Flyback power converter based on primary-side feedback

Abstract

Provided is a primary-side feedback-based flyback power converter, comprising a transformer, a power switch tube, a bipolar junction transistor, a first current source, a switch, first and second switch tubes, and a switch control circuit. The first electrode of the first switch tube is connected to the first output end of the switch control circuit, the second electrode is connected to the first electrode of the power switch tube, and the third electrode is connected to the base of the bipolar junction transistor; the first electrode of the second switch tube is connected to the second output end of the switch control circuit, the second electrode is connected to the base of the bipolar junction transistor, and the third electrode is grounded; the first electrode of the switch is connected to the first current source, and the second electrode is connected to the base 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 is connected to the primary winding of the transformer, and the third electrode is connected to the bus voltage or the primary winding of the transformer via a starting resistor.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of circuit, in particular to a flyback power converter based on primary side feedback. BACKGROUND

[0002] In the field of small and medium power power converter, the flyback power converter based on primary side feedback occupies the absolute dominant position in the application market with its simple circuit, small space volume, low system cost, high conversion efficiency and other advantages. In recent years, energy saving and environmental protection has become a consensus, and lower standby power consumption technology has been valued by consumers. Bipolar junction transistor (BJT) is widely used in the market below 10W due to its good switching characteristics and low price advantage.

[0003] With the increasing functions of mobile devices such as mobile phones and tablet computers, the capacity of the battery that powers the mobile device has increased explosively, and the output power of the charger or adapter that powers the mobile device has continuously increased from the original 5W-10W to 20W, 30W, 45W, 65W or even higher. How to improve the overall efficiency and power density of the power converter on the basis of low cost and low standby power consumption, so that the power converter not only meets the development needs of the miniaturization of the charger or adapter, but also meets the increasingly stringent power efficiency standards, has become the focus of current research. SUMMARY

[0004] The flyback power converter based on primary side feedback according to the embodiment of the present application comprises a transformer, a power switch tube, a bipolar junction transistor, a first current source, a switch, first and second switch tubes, and a switch control circuit, wherein: the first electrode of the first switch tube is connected to the first output end of the switch control circuit, the second electrode is connected to the first electrode of the power switch tube, and the third electrode is connected to the base of the bipolar junction transistor; the first electrode of the second switch tube is connected to the second output end of the switch control circuit, the second electrode is connected to the base of the bipolar junction transistor, and the third electrode is grounded; the first electrode of the switch is connected to the first current source, and the second electrode is connected to the base 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 is connected to the primary winding of the transformer, and the third electrode is connected to the second current source or the third output end of the switch control circuit and is connected to the 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 is connected to the second electrode of the switch, the third electrode of the first switch tube, and the second electrode of the second switch tube, and the emitter is grounded through a current sensing resistor. BRIEF DESCRIPTION OF DRAWINGS

[0005] The present application can be better understood from the following description of specific embodiments thereof, taken in conjunction with the accompanying drawings in which:

[0006] Figure 1A An example circuit diagram of the primary-side feedback based flyback power converter according to the first embodiment of the present application is shown.

[0007] Figure 1B Another example circuit diagram of the primary-side feedback based flyback power converter according to the first embodiment of the present application is shown.

[0008] Figure 2 An example circuit diagram of the primary-side feedback based flyback power converter according to the second embodiment of the present application is shown. Figure 1A An example timing diagram of the operation of the primary-side feedback based flyback power converter shown in FIG. 1B is shown.

[0009] Figure 3A Another example circuit diagram of the primary-side feedback based flyback power converter according to the second embodiment of the present application is shown.

[0010] Figure 3B An example timing diagram of the operation of the primary-side feedback based flyback power converter shown in FIG. 3B is shown.

[0011] Figure 4 An example timing diagram of the operation of the primary-side feedback based flyback power converter shown in FIG. 3B is shown. Figure 3A An example timing diagram of the operation of the primary-side feedback based flyback power converter shown in FIG. 1B is shown.

