CN115296544A - Flyback power converter based on primary side feedback - Google Patents

Flyback power converter based on primary side feedback Download PDF

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Publication number
CN115296544A
CN115296544A CN202210873071.7A CN202210873071A CN115296544A CN 115296544 A CN115296544 A CN 115296544A CN 202210873071 A CN202210873071 A CN 202210873071A CN 115296544 A CN115296544 A CN 115296544A
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China
Prior art keywords
switch
electrode
primary
bipolar junction
switching tube
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CN202210873071.7A
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Chinese (zh)
Inventor
张秀红
方烈义
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On Bright Electronics Shanghai Co Ltd
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On Bright Electronics Shanghai Co Ltd
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Priority to CN202210873071.7A priority Critical patent/CN115296544A/en
Priority to TW111137378A priority patent/TWI832463B/en
Publication of CN115296544A publication Critical patent/CN115296544A/en
Pending legal-status Critical Current

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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
    • H02M1/0003—Details of control, feedback or regulation circuits
    • 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
    • H02M1/0048—Circuits or arrangements for reducing losses
    • H02M1/0054—Transistor switching losses
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • 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
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without possibility of reversal 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
    • H02M7/217—Conversion of ac power input into dc power output without possibility of reversal 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
    • H02M7/219—Conversion of ac power input into dc power output without possibility of reversal 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 in a bridge configuration
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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

Abstract

The flyback power converter based on primary side feedback comprises a transformer, a power switch tube, a bipolar junction transistor, a first current source, a switch, a first switch tube, a second switch tube and a switch control circuit. A first electrode of the first switching tube is connected to a first output end of the switch control circuit, a second electrode of the first switching tube is connected to a first electrode of the power switching tube, and a third electrode of the first switching tube is connected to a base electrode of the bipolar junction transistor; a first electrode of the second switching tube is connected to a second output end of the switch control circuit, a second electrode of the second switching tube is connected to a base electrode of the bipolar junction transistor, and a third electrode of the second switching tube is grounded; a first electrode of the switch is connected to a first current source, and a second electrode of the switch is connected to a base electrode of the bipolar junction transistor; the first electrode of the power switch tube is connected to the second electrode of the first switch tube and the fourth output end of the switch control circuit, the second electrode of the power switch tube is connected to the primary winding of the transformer, and the third electrode of the power switch tube is connected to the bus voltage or the primary winding of the transformer through the starting resistor.

Description

Flyback power converter based on primary side feedback
Technical Field
The invention relates to the field of circuits, in particular to a flyback power converter based on primary side feedback.
Background
In the field of medium and small power converters, a flyback power converter based on primary side feedback occupies an absolute leading position of an application market by the advantages of simple circuit, small space volume, low system cost, high conversion efficiency and the like. In recent years, energy saving and environmental protection are well known, a lower standby power consumption technology is emphasized by consumers, and a Bipolar Junction Transistor (BJT) is widely used in a low power market of 10W or less due to its excellent switching characteristics and low price advantage.
With the increasing functions of mobile devices such as mobile phones and tablet computers, the capacity of batteries for supplying power to the mobile devices is increased explosively, and the output power of chargers or adapters for supplying power to the mobile devices is increasing continuously, which has been developed from 5W to 10W to 20W, 30W, 45W, 65W or even higher. How to improve the overall system efficiency and power density of the power converter on the basis of low cost and low standby power consumption makes the power converter meet the development requirement of miniaturization of a charger or an adapter and meet the increasingly stringent power energy efficiency standard, and becomes the key point of current research.
Disclosure of Invention
According to the flyback power converter based on the primary side feedback of the embodiment of the invention, including transformer, power switch tube, bipolar junction transistor, first current source, switch, first and second switch tube and switch control circuit, wherein: the first electrode of the first switching tube is connected to the first output end of the switch control circuit, the second electrode of the first switching tube is connected to the first electrode of the power switching tube, and the third electrode of the first switching tube is connected to the base electrode of the bipolar junction transistor; a first electrode of the second switching tube is connected to a second output end of the switch control circuit, a second electrode of the second switching tube is connected to a base electrode of the bipolar junction transistor, and a third electrode of the second switching tube is grounded; the first electrode of the switch is connected to the first current source, and the second electrode of the switch is connected to the base electrode of the bipolar junction transistor; a first electrode of the power switch tube is connected to a second electrode of the first switch tube and a fourth output end of the switch control circuit, a second electrode of the power switch tube is connected to a primary winding of the transformer, and a third electrode of the power switch tube is connected to a second current source or a third output end of the switch control circuit and is connected to a bus voltage or the primary winding of the transformer through a starting resistor; the collector of the bipolar junction transistor is connected to the primary winding of the transformer, the base of the bipolar junction transistor is connected to the second electrode of the switch, the third electrode of the first switching tube, the second electrode of the second switching tube and the emitter of the bipolar junction transistor are grounded through the current sensing resistor.
