Flyback power converter based on primary-side feedback

Abstract

A primary-side feedback based flyback power converter is provided, which includes a transformer, first and second power switching transistors, a current source, first, second and third switching transistors, an emitter switching transistor, and a switching control circuit. The first, second and third switching transistors have their first electrodes connected to the first, second and third outputs of the switching control circuit, respectively, the second switching transistor has its second electrode connected to the base of the first power switching transistor, and its third electrode connected to the base of the second power switching transistor or to a floating ground, the third switching transistor has its second electrode connected to the base of the second power switching transistor, and its third electrode connected to a floating ground, the first power switching transistor has its collector connected to a bus voltage or to a primary winding of the transformer, its base connected to the second electrode of the second switching transistor, and its emitter connected to the base of the second power switching transistor, and a drive current for the first power switching transistor is provided by the current source under control of the first switching transistor.

Description

Technical Field

[0001] This invention relates to the field of integrated circuits, and more particularly to a flyback power converter based on primary-side feedback. Background Technology

[0002] In the field of low-to-medium power converters, flyback power converters based on primary-side feedback dominate the market due to their advantages such as simple circuitry, small size, low system cost, and high conversion efficiency. In recent years, power switching transistors (also known as bipolar transistors) have been widely used in the low-power market below 10W due to their excellent switching characteristics and low price.

[0003] With the increasing functionality of mobile devices such as smartphones and tablets, the capacity of batteries powering these devices has exploded, and the output power of chargers and adapters for these devices has continuously increased, from the original 5W-10W to 20W, 30W, 45W, 65W, and even higher. How to improve the overall system efficiency and power density of power converters while maintaining low cost, so that power converters can meet both the miniaturization needs of chargers and adapters and increasingly stringent power efficiency standards, has become a key research focus today. Summary of the Invention

[0004] According to an embodiment of the present invention, a flyback power converter based on primary-side feedback includes a transformer, first and second power switches, a current source, first, second, and third switches, an emitter switch, and a switching control circuit. The first electrodes of the first, second, and third switches are respectively connected to the first, second, and third output terminals of the switching control circuit. The second electrode of the second switch is connected to the base of the first power switch, and its third electrode is connected to the base of the second power switch or grounded. The second electrode of the third switch is connected to the base of the second power switch, and its third electrode is grounded. The collector of the first power switch is connected to the bus voltage. The primary winding and base of the transformer are connected to the second electrode of the second switching transistor, and the emitter is connected to the base of the second power switching transistor. The drive current for the first power switching transistor is provided by a current source under the control of the first switching transistor. The collector of the second power switching transistor is connected to the bus voltage, or the primary winding of the transformer is connected to the second electrode of the third switching transistor, and the emitter is connected to the second electrode of the emitter switching transistor. The first electrode of the emitter switching transistor is connected to the fourth output terminal of the switch control circuit, the second electrode is connected to the emitter of the second power switching transistor, and the third electrode is connected to the current sensing resistor and connected to the floating ground or connected to the primary side ground of the transformer via the current sensing resistor. Attached Figure Description

[0005] The invention can be better understood from the following description of specific embodiments of the invention in conjunction with the accompanying drawings, wherein:

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

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

[0008] Figure 2A An example circuit diagram of a flyback power converter based on primary-side feedback according to a second embodiment of the present invention is shown.

[0009] Figure 2B Another example circuit diagram of a flyback power converter based on primary-side feedback according to a second embodiment of the present invention is shown.

[0010] Figure 3A An example circuit diagram of a flyback power converter based on primary-side feedback according to a third embodiment of the present invention is shown.

[0011] Figure 3B Another example circuit diagram of a flyback power converter based on primary-side feedback according to a third embodiment of the present invention is shown.

[0012] Figure 4A An example circuit diagram of a flyback power converter based on primary-side feedback according to a fourth embodiment of the present invention is shown.

[0013] Figure 4B Another example circuit diagram of a flyback power converter based on primary-side feedback according to a fourth embodiment of the present invention is shown.

[0014] Figure 5A and 5B It shows Figures 1A to 4B The diagram shows the waveforms of multiple signals in a flyback power converter based on primary-side feedback.

[0015] Figure 6A It shows Figure 1A , 2A Example block diagrams of the control chip in a flyback power converter based on primary-side feedback, shown in Figures 3A and 4A.

[0016] Figure 6B It shows Figure 1B , 2B Example block diagrams of the control chip in a flyback power converter based on primary-side feedback, shown in 3B and 4B.