[0012] Figure 5 An example timing diagram of the operation of the primary-side feedback based flyback power converter shown in FIG. 1B is shown. Figure 1A An example timing diagram of the operation of the primary-side feedback based flyback power converter shown in FIG. 3B is shown.

[0013] Figure 6 An example timing diagram of the operation of the primary-side feedback based flyback power converter shown in FIG. 3B is shown. Figure 3A An example timing diagram of the operation of the primary-side feedback based flyback power converter shown in FIG. 1B is shown.

[0014] Figure 7 An example timing diagram of the operation of the primary-side feedback based flyback power converter shown in FIG. 1B is shown. Figure 1A An example timing diagram of the operation of the primary-side feedback based flyback power converter shown in FIG. 3B is shown. Figure 3A An example timing diagram of the operation of the primary-side feedback based flyback power converter shown in FIG. 1B is shown.

[0015] Figure 8A An example timing diagram of the operation of the primary-side feedback based flyback power converter shown in FIG. 1B is shown. Figure 1A An example timing diagram of the operation of the primary-side feedback based flyback power converter shown in FIG. 3B is shown.

[0016] Figure 8B An example timing diagram of the operation of the primary-side feedback based flyback power converter shown in FIG. 3B is shown. Figure 3A An example timing diagram of the operation of the primary-side feedback based flyback power converter shown in FIG. 3B is shown.

[0017] Figure 9A It shows Figure 1A The diagram shown in / 1B is an example package schematic of the power switch, bipolar junction transistor, and control chip in a primary-side feedback-based flyback power converter.

[0018] Figure 9B It shows Figure 3A The example package diagram shown in / 3B illustrates the power switch, bipolar junction transistor, and control chip in a primary-side feedback-based flyback power converter. Detailed Implementation

[0019] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a comprehensive understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific configuration presented below, but covers any modifications, substitutions, and improvements to elements and components without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description in order to avoid unnecessarily obscuring the invention. Furthermore, it should be noted that the term "connected to B" as used herein can mean "directly connected to B" or "indirectly connected to B via one or more other elements."

[0020] Currently, the main reason why bipolar junction transistors (BJTs) can only be used in the low-power market is that the conduction of BJTs is current-driven, and sufficient drive current is required for the BJT to conduct. In addition, the large drive loss, large conduction loss, and slow turn-off speed of BJTs also limit their application in the high-power market.

[0021] In view of the above, a flyback power converter based on primary-side feedback according to an embodiment of the present invention is proposed, wherein a combination of multiple switching transistors is used to drive a bipolar junction transistor (BJT) to reduce the drive current loss of the BJT, improve the turn-on speed and / or turn-off speed of the BJT, and / or reduce the turn-off loss of the BJT.

[0022] Figure 1A An example circuit diagram of a flyback power converter 100A based on primary-side feedback according to a first embodiment of the present invention is shown. Figure 1A As shown, the flyback power converter 100A based on primary-side feedback includes a transformer T, a power switch Q1, a bipolar junction transistor Q2, and a first current source I. SB1, the first electrode of the first switch tube M1 is connected to the first output terminal of the switch control circuit 102, the second electrode is connected to the source of the power switch tube Q1, and the third electrode is connected to the base of the bipolar junction transistor Q2; the first electrode of the second switch tube M2 is connected to the second output terminal of the switch control circuit 102, the second electrode is connected to the base of the bipolar junction transistor Q2, and the third electrode is grounded; the first electrode of the switch S is connected to the first current source I SB1 , the second electrode is connected to the base 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 the bus voltage via the start-up 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 bipolar junction transistor 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 switch tube M1, and the second electrode of the second switch tube M2, and the emitter is grounded via the current sensing resistor Rs. Here, the first current source I SB1 , the switch S, the first and second switch tubes M1 and M2, and the switch control circuit 102 can be included in the control chip U1A.

