TWM638854U - Flyback Power Converter Based on Primary Side Feedback - Google Patents

Abstract

A flyback power converter based on primary side feedback is provided, including a transformer, first and second power switch tubes, first and second current sources, first, second, third, and fourth switch tubes, and switch control circuit. The first electrodes of the first, second, third, and fourth switch tubes are respectively connected to the first, second, third, and fourth output ends of the switch control circuit, and the second electrodes of the second switch tube are connected to the 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, and the second electrode of the fourth switch tube is connected to the base of the second power switch tube. The third electrode of the four switching tubes is grounded, the collector of the first power switching tube is connected to the primary winding of the transformer, the base is connected to the second electrode of the second switching tube, and the emitter is connected to the base of the second power switching tube, The collector of the second power switch tube is connected to the primary winding of the transformer, and the emitter is grounded through the current sensing resistor.

Description

Flyback Power Converter Based on Primary Side Feedback

This creation relates to the field of integrated circuits, in particular to a flyback power converter based on primary side feedback.

In the field of small and medium power power converters, flyback power converters based on primary side feedback occupy an absolute dominant position in the application market due to their advantages of simple circuit, small space, low system cost, and high conversion efficiency. In recent years, power switching tubes (also known as bipolar transistors) have been widely used in low-power markets below 10W because of their good switching characteristics and low price advantages.

With more and more functions of mobile devices such as mobile phones and tablets, the capacity of batteries powering mobile devices has increased explosively, and the output power of chargers or adapters powering mobile devices has continued to increase, from the original 5W~ 10W develops to 20W, 30W, 45W, 65W or even higher. How to improve the overall efficiency and power density of the power converter system on the basis of low cost, so that the power converter can not only meet the development needs of the charger or adapter miniaturization, but also meet the increasingly stringent power energy efficiency standards, has become the research topic of today. focus.

The primary-side feedback-based flyback power converter according to an embodiment of the invention includes a transformer, a first and a second power switch tube, a first and a second current source, a first, a second, a third, and a fourth A switch tube, 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 first power switch The base of the switching tube, the second electrode of the fourth switching tube is connected to the base of the second power switching tube, the third electrode of the second switching tube is grounded or connected to the second electrode of the fourth switching tube, and the fourth switching tube The third electrode of the first power switching tube is connected to the ground, the collector of the first power switching tube is connected to the primary winding of the transformer, the base is connected to the second electrode of the second switching tube, and the emitter is connected to the base of the second power switching tube for the first The first drive current of 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, and the base is connected to the first switch tube. The second electrodes and emitters of the four switching tubes are grounded through the current sensing resistor, and the second driving current for the second power switching tube is provided by the second current source under the control of the third switching tube.

1,2,3,4,5,6,7,8: pins

100A, 100B: flyback power converter

102: switch control circuit

104: chip power supply circuit

106: Feedback control circuit

108: Constant voltage control circuit

110: Constant current control circuit

112: Current sensing control circuit

114: Oscillator circuit

116: logic control circuit

118: Protection circuit

CS: current sense pin

D1: the first switch tube

D2: The second switch tube

D3: The third switch tube

D4: The fourth switch tube

FB, VDD: pin

GND: ground pin

I _B1 : the first driving current

I _B2 : the second driving current

Ic: current

Io: current constant

Iref: reference current

Is: Primary current

I _SB1 : the first current source

I _SB2 : Second current source

I _SBN : Reference current source

OVP: overvoltage protection pin

PWM: pulse width modulation

Q1: The first power switch tube

Q2: The second power switch tube

Rs: current sense resistor

T: Transformer

U1, U1A, U1B: control chip

UVLO: undervoltage lockout

UVP: under voltage protection

Vcs: voltage

Vref: reference voltage

α: predetermined coefficient

This creation can be better understood from the following description of the specific implementation manner of this creation in conjunction with the drawings, wherein:

FIG. 1A shows an example circuit diagram of a primary-side feedback-based flyback power converter according to an embodiment of the present invention.

