Flyback switching power supply resonant EMI optimization circuit and method

Abstract

The present application relates to a flyback switching power supply resonant EMI optimization circuit and method, which is integrated in a power chip of a flyback switching power supply circuit, and includes: a signal inversion module, which is used to generate an inverted signal SWB that is inverted with the switch signal SW of the first power tube; a sampling timing module, which is used to sample the output feedback voltage signal VS of the secondary coil to determine whether the secondary coil is turned off and collect the turn-off time of the secondary coil; a zero-crossing detection module, which is used to detect whether the output feedback voltage signal VS is zero-crossing; a logic AND gate, which receives signals from the signal inversion module, the sampling timing module and the zero-crossing detection module and outputs and judgment signals; a trigger module, which receives and judges signals and is connected to the second power tube to drive the second power tube to turn on or off; when the logic AND gate outputs a high-level signal, the trigger module drives the second power tube to turn on under the action of the high-level signal to release the resonant energy. It can reduce resonant interference, reduce power loss and improve efficiency.

Description

Technical Field

[0001] The invention relates to a flyback switching power supply resonance EMI optimization circuit and method, belonging to the technical field of flyback switching power supplies. Background Art

[0002] With the development of science and technology, power electronics technology is also constantly developing and innovating. Switching power supplies based on power electronics technology have been widely used in various electronic and electrical equipment, such as communication equipment, military equipment, industrial equipment, household appliances and digital products. However, as the part that is most closely connected to the power grid, its EMC (electromagnetic compatibility) characteristics have become very important. On the one hand, the switching power supply needs to have good adaptability to external electromagnetic interference, and on the other hand, it needs to be able to reduce interference to the power grid and surrounding electronic equipment.

[0003] The phenomenon of electronic products interfering with surrounding electronic equipment when they are working is called EMI (electromagnetic interference). Electromagnetic interference has many hazards. First, it will affect the performance of electronic equipment. Once electromagnetic interference enters the power grid, it will cause serious harmonic pollution and interfere with other electronic equipment on the power grid. Severe electromagnetic interference will cause high voltage breakdown or burning of electronic equipment.

[0004] There are a lot of parasitic capacitors in the flyback switching power supply system. When the power supply works in DCM mode (discontinuous mode), the LC oscillation circuit composed of parasitic capacitors and coils will resonate during the dead time. Therefore, it is easy to generate resonance with a frequency of hundreds of kHz, and resonance with a frequency of hundreds of kHz can easily bring conducted interference to the power supply, making the EMC characteristics of the switching power supply worse, resulting in large losses and low efficiency. Summary of the invention

[0005] The object of the present invention is to provide a flyback switching power supply resonant EMI optimization circuit and method, which can reduce resonant interference, reduce power loss and improve efficiency.

[0006] To achieve the above object, the present invention provides the following technical solution: a flyback switching power supply resonant EMI optimization circuit, integrated in a power chip of the flyback switching power supply circuit, the flyback switching power supply circuit comprising an auxiliary coil, a first power tube and a second power tube connected to the auxiliary coil, the flyback switching power supply resonant EMI optimization circuit comprising:

[0007] A signal inversion module, used to generate an inverted signal SWB which is inverted to the switching signal SW of the first power tube;

[0008] A sampling timing module, used for sampling the output feedback voltage signal VS of the secondary coil induced by the auxiliary coil of the flyback switching power supply, so as to determine whether the secondary coil is turned off, and to collect the turn-off time of the secondary coil;

[0009] A zero-crossing detection module, used to detect whether the output feedback voltage signal VS crosses zero;

[0010] A logic AND gate, receiving signals from the signal inversion module, the sampling timing module and the zero-crossing detection module and outputting an AND judgment signal;

[0011] A trigger module receives the judgment signal and is connected to the second power tube to drive the second power tube to turn on or off;

[0012] When the logic AND gate outputs a high level signal, the trigger module drives the second power tube to turn on under the action of the high level signal to release the resonance energy.

