Multi-channel output flyback switching power supply circuit

Abstract

The present invention relates to a multi-channel output flyback switching power supply circuit, which comprises: an AC power supply, an EMI circuit, a rectifier circuit and a flyback circuit, wherein the AC power supply is used to provide initial AC power, an input end of the EMI circuit is connected to the AC power supply, and is used to filter out electromagnetic interference signals in the AC power supply to prevent the signals from affecting subsequent circuits, the rectifier circuit is connected to the output end of the EMI circuit, and the flyback circuit is connected to the output end of the rectifier circuit; the flyback circuit comprises: a flyback control chip and a transformer, wherein the primary side and the secondary side of the transformer are connected to a flyback primary circuit, and the primary side winding and the secondary side winding of the transformer are connected to a flyback secondary side circuit.

Description

Technical Field

[0001] The present application relates to the field of liquid crystal display, and in particular to a multi-channel output flyback switching power supply circuit. Background Art

[0002] With the increasing global awareness of environmental protection and the growing demand for energy conservation, green environmental protection technology has become an important goal pursued by all walks of life. In this context, LCD technology, as one of the core ways of modern information display, is also constantly evolving to meet the requirements of higher efficiency and lower energy consumption. Especially for large-size LCD displays for home and commercial use, reducing power consumption can not only reduce users' electricity bills, but also bring better market competitiveness to enterprises.

[0003] The mainstream LCD monitors on the market currently use backlit LCD display technology, which mainly relies on two core components: display module and backlight module. Among them, the display module is responsible for image formation and control; while the backlight module provides a uniform light source for the entire screen.

[0004] Furthermore, the backlight power supply and driver power supply in most current low-power TV products generally still adopt the PFC+LLC architecture setting, and the circuit using this structure setting is relatively complex and increases the cost of inductors and other circuit components.

[0005] At the same time, most low-power TV products have certain requirements for the size of the back frame. If the back frame is too large, it will not only take up too much space and increase packaging and transportation costs, but also cause inconvenience during installation and use; if the back frame is too small, it may not be able to effectively accommodate the internal display module, backlight module and other related circuit components, resulting in assembly difficulties and may even affect the heat dissipation performance and overall stability of the display; however, the backlight power supply and driver power supply set up with PFC+LLC architecture are not suitable for low-power TV products with tight board frame size because they need to add additional inductors and other circuit components. Summary of the invention

[0006] The main purpose of the present application is to provide a multi-output flyback switching power supply circuit, which aims to solve the problem in the prior art that when low-power TV products adopt a PFC+LLC architecture, additional inductors and other circuit components need to be added, resulting in complex circuits, increased costs, and unsuitability for low-power TV products with tight board frame size.

[0007] To achieve the above-mentioned purpose, the present application provides a multi-channel output flyback switching power supply circuit, including: an AC power supply, an EMI circuit, a rectifier circuit and a flyback circuit, wherein the AC power supply is used to provide initial AC power, the input end of the EMI circuit is connected to the AC power supply, and is used to filter out electromagnetic interference signals in the AC power supply, the rectifier circuit is connected to the output end of the EMI circuit, and the flyback circuit is connected to the output end of the rectifier circuit; the flyback circuit includes: a flyback control chip and a transformer, the primary side and the secondary side of the transformer are both connected to the flyback primary circuit, and the primary side winding and the secondary side winding of the transformer are both connected to the flyback secondary side circuit.

[0008] In one embodiment, the flyback primary circuit includes: a MOS tube, a drain of the MOS tube is connected to a first diode and a stripline bead, a source of the MOS tube is connected to a chip select pin of a flyback control chip through a first resistor, and a gate of the MOS tube is connected to an output pin of the flyback control chip; The cathode of the first diode is connected to one end of the first capacitor, the other end of the first capacitor is connected to one end of the primary side to form an RC absorption network, and the stripline magnetic bead is connected to the other end of the primary side to form a magnetic coupling with the primary side.

[0009] In one embodiment, a second capacitor and a second resistor are connected in parallel between the drain and source of the MOS tube, the second capacitor and the second resistor form an RC buffer circuit, the gate of the MOS tube is connected to a second diode, the cathode of the second diode is connected to a third resistor, the third resistor is connected to the output pin of the flyback control chip, a fourth resistor is connected between the output pin of the flyback control chip and the anode of the second diode, and a fifth resistor is connected between the fourth resistor and the second resistor.