FIG. 1B shows another example circuit diagram of a primary-side feedback-based flyback power converter according to an embodiment of the present invention.

FIG. 2 shows the working waveform diagram of multiple signals in the primary-side feedback-based flyback power converter shown in FIG. 1A/1B .

FIG. 3A shows an example block diagram of a control chip in the primary-side feedback-based flyback power converter shown in FIG. 1A .

FIG. 3B shows an example block diagram of a control chip in the primary-side feedback-based flyback power converter shown in FIG. 1B .

FIG. 4A shows a schematic diagram of an example alternative implementation of circuit parts related to the first/second current source and the first/third switch tube.

FIG. 4B shows a schematic diagram of another exemplary alternative implementation of circuit parts related to the first/second current source and the first/third switch tube.

Figure 4C shows the circuit related to the first/second current source and the first/third switch tube A schematic diagram of yet another example alternative implementation of a section.

FIG. 5 shows a schematic diagram of an example package of the first and second power switch tubes in the primary-side feedback-based flyback power converter shown in FIG. 1A/1B .

FIG. 6 shows a schematic diagram of an example package of the first and second power switch tubes and the control chip in the primary-side feedback-based flyback power converter shown in FIG. 1A/1B .

Features and exemplary embodiments of various aspects of the present invention will be described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the invention may be practiced without some of these specific details. The following description of the embodiments is only to provide a better understanding of the invention by showing an example of the invention. The invention is in no way limited to any specific configuration set forth below, but rather covers any modifications, substitutions and improvements of elements and parts without departing from the spirit of the invention. In the drawings and the following description, well-known structures and techniques have not been shown in order to avoid unnecessarily obscuring the present invention. In addition, it should be noted that the term "A is connected to B" used herein may mean "A and B are directly connected" or "A and B are indirectly connected via one or more other elements".

At present, the main reason why the power switch tube can only be used in the low-power market is that the conduction of the power switch tube is driven by current, and there must be sufficient driving current 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, these factors also limit its application in the higher power market.

In view of the above situation, a flyback power converter based on primary side feedback is proposed according to the embodiment of this invention, in which four switching tubes are used to drive the power switching tube in combination to reduce the driving current loss of the power switching tube and increase the power Turn-on speed and/or turn-off speed of the switch tube, and/or reduce turn-off loss of the power switch tube.

FIG. 1A shows an example circuit diagram of a primary-side feedback-based flyback power converter 100A according to an embodiment of the present invention. As shown in FIG. 1A , the flyback power converter 100A based on primary side feedback includes a transformer T, first and second power switch tubes Q1 and Q2, first and second current sources I _SB1 and I _SB2 , first, The second, third, and fourth switch tubes D1 to D4, and the 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 switch control circuit The first, second, third, and fourth output terminals of 102, the second electrodes of the first and third switching tubes D1 and D3 are respectively connected to the first and second current sources _ISB1 and _ISB2 , and the second switch The second electrode of the tube D2 is connected to the third electrode of the first switching tube D1 and the base of the first power switching tube Q1, and the second electrode of the fourth switching tube D4 is connected to the third electrode of the third switching tube D3 and the base of the first power switching tube Q1. The base of the second power switching tube Q2, the third electrodes of the second and fourth switching tubes D2 and D4 are grounded, the collector of the first power switching tube Q1 is connected to the primary winding of the transformer T, and the base is connected to the first switching tube The third electrode of D1 and the second electrode and emitter of the second switching tube D2 are connected to the base of the second power switching tube Q2, and the collector of the second power switching tube Q2 is connected to the primary winding and base of the transformer T The third electrode of the third switching tube D3 and the second electrode and emitter of the fourth switching tube D4 are grounded via the current sensing resistor Rs.