[0013] Furthermore, the inversion module includes an inverter, and the inverter inverts the switch signal SW of the first power tube and outputs a reverse signal SWB.

[0014] Furthermore, the sampling timing module includes a sampling circuit and a timing circuit. The sampling circuit outputs a detection signal Ssec when it detects that the secondary coil is turned on or off. The timing circuit starts timing, and when the timing duration reaches a preset duration in the timing circuit, the timing circuit outputs a high level signal.

[0015] Furthermore, the inverted signal SWB can also reset the timing circuit.

[0016] Further, the zero-crossing detection module includes a zero-crossing detection circuit, and when the zero-crossing detection circuit detects that the output feedback voltage signal VS crosses zero, the output voltage zero-crossing detection signal ZERO.

[0017] Furthermore, the trigger module includes an RS trigger and a driving circuit connected to the RS trigger and the second power tube, the S end of the RS trigger is connected to the output end of the logic AND gate, the R end of the RS trigger is connected to the switching signal SW of the first power tube, and the Q end of the RS trigger is connected to the driving circuit.

[0018] Furthermore, the flyback switching power supply circuit also includes an anti-backflow diode, a first end of the anti-backflow diode is connected to one end of the auxiliary coil, and a second end of the anti-backflow diode is connected to the drain of the second power tube.

[0019] Furthermore, the anti-backflow diode and the second power tube may be integrated in the power chip, or the anti-backflow diode and the second power tube may be externally arranged.

[0020] The present invention also provides a flyback switching power supply resonant EMI optimization method, which is used in a flyback switching power supply circuit, wherein the flyback switching power supply circuit includes an auxiliary coil, a first power tube and a second power tube connected to the auxiliary coil, and adopts the flyback switching power supply resonant EMI optimization circuit as described above, and the method includes the following steps:

[0021] Acquire a switch signal SW of the first power tube and an output feedback voltage signal VS of a secondary coil induced by an auxiliary coil of the flyback switching power supply;

[0022] The signal inversion module inverts the switch signal SW to obtain an inverted signal SWB;

[0023] The sampling timing module samples the secondary coil of the flyback switching power supply. If the secondary coil is turned off, a low-level conduction detection signal Ssec is output. At the same time, the sampling timing module starts timing. When the timing duration reaches a preset duration, the sampling timing module outputs a high-level signal.

[0024] The zero-crossing detection module detects whether the output feedback voltage signal VS crosses zero, and if the feedback voltage signal VS crosses zero, outputs a high-level zero-crossing detection signal ZERO;

[0025] When the sampling timing module output signal, the inverting signal SWB and the zero-crossing detection signal ZERO are all at high levels, the logic AND gate outputs a high level and then controls the second power tube to turn on to release the resonance energy.

[0026] The beneficial effect of the present invention is that when the first power tube is turned off, the primary coil is turned off and the secondary coil is not turned on, the timing of the dead time is used to determine the switch of the second power tube, and then the resonant energy in the dead time is discharged, thereby achieving the effect of interrupting the resonance.

[0027] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The schematic diagram is a circuit diagram of a flyback switching power supply circuit in the prior art.

[0029] Figure 2 It is a resonant waveform diagram of the existing flyback switching power supply circuit.

[0030] Figure 3 This is a schematic diagram of the application of the resonant EMI optimization circuit of the flyback switching power supply of the present invention in the flyback switching power supply.

[0031] Figure 4 It is a module block diagram of the flyback switching power supply resonant EMI optimization circuit of the present invention.

[0032] Figure 5 It is a schematic diagram of a resonant EMI optimization circuit of a flyback switching power supply of the present invention.

