CN112311227A - Switch power supply and ringing elimination circuit and ringing elimination method thereof - Google Patents
Switch power supply and ringing elimination circuit and ringing elimination method thereof Download PDFInfo
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- CN112311227A CN112311227A CN201910705901.3A CN201910705901A CN112311227A CN 112311227 A CN112311227 A CN 112311227A CN 201910705901 A CN201910705901 A CN 201910705901A CN 112311227 A CN112311227 A CN 112311227A
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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
- 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
Abstract
The invention discloses a switching power supply, a ringing elimination circuit and a ringing elimination method thereof. The ringing cancellation circuit includes a voltage transfer circuit, a control circuit, and a ringing detection circuit. The voltage transmission circuit is used for providing a reference voltage to a conductive path of the switch node, the ringing detection circuit is connected with the switch node to obtain a switch voltage, and a ringing detection signal is obtained according to a switch control signal and the switch voltage, and the control circuit is used for switching on or switching off the conductive path according to the switch control signal and the ringing detection signal. When the ringing detection signal represents that the switching voltage is less than a preset value in the turn-off stage of each switching period of the power switching tube, the control circuit conducts the conductive path and provides the reference voltage to the switching node, so that high-frequency oscillation at the switching node is inhibited, ringing is reduced, unnecessary noise is reduced, and the efficiency and the reliability of the circuit are improved.
Description
Technical Field
The invention relates to the technical field of power electronics, in particular to a switching power supply, a ringing elimination circuit of the switching power supply and a ringing elimination method of the switching power supply.
Background
The switching power supply generally has two operation modes, i.e., a Continuous Conduction Mode (CCM) and a Discontinuous Conduction Mode (DCM). The difference between the two is that: in the continuous conduction mode, the switching signal controls the power switching tube to be conducted again when the inductor discharge is not completely finished; in the discontinuous conduction mode, the switching signal controls the power switch tube to be conducted after the inductor finishes discharging.
As shown in fig. 1, a conventional switching power supply circuit, a switching power supply 100 includes an inductor L1, a power switch M0, a freewheeling diode D1, and a control circuit 110. The inductor L1 and the power switch tube M0 are connected in series between the DC input voltage Vin and the ground, the anode of the freewheeling diode D1 is connected to the node between the inductor L1 and the power switch tube M0, and the cathode is connected to the DC output voltage Vout terminal. The control circuit 110 is configured to control the power switch M0 to turn on and off, so that the inductor L1 obtains a dc output voltage Vout according to the dc input voltage Vin.
In the discontinuous conduction mode, when the inductor L1 has been discharged and the power switch M0 is not conducting, the LC loop formed by the inductor L1 and the parasitic capacitance of the power switch M0 may generate a high frequency oscillation at the switch node SW between the inductor L1 and the power switch M0, as shown in fig. 2, the high frequency oscillation may form ringing in the circuit, generate electromagnetic interference in the system, affect the reliability of the system, and reduce the service life of the system.
Disclosure of Invention
In view of the above, an object of the present invention is to provide a switching power supply, a ringing cancellation circuit thereof, and a ringing cancellation method thereof, which can effectively reduce the peak in the switching voltage and improve the reliability of the circuit.
According to a first aspect of the present invention, there is provided a ringing cancellation circuit for a switching power supply, the switching power supply comprising a power switching tube and an inductor connected in series between an input voltage ground, a switching node between the power switching tube and the inductor providing an output voltage, wherein the ringing cancellation circuit comprises: a voltage transfer circuit for providing a reference voltage to a conductive path of the switch node; the ringing detection circuit is connected with the switch node to obtain a switch voltage, and a ringing detection signal is obtained according to a switch control signal and the switch voltage; and the control circuit is used for switching on or switching off the conductive path according to the switch control signal and the ringing detection signal, wherein in the switching-off stage of each switching cycle of the power switching tube, when the ringing detection signal indicates that the switching voltage is smaller than a preset value, the control circuit switches on the conductive path.
Preferably, the control circuit includes: a first driver for generating a first control signal according to the switching control signal; a second driver for generating a second control signal according to the ringing detection signal; the charging and discharging unit is used for charging or discharging a charging node according to the first control signal; and a reference capacitor having a first plate connected to the charging node and a second plate for receiving the second control signal, wherein the charging node is connected to the control terminal of the voltage transfer circuit to provide a switching signal, and the conductive path is turned on when the switching signal is active.