FIG. 1B shows another example circuit diagram of a primary-side feedback-based flyback power converter 100B according to an embodiment of the present invention. The main difference in structure between the primary-side feedback-based flyback power converter 100B shown in FIG. 1B and the primary-side feedback-based flyback power converter 100A shown in FIG. 1A is that the second switching tube D2 The three electrodes are connected to the third electrode of the third switching tube D3 and the second electrode of the fourth switching tube D4 (that is, connected to the emitter of the first power switching tube Q1 and the base of the second power switching tube Q2), and other Partial connections are the same as the corresponding parts shown in FIG. 1 , and will not be repeated here.

Fig. 2 shows the working waveform diagram of a plurality of signals in the flyback power converter 100A/100B based on the primary side feedback shown in Fig. 1A/1B, wherein D1 to D4 respectively represent the The turn-on and turn-off drive signals of the four switch tubes D1 to D4, I _B1 represents the first drive current for the second power switch tube Q2, I _B2 represents the second drive current for the second power switch tube Q2, Is Indicates the primary current flowing through the current sense resistor Rs.

As shown in FIG. 1A/B and FIG. 2 , in some embodiments, at the beginning of a pulse width modulation (Pulse Width Modulation, PWM) switching cycle, the first switching tube D1 changes from the off state to the on state, and the second A driving current I _B1 is conducted to the base of the first power switch tube Q1, so that the first power switch tube Q1 changes from the off state to the on state; since the emitter of the first power switch tube Q1 is connected to the second power switch tube The base of Q2, the current injected into the base of the second power switch Q2 from the emitter of the first power switch Q1 is enough to make the second power switch Q2 change from the off state to the on state, so that the current sense The primary current Is of the measuring resistor Rs increases. When the primary current Is flowing through the current sensing resistor Rs reaches a predetermined level, the first switch tube D1 changes from the on state to the off state, and the second switch tube D2 changes from the off state to the on state, so that the first power The switch tube Q1 changes from the on state to the off state; at this time, the third switch tube D3 changes from the off state to the on state, and the second drive current I _B2 is conducted to the second power switch tube Q2, so that the second power switch tube Q2 remain in the on state. When the primary current Is flowing through the current sensing resistor Rs reaches a predetermined level, the third switch tube D3 changes from the on state to the off state, and the fourth switch tube D4 changes from the off state to the on state, so that the second power The switch tube Q2 changes from the on state to the off state until the next PWM switching cycle starts.

As shown in FIG. 1A/1B and FIG. 2 , in some embodiments, when the second power switch tube Q2 changes from the off state to the on state, the first switch tube D1 and the first power switch tube Q1 are in conduction. state and the second, third, and fourth switching tubes D2 to D4 are in the off state, the base current of the second power switching tube Q2 is supplied by the first current source _ISB1 via the first switching tube D1 and the first power switching tube Q1 provides (that is, uses the first driving current I _B1 as the driving current of the second power switch transistor Q2 ).

As shown in FIG. 1A/1B and FIG. 2, in some embodiments, during the period when the second power switch Q2 is in the on state, before the voltage Vcs of the current sensing resistor Rs reaches a predetermined setting value (that is, flows through the current sense Before the primary side current Is of the measuring resistor Rs reaches a predetermined level), the first switch tube D1 and the first power switch tube Q1 are in the conduction state and the second, third, and fourth switch tubes D2 to D4 are in the off state. The base current of the second power switch tube Q2 is provided by the first current source _ISB1 via the first switch tube D1 and the first power switch tube Q1 (that is, the first drive current I _B1 is used as the drive current of the second power switch tube Q2 ).

As shown in FIG. 1A/1B and FIG. 2 , in some embodiments, during the period when the second power switch tube Q2 is in the on state, after the voltage Vcs on the current sensing resistor Rs reaches a predetermined setting value (that is, the current flows After the primary side current Is of the sensing resistor Rs reaches a predetermined level), the first switch tube D1, the fourth switch tube D4, and the first power switch tube Q1 are in the off state, and the second and third switch tubes D2 and D3 are in the off state. In the ON state, the base current of the second power switch Q2 is provided by the second current source I _SB2 via the third switch D3 (that is, the second drive current I _B2 is used as the drive current of the second power switch Q2 ).