[0033] Figure 6 It is a circuit waveform diagram of the flyback switching power supply resonant EMI optimization circuit of the present invention. DETAILED DESCRIPTION

[0034] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0035] See also Figure 1 , which is a flyback switching power supply in the prior art, including a rectifier circuit for converting AC to DC, a first capacitor C1, a second capacitor C2 and a primary coil NP connected to the rectifier circuit, a secondary coil NS and an auxiliary coil NA having mutual inductance with the primary coil NP, and a power chip POWER IC connected to the auxiliary coil NA.

[0036] The flyback switching power supply further includes a first resistor R1 connected to both ends of the primary coil NP, a third capacitor C3 connected in parallel with the first resistor R1, a fourth diode D5 connected to the third capacitor C3 and the primary coil NP loop, a fifth capacitor C5 connected to both ends of the secondary coil NS, and a seventh diode D7 connected to the fifth capacitor C5 and the secondary coil NS loop. The flyback switching power supply further includes a first parasitic capacitor Cpara1 connected to both ends of the primary coil NP and a second parasitic capacitor Cpara2 connected to both ends of the secondary coil NS.

[0037] The flyback switching power supply further includes a third parasitic capacitor Cpara3 connected to the auxiliary coil NA, a second resistor R2, a third resistor R3, a fourth resistor R4, a sixth diode D6, a fourth capacitor C4, and a power tube Q1. Both ends of the third parasitic capacitor Cpara3 are connected to the auxiliary coil NA, a first end of the second resistor R2 is connected to one end of the auxiliary coil NA, a first end of the third parasitic capacitor Cpara3 is connected, and the second resistor R2 The second end of the sixth diode D6 is connected to the first end of the third resistor R3, the second end of the third resistor R3 is connected to the other end of the auxiliary coil NA and the second end of the third parasitic capacitor Cpara3, the first end of the sixth diode D6 is connected to the first end of the second resistor R2, the second end of the sixth diode D6 is connected to the first end of the fourth capacitor C4 and the VCC pin of the power supply chip, the other end of the fourth capacitor C4 is connected to the second end of the third resistor R3, the first end of the fourth resistor R4 is connected to the CS pin of the power supply chip, the third resistor R3, the fourth capacitor C4 and the second ends of the fourth resistor R4 are connected in parallel and grounded, the GND pin of the power supply chip is also grounded, the drain of the power tube Q1 is connected to the DRAIN pin of the power supply chip and the primary coil NP, the gate of the power tube Q1 is connected to the GATE pin of the power supply chip, the source of the power tube Q1 is connected to the CS pin of the power supply chip and the first end of the fourth resistor R4, and the VS pin of the power supply chip is connected to the second end of the second resistor R2 and the first end of the third resistor R3.

[0038] See also Figure 2 , Vdc is the DC voltage on capacitor C2, Vfb is the voltage on the secondary coil that is inducted by the transformer to the primary coil, then:

[0039]

[0040] Due to the existence of the first parasitic capacitor Cpara1, the second parasitic capacitor Cpara2, and the third parasitic capacitor Cpara3, resonance will occur in the LC oscillation circuit formed with the primary coil NP, the secondary coil NS, and the auxiliary coil NA respectively during the dead time. As the switching frequency decreases and the dead time increases, the resonance time becomes longer, which makes it more likely to cause the EMC characteristics to deteriorate and the efficiency to decrease.

[0041] See also Figure 3In order to solve the above technical problems, the flyback switching power supply circuit of the present invention also includes a flyback switching power supply resonant EMI optimization circuit integrated in a power supply chip. At the same time, the flyback switching power supply circuit also includes a second power tube Q2 and an anti-backflow diode D8 for preventing current backflow. The anti-backflow diode and the second power tube can be integrated in the power supply chip, or the anti-backflow diode and the second power tube can be externally connected. In this embodiment, the anti-backflow diode D8 is externally connected to the second power tube Q2. The first end of the anti-backflow diode D8 is connected to one end of the auxiliary coil NA, the second end of the anti-backflow diode D8 is connected to the drain of the second power tube Q2, the gate of the second power tube Q2 is connected to the control end GATE2 of the flyback switching power supply resonant EMI optimization circuit, and the source of the second power tube Q2 is connected to the second end of the third resistor R3 and grounded.

