flyback switching power supply circuit, adapter and charger

Abstract

This application provides a flyback switching power supply circuit, adapter, and charger, relating to the field of switching power supply technology. The circuit includes a feedback circuit module, a transformer and a first MOSFET, a switching circuit submodule, and a comparator. The level drive terminal of the switching circuit submodule is connected to the gate of the first MOSFET. The inverting and non-inverting terminals of the comparator are respectively connected to the source of the first MOSFET and the feedback voltage receiver. The comparator's comparison output terminal is connected to the control terminal of the switching circuit submodule. The switching circuit submodule is configured to output a first drive voltage based on the high level output of the comparator when the load is determined to be in a light load or overload range, and to output a second drive voltage greater than the first drive voltage based on the high level output of the comparator when the load is determined to be in a heavy load range. This application embodiment can dynamically adjust the gate drive voltage of the first MOSFET according to the load conditions, thereby achieving the best balance between efficiency and reliability under different load conditions.

Description

Technical Field

[0001] This application relates to, but is not limited to, the field of switching power supply technology, and particularly to a flyback switching power supply circuit, adapter, and charger. Background Technology

[0002] Flyback switching circuits are widely used in various adapters, chargers, and industrial power supplies due to their simple structure, low cost, and ability to achieve electrical isolation. Flyback switching circuits typically use a fixed voltage drive; however, to reduce the conduction losses of the MOSFETs in the flyback switch, a higher drive voltage (e.g., 12V) is often desired to significantly reduce Rds(on). However, a higher drive voltage leads to increased gate charging and discharging switching losses, particularly under light load conditions, which is detrimental to average efficiency. Furthermore, under overload or short-circuit conditions, the power supply operates in continuous conduction mode, resulting in a common time between the primary-side switch turn-off and the secondary-side synchronous rectifier turn-on, generating significant stress and potentially damaging the synchronous rectifier. Simultaneously, excessive primary-side peak current can also threaten the primary-side switch and may cause transformer magnetic saturation. Existing drive schemes are mostly fixed-voltage drives or only statically set the drive voltage according to the power device type, failing to cope with dynamically changing load conditions to achieve multiple optimization goals of efficiency and reliability. Utility Model Content

[0003] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims. Embodiments of this application provide a flyback switching power supply circuit that optimizes the average efficiency of the flyback switching circuit under different load conditions, while reducing the stress on the synchronous rectifier diode under overload conditions and improving reliability.

[0004] In a first aspect, the flyback switching power supply circuit according to the embodiments of this application includes: A transformer power supply circuit module, comprising a transformer and a first MOSFET, wherein the drain of the first MOSFET is connected to the primary control terminal of the transformer, and the secondary coil of the transformer is used to connect to the load. A feedback circuit module, wherein the feedback circuit module is used to sample the voltage of the load and output a feedback voltage; The control circuit module includes a switching circuit submodule and a comparator. The level drive terminal of the switching circuit submodule is connected to the gate of the first MOSFET, and the source of the first MOSFET is connected to the inverting terminal of the comparator. The non-inverting terminal of the comparator is used to receive the feedback voltage. The comparison output terminal of the comparator is connected to the control terminal of the switching circuit submodule. The switching circuit submodule is configured to output a preset first drive voltage based on the high level output of the comparator when the load is determined to be in a light load range or an overload range, and to output a preset second drive voltage based on the high level output of the comparator when the load is determined to be in a heavy load range, wherein the second drive voltage is greater than the first drive voltage.

[0005] Therefore, the above embodiments of this application have at least the following beneficial effects: by setting a feedback circuit module, the feedback voltage can characterize the actual load state of the load. At this time, by switching circuit sub-modules and comparators, a preset first driving voltage is controlled to be output when the load is in the light load range and overload range, and a preset second driving voltage is controlled to be output when the load is in the heavy load range. This allows for dynamic adjustment of the driving voltage of the first MOSFET under different load conditions, thereby optimizing the average efficiency of the power supply output by the flyback switching power supply circuit across the entire load range. Therefore, compared with related technologies, the embodiments of this application can optimize the average efficiency of the flyback switching circuit under different load conditions, while reducing the stress on the synchronous rectifier under overload conditions and improving reliability.

[0006] According to some embodiments of the first aspect of this application, the input terminal of the switching circuit submodule is connected to the source of the first MOS transistor, and the switching circuit submodule is further configured to determine whether the load is in the light load range, the overload range, or the heavy load range based on the source voltage at the turn-off time of the first MOS transistor.