As shown in FIG. 1A/1B and FIG. 2, in some embodiments, when the second power switch tube Q2 is in the off state, the first switch tube D1, the third switch tube D3, and the first power switch tube Q1 are in the off state. In the off state, the second and fourth switch tubes D2 and D4 are in the on state.

In the flyback power converter 100A/100B based on primary side feedback shown in FIG. 1A/1B, the first and second switch tubes D1 and D2 are used to control whether the first drive current I _B1 is used as the second power The driving current of the switching tube Q2 (the first driving current I _B1 is also used as the driving current of the first power switching tube Q1, so the first and second switching tubes D1 and D2 are actually used to control the conduction and switching of the first power switching tube Q1 off), the third and fourth switching tubes D3 and D4 are used to control whether the second driving current I _B2 is used as the driving current of the second power switching tube Q2. When the second power switch tube Q2 is in the conduction state, the first and second drive currents I _B1 and I _B2 are used as the drive current of the second power switch tube Q2 in different periods. In the process of the second power switch tube Q2 changing from the off state to the on state, the first drive current I _B1 is used as the drive current of the second power switch tube Q2, in this case the first drive current I _B1 should be sufficient is large, so that the second power switch tube Q2 can quickly enter the saturation region, so as to minimize the turn-on loss of the second power switch tube Q2 and increase the switching speed of the second power switch tube Q2. However, if the driving current of the second power switch tube Q2 is too high, the turn-off speed of the second power switch tube Q2 will be reduced, and the turn-off loss of the second power switch tube Q2 will be increased. Before the process of the off-state starts, the driving current of the second power switch tube Q2 is switched from the first driving current I _B1 to the second driving current I _B2 (also referred to as the pre-shutdown driving current), which can make the second power switch The minority carriers stored in the base region rapidly recombine when the tube Q2 is in the on-state to reduce the turn-off time of the second power switch tube Q2, reduce the turn-off loss of the second power switch tube Q2, and improve the flyback power conversion The system efficiency and output power of the converter 100A/100B.

Specifically, in the process of changing the second power switch tube Q2 from the off state to the on state, the first drive current I _B1 is used as the drive current of the second power switch tube Q2, due to the amplification effect of the first power switch tube Q1 , the base current of the second power switch tube Q2 is hfe*I _B1 (hfe is the amplification factor of the first power switch tube Q1), and the larger base current impels the second power switch tube Q2 to enter the saturation region rapidly, reducing the The turn-on loss of the second power switch tube Q2; during the period when the second power switch tube Q2 is in the conduction state, the primary side current Is=Ic+hfe*I _B1 flowing through the current sensing resistor Rs (Ic is the primary current Is=Ic+hfe*I B1 flowing through the transformer T winding current); after the voltage Vcs on the current sensing resistor Rs reaches a predetermined setting value (for example, 90% of the maximum voltage value Vcsmax on the current sensing resistor Rs), use the second drive current I _B2 as the second power switch The drive current of tube Q2, because I _B2 << I _B1 , so when using the second drive current I _B2 to maintain the second power switch tube Q2 in the on state, the second power switch tube Q2 stores the carriers in the base region Less, when the second power switch tube Q2 is turned off, the carriers with fewer base regions can quickly recombine to reduce the turn-off time of the second power switch tube Q2 and reduce the turn-off loss of the second power switch tube Q2 .

