CN111082676B - Switching power supply and control circuit and control method thereof - Google Patents

Switching power supply and control circuit and control method thereof Download PDF

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Publication number
CN111082676B
CN111082676B CN201911395758.9A CN201911395758A CN111082676B CN 111082676 B CN111082676 B CN 111082676B CN 201911395758 A CN201911395758 A CN 201911395758A CN 111082676 B CN111082676 B CN 111082676B
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voltage
signal
control
sampling
control signal
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CN111082676A (en
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王建龙
赵光焕
厉剑波
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Hangzhou Silan Microelectronics Co Ltd
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Hangzhou Silan Microelectronics Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
    • H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
    • H02H7/125—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for rectifiers
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention discloses a switching power supply and a control circuit and a control method thereof, wherein the control circuit comprises a control unit, a voltage limiting threshold value adjusting unit, a voltage limiting protection unit and a driving unit, the control unit is used for generating a first control signal, the voltage limiting threshold value adjusting unit is used for obtaining a first reference voltage according to a target voltage signal, the voltage limiting protection unit is used for outputting a second control signal according to the sampling voltage of the output voltage, the first reference voltage and the first control signal, the driving unit is used for outputting a driving signal for controlling a power switching tube according to the second control signal, the voltage limiting threshold value adjusting unit is also used for adjusting the voltage limiting protection threshold value of the output voltage in real time through the detection of a load state, when the switching power supply works under different load conditions and meets the power grid fluctuation, the output voltage can be always kept below the set voltage limiting protection threshold value, the power device at the rear end is prevented from being overshot by larger current, the reliability is improved, and the service life is prolonged.

Description

Switching power supply and control circuit and control method thereof
Technical Field
The invention relates to the technical field of switching power supply control, in particular to a switching power supply and a control circuit and a control method thereof.
Background
The switching power supply is a power supply that utilizes modern power electronic technology to control the on/off time ratio of a power switching tube to maintain stable output voltage, and generally includes a Pulse Width Modulation (PWM) control circuit and a power switching tube (e.g., a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET)). The conventional switching power supply is implemented in an analog control mode, a digital control mode and a digital-analog hybrid control mode. In recent years, digital control has become widely used and accepted due to advantages such as programmability, design continuity, and a small number of components.
Due to the existence of nonlinear elements and energy storage elements in a large number of electric devices, the waveform of input alternating current is severely distorted, and the input power factor at the side of a power grid is low. Therefore, a PFC (Power Factor Correction) control system must be added to the electric equipment. In a PFC control system, the on and off of a power switch tube are controlled through a PWM control signal to realize the control of system power factors and output voltage, meanwhile, the output voltage needs to be detected and protected in real time, and if the detected output voltage is higher than a set protection threshold value, the PWM control signal is closed in time to prevent the failure of a rear-end device caused by overhigh output voltage.
Fig. 1 shows a waveform diagram of a conventional PFC overvoltage protection. The traditional PFC overvoltage protection can be divided into software protection and hardware protection, wherein the software protection is implemented by carrying out resistance voltage division on an output voltage signal and then sending the output voltage signal into a digital-analog sampling port of a microcontroller, then carrying out software filtering on a sampling result, and if a filtering value is higher than a set protection threshold value, closing PWM control signal output. The hardware protection compares the output voltage signal after voltage division with a reference voltage signal (namely an overvoltage protection threshold) set by hardware through a hardware comparator, when the output voltage after voltage division is higher than the reference voltage, the comparator is turned over, and the microcontroller closes the PWM control signal.
In many applications, in order to improve the efficiency of the PFC control system and reduce the temperature rise of the power device, the target voltage of the PFC overvoltage protection is automatically adjusted, for example, the target voltage is lower when the load is light, and the target voltage is increased when the load is heavy. However, the traditional PFC software overvoltage protection requires filtering processing on signals, so that the protection speed is slow, and the PWM control signal can be turned off only when the actual output voltage is higher than the protection threshold. And the protection threshold value of the PFC hardware overvoltage protection cannot be adjusted, so the set protection threshold value is higher than the highest target voltage of a PFC control system, and enough margin needs to be reserved to prevent the false triggering. However, as shown in fig. 1, if the power supply is often operated in an environment with a light load and severe and frequent grid fluctuation, output voltage overshoot frequently occurs, but the set hardware overvoltage protection cannot be triggered, so that the power device and the filter capacitor at the rear end frequently bear the voltage overshoot, and the service life of the power device and the filter capacitor is easily affected.
Disclosure of Invention
In view of the above, the present invention provides a switching power supply, a control circuit thereof and a control method thereof, which adjust a voltage limiting protection threshold of an output voltage in real time by detecting a load state, so that when the switching power supply operates under different load conditions and encounters power grid fluctuation, the output voltage can be always kept below the set voltage limiting protection threshold, a power device at a rear end is prevented from being overshot by a large current, reliability of the switching power supply is improved, and a service life of the switching power supply is prolonged.
According to a first aspect of embodiments of the present invention, there is provided a control circuit of a switching power supply, the control circuit including: an output voltage sampling unit which samples the output voltage to obtain a sampling voltage of the output voltage; a load state detection unit which obtains the target voltage signal by detecting a load state of the switching power supply, the target voltage signal varying according to a variation of the load state; a control unit generating a first control signal; the voltage limiting threshold adjusting unit is used for obtaining a first reference voltage according to the target voltage signal; the voltage limiting protection unit is connected with the control unit and outputs a second control signal according to the sampling voltage of the output voltage, the first reference voltage and the first control signal; and the driving unit is connected with the voltage limiting protection unit so as to output a driving signal for controlling the power switch tube according to the second control signal, and when the sampling voltage of the output voltage is greater than or equal to the first reference voltage, the driving unit turns off the power switch tube according to the second control signal, wherein the voltage limiting threshold value adjusting unit also adjusts the first reference voltage according to the load state of the switch power supply.
Preferably, the voltage limiting threshold adjusting unit includes: the software adjusting module receives the target voltage signal and obtains a voltage limiting protection threshold value according to the target voltage signal; and the digital-to-analog conversion module is used for receiving the voltage limiting protection threshold value and performing digital-to-analog conversion on the voltage limiting protection threshold value to generate the first reference voltage.
Preferably, the software adjusting module obtains the voltage-limiting protection threshold according to a maximum value of the target voltage signal, an amplitude of a voltage ripple, and a preset first protection margin.
Preferably, the control circuit further comprises: an input voltage sampling unit which samples an input voltage of the switching power supply to obtain a sampling voltage of the input voltage; the switching power supply comprises an input current sampling unit for sampling the input current of the switching power supply to obtain the sampling voltage of the input current, wherein the control unit generates the first control signal according to the sampling voltage of the input current, a target voltage signal, the sampling voltage of the input voltage and the sampling voltage of the output voltage.
Preferably, the control unit includes: a duty signal generation unit that generates a duty signal from the sampling voltage of the input current, the sampling voltage of the input voltage, the sampling voltage of the output voltage, and the target voltage; and a PWM generating unit generating the first control signal and a PWM reset signal according to the duty signal, wherein the duty signal generating unit includes: the first adding module is used for obtaining a first error according to the sampling voltage of the output voltage and the target voltage signal; the first linear control module is used for obtaining an input current effective value according to the first error; the phase calculation module is used for obtaining an input voltage phase value according to the sampling voltage of the input voltage; the multiplication module is used for obtaining a target current signal according to the input current effective value and the input voltage phase value; the second addition module is used for obtaining a second error according to the sampling voltage of the input current and the target current signal; and a second linear control module generating the duty cycle signal according to the second error.
Preferably, the first linear control module and the second linear control module each include a PI controller.
Preferably, the voltage limiting protection unit includes: the comparison module compares the first reference voltage with the sampling voltage of the output voltage and generates a first indication signal according to a comparison result; the fault management module is connected with the comparison module and generates the second control signal according to the first indication signal, the first control signal and the PWM reset signal; when the sampling voltage of the output voltage is larger than or equal to the first reference voltage, judging that the output voltage is overvoltage, outputting the second control signal by the fault management module to turn off the power switch tube, and outputting the second control signal by the fault management module according to the PWM reset signal to turn on the power switch tube in the next control period.
Preferably, the fault management module comprises: a first latch generating a first fail signal according to the PWM reset signal and the first indication signal; and the AND gate generates the second control signal according to the first control signal and the first fault signal, wherein when the first indication signal is valid, the first fault signal is valid, when the PWM reset signal is valid and the first indication signal is invalid, the first fault signal is invalid, when the first fault signal is invalid, the state of the second control signal is consistent with the state of the first control signal, and when the first fault signal is valid, the second control signal is invalid.
