Control circuit for switching power supply, switching power supply and control method

Abstract

A control circuit for a switching power supply, a switching power supply and a control method. The control circuit comprises: an output short circuit detection unit, receiving a detection signal of an output electrical parameter of the switching power supply, and outputting a short circuit indication signal according to the detection signal; a magnetic field detection unit, detecting the magnetic field strength outside the switching power supply, and outputting a magnetic field strength detection signal; a control unit connected with the magnetic field detection unit and the output short circuit detection unit, controlling the switching power supply based on the short circuit indication signal and the magnetic field strength detection signal. The above scheme can improve the reliability of the switching power supply.

Description

Technical Field

[0001] This invention relates to the field of switching power supply technology, and more specifically to a control circuit, a switching power supply, and a control method for a switching power supply. Background Technology

[0002] With the widespread application of power equipment, switching power supplies, as an important component, are widely used due to their advantages such as small size, fast response, and low loss. However, in practical applications, switching power supplies face the problem of interference from strong external magnetic fields. This interference can cause the transformer in the switching power supply to demagnetize, preventing the switching power supply from functioning properly.

[0003] Traditional solutions typically involve adding a magnetic field shielding enclosure to the switching power supply or using special materials and processes to fabricate inductors or transformers within the power supply. While these methods can reduce the interference of magnetic fields on the switching power supply to some extent, they also significantly increase the size of the power supply and the overall manufacturing cost.

[0004] Currently, the industry's solutions mainly rely on algorithms to determine whether the switching power supply is in a strong magnetic field environment, or directly use Hall effect devices to detect the magnetic field of the switching power supply, and adjust the parameters of the switching power supply according to the judgment or detection results to ensure that the switching power supply works normally under a strong magnetic field.

[0005] However, adjusting the parameters of the switching power supply based on the judgment or test results, while reducing the size of the switching power supply and the increase in overall manufacturing cost, will reduce the reliability of the switching power supply. Summary of the Invention

[0006] The problem this invention aims to solve is: how to improve the reliability of switching power supplies in strong magnetic field environments.

[0007] To address the above problems, embodiments of the present invention provide a control circuit for a switching power supply, the control circuit comprising: The output short-circuit detection unit receives the detection signal of the output electrical parameters of the switching power supply and outputs a short-circuit indication signal according to the detection signal; The magnetic field detection unit detects the magnetic field strength outside the switching power supply and outputs a magnetic field strength detection signal. The control unit is connected to the magnetic field detection unit and the output short circuit detection unit, and controls the switching power supply based on the short circuit indication signal and the magnetic field strength detection signal.

[0008] In one possible embodiment, the control unit controls at least one of the operating frequency of the switching power supply and a current limiting threshold; wherein the current limiting threshold is the maximum value allowed to flow through the power switching transistor in the switching power supply, and the power switching transistor is used to control the energy transfer of the switching power supply.

[0009] In one possible embodiment, the control unit controls the switching power supply to switch to a second state when the short-circuit indication signal indicates that the switching power supply does not have an output short circuit and the magnetic field strength detection signal indicates that the magnetic field strength outside the switching power supply is greater than the magnetic field strength threshold; and controls the switching power supply to a first state when the short-circuit indication signal indicates that the switching power supply has an output short circuit or the magnetic field strength outside the switching power supply is less than or equal to the magnetic field strength threshold. Wherein, at least one of the operating frequency and the current limiting threshold in the second state is greater than at least one of the operating frequency and the current limiting threshold in the first state.

[0010] In one possible embodiment, the output short-circuit detection unit includes: a first comparator that compares the detection signal with a detection threshold to output a short-circuit indication signal.

[0011] In one possible embodiment, the control unit includes: an AND gate circuit connected to the output short-circuit detection unit and the magnetic field detection unit, which generates an adjustment control signal based on the short-circuit indication signal and the magnetic field strength detection signal; and a control module connected to the AND gate circuit, which controls the switching power supply based on the adjustment control signal.

[0012] In one possible embodiment, the control module includes at least one of the following: a current limiting threshold sub-circuit, connected to the AND gate circuit, for controlling the current limiting threshold of the switching power supply based on the current sampling result of the power switching transistor in the switching power supply and the adjustment control signal; and an operating frequency sub-circuit, connected to the AND gate circuit, for controlling the operating frequency of the switching power supply based on the detection signal and the adjustment control signal.

[0013] In one possible embodiment, the control module further includes a PWM logic and drive unit connected to the current limiting threshold adjustment sub-circuit and the operating frequency adjustment sub-circuit, which outputs a PWM drive signal based on the current limiting threshold and the operating frequency.

[0014] In one possible embodiment, the control circuit further includes: an error amplification unit, which compares the output electrical parameters of the switching power supply with a reference voltage to obtain an error signal; and an optocoupler, which transmits the error signal to the output short-circuit detection unit.