[0010] In one embodiment, a sixth resistor is connected between the first diode and the first capacitor, a seventh resistor is connected in parallel at both ends of the sixth resistor, and an eighth resistor is connected between the first diode and the primary side.

[0011] In one embodiment, one end of the secondary side is grounded, the other end of the secondary side is connected to a ninth resistor, a third diode is connected between the ninth resistor and the power pin of the flyback control chip, the cathode of the third diode is grounded through a third capacitor, and a tenth resistor and a fourth capacitor are connected in parallel between the positive and negative electrodes of the third diode; A fourth diode is further connected between the secondary side and the power pin of the flyback control chip, the cathode of the fourth diode is connected to an eleventh resistor, and the eleventh resistor is grounded through a fifth capacitor; The power pin of the flyback control chip is also connected to the output end of the EMI circuit through the twelfth resistor and the thirteenth resistor respectively, the output end of the EMI circuit is also connected to the output voltage feedback pin of the flyback control chip through the fourteenth resistor and the fifteenth resistor respectively, and the compensation pin of the flyback control chip is electrically connected to the secondary side of the optocoupler switch.

[0012] In one embodiment, the flyback secondary side circuit includes: a first voltage output circuit and a second voltage output circuit, the first voltage output circuit is electrically connected to the primary side winding, and the second voltage output circuit is electrically connected to the secondary side winding; the first voltage output circuit includes: a fifth diode, the anode of the fifth diode is connected to the primary side winding, the cathode of the fifth diode is connected to the first voltage output end, the cathode of the fifth diode is also connected to an electrolytic capacitor, and a resistor voltage divider network is connected in parallel at both ends of the electrolytic capacitor; The first voltage output end is grounded through the sixteenth resistor and the seventeenth resistor respectively, the six capacitor is connected in parallel at both ends of the seventeenth resistor, the sixth capacitor is connected to the voltage zener diode, the positive electrode of the voltage zener diode is connected to the base of the transistor, the collector of the transistor is connected to the first voltage output end through the eighteenth resistor and the nineteenth resistor respectively, the emitter of the transistor is grounded, and the positive electrode of the voltage zener diode and the base of the transistor are connected to one end of the twentieth resistor, and the other end of the twentieth resistor is grounded.

[0013] In one embodiment, the second voltage output circuit includes: a Schottky diode, wherein the anode of the Schottky diode is connected to the secondary winding, the cathode of the Schottky diode is connected to the CLC filter circuit, and the CLC filter circuit is connected to one end of the second voltage output terminal; The secondary side winding is also connected to a seventh capacitor, which is connected to the primary side of the optocoupler switch through a twenty-first resistor and a twenty-second resistor. A twenty-third resistor is connected between the positive and negative poles of the primary side, and the twenty-third resistor is connected to the cathode of the fourth diode. The anode of the fourth diode is grounded. The reference voltage end of the fourth diode D3 is connected to the second voltage output end through a twenty-fourth resistor, and the twenty-fourth resistor is also grounded through a twenty-fifth resistor.

[0014] In one embodiment, a low-pass filter network is connected in parallel between the cathode of the fourth diode and the second voltage output voltage, so as to provide a large current required for transient response and effectively filter out high-frequency noise.

[0015] In one embodiment, the first voltage output terminal is also used to connect to an external backlight driving circuit, and the second voltage output terminal is used to connect to an external display driving and main control circuit.

[0016] The beneficial effects of the technical solution of the present invention are: On the one hand, the AC power supply provides the initial power source for the entire circuit; at the same time, through the effective filtering of the EMI circuit, it can greatly reduce the impact of electromagnetic interference on subsequent circuits, and improve the stability and reliability of the power supply; and through the rectifier circuit, the AC power is converted into DC power, providing a stable input voltage for the flyback circuit; on the other hand, in the flyback circuit part, through the clever cooperation of the flyback control chip and the transformer, efficient conversion of the primary and secondary side circuits is achieved.

[0017] At the same time, when the power switch tube is turned off, the energy stored on the primary side will be released to the primary side winding. Due to electromagnetic induction, the primary side winding generates an induced electromotive force. After being rectified by the rectifier tube, the AC component is converted into DC. Then, it is filtered and smoothed by the filter capacitor, and finally a stable DC output voltage is obtained at both ends of the filter capacitor, which can be used as the power supply for subsequent loads. The voltage signal induced by the secondary winding will be processed by the voltage divider circuit to obtain a sampling voltage proportional to the output voltage, and it will be compared with the reference voltage set inside the chip to generate an error signal. Then, the flyback control chip automatically adjusts the on and off time of the power switch tube according to the size and polarity of the error signal, that is, adjusts the duty cycle, so as to achieve precise control of the output voltage and maintain the output voltage at the set stable value; and when the output voltage increases, the voltage induced by the secondary winding also increases accordingly. After voltage division and error amplification, the flyback control chip will reduce the duty cycle, shorten the on time of the power switch tube, and thus reduce the output voltage; conversely, when the output voltage decreases, the flyback control chip will increase the duty cycle, increase the on time of the power switch tube, and increase the output voltage.

[0018] Through the synergy of the secondary side, power pins and EMI circuits, two different voltage acquisition methods are provided for the power pin of the flyback control chip. One of the methods is to obtain the power supply voltage through the AC high voltage before the rectifier circuit and the resistor voltage divider. The other method is to use the cooperation between the secondary side and the power supply winding. At the same time, the voltage generated by the secondary side is also used for OVP detection of the chip select pin. The output voltage feedback pin of the flyback control chip is responsible for starting and shutting down the output function. This pin is also before the rectifier circuit and detects the size of the input voltage through the voltage divider resistor. When the input voltage rises to the start voltage threshold, the flyback control chip is activated and controls the output pin to output the PWM waveform; conversely, when the input voltage drops to the undervoltage threshold, the output of the output pin will be turned off.

[0019] At the same time, the compensation pin of the flyback control chip adjusts the output through the electrical signal transmitted by the optocoupler switch. According to the signal level received by the compensation pin, the flyback control chip will adjust the frequency and duty cycle of the PWM output accordingly. When the voltage of the compensation pin decreases, the flyback control chip will reduce the frequency and duty cycle of the PWM signal; and when the voltage of the compensation pin increases, the flyback control chip will increase the frequency and duty cycle of the PWM signal to maintain the stability of the output voltage. When a short circuit occurs at the output end of the voltage device, the output voltage will drop to near zero instantly, causing the voltage of the compensation pin to increase instantly, thereby triggering the short-circuit protection mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a system block diagram of a flyback multi-output switching power supply circuit in an embodiment of the present application; Figure 2 This is a circuit structure diagram of an input end + EMI circuit according to an embodiment of the present application; Figure 3 A circuit diagram of a flyback primary side circuit according to an embodiment of the present application; Figure 4 A circuit diagram of a flyback secondary side circuit according to an embodiment of the present application; Figure 5 is a circuit structure diagram of a first voltage output circuit according to an embodiment of the present application; The purpose, features and advantages of this application will be further described in conjunction with the embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0021] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0022] In addition, if the descriptions of "first", "second", etc. are involved in this application, they are only used for descriptive purposes (such as for distinguishing the same or similar elements), and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0023] See also Figure 1-Figure 3 The present invention proposes a multi-channel output flyback switching power supply circuit, including: an AC power supply, an EMI circuit, a rectifier circuit and a flyback circuit, wherein the AC power supply is used to provide initial AC power, the input end of the EMI circuit is connected to the AC power supply, and is used to filter out electromagnetic interference signals in the AC power supply to prevent it from affecting subsequent circuits, the rectifier circuit is connected to the output end of the EMI circuit, and the flyback circuit is connected to the output end of the rectifier circuit; the flyback circuit includes: a flyback control chip U1 and a transformer T1, the primary side T1A and the secondary side T1B of the transformer T1 are connected to the flyback primary circuit, and the primary side winding T1C and the secondary side winding T1D of the transformer T1 are both connected to the flyback secondary side circuit.

[0024] In this embodiment, the AC power supply provides the initial power source for the entire circuit; at the same time, through the effective filtering of the EMI circuit, the impact of electromagnetic interference on subsequent circuits can be greatly reduced, thereby improving the stability and reliability of the power supply; and the AC power is converted into DC power through the rectifier circuit, providing a stable input voltage for the flyback circuit.

[0025] Furthermore, in the flyback circuit part, through the clever cooperation of the flyback control chip U1 and the transformer T1, efficient conversion of the primary and secondary side circuits is achieved.

[0026] Specifically, one end of the primary side T1A is connected to the output end of the rectifier circuit, and the other end is grounded through the power switch tube controlled by the flyback control chip U1. When the power switch tube is turned on, current flows through the primary side T1A. At this time, due to electromagnetic induction, the secondary side T1B generates an induced electromotive force, which provides the flyback control chip U1 with the energy required for operation and maintains its normal operation.

[0027] At the same time, when the power switch tube is turned off, the energy stored in the primary side T1A will be released to the primary side winding T1C. Due to electromagnetic induction, the primary side winding T1C generates an induced electromotive force. After being rectified by the rectifier tube D2, the AC component is converted into DC. Then, it is filtered and smoothed by the filter capacitor, and finally a stable DC output voltage is obtained at both ends of the filter capacitor, which can be used as the power supply for subsequent loads.

[0028] The voltage signal induced by the secondary winding T1D will be processed by the voltage divider circuit to obtain a sampling voltage proportional to the output voltage, and it will be compared with the reference voltage set inside the chip to generate an error signal. Then, the flyback control chip U1 automatically adjusts the on and off time of the power switch tube according to the size and polarity of the error signal, that is, adjusts the duty cycle, so as to achieve precise control of the output voltage and maintain the output voltage at the set stable value; and when the output voltage increases, the voltage induced by the secondary winding T1D also increases accordingly. After voltage division and error amplification, the flyback control chip U1 will reduce the duty cycle, shorten the on time of the power switch tube, and thus reduce the output voltage; conversely, when the output voltage decreases, the flyback control chip U1 will increase the duty cycle, increase the on time of the power switch tube, and increase the output voltage.

[0029] In one of the embodiments, the flyback control chip U1 adopts the LD5537B1 model; when the output voltage exceeds the set value, the LD5537B1 will automatically reduce the duty cycle of the drive pulse to reduce the output voltage; when the output current exceeds the set value, it will quickly turn off the MOS tube Q1 to prevent damage to the power supply and load equipment. At the same time, it has a soft start function, which can effectively reduce the surge current during startup and extend the service life of the power supply.

[0030] See also Figure 3 In one embodiment, the flyback primary circuit includes: a MOS tube Q1, a drain of the MOS tube Q1 is connected to a first diode D2 and a stripline bead B1, a source of the MOS tube Q1 is connected to a chip select pin CS of a flyback control chip U1 through a first resistor R39, and is grounded, and a gate of the MOS tube Q1 is connected to an output pin OUT of the flyback control chip U1.

[0031] Among them, the cathode of the first diode D2 is connected to the first capacitor C2, and the other end of the first capacitor C2 is connected to one end of the primary side T1A to form an RC absorption network for absorbing the reverse electromotive force and peak voltage generated in the primary side T1A when the MOS tube Q1 is cut off. The strip line magnetic bead B1 is connected to the other end of the primary side T1A and forms a tight magnetic coupling with the primary side T1A.

[0032] Specifically, when the MOS tube Q1 is turned on, current flows through the primary side T1A and stores energy. At this time, due to electromagnetic induction, the secondary side T1B generates an induced electromotive force, which provides the energy required for the flyback control chip U1 to work and maintain its normal operation. At the same time, the close magnetic coupling between the strip line bead B1 and the primary side T1A helps to reduce leakage magnetic field and reduce electromagnetic radiation.

[0033] When the MOS tube Q1 is turned off, the energy stored in the primary side T1A will be released to the primary side winding T1C through magnetic field coupling. In this process, a reverse electromotive force will be generated in the primary side T1A, which will make the first diode D2 forward biased and conductive, thereby transferring the energy in the primary side T1A to the first capacitor C2. At the same time, since the first capacitor C2 can absorb this part of the energy, and the strip line bead B1 helps to reduce electromagnetic interference; therefore, the entire circuit can effectively suppress the generation of spike voltage and protect the MOS tube Q1 from overvoltage shock.

[0034] Among them, a second capacitor C6 and a second resistor R25 are connected in parallel between the drain and the source of the MOS tube Q1, and the second capacitor C6 and the second resistor R25 form an RC buffer circuit. The gate of the MOS tube Q1 is connected to the second diode D5, and the cathode of the second diode D5 is connected to the third resistor R35. The third resistor R35 is connected to the output pin OUT of the flyback control chip U1. A fourth resistor R36 is connected between the output pin OUT of the flyback control chip U1 and the anode of the second diode D5. A fifth resistor R28 is connected between the fourth resistor R36 and the second resistor R25.

[0035] In this embodiment, a second capacitor C6 and a second resistor R25 connected in parallel between the drain and source of the MOS tube Q1 form an RC buffer circuit to absorb the voltage spike generated when the MOS tube Q1 is turned off, thereby preventing the MOS tube Q1 from being damaged due to overvoltage. At the same time, it can also slow down the voltage rise rate of the MOS tube Q1 and reduce electromagnetic interference (EMI).

[0036] Furthermore, a second diode D5 is connected to the gate of the MOS tube Q1, and a cathode of the diode is connected to a third resistor R35, which is in turn connected to an output pin OUT of the flyback control chip U1. Thus, when the MOS tube Q1 needs to be quickly turned off, a pulse signal output by the output pin OUT turns on the second diode D5, providing a fast discharge path for the gate of the MOS tube Q1, thereby preventing the MOS tube Q1 from being in a linear region for a long time during the shutdown process, and reducing shutdown loss and heat generation.

[0037] In addition, through the fourth resistor R36 connected between the output pin OUT of the flyback control chip U1 and the anode of the second diode D5, and the fifth resistor R28 connected between the fourth resistor R36 and the second resistor R25, it is ensured that the MOS tube Q1 can obtain appropriate gate charge when it is turned on and off, thereby achieving efficient and stable switching operation.

[0038] In one embodiment, a sixth resistor R13 is connected between the first diode D2 and the first capacitor C2, a seventh resistor R15 is connected in parallel across the sixth resistor R13, and an eighth resistor R6 is connected between the first diode D2 and the primary side T1A.

[0039] In this embodiment, the charging and discharging rates of the first capacitor C2 are adjusted by adding the sixth resistor R13 and the seventh resistor R15. Specifically, when the MOS tube Q1 is turned off, the energy stored in the primary side T1A is released to the primary side winding T1C through magnetic field coupling; at the same time, a reverse electromotive force is generated on the first diode D2, so that the first capacitor C2 is charged; and the sixth resistor R13 and the seventh resistor R15 can control the size and rate of the charging current to prevent the first capacitor C2 from generating an excessively high voltage due to over-fast charging.

[0040] In addition, the eighth resistor R6 is added to prevent the primary side T1A from generating an excessively high voltage spike when the current suddenly changes, so as to limit the current change rate in the primary side T1A when the MOS tube Q1 suddenly changes from the on state to the off state, reduce the voltage spike, and protect other components in the circuit from overvoltage shock.

[0041] In one embodiment, one end of the secondary side T1B is grounded, and the other end of the secondary side T1B is connected to a ninth resistor R22. A third diode D4 is connected between the ninth resistor R22 and a power pin VCC of the flyback control chip U1. The cathode of the third diode D4 is grounded through a third capacitor CE5. A tenth resistor R23 and a fourth capacitor C7 are connected in parallel between the positive and negative electrodes of the third diode D4.

[0042] A fourth diode D6 is further connected between the secondary side T1B and the power pin VCC of the flyback control chip U1 . The cathode of the fourth diode D6 is connected to an eleventh resistor R31 . The eleventh resistor R31 is grounded via a fifth capacitor C14 .

[0043] The power pin VCC of the flyback control chip U1 is also connected to the output end of the EMI circuit through the twelfth resistor R20 and the thirteenth resistor R21. The output end of the EMI circuit is also connected to the output voltage feedback pin BNO of the flyback control chip U1 through the fourteenth resistor R18 and the fifteenth resistor R19 respectively, and the compensation pin COMP of the flyback control chip U1 is connected to the secondary side U2B of the optocoupler switch.

[0044] In this embodiment, through the synergistic effect of the secondary side T1B, the power pin VCC and the EMI circuit, two different voltage acquisition methods are provided for the power pin VCC of the flyback control chip U1.

[0045] Specifically, one way is to obtain the VCC voltage through the AC high voltage before the rectifier circuit and the resistor voltage divider. Another way is to use the cooperation between the secondary side T1B and the power supply winding. At the same time, the voltage generated by the secondary side T1B is also used for the OVP (detection) of the chip select pin CS. The output voltage feedback pin BNO of the flyback control chip U1 is responsible for starting and shutting down the output function. This pin is also before the rectifier circuit and detects the size of the input voltage through the voltage divider resistor. When the input voltage rises to the start voltage threshold, the flyback control chip is activated and controls the output pin OUT to output the PWM waveform; conversely, when the input voltage drops to the undervoltage threshold, the output of the output pin OUT will be turned off.

[0046] The compensation pin COMP of the flyback control chip U1 adjusts the output through the electrical signal transmitted by the optocoupler switch. According to the signal level received by the compensation pin COMP, the flyback control chip U1 will adjust the frequency and duty cycle of the PWM output accordingly. When the voltage of the compensation pin COMP decreases, the flyback control chip U1 will reduce the frequency and duty cycle of the PWM signal; and when the voltage of the compensation pin COMP increases, the flyback control chip U1 will increase the frequency and duty cycle of the PWM signal to maintain the stability of the output voltage. When a short circuit occurs at the output end of the voltage device, the output voltage will instantly drop to near zero, causing the voltage of the compensation pin COMP to instantly increase, thereby triggering the short-circuit protection mechanism.

[0047] See also Figure 4-Figure 5 In one embodiment, the flyback secondary side circuit includes: a first voltage output circuit and a second voltage output circuit, and the first voltage output circuit and the second voltage output circuit are electrically connected to the primary side winding T1C and the secondary side winding T1D respectively.

[0048] The first voltage output circuit includes: a fifth diode D1, the anode of the fifth diode D1 is connected to the primary side winding T1C, the cathode of the fifth diode D1 is connected to the first voltage output end, the cathode of the fifth diode D1 is also connected to an electrolytic capacitor CE1, a resistor voltage divider network is connected in parallel at both ends of the electrolytic capacitor CE1, and the electrolytic capacitor CE1 is grounded.

[0049] The first voltage output end is grounded through a sixteenth resistor R5 and a seventeenth resistor R8, a sixth capacitor C8 is connected in parallel at both ends of the seventeenth resistor R8, the sixth capacitor C8 is connected to a voltage zener diode ZD1, the anode of the voltage zener diode ZD1 is connected to the base of the transistor Q2, the collector of the transistor Q2 is connected to the first voltage output end through an eighteenth resistor R14 and a nineteenth resistor R7, the emitter of the transistor Q2 is grounded, and the anode of the voltage zener diode ZD1 and the base of the transistor Q2 are both connected to one end of the twentieth resistor R9, and the other end of the twentieth resistor R9 is grounded.

[0050] In this embodiment, when the MOS tube Q1 is turned on, the flyback energy is transferred to the secondary side winding T1C through the primary side winding T1A, and flows out to the first voltage load end after being rectified by the fifth diode D1. During the period when the MOS tube Q1 is turned off, thanks to the freewheeling effect of the fifth diode D1, the energy will not flow back to the primary side of the transformer or be lost to other paths. At the same time, with the application of the ultra-fast recovery diode, the voltage spike caused by the insufficient reverse recovery time on the secondary side during the switching process of the MOS tube Q1 is effectively reduced, ensuring the stable operation of the circuit. Furthermore, the electrolytic capacitor CE1 is used as a filtering element to smooth the voltage at the first voltage output end, reduce the voltage ripple, and improve the power quality.

[0051] Among them, the voltage stabilization mechanism of the first voltage output circuit is to achieve current limiting and voltage stabilization functions through a resistor voltage divider network. Specifically, the voltage divider network samples and controls the output voltage at a level of 15V, and then uses the voltage regulator diode ZD1 to accurately clamp this voltage. When the output voltage drops, the clamping effect of the voltage regulator diode ZD1 ensures that the voltage on the lower bias resistor is forcibly pulled up to 15V, thereby maintaining the stability of the voltage at the first voltage output terminal through the voltage divider ratio. On the contrary, when the output voltage rises and causes the voltage on the lower bias resistor to exceed 15V, the voltage regulator diode ZD1 will be turned on and current will be introduced into the base of the transistor Q2, so that the transistor Q2 is turned on, and its emitter and collector are respectively connected to the positive and negative electrodes of the first voltage output terminal, forming an effective current path, and guiding excess energy to the ground, thereby limiting the further rise of the voltage and protecting the circuit from overvoltage shock.

[0052] In one embodiment, the second voltage output circuit includes: a Schottky diode D3, wherein the anode of the Schottky diode D3 is connected to the secondary winding T1D, and the cathode of the Schottky diode D3 is connected to the CLC filter circuit, and the CLC filter circuit is connected to the second voltage output terminal; The secondary side winding T1D is also connected to a seventh capacitor C5, and the seventh capacitor C5 is connected to the primary side U2A in the optocoupler switch through a twenty-first resistor R16 and a twenty-second resistor R24. A twenty-third resistor R30 is connected between the positive and negative poles of the primary side U2A, and the twenty-third resistor R30 is connected to the cathode of the sixth diode U3. The anode of the sixth diode U3 is grounded, and the reference voltage end of the sixth diode U3 is connected to one end of the second voltage output end through a twenty-fourth resistor R37, and the twenty-fourth resistor R37 is also grounded through a twenty-fifth resistor R42.

[0053] Furthermore, a low ESR filtering network is connected in parallel between the cathode of the sixth diode U3 and the port of the second voltage output voltage, so as to provide a large current required for transient response and effectively filter out high-frequency noise.

[0054] In this embodiment, when the MOS tube Q1 is switched, the transformer transfers energy to the secondary side due to the reverse effect caused by the cutoff of the Schottky diode. In the second voltage output circuit, the Schottky diode D3 is responsible for rectification and transmits the pulsating DC voltage to the CLC filter circuit to smooth the voltage fluctuation. At the same time, the seventh capacitor C5 is connected to the light-emitting diode in the optocoupler switch through the twenty-first resistor R16 and the twenty-second resistor R24, respectively, to form a feedback network. When the voltage at the second voltage output end changes, the feedback network will adjust the brightness of the light-emitting diode in the optocoupler switch accordingly, thereby affecting the control chip's regulation of the pulse width modulation (PWM) signal.

[0055] Specifically, when the second voltage output voltage rises, the voltage divided by the twenty-fourth resistor R37 and the twenty-fifth resistor R42 will also rise, resulting in an increase in the voltage on the twenty-third resistor R30 connected to the light-emitting diode end of the optocoupler switch. This will increase the current flowing through the optocoupler switch, thereby increasing the voltage of the chip compensation pin COMP. In response, the chip will increase the duty cycle of the PWM signal to reduce the output voltage back to the set value. On the contrary, if the second voltage output voltage drops, the control process is exactly the opposite: the current flowing through the optocoupler switch decreases, the voltage of the compensation pin COMP decreases, and the duty cycle of the PWM signal decreases, thereby increasing the output voltage to the desired level.

[0056] In one embodiment, the first voltage output terminal is also used to connect to an external backlight driving circuit, and the second voltage output terminal is used to connect to an external display driving and main control circuit.

[0057] It should be noted that, in this article, the terms "include", "comprises" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, device, article or multi-output flyback switching power supply circuit including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, device, article or multi-output flyback switching power supply circuit. In the absence of more restrictions, an element defined by the sentence "includes one..." does not exclude the existence of other identical elements in the process, device, article or multi-output flyback switching power supply circuit including the element.

[0058] The above description is only a preferred embodiment of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A multi-output flyback switching power supply circuit, characterized in that: include: An AC power supply, an EMI circuit, a rectifier circuit and a flyback circuit, wherein the AC power supply is used to provide initial AC power, the EMI circuit input end is connected to the AC power supply and is used to filter out electromagnetic interference signals in the AC power supply, the rectifier circuit is connected to the output end of the EMI circuit, and the flyback circuit is connected to the output end of the rectifier circuit; the flyback circuit includes: a flyback control chip and a transformer, the primary side and the secondary side of the transformer are both connected to the flyback primary circuit, and the primary side winding and the secondary side winding of the transformer are connected to the flyback secondary side circuit.

2. A multi-output flyback switching power supply circuit according to claim 1, characterized in that: The flyback primary circuit comprises: a MOS tube, a drain of the MOS tube is connected to a first diode and a stripline bead, a source of the MOS tube is connected to a chip select pin of a flyback control chip via a first resistor, and a gate of the MOS tube is connected to an output pin of the flyback control chip; The cathode of the first diode is connected to one end of the first capacitor, the other end of the first capacitor is connected to one end of the primary side to form an RC absorption network, and the stripline magnetic bead is connected to the other end of the primary side and forms a magnetic coupling with the primary side.

3. A multi-output flyback switching power supply circuit according to claim 2, characterized in that: A second capacitor and a second resistor are connected in parallel between the drain and source of the MOS tube, the second capacitor and the second resistor form an RC buffer circuit, the gate of the MOS tube is connected to a second diode, the cathode of the second diode is connected to a third resistor, the third resistor is connected to the output pin of the flyback control chip, a fourth resistor is connected between the output pin of the flyback control chip and the anode of the second diode, and a fifth resistor is connected between the fourth resistor and the second resistor.

4. A multi-output flyback switching power supply circuit according to claim 3, characterized in that: A sixth resistor is connected between the first diode and the first capacitor, a seventh resistor is connected in parallel at both ends of the sixth resistor, and an eighth resistor is connected between the first diode and the primary side.

5. The multi-output flyback switching power supply circuit according to claim 1, characterized in that: One end of the secondary side is grounded, the other end of the secondary side is connected to a ninth resistor, a third diode is connected between the ninth resistor and the power pin of the flyback control chip, the cathode of the third diode is grounded through a third capacitor, and a tenth resistor and a fourth capacitor are connected in parallel between the positive and negative electrodes of the third diode; A fourth diode is further connected between the secondary side and the power pin of the flyback control chip, the cathode of the fourth diode is connected to an eleventh resistor, and the eleventh resistor is grounded through a fifth capacitor; The power pin of the flyback control chip is also connected to the output end of the EMI circuit through the twelfth resistor and the thirteenth resistor respectively, the output end of the EMI circuit is also connected to the output voltage feedback pin of the flyback control chip through the fourteenth resistor and the fifteenth resistor respectively, and the compensation pin of the flyback control chip is electrically connected to the secondary side of the optocoupler switch.

6. The multi-output flyback switching power supply circuit according to claim 1, characterized in that: The flyback secondary side circuit comprises: a first voltage output circuit and a second voltage output circuit, the first voltage output circuit is electrically connected to the primary side winding, and the second voltage output circuit is electrically connected to the secondary side winding; the first voltage output circuit comprises: a fifth diode, the anode of the fifth diode is connected to the primary side winding, the cathode of the fifth diode is connected to the first voltage output terminal, the cathode of the fifth diode is also connected to an electrolytic capacitor, and a resistor voltage divider network is connected in parallel at both ends of the electrolytic capacitor; The first voltage output end is grounded through the sixteenth resistor and the seventeenth resistor respectively, the six capacitor is connected in parallel at both ends of the seventeenth resistor, the sixth capacitor is connected to the voltage zener diode, the positive electrode of the voltage zener diode is connected to the base of the transistor, the collector of the transistor is connected to the first voltage output end through the eighteenth resistor and the nineteenth resistor respectively, the emitter of the transistor is grounded, and the positive electrode of the voltage zener diode and the base of the transistor are connected to one end of the twentieth resistor, and the other end of the twentieth resistor is grounded.

7. The multi-output flyback switching power supply circuit according to claim 6, characterized in that: The second voltage output circuit comprises: a Schottky diode, wherein the anode of the Schottky diode is connected to the secondary winding, the cathode of the Schottky diode is connected to the CLC filter circuit, and the CLC filter circuit is connected to the second voltage output terminal; The secondary side winding is also connected to a seventh capacitor, and the seventh capacitor is connected to the primary side of the optocoupler switch through a twenty-first resistor and a twenty-second resistor respectively. A twenty-third resistor is connected between the positive and negative poles of the primary side, and the twenty-third resistor is connected to the cathode of the sixth diode. The anode of the sixth diode is grounded, and the reference voltage end of the sixth diode is connected to the second voltage output end through a twenty-fourth resistor, and the twenty-fourth resistor is also grounded through a twenty-fifth resistor.

8. The multi-output flyback switching power supply circuit according to claim 7, characterized in that: A low-pass filter network is connected in parallel between the cathode of the sixth diode and the second voltage output voltage.

9. The multi-output flyback switching power supply circuit according to claim 8, characterized in that: The first voltage output terminal is also used to connect to an external backlight driving circuit, and the second voltage output terminal is also used to connect to an external display driving and main control circuit.

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