CN114531016A - Switching converter, zero-crossing detection circuit and zero-crossing detection method thereof - Google Patents

Switching converter, zero-crossing detection circuit and zero-crossing detection method thereof Download PDF

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CN114531016A
CN114531016A CN202011321237.1A CN202011321237A CN114531016A CN 114531016 A CN114531016 A CN 114531016A CN 202011321237 A CN202011321237 A CN 202011321237A CN 114531016 A CN114531016 A CN 114531016A
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signal
zero
crossing
switch
sampling
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CN114531016B (en
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孙健
张宝全
李精文
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SG Micro Beijing Co Ltd
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SG Micro Beijing Co 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
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/175—Indicating the instants of passage of current or voltage through a given value, e.g. passage through zero
    • 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
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H02M3/1582—Buck-boost converters
    • 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
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H02M3/1588—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load comprising at least one synchronous rectifier element
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention discloses a switching converter, a zero-crossing detection circuit and a zero-crossing detection method thereof. The zero-crossing detection circuit comprises a voltage sampling module, a bias module and a zero-crossing comparator, wherein the voltage sampling module generates a sampling signal equal to the direct-current output voltage, the bias module generates a corresponding bias signal according to the sampling signal, and the zero-crossing comparator compares a superposed signal of a signal to be detected and the bias signal with a zero-crossing reference value so as to obtain a zero-crossing indication signal. The zero-crossing detection circuit of the invention generates a sampling signal equal to the DC output voltage in a simulation way in the chip, and adjusts the compensation quantity of the bias module in a self-adaptive way according to the sampling signal, so that the compensation quantity is basically equal to the variation quantity of the switch node voltage in the time delay period, the influence of the zero-crossing comparator and the subsequent logic control time delay on the zero-crossing detection precision can be reduced in different application occasions, the zero-crossing detection precision is improved, the circuit loss of the switch converter is reduced, and the efficiency of the switch converter is improved.

Description

Switching converter, zero-crossing detection circuit and zero-crossing detection method thereof
Technical Field
The invention relates to the technical field of semiconductor integrated circuits, in particular to a switching converter, a zero-crossing detection circuit of the switching converter and a zero-crossing detection method of the switching converter.
Background
At present, wearable equipment and Internet of things equipment are powered by lithium batteries, so that the efficiency of switching power supply products is more and more important. Modern electronic devices use power supplies broadly divided into linear regulated power supplies and switching regulated power supplies. The adjusting tube of the linear voltage-stabilized power supply works in an amplifying region, has the advantages of no introduction of additional interference, good reliability and low cost, but has the defects of larger volume and low conversion efficiency. Compared with a linear voltage-stabilized power supply, the switching voltage-stabilized power supply has the characteristics of being capable of boosting and reducing voltage and high in power supply efficiency. The switching converter adopts the switching tube to control the electric energy transmission from the input end to the output end, so that constant output voltage and/or output current can be provided at the output end, and the switching converter has the advantages of good light load efficiency, quick transient response and easiness in realization, and is widely applied in recent years.
In order to improve the conversion efficiency of the switching converter, the conventional switching converter generally adopts a synchronous rectification structure, i.e., a synchronous rectification transistor is used to replace a conventional diode to complete the rectification of the inductive current. However, when the output load is small, the inductive current in the synchronous rectification switching converter is reversed to cause energy loss, and for this purpose, a zero-crossing detection circuit is required to detect the reverse current of the synchronous rectification transistor, and when the zero-crossing detection circuit detects that the current of the synchronous rectification transistor is reversed, the zero-crossing detection circuit sends a signal to turn off the synchronous rectification transistor to prevent the reverse direction of the inductive current.
Fig. 1 shows a schematic circuit diagram of a switching converter according to the prior art. As shown in fig. 1, the main circuit of the switching converter 100 includes a power transistor MD1 and a rectifier MD2 connected in series between an input terminal and a ground terminal, an inductor Lx connected between a common terminal and an output terminal of the power transistor MD1 and the rectifier MD2, and an output capacitor Co connected between the output terminal and the ground terminal. The switching converter 100 has an input terminal receiving a dc input voltage Vin and an output terminal providing a dc output voltage Vout. The logic control circuit 110 is used to provide a switch control signal SW to the power tube MD1 and the rectifying tube MD2 to control the on and off of the power tube MD1 and the rectifying tube MD 2.
