Control device and method for switching power supply, switching power supply

Abstract

The application discloses a control device and method of a switching power supply, the switching power supply comprising a transformer and a primary side switch tube; the control device is used for generating a switching control signal, controlling the primary side switch tube, and transmitting energy from a primary side winding of the transformer to a secondary side winding; the control device comprises a feedback circuit used for generating a feedback voltage based on an output voltage of the switching power supply and a reference voltage; a control circuit is used for controlling a frequency of the switching control signal to be a first frequency or a second frequency in response to a starting time and the feedback voltage; the second frequency is generated according to the feedback voltage, and the first frequency is a preset frequency and is smaller than the second frequency. By using the scheme, the voltage and current stress of a power device can be effectively reduced when an output short circuit fault occurs in the starting process of the switching power supply, the device is prevented from being damaged, and the reliability of the switching power supply is improved.

Description

Technical Field

[0001] This application relates to the field of switching power supplies, specifically to a control device and method for a switching power supply, and a switching power supply itself. Background Technology

[0002] Switching power supplies are widely used in industrial fields. However, in actual operation, output short-circuit faults are one of the most common abnormalities. Output short-circuit faults cause the power devices in the switching power supply to be subjected to excessive current and voltage stress. Especially when a short circuit occurs during startup, because the control loop has not yet established steady-state regulation, extreme current spikes and turn-off overshoots occur in the initial stage, which can easily exceed the safe operating area of ​​the power transistors, causing device damage or startup failure. Summary of the Invention

[0003] This application provides a control device and method for a switching power supply, as well as a switching power supply, so as to effectively reduce the voltage and current stress on power devices when an output short-circuit fault occurs during the startup process of the switching power supply, avoid device damage, and improve the reliability of the switching power supply.

[0004] On one hand, this application provides a control device for a switching power supply, the switching power supply including: a transformer and a primary-side switching transistor; the control device is used to generate a switching control signal to control the primary-side switching transistor to transfer energy from the primary winding to the secondary winding of the transformer; the control device includes: Feedback circuit for using the output voltage of the switching power supply and reference voltage Generate feedback voltage ; Control circuit, responsive to startup time and the feedback voltage The frequency of the switch control signal is controlled to be either a first frequency or a second frequency; wherein the second frequency is determined based on the feedback voltage. The first frequency is a preset frequency and is less than the second frequency.

[0005] Optionally, the control circuit controls the frequency of the switch control signal to a first frequency or a second frequency, including: The startup time of the switching power supply The feedback voltage is less than or equal to the set startup time threshold and Before the voltage drops to a first voltage threshold, the frequency of the switch control signal is controlled at a first frequency. The startup time of the switching power supply The feedback voltage is less than or equal to the set startup time threshold and After the voltage drops to the first voltage threshold, the frequency of the switch control signal is controlled to be the second frequency.

[0006] Optionally, the control circuit controls the frequency of the switch control signal to a first frequency or a second frequency, including: The startup time of the switching power supply The feedback voltage is greater than the set startup time threshold and Before the voltage exceeds the second voltage threshold, the frequency of the switch control signal is controlled to be the first frequency. The startup time of the switching power supply The feedback voltage is greater than the set startup time threshold and After the voltage exceeds the second voltage threshold, the frequency of the switch control signal is set to the second frequency.

[0007] Optionally, the control circuit also responds to the startup time. Greater than or equal to the protection time threshold And the feedback voltage If the voltage is less than the second voltage threshold, stop outputting the switch control signal.

[0008] Optionally, the control circuit includes: The feedback clock signal generation module is used to generate a clock signal based on the feedback voltage. Generate a feedback clock signal; The clock selection module includes a first input terminal and a second input terminal; the first input terminal of the clock selection module is connected to a preset startup clock signal; the second input terminal of the clock selection module is connected to the feedback clock signal; the clock selection module selects the startup time and the feedback voltage according to the startup time and the feedback voltage. Choose to output the startup clock signal or the feedback clock signal; A control signal generation module is used to generate a switch control signal of the first frequency when the clock selection module outputs the power-on clock signal, and to generate a switch control signal of the second frequency when the clock selection module outputs the feedback clock signal.

[0009] Optionally, the control circuit further includes: The voltage selection module includes a first input terminal and a second input terminal; the first input terminal of the voltage selection module is connected to a preset start-up voltage. The second input terminal of the voltage selection module is connected to a current detection signal Vcs, which represents the current flowing through the primary-side switching transistor; the voltage selection module is used to select the voltage based on the startup time. and the feedback voltage Select the output startup voltage Or the current detection signal ; The control signal generation module is also used to control the conduction time of the switch control signal according to the output signal of the voltage selection module.

[0010] Optionally, the voltage selection module is configured to select the voltage based on the startup time. and the feedback voltage Select the output startup voltage Or the current detection signal ,include: When the clock selection module outputs the startup clock signal, the voltage selection module outputs the startup voltage. ;or, When the clock selection module outputs the feedback clock signal, the voltage selection module outputs the current detection signal. .

[0011] Optionally, the control signal generation module includes: A proportional amplifier is used to adjust the feedback voltage. Perform proportional amplification and output feedback amplified voltage V2; A voltage comparator, wherein the first input terminal of the voltage comparator is connected to the output terminal of the proportional amplifier, and the second input terminal of the voltage comparator is connected to the output terminal of the voltage selection module; An RS flip-flop is provided, wherein the R terminal of the RS flip-flop is connected to the output terminal of the voltage comparator, the S terminal of the RS flip-flop is connected to the output terminal of the clock selection module, and the Q terminal of the RS flip-flop is used to output the switch control signal.

[0012] Optionally, the feedback circuit includes: an error amplification module, an optocoupler module, and a feedback voltage generation module; The error amplification module is used to amplify the output voltage of the switching power supply. and the reference voltage V REF Generate an error signal; The optocoupler module is used to transmit the error signal to the primary side; The feedback voltage generation module is used to generate the feedback voltage based on the error signal transmitted to the primary side. .

[0013] Optionally, the feedback voltage generation module includes a current sampling unit for sampling the current flowing through the output side of the optocoupler module to generate the feedback voltage. .

[0014] Optionally, the power supply for the error amplification module is the output voltage. supply.

[0015] Optionally, the control device further includes: a feedback control module, used for controlling the output voltage When the current is less than a set threshold, the current flowing through the optocoupler module is disconnected.

[0016] Optionally, the feedback control module includes: a first comparator and a first switching unit; The first input terminal of the first comparator is connected to the output terminal of the switching power supply, and the second input terminal of the first comparator is connected to a preset loop disconnect voltage. The output of the first comparator is connected to the control terminal of the first switching unit. The first switching unit is used to control the current flowing through the optocoupler module.

[0017] On the other hand, embodiments of this application also provide a switching power supply, including the control device for the switching power supply.

