CN110611432B - Control circuit and control method of switching converter - Google Patents

Control circuit and control method of switching converter Download PDF

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CN110611432B
CN110611432B CN201910992356.0A CN201910992356A CN110611432B CN 110611432 B CN110611432 B CN 110611432B CN 201910992356 A CN201910992356 A CN 201910992356A CN 110611432 B CN110611432 B CN 110611432B
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compensation signal
main power
signal
circuit
control circuit
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CN110611432A (en
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邓建
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Hangzhou Silergy Semiconductor Technology Ltd
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Hangzhou Silergy Semiconductor Technology Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/14—Arrangements for reducing ripples from dc input or output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33538—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only of the forward type
    • H02M3/33546—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only of the forward type with automatic control of the output voltage or current
    • H02M3/33553—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only of the forward type with automatic control of the output voltage or current with galvanic isolation between input and output of both the power stage and the feedback loop
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0016—Control circuits providing compensation of output voltage deviations using feedforward of disturbance parameters
    • H02M1/0022—Control circuits providing compensation of output voltage deviations using feedforward of disturbance parameters the disturbance parameters being input voltage fluctuations

Abstract

A control circuit and a control method of a switching converter are disclosed. And generating a feedforward compensation signal with a trend opposite to the change trend of the input voltage according to the duty ratio information of the main power tube in the switching converter, and controlling the conduction time of the main power tube in the switching converter according to the feedforward compensation signal and the feedback compensation signal so as to compensate the change of the input voltage and reduce the ripple wave of the output voltage when the input voltage changes.

Description

Control circuit and control method of switching converter
Technical Field
The invention relates to the technical field of power electronics, in particular to a control circuit and a control method of a switching converter.
Background
The conventional switching converter has various circuit topologies, and the output power is related to not only the control quantity (peak current, on time, etc.), but also the input and output voltage. In the prior art, a feedback compensation signal obtained by compensating for an error between an output voltage and an output voltage reference value is generally used as a control signal of a peak current, and the peak current is controlled according to a fixed curve so as to change a switch state.
Fig. 1 shows a control circuit diagram of a switching converter in the prior art. A flyback converter will be described as an example. The input voltage Vac is power frequency alternating current, forms pulsating bus voltage Vin on the capacitor Cin after being rectified by the bridge diode, and modulates the bus voltage Vin into output voltage Vout meeting the voltage regulation rate by controlling the switching state of the main power tube Q so as to output the output voltage Vout to a load. The control circuit obtains a feedback signal V by sampling the output voltage VoutFBAnd an output voltage reference value VREFComparing to obtain error signal, and outputting feedback compensation signal V via feedback compensation circuitCOMP. The peak current regulating circuit receives the feedback compensation signal VCOMPThereby adjusting the peak current reference value VPK,REF. When the inductive current sampling signal reaches the peak current reference value VPK,REFAnd when the main power tube Q is switched off, the comparator outputs a Reset signal Reset to the PWM generating circuit so as to control the main power tube Q to be switched off. In the critical current mode, when the inductive current reaches zero, the main power tube Q is controlled to be conducted. In the Discontinuous (DCM) mode, there are various ways to control the conduction of the main power transistor Q. However, when the input voltage Vac fluctuates or the ripple is large, the feedback loop cannot respond in time, which increases the ripple of the output voltage Vout and fails to satisfy the voltage regulation requirement.
Disclosure of Invention
In view of the above, an object of the present invention is to provide a control circuit and a control method for a switching converter, which generate a feedforward compensation signal having a trend opposite to a change trend of an input voltage according to duty ratio information of a main power tube in the switching converter, and control a turn-on time of the main power tube in the switching converter according to the feedforward compensation signal and a feedback compensation signal, so as to compensate a change of the input voltage and reduce a ripple of an output voltage when the input voltage changes. And generating a feedforward compensation signal opposite to the change trend of the input voltage to control the conduction time of a main power tube in the switching converter, thereby compensating the change of the input voltage and reducing the ripple of the output voltage when the input voltage changes.
In a first aspect, an embodiment of the present invention provides a control circuit for a switching converter, where the control circuit includes:
a feedforward compensation circuit configured to generate a feedforward compensation signal having a trend opposite to a change of an input voltage according to duty ratio information of a main power transistor in the switching converter, an
A feedback compensation circuit configured to generate a feedback compensation signal according to an error between an output signal of the switching converter and an output signal reference value, wherein
And the control circuit controls the conduction time of the main power tube according to the feedforward compensation signal and the feedback compensation signal.
