CN114389458A - Control circuit and switching converter using same - Google Patents

Control circuit and switching converter using same Download PDF

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Publication number
CN114389458A
CN114389458A CN202111680591.8A CN202111680591A CN114389458A CN 114389458 A CN114389458 A CN 114389458A CN 202111680591 A CN202111680591 A CN 202111680591A CN 114389458 A CN114389458 A CN 114389458A
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Prior art keywords
voltage
auxiliary
switching
tube
switching tube
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CN202111680591.8A
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Chinese (zh)
Inventor
陈佳滨
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Hangzhou Silergy Semiconductor Technology Ltd
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Hangzhou Silergy Semiconductor Technology Ltd
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Priority to CN202111680591.8A priority Critical patent/CN114389458A/en
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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
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/3353—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having at least two simultaneously operating switches on the input side, e.g. "double forward" or "double (switched) flyback" converter
    • 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
    • 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
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H02M1/34—Snubber circuits

Abstract

The application discloses a control circuit and a switching converter applying the same. According to the technical scheme of the embodiment of the invention, the auxiliary switching tube is controlled to be conducted for a preset time period before the main switching tube is conducted, and meanwhile, the conduction time of the auxiliary switching tube is adjusted according to the input voltage and the output voltage information of the switch converter, so that the main switching tube discharges the parasitic capacitor of the main switching tube through a discharge current before being conducted, zero voltage conduction is realized, and the conduction loss is effectively reduced.

Description

Control circuit and switching converter using same
Technical Field
The invention relates to the power electronic technology, in particular to a switching converter and a control circuit thereof.
Background
A switching converter is a power converter that stores energy in a magnetic element when a main power transistor is on and delivers the energy stored in the magnetic element to a load when the main power transistor is off. When the main power tube is turned off, resonance occurs between a magnetic element in the switching converter and the junction capacitance of the main power tube, so that conduction loss occurs when the main power tube is turned on again, and the power conversion efficiency is low. In order to reduce the conduction loss of the main power tube, the conduction of the main power tube is controlled by adopting a quasi-resonance mode in the prior art, namely the conduction is carried out when the drain-source voltage of the main power tube is reduced to the lowest point, so as to realize zero voltage switching-on. However, when the input voltage of the switching converter changes, the main power tube is difficult to realize zero voltage switching, thereby increasing the switching loss and reducing the system efficiency.
Disclosure of Invention
In view of this, embodiments of the present invention provide a switching converter and a control circuit thereof, which control an auxiliary switching tube to be turned on for a predetermined time period before a main power tube is turned on, so as to effectively reduce turn-on loss of the main switching tube and improve system efficiency.
According to a first aspect of the embodiments of the present invention, there is provided a control circuit of a switching converter, the switching converter including a main switching tube and an auxiliary switching tube, the control circuit including:
the zero voltage controller is configured to generate an auxiliary tube control signal according to input and output voltage information of the switching converter so as to control the auxiliary switching tube to be conducted for a first time period; and
and the primary side controller is configured to generate a main pipe control signal to control the main switching pipe to be conducted for a second time period.
Preferably, the reference ground of the zero-voltage controller is coupled to the common end of the magnetic element of the switching converter and the main switching tube, and the reference ground of the primary side controller is coupled to the reference ground of the switching converter.
Preferably, the reference ground of the zero-voltage controller and the reference ground of the primary side controller are the same.
Preferably, the zero voltage controller is integrated into a first control chip to generate the auxiliary pipe control signal, and the primary side controller is integrated into a second control chip to generate the main pipe control signal.
Preferably, the length of the first time period is controlled within a preset range so that the drain-source voltage of the main switching tube drops to zero after the first time period ends and before the second time period begins.
Preferably, before the auxiliary switch tube is turned on, the drain-source voltage of the main switch tube has at least one valley bottom.
Preferably, the length of the first time period has the same variation trend with the input voltage of the switching converter and has the opposite variation trend with the output voltage of the switching converter.
Preferably, the zero voltage controller includes:
an input configured to receive an input voltage of the switching converter;
an output configured to generate the auxiliary pipe control signal; and
a reference terminal coupled to a magnetic element of the switching converter and a common terminal of the main switching tube.