[0018] On the other hand, embodiments of this application also provide a control method for a switching power supply, the switching power supply including: a transformer and a primary-side switching transistor; the control method is used to generate a switching control signal to control the primary-side switching transistor to transfer energy from the primary winding to the secondary winding of the transformer; the method includes: Based on the output voltage of the switching power supply and reference voltage Generate feedback voltage ; Response to startup time and the feedback voltage The frequency of the switch control signal is controlled to be either a first frequency or a second frequency; wherein the second frequency is determined based on the feedback voltage. The first frequency is a preset frequency and is less than the second frequency.

[0019] Optionally, the frequency of the control signal for the switch is a first frequency or a second frequency, including: The startup time of the switching power supply The feedback voltage is less than or equal to the set startup time threshold and Before the voltage drops to a first voltage threshold, the frequency of the switch control signal is controlled to be a first frequency. The startup time of the switching power supply The feedback voltage is less than or equal to the set startup time threshold and After the voltage drops to the first voltage threshold, the frequency of the switch control signal is controlled to be the second frequency.

[0020] Optionally, the frequency of the control signal for the switch is a first frequency or a second frequency, including: The startup time of the switching power supply The feedback voltage is greater than the set startup time threshold and Before the voltage exceeds the second voltage threshold, the frequency of the switch control signal is controlled to be the first frequency. The startup time of the switching power supply The feedback voltage is greater than the set startup time threshold and After the voltage exceeds the second voltage threshold, the frequency of the switch control signal is set to the second frequency.

[0021] Optionally, the method further includes: responding to the startup time Greater than or equal to the protection time threshold And the feedback voltage If the voltage is less than the second voltage threshold, stop outputting the switch control signal.

[0022] The control device and method for switching power supplies provided in this application embodiment, through a set startup logic, wherein during startup, the power system first operates at a lower startup clock signal frequency and startup voltage until the output voltage of the switching power supply reaches the set voltage, at which point the system selects to operate at a higher feedback clock signal frequency. This ensures that the power system can start normally without short-circuit conditions, without affecting the load-carrying capacity of the power system. Under short-circuit startup conditions, it can effectively reduce the voltage and current stress on power devices, avoid device damage, and improve the reliability of the switching power supply.

[0023] Furthermore, it can provide immediate protection when a short circuit occurs during power system startup and normal operation without waiting for a delay, and it will not increase the primary-side switching current or system frequency, thereby effectively reducing the voltage and current stress on the system.

[0024] Moreover, the proposed solution does not require additional system components or power supply integrated chip pins of the same type, and does not increase the cost of the same type of power supply. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of a conventional flyback power supply in the prior art; Figure 2yes Figure 1 The diagram shows the short-circuit protection timing of the flyback power supply. Figure 3 This is a schematic block diagram of a control device for a switching power supply provided in an embodiment of this application; Figure 4 This is a schematic diagram of the startup logic of a switching power supply system having the control device provided in the embodiments of this application; Figure 5 This is a schematic diagram of the control circuit in the control device of the switching power supply provided in this application embodiment; Figure 6 This is another schematic diagram of the control circuit in the control device of the switching power supply provided in the embodiments of this application; Figure 7 This is a schematic diagram of a specific structure of the control circuit in the control device of the switching power supply provided in the embodiments of this application; Figure 8 This is a schematic diagram of the feedback circuit in the control device of the switching power supply provided in this application embodiment.

[0027] Figure 9 This is another principle block diagram of the control device for the switching power supply provided in the embodiments of this application; Figure 10 This is a schematic diagram of the feedback control module in the control device of the switching power supply provided in this application embodiment; Figure 11 This is a schematic diagram of the short-circuit start-up logic of a switching power supply system having the control device provided in the embodiments of this application; Figure 12 This is a schematic diagram of the short-circuit protection logic of a switching power supply system having the control device provided in the embodiments of this application; Figure 13 This is a schematic diagram of a switching power supply having the control device provided in the embodiments of this application; Figure 14 This is another schematic diagram of a switching power supply having the control device provided in the embodiments of this application; Figure 15 This is another schematic diagram of a switching power supply having the control device provided in the embodiments of this application; Figure 16 This is another schematic diagram of a switching power supply having the control device provided in the embodiments of this application; Figure 17 This is another schematic diagram of a switching power supply having the control device provided in the embodiments of this application; Figure 18 This is another schematic diagram of a switching power supply having the control device provided in the embodiments of this application; Figure 19This is a flowchart of a control method for a switching power supply provided in an embodiment of this application. Detailed Implementation

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] The following section will first take a peak current controlled flyback power supply as an example to briefly explain the existing switching power supply and its short-circuit protection methods.

[0030] like Figure 1 As shown, this is a conventional peak current controlled flyback power supply.

[0031] The power supply system mainly consists of a rectifier circuit 11, a transformer, output rectifier diodes D1 and D2, a primary-side switching transistor Q1, a primary-side drive module 12, a feedback circuit, and a control circuit.

[0032] Where Vbulk is the bus voltage, Np, Ns, and Na are the primary, secondary, and auxiliary windings of the transformer, respectively, and capacitors C1 and C2 are the output filter capacitors for the secondary and auxiliary windings, respectively. The DC output voltage is... The auxiliary winding provides power to the external circuit; its output voltage is VDD, providing power to the internal DC power supply and providing undervoltage lockout functionality. Capacitor C3 is the output filter capacitor for rectifier circuit 11. A buffer circuit 13 is also provided on the primary side of the transformer to suppress voltage spikes generated when the primary-side switch Q1 is turned off. The primary-side switch Q1 is typically a MOSFET, with its gate connected to the output of the primary-side drive module 12, its drain connected to the primary side of the transformer, and a resistor connected between its source and ground. .

[0033] The feedback circuit is implemented through a voltage sampling module and an optocoupler module 14. The voltage sampling module uses voltage divider resistors R1 and R2 to measure the output voltage of the DC power supply. Voltage division sampling is performed, and the sampled voltage is fed back to the primary side through the voltage reference source and optocoupler module 14 to obtain the feedback voltage. . Figure 1 Resistors R3 and R4 are current-limiting resistors, and resistor R5 and capacitor C5 form a loop compensation network. Current source ISS, resistors R6 and R7 are based on the drive current at the input of optocoupler module 14. Generate feedback voltage .

[0034] The control circuit is based on feedback voltage. and the source voltage of the primary-side switching transistor Output control signals to the primary-side drive module 12. For example... Figure 1 As shown, the control circuit mainly includes a feedback clock signal generation module 16, a comparator 15, and an RS flip-flop 17. The feedback clock signal generation module 16 is based on the feedback voltage. Generate feedback clock signal (at output voltage) When the frequency is low, the frequency of the feedback clock signal is reduced; conversely, the frequency of the feedback clock signal is increased. The feedback clock signal is then output to the S terminal (set terminal) of RS flip-flop 17, and the non-inverting input terminal of comparator 15 is connected to the feedback voltage adjusted by the proportional coefficient K. The obtained reference voltage The negative input terminal of comparator 15 is connected to a current sensing resistor R. CS Current detection signal on The output of comparator 15 is connected to the R terminal (reset terminal) of RS flip-flop 17. The Q output of RS flip-flop 17 outputs a control signal to the primary-side drive module 12.