Further, the feedforward compensation circuit is configured to generate the feedforward compensation signal also in accordance with the feedback compensation signal.
Further, the control circuit further includes:
and the conduction time control circuit is configured to adjust the conduction time of the main power tube according to the feedforward compensation signal.
Further, the conduction time control circuit is configured to adjust a peak current reference value of an inductor current in the switching converter according to the feedforward compensation signal to adjust the conduction time of the main power tube.
Further, the on-time control circuit includes:
a peak current adjustment circuit configured to adjust the peak current reference value in accordance with the feedforward compensation signal; and
a comparison circuit configured to generate a reset signal to control the main power tube to turn off when an inductor current of the switching converter reaches the peak current reference value.
Further, the feedforward compensation circuit includes:
the inverting input end of the operational amplifier receives the first conditioning signal and outputs the feedforward compensation signal; and
the first conditioning circuit is configured to generate the first conditioning signal according to a feedforward compensation signal output by the operational amplifier and duty ratio information of the switching converter, and feed the first conditioning signal back to an inverting input end of the operational amplifier.
Further, the first conditioning circuit comprises:
a first switching unit configured to be controlled by a switching state of the main power transistor to generate a first node voltage; and
a first filter circuit configured to obtain an average value of the first node voltage in one switching period, wherein
The first node voltage is zero when the main power tube is switched on, and is equal to the feedforward compensation signal when the main power tube is switched off.
Further, the first switching unit includes:
a first switch and a second switch connected in series between the output terminal of the operational amplifier and a reference ground, wherein
The first switch is in a conducting state during the period that the main power tube is turned off, the second switch is in a conducting state during the period that the main power tube is turned on, and the voltage of the common connection point of the first switch and the second switch is the voltage of the first node.
Further, the first filter circuit includes:
a first resistor connected to the first node voltage; and
and the first capacitor is connected between the first resistor and the reference ground, wherein the voltage on the first capacitor is the first conditioning signal.
Further, the non-inverting input of the operational amplifier receives the feedback compensation signal.
Further, the feedforward compensation circuit further includes:
and the second conditioning circuit is configured to generate a second conditioning signal according to the feedback compensation signal and the duty ratio information of the switching converter and input the second conditioning signal to the non-inverting input end of the operational amplifier when the feedback compensation signal is larger than a first threshold value.
Further, the second conditioning circuit comprises:
a second switching unit configured to be controlled by a switching state of the main power transistor to generate a second node voltage;
a second filter circuit configured to obtain an average value of the second node voltage in one switching period; and
a threshold circuit connected between the feedback compensation signal and the second switching unit and generating the first threshold, wherein
The second node voltage is a difference between the feedback compensation signal and the first threshold when the main power tube is switched on, and is equal to zero when the main power tube is switched off.
Further, the second switching unit includes:
a third switch and a fourth switch connected in series between the threshold circuit and a reference ground, wherein
The third switch is in a conducting state during the conduction period of the main power tube, the fourth switch is in a conducting state during the period that the inductive current of the switch converter is reduced from a peak current reference value to zero or the main power tube is in a turn-off state, and the voltage of the common connection point of the third switch and the fourth switch is the second node voltage.
Further, the second filter circuit includes:
a second resistor connected to the second node voltage; and
and the second capacitor is connected between the second resistor and the reference ground, wherein the voltage on the second capacitor is the second conditioning signal.
Further, the control circuit further comprises a superposition circuit for superposing the feedforward compensation signal and the feedback compensation signal to control the conduction time of the main power tube.
Further, the switching converter operates in a current critical mode or a discontinuous mode.
In a second aspect, an embodiment of the present invention provides a method for controlling a switching converter, including: and generating a feedforward compensation signal opposite to the change trend of the input voltage according to the duty ratio information of the main power tube in the switching converter, and controlling the conduction time of the main power tube in the switching converter according to the feedforward compensation signal and a feedback compensation signal, wherein the feedback compensation signal represents the error between the output signal of the switching converter and the reference value of the output signal.
Further, the feedforward compensation signal is also generated according to the feedback compensation signal.
Further, the control method includes:
acquiring a first node voltage according to the switching state of the switching converter, wherein the first node voltage is zero when the main power tube is switched on and is equal to the feedforward compensation signal when the main power tube is switched off; and
and acquiring the average value of the first node voltage in one switching period.
Further, the control method further includes:
and obtaining the feedforward compensation signal according to the condition that the average value corresponding to the first node voltage is equal to the feedback compensation signal.