[0023] Figure 1B An example circuit diagram of the primary-side feedback based flyback power converter 100B according to the first embodiment of the present application is shown. Figure 1B The primary-side feedback based flyback power converter 100B shown is similar to the primary-side feedback based flyback power converter 100A shown in Figure 1A The main difference in structure between the primary-side feedback based flyback power converter 100B shown and the primary-side feedback based flyback power converter 100A shown in Figure 1A is that the gate of the power switch tube Q1 is connected to the primary winding of the transformer T (i.e., connected to the drain of the power switch tube Q1 and the collector of the bipolar junction transistor Q2) via the start-up resistor Rst, and the connection relationship of other parts is the same as the corresponding parts of the primary-side feedback based flyback power converter 100A shown in

[0024] In the primary-side feedback based flyback power converter 100A / 100B shown in Figure 1A , when the power switch tube Q1 and the first switch tube M1 are in the on state and the second switch tube M2 and the switch S are in the off state, the current flowing through the power switch tube Q1 and the first switch tube M1 provides the first driving current for the bipolar junction transistor Q2; when the first switch tube M1 and the second switch tube M2 are in the off state and the power switch tube Q1 and the switch S are in the on state, the first current source I SB1 provides the second driving current for the bipolar junction transistor Q2.

[0025] Figure 2 An example circuit diagram of the primary-side feedback based flyback power converter 100B according to the first embodiment of the present application is shown.Figure 1A The waveform diagram shown in Figure 1B illustrates the operating waveforms of multiple signals in the primary-side feedback-based flyback power converter 100A / 100B. Here, Vg1 represents the drive signal controlling the on / off state of the first switch M1, Vg2 represents the drive signal controlling the on / off state of the second switch M2, S1 represents the drive signal controlling the on / off state of switch S, and Vg3 represents the drive signal controlling the on / off state of power switch Q1. B2 Let R represent the second drive current used for the bipolar junction transistor Q, and Is represent the primary current flowing through the current sensing resistor Rs. Here, it is assumed that each of the power switch Q1, the first and second switches M1 and M2, and the switch S is in the on state when its drive signal is high and in the off state when its drive signal is low.

[0026] like Figure 1A / 1B and Figure 2 As shown, in some embodiments, when the flyback power converter 100A / 100B based on primary-side feedback is first powered on, the power switch Q1 changes from the off state to the on state, while the first switch M1 remains off. 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 power supply capacitor of the control chip U1A / U1B via the diode D1 inside the control chip U1A / U1B. Subsequently, the control chip U1A / U1B starts up. At the beginning of a pulse width modulation (PWM) cycle, the power switch Q1 and the first switch M1 are in the on state, while the second switch M2 and the switch S are in the off state. The first drive current I... B1 The current is conducted to the base of the bipolar junction transistor Q2, causing Q2 to change from the off state to the on state, thereby increasing the primary current Is flowing through the current sensing resistor Rs. When the primary current Is flowing through the current sensing resistor Rs reaches a first predetermined level, the power switch Q1 remains on, the first switch M1 changes from the on state to the off state, the switch S changes from the off state to the on state, the second switch M2 remains off, and the second drive current I... B2 The current is conducted to the bipolar junction transistor Q2, keeping Q2 in the on state. When the primary current Is flowing through the current sensing resistor Rs reaches the second predetermined level, the second switch M2 changes from the off state to the on state, grounding the base of the bipolar junction transistor Q2, causing Q2 to change from the on state to the off state, until the next pulse width modulation (PWM) cycle begins.

[0027] like Figure 1A / 1B and Figure 2As shown, in some embodiments, while the bipolar junction transistor Q2 is in the on state, before the voltage Vcs across the current sensing resistor Rs reaches a first predetermined threshold (i.e., before the primary current Is flowing through the current sensing resistor Rs reaches a first predetermined level), power switch Q1 and first switch M1 are in the on state, and switch S and second switch M2 are in the off state. The base current of the bipolar junction transistor Q2 is provided by the current Ic from the primary winding of the transformer T via power switch Q1 and first switch M1 (i.e., using the first drive current Ic). B1 As the drive current of bipolar junction transistor Q2.

[0028] like Figure 1A / 1B and Figure 2 As shown, in some embodiments, while the bipolar junction transistor Q2 is in the on state, after the voltage Vcs across the current sensing resistor Rs reaches a first predetermined threshold (i.e., after the primary current Is flowing through the current sensing resistor Rs reaches a 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 state. The base current of the bipolar junction transistor Q2 is supplied by the first current source I. SB1 Provided via switch S (i.e., using the second drive current I) B2 As the drive current of bipolar junction transistor Q2.