FIG. 3A shows an example block diagram of the control chip U1A in the primary-side feedback-based flyback power converter 100A shown in FIG. 1A . FIG. 3B shows the control chip U1B in the primary-side feedback-based flyback power converter 100B shown in FIG. 1B. Example block diagram. In the following, for simplicity, the control chips U1A and U1B are collectively referred to as the control chip U1. As shown in FIG. 3A/3B, the first to fourth switch tubes D1 to D4 and the switch control circuit 102 may be included in the control chip U1, and the control chip U1 may also include:

Chip power supply circuit 104: connected to the VDD pin of the control chip U1, including three parts: undervoltage protection (Under Voltage Lock Out, UVLO), overvoltage protection pin (Over Voltage Protection, OVP), reference voltage and reference current (Vref&Iref) , for providing the working voltage, the reference voltage Vref, and the reference current Iref for the internal circuit of the chip. When the voltage at the VDD pin exceeds the UVLO voltage, the internal circuit of the chip starts to work. When the voltage at the VDD pin exceeds the OVP threshold, the internal circuit of the chip enters an automatic recovery protection state to prevent damage to the control chip U1.

Feedback control circuit 106: connected to the FB pin of the control chip U1, a constant voltage (Constant Pressure, CV) control circuit 108, and a logic control circuit 116, including a sampler, an error amplifier (Error Amplifier, EA), a voltage drop compensation, And output overvoltage/undervoltage protection (OVP/UVP) and other parts. The sampler generates an output voltage sampling signal and provides the output voltage sampling signal to the operational amplifier according to the output voltage feedback signal received from the auxiliary winding of the transformer T representing the system output voltage on the secondary winding of the transformer T. 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 a constant voltage (CV) control circuit 108 and a voltage drop compensation part. The drop compensation section generates a drop compensation signal based on the error amplifier signal (this loop is positive feedback). The output OVP and UVP part generates the OVP signal and the UVP signal according to the output voltage feedback signal, and provides the OVP signal and the UVP signal to the logic control circuit 116 .

CV control circuit 108 : connected to the CS current sensing pin of the control chip U1 and the feedback control circuit 106 , used to control the output voltage of the flyback power converter 100A/100B based on the primary side feedback to be constant.

Constant Current (CC) control circuit 110: connected to the FB pin of the control chip U1 and the logic control circuit 116, used to control the The output current of the flyback power converter 100A/100B is constant, and the output current of the flyback power converter 100A/100B based on primary side feedback can be adjusted through the current sensing resistor Rs.

Current sensing control circuit 112: connected to the CS current sensing pin of the control chip U1 and the logic control circuit 116, including leading-edge blanking (Leading-Edge Blanking, LEB) and over-current protection (Over Current Protection, OCP) comparator two A part is used to realize the overcurrent protection of the flyback power converter 00A/100B based on the primary side feedback.

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

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

The protection circuit 118 is used to enable the control chip U1 to enter an automatic recovery protection state when abnormal fault information is detected, so as to prevent the control chip U1 from being damaged.

Here, it should be noted that the switch control circuit 102 is used to generate four control signals for respectively controlling the on and off of the first to fourth switch transistors D1 to D4 according to the logic control signal provided by the logic control circuit 116, the first The first to fourth switching transistors D1 to D4 are turned on and off under the control of the switch control circuit 102 to form the first and second driving currents I _B1 and I _B2 . The first to fourth switch tubes D1, D2, D3, and D4 can use N-type metal-oxide-semiconductor field-effect transistors (N-Metal-Oxide-Semiconductor Field-Effect Transistor, N-MOSFET) or bipolar junction transistors (Bipolar Junction Transistor, BJT) to achieve. The first and third switching transistors D1 and D3 can also be realized by using P-type metal-oxide-semiconductor field-effect transistors (P-Metal-Oxide-Semiconductor Field-Effect Transistor, MOSFET, P-MOSFET).