[0007] According to some embodiments of the first aspect of this application, the input terminal of the switching circuit submodule is connected to the feedback voltage output terminal of the feedback circuit module, and the switching circuit submodule is further configured to determine whether the load is in the light load range, the overload range, or the heavy load range based on the feedback voltage output by the feedback voltage output terminal.

[0008] According to some embodiments of the first aspect of this application, the switching circuit submodule includes a first switching switch, a first Zener diode, a second Zener diode, a push-pull amplifier, and a first level switch; the first terminal of the first switching switch and the first terminal of the first Zener diode are both grounded, and the second terminal of the first switching switch is connected to the first terminal of the second Zener diode; the second terminals of the first Zener diode and the second Zener diode are both connected to the comparator output terminal of the comparator and the first connection terminal of the push-pull amplifier, and the second connection terminal of the push-pull amplifier is grounded; the third connection terminal of the push-pull amplifier is connected to the gate of the first MOS transistor, and the first level switch is configured to turn on the first switching switch when the load is in the light load range and the overload range, and to turn off the first switching switch when the load is in the heavy load range.

[0009] According to some embodiments of the first aspect of this application, the switching circuit submodule includes a second switching switch, a first voltage regulator, a second voltage regulator, a push-pull amplifier, and a second level switch. The second terminals of the first voltage regulator and the second voltage regulator are connected in parallel. The second terminal of the second switching switch is connected to the comparison output terminal of the comparator. The first connection terminal of the push-pull amplifier is connected to the parallel connection of the first voltage regulator and the second voltage regulator. The second connection terminal of the push-pull amplifier is grounded. The third connection terminal of the push-pull amplifier is connected to the gate of the first MOSFET. The second level switch is configured to connect the first terminal of the second switching switch to the first voltage regulator when the load is in the light load range and the overload range, and to connect the first terminal of the second switching switch to the second voltage regulator when the load is in the heavy load range.

[0010] According to some embodiments of the first aspect of this application, the feedback circuit module includes an operational amplifier, a first voltage divider resistor, a second voltage divider resistor, and an optocoupler. The first terminals of the first and second voltage divider resistors are connected in series, and the second terminal of the first voltage divider resistor is connected to the secondary output terminal of the transformer power supply circuit module. The signal input terminal of the operational amplifier is connected to the series connection of the first and second voltage divider resistors. The two input terminals of the optocoupler are respectively connected to the secondary output terminal and the signal output terminal of the operational amplifier. The first output terminal of the optocoupler is connected to the non-inverting input of the comparator. The second output terminal of the optocoupler is grounded.

[0011] According to some embodiments of the first aspect of this application, the transformer power supply circuit module further includes a rectifier bridge, a first filter capacitor, a synchronous rectifier diode, and a second filter capacitor. The rectifier bridge and the first filter capacitor are connected in parallel. The first end of the first filter capacitor is connected to the first end of the primary winding of the transformer. The two ends of the secondary winding of the transformer are respectively connected to the two ends of the second filter capacitor. The synchronous rectifier diode is disposed between the second filter capacitor and the secondary winding. The second end of the second filter capacitor is grounded. The first end of the second filter capacitor is used to connect to the load.

[0012] According to some embodiments of the first aspect of this application, the first driving voltage is set to 6~10V, and the second driving voltage is set to 10~15V.

[0013] Secondly, the adapter proposed according to the embodiments of this application includes the flyback switching power supply circuit described in any of the first aspects.

[0014] Thirdly, the charger proposed according to the embodiments of this application includes the flyback switching power supply circuit described in any of the first aspects. Attached Figure Description

[0015] The accompanying drawings are used to provide a further understanding of the technical solutions of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of this application and do not constitute a limitation on the technical solutions of this application.