[0015] In one possible embodiment, the error amplification unit includes: an error amplifier connected to the output terminal of the switching power supply, which compares the output voltage of the switching power supply with a reference voltage; The first switching transistor is connected to the output terminal of the error amplifier and is located between the optocoupler and the error amplifier. Under the control of the output signal of the error amplifier, it generates the error signal.

[0016] In one possible embodiment, the control circuit further includes a protection circuit connected to the optocoupler, which controls the current flowing through the optocoupler to zero in the event of a short circuit at the output of the switching power supply.

[0017] In one possible embodiment, the protection circuit includes: a second switching transistor connected to the input side of the optocoupler; The second comparator has its output terminal connected to the control terminal of the second switching transistor and its input terminal connected to the output terminal of the switching power supply. It compares the output voltage of the switching power supply with a preset protection voltage.

[0018] This invention also provides a switching power supply, which includes: any of the above-described control circuits for a switching power supply.

[0019] This invention also provides a control method for a switching power supply, the method comprising: receiving a detection signal of the output electrical parameters of the switching power supply, and obtaining a short-circuit indication signal based on the detection signal; detecting the magnetic field strength outside the switching power supply, and obtaining a magnetic field strength detection signal; and controlling the switching power supply based on the short-circuit indication signal and the magnetic field strength detection signal.

[0020] In one possible embodiment, controlling the switching power supply based on the short-circuit indication signal and the magnetic field strength detection signal includes: controlling at least one of the operating frequency and current limiting threshold of the switching power supply based on the short-circuit indication signal and the magnetic field strength detection signal; wherein the current limiting threshold is the maximum value allowed to flow through the power switching transistor in the switching power supply, and the power switching transistor is used to control the energy transfer of the switching power supply.

[0021] In one possible embodiment, controlling at least one of the operating frequency and current limiting threshold of the switching power supply based on the short-circuit indication signal and the magnetic field strength detection signal includes: controlling the switching power supply to switch to a second state when the short-circuit indication signal indicates that the switching power supply does not have an output short circuit and the magnetic field strength detection signal indicates that the magnetic field strength outside the switching power supply is greater than a first magnetic field strength threshold; and controlling the switching power supply to a first state when the short-circuit indication signal indicates that the switching power supply has an output short circuit or the magnetic field strength outside the switching power supply is less than or equal to the magnetic field strength threshold. Wherein, at least one of the operating frequency and current limiting threshold of the switching power supply in the second state is greater than the corresponding parameter value in the first state.

[0022] Compared with the prior art, the technical solution of the embodiments of the present invention has the following advantages: By applying the solution of this invention, an output short-circuit detection unit is set up, and this output short-circuit detection unit can be connected to the control unit together with the magnetic field detection unit. This allows the control unit to determine whether to control the switching power supply based on the short-circuit indication signal and the magnetic field strength detection signal. In this way, during the control of the switching power supply in a strong magnetic field environment, the existence of an output short circuit in the switching power supply can be taken into account. This avoids the reliability risk caused by strong magnetic field protection when the switching power supply has an output short circuit, and improves the reliability of the switching power supply in a strong magnetic field environment. Attached Figure Description

[0023] Figures 1 to 8 These are schematic diagrams of the control circuit structure in different embodiments of the present invention; Figure 9 This is a schematic diagram of the structure of a switching power supply according to an embodiment of the present invention; Figure 10 This is a flowchart of a switching power supply control method according to an embodiment of the present invention. Detailed Implementation

[0024] One current industry solution is to rely on algorithms to determine whether the switching power supply is in a strong magnetic field environment, and adjust the switching frequency of the power switching transistors in the switching power supply based on the determination result.

[0025] Using this method, the switching power supply may experience an output short circuit in a strong magnetic field environment. In this case, the switching frequency will increase, which may lead to overcurrent, overheating, core saturation, or even burnout of the power switching transistor. This will cause the switching power supply to lose its safe and stable working ability, resulting in reliability risks and reducing the reliability of the switching power supply.

[0026] Another industry solution involves directly detecting the external magnetic field using a Hall effect sensor and adjusting the switching frequency and current-limiting threshold of the power switch in the power supply based on the detection. This current-limiting threshold refers to the maximum allowable current to flow through the power switch, which controls the energy transfer of the power supply. For example, when the power supply is isolated, the current-limiting threshold is the primary-side current. When the power supply is non-isolated, the current-limiting threshold is the current flowing through the inductor.

[0027] Using this method, the switching power supply may experience an output short circuit in a strong magnetic field environment. In this case, the increase in switching frequency and current limiting threshold will lead to overcurrent, overheating, core saturation, or even burnout failure of the power switching transistor, thereby causing the switching power supply to lose its safe and stable working capability, creating reliability risks, and thus reducing the reliability of the switching power supply.

[0028] In other words, current industry solutions, in the process of addressing strong magnetic field interference, introduce reliability risks, thereby reducing the reliability of switching power supplies.