The switching converter 100 further includes a zero-crossing comparator 120, wherein the zero-crossing comparator 120 is configured to compare the switching node voltage Vsw with a zero-crossing reference value (e.g., a reference ground voltage), and when the switching node voltage Vsw is detected to be greater than the zero-crossing reference value, the inductor current ILx is considered to be negative, the zero-crossing indication signal ZCD is provided to the logic control circuit 110, and the logic control circuit 110 turns off the rectifier tube MD2 according to the zero-crossing indication signal ZCD, so as to prevent the inductor current from reversing. However, since the comparator has a certain delay, the accuracy of zero-crossing detection is affected by the inherent delay of the zero-crossing comparator, when the switching converter is in a light-load state, the zero-crossing point may be advanced or delayed, the inductive current loses energy on the body diode of the rectifier tube when the zero-crossing point is advanced, and the zero-crossing point is delayed to reverse the inductive current, so that the overall performance index of the system is affected, and the efficiency of the whole circuit is reduced.
In view of the above problems, the existing solution is to superimpose a fixed offset signal on the input of the zero-crossing comparator to offset the inherent delay of the zero-crossing comparator. As shown in fig. 1, the current source 130 and the resistor Rc are used to superimpose a bias signal on the switching node voltage Vsw, but such a bias signal is not suitable for all applications, and once the temperature, the value of the inductor or the output voltage changes, the bias signal will not be able to eliminate the effect of the delay of the zero-crossing comparator.
Disclosure of Invention
In view of this, an object of the present invention is to provide a switching converter, a zero-crossing detection circuit and a zero-crossing detection method thereof, which can reduce the influence of a zero-crossing comparator and subsequent logic control delay on the zero-crossing detection precision, improve the zero-crossing detection precision, reduce the circuit loss of the switching converter, and improve the efficiency of the switching converter in different application situations.
According to a first aspect of the present invention, there is provided a zero-crossing detection circuit for providing a zero-crossing indication signal according to a signal to be detected, the signal to be detected being responsive to an inductor current provided by an inductor, the inductor being charged when a power tube is on and a rectifier tube is off, and being discharged to enable a follow current when the power tube is off, the power tube and the rectifier tube being configured to convert a dc input voltage to a dc output voltage, wherein the zero-crossing detection circuit comprises: the voltage sampling module is used for generating a sampling signal equal to the direct current output voltage; the offset module is used for generating a corresponding offset signal according to the sampling signal; and the zero crossing comparator is used for comparing the superposed signal of the signal to be detected and the bias signal with a zero crossing reference value so as to judge whether the inductive current is reduced to zero or not and provide a zero crossing indication signal representing a judgment result.
Optionally, the voltage sampling module samples and holds the dc input voltage according to a switch control signal that controls on and off of the power tube and the rectifier tube and the zero-crossing indication signal, so as to obtain the sampling signal.
Optionally, the voltage sampling module includes: a switching signal generating unit for generating a first switching signal and a second switching signal according to the switching control signal and the zero-crossing indication signal; and a sample-and-hold unit for generating the sampling signal according to the dc input voltage under control of the first switching signal and the second switching signal.
Optionally, the switching signal generating unit includes a first and gate, a second and gate, a first inverter and a second inverter, wherein a first input end of the first and gate receives the switching control signal, an input end of the first inverter receives the zero-crossing indication signal, an output end of the first and gate is connected to a second input end of the first and gate, an output end of the second and gate outputs the first switching signal, an input end of the second inverter receives the switching control signal, an output end of the second inverter is connected to the first input end of the second and gate, a second input end of the second and gate is connected to the output end of the first inverter, and an output end of the second and gate outputs the second switching signal.
Optionally, the sample-and-hold unit includes: the first switch and the second switch are sequentially connected between the direct current input voltage and the ground; a first resistor, a first end of which is connected to a common end of the first switch and the second switch; the first end of the first capacitor is connected to the second end of the first resistor, and the second end of the first capacitor is grounded; a first end of the second resistor is connected to a common end of the first resistor and the first capacitor; and a second capacitor, a first end of which is connected to a second end of the second resistor, and a second end of which is grounded, wherein the first switch and the second switch are respectively controlled by the first switch signal and the second switch signal, and a common terminal of the second resistor and the second capacitor is used for providing the sampling signal.