Preferably, the voltage-limiting protection unit is further configured to control the driving unit to turn off the power switch tube when the number of times that the sampling voltage of the output voltage is greater than or equal to the first reference voltage within a first preset time reaches a preset value and a fault clearing signal is not received.
Preferably, the voltage limiting protection unit further comprises: the second indication signal generation unit is used for counting the first indication signal, obtaining a count value, generating a second indication signal according to the count value, and enabling the second indication signal to be effective when the count value is greater than or equal to a preset value within a first preset time, wherein the second indication signal generation unit comprises: the counting module is used for counting the first indicating signal to obtain a counting value, generating an intermediate indicating signal according to the counting value, and enabling the intermediate indicating signal to be effective when the counting value is larger than or equal to a preset value within first preset time; the latch module is connected with the counting module and used for latching the intermediate indication signal and generating a second indication signal according to the intermediate indication signal; the first timer is used for repeatedly timing, generating a counting reset signal after the first preset time, resetting the counting value according to the counting reset signal by the counting module and restarting counting; and the second timer starts timing when the intermediate indication signal is effective and generates a fault clearing signal after a second preset time, and the latch module generates a second indication signal according to the fault clearing signal and the intermediate indication signal.
Preferably, the fault management module further comprises: and a second latch configured to generate a second fail signal based on the PWM reset signal and the second indication signal, wherein the second fail signal is enabled when the second indication signal is enabled, the second fail signal is disabled when the PWM reset signal is enabled and the second indication signal is disabled, a state of the second control signal is identical to a state of the first control signal when both the first fail signal and the second fail signal are disabled, and the second control signal is disabled when one of the first fail signal and the second fail signal is enabled.
Preferably, the control circuit further includes a hardware overvoltage protection unit, which receives a sampling voltage of the output voltage, the hardware overvoltage protection unit generates a first trigger signal when the sampling voltage of the output voltage is greater than or equal to a second reference voltage, the driving unit turns off the power switch tube according to the first trigger signal, and the control unit controls the first control signal to be in an invalid state according to the first trigger signal, where the second reference voltage represents a first overvoltage protection threshold, and the second reference voltage is greater than the first reference voltage.
Preferably, the control circuit further includes a software overvoltage protection unit, which receives the sampling voltage of the output voltage, the software overvoltage protection unit generates a second trigger signal when the sampling voltage of the output voltage is greater than or equal to a third reference voltage, and the control unit controls the first control signal to be in an invalid state according to the first trigger signal, where the third reference voltage represents a second overvoltage protection threshold, and the first reference voltage is greater than the third reference voltage.
Preferably, the threshold adjusting unit is further configured to obtain the second overvoltage protection threshold according to the target voltage signal.
Preferably, the threshold value adjusting unit includes: and the software adjusting module is used for receiving the target voltage signal and obtaining the second overvoltage protection threshold according to the maximum value of the target voltage signal, the amplitude of the voltage ripple and a preset second protection margin.
According to a second aspect of the embodiments of the present invention, there is provided a switching power supply including the control circuit described above.
Preferably, the switching power supply further includes: a rectifier bridge rectifying an alternating input voltage to obtain the input voltage; the inductor, the diode and the sampling resistor are connected to two ends of the rectifier bridge in series, and the anode of the diode is connected with the power switch tube and the middle node of the inductor; and the output capacitor is connected between the intermediate node and the cathode of the diode and used for stabilizing the output voltage.
According to a third aspect of the embodiments of the present invention, there is provided a control method of a switching power supply, the control method including: sampling the output voltage to obtain a sampled voltage of the output voltage; preferably, a load state of the switching power supply is detected to obtain the target voltage signal, and the target voltage signal changes according to the change of the load state; generating a first control signal; obtaining a first reference voltage according to the target voltage signal; outputting a second control signal according to the sampling voltage of the output voltage, the first reference voltage and the first control signal; and outputting a driving signal for controlling a power switch tube according to the second control signal, and when the sampling voltage of the output voltage is greater than or equal to the first reference voltage, the driving unit turns off the power switch tube according to the second control signal, wherein the control method further comprises adjusting the first reference voltage according to the load state of the switching power supply.
Preferably, the step of obtaining a first reference voltage according to the target voltage signal includes: receiving the target voltage signal, and obtaining a voltage limiting protection threshold value according to the target voltage signal; and performing digital-to-analog conversion on the voltage limiting protection threshold value to generate the first reference voltage.
Preferably, the step of obtaining the voltage-limiting protection threshold according to the target voltage signal includes: and obtaining the voltage limiting protection threshold according to the maximum value of the target voltage signal, the amplitude of the voltage ripple and a preset first protection margin.
Preferably, the control method further includes: sampling an input voltage of the switching power supply to obtain a sampled voltage of the input voltage; sampling an input current of the switching power supply to obtain a sampled voltage of the input current; and generating the first control signal according to the sampling voltage of the input current, the target voltage signal, the sampling voltage of the input voltage and the sampling voltage of the output voltage.
Preferably, the step of generating the first control signal according to the sampled voltage of the input current, the target voltage signal, the sampled voltage of the input voltage, and the sampled voltage of the output voltage includes: generating a duty ratio signal according to the sampling voltage of the input current, the sampling voltage of the input voltage, the sampling voltage of the output voltage and the target voltage signal; and generating the first control signal and a PWM reset signal according to the duty signal, wherein the generating the duty signal according to the sampling voltage of the input current, the sampling voltage of the input voltage, the sampling voltage of the output voltage, and the target voltage signal includes: obtaining a first error according to the sampling voltage of the output voltage and the target voltage signal; obtaining an input current effective value according to the first error; obtaining an input voltage phase value according to the sampling voltage of the input voltage; obtaining a target current signal according to the input current effective value and the input voltage phase value; obtaining a second error according to the sampling voltage of the input current and the target current signal; and generating the duty cycle signal according to the second error.
Preferably, the step of outputting a second control signal according to the sampling voltage of the output voltage, the first reference voltage, and the first control signal includes: comparing the first reference voltage with the sampling voltage of the output voltage, and generating a first indication signal according to the comparison result; generating the second control signal according to the first indication signal, the first control signal and a PWM reset signal; when the sampling voltage of the output voltage is larger than or equal to the first reference voltage, judging that the output voltage is overvoltage, outputting the second control signal to turn off the power switch tube, and outputting the second control signal to turn on the power switch tube according to the PWM reset signal in the next control period.
Preferably, the step of generating the second control signal according to the first indication signal, the first control signal and a PWM reset signal includes: generating a first fault signal according to the PWM reset signal and the first indication signal; and generating the second control signal according to the first control signal and the first fault signal, wherein when the first indication signal is valid, the first fault signal is valid, when the PWM reset signal is valid and the first indication signal is invalid, the first fault signal is invalid, when the first fault signal is invalid, the state of the second control signal is consistent with the state of the first control signal, and when the first fault signal is valid, the second control signal is invalid.
Preferably, the control method further includes: and when the times that the sampling voltage of the output voltage is greater than or equal to the first reference voltage within the first preset time reaches a preset value and a fault clearing signal is not received, the power switch tube is turned off.
Preferably, the step of generating a second control signal according to the sampling voltage of the output voltage, a first reference voltage and the first control signal further comprises: counting the first indicating signal to obtain a counting value, generating an intermediate indicating signal according to the counting value, and enabling the intermediate indicating signal to be effective when the counting value is larger than or equal to a preset value within first preset time; latching the intermediate indication signal and generating a second indication signal according to the intermediate indication signal; generating a counting reset signal after the first preset time, resetting the counting value according to the counting reset signal, and restarting counting; starting timing when the intermediate indication signal is effective, generating a fault clearing signal after a second preset time, and generating a second indication signal according to the fault clearing signal and the intermediate indication signal; generating the second control signal according to the first indication signal, the second indication signal and the first control signal.
Preferably, the step of generating the second control signal according to the first indication signal, the second indication signal and the first control signal further comprises: and generating a second fault signal according to the PWM reset signal and the second indication signal, wherein the second fault signal is enabled when the second indication signal is enabled, the second fault signal is disabled when the PWM reset signal is enabled and the second indication signal is disabled, the state of the second control signal is consistent with the state of the first control signal when both the first fault signal and the second fault signal are disabled, and the second control signal is disabled when one of the first fault signal and the second fault signal is enabled.