Preferably, the zero voltage controller includes:
an input terminal coupled to a magnetic element of the switching converter and a common terminal of the main switching tube;
an output configured to generate the auxiliary pipe control signal; and
a reference terminal coupled to a reference ground potential of the switching converter.
Preferably, during a switching cycle, the zero voltage controller is configured to sample a voltage at a common terminal of the magnetic element and the main switching tube to generate a first voltage, sample a maximum value of the voltage at the common terminal of the magnetic element and the main switching tube to generate a second voltage, and generate a third voltage by subtracting the second voltage from the first voltage, wherein the first voltage is indicative of an input voltage of the switching converter and the third voltage is indicative of an output voltage of the switching converter.
Preferably, the switching converter includes a transformer including a primary winding and an auxiliary winding, and the zero voltage controller includes:
an input terminal coupled to a common terminal of the auxiliary winding and the auxiliary switching tube;
an output configured to generate the auxiliary pipe control signal; and
a reference terminal coupled to a reference ground potential of the switching converter.
Preferably, in one switching cycle, the zero voltage controller is configured to sample the voltage at the common terminal of the auxiliary winding and the auxiliary switching tube to generate a fourth voltage, sample a maximum value of the voltage at the common terminal of the auxiliary winding and the auxiliary switching tube to generate a fifth voltage, and subtract the fifth voltage and the fourth voltage to generate a sixth voltage, wherein the fourth voltage is representative of the output voltage of the switching converter and the sixth voltage is representative of the input voltage of the switching converter.
Preferably, the switching converter operates in a current chopping mode.
According to a second aspect of the invention, a switching converter is provided. The switching converter includes:
any of the control circuits of the first aspect;
the power stage circuit comprises a main switching tube and a magnetic element; and
and the clamping circuit comprises an auxiliary switching tube.
Preferably, the clamping circuit is connected in series with the main switching tube, and includes an auxiliary switching tube and a clamping capacitor connected between the input end of the switching converter and the main switching tube.
Preferably, the clamping circuit is connected in parallel with the main switching tube, and comprises an auxiliary switching tube and a clamping capacitor which are connected in series between a first end and a second end of the main switching tube.
Preferably, the magnetic element is a transformer, the transformer includes a primary winding, at least one secondary winding, and an auxiliary winding, the clamping circuit is connected in parallel to two ends of the auxiliary winding, and includes an auxiliary switching tube and a clamping capacitor connected in series between a first end and a second end of the auxiliary winding.
According to the technical scheme of the embodiment of the invention, the auxiliary switching tube is controlled to be conducted for the preset time period before the main power tube is conducted, so that the main switching tube discharges the parasitic capacitance of the main switching tube through a discharge current before being conducted, zero voltage conduction is realized, the conduction loss is effectively reduced, and the system efficiency 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, in which:
fig. 1 is a circuit diagram of a switching converter according to a first embodiment of the present invention;
fig. 2 is a circuit diagram of a switching converter according to a second embodiment of the present invention;
fig. 3 is a circuit diagram of a switching converter according to a third embodiment of the present invention;
FIG. 4 is a schematic structural diagram of a zero voltage controller according to an embodiment of the present invention;
fig. 5 is a waveform diagram illustrating the operation of a switching converter according to an embodiment of the present invention.
Detailed Description
The present invention will be described below based on examples, but the present invention is not limited to only these examples. In the following detailed description of the present invention, certain specific details are set forth. It will be apparent to one skilled in the art that the present invention may be practiced without these specific details. Well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.
Further, those of ordinary skill in the art will appreciate that the drawings provided herein are for illustrative purposes and are not necessarily drawn to scale.
Meanwhile, it should be understood that, in the following description, a "circuit" refers to a conductive loop constituted by at least one element or sub-circuit through electrical or electromagnetic connection. When an element or circuit is referred to as being "connected to" another element or element/circuit is referred to as being "connected between" two nodes, it may be directly coupled or connected to the other element or intervening elements may be present, and the connection between the elements may be physical, logical, or a combination thereof. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, it is intended that there are no intervening elements present.
Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, what is meant is "including, but not limited to".
In the description of the present invention, it is to be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. In addition, in the description of the present invention, "a plurality" means two or more unless otherwise specified.