Optionally, the first switch is turned on during the period that the power transistor is turned on, the second switch is turned off, the dc input voltage charges the first capacitor and the second capacitor, the first switch is turned off during the period that the rectifier transistor is turned on, the second switch is turned on, the first capacitor and the second capacitor are discharged, and the first switch and the second switch are turned off during the period that the power transistor and the rectifier transistor are turned off, the sampling signal is kept unchanged.
Optionally, the bias module includes: the transconductance amplifier is used for generating corresponding bias current according to the sampling signal; and a bias resistor for converting the bias current into a voltage signal to generate the bias signal.
According to a second aspect of the present invention, there is provided a switching converter comprising: the main circuit comprises a power tube and a rectifying tube, wherein the power tube and the rectifying tube are used for controlling the transmission of electric energy from an input end to an output end so as to generate direct-current output voltage according to direct-current input voltage; the zero-cross detection circuit described above; and the logic control circuit provides a switch control signal according to the zero-crossing indication signal so as to control the conduction and the disconnection of the power tube and the rectifying tube.
Optionally, the main circuit adopts a topology selected from any one of the following: step-down, step-up, non-inverting step-up and step-down, forward, and flyback.
According to a third aspect of the present invention, there is provided a zero-crossing detection method for generating a zero-crossing indication signal according to a signal to be detected, the signal to be detected being responsive to an inductor current provided by an inductor, the inductor being charged when a power tube is turned on and a rectifier tube is turned off, and being discharged to realize a follow current when the power tube is turned on, the power tube and the rectifier tube being configured to convert a dc input voltage into a dc output voltage, wherein the zero-crossing detection method comprises: generating a sampling signal equal to the dc output voltage; generating a corresponding bias signal according to the sampling signal; and comparing the superposed signal of the signal to be detected and the bias signal with a zero-crossing reference value to judge whether the inductive current is reduced to zero or not and providing a zero-crossing indication signal representing a judgment result.
Optionally, the generating a sampling signal equal to the dc output voltage includes: and sampling and holding the direct current input voltage according to a switch control signal for controlling the on and off of the power tube and the rectifying tube and the zero-crossing indication signal to obtain the sampling signal.
Optionally, the sampling and holding the dc input voltage according to the switching control signal for controlling the on and off of the power tube and the rectifying tube and the zero-crossing indication signal to obtain the sampling signal includes: the method includes turning on a first switch during a turn-on period of the power transistor, turning off a second switch, charging a first capacitor and a second capacitor based on the DC input voltage, turning off the first switch during a turn-on period of the rectifier transistor, turning on the second switch, discharging the first capacitor and the second capacitor, and turning off the first switch and the second switch during a turn-off period of the power transistor and the rectifier transistor so that the sampling signal remains unchanged.
Optionally, the generating a corresponding bias signal according to the sampling signal includes: generating a corresponding bias current according to the sampling signal; and converting the bias current to a voltage signal to generate the bias signal.
The zero-crossing detection circuit of the switching converter comprises a voltage sampling module, a bias module and a zero-crossing comparator, wherein the voltage sampling module is used for generating a sampling signal equal to direct-current output voltage, the bias module generates a corresponding bias signal according to the sampling signal, and the zero-crossing comparator compares a superposed signal of a signal to be detected and the bias signal with a zero-crossing reference value so as to obtain a zero-crossing indication signal. Compared with the prior art, the zero-crossing detection circuit provided by the embodiment of the invention generates a sampling signal equal to the DC output voltage in a simulation mode in a chip, and adaptively adjusts the compensation quantity of the offset module according to the sampling signal, so that the compensation quantity is basically equal to the variation quantity of the switch node voltage in the delay period, an optimal compensation effect can be provided for the switch node voltage regardless of the change of the DC output voltage, the influence of a zero-crossing comparator and subsequent logic control delay on the zero-crossing detection precision can be reduced in different application occasions, the zero-crossing detection precision is improved, the circuit loss of the switching converter is reduced, and the efficiency of the switching converter is improved.
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.
Fig. 1 shows a schematic circuit diagram of a switching converter according to the prior art;
fig. 2 shows a schematic circuit diagram of a switching converter according to a first embodiment of the invention;
fig. 3 shows a schematic circuit diagram of a voltage sampling module in a zero crossing detection circuit according to a first embodiment of the invention;
fig. 4 shows a schematic flow chart of a zero-crossing detection method of a switching converter according to a second embodiment of the invention.
