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CN118137428B - Overcurrent protection circuit and flyback switching power supply - Google Patents

Overcurrent protection circuit and flyback switching power supply Download PDF

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Publication number
CN118137428B
CN118137428B CN202410571539.6A CN202410571539A CN118137428B CN 118137428 B CN118137428 B CN 118137428B CN 202410571539 A CN202410571539 A CN 202410571539A CN 118137428 B CN118137428 B CN 118137428B
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China
Prior art keywords
voltage
resistor
power supply
signal
switching power
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CN118137428A (en
Inventor
秦赓
马辉
姚桂花
张华�
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Shenzhen Delian Minghai New Energy Co ltd
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Shenzhen Delian Minghai New Energy Co ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
    • G01R19/16533—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the application
    • G01R19/16538—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the application in AC or DC supplies
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H1/00—Details of emergency protective circuit arrangements
    • H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/08—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current
    • H02H3/087—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current for dc applications
    • 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
    • H02H7/1213—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 DC-DC converters
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0009—Devices or circuits for detecting current in a converter
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0048—Circuits or arrangements for reducing losses
    • 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
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters

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

Abstract

The application relates to an overcurrent protection circuit and a flyback switching power supply. The overcurrent protection circuit includes: a controller and a voltage dividing module; the voltage dividing module is configured to: outputting a voltage division signal according to a reference power VCC; the current sensing resistor Rsense is configured to: detecting a current signal of a flyback switching power supply; the controller is configured to: and receiving a target voltage signal obtained by superposing the voltage division signal and the current signal, and controlling the flyback switching power supply to stop working when the target voltage signal is larger than a preset value. According to the overcurrent protection circuit, the voltage division signal output by the voltage division module and the current signal detected by the current detection resistor Rsense are overlapped to form a target voltage signal, so that whether overcurrent is judged according to the target voltage signal, if overcurrent is caused, the flyback switching power supply is controlled by the controller to stop working, so that the voltage drop at two ends of the current detection resistor can be reduced when overcurrent is caused, the power consumption of the current detection resistor is further reduced, the overcurrent protection effect can be realized, and the design cost of the circuit is reduced.

