedback switching power supply. This circuit outputs the line compensation current as multiple continuous segments with continuous nodes between the segments, used to fit a cubic equation curve between the line compensation current and the switching frequency. This circuit uses the line compensation current to compensate for the feedback terminal of the switching power supply control chip, taking into account the effects of both the switching frequency and the primary peak current of the switching power supply on the output current. This circuit can adaptively compensate for line loss changes in response to output current, effectively improving the line loss compensation effect on the line-end voltage and thus enhancing constant voltage accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention.

[0022] Figure 1 This is a commonly used primary-side feedback switching power supply schematic; Figure 2a This is a comparison diagram of the line end voltage with line loss compensation and the line end voltage without line loss compensation under ideal conditions. Figure 1 ; Figure 2b This is the second diagram comparing the line-end voltage with line loss compensation and the line-end voltage without line loss compensation under ideal conditions; Figure 3a Comparison of the line-end voltage with line loss compensation and the line-end voltage without line loss compensation in the existing technology Figure 1 ; Figure 3b Figure 2 is a comparison of the line-end voltage with and without line-loss compensation in the prior art; Figure 4 The switching frequency and V cs Schematic diagram of the relationship between Figure 5 is a schematic diagram of a relationship curve of a cubic equation between line compensation current and switching frequency proposed in some embodiments of the present invention; Figure 6 is a schematic structural diagram of a line loss compensation circuit proposed in some embodiments of the present invention; Figure 7 In some embodiments of the present invention, V cap_fsw_fb Schematic diagram of the relationship with the switching frequency f; Figure 8 Schematic diagram of the line compensation structure in which the line compensation current flows into the feedback terminal; Figure 9 This is a schematic diagram of the segmented output of line compensation current in some embodiments of the present invention. Figure 1 ; Figure 10Schematic diagram of the line compensation structure where the line compensation current flows out of the feedback terminal; Figure 11 Schematic diagram 2 of segmented output of line compensation current in some embodiments of the present invention; Figure 12 1 is a schematic diagram comparing the line end voltage with line loss compensation in some embodiments of the present invention and the line end voltage with line loss compensation in the prior art; Figure 13 is a circuit diagram of a line loss compensation circuit proposed in some embodiments of the present invention; Figure 14 is a circuit diagram of a line loss compensation circuit proposed in some other embodiments of the present invention; Figure 15 is a circuit diagram of a line loss compensation circuit proposed in some embodiments of the present invention; Figure 16 is a schematic structural diagram of a line loss compensation circuit proposed in other embodiments of the present invention; Figure 17 is a schematic structural diagram of the first conversion module in some embodiments of the present invention.

[0023] Description of reference numerals: FB-feedback terminal, CV-constant voltage mode, CC-constant current mode; CV_1 - Variation of line-end voltage with output current without line loss compensation, CV_2 - Variation of line-end voltage with output current in an ideal state with line loss compensation, CV_3 - Variation of line-end voltage with output current in the prior art with line loss compensation, CV_4 - Variation of line-end voltage with output current in the present invention with line loss compensation; Ifb1_n represents the first current signal output by the nth first compensation module, and Ifb2 represents the second current signal. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0025] Hereinafter, the terms "second," "first," etc., are used for descriptive convenience only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature qualified as "second," "first," etc., may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0026] In the embodiments of the present invention, unless otherwise clearly specified or limited, the term "connection" should be understood in a broad sense, and may refer to direct connection or indirect connection through an intermediate medium.

[0027] In the embodiments of the present invention, "and / or" describes the association relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0028] AC / DC (AC to DC) chargers are widely used in mobile phones, tablets and other fields. In related technologies, a line loss compensation technology is proposed to compensate for the line end voltage V caused by the wire. o loss, causing the line voltage V o Remain unchanged. Figure 2a and Figure 2b They are the line end voltage V without wireless loss compensation o and the line-end voltage V with line loss compensation o Two comparative schematic diagrams, in Figure 2a and Figure 2b In the example, the line voltage V without loss compensation is o With the output current I out The change of is represented by CV_1, and the ideal line-end voltage V with line loss compensation is o With the output current I out The change of is represented by CV_2.

[0029] However, during the creation of the present invention, it was found that Figure 2a and Figure 2b The CV_2 shown is only an ideal state. Based on the existing line loss compensation technology, Figure 2a Compensated line voltage V o With the output current I out The actual relationship is Figure 3a As shown in CV_3, Figure 2b Compensated line voltage V o With the output current I out The actual relationship is Figure 3b As shown in CV_3 in the figure, it can be seen that as the output current I out The change of line terminal voltage V o The fluctuation is large, affecting the constant pressure accuracy.

[0030] In various embodiments of the present invention, the unit of voltage can be expressed in volts (V), millivolts (mV), etc., the unit of current can be expressed in amperes (A), milliamperes (mA), etc., and the unit of frequency can be expressed in hertz (Hz). The present invention does not limit this. Figure 2a 、 Figure 2b 、 Figure 3a 、 Figure 3b In the middle, the line end voltage V oThe unit is volt (v), the output current I out The unit of voltage and current is ampere (A), but this does not limit the voltage and current.