Further, the control method further includes:
acquiring a second node voltage according to the switching state of the switching converter, wherein the second node voltage is a difference value between the feedback compensation signal and the first threshold when the main power tube is switched on, and is equal to zero when the main power tube is switched off; and
and acquiring the average value of the voltage of the second node in a switching period.
Further, the control method further includes:
and obtaining the feedforward compensation signal according to the condition that the average value corresponding to the second node voltage is equal to the average value corresponding to the first node voltage.
Further, the control method includes: when the switching converter works in a discontinuous mode, the feedforward compensation signal and the feedback compensation signal are superposed to control the conduction time of the main power tube.
Further, the feedforward compensation signal is zero when the feedback compensation signal is less than a first threshold.
In summary, according to the technical solution of the embodiments of the present invention, a feedforward compensation signal having a trend opposite to a change trend of an input voltage is generated according to duty ratio information of a main power tube in a switching converter, and on-time of the main power tube in the switching converter is controlled according to the feedforward compensation signal and a feedback compensation signal, so as to compensate for a change of the input voltage, and reduce a ripple of an output voltage when the input voltage changes.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:
FIG. 1 is a control circuit diagram of a prior art switching converter;
FIG. 2 is a block diagram of a control circuit of a switching converter according to an embodiment of the present invention;
FIG. 3 is a first control circuit diagram of a switching converter according to an embodiment of the present invention;
FIG. 4 is a waveform diagram illustrating the operation of a first control circuit of the switching converter according to the embodiment of the present invention;
FIG. 5 is a waveform illustrating simulation of operation of a switching converter according to an embodiment of the present invention; and
fig. 6 is a second control circuit diagram of the switching converter according to the embodiment of the present invention.
Detailed Description
The present invention will be described below based on examples, but the present invention is not limited to only these examples. In the following detailed description of the present invention, certain specific details are set forth. It will be apparent to one skilled in the art that the present invention may be practiced without these specific details. Well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.
Further, those of ordinary skill in the art will appreciate that the drawings provided herein are for illustrative purposes and are not necessarily drawn to scale.
Meanwhile, it should be understood that, in the following description, a "circuit" refers to a conductive loop constituted by at least one element or sub-circuit through electrical or electromagnetic connection. When an element or circuit is referred to as being "connected to" another element or element/circuit is referred to as being "connected between" two nodes, it may be directly coupled or connected to the other element or intervening elements may be present, and the connection between the elements may be physical, logical, or a combination thereof. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, it is intended that there are no intervening elements present.
Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, what is meant is "including, but not limited to".
In the description of the present invention, it is to be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. In addition, in the description of the present invention, "a plurality" means two or more unless otherwise specified.
Fig. 2 shows a block diagram of a control circuit of a switching converter according to an embodiment of the present invention. In the figure, the switch converter 1 may be a flyback converter as shown in fig. 1, or may be a converter with other topology structures, such as a boost converter, buck-boost converter, cuk converter, and the like. The control circuit includes a feedback compensation circuit 11 and a feedforward compensation circuit 12. The feedback compensation circuit 11 samples the output voltage Vout to obtain a feedback signal and an output voltage reference value VREFIs compensated to generate a feedback compensation signal VCOMPIt is to be understood that any compensation means known in the art may be employed. The feedforward compensation circuit 12 is used for generating a feedforward compensation signal VCFWDWhich is opposite to the trend of the input voltage Vac of the switching converter 1. In some embodiments, the feedforward compensation signal V may be generated from a signal related to both the input voltage Vac and the output voltage Vout of the switching converter 1 or from a signal related to the duty cycleCFWD. In some cases, the feedforward compensation signal VCFWDAnd also with the feedback compensation signal VCOMPIt is related. The control circuit further includes an on-time control circuit 13 and a PWM generation circuit 14. Feedforward compensation signal VCFWDAnd a feedback compensation signal VCOMPWhich act in concert to control the adjustment signal Vs output by the on-time control circuit 13 to adjust the peak current or on-time of the switching converter. The PWM generation circuit 14 receives the adjustment signal Vs to control the switching state of the main power transistor in the switching converter 1.
Of course, it should be understood by those skilled in the art that the control of the switching state of the main power transistor may be performed by peak control, or other control methods in the prior art, such as on-time control, which will not be described in detail herein.
