Harmonic improved flyback converter and switching power supply

Abstract

The utility model relates to harmonic circuit technical field especially is involved in a kind of harmonic improved flyback conversion circuit and switching power supply, including transformer T1, rectifier bridge, capacitor C1-C3, diode D1-D2 and switch tube S1, transformer T1 has a primary winding, primary winding is equipped with intermediate tap, the primary winding is divided into the first part N1a and second part N1b with the number of turns ratio of N1a:N1b;Rectifier bridge is composed of diode DB1, DB2, DB3 and DB4, and the live wire and zero line of alternating current power supply are connected to the alternating current input end. Through the intermediate tap of transformer primary winding, compensation is directly carried out, and the number of turns ratio of N1a:N1b can be adjusted to adjust the harmonic size through tap compensation, which is more flexible, and no additional auxiliary winding is needed, reducing the complexity and cost of the circuit, and also effectively reducing the influence of harmonic on circuit performance, improving the stability and reliability of the circuit.

Description

Technical Field

[0001] This utility model relates to the field of harmonic circuit technology, and in particular to a harmonic-improved flyback converter circuit and a switching power supply. Background Technology

[0002] Total harmonic distortion (THD) is an indicator of harmonic distortion in electrical signals. It is commonly defined as the ratio of the sum of the power of all harmonic components to the power of the fundamental frequency signal. Sometimes it is also expressed as the distortion factor. A higher THD indicates a larger proportion of harmonic components. Harmonic distortion refers to the unwanted signals superimposed on the input signal due to nonlinear factors. These unwanted signals are multiples of the original input signal's frequency.

[0003] Harmonic distortion is a critical issue in power supply circuits. Existing harmonic compensation techniques typically require additional harmonic suppression circuitry, which increases cost and circuit complexity. For example, the filter circuit with harmonic compensation proposed in patent CN114142747A uses components such as freewheeling capacitors, freewheeling switches, and unidirectional switches for harmonic compensation. However, this solution is limited by the auxiliary power supply level, making harmonic compensation easily restricted; moreover, it requires a relatively complex circuit structure and control method, resulting in higher costs. Utility Model Content

[0004] To address the issues of complex and costly existing harmonic suppression circuits, this invention provides a harmonic-improved flyback converter circuit. By utilizing the turns ratio of the center tap of the primary winding of the flyback converter transformer, the harmonic compensation magnitude can be flexibly adjusted. It employs only low-cost passive components to achieve a higher power factor and lower harmonic current in the switching power supply.

[0005] This invention provides a harmonic-improved flyback converter circuit, including...

[0006] Transformer T1 has a primary winding with an intermediate tap, which divides the primary winding into a first part N1a and a second part N1b with a turns ratio of N1a:N1b.

[0007] The rectifier bridge consists of diodes DB1, DB2, DB3 and DB4, and its AC input terminal is connected to the live wire and neutral wire of the AC power supply.

[0008] Capacitor C1 is connected between the positive output terminal and the negative input terminal of the rectifier bridge;

[0009] Capacitor C2 is connected at one end to the positive output terminal of the rectifier bridge, and at the other end to the cathode of diode D1 and the anode of diode D2.

[0010] Capacitor C3 is connected to the neutral wire at one end and to the anode of diode D1 and the cathode of diode D3 at the other end.

[0011] Diode D1 is connected between capacitor C2 and capacitor C3;

[0012] Diode D2, with its anode connected to capacitor C2 and the cathode of diode D1, and its cathode connected to the center tap of the primary winding;

[0013] The switching transistor S1 is connected at one end to the secondary input terminal of the rectifier bridge and at the other end to the output terminal of the primary winding.

[0014] During the positive half-cycle of the input voltage, capacitor C3 and the AC voltage Vac of the AC power supply jointly charge capacitor C1; during the negative half-cycle of the input voltage, capacitor C2 and the AC voltage jointly charge capacitors C1 and C3. Compensation is performed directly using the center tap of the primary winding of transformer T1. This tap compensation method allows for adjustment of harmonic magnitudes according to different ratios, offering greater flexibility and eliminating the need for additional auxiliary windings, thus reducing circuit complexity and cost. Capacitor C3 is connected to the AC input terminal; it can be connected to either the neutral or live wire, providing harmonic compensation in both cases.