[0029] To address this problem, the present invention provides a control circuit for a switching power supply. This control circuit includes an output short-circuit detection unit. The control unit can control the switching power supply based on the short-circuit indication signal and the magnetic field strength detection signal, thereby avoiding the reliability risk caused by the switching power supply still performing strong magnetic field protection when there is an output short circuit in a strong magnetic field environment, and improving the reliability of the switching power supply.

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0031] Reference Figure 1 This invention provides a control circuit 10 for a switching power supply. Specifically, refer to... Figure 1 The control circuit 10 may include: an output short-circuit detection unit 11, a magnetic field detection unit 12, and a control unit 13. Wherein: The output short-circuit detection unit 11 receives the detection signal of the output electrical parameters of the switching power supply and outputs a short-circuit indication signal according to the detection signal. The magnetic field detection unit 12 detects the magnetic field strength outside the switching power supply and outputs a magnetic field strength detection signal. The control unit 13 is connected to the magnetic field detection unit 12 and the output short circuit detection unit 11, and controls the switching power supply based on the short circuit indication signal and the magnetic field strength detection signal.

[0032] In specific implementations, the detection signals for the output electrical parameters of the switching power supply can be either signals reflecting the magnitude of the output voltage or signals reflecting the magnitude of the output current. By setting up an output short-circuit detection unit 11, the unit can receive the detection signals for the output electrical parameters of the switching power supply and obtain a short-circuit indication signal. This short-circuit indication signal, along with the magnetic field strength detection signal output by the magnetic field detection unit 12, is output to the control unit 13, enabling the control unit 13 to control the switching power supply based on the short-circuit indication signal and the magnetic field strength detection signal.

[0033] Therefore, in the process of controlling the switching power supply in a strong magnetic field environment, the control unit 13 of this invention takes into account not only the magnetic field strength outside the switching power supply, but also the factor of whether the switching power supply has an output short circuit. Thus, when the switching power supply is in a strong magnetic field environment, the reliability risk caused by still performing strong magnetic field protection when the switching power supply has an output short circuit can be avoided, thereby improving the reliability of the switching power supply.

[0034] In a specific implementation, based on the short-circuit indication signal and the magnetic field strength detection signal, the control unit 13 can control at least one of the operating frequency and current limiting threshold of the switching power supply. The current limiting threshold is the maximum value allowed to flow through the power switching transistor in the switching power supply, and the power switching transistor is used to control the energy transfer of the switching power supply.

[0035] Specifically, based on the short-circuit indication signal and the magnetic field strength detection signal, the control unit 13 can control only the operating frequency of the switching power supply, or only the current limiting threshold of the switching power supply, or both the operating frequency and the current limiting threshold of the switching power supply. Controlling the operating frequency of the switching power supply includes, but is not limited to, changing the maximum operating frequency of the power switching transistor in the switching power supply, thereby reducing the impact of the strong magnetic field on the operation of the power switching transistor.

[0036] For example, the control unit 13 can control the switching power supply to a second state when the short-circuit indication signal indicates that the switching power supply does not have an output short circuit and the magnetic field strength detection signal indicates that the magnetic field strength outside the switching power supply is greater than a magnetic field strength threshold; and control the switching power supply to a first state when the short-circuit indication signal indicates that the switching power supply has an output short circuit or the magnetic field strength outside the switching power supply is less than or equal to the magnetic field strength threshold. In the second state, at least one of the operating frequency and the current limiting threshold is greater than at least one of the operating frequency and the current limiting threshold in the first state.

[0037] Specifically, when there is no output short circuit in the switching power supply and the magnetic field strength detection signal indicates that the magnetic field strength outside the switching power supply is greater than the magnetic field strength threshold, the control unit 13 can control the switching power supply to increase the maximum operating frequency of the power switching transistor and / or increase the current limiting threshold. When only the maximum operating frequency of the power switching transistor is increased, the maximum operating frequency of the power switching transistor in the first state is less than the maximum operating frequency of the power switching transistor in the second state. When only the current limiting threshold of the power switching transistor is increased, the current limiting threshold of the switching power supply in the first state is less than the current limiting threshold of the switching power supply in the second state. When both the maximum operating frequency and the current limiting threshold of the power switching transistor are increased, the maximum operating frequency of the power switching transistor in the first state is less than the maximum operating frequency of the power switching transistor in the second state, and the current limiting threshold of the switching power supply in the first state is less than the current limiting threshold of the switching power supply in the second state.

[0038] In specific implementations, the output short circuit detection unit 11 can have various structures, which are not limited here, as long as it can detect whether there is an output short circuit in the switching power supply based on the detection signal of the output electrical parameters of the switching power supply.

[0039] In one embodiment of the present invention, reference is made to... Figure 2 The output short-circuit detection unit 11 may include a first comparator 111. The first comparator 111 is capable of comparing the detection signal with a detection threshold to output a short-circuit indication signal.