Fig. 3 shows a first control circuit diagram of a switching converter according to an embodiment of the present invention. As shown in fig. 3, the switching converter 1 will be described by taking a flyback converter as an example. As described above, the control circuit includes the feedback compensation circuit 11, the feedforward compensation circuit 12, the on-time control circuit 13, and the PWM generation circuit 14. Wherein the feedback compensation circuit 11 will output a voltage feedback signal VFBAnd an output voltage reference value VREFIs compensated to generate a feedback compensation signal VCOMPThe compensation network may adopt any structure in the prior art. In the present embodiment, the feedforward compensation circuit 12 includes: an operational amplifier Ap1 and a first conditioning circuit connected between the inverting input terminal and the output terminal of the operational amplifier Ap1 for adjusting the feed forward compensation signal V according to the output of the operational amplifierCFWDAnd the duty cycle information acquires a first conditioning signal Vcd1 and feeds back the first conditioning signal Vcd1 to the inverting input of the operational amplifier Ap 1.
Specifically, the first conditioning circuit includes a first switching unit 121 and a first filtering circuit 122. The first switch unit 121 is used for obtaining a first node voltage V according to the switching state of the main power transistor QSW1Wherein the first node voltage VSW1Is zero when the main power tube Q is switched on and is equal to the feedforward compensation signal V when the main power tube Q is switched offCFWD. The first filter circuit 122 is used for obtaining a first node voltage VSW1Average value over one switching period. Wherein the first switching unit 121 includes a first switch S1 and a second switch S2 connected in series between the output terminal of the operational amplifier Ap1 and the reference ground, and a common connection point of the first switch S1 and the second switch S2 is SW 1. The first switch S1 is turned on when the main power transistor Q is turned off, and the second switch S2 is turned on when the main power transistor Q is turned on to obtain a first node voltage VSW1. In the present embodiment, the first switch S1 is controlled by a signal PWMB opposite to the driving signal of the main power transistor Q, and the second switch S2 is controlled by a signal PWM identical to the driving signal of the main power transistor Q. Of course, the first switch S1 may also be controlled by the turn-off time Tdis of the main power transistor Q, where the turn-off time Tdis refers to the time when the inductor current of the switching converter drops from the peak value to zero. In one implementation, switching converter 1 operates in a critical current mode, and main power transistor Q is turned on when the inductor current reaches zero, so that off-time Tdis is the same as the active level time corresponding to signal PWMB. In another implementation, switching converter 1 operates in DCM mode, so that off-time Tdis is different from the active level time (the time when the main power transistor is in the off state) corresponding to signal PWMB, and off-time Tdis is the time when the inductor current drops from the peak to zero (excluding the time when the inductor current continues to be zero). The first filter circuit 122 has an input coupled to the common junction SW1 and an output for generating a first conditioned signal Vcd 1. In the present embodiment, the first filter circuit 122 is composed of a first resistor R1 and a first capacitor C1, wherein one end of the first resistor R1 is connected to the common connection point SW1, the other end is connected to the first capacitor C1, the other end of the first capacitor C1 is connected to the reference ground, and the first capacitor C is connected to the reference groundThe voltage at 1 is the first conditioning signal Vcd 1. The inverting input terminal of the operational amplifier Ap1 receives the first conditioning signal Vcd1, and the non-inverting input terminal receives the feedback compensation signal VCOMPThe output end outputs a feedforward compensation signal VCFWD. The on-time control circuit 13 receives the feedforward compensation signal VCFWDAnd adjusting the conduction time of the main power tube Q. In the embodiment, the flyback converter adopts peak current control to adjust the turn-off time of the main power tube Q. The on-time control circuit 13 includes a peak current adjusting circuit and a comparator Cmpr. The peak current regulating circuit is based on the received feedforward compensation signal VCFWDAdjusting peak current reference value VPK,REFThe input ends of the comparators Cmpr respectively receive a peak current reference value VPK,REFAnd an inductor current sampling signal Vi. It should be understood that in the present embodiment, the inductor current sampling signal Vi is directly obtained through the sampling resistor connected in series with the main power tube Q, and the inductor current sampling signal may be obtained in other manners. When the inductive current sampling signal Vi reaches the peak current reference value VPK,REFThe output of the comparator Cmpr generates a Reset signal Reset. The PWM generating circuit 14 receives the Reset signal Reset and outputs a corresponding driving signal to turn off the main power transistor Q, thereby adjusting the on-time of the main power transistor Q in response to the variation of the input and output voltages. It should be understood that the present embodiment is described with reference to peak current as an example, and other on-time control methods are also applicable.