[0016] Figure 1 This is a schematic diagram of the circuit structure of one embodiment of the flyback switching power supply circuit provided in this application; Figure 2 This is a schematic diagram of the circuit structure of another embodiment of the flyback switching power supply circuit provided in this application; Figure 3 This is a schematic diagram of the circuit structure of another embodiment of the flyback switching power supply circuit provided in this application; Figure 4 This is a schematic diagram of the circuit structure of another embodiment of the flyback switching power supply circuit provided in this application; Figure 5 This is a schematic diagram of the gate charge characteristic curve of the first MOS transistor in various embodiments of the flyback switching power supply circuit provided in this application; Figure 6 This is a schematic diagram illustrating the effect of the turn-off speed of the first MOSFET on the generated peak current in various embodiments of the flyback switching power supply circuit provided in this application. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit this application. The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0019] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a thorough understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of the specific details, or other methods, components, apparatuses, steps, etc., can be employed. In other instances, well-known methods, apparatuses, implementations, or operations are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0020] Flyback switching circuits are widely used in various adapters, chargers, and industrial power supplies due to their simple structure, low cost, and ability to achieve electrical isolation. Their core performance indicators include conversion efficiency and reliability. In existing technologies, to improve the average efficiency of flyback switching circuits, common methods include transformer optimization, selection of power MOSFETs with low on-resistance (Rds(on)), and the use of soft-switching techniques such as quasi-resonant (QR) or active clamping. Simultaneously, in terms of drive, to reduce MOSFET conduction losses, a higher drive voltage (e.g., 12V) is typically desired to significantly reduce Rds(on). However, a higher drive voltage leads to increased gate charging and discharging switching losses, especially under light load conditions, which reduces the average efficiency of the output flyback switching circuit. Furthermore, under overload or short-circuit conditions, the flyback switching circuit may operate in continuous conduction mode (CCM) or experience continuous current, resulting in a cross-conduction between the primary-side switch turn-off and the secondary-side synchronous rectifier turn-on. This commonality generates significant stress, potentially damaging the synchronous rectifier diodes connected to the transformer's secondary winding. Simultaneously, excessive primary-side peak current can threaten the switching transistors connected to the transformer's primary winding and may lead to transformer magnetic saturation. However, existing drive schemes are mostly fixed-voltage drives, or statically set only based on the power device type (e.g., SiMOS, GaN), failing to cope with dynamically changing load conditions to achieve multiple optimization objectives. This application provides a flyback switching power supply circuit capable of real-time load state identification and dynamic adjustment of the drive voltage under different load conditions, thereby achieving an optimal balance between efficiency and reliability under varying load conditions.

[0021] Firstly, referring to Figures 1 to 4 As shown, the flyback switching power supply circuit according to an embodiment of this application includes: The transformer power supply circuit module includes a transformer and a first MOSFET. The drain of the first MOSFET is connected to the primary control terminal of the transformer, and the secondary coil of the transformer is used to connect the load. Feedback circuit module, used to sample the voltage of the load and output feedback voltage; The control circuit module includes a switching circuit submodule and a comparator. The level drive terminal of the switching circuit submodule is connected to the gate of a first MOSFET, and the source of the first MOSFET is connected to the inverting terminal of the comparator. The non-inverting terminal of the comparator is used to receive feedback voltage. The comparison output terminal of the comparator is connected to the control terminal of the switching circuit submodule. The switching circuit submodule is configured to output a preset first drive voltage based on the high level output of the comparator when the load is determined to be in the light load range and the overload range, and to output a preset second drive voltage based on the high level output of the comparator when the load is determined to be in the heavy load range, wherein the second drive voltage is greater than the first drive voltage.

[0022] Therefore, by setting a feedback circuit module so that the feedback voltage can characterize the actual load state, the switching circuit submodule and comparator control the output of a preset first drive voltage when the load is in the light load and overload ranges, and control the output of a preset second drive voltage when the load is in the heavy load range. This allows for dynamic adjustment of the drive voltage of the first MOSFET under different load conditions, thereby optimizing the average efficiency of the flyback switching power supply circuit across the entire load range. Therefore, compared with related technologies, the embodiments of this application can optimize the average efficiency of the flyback switching circuit under different load conditions.

[0023] The transformer power supply circuit module utilizes the transformer's "energy storage-energy release" cycle and controls the transformer's energy transfer through the switching on and off of the first MOSFET. Because the energy transfer between the transformer's primary winding (input side) and secondary winding (output side) is asynchronous, the conversion from input voltage to output voltage is ultimately achieved. This application does not limit the electrical components included in the transformer power supply circuit module. For example, such as... Figures 1 to 4 As shown, the transformer power supply circuit module also includes a rectifier bridge, a synchronous rectifier diode D2, a first filter capacitor C1, and a second filter capacitor C2. The input terminal of the rectifier bridge is connected to an external power supply. The positive output terminal of the rectifier bridge is connected to the first terminal of the first filter capacitor C1. The second terminal of the first filter capacitor C1 and the negative output terminal of the rectifier bridge are both grounded. The first terminal of the first filter capacitor C1 is also connected to the first terminal of the primary winding of the transformer T1. The second terminal of the primary winding (i.e., the primary control terminal) is connected to the drain of the first MOSFET. The first terminal of the secondary winding of the transformer T1 is connected in sequence to the synchronous rectifier diode D2 and the second filter capacitor C2. The second terminal of the secondary winding and the second terminal of the second filter capacitor C2 away from the second terminal of the synchronous rectifier diode D2 are grounded. In some embodiments, a resistor RL is also connected in parallel with the second filter capacitor C2. An external load is connected at the connection point between the synchronous rectifier diode D2 and the second filter capacitor C2.

[0024] The embodiments of this application do not limit the structure of the feedback circuit module, and those skilled in the art can selectively configure the feedback circuit module according to actual needs.

[0025] When the first MOSFET turn-on logic is met (e.g., in some embodiments, the feedback voltage is greater than the source voltage; in other embodiments, the feedback voltage is greater than the source voltage and a turn-on enable signal is received, wherein the turn-on enable signal is used to detect a valley or reach a specified switching frequency, i.e., to reach the desired turn-on time of the first MOSFET), the comparator outputs a high level Vcc; when the first MOSFET turn-off logic is met, i.e., when the inverting input of the comparator is greater than the non-inverting input, the comparator outputs a low level. This application does not restrict which component provides the comparator's turn-on enable signal; it can be provided by a switching circuit submodule or by an independent component. This application does not impose any restrictions on this.

[0026] The switching circuit submodule has two selectable voltage supply branches: a first voltage supply branch and a second voltage supply branch. The first voltage supply branch conducts when the load is in the light load and overload ranges, while the second voltage supply branch conducts when the load is in the heavy load range. Each voltage supply branch has a different minimum voltage threshold, and the target output voltages are the first driving voltage and the second driving voltage, respectively. The minimum voltage threshold is greater than the low level of the comparator output, so the corresponding target voltage can be output by the voltage supply branch that only conducts when the level is high. This application does not limit the circuit structure of each voltage supply branch; those skilled in the art can choose electronic components (such as Zener diodes or voltage regulators) with constant output and a minimum voltage threshold for the input voltage to assemble the circuit.

[0027] In some embodiments, the feedback voltage and the turn-off voltage threshold of the first MOSFET are in a preset ratio k. In this case, the feedback voltage * k serves as the input to the non-inverting input of the comparator. In other embodiments, the feedback voltage represents the turn-off voltage threshold of the first MOSFET. This application does not limit the specific implementation of the embodiments, and those skilled in the art can selectively set the values ​​according to actual conditions.

[0028] Understandably, referring to Figure 3 and Figure 4 As shown, the input terminal of the switching circuit submodule is connected to the source of the first MOSFET. The switching circuit submodule is also configured to determine whether the load is in the light load range, overload range, or heavy load range based on the source voltage of the first MOSFET at the turn-off time.

[0029] The source voltage represents the sampling voltage at the source of the first MOSFET.

[0030] The source voltage at the turn-off moment of the first MOSFET represents the peak current of the first MOSFET. For example... Figure 3 and Figure 4As shown, a sampling resistor RCS is placed at the source of the first MOSFET. In this case, the source voltage VCS of the first MOSFET can be obtained. Assume the switching frequency of the first MOSFET is... Then power loss Satisfy the following formula: (1); in, Let VCS be the magnetizing inductance of transformer T1. Therefore, the power consumption of the load can be determined based on the voltage VCS and RCS of the sampling resistor RCS. With RCS and the voltage divider resistors R1 and R2 in the feedback loop fixed, the larger the VCS, the larger the feedback voltage and the larger the load.

[0031] For example, taking the source voltage VCS as an example, if the VCS is continuously higher than an overload threshold VCS_ovl (e.g., 120% of the maximum output current) for a period of time T_ovl, it is determined that the load is in the overload range; if the VCS is lower than a light load threshold VCS_light, it is determined that the load is in the light load range; if the VCS is higher (e.g., higher than a heavy load threshold VCS_heavy), it is determined that the load is in the heavy load range.

[0032] Understandably, referring to Figure 1 and Figure 2 As shown, the input terminal of the switching circuit submodule is connected to the feedback voltage output terminal of the feedback circuit module. The switching circuit submodule is also configured to determine whether the load is in the light load range, overload range, or heavy load range based on the feedback voltage output from the feedback voltage output terminal.

