Flyback power converter based on primary-side feedback

Abstract

Provided is a primary-side feedback-based flyback power converter, comprising a transformer, first and second power switching tubes, first and second current sources, first, second, third, and fourth switching tubes, and a switching control circuit. First electrodes of the first, second, third, and fourth switching tubes are respectively connected to first, second, third, and fourth outputs of the switching control circuit, a second electrode of the second switching tube is connected to a base of the first power switching tube, a second electrode of the fourth switching tube is connected to a base of the second power switching tube, a third electrode of the second switching tube is grounded or connected to the second electrode of the fourth switching tube, a third electrode of the fourth switching tube is grounded, a collector of the first power switching tube is connected to a primary winding of the transformer, the base is connected to the second electrode of the second switching tube, and an emitter is connected to the base of the second power switching tube, a collector of the second power switching tube is connected to the primary winding of the transformer, and the emitter is grounded via a current sensing resistor.

Description

TECHNICAL FIELD

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

[0002] In the field of small and medium power power converter, 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, power switch tube (also known as bipolar transistor) is widely used in the market below 10W small power 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 for powering the mobile devices has increased explosively, and the output power of the charger or adapter for powering the mobile devices has been continuously improved 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 so that the power converter meets the development needs of the miniaturization of the charger or adapter and 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 embodiments of the present application comprises a transformer, first and second power switch tubes, first and second current sources, first, second, third and fourth switch tubes, and a switch control circuit, wherein: the first electrodes of the first, second, third and fourth switch tubes are respectively connected to the first, second, third and fourth output terminals 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 second electrode of the fourth switch tube is connected to the base of the second power switch tube, the third electrode of the second switch tube is grounded or connected to the second electrode of the fourth switch tube, the third electrode of the fourth switch tube is grounded, the collector of the first power switch tube is connected to 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 first drive current for the first and second power switch tubes is provided by the first current source under the control of the first switch tube, the collector of the second power switch tube is connected to the primary winding of the transformer, the base is connected to the second electrode of the fourth switch tube, and the emitter is grounded via a current sensing resistor, and the second drive current for the second power switch tube is provided by the second current source under the control of the third switch tube. BRIEF DESCRIPTION OF DRAWINGS

[0005] The present application can be better understood from the following description of specific embodiments thereof, given by way of example and with reference to the accompanying drawings, in which:

[0006] Figure 1A An example circuit diagram of a primary-side feedback based flyback power converter is shown.

[0007] Figure 1B Another example circuit diagram of a primary-side feedback based flyback power converter is shown.

[0008] Figure 2 An example schematic diagram of a primary-side feedback based flyback power converter is shown. Figure 1A An example waveform diagram of a plurality of signals in the primary-side feedback based flyback power converter shown in FIG. 1A is shown.

[0009] Figure 3A An example schematic diagram of a primary-side feedback based flyback power converter is shown. Figure 1A An example block diagram of a control chip in the primary-side feedback based flyback power converter shown in FIG. 1A is shown.

[0010] Figure 3B An example schematic diagram of a primary-side feedback based flyback power converter is shown. Figure 1B An example block diagram of a control chip in the primary-side feedback based flyback power converter shown in FIG. 1A is shown.

[0011] Figure 4A An example schematic diagram of a primary-side feedback based flyback power converter is shown.

[0012] Figure 4B An example schematic diagram of a primary-side feedback based flyback power converter is shown.

[0013] Figure 4C An example schematic diagram of a primary-side feedback based flyback power converter is shown.

[0014] Figure 5 An example schematic diagram of a primary-side feedback based flyback power converter is shown. Figure 1A An example package schematic diagram of the first and second power switches in the primary-side feedback based flyback power converter shown in FIG. 1A is shown.

[0015] Figure 6 An example package schematic diagram of the first and second power switches in the primary-side feedback based flyback power converter shown in FIG. 1A is shown. Figure 1A An example package schematic diagram of the first and second power switches and the control chip in the primary-side feedback based flyback power converter shown in FIG. 1A is shown. DETAILED DESCRIPTION

[0016] Features and exemplary embodiments of various aspects of the present application will be described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one of ordinary skill in the art that the present application can be practiced without some or all of these specific details. The description of the embodiments is merely intended to provide a better understanding of the present application by showing examples of the present application. The present application is not limited to any particular configuration set forth below, but covers any modifications, alternatives, and equivalents of the elements and processes described below. In the drawings and the following description, well-known structures and techniques have not been shown or described in detail in order to avoid unnecessarily obscuring the present application. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. It is to be understood that the use of the singular includes the plural unless specifically stated otherwise.