Preferably, the first control signal is active during a first time period of an off phase of each switching cycle, and the charging and discharging unit pulls up the charging node to a first voltage, and the second control signal is active during a second time period of the off phase of each switching cycle, and the charging node is continuously pulled up to a second voltage, so that the switching signal is active.
Preferably, the charge and discharge unit includes: a first transistor and a second transistor connected in series between the reference voltage and ground, control terminals of the first and second transistors being connected to each other to receive the first control signal, an intermediate node of the first and second transistors being connected to the charging node.
Preferably, the charge and discharge unit further includes: a third transistor connected between the second terminal of the first transistor and the charge node, the third transistor connected as a diode structure.
Preferably, the first transistor is a P-type field effect transistor, and the second transistor and the third transistor are N-type field effect transistors.
Preferably, the ringing detection circuit includes: a first voltage dividing resistor and a second voltage dividing resistor connected in series between the switching node and ground, wherein an intermediate node of the first voltage dividing resistor and the second voltage dividing resistor is used for providing a voltage feedback signal representing the switching voltage; the level conversion unit is used for obtaining a detection signal according to the voltage feedback signal; and the logic unit is used for obtaining the ringing detection signal according to the switch control signal and the detection signal.
Preferably, in the first time period, the voltage feedback signal is greater than or equal to a preset reference voltage, the level shift unit outputs the detection signal as a high level, and in the second time period, the voltage feedback signal is smaller than the preset reference voltage, and the level shift unit turns over to output the detection signal as a low level.
Preferably, the logic unit is implemented by a nor gate, and performs a nor operation on the logic values of the switch control signal and the detection signal to obtain the ringing detection signal.
Preferably, the voltage transfer circuit includes: a fourth transistor and a fifth transistor connected in series between the reference voltage and the switch node, control terminals of the fourth transistor and the fifth transistor being connected to each other to receive the switching signal, wherein when the switching signal is active, the fourth transistor and the fifth transistor are turned on to transfer the reference voltage to the switch node.
Preferably, the voltage transfer circuit further comprises: and the protection resistor is connected between the reference voltage and the first end of the fourth transistor.
Preferably, the fourth transistor and the fifth transistor are N-type field effect transistors.
Preferably, the drain-source voltage of the fifth transistor is greater than 5V.
Preferably, the reference voltage comprises a power supply, a positive supply voltage or a highest positive supply voltage.
According to a second aspect of the present invention, there is provided a ringing cancellation method for a switching power supply, the switching power supply comprising a power switching tube and an inductor connected in series between an input voltage ground, a switching node between the power switching tube and the inductor providing an output voltage, wherein the ringing cancellation method comprises: obtaining a switching voltage according to the switching node, and obtaining a ringing detection signal according to a switching control signal and the switching voltage; providing a conductive path from a reference voltage to the switch node; and switching on or switching off the conductive path according to the switch control signal and the ringing detection signal, wherein in the switching-off stage of each switching period of the power switch tube, when the ringing detection signal indicates that the switching voltage is less than a preset value, the conductive path is switched on.
Preferably, the turning on or off the conductive path according to the switch control signal and the ringing detection signal includes: generating a first control signal according to the switch control signal; generating a second control signal according to the ringing detection signal; charging or discharging a charging node according to the first control signal; and providing a reference capacitor, a first plate of the reference capacitor being connected to the charging node, a second plate of the reference capacitor being configured to receive the second control signal, wherein the charging node is configured to provide a switching signal, and the conductive path is conductive when the switching signal is active.
Preferably, the ringing elimination method further includes: the first control signal is active during a first time period of the off phase of each switching cycle, the charging node is pulled up to a first voltage, and the second control signal is active during a second time period of the off phase of each switching cycle, the charging node is continuously pulled up to a second voltage to enable the switching signal.
Preferably, the obtaining a ringing detection signal according to a switch control signal and the switch voltage includes: obtaining a voltage feedback signal for representing the switching voltage according to the switching voltage; carrying out level conversion on the voltage feedback signal to obtain a detection signal; and carrying out NOR operation on the logic values of the switch control signal and the detection signal to obtain the ringing detection signal.