[0033] For example, if the feedback voltage V_fb remains above an overload threshold V_ovl (e.g., 120% of the maximum output current) for a period of time T_ovl, the load is determined to be in the overload range. If V_fb is low (e.g., below a light load threshold V_light), the load is determined to be in the light load range; if V_fb is high (e.g., above a heavy load threshold V_heavy), the load is determined to be in the heavy load range.

[0034] Understandably, referring to Figure 1 and Figure 3As shown, the switching circuit submodule includes a first switching switch, a first Zener diode, a second Zener diode, a push-pull amplifier, and a first level switch. The first terminal of the first switching switch and the first terminal of the first Zener diode are both grounded, and the second terminal of the first switching switch and the first terminal of the second Zener diode are connected. The second terminals of the first Zener diode and the second Zener diode are both connected to the comparator output terminal of the comparator and the first connection terminal of the push-pull amplifier, and the second connection terminal of the push-pull amplifier is grounded. The third connection terminal of the push-pull amplifier is connected to the gate of the first MOSFET. The first level switch is configured to turn on the first switching switch when the load is in the light load range and the overload range, and to turn off the first switching switch when the load is in the heavy load range.

[0035] The embodiments of this application do not limit the specific structure of the first level switch. The first level switch can be an MCU, a PLC, or a circuit formed by a combination of multi-level comparators, etc. The embodiments of this application do not limit this, and those skilled in the art can selectively set it according to actual needs.

[0036] In some embodiments, such as Figure 1 As shown, the input terminal of the first level switch is used to receive feedback voltage. Based on the feedback voltage, it is determined whether the load is in a light load range, an overload range, or a heavy load range, thereby selecting to control the on / off state of the first switching switch. In other embodiments, such as... Figure 3 As shown, the input terminal of the first level switch is used to receive the source voltage. Based on the source voltage, it is determined whether the load is in the light load range, overload range, or heavy load range, thereby selecting to control the on / off state of the first switching switch.

[0037] The embodiments of this application do not limit the specific structure of the first switching switch, and those skilled in the art can selectively set it according to actual needs.

[0038] The clamping voltage of the first Zener diode is greater than that of the second Zener diode. For example, the first Zener diode can be 12V, and the second Zener diode can be 8V. When VFB is in the light load and overload range, when the first switching switch is on, the drive level is determined by the second Zener diode, and the drive high level of the first MOSFET is VZD2=8V; when VFB is in the heavy load range, when the first switching switch is off, the drive level is determined by the first Zener diode, and the drive high level of the first MOSFET is VZD1=12V.

[0039] For example, refer to Figure 1 and Figure 3 As shown, the first switch is S1, the first Zener diode is ZD1, and the second Zener diode is ZD2. Figure 1 and Figure 3As shown, ZD2 and S1 are connected in series. ZD2 and S1 are then connected in parallel with ZD1, with one parallel terminal connected to ground and the other parallel terminal connected between the first connection terminal of the push-pull amplifier and the output terminal of comparator U1. The breakdown voltage of ZD1 and ZD2 is greater than the low level of the U1 output. Therefore, when the U1 output is low, neither ZD1 nor ZD2 is broken down, and Q1 is turned off. When the U1 output is high, S1 is closed, and ZD2 breaks down; when S1 is open, ZD1 breaks down.

[0040] The embodiments of this application do not limit the structure of the push-pull amplifier, such as Figures 1 to 4 As shown, the push-pull amplifier consists of an NPN transistor Q2 and a PNP transistor Q3 interconnected to form a circuit with four terminals. The bases of Q2 and Q3 are connected to form the first terminal; the collector of Q2 serves as the fourth terminal; the emitter of Q3 is connected to the emitter of Q2 to form the third terminal; and the collector of Q3 serves as the second terminal. In some embodiments, such as... Figures 1 to 4 As shown, the fourth connection terminal of the push-pull amplifier is connected to the external power supply Vcc. Pulling the push-pull amplifier up to Vcc can increase the sink current (Isource) and increase the driving capability. In some other embodiments, the fourth terminal of the push-pull amplifier may not be connected.