In the primary-side feedback-based flyback power converter 100A/100B shown in FIG. 1A/B, although the first current source _ISB1 and the first switch tube D1 are shown as directly connected together, the first I _SB1 does not have to be directly connected to a switch tube, as long as the first current source I _SB1 can provide the first driving current I _B1 when the second power switch tube Q2 is in the on state, and when the second power switch tube Q2 is in the off state It is sufficient not to provide the first driving current I _B1 ; 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 is not necessarily directly connected. One switch tube, as long as the second current source I _SB2 can provide the second drive current I _B2 when the second power switch tube Q2 is in the on state, and will not provide the second drive current I B2 when the second power switch tube Q2 is in the off state _B2 will do. In addition, the first driving current I _B1 can be a ramp-up current, a constant current, or a current that changes in a certain proportion with the primary current Is flowing through the current sensing resistor Rs, that is, I _SB1 =Io+α*Is, where , Io is a current constant, α is a predetermined coefficient; the second driving current I _B2 may be a constant current.

In other _words , in the flyback power converter 100A/100B based on the primary side feedback shown in FIG _. Relevant circuit parts can also be implemented in other forms, wherein the first drive current I B1 for the first power switch tube Q1 and the second power switch tube _Q2 is controlled by the first current source I _SB1 in the first switch tube D1 The second drive current I _B2 for the second power switch tube Q2 is provided by the second current source _ISB2 under the control of the third switch tube D3.

FIG. 4A shows a schematic diagram of an exemplary alternative implementation of circuit parts related to the first/second current source _ISB1 / _ISB2 and the first/third switching transistor D1 / D3 . As shown in FIG. 4A, the first/second drive current I _B1 /I _B2 is provided by the first/second current source I _SB1 /I _SB2 under the control of the first/third switch tube D1/D3, wherein: when When the first/third switch tube D1/D3 is in the conduction state, the current of the first/second current source I _SB1 / _ISB2 all flows through the first/third switch tube D1/D3 and is used as the first/second drive Current I _B1 /I _B2 ; when the first/third switch tube D1/D3 is in an off state, the current of the first/second current source I _SB1 / _ISB2 does not flow through the first/third switch tube D1/ D3, the first/second driving current I _B1 /I _B2 is zero. In this case, the area of the first/third switching transistor D1/D3 is relatively large.

FIG. 4B shows a schematic diagram of another exemplary alternative implementation of circuit parts related to the first/second current source _ISB1 / _ISB2 and the first/third switch transistor D1 / D3 . As shown in Figure 4B, the first/second current source _ISB1 / _ISB2 is implemented as a mirror current source, and the reference current source _ISBN for the mirror current source is under the control of the first/third switch tube D1/D3 Included in the mirror current source or not included in the mirror current source, wherein: when the first/third switch tube D1/D3 is in the conduction state, the current of the reference current source _ISBN is generated by mirroring as the first/second The mirror current of the two current sources I _SB1 / _ISB2 , the current of the reference current source I _SBN is only 1/n of the first driving current I _B1 ; when the first/third switching tube D1/D3 is in the off state, the reference The current of the current source I _SBN is not mirrored, and the first/second driving current I _B1 /I _B2 is zero. In this case, the current flowing through the first switch tube D1 is relatively small, and the area of the first switch tube D1 is greatly reduced compared to the situation shown in FIG. 4A .

FIG. 4C shows a schematic diagram of yet another alternative implementation of circuit parts related to the first/second current source _ISB1 / _ISB2 and the first/third switch tube D1 / D3 . As shown in FIG. 4C, the first/second current source _ISB1 / _ISB2 is implemented as a mirror current source, and the first/third switch tube D1/D3 is used for switching control of the mirror current source, wherein: when the first/third When the third switching tube D1/D3 is in the conducting state, the current of the reference current source I _SBN used for the first/second current source I _SB1 /I _SB2 is mirrored and generated as the first/second current source I _SB1 /I _SB2 mirror current, the current of the reference current source _ISBN is only 1/n of the first drive current I _B1 ; when the first/third switch tube D1/D3 is in the off state, the current of the reference current source _ISBN is not mirror image. In this case, the current flowing through the first/third switch tube D1/D3 is 1/n of the first driving current I _B1 , and the area of the first/third switch tube D1/D3 is relatively as shown in FIG. 4A The situation is greatly reduced.