Fig. 1 is a circuit diagram of a switching converter according to a first embodiment of the present invention. The switching converter of the embodiment of the invention is a flyback switching converter, and comprises a power stage circuit, a clamping circuit 1 and a control circuit 10. The control circuit 10 includes a zero voltage controller 100 and a primary side controller 101. The power stage circuit comprises a transformer T, a main switching tube Sm connected with a primary winding of the transformer T in series, a follow current tube SR connected with a secondary winding of the transformer T in series and an output capacitor Co. As shown in fig. 1, a first terminal (e.g., a different-name terminal) of a primary winding of the transformer T receives an input voltage Vin, and a second terminal (e.g., a same-name terminal) of the primary winding of the transformer T is connected to a first terminal of a main switching tube Sm. The second terminal of the main switching tube Sm is coupled to the primary side reference ground. A first end (e.g., a dotted end) of the secondary winding of transformer T is connected to a first end of the follow current tube SR. An output capacitor Co is connected between the second terminal of the freewheeling tube SR and the second terminal (e.g., the synonym terminal) of the secondary winding of transformer T. A dc output voltage Vout is provided across the output capacitor Co. The clamping circuit 1 is connected in series with a main switching tube Sm of the transformer T, and includes an auxiliary switching tube Sa and a clamping capacitor Cc connected in series with the main switching tube Sm. By arranging the active clamping circuit, the withstand voltage of the switching tube can be reduced, and the ZVS range is expanded, so that the switching converter can be applied to a wide input voltage range. In this embodiment, the flyback switching converter further includes a secondary controller 103 for controlling the freewheeling tube SR. It should be understood that the freewheeling tube in the embodiment of the present invention may be replaced by a diode, and other electrically controlled switches may also be used to implement the above functions. In fig. 1, the primary winding of the transformer T may be equivalent to an excitation inductance Lm and a leakage inductance Lk connected in series, which are shown by dashed lines, respectively. According to various implementations, the input voltage Vin may be an unrectified alternating input voltage, such as 220V Alternating Current (AC), or may be a direct input voltage. The zero voltage controller 100 is configured to generate an auxiliary control signal V according to input and output voltage information of the switching converterSaThe primary side controller 101 is configured to generate a master control to control the auxiliary switching tube Sa to be turned on for a first period of timeSignal VSmSo as to control the main switch tube Sm to be conducted for the second time period. In this embodiment, the reference ground of the zero voltage controller 100 is the common terminal of the primary winding and the main switching tube Sm, and the reference ground of the primary side controller 101 is the reference ground of the switching converter.
In the present embodiment, the length of the first time period is within a preset range so that the drain-source voltage of the main switch tube Sm drops to zero after the end of the first time period and before the start of the second time period. Further, the drain-source voltage of the main switch tube Sm has at least one valley before the auxiliary switch tube Sa is turned on. For example, the switching converter operates in the quasi-resonant mode, and the zero voltage controller 100 controls the auxiliary switching tube Sa to start conducting by detecting the number of valleys of the drain-source voltage of the main switching tube Sm, and conducts for the first period of time.
In the present embodiment, before the main switching tube Sm is turned on, the zero voltage controller 100 controls the auxiliary switching tube Sa to be turned on for a predetermined time period, so that the clamp circuit starts to operate. During the conduction period of the auxiliary switching tube Sa, the clamping capacitor Cc reversely excites the primary winding Lm, after excitation is finished, the primary winding Lm continues current through the parasitic capacitor of the main switching tube Sm until the voltage on the parasitic capacitor of the main switching tube Sm is released, and meanwhile, the negative current flowing through the primary winding Lm drops to zero, at this time, the primary controller 102 controls the conduction of the main switching tube Sm, and the main switching tube Sm realizes zero-voltage switching-on, so that energy in the leakage inductance Lk is recovered to improve Electromagnetic Interference (EMI), and the voltages of two power ends of the main switching tube Sm when the main switching tube Sm is switched on are reduced, so that the switching-on loss is reduced.
In the present embodiment, the zero voltage controller 100 is integrated into the first control chip to generate the auxiliary control signal VSaThe primary controller 101 is integrated into the second control chip to generate the master control signal VSmAnd the reference ground potential of the first control wafer is the common end of the primary winding and the main switching tube Sm, and the reference ground potential of the second control wafer is the reference ground of the switching converter.