[0035] Figure 2 It shows Figure 1 The diagram shows the short-circuit protection timing of the flyback power supply.

[0036] During normal operation, the output voltage Stabilize at the set voltage When the output is short-circuited, the output voltage... From the set voltage Suddenly it becomes 0, the current flowing through optocoupler module 14 becomes its minimum value (almost 0), and the feedback voltage V COMP The voltage is increased to its maximum. Correspondingly, the reference voltage input to the non-inverting input of comparator 15... This also rises to its maximum, causing the switching power supply to operate at high frequency and high current (i.e., maximum switching frequency and maximum peak current). Simultaneously, to prevent false triggering during normal startup or sudden load changes, the protection circuit needs to wait for a certain delay time (i.e.,... Figure 2 The overload protection time in the circuit will trigger the protection; therefore, when the feedback voltage... The system will only determine the abnormal state after the temperature rises continuously for a period of time, at which point the switch will stop working and enter protection mode.

[0037] However, this protection method has significant drawbacks: when the output is short-circuited, the system continues to operate at maximum primary-side current and highest switching frequency for a period of time. During this period, the primary-side switch Q1 continuously withstands extreme stress, leading to increased system temperature, damage to components, and serious impact on normal system operation. Especially when a short circuit occurs during startup, it increases the voltage and current stress on power devices, causing device damage or startup failure.

[0038] To address the problems existing in current switching power supply protection methods, this application provides a control device for a switching power supply. The switching power supply includes a transformer and a primary-side switching transistor. The control device generates a control signal to control the primary-side switching transistor, allowing energy to be transferred from the primary winding of the transformer to the secondary winding.

[0039] like Figure 3 The diagram shown is a schematic block diagram of a control device for a switching power supply provided in an embodiment of this application.

[0040] The control device 300 of the switching power supply includes: a feedback circuit 301 and a control circuit 302. Wherein: Feedback circuit 301 is used for feedback based on the output voltage of the switching power supply and reference voltage Generate feedback voltage ; Control circuit 302 responds to startup time and feedback voltage The frequency of the switch control signal is controlled to be either a first frequency or a second frequency; wherein the second frequency is determined based on the feedback voltage. The first frequency is a preset frequency and is less than the second frequency. The startup time... This refers to the time it takes for the output voltage to rise from 0 to a stable value.

[0041] Taking into account different loads, the output voltage at startup is adjusted. The different rates of ascent correspond to different feedback voltages. The rate of increase will also differ. Feedback voltage under light load startup conditions. The rise rate is relatively fast, and the feedback voltage is high under heavy load startup conditions. The rate of increase is relatively slow. Therefore, different frequency switching conditions can be set according to different loads.

[0042] For example, in some embodiments, the frequency of the control signal controlled by the control circuit 302 to the switch control signal may be a first frequency or a second frequency, such as: Figure 4 As shown in Figure (a), the startup time of the switching power supply Less than or equal to the set startup time threshold At this time, the power supply is started under light or normal load. This is during the startup time of the switching power supply. Less than or equal to the set startup time threshold (or soft-start time) and feedback voltage Reduced to the first voltage threshold Previously, the frequency of the control switch signal was the first frequency; during the startup time of the switching power supply. Less than or equal to the set startup time threshold And feedback voltage Reduced to the first voltage threshold After that, the frequency of the control switch control signal is the second frequency.

[0043] For example, in some embodiments, such as Figure 4 As shown in (b), the startup time of the switching power supply Greater than the set startup time threshold At this time, the system is under heavy load startup. The control circuit 302 controls the switch, and the frequency of the control signal is either a first frequency or a second frequency, including during the startup time of the switching power supply. Greater than the set startup time threshold And feedback voltage Greater than the second voltage threshold Previously, the frequency of the control switch signal was the first frequency; during the startup time of the switching power supply. Greater than the set startup time threshold And feedback voltage Greater than the second voltage threshold Subsequently, the frequency of the control switch signal is the second frequency. Furthermore, in the power-on state, if the startup time of the switching power supply... Greater than or equal to the protection time threshold Then, feedback voltage The second voltage threshold has not yet been reached. This means a short circuit has occurred. Therefore, in some embodiments, the control circuit 302 also responds to the startup time of the switching power supply. Greater than or equal to the protection time threshold And feedback voltage Less than the second voltage threshold The power supply stops outputting the switch control signal to put the switching power supply into a protection state.

[0044] Through the above-mentioned startup control logic and short-circuit protection method, it can be ensured that the switching power supply can start normally when no short circuit occurs, without affecting the load capacity of the system; and when a short circuit occurs during startup, it can be effectively protected in a timely manner without increasing the current of the primary-side switching transistor and the switching frequency, thereby effectively reducing the voltage and current stress of the system.

[0045] In some embodiments, the first frequency of the switch control signal can be generated based on a set power-on clock signal (denoted as power-on CLK), and the second frequency of the switch control signal can be generated based on a feedback clock signal (denoted as feedback CLK). The following describes the process in conjunction with... Figure 5 Please provide a detailed explanation.

[0046] like Figure 5The diagram shown is a schematic diagram of the control circuit in the control device of the switching power supply provided in this application embodiment.

[0047] In this example, the control circuit 302 includes: a feedback clock signal generation module 321, a clock selection module 322, and a control signal generation module 320. Wherein: The feedback clock signal generation module 321 is used to generate clock signals based on the feedback voltage. Generate feedback CLK; The clock selection module 322 includes a first input terminal and a second input terminal; the first input terminal of the clock selection module 322 is connected to the power-on CLK; the second input terminal is connected to the feedback CLK. The clock selection module 322 is used to select the power-on time based on the power-on time. and feedback voltage Choose to output either a startup clock signal or a feedback clock signal. The specific judgment principle is as described above, and can be divided into several different cases.

[0048] The control signal generation module 320 is used to generate a first frequency switching control signal when the clock module 322 outputs a power-on CLK; and to generate a second frequency switching control signal when the clock selection module 322 outputs a feedback CLK.

[0049] exist Figure 5 In the illustrated embodiment, the first frequency switching control signal and the second frequency switching control signal can be PWM signals with different frequencies.

[0050] like Figure 6 The diagram shown is a schematic diagram of another structure of the control circuit in the control device of the switching power supply provided in the embodiment of this application.