[0015] Furthermore, a diode D5 is connected in parallel across capacitor C3. The anode of diode D5 is connected to the cathode of diode D3, and the cathode is connected to the neutral wire. To prevent the power circuit from directly passing through D3 and C3 and causing a current surge to C3 when the voltage drop of diode DB4 is higher than that of diode D3, capacitor C3 is clamped under extreme conditions to prevent the harmonic reduction effect from deteriorating due to possible reverse charging.

[0016] Furthermore, diode D3 is a high-dropout rectifier diode, and the rectifier bridge is a low-dropout rectifier bridge. The voltage drop of diode D3 is greater than the voltage drop of any one of diodes DB1, DB2, DB3, and DB4. This allows for more precise control of the current flow.

[0017] Furthermore, the turns ratio N1a:N1b of the first part N1a and the second part N1b is adjustable, which is used to adjust the voltage across capacitor C2. By adjusting this turns ratio, different circuit requirements can be flexibly adapted to, so that the voltage across capacitor C2 reaches the optimal operating state, better cope with different load changes and operating environments, and further improve the performance and reliability of the entire flyback converter circuit.

[0018] Furthermore, the voltage VC2 across capacitor C2 is: VC2 = VC1 × N1a / (N1a + N1b). By adjusting the turns ratio of N1a:N1b, the voltage across capacitor C2 is controlled to satisfy the relationship, making the voltage distribution of the entire circuit more reasonable, thereby effectively reducing harmonic interference and improving the power factor of the circuit.

[0019] Furthermore, the switching transistor S1 is a MOSFET, and its gate is connected to the PWM control signal. MOSFETs have advantages such as fast switching speed, high input impedance, and low drive power. By using a MOSFET as the switching transistor S1 and connecting the gate to the PWM control signal, the turn-on and turn-off times of the switching transistor S1 can be precisely controlled. By adjusting the duty cycle of the PWM control signal, the output voltage and current of the flyback converter circuit can be flexibly adjusted to meet the needs of different loads.

[0020] Furthermore, transformer T1 also has a secondary winding, with its two ends connected to a secondary load circuit. The secondary load circuit includes diode D4, capacitor C4, and load R1. The same-name terminal of the secondary winding is connected to the anode of diode D4, and the opposite-name terminal is connected to ground. The cathode of diode D4 is connected to capacitor C4 and load R1, and the cathode of capacitor C4 is connected to ground. Diode D4 and capacitor C4 constitute an output filtering circuit, making the voltage output to load R1 more stable. Load R1 consumes electrical energy to achieve its function.

[0021] A switching power supply includes the aforementioned harmonic-improved flyback converter circuit, and further includes a control circuit for generating a PWM control signal to drive the switching transistor S1. The control circuit can dynamically adjust the parameters of the PWM control signal according to the real-time load demand and the operating state of the flyback converter circuit.

[0022] The beneficial effects of this utility model are as follows:

[0023] This invention provides a harmonic-improved flyback converter circuit and switching power supply. It directly compensates for harmonics through the middle tap of the transformer primary winding. The tap compensation can adjust the harmonic magnitude by adjusting the turns ratio of N1a:N1b, which is more flexible and does not require additional auxiliary windings. This reduces circuit complexity and cost, and can also effectively reduce the impact of harmonics on circuit performance, thereby improving the stability and reliability of the circuit. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of this utility model or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is the circuit diagram for Example 1;

[0026] Figure 2 This is the circuit diagram for Embodiment 2;

[0027] Figure 3 This is a schematic diagram of the path when the positive half-cycle is input;

[0028] Figure 4 This is a schematic diagram of the path when the negative half-cycle is input; Detailed Implementation

[0029] The technical solution of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this utility model, but not all embodiments.

[0030] Example 1, as Figure 1 As shown, to simplify the circuit structure, reduce costs, and flexibly adjust the harmonic compensation magnitude, a harmonic-improved flyback converter circuit is designed, including a transformer T1, a rectifier bridge, capacitors C1-C3, diodes D1-D2, and a switching transistor S1. The transformer T1 has a primary winding with a center tap, dividing the primary winding into a first part N1a and a second part N1b with a turns ratio of N1a:N1b. The rectifier bridge consists of diodes DB1, DB2, DB3, and DB4, and its AC input terminal is connected to the live and neutral wires of the AC power supply. The capacitors... C1 is connected between the positive output and negative input terminals of the rectifier bridge; one end of capacitor C2 is connected to the positive output terminal of the rectifier bridge, and the other end is connected to the cathode of diode D1 and the anode of diode D2; one end of capacitor C3 is connected to the neutral wire, and the other end is connected to the anode of diode D1 and the cathode of diode D3; diode D1 is connected between capacitor C2 and capacitor C3; the anode of diode D2 is connected to capacitor C2 and the cathode of diode D1, and the cathode is connected to the center tap of the primary winding; one end of switching transistor S1 is connected to the secondary input terminal of the rectifier bridge, and the other end is connected to the output terminal of the primary winding.

[0031] Compensation is achieved directly through the center tap of the transformer's primary winding. Tap compensation allows for adjustment of harmonic magnitude by changing the turns ratio of N1a:N1b, offering greater flexibility. Furthermore, it eliminates the need for additional auxiliary windings and utilizes only low-cost passive components (such as capacitors and diodes), significantly reducing circuit cost. The overall circuit structure is simpler, reducing the number of components and connection complexity, thus improving circuit reliability and maintainability.

[0032] The switching transistor S1 is a MOSFET, and its gate is connected to the PWM control signal. MOSFETs have advantages such as fast switching speed, high input impedance, and low drive power. By using a MOSFET as the switching transistor S1 and connecting the gate to the PWM control signal, the on and off times of the switching transistor S1 can be precisely controlled. By adjusting the duty cycle of the PWM control signal, the output voltage and current of the flyback converter circuit can be flexibly adjusted to meet the needs of different loads.

[0033] The turns ratio N1a:N1b of the first part N1a and the second part N1b is adjustable and used to adjust the voltage across capacitor C2. The voltage across capacitor C2 is VC2 = VC1 × N1a / (N1a + N1b). When it is necessary to increase the voltage VC2, the turns ratio of the first part N1a to the second part N1b can be increased appropriately; conversely, if it is necessary to decrease the voltage, the turns ratio can be decreased.

[0034] Transformer T1 also has a secondary winding, with its two ends connected to a secondary load circuit. The secondary load circuit includes diode D4, capacitor C4, and load R1. The same-name terminal of the secondary winding is connected to the anode of diode D4, and the opposite-name terminal is connected to ground. The cathode of diode D4 is connected to capacitor C4 and load R1, and the cathode of capacitor C4 is connected to ground. Diode D4 and capacitor C4 constitute an output filtering circuit, making the voltage output to load R1 more stable. Load R1 consumes electrical energy to achieve its function.

[0035] A switching power supply includes the aforementioned harmonic-improved flyback converter circuit and a control circuit for generating a PWM control signal to drive the switching transistor S1. The control circuit can dynamically adjust the parameters of the PWM control signal according to the real-time load demand and the operating state of the flyback converter circuit. For example, when the load increases, the control circuit can automatically increase the duty cycle of the PWM control signal, extending the conduction time of the switching transistor S1, thereby increasing the output power of the flyback converter circuit to meet the load's power requirements.

[0036] like Figure 4 As shown, during the negative half-cycle of the input, when the voltage of capacitor C2 (VC2+) and the AC voltage (Vac) reach the voltage of VC1, capacitor C2 and the AC voltage (Vac) together charge capacitor C1 and simultaneously charge capacitor C3. As the charging process proceeds, the voltages of capacitors C1 and C3 gradually increase, until the voltage of capacitor C3 reaches the voltage of capacitor C2. As the AC voltage (Vac) rises, it directly charges capacitor C1 through rectifier bridges DB2 and DB3. When the voltage of capacitor C3 reaches the voltage of capacitor C2, the circuit enters a new stable state. At this point, if the AC voltage (Vac) continues to rise, in addition to charging capacitor C1, some energy will be transferred to the secondary load circuit through transformer T1. The secondary load circuit converts and distributes the received energy according to the load's needs, providing stable power to the load.

[0037] like Figure 3 As shown, during the positive half-cycle of the input, when the voltage of capacitor C3 and the AC voltage Vac reach VC1, capacitor C3 and AC voltage Vac together charge capacitor C1. The voltage of capacitor C3 discharges quickly and is completely discharged. As the AC voltage Vac continues to increase, the AC voltage Vac continues to charge C1 through rectifier bridges DB1 and DB4.