In a preferred embodiment, the zero voltage controller 100 samples the input voltage Vin and the output voltage Vout of the switching converter, and adjusts the on-time of the auxiliary switching tube Sa according to the input voltage and the output voltage information to control the on-time of the auxiliary switching tube Sa to be within a preset range, so that the drain-source voltage of the main switching tube Sm drops to zero after the auxiliary switching tube Sa is turned off and before the main switching tube Sm is turned on. Further, the on-time of the auxiliary switch tube Sa has the same trend with the input voltage Vin and the opposite trend with the output voltage Vout.
Further, the zero voltage controller 100 has an input end for receiving the sampling signal Vs (input voltage Vin) to obtain the input voltage and the output voltage information; the reference end is connected to the common end of the primary winding and the main switching tube Sm, and the common end is the reference ground potential of the zero voltage controller 100; and an output terminal for generating an auxiliary control signal VSaSo as to control the auxiliary switch tube Sa to be turned on or off. In the present embodiment, the zero voltage controller 100 may directly sample the input voltage Vin to obtain the input voltage information. Because the reference ground potential of the zero-voltage controller 100 is the common end of the primary winding and the main switching tube Sm, the zero-voltage controller 100 samples the input voltage Vin to obtain the voltage on the primary winding, so as to obtain the output voltage information according to the voltage on the primary winding.
Further, the zero voltage controller 100 controls the on time of the auxiliary switching tube Sa to be within a preset range so that the drain-source voltage of the main switching tube Sm drops to zero after the auxiliary switching tube Sa is turned off and before the main switching tube Sm is turned on.
In the present embodiment, the switching converter operates in the current interruption mode, and the zero voltage controller 100 controls the auxiliary switching tube Sa to be turned on for a predetermined time period before the main switching tube Sm is turned on, so as to realize the zero voltage turning on.
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 control signal to control the switching tube to be switched on and off.
Different from the control mode of the switch converter in the prior art, the switch converter in the embodiment of the invention controls the auxiliary switch tube Sa to be conducted for a preset time period before the main switch tube Sm is conducted, and simultaneously regulates the conduction time of the auxiliary switch tube Sa according to the input voltage and the output voltage information of the switch converter, so that the main switch tube discharges the parasitic capacitor of the main switch tube before being conducted through a discharge current, zero-voltage conduction is realized, and the conduction loss is effectively reduced.
Fig. 2 is a circuit diagram of a switching converter according to a second embodiment of the present invention. As shown in fig. 2, the switching converter according to the embodiment of the present invention is a flyback switching converter, and includes a power stage circuit, a clamp circuit 1, and a control circuit. The control circuit includes a zero voltage controller 100 and a primary side controller 101. The power stage circuit, the primary side controller 101, the secondary side controller 103 and the control method of the switching converter are substantially the same as those of the switching converter of the first embodiment, and detailed description thereof is omitted. In contrast, the clamping circuit 1 is connected in parallel with the main switching tube Sm, and includes an auxiliary switching tube Sa and a clamping capacitor Cc connected in series between a first end and a second end of the main switching tube Sm. In this embodiment, the reference ground of the zero voltage controller 100 and the primary side controller 101 are the same.
In this embodiment, the zero voltage controller 100 includes an input end connected to the common end of the primary winding and the main switching tube Sm for sampling the input voltage and the output voltage information of the switching converter; an output terminal for generating an auxiliary control signal VSaThe auxiliary switching tube Sa is controlled to be switched on or switched off; and a reference terminal connected to a reference ground of the switching converter.
In a preferred embodiment, the zvs controller 100 generates a first voltage by sampling and holding the voltages of the primary winding and the common terminal of the main switching tube Sm during a switching cycle, wherein the first voltage is representative of the input voltage information, according to the principle of volt-second balance on the primary winding. The zero voltage controller 100 generates a second voltage by sampling and holding the maximum value of the voltages on the primary winding and the common terminal of the main switching tube Sm in one switching period, and generates a third voltage by subtracting the second voltage from the first voltage, wherein the third voltage represents the output voltage information.