[0051] and Figure 5 The example shown is different, Figure 6 In the example shown, the control circuit 302 further includes a voltage selection module 324. The voltage selection module 324 includes a first input terminal and a second input terminal; the first input terminal of the voltage selection module 324 is connected to a preset start-up voltage. The second input of the voltage selection module 324 is connected to the source terminal of the primary-side switching transistor Q1, and a current detection signal is input. Current detection signal This characterizes the current flowing through the primary-side switch Q1. The voltage selection module 324 is used to select the voltage based on the startup time. and feedback voltage Select output start voltage Or current detection signal The specific judgment principles are as described above, and can be divided into several different situations.

[0052] It should be noted that the startup voltage It can be set to a fixed value or designed to gradually increase over a certain period of time. It can be adjusted according to the actual load capacity requirements and current stress requirements of the system. This application does not limit this aspect.

[0053] Accordingly, Figure 6 In the embodiment shown, the control signal generation module 320 is used to control the conduction time of the switch control signal according to the output signal of the voltage selection module 324.

[0054] exist Figure 6 In the illustrated embodiment, the first frequency switching control signal and the second frequency switching control signal can be PWM signals with different frequencies and duty cycles.

[0055] In this embodiment of the invention, the voltage selection module 324 selects the voltage based on the startup time. and feedback voltage Select output start voltage Or current detection signal This includes: when the clock selection module 322 outputs the power-on CLK, the voltage selection module 324 outputs the power-on voltage. This causes the control signal generation module 320 to output a switching control signal at a first frequency; or, when the clock selection module 322 outputs feedback CLK, the voltage selection module 324 outputs a current detection signal. This allows the control signal generation module 320 to output a switching control signal at a second frequency. The clock selection module 322 and voltage selection module 324 work together to control the control signal generation module 320: During startup, a low-frequency clock is selected and the control voltage is clamped to a low level, forcing the power transistor to operate in a "low frequency, low duty cycle" state to limit startup energy surges; once the output voltage reaches a preset threshold, the clock is switched to a high-frequency clock and the control voltage clamp is released, allowing the system to enter a "high frequency, normal duty cycle" steady-state operating mode to ensure efficiency and dynamic response under steady-state conditions. Through the collaboration of the clock selection module 322 and voltage selection module 324, both startup energy surges are suppressed, and the smooth establishment of the output voltage is ensured. Figure 7 The diagram shown is a specific structural schematic of the control circuit in the control device of the switching power supply provided in this application embodiment.

[0056] In this embodiment, the control circuit 302 includes a feedback clock signal generation module 321, a clock selection module 322, a voltage selection module 324, and a control signal generation module 320.

[0057] The control signal generation module 320 includes: a proportional amplifier 3201, a voltage comparator 3202, and an RS flip-flop 3203. The proportional amplifier 3201 is used for the feedback voltage Perform proportional amplification and output feedback amplified voltage V2; The first input terminal (e.g., the positive input terminal) of the voltage comparator 3202 is connected to the output terminal of the proportional amplifier 3201, and the second input terminal (e.g., the negative input terminal) of the voltage comparator 3202 is connected to the output terminal of the voltage selection module 324. The R terminal of the RS flip-flop 3203 is connected to the output terminal of the voltage comparator 3202, the S terminal of the RS flip-flop 3203 is connected to the output terminal of the clock selection module 322, and the Q terminal of the RS flip-flop 3203 is used to output the switch control signal.

[0058] In this embodiment, the startup CLK frequency is a low value, lower than the operating frequency during switching power supply feedback regulation, and can be adjusted according to the actual load capacity requirements of the system. Startup voltage It can be set to a fixed value, or it can be designed to gradually increase over a certain period of time.

[0059] The selection logic of both clock selection module 322 and voltage selection module 324 is based on the startup time. and feedback voltage Decision. The signal selection logic is as follows: timing begins when power is on, and the signal selection time is determined during startup. Less than or equal to the set startup time threshold And feedback voltage Reduced to the first voltage threshold Previously, the startup CLK and startup voltage were selected. To operate, the frequency of the switching control signal is set to the first frequency; during the startup time of the switching power supply. Less than or equal to the set startup time threshold And feedback voltage Reduced to the first voltage threshold Then, the CLK and current sensing signals are selected as the feedback signals. It operates to switch the frequency of the switch control signal to a second frequency.

[0060] During the startup time of the switching power supply Greater than the set startup time threshold And feedback voltage Greater than the second voltage threshold Previously, the startup CLK and startup voltage were selected. To operate, the frequency of the switching control signal is set to the first frequency; during the startup time of the switching power supply. Greater than the set startup time threshold And feedback voltage Greater than the second voltage threshold Then, the CLK and current sensing signals are selected as the feedback signals. The system operates to switch the frequency of the switch control signal to a second frequency. Regardless of whether the load is light or heavy, if the timing is greater than or equal to the protection time threshold... And feedback voltage The second voltage threshold has not yet been reached. If the switch control signal is not output, the system will enter a protection state.

[0061] like Figure 8 As shown, is Figure 3 A schematic diagram of a feedback circuit 301 in the control device 300 shown.

[0062] The feedback circuit 301 may include: an error amplification module 311, an optocoupler module 312, and a feedback voltage generation module 313. Wherein: Error amplifier module 311 is used for output voltage based on switching power supply and reference voltage V REF Error signal; Optical coupler module 312 is used to transmit the error signal to the primary side; Feedback voltage generation module 313 is used to generate feedback voltage based on the error signal transmitted to the primary side. For example, the feedback voltage generation module 313 may include a current sampling unit for sampling the current flowing through the output side of the optocoupler module 312 to generate a feedback voltage. .

[0063] In some embodiments, the error amplification module 311 can be implemented, for example, using a transconductance amplifier or a voltage-type operational amplifier, and its power supply can be provided by the output voltage. It provides the ability to power down the error amplifier module 311 more quickly during a short circuit, controlling the current signal flowing through the optocoupler to be 0, thereby enabling faster short circuit protection.

[0064] In some embodiments, the feedback voltage generation module 313 may generate the voltage in various ways, and this application embodiment does not limit the specific methods used.

[0065] like Figure 9 This is another principle block diagram of the control device for the switching power supply provided in the embodiments of this application.

[0066] and Figure 3 The difference in the illustrated embodiment is that, Figure 9 In the illustrated embodiment, the control device 300 of the switching power supply may further include a feedback control module 303, used for controlling the output voltage. When the current is less than the set threshold, the current flowing through the optocoupler module 312 in the feedback circuit 301 is disconnected, thereby breaking the feedback loop.

[0067] like Figure 10 As shown, is Figure 9 A schematic diagram of a feedback control module in the control device shown.

[0068] In this embodiment, the feedback control module 303 includes: a first comparator 331 and a first switching unit 332. Wherein: The first input terminal of the first comparator 331 is connected to the output terminal of the switching power supply, and the output voltage is applied. The second input terminal of the first comparator 331 is connected to a preset loop disconnect voltage. The output of the first comparator 331 is connected to the control terminal of the first switching unit 332. The first switching unit 332 is used to control the current flowing through the optocoupler module 312.