Detailed Description
The invention will be described in more detail below with reference to the accompanying drawings. Like elements in the various figures are denoted by like reference numerals. For purposes of clarity, the various features in the drawings are not necessarily drawn to scale. Moreover, certain well-known elements may not be shown in the figures.
In the following description, numerous specific details of the invention, such as structure, materials, dimensions, processing techniques and techniques of components, are set forth in order to provide a more thorough understanding of the invention. However, as will be understood by those skilled in the art, the present invention may be practiced without these specific details.
It should be understood that in the following description, "circuitry" may comprise singly or in combination hardware circuitry, programmable circuitry, state machine circuitry, and/or elements capable of storing instructions executed by programmable circuitry. When an element or circuit is referred to as being "connected" or "coupled" to another element, or being "connected" or "coupled" between two nodes, it may be directly coupled or connected to the other element or intervening elements may also be present, and the connection or coupling 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.
In the present application, the switching transistor is a transistor that operates in a switching mode to provide a current path, and includes one selected from a bipolar transistor or a field effect transistor. The first end and the second end of the switching tube are respectively a high potential end and a low potential end on a current path, and the control end is used for receiving a driving signal to control the switching tube to be switched on and off.
Fig. 2 shows a schematic circuit diagram of a switching converter according to a first embodiment of the invention. As shown in fig. 2, the main circuit of the switching converter 200 includes a power transistor MD1 and a rectifier MD2 connected in series between an input terminal and a ground terminal, an inductor Lx connected between a common terminal and an output terminal of the power transistor MD1 and the rectifier MD2, and an output capacitor Co connected between the output terminal and the ground terminal. The switching converter 200 has an input terminal receiving a dc input voltage Vin and an output terminal providing a dc output voltage Vout.
The power transistor MD1 and the rectifier MD2 are, for example, N-channel or P-channel field effect transistors. In this embodiment, an N-channel field effect transistor is taken as an example, wherein the first terminal of the power transistor MD1 and the second terminal of the rectifying transistor MD2 are source electrodes, the second terminal thereof is a drain electrode, and the control terminal thereof is a gate electrode.
The logic control circuit 210 is configured to generate a switch control signal SW, and the switch control signal SW is configured to control the power transistor MD1 and the rectifying transistor MD2 to be turned on and off. The inductor Lx is charged when the power tube MD1 is turned on and the rectifier tube MD2 is turned off, and is discharged when the power tube MD1 is turned off and the rectifier tube MD2 is turned on to realize free-wheeling.
The zero-crossing detection circuit 220 is coupled to the inductor Lx (e.g., coupled to a common terminal of the power tube MD1 and the rectifier tube MD 2) to obtain a signal to be detected that is capable of characterizing the inductor current flowing through the inductor Lx, and is configured to provide a zero-crossing indication signal ZCD, which is used to characterize whether the inductor current flowing through the inductor Lx has decreased to 0, based on the signal to be detected and a zero-crossing reference value.
The operation principle of the zero-crossing detection circuit 220 may be equivalent to, for example, the following process: when the signal to be detected is greater than the zero-crossing reference value, the zero-crossing detection circuit 220 provides an effective zero-crossing indication signal ZCD to indicate that the zero-crossing of the inductor current is detected; when the signal to be detected is less than/equal to the zero crossing reference value, the zero crossing detection circuit 220 provides an invalid zero crossing indication signal ZCD to indicate that the inductor current has not crossed zero.
When the zero crossing indicating signal ZCD indicates that the current flowing through the inductor Lx has dropped to 0 (zero crossing), indicating that the inductor Lx cannot continue to supply enough energy, the rectifier tube MD2 needs to be turned off to prevent the inductor current from reversing, so the zero crossing indicating signal ZCD can be used to determine whether the rectifier tube MD2 is turned off.
In some embodiments, as shown in fig. 2, the zero-crossing detection circuit 220 is connected to the logic control circuit 210, when the signal to be detected is greater than the zero-crossing reference value, the zero-crossing detection circuit 220 provides a valid zero-crossing indication signal ZCD to the logic control circuit 210, and the logic control circuit 210 turns off the rectifying tube MD2 according to the zero-crossing indication signal ZCD to prevent the inductor current from reversing.
In the embodiment of the present invention, the logic control circuit 210 may operate in an intermittent conduction mode or a continuous conduction mode. The discontinuous conduction mode is: after the inductor current provided by the inductor Lx is detected to drop to 0, the power tube MD1 is switched from the off state to the on state after a delay. The continuous conduction mode is as follows: when the inductor current provided by the inductor Lx is detected to drop to a certain value, the power tube MD1 is immediately switched from the off state to the on state, and the inductor current of the inductor Lx does not cross zero all the time in the continuous on mode.