Fig. 3 is a circuit diagram of a switching converter according to a third embodiment of the present invention. As shown in fig. 3, the switching converter according to the embodiment of the present invention is a flyback switching converter, and includes a power stage circuit, a clamp circuit 1, and a control circuit. The control circuit includes a zero voltage controller 100 and a primary side controller 101. In this embodiment, the transformer includes an auxiliary winding. The auxiliary winding is coupled to the primary winding of the transformer. The power stage circuit, the primary side controller 101, the secondary side controller 103 and the control method of the switching converter are substantially the same as those of the switching converter of the first embodiment, and detailed description thereof is omitted. In contrast, the clamping circuit 1 is connected in parallel across the auxiliary winding and includes an auxiliary switching tube Sa and a clamping capacitor Cc connected in series between a first end and a second end of the auxiliary winding. In this embodiment, the reference ground of the zero voltage controller 100 and the primary side controller 101 are the same.
In the present embodiment, the zero voltage controller 100 includes an input terminal connected to the common terminal of the auxiliary winding and the auxiliary switching tube Sa for sampling the input voltage and the output voltage information of the switching converter; an output terminal for generating an auxiliary tube driving signal VSaThe auxiliary switching tube Sa is controlled to be switched on or switched off; and a reference terminal connected to the primary side reference ground of the switching converter.
In a preferred embodiment, since the auxiliary winding is coupled to the primary winding, the zvs 100 generates a fourth voltage by sampling and holding the voltages of the auxiliary winding and the common terminal of the auxiliary switching tube Sa during a switching period, wherein the fourth voltage is indicative of the output voltage information. The zero voltage controller 100 generates a fifth voltage by sampling and holding the maximum value of the voltages at the auxiliary winding and the common terminal of the auxiliary switching tube Sa in one switching period, and generates a sixth voltage by subtracting the fifth voltage from the fourth voltage, wherein the sixth voltage represents the input voltage information.
It should be understood that in the above embodiment, since the connection mode of the clamp circuit 1 in the switching converter is changed, the sampling point of the zero voltage controller needs to be adaptively adjusted accordingly. In addition, the switching converter in the embodiment of the present invention may also be other switching converters such as a Buck converter and a Boost converter, and is not limited to the flyback switching converter. In the above embodiments, the magnetic elements are all transformers, and in other embodiments, the magnetic elements may be inductors or the like.
Fig. 4 is a schematic structural diagram of a zero voltage controller according to an embodiment of the present invention. The zero voltage controller 100 includes a detection circuit 41 and a control signal generation circuit 42. The detection circuit 41 is configured to receive the sampling signal Vs to generate an input sampling signal SVin representing input voltage information and an output sampling signal SVout representing output voltage information. The control signal generating circuit 42 is configured to generate the auxiliary control signal V according to the input sampling signal SVin and the output sampling signal SVoutSaThe on-time of the auxiliary switching tube Sa is adjusted, so that the main switching tube discharges the parasitic capacitance of the main switching tube through a discharge current before the main switching tube is turned on, zero voltage switching-on is achieved, and switching-on loss is effectively reduced. The zero voltage controller 100 adjusts the length of the on time of the auxiliary switch tube Sa according to the input sampling signal SVin and the output sampling signal SVout, that is, the auxiliary tube control signal VSaIs used to measure the effective length of (a). In the auxiliary control signal VSaWhen the auxiliary switch tube Sa is active, the zero voltage controller 100 controls the auxiliary switch tube Sa to be turned on.
In a preferred embodiment, the flyback converter in this embodiment operates in a Discontinuous Conduction Mode (DCM) and adopts a Quasi-Resonant (QR) control manner. The zero voltage controller 100 generates a valley detection signal Vring according to the sampling signal Vs to control the auxiliary switching tube Sa to be turned on when the drain-source voltage of the main switching tube is reduced to the valley, so that the switching loss of the auxiliary switching tube Sa is reduced, and the working efficiency of the flyback converter is further improved. In this embodiment, before the auxiliary switch Sa starts to be turned on, the drain-source voltage of the main switch has at least one valley. Taking the flyback converter in fig. 1 as an example, the detection circuit 41 can obtain the trough detection signal Vring according to the sampling signal Vs, that is, the input voltage Vin, and the control signal generation circuit 42 generates the effective auxiliary tube control signal V according to the trough detection signal VringSaSo as to control the auxiliary switch tube Sa to conduct.