[0069] The control device for the switching power supply provided in this embodiment of the invention can only ensure that the voltage and current stress is effectively reduced during short-circuit startup. Moreover, the feedback control module 303 can disconnect the feedback loop when a short circuit occurs during normal operation of the switching power supply system, immediately enter the protection state, without waiting for delay, and will not increase the drain current and switching frequency of the primary-side switching transistor of the transformer.

[0070] like Figure 11 The diagram shown is a schematic diagram of the short-circuit start-up logic of a switching power supply system having the control device provided in the embodiments of this application.

[0071] When the switching power supply output is short-circuited, the switching power supply starts up, and the system defaults to using the startup CLK and startup voltage. When the power supply is in operation, the output voltage of the switching power supply is... The current flowing through the optocoupler module 312 remains zero, therefore, the set protection time threshold is met. Within this period, the system operates at a low frequency of boot CLK until the boot time. The timer has reached the protection time threshold. The system enters short-circuit protection mode. Therefore, during short-circuit startup, the system can effectively reduce voltage and current stress.

[0072] like Figure 12 The diagram shown is a schematic diagram of the short-circuit protection logic of a switching power supply system with the control device provided in the embodiments of this application.

[0073] When the switching power supply is running, assuming When the switching power supply is short-circuited, the output voltage... If the value suddenly drops to 0, the feedback loop immediately stops working, and the system enters a short-circuit protection state.

[0074] Figure 11 and Figure 12 voltage in This indicates the set target voltage, i.e., the output voltage when the switching power supply is operating normally. Ideal voltage and current to be achieved This represents the current flowing through the primary switching transistor of the switching power supply transformer.

[0075] Therefore, the control device for the switching power supply provided in this application will immediately enter a short-circuit protection state when a short circuit suddenly occurs during the operation of the switching power supply, without increasing the system operating frequency or primary current. This effectively reduces voltage and current stress.

[0076] The control device for the switching power supply provided in this application embodiment can not only immediately put the system into short-circuit protection state when a short circuit occurs during the operation of the switching power supply, but also effectively reduce voltage and current stress without affecting the load-carrying capacity of the switching power supply.

[0077] The following is based on the previous... Figure 4 Provide a detailed description of the load-carrying capacity of the switching power supply with this control device.

[0078] like Figure 4 As shown, Figure 4 (a) is a schematic diagram of the startup logic during light load startup; Figure 4 (b) is a schematic diagram of the startup logic during heavy load startup.

[0079] During startup, the system defaults to using the startup CLK and startup voltage. To carry out the work.

[0080] like Figure 4 As shown in (a), under light load startup conditions, the system defaults to using startup CLK and startup voltage. To operate, output voltage Gradually increase, at the output voltage achieve Figure 7 The operating voltage of the error amplification module 311 in the middle The error amplifier module 311 starts working, the feedback loop is established, and the feedback voltage... Rise; at the output voltage Achieve the set target voltage At that time, due to the load, the feedback voltage It will gradually drop back, until it falls back to the first voltage threshold. At that time, the system begins to use feedback CLK and current detection signals. To begin operation, the frequency of the switch control signal is switched from the first frequency to the second frequency.

[0081] It can be seen that under light load startup conditions, the feedback voltage The startup time of the switching power supply is less than the set startup time threshold. The first voltage threshold can be reached within [timeframe]. First voltage threshold It can be set as the output voltage. Achieve the set target voltage The corresponding feedback voltage The voltage value. That is, the output voltage. Achieve the set target voltage The frequency of the aforementioned switch control signal is switched only when the frequency of the switch control signal is changed from the first frequency to the second frequency.

[0082] like Figure 4 As shown in (b), under heavy load startup conditions, the system defaults to using startup CLK and startup voltage. To operate, output voltage Gradually increase, feedback voltage During the startup time of the switching power supply Greater than the set startup time threshold Then, the output voltage Only then did it reach Figure 7 The operating voltage of the error amplification module 311 in the middle The error amplifier module 311 starts working, the feedback loop is established, and the feedback voltage... Increase. To make the output voltage rise. Raise to target voltage as soon as possible Establish a stable output at the feedback voltage. Reaching the second voltage threshold Then, the frequency of the aforementioned switch control signal is switched, changing the frequency of the switch control signal from the first frequency to the second frequency.

[0083] Therefore, it can be seen that the device using the switching power supply provided in the embodiments of this application does not affect the load-carrying capacity of the power supply under both light-load and heavy-load start-up conditions.

[0084] It should be noted that the control device for the switching power supply provided in this application embodiment can be applied to switching power supplies controlled in various ways. In the following embodiments, a peak current controlled flyback power supply will be used as an example for explanation.

[0085] Accordingly, this application also provides a switching power supply having the control device.

[0086] like Figure 13 The diagram shown is a structural schematic of a switching power supply with the above-described control device provided in an embodiment of this application.

[0087] The power supply system mainly includes: rectifier circuit 11, transformer, output rectifier diodes D1 and D2, primary-side switching transistor Q1, primary-side drive module 12, and control device 300.

[0088] In some embodiments, the primary-side driving module 12 may also be integrated into the control device 300.

[0089] Figure 13 In this diagram, Vbulk is the bus voltage, Np, Ns, and Na are the primary, secondary, and auxiliary windings of the transformer, respectively, and capacitors C1 and C2 are the output filter capacitors for the secondary and auxiliary windings, respectively. The DC output voltage is... The auxiliary winding is used to provide power to the external circuit; its output voltage is VDD, which can provide power to the internal DC power supply and provide undervoltage lockout. Capacitor C3 is the output filter capacitor of rectifier circuit 11. A buffer circuit 13 is also provided on the primary side of the transformer to suppress voltage spikes generated when the primary-side switch Q1 is turned off. The primary-side switch Q1 is typically a MOSFET, with its gate connected to the output of the primary-side drive module 12, its drain connected to the primary side of the transformer, and a resistor connected between its source and ground. .

[0090] Also refer to the previous Figure 3 , Figure 6 , Figure 7 , Figure 8 and Figure 9 , Figure 13 The feedback circuit 301 in the illustrated embodiment includes: an error amplification module 311, an optocoupler module 312, and a feedback voltage generation module 313. The error amplification module 311 can be a transconductance amplifier Gm, and the feedback voltage generation module 313 can be a current sensing resistor. .

[0091] The power supply port of the transconductance amplifier Gm is connected to the output terminal of the switching power supply, meaning that the output terminal of the switching power supply provides the operating power to the transconductance amplifier Gm. The negative input terminal of the transconductance amplifier Gm is connected to a first voltage V1, which is based on the output voltage of the switching power supply. The voltage divider, such as Figure 13 As shown, the output voltage is affected by the voltage divider resistors R31 and R32 connected in series between the output terminal of the switching power supply and the secondary ground of the transformer. The voltage V1 is obtained by voltage division. The first reference voltage is connected to the non-inverting input terminal of the transconductance amplifier Gm. The transconductance amplifier Gm is based on the voltage difference at the input terminals (i.e., Output error signal.