[0017] Figure 7A A schematic diagram of an example implementation of the circuit portion related to the current source and the first switching transistor is shown.

[0018] Figure 7B A schematic diagram of another example implementation of the circuit portion related to the current source and the first switching transistor is shown.

[0019] Figure 8 It shows Figures 1A to 4B The diagram shows an example package schematic of the first and second power switches in a primary-side feedback-based flyback power converter.

[0020] Figure 9 It shows Figures 1A to 4B The diagram shows an example package of the first and second power switches and the control chip in a primary-side feedback-based flyback power converter. Detailed Implementation

[0021] 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."

[0022] Currently, the main reason why power switching transistors can only be used in the low-power market is that their conduction is current-driven, requiring sufficient drive current to turn them on. Furthermore, the high drive losses, high conduction losses, and slow turn-off speed of power switching transistors also limit their application in the higher-power market.

[0023] 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 three switching transistors are used to drive the power switching transistor in combination, so as to reduce the drive current loss of the power switching transistor, improve the turn-on speed and / or turn-off speed of the power switching transistor, and / or reduce the turn-off loss of the power switching transistor.

[0024] 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 1AAs shown, the flyback power converter 100A based on primary-side feedback includes a transformer T, first and second power switches Q1 and Q2, and a current source I. SB1 The circuit consists of first, second, and third switching transistors D1 to D3, emitter switch Q3, and switch control circuit 102, wherein the first electrodes of the first, second, and third switching transistors D1 to D3 are respectively connected to the first, second, and third output terminals of switch control circuit 102; the second electrode of the first switching transistor D1 is connected to current source I. SB1 The third electrode is connected to the second electrode of the second switching transistor and the base of the first power switching transistor Q1; the second electrode of the second switching transistor D2 is connected to the third electrode of the first switching transistor D1 and the base of the first power switching transistor Q1, and the third electrode is connected to the second electrode of the third switching transistor D3 and the base of the second power switching transistor Q2; the second electrode of the third switching transistor D3 is connected to the third electrode of the second switching transistor D2 and the base of the second power switching transistor Q2, and the third electrode is connected to floating ground; the collector of the first power switching transistor Q1 is connected to the bus voltage Vbulk, the base is connected to the third electrode of the first switching transistor D1 and the second electrode of the second switching transistor D2, and the emitter is connected to the base of the second power switching transistor Q2; the collector of the second power switching transistor Q2 is connected to the bus voltage Vbulk, the base is connected to the third electrode of the second switching transistor D2 and the second electrode of the third switching transistor D3, and the emitter is connected to the second electrode of the emitter switch Q3; the first electrode of the emitter switch Q3 is connected to the fourth output terminal of the switch control circuit 102, the second electrode is connected to the emitter of the second power switching transistor Q2, and the third electrode is connected to the current sensing resistor Rs and connected to floating ground.

[0025] Figure 1B An example circuit diagram of a flyback power converter 100B based on primary-side feedback according to a first embodiment of the present invention is shown. Figure 1B The flyback power converter 100B 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 third electrode of the second switch D2 is connected to floating ground (instead of being connected to the second electrode of the third switch D3 and the base of the second power switch Q2). The connection relationships of other parts are the same as... Figure 1A The corresponding parts shown are the same, so they will not be repeated here.

[0026] Figure 2A An example circuit diagram of a flyback power converter 200A based on primary-side feedback according to a second embodiment of the present invention is shown. Figure 2A The flyback power converter 200A based on primary-side feedback shown is... Figure 1AThe main structural difference of the primary-side feedback-based flyback power converter 100A shown is that the base of the second power switch Q2 is connected to the bus voltage Vbulk via a start-up resistor Rst. Figure 1A In the circuit, the base of the first power switch Q1 is connected to the bus voltage Vbulk via the start-up resistor Rst. The connection relationships of the other parts are similar to those in the circuit. Figure 1A The corresponding parts shown are the same, so they will not be repeated here.

[0027] Figure 2B An example circuit diagram of a flyback power converter 200B based on primary-side feedback according to a second embodiment of the present invention is shown. Figure 2B The flyback power converter 200B based on primary-side feedback shown is... Figure 2A The main structural difference of the primary-side feedback-based flyback power converter 200A shown is that the third electrode of the second switch D2 is connected to floating ground (instead of being connected to the second electrode of the third switch D3 and the base of the second power switch Q2). The connection relationships of other parts are the same as... Figure 2A The corresponding parts shown are the same, so they will not be repeated here.