Preferably, in the first time period, the voltage feedback signal is greater than or equal to a preset reference voltage, the detection signal is at a high level, and in the second time period, the voltage feedback signal is less than the preset reference voltage, and the detection signal is inverted to a low level.
Preferably, the reference voltage comprises a power supply, a positive supply voltage or a highest positive supply voltage.
According to a third aspect of the present invention, there is provided a switching power supply comprising: the power switch tube and the inductor are connected between an input voltage and the ground in series, and a switch node of the power switch tube and the inductor provides an output voltage; and the ringing cancellation circuit described above.
The embodiment of the invention provides a switching power supply, a ringing elimination circuit and a ringing elimination method thereof, and has the following beneficial effects.
The ringing cancellation circuit includes a voltage transfer circuit, a control circuit, and a ringing detection circuit. The voltage transmission circuit is used for providing a reference voltage to a conductive path of the switch node, the ringing detection circuit is connected with the switch node to obtain a switch voltage, and a ringing detection signal is obtained according to a switch control signal and the switch voltage, and the control circuit is used for switching on or switching off the conductive path according to the switch control signal and the ringing detection signal. When the ringing detection signal represents that the switching voltage is less than a preset value in the turn-off stage of each switching period of the power switching tube, the control circuit conducts the conductive path and provides the reference voltage to the switching node, so that high-frequency oscillation at the switching node is inhibited, ringing is reduced, unnecessary noise is reduced, and the efficiency and the reliability of the circuit are improved.
In addition, the ringing eliminating circuit can be integrated in the control chip, and no peripheral element is required to be added, thereby being beneficial to saving space and reducing cost.
Further, the N-type transistor M4 in the voltage transfer circuit is a low voltage device, and the N-type transistor M5 is a high voltage device. Through the combination of the high-voltage device and the low-voltage device, the voltage resistance of the circuit is improved, the circuit can be applied to the condition that the voltage at the switch node is high, and the low-voltage device in the circuit is prevented from being broken down when the voltage at the node is high.
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 circuit schematic of a switching power supply circuit according to the prior art.
Fig. 2 shows an operation waveform diagram of a switching power supply according to the related art.
Fig. 3 shows a circuit schematic of a switching power supply circuit according to a first embodiment of the present invention.
Fig. 4 shows a circuit schematic of the ring detection circuit of fig. 3.
Fig. 5 shows a circuit schematic of the control circuit of fig. 3.
FIG. 6 shows a circuit schematic of the voltage transfer circuit of FIG. 3.
Fig. 7 is a waveform diagram showing an operation of the switching power supply according to the first embodiment of the present invention.
Fig. 8 is a flowchart illustrating a ringing cancellation method of a switching power supply according to a second embodiment of the present 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, a "circuit" refers to a conductive loop formed by at least one element or sub-circuit through an 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.
Fig. 3 shows a circuit schematic of a switching power supply circuit according to a first embodiment of the present invention. The switching power supply adopts Boost topology. As shown in fig. 3, the switching power supply 200 includes an inductor L1, a power switch M0, and a freewheeling diode D1.
The inductor L1 and the power switch tube M0 are connected in series between the DC input voltage Vin and the ground, the anode of the freewheeling diode D1 is connected to the switch node between the inductor L1 and the power switch tube M0, and the cathode is connected to the DC output voltage Vout terminal. The switch control signal N _ ON is a logic signal for controlling the ON and off of the power switch M0, and the ON and off states of the power switch M0 can adjust the switching voltage Vsw of the switching node and the current flowing through the power switch M0. During the conduction period of the power switch tube M0, the dc input voltage Vin charges the inductor L1, and during the turn-off period of the power switch tube M0, the inductor L1 supplies power to the load.
Further, the switching power supply 200 further includes an output capacitor (not shown), which can stabilize and filter the output voltage Vout.
The switching power supply 200 further includes a ringing cancellation circuit 210, and the ringing cancellation circuit 210 includes a ringing detection circuit 211, a control circuit 212, and a voltage delivery circuit 213.
The ringing detection circuit 211 is configured to obtain a switching voltage Vsw according to a switching node SW between the inductor L1 and the power switch M0, and obtain a ringing detection signal Vnor according to the switching control signal N _ ON and the switching voltage Vsw.
The control circuit 212 is configured to obtain a switch signal G3 according to the switch control signal N _ ON and the ringing detection signal Vnor.