Description

Overcurrent protection circuit and flyback switching power supply
Technical Field
The invention relates to the technical field of power supply circuits, in particular to an overcurrent protection circuit and a flyback switching power supply.
Background
The power supply is used for converting the externally input high-voltage alternating voltage into direct voltage applicable to the electronic equipment. According to different working principles, the power supply is mainly divided into two main types of linear power supply and switching power supply. The switching power supply uses a pulse width modulation (Pulse Width Modulation, PWM) control chip (INTEGRATED CIRCUIT, IC) to control the time ratio of on and off of the transistor, so as to maintain a stable output voltage, and is widely used in various electronic devices and apparatuses.
The flyback switching power supply is a switching power supply using a flyback high-frequency transformer to isolate an input/output loop, and a PWM (pulse-width modulation) IC (integrated circuit) used by the flyback switching power supply generally has an overcurrent protection function, and the chip generally has a Current Sense (CS) pin. The overcurrent protection principle is as follows: the lower end of the switching tube is connected in series with a current detection resistor, current can generate corresponding voltage through the current detection resistor, the voltage is output to a CS pin, and when the voltage is larger than an overcurrent protection threshold voltage, the PWM IC turns off a driving signal, and the phenomenon is called wave sealing.
However, the threshold voltage of the overcurrent protection is usually 1V, and when the current approaches the protection value, the voltage of the current detection resistor approaches 1V, so that the power consumption of the current detection resistor is higher, and the power consumption is shared by adopting a high-power resistor or multiple parallel current detection resistor areas, so that the design cost of the circuit is higher.
Disclosure of Invention
The overcurrent protection circuit and the flyback switching power supply provided by the embodiment of the application can solve at least part of defects in the prior art.
In a first aspect, an embodiment of the present application provides an overcurrent protection circuit applied to a flyback switching power supply, where the flyback switching power supply has a current detection resistor Rsense. The overcurrent protection circuit includes: a controller and a voltage dividing module; the voltage division module is respectively connected with a reference power supply VCC, the current detection resistor Rsense and the controller, and the controller is also connected with the flyback switching power supply; the voltage dividing module is configured to: outputting a voltage division signal according to the reference power supply VCC; the current sensing resistor Rsense is configured to: detecting a current signal of the flyback switching power supply; the controller is configured to: and receiving a target voltage signal, and controlling the flyback switching power supply to stop working when the target voltage signal is larger than a preset value, wherein the target voltage signal is a signal obtained by superposing the voltage dividing signal and the current signal.
Optionally, the controller has: a detection pin and a driving pin; the voltage dividing module includes: a first resistor R1, a second resistor R2 and a third resistor R3; the detection pin is respectively connected with the first end of the first resistor R1, the first end of the second resistor R2 and the first end of the third resistor R3, and forms a target connection node; wherein the voltage of the target connection node corresponds to the target voltage signal; the second end of the first resistor R1 is connected with the reference power supply VCC, the second end of the second resistor R2 is connected with the first end of the current detection resistor Rsense, the second end of the current detection resistor Rsense is connected to the ground, and the second end of the third resistor R3 is connected to the ground; the driving pin is connected with the flyback switching power supply; the controller is configured to: and detecting the voltage of the target connection node, and outputting a control signal when the voltage of the target connection node is larger than the preset value, and transmitting the control signal to the flyback switching power supply through the driving pin so as to control the flyback switching power supply to stop working.
Optionally, the voltage of the target connection node includes: a first voltage Vp1 and a second voltage Vp2; the first voltage Vp1 is: Wherein the said For indicating the current flowing through the sense resistor Rsense; the second voltage Vp2 is:。
Optionally, the voltage of the target connection node The expression of (2) is:。
Optionally, the overcurrent protection circuit further includes: a switching tube Q1; the control end of the switching tube Q1 is connected with the driving pin; the first end of the switching tube Q1 is connected with a transformer winding to receive the input voltage of the flyback switching power supply; the second end of the switching tube Q1 is respectively connected with the first end of the current detection resistor Rsense and the second end of the second resistor R2; the switching tube Q1 is configured to: when the control signal is received, the switching tube Q1 is cut off, so that the flyback switching power supply stops working.
Optionally, the overcurrent protection circuit further includes: a voltage follower module; the voltage following module is respectively connected with the flyback switching power supply and the controller; the voltage follower module is configured to: outputting a following voltage signal according to the input voltage of the flyback switching power supply; the controller is configured to: and receiving a target voltage signal, and controlling the flyback switching power supply to stop working when the target voltage signal is larger than the preset value, wherein the target voltage signal is a signal obtained by superposing the voltage dividing signal, the current signal and the follow-up voltage signal.
Optionally, the voltage following module includes: a fourth resistor R4, a fifth resistor R5 and a voltage follower; the first end of the fourth resistor R4 is connected with the flyback switching power supply, the second end of the fourth resistor R4 is respectively connected with the input end of the voltage follower and the first end of the fifth resistor R5, and the second end of the fifth resistor R5 is connected to the ground; the output end of the voltage follower is connected with the target connection node; wherein the voltage of the target connection node corresponds to the target voltage signal; the controller is configured to: and detecting the voltage of the target connection node, and outputting a control signal when the voltage of the target connection node is larger than the preset value, and transmitting the control signal to the flyback switching power supply through the driving pin so as to control the flyback switching power supply to stop working.