[0028] exist Figures 1A to 2B In the flyback power converters 100A to 200B based on primary-side feedback shown, the control of the on and off of the first and second power switches Q1 and Q2 can be achieved using only the primary winding Np and the secondary winding Ns of the transformer T.

[0029] In some embodiments, the auxiliary winding N of transformer T can be further increased. AUX It serves as a shielding winding to reduce electromagnetic interference. For example, a voltage divider network used for feedback sampling can be connected to the auxiliary winding N of transformer T. AUX This is between the GND pin of the control chip used to control the on / off state of the first and second power switches Q1 and Q2. At this time, the auxiliary winding N of the transformer T... AUX It is not a power supply winding, and it does not have an absolute turns ratio with the primary winding Np and secondary winding Ns of transformer T. It exists only as a shielding layer, and its turns are adjusted according to the electromagnetic interference test results.

[0030] Figure 3A An example circuit diagram of a flyback power converter 300A based on primary-side feedback according to a third embodiment of the present invention is shown. Figure 3A The flyback power converter 300A based on primary-side feedback shown is... Figure 1AThe main structural difference of the primary-side feedback-based flyback power converter 100A shown is that the collectors of the first power switch Q1 and the second power switch Q2 are connected to the first terminal of the primary winding Np of the transformer T, and the second terminal of the primary winding Np of the transformer T is connected to the bus voltage Vbulk; the voltage divider resistor network is connected to the auxiliary winding N of the transformer T. AUX Between the first terminal and the floating ground, the auxiliary winding N of transformer T AUX The second terminal is connected to the primary side ground of transformer T; one end of the current sensing resistor Rs is connected to the third electrode of emitter switch Q3 and then to floating ground, and the other end is connected to the primary side ground of transformer T. The connection relationships of other parts are the same as those of the transformer T. Figure 1A The corresponding parts shown are the same, so they will not be repeated here.

[0031] Figure 3B An example circuit diagram of a flyback power converter 300B based on primary-side feedback according to a third 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 third electrode of the second switch D2 is connected to floating ground (instead of being connected to the second electrode of the third switch D3 and the base of the second power switch 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.

[0032] Figure 4A An example circuit diagram of a flyback power converter 400A based on primary-side feedback according to a fourth embodiment of the present invention is shown. Figure 4A The flyback power converter 400A 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 second power switch Q2 is connected to the bus voltage Vbulk via a start-up resistor Rst. Figure 3A In the circuit, the base of the first power switch Q1 is connected to the bus voltage Vbulk via the start-up resistor Rst. The connection relationships of the other parts are similar to those in the circuit. Figure 3A The corresponding parts shown are the same, so they will not be repeated here.

[0033] Figure 4B An example circuit diagram of a flyback power converter 400B based on primary-side feedback according to a fourth embodiment of the present invention is shown. Figure 4B The flyback power converter 400B based on primary-side feedback shown is... Figure 4AThe main structural difference of the primary-side feedback-based flyback power converter 400A shown is that the third electrode of the second switch D2 is connected to floating ground (instead of being connected to the second electrode of the third switch D3 and the base of the second power switch Q2). The connection relationships of other parts are the same as... Figure 4A The corresponding parts shown are the same, so they will not be repeated here.

[0034] exist Figures 1A to 4B In any of the primary-side feedback-based flyback power converters shown, the first to third switches D1 to D3, the switch control circuit 102, and the emitter switch Q3 can be included in the corresponding control chips U1A to U4B for controlling the on and off of the first and second power switches Q1 and Q2. For ease of description, control chips U1A to U4B are collectively referred to as control chip U. In this case, the emitter of the second power switch Q2 can be connected to the second electrode of the emitter switch Q3 via the SW pin of control chip U, and the emitter switch Q3 can be connected to the current sensing resistor Rs via the GND pin (i.e., the floating ground inside control chip U) of control chip U, forming a current path for the power loop. It will be apparent to those skilled in the art that the present invention can be implemented without combining... Figures 1A to 4B This will be implemented in some of the specific details described above.

[0035] Figure 5A and 5B It shows Figures 1A to 4B The diagram shows the waveforms of multiple signals in a primary-side feedback-based flyback power converter. D1 to D3 represent the drive signals used to turn on and off the first to third switches D1 to D3, respectively. B1 It is the drive current I used for the first power switch Q1. Base Q1 represents the drive current for the second power switch Q2, Q2 represents the drive signal for the emitter switch Q3, Q4 represents the drive signal for the VDD charging control switch Q4 (the VDD charging control switch Q4 is used to control the charging and discharging of the VDD power supply capacitor connected to the VDD pin of the control chip U), VDD represents the voltage at the VDD pin of the control chip U, Ic represents the primary current for the power circuit, and Vcs represents the voltage across the current sensing resistor Rs.