[0092] A resistor R34 and a capacitor C34 connected in series between the output of the transconductance amplifier Gm and ground serve as an RC frequency compensation network. A dominant pole is constructed at the high-impedance output to ensure the stability of the voltage feedback loop and avoid oscillation.

[0093] like Figure 13 As shown, the error signal output from the transconductance amplifier Gm is connected to the input terminal of the optocoupler module 312 through resistor R33 to generate a drive current. .

[0094] The optocoupler module 312 includes a light-emitting diode (LED) as the light-emitting end and a phototransistor as the light-receiving end. The light-emitting end receives a drive current. The current flowing through the light-receiving end generates a feedback voltage via the feedback voltage generation module 313. .

[0095] Figure 13 In the illustrated embodiment, the anode of the light-emitting diode (LED) is connected to resistor R33, and the cathode of the LED is connected to the secondary ground. The collector of the phototransistor is connected to the internal power supply VDD generated by the auxiliary winding of the transformer, and the emitter of the phototransistor is connected to resistor R33. Connect to primary ground, resistor The current flowing through the phototransistor is detected to generate a feedback voltage. .

[0096] Figure 13 In the embodiment shown, the control circuit 302 includes: a feedback clock signal generation module 321, a clock selection module 322, a voltage selection module 324, a proportional amplifier 3201, a voltage comparator 3202, and an RS flip-flop 3203.

[0097] The following is combined Figure 13 Provide a detailed explanation of the working process and control logic of this switching power supply.

[0098] Reference Figure 13 When the power supply is started, the rectifier circuit 11 converts AC power into DC power, the transformer realizes the energy transfer from the primary side Np to the secondary side Na, and the auxiliary winding Na provides the internal power supply VDD.

[0099] Feedback circuit 301 converts the output voltage of the switching power supply The information is transmitted to the primary-side control circuit 302, which generates a control signal, i.e., a PWM signal, to control the primary-side switching transistor Q1, so as to achieve stable output of the system.

[0100] In this embodiment, the startup CLK frequency is a low value, lower than the operating frequency during switching power supply feedback control, and can be adjusted according to the actual load capacity requirements of the system. Startup voltage It can be set to a fixed value, or it can be designed to gradually increase over a certain period of time.

[0101] The selection logic of both clock selection module 322 and voltage selection module 324 is based on the startup time. and feedback voltage Decision. The signal selection logic can be referred to above. Figure 6 The corresponding descriptions will not be repeated here.

[0102] The control device for the switching power supply provided in this application embodiment can not only immediately put the system into short-circuit protection state when a short circuit occurs during the operation of the switching power supply, but also effectively reduce voltage and current stress without affecting the load-carrying capacity of the switching power supply.

[0103] like Figure 14 The diagram shown is another structural schematic of a switching power supply having the short-circuit protection device provided in the embodiments of this application.

[0104] and Figure 13 The difference in the illustrated embodiment is that, in this embodiment, the error amplification module 311 uses a voltage-type operational amplifier EA, and the power supply port of the voltage-type operational amplifier EA is connected to the output voltage of the switching power supply. Furthermore, a compensation loop consisting of resistor R35 and capacitor C35 connected in series between the output and negative input terminals of the voltage-type operational amplifier EA can be used to change the internal frequency characteristics of the circuit, ensuring that the amplifier operates stably without oscillation.

[0105] like Figure 15 The diagram shown is a schematic diagram of another structure of a switching power supply having the control device provided in the embodiments of this application.

[0106] and Figure 13 Compared with the embodiments shown, Figure 15 In the illustrated embodiment, Figure 7 The feedback voltage generation module 313 can directly collect the collector current flowing through the phototransistor at the light-receiving end of the optocoupler module 312, convert it into voltage, and obtain the feedback voltage. . Specifically, Figure 7 The feedback voltage generation module 313 includes a current sampling unit 3131 and a signal conversion module 3132.

[0107] The current sampling unit 3131 is connected to the collector of the phototransistor at the light-receiving end of the optocoupler module 312 and the current source IS, respectively, and the emitter of the phototransistor is connected to the primary ground. The current sampling unit 3131 is used to collect the current flowing through the optocoupler module 312.

[0108] Signal conversion unit 3132 is used to convert the current sampled by current sampling unit 3131 into voltage to obtain feedback voltage. .

[0109] It should be noted that, Figure 15 The diagram shows the direct acquisition of the collector current flowing through the phototransistor at the light-receiving end of the optocoupler module 312, which is then converted into a voltage to obtain the feedback voltage. The same method applies Figure 14 The error amplification module 311 shown is implemented using a voltage-type operational amplifier EA.

[0110] like Figure 16 The diagram shown is a schematic diagram of another structure of a switching power supply having the control device provided in the embodiments of this application.

[0111] and Figure 13 The difference between the embodiments shown is that, Figure 16 In the illustrated embodiment, Figure 3 In addition to the error amplification module 311, optocoupler module 312, and feedback voltage generation module 313, the feedback circuit 301 also includes an operational amplifier module 314. The non-inverting input of the operational amplifier module 314 is connected to a second reference voltage. The negative input terminal of the operational amplifier module 314 is connected to the emitter of the phototransistor. The operational amplifier module 314 is used to control the resistance... The voltage generated is amplified and output as the feedback voltage. .

[0112] A feedback resistor R35 is connected between the output terminal and the negative input terminal of the operational amplifier module 314. The gain of the operational amplifier module 314 can be adjusted by adjusting the value of the feedback resistor R35.

[0113] Compared to Figure 13 As shown, directly from the resistor Obtain feedback voltage In this way, Figure 16 The embodiment shown adds an operational amplifier module 314, which allows for more flexible gain configuration to meet the application needs of different scenarios.

[0114] like Figure 17 The diagram shown is a schematic diagram of another structure of a switching power supply having the control device provided in the embodiments of this application.

[0115] Compared to Figure 13 In the illustrated embodiment, Figure 17 The illustrated embodiment adds Figure 8 The feedback control module 303 shown in this embodiment includes a first comparator 331 and a first switching unit 332. The first switching unit 332 is implemented using a MOSFET Q2.

[0116] In this circuit, the non-inverting input of the first comparator 331 is connected to the output of the switching power supply, and the negative input of the first comparator 331 is connected to a preset loop disconnect voltage. The output of the first comparator 331 is connected to the gate of the MOSFET Q2.