[0042] Please combine Figure 4 and Figure 5 The flyback switching power supply resonant EMI optimization circuit includes a signal inversion module 1, a sampling timing module 2, a zero-crossing detection module 3, a logic AND gate 4 and a trigger module 5, wherein the signal inversion module 1 is used to reverse the switching signal of the first power tube Q1, the sampling timing module 2 is used to sample the output feedback voltage signal VS of the secondary coil induced by the auxiliary coil of the flyback switching power supply circuit to determine whether the secondary coil is turned off and collect the turn-off time of the secondary coil, the zero-crossing detection module 3 is used to detect whether the output feedback voltage signal VS is zero-crossing, the logic AND gate 4 is connected to the signal inversion module 1, the sampling timing module 2 and the zero-crossing detection module 3, and the trigger module 5 is connected to the second power tube Q2 and is used to drive the second power tube Q2 to turn on or off. When the logic AND gate 4 outputs a high-level signal, the trigger module 5 drives the second power tube Q2 to turn on under the action of the high-level signal to release the resonant energy.

[0043] Specifically, the inverting module 1 includes an inverter, which inverts the switching signal of the first power tube Q1 and outputs an inverted signal SWB. Meanwhile, when the primary coil NP is turned on, the reverse signal SWB can also reset the timing circuit.

[0044] The sampling timing module 2 includes a sampling circuit connected to the auxiliary coil of the flyback switching power supply, and a timing circuit for connecting the sampling circuit and a logic AND gate 4. When the sampling circuit detects that the secondary coil is turned off, it outputs a low-level conduction detection signal Ssec. At the same time, the timing circuit starts timing. When the timing duration reaches a preset duration preset in the timing circuit, the sampling timing module outputs a high-level signal.

[0045] The zero-crossing detection module 3 comprises a zero-crossing detection circuit. When the zero-crossing detection circuit detects that the feedback voltage detection signal VS crosses zero, the zero-crossing detection circuit outputs a voltage zero-crossing detection signal ZERO.

[0046] The trigger module 5 includes an RS trigger and a driving circuit connected to the RS trigger and the second power tube. The S end of the RS trigger is connected to the output end of the logic AND gate 4, the R end of the RS trigger is connected to the switching signal SW of the first power tube Q1, and the Q end of the RS trigger is connected to the driving circuit.

[0047] The implementation process of the flyback switching power supply resonant EMI optimization circuit of the present invention is: in DCM mode (discontinuous mode), after the secondary coil NS is turned off, the primary coil NP is not turned on, that is, resonance will occur during the dead time. At this time, the switch signal SW of the first power tube Q1 is 0, and the inverting signal SWB is 1; the sampling circuit detects that the secondary coil NS is turned off, that is, Ssec=0, the timing circuit starts timing, and sets the maximum timing duration tdmax. When the timing duration reaches the maximum timing duration tdmax, the sampling timing module output signal is high level. The zero-crossing detection circuit starts to detect whether the output feedback voltage signal VS is zero-crossing. When the output feedback voltage detection signal VS is zero-crossing, that is, the second half cycle of Vd resonance, the voltage zero-crossing detection signal ZERO=1. When the inverting signal SWB, the voltage zero-crossing detection signal ZERO and the output signal of the sampling timing module are all at high level, the logic AND gate 4 outputs the signal SW1=1, and then the RS trigger outputs the signal SW2=1, and then the driving circuit outputs the driving signal GATE2=1 to the second power tube Q2, turning on the second power tube Q2. After Q2 is turned on, the auxiliary coil NA releases the energy on the coil through the eighth diode D8 and the second power tube Q2, so that the flyback switching power supply releases the resonant energy through the auxiliary coil NA, thereby achieving the effect of interrupting the resonance.