[0036] Specifically, Figure 5A It shows Figures 1A to 4B The diagram shows the waveforms of multiple signals during the non-charging duty cycle of the primary-side feedback-based flyback power converters 100A to 400B. Figure 5AAs shown, during the operating cycle when the VDD power supply capacitor of the control chip U is in a non-charging state (i.e., the non-charging operating cycle), the emitter switch Q3 is always in the on state, and the VDD charging control switch Q4 is always in the off state. Additionally, Figure 5B It shows Figures 1A to 4B The diagram shows the waveforms of multiple signals during the charging cycle of the primary-side feedback-based flyback power converters 100A to 400B. Figure 5B As shown, during the working cycle (i.e., the charging working cycle) when the VDD power supply capacitor of the control chip U is in the charging state, the emitter switch Q3 changes from the on state to the off state before the process of the second power switch Q2 changing from the on state to the off state begins. The emitter current I of the second power switch Q2... S2 The VDD power supply capacitor is charged via the VDD charging control switch Q4, which also maintains the operating current of the control chip U.

[0037] like Figures 1A to 4B and Figure 5A and 5B As shown, in some embodiments, during the process of the second power switch Q2 changing from the off state to the on state, the first switch D1 and the first power switch Q1 are in the on state while the second and third switches D2 and D3 are in the off state. The base current of the second power switch Q2 is supplied by current source I. SB1 It is supplied via the first switching transistor D1 and the first power switching transistor Q1.

[0038] like Figures 1A to 4B and Figure 5A and 5B As shown, in some embodiments, during the period when the second power switch Q2 is in the on state, before the voltage Vcs on the current sensing resistor Rs reaches a predetermined set value, the first switch D1 and the first power switch Q1 are in the on state, and the second and third switches D2 and D3 are in the off state. The base current of the second power switch Q2 is supplied by the current source I. SB1 It is supplied via the first switching transistor D1 and the first power switching transistor Q1.

[0039] like Figures 1A to 4B and Figure 5A and 5B As shown, in some embodiments, during the period when the second power switch Q2 is in the on state, after the voltage Vcs on the current sensing resistor Rs reaches a predetermined set value, the first switch D1, the third switch D3, and the first power switch Q1 are in the off state, the second switch D2 is in the on state, the base of the second power switch Q2 is in the floating state, and the minority carriers in the base region of the second power switch Q2 maintain the second power switch Q2 in the on state.

[0040] like Figures 1A to 4B and Figure 5A and 5B As shown, in some embodiments, while the second power switch Q2 is in the off state, the first switch D1 and the first power switch Q1 are in the off state, and the second and third switches D2 and D3 are in the on state.

[0041] like Figures 1A to 4B and Figure 5A and 5B As shown, in some embodiments, at the start of a pulse width modulation (PWM) switching cycle, the first switch D1 changes from the off state to the on state, while the second and third switches D2 and D3 remain off, driving the current I... B1 The current is conducted to the base of the first power switch Q1, causing Q1 to change from the off state to the on state. Since the emitter of the first power switch Q1 is connected to the base of the second power switch Q2, the current injected from the emitter of the first power switch Q1 into the base of the second power switch Q2 is sufficient to cause the second power switch Q2 to change from the off state to the on state, thereby increasing the current flowing through the current sensing resistor Rs. When the voltage Vcs on the current sensing resistor Rs reaches a first predetermined level, the first switch D1 changes from the on state to the off state, the second switch D2 changes from the off state to the on state, and the third switch remains in the off state. This causes the first power switch Q1 to change from the on state to the off state, the base of the second power switch Q2 to be in a floating state, and the minority carriers in the base region of the second power switch Q2 maintain the second power switch Q2 in the on state. When the voltage Vcs on the current sensing resistor Rs reaches the second predetermined level, the first switch D1 remains off, the second switch D2 remains on, and the third switch D3 changes from off to on, causing the second power switch Q2 to change from on to off until the next PWM switching cycle begins.

[0042] exist Figures 1A to 4B In the primary-side feedback-based flyback power converters 100A to 400B shown, when the voltage at the VDD pin of the control chip U exceeds the preset supply voltage, there is no need to charge the VDD supply capacitor; the emitter switch Q3 is in the on state, the VDD charging control switch Q4 is in the off state, and the VDD supply capacitor supplies power to the control chip U. When the voltage at the VDD pin of the control chip U is lower than the preset supply voltage, the emitter switch Q3 is in the off state, the VDD charging control switch Q4 is in the on state, and the emitter current I of the second power switch Q2... S2 Charge the VDD power supply capacitor and maintain the operating current of the control chip U.