[0017] At present, the main reason why power switch tubes can only be applied to the small power market is that the conduction of the power switch tube is current driven, and sufficient driving current is required to make the power switch tube conduct. In addition, the driving loss of the power switch tube is large, the conduction loss is large, and the turn-off speed is slow, which also limits its application in higher power market.

[0018] In view of the above, a primary-side feedback based flyback power converter according to an embodiment of the present application is proposed, in which four switch tubes are used to combine the driving of the power switch tube, so as to reduce the driving current loss of the power switch tube, improve the turn-on speed and / or turn-off speed of the power switch tube, and / or reduce the turn-off loss of the power switch tube.

[0019] Figure 1A An example circuit diagram of a primary-side feedback based flyback power converter 100A according to an embodiment of the present application is shown. As shown in Figure 1A The primary-side feedback based flyback power converter 100A includes a transformer T, first and second power switch tubes Q1 and Q2, first and second current sources I SB1 and I SB2 , first, second, third, and fourth switch tubes D1 to D4, and a switch control circuit 102, wherein the first electrodes of the first, second, third, and fourth switch tubes D1 to D4 are respectively connected to the first, second, third, and fourth output terminals of the switch control circuit 102, and the second electrodes of the first and third switch tubes D1 and D3 are respectively connected to the first and second current sources I SB1 and I SB2The second electrode of the second switch D2 is connected to the third electrode of the first switch D1 and the base of the first power switch Q1. The second electrode of the fourth switch D4 is connected to the third electrode of the third switch D3 and the base of the second power switch Q2. The third electrodes of the second and fourth switches D2 and D4 are grounded. The collector of the first power switch Q1 is connected to the primary winding of the transformer T, the base is connected to the third electrode of the first switch D1 and the second electrode of the second switch D2, and the emitter is connected to the base of the second power switch Q2. The collector of the second power switch Q2 is connected to the primary winding of the transformer T, the base is connected to the third electrode of the third switch D3 and the second electrode of the fourth switch D4, and the emitter is grounded via the current sensing resistor Rs.

[0020] Figure 1B Another example circuit diagram of a flyback power converter 100B based on primary-side feedback according to an 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 the third electrode of the third switch D3 and the second electrode of the fourth switch D4 (i.e., connected to the emitter of the first power switch Q1 and the base of the second power switch Q1). The connection relationships of other parts are the same as those of the corresponding parts shown in Figure 1, and will not be described again here.

[0021] Figure 2 It shows 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, D1 to D4 represent the drive signals used to turn on and off the first to fourth switching transistors D1 to D4, respectively. B1 I represents the first drive current used for the second power switch Q2. B2 This represents the second drive current used for the second power switch Q2, and Is represents the primary current flowing through the current sensing resistor Rs.

[0022] like Figure 1A / B and Figure 2 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, and the first drive current I... B1The 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 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 predetermined level, the first switch D1 changes from the on state to the off state, and the second switch D2 changes from the off state to the on state, causing the first power switch Q1 to change from the on state to the off state. At this time, the third switch D3 changes from the off state to the on state, and the second drive current I... B2 The current is conducted to the second power switch Q2, keeping it in the on state. When the primary current Is flowing through the current sensing resistor Rs reaches a predetermined level, the third switch D3 changes from the on state to the off state, and the fourth switch D4 changes from the off state to the on state, causing the second power switch Q2 to change from the on state to the off state until the start of the next PWM switching cycle.

[0023] like Figure 1A / 1B and Figure 2 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, third, and fourth switches D2 to D4 are in the off state. The base current of the second power switch Q2 is supplied by the first current source I. SB1 Provided via the first switching transistor D1 and the first power switching transistor Q1 (i.e., using the first drive current I). B1 As the drive current for the second power switch Q2.

[0024] like Figure 1A / 1B and Figure 2 As shown, in some embodiments, while the second power switch Q2 is in the on state, before the voltage Vcs of the current sensing resistor Rs reaches a predetermined set value (i.e., before the primary current Is flowing through the current sensing resistor Rs reaches a predetermined level), the first switch D1 and the first power switch Q1 are in the on state, and the second, third, and fourth switches D2 to D4 are in the off state. The base current of the second power switch Q2 is supplied by the first current source I. SB1 Provided via the first switching transistor D1 and the first power switching transistor Q1 (i.e., using the first drive current I). B1 As the drive current for the second power switch Q2.