[0031] in, Figure 2a 、 Figure 2b 、 Figure 3a 、 Figure 3b In the figure, the dotted line segment indicates that when the machine is started, the output voltage starts to rise from 0V, and the constant current and constant voltage functions have not yet taken effect.

[0032] The line loss compensation concept of the present invention is described below.

[0033] like Figure 1 As shown, in the constant voltage mode (denoted by CV in each figure), the line terminal voltage V o The calculation formula is , formula (1); Among them, V o is the line terminal voltage, V out is the output voltage, V b For example Figure 1 The rectifier diode voltage between the secondary winding and capacitor C02 is shown, I out is the output current, R cable is the equivalent resistance of the secondary output wire.

[0034] exist Figure 1 The switching power supply includes the primary side, the secondary side, and the auxiliary winding N aux and control chip, the primary side part may include the primary winding N p , capacitor C4, resistor R3, MOS switch Q5, current sampling resistor R cs , diode D3, capacitor C3 and resistors Rx and Ry, the secondary side part may include a secondary winding N s , capacitor C2. The control chip can be connected to the primary side of the switching power supply through its power supply terminal VDD, feedback terminal FB, control terminal GATE and current sampling terminal CS. For specific connection methods, please refer to Figure 1 The schematic diagram may also refer to the schematic diagrams of other existing switching power supply structures, but this is not part of the present invention and will not be described in detail here. Among them, AC-VIN is the input voltage of the switching power supply. In the various figures of the present invention, GND represents ground.

[0035] Line loss compensation is essentially to compensate for the loss voltage on the line. The line loss voltage V S =I out *R cable In the constant voltage mode of the switching power supply, the line loss voltage V S As small as possible, so that the line voltage Vo =V out -V b However, in constant voltage mode, the output voltage V out remains constant, while the output current I out It changes according to the load. When the output current I out At different times, the line loss voltage V S Also different, the final output line voltage V o Therefore, the output current I out The size of significantly affects the final line loss compensation effect.

[0036] Ideally, the input power of the primary winding of the switching power supply is equal to the output power of the secondary winding. Therefore, according to the law of conservation of energy, , formula (2), where, is the conversion efficiency of the switching power supply, L p is the inductance of the primary winding, I pk is the peak current of the primary winding, and f is the switching frequency. The switching frequency f of the switching power supply can be understood as Figure 1 The switching frequency of the MOS switch Q5.

[0037] Obviously, when the switching power supply operates in constant voltage mode, the output voltage remains basically unchanged. At this time, the output current I out Affected by the peak current of the primary winding and the switching frequency f, the output current I out It has a quadratic relationship with the peak current and a linear relationship with the switching frequency f. For example, when a switching power supply controller operates in PFM (Pulse Frequency Modulation) mode, it will simultaneously adjust the switching frequency f and the peak current of the primary winding to meet power requirements.

[0038] refer to Figure 4 , the present invention makes , formula (3), , where V cs Reflects R cs The voltage drop across the switch is: a and b are constants, f is the switching frequency, V cs_max Indicates V cs The maximum value, V cs_min Indicates V cs When f0≤f≤f1, the switching power supply is in constant voltage mode; when f>f1, the switching power supply is in constant current mode, f0 is V cs_min The corresponding switching frequency. , formula (4), where, in the power MOS (such as Figure 1 When Q5 in the csWill increase linearly to reach the value based on V cap_fsw_cs When the reference voltage is set, the chip will turn off the power MOS. Based on formulas (1)-(4), we can get: , formula (5).

[0039] Since the line terminal voltage V o Much larger than the line loss voltage V S , which is much larger than I out *R cable , so formula (5) can be further transformed into: , Formula (6). Based on Formula (6), it can be known that when V o and V b When the output current I out It has a cubic relationship with the switching frequency f.

[0040] Based on Figure 1 In the structure of the switching power supply shown in the figure, the number of turns of the secondary winding is proportional to the number of turns of the auxiliary winding. Therefore, the output voltage V out The feedback voltage of the switching power supply control chip Vref It also satisfies certain relationships, as shown in formula (7): , formula (7), After calculation, it is a fixed value. Rx Represents the resistance connected between the feedback terminal and the auxiliary winding. Ry Represents the resistance connected between the feedback terminal and ground.

[0041] Therefore, the line compensation current I cable Feedback voltage of the switching power supply control chip Vref Compensation can be performed to achieve compensation of the output voltage, that is, to achieve compensation of the line end voltage V o compensation.

[0042] Due to the line loss voltage V S =I out *R cable , output current I out The output line compensation current I is the cubic relationship with the switching frequency f. cable Theoretically, it should also satisfy the cubic relationship with the switching frequency f, so that the output current I can be adaptively adjusted. out The change of line loss voltage V S The line terminal voltage V o In other words, due to the output current I out The relationship between the switching frequency f and the line compensation current I is the cubic relationship between the switching frequency f and the line compensation current I is the cubic relationship between the switching frequency f and the line compensation current I is the cubic relationship between the switching frequency f and the line compensation current I. cable (Line compensation current Icable The relationship curve of the cubic equation between the switching frequency f can be shown as Figure 5 As shown), the output current I out The line loss is compensated by the change of out How does it change, the final output V o are close to V out , that is, maintain V o Constant, improving constant pressure accuracy.