Fig. 4 is a waveform diagram showing the operation of the control circuit shown in fig. 3. Referring to fig. 3 and 4, the switching converter 1 is illustrated as operating in the critical current mode, and the operation principle of the feedforward compensation circuit 12 is as follows:
in a switching period, when the inductor current sampling signal Vi is reduced to zero, the main power tube Q is switched on, the signal PWM is effective, the signal PWMB is ineffective, the first switch S1 is switched off, the second switch S2 is switched on, and the first node voltage V isSW1Is zero; when the inductive current sampling signal Vi reaches the peak current reference value VPK,REFAt this time, the main power transistor Q is turned off, and at this time, the signal PWMB is active and the signal PWM is inactive, so that the first switch S1 is turned on and the second switch S2 is turned off, thereby the first node voltage V is turned onSW1Equal to the feedforward compensation signal VCFWD. First node voltage VSW1The average value after being filtered by the first filter circuit is the first conditioning signal Vcd 1:
Vcd1＝VCFWD×(1-D) (1)
where D is the duty cycle of the switching converter. Meanwhile, since the signal values of the two input ends of the operational amplifier Ap are equal, that is:
VCOMP＝Vcd1 (2)
thus, the final feedforward compensation signal VCFWDComprises the following steps:
VCFWD＝VCOMP/(1-D) (3)
in the critical current mode, the duty ratio D is vout/(nvut + Vin), where n is the turn ratio of the primary side and the secondary side of the transformer of the flyback converter. At time t0, the input voltage Vac rises, (1-D) increases, and the feedback compensation signal VCOMPRemains substantially constant at that instant, so that the feedforward compensation signal VCFWDReduced, therefore peak current reference value VPK,REFThe on-time is correspondingly reduced, the output voltage Vout is maintained unchanged, the dynamic response of the system is accelerated, and the ripple of the output voltage Vout is reduced.
Fig. 5 is a waveform diagram showing an operation simulation of the switching converter according to the embodiment of the present invention. Wherein, fig. 5(a) is a simulation waveform diagram without adding feedforward compensation control, and fig. 5(b) is a simulation waveform diagram with adding feedforward compensation control. The abscissa is time t and the ordinate is input voltage Vin and output voltage Vout in sequence. As shown in the figure, under the condition that the variation amplitude and the period of the input voltage Vin are the same, when the feedforward compensation control is not added, the ripple variation range of the output voltage Vout is 9.90V-10.14V; after the feedforward compensation control is added, the ripple variation range of the output voltage Vout is obviously reduced. Thereby verifying the effectiveness of incorporating the feedforward compensation control scheme.
It should be understood that the present invention provides only one preferred way of feed forward compensation, and that the object of the present invention can be achieved by generating a feed forward compensation signal based on a feedback compensation signal and other signals having a trend opposite to the input voltage.
The principle of reducing the ripple of the output voltage Vout is explained in detail below. Without feed forward compensation added, the output power Po of the switching converter can be expressed as:
Figure BDA0002238666190000101
where k1 is k × nVout, Lm is the excitation inductance of the transformer, Ipk is the peak value of the inductor current, and fs is the switching frequency of the switching converter.
After adding the feedforward compensation, substituting equation (3) into equation (4), the output power Po' can be expressed as:
Po’＝k1VCOMP/(1-D)×(1-D)＝k1VCOMP(5)
it can be seen that the addition of the feedforward compensation eliminates the influence of the input voltage Vac on the output power, so that the output power is only equal to the feedback compensation signal VCOMPRelated, so that when the input voltage Vac varies, the compensation signal V is fed backCOMPThe output power is substantially constant, thereby reducing the ripple of the output voltage.
Meanwhile, it can be seen from the formula (4) that when the input voltage Vac is large and the input voltage Vac changes by Δ V1, the output power Po changes less and the output voltage Vout also changes less; when the input voltage Vac is smaller, the output power Po changes by Δ V1, which results in a larger change of the output voltage Vout, and this makes the gain of the same control loop achieve different effects. After the feedforward compensation control is added, the influence of the change on the output is the same no matter what the magnitude of the input voltage Vac, that is, the loop gain is the same, so the loop design is simplified.
When the switching converter enters a Discontinuous (DCM) mode, in order to avoid the situation that the frequency is very low due to very light load, the compensation loop delays greatly, and the system is unstable, the feedforward compensation control works only in the state that the DCM is relatively light (i.e. the zero current time after the inductor current drops to zero is short).