Drawings
The invention may be better understood from the following description of specific embodiments thereof taken in conjunction with the accompanying drawings, in which:
fig. 1A shows an exemplary circuit diagram of a flyback power converter based on primary-side feedback according to a first embodiment of the present invention.
Fig. 1B shows another exemplary circuit diagram of a flyback power converter based on primary-side feedback according to a first embodiment of the present invention.
Fig. 2 is a waveform diagram illustrating the operation of a plurality of signals in the flyback power converter based on primary side feedback shown in fig. 1A/1B.
Fig. 3A shows an exemplary circuit diagram of a flyback power converter based on primary-side feedback according to a second embodiment of the present invention.
Fig. 3B shows another exemplary circuit diagram of a flyback power converter based on primary-side feedback according to a second embodiment of the present invention.
Fig. 4 is a waveform diagram illustrating the operation of a plurality of signals in the flyback power converter based on primary-side feedback shown in fig. 3A/3B.
Fig. 5 shows an exemplary block diagram of a control chip in the flyback power converter based on primary-side feedback shown in fig. 1A/1B.
Fig. 6 is a block diagram of an example of a control chip in the flyback power converter based on primary-side feedback shown in fig. 3A/3B.
Fig. 7 shows a schematic diagram of an example implementation of the circuit parts related to the switches and the first current source in the flyback power converter based on primary side feedback shown in fig. 1A/1B and fig. 3A/3B.
Fig. 8A is a schematic diagram of an exemplary package of a power switch and a bjt in the flyback power converter based on primary-side feedback shown in fig. 1A/1B.
Fig. 8B is a schematic diagram of an exemplary package of a power switch and a bjt in the flyback power converter based on primary-side feedback shown in fig. 3A/3B.
Fig. 9A is a schematic diagram of an exemplary package of the power switch tube and the bjt and the control chip in the flyback power converter based on primary-side feedback shown in fig. 1A/1B.
Fig. 9B is a schematic diagram of an exemplary package of the power switch tube and the bjt and the control chip in the flyback power converter based on primary-side feedback shown in fig. 3A/3B.
Detailed Description
Features and exemplary embodiments of various aspects of the present invention will be described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is in no way limited to any specific configuration set forth below, but rather covers any modification, substitution, and improvement of elements and components without departing from the spirit of the invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the present invention. Note that, the term "a and B are connected" as used herein may mean "a and B are directly connected" or "a and B are indirectly connected via one or more other elements".
The major reason why bjts are currently only available in the low power market is that the turn-on of bjts is current driven and there must be enough drive current to turn on bjts. In addition, bipolar junction transistors have large driving losses, large turn-on losses, and slow turn-off speeds, which also limit their use in higher power markets.
In view of the above situation, a primary-side feedback-based flyback power converter according to an embodiment of the present invention is proposed, in which a plurality of switching tubes are used to drive a bjt so as to reduce the driving current loss of the bjt, increase the turn-on speed and/or turn-off speed of the bjt, and/or reduce the turn-off loss of the bjt.