[0029] like Figure 1A / 1B and Figure 2 As shown, in some embodiments, when the first switch M1 and switch S are in the off state, the power switch Q1 is in the on state, and the second switch M2 is in the on state, the bipolar junction transistor Q2 is in the off state.

[0030] exist Figure 1A In the flyback power converter 100A / 100B based on primary-side feedback shown in / 1B, power switch Q1 and first switch M1 are used to control the first drive current I. B1 Whether it is used as the drive current for bipolar junction transistor Q2, switch S is used to control the second drive current I. B2 Whether it is used as the drive current for bipolar junction transistor Q2. During the period when bipolar junction transistor Q2 is in the on state, the first and second drive currents I are used in time slots. B1 and I B2 This serves as the drive current for the bipolar junction transistor Q2. During the transition of the bipolar junction transistor Q2 from the off state to the on state, the first drive current I is used. B1 When used as the drive current for bipolar junction transistor Q2, the first drive current I B1to be large enough to enable the bipolar junction transistor Q2 to quickly enter the saturation region to minimize the turn-on loss of the bipolar junction transistor Q2 and improve the switching speed of the bipolar junction transistor Q2. However, the driving current of the bipolar junction transistor Q2 is too large to reduce the turn-off speed of the bipolar junction transistor Q2 and increase the turn-off loss of the bipolar junction transistor Q2. Therefore, before the process of changing the bipolar junction transistor Q2 from the on state to the off state begins, the driving current of the bipolar junction transistor Q2 is changed from the first driving current I B1 to the second driving current I B2 (also known as the pre-off driving current) to enable the minority carriers stored in the base region of the bipolar junction transistor Q2 during the on state of the bipolar junction transistor Q2 to quickly recombine to reduce the turn-off time of the bipolar junction transistor Q2, reduce the turn-off loss of the bipolar junction transistor Q2, and improve the system efficiency and output power of the primary-side feedback-based flyback power converter 100A / 100B.

[0031] Specifically, during the process of changing the bipolar junction transistor Q2 from the off state to the on state, when the first driving current I B1 is used as the driving current of the bipolar junction transistor Q2, the power switch Q1 and the first switch M1 are in the on state, the first driving current I B1 is generated by the drain current I D of the power switch Q1, and the drain current I D generates a loss Ploss = I D . 2 *R Q1_dson , R Q1_dson is the on resistance of the power switch Q1 and is relatively small, so a very small driving loss Ploss can generate a relatively large first driving current I B1 , which enables the bipolar junction transistor Q2 to quickly enter the saturation region and reduces the turn-on loss of the bipolar junction transistor Q2; during the on state of the bipolar junction transistor Q2, the primary-side current Is = Ic + hfe * I B1 (Ic is the current flowing through the primary winding of the transformer T, and hfe is the amplification factor of the bipolar junction transistor Q2) flows through the current sensing resistor Rs; after the voltage Vcs on the current sensing resistor Rs reaches the first predetermined threshold (e.g., 90% of the maximum voltage value Vcsmax on the current sensing resistor Rs), the second driving current I B2 is used as the driving current of the bipolar junction transistor Q2, since I B2 <<I B1 , the second driving current I B2During the period when the bipolar junction transistor Q2 is in the on state, there are fewer carriers stored in the base region of the bipolar junction transistor Q2. When the bipolar junction transistor Q2 is turned off, the fewer carriers in its base region can recombine quickly, thereby reducing the turn-off time of the bipolar junction transistor Q2 and reducing the turn-off loss of the bipolar junction transistor Q2.