[0117] Accordingly, in the output voltage Less than the loop disconnect voltage When the first comparator 331 outputs a low level, the MOSFET Q2 enters the cutoff state, thereby disconnecting the current to the LED of the optocoupler module 312; when the output voltage... Greater than the loop disconnect voltage When the output of the first comparator 331 is high, the MOSFET Q2 enters the conducting state, thereby connecting the current of the light-emitting diode of the optocoupler module 312.

[0118] and Figure 13 Compared to the embodiments shown, Figure 17 In the illustrated embodiment, the condition for the feedback loop to start working requires not only the voltage at the transconductance power supply terminal on the secondary side (i.e., the output voltage of the switching power supply) but also... To reach the operating voltage, the output voltage also needs to be adjusted. Meet the conditions Only then can a feedback signal be established.

[0119] like Figure 18 The diagram shown is a schematic diagram of another structure of a switching power supply having the control device provided in the embodiments of this application.

[0120] Compared to Figure 13 The embodiment shown, Figure 18 The illustrated embodiment adds Figure 8 The feedback control module 303 shown in this embodiment includes: a MOSFET Q3, resistors R36 and R37, and a diode D3 connected between the drain of the MOSFET Q3 and the secondary ground. Resistor R36 is connected between the source of the MOSFET Q3 and the secondary ground, and resistor R37 is connected between the output of the transconductance amplifier Gm and the gate of the MOSFET Q3.

[0121] The switching power supply and its control device provided in this application combine short-circuit protection and feedback circuitry. When a short circuit occurs at the system output, the feedback signal drops directly to 0, causing the feedback circuit to immediately stop working, thus putting the system into short-circuit protection mode. Furthermore, it effectively reduces voltage and current stress without affecting the system's load-carrying capacity.

[0122] Accordingly, this application also provides a control method for a switching power supply, the switching power supply including: a transformer and a primary-side switching transistor; the control method is used to generate a switching control signal to control the primary-side switching transistor to transfer energy from the primary winding of the transformer to the secondary winding.

[0123] like Figure 19 The diagram shown is a flowchart of a control method for a switching power supply provided in an embodiment of this application. The method includes the following steps: Step 191: Generate a feedback voltage based on the output voltage and reference voltage of the switching power supply; Step 192: In response to the startup time and the feedback voltage, control the frequency of the switch control signal to a first frequency or a second frequency; wherein the second frequency is generated according to the feedback voltage, and the first frequency is a preset frequency and is less than the second frequency.

[0124] Depending on the application scenario with different loads, the frequency of the control signal for the switch can be either a first frequency or a second frequency.

[0125] For example, in some embodiments, before the startup time of the switching power supply is less than or equal to a set startup time threshold and the feedback voltage drops to a first voltage threshold, the frequency of the switching control signal is controlled to be a first frequency; after the startup time of the switching power supply is less than or equal to the set startup time threshold and the feedback voltage drops to the first voltage threshold, the frequency of the switching control signal is controlled to be a second frequency.

[0126] For example, in some embodiments, before the startup time of the switching power supply is greater than a set startup time threshold and the feedback voltage is greater than a second voltage threshold, the frequency of the switching control signal is controlled to be a first frequency; after the startup time of the switching power supply is greater than the set startup time threshold and the feedback voltage is greater than the second voltage threshold, the frequency of the switching control signal is controlled to be a second frequency.

[0127] In some embodiments, the frequency of the switch control signal can be controlled according to different clock signals. For example, a first frequency switch control signal can be generated according to a preset startup clock signal; a second frequency switch control signal can be generated according to a feedback clock signal; the feedback clock signal is a clock signal generated based on the feedback voltage.

[0128] In some embodiments, the frequency and conduction time of the switch control signal can be controlled according to different clock signals and different voltage signals. For example, a first frequency switch control signal is generated according to a preset start-up clock signal and a preset start-up voltage, and its conduction time is controlled; a second frequency switch control signal is generated according to a feedback clock signal and a current detection signal, and its conduction time is controlled; the feedback clock signal is a clock signal generated based on the feedback voltage, and the current detection signal represents the current flowing through the primary-side switch.

[0129] The control method provided in this application embodiment can not only immediately enter the protection state when a short circuit occurs during normal operation of the switching power supply system, but also effectively reduce voltage and current stress without affecting the load-carrying capacity of the switching power supply.

[0130] The control method for switching power supplies provided in this application can be applied to switching power supplies controlled in various ways.

[0131] In the description of the embodiments of this application, unless otherwise expressly specified and limited, ordinal numbers, such as "first" and "second," are used only to distinguish and describe related objects, and should not be construed as indicating or implying the relative importance or order between related objects. Furthermore, ordinal numbers do not represent the number of related objects.

[0132] In the description of the embodiments in this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. Other quantifiers are similar.

[0133] The terms "or" and "and / or" used in this application are used to describe the relationship between related objects, indicating a non-exclusive inclusion. For example, "A and / or B" can include: "A alone", "B alone", or "A with B". Additionally, the character " / " in this document indicates that the preceding and following related objects are in an "or" relationship.

[0134] In the several embodiments provided in this application, it should be understood that the disclosed apparatus can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for example, the division of modules is merely a logical functional division, and there may be other division methods in actual implementation, which this application does not limit.

[0135] In the embodiments of this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0136] Furthermore, the functional modules in the various embodiments of this application can be integrated into one processing unit, or they can be separate physical units, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or in the form of hardware and software functional units.

[0137] Integrated units implemented as hardware and software functional units can be implemented by a processor calling software; for example, the system includes a processor connected to memory, which stores instructions. The processor calls the instructions stored in memory to implement any of the above methods or to implement the functions of each module of the system. The processor is, for example, a general-purpose processor, such as a CPU or microprocessor, and the memory is either internal or external to the system. The software described above can be stored in a computer-readable storage medium.

[0138] Although embodiments of this application have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting this application. Any person skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments without departing from the spirit and scope of this application.

Claims

1. A control device for a switching power supply, the switching power supply comprising: Transformer and primary-side switching transistor; The control device is used to generate a switching control signal to control the primary-side switching transistor, thereby transferring energy from the primary winding to the secondary winding of the transformer; characterized in that the control device comprises: Feedback circuit, used for feedback based on the output voltage of the switching power supply ( ) and reference voltage ( ) generates feedback voltage ( ); Control circuit, responding to startup time ( ) and the feedback voltage ( The frequency of the switch control signal is controlled to be either a first frequency or a second frequency; wherein the second frequency is determined based on the feedback voltage ( The first frequency is a preset frequency and is less than the second frequency.

2. The control device according to claim 1, characterized in that, The control circuit controls the frequency of the switch control signal to a first frequency or a second frequency, including: During the startup time of the switching power supply ( The feedback voltage is less than or equal to the set startup time threshold and the feedback voltage is less than or equal to the set startup time threshold. Before the voltage drops to the first voltage threshold, the frequency of the switch control signal is controlled to be a first frequency; During the startup time of the switching power supply ( The feedback voltage is less than or equal to the set startup time threshold and the feedback voltage is less than or equal to the set startup time threshold. After the voltage drops to the first voltage threshold, the frequency of the switch control signal is controlled to be the second frequency.