Fig. 1A shows an exemplary circuit diagram of a flyback power converter 100A based on primary-side feedback according to a first embodiment of the present invention. As shown in fig. 1A, a flyback power converter 100A based on primary-side feedback includes a transformer T, a power switch Q1, a bjt Q2, and a first current source I SB1 Switch S, first and second switching tubes M1 and M2, and switch control circuit 102, wherein: a first electrode of the first switching tube M1 is connected to a first output end of the switch control circuit 102, a second electrode is connected to a source electrode of the power switching tube Q1, and a third electrode is connected to a base electrode of the bipolar junction transistor Q2; a first electrode of the second switching tube M2 is connected to the second output terminal of the switch control circuit 102, a second electrode is connected to the base electrode of the bipolar junction transistor Q2, and a third electrode is grounded; a first electrode of the switch S is connected to a first current source I SB1 The second electrode is connected to the base electrode of the bipolar junction transistor Q2; the drain of the power switch tube Q1 is connected to the primary winding of the transformer T, the gate is connected to the third output terminal of the switch control circuit 102 and to the bus voltage via the starting resistor Rst, and the source is connected to the second electrode of the first switch tube M1 and the fourth output terminal of the switch control circuit 102; the collector of the bjt Q2 is connected to the primary winding of the transformer T, the base is connected to the second electrode of the switch S, the third electrode of the first switching tube M1, and the second electrode and the emitter of the second switching tube M2 are grounded via the current sensing resistor Rs. Here, the first current source I SB1 The switch S, the first and second switching tubes M1 and M2, and the switch control circuit 102 may be included in the control chip U1A.
Fig. 1B shows an exemplary circuit diagram of a flyback power converter 100B based on primary-side feedback according to the first embodiment of the present invention. The primary-side feedback-based flyback power converter 100B shown in fig. 1B is mainly different from the primary-side feedback-based flyback power converter 100A shown in fig. 1A in structure in that the gate of the power switch Q1 is connected to the primary winding of the transformer T (i.e., connected to the drain of the power switch Q1 and the collector of the bjt Q2) via the starting resistor Rst, and connection relationships of other parts are the same as those of the corresponding parts shown in fig. 1A, and are not described again here.
In the flyback power converter 100A/100B based on the primary-side feedback shown in fig. 1A/1B, when the power switch Q1 and the first switch transistor M1 are in the on state and the second switch transistor M2 and the switch S are in the off state, the current flowing through the power switch transistor Q1 and the first switch transistor M1 provides a first driving current for the bjt Q2; when the first switch tube M1 and the second switch tube M2 are in an off state and the power switch tube Q1 and the switch S are in an on state, the first current source I SB1 A second drive current is provided for bipolar junction transistor Q2.
Fig. 2 shows a working waveform diagram of a plurality of signals in the primary-side feedback-based flyback power converter 100A/100B shown in fig. 1A/1B, where Vg1 represents a driving signal for controlling on and off of the first switching tube M1, vg2 represents a driving signal for controlling on and off of the second switching tube M2, S1 represents a driving signal for controlling on and off of the switch S, vg3 represents a driving signal for controlling on and off of the power switching tube Q1, and I B2 Representing the second drive current for the bjt Q and Is representing the primary current through the current sense resistor Rs. Here, it is assumed that each of the power switch tube Q1, the first and second switch tubes M1 and M2, and the switch S is in an on state when its driving signal is at a high level and in an off state when its driving signal is at a low level.
As shown in fig. 1A/1B and fig. 2, in some embodiments, when the flyback power converter 100A/100B based on primary-side feedback is just powered on, the power switch Q1 is turned from the off state to the on state, the first switch M1 is still in the off state, the current flowing through the power switch Q1 flows into the control chip U1A/U1B through the fourth output terminal of the switch control circuit 102 and charges the supply capacitor of the control chip U1A/U1B through the diode D1 in the control chip U1A/U1B, and then the supply capacitor charges with the current flowing through the power switch Q1 and the diode D1 in the control chip U1A/U1BStarting the rear control chip U1A/U1B; when a Pulse Width Modulation (PWM) period begins, the power switch tube Q1 and the first switch tube M1 are in a conducting state, the second switch tube M2 and the switch S are in an off state, and the first driving current I B1 Conducting the current to the base of the bjt Q2 to turn the bjt Q2 from an off state to an on state, thereby increasing the primary current Is flowing through the current sensing resistor Rs; when the primary side current Is flowing through the current sensing resistor Rs reaches a first predetermined level, the power switch tube Q1 maintains a conducting state, the first switch tube M1 Is changed from a conducting state to an off state, the switch S Is changed from the off state to the conducting state, the second switch tube M2 maintains the off state, and the second driving current I B2 To bipolar junction transistor Q2 such that bipolar junction transistor Q2 remains in a conductive state; when the primary side current Is flowing through the current sensing resistor Rs reaches a second predetermined level, the second switching tube M2 Is changed from an off state to an on state, and the base of the bjt Q2 Is grounded, so that the bjt Q2 Is changed from the on state to the off state until the start of the next Pulse Width Modulation (PWM) cycle.