[0040] In some embodiments, the output signal of the first comparator 111 can be directly used as a short-circuit indication signal. In this case, when there is an output short circuit in the switching power supply, the short-circuit indication signal is low, and when there is no output short circuit in the switching power supply, the short-circuit indication signal is high.

[0041] In a specific implementation, the detection signal can be a voltage signal VFB that characterizes the magnitude of the output voltage of the switching power supply, and correspondingly, the detection threshold can be a preset short-circuit reference voltage V. REF At this time, the output voltage of the first comparator 111 switching power supply is equal to the preset short-circuit reference voltage V. REF The values ​​are compared to obtain the output short-circuit indication signal. The preset short-circuit reference voltage V is used. REF The value is usually small; for example, a preset short-circuit reference voltage V can be set. REF The value is 0.5V.

[0042] When VFB < V REF When VFB ≥ V REFWhen the output voltage of the switching power supply is not pulled down to zero, it indicates that there is no output short circuit in the switching power supply. At this time, the first comparator 111 can output a short circuit indication signal indicating that there is no output short circuit in the switching power supply to the control unit 13.

[0043] It is understandable that, in the specific process of determining whether a switching power supply has an output short circuit, a preset short-circuit reference voltage V is used. REF It is itself a boundary value, and can also be used when VFB equals V. REF At that time, it is determined that the switching power supply has an output short circuit. In other words, at the boundary value, it can be determined that the switching power supply has an output short circuit, or it can be determined that the switching power supply does not have an output short circuit. How to determine it can be set by those skilled in the art. However, regardless of how it is determined, the above solution is within the protection scope of this invention.

[0044] In other embodiments, refer to Figure 3 The output short-circuit detection unit 11 may also include an inverter 112, the input of which is connected to the output of the first comparator 111. Thus, the output signal of the first comparator 111 can be inverted and used as a short-circuit indication signal, which is then output to the control unit 13.

[0045] In specific implementations, the control unit 13 can have various structures, and no limitation is made here.

[0046] In some embodiments, refer to Figure 4 The control unit 13 may include: an AND gate circuit 131 and a control module 132. Wherein: AND gate circuit 131 is connected to the output short-circuit detection unit 11 and the magnetic field detection unit 12, and generates an adjustment control signal based on the short-circuit indication signal and the magnetic field strength detection signal; The control module 132, connected to the AND gate circuit 131, is used to control the switching power supply based on the adjustment control signal.

[0047] Specifically, the AND gate 131 can perform an AND operation on the short-circuit indication signal and the magnetic field strength detection signal, or an AND operation on the inverse of the short-circuit indication signal and the magnetic field strength detection signal, thereby obtaining an adjustment control signal. Under the control of this adjustment control signal, the control module 132 can control at least one of the operating frequency and current limiting threshold of the switching power supply.

[0048] When the output short-circuit indication signal is low, or when the magnetic field strength detection signal is low, the adjustment control signal is low, and the control module 132 controls the switching power supply to remain in the first state. When both the output short-circuit indication signal and the magnetic field strength detection signal are high, the adjustment control signal is high, and the control module 132 controls the switching power supply to switch from the first state to the second state.

[0049] In some embodiments, refer to Figure 5 The control module 132 may include at least one of the following: The current limiting threshold sub-circuit 1321 is connected to the AND gate circuit 131 and controls the current limiting threshold of the switching power supply based on the current sampling result of the power switching transistor in the switching power supply and the adjustment control signal. The operating frequency sub-circuit 1322 is connected to the AND gate circuit 131 and controls the operating frequency of the switching power supply based on the detection signal and the adjustment control signal.

[0050] In practical implementation, when using the current limiting threshold sub-circuit 1321 to control the current limiting threshold of the switching power supply, the current limiting threshold sub-circuit 1321 can increase the current limiting threshold when there is no output short circuit in the switching power supply and the magnetic field strength detection signal indicates that the magnetic field strength outside the switching power supply is greater than the magnetic field strength threshold. Conversely, when there is an output short circuit in the switching power supply or the magnetic field strength detection signal indicates that the magnetic field strength outside the switching power supply is less than or equal to the magnetic field strength threshold, the current limiting threshold remains unchanged.

[0051] In specific implementation, when the operating frequency sub-circuit 1322 is used to control the operating frequency of the switching power supply, the operating frequency sub-circuit 1322 can increase the operating frequency of the power switching transistor when there is no output short circuit in the switching power supply and the magnetic field strength detection signal indicates that the magnetic field strength outside the switching power supply is greater than the magnetic field strength threshold. However, when there is an output short circuit in the switching power supply or the magnetic field strength detection signal indicates that the magnetic field strength outside the switching power supply is less than or equal to the magnetic field strength threshold, the current operating frequency remains unchanged.