In order to smoothly transition with the peak current control curve generated by the compensation loop when the feedforward compensation control only works in the relatively light DCM, the feedforward compensation control only works on the feedback compensation signal V in the embodimentCOMPGreater than a first threshold value VCOMP,DCIs active only when the compensation signal V is fed backCOMPLess than a first threshold value VCOMP,DCTime, feedforward compensation signal VCFWD0, the conduction time is only compensated by the feedback signal VCOMPAnd (5) controlling. Wherein the first threshold value VCOMP,DCThe system is set according to actual circuit system parameters, and a demarcation point of feedforward compensation control is added when the system is used for ensuring the stability of the system.
Fig. 6 shows a second control circuit diagram of the switching converter according to the embodiment of the present invention. As shown in the drawing, the present embodiment is described by taking the flyback converter 2 as an example. Similarly, the switching converter 2 in the figure may also be a boost converter, buck-boost converter, cuk converter, or the like. The control circuit of the flyback converter 2 includes a feedback compensation circuit 21, a feedforward compensation circuit 22, an on-time control circuit 23 and a PWM generation circuit 24, wherein the circuit topology and the operation principle of the feedback compensation circuit 21, the on-time control circuit 23 and the PWM generation circuit 24 are substantially the same as those of the control circuit shown in fig. 3, and will not be described in detail herein.
The feedforward compensation circuit 22 includes an operational amplifier Ap2 and a first conditioning circuit. The first conditioning circuit is connected between the inverting input terminal and the output terminal of the operational amplifier Ap2, and is used for adjusting the feedforward compensation signal V according to the output of the operational amplifier Ap2CFWDAnd the duty cycle information acquires a first conditioning signal Vcd1 and feeds back the first conditioning signal Vcd1 to the inverting input of the operational amplifier Ap 2. Likewise, the first conditioning circuit includes a first switching unit 221 and a first filter circuit 222, wherein the first switching unit 221 includes a first switch S1 and a second switch S2, and the first filter circuit 222 includes a first resistor R1 and a first capacitor C1. The specific structure and function of the first conditioning circuit are the same as those of the above embodiments, and will not be described here. Also, in one implementation, the switching converter 2 operates in the critical current mode with the main power transistor Q at inductor current zeroOn, and thus off time Tdis is the same as the active level time corresponding to signal PWMB. In another implementation, switching converter 2 operates in DCM mode, so that off-time Tdis is different from the active level time (the time when the main power transistor is in the off state) corresponding to signal PWMB, and off-time Tdis is the time when the inductor current drops from the peak to zero (excluding the time when the inductor current continues to be zero).
In this embodiment, in order to realize that the feedforward compensation control is added only when DCM is relatively light when the switching converter is changed from heavy load to light load, the feedforward compensation circuit 22 further includes a second conditioning circuit connected between the output terminal of the feedback compensation circuit 21 and the non-inverting input terminal of the operational amplifier Ap2 for providing the feedback compensation signal VCOMPGreater than a first threshold value VCOMP,DCAccording to the feedback compensation signal VCOMPAnd duty cycle information to produce a second conditioning signal Vcd2 for input to the non-inverting input of an operational amplifier Ap 2.
Specifically, the second conditioning circuit includes a second switching unit 223, a second filtering circuit 224, and a threshold circuit. Wherein the threshold circuit is used for generating a first threshold value VCOMP,DCSo that the feedforward compensation control is only on the feedback compensation signal VCOMPGreater than a first threshold value VCOMP,DCIt is functional. In this embodiment, the threshold circuit has a voltage value VCOMP,DCWherein the positive terminal of the threshold circuit receives the feedback compensation signal VCOMPAnd a negative terminal is connected to an input terminal of the second switching unit 223. The second switching unit 223 is used for obtaining a second node voltage V according to the switching state of the main power transistor QSW2Which compensates the signal V for the feedback when the main power tube Q is turned onCOMPAnd a first threshold value VCOMP,DCA difference of (i.e. V)COMP-VCOMP,DCAnd equals zero when the main power tube Q is turned off. The second filter circuit 224 is used for obtaining a second node voltage VSW2Average value over one switching period. Specifically, the second switching unit 223 includes a third switch S3 and a fourth switch S4 connected in series between the negative terminal of the threshold circuit and the reference ground, and a common connection point of the third switch S3 and the fourth switch S4 is SW 2. Wherein, the firstThe switch S3 is turned on when the main power transistor Q is turned on, and the fourth switch S4 is turned on when the main power transistor Q is turned off to obtain a second node voltage VSW2. In the present embodiment, the third switch S3 is controlled by the same signal PWM as the driving signal of the main power transistor Q, and the fourth switch S4 is controlled by the opposite signal PWMB to the driving signal of the main power transistor Q. In another embodiment, the fourth switch S4 is controlled to be in the on state by the off time Tdis, which is the time when the inductor current drops from the peak value to zero (excluding the time when the current is continuously zero) when the main power transistor is in the DCM mode, to improve the compensation effect. It should be understood that other switching units and control schemes may also implement the above-described functions. The second filter circuit 224 has an input coupled to the common junction SW2 and an output that generates a second conditioning signal Vcd 2. In this embodiment, the second filter circuit 224 is composed of a second resistor R2 and a second capacitor C2, wherein one end of the second resistor R2 is connected to the common connection point SW2, the other end of the second resistor R2 is connected to the second capacitor C2, the other end of the second capacitor C2 is connected to the reference ground, and the voltage on the second capacitor C2 is the second conditioning signal Vcd 2.