Preferably, the control method further includes: and generating a first trigger signal when the sampling voltage of the output voltage is greater than or equal to a second reference voltage, turning off the power switch tube according to the first trigger signal, and controlling the first control signal to be in an invalid state, wherein the second reference voltage represents a first overvoltage protection threshold value, and the second reference voltage is greater than the first reference voltage.
Preferably, the control method further includes: and generating a second trigger signal when the sampling voltage of the output voltage is greater than or equal to a third reference voltage, and controlling the first control signal to be in an invalid state according to the first trigger signal, wherein the third reference voltage represents a second overvoltage protection threshold value, and the first reference voltage is greater than the third reference voltage.
Preferably, the control method further includes obtaining the second overvoltage protection threshold according to the target voltage signal.
Preferably, the step of obtaining the second overvoltage protection threshold according to the target voltage signal includes: and obtaining the second overvoltage protection threshold according to the maximum value of the target voltage signal, the amplitude of the voltage ripple and a preset second protection margin.
The switching power supply, the control circuit and the control method thereof have the following beneficial effects.
The switch power supply of the embodiment of the invention can modify the voltage-limiting protection threshold value in real time according to the load state information, can ensure that the output voltage of the switch power supply is always controlled within a certain range when the switch power supply works under different load conditions and meets the power grid fluctuation, prevents the output voltage from generating larger fluctuation, and protects devices such as a rear-end filter capacitor, a load and the like.
In a further embodiment, the switching power supply can adjust the overvoltage protection threshold of the software overvoltage protection in real time according to the load state information, so that the safety and the stability of the switching power supply are further improved when the switching power supply encounters power grid fluctuation under different load conditions.
In a further embodiment, the switching power supply of the embodiment of the invention provides two-stage hardware overvoltage protection, when the output voltage is overshot due to external interference, the output voltage can be ensured to be always below a set voltage-limiting protection threshold value, the overshoot amplitude of the output voltage is reduced, frequent overvoltage impact on a filter capacitor, a load and the like at the rear end is avoided to the greatest extent, and the stability of a system and the service life of devices are improved. And even though accidental false triggering occurs in the cycle-by-cycle mode, the power switch tube of the main circuit can be quickly opened in the next PWM control cycle, so that the output voltage is prevented from being too low, the normal work of a power supply system is not influenced, the frequent shutdown of the system due to overvoltage protection can be avoided under the condition that the power grid fluctuates frequently and violently, and the user experience of related products is improved.
In a further embodiment, when the output voltage exceeds the voltage limiting protection threshold value for multiple times within a certain time, the switching power supply enters a single protection mode, and the switching power supply can be restarted only by clearing the protection mode flag bit through software, that is, the switching power supply can be restarted only by receiving a fault clearing signal. Even under the condition of frequent overvoltage, the output voltage can be ensured to be always near the set voltage limiting protection threshold value for carrying out small-amplitude fluctuation, devices such as a filter capacitor and a load at the rear end are prevented from being impacted by overvoltage to the greatest extent, and the stability of the system and the service life of the devices are improved.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings.
FIG. 1 illustrates a waveform diagram of a conventional overvoltage protection;
fig. 2 shows a schematic configuration diagram of a switching power supply according to a first embodiment of the present invention;
FIG. 3 shows a schematic diagram of the control unit of FIG. 2;
fig. 4 is a schematic diagram showing a structure of the duty signal generating unit in fig. 3;
FIG. 5 is a schematic diagram of the voltage limiting threshold adjustment unit of FIG. 2;
FIG. 6 is a schematic diagram of the voltage limiting protection unit shown in FIG. 2;
fig. 7 illustrates a schematic structural diagram of the second indication signal generation unit in fig. 6;
FIG. 8 shows a schematic diagram of the structure of the fault management module of FIG. 6;
fig. 9 shows a schematic configuration diagram of a switching power supply according to a second embodiment of the present invention;
FIG. 10 is a schematic diagram showing the structure of the voltage limiting threshold adjusting unit in FIG. 9;
fig. 11 shows an operation timing diagram of the switching power supply according to the embodiment of the present invention;
fig. 12 shows a method flowchart of a control method of a switching power supply according to a third embodiment of the present invention;
fig. 13 is a detailed flowchart illustrating a control method according to a third embodiment of the present invention;
fig. 14 is a flowchart showing a cycle-by-cycle protection mode of the control method according to the third embodiment of the invention;
fig. 15 shows a flow chart of a single protection mode of the control method according to the third embodiment of the present invention.
Detailed Description
The invention will be described in more detail below with reference to the accompanying drawings. Like elements in the various figures are denoted by like reference numerals. For purposes of clarity, the various features in the drawings are not necessarily drawn to scale. Moreover, certain well-known elements may not be shown in the figures.
In the following description, numerous specific details of the invention, such as structure, materials, dimensions, processing techniques and techniques of components, are set forth in order to provide a more thorough understanding of the invention. However, as will be understood by those skilled in the art, the present invention may be practiced without these specific details.
It should be understood that in the following description, a "circuit" refers to a conductive loop formed by at least one element or sub-circuit through an electrical or electromagnetic connection. When an element or circuit is referred to as being "connected to" another element or element/circuit is referred to as being "connected between" two nodes, it may be directly coupled or connected to the other element or intervening elements may be present, and the connection between the elements may be physical, logical, or a combination thereof. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, it is intended that there are no intervening elements present.
Fig. 2 shows a schematic configuration diagram of a switching power supply according to a first embodiment of the present invention. The switching power supply of the embodiment adopts a Boost topology and works in a floating mode. Of course, the switching power supply of the embodiment of the invention can also be used in a Buck topology, a Boost-Buck topology and the like. As shown in fig. 2, the switching power supply includes a rectifier bridge 110, a main circuit 120, an output capacitor Cout, a load 130, and a control circuit 200. Wherein the input terminal of the main circuit 120 is connected to the output terminal of the rectifier bridge 110, and the output terminal is connected to the load 130. The main circuit 120 includes an inductor Lf, a power switch tube T1, a fast recovery diode VD, and a sampling resistor Rsen.
Further, the input end of the rectifier bridge 110 is connected to the AC power source AC, the rectifier bridge 110 is configured to convert an AC input signal into an input voltage Vin, the inductor Lf is connected in series with the power switch tube T1 and the sampling resistor Rsen between the positive output end and the negative output end of the rectifier bridge 110, the fast recovery diode VD mainly plays an isolation role, and prevents the output capacitor Cout from being shorted to ground when the power switch tube T1 is turned on, and the output capacitor Cout is connected in parallel with the load 130 and configured to stabilize the output voltage Vout. The control terminal of the power switch T1 is connected to the control circuit 200, and the control circuit 200 is used for controlling the power switch T1 to be turned on and off, so that the main circuit 120 obtains the output voltage Vout according to the input voltage Vin. During the on-time of the power switch T1, the AC power source AC charges the inductor Lf, and during the off-time of the power switch T1, the inductor Lf supplies power to the load 130. The control circuit 200 is further configured to perform real-time detection on the output voltage Vout and perform overvoltage protection on the power supply, and if the detected output voltage Vout is higher than the set voltage-limiting protection threshold and/or overvoltage protection threshold, turn off the power switch T1 in the main circuit 120 in time to prevent the output voltage Vout from being too high to cause failure of the power switch T1 and the backend device.
Further, the power switch Transistor T1 in the present embodiment is implemented by, for example, an IGBT (Insulated Gate Bipolar Transistor) and a MOSFET. The IGBT is a composite voltage-driven power semiconductor device composed of BJT (Bipolar Junction Transistor) and MOSFET, and has the advantages of both high input impedance of MOSFET and low on-state voltage drop of GTR (Transistor), and has low driving power and reduced saturation voltage.
Specifically, the control circuit 200 includes: a control unit 210, a voltage limiting threshold value adjusting unit 220, a voltage limiting protection unit 230, and a driving unit 260. The control unit 210 is configured to generate the first control signal PWM1 according to a sampled voltage Vin _ sa of the input voltage, a sampled voltage Vout _ sa of the output voltage, a sampled voltage Iin _ sa of the input current, and the target voltage signal of the main circuit 120. The voltage limiting threshold adjusting unit 220 obtains a first reference voltage Vref used for representing a voltage limiting protection threshold according to the target voltage signal. The voltage-limiting protection unit 230 obtains a second control signal PWM2 according to the sampled voltage Vout _ sa of the output voltage, the first reference voltage Vref, and the first control signal PWM 1. The driving unit 260 provides a driving signal Vgate to the control terminal of the power switch T1 according to the second control signal PWM2 to drive the power switch T1 in the main circuit 120, so that the main circuit 120 obtains an output voltage Vout according to the input voltage Vin.