[0041] Understandably, referring to Figure 2 and Figure 4 As shown, the switching circuit submodule includes a second switching switch, a first voltage regulator, a second voltage regulator, a push-pull amplifier, and a second level switch. The second terminals of the first and second voltage regulators are connected in parallel. The second terminal of the second switching switch is connected to the comparison output terminal of the comparator. The first terminal of the push-pull amplifier is connected to the parallel connection of the first and second voltage regulators. The second terminal of the push-pull amplifier is grounded. The third terminal of the push-pull amplifier is connected to the gate of the first MOSFET. The second level switch is configured to connect the first terminal of the second switching switch to the first voltage regulator when the load is in the light load range and the overload range, and to connect the first terminal of the second switching switch to the second voltage regulator when the load is in the heavy load range.

[0042] Both the first and second voltage regulators are low-dropout linear regulators. For example... Figure 2 As shown, in some embodiments, the input of the second level switch is used to receive feedback voltage to determine which of the three load ranges (light load, overload, or heavy load) the load is in, such as... Figure 4 As shown, in some other embodiments, the input of the second level switch is used to receive the source voltage to determine which of the following ranges the load is in: light load, overload, or heavy load.

[0043] For example, such as Figure 2 and Figure 4 As shown, the first regulator is LDO1, the second regulator is LDO2, and the second switching switch is S1. LDO1 and LDO2 are connected in parallel, and S1 is used to select LDO1 and LDO2. When the second level switch is on, comparators U1 and LDO2 are connected, and the output signal of U1 passes through LDO2 and a push-pull amplifier to the gate of the first MOSFET Q1. When the second level switch is on, comparators U1 and LDO1 are connected, and the output signal of U1 passes through LDO1 and a push-pull amplifier to the gate of the first MOSFET Q1. When U1 outputs a low level, neither LDO1 nor LDO2 has an output. When U1 outputs a high level, S1 is on LDO1, and the output voltage is set according to the target voltage set in LDO1. When S1 is on LDO2, the output voltage is set according to the target voltage set in LDO2.

[0044] Understandably, referring to Figures 1 to 4 As shown, the feedback circuit module includes an operational amplifier, a first voltage divider resistor, a second voltage divider resistor, and an optocoupler. The first terminals of the first and second voltage divider resistors are connected in series, and the second terminal of the first voltage divider resistor is connected to the secondary output terminal of the transformer power supply circuit module. The signal input terminal of the operational amplifier is connected to the series connection of the first and second voltage divider resistors. The two input terminals of the optocoupler are connected to the secondary output terminal and the signal output terminal of the operational amplifier, respectively. The first output terminal of the optocoupler is connected to the non-inverting input of the comparator. The second output terminal of the optocoupler is grounded.

[0045] For example, such as Figures 1 to 4 As shown, the optocoupler is set as U2, the operational amplifier is set as U3, the first voltage divider resistor and the second voltage divider resistor are R1 and R2 respectively, and the output voltage Vo and the reference voltage Vref are amplified by the operational amplifier to output the error signal Verror; U2, based on the error signal Verror output by U3 and the output voltage Vo, is fed back to the primary side through the optocoupler to obtain the VFB signal, and thus obtain the correspondence with the load. In some embodiments, the output terminal of U2 (i.e., Figures 1 to 4 Terminal 4 in the circuit is connected to the first end of the second resistor RFB, and the second end of RFB is connected to the bias voltage. Taking the voltage division ratio of R1 and R2 as R2 / (R1+R2)=0.125 and Vref as 2.5V as an example, the current IF of U2 is IF=(Vo-Verror) / R4, where R4 is the third voltage divider resistor; assuming that U2 has a current transfer ratio CTR=IC / IF, then VFB=Vbias-IC*RFB; where Vbias is... Figures 1 to 4 The bias voltage in the middle.

[0046] Understandably, referring to Figures 1 to 4As shown, the transformer power supply circuit module also includes a rectifier bridge, a first filter capacitor, a synchronous rectifier tube, and a second filter capacitor. The rectifier bridge and the first filter capacitor are connected in parallel. The first end of the first filter capacitor is connected to the first end of the primary winding of the transformer. The two ends of the secondary winding of the transformer are respectively connected to the two ends of the second filter capacitor. The synchronous rectifier tube is placed between the second filter capacitor and the secondary winding. The second end of the second filter capacitor is grounded. The first end of the second filter capacitor is used to connect to the load.

[0047] This application embodiment does not restrict the location of the synchronous rectifier tube, and can be as follows: Figures 1 to 4 As shown, it is positioned on the high side of the secondary coil, that is, between the secondary coil and the end of the second filter capacitor furthest from ground. It can also be positioned on the low side of the secondary coil.