Optionally, the voltage follower includes: an operational amplifier U1, a sixth resistor R6, and a seventh resistor R7; the non-inverting input end of the operational amplifier U1 is respectively connected with the second end of the fourth resistor R4 and the first end of the fifth resistor R5; the first end of the sixth resistor R6 is connected with the inverting input end of the operational amplifier U1, and the second end of the sixth resistor R6 is connected with the output end of the operational amplifier U1; the first end of the seventh resistor R7 is connected to the output end of the operational amplifier U1, and the second end of the seventh resistor R7 is connected to the target connection node.
Optionally, the voltage of the target connection node includes: a first voltage Vp1, a second voltage Vp2, and a third voltage Vp3; the first voltage Vp1 is: Wherein the said For indicating the current flowing through the sense resistor Rsense; the second voltage Vp2 is: ; the third voltage Vp3 is: Wherein the said For indicating the input voltage of the flyback switching power supply.
In a second aspect, an embodiment of the present application provides a flyback switching power supply. The flyback switching power supply includes: the overcurrent protection circuit.
At least one advantageous aspect of the overcurrent protection circuit provided by the embodiment of the application is that: the voltage division module outputs a voltage division signal according to the reference power VCC, the current signal of the flyback switching power supply is detected through the current detection resistor Rsense, the voltage division signal and the current signal are overlapped to form a target voltage signal, the controller is used for judging whether the overcurrent is caused or not according to the target voltage signal, if the overcurrent is caused, the flyback switching power supply is controlled by the controller to stop working, the current detection resistor can be designed to be a lower value, so that the voltage drop at two ends of the current detection resistor can be reduced when the overcurrent is caused, the power consumption of the current detection resistor is reduced, the overcurrent protection effect can be realized, and meanwhile, the power consumption is not required to be shared by a high-power resistor or multiple current detection resistor areas, and the design cost of a circuit can be reduced.
Drawings
One or more embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements, and in which the figures of the drawings are not to be taken in a limiting sense, unless otherwise indicated.
FIG. 1 is a schematic diagram of the amount by which a true envelope current exceeds a current threshold;
FIG. 2 is a schematic diagram showing the actual amount of current in the envelope exceeding the current threshold becoming greater as the input voltage becomes higher;
FIG. 3 is a functional block diagram of an over-current protection circuit according to an embodiment of the present application;
FIG. 4 is a schematic circuit diagram of an over-current protection circuit according to an embodiment of the present application;
FIG. 5 is a schematic diagram of a voltage division module for reducing the resistance of a current detection resistor according to an embodiment of the present application;
FIG. 6 is a functional block diagram of an over-current protection circuit according to another embodiment of the present application;
FIG. 7 is a schematic circuit diagram of an over-current protection circuit according to another embodiment of the present application;
FIG. 8 is a schematic diagram of a real current reduction in a seal wave according to an embodiment of the present application.
Detailed Description
In order that the invention may be readily understood, a more particular description thereof will be rendered by reference to specific embodiments that are illustrated in the appended drawings. It will be understood that when an element is referred to as being "fixed" to another element, it can be directly on the other element or one or more intervening elements may be present therebetween. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or one or more intervening elements may be present therebetween. The terms "upper," "lower," "inner," "outer," "bottom," and the like as used in this specification are used in an orientation or positional relationship based on that shown in the drawings, merely to facilitate the description of the invention and to simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the invention. Furthermore, the terms "first," "second," "third," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used in this specification includes any and all combinations of one or more of the associated listed items.
In addition, the technical features mentioned in the different embodiments of the invention described below can be combined with one another as long as they do not conflict with one another.
PWM ICs used in flyback switching power supplies generally have an overcurrent protection function, such as UC2844, NCP1252, and the like. A chip of this type is generally provided with a Current Sense (CS) pin, which is used as a detection pin in the present application, and the overcurrent protection principle is as follows: the lower end of the switching tube is connected in series with a current detection resistor, current can generate corresponding voltage through the current detection resistor, the voltage is output to a CS pin, and when the voltage is larger than an overcurrent protection threshold voltage, the PWM IC turns off a driving signal, and the phenomenon is called wave sealing.
But typically overcurrent protection threshold voltageIs 1V, from current exceeding current thresholdBy the time of wave sealing, there is delay time Tdelay, which is caused by the chip technology and cannot be eliminated. Leading to the following drawbacks of the prior art:
defect 1: when the current approaches the current threshold At the time of current detection resistorThe voltage drop over the resistor is approximately 1VThe power received is: thereby resulting in a current sensing resistor The power consumption of the circuit is higher, and the power consumption is shared by adopting a high-power resistor or multiple parallel current detection resistor areas at present, so that the design cost of the circuit is higher.
Defect 2: when the input voltage is low, the current detecting resistorThe 1V drop in voltage will result in a decrease in the overall efficiency of the flyback switching power supply.
Defect 3: due to the delay time Tdelay, when Feng Bo is true, the true envelope current has exceeded the current thresholdAs shown in FIG. 1, FIG. 1 is a schematic diagram of the amount by which the true seal current exceeds the current threshold, where ΔI is used to indicate that the true seal current exceeds the current thresholdThe Δi is determined by Tdelay, the input voltage Vin, and the transformer excitation inductance Lm, and includes: In a specific design, tdelay and Lm are fixed values, and it can be seen that the input voltage Vin is a factor affecting Δi. When the input voltage Vin becomes higher, Δi becomes larger, as shown in fig. 2, fig. 2 is a schematic diagram that the amount of real envelope current exceeding the current threshold becomes larger as the input voltage becomes higher, so that the energy stored on the transformer of the flyback switching power supply is obtained as follows: where Im is used to indicate the excitation current at the time of closing, it can be seen that the larger Δi is, the more energy is stored on the transformer.