The control signal generating circuit 42 sets the length of the conducting time of the auxiliary switch tube Sa within a preset range according to the information of the input voltage Vin and the output voltage Vout, that is, the auxiliary tube control signal VSaIs used to measure the effective length of (a). For example, the length of the on-time of the auxiliary switch tube Sa may be set to be within a preset range (t0-th1, t0+ th2), where th1 and th2 are time thresholds, which may be equal or unequal, and the on-time t0 may be set according to the type and operation principle of the switching converter, so that the on-time of the auxiliary switch tube Sa is located near time t0, so that the drain-source voltage of the main switch tube Sm drops to zero after the auxiliary switch tube Sa is turned off and before the main switch tube Sm is turned on.
Taking the flyback converter as an example in this embodiment, the time t0 can be expressed as follows:
Figure BDA0003432434900000091
wherein, K1 is a proportional parameter, and is related to the equivalent inductance of the transformer, the junction capacitance between the secondary reference ground and the follow current tube, etc., N is the transformation ratio of the transformer, SVin is the input sampling signal, and SVout is the output sampling signal.
In this embodiment, the on-time of the auxiliary switch tube Sa (auxiliary tube control signal V)SaEffective length of) can be directly set according to formula (1), the on time of the auxiliary switching tube Sa can be slightly less than or greater than time t0, and can be specifically adjusted according to time thresholds th1 and th 2.
Fig. 5 is a waveform diagram illustrating the operation of a switching converter according to an embodiment of the present invention. In this embodiment, taking the flyback converter in fig. 1 as an example, the drain terminal voltage Vdrain of the main switch tube Sm and the voltage V on the primary windingbus-drainMaster control signal VSmAnd auxiliary pipe control signal VSaShown in sequence from top to bottom. As shown in FIG. 5, at time t1, master control signal VSmEffectively, the main switch tube Sm is changed into a conducting state from a turn-off state, and the primary side current IPAnd gradually increases, the primary winding begins to store energy. At time t2, master control signal VSmWhen the main switch tube Sm is invalid, the main switch tube Sm is switched from the on state to the off state, the main switch tube Sm is switched off, and the primary side current IPAnd the voltage Vdrain of the main switch tube Sm is gradually increased relative to the input voltage Vin. At time t3, voltage V on the primary windingbus-drainA wave trough appears, namely the drain-source voltage of the main switch tube Sm is in the wave trough, and the auxiliary tube control signal VSaEffectively, the auxiliary switch tube Sa is turned on. Primary side current I during the on period of the auxiliary switch tube SaPThe reverse increase accelerates the discharge speed of the junction capacitor of the main switching tube Sm, so that the resonance between the leakage inductance and the junction capacitor of the main switching tube Sm can be reduced to zero (the resonance can be considered to be zero when the leakage inductance is close to or close to zero). At time t4, the auxiliary switch Sa is turned on for a predetermined period of time, and the auxiliary tube control signal VSaThe auxiliary switching tube Sa is turned off when the active switch is switched to the inactive switch. At time t5, the primary current IPReducing to zero, the drain end voltage Vdrain of the main switch tube Sm resonates to zero, and the main tube controls the signal VSmEffectively, the main switch tube Sm is changed into a conducting state from a turn-off state, and a new working cycle is started.
According to the technical scheme of the embodiment of the invention, the auxiliary switching tube Sa is controlled to be conducted for the preset time period before the main switching tube Sm is conducted, and meanwhile, the conduction time of the auxiliary switching tube Sa is adjusted according to the input voltage and the output voltage information of the switch converter, so that the main switching tube discharges the parasitic capacitor of the main switching tube Sa through a discharge current before being conducted, zero-voltage conduction is realized, and the conduction loss is effectively reduced.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (17)

1. A control circuit for a switching converter, the switching converter including a main switching transistor and an auxiliary switching transistor, the control circuit comprising:
the zero voltage controller is configured to generate an auxiliary tube control signal according to input and output voltage information of the switching converter so as to control the auxiliary switching tube to be conducted for a first time period; and
and the primary side controller is configured to generate a main pipe control signal to control the main switching pipe to be conducted for a second time period.
2. The control circuit of claim 1, wherein the reference ground of the zero voltage controller is coupled to a common terminal of the magnetic element of the switching converter and the main switching tube, and the reference ground of the primary side controller is coupled to the reference ground of the switching converter.