[0038] The required harmonic ratio can be adjusted by using the winding turns ratio. This adjustment method can effectively improve the power factor of the circuit, reduce reactive power loss, and improve the efficiency of power utilization. Furthermore, the method of adjusting the harmonic ratio by using the winding turns ratio can also reduce electromagnetic interference in the circuit and improve the stability and reliability of the entire circuit system. It is especially suitable for application scenarios with high power quality requirements.

[0039] Example 2, as Figure 2 As shown, a diode D5 is connected in parallel across capacitor C3. The anode of diode D5 is connected to the cathode of diode D3, and the cathode is connected to the neutral wire. The purpose of connecting diode D5 in parallel across capacitor C3 is to prevent the power circuit from directly passing through diode D3 and capacitor C3 when the voltage drop of diode DB4 is higher than that of diode D3, thus avoiding current surges to capacitor C3. The added diode D5 can clamp the capacitor under extreme conditions, preventing the harmonic reduction effect from deteriorating due to possible reverse charging.

[0040] Preferably, diode D3 is a high-dropout rectifier diode, and the rectifier bridge is a low-dropout rectifier bridge. The voltage drop of diode D3 is greater than the voltage drop of any one of diodes DB1, DB2, DB3 and DB4, so as to avoid the power circuit running through capacitor C3 and diode D3.

[0041] The above description is illustrative only and not restrictive of this utility model. Those skilled in the art will understand that many modifications, variations or equivalents can be made without departing from the spirit and scope defined by the appended claims, and all such modifications, variations or equivalents will fall within the protection scope of this utility model.

Claims

1. A harmonic-improved flyback converter circuit, characterized in that, include Transformer T1 has a primary winding with an intermediate tap, which divides the primary winding into a first part N1a and a second part N1b with a turns ratio of N1a:N1b. The rectifier bridge consists of diodes DB1, DB2, DB3 and DB4, and its AC input terminal is connected to the live wire and neutral wire of the AC power supply. Capacitor C1 is connected between the positive output terminal and the negative input terminal of the rectifier bridge; Capacitor C2 is connected at one end to the positive output terminal of the rectifier bridge, and at the other end to the cathode of diode D1 and the anode of diode D2. Capacitor C3 is connected to the neutral wire at one end and to the anode of diode D1 and the cathode of diode D3 at the other end. Diode D1 is connected between capacitor C2 and capacitor C3; Diode D2, with its anode connected to capacitor C2 and the cathode of diode D1, and its cathode connected to the center tap of the primary winding; The switching transistor S1 is connected at one end to the secondary input terminal of the rectifier bridge and at the other end to the output terminal of the primary winding.

2. The harmonic-improved flyback converter circuit according to claim 1, characterized in that: A diode D5 is connected in parallel across capacitor C3. The anode of diode D5 is connected to the cathode of diode D3, and the cathode is connected to the neutral wire.

3. The harmonic-improved flyback converter circuit according to claim 1, characterized in that: Diode D3 is a high-voltage drop rectifier diode, and the rectifier bridge is a low-voltage drop rectifier bridge. The voltage drop of diode D3 is greater than any of diodes DB1, DB2, DB3, and DB4.

4. The harmonic-improved flyback converter circuit according to claim 1, characterized in that: The turns ratio of the first part N1a and the second part N1b is N1a:N1b, which is adjustable and used to adjust the voltage across capacitor C2.

5. The harmonic-improved flyback converter circuit according to claim 4, characterized in that: The voltage VC2 across capacitor C2 is: VC2 = VC1 × N1a / (N1a + N1b).

6. The harmonic-improved flyback converter circuit according to claim 1, characterized in that: The switching transistor S1 is a MOSFET, and its gate is connected to the PWM control signal.

7. The harmonic-improved flyback converter circuit according to claim 6, characterized in that: Transformer T1 also has a secondary winding, with both ends of the secondary winding connected to the secondary load circuit.

8. The harmonic-improved flyback converter circuit according to claim 7, characterized in that: The secondary load circuit includes diode D4, capacitor C4, and load R1. The same-name terminal of the secondary winding is connected to the anode of diode D4, and the opposite-name terminal is connected to the reference ground. The cathode of diode D4 is connected to capacitor C4 and load R1, and the cathode of capacitor C4 is connected to the reference ground.

9. A switching power supply, characterized in that, A flyback converter circuit with harmonic enhancement according to any one of claims 1-8.

10. A switching power supply according to claim 9, characterized in that: It also includes a control circuit for generating a PWM control signal to drive the switching transistor S1.

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