Therefore, it can be explained that when the input voltage changes, the real current of the flyback switching power supply exceeds the current threshold value and the overload protection power (corresponding to the energy stored on the transformer) both change, and the higher the input voltage, the larger the actual overload protection power. In a high-voltage battery energy storage system, the total series number of batteries and the working voltage range of a single battery core are greatly changed, the ratio between the lowest value and the highest value of input voltage can reach 1:4, and when the input voltage is highest, overload protection power can far exceed design power, and power devices such as a transformer, a switching tube and an output rectifying diode can be seriously heated, so that the safety is influenced.
In order to solve the above-mentioned defect 1 and defect 2, the present application provides an overcurrent protection circuit, which is applied to a flyback switching power supply, the flyback switching power supply has a current detection resistor Rsense, as shown in fig. 3, fig. 3 is a functional block diagram of the overcurrent protection circuit provided by the embodiment of the present application, and the overcurrent protection circuit 30 includes: a controller 31 and a voltage dividing module 32.
The controller 31 is a pulse width modulation (Pulse Width Modulation, PWM) control chip (INTEGRATED CIRCUIT, IC).
The voltage dividing module 32 is respectively connected with the reference power supply VCC, the current detection resistor Rsense and the controller 31, and the controller 31 is also connected with the flyback switching power supply.
The reference power VCC provides a voltage to the voltage dividing module 32, the voltage dividing module 32 being configured to: the divided voltage signal is output according to the reference power VCC.
The current detection resistor Rsense is connected with the flyback switching power supply, and is configured to: and detecting a current signal of the flyback switching power supply.
The controller 31 is configured to: and receiving a target voltage signal, and controlling the flyback switching power supply to stop working when the target voltage signal is larger than a preset value, wherein the target voltage signal is a signal obtained by superposing a voltage division signal and a current signal.
It should be noted that the preset value is an overcurrent protection threshold voltage, and the value is generally set to 1V.
The voltage division module outputs a voltage division signal according to the reference power VCC, the current signal of the flyback switching power supply is detected through the current detection resistor Rsense, the voltage division signal and the current signal are overlapped to form a target voltage signal, the controller is used for judging whether the overcurrent is caused or not according to the target voltage signal, if the overcurrent is caused, the flyback switching power supply is controlled by the controller to stop working, the current detection resistor can be designed to be a lower value, so that the voltage drop at two ends of the current detection resistor can be reduced when the overcurrent is caused, the power consumption of the current detection resistor is reduced, the overcurrent protection effect can be realized, and meanwhile, the power consumption is not required to be shared by a high-power resistor or multiple current detection resistor areas, and the design cost of a circuit can be reduced.
As shown in fig. 4, fig. 4 is a schematic circuit diagram of an overcurrent protection circuit according to an embodiment of the present application.
In one embodiment, as shown in fig. 4, the controller 31 has: a sense pin 311 and a drive pin 312. The voltage dividing module 32 includes: a first resistor R1, a second resistor R2 and a third resistor R3.
The detection pin 311 is connected to the first end of the first resistor R1, the first end of the second resistor R2, and the first end of the third resistor R3, respectively, and forms a target connection node P, where the voltage of the target connection node P corresponds to the target voltage signal.
The second end of the first resistor R1 is connected to the reference power VCC, the second end of the second resistor R2 is connected to the first end of the current sensing resistor Rsense, the second end of the current sensing resistor Rsense is connected to the ground GND, and the second end of the third resistor R3 is connected to the ground GND.
The drive pin 312 is connected to a flyback switching power supply, and the controller 31 is configured to: and detecting the voltage of the target connection node P, outputting a control signal when the voltage of the target connection node P is larger than a preset value, and transmitting the control signal to the flyback switching power supply through the driving pin 312 to control the flyback switching power supply to stop working.
The reference power supply VCC generates a voltage (second voltage Vp 2) through R1 and R3// R2, and after being superimposed with a current signal of the flyback switching power supply detected by the current detection resistor Rsense, a voltage at the target connection node P is obtained, so that the controller determines whether to overcurrent or not according to the voltage of the target connection node P.
In one embodiment, as shown in fig. 4, the overcurrent protection circuit 30 further includes: the switching transistor Q1 is, for example and not by way of limitation, an N-type MOS transistor or a P-type MOS transistor.
The control end of the switching tube Q1 is connected to the driving pin 312, the first end of the switching tube Q1 is connected to the transformer winding to receive the input voltage of the flyback switching power supply, the second end of the switching tube Q1 is connected to the first end of the current detection resistor Rsense and the second end of the second resistor R2, and the switching tube Q1 is configured to: when receiving the control signal, the switching tube Q1 is cut off, so that the flyback switching power supply stops working.
The flyback switching power supply can be normally operated or stopped by controlling the on or off of the switching tube Q1, and the flyback switching power supply can be stopped under the condition that the switching tube Q1 is cut off, so that the flyback switching power supply can be protected.
In one embodiment, as shown in fig. 4, the overcurrent protection circuit 30 further includes: a capacitor C1.
Wherein, the first end of the capacitor C1 is connected to the detection pin 311, the second end of the capacitor C1 is connected to the ground GND, and the capacitor C1 is configured to: the dc signal and the high frequency noise in the overcurrent protection circuit 30 are filtered and eliminated.
By adding the capacitor C1 to the circuit, the dc signal and the high-frequency noise in the overcurrent protection circuit can be filtