A quasi-resonant flyback AC-DC control circuit

Abstract

This utility model relates to the field of circuit control technology, specifically a quasi-resonant flyback AC-DC control circuit, including a flyback circuit. The flyback circuit includes a flyback transformer T, with a MOSFET Q1 electrically connected to the flyback transformer T. A capacitor C1 and a diode VD2 are connected in parallel on one side of the transformer T, and a load is electrically connected to the other side of the transformer T. A diode VD1 and an optocoupler are electrically connected between the transformer T and the load. A voltage regulator circuit, a filter circuit, a rectifier circuit, and a power transformer are electrically connected sequentially on the flyback circuit. During operation, when the main switch is turned off, the energy stored on the primary side of the power transformer is released to the load through the secondary side. Simultaneously, the primary inductance of T and the capacitor C1 form a resonant circuit, generating an oscillating voltage. When the oscillating voltage drops to its lowest point, the flyback circuit controls the main switch to turn on, thereby achieving near-zero voltage turn-on and reducing turn-on losses.

Description

Technical Field

[0001] This utility model relates to a control circuit, and more particularly to a quasi-resonant flyback AC-DC control circuit, belonging to the field of circuit control technology. Background Technology

[0002] Quasi-resonant flyback switching power supplies operate in DCM or CRCM mode. When the secondary diode current drops to zero, an RLC resonant circuit is formed by the capacitor, primary inductor, and parasitic resistance. Traditional linear regulators refer to the product of the voltage difference between the input and output and the current flowing to the input as the power loss, which is converted into heat. Without a heat sink, it can only withstand about 2W at most. Of course, high loss means poor efficiency. When considering adding an AC / DC converter, the input of the linear regulator IC cannot withstand the direct rectification of 140V voltage from 100VAC.

[0003] In AC / DC conversion using a switching method, replacing the unusable linear regulator IC in the DC / DC section can be achieved by using high-voltage transistors or other methods to avoid directly connecting the linear regulator. However, when reducing the voltage from 140V DC to, for example, 12V, there are practically no other options considering heat treatment, resulting in high power consumption and low efficiency.

[0004] Therefore, it is urgent to improve the control circuit of the quasi-resonant flyback AC-DC converter to solve the above-mentioned problems. Utility Model Content

[0005] The purpose of this invention is to provide a quasi-resonant flyback AC-DC control circuit. During operation, when the main switch is turned off, the energy stored on the primary side of the power transformer is released to the load through the secondary side. At the same time, the primary inductance of T and the capacitor C1 form a resonant circuit to generate an oscillating voltage. When the oscillating voltage is detected to drop to the bottom, the flyback circuit controls the main switch to turn on, thereby achieving near-zero voltage turn-on and reducing turn-on losses.

[0006] To achieve the above objectives, the main technical solutions adopted by this utility model include:

[0007] A quasi-resonant flyback AC-DC control circuit includes a flyback circuit, the flyback circuit including a flyback transformer T, a MOSFET Q1 electrically connected to the flyback transformer T, a capacitor C1 and a diode VD2 connected in parallel on one side of the transformer T, a load electrically connected to the other side of the transformer T, and a diode VD1 and an optocoupler electrically connected between the transformer T and the load.

[0008] The flyback circuit is electrically connected in sequence to a voltage regulator circuit, a filter circuit, a rectifier circuit, and a power transformer.

[0009] Preferably, a resistor R1 is connected in parallel with the capacitor C1, and the capacitor C1 and the resistor R1 are connected in parallel and then connected in series with the diode VD2.

[0010] Preferably, the rectifier circuit includes a bridge rectifier bridge, which includes diodes VD3, VD4, VD5, and VD6.

[0011] Preferably, the voltage regulator circuit includes a transistor Q2 and an operational amplifier Q3. A resistor R2 and a resistor R3 are electrically connected between the negative terminals of the transistor Q2 and the operational amplifier Q3. A resistor RW is electrically connected between the resistor R2 and the resistor R3. The negative terminal of the operational amplifier Q3 is slidably connected to the resistor RW.

[0012] Preferably, a resistor RL is connected in parallel on one side of the resistor R2, and a resistor R4 is electrically connected to the positive pin of the operational amplifier Q3. The resistor R4 is grounded through a diode VD3.

[0013] Preferably, the filter circuit includes a transistor Q4, a capacitor C2 electrically connected to the transistor Q4, a resistor R6 electrically connected between the capacitor C2 and the transistor Q4, and a resistor R5 electrically connected between the capacitor C2 and the transistor Q4.

[0014] This utility model has at least the following beneficial effects:

[0015] During operation, when the main switch is turned off, the energy stored on the primary side of the power transformer is released to the load through the secondary side. At the same time, the primary inductance of T and the capacitor C1 form a resonant circuit, generating an oscillating voltage. When the oscillating voltage drops to its lowest point, the flyback circuit controls the main switch to turn on, thereby achieving near-zero voltage turn-on and reducing turn-on losses. Attached Figure Description

[0016] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0017] Figure 1 This is the circuit diagram of this utility model;

[0018] Figure 2 This is the flyback circuit diagram of this utility model;

[0019] Figure 3 The waveform diagrams are shown for each part of the flyback method of this utility model;

[0020] Figure 4 This is a diagram of the voltage regulator circuit of this utility model;

[0021] Figure 5 This is the filter circuit diagram of this utility model.

[0022] In the diagram, 1 is the power transformer; 2 is the rectifier circuit; 3 is the filter circuit; 4 is the voltage regulator circuit; and 5 is the flyback circuit. Detailed Implementation

[0023] The following will describe in detail the implementation of this application with reference to the accompanying drawings and embodiments, so that the implementation process of how this application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0024] like Figures 1-5 As shown, the quasi-resonant flyback AC-DC control circuit provided in this embodiment includes a flyback circuit 5, which includes a flyback transformer T. A MOSFET Q1 is electrically connected to the flyback transformer T. A capacitor C1 and a diode VD2 are connected in parallel on one side of the transformer T. A load is electrically connected to the other side of the transformer T. A diode VD1 and an optocoupler are electrically connected between the transformer T and the load. A resistor R1 is connected in parallel with the capacitor C1. The parallel connection of the capacitor C1 and the resistor R1 is then connected in series with the diode VD2. Traditional linear regulators refer to the product of the voltage difference between the input and output and the current flowing to the input as the power loss, which is converted into heat. Without a heat sink, it can only withstand a maximum of about 2W. Of course, high power loss means... Due to its poor efficiency, when considering adding an AC / DC converter, the input of the linear regulator IC cannot withstand the direct rectification of 140V voltage from 100VAC. In AC / DC conversion using a switching method, replacing the unusable linear regulator IC in the DC / DC section can be done by using high-voltage transistors or other methods to avoid direct connection to the linear regulator. However, when reducing the DC voltage from 140V to, for example, 12V, there is practically no other option considering heat treatment. Therefore, when using a linear regulator to convert DC / DC, a transformer is generally used. If the transformer can be adjusted to its ideal optimal state and the input and output drop of the linear regulator is not too large, the efficiency will not be so bad, and it can be used within the allowable heat dissipation range.

[0025] Quasi-resonant type uses a dedicated IC for control, but it has lower noise and lower loss than PWM. Therefore, some applications use quasi-resonant type and use optocouplers to isolate the feedback on the secondary side (output), thus forming an isolated power supply and achieving the purpose of safety isolation.

[0026] When MOSFET Q1 is ON, current flows through the primary winding of the transformer, accumulating electrical energy. At this time, diode is OFF.

[0027] When MOSFET Q1 is OFF, the stored electrical energy is output from the secondary winding of the transformer through the diode, and then rectified / smoothed to generate DC voltage. This operating mode is also called ON / OFF mode, and the waveforms of each part are as follows: Figure 3 As shown;

[0028] The flyback circuit 5 is electrically connected in sequence to the voltage regulator circuit 4, the filter circuit 3, the rectifier circuit 2, and the power transformer 1. During operation, when the main switch is turned off, the energy stored on the primary side of the power transformer 1 is released to the load through the secondary side. At the same time, the primary inductance of T and the capacitor C1 form a resonant circuit to generate an oscillating voltage. When the oscillating voltage is detected to drop to the bottom, the flyback circuit 5 controls the main switch to turn on, thereby achieving near-zero voltage turn-on and reducing turn-on losses.

[0029] Furthermore, the rectifier circuit 2 includes a bridge rectifier bridge, which includes diodes VD3, VD4, VD5, and VD6. A rectifier bridge is a combination of electronic components whose core function is to convert AC voltage into DC voltage. The rectifier bridge consists of four diodes, including diodes VD3, VD4, VD5, and VD6, forming a bridge structure. This structure allows current to flow in one direction while preventing it from flowing in the opposite direction. The working principle of the rectifier bridge is based on the unidirectional conductivity of diodes. When the positive half-cycle of the AC power supply is applied to the rectifier bridge, two diodes conduct, allowing current to flow from the input terminal to the output terminal.

[0030] During the negative half-cycle, the other two diodes conduct, and the current still flows from the input to the output. However, the current path is different from that during the positive half-cycle. In this way, the rectifier bridge can ensure that the output current always maintains the same direction regardless of how the AC waveform changes, thus achieving the conversion from AC to DC.