[0043] exist Figures 1A to 4B In the primary-side feedback-based flyback power converters 100A to 400B shown, first and second switches D1 and D2 are used to control the on and off states of the first power switch Q1, and a third switch D3 is used to control the off state of the second power switch Q2. During the transition of the second power switch Q2 from the off state to the on state, a drive current I is used. B1 As the drive current for the second power switch Q2, in this case the drive current I B1 The current must be large enough to allow the second power switch Q2 to quickly enter the saturation region, thereby minimizing its turn-on losses and maximizing its switching speed. During the on-state of the second power switch Q2, the drive current I is still used. B1 This serves as the drive current for the second power switch Q2. However, excessive drive current for the second power switch Q2 will reduce its turn-off speed and increase its turn-off losses. Therefore, before the second power switch Q2 changes from the on state to the off state, when the voltage Vcs on the current sensing resistor Rs reaches the first predetermined level, the first switch D1 changes from the on state to the off state, the second switch D2 changes from the off state to the on state, and the third switch D3 remains in the off state. The base of the second power switch Q2 is in a floating state, and only the minority carriers in the base region of the second power switch Q2 maintain the on state of the second power switch Q2. When the voltage Vcs on the current sensing resistor Rs reaches the second predetermined level, the first switch D1 remains in the off state, the second switch D2 remains in the on state, and the third switch D3 changes from the off state to the on state. The minority carriers stored in the base region of the second power switch Q2 recombine rapidly to reduce the turn-off time of the second power switch Q2, reduce the turn-off loss of the second power switch Q2, and improve the system efficiency and output power of the primary-side feedback-based power converter 100A to 400B.

[0044] Specifically, during the process of the second power switch Q2 changing from the off state to the on state, the drive current I is used. B1 As the drive current for the second power switch Q2, due to the amplification effect of the first power switch Q1, the base current of the second power switch Q2 is hfe*I. B1 (hfe is the amplification factor of the first power switch Q1). The larger base current causes the second power switch Q2 to quickly enter the saturation region, reducing the turn-on loss of the second power switch Q2. During the conduction state of the second power switch Q2, the current flowing through the current sensing resistor Rs is Ics = Ic + hfe * I. B1(Ic is the primary current of the power circuit); after the voltage Vcs on the current sensing resistor Rs reaches a predetermined value (e.g., 90% of the maximum voltage value Vcsmax on the current sensing resistor Rs), the base of the second power switch Q2 is in a floating state. At this time, only the minority carriers in the base region of the second power switch Q2 maintain the conduction state of the second power switch Q2; after the voltage Vcs on the current sensing resistor Rs reaches a second predetermined level (e.g., the maximum voltage value Vcsmax on the current sensing resistor Rs), the minority carriers stored in the base region of the second power switch Q2 recombine rapidly, reducing the turn-off time of the second power switch Q2 and reducing the turn-off loss of the second power switch Q2.

[0045] Figure 6A It shows Figure 1A , 2A Example block diagrams of control chips U1A, U2A, U3A, and U4A in flyback power converters 100A, 200A, 300A, and 400B based on primary-side feedback, shown in Figures 3A and 4A. Figure 6B It shows Figure 1B , 2B Example block diagrams of control chips U1B, U2B, U3B, and U4B in flyback power converters 100B, 200B, 300B, and 400B based on primary-side feedback, shown in figures 3B and 4B. As mentioned above, for ease of description, control chips U1A to U4A and U1B to U4B can be collectively referred to as control chip U. Figure 6A and 6B As shown, in addition to the first to third switching transistors D1 to D3, the switching control circuit 102, and the emitter switch Q3 being included in the control chip U, the control chip U may also include:

[0046] Chip power supply circuit 104: Connected to the VDD pin of the control chip U, it includes three parts: undervoltage lockout (UVLO), overvoltage protection (OVP), and reference voltage and reference current (Vref & Iref). It provides the operating voltage, reference voltage Vref, and reference current Iref to the internal circuitry of the chip. When the voltage at the VDD pin exceeds the UVLO voltage, the internal circuitry of the chip begins to operate. When the voltage at the VDD pin exceeds the OVP threshold, the internal circuitry of the chip enters an automatic recovery protection state to prevent damage to the control chip U.