Specifically, the voltage limiting protection unit 230 compares the sampling voltage Vout _ sa of the output voltage with the first reference voltage Vref, and generates the second control signal PWM2 according to the comparison result. In each PWM control period, when the comparison result indicates that the sampling voltage Vout _ sa of the output voltage is greater than or equal to the first reference voltage Vref, the voltage limiting protection unit 230 generates an invalid second control signal PWM2, and the driving unit 260 turns off the power switch T1 in the main circuit 120 according to the invalid second control signal PWM 2.
In this embodiment, the first control signal PWM1 is a square wave signal with a certain duty ratio, and the first control signal PWM1 is active at a high level and inactive at a low level.
Further, the switching power supply further includes an input current sampling unit 241, an input voltage sampling unit 242, an output voltage sampling unit 243, and a load state detection unit 244. The input current sampling unit 241, the input voltage sampling unit 242, and the output voltage sampling unit 243 detect the input current Iin, the input voltage Vin, and the output voltage Vout of the main circuit 120 to obtain a sampling voltage Iin _ sa of the input current, a sampling voltage Vin _ sa of the input voltage, and a sampling voltage Vout _ sa of the output voltage, respectively. The load state detection unit 244 is configured to detect a load state of the main circuit 120 (for example, obtain load state information by detecting a load current or a load power, etc.) to obtain a target voltage signal. As a non-limiting example, the load state detection unit 244 is, for example, a PI controller, whose inputs are a target load state and a load state detected in real time, respectively, and whose output is a target voltage signal. The load state detection unit 244 obtains the target voltage signal through feedback adjustment according to the load state detected in real time. The control unit 210 calculates the first control signal PWM1 according to the sampled voltage Iin _ sa, the sampled voltage Vin _ sa, the sampled voltage Vout _ sa, and the target voltage signal.
Further, the control circuit 200 further includes a hardware overvoltage protection unit 270, where the hardware overvoltage protection unit 270 compares the sampling voltage Vout _ sa of the output voltage with an internal second reference voltage representing a first overvoltage protection threshold, when the sampling voltage Vout _ sa of the output voltage is greater than or equal to the internal second reference voltage, the hardware overvoltage protection unit 270 generates an effective first trigger signal, the driving unit 260 turns off the power switch T1 in the main circuit 120 according to the effective first trigger signal, and the control unit 210 outputs an ineffective first control signal PWM1 according to the effective first trigger signal. As an example, the hardware overvoltage protection unit 270 compares the sampled voltage Vout _ sa of the output voltage with the fixed internal second reference voltage using a standard comparator.
Further, the switching power supply further includes a software overvoltage protection unit 280, where the software overvoltage protection unit 280 is configured to compare the sampled voltage Vout _ sa of the output voltage with an internal third reference voltage representing a second overvoltage protection threshold, and when the sampled voltage Vout _ sa of the output voltage is greater than or equal to the internal third reference voltage, the software overvoltage protection unit 280 generates a valid second trigger signal, and the control unit 210 outputs an invalid first control signal PWM1 according to the valid second trigger signal. For example, the software overvoltage protection unit 280 converts the sampling voltage Vout _ sa into a digital value by using an AD converter, and generates the second trigger signal through software filtering and comparing operation.
Similarly, the first over-voltage protection threshold in this embodiment is greater than the voltage limiting protection threshold, and the voltage limiting protection threshold is greater than the second over-voltage protection threshold, and the corresponding internal second reference voltage is greater than the first reference voltage, and the first reference voltage is greater than the internal third reference voltage.
Fig. 3 shows a schematic diagram of the control unit in fig. 2. As shown in fig. 3, the control unit 210 includes a duty signal generation unit 211 and a PWM generation unit 212. The duty signal generating unit 211 is configured to generate a duty signal according to the received sampling voltage Iin _ sa of the input current, the sampling voltage Vin _ sa of the input voltage, the sampling voltage Vout _ sa of the output voltage, and the target voltage signal. The PWM generating unit 212 is configured to generate the first control signal PWM1 according to the duty ratio signal and the first trigger signal and the second trigger signal. The PWM generating unit 212 outputs the first control signal PWM1 that is active when all of the first and second trigger signals are inactive, and outputs the first control signal PWM1 that is inactive when one of the first and second trigger signals is active. In addition, the PWM generating unit 212 also outputs a PWM reset signal to the voltage limiting protection unit 230 at the beginning of each PWM control period.
In this embodiment, the first trigger signal and the second trigger signal are active at a high level and inactive at a low level.
Fig. 4 shows a schematic structural diagram of the duty ratio signal generating unit in fig. 3. As shown in fig. 4, the duty signal generation unit 211 includes, as a non-limiting example, an addition module 2111, a linear control module 2112, a multiplication module 2113, a phase calculation module 2114, an addition module 2115, and a linear control module 2116. The adding module 2111 is configured to calculate a first error according to the sampled voltage Vout _ sa of the output voltage and the target voltage signal, the linear control module 2112 obtains an effective value of the input current according to the first error, the phase calculation module 2114 obtains a phase value of the sampled voltage Vin _ sa of the input voltage according to the sampled voltage Vin _ sa of the input voltage, the multiplication module 2113 obtains a target current signal according to the effective value of the input current and the phase value of the sampled voltage Vin _ sa of the input voltage, the adding module 2115 calculates a second error between the sampled voltage Iin _ sa of the input current and the target current signal, and the linear control module 2116 generates a duty ratio signal according to the second error. The linear control module 2112 and the linear control module 2116 are, for example, PI controllers (Proportional Integral controllers), and the first error and the second error are close to 0 in a steady state by setting a Proportional coefficient, an Integral coefficient, a maximum-minimum limiter, and the like in the linear control module 2112 and the linear control module 2116. The operating principle of the PI controller is common knowledge of those skilled in the art, and is not described herein again.
Fig. 5 is a schematic diagram showing a structure of the voltage limiting threshold adjusting unit in fig. 2. As shown in fig. 5, the voltage limiting threshold adjusting unit 220 includes a software adjusting module 221 and a digital-to-analog converting module 222.
The software adjusting module 221 receives the target voltage signal, and obtains a voltage limiting protection threshold value through software calculation according to the target voltage signal. Specifically, the software adjusting module 221 adds a preset protection margin on the basis of the summation of the maximum value of the target voltage signal and the voltage ripple amplitude, and finally obtains the voltage limiting protection threshold, thereby implementing flexible adjustment of the voltage limiting protection threshold.
The digital-to-analog conversion module 222 receives the voltage-limiting protection threshold, and performs digital-to-analog conversion on the voltage-limiting protection threshold to generate a first reference voltage Vref, thereby implementing flexible adjustment on the voltage-limiting protection threshold.
Fig. 6 is a schematic structural diagram of the voltage limiting protection unit in fig. 2. As shown in fig. 6, the voltage limiting protection unit 230 includes a comparison module 231, a second indication signal generation unit 232, and a fault management module 233. The comparison module 231 compares the first reference voltage Vref with the sampled voltage Vout _ sa of the output voltage, and when the sampled voltage Vout _ sa of the output voltage is greater than or equal to the first reference voltage Vref, the comparison module 231 generates a valid first indication signal. The second indication signal generating unit 232 is configured to generate an effective second indication signal when the count value of the first indication signal is greater than or equal to the preset value within the first preset time. The fault management module 233 determines the state of the second control signal PWM2 according to the first indication signal, the second indication signal, and the first control signal PWM 1. The power switch tube voltage limiting protection method can ensure that when the output voltage is increased due to abnormal disturbance, the output voltage is not higher than a set voltage limiting protection threshold all the time, and can quickly recover the normal work of the power switch tube, thereby avoiding the situation that the output voltage is too low due to long-time turn-off of the power switch tube.
The fault management module 233 is responsible for output management of the second control signal PWM2, and if the fault management module 233 receives the valid first indication signal and the valid second indication signal, the fault management module 233 outputs the invalid second control signal PWM2, and at this time, the second control signal PWM2 is maintained in a low level state; if the fault management module 233 does not receive valid first and second indication signals, the output second control signal PWM2 and first control signal PWM1 are in a consistent state.