[0031] Furthermore, such as Figure 4 As shown, the voltage regulator circuit 4 includes a transistor Q2 and an operational amplifier Q3. Resistors R2 and R3 are electrically connected between the negative pins of transistor Q2 and operational amplifier Q3, and resistor RW is electrically connected between resistors R2 and R3. The negative pin of operational amplifier Q3 is slidably connected to resistor RW. A resistor RL is connected in parallel on one side of resistor R2. Resistor R4 is electrically connected to the positive pin of operational amplifier Q3. Resistor R4 is grounded through diode VD3. Through the internal transistor Q2 and operational amplifier Q3, the voltage regulator circuit 4 can monitor and adjust the output voltage in real time. When the input voltage changes, the regulator will adjust its operating state according to the information provided by the feedback loop, thereby ensuring that the output voltage remains at a preset stable value. This process helps protect electronic equipment from power fluctuations and improves the reliability and stability of the equipment.

[0032] Furthermore, such as Figure 5 As shown, the filter circuit 3 includes a transistor Q4, a capacitor C2 electrically connected to the transistor Q4, a resistor R6 electrically connected between the capacitor C2 and the transistor Q4, and a resistor R5 electrically connected between the capacitor C2 and the transistor Q4. The filter circuit 3 is often used to filter out the ripple in the rectified output voltage. This ripple is the pulse component generated during the rectification process. The filter circuit 3 forms various complex filter circuits through the combination of capacitor C2 and transistor Q4 to reduce the AC component in the pulsating DC voltage and retain its DC component. This reduces the ripple coefficient of the output voltage and makes the waveform smoother.

[0033] like Figures 1-5 As shown, the principle of the quasi-resonant flyback AC-DC control circuit provided in this embodiment is as follows:

[0034] A MOSFET Q1 is electrically connected to the flyback transformer T. A capacitor C1 and a diode VD2 are connected in parallel on one side of the transformer T. A load is electrically connected to the other side of the transformer T. A diode VD1 and an optocoupler are electrically connected between the transformer T and the load. A resistor R1 is connected in parallel with the capacitor C1. The parallel connection of the capacitor C1 and the resistor R1 is then connected in series with the MOSFET Q1. The quasi-resonant type is controlled by a dedicated IC, but it has lower noise and lower losses than PWM. Therefore, some applications use the quasi-resonant type. The optocoupler isolates the feedback at the secondary side (output), thus forming an isolated power supply and achieving the purpose of safety isolation.

[0035] During operation, when the main switch is turned off, the energy stored in the primary side of the power transformer 1 is released to the load through the secondary side. At the same time, the primary inductance of T and the capacitor C1 form a resonant circuit, generating an oscillating voltage. When the oscillating voltage is detected to drop to the bottom, the flyback circuit 5 controls the main switch to turn on, thereby achieving near-zero voltage turn-on and reducing turn-on losses.

[0036] If certain terms are used in the specification and claims to refer to specific components, those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The term "comprising" as used throughout the specification and claims is an open-ended term and should be interpreted as "comprising but not limited to." "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error.

[0037] It should be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes that element.

[0038] The foregoing description illustrates and describes several preferred embodiments of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A quasi-resonant flyback AC-DC control circuit comprising a flyback circuit (5), characterized in that, The flyback circuit (5) includes a flyback transformer T, a MOS transistor Q1 is electrically connected to the flyback transformer T, a capacitor C1 and a diode VD2 are connected in parallel on one side of the transformer T, a load is electrically connected to the other side of the transformer T, and a diode VD1 and an optocoupler are electrically connected between the transformer T and the load. The flyback circuit (5) is electrically connected in sequence to a voltage regulator circuit (4), a filter circuit (3), a rectifier circuit (2), and a power transformer (1).

2. A quasi-resonant flyback AC-DC control circuit according to claim 1, characterized in that: The capacitor C1 is connected in parallel with a resistor R1, and the capacitor C1 and the resistor R1 are connected in parallel and then connected in series with the diode VD2.

3. The quasi-resonant flyback AC-DC control circuit according to claim 1, characterized in that: The rectifier circuit (2) includes a bridge rectifier bridge, which includes diodes VD3, VD4, VD5 and VD6.

4. The quasi-resonant flyback AC-DC control circuit according to claim 1, characterized in that: The voltage regulator circuit (4) includes a transistor Q2 and an operational amplifier Q3. Resistors R2 and R3 are electrically connected between the negative pins of the transistor Q2 and the operational amplifier Q3. Resistor RW is electrically connected between the resistor R2 and the resistor R3. The negative pin of the operational amplifier Q3 is slidably connected to the resistor RW.

5. The quasi-resonant flyback AC-DC control circuit according to claim 4, characterized in that: A resistor RL is connected in parallel on one side of the resistor R2, and a resistor R4 is electrically connected to the positive pin of the operational amplifier Q3. The resistor R4 is grounded through a diode VD3.

6. The quasi-resonant flyback AC-DC control circuit according to claim 1, characterized in that: The filter circuit (3) includes a transistor Q4, a capacitor C2 electrically connected to the transistor Q4, a resistor R6 electrically connected between the capacitor C2 and the transistor Q4, and a resistor R5 electrically connected between the capacitor C2 and the transistor Q4.

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