[0048] For example, such as Figures 1 to 4 As shown, the first filter capacitor is C1, the second filter capacitor is C2, the transformer is T1, and the first MOSFET is Q1. Q1 controls T1 so that T1 cyclically stores and releases the current after rectifier bridge and C1 filter, thereby realizing the current output of the secondary coil.

[0049] Understandably, the first driving voltage is set to 6~10V, and the second driving voltage is set to 10~15V.

[0050] The embodiments of this application do not limit the specific values ​​of the first driving voltage and the second driving voltage. For example, the first driving voltage is 8V and the second driving voltage is 10V; or the first driving voltage is 8V and the second driving voltage is 15V; or the first driving voltage is 6V and the second driving voltage is 10V; or the first driving voltage is 6V and the second driving voltage is 15V; or the first driving voltage is 10V and the second driving voltage is 15V; or the first driving voltage is 10V and the second driving voltage is 12V. The embodiments of this application do not limit these values, and those skilled in the art can selectively set them according to actual needs.

[0051] Setting the first and second drive voltages to 6~10V and 10~15V respectively can minimize the switching losses of the first MOSFET. Taking a first drive voltage of 8V and a second drive voltage of 12V as an example, when the drive voltage of the first MOSFET is 8V, Qg=28nC, Rdson=0.245Ω@VG=7V, ID=8A; when the drive voltage of the first MOSFET is 12V, Qg=40nC, Rdson=0.22Ω@VG=10V, ID=8A. The drive losses of the first MOSFET then satisfy the following formula: (2); Reference Figures 1 to 4It can be seen that the driving charge actually flows to the gate of Q1 through VCC and the push-pull amplifier, and the switching frequency fsw determines the driving loss. When the driving voltage is reduced from 12V to 8V, the driving loss decreases significantly.

[0052] Conduction loss: (3); According to formula (3) and combined with Figure 5 As shown in the schematic diagram of the gate charge characteristics of the first MOSFET, the gate voltage of the first MOSFET is 12V, and the on-resistance Rdson is smaller than that of 8V, resulting in a slight reduction in conduction loss under heavy load.

[0053] In summary, since the gate voltage of the first MOSFET needs to reach the threshold voltage to conduct, and the turn-on speed is slower at lower drive levels, reducing the drive voltage can reduce the turn-on speed under overload conditions (e.g., above 120%). In this state, the flyback switching power supply circuit typically operates in CCM mode. Reducing the turn-on speed significantly reduces the energy stored in the leakage inductance when the primary and secondary sides are in common operation, and significantly reduces the stress on the output rectifier diodes. During turn-off, the gate voltage of the first MOSFET needs to be reduced to the threshold voltage Vgsth (e.g., 3V) through Roff to turn it off. Therefore, a lower first drive voltage will result in a faster turn-off speed than a lower second drive voltage. And if... Figure 6 As shown, at time t0, the controller outputs a drive signal via VG according to the set drive level. At time t1, the threshold voltage Vgs is reached, and the first MOSFET truly begins to conduct; at time t2, when the level switch detects that the VCS voltage has reached the threshold low voltage VCS_th determined by the feedback voltage VFB, VG sends a turn-off signal. At time t3, the gate voltage of the first MOSFET drops to the threshold voltage Vgsth, and the first MOSFET truly turns off. At this time, as... Figure 6 As shown, a fast turn-off results in a smaller peak current on the primary side compared to a slow turn-off. Therefore, compared to the prior art, the flyback switching power supply circuit of this application embodiment has lower noise (i.e., audible sound) under light load.

[0054] Secondly, the adapter proposed according to the embodiments of this application includes the flyback switching power supply circuit described above.

[0055] Thirdly, the charger proposed according to the embodiments of this application includes the flyback switching power supply circuit described above.

[0056] The above is a detailed description of the preferred embodiments of this application. However, this application is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of this application. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A flyback switching power supply circuit, characterized by comprising: include: A transformer power supply circuit module, comprising a transformer and a first MOSFET, wherein the drain of the first MOSFET is connected to the primary control terminal of the transformer, and the secondary coil of the transformer is used to connect to the load. A feedback circuit module, wherein the feedback circuit module is used to sample the voltage of the load and output a feedback voltage; The control circuit module includes a switching circuit submodule and a comparator. The level drive terminal of the switching circuit submodule is connected to the gate of the first MOSFET, and the source of the first MOSFET is connected to the inverting terminal of the comparator. The non-inverting terminal of the comparator is used to receive the feedback voltage. The comparison output terminal of the comparator is connected to the control terminal of the switching circuit submodule. The switching circuit submodule is configured to output a preset first drive voltage based on the high level output of the comparator when the load is determined to be in a light load range or an overload range, and to output a preset second drive voltage based on the high level output of the comparator when the load is determined to be in a heavy load range, wherein the second drive voltage is greater than the first drive voltage.