Fig. 7 illustrates a schematic configuration diagram of the second indication signal generation unit in fig. 6. As shown in fig. 7, the second indication signal generating unit 232 includes a counting module 2321, a first timer 2322, a latching module 2323, and a second timer 2324. The counting module 2321 is configured to count the valid first indication signals. When the count value of the first indication signal which is valid in the first preset time is greater than or equal to the preset value, the counting module 2321 generates a valid intermediate indication signal; otherwise, an invalid intermediate indication signal is generated. The latch module 2323 is configured to latch the valid intermediate indication signal and generate a valid second indication signal according to the valid intermediate indication signal. The first timer 2322 is configured to repeatedly count time and generate an effective counting reset signal when a first preset time is reached, and the counting module 2321 resets the counting value of the first indication signal according to the effective counting reset signal and restarts counting. The second timer 2324 starts timing when receiving a valid intermediate indication signal and generates a valid fault clearing signal after a second preset time, the latch module 2323 generates an invalid second indication signal according to the valid fault clearing signal, and the second timer 2324 stops working and starts working when receiving the next valid intermediate indication signal.
In this embodiment, the first indicator signal, the intermediate indicator signal, and the second indicator signal are active low and inactive high, and the count reset signal and the fault clear signal are active high and inactive low.
Fig. 8 shows a schematic diagram of the structure of the fault management module in fig. 6. In the present embodiment, the fault management module 233 has two modes of cycle-by-cycle protection and single-time protection. Specifically, as shown in fig. 8, the fault management module 233 includes a first latch 2331, a second latch 2332, and an and gate 2333. The first latch 2331 includes a first set terminal for receiving the first indication signal, a first reset terminal for receiving the PWM reset signal, and a first output terminal. The second latch 2332 includes a second set terminal for receiving the second indication signal, a second reset terminal for receiving the PWM reset signal, and a second output terminal. And gate 2333 includes first to third input terminals for receiving first control signal PWM1, a second input terminal connected to a first output terminal of first latch 2331, a third input terminal connected to a second output terminal of second latch 2332, and a third output terminal connected to an input terminal of driving unit 260. The and gate 2333 is used to generate a second control signal PWM2 according to the output signals of the first and second latches 2331 and 2332 and the first control signal PWM 1.
For example, the first latch 2331 generates a valid first fail signal upon receiving a valid first indication signal and sets the cycle-by-cycle protected mode flag bit, and gate 2333 generates an invalid second control signal PWM2 based on the valid first fail signal. When first latch 2331 receives the active PWM reset signal and the inactive first indication signal, it generates an inactive first fail signal and simultaneously resets the cycle-by-cycle protection mode flag bit, and gate 2333 generates second control signal PWM2 in accordance with the state of PWM1 (assuming that the second fail signal output from second latch 2332 is in an inactive state at this time), and second control signal PWM2 is identical to first control signal PWM1 at this time. In the cycle-by-cycle protection, when the output voltage exceeds the voltage-limiting protection threshold, software intervention is not required in each PWM control cycle, the power switch tube T1 in the main circuit can be turned off or turned on only by the cycle-by-cycle protection inside the fault management module 233, so as to prevent the output voltage from overshooting and damaging the power switch tube T1 and subsequent devices, and the power switch tube T1 in the main circuit can also be turned on quickly, so as to prevent the output voltage from being too low.
For another example, when receiving the second indication signal being active, second latch 2332 generates a second fail signal that is active, sets the one-shot protection mode flag bit, and gate 2333 generates a second control signal PWM2 that is inactive based on the second fail signal being active, and second control signal PWM2 is always at a low level. The second latch 2332 is further configured to generate an inactive second fail signal when receiving an active PWM reset signal and an inactive second indication signal, and gate 2333 outputs the second control signal PWM2 and the first control signal PWM1 in accordance with the inactive second fail signal (assuming that the first fail signal output from the first latch 2331 is in an inactive state). In the single protection mode, the flag bit of the single protection mode needs to be cleared by software to recover the output of the control signal, namely, compared with the cycle-by-cycle protection, once the single protection is effective, the flag bit of the single protection mode can be reset only when an effective fault clearing signal is detected, and the switching power supply recovers the normal working state.
Fig. 9 shows a schematic configuration diagram of a switching power supply according to a second embodiment of the present invention. As shown in fig. 9, a switching power supply of a second embodiment of the present invention is substantially the same as the switching power supply of the first embodiment described above, except that: the voltage-limiting threshold adjusting unit 320 in the switching power supply of this embodiment is further configured to obtain a second overvoltage protection threshold of the software overvoltage protection unit 380 according to the target voltage signal provided by the load state detecting unit 344.
Further, fig. 10 shows a schematic structural diagram of the voltage limiting threshold adjusting unit in fig. 9. As shown in fig. 10, the voltage limiting threshold adjusting unit 320 includes a software adjusting module 321 and a digital-to-analog converting module 322, where the software adjusting module 321 receives the target voltage signal and obtains a voltage limiting protection threshold and a second overvoltage protection threshold through software calculation according to the target voltage signal. Specifically, the software adjusting module 321 adds a preset protection margin to the sum of the maximum value of the target voltage signal and the voltage ripple amplitude to obtain a second overvoltage protection threshold, and then adds another protection margin to the second overvoltage protection threshold to finally obtain a voltage limiting protection threshold.
The digital-to-analog conversion module 322 receives the voltage-limiting protection threshold, and performs digital-to-analog conversion on the voltage-limiting protection threshold to generate a first reference voltage Vref, thereby implementing flexible adjustment on the voltage-limiting protection threshold and a second overvoltage protection threshold.
Besides, the structures and operating principles of the control unit 310, the voltage limiting threshold adjusting unit 320, the voltage limiting protection unit 330, the driving unit 360, the hardware overvoltage protection unit 370, the software overvoltage protection unit 380, the input current sampling unit 341, the input voltage sampling unit 342, the output voltage sampling unit 343, and the load state detecting unit 344 in the switching power supply of the second embodiment are the same as those in the switching power supply of the first embodiment, and are not described herein again.
Fig. 11 is a timing diagram illustrating the operation of the switching power supply according to the embodiment of the present invention. In the timing diagram of fig. 11, the switching power supply operates in a plurality of successive PWM control periods, and each PWM control period is the period from one active PWM reset signal to the next active PWM reset signal. For example, the first PWM control cycle is a time period between times t0-t 2. In fig. 11, the first control signal PWM1 is a square wave signal with a certain duty ratio, and both the second control signal PWM2 and the first control signal PWM1 are active at a high level and inactive at a low level. The fault clearing signal and the PWM reset signal are active at a high level and inactive at a low level. The first indication signal and the second indication signal are both active at low level and inactive at high level.
As described above, the control circuit of the switching power supply of the embodiment of the present invention includes the cycle-by-cycle protection mode and the single-shot protection mode. In the cycle-by-cycle protection mode, when the sampled voltage Vout-sa of the output voltage exceeds the first reference voltage Vref, the power switch tube T1 in the main circuit 120 can be turned off or turned on only by the fault management module without software intervention in each PWM control cycle, so as to prevent the output voltage from overshooting and damaging the power switch tube T1 and subsequent devices, and the power switch tube T1 in the main circuit 120 can also be turned on quickly, so as to prevent the output voltage from being too low. In the single protection mode, when the times that the output voltage exceeds the voltage limiting protection threshold value in a plurality of PWM control periods reach a preset value, the single protection mode is started, and compared with the period-by-period protection mode, once the single protection mode takes effect, the flag bit of the single protection mode can be reset only when an effective fault clearing signal is detected, and the switching power supply recovers the normal working state.
At time t0, the PWM reset signal is in an active state, the first indication signal and the second indication signal are inactive, the second control signal output by the fault management module is active, and the sampled voltage Vout-sa of the output voltage gradually increases.
At time T1, the sampling voltage Vout-sa of the output voltage is greater than or equal to the first reference voltage Vref, the output of the comparison module is inverted, the first indication signal is inverted to an active state, the fault management module generates an invalid second control signal, the power switch T1 in the main circuit 120 is turned off, and the sampling voltage Vout-sa of the output voltage is gradually reduced.
At time t2, the PWM reset signal is again inverted to an active state, and at this time, the first indication signal and the second indication signal are in an inactive state, so that the second control signal output by the fault management module is active, and the sampling voltage Vout-sa of the output voltage gradually increases. The working processes of the time t0-t1 and the time t1-t2 are repeated at the later time t2-t3, time t4-t5, time t3-t4 and time t5-t6 respectively, and are not described again.
At time T6, the PWM reset signal is turned to the active state again, when the number of times that the first indication signal is active reaches the preset value, the second indication signal is turned from the inactive state to the active state, the fault management module generates an inactive second control signal, the power switch T1 in the main circuit 120 is turned off, and the sampling voltage Vout-sa of the output voltage is gradually reduced.