In summary, in the embodiment, two input terminals of the operational amplifier Ap2 respectively receive the first conditioning signal Vcd1 and the second conditioning signal Vcd2 and output the feedforward compensation signal VCFWDWherein
Vcd1＝VCFWD×(1-D) (8)
Vcd2＝(VCOMP-VCOMP,DC)×D (9)
From the principle of operational amplifiers, Vcd1 — Vcd2 can be found:
VCFWD＝(VCOMP-VCOMP,DC)×D/(1-D) (10)
in this embodiment, the control circuit further comprises an adding circuit for adding the feedforward compensation signal VCFWDAnd a feedback compensation signal VCOMPAnd (3) superposing to obtain a compensation signal Vd:
Vd＝VCOMP+VCFWD＝VCOMP,DC+(VCOMP-VCOMP,DC)/(1-D) (11)
the on-time control circuit 23 adjusts the on-time of the main power transistor Q according to the compensation signal Vd. When the input voltage Vac rises, (1-D) increases, feeding forward the compensation signal VCFWDIs automatically reduced, and the compensation signal V is fed backCOMPAt this moment, the compensation signal Vd is substantially constant, and therefore the peak current reference value V is reducedPK,REFThe on-time is correspondingly reduced, the output voltage Vout is maintained unchanged, the dynamic response of the system is accelerated, and the ripple of the output voltage Vout is reduced.
The above embodiments are described only by way of example with reference to being controlled by the signal PWMB, it being understood that the principle of operation of the feedforward compensation circuit controlled by the off-time Tdis is similar and will not be derived in detail here.
It should be understood that the present invention only shows one preferred way of feed forward compensation, and that the object of the present invention can be achieved by adding other signals with the inverse trend of the input voltage to the feedback compensation signal to generate the feed forward compensation signal.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (24)

1. A control circuit for a switching converter, the control circuit comprising:
a feedforward compensation circuit configured to generate a feedforward compensation signal to suppress a ripple of an output voltage due to a variation of an input voltage of the switching converter according to duty ratio information of a main power transistor in the switching converter, an
A feedback compensation circuit configured to generate a feedback compensation signal according to an error between an output signal of the switching converter and an output signal reference value, wherein
The control circuit controls the conduction time of the main power tube according to the feedforward compensation signal and the feedback compensation signal, and the feedforward compensation signal and the input voltage have opposite change trends.
2. The control circuit of claim 1, wherein the feedforward compensation circuit is configured to generate the feedforward compensation signal further in accordance with the feedback compensation signal.
3. The control circuit of claim 1, further comprising:
and the conduction time control circuit is configured to adjust the conduction time of the main power tube according to the feedforward compensation signal.
4. The control circuit of claim 3, wherein the on-time control circuit is configured to adjust a peak current reference value of an inductor current in the switching converter to adjust the on-time of the main power transistor based on the feed-forward compensation signal.
5. The control circuit of claim 4, wherein the on-time control circuit comprises:
a peak current adjustment circuit configured to adjust the peak current reference value in accordance with the feedforward compensation signal; and
a comparison circuit configured to generate a reset signal to control the main power tube to turn off when an inductor current of the switching converter reaches the peak current reference value.
6. The control circuit of claim 1, wherein the feedforward compensation circuit comprises:
the inverting input end of the operational amplifier receives the first conditioning signal and outputs the feedforward compensation signal; and
the first conditioning circuit is configured to generate the first conditioning signal according to a feedforward compensation signal output by the operational amplifier and duty ratio information of the switching converter, and feed the first conditioning signal back to an inverting input end of the operational amplifier.
7. The control circuit of claim 6, wherein the first conditioning circuit comprises:
a first switching unit configured to be controlled by a switching state of the main power transistor to generate a first node voltage; and
a first filter circuit configured to obtain an average value of the first node voltage in one switching period, wherein
The first node voltage is zero when the main power tube is switched on, and is equal to the feedforward compensation signal when the main power tube is switched off.