[0043] Based on the above line loss compensation concept, the present invention proposes a line loss compensation circuit for a primary side feedback switching power supply in some embodiments, which converts the line compensation current I cable The output is multiple continuous segments and the nodes between each segment are continuous, which is used to fit the line compensation current I cable The relationship curve between the cubic equation and the switching frequency f. In this way, the line compensation current I cable When compensating the feedback terminal of the switching power supply control chip, both the switching frequency f and the primary peak current I of the switching power supply are taken into account. pk For output current I out The output current I out Compensate for line loss by adjusting the change of line voltage V o The line loss compensation effect is improved, thereby improving the constant voltage accuracy.

[0044] In some embodiments, the structural diagram of the line loss compensation circuit can be as follows: Figure 6 As shown, the line loss compensation circuit includes N first compensation modules and second compensation modules, where N ≥ 1. Each first compensation module is configured to generate a first current signal based on a first voltage signal linearly proportional to the switching frequency f of the switching power supply in constant voltage mode, and a corresponding first resistor and first current source. The second compensation module generates a second current signal based on the first voltage signal and the second resistor, and then generates a line compensation current Icable in segments based on the N first and second current signals to compensate the feedback terminal of the switching power supply control chip.

[0045] In such Figure 6 In the embodiment shown, the voltage signals inputted by the first compensation module and the second compensation module are the same, for example, both are first voltage signals. In some feasible implementations, the first voltage signal may be V cap_fsw_fb In some other feasible implementations, the first voltage signal may be V cap_fsw_cs In the constant voltage mode, the first voltage signal is linearly proportional to the switching frequency f. cap_fsw_fb For example, V cap_fsw_fb The relationship with the switching frequency f can be referred to Figure 7When f2≤f≤f1, V cap_fsw_fb It has a linear relationship with the switching frequency f and increases with the increase of f. When the switching frequency f>f1, the switching power supply is in constant current mode. Where f1 and f2 are the set frequency thresholds, and f2≤f0.

[0046] In each of the figures, Ifb1_n represents the first current signal output by the nth first compensation module, where n is in the range of 1 ≤ n ≤ N. For example, the first current signal output by the first first compensation module is Ifb1_1, the first current signal output by the second first compensation module is Ifb1_2, the first current signal output by the third first compensation module is Ifb1_3, and so on. In other words, the N first compensation modules actually generate a total of N first current signals, namely Ifb1_1, Ifb1_2, Ifb1_3, ..., Ifb1_n.

[0047] The line loss compensation circuit of this embodiment is designed with N first compensation modules and second compensation modules. Since the first voltage signal is linearly proportional to the switching frequency f, and the first current signal output by the first compensation module and the second current signal generated by the second compensation module are both generated based on the first voltage signal, the first current signal and the second current signal are both related to the switching frequency f. In addition, since the second compensation module outputs the line compensation current I based on the N first current signals and the second current signals, cable , thus establishing the switching frequency f and line compensation current I cable The N first current signals and the second current signals together determine the line compensation current I cable The number of turning points relative to the switching frequency f, so that the line loss compensation circuit can output multiple segments of line compensation current I with continuous nodes between each segment. cable , used to fit the line compensation current I cable The relationship curve of the cubic equation between the switching frequency f is used to compensate the feedback end, thereby achieving the line voltage V o Based on this fitting idea, the larger the number of N is, the better the fitting effect is, that is, the line compensation current I cable The closer the multiple segments of the corresponding switching frequency f are to the relationship curve of the cubic equation, the better the line compensation current I cable An implementation example of a cubic equation relationship curve between switching frequency f is: Figure 5 shown.

[0048] In one feasible implementation, the line compensation current I cable The feedback terminal FB of the switching power supply control chip is a pull-up current, and the line compensation structure is as follows: Figure 8 As shown. Line compensation current I cableIt flows from the line loss compensation circuit to the feedback terminal, and then flows out of the chip through the feedback terminal FB. The sampled feedback terminal voltage Vref Higher than the actual value, there are: , formula (8); Right now, , formula (9).

[0049] In each formula, / / is the parallel symbol, Rx / / Ry means resistors Rx and Ry are connected in parallel, I cable (Rx / / Ry) represents I cable Multiplying by the resistance value (Rx / / Ry) equals the line compensation voltage.

[0050] In order to ensure the line voltage V o In the full load range, in constant voltage mode, that is, when the output voltage is constant, the line compensation current I cable With the output current I out Inversely proportional, then: when the load is fully loaded, the output current I out At maximum, the line compensation current I cable When the load is no-load, , the line compensation current is the largest, max_I cable Based on this compensation idea, it is optional that N≥2, line compensation current I cable The relationship with the switching frequency f is as follows Figure 9 As shown, it is used to fit Figure 5 The cubic equation relationship curve between the line compensation current and the switching frequency f is shown. In this relationship curve, the line compensation current I cable It is inversely proportional to the switching frequency f.