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

FIG. 5 shows a schematic diagram of an example package of the first and second power switch tubes Q1 and Q2 in the primary-side feedback-based flyback power converter 100A/100B shown in FIG. 1A/B. As shown in FIG. 5, the first and second power switch transistors Q1 and Q2 may be included in the same single-substrate island chip package (wherein, the collectors of the first and second power switch transistors Q1 and Q2 are connected), and The detailed pin information of the single-base island chip package is as follows: pin 1 is the first current pin, which is used to receive the first driving current I _B1 and is connected to the base region of the first power switch tube Q1; pin 2 is The second current pin is used to receive the second driving current I _B2 , and is connected to the emitter area of the first power switch tube Q1 and the base area of the second power switch tube Q2; 3/4 pins are emitter pins , connected to the emitter region of the second power switch tube Q2, in order to increase the heat dissipation area and reduce the temperature, multiple bonding wires and multi-pin packaging can be used, for example, two pins are connected by two sets of bonding wires, and each group of bonding wires contains The specific number of bonding wires can be determined according to the area of the emitter area of the second power switch tube Q2; pins 5~8 are collector pins, connected to the collector areas of the first and second power switch tubes Q1 and Q2 , for the convenience of heat dissipation and printed circuit board layout, a multi-pin package is 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 used The conductive glue is connected to the chip base island, no need to wire, and the impedance is the smallest.

FIG. 6 shows an example package diagram of the first and second power switch transistors Q1 and Q2 and the control chip U1 in the primary-side feedback-based flyback power converter 100A/100B shown in FIG. 1A/B. As shown in FIG. 6 , 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 an iterative form. The specific package form can be adjusted according to the number and shape of the base islands, and is not limited to the 8-pin package form. The detailed pin information of the example package shown in Figure 6 is as follows: pins 1, 2, and 3 are control pins for controlling chip U1, connected to The internal pad of the control chip U1; the 4th pin is the emitter pin, which is connected to the emitter area of the second power switch tube Q2. The specific number of roots can be determined according to the area of the emitter region of the second power switch tube Q2; pins 5 to 8 are collector pins, connected to the collector regions of the first and second power switch tubes Q1 and Q2, for Heat dissipation and printed circuit board layout are convenient, and multi-pin packaging is adopted. The collector areas of the first and second power switch tubes Q1 and Q2 are located on the back of the transistor, and are connected to the base island with conductive glue, no need for wiring, and the impedance is the smallest.

The example package shown in Figure 6 can add redundant pins without increasing the cost of system pins. The entire system circuit is simple, with few peripheral components and low system cost.

To sum up, in the flyback power converter based on primary side feedback according to the embodiment of this invention, four switching tubes are used to drive the power switching tubes in combination, which reduces the driving current loss of the power switching tubes and improves the power The turn-on speed of the switch tube. In addition, by setting the pre-turn-off drive current before the power switch tube turns from the on state to the off state, the carriers in the base region during the on state of the power switch tube are reduced, so that the power can be quickly extracted when the power switch tube is turned off. The remaining minority carriers in the base region of the switch tube can increase the turn-off speed and reduce the turn-off loss, so that the application range of the power switch tube in the medium power system can be improved.

This creation can be realized in other specific forms without departing from its spirit and essential characteristics. The current embodiments are to be considered in all respects as illustrative rather than restrictive, the scope of the invention is defined by the appended claims rather than the above description, and what falls within the meaning and range of equivalents of the claims All changes are included within the scope of this work.