[0052] In some embodiments, refer to Figure 6 The control module 132 may further include a PWM logic and drive unit 1323. The PWM logic and drive unit 1323 is connected to the current limiting threshold sub-circuit 1321 and the operating frequency sub-circuit 1322, and outputs a PWM drive signal based on the current limiting threshold and the operating frequency.

[0053] In practical implementation, the PWM logic and drive unit 1323 can generate a PWM signal based on the current limiting threshold indicated by the current limiting threshold sub-circuit 1321 and the maximum operating frequency of the power switch indicated by the operating frequency sub-circuit 1322. The current limiting threshold and the maximum operating frequency of the power switch determine the duty cycle of the PWM signal. The duty cycle of the PWM signal affects the turn-on and turn-off time of the power switch. Therefore, the PWM drive signal output by the PWM logic and drive unit 1323 can be used to adjust the on / off state of the power switch, thereby achieving the effect of controlling the switching power supply.

[0054] In some embodiments, refer to Figure 7 The control circuit 10 may further include an error amplification unit 15 and an optocoupler 16. The error amplification unit 15 compares the output electrical parameters of the switching power supply with a reference voltage to generate an error signal; the optocoupler 16 isolates and transmits the error signal to generate a detection signal.

[0055] Specifically, the error amplification unit 15 can compare the output electrical parameters of the switching power supply with the reference voltage V. R_EA The comparison is performed to output an error signal, which is the drive current flowing through optocoupler 16, and is isolated and transmitted to the output side of optocoupler 16 to generate a detection signal.

[0056] In this embodiment, the control circuit 10 uses an error amplifier unit 15 and an optocoupler 16 to generate the detection signal in order to share the feedback circuit of the switching power supply. Of course, the control circuit 10 can also directly generate the detection signal based on the output electrical parameters of the switching power supply.

[0057] For example, refer to Figure 8 The error amplification unit 15 may include an error amplifier EA and a first switching transistor K1. The error amplifier EA is connected to the output terminal of the switching power supply and compares the output voltage of the switching power supply with a reference voltage. The first switching transistor K1 is connected to the output terminal of the error amplifier EA and is located between the optocoupler 16 and the error amplifier EA. Under the control of the output signal of the error amplifier EA, the error signal is the current flowing through the optocoupler 16.

[0058] In a specific implementation, the output terminal of the error amplifier EA is connected to the gate of the first switching transistor K1, and the other end of the first switching transistor K1 is connected to the optocoupler 16. The output signal generated by the error amplifier EA controls the first switching transistor K1, thereby adjusting the current flowing through the optocoupler 16.

[0059] In some embodiments, refer to Figure 7 The control circuit 10 may further include a protection circuit 17, which is connected to the optocoupler 16 and controls the current flowing through the optocoupler 16 to be zero when the output of the switching power supply is short-circuited.

[0060] For example, refer to Figure 8The protection circuit 17 may include a second switch K2 and a second comparator CMP_EA. The second switch K2 is connected to the input side of the optocoupler 16, and the output side of the optocoupler 16 is connected to the output short-circuit detection unit 11. The output terminal of the second comparator CMP_EA is connected to the control terminal of the second switch K2, and its input terminal is connected to the output terminal of the switching power supply, comparing the output voltage of the switching power supply with a preset protection voltage V. EA_set Compare them.

[0061] Specifically, when the output voltage Vo of the switching power supply <V EA_set At this time, the second comparator CMP_EA can control the second switch K2 to turn off, and the input current I of optocoupler 16... D The current is reduced to 0, thus making the feedback current of optocoupler 16 zero. At this time, the system does not rely on the power failure of error amplifier EA to enter protection, but instead cuts off the current path flowing through optocoupler 16, forcibly shutting off optocoupler 16, thereby quickly cutting off the output and realizing output short-circuit protection.

[0062] Therefore, by setting up protection circuit 17, the switching power supply can enter the short-circuit protection state more quickly when the output of the switching power supply is short-circuited, without performing strong magnetic field protection operation. Wherein, V EA_set The value can be set according to the actual application to achieve a faster short-circuit protection response.

[0063] In specific implementations, the magnetic field detection unit 12 can be implemented using various structures, and no restrictions are imposed here.

[0064] In one embodiment, the magnetic field detection unit 12 may include a Hall effect sensor. The Hall effect sensor can be used to detect the external magnetic field strength of the switching power supply and convert it into an internal voltage signal, which is then amplified and compared to generate a corresponding magnetic field strength detection result signal.

[0065] The Hall detection device is a chip-level Hall device integrated into the switching power supply chip.

[0066] By employing the control circuit 10 in this embodiment of the invention, the switching power supply can be controlled in conjunction with the output short circuit condition during the detection of the external magnetic field strength of the switching power supply. This can effectively reduce the damage caused by the output short circuit under strong magnetic field conditions, distinguish the output short circuit condition under strong magnetic field conditions, and improve the reliability of the switching power supply.