[0025] like Figure 1A / 1B and Figure 2As shown, in some embodiments, during the period when the second power switch Q2 is in the on state, after the voltage Vcs across the current sensing resistor Rs reaches a predetermined set value (i.e., after the primary current Is flowing through the current sensing resistor Rs reaches a predetermined level), the first switch D1, the fourth switch D4, 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. The base current of the second power switch Q2 is supplied by the second current source I. SB2 Provided via the third switch D3 (i.e., using the second drive current I) B2 As the drive current for the second power switch Q2.

[0026] like Figure 1A / 1B and Figure 3A As shown, in some embodiments, while the second power switch Q2 is in the off state, the first switch D1, the third switch D3, and the first power switch Q1 are in the off state, and the second and fourth switches D2 and D4 are in the on state.

[0027] exist Figure 1A In the flyback power converter 100A / B based on primary-side feedback shown in / 1B, the first and second switching transistors D1 and D2 are used to control the first drive current I. B1 Is it used as the drive current for the second power switch Q2 (the first drive current I)? B1 Also used as the drive current for the first power switch Q1, so the first and second switches D1 and D2 are actually used to control the on and off of the first power switch Q1, and the third and fourth switches D3 and D4 are used to control the second drive current I. B2 Whether it is used as the drive current for the second power switch Q2. During the period when the second power switch 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 second power switch Q2. During the transition of the second power switch Q2 from the off state to the on state, the first drive current I is used. B1 As the drive current of the second power switch Q2, in this case the first drive current I B1 The current needs to be large enough so that the second power switch Q2 can quickly enter the saturation region, thereby minimizing its turn-on losses and increasing its switching speed. 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 process of the second power switch Q2 changing from the on state to the off state begins, the drive current of the second power switch Q2 is reduced from the first drive current I. B1 Switching to the second drive current IB2 The second drive current Ic2 (also referred to as a pre- turn-off drive current) can cause the minority carriers stored in the base region of the second power switch Q2 during the on state of the second power switch Q2 to rapidly recombine 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 power converter 100A / B.

[0028] Specifically, during the process of the second power switch Q2 changing from the off state to the on state, the first drive current Ic1 is used. B1 As the drive current of 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*Ic1. 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 on state of the second power switch Q2, the primary side current Is flowing through the current sensing resistor Rs is Is = Ic + hfe*Ic1. B1 (Ic is the current flowing through the primary winding of the transformer T); after the voltage Vcs on the current sensing resistor Rs reaches a predetermined set value (for example, 90% of the maximum voltage value Vcsmax on the current sensing resistor Rs), the second drive current Ic2 is used. B2 As the drive current of the second power switch Q2, due to Ic2 B2 <<I B1 Therefore, during the use of the second drive current Ic2 B2 During the maintenance of the second power switch Q2 in the on state, the second power switch Q2 stores fewer carriers in the base region, and the fewer carriers in the base region of the second power switch Q2 can rapidly recombine to reduce the turn-off time of the second power switch Q2 and reduce the turn-off loss of the second power switch Q2 when the second power switch Q2 is turned off.

[0029] Figure 3B An example block diagram of the control chip U1A in the primary side feedback based flyback power converter 100A is shown. Figure 1B An example block diagram of the control chip U1B in the primary side feedback based flyback power converter 100B is shown. Figure 3A An example block diagram of the control chip U1B in the primary side feedback based flyback power converter 100B is shown. Figure 1A As shown in FIGS. 3A and 3B, the first to fourth switches D1 to D4 and the switch control circuit 102 can be included in the control chip U1, and the control chip U1 can further include: Figure 1A

[0030] ​Chip power supply circuit 104: connected to the VDD pin of control chip U1, including three parts of under-voltage lockout (UVLO), over-voltage protection (OVP), reference voltage and reference current (Vref & Iref), for providing working voltage, reference voltage Vref and reference current Iref for internal circuits of the chip. When the voltage at the VDD pin exceeds the UVLO voltage, 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 U1 from being damaged.

[0031] Feedback control circuit 106: connected to the FB pin of control chip U1, constant voltage (CV) control circuit 108 and logic control circuit 116, including parts of sampler, operational amplifier (EA), voltage drop compensation and output over-voltage / under-voltage protection (OVP / UVP). The sampler generates an output voltage sampling signal according to the output voltage feedback signal received from the auxiliary winding of transformer T, which represents the system output voltage on the secondary winding of 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 constant voltage (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 and 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.