As shown in fig. 1A/1B and 2, in some embodiments, during the on state of the bjt Q2, before the voltage Vcs across the current sensing resistor Rs reaches the first predetermined threshold (i.e., before the primary side current Is flowing through the current sensing resistor Rs reaches the first predetermined level), the power switch Q1 and the first switch M1 are in the on state and the switch S and the second switch M2 are in the off state, the base current of the bjt Q2 Is provided by the current Ic from the primary winding of the transformer T via the power switch Q1 and the first switch M1 (i.e., using the first driving current I B1 As the drive current for bipolar junction transistor Q2).
As shown in fig. 1A/1B and fig. 2, in some embodiments, during the on state of the bjt Q2, after the voltage Vcs across the current sensing resistor Rs reaches the first predetermined threshold (i.e., after the primary current Is flowing through the current sensing resistor Rs reaches the first predetermined level), the first switch M1 and the second switch M2 are in the off state, and the switch S and the power switch Q1 are in the on stateIn the conducting state, the base current of the bipolar junction transistor Q2 is supplied by the first current source I SB1 Supplied via switch S (i.e. using the second drive current I) B2 As the drive current for bipolar junction transistor Q2).
As shown in fig. 1A/1B and fig. 2, in some embodiments, when the first switch transistor M1 and the switch S are in an off state, the power switch transistor Q1 is in an on state, and the second switch transistor M2 is in an on state, the bjt Q2 is in an off state.
In the flyback power converter 100A/100B based on primary-side feedback shown in FIG. 1A/1B, the power switch tube Q1 and the first switch tube M1 are used for controlling the first driving current I B1 Whether or not to be used as the drive current for bjt Q2, switch S being used to control the second drive current I B2 Whether or not to be used as the drive current for bjt Q2. Using the first and second drive currents I for a period of time during which the bipolar junction transistor Q2 is in an on state B1 And I B2 As the drive current for bipolar junction transistor Q2. In the process of changing the bipolar junction transistor Q2 from the off state to the on state, the first drive current I is used B1 The first drive current I is the drive current of the bipolar junction transistor Q2 B1 Is large enough to allow the bjt Q2 to quickly enter the saturation region, so as to reduce the turn-on loss of the bjt Q2 to the maximum and increase the switching speed of the bjt Q2. However, since an excessive driving current of the bjt Q2 decreases the turn-off speed of the bjt Q2 and increases the turn-off loss of the bjt Q2, the driving current of the bjt Q2 is changed from the first driving current I before the process of changing the bjt Q2 from the on state to the off state starts B1 Switching to a second drive current I B2 (also called pre-off drive current), minority carriers stored in the base region can be quickly recombined during the period that the power bipolar junction transistor Q2 is in the conducting state, so as to reduce the off time of the bipolar junction transistor Q2, reduce the off loss of the bipolar junction transistor Q2, and improve the primary side feedback-based flyback power converter 100A/1System efficiency and output power of 00B.
Specifically, in the process of the bipolar junction transistor Q2 changing from the off state to the on state, when the first drive current I is used B1 When the bipolar junction transistor Q2 is driven by the first driving current I, the power switch tube Q1 and the first switch tube M1 are in a conducting state B1 By the drain current I of the power switch tube Q1 D Generation of drain current I D Resulting loss Ploss = I D 2 *R Q1_dson Due to R Q1_dson The on-resistance of the power switch tube Q1 is relatively small, so that a small drive loss Ploss can generate a large first drive current I B1 The bipolar junction transistor Q2 is enabled to rapidly enter a saturation region, and the turn-on loss of the bipolar junction transistor Q2 is reduced; a primary side current Is = Ic + hfe I flowing through the current sensing resistor Rs during the on state of the bjt Q2 B1 (Ic is the current flowing through the primary winding of transformer T, hfe is the amplification of bipolar junction transistor Q2); after the voltage Vcs across the current sense resistor Rs reaches a first predetermined threshold (e.g., 90% of the maximum voltage value Vcsmax across the current sense resistor Rs), the second drive current I is used B2 As the driving current of the bipolar junction transistor Q2, due to I B2 <<I B1 So that the second drive current I is used B2 And during the period of maintaining the bipolar junction transistor Q2 in the conducting state, the bipolar junction transistor Q2 has less carriers stored in the base region, and the less carriers in the base region can be quickly combined when the bipolar junction transistor Q2 is turned off, so that the turn-off time of the bipolar junction transistor Q2 is shortened, and the turn-off loss of the bipolar junction transistor Q2 is reduced.