[0047] 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 a sampler, operational amplifier (EA), voltage drop compensation, and output overvoltage / undervoltage protection (OVP / UVP). The sampler generates an output voltage sampling signal based on the output voltage feedback signal received from the primary winding Np of transformer T, which characterizes the system output voltage on the secondary winding Ns of transformer T, and provides the output voltage sampling signal to the operational amplifier. The operational amplifier generates an error amplification signal based on the output voltage sampling signal and the reference voltage Vref, and provides the error amplification signal to the constant voltage (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 OVP and UVP signals based on the output voltage feedback signal and provides the OVP and UVP signals to the logic control circuit 116.

[0048] CV control circuit 108: connected to the CS pin of the control chip U and the feedback control circuit 106, used to control the output voltage of the flyback power converter based on primary-side feedback to be constant.

[0049] Constant current (CC) control circuit 110: connected to the FB pin of the control chip U and the logic control circuit 116, used to control the output current of the primary-side feedback-based flyback power converter to be constant, and the magnitude of the output current of the primary-side feedback-based flyback power converter can be adjusted by the current sensing resistor Rs.

[0050] Current sensing control circuit 112: connected to the CS pin of control chip U and logic control circuit 116, including two parts: leading edge blanking (LEB) and overcurrent protection (OCP) comparator, used to implement overcurrent protection of flyback switching power converter based on primary side feedback.

[0051] Oscillator (OSC) circuit 114: used to generate a high-frequency sawtooth wave signal and provide it to the logic control circuit 116, which then uses it to generate a square wave signal with an adjustable duty cycle.

[0052] Logic control circuit 116: used to perform logical analysis on the input signals from various circuit modules and output logic control signals to switch control circuit 102.

[0053] Protection circuit 118: When abnormal fault information is detected, the control chip U enters the automatic recovery protection state to avoid damage to the control chip U.

[0054] exist Figure 6A and 6BDuring the startup process of the control chip U shown, the emitter switch Q3 is in the off state. The startup current flows from the bus voltage Vbulk through the startup resistor Rst, the first and second power switches Q1 and Q2 (or only the second power switch Q2), and the VDD charging control switch Q4 to charge the VDD power supply capacitor. When the voltage at the VDD pin of the control chip U exceeds UVLO, the emitter switch Q3 changes from the off state to the on state. Here, the VDD charging control switch Q4 can be implemented using a P-type metal-oxide-semiconductor field-effect transistor (P-MOSFET) or a diode.

[0055] It should be noted that the switch control circuit 102 generates three control signals based on the logic control signals provided by the logic control circuit 116, which are used to control the on and off states of the first to third switching transistors D1 to D3. The first to third switching transistors D1 to D3 are turned on and off under the control of the switch control circuit 102, and the first and second power switching transistors Q1 and Q2 are turned on and off under the control of the first to third switching transistors D1 to D3. The first to third switching transistors D1, D2, and D3 can be implemented using N-type metal-oxide-semiconductor field-effect transistors (N-MOSFETs) or bipolar junction transistors (BJTs). The first switching transistor D1 can also be implemented using a P-type metal-oxide-semiconductor field-effect transistor (P-MOSFET).

[0056] exist Figures 1A to 4B In the primary-side feedback-based flyback power converters 100A to 400B shown, although current source I SB1 The first switching transistor D1 is shown as being directly connected, but the current source I... SB1 It is not necessary to directly connect a switching transistor, as long as the current source I... SB1 It can provide drive current I when the second power switch Q2 is in the on state. B1 No drive current I is provided when the second power switch Q2 is in the off state. B1 That's it; drive current I B1 It can be a ramp-up current, a constant current, or a current that varies proportionally with the current Ics flowing through the current sensing resistor Rs, i.e., I SB1 =Io + α*Ics, where Io is a current constant and α is a predetermined coefficient.

[0057] in other words, Figures 1A to 4B The flyback power converters 100A to 400B based on primary-side feedback shown are connected to current source I. SB1 The circuit related to the first switching transistor D1 can also be implemented in other forms, wherein the drive current I for the first power switching transistor Q1 and the second power switching transistor Q2 is...B1 From current source I SB1 Provided under the control of the first switching transistor D1. Figure 7A It shows the relationship with current source I SB1 A schematic diagram illustrating an example implementation of the circuitry related to the first switching transistor D1. (See attached diagram.) Figure 7A As shown, the driving current I B12 From current source I SB1 The current source I is provided under the control of the first switch D1, wherein: when the first switch D1 is in the on state, the current source I... SB1 All the current flows through the first switching transistor D1 and is used as the drive current I. B1 In this case, the area of ​​the first switching transistor D1 is relatively large.