[0067] This invention also provides a switching power supply, which includes, but is not limited to, the control circuit 10 in the above embodiments.

[0068] In specific implementations, the switching power supply can be either an isolated switching power supply or a non-isolated switching power supply. In an isolated switching power supply, the magnetic component is a transformer, while in a non-isolated switching power supply, the magnetic component is an inductor. Isolated switching power supplies can have various topologies, such as flyback, forward, and LLC resonant. Non-isolated switching power supplies also have various topologies, such as buck converters, boost converters, and buck-boost converters.

[0069] Both isolated and non-isolated switching power supplies include power switching transistors. These transistors are configured to periodically turn on and off to control energy transfer to the magnetic components, and to regulate and stabilize the output voltage or current by adjusting the on-time or switching frequency.

[0070] Taking a flyback switching power supply as an example, refer to Figure 9 The input terminal of the switching power supply is connected to an AC signal. After rectification and filtering, the AC signal is input to the primary winding Np of transformer T. The corresponding terminal of the primary winding Np is connected to the power switch Q1. The power switch Q1 can be turned on or off rapidly at high frequency under the drive of PWM logic and drive unit 14.

[0071] When the power switch Q1 is turned on, the magnetic core of the primary winding Np stores energy. When the power switch Q1 is turned off, the energy in the magnetic core is released through the secondary winding Ns, and the released energy is output through the secondary winding Ns.

[0072] In practical implementation, one end of the power switch Q1 can be grounded through the current sampling resistor RCS. The power switch Q1 can be integrated into a switching chip, which has a current sampling pin (i.e., the current sampling terminal CS), a gate drive pin GATE, and a voltage feedback pin FB (i.e., the voltage feedback node).

[0073] On the secondary winding Ns side of transformer T1, the output voltage Vo is divided by the first voltage divider resistor R1 and the second voltage divider resistor R2. The divided voltage is then captured by the error amplifier EA and compared with the internal reference voltage V. R_EA In comparison, the current flowing through optocoupler 16 is adjusted by controlling the first switching transistor K1, and then transmitted to the feedback pin FB via optocoupler 16. The voltage at the feedback pin FB affects the operation of the first comparator 111, the control circuit 132, and the PWM logic and drive unit 14.

[0074] In some embodiments, the switching power supply may further include a compensation network. This compensation network may include a compensation resistor R. F and compensation capacitor C F Compensation resistor R FOne end is connected to the output of the error amplifier EA, and the other end is connected to the compensation capacitor C. F Series connection. Compensation capacitor C F The other end is connected to the connection terminals of the first voltage divider resistor R1 and the second voltage divider resistor R2. This compensation network can be used to stabilize the loop and prevent oscillation.

[0075] In some embodiments, the switching power supply may further include a Zener diode D3. The anode of the Zener diode D3 is grounded, and the cathode is connected to one end of the second switching transistor K2. The Zener diode D3 can provide a stable bias voltage for the second switching transistor K2, thereby enabling the second switching transistor K2 to operate in a suitable amplification region and ensuring its linear amplification of error signals.

[0076] Specifically, the switching power supply may further include a feedback voltage generation unit 20. This feedback voltage generation unit 20 can convert the signal at the feedback pin FB to generate a detection signal that is input to the first comparator 111 of the output short-circuit detection unit.

[0077] In a specific implementation, the feedback voltage generation unit 20 may include a feedback voltage generation subunit 21 and a proportional conversion subunit 22. The feedback voltage generation subunit 21 converts the signal at the feedback pin FB. The sampling voltage of the proportional conversion subunit 22 is proportionally converted to obtain the converted voltage VFB, which is used as a detection signal.

[0078] In some embodiments, the feedback voltage sampling unit 20 may further include an enable subunit 23. The enable subunit 23 is connected to the feedback voltage generating subunit 21 and is adapted to output an enable signal to the feedback voltage generating subunit 21 to control the operation of the feedback voltage generating subunit 21.

[0079] Specifically, the feedback voltage generation subunit 21 can generate a voltage VFB after receiving the enable signal output by the enable subunit 23, for subsequent short-circuit judgment. In this way, the operation of the entire control circuit can be controlled through the enable subunit 23, so that the switching power supply enters the magnetic field detection mode when magnetic field detection is required, and maintains the normal operation mode when magnetic field detection is not required, thereby reducing the impact on the normal operation of the switching power supply.

[0080] The voltage VFB is input to the first comparator 111, which determines whether the switching power supply has an output short circuit and obtains a short-circuit indication signal. This short-circuit indication signal is inverted by the inverter 112 and then output to the AND gate 131. The AND gate 131 ANDs the short-circuit indication signal and the magnetic field strength detection signal, which then controls the outputs of the current limiting threshold sub-circuit 1321 and the operating frequency sub-circuit. The outputs of the current limiting threshold sub-circuit 1321 and the operating frequency sub-circuit control the duty cycle of the PWM signal output by the PWM logic and the drive unit 14, thereby changing the on / off duration of the power switch Q1.