[0051] In another feasible embodiment, the line compensation current I cable The feedback terminal FB of the switching power supply control chip is a pull-down current, and the line compensation structure is as follows: Figure 10 As shown, the line compensation current I cable The voltage flows from the feedback terminal FB to the line loss compensation circuit, that is, from the feedback terminal FB to the control chip. The sampled Vref is lower than the actual value, so: , formula (10); Right now, , formula (11); In order to ensure the output terminal voltage V o In the full load range, in constant voltage mode, that is, when the output voltage is constant, the line compensation current I cable With the output current I out When the load is fully loaded, the output current I out At maximum, the line compensation current I cableIt is also the largest, max_I cable , ;When the load is unloaded, the output current I out Small, line compensation current I cable Based on this compensation idea, it is optional that N≥2, the line compensation current I cable The relationship with the switching frequency f is as follows Figure 11 As shown, it is used to fit the line compensation current I cable The relationship curve of the cubic equation between the switching frequency f and the switching frequency f is not shown in the figure. In this relationship curve, the line compensation current I cable It is proportional to the switching frequency f.

[0052] like Figure 9 and Figure 11 As shown, as the switching frequency f changes, the line compensation current I cable It is presented as multiple segments with continuous nodes between each segment, effectively fitting the Figure 5 The line compensation current I cable The relationship curve of the cubic equation between the switching frequency f is used to compensate the feedback terminal FB, thereby achieving the line voltage V o In some embodiments, the line compensation current I cable After the feedback terminal is compensated, the line terminal voltage V o With the output current I out The relationship as Figure 12 As shown in CV_4; Figure 12 CV_3 in FIG shows a line terminal voltage V after compensation in the prior art. o With the output current I out Obviously, compared with the line terminal voltage V after compensation in the prior art, o The waveform (shown as CV_3) of the line terminal voltage V after compensation in the embodiment of the present invention o The waveform (represented by CV_4) is significantly smoother and closer to the ideal line-end voltage V with line loss compensation. o The waveform (such as Figure 2a and Figure 2b CV_2 in the output), which increases the output line voltage V o Constant pressure accuracy.

[0053] Next, take the first voltage signal as V cap_fsw_fb , taking two first compensation modules and one second compensation module as an example, the circuit of this embodiment is described.

[0054] Among them, the input end of each first compensation module inputs V cap_fsw_fb, and each first compensation module is connected to its corresponding first resistor and first current source. The first compensation module may include a first current source and a first current generating unit, the first current generating unit being connected to the first current source corresponding to the first compensation module; the first current generating unit is used to generate a first current signal Ifb1_n based on the first voltage signal and the current value generated by the corresponding first resistor and the first current source. The first current signals Ifb1_n generated by each of the N first compensation modules will eventually flow to the second compensation module. For example, the output ends of the N first compensation modules are all connected to the node for outputting the second current signal Ifb2 in the second compensation module, and the first current signal Ifb1_n flows to the node for outputting the second current signal Ifb2 in the second compensation module to compensate for the second current signal Ifb2, thereby changing the current line compensation current I cable The slope of the line compensation current I cable Compared with the switching frequency f, a turning point is generated to achieve line compensation current I cable segmentation.

[0055] Among them, the product of the first resistor and the first current source corresponding to each first compensation module is different, which can distinguish the line compensation current I cable Optional, II1 (n)* R1 (n) >I1 (n-1)* R1 (n-1) ......>I1 (1)* R1 (1) , where I1 (n) represents the current value generated by the first current source corresponding to the nth first compensation module among the N first compensation modules, * represents the product, R1 (n) represents the resistance value of the first resistor corresponding to the nth first compensation module among the N first compensation modules.

[0056] by Figure 13 and Figure 14 Taking the structure shown in FIG. 1 as an example, the calculation method of the first current signal generated by the first current generating unit in the first compensation module based on its corresponding first resistor and the first current source is described. Figure 13 and Figure 14 The first current generating unit may include a first operational amplifier, a first resistor, a first switch, and a first current mirror; wherein the first input terminal of the first operational amplifier is connected to the voltage V cap_fsw_fb , the second input terminal is grounded through a first resistor and connected to the first current source; the gate of the first switch is connected to the output terminal of the first operational amplifier, the source is connected to the second input terminal of the first operational amplifier, and the drain is connected to the input branch of the first current mirror; the output branch of the first current mirror is used to output the second current signal Ifb2 to the node (at the second compensation module) in the second compensation module. Figure 13 and Figure 14 , the node is represented by Q) outputs the first current signal Ifb1_n.

[0057] The first operational amplifier in the nth first compensation module is shown in the figure by A1. (n) Indicates that the first input terminal can be a positive input terminal, and the second input terminal can be a negative input terminal. In this structure, Ifb1_n=K1 (n) * (V cap_fsw_fb / R1 (n) -I1 (n) ), formula (12), where K1 (n) Indicates the mirror ratio of the first current mirror in the nth first compensation module. For example: In the first compensation module, the corresponding first resistor has a resistance value of R1. (1) , the current value generated by the corresponding first current source is I1 (1) , the first switch is represented by N1 (1) The first current mirror is composed of MOS tubes P5 and P6, and the mirror ratio of the first current mirror is K1 (1) The first current signal Ifb_1 output by the first compensation module is K1 (1) * (V cap_fsw_fb / R1 (1) -I1 (1) ).

[0058] In the second first compensation module, the corresponding first resistor has a resistance value of R1 (2) , the current value generated by the corresponding first current source is I1 (2) , the first switch is represented by N1 (2) The first current mirror is composed of MOS tubes P7 and P8, and the mirror ratio of the first current mirror is K1 (2) The first current signal Ifb_2 output by the second first compensation module is K1 (2) * (V cap_fsw_fb / R1 (2) -I1 (2) ).

[0059] The second compensation module may include a second current generating unit and a line compensation current generating unit, wherein the second current generating unit is used to generate a second current signal Ifb2, Ifb2 ≥ 0. The line compensation current generating unit is based on the N first current signals and the second current signal and the line compensation current maximum value max_I cable , segmented line compensation current I cable , to compensate the feedback end of the switching power supply, thereby achieving the line voltage V o Line loss compensation.

[0060] In some implementations of this embodiment, the generation structure of the second current signal can be as follows: Figure 13 As shown, the second current generating unit is based on the input V cap_fsw_fb The second current generating unit generates a second current signal Ifb2 with a second resistor. Specifically, the second current generating unit includes a second operational amplifier, a second resistor, a second switch, and a second current mirror. The first input terminal of the second operational amplifier is connected to the first voltage signal, and the second input terminal is grounded via the second resistor. The gate of the second switch is connected to the output terminal of the second operational amplifier, the source terminal is connected to the second input terminal of the second operational amplifier, and the drain terminal is connected to the input branch of the second current mirror. The output branch of the second current mirror is used to output the second current signal Ifb2.

[0061] In this embodiment, the second operational amplifier is represented by A2 in the drawings. Specifically, the first input terminal can be a non-inverting input terminal, and the second input terminal can be an inverting input terminal. The second switch is represented by N2, and the second current mirror is composed of MOS transistors P1 and P2. Ifb2=K2*(V cap_fsw_fb / R2), formula (13), where K2 represents the mirror ratio of the second current mirror, and R2 is the resistance value of the second resistor.

[0062] In some other implementations of this embodiment, the generation structure of the second current signal Ifb2 may also be as follows: Figure 14 As shown in the structure, the second compensation module also includes a second current source. Figure 13 In the illustrated embodiment, a second current source is added. The second current generating unit generates a second current signal Ifb2 based on the input first voltage signal, the second resistor, and the current value generated by the second current source. Specifically, the first input terminal of the second operational amplifier in the second current generating unit is connected to the first voltage signal, while the second input terminal is connected to ground and to the second current source via a second resistor. The gate of the second switch in the second current generating unit is still connected to the output terminal of the second operational amplifier, the source terminal is connected to the second input terminal of the second operational amplifier, and the drain terminal is connected to the input branch of the second current mirror. The output branch of the second current mirror is used to output the second current signal Ifb2.

[0063] In this embodiment, Ifb2=K2*(V cap_fsw_fb / R2-I2), formula (14), where K2 represents the mirror ratio of the second current mirror, R2 is the resistance value of the second resistor, I2 is the current value generated by the second current source, and I1 (1)* R1 (1) >I2*R2.

[0064] Continue to refer Figure 13 and Figure 14The line compensation current generating unit may include a third current source and a third current mirror (in the figure, the third current mirror is composed of MOS transistors P3 and P4), wherein the third current source is used to generate the maximum value of the line compensation current max_I cable The input branch of the third current mirror is connected to the node Q, which is used to access the N first current signals, the second current signal Ifb2 and the maximum line compensation current max_I cable The current generated, the output branch is used to output the line compensation current I cable .

[0065] by Figure 14 Taking the structure shown in the figure as an example, it is assumed that the mirror ratio K3 of the third current mirror is equal to 1. As the switching frequency f changes, that is, as V cap_fsw_fb The line compensation current generating unit is based on the two first current signals Ifb1_1, Ifb1_2 and the second current signal Ifb2 and the line compensation current maximum value max_I cable , generating line compensation current I cable The piecewise function of is shown in the following formula: , formula (15).

[0066] The line compensation current I corresponding to the piecewise function cable The relationship with the switching frequency f can be referred to Figure 9 : when When the second switch N2 and the first switch N1 corresponding to the first compensation module (1) The first switch N1 corresponding to the second first compensation module (2) Both are in the off state, the line compensation current I cable max_I cable , the corresponding segments are as follows Figure 9 As shown in L1; when When the second switch N2 is turned on, the first switch N1 corresponding to the first compensation module (1) The first switch N1 corresponding to the second first compensation module (2) Both are in the off state, the line compensation current I cable for , the corresponding segments are as follows Figure 9 As shown in L2; when When the second switch N2 and the first switch N1 corresponding to the first compensation module (1) The first switch N1 corresponding to the second first compensation module is turned on. (2) In the off state, the line compensation current I cable for: , the corresponding segments are as follows Figure 9 As shown in L3; when When the second switch N2 and the first switch N1 corresponding to the first compensation module (1) The first switch N1 corresponding to the second first compensation module (2) All are conducting, line compensation current I cable for: , the corresponding segments are as follows Figure 9 As shown in L4.

[0067] When V cap_fsw_fb >max_V set When the line compensation current I cable Reduced to 0, the corresponding segment is as follows Figure 9 As shown in L5. max_V set is the set value.

[0068] above Figure 13 and Figure 14 In the disclosed embodiment, the first voltage signal connected to the first compensation module and the second compensation module is the same, and the first voltage signal connected to them is V cap_fsw_fb In other embodiments, the first voltage signal may also be V cap_fsw_cs .