[0048] When the primary coil NP is turned on, that is, SW=1, the inverting signal SWB=0. At this time, the switch signal SW resets the RS trigger, that is, SW2=0, driving the second power tube Q2 to turn off; at the same time, the inverting signal SWB serves as a reset signal for the timing circuit. When the primary coil is turned on, the timing circuit is reset and the timing is restarted when entering the dead zone next time.

[0049] Please combine Figure 6, where GATE1 is the switch control signal of the first power tube Q1, Vd is the drain voltage waveform of the switch tube Q1, Ssec is the secondary coil conduction detection signal, VS is the output feedback voltage signal of the secondary coil induced by the auxiliary coil, ZERO is the detection signal that the VS voltage is less than zero in the dead zone, that is, the signal of the negative half cycle of the resonant energy, and GATE2 is the switch control signal of the second power tube Q2. When the output load decreases, the power chip controls the switching frequency to decrease, and the dead zone time increases accordingly. After entering the dead zone, the LC oscillation circuit composed of parasitic capacitance and coil starts to work, generating harmonic oscillation at the drain end of the first power tube Q1. At the same time, the timing circuit in the resonant energy release circuit starts timing. In the T1 and T2 cycles, due to the short dead time, the SW2=1 signal is not generated to control the opening of the second power tube Q2; in the T3 and T4 cycles, due to the long dead time, the Vd resonant voltage is in the second half cycle and the primary coil NP is turned on before the SW2=1 signal is generated, the second power tube Q2 is turned on, the resonant energy is released through the auxiliary coil, the Vd voltage no longer resonates, and is equal to the Vdc voltage. When SW=1, the primary coil is turned on, SW2=0, and the power tube Q2 is turned off.

[0050] The present invention also provides a resonance energy release control method, the method comprising the following steps:

[0051] Acquire a switch signal SW of the first power tube and an output feedback voltage signal VS of a secondary coil induced by an auxiliary coil of the flyback switching power supply;

[0052] The signal inversion module inverts the switch signal SW to obtain an inverted signal SWB;

[0053] The sampling timing module samples the secondary coil of the flyback switching power supply. If the secondary coil is turned off, a low-level conduction detection signal Ssec is output. At the same time, the sampling timing module starts timing. When the timing duration reaches a preset duration, the output signal is high level.

[0054] The zero-crossing detection module detects whether the output feedback voltage signal VS crosses zero, and if the feedback voltage signal VS crosses zero, outputs a high-level zero-crossing detection signal ZERO;

[0055] When the output signal, the inverted signal SWB and the zero-crossing detection signal ZERO are all at high levels, that is, in the negative half cycle of the resonant energy, the logic AND gate outputs a high level, the trigger drives the second power tube to turn on, and the auxiliary coil releases the energy on the coil through the eighth diode D8 and the second power tube Q2, so that the flyback switching power supply releases the resonant energy through the auxiliary coil NA;

[0056] When the primary coil NP of the flyback switching power supply is turned on, the switching signal SW of the first power tube Q1 is at a high level, triggering the reset of the trigger to turn off the second power tube Q2. At the same time, the switching signal SW of the first power tube Q1 outputs a low level signal through the inverter to reset the timing circuit and wait for the next cycle to be re-timing.

[0057] In summary, when the first power tube Q1 is turned off, the primary coil NP is turned off and the secondary coil NS is not turned on, the dead time is used to determine the switch of the second power tube Q2, and then the resonant energy in the dead time is discharged, thereby achieving the effect of interrupting the resonance.