At time T7, the PWM reset signal is again toggled to the active state, and the second indication signal is still active, so the fault management module generates an inactive second control signal and the power switch T1 in the main circuit 120 is still in the off state.
At time t8, the fault clear signal is inverted to the active state, and the latch module in the second indication signal generation unit inverts the second indication signal from the active state to the inactive state according to the active fault clear signal.
At time t9, the PWM reset signal is again inverted to an active state, and at this time, the first indication signal and the second indication signal are in an inactive state, so that the second control signal output by the fault management module is active, and the sampling voltage Vout-sa of the output voltage gradually increases.
At time T10, the sampling voltage Vout-sa of the output voltage is greater than or equal to the first reference voltage Vref, the output of the comparison module is inverted, the first indication signal is inverted to an active state, the fault management module generates an invalid second control signal, the power switch T1 in the main circuit 120 is turned off, and the sampling voltage Vout-sa of the output voltage is gradually reduced.
Fig. 12 shows a method flowchart of a control method of a switching power supply according to a third embodiment of the present invention. The switching power supply of this embodiment may be the switching power supply of the above embodiment, and includes a rectifier bridge 110, a main circuit 120, an output capacitor Cout, a load 130, and a control circuit. The input terminal of the main circuit 120 is connected to the rectifier bridge 110, and the output terminal is connected to the load 130. The main circuit 120 includes an inductor Lf, a power switch tube T1, a fast recovery diode VD, and a sampling resistor Rsen. The control circuit is not only used for controlling the on and off of the power switch tube, but also used for detecting the output voltage of the main circuit in real time and performing output voltage overvoltage protection on the circuit, and if the detected output voltage is higher than a set voltage limiting protection threshold value or an overvoltage protection threshold value, the power switch tube T1 in the main circuit 120 is turned off in time to prevent the failure of the power switch tube T1 and rear-end devices caused by overhigh output voltage. As shown in fig. 12, the control method includes the following steps S110 to S150.
In step S110, the output voltage is sampled to obtain a sampled voltage of the output voltage.
In step S120, a first control signal is generated.
In a further embodiment, the control method further comprises generating the first control signal from a sampled voltage of the input current, the target voltage signal, a sampled voltage of the input voltage, and a sampled voltage of the output voltage.
In step S130, a first reference voltage is obtained according to the target voltage signal. For example, the voltage-limiting protection threshold may be obtained according to a maximum value of the target voltage signal, an amplitude of a voltage ripple, and a preset protection margin, and digital-to-analog conversion may be performed on the voltage-limiting protection threshold to obtain the first reference voltage.
In a further embodiment, the control method further includes adjusting the first reference voltage according to a load state of the switching power supply, for example, a target voltage signal may be obtained according to load state information such as a load current or a load power of the main circuit 120, and then the first reference voltages in different load states are obtained.
In a further embodiment, the control method further comprises the step of adjusting the second overvoltage protection threshold of the software overcurrent protection in real time according to the load state, so that the safety and the stability of the switching power supply when the switching power supply encounters power grid fluctuation under different load conditions are further improved.
In step S140, a second control signal is obtained according to the sampling voltage of the output voltage, the first reference voltage and the first control signal.
In step S150, a driving signal for controlling the power switch tube is generated according to the second control signal.
Further, the control method further comprises generating an invalid second control signal when the sampling voltage of the output voltage is greater than or equal to the first reference voltage in each PWM control period, and turning off the power switch tube according to the invalid second control signal, and outputting an valid second control signal according to a PWM reset signal to turn on the power switch tube when a next PWM control period adjacent to the PWM control period starts.
Further, the control method further comprises the step of turning off the power switch tube when the number of times that the sampling voltage of the output voltage is greater than or equal to the first reference voltage within a first preset time reaches a preset value and a fault clearing signal is not received.
Fig. 13 is a detailed flowchart illustrating a control method according to a third embodiment of the present invention. Specifically, the control method of the present embodiment further includes steps S210 to S260.
In step S210, it is determined whether the sampled voltage of the output voltage is equal to or greater than a first reference voltage. If the sampling voltage of the output voltage is greater than or equal to the first reference voltage, continuing to step S220; if the sampling voltage of the output voltage is less than the first reference voltage, the step S230 is continued.
In step S220, an effective first indication signal is output, the counting module counts the effective first indication signal, and the count value of the counting module is incremented by 1. In this embodiment, when the sampling voltage of the output voltage is greater than or equal to the first reference voltage, the comparison module generates an effective first indication signal. The fault management module generates an invalid second control signal based on the valid first indication signal. And the counting module counts the pulses of the first indicating signal to obtain a count value.
In step S230, it is determined whether a first preset time is reached. If the first preset time is reached, continuing to step S240; if the first preset time is not reached, the control flow is exited, and the process is restarted, and the determination logic of step S210 is continuously executed.
In step S240, it is determined whether the count value of the first indication signal is greater than or equal to a preset value. If the count value of the first indication signal is greater than or equal to the preset value, continuing to step S250; if the count value of the first indication signal is smaller than the preset value, the step S260 is continued.
In step S250, a valid second indication signal is generated. In this embodiment, the counting module counts the first indication signal within a first preset time, and when a count value of the first indication signal within the first preset time is greater than or equal to a preset value, the counting module generates a valid second indication signal. And the fault management module generates an invalid second control signal according to the valid second indication signal, and the switching power supply enters a single-time protection mode.
In step S260, the count value of the first instruction signal is cleared. In this embodiment, after each first preset time, the count value of the first indication signal is cleared and the count is restarted, and then the control flow exits and is restarted, and the determination logic of step S210 is continuously executed.
Fig. 14 and 15 show schematic flowcharts of the cycle-by-cycle protection mode and the single-shot protection mode of the control method according to the third embodiment of the present invention, respectively.
As shown in fig. 14, the cycle-by-cycle protection mode of the control method includes steps S310 to S380.
In step S310, a first control signal is received.
In step S320, it is determined whether a valid PWM reset signal is received. If a valid PWM reset signal is received, continue to step S330; if the valid PWM reset signal is not received, step S340 is continued.
In step S330, the first fault signal is cleared.
In step S340, it is determined whether a valid first indication signal is received. If the valid first indication signal is received, continuing to step S350; if the valid first indication signal is not received, the step S360 is continued.
In step S350, a valid first fault signal is generated. In this embodiment, the fault management module further comprises a first latch that generates a first fault signal upon receiving a valid first indication signal.
In step S360, it is determined whether a valid first fault signal is received. If a valid first fault signal is received, continue to step S370; if a valid first failure signal is not received, step S380 is continued.
In step S370, the inactive second control signal PWM2 is output. In this embodiment, the fault management module further comprises an and gate that generates an inactive second control signal PWM2 when receiving an active first fault signal.
In step S380, the output second control signal is consistent with the state of the first control signal.
In this embodiment, the first latch clears the first fault signal when receiving the valid PWM reset signal and simultaneously receiving the invalid first indication signal, and the state of the second control signal output by the and gate is consistent with the state of the first control signal.
In the cycle-by-cycle protection mode, when the output voltage exceeds the voltage-limiting protection threshold, software intervention is not needed in each PWM control cycle, the power switch tube in the main circuit can be turned off only through the cycle-by-cycle protection in the fault management module, the power switch tube and subsequent devices are prevented from being damaged by output voltage overshoot, the power switch tube in the main circuit can be quickly turned on in the next PWM control cycle, and the output voltage is prevented from being too low.
As shown in fig. 15, the single protection mode of the control method includes steps S410 to S480.
In step S410, a first control signal is received.
In step S420, it is determined whether a valid PWM reset signal is received. If a valid PWM reset signal is received, continue to step S430; if the valid PWM reset signal is not received, the process continues to step S440.
In step S430, the second fault signal is cleared.
In step S440, it is determined whether a valid second indication signal is received. If a valid second indication signal is received, continuing to step S450; if a valid second indication signal is not received, the process continues to step S460.
In step S450, a valid second fault signal is generated. In this embodiment, the fault management module further comprises a second latch that generates a second fault signal when a valid second indication signal is received.
In step S460, it is determined whether a valid second failure signal is received. If a valid second failure signal is received, continue to step S470; if a valid second failure signal is not received, step S480 continues.
In step S470, the invalid second control signal is output. In this embodiment, the fault management module further comprises an and gate that generates an inactive second control signal PWM2 when receiving an active second fault signal.