8. The control circuit according to claim 7, wherein the first switching unit includes:
a first switch and a second switch connected in series between the output terminal of the operational amplifier and a reference ground, wherein
The first switch is in a conducting state during the period that the main power tube is turned off, the second switch is in a conducting state during the period that the main power tube is turned on, and the voltage of the common connection point of the first switch and the second switch is the voltage of the first node.
9. The control circuit of claim 7, wherein the first filtering circuit comprises:
a first resistor connected to the first node voltage; and
and the first capacitor is connected between the first resistor and the reference ground, wherein the voltage on the first capacitor is the first conditioning signal.
10. The control circuit of claim 6, wherein a non-inverting input of the operational amplifier receives the feedback compensation signal.
11. The control circuit of claim 6, wherein the feedforward compensation circuit further comprises:
and the second conditioning circuit is configured to generate a second conditioning signal according to the feedback compensation signal and the duty ratio information of the switching converter and input the second conditioning signal to the non-inverting input end of the operational amplifier when the feedback compensation signal is larger than a first threshold value.
12. The control circuit of claim 11, wherein the second conditioning circuit comprises:
a second switching unit configured to be controlled by a switching state of the main power transistor to generate a second node voltage;
a second filter circuit configured to obtain an average value of the second node voltage in one switching period; and
a threshold circuit connected between the feedback compensation signal and the second switching unit and generating the first threshold, wherein
The second node voltage is a difference between the feedback compensation signal and the first threshold when the main power tube is switched on, and is equal to zero when the main power tube is switched off.
13. The control circuit according to claim 12, wherein the second switching unit comprises:
a third switch and a fourth switch connected in series between the threshold circuit and a reference ground, wherein
The third switch is in a conducting state during the conduction period of the main power tube, the fourth switch is in a conducting state during the period that the inductive current of the switch converter is reduced from a peak current reference value to zero or the main power tube is in a turn-off state, and the voltage of the common connection point of the third switch and the fourth switch is the second node voltage.
14. The control circuit of claim 12, wherein the second filtering circuit comprises:
a second resistor connected to the second node voltage; and
and the second capacitor is connected between the second resistor and the reference ground, wherein the voltage on the second capacitor is the second conditioning signal.
15. The control circuit of claim 11, further comprising a superposition circuit for superposing the feedforward compensation signal and the feedback compensation signal to control the on-time of the main power transistor.
16. The control circuit of claim 11, wherein the switching converter operates in a current critical mode or a discontinuous mode.
17. A method of controlling a switching converter, comprising: and generating a feedforward compensation signal according to the duty ratio information of the main power tube in the switching converter so as to restrain the ripple of the output voltage caused by the change of the input voltage of the switching converter, and controlling the conduction time of the main power tube in the switching converter according to the feedforward compensation signal and a feedback compensation signal, wherein the feedforward compensation signal and the feedback compensation signal have opposite change trends, and the feedback compensation signal represents the error of the output signal of the switching converter and the reference value of the output signal.
18. The control method of claim 17, wherein the feedforward compensation signal is also generated based on the feedback compensation signal.
19. The control method according to claim 18, characterized by comprising:
acquiring a first node voltage according to the switching state of the switching converter, wherein the first node voltage is zero when the main power tube is switched on and is equal to the feedforward compensation signal when the main power tube is switched off; and
and acquiring the average value of the first node voltage in one switching period.
20. The control method according to claim 19, characterized by further comprising:
and obtaining the feedforward compensation signal according to the condition that the average value corresponding to the first node voltage is equal to the feedback compensation signal.
21. The control method according to claim 19, characterized by further comprising:
acquiring a second node voltage according to the switching state of the switching converter, wherein the second node voltage is a difference value between the feedback compensation signal and a first threshold value when the main power tube is switched on, and is equal to zero when the main power tube is switched off; and
and acquiring the average value of the voltage of the second node in a switching period.
22. The control method according to claim 21, characterized by further comprising:
and obtaining the feedforward compensation signal according to the condition that the average value corresponding to the second node voltage is equal to the average value corresponding to the first node voltage.
23. The control method according to claim 17, characterized by comprising: when the switching converter works in a discontinuous mode, the feedforward compensation signal and the feedback compensation signal are superposed to control the conduction time of the main power tube.
24. The control method of claim 23, wherein the feedforward compensation signal is zero when the feedback compensation signal is less than a first threshold.
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