[0032] Figure 3A An example circuit diagram of a flyback power converter 300A based on primary-side feedback according to a second embodiment of the present invention is shown. Figure 3A The flyback power converter 300A based on primary-side feedback shown is... Figure 1A The main structural difference of the primary-side feedback-based flyback power converter 100A shown is that the power switch Q1 is implemented using a bipolar junction transistor (BJT). Figure 1A The power switch Q1 in the circuit is implemented using an N-type metal-oxide-semiconductor field-effect transistor (N-MOSFET), which is used for the first drive current I of the bipolar junction transistor Q2. B1 From the second current source I SB2 The power is amplified by the power switch Q1, and I is generated. B1 =hfe*I SB2 (hfe is the amplification factor of power switch Q1). A larger drive current causes bipolar junction transistor Q2 to quickly enter the saturation region, thus reducing the turn-on loss of Q2. The connection relationships of other parts are... Figure 1A The corresponding parts shown are the same, so they will not be repeated here.

[0033] Figure 3B Another example circuit diagram of a primary-side feedback-based flyback power converter 300B according to a second embodiment of the present invention is shown. Figure 3B The flyback power converter 300B based on primary-side feedback shown is... Figure 3A The main structural difference of the primary-side feedback-based flyback power converter 300A shown is that the base of the power switch Q1 is connected to the primary winding of the transformer T via the start-up resistor Rst (i.e., connected to the collector of the power switch Q1 and the collector of the bipolar junction transistor Q2). The connection relationships of other parts are the same as... Figure 3A The corresponding parts shown are the same, so they will not be repeated here.

[0034] Figure 4 It shows Figure 3A The waveform diagram of multiple signals in the primary-side feedback-based flyback power converter 300A / 300B shown in / 3B is an example of the operating waveforms of various signals. SB2Vg1 represents the drive current used to control the on and off states of power switch Q1; Vg2 represents the drive signal used to control the on and off states of first switch M1; Vg2 represents the drive signal used to control the on and off states of second switch M2; S1 represents the drive signal used to control the on and off states of switch S; I represents the drive signal used to control the on and off states of switch S. B2 Let represent the second drive current used for bipolar junction transistor Q2, and Is represent the primary current flowing through the current sensing resistor Rs. Here, it is still assumed that each of the first and second switches M1 and M2, and switch S, is in the on state when its drive signal is high and in the off state when its drive signal is low.

[0035] like Figure 3A / 3B and Figure 4 As shown, 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 will not be described again here.

[0036] Figure 5 It shows Figure 1A Example block diagram of the control chip U1A / U1B in the primary-side feedback-based flyback power converter 100A / 100B shown in / 1B. Figure 5 As shown, since the power switch Q1 is implemented by an N-MOSFET, the switching control circuit 102 in the control chip U1A / U1B controls the turn-on and turn-off of the power switch Q1.

[0037] Figure 6 It shows Figure 3A Example block diagram of the control chip U3A / U3B in the primary-side feedback-based flyback power converter 300A / 300B shown in / 3B. Figure 6 As shown, since the power switch Q1 is implemented using a bipolar junction transistor, the current is supplied by the second current source I in the control chip U3A / U3B. SB2 This is used to control the on and off states of the power switch Q1.

[0038] Aside from the different mechanisms used to control the on and off states of the power switch Q1, the control chips U1A / U1B and U3A / 3B have essentially the same functions. Below, control chips U1A / U1B and U3A / U3B will be collectively referred to as control chip U, and will be combined with... Figure 5 / Figure 6 Describe the various functional modules of the control chip U. For example... Figure 5 / Figure 6 As shown, the control chip U may include:

[0039] Chip power supply circuit 104: connected to the VDD pin of control chip U, including under-voltage lockout (UVLO), over-voltage protection (OVP), reference voltage and reference current (Vref & Iref) three parts, for providing operating voltage, reference voltage Vref and reference current Iref for internal circuits of the chip. When the voltage at the VDD pin exceeds the UVLO threshold, the internal circuits of the chip start to work. When the voltage at the VDD pin exceeds the OVP threshold, the internal circuits of the chip enter the automatic recovery protection state to prevent the control chip U from being damaged.