2. The flyback switching power supply circuit according to claim 1, characterized in that, The input terminal of the switching circuit submodule is connected to the source of the first MOS transistor. The switching circuit submodule is also configured to determine whether the load is in the light load range, the overload range, or the heavy load range based on the source voltage of the first MOS transistor at the turn-off time.

3. The flyback switching power supply circuit according to claim 1, characterized in that, The input terminal of the switching circuit submodule is connected to the feedback voltage output terminal of the feedback circuit module. The switching circuit submodule is also configured to determine whether the load is in the light load range, the overload range, or the heavy load range based on the feedback voltage output by the feedback voltage output terminal.

4. The flyback switching power supply circuit according to any one of claims 1 to 3, characterized in that, The switching circuit submodule includes a first switching switch, a first Zener diode, a second Zener diode, a push-pull amplifier, and a first level switch. The first terminal of the first switching switch and the first terminal of the first Zener diode are both grounded. The second terminal of the first switching switch is connected to the first terminal of the second Zener diode. The second terminals of the first Zener diode and the second Zener diode are both connected to the comparator output terminal and the first connection terminal of the push-pull amplifier. The second connection terminal of the push-pull amplifier is grounded. The third connection terminal of the push-pull amplifier is connected to the gate of the first MOSFET. The first level switch is configured to turn on the first switching switch when the load is in a light load range or an overload range, and to turn off the first switching switch when the load is in a heavy load range.

5. The flyback switching power supply circuit according to any one of claims 1 to 3, characterized in that, The switching circuit submodule includes a second switching switch, a first voltage regulator, a second voltage regulator, a push-pull amplifier, and a second level switch. The second terminals of the first voltage regulator and the second voltage regulator are connected in parallel. The second terminal of the second switching switch is connected to the comparison output terminal of the comparator. The first connection terminal of the push-pull amplifier is connected to the parallel connection of the first voltage regulator and the second voltage regulator. The second connection terminal of the push-pull amplifier is grounded. The third connection terminal of the push-pull amplifier is connected to the gate of the first MOSFET. The second level switch is configured to connect the first terminal of the second switching switch to the first voltage regulator when the load is in the light load range and the overload range, and to connect the first terminal of the second switching switch to the second voltage regulator when the load is in the heavy load range.

6. The flyback switching power supply circuit according to claim 1, characterized in that, The feedback circuit module includes an operational amplifier, a first voltage divider resistor, a second voltage divider resistor, and an optocoupler. The first terminals of the first and second voltage divider resistors are connected in series, and the second terminal of the first voltage divider resistor is connected to the secondary output terminal of the transformer power supply circuit module. The signal input terminal of the operational amplifier is connected to the series connection of the first and second voltage divider resistors. The two input terminals of the optocoupler are connected to the secondary output terminal and the signal output terminal of the operational amplifier, respectively. The first output terminal of the optocoupler is connected to the non-inverting input of the comparator. The second output terminal of the optocoupler is grounded.

7. The flyback switching power supply circuit according to claim 1, characterized in that, The transformer power supply circuit module further includes a rectifier bridge, a first filter capacitor, a synchronous rectifier tube, and a second filter capacitor. The rectifier bridge and the first filter capacitor are connected in parallel. The first end of the first filter capacitor is connected to the first end of the primary winding of the transformer. The two ends of the secondary winding of the transformer are respectively connected to the two ends of the second filter capacitor. The synchronous rectifier tube is disposed between the secondary windings of the second filter capacitor. The second end of the second filter capacitor is grounded. The first end of the second filter capacitor is used to connect to the load.

8. The flyback switching power supply circuit according to claim 1, characterized in that, The first driving voltage is set to 6~10V, and the second driving voltage is set to 10~15V.

9. An adapter, characterized in that, Includes the flyback switching power supply circuit as described in any one of claims 1 to 8.

10. A charger, characterized in that, Includes the flyback switching power supply circuit as described in any one of claims 1 to 8.

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