[0081] The drive unit 1323 can adjust the duty cycle of the drive signal of the first switching transistor K1 according to the feedback signal transmitted by the optocoupler 16. When the output voltage of the switching power supply increases, the output of the error amplifier EA is at a low level, the conduction time of the first switching transistor K1 is extended, the output current of the optocoupler 16 increases, and the primary-side control chip reduces the duty cycle, thereby reducing the output voltage; conversely, the output voltage decreases, ultimately stabilizing the output voltage at the set value.

[0082] Additionally, in protection circuit 17, one input terminal of the second comparator CMP_EA can be connected to the output terminal of the switching power supply, thereby using the second comparator CMP_EA to detect whether the output of the switching power supply is short-circuited. Once the output of the switching power supply is short-circuited, the second comparator CMP_EA will control the second switching transistor K2 to turn off, and the current I on the input side of optocoupler 16 will decrease. D The current is reduced to 0, thereby making the feedback current of optocoupler 16 0, thus achieving output short-circuit protection.

[0083] The control circuit in this embodiment of the invention can detect the external magnetic field strength of the switching power supply and, in conjunction with the short circuit condition of the switching power supply output, determine whether to perform a strong magnetic field protection operation. This enables the differentiation of output short circuit conditions under strong magnetic field environments and improves the reliability of the switching power supply.

[0084] Reference Figure 10 The present invention also provides a control method for a switching power supply, the method comprising the following steps: Step S110: Receive the detection signal of the output electrical parameters of the switching power supply, and obtain a short-circuit indication signal based on the detection signal.

[0085] Specifically, the detection signal for the output electrical parameters of the switching power supply can be either a detection signal reflecting the magnitude of the output voltage or a detection signal reflecting the magnitude of the output current. The short-circuit indication signal is used to indicate whether a short circuit exists at the output of the switching power supply.

[0086] In practice, the presence of a short circuit in the output of the switching power supply can be determined by comparing the output electrical parameters of the switching power supply with a preset detection threshold.

[0087] Step S120: Detect the magnetic field strength outside the switching power supply and obtain the magnetic field strength detection signal.

[0088] In practice, the magnetic field strength outside the switching power supply can be compared with a preset magnetic field strength threshold to obtain a magnetic field strength detection signal. This magnetic field strength detection signal indicates whether the magnetic field outside the switching power supply is a strong or weak magnetic field.

[0089] Step S130: Based on the short-circuit indication signal and the magnetic field strength detection signal, control the switching power supply.

[0090] In a specific implementation, controlling the switching power supply based on the short-circuit indication signal and the magnetic field strength detection signal may include: controlling at least one of the operating frequency and current limiting threshold of the switching power supply based on the short-circuit indication signal and the magnetic field strength detection signal. The current limiting threshold is the maximum value allowed to flow through the power switching transistor in the switching power supply, and the power switching transistor is used to control the energy transfer of the switching power supply.

[0091] In specific implementation, the switching power supply can be controlled to switch to a second state when the short-circuit indication signal indicates that there is no output short circuit in the switching power supply and the magnetic field strength detection signal indicates that the magnetic field strength outside the switching power supply is greater than a first magnetic field strength threshold; and when the short-circuit indication signal indicates that there is an output short circuit in the switching power supply or the magnetic field strength outside the switching power supply is less than or equal to the magnetic field strength threshold, the switching power supply can be controlled to a first state; wherein, at least one of the operating frequency and current limiting threshold of the switching power supply in the second state is greater than the corresponding parameter value in the first state.

[0092] For steps S110 to S130, please refer to the above description of the corresponding circuits for implementation; they will not be repeated here.

[0093] The control method of the switching power supply in the embodiments of the present invention determines whether to switch the state of the switching power supply when it is in a strong magnetic field environment, based on the output short circuit of the switching power supply. This enables the differentiation of the output short circuit condition under a strong magnetic field environment and improves the reliability of the switching power supply.

[0094] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A control circuit for a switching power supply, characterized in that, include: The output short-circuit detection unit receives the detection signal of the output electrical parameters of the switching power supply and outputs a short-circuit indication signal according to the detection signal; The magnetic field detection unit detects the magnetic field strength outside the switching power supply and outputs a magnetic field strength detection signal. The control unit is connected to the magnetic field detection unit and the output short circuit detection unit, and controls the switching power supply based on the short circuit indication signal and the magnetic field strength detection signal.

2. The control circuit for a switching power supply as described in claim 1, characterized in that, The control unit controls at least one of the operating frequency and current limiting threshold of the switching power supply. The current limiting threshold is the maximum value allowed to flow through the power switching transistor in the switching power supply, and the power switching transistor is used to control the energy transfer of the switching power supply.