[0040] Feedback control circuit 106: connected to the FB pin of control chip U, constant voltage (CV) control circuit 108 and logic control circuit 116, including sampler, operational amplifier (EA), voltage drop compensation and output over-voltage / under-voltage protection (OVP / UVP) parts. The sampler generates an output voltage sampling signal according to the output voltage feedback signal received from the auxiliary winding of the transformer T, which represents the system output voltage on the secondary winding of the transformer T, and provides the output voltage sampling signal to the operational amplifier. The operational amplifier generates an error amplification signal according to the output voltage sampling signal and the reference voltage Vref, and provides the error amplification signal to the CV control circuit 108 and the voltage drop compensation part. The voltage drop compensation part generates a voltage drop compensation signal based on the error amplification signal (this loop is positive feedback). The output OVP / UVP part generates OVP signal and UVP signal according to the output voltage feedback signal, and provides the OVP signal and UVP signal to the logic control circuit 116.

[0041] CV control circuit 108: connected to the CS pin of control chip U and feedback control circuit 106, for controlling the output voltage of the primary-side feedback-based flyback power converter 100A / 100B to be constant.

[0042] Constant current (CC) control circuit 110: connected to the FB pin of control chip U and logic control circuit 116, for controlling the output current of the primary-side feedback-based flyback power converter 100A / 100B to be constant, and the size of the output current of the primary-side feedback-based flyback power converter 100A / 100B can be adjusted through the current sensing resistor Rs.

[0043] Current sensing control circuit 112: connected to the CS pin of control chip U and logic control circuit 116, including leading edge blanking (LEB) and over-current protection (OCP) two parts, for realizing over-current protection of the primary-side feedback-based flyback switching power converter 100A / 100B.

[0044] Oscillator (OSC) circuit 114: for generating a high-frequency sawtooth wave signal provided to the logic control circuit 116 for the logic control circuit 116 to generate a duty cycle adjustable square wave signal.

[0045] Logic control circuit 116: for logical analysis of input signals from various circuit modules, and outputting logic control signals to switch control circuit 102.

[0046] Protection circuit 118: for entering the automatic recovery protection state of control chip U when detecting abnormal fault information, to avoid damage to control chip U.

[0047] In Figure 5 / Figure 6 The starting process of control chip U is shown in the figure. The first switch tube M1 is in the off state, and the starting current of control chip U is supplied from the bus voltage or the primary winding of transformer T to the supply capacitor of control chip U via starting resistor Rst, power switch tube Q1, and diode D1 inside control chip U. When the voltage at the VDD pin of control chip U exceeds the UVLO threshold value, the first switch tube M1 changes from the off state to the on state. Here, diode D1 can be replaced by a P-type metal oxide semiconductor field effect transistor (P-MOSFET).

[0048] It should be noted that switch control circuit 102 can generate control signals for controlling the on and off of switch S, first and second switch tubes M1 and M2, and power switch tube Q1, respectively, according to the logic control signals provided by logic control circuit 116, so that switch S, first and second switch tubes M1 and M2, and power switch tube Q1 are controlled to be on and off under the control of switch control circuit 102, thereby forming first and second drive currents I B1 and I B2 . Switch S and first and second switch tubes M1 and M2 can be implemented by N-MOSFET or bipolar junction transistor.

[0049] In Figure 1A / 1B, the first current source I SB1 and switch S are shown as being directly connected together, but the first current source I SB1 does not necessarily have to be directly connected to a switch, as long as the first current source I SB1 can provide the second drive current I B2 when the bipolar junction transistor Q2 is in the on state, and does not provide the first drive current I B2 when the bipolar junction transistor Q2 is in the off state. Figure 7 A schematic diagram showing an example implementation of the circuit part related to the first current source I SB1 and switch S is shown.

[0050] In some embodiments, multiple switch control circuits can be used to control the switching S, the first switching transistor M1, and the second switching transistor M2 to turn on and off respectively. Additionally, the power switching transistor Q1 and the bipolar junction transistor Q2 can be two independent power switching transistors, or they can be formed in a single chip package; alternatively, the control chip U can be formed in a three-chip package with the power switching transistor Q1 and the bipolar junction transistor Q2.