3. The control device according to claim 1, characterized in that, The control circuit controls the frequency of the switch control signal to a first frequency or a second frequency, including: During the startup time of the switching power supply ( The feedback voltage is greater than the set startup time threshold and the feedback voltage is greater than the set startup time threshold. Before the voltage exceeds the second voltage threshold, the frequency of the switch control signal is controlled to be the first frequency; During the startup time of the switching power supply ( The feedback voltage is greater than the set startup time threshold and the feedback voltage is greater than the set startup time threshold. After the voltage exceeds the second voltage threshold, the frequency of the switch control signal is set to the second frequency.

4. The control device according to claim 2 or 3, characterized in that, The control circuit also responds to the startup time ( ) greater than or equal to the protection time threshold ( And the feedback voltage ( If the voltage is less than the second voltage threshold, stop outputting the switch control signal.

5. The control device according to any one of claims 1-3, characterized in that, The control circuit includes: The feedback clock signal generation module is used to generate a clock signal based on the feedback voltage ( Generate a feedback clock signal; A clock selection module includes a first input terminal and a second input terminal; the first input terminal of the clock selection module is connected to a preset startup clock signal; the second input terminal of the clock selection module is connected to the feedback clock signal; the clock selection module selects the startup time and the feedback voltage according to the startup time and the feedback voltage. Select to output either the startup clock signal or the feedback clock signal; A control signal generation module is used to generate a switch control signal of the first frequency when the clock selection module outputs the power-on clock signal, and to generate a switch control signal of the second frequency when the clock selection module outputs the feedback clock signal.

6. The control device according to claim 5, characterized in that, The control circuit also includes: The voltage selection module includes a first input terminal and a second input terminal; the first input terminal of the voltage selection module is connected to a preset start-up voltage (…). The second input terminal of the voltage selection module is connected to a current detection signal (Vcs), which represents the current flowing through the primary-side switching transistor; the voltage selection module is used to select the voltage based on the startup time (Vcs). ) and the feedback voltage ( Select the output startup voltage ( ) or the current detection signal ( ); The control signal generation module is also used to control the conduction time of the switch control signal according to the output signal of the voltage selection module.

7. The control device according to claim 6, characterized in that, The voltage selection module is used to select the voltage according to the start time ( ) and the feedback voltage ( Select the output startup voltage ( ) or the current detection signal ( ),include: When the clock selection module outputs the startup clock signal, the voltage selection module outputs the startup voltage ( );or, When the clock selection module outputs the feedback clock signal, the voltage selection module outputs the current detection signal. ).

8. The control device according to claim 6 or 7, characterized in that, The control signal generation module includes: A proportional amplifier is used to adjust the feedback voltage ( The voltage is proportionally amplified and the output feedback amplified voltage (V2) is generated. A voltage comparator, wherein the first input terminal of the voltage comparator is connected to the output terminal of the proportional amplifier, and the second input terminal of the voltage comparator is connected to the output terminal of the voltage selection module; An RS flip-flop is provided, wherein the R terminal of the RS flip-flop is connected to the output terminal of the voltage comparator, the S terminal of the RS flip-flop is connected to the output terminal of the clock selection module, and the Q terminal of the RS flip-flop is used to output the switch control signal.

9. The control device according to any one of claims 1-3, characterized in that, The feedback circuit includes: an error amplification module, an optocoupler module, and a feedback voltage generation module; The error amplification module is used to amplify the output voltage of the switching power supply ( ) and the reference voltage (V REF Generate error signals; The optocoupler module is used to transmit the error signal to the primary side; The feedback voltage generation module is used to generate the feedback voltage based on the error signal transmitted to the primary side. ).

10. The control device according to claim 9, characterized in that, The feedback voltage generation module includes a current sampling unit for sampling the current flowing through the output side of the optocoupler module to generate the feedback voltage. ).

11. The control device according to claim 9, characterized in that, The power supply for the error amplification module is provided by the output voltage ( )supply.

12. The control device according to claim 11, characterized in that, The control device further includes: Feedback control module, used to control the output voltage ( When the current is less than the set threshold, the current flowing through the optocoupler module is disconnected.

13. The control device according to claim 12, characterized in that, The feedback control module includes: a first comparator and a first switching unit; The first input terminal of the first comparator is connected to the output terminal of the switching power supply, and the second input terminal of the first comparator is connected to a preset loop disconnect voltage. The output of the first comparator is connected to the control terminal of the first switching unit. The first switching unit is used to control the current flowing through the optocoupler module.

14. A switching power supply, characterized in that, Includes the control device for the switching power supply as described in any one of claims 1 to 13.

15. A control method for a switching power supply, the switching power supply comprising: Transformer and primary-side switching transistor; The control method is used to generate a switching control signal to control the primary-side switching transistor, thereby transferring energy from the primary winding to the secondary winding of the transformer; characterized in that the method includes: Based on the output voltage of the switching power supply ( ) and reference voltage ( ) generates feedback voltage ( ); Response to startup time ( ) and the feedback voltage ( The frequency of the switch control signal is controlled to be either a first frequency or a second frequency; wherein the second frequency is determined based on the feedback voltage ( The first frequency is a preset frequency and is less than the second frequency.

16. The control method according to claim 15, characterized in that, The frequency of the control signal for the switch is either a first frequency or a second frequency, including: During the startup time of the switching power supply ( The feedback voltage is less than or equal to the set startup time threshold and the feedback voltage is less than or equal to the set startup time threshold. Before the voltage drops to the first voltage threshold, the frequency of the switch control signal is controlled to be a first frequency; During the startup time of the switching power supply ( The feedback voltage is less than or equal to the set startup time threshold and the feedback voltage is less than or equal to the set startup time threshold. After the voltage drops to the first voltage threshold, the frequency of the switch control signal is controlled to be the second frequency.

17. The control method according to claim 15, characterized in that, The frequency of the control signal for the switch is either a first frequency or a second frequency, including: During the startup time of the switching power supply ( The feedback voltage is greater than the set startup time threshold and the feedback voltage is greater than the set startup time threshold. Before the voltage exceeds the second voltage threshold, the frequency of the switch control signal is controlled to be the first frequency; During the startup time of the switching power supply ( The feedback voltage is greater than the set startup time threshold and the feedback voltage is greater than the set startup time threshold. After the voltage exceeds the second voltage threshold, the frequency of the switch control signal is set to the second frequency.

18. The control method according to claim 16 or 17, characterized in that, The method further includes: In response to the startup time ( ) greater than or equal to the protection time threshold ( And the feedback voltage ( If the voltage is less than the second voltage threshold, stop outputting the switch control signal.

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