[0058] Figure 7B It shows the relationship with current source I SB1 A schematic diagram of another example implementation of the circuitry related to the first switching transistor D1. (See diagram below.) Figure 7B As shown, current source I SB1 Implemented as a mirror current source, used as the reference current source I for the mirror current source. SBN Under the control of the first switch D1, it may be included in or not included in the mirror current source, wherein: when the first switch D1 is in the on state, the reference current source I... SBN The current is generated by the mirror as the driving current I. B1 The mirror current, the reference current source I SBN The current is only the drive current I B1 1 / n; when the first switch D1 is in the off state, the reference current source I SBN The current is not mirrored, and the driving current I B1 The current is zero. In this case, the current flowing through the first switching transistor D1 is relatively small, and the area of ​​the first switching transistor D1 is relatively small. Figure 7A The situation shown is greatly reduced. Furthermore, Figure 7B A diode was added to prevent the startup current from flowing to the mirror current source when the startup resistor Rst is directly connected to the base of the first power switch Q1.

[0059] In some embodiments, the first switch control circuit can control the on and off of the first and second power switches D1 and D2, and the second switch control circuit can control the on and off of the third power switch D3. Alternatively, the first and second power switches Q1 and Q2 can be two independent power switches, or they can be formed in a single chip package; or the control chip U can be formed in a three-chip package with the first and second power switches Q1 and Q2.

[0060] Figure 8 It shows Figures 1A to 4B The diagram shows an example package schematic of the first and second power switches Q1 and Q2 in a primary-side feedback-based flyback power converter 100A to 400B. Figure 8 As shown, the first and second power switches Q1 and Q2 can be included in the same single-base island chip package (where the collectors of the first and second power switches Q1 and Q2 are connected), and the detailed pin information of this single-base island chip package is as follows:

[0061] Pin 1 is the first current pin, used to receive the drive current I. B1 It is connected to the base region of the first power switch Q1;

[0062] Pin 2 is the second current pin, which is connected to the emitter region of the first power switch Q1 and the base region of the second power switch Q2;

[0063] Pins 3 and 4 are emitter pins, which are connected to the emitter region of the second power switch 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 pins can be connected by two sets of wire bonding respectively. The specific number of wires in each set of wire bonding can be determined according to the area of ​​the emitter region of the second power switch Q2.

[0064] Pins 5 to 8 are collector pins, connected to the collector areas of the first and second power switches Q1 and Q2. For heat dissipation and convenient printed circuit board layout, a multi-pin package is used. The collector areas of the first and second power switches Q1 and Q2 are located on the back of the transistor, so the first and second power switches Q1 and Q2 can be connected to the chip base island using conductive glue without wire bonding, resulting in minimal impedance.

[0065] Figure 9 It shows Figures 1A to 4B The diagram shows an example package of the first and second power switches Q1 and Q2, and the control chip U, in a primary-side feedback-based flyback power converter 100A to 400B. Figure 9 As shown, the first and second power switches Q1 and Q2 are packaged in a flat configuration, while the control chip U and the second power switch Q2 are packaged in a stacked configuration. The specific package configuration can be adjusted according to the number and shape of the base islands, and is not limited to an 8-pin package. Detailed pin information for the example package shown in Figure 6 is as follows:

[0066] Pins 1, 2, and 3 are control pins for the control chip U, and are connected to the internal pads of the control chip U.

[0067] Pin 4 is the emitter pin, which is connected to the emitter region of the second power switch Q2. In order to increase the heat dissipation area and reduce the temperature, multiple wires can be used to reduce the wire impedance. The specific number of wires can be determined according to the area of ​​the emitter region of the second power switch Q2.

[0068] Pins 5 to 8 are collector pins, which are connected to the collector areas of the first and second power switching transistors Q1 and Q2. For heat dissipation and convenient printed circuit board layout, a multi-pin package is used. The collector areas of the first and second power switching transistors Q1 and 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 minimizes impedance.

[0069] Figure 9 The example package shown can add extra pins without increasing the system pin cost, resulting in a simple system circuit, fewer external components, and low system cost.