[0051] Figure 8A It shows Figure 1A The example package diagram shown in / 1B illustrates the power switch Q1 and bipolar junction transistor Q2 in the primary-side feedback-based flyback power converter 100A / 100B. (See also:) Figure 8A As shown, power switch Q1 and bipolar junction transistor Q2 can be included in the same single-base island chip package (where the drain of power switch Q1 and the collector of bipolar junction transistor Q2 are connected), and the detailed pin information of this single-base island chip package is as follows:

[0052] Pin 1 is the gate drive pin, which is connected to the gate region of power switch Q1;

[0053] Pin 2 is the source pin, which is connected to the source region of the power switch Q1;

[0054] Pin 3 is the base pin, which is connected to the base region of the bipolar junction transistor Q2;

[0055] Pin 4 is the emitter pin, which is connected to the emitter region of the bipolar junction transistor Q2. In order to increase the heat dissipation area and reduce the temperature, multiple wire bonding and multi-pin packaging can be used. For example, two wire bondings can be used to connect one pin. The specific number of wire bondings can be determined according to the area of ​​the emitter region of the bipolar junction transistor Q2.

[0056] Pins 5 to 8 are collector / drain pins, connected to the drain region of power switch Q1 and the collector region of bipolar junction transistor Q2. For heat dissipation and convenient printed circuit board layout, a multi-pin package is used. The drain region of power switch Q1 and the collector region of bipolar junction transistor Q2 are located on the back of the transistor, so power switch Q1 and bipolar junction transistor Q2 can be connected by conductive glue and chip base island without wire bonding, resulting in minimal impedance.

[0057] Figure 8B It shows Figure 3A The example package diagram shown in / 3B is of the power switch Q1 and bipolar junction transistor Q2 in the primary-side feedback-based flyback power converter 300A / 300B. Figure 8B The example encapsulation shown is Figure 8A The difference in the example package shown is that a bipolar junction transistor is used instead of an N-MOSFET as the power switch Q1.Figure 8A The gate drive pin, source pin, and collector / drain pin in the original text are used to replace the base drive pin, emitter pin, and collector pin of the power switch Q1, respectively.

[0058] Figure 9A It shows Figure 1A The example package diagram shown in Figure 1B illustrates the power switch Q1 and bipolar junction transistor Q2, as well as the control chip U1A / U1B, in a primary-side feedback-based flyback power converter 100A / 100B. Figure 9A As shown, the power switch Q1 and bipolar junction transistor Q2 are packaged in a planar configuration, while the control chips U1A / U1B and the bipolar junction switch Q2 are packaged in a stacked configuration. The specific package configuration can be adjusted based on the number and shape of the base islands, and is not limited to an 8-pin package. Figure 9A The detailed pin information for the example package shown is as follows:

[0059] Pins 1, 2, and 3 are control pins for the control chips U1A / U1B, and are connected to the internal pads of the control chips U1A / U1B.

[0060] Pin 4 is the emitter pin, which is connected to the emitter region of the bipolar junction transistor Q2. In order to increase the heat dissipation area and reduce the temperature, multiple wire bonding can be used to reduce the wire bonding impedance. The specific number of wire bonding can be determined according to the area of ​​the emitter region of the bipolar junction transistor Q2.

[0061] Pins 5 to 8 are collector pins, connected to the drain region of power switch Q1 and the collector region of bipolar junction transistor Q2. For heat dissipation and convenient printed circuit board layout, a multi-pin package is used. The drain region of power switch Q1 and the collector region of bipolar junction transistor Q2 are located on the back of the transistor and are connected by conductive glue and base island, which does not require wire bonding and has the lowest impedance.

[0062] Figure 9B It shows Figure 3A The example package diagram shown in / 3B is of the power switch Q1 and bipolar junction transistor Q2 in the primary-side feedback-based flyback power converter 300A / 300B.

[0063] Figure 9B The example encapsulation shown is Figure 9A The difference in the example package shown is that a bipolar junction transistor (BJT) is used as the power switch Q1. The connection between the power switch Q1 and the BJT Q2, as well as their respective pin connections, are similar and will not be described again here.