[0058] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0059] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A flyback switching power supply resonant EMI optimization circuit, integrated in a power chip of a flyback switching power supply circuit, characterized in that: The flyback switching power supply circuit includes an auxiliary coil, a first power tube and a second power tube connected to the auxiliary coil, and the flyback switching power supply resonant EMI optimization circuit includes: A signal inversion module, used to generate an inverted signal SWB which is inverted to the switching signal SW of the first power tube; A sampling timing module, used for sampling the output feedback voltage signal VS of the secondary coil induced by the auxiliary coil of the flyback switching power supply, so as to determine whether the secondary coil is turned off, and to collect the turn-off time of the secondary coil; A zero-crossing detection module, used to detect whether the output feedback voltage signal VS crosses zero; A logic AND gate, receiving signals from the signal inversion module, the sampling timing module and the zero-crossing detection module and outputting an AND judgment signal; A trigger module receives the judgment signal and is connected to the second power tube to drive the second power tube to turn on or off; When the logic AND gate outputs a high level signal, the trigger module drives the second power tube to turn on under the action of the high level signal to release the resonance energy.

2. The flyback switching power supply resonant EMI optimization circuit as claimed in claim 1, characterized in that: The inversion module includes an inverter, which inverts the switch signal SW of the first power tube and outputs a reverse signal SWB.

3. The flyback switching power supply resonant EMI optimization circuit as claimed in claim 2, characterized in that: The sampling timing module includes a sampling circuit and a timing circuit. The sampling circuit outputs a detection signal Ssec when detecting that the secondary coil is turned on or off. The timing circuit starts timing, and when the timing duration reaches the preset duration in the timing circuit, the timing circuit outputs a high level signal.

4. The flyback switching power supply resonant EMI optimization circuit as claimed in claim 3, characterized in that: The inverted signal SWB can also reset the timing circuit.

5. The flyback switching power supply resonant EMI optimization circuit as claimed in claim 1, characterized in that: The zero-crossing detection module includes a zero-crossing detection circuit. When the zero-crossing detection circuit detects that the output feedback voltage signal VS crosses zero, the zero-crossing detection circuit outputs a voltage zero-crossing detection signal ZERO.

6. The flyback switching power supply resonant EMI optimization circuit as claimed in claim 1, characterized in that: The trigger module includes an RS trigger and a driving circuit connected to the RS trigger and the second power tube, the S end of the RS trigger is connected to the output end of the logic AND gate, the R end of the RS trigger is connected to the switching signal SW of the first power tube, and the Q end of the RS trigger is connected to the driving circuit.

7. The flyback switching power supply resonant EMI optimization circuit as claimed in claim 1, characterized in that: The flyback switching power supply circuit also includes an anti-backflow diode, a first end of the anti-backflow diode is connected to one end of the auxiliary coil, and a second end of the anti-backflow diode is connected to the drain of the second power tube.

8. The flyback switching power supply resonant EMI optimization circuit as claimed in claim 7, characterized in that: The anti-backflow diode and the second power tube can be integrated in the power chip, or the anti-backflow diode and the second power tube can be externally arranged.

9. A flyback switching power supply resonant EMI optimization method, used in a flyback switching power supply circuit, the flyback switching power supply circuit comprising an auxiliary coil, a first power tube and a second power tube connected to the auxiliary coil, characterized in that: Using the flyback switching power supply resonant EMI optimization circuit according to any one of claims 1 to 8, the method comprises the following steps: Acquire a switch signal SW of the first power tube and an output feedback voltage signal VS of a secondary coil induced by an auxiliary coil of the flyback switching power supply; The signal inversion module inverts the switch signal SW to obtain an inverted signal SWB; The sampling timing module samples the secondary coil of the flyback switching power supply. If the secondary coil is turned off, a low-level conduction detection signal Ssec is output. At the same time, the sampling timing module starts timing. When the timing duration reaches a preset duration, the sampling timing module outputs a high-level signal. The zero-crossing detection module detects whether the output feedback voltage signal VS crosses zero, and if the feedback voltage signal VS crosses zero, outputs a high-level zero-crossing detection signal ZERO; When the sampling timing module output signal, the inverting signal SWB and the zero-crossing detection signal ZERO are all at high levels, the logic AND gate outputs a high level and then controls the second power tube to turn on to release the resonance energy.

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