Circuit capable of reducing VCC resonance peak of flyback power transformer

Abstract

The invention discloses a circuit capable of reducing a VCC resonance peak of a flyback power supply transformer, which mainly comprises a switching power supply isolation transformer and a primary switching power supply PWM control circuit, and a damping oscillation circuit is connected in series between the switching power supply isolation transformer and the primary switching power supply PWM control circuit. According to the invention, the flow direction of reverse current is changed by controlling the conduction of the triode Q1, and the current is guided to be absorbed and blocked through the damping oscillation circuit, so that the resonance of the VCC winding is reduced, the damping oscillation of other windings is further changed, and the purpose of optimizing the EMC of the power supply is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of flyback power supplies, and specifically refers to a circuit that can reduce the VCC resonance spike of a flyback power supply transformer. Background Art

[0002] In current flyback power supply design solutions, problems of EMC radiation interference caused by leakage inductance resonance are commonly encountered. Due to transformer production technology issues, when the switching transistor turns off, the leakage inductance of the transformer will form an LC resonance circuit with the output capacitance of the switching transistor, the parasitic capacitance of the transformer, etc., thus generating resonance spikes. At the same time, the high-frequency current changes (di / dt) and voltage changes (dv / dt) generated during the fast on-off of the switching transistor and the reverse recovery of the diode will propagate through the parasitic capacitance of the transformer and other channels, resulting in electromagnetic interference (EMI) problems and affecting EMC performance. The traditional RC absorption circuit is difficult to effectively solve the power EMC-related problems derived therefrom. Therefore, it is an urgent problem to be solved to develop a circuit that can reduce the VCC resonance spike of a flyback power supply transformer. Summary of the Invention

[0003] The purpose of the present invention is to solve the above problems and provide a circuit that can reduce the VCC resonance spike of a flyback power supply transformer.

[0004] The purpose of the present invention is achieved through the following technical solutions: A circuit that can reduce the VCC resonance spike of a flyback power supply transformer mainly consists of a switching power supply isolation transformer and a primary switching power supply PWM control circuit, and a damping oscillation circuit is connected in series between the switching power supply isolation transformer and the primary switching power supply PWM control circuit.

[0005] Further, the damping oscillation circuit is composed of an RC filter circuit, a triode Q1, a rectifier diode D3, and resistors R4 and R10; the emitter of the triode Q1 is connected to the primary switching power supply PWM control circuit, its collector is connected to the switching power supply isolation transformer after passing through the RC filter circuit, and its base is connected to the switching power supply isolation transformer after passing through the resistor R10 and the rectifier diode D3; one end of the resistor R4 is connected to the emitter of the triode Q1, and the other end is connected to the cathode of the rectifier diode D3.

[0006] The primary switching power supply PWM control circuit includes a power chip U1 and a capacitor EC5. The VCC pin of the power chip U1 is connected to the emitter of the triode Q1. One end of the capacitor EC5 is connected to the VCC pin of the power chip U1, and the other end is grounded; when no spike is formed in the power chip U1, the triode Q1 is in the off state; when a spike is formed in the power chip U1, the triode Q1 is in the on state.

[0007] The primary side of the switching power supply isolation transformer is provided with a primary winding and a parallel winding. One terminal of the parallel winding is connected to the anode of the rectifier diode D3, and the other terminal is grounded.

[0008] The described RC filter circuit is composed of a resistor R5 and a capacitor C3 connected in parallel. The resistance value of the resistor R5 is 10 kΩ, and the value of the capacitor C3 is 0.01 μF / 1 KV.

[0009] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0010] (1) By controlling the conduction of the triode Q1, the present invention changes the flow direction of the reverse current, guides the current to be absorbed and blocked by the damping oscillation circuit, reduces the resonance of the VCC winding, and then changes the damping oscillation of other windings, achieving the purpose of optimizing the power supply EMC.

[0011] (2) By reducing the VCC resonance peak, the present invention reduces the high-frequency noise and electromagnetic interference generated during the operation of the power supply, helps the power supply meet the relevant electromagnetic compatibility standards, reduces the interference to other surrounding electronic devices, and at the same time improves the anti-interference ability of the power supply itself.