In step S480, the output second control signal coincides with the state of the first control signal. In this embodiment, the second latch clears the second fault signal when receiving the valid PWM reset signal and simultaneously receiving the invalid second indication signal, and the state of the second control signal output by the and gate is consistent with the state of the first control signal.
In the single-protection mode, when the output voltage exceeds the voltage-limiting protection threshold value for a plurality of times within a certain time (including a plurality of PWM control periods), the switching power supply enters the single-protection mode, and the switching power supply is required to be restarted until a fault clearing signal is received. Even under the condition of frequent overvoltage of the output voltage, the output voltage can be ensured to be always close to the set voltage limiting protection threshold value for carrying out small-amplitude fluctuation, devices such as a filter capacitor, a load and the like at the rear end are prevented from being impacted by overvoltage to the greatest extent, and the stability of the system and the service life of the devices are improved.
In summary, the switching power supply according to the embodiment of the invention can modify the voltage-limiting protection threshold in real time according to the load state information, so as to ensure that the output voltage of the main circuit is always controlled within a certain range when the switching power supply works under different load conditions and meets the power grid fluctuation, prevent the output voltage from generating large fluctuation, and protect devices such as a back-end filter capacitor and a load.
In a further embodiment, the switching power supply can adjust the overvoltage protection threshold of the software overvoltage protection in real time according to the load state, so that the safety and the stability of the switching power supply are further improved when the switching power supply encounters power grid fluctuation under different load conditions.
In a further embodiment, the switching power supply of the embodiment of the invention provides two-stage hardware overvoltage protection, when the output voltage triggers overshoot due to some external interference, the output voltage can be ensured to be always below a set voltage-limiting protection threshold value, the voltage overshoot amplitude is reduced, frequent overvoltage impact on a filter capacitor, a load and the like at the rear end is avoided to the greatest extent, and the stability of a system and the service life of devices are improved. And even though accidental false triggering occurs in the cycle-by-cycle mode, the power switch tube of the main circuit can be quickly opened in the next PWM control cycle, so that the output voltage is prevented from being too low, the normal work of a power supply system is not influenced, the frequent shutdown of the system due to overvoltage protection can be avoided under the condition that the power grid fluctuates frequently and violently, and the user experience of related products is improved.
In a further embodiment, when the output voltage exceeds the voltage limiting protection threshold value for multiple times within a certain time, the switching power supply enters a single protection mode, and the switching power supply can be restarted only by clearing the protection mode flag bit through software, that is, the switching power supply can be restarted only by receiving a fault clearing signal. Even under the condition of frequent overvoltage, the output voltage can be ensured to be always near the set voltage limiting protection threshold value for carrying out small-amplitude fluctuation, devices such as a filter capacitor and a load at the rear end are prevented from being impacted by overvoltage to the greatest extent, and the stability of the system and the service life of the devices are improved.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
While embodiments in accordance with the invention have been described above, these embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments described. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The invention is limited only by the claims and their full scope and equivalents.

Claims (31)

1. A control circuit for a switching power supply, the control circuit comprising:
an output voltage sampling unit which samples the output voltage to obtain a sampling voltage of the output voltage;
a load state detection unit which obtains a target voltage signal by detecting a load state of the switching power supply, the target voltage signal varying according to a variation of the load state;
a control unit generating a first control signal;
the voltage limiting threshold adjusting unit is used for obtaining a first reference voltage representing a voltage limiting protection threshold according to the target voltage signal;
the voltage limiting protection unit is connected with the control unit and outputs a second control signal according to the sampling voltage of the output voltage, the first reference voltage and the first control signal; and
the driving unit is connected with the voltage limiting protection unit so as to output a driving signal for controlling the power switch tube according to the second control signal, and when the sampling voltage of the output voltage is greater than or equal to the first reference voltage, the driving unit turns off the power switch tube according to the second control signal,
the voltage limiting threshold value adjusting unit also adjusts the voltage limiting protection threshold value in real time according to the load state of the switching power supply, so that the output voltage is always kept below the voltage limiting protection threshold value.
2. The control circuit according to claim 1, wherein the voltage limiting threshold adjusting unit comprises:
the software adjusting module receives the target voltage signal and obtains a voltage limiting protection threshold value according to the target voltage signal; and
and the digital-to-analog conversion module is used for receiving the voltage limiting protection threshold value and performing digital-to-analog conversion on the voltage limiting protection threshold value to generate the first reference voltage.
3. The control circuit of claim 2, wherein the software adjusting module obtains the voltage-limiting protection threshold according to a maximum value of the target voltage signal, an amplitude of a voltage ripple, and a preset first protection margin.
4. The control circuit of claim 1, further comprising:
an input voltage sampling unit which samples an input voltage of the switching power supply to obtain a sampling voltage of the input voltage;
an input current sampling unit sampling an input current of the switching power supply to obtain a sampling voltage of the input current,
wherein the control unit generates the first control signal according to a sampling voltage of the input current, a target voltage signal, a sampling voltage of the input voltage, and a sampling voltage of the output voltage.
5. The control circuit of claim 4, wherein the control unit comprises:
a duty signal generation unit that generates a duty signal from the sampling voltage of the input current, the sampling voltage of the input voltage, the sampling voltage of the output voltage, and the target voltage; and
a PWM generating unit generating the first control signal and a PWM reset signal according to the duty ratio signal,
wherein the duty signal generating unit includes:
the first adding module is used for obtaining a first error according to the sampling voltage of the output voltage and the target voltage signal;
the first linear control module is used for obtaining an input current effective value according to the first error;
the phase calculation module is used for obtaining an input voltage phase value according to the sampling voltage of the input voltage;
the multiplication module is used for obtaining a target current signal according to the input current effective value and the input voltage phase value;
the second addition module is used for obtaining a second error according to the sampling voltage of the input current and the target current signal; and
and the second linear control module generates the duty ratio signal according to the second error.
6. The control circuit of claim 5, wherein the first linear control module and the second linear control module each comprise a PI controller.
7. The control circuit of claim 1, wherein the voltage limiting protection unit comprises:
the comparison module compares the first reference voltage with the sampling voltage of the output voltage and generates a first indication signal according to a comparison result;
the fault management module is connected with the comparison module and generates the second control signal according to the first indication signal, the first control signal and the PWM reset signal;
when the sampling voltage of the output voltage is larger than or equal to the first reference voltage, judging that the output voltage is overvoltage, outputting the second control signal by the fault management module to turn off the power switch tube, and outputting the second control signal by the fault management module according to the PWM reset signal to turn on the power switch tube in the next control period.
8. The control circuit of claim 7, wherein the fault management module comprises:
a first latch generating a first fail signal according to the PWM reset signal and the first indication signal;
an AND gate that generates the second control signal based on the first control signal and the first fault signal,
wherein the first fault signal is active when the first indication signal is active, the first fault signal is inactive when the PWM reset signal is active and the first indication signal is inactive,
when the first fault signal is invalid, the state of the second control signal is consistent with the state of the first control signal, and when the first fault signal is valid, the second control signal is invalid.
9. The control circuit of claim 8, wherein the voltage limiting protection unit is further configured to control the driving unit to turn off the power switch tube when the number of times that the sampling voltage of the output voltage is greater than or equal to the first reference voltage within a first preset time reaches a preset value and a fault clearing signal is not received.
10. The control circuit of claim 9, wherein the voltage limiting protection unit further comprises:
a second indication signal generating unit, counting the first indication signal to obtain a count value, generating a second indication signal according to the count value, when the count value is greater than or equal to a preset value within a first preset time, the second indication signal is valid,
wherein the second indication signal generation unit includes:
the counting module is used for counting the first indicating signal to obtain a counting value, generating an intermediate indicating signal according to the counting value, and enabling the intermediate indicating signal to be effective when the counting value is larger than or equal to a preset value within first preset time;
the latch module is connected with the counting module and used for latching the intermediate indication signal and generating a second indication signal according to the intermediate indication signal;
the first timer is used for repeatedly timing, generating a counting reset signal after the first preset time, resetting the counting value according to the counting reset signal by the counting module and restarting counting; and
the second timer starts timing when the intermediate indication signal is effective, generates a fault clearing signal after a second preset time, and the latch module generates a second indication signal according to the fault clearing signal and the intermediate indication signal.