[0069] Figure 13 and Figure 14 The difference lies in whether the second compensation module includes a second current source, so Ifb2 is slightly different, wherein Ifb2≥0.

[0070] Figure 13 and Figure 14 The circuit structure shown corresponds to Figure 8 The line compensation structure shown, the line compensation current I cable From the line loss compensation circuit to the feedback terminal FB. Figure 10 The line compensation structure shown in the figure continues with N=2 as an example. The line compensation current I cable The structural diagram of the line loss compensation circuit from the feedback terminal FB can be as follows Figure 15 As shown, in Figure 15 In the third current mirror, the MOS tubes N3 and N4 are composed of the line compensation current I cable The relationship with the switching frequency f can be referred to Figure 11 .

[0071] when When the second switch N2 and the first switch N1 corresponding to the first compensation module (1) The first switch N1 corresponding to the second first compensation module (2) Both are in the off state, the line compensation current I cableis 0, the corresponding segment is Figure 11 As shown in L1; when When the second switch N2 is turned on, the first switch N1 corresponding to the first compensation module (1) The first switch N1 corresponding to the second first compensation module (2) Both are in the off state, the line compensation current I cable for , the corresponding segments are as follows Figure 11 As shown in L2; when When the second switch N2 and the first switch N1 corresponding to the first compensation module (1) The first switch N1 corresponding to the second first compensation module is turned on. (2) In the off state, the line compensation current I cable for: , the corresponding segments are as follows Figure 11 As shown in L3; when When the second switch N2 and the first switch N1 corresponding to the first compensation module (1) The first switch N1 corresponding to the second first compensation module (2) All are conducting, line compensation current I cable for: , the segment is as follows Figure 11 As shown in L4; When V cap_fsw_fb >max_V set When the line compensation current I cable max_I cable , the corresponding segments are as follows Figure 11 As shown in L5. max_V set is the set value.

[0072] In other embodiments, the structural diagram of the line loss compensation circuit of the present invention can be as follows: Figure 16 As shown, the line loss compensation circuit includes N first compensation modules and second compensation modules, where N ≥ 1. Each first compensation module is configured to generate a first current signal based on a second voltage signal that is linearly proportional to the switching frequency f of the switching power supply in constant voltage mode, and a first resistor and a first current source corresponding thereto; the second compensation module generates a second current signal Ifb2 based on the first voltage signal that is linearly proportional to the switching frequency f of the switching power supply in constant voltage mode and the second resistor, and generates a line compensation current I in segments based on the N first current signals and the second current signal Ifb2. cable , to compensate the feedback terminal FB of the switching power supply control chip.

[0073] Different from some of the above embodiments, Figure 16 In the embodiment shown, the voltage signals inputted by the first compensation module and the second compensation module are different, which can be understood as two signals. Optionally, the first voltage signal is V cap_fsw_fb , the second voltage signal is V cap_fsw_cs ; Or, the first voltage signal is V cap_fsw_cs , the second voltage signal is V cap_fsw_fb .

[0074] In an actual circuit, the first voltage signal and the second voltage signal may be equal or unequal, and may be designed based on actual parameter requirements. In some optional embodiments, the first voltage signal and the second voltage signal are equal in a steady state.

[0075] Other relevant explanations of this embodiment can refer to the above embodiments, which will not be elaborated here. The circuit structures of the first compensation module and the second compensation module can also refer to Figure 13-15 The focus of this embodiment is to emphasize that the voltage signals connected to the first compensation module and the second compensation module are different. Figure 13-15 As shown in the structure, when the voltage connected to the first operational amplifier in the first compensation module is V cap_fsw_fb When the voltage connected to the second operational amplifier in the second compensation module is V cap_fsw_cs ; When the voltage connected to the first operational amplifier in the first compensation module is V cap_fsw_cs When the voltage connected to the second operational amplifier in the second compensation module is V cap_fsw_fb .

[0076] In this embodiment, since the first voltage signal and the second voltage signal are both voltage signals linearly proportional to the switching frequency f, the first current signal is generated based on the second voltage signal, and the second current signal is generated based on the first voltage signal, the first current signal and the second current signal are both related to the switching frequency f. In addition, since the second compensation module outputs the line compensation current I based on the N first current signals Ifb1_n and the second current signal Ifb2, cable , thus establishing the switching frequency f and line compensation current I cable The N first current signals and the second current signal Ifb2 together determine the line compensation current I cable The number of turning points relative to the switching frequency f, so that the line loss compensation circuit can output multiple segments of line compensation current I with continuous nodes between each segment. cable , used to fit the line compensation current I cable The relationship curve of the cubic equation between the switching frequency f is used to compensate the feedback terminal FB. Based on this fitting idea, the larger the number of N, the better the fitting effect, that is, the line compensation current I cableThe closer the multiple segments corresponding to the switching frequency f are to the relationship curve of the cubic equation.

[0077] In the embodiment of the present invention, the first voltage signal is V cap_fsw_fb , the second voltage signal is V cap_fsw_cs Taking FPGA as an example, the difference between the two and their respective implementation circuits are explained.

[0078] The line loss compensation circuit of this embodiment may further include a first conversion module, which may generate a first voltage signal V according to the reference voltage, the switching frequency and the full load frequency. cap_fsw_fb Among them, reference Figure 17 The first conversion module may include: a frequency-to-voltage unit for outputting a third voltage signal according to a reference voltage, a switching frequency, and a full-load frequency; a filtering unit for inputting the third voltage signal and outputting V under the control of the switching frequency. cap_fsw_fb .

[0079] The reference voltage can be driven and enhanced by a buffer amplifier (Buffer) and then input into the frequency-to-voltage unit. The reference voltage is a set value. Therefore, the first voltage signal V cap_fsw_fb It is an absolute voltage generated based on the switching frequency. Its voltage value is only related to the switching frequency f and can effectively reflect the change of the switching frequency f. For example, it increases with the increase of the switching frequency. cap_fsw_fb The value of is between 0 and the reference voltage. If the reference voltage is 2V, then 0≤V cap_fsw_fb ≤2V.

[0080] exist Figure 17 In the example, the full load frequency is expressed as Fset, and the full load frequency is a set value, which can be f1. The specific value can be the same as the above max_V set Corresponding. When f≥Fset, V cap_fsw_fb Equal to the reference voltage; when f<Fset, V cap_fsw_fb Proportional to f, the lower f is, the higher V cap_fsw_fb The lower the frequency is, the better. The frequency-to-voltage unit can be realized by some existing frequency-to-voltage circuits on the market, and this embodiment does not limit its structure. The filtering unit can be realized by Figure 17 The structure shown is implemented, that is, the filtering unit may include a third switch S3, a fourth switch S4, an inverter INV, a first capacitor C01 and a second capacitor C02. The first end of the third switch S3 is used to receive the third voltage signal, the second end of the third switch S3 is grounded via the first capacitor C01 and connected to the first end of the fourth switch S4, and the control end of the third switch S3 is used to receive the switching frequency f; the second end of the fourth switch S4 is grounded via the second capacitor C02, and the control end of the fourth switch S4 is used to receive the signal of the switching frequency f after passing through the inverter; the voltage on the second capacitor C02 is Vcap_fsw_fb The third switch S3 and the fourth switch S4 may be implemented by MOS transistors, which is not limited in the present invention.

[0081] If the second voltage signal is V cap_fsw_cs , or based on Figure 17 A similar structure as shown converts the switching frequency f to V cap_fsw_cs Among them, due to V cap_fsw_cs Can be used to convert current sampling voltage V cs The reference voltage is V cs Provides different reference voltage values. Based on V cap_fsw_cs This function is usually used when the chip is initially powered on. cap_fsw_cs With V cap_fsw_fb Need to have different default values. Therefore, V cap_fsw_fb With V cap_fsw_cs Although they are all converted by the switching frequency f, V cap_fsw_fb With V cap_fsw_cs Essentially, it is a two-way voltage signal. In some application embodiments, when the chip enters constant voltage mode, V cap_fsw_fb Slowly build up from 0V to steady state, and V cap_fsw_cs become the same voltage.

[0082] Based on the same inventive concept, an embodiment of the present invention further provides a control chip, including a feedback terminal FB and the line loss compensation circuit of the embodiment of the present invention. cap_fsw_cs Under the limitation of , the control chip may further include a current sampling terminal CS.

[0083] Based on the same inventive concept, an embodiment of the present invention further provides a primary-side feedback switching power supply, comprising the control chip as described in the embodiment of the present invention.

[0084] In summary, the embodiment of the present invention proposes a line loss compensation circuit for a primary-side feedback switching power supply. The line loss compensation circuit is based on a first voltage signal or a second voltage signal that is linearly proportional to the switching frequency f, and can output a line compensation current I in segments corresponding to the switching frequency f. cable , the segment line compensation current I cable Used to fit the line compensation current I cable The relationship curve of the cubic equation between the switching frequency f, which is actually reflected in the output current I out The cubic function equation relationship with the switching frequency f. In this way, the segmented output line compensation current I cable When compensating the feedback terminal of the switching power supply control chip, the switching frequency f and the primary peak current I of the switching power supply are also taken into account. pk For output current I outThe output current I out Compensate for line loss by adjusting the change of line voltage V o The line loss compensation effect is improved, thereby improving the constant voltage accuracy.

[0085] During this process, due to the output current I out changes, the switching frequency f changes accordingly, and the line compensation current I cable Also changes accordingly, so the line compensation current I cable The size can be adjusted with I out The line loss compensation is fast and the line loss can be adjusted adaptively according to the change of the line loss.

[0086] In the circuit structure of the line loss compensation circuit proposed in the present invention, the circuits for generating currents by the N first compensation modules and the second compensation modules are independent of each other, such as each corresponding to an operational amplifier, a resistor, and a current source to generate current, so that the line compensation current I can be conveniently adjusted. cable The slope and starting point are determined to achieve a simple circuit and a small occupied area.

[0087] It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the various embodiments can be referenced to each other.

[0088] The technical solutions provided by the present invention have been described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is intended only to facilitate understanding of the present invention, and the contents of this specification should not be construed as limiting the present invention. Furthermore, those skilled in the art will appreciate that various modifications may be made to the specific implementation methods and scope of application according to the present invention. It is not necessary and impossible to exhaustively enumerate all implementation methods herein, and any obvious variations or modifications derived therefrom remain within the scope of protection of the present invention.