[0012] (3) When no peak is formed in the power chip U1, the triode Q1 is in the off state, and the circuit power consumption is low at this time; when a peak appears, the triode Q1 quickly conducts to process the peak quickly. This fast response mechanism enables the circuit to respond to the appearance of the peak in a timely manner and improves the dynamic performance of the power supply. Description of the Drawings

[0013] Figure 1 It is a schematic diagram of the overall circuit structure of the present invention. Detailed Embodiment

[0014] The following further elaborates on the present invention in conjunction with embodiments, but the implementation manners of the present invention are not limited thereto.

[0015] Embodiment

[0016] As Figure 1 shown, the circuit for reducing the VCC resonance peak of the flyback power supply transformer described in this embodiment mainly consists of a switching power supply isolation transformer 1, a primary switching power supply PWM control circuit 3, and a damping oscillation circuit 2 connected in series between the switching power supply isolation transformer 1 and the primary switching power supply PWM control circuit 3.

[0017] The switching power supply isolation transformer 1 is used to provide different voltages for different loads. By reasonably designing the turns ratio of the windings, the switching power supply isolation transformer 1 can convert the mains power or other input voltages into various required output voltages to meet the power supply needs of different loads. The primary side of the switching power supply isolation transformer 1 is provided with two windings, namely the primary winding and the parallel winding. The primary winding has three terminals, namely terminal 1, terminal 2, and terminal 3. Terminal 1 and terminal 3 of the primary winding are connected to the primary input rectifier circuit of the switching power supply. The parallel winding has two terminals, namely terminal 4 and terminal 5. When the primary winding is energized, the parallel winding will induce a corresponding induced voltage and induced current according to the current flow direction of the primary winding, and the secondary winding of the switching power supply isolation transformer 1 is externally connected to the secondary rectifier circuit of the switching power supply.

[0018] The primary switching power supply PWM control circuit 3 includes a power chip U1, a capacitor EC5, and other auxiliary circuits. The power chip U1 is a DK065G chip, which is a quasi-resonant flyback control AC-DC power switch chip highly integrated with 650V / 260mΩ GaN HEMT, and a GaN-MOS tube is encapsulated inside it. The capacitor EC5 is preferably implemented by a capacitor with parameters of 10uF / 50V, that is, the capacitance of the capacitor EC5 is 10 microfarads and its rated voltage is 50 volts.

[0019] The damping oscillation circuit 2 is the core part of this embodiment, and it is composed of an RC filter circuit, a triode Q1, a rectifier diode D3, and resistors R4 and R10. To ensure the accurate operation of this embodiment, the triode Q1 is preferably implemented by a PNP type triode of MMBT5401.

[0020] When connecting, the anode of the rectifier diode D3 is connected to terminal 5 of the parallel winding, and terminal 4 of the parallel winding is grounded; the cathode of the rectifier diode D3 is connected to the VCC pin of the power chip U1 after passing through a resistor R4 with a resistance value of 1.8 ohms. The emitter of the triode Q1 is connected to the VCC pin of the power chip U1, its base is connected to the cathode of the rectifier diode D3 after passing through a resistor R10, and its collector is connected to the anode of the rectifier diode D3 after passing through the RC filter circuit. The RC filter circuit is composed of a resistor R5 and a capacitor C3 in parallel. The resistance value of the resistor R5 is 10 kΩ, and the capacitance of the capacitor C3 needs to be 0.01 μF, and its withstand voltage value is 1 kV.

[0021] The principle of this embodiment is as follows: When the GaN-MOS integrated in the power chip U1 is turned on, the parallel winding of the switch-mode power supply isolation transformer 1 induces corresponding voltage and current according to the alternating magnetic field of the primary coil. This current is filtered by the rectifier diode D3, resistor R4, and capacitor EC5 to provide voltage and current for the VCC terminal of the power chip U1. At this time, the capacitor EC5 is charged and stores energy.

[0022] When the GaN-MOS integrated in the power chip U1 is turned off, a reverse current appears in the VCC circuit due to the leakage inductance energy, forming a spike. At this time, this reverse current flows reversely from the VCC terminal of the power chip U1 through the resistor R4 and acts on the cathode of the rectifier diode D3. Since this spike voltage and current are relatively large, the rectifier diode D3 will be Zener breakdown in a short time, so that the reverse spike current forms an electrical loop with the connection terminals 5 and 4 of the parallel winding after passing through the rectifier diode D3. At the same time, since a voltage drop will be formed when the spike current flows through the resistor R4, the emitter current of the triode Q1 is greater than the base and collector currents, and the triode Q1 is turned on. At this time, the large reverse spike current will pass through the emitter, collector of the triode Q1, the RC filter circuit, and then through the connection terminals 5 and 4 of the parallel winding to ground. And the voltage acting on the cathode of the rectifier diode D3 will decrease at this time, and the rectifier diode D3 will return to its normal working state to maintain the continuous conduction of the triode Q1.