[0032] CV control circuit 108: connected to the CS pin of control chip U1 and feedback control circuit 106, for controlling the output voltage of the primary-side feedback-based flyback power converter 100A / 100B to be constant.

[0033] Constant current (CC) control circuit 110: connected to the FB pin of control chip U1 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.

[0034] Current sensing control circuit 112: connected to the CS pin of control chip U1 and logic control circuit 116, including two parts of leading edge blanking (LEB) and over-current protection (OCP) comparator, for realizing over-current protection of the primary-side feedback-based flyback switching power converter 100A / 100B.

[0035] 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.

[0036] Logic control circuit 116: for logically analyzing input signals from various circuit modules and outputting logic control signals to the switch control circuit 102.

[0037] Protection circuit 118: for entering the control chip U1 into an automatic recovery protection state when an abnormal fault information is detected, so as to avoid damaging the control chip U1.

[0038] Here, it should be noted that the switch control circuit 102 is used to generate four control signals for controlling the turn-on and turn-off of the first to fourth switch tubes D1 to D4 according to the logic control signals provided by the logic control circuit 116, and the first to fourth switch tubes D1 to D4 are turned on and turned off under the control of the switch control circuit 102, thereby forming the first and second drive currents I B1 and I B2 . The first to fourth switch tubes D1, D2, D3, and D4 can be implemented by N-type metal oxide semiconductor field effect transistors (N-MOSFETs) or bipolar transistors (BJTs). The first and third switch tubes D1 and D3 can also be implemented by P-type metal oxide semiconductor field effect transistors (P-MOSFETs).

[0039] In Figure 4A the primary side feedback based flyback power converter 100A / 100B shown in FIG. 1A / 1B, although the first current source I SB1 and the first switch tube D1 are shown as being directly connected together, the first current source I SB1 does not necessarily have to be directly connected to a switch tube, as long as the first current source I SB1 is capable of providing the first drive current I B1 when the power switch tube Q2 is in the on state and not providing the first drive current I B1 when the power switch tube Q2 is in the off state; similarly, although the second current source I SB2 and the third switch tube D3 are shown as being directly connected together, the second current source I SB2 does not necessarily have to be directly connected to a switch tube, as long as the second current source I SB2 is capable of providing the second drive current I B2 when the power switch tube Q2 is in the on state and not providing the second drive current I B2 when the power switch tube Q2 is in the off state. In addition, the first drive current I B1It can be a ramp-up current, a constant current, or a current that varies proportionally with the primary current Is of the current-sensing resistor Rs, i.e., I SB1 =Io + α*Is, where Io is a current constant and α is a predetermined coefficient; the second driving current I B2 It can be a constant current.

[0040] in other words, Figure 4A The flyback power converter 100A / 100B based on primary-side feedback shown in Figure / B is related to the first / second current source I. SB1 / I SB2 The circuitry related to the first / third switching transistors D1 / D3 can also be implemented in other forms, wherein the first drive current I for the first power switching transistor Q1 and the second power switching transistor Q2 is... B1 From the first current source I SB1 The second drive current I, provided under the control of the first switch D1, is used for the second power switch Q2. B2 From the second current source I SB2 Provided under the control of the third switch D3.

[0041] Figure 4B It shows the relationship with the first / second current source I SB1 / I SB2 A schematic diagram illustrating an example alternative implementation of the circuitry related to the first / third switching transistors D1 / D3. (See attached diagram.) Figure 4B As shown, the first / second drive current I B1 / I B2 From the first / second current source I SB1 / I SB2 Provided under the control of the first / third switching transistors D1 / D3, wherein: when the first / third switching transistors D1 / D3 are in the on state, the first / second current source I... SB1 / I SB2 All current flows through the first / third switching transistors D1 / D3 and is used as the first / second drive current I. B1 / I B2 When the first / third switching transistors D1 / D3 are in the off state, the first / second current source I... SB1 / I SB2 The current does not flow through the first / third switching transistors D1 / D3, and the first / second drive current I B1 / I B2 The value is zero. In this case, the area of ​​the first / third switching transistors D1 / D3 is relatively large.

[0042] Figure 4A It shows the relationship with the first / second current source I SB1 / I SB2A schematic diagram illustrating another example of an alternative implementation of the circuitry related to the first / third switching transistors D1 / D3. (See diagram below.) Figure 4C As shown, the first / second current source I SB1 / I SB2 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 / third switching transistors D1 / D3, it may be included in or not included in the mirror current source, wherein: when the first / third switching transistors D1 / D3 are in the on state, the reference current source I... SBN The current is generated by the mirror as the first / second drive current I. SB1 / I SB2 The mirror current, the reference current source I SBN The current is only the first drive current I B1 1 / n; when the first / third switching transistors D1 / D3 are in the off state, the reference current source I SBN The current is not mirrored, the first / second drive current I B1 / I B2 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 4C The situation shown is greatly reduced.