The voltage transmitting circuit 213 is used to provide a conductive path from a reference voltage value to the switch node SW. The voltage transfer circuit 213 is configured to turn on or off the conductive path according to a switching signal G3.
Further, in the turn-off phase of each switching cycle of the power switch M0, when the ringing detection signal indicates that the switching voltage Vsw is smaller than the predetermined value, the control circuit 212 turns on the conductive path to short-circuit the switching node SW with the reference voltage, thereby suppressing the high-frequency oscillation at the switching node SW, reducing the ringing, reducing the unnecessary noise, and improving the circuit efficiency and reliability.
The different level states of the switch control signal N _ ON represent the ON-phase and the off-phase of each switching cycle of the power switch transistor M0, respectively. For example, when the switch control signal N _ ON is "high", the power switch M0 is in the conducting phase; when the switch control signal N _ ON is "low", the power switch transistor M0 is in the off phase.
Fig. 4 shows a circuit schematic of the ring detection circuit of fig. 3. As a non-limiting example, the ringing detection circuit 211 includes voltage dividing resistors R1 and R2, a level shift unit 2112, and a logic unit 2113. Voltage dividing resistors R1 and R2 are connected in series between the switch node SW and ground, and the intermediate node between the voltage dividing resistors R1 and R2 is used to provide a voltage feedback signal VA indicative of the switch voltage. The level shifting unit 2112 is configured to perform level shifting according to the voltage feedback signal VA to obtain a detection signal VB of a logic signal. The logic unit 2113 is, for example, a nor gate, and is used for obtaining the ringing detection signal Vnor according to the switch control signal N _ ON and the detection signal VB.
Fig. 5 shows a circuit schematic of the control circuit of fig. 3. As a non-limiting example, the control circuit 212 includes a first driver 2121, a second driver 2122, a charge and discharge unit 2123, and a reference capacitor Cb. The first driver 2121 is configured to generate a first control signal G1 according to the switch control signal N _ ON. The second driver 2122 is configured to generate a second control signal G2 according to the ringing detection signal Vnor. The charging and discharging unit 2123 has a control terminal for receiving the first control signal G1, an output terminal connected to the first plate of the reference capacitor Cb, and a charging and discharging unit 2123 for performing a charging or discharging operation on the charging node according to the first control signal G1. The second plate of the reference capacitor Cb is arranged to receive the second control signal G2. The charging node is connected to the control terminal of the voltage transfer circuit 213 to provide a switch signal G3, and when the switch signal G3 is asserted, the conductive path of the voltage transfer circuit is turned on to provide the reference voltage to the switch node SW.
The charge/discharge unit 2123 includes a P-type transistor M1, an N-type transistor M3, and an N-type transistor M2 connected in series between the reference voltage VCC and ground. The control terminals of the P-type transistor M1 and the N-type transistor M2 are connected to each other to receive the first control signal, the first terminal of the P-type transistor M1 is connected to the reference voltage VCC, and the first terminal of the N-type transistor M2 is connected to the ground. An intermediate node between the N-type transistor M3 and the N-type transistor M2 is connected to the charging node. The N-type transistor M3 forms a diode structure to prevent the current of the charging node from flowing backward to the reference voltage VCC when the voltage of the charging node is greater than the reference voltage VCC.
In the present embodiment, when the first control signal G1 and the second control signal G2 are at "low level", the P-type transistor M1 is turned on, the reference voltage VCC charges the reference capacitor Cb, and the charging node is pulled up to the first voltage V1 — VCC. When the second control signal G2 changes to "high", the charging node is continuously pulled up to the second voltage V2 — 2 × VCC-Vgs. Where Vgs is the turn-on voltage of the N-type transistor M2.
FIG. 6 shows a circuit schematic of the voltage transfer circuit of FIG. 3. As shown in fig. 6, the voltage transfer circuit 213 includes a protection resistor R3, an N-type transistor M4, and an N-type transistor M5 connected in series. The control terminals of the N-type transistor M4 and the N-type transistor M5 are connected to receive the switching signal G3. When the charging node is pulled up to the second voltage, the switching signal G3 is asserted, and the N-type transistors M4 and M5 are turned on to supply the reference voltage VCC to the switching node SW, thereby suppressing high frequency oscillation at the switching node SW and reducing ringing. Further, the protection resistor R3 is an ESD protection resistor, and when ESD occurs, the protection resistor R3 functions as a current limiting and voltage reducing.
Further, the N-type transistor M4 is a low voltage device, and the N-type transistor M5 is a high voltage device. The N-type transistor M5 is connected to the second terminal of the switch node SW for withstanding high voltage. Furthermore, the drain-source voltage Vds of the N-type transistor M5 is greater than 5V (e.g., 12V, 24V, 40V, or 60V), which improves the voltage endurance of the circuit, and can be applied to the case where the voltage at the switch node SW is a high voltage, thereby avoiding the damage to the low-voltage device in the circuit when the voltage at the switch node SW is a high voltage.
Fig. 7 is a waveform diagram showing an operation of the switching power supply according to the first embodiment of the present invention. The operation principle of the switching power supply according to the first embodiment of the present invention in each switching cycle will be described in detail with reference to fig. 3 to 7.
In the time period T0, the switch control signal N _ ON is at "high level", and the power switch M0 is in the ON phase. The switching voltage Vsw is 0, the level conversion unit 2112 outputs a detection signal of "low level", the logic unit 2113 outputs a ringing detection signal of "low level" based on the switching control signal of high level and the detection signal of low level, and the second driver 2122 outputs the second control signal G2 of "low level" based on the ringing detection signal of low level. Meanwhile, the first driver 2121 outputs the first control signal G1 as "high" according to the high-level switch control signal, the N-type transistor M2 is turned on, and the node voltage is pulled down to ground. Therefore, the switch signal G3 is in an inactive state, the N-type transistors M4 and M5 are turned off, and the conductive path from the reference voltage VCC to the switch node SW is turned off.
In the period T1, the switch control signal N _ ON transits from "high level" to "low level", the first driver 2121 outputs the first control signal G1 as "low level" according to the low level switch control signal, the P-type transistor M1 is turned ON, and the node voltage is pulled up to the first voltage V1 as VCC-Vgs. At this time, the inductor current decreases, and the switching voltage Vsw becomes Vout + Vd. Vd is a voltage across the freewheeling diode D1. After the voltage division by the voltage dividing resistors R1 and R2, the voltage feedback signal VA is greater than the preset reference voltage (e.g., 30.3V), and the level shifting unit 2112 flips to output the detection signal VB as a "high level". The logic unit 2113 outputs the ring detection signal as "low level" according to the low level switch control signal and the high level detection signal, so that the second control signal is still at "low level" and the voltage on the second plate of the reference capacitor Cb is approximately equal to 0. The voltage at the charging node is still less than the turn-on thresholds of the N-type transistors M4 and M5, so the switch signal G3 is still inactive, the N-type transistors M4 and M5 are turned off, and the conduction path from the reference voltage VCC to the switch node SW is turned off.
In the time period T2, the inductor current drops to zero, the switching voltage Vsw starts oscillating, and when Vsw becomes smaller and is divided by the voltage dividing resistors R1 and R2, the voltage feedback signal VA is smaller than the preset reference voltage (e.g., 8V), and the level shifting unit 2112 inverts to output the detection signal VB as "low level". The logic unit 2113 outputs the ring detection signal as "high level" according to the low level switch control signal and the low level detection signal, so that the second control signal jumps to "high level", the voltage on the second plate of the reference capacitor Cb is approximately equal to the reference voltage VCC, so that the charging node is continuously pulled up to the second voltage V2-2 VCC-Vgs, the voltage of the charging node is greater than the turn-on threshold of the N-type transistors M4 and M5, the switch signal G3 is in an active state, the N-type transistors M4 and M5 are turned on, the reference voltage VCC is provided to the switch node SW, and the switch voltage Vsw is approximately equal to the reference voltage VCC, thereby suppressing the high frequency oscillation at the switch node SW and reducing the ring.
In the above embodiments, the power switch M0, the P-type transistor M1, and the N-type transistors M2-M5 are, for example, field-effect transistors (MOS field-effect transistors). The "control terminal", "first terminal", and "second terminal" in this embodiment are, for example, a "gate", "source", and "drain" of a field effect transistor.
It should be understood that the transistor in the above-described embodiments is realized by a field effect transistor, but the present invention is not limited thereto. In other embodiments of the present invention, the transistors of the above embodiments can also be implemented by a bipolar transistor, and the "control terminal", "first terminal", and "second terminal" in the embodiments are the "base", "emitter", and "collector" of the bipolar transistor, respectively.
In the above embodiments, the reference voltage VCC may be a power supply, a positive power supply voltage, or the highest positive power supply voltage, or the like.
Fig. 8 is a flowchart illustrating a ringing cancellation method of a switching power supply according to a second embodiment of the present invention. The switching power supply comprises an inductor L1, a power switch tube M0 and a freewheeling diode D1. The inductor L1 and the power switch tube M0 are connected in series between the DC input voltage Vin and the ground, the anode of the freewheeling diode D1 is connected to the switch node between the inductor L1 and the power switch tube M0, and the cathode is connected to the DC output voltage Vout terminal. The switch control signal N _ ON is a logic signal for controlling the ON and off of the power switch M0, and the ON and off states of the power switch M0 can adjust the switching voltage Vsw of the switching node and the current flowing through the power switch M0. During the conduction period of the power switch tube M0, the dc input voltage Vin charges the inductor L1, and during the turn-off period of the power switch tube M0, the inductor L1 supplies power to the load.
As shown in fig. 8, the ringing elimination method includes steps S310 to S320.
In step S310, a ringing detection signal is obtained according to the switching voltage and the switching control signal.
In step S320, a conductive path is provided from a reference voltage to the switch node.
In step S330, the conductive path is turned on or off according to the switch control signal and the ringing detection signal. Wherein, in the off phase of each switching cycle of the power switch tube, when the ringing detection signal indicates that the switching voltage is less than a predetermined value, the conductive path is conducted.
Further, the turning on or off the conductive path according to the switch control signal and the ringing detection signal includes: and generating a first control signal and a second control signal according to the switch control signal and the ringing detection signal respectively, charging or discharging a charging node according to the first control signal, and providing a reference capacitor, wherein a first polar plate of the reference capacitor is connected to the charging node, and a second polar plate is used for receiving the second control signal. Wherein the charging node is configured to provide a switching signal, and the conductive path is conducted when the switching signal is active.
Further, the obtaining a ringing detection signal according to a switch control signal and the switch voltage includes: and obtaining a voltage feedback signal for representing the switching voltage according to the switching voltage, then carrying out level conversion on the voltage feedback signal to obtain a detection signal with a logic value, and finally carrying out NOR operation on the logic values of the switching control signal and the detection signal to obtain the ringing detection signal.
In the present embodiment, when the first control signal G1 and the second control signal G2 are at "low level", the P-type transistor M1 is turned on, the reference voltage VCC charges the reference capacitor Cb, and the charging node is pulled up to the first voltage V1 — VCC. When the second control signal G2 changes to "high", the charging node is continuously pulled up to the second voltage V2 — 2 × VCC-Vgs. Where Vgs is the turn-on voltage of the N-type transistor M2.
In the first time period of the off phase of each switching cycle, the switching control signal changes from "high" to "low", the first control signal is "low", and the charging node is pulled up to the first voltage V1 ═ VCC-Vgs. At this time, the inductor current decreases, and the switching voltage Vsw becomes Vout + Vd. Vd is a voltage across the freewheeling diode D1. After the voltage is divided by the voltage dividing resistor, the voltage feedback signal is greater than a preset reference voltage (for example, 30.3V), and the detection signal is at a high level. And performing NOR calculation according to the switch control signal at low level and the detection signal at high level to obtain that the ringing detection signal is at "low level", so that the second control signal is also at "low level", and the voltage on the second plate of the reference capacitor is approximately equal to 0. The voltage of the charging node is less than the conduction threshold of the conductive path, so the switch signal is in an inactive state and the conductive path from the reference voltage VCC to the switch node SW is turned off.
In a second time period of the turn-off phase of each switching cycle, the inductor current drops to zero, the switching voltage Vsw gradually decreases, the voltage feedback signal is smaller than a preset reference voltage (for example, 8V) after being divided by the voltage dividing resistor, and the detection signal is at a "low level". And performing NOR calculation according to the low-level switch control signal and the low-level detection signal to obtain that the ringing detection signal is at a high level, so that the second control signal jumps to a high level, the voltage on the second plate of the reference capacitor is approximately equal to the reference voltage VCC, so that the charging node is continuously pulled up to the second voltage V2-2 VCC-Vgs, the voltage of the charging node is greater than the conduction threshold of the conduction path, the switch signal is in an active state, the reference voltage VCC is provided to the switch node SW, and the switch voltage Vsw is approximately equal to the reference voltage VCC, so that high-frequency oscillation at the switch node SW is inhibited, and ringing is reduced.
In summary, embodiments of the present invention provide a switching power supply, a ring elimination circuit thereof, and a ring elimination method thereof. The ringing cancellation circuit includes a voltage transfer circuit, a control circuit, and a ringing detection circuit. The voltage transmission circuit is used for providing a reference voltage to a conductive path of the switch node, the ringing detection circuit is connected with the switch node to obtain a switch voltage, and a ringing detection signal is obtained according to a switch control signal and the switch voltage, and the control circuit is used for switching on or switching off the conductive path according to the switch control signal and the ringing detection signal. When the ringing detection signal represents that the switching voltage is less than a preset value in the turn-off stage of each switching period of the power switching tube, the control circuit conducts the conductive path and provides the reference voltage to the switching node, so that high-frequency oscillation at the switching node is inhibited, ringing is reduced, unnecessary noise is reduced, and the efficiency and the reliability of the circuit are improved.
In addition, the ringing eliminating circuit can be integrated in the control chip, and no peripheral element is required to be added, thereby being beneficial to saving space and reducing cost.
Further, the N-type transistor M4 in the voltage transfer circuit is a low voltage device, and the N-type transistor M5 is a high voltage device. Through the combination of the high-voltage device and the low-voltage device, the voltage resistance of the circuit is improved, the circuit can be applied to the condition that the voltage at the switch node is high, and the low-voltage device in the circuit is prevented from being broken down when the voltage at the node is high.
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 a 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 (21)
1. A ringing cancellation circuit for a switching power supply, said switching power supply including a power switching tube and an inductor connected in series between an input voltage ground, a switching node between said power switching tube and said inductor providing an output voltage, said ringing cancellation circuit comprising:
a voltage transfer circuit for providing a reference voltage to a conductive path of the switch node;
the ringing detection circuit is connected with the switch node to obtain a switch voltage, and a ringing detection signal is obtained according to a switch control signal and the switch voltage;
a control circuit for turning on or off the conductive path according to the switch control signal and the ringing detection signal,
wherein, in the turn-off phase of each switching period of the power switch tube, when the ringing detection signal indicates that the switching voltage is less than a predetermined value, the control circuit turns on the conductive path.
2. The ring cancellation circuit of claim 1, wherein the control circuit comprises:
a first driver for generating a first control signal according to the switching control signal;
a second driver for generating a second control signal according to the ringing detection signal;
the charging and discharging unit is used for charging or discharging a charging node according to the first control signal;
a reference capacitor having a first plate coupled to the charging node and a second plate for receiving the second control signal,
wherein the charging node is coupled to a control terminal of the voltage delivery circuit to provide a switching signal, the conductive path being conductive when the switching signal is active.
3. The ring elimination circuit of claim 2, wherein the first control signal is asserted and the charge and discharge unit pulls the charge node up to a first voltage during a first time period of an off phase of each switching cycle,
during a second time period of the off phase of each switching cycle, the second control signal is active and the charging node continues to be pulled up to a second voltage to assert the switching signal.
4. The ring elimination circuit as recited in claim 2, wherein the charge and discharge unit comprises:
a first transistor and a second transistor connected in series between the reference voltage and ground,
control terminals of the first and second transistors are coupled to receive the first control signal,
the first transistor and the second transistor intermediate node are connected to the charging node.
5. The ring elimination circuit as recited in claim 4, wherein the charge and discharge unit further comprises:
a third transistor connected between the second terminal of the first transistor and the charge node, the third transistor connected as a diode structure.
6. The ring elimination circuit as recited in claim 5, wherein the first transistor is a P-type field effect transistor, and the second and third transistors are N-type field effect transistors.
7. The ring cancellation circuit of claim 3, wherein the ring detection circuit comprises:
a first voltage dividing resistor and a second voltage dividing resistor connected in series between the switching node and ground, wherein an intermediate node of the first voltage dividing resistor and the second voltage dividing resistor is used for providing a voltage feedback signal representing the switching voltage;
the level conversion unit is used for obtaining a detection signal according to the voltage feedback signal; and
and the logic unit is used for obtaining the ringing detection signal according to the switch control signal and the detection signal.
8. The ring elimination circuit as recited in claim 7, wherein, during the first period of time, the voltage feedback signal is greater than/equal to a preset reference voltage, the level conversion unit outputs the detection signal as a high level,
in the second time period, the voltage feedback signal is smaller than a preset reference voltage, and the level conversion unit is turned over to output the detection signal as a low level.
9. The ring elimination circuit as recited in claim 7, wherein the logic unit is implemented by a nor gate, and the logic values of the switch control signal and the detection signal are nor-operated to obtain the ring detection signal.
10. The ring cancellation circuit of claim 1, wherein the voltage delivery circuit comprises:
a fourth transistor and a fifth transistor connected in series between the reference voltage and the switch node,
control terminals of the fourth transistor and the fifth transistor are connected to each other to receive the switching signal,
when the switching signal is active, the fourth transistor and the fifth transistor are turned on to transmit the reference voltage to the switching node.
11. The ring cancellation circuit of claim 10, wherein the voltage delivery circuit further comprises:
and the protection resistor is connected between the reference voltage and the first end of the fourth transistor.
12. The ring elimination circuit as recited in claim 10, wherein the fourth transistor and the fifth transistor are N-type field effect transistors.
13. A ring elimination circuit as set forth in claim 10, wherein the drain-source voltage of the fifth transistor is greater than 5V.
14. The ring cancellation circuit of claim 1, wherein the reference voltage comprises a power supply, a positive supply voltage, or a highest positive supply voltage.
15. A ringing cancellation method for a switching power supply, said switching power supply comprising a power switching tube and an inductor connected in series between an input voltage ground, a switching node between said power switching tube and said inductor providing an output voltage, said ringing cancellation method comprising:
obtaining a switching voltage according to the switching node, and obtaining a ringing detection signal according to a switching control signal and the switching voltage;
providing a conductive path from a reference voltage to the switch node;
turning on or off the conductive path according to the switch control signal and the ringing detection signal,
wherein, in the off phase of each switching cycle of the power switch tube, when the ringing detection signal indicates that the switching voltage is less than a predetermined value, the conductive path is conducted.
16. The ring cancellation method according to claim 15, wherein said turning on or off the conductive path according to the switch control signal and the ring detection signal comprises:
generating a first control signal according to the switch control signal;
generating a second control signal according to the ringing detection signal;
charging or discharging a charging node according to the first control signal; and
providing a reference capacitor having a first plate connected to the charging node and a second plate for receiving the second control signal,
wherein the charging node is configured to provide a switching signal, and the conductive path is conductive when the switching signal is active.
17. A ring elimination method as set forth in claim 16, further comprising:
the first control signal is active, the charging node is pulled up to a first voltage during a first time period of an off phase of each switching cycle,
during a second time period of the off phase of each switching cycle, the second control signal is active and the charging node continues to be pulled up to a second voltage to assert the switching signal.
18. The ring elimination method as recited in claim 17, wherein said deriving a ring detection signal from a switch control signal and the switch voltage comprises:
obtaining a voltage feedback signal for representing the switching voltage according to the switching voltage;
carrying out level conversion on the voltage feedback signal to obtain a detection signal; and
and carrying out NOR operation on the logic values of the switch control signal and the detection signal to obtain the ringing detection signal.
19. The ring elimination method as set forth in claim 18,
in the first time period, the voltage feedback signal is greater than/equal to a preset reference voltage, the detection signal is at a high level,
and in the second time period, the voltage feedback signal is smaller than a preset reference voltage, and the detection signal is inverted to a low level.
20. A ring elimination method as recited in claim 15, wherein the reference voltage comprises a power supply, a positive supply voltage, or a highest positive supply voltage.
21. A switching power supply, comprising:
the power switch tube and the inductor are connected between an input voltage and the ground in series, and a switch node of the power switch tube and the inductor provides an output voltage; and a ring-down cancellation circuit as claimed in any one of claims 1 to 14.
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| CN114137886A (en) * | 2021-12-08 | 2022-03-04 | 杭州涂鸦信息技术有限公司 | Door magnet monitoring circuit, door magnet monitoring device and installation method thereof |
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