[0023] The large reverse spike current is absorbed by the RC filter circuit after passing through the emitter and collector of the triode Q1, so that the large reverse spike current quickly stabilizes, thus achieving the purpose of eliminating the resonance spike and improving the EMC.

[0024] That is to say, in this embodiment, the triode Q1 is in the off state when the power chip U1 does not form a spike; when the power chip U1 forms a spike, the triode Q1 is in the on state.

[0025] Other auxiliary circuits of the primary switch-mode power supply PWM control circuit 3 include a linear optocoupler U1A, resistor R8, resistor R9, resistor RS3, resistor RS4, resistor RS5, capacitor C5, and capacitor C6. Among them, the linear optocoupler U1A is preferably implemented by the EL817 type. The resistance value of the resistor R8 is 140 KΩ, the resistor R9 is 12 KΩ, the resistor RS3, resistor RS4, and resistor RS5 are all 0.82 KΩ, the parameter of the capacitor C5 is 102 / 50V, and the parameter of the capacitor C6 is 22PF / 1KV.

[0026] When connected, one end of resistor R8 is connected to the VS pin of power chip U1, and the other end is connected to the terminal 5 of the parallel winding; one end of resistor R9 is connected to the VS pin of power chip U1, and the other end is grounded; one end of linear optocoupler U1A is connected to the FB pin of power chip U1, and the other end is grounded; one end of capacitor C5 is connected to the FB pin of power chip U1, and the other end is grounded; after resistors RS3, RS4 and RS5 are connected in parallel, one end is connected to the CS pin of power chip U1, and the other end is grounded; one end of capacitor C6 is connected to the SW pin of power chip U1 and the terminal 3 of the primary winding respectively, and the other end is grounded.

[0027] As described above, the present invention can be implemented with high efficiency.

Claims

1. A circuit capable of reducing the resonance peak of a flyback power transformer VCC, mainly comprising a switching power isolation transformer (1) and a primary switching power PWM control circuit (3), characterized in that: A damping oscillation circuit (2) is connected in series between a switching power supply isolation transformer (1) and a primary switching power supply PWM control circuit (3).

2. A circuit capable of reducing the resonance peak of the flyback power transformer VCC according to claim 1, characterized in that: The damped oscillation circuit (2) is composed of an RC filter circuit, a transistor Q1, a rectifier diode D3, and resistors R4 and R10; the emitter of the transistor Q1 is connected to the primary switch power PWM control circuit (6), the collector thereof is connected to the switch power isolation transformer (2) after passing through the RC filter circuit, and the base thereof is connected to the switch power isolation transformer (2) after passing through the resistor R10 and the rectifier diode D3; one end of the resistor R4 is connected to the emitter of the transistor Q1, and the other end is connected to the cathode of the rectifier diode D3.

3. A circuit capable of reducing the resonance peak of the flyback power transformer VCC according to claim 2, characterized in that: The primary switch power supply PWM control circuit (3) comprises a power chip U1 and a capacitor EC5, wherein the VCC pin of the power chip U1 is connected to the emitter of the transistor Q1, one end of the capacitor EC5 is connected to the VCC pin of the power chip U1, and the other end is grounded; when the power chip U1 does not form a spike, the transistor Q1 is in an off state; when the power chip U1 forms a spike, the transistor Q1 is in an on state.

4. A circuit capable of reducing the resonance peak of the flyback power transformer VCC according to claim 3, characterized in that: The primary end of the switching power supply isolation transformer (1) is provided with a primary winding and a parallel winding, one terminal of the parallel winding is connected to the anode of the rectifier diode D3, and the other terminal is grounded.

5. A circuit capable of reducing the resonance peak of a flyback power transformer VCC according to any one of claims 2 to 4, characterized in that: The RC filter circuit is composed of a resistor R5 and a capacitor C3 connected in parallel. The resistance of the resistor R5 is 10 kilo-ohms, and the value of the capacitor C3 is 0.01 μF / 1KV.

6. A circuit capable of reducing the resonance peak of the flyback power transformer VCC according to claim 5, characterized in that: The transistor Q1 is of PNP type.

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