Claims

1. A line loss compensation circuit, characterized in that: Applied to a primary-side feedback switching power supply, the line loss compensation circuit includes: N first compensation modules, each of the first compensation modules being configured to generate a first current signal based on a first voltage signal linearly proportional to a switching frequency of the switching power supply in a constant voltage mode or a second voltage signal linearly proportional to the switching frequency of the switching power supply in a constant voltage mode, and a first resistor and a first current source corresponding thereto; N ≥ 1; The second compensation module generates a second current signal based on the first voltage signal and the second resistor, and generates a line compensation current based on N first current signals and the second current signals in segments to compensate the feedback end of the switching power supply.

2. The line loss compensation circuit according to claim 1, wherein: in, The first voltage signal and the second voltage signal are equal in a steady state.

3. The line loss compensation circuit according to claim 1 or 2, characterized in that: I1 (n)* R1 (n) >I1 (n-1)* R1 (n-1) ......>I1 (1)* R1 (1) , where I1 (n) represents the current value generated by the first current source corresponding to the nth first compensation module among the N first compensation modules, * represents the product, R1 (n) represents the resistance value of the first resistor corresponding to the nth first compensation module among the N first compensation modules.

4. The line loss compensation circuit according to claim 3, wherein: in, N≥2。 5. The line loss compensation circuit according to claim 1, wherein: The line compensation current flows from the line loss compensation circuit to the feedback end; Alternatively, the line compensation current flows from the feedback end to the line loss compensation circuit.

6. The line loss compensation circuit according to claim 3, wherein: The second compensation module includes: a second current generating unit and a second current source; The second current generating unit is configured to generate a second current signal according to the first voltage signal input, the second resistor, and a current value generated by the second current source; Among them, I1 (1)* R1 (1) >I2*R2, I2 is the current value generated by the second current source, and R2 is the resistance value of the second resistor.

7. The line loss compensation circuit according to claim 1, wherein: The first compensation module includes: a first current source and a first current generating unit, wherein the first current generating unit is connected to the first current source; The first current generating unit is configured to transmit a first current signal to a node in the second compensation module for outputting the second current signal based on the first voltage signal or the second voltage signal and the current value generated by the corresponding first resistor and the first current source.

8. The line loss compensation circuit according to claim 7, wherein: The first current generating unit includes: a first operational amplifier, a first resistor, a first switch and a first current mirror; A first input terminal of the first operational amplifier is connected to the first voltage signal or the second voltage signal, and a second input terminal is grounded through the first resistor and connected to the first current source; The gate of the first switch is connected to the output end of the first operational amplifier, the source is connected to the second input end of the first operational amplifier, and the drain is connected to the input branch of the first current mirror; the output branch of the first current mirror is used to output the first current signal.

9. The line loss compensation circuit according to claim 6, wherein: The second current generating unit includes: a second operational amplifier, a second resistor, a second switch and a second current mirror; A first input terminal of the second operational amplifier is connected to the first voltage signal, and a second input terminal is grounded through the second resistor and connected to the second current source; The gate of the second switch is connected to the output end of the second operational amplifier, the source is connected to the second input end of the second operational amplifier, and the drain is connected to the input branch of the second current mirror; the output branch of the second current mirror is used to output the second current signal.

10. The line loss compensation circuit according to claim 1, 6 or 9, characterized in that: The second compensation module further includes: The line compensation current generating unit generates the line compensation current in segments based on the N first current signals and the second current signals and a maximum value of the line compensation current.

11. The line loss compensation circuit according to claim 10, wherein: The line compensation current generating unit includes: a third current source, configured to generate a maximum value of the line compensation current; The third current mirror has an input branch for receiving a current generated based on the first current signal, the second current signal and the maximum value of the line compensation current, and an output branch for outputting the line compensation current.

12. The line loss compensation circuit according to claim 1 or 2, characterized in that: Also includes: A first conversion module is configured to generate the first voltage signal according to a reference voltage, the switching frequency, and a full load frequency.

13. The line loss compensation circuit according to claim 12, wherein: The first conversion module includes: a frequency-to-voltage unit, configured to output a third voltage signal according to a reference voltage, the switching frequency, and a full-load frequency; The filtering unit is configured to input the third voltage signal and output the first voltage signal under the control of the switching frequency.

14. The line loss compensation circuit according to claim 13, wherein: The filtering unit includes a third switch, a fourth switch, an inverter, a first capacitor and a second capacitor. The first end of the third switch is used to receive the third voltage signal, the second end of the third switch is grounded via the first capacitor and connected to the first end of the fourth switch, and the control end of the third switch is used to receive the switching frequency; The second end of the fourth switch is grounded via the second capacitor, and the control end of the fourth switch is used to receive the signal of the switching frequency after passing through the inverter; The voltage on the second capacitor is the first voltage signal.

15. A control chip, characterized in that: include: A feedback terminal FB and a line loss compensation circuit as described in any one of claims 1 to 14.

16. A primary-side feedback switching power supply, characterized in that: Comprising the control chip as described in any one of claim 15.

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