11. The control circuit of claim 10, wherein the fault management module further comprises:
a second latch to generate a second fail signal according to the PWM reset signal and the second indication signal,
wherein the second fail signal is active when a second indication signal is active, and the second fail signal is inactive when the PWM reset signal is active and the second indication signal is inactive,
when both the first fault signal and the second fault signal are invalid, the state of the second control signal is consistent with the state of the first control signal, and when one of the first fault signal and the second fault signal is valid, the second control signal is invalid.
12. The control circuit according to claim 1, further comprising a hardware overvoltage protection unit receiving a sampled voltage of the output voltage, wherein the hardware overvoltage protection unit generates a first trigger signal when the sampled voltage of the output voltage is greater than or equal to a second reference voltage, the driving unit turns off the power switch tube according to the first trigger signal, and the control unit controls the first control signal to be in an inactive state according to the first trigger signal,
wherein the second reference voltage characterizes a first over-voltage protection threshold, the second reference voltage being greater than the first reference voltage.
13. The control circuit of claim 1, further comprising a software over-voltage protection unit receiving the sampled voltage of the output voltage, wherein the software over-voltage protection unit generates a second trigger signal when the sampled voltage of the output voltage is greater than or equal to a third reference voltage, and the control unit controls the first control signal to be in an invalid state according to the second trigger signal,
wherein the third reference voltage characterizes a second over-voltage protection threshold, and the first reference voltage is greater than the third reference voltage.
14. The control circuit of claim 13, wherein the threshold adjustment unit is further configured to obtain the second over-voltage protection threshold according to the target voltage signal.
15. The control circuit of claim 14, wherein the threshold adjustment unit comprises:
and the software adjusting module is used for receiving the target voltage signal and obtaining the second overvoltage protection threshold according to the maximum value of the target voltage signal, the amplitude of the voltage ripple and a preset second protection margin.
16. A switching power supply comprising a control circuit as claimed in any one of claims 1 to 15.
17. The switching power supply according to claim 16, further comprising:
a rectifier bridge rectifying an alternating input voltage to obtain an input voltage;
the inductor, the power switch tube and the sampling resistor are connected in series at two ends of the rectifier bridge;
the anode of the diode is connected with the power switch tube and the middle node of the inductor;
and the output capacitor is connected between the sampling resistor and the intermediate node of the power switch tube and the cathode of the diode and is used for stabilizing the output voltage.
18. A control method of a switching power supply, characterized by comprising:
sampling the output voltage to obtain a sampled voltage of the output voltage;
detecting a load state of the switching power supply to obtain a target voltage signal, wherein the target voltage signal changes according to the change of the load state;
generating a first control signal;
obtaining a first reference voltage representing a voltage limiting protection threshold according to the target voltage signal;
outputting a second control signal according to the sampling voltage of the output voltage, the first reference voltage and the first control signal; and
outputting a driving signal for controlling a power switch tube according to the second control signal, and turning off the power switch tube according to the second control signal when the sampling voltage of the output voltage is greater than or equal to the first reference voltage,
the control method further comprises the step of adjusting the voltage limiting protection threshold in real time according to the load state of the switching power supply, so that the output voltage is always kept below the voltage limiting protection threshold.
19. The control method of claim 18, wherein the step of deriving the first reference voltage from the target voltage signal comprises:
receiving the target voltage signal, and obtaining a voltage limiting protection threshold value according to the target voltage signal; and
and performing digital-to-analog conversion on the voltage-limiting protection threshold value to generate the first reference voltage.
20. The control method of claim 19, wherein the step of deriving a voltage limiting protection threshold from the target voltage signal comprises:
and obtaining the voltage limiting protection threshold according to the maximum value of the target voltage signal, the amplitude of the voltage ripple and a preset first protection margin.
21. The control method according to claim 18, characterized by further comprising:
sampling an input voltage of the switching power supply to obtain a sampled voltage of the input voltage;
sampling an input current of the switching power supply to obtain a sampled voltage of the input current; and
and generating the first control signal according to the sampling voltage of the input current, the target voltage signal, the sampling voltage of the input voltage and the sampling voltage of the output voltage.
22. The control method of claim 21, wherein the step of generating the first control signal based on the sampled voltage of the input current, the target voltage signal, the sampled voltage of the input voltage, and the sampled voltage of the output voltage comprises:
generating a duty ratio signal according to the sampling voltage of the input current, the sampling voltage of the input voltage, the sampling voltage of the output voltage and the target voltage signal; and
generating the first control signal and a PWM reset signal according to the duty ratio signal,
wherein the step of generating a duty cycle signal from the sampled voltage of the input current, the sampled voltage of the input voltage, the sampled voltage of the output voltage, and the target voltage signal comprises:
obtaining a first error according to the sampling voltage of the output voltage and the target voltage signal;
obtaining an input current effective value according to the first error;
obtaining an input voltage phase value according to the sampling voltage of the input voltage;
obtaining a target current signal according to the input current effective value and the input voltage phase value;
obtaining a second error according to the sampling voltage of the input current and the target current signal; and
generating the duty cycle signal according to the second error.
23. The control method of claim 18, wherein the step of outputting a second control signal according to the sampled voltage of the output voltage, the first reference voltage, and the first control signal comprises:
comparing the first reference voltage with the sampling voltage of the output voltage, and generating a first indication signal according to the comparison result;
generating the second control signal according to the first indication signal, the first control signal and a PWM reset signal;
when the sampling voltage of the output voltage is greater than or equal to the first reference voltage, judging that the output voltage is overvoltage, outputting the second control signal to turn off the power switch tube,
and in the next control period, outputting the second control signal according to the PWM reset signal to conduct the power switch tube.
24. The control method of claim 23, wherein the step of generating the second control signal according to the first indication signal, the first control signal, and a PWM reset signal comprises:
generating a first fault signal according to the PWM reset signal and the first indication signal;
generating the second control signal based on the first control signal and the first fault signal,
wherein the first fault signal is active when the first indication signal is active, the first fault signal is inactive when the PWM reset signal is active and the first indication signal is inactive,
when the first fault signal is invalid, the state of the second control signal is consistent with the state of the first control signal, and when the first fault signal is valid, the second control signal is invalid.
25. The control method according to claim 24, characterized by further comprising: and when the times that the sampling voltage of the output voltage is greater than or equal to the first reference voltage within the first preset time reaches a preset value and a fault clearing signal is not received, the power switch tube is turned off.
26. The method of claim 25, wherein the step of generating a second control signal based on the sampled voltage of the output voltage, a first reference voltage, and the first control signal further comprises:
counting the first indicating signal to obtain a counting value, generating an intermediate indicating signal according to the counting value, and enabling the intermediate indicating signal to be effective when the counting value is larger than or equal to a preset value within first preset time;
latching the intermediate indication signal and generating a second indication signal according to the intermediate indication signal;
generating a counting reset signal after the first preset time, resetting the counting value according to the counting reset signal, and restarting counting; and
starting timing when the intermediate indication signal is effective, generating a fault clearing signal after a second preset time, and generating a second indication signal according to the fault clearing signal and the intermediate indication signal;
generating the second control signal according to the first indication signal, the second indication signal and the first control signal.
27. The method of claim 26, wherein the step of generating the second control signal based on the first indicator signal, the second indicator signal, and the first control signal further comprises:
generating a second fault signal based on the PWM reset signal and the second indication signal,
wherein the second fail signal is active when a second indication signal is active, and the second fail signal is inactive when the PWM reset signal is active and the second indication signal is inactive,
when both the first fault signal and the second fault signal are invalid, the state of the second control signal is consistent with the state of the first control signal, and when one of the first fault signal and the second fault signal is valid, the second control signal is invalid.
28. The control method according to claim 18, characterized by further comprising: when the sampling voltage of the output voltage is greater than or equal to a second reference voltage, generating a first trigger signal, switching off the power switch tube according to the first trigger signal, and controlling the first control signal to be in an invalid state,
wherein the second reference voltage characterizes a first over-voltage protection threshold, the second reference voltage being greater than the first reference voltage.
29. The control method according to claim 18, characterized by further comprising: generating a second trigger signal when the sampling voltage of the output voltage is greater than or equal to a third reference voltage, and controlling the first control signal to be in an invalid state according to the second trigger signal,
wherein the third reference voltage characterizes a second over-voltage protection threshold, and the first reference voltage is greater than the third reference voltage.
30. The control method of claim 29, further comprising deriving the second over-voltage protection threshold from the target voltage signal.
31. The control method of claim 30, wherein the step of deriving the second over-voltage protection threshold from the target voltage signal comprises:
and obtaining the second overvoltage protection threshold according to the maximum value of the target voltage signal, the amplitude of the voltage ripple and a preset second protection margin.
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