[0043] Figure 4A It shows the relationship with the first / second current source I SB1 / I SB2 A schematic diagram illustrating another example of an alternative implementation of the circuitry related to the first / third switching transistors D1 / D3. (See diagram below.) Figure 5 As shown, the first / second current source I SB1 / I SB2 Implemented as a mirror current source, the first / third switching transistors D1 / D3 are used for switching control of the mirror current source, wherein: when the first / third switching transistors D1 / D3 are in the on state, they are used for the first / second current source I. SB1 / I SB2 Reference current source I SBN The current is generated by the mirror as the first / second drive current I. SB1 / I SB2 The mirror current, the reference current source I SBN The current is only the first drive current I B1 1 / n; when the first / third switching transistors D1 / D3 are in the off state, the reference current source I SBN The current is not mirrored. In this case, the current flowing through the first / third switching transistors D1 / D3 is the first drive current I. B1 The area of ​​the first / third switching transistors D1 / D3 is relative to 1 / n. Figure 1A The situation shown is greatly reduced.

[0044] In some embodiments, the turn-on and turn-off of the first and second switch tubes D1 and D2 can be controlled by the first switch control circuit, and the turn-on and turn-off of the third and fourth switch tubes D3 and D4 can be controlled by the second switch control circuit. In addition, the first and second power switch tubes Q1 and Q2 can be two independent power switch tubes, or can be formed in one chip package; or the control chip U1 can be formed in a three-chip package with the first and second power switch tubes Q1 and Q2.

[0045] Figure 5 An example packaging schematic diagram of the first and second power switch tubes Q1 and Q2 in the primary side feedback based flyback power converter 100A / B is shown. Figure 6 As shown, the first and second power switch tubes Q1 and Q2 can be included in the same single base island chip package (where the collector of the first and second power switch tubes Q1 and Q2 is connected), and the detailed pin information of the single base island chip package is as follows: Figure 1A

[0046] 1 pin is a first current pin for receiving a first drive current I B1 , connected to the base region of the first power switch tube Q1;

[0047] 2 pin is a second current pin for receiving a second drive current I B2 , connected to the emitter region of the first power switch tube Q1 and the base region of the second power switch tube Q2;

[0048] 3 / 4 pin is an emitter pin connected to the emitter region of the second power switch tube Q2. In order to increase the heat dissipation area and reduce the temperature, a plurality of wires and a plurality of pins can be used, for example, two pins are connected by two groups of wires, and the specific number of wires included in each group of wires can be determined according to the area of the emitter region of the second power switch tube Q2;

[0049] 5-8 pins are collector pins connected to the collector regions of the first and second power switch tubes Q1 and Q2. In order to dissipate heat and facilitate printed circuit board layout, a plurality of pin packages are used, and the collector regions of the first and second power switch tubes Q1 and Q2 are located on the back of the transistor, so the first and second power switch tubes Q1 and Q2 can be connected without wires using conductive adhesive and chip base island, with minimal impedance.

[0050] Figure 6 An example packaging schematic diagram of the first and second power switch tubes Q1 and Q2 and the control chip U1 in the primary side feedback based flyback power converter 100A / B is shown. Figure 6 As shown, the first and second power switch tubes Q1 and Q2 can be included in the same single base island chip package (where the collector of the first and second power switch tubes Q1 and Q2 is connected), and the detailed pin information of the single base island chip package is as follows: Figure 6 ​As shown, the first and second power switch tubes Q1 and Q2 are packaged in a flat form, and the control chip U1 and the second power switch tube Q2 are packaged in a stacked form. The specific packaging form can be adjusted according to the number and shape of the base islands, and is not limited to the 8-pin packaging form. ​ The detailed pin information of the example package shown is as follows:

[0051] The 1, 2 and 3 pins are control pins for the control chip U1, and are connected to the internal pads of the control chip U1.

[0052] The 4 pin is an emitter pin, and is connected to the emitter region of the second power switch tube Q2. In order to increase the heat dissipation area and reduce the temperature, a plurality of wire bonding methods can be used to reduce the wire bonding impedance. The specific number of wire bonds can be determined according to the area of the emitter region of the second power switch tube Q2.

[0053] The 5-8 pins are collector pins, and are connected to the collector regions of the first and second power switch tubes Q1 and Q2. In order to dissipate heat and facilitate the layout of the printed circuit board, a multi-pin package is used. The collector regions of the first and second power switch tubes Q1 and Q2 are located on the back of the transistor, and are connected by conductive adhesive without wire bonding, thereby minimizing the impedance.

[0054] ​ The example package shown can increase the number of excess pins without increasing the cost of system pins. The entire system circuit is simple, has few peripheral devices, and has low system cost.

[0055] In summary, in the primary-side feedback-based flyback power converter according to the embodiment of the present application, four switch tubes are used to combine and drive the power switch tube, thereby reducing the drive current loss of the power switch tube and improving the turn-on speed of the power switch tube. In addition, by setting a pre-off drive current before the power switch tube changes from the on state to the off state, the number of carriers in the base region of the power switch tube during the on state is reduced, so that the remaining minority carriers in the base region of the power switch tube can be quickly extracted during the off state, the off speed is improved, the off loss is reduced, and the application range of the power switch tube in a medium-power system can be improved.

[0056] The present application can be implemented in other specific forms without departing from the spirit and essential characteristics thereof. The current embodiments are considered in all respects as illustrative and not restrictive, the scope of the present application being defined by the appended claims rather than the description above, and all changes coming within the meaning and equivalency range of the claims are intended to be embraced therein.

Claims

1. A primary-side feedback based flyback power converter, characterized by, The power supply comprises a transformer, a first power switch tube and a second power switch tube, a first current source and a second current source, a first switch tube, a second switch tube, a third switch tube, and a fourth switch tube, and a switch control circuit, wherein: the first electrodes of the first switch tube, the second switch tube, the third switch tube, and the fourth switch tube are connected to the first output end, the second output end, the third output end, and the fourth output end of the switch control circuit respectively, the second electrode of the second switch tube is connected to the base of the first power switch tube, the second electrode of the fourth switch tube is connected to the base of the second power switch tube, the third electrode of the second switch tube is grounded or connected to the second electrode of the fourth switch tube, the third electrode of the fourth switch tube is grounded, the collector of the first power switch tube is connected to 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 first drive current for the first power switch tube and the second power switch tube is provided by the first current source under the control of the first switch tube, the collector of the second power switch tube is connected to the primary winding of the transformer, the base is connected to the second electrode of the fourth switch tube, and the emitter is grounded via a current sensing resistor, the second drive current for the second power switch tube is provided by the second current source under the control of the third switch tube, the first current source is implemented as a mirror current source, and the first switch tube is used to control whether a reference current source for the first current source is included in the mirror current source or the switch control for implementing the mirror current source, the second current source is implemented as a mirror current source, and the third switch tube is used to control whether a reference current source for the second current source is included in the mirror current source or the switch control for implementing the mirror current source, the switch control circuit is used to generate four control signals for controlling the turn-on and turn-off of the first switch tube, the second switch tube, the third switch tube, and the fourth switch tube, in the process of the second power switch tube changing from the turn-off state to the turn-on state, and during the second power switch tube being in the turn-on state and before the voltage on the current sensing resistor reaches a predetermined set value, the first switch tube and the first power switch tube are in the turn-on state, and the second switch tube, the third switch tube, and the fourth switch tube are in the turn-off state, the base current of the second power switch tube is provided by the first current source via the first switch tube and the first power switch tube, in the process of the second power switch tube being in the turn-on state, after the voltage on the current sensing resistor reaches the predetermined set value, the first switch tube, the fourth switch tube, and the first power switch tube are in the turn-off state, the second switch tube and the third switch tube are in the turn-on state, and the base current of the second power switch tube is provided by the second current source via the third switch tube.

2. The primary-side feedback based flyback power converter of claim 1, wherein, During the period when the second power switch is in the off state, the first switch, the third switch, and the first power switch are in the off state, and the second switch and the fourth switch are in the on state.

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

4. The primary-side feedback based flyback power converter of claim 1, wherein, A control chip is further included, and the first switch, the second switch, the third switch, and the fourth switch and the switch control circuit are included in the control chip.

5. 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-base island chip package.

6. The primary-side feedback based flyback power converter of claim 5, wherein, The single-base island chip package has a first current pin, a second current pin, at least one emitter pin, and at least one collector pin.

7. The primary-side feedback based flyback power converter of claim 4, wherein, The first power switch and the second power switch and the control chip are included in the same chip package.

8. The primary-side feedback based flyback power converter of claim 7, 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.

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