Those skilled in the art will appreciate that the logic control circuit 210 may be implemented by different architectures. Meanwhile, the control principle of the synchronous rectification buck-type switching converter 200 should be well known to those skilled in the art.
Further, the zero crossing detection circuit 220 includes a voltage sampling module 201, a bias module 202, and a zero crossing comparator 203. The voltage sampling module 201 is configured to sample and hold the dc input voltage Vin according to the switch control signal SW and the zero-crossing indication signal ZCD to generate a sampling signal Vs equal to the dc output voltage Vout. The bias module 202 is configured to generate a corresponding bias signal Vbias according to the sampling signal Vs. The zero crossing comparator 203 compares the superimposed signal of the switching node voltage Vsw and the bias signal Vbias at the common terminal of the power tube MD1 and the rectifier tube MD2 with a zero crossing reference value to generate the zero crossing indication signal ZCD. Wherein the zero-crossing reference value is, for example, a reference ground voltage, and when a superimposed signal of the switching node voltage Vsw and the bias signal Vbias is greater than the reference ground voltage, an output of the zero-crossing comparator 203 is inverted to generate an effective (e.g., high level) zero-crossing indication signal ZCD.
Further, the bias module 202 includes a transconductance amplifier 221 and a bias resistor Rc. A first terminal of the transconductance amplifier 221 is connected to the power supply voltage Vdd, and the transconductance amplifier 221 is configured to generate a corresponding bias current Ic according to the sampling signal Vs. One end of the bias resistor Rc is connected to the common end of the power transistor MD1 and the rectifier MD2, the other end is connected to the second end of the transconductance amplifier 221 and one end of the zero-crossing comparator 203, and the bias resistor Rc is configured to convert the bias current Ic into a voltage signal to generate a bias signal Vbias, and to provide a superimposed signal of the bias signal Vbias and the switching node voltage Vsw to one end of the zero-crossing comparator 203.
The switching node voltage of the common terminal of the power tube MD1 and the rectifying tube MD2 is obtained by the following formula:
vsw ILx × Ron _ LS equation 1
Vsw is the switching node voltage of the common terminal of the power tube MD1 and the rectifier tube MD2, ILx is the inductor current, and Ron _ LS is the on-resistance of the rectifier tube MD 2.
The voltages at the non-inverting input and the inverting input of the zero-crossing comparator 203 are:
VA + Vsw + Vs × gm × Rc formula 2
VB 0 formula 3
Where VA denotes a voltage at the non-inverting input terminal of the zero-cross comparator 203, VB denotes a voltage at the inverting input terminal of the zero-cross comparator 203, Vs denotes a voltage value of the sampling signal, gm denotes a transconductance of the transconductance amplifier 221, which is a constant, and Rc denotes a resistance value of the bias resistor.
The zero-crossing indication signal ZCD is high when the voltage VA at the non-inverting input terminal of the zero-crossing comparator 203 is higher than the voltage VB at the inverting input terminal. Because the zero-crossing comparator and the subsequent logic control have fixed delay Td, the compensation amount is set through the bias current Ic and the bias resistor Rc, the voltage VA is larger than VB in advance when the switching node voltage Vsw is still negative, and after the subsequent delay, the switching node voltage Vsw is just equal to zero when the rectifier tube MD2 is turned off, so that the aim of turning off the rectifier tube MD2 in time is fulfilled.
In combination with equation 1, it can be obtained that there is a correlation between the change rate of the switching node voltage Vsw (i.e. the change rate of the inductor current) and the dc output voltage Vout, that is:
KVsw＝KILx Ron _ LS ═ (Vout/L) × Ron _ LS equation 4
Wherein, KVswRepresenting the rate of change of the switching node voltage Vsw, KILThe change rate of the inductor current is shown, and the inductance of the inductor Lx is shown as L, so that the change amount of the switching node voltage during the delay time is:
Δ Vsw is (Vout/L) × Ron _ LS × Td formula 5
Wherein Td represents the fixed time delay of the zero-crossing comparator and the subsequent logic control, and since the sampling signal Vs is substantially equal to the dc output voltage Vout, the offset current Ic and the offset resistor Rc set the compensation amount as follows:
vbias Vs × gm × Rc Vout × gm × Rc formula 6
Combining equation 5 and equation 6 yields:
(Vout/L) × Ron _ LS × Td ═ Vout × gm × Rc formula 7
The circuit parameters of the bias module can be obtained according to equation 7 as follows:
gm × Rc ═ Ron _ LS × Td/L equation 8
All the other parameters except the inductance L in the formula 8 are fixed parameters in the circuit and basically do not change, so that the compensation quantity of the bias module is basically equal to the variation quantity of the switch node voltage in the time delay period, and the optimal compensation effect can be provided for the switch node voltage regardless of the change of the direct current output voltage, so that the zero-crossing detection precision is improved, the circuit loss of the switch converter is reduced, and the system efficiency is improved.