3. The control circuit for a switching power supply as described in claim 2, characterized in that, The control unit controls the switching power supply to a second state when the short circuit indication signal indicates that the switching power supply does not have an output short circuit and the magnetic field strength detection signal indicates that the magnetic field strength outside the switching power supply is greater than the magnetic field strength threshold; and controls the switching power supply to a first state when the short circuit indication signal indicates that the switching power supply has an output short circuit or the magnetic field strength outside the switching power supply is less than or equal to the magnetic field strength threshold. Wherein, at least one of the operating frequency and the current limiting threshold in the second state is greater than at least one of the operating frequency and the current limiting threshold in the first state.

4. The control circuit for a switching power supply as described in any one of claims 1-3, characterized in that, The output short-circuit detection unit includes: The first comparator compares the detection signal with a detection threshold to output a short-circuit indication signal.

5. The control circuit for a switching power supply as described in any one of claims 1-3, characterized in that, The control unit includes: An AND gate circuit is connected to the output short-circuit detection unit and the magnetic field detection unit, and generates an adjustment control signal based on the short-circuit indication signal and the magnetic field strength detection signal; A control module, connected to the AND gate circuit, is used to control the switching power supply based on the adjustment control signal.

6. The control circuit for a switching power supply as described in claim 5, characterized in that, The control module includes at least one of the following: A current limiting threshold sub-circuit, connected to the AND gate circuit, controls the current limiting threshold of the switching power supply based on the current sampling results of the power switching transistor in the switching power supply and the adjustment control signal. The operating frequency sub-circuit, connected to the AND gate circuit, controls the operating frequency of the switching power supply based on the detection signal and the adjustment control signal.

7. The control circuit for a switching power supply as described in claim 6, characterized in that, The control module further includes a PWM logic and drive unit, which is connected to the current limiting threshold sub-circuit and the operating frequency sub-circuit, and outputs a PWM drive signal based on the current limiting threshold and the operating frequency.

8. The control circuit for a switching power supply as described in any one of claims 1-3, characterized in that, The control circuit also includes: The error amplification unit compares the output electrical parameters of the switching power supply with the reference voltage and obtains the error signal. An optocoupler isolates and transmits the error signal for use in generating the detection signal.

9. The control circuit of the switching power supply as described in claim 8, characterized in that, The error amplification unit includes: An error amplifier is connected to the output terminal of the switching power supply to compare the output voltage of the switching power supply with a reference voltage. The first switching transistor is connected to the output terminal of the error amplifier and is located between the optocoupler and the error amplifier. Under the control of the output signal of the error amplifier, it generates the error signal.

10. The control circuit for a switching power supply as described in claim 8, characterized in that, The control circuit also includes: A protection circuit, connected to the optocoupler, controls the current flowing through the optocoupler to zero when the output of the switching power supply is short-circuited.

11. The control circuit for a switching power supply as described in claim 10, characterized in that, The protection circuit includes: The second switch is connected to the input side of the optocoupler; The second comparator has its output terminal connected to the control terminal of the second switching transistor and its input terminal connected to the output terminal of the switching power supply. It compares the output voltage of the switching power supply with a preset protection voltage.

12. A switching power supply, characterized in that, include: The control circuit for a switching power supply according to any one of claims 1 to 11.

13. A control method for a switching power supply, characterized in that, include: Receive the detection signal of the output electrical parameters of the switching power supply, and obtain a short circuit indication signal based on the detection signal; The magnetic field strength outside the switching power supply is detected, and a magnetic field strength detection signal is obtained; The switching power supply is controlled based on the short-circuit indication signal and the magnetic field strength detection signal.

14. The control method for a switching power supply as described in claim 13, characterized in that, The step of controlling the switching power supply based on the short-circuit indication signal and the magnetic field strength detection signal includes: Based on the short-circuit indication signal and the magnetic field strength detection signal, control at least one of the operating frequency and current limiting threshold of the switching power supply; The current limiting threshold is the maximum value allowed to flow through the power switching transistor in the switching power supply, and the power switching transistor is used to control the energy transfer of the switching power supply.

15. The control method for a switching power supply as described in claim 14, characterized in that, The step of controlling at least one of the operating frequency and current limiting threshold of the switching power supply based on the short-circuit indication signal and the magnetic field strength detection signal includes: When the short circuit indication signal indicates that the switching power supply does not have an output short circuit and the magnetic field strength detection signal indicates that the magnetic field strength outside the switching power supply is greater than a first magnetic field strength threshold, the switching power supply is controlled to be in a second state; and when the short circuit indication signal indicates that the switching power supply has an output short circuit or the magnetic field strength outside the switching power supply is less than or equal to the magnetic field strength threshold, the switching power supply is controlled to be in a first state. Wherein, at least one of the operating frequency and current limiting threshold of the switching power supply in the second state is greater than the corresponding parameter value in the first state.

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