Fig. 3A shows an exemplary circuit diagram of a flyback power converter 300A based on primary-side feedback according to a second embodiment of the present invention. The primary-side feedback-based flyback power converter 300A shown in fig. 3A is structurally different from the primary-side feedback-based flyback power converter 100A shown in fig. 1A mainly in that the power switch Q1 is implemented by a bipolar junction transistor (the power switch Q1 in fig. 1A is implemented by an N-type metal oxide semiconductor field effect transistor (N-MOSFET)), and is implemented by a bipolar junction transistor (bjt)First drive current I in bipolar junction transistor Q2 B1 By a second current source I SB2 Is amplified by a power switch tube Q1 to generate I B1 ＝hfe*I SB2 (hfe is the amplification factor of the power switch tube Q1), the larger driving current causes the bipolar junction transistor Q2 to rapidly enter a saturation region, and the turn-on loss of the bipolar junction transistor Q2 is also reduced; the connection relationship of other parts is the same as that of the corresponding part shown in fig. 1A, and is not described herein again.
Fig. 3B shows another exemplary circuit diagram of a flyback power converter 300B based on primary-side feedback according to a second embodiment of the present invention. The primary-side feedback-based flyback power converter 300B shown in fig. 3B is mainly different from the primary-side feedback-based flyback power converter 300A shown in fig. 3A in structure in that the base of the power switch Q1 is connected to the primary winding of the transformer T (i.e., connected to the collector of the power switch Q1 and the collector of the bjt Q2) via the starting resistor Rst, and connection relationships of other parts are the same as those of the corresponding parts shown in fig. 3A, and are not described again here.
FIG. 4 is a waveform diagram illustrating the operation of a plurality of signals in the flyback power converter 300A/300B based on primary-side feedback shown in FIG. 3A/3B, wherein I SB2 Showing a driving current for controlling the on and off of the power switch tube Q1, vg1 showing a driving signal for controlling the on and off of the first switch tube M1, vg2 showing a driving signal for controlling the on and off of the second switch tube M2, S1 showing a driving signal for controlling the on and off of the switch S, I B2 A second drive current for bjt Q2 Is shown and Is represents the primary current through current sense resistor Rs. Here, it is still assumed that each of the first and second switching tubes M1 and M2 and the switch S is in an on state when its driving signal is high level and in an off state when its driving signal is low level.
As shown in fig. 3A/3B and fig. 4, the control process of the flyback power converter 300A/300B based on primary side feedback is similar to that of the flyback power converter 300A/300B based on primary side feedback, and is not described herein again.
FIG. 5 shows an exemplary block diagram of the control chip U1A/U1B in the flyback power converter 100A/100B based on primary-side feedback shown in FIG. 1A/1B. As shown in FIG. 5, since the power switch Q1 is implemented by an N-MOSFET, the switch control circuit 102 in the control chip U1A/U1B controls the on/off of the power switch Q1.
Fig. 6 shows an exemplary block diagram of the control chip U3A/U3B in the flyback power converter 300A/300B based on primary-side feedback shown in fig. 3A/3B. As shown in FIG. 6, since the power switch Q1 is implemented by a BJT, it is controlled by the second current source I in the chip U3A/U3B SB2 To control the on/off of the power switch Q1.
The control chips U1A/U1B and U3A/3B include substantially similar functionality, except that the mechanism for controlling the turn-on and turn-off of the power switch Q1 is different. Hereinafter, the control chips U1A/U1B and U3A/U3B are collectively referred to as a control chip U, and the respective functional modules of the control chip U are described with reference to fig. 5/6. As shown in fig. 5/6, the control chip U may include:
chip power supply circuit 104: the VDD pin connected to the control chip U comprises an under-voltage lockout (UVLO), an over-voltage protection (OVP), a reference voltage and a reference current (Vref & Iref), and is used for providing a working voltage, the reference voltage Vref and the reference current Iref for the internal circuit of the chip. When the voltage at the VDD pin exceeds the UVLO threshold, the internal circuit of the chip starts to work. When the voltage at the VDD pin exceeds the OVP threshold value, the internal circuit of the chip enters an automatic recovery protection state to prevent the control chip U from being damaged.