[0064] In summary, in the flyback power converter based on the primary side feedback according to the embodiment of the application, the combination of multiple switch tubes is used to drive the bipolar junction transistor, the drive current loss of the bipolar junction transistor is reduced, and the turn-on speed of the bipolar junction transistor is improved. In addition, by setting the pre-off drive current before the process of the bipolar junction transistor changing from the on state to the off state, the carriers in the base region of the bipolar junction transistor during the on state are reduced, so that the remaining minority carriers in the base region of the bipolar junction transistor can be quickly extracted at the time of off, the off speed is improved, the off loss is reduced, and the application range of the bipolar junction transistor can be expanded.

[0065] The application can be implemented in other specific forms without departing from the spirit and essential characteristics thereof. The current embodiments are considered in all aspects as illustrative and not restrictive, the scope of the application is defined by the appended claims rather than the above description, and all changes falling within the meaning and equivalent of the claims are included in the scope of the application.

Claims

1. A primary-side feedback based flyback power converter, characterized by, The power switch tube, the first switch tube, the second switch tube, the switch, the first current source, and the switch control circuit are included in a control chip. The first electrode of the first switch tube is connected to the first output terminal of the switch control circuit, the second electrode is connected to the first electrode of the power switch tube, and the third electrode is connected to the base of the bipolar junction transistor. The first electrode of the second switch tube is connected to the second output terminal of the switch control circuit, the second electrode is connected to the base of the bipolar junction transistor, and the third electrode is grounded. The first electrode of the switch is connected to the first current source, and the second electrode is connected to the base 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 terminal of the switch control circuit, the second electrode is connected to the primary winding of the transformer, and the third electrode is connected to the second current source or the third output terminal of the switch control circuit and is connected to the bus voltage or the primary winding of the transformer via a start-up resistor. The collector of the bipolar junction transistor is connected to the primary winding of the transformer, the base is connected to the second electrode of the switch, the third electrode of the first switch tube, and the second electrode of the second switch tube, and the emitter is grounded via a current sensing resistor. The switch, the first switch tube, the second switch tube, the switch control circuit, and the first current source are included in a control chip, and during the start-up process of the control chip, the first switch tube is in an off state, and the start-up current for the control chip charges the power supply capacitor of the control chip from the bus voltage or the primary winding of the transformer via the start-up resistor, the power switch tube, and a diode inside the control chip.

2. The primary-side feedback based flyback power converter of claim 1, wherein, During the on state of the bipolar junction transistor, when the first switch tube and the power switch tube are in an on state and the switch and the second switch tube are in an off state before the voltage on the current sensing resistor reaches a first predetermined threshold, the current flowing through the first switch tube and the power switch tube provides a drive current for the bipolar junction transistor.

3. The primary-side feedback based flyback power converter of claim 1, wherein, During the on state of the bipolar junction transistor, when the first switch tube and the second switch tube are in an off state and the switch and the power switch tube are in an on state after the voltage on the current sensing resistor reaches the first predetermined threshold, the first current source provides a drive current for the bipolar junction transistor.

4. The primary-side feedback based flyback power converter of claim 1, wherein, When the first switch tube and the switch are in an off state, the power switch tube and the second switch tube are in an on state, and the bipolar junction transistor is in an off state.

5. The primary-side feedback based flyback power converter of claim 1, wherein, The power switch tube 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 switch tube, and the second switch tube are implemented as an N-type metal oxide field effect transistor or a bipolar junction transistor.

7. 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.

8. The primary-side feedback based flyback power converter of claim 7, wherein, The single-base chip package has a gate driving pin, a source pin, a base pin, an emitter pin, and at least one collector or drain pin.

9. The primary-side feedback based flyback power converter of claim 1, wherein, The power switch tube, the bipolar junction transistor, and the control chip are included in the same chip package.

10. The primary-side feedback based flyback power converter of claim 9, wherein, The power switch tube and the bipolar junction transistor are packaged in a flat form, and the control chip and the bipolar junction transistor are packaged in a stacked form.

11. The primary-side feedback based flyback power converter of claim 9, wherein, The chip package includes at least one control pin for the control chip, an emitter pin, and at least one collector or drain pin.

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