3. The control circuit of claim 1, wherein the reference ground of the zero voltage controller and the reference ground of the primary side controller are the same.
4. The control circuit of claim 1, wherein the zero voltage controller is integrated into a first control die to generate the auxiliary pipe control signal and the primary side controller is integrated into a second control die to generate the main pipe control signal.
5. The control circuit of claim 1, wherein the length of the first time period is controlled to be within a preset range so that the drain-source voltage of the main switching tube decreases to zero after the end of the first time period and before the beginning of the second time period.
6. The control circuit of claim 1, wherein the drain-source voltage of the main switch tube has at least one valley before the auxiliary switch tube is turned on.
7. The control circuit of claim 1, wherein the length of the first time period has the same trend of change as the input voltage of the switching converter and an opposite trend of change as the output voltage of the switching converter.
8. The control circuit of claim 1, wherein the zero voltage controller comprises:
an input configured to receive an input voltage of the switching converter;
an output configured to generate the auxiliary pipe control signal; and
a reference terminal coupled to a magnetic element of the switching converter and a common terminal of the main switching tube.
9. The control circuit of claim 1, wherein the zero voltage controller comprises:
an input terminal coupled to a magnetic element of the switching converter and a common terminal of the main switching tube;
an output configured to generate the auxiliary pipe control signal; and
a reference terminal coupled to a reference ground potential of the switching converter.
10. The control circuit of claim 9, wherein the zero voltage controller is configured to sample a voltage at the common terminal of the magnetic element and the main switching tube to generate a first voltage, sample a maximum value of the voltage at the common terminal of the magnetic element and the main switching tube to generate a second voltage, and subtract the second voltage from the first voltage to generate a third voltage, wherein the first voltage is indicative of an input voltage of the switching converter and the third voltage is indicative of an output voltage of the switching converter, during a switching cycle.
11. The control circuit of claim 1, wherein the switching converter comprises a transformer including a primary winding and an auxiliary winding, and wherein the zero voltage controller comprises:
an input terminal coupled to a common terminal of the auxiliary winding and the auxiliary switching tube;
an output configured to generate the auxiliary pipe control signal; and
a reference terminal coupled to a reference ground potential of the switching converter.
12. The control circuit of claim 11 wherein, during a switching cycle, the zero voltage controller is configured to sample the voltage at the common terminal of the auxiliary winding and the auxiliary switching tube to produce a fourth voltage, sample a maximum value of the voltage at the common terminal of the auxiliary winding and the auxiliary switching tube to produce a fifth voltage, and subtract the fifth voltage and the fourth voltage to produce a sixth voltage, wherein the fourth voltage is representative of the output voltage of the switching converter and the sixth voltage is representative of the input voltage of the switching converter.
13. The control circuit of claim 1, wherein the switching converter operates in a current chopping mode.
14. A switching converter, comprising:
the control circuit of any of claims 1-13; and
the power stage circuit comprises a main switching tube and a magnetic element; and
and the clamping circuit comprises an auxiliary switching tube.
15. The switching converter according to claim 14, wherein said clamping circuit is connected in series with said main switching transistor and includes an auxiliary switching transistor and a clamping capacitor connected between said switching converter input and said main switching transistor.
16. The switching converter of claim 14, wherein said clamping circuit is coupled in parallel with said main switching tube and includes an auxiliary switching tube and a clamping capacitor coupled in series between a first terminal and a second terminal of said main switching tube.
17. The switching converter according to claim 14, wherein said magnetic element is a transformer, said transformer includes a primary winding, at least one secondary winding, and an auxiliary winding, said clamping circuit is connected in parallel across said auxiliary winding, and includes an auxiliary switching tube and a clamping capacitor connected in series between a first end and a second end of said auxiliary winding.
CN202111680591.8A 2021-12-24 2021-12-24 Control circuit and switching converter using same Pending CN114389458A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115833610A (en) * 2023-02-09 2023-03-21 恩赛半导体(成都)有限公司 Power supply conversion circuit and electronic device

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115833610A (en) * 2023-02-09 2023-03-21 恩赛半导体(成都)有限公司 Power supply conversion circuit and electronic device

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