The feedback control circuit 106: and an FB pin connected to the control chip U, a Constant Voltage (CV) control circuit 108, and a logic control circuit 116, which include a sampler, an operational amplifier (EA), a voltage drop compensation, and an output over/under voltage protection (OVP/UVP). The sampler generates an output voltage sampling signal from an output voltage feedback signal received from the auxiliary winding of the transformer T, which is characteristic of the system output voltage on the secondary winding of the transformer T, and supplies the output voltage sampling signal to the operational amplifier. The operational amplifier generates an error amplification signal from the output voltage sampling signal and the reference voltage Vref, and supplies the error amplification signal to the CV control circuit 108 and the voltage drop compensation section. The voltage drop compensation section generates a voltage drop compensation signal based on the error amplification signal (this loop is positive feedback). The output OVP/UVP section generates an OVP signal and a UVP signal from the output voltage feedback signal and provides the OVP signal and the UVP signal to the logic control circuit 116.
CV control circuit 108: and the CS pin and the feedback control circuit 106 are connected to the control chip U and are used for controlling the output voltage of the flyback power converter 100A/100B based on primary side feedback to be constant.
Constant Current (CC) control circuit 110: and the FB pin and logic control circuit 116 are connected to the control chip U and are used for controlling the output current of the flyback power converter 100A/100B based on primary side feedback to be constant, and the magnitude of the output current of the flyback power converter 100A/100B based on primary side feedback can be adjusted through the current sensing resistor Rs.
Current sense control circuit 112: the CS pin and logic control circuit 116 connected to the control chip U includes two parts, namely Leading Edge Blanking (LEB) and over-current protection (OCP), and is used to implement over-current protection of the flyback switching power converter 100A/100B based on primary side feedback.
Oscillator (OSC) circuit 114: the signal for generating the high frequency sawtooth wave is provided to the logic control circuit 116, and is used by the logic control circuit 116 to generate the square wave signal with the adjustable duty ratio.
The logic control circuit 116: for performing logic analysis on the input signals from the circuit modules and outputting logic control signals to the switch control circuit 102.
The protection circuit 118: and the automatic recovery protection device is used for enabling the control chip U to enter an automatic recovery protection state when the abnormal fault information is detected, so that the control chip U is prevented from being damaged.
In the starting process of the control chip U shown in fig. 5/6, the first switching tube M1 is in an off state, and the starting current for the control chip U charges the power supply capacitor of the control chip U from the bus voltage or the primary winding of the transformer T through the starting resistor Rst, the power switching tube Q1, and the diode D1 located inside the control chip U; when the voltage at the VDD pin of the control chip U exceeds the UVLO threshold, the first switching tube M1 changes from the off state to the on state. Here, the diode D1 may be replaced with a P-type metal oxide semiconductor field effect transistor (P-MOSFET).
It should be noted that the switch control circuit 102 can generate control signals for controlling the on and off of the switch S, the first and second switching tubes M1 and M2, and the power switching tube Q1 respectively according to the logic control signal provided by the logic control circuit 116, so that the switch S, the first and second switching tubes M1 and M2, and the power switching tube Q1 are turned on and off under the control of the switch control circuit 102, thereby forming the first and second driving currents I B1 And I B2 . The switch S and the first and second switching transistors M1 and M2 may be implemented using N-MOSFETs or bipolar junction transistors.
In the flyback power converter 100A/100B based on primary-side feedback shown in FIG. 1A/1B, although the first current source I SB1 And switch S are shown as being directly connected together, but with a first current source I SB1 It is not necessary to connect a switch directly, as long as the first current source I SB1 Capable of providing a second drive current I when the bipolar junction transistor Q2 is in a conductive state B2 The first driving current I is not provided when the bipolar junction transistor Q2 is in an off state B2 And (4) finishing. FIG. 7 shows a first current source I SB1 Schematic diagram of an example implementation of the circuit part related to the switching tube S.
In some embodiments, the switch S, the first switch tube M1, and the second switch tube M2 can be respectively controlled to be turned on and off by a plurality of switch control circuits. In addition, the power switch tube Q1 and the bipolar junction transistor Q2 may be two independent power switch tubes, or may be formed in one chip package; or the control chip U may be formed in a three-chip package with the power switch Q1 and the bjt Q2.
Fig. 8A shows an exemplary package schematic of the power switch Q1 and the bjt Q2 in the flyback power converter 100A/100B based on primary-side feedback shown in fig. 1A/1B. As shown in fig. 8A, the power switch Q1 and the bjt Q2 may be included in the same single-base island chip package (where the drain of the power switch Q1 is connected to the collector of the bjt Q2), and the detailed pin information of the single-base island chip package is as follows:
the 1 pin is a gate drive pin and is connected to a gate region of the power switch tube Q1;
pin 2 is a source electrode pin and is connected to a source electrode area of the power switch tube Q1;
pin 3 is a base pin and is connected to the base region of the bipolar junction transistor Q2;
the 4 pins are emitter pins and are connected to the emitter region of the bipolar junction transistor Q2, in order to increase the heat dissipation area and reduce the temperature, a plurality of wire bonding and multi-pin packaging can be adopted, for example, one pin is connected through two wire bonding, and the specific number of the wire bonding can be determined according to the area of the emitter region of the bipolar junction transistor Q2;
pins 5-8 are collector/drain pins connected to the drain region of the power switch tube Q1 and the collector region of the bipolar junction transistor Q2, and for convenience of heat dissipation and printed circuit board layout, multi-pin packaging is adopted, the drain region of the power switch tube Q1 and the collector region of the bipolar junction transistor Q2 are located on the back of the transistor, so that the power switch tube Q1 and the bipolar junction transistor Q2 can be connected by adopting conductive glue and a chip base island, wire bonding is not needed, and the impedance is minimum.
Fig. 8B shows an exemplary package schematic diagram of the power switch Q1 and the bjt Q2 in the flyback power converter 300A/300B based on primary-side feedback shown in fig. 3A/3B. The example package shown in fig. 8B is different from the example package shown in fig. 8A in that a bipolar junction transistor is used instead of the N-MOSFET as the power switch Q1, and the gate driving pin, the source pin, and the collector/drain pin in fig. 8A are replaced with a base driving pin, an emitter pin, and a collector pin for the power switch Q1, respectively.
Fig. 9A shows an exemplary package schematic diagram of the power switch Q1 and the bjt Q2 and the control chip U1A/U1B in the flyback power converter 100A/100B based on primary-side feedback shown in fig. 1A/1B. As shown in fig. 9A, the power switch Q1 and the bjt Q2 are packaged in a tiled manner, and the control chip U1A/U1B and the bjt Q2 are packaged in an iterative manner. The specific packaging form can be adjusted according to the number and the shape of the base islands, and is not limited to the 8-pin packaging form. The detailed pin information for the example package shown in fig. 9A is as follows:
1. pins 2 and 3 are control pins for controlling the chip U1A/U1B and are connected to an internal welding pad of the control chip U1A/U1B;
the 4 pins are emitter pins and are connected to the emitter region of the bipolar junction transistor Q2, in order to increase the heat dissipation area and reduce the temperature, the routing impedance can be reduced by adopting a multi-routing mode, and the specific number of routing can be determined according to the area of the emitter region of the bipolar junction transistor Q2;
pins 5-8 are collector pins connected to the drain region of the power switch tube Q1 and the collector region of the bipolar junction transistor Q2, and for convenience of heat dissipation and printed circuit board layout, multi-pin packaging is adopted, the drain region of the power switch tube Q1 and the collector region of the bipolar junction transistor Q2 are located on the back of the transistor and are connected by conductive glue and a base island, wire bonding is not needed, and impedance is minimum.
Fig. 9B shows an exemplary package schematic of the power switch Q1 and the bjt Q2 in the flyback power converter 300A/300B based on primary-side feedback shown in fig. 3A/3B.
The example package shown in fig. 9B differs from the example package shown in fig. 9A in that a bjt is used as the power switch Q1, and the connection between the power switch Q1 and the bjt Q2 and their respective pins are similar, and therefore, the description thereof is omitted here.
In summary, in the flyback power converter based on the primary-side feedback according to the embodiment of the invention, the bipolar junction transistor is driven by the combination of the plurality of switching tubes, so that the driving current loss of the bipolar junction transistor is reduced, and the switching speed of the bipolar junction transistor is increased. In addition, the pre-turn-off driving current is set before the process of changing the bipolar junction transistor from the on state to the off state is started, so that the current carriers of the base region of the bipolar junction transistor in the on state are reduced, the residual minority current carriers in the base region of the bipolar junction transistor can be quickly extracted during turn-off, the turn-off speed is improved, the turn-off loss is reduced, and the application range of the bipolar junction transistor can be expanded.
The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The present embodiments are to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (12)

1. The utility model provides a flyback power converter based on primary side feedback which characterized in that, includes transformer, power switch tube, bipolar junction transistor, first current source, switch, first and second switch tube and switch control circuit, wherein:
the first electrode of the first switching tube is connected to the first output end of the switch control circuit, the second electrode of the first switching tube is connected to the first electrode of the power switching tube, and the third electrode of the first switching tube is connected to the base electrode of the bipolar junction transistor;
a first electrode of the second switching tube is connected to a second output end of the switch control circuit, a second electrode of the second switching tube is connected to a base electrode of the bipolar junction transistor, and a third electrode of the second switching tube is grounded;
a first electrode of the switch is connected to the first current source, and a second electrode of the switch is connected to a base of the bipolar junction transistor;
a first electrode of the power switch tube is connected to a second electrode of the first switch tube and a fourth output end of the switch control circuit, a second electrode of the power switch tube is connected to a primary winding of the transformer, and a third electrode of the power switch tube is connected to a second current source or a third output end of the switch control circuit and is connected to a bus voltage or the primary winding of the transformer through a starting resistor;
the collector of the bipolar junction transistor is connected to the primary winding of the transformer, the base of the bipolar junction transistor is connected to the second electrode of the switch, the third electrode of the first switching tube, the second electrode of the second switching tube and the emitter of the bipolar junction transistor are grounded through a current sensing resistor.
2. The primary-side feedback based flyback power converter of claim 1 wherein current flowing through the power switch transistor and the first switch transistor provides drive current for the bjt when the power switch transistor and the first switch transistor are in a conducting state and the switch and the second switch transistor are in an off state before the voltage across the current sense resistor reaches a first predetermined threshold during the bjt being in a conducting state.
3. The primary-side feedback based flyback power converter of claim 1 wherein the first current source provides a drive current for the bjt when the first and second switches are in the off state and the switch and the power switch are in the on state after the voltage across the current sense resistor reaches a first predetermined threshold during the bjt is in the on state.
4. The primary-side feedback-based flyback power converter of claim 1 wherein the bjt is in an off state when the first switching tube and the switch are in an off state and the power switching tube and the second switching tube are in an on state.
5. The primary-side feedback-based flyback power converter as in claim 1, wherein the power switch is implemented as an N-type metal oxide field effect transistor or a bipolar junction transistor.
6. The primary-side-feedback-based flyback power converter of claim 1, wherein the switch, the first switching tube, and the second switching tube are implemented as N-type metal oxide field effect transistors or bipolar junction transistors.
7. The primary-side feedback based flyback power converter of claim 1 further comprising a control chip, wherein the switch, the first and second switching tubes, the switch control circuit, and the first current source are included in the control chip.
8. The primary-side feedback-based flyback power converter of claim 1 wherein the power switch tube and the bipolar junction transistor are included in the same single-base island chip package.
9. The primary feedback-based flyback power converter of claim 8 wherein the single base island chip package has a gate drive pin, a source pin, a base pin, an emitter pin, and at least one collector or drain pin.
10. The primary-side feedback-based flyback power converter of claim 7, wherein the power switch tube, the bjt, and the control chip are included in the same chip package.
11. The primary-side feedback-based flyback power converter of claim 10, wherein the power switching tube and the bjt are packaged in a tiled format and the control chip and the bjt are packaged in an iterative format.
12. The primary feedback-based flyback power converter of claim 10 wherein the chip package comprises at least one control pin for the control chip, an emitter pin, and at least one collector or drain pin.
CN202210873071.7A 2022-07-22 2022-07-22 Flyback power converter based on primary side feedback Pending CN115296544A (en)

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US8873254B2 (en) * 2012-03-12 2014-10-28 Linear Technology Corporation Isolated flyback converter with sleep mode for light load operation
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TWM505122U (en) * 2014-08-15 2015-07-11 Noveltek Semiconductor Corp Primary-side regulated flyback converter and power control circuit thereof
US11303195B2 (en) * 2019-10-22 2022-04-12 Semiconductor Components Industries, Llc Partial zero voltage switching (ZVS) for flyback power converter and method therefor
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