100A: flyback power converter

102: switch control circuit

CS: current sense pin

D1: the first switch tube

D2: The second switch tube

D3: The third switch tube

D4: The fourth switch tube

FB, VDD: pin

GND: ground pin

I _B1 : the first driving current

I _B2 : the second driving current

Ic: current

I _S1 : emitter current of the first power switch tube

I _S2 : the emitter current of the second power switch tube

I _SB1 : the first current source

I _SB2 : Second current source

Q1: The first power switch tube

Q2: The second power switch tube

Rs: current sense resistor

U1A: Control chip

Claims (15)

A flyback power converter based on primary side feedback, characterized in that it includes a transformer, first and second power switch tubes, first and second current sources, first, second, third, and fourth switches Tube, and 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, and the second switch tube The second electrode of the first power 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, and the third electrode of the second switch tube 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 through a current sensing resistor for the second power switch. The second driving current of the switch tube is provided by the second current source under the control of the third switch tube. The primary-side feedback-based flyback power converter according to claim 1, wherein, during the process of the second power switch tube changing from the off state to the on state, the first switch tube and the The first power switch tube is in the on state and the second, third, and fourth switch tubes are in the off state, and the base current of the second power switch tube is supplied by the first current source through the first A switch tube and the first power switch tube are provided. The primary-side feedback-based flyback power converter according to claim 1, wherein, during the period when the second power switch is in the on state, before the voltage on the current sensing resistor reaches a predetermined setting value, The first switching tube and the first work The power switch tube is in the on state and the second, third, and fourth switch tubes are in the off state, and the base current of the second power switch tube is supplied by the first current source through the first switch tube and the first power switch tube is provided. The primary-side feedback-based flyback power converter according to claim 1, wherein, during the period when the second power switch is in the on state, after the voltage on the current sensing resistor reaches a predetermined setting value, The first switch tube, the fourth switch tube, and the first power switch tube are in an off state, the second and third switch tubes are in a conduction state, and the base of the second power switch tube The current is provided by the second current source via the third switch tube. The primary-side feedback-based flyback power converter according to claim 1, wherein, during the period when the second power switch tube is in the off state, the first switch tube, the third switch tube, and The first power switch tube is in an off state, and the second and fourth switch tubes are in a conduction state. The primary-side feedback-based flyback power converter according to claim 1, wherein the first, second, third, and fourth switching transistors are implemented as power switching transistors or field effect transistors. The primary-side feedback-based flyback power converter according to claim 1, further comprising a control chip, the first, second, third, and fourth switch tubes and the switch control circuit are included in the control wafer. The primary-side feedback-based flyback power converter according to claim 1, wherein the first and second power switch tubes are included in the same single-island chip package. The flyback power converter based on primary side feedback as described in claim 8, wherein the single-base island chip package has a first current pin, a second current pin, at least one emitter pin, and at least a collector pin. The primary-side feedback-based flyback power converter as described in claim 7, wherein the first and second power switch tubes and the control chip are included in in the same chip package. The primary-side feedback-based flyback power converter according to claim 10, wherein the first and second power switch tubes are packaged in a tiled form, and the control chip and the second power switch tube Packaged in an iterative form. The primary-side feedback-based flyback power converter according to claim 1, wherein the second electrode of the first switch tube is connected to the first current source, and the third electrode of the first switch tube The electrode is connected to the second electrode of the second switch tube. The primary-side feedback-based flyback power converter according to claim 1, wherein the second electrode of the third switching tube is connected to the second current source, and the third switching tube of the third switching tube The electrode is connected to the second electrode of the fourth switch tube. The primary-side feedback-based flyback power converter according to claim 1, wherein the first current source is implemented as a mirror current source, and the first switch tube is used to control the current source used for the first current source Whether the reference current source is included in the mirror current source or is used to implement switch control of the mirror current source. The primary-side feedback-based flyback power converter according to claim 1, wherein the second current source is implemented as a mirror current source, and the third switch tube is used to control the current source used for the third current source Whether the reference current source is included in the mirror current source or is used to implement switch control of the mirror current source.

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