[0070] In summary, in the primary-side feedback-based flyback power converter according to embodiments of the present invention, three switching transistors are used to drive the power switching transistor in combination, which reduces the drive current loss of the power switching transistor and improves the turn-on speed of the power switching transistor. Furthermore, by maintaining the conduction state of the power switching transistor by its base region carriers before the transition from the on to the off state begins, the remaining minority carriers in the base region of the power switching transistor can be rapidly extracted during turn-off, improving the turn-off speed and reducing turn-off losses. This expands the application range of the power switching transistor in medium-power systems.

[0071] This invention may be implemented in other specific forms without departing from its spirit and essential characteristics. The present embodiments are to be regarded in all respects as exemplary rather than limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description, and all modifications falling within the meaning and scope of the claims and their equivalents are included within the scope of the invention.

Claims

1. A primary-side feedback based flyback power converter, characterized by, The control chip comprises a transformer, a first power switch tube, a second power switch tube, a current source, a first switch tube, a second switch tube, a third switch tube, an emitter switch tube, and a switch control circuit, wherein: the first electrode of the first switch tube, the second switch tube, and the third switch tube are respectively connected to the first output end, the second output end, and the third output end of the switch control circuit, the second electrode of the second switch tube is connected to the base of the first power switch tube, the third electrode is connected to the base of the second power switch tube or is connected to the floating ground, and the second electrode of the third switch tube is connected to the base of the second power switch tube, and the third electrode is connected to the floating ground, the collector of the first power switch tube is connected to the bus voltage or the primary winding of the transformer, the base is connected to the second electrode of the second switch tube, and the emitter is connected to the base of the second power switch tube, the driving current for the first power switch tube is provided by the current source under the control of the first switch tube, the collector of the second power switch tube is connected to the bus voltage or the primary winding of the transformer, the base is connected to the second electrode of the third switch tube, and the emitter is connected to the second electrode of the emitter switch tube, the first electrode of the emitter switch tube is connected to the fourth output end of the switch control circuit, the second electrode is connected to the emitter of the second power switch tube, and the third electrode is connected to the current sensing resistor and is connected to the floating ground or is connected to the primary side ground of the transformer via the current sensing resistor, and the first switch tube, the second switch tube, the third switch tube, the switch control circuit, and the emitter switch tube are included in the control chip for controlling the turn-on and turn-off of the first power switch tube and the second power switch tube, the first switch tube and the second switch tube are used for controlling the turn-on and turn-off of the first power switch tube, and the third switch tube is used for controlling the turn-off of the second power switch tube.

2. The primary-side feedback based flyback power converter of claim 1, wherein, In the process of changing the second power switch tube from the off state to the on state, the first switch tube and the first power switch tube are in the on state, and the second switch tube and the third switch tube are in the off state, and the base current of the second power switch tube is provided by the current source via the first switch tube and the first power switch tube.

3. The primary-side feedback based flyback power converter of claim 1, wherein, During the period when the second power switch tube is in the on state, before the voltage on the current sensing resistor reaches the predetermined setting value, the first switch tube and the first power switch tube are in the on state, and the second switch tube and the third switch tube are in the off state, and the base current of the second power switch tube is provided by the current source via the first switch tube and the first power switch tube.

4. The primary-side feedback based flyback power converter of claim 1, wherein, During the period when the second power switch tube is in the on state, after the voltage on the current sensing resistor reaches the predetermined setting value, the first switch tube, the third switch tube, and the first power switch tube are in the off state, the second switch tube is in the on state, and the on state of the second power switch tube is maintained by the base current of the second power switch tube.

5. The primary-side feedback based flyback power converter of claim 1, wherein, During the off state of the second power switch, the first switch and the first power switch are in an off state, and the second switch and the third switch are in an on state.

6. The primary-side feedback based flyback power converter of claim 1, wherein, The first switch, the second switch, and the third switch are implemented as power switches or field effect transistors.

7. The primary-side feedback based flyback power converter of claim 1, wherein, The first power switch and the second power switch are included in the same single die chip package.

8. The primary-side feedback based flyback power converter of claim 7, wherein, The single die chip package has a first current pin, a second current pin, at least one emitter pin, and at least one collector pin.

9. The primary-side feedback based flyback power converter of claim 1, wherein, The first power switch and the second power switch 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 first power switch and the second power switch are packaged in a side-by-side form, and the control chip and the second power switch are packaged in a stacked form.

11. The primary-side feedback based flyback power converter of claim 1, wherein, The second electrode of the first switch is connected to the current source, and the third electrode is connected to the second electrode of the second switch.

12. The primary-side feedback based flyback power converter of claim 1, wherein, The current source is implemented as a mirror current source, and the first switch is used to control whether a reference current source for the mirror current source is included in the mirror current source.

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