Fig. 3 shows a schematic circuit diagram of a voltage sampling module in a zero-crossing detection circuit according to a first embodiment of the present invention. As shown in fig. 3, the voltage sampling module 201 includes a switching signal generating unit 211 and a sample-and-hold unit 212. The switching signal generating unit 211 is configured to generate switching signals Vk1 and Vk2 according to the switching control signal SW and the zero-crossing indication signal ZCD. The sample-and-hold unit 212 is configured to generate a sampling signal Vs according to the dc input voltage Vin under the control of the switching signals Vk1 and Vk 2.
Here, the switching signal generating unit 211 includes AND gates AND1 AND2, AND inverters INV1 AND INV 2. One input terminal of the AND gate AND1 is configured to receive the switching control signal SW, an input terminal of the inverter INV1 is configured to receive the zero crossing indication signal ZCD, an output terminal is connected to another input terminal of the AND gate AND1, AND an output terminal of the AND gate AND1 is configured to output the switching signal Vk 1. The inverter INV2 has an input terminal receiving the switching control signal SW, an output terminal connected to one input terminal of the AND gate AND2, another input terminal of the AND gate AND2 connected to the output terminal of the inverter INV1, AND an output terminal of the AND gate AND2 for outputting the switching signal Vk 2.
The sample-and-hold unit 212 includes switches K1 and K2, resistors R1 and R2, and capacitors C1 and C2. Switches K1 and K2 are sequentially connected between the dc input voltage Vin and ground, one end of a resistor R1 is connected to a common terminal of the switches K1 and K2, the other end of the resistor R1 is connected to one end of a capacitor C1, the other end of the capacitor C1 is grounded, one end of a resistor R2 is connected to a common terminal of the resistor R1 and the capacitor C1, the other end of the resistor R2 is connected to one end of the capacitor C2, the other end of the capacitor C2 is grounded, and the common terminal of the resistor R2 and the capacitor C2 is used for providing the sampling signal Vs. The on and off of the switches K1 and K2 are controlled by the switching signals Vk1 and Vk2, respectively.
When the switching converter operates in a continuous conduction mode, the inductor current of the inductor Lx does not cross zero all the time, the zero crossing indication signal ZCD is always at a low level, the voltage sampling module 201 turns on the switch K1 during the conduction period of the power transistor MD1, charges the capacitors C1 and C2 based on the dc input voltage Vin, turns on the switch K2 during the conduction period of the rectifier tube MD2, and discharges the capacitors C1 and C2, so that the sampling signal Vs equal to the dc output voltage Vout can be obtained.
When the switching converter operates in the discontinuous conduction mode, the voltage sampling module 201 turns on the switch K1 during the conduction period of the power tube MD1, charges the capacitors C1 and C2 based on the dc input voltage Vin, turns on the switch K2 during the conduction period of the rectifier tube MD2, discharges the capacitors C1 and C2, and simultaneously turns off the switches K1 and K2 during the turn-off period of both the power tube MD1 and the rectifier tube MD2, so as to obtain the sampling signal Vs equal to the dc output voltage Vout through the holding voltages of the capacitors C1 and C2.
Fig. 4 shows a schematic flow diagram of a zero-crossing detection method of a switching converter according to a second embodiment of the invention. The switching converter is for example the switching converter shown in fig. 2. The zero-crossing detection method comprises the following steps:
in step S01, a sampling signal equal to the dc output voltage is generated.
In step S02, a corresponding offset signal is generated based on the sampled signal.
In step S03, the superimposed signal of the signal to be detected and the bias signal is compared with a zero-crossing reference value to generate a zero-crossing indication signal.
The step S01 specifically includes sampling and holding the dc input voltage according to a switching control signal for controlling the on and off of the power transistor and the rectifier transistor and a zero-crossing indication signal to obtain the sampling signal. The method comprises the steps of conducting a first switch during the conduction period of a power tube, turning off a second switch, charging a first capacitor and a second capacitor based on direct-current input voltage, turning off the first switch during the conduction period of a rectifier tube, conducting the second switch, discharging the first capacitor and the second capacitor, turning off the first switch and the second switch during the turning-off period of the power tube and the rectifier tube, and keeping the voltage unchanged through the first capacitor and the second capacitor to obtain a sampling signal equal to the direct-current output voltage.
The step S02 specifically includes obtaining a corresponding bias current according to the sampling signal, and then converting the bias current into a voltage signal to generate the bias signal.
The step S03 specifically includes comparing the superimposed signal of the switch node voltage and the bias signal between the power transistor and the rectifier transistor with the zero-crossing reference value to determine whether the inductor current has dropped to zero, and providing a zero-crossing indication signal representing the determination result. When the superposed signal of the switch node voltage and the bias signal is greater than the zero-crossing reference value, providing an effective zero-crossing indication signal to indicate that the zero-crossing of the inductive current is detected; when the superimposed signal of the switch node voltage and the bias signal is less than/equal to the zero-crossing reference value, an invalid zero-crossing indication signal is provided to indicate that the inductor current has not crossed zero.
In summary, the zero-crossing detection circuit of the switching converter according to the embodiment of the present invention includes a voltage sampling module, a bias module, and a zero-crossing comparator, where the voltage sampling module is configured to generate a sampling signal equal to the dc output voltage, the bias module generates a corresponding bias signal according to the sampling signal, and the zero-crossing comparator compares a superimposed signal of a signal to be detected and the bias signal with a zero-crossing reference value, so as to obtain a zero-crossing indication signal. Compared with the prior art, the zero-crossing detection circuit provided by the embodiment of the invention generates a sampling signal equal to the DC output voltage in a simulation mode in a chip, and adaptively adjusts the compensation quantity of the offset module according to the sampling signal, so that the compensation quantity is basically equal to the variation quantity of the switch node voltage in the delay period, an optimal compensation effect can be provided for the switch node voltage regardless of the change of the DC output voltage, the influence of a zero-crossing comparator and subsequent logic control delay on the zero-crossing detection precision can be reduced in different application occasions, the zero-crossing detection precision is improved, the circuit loss of the switching converter is reduced, and the efficiency of the switching converter is improved.
In the above embodiment, although the switching converter with the buck topology is described with reference to fig. 2, it is understood that the zero crossing detection circuit 220 according to the embodiment of the present invention may also be used in switching converters with other topologies, including but not limited to buck, boost, buck-boost, forward, flyback, and the like topologies.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in the process, method, article, or apparatus that comprises the element.
While embodiments in accordance with the invention have been described above, these embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments described. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The invention is limited only by the claims and their full scope and equivalents.

Claims (13)

1. A zero-crossing detection circuit for providing a zero-crossing indication signal in accordance with a signal to be detected, the signal to be detected being responsive to an inductor current provided by an inductor, the inductor being charged when a power tube is on and a rectifier tube is off and being discharged to enable a follow current when the power tube is off, the power tube and rectifier tube being for converting a dc input voltage to a dc output voltage, wherein the zero-crossing detection circuit comprises:
the voltage sampling module is used for generating a sampling signal equal to the direct current output voltage;
the offset module is used for generating a corresponding offset signal according to the sampling signal; and
and the zero crossing comparator is used for comparing the superposed signal of the signal to be detected and the bias signal with a zero crossing reference value so as to judge whether the inductive current is reduced to zero or not and provide a zero crossing indication signal representing a judgment result.
2. A zero-crossing detection circuit as claimed in claim 1, wherein the voltage sampling module samples and holds the dc input voltage according to a switch control signal controlling the on and off of the power tube and the rectifying tube and the zero-crossing indication signal to obtain the sampling signal.
3. A zero-crossing detection circuit as claimed in claim 2, wherein the voltage sampling module comprises:
a switching signal generating unit for generating a first switching signal and a second switching signal according to the switching control signal and the zero-crossing indication signal; and
and the sampling and holding unit is used for generating the sampling signal according to the direct current input voltage under the control of the first switching signal and the second switching signal.
4. A zero-crossing detection circuit as claimed in claim 3, wherein the switching signal generation unit includes a first AND gate, a second AND gate, a first inverter and a second inverter,
wherein a first input end of the first and gate receives the switch control signal, an input end of the first inverter receives the zero-crossing indication signal, an output end of the first inverter is connected with a second input end of the first and gate, an output end of the second and gate outputs the first switch signal,
the input end of the second inverter receives the switch control signal, the output end of the second inverter is connected with the first input end of the second AND gate, the second input end of the second AND gate is connected with the output end of the first inverter, and the output end of the second AND gate outputs the second switch signal.
5. A zero-crossing detection circuit as claimed in claim 3, wherein the sample-and-hold unit comprises:
the first switch and the second switch are sequentially connected between the direct current input voltage and the ground;
a first resistor, a first end of which is connected to a common end of the first switch and the second switch;
the first end of the first capacitor is connected to the second end of the first resistor, and the second end of the first capacitor is grounded;
a first end of the second resistor is connected to a common end of the first resistor and the first capacitor; and
a second capacitor, the first end is connected to the second end of the second resistor, the second end is grounded,
the on and off of the first switch and the second switch are controlled by the first switch signal and the second switch signal respectively, and a common end of the second resistor and the second capacitor is used for providing the sampling signal.
6. A zero-crossing detection circuit as claimed in claim 4, wherein the first switch is turned on and the second switch is turned off during the conduction of the power transistor, the DC input voltage charges the first and second capacitors,
the first switch is turned off and the second switch is turned on during the on period of the rectifier tube, discharging the first capacitor and the second capacitor, and
the first switch and the second switch are turned off during the period that the power tube and the rectifying tube are turned off, and the sampling signal is kept unchanged.
7. A zero-crossing detection circuit as claimed in claim 1, wherein the biasing module comprises:
the transconductance amplifier is used for generating corresponding bias current according to the sampling signal; and
a bias resistor for converting the bias current into a voltage signal to generate the bias signal.
8. A switching converter, comprising:
the main circuit comprises a power tube and a rectifying tube, wherein the power tube and the rectifying tube are used for controlling the transmission of electric energy from an input end to an output end so as to generate direct-current output voltage according to direct-current input voltage;
a zero-crossing detection circuit as claimed in any one of claims 1-7; and
and the logic control circuit provides a switch control signal according to the zero-crossing indication signal so as to control the conduction and the disconnection of the power tube and the rectifying tube.
9. The switching converter of claim 8, the main circuit employing a topology selected from any one of: step-down, step-up, non-inverting step-up and step-down, forward, and flyback.
10. A zero-crossing detection method for generating a zero-crossing indication signal according to a signal to be detected, the signal to be detected being responsive to an inductor current provided by an inductor, the inductor being charged when a power tube is turned on, a rectifier tube being charged when the rectifier tube is turned off, and the rectifier tube being discharged when the power tube is turned on to realize a follow current, the power tube and the rectifier tube being configured to convert a dc input voltage to a dc output voltage, wherein the zero-crossing detection method comprises:
generating a sampling signal equal to the dc output voltage;
generating a corresponding bias signal according to the sampling signal; and
and comparing the superposed signal of the signal to be detected and the bias signal with a zero-crossing reference value to judge whether the inductive current is reduced to zero or not and providing a zero-crossing indication signal representing a judgment result.
11. A zero-crossing detection method as claimed in claim 10, wherein the generating a sampled signal equal to the dc output voltage comprises:
and sampling and holding the direct current input voltage according to a switch control signal for controlling the on and off of the power tube and the rectifying tube and the zero-crossing indication signal to obtain the sampling signal.
12. A zero-crossing detection method as claimed in claim 11, wherein the sampling and holding the dc input voltage according to the switching control signal controlling the on and off of the power tube and the rectifier tube and the zero-crossing indication signal to obtain the sampling signal comprises:
turning on a first switch, turning off a second switch, charging a first capacitor and a second capacitor based on the DC input voltage,
turning off the first switch, turning on the second switch, discharging the first capacitor and the second capacitor during the on period of the rectifier tube, and
and turning off the first switch and the second switch during the period that the power tube and the rectifying tube are turned off so that the sampling signal is kept unchanged.
13. A zero-crossing detection method as claimed in claim 10, wherein the generating a corresponding bias signal from the sampled signal comprises:
generating a corresponding bias current according to the sampling signal; and
converting the bias current to a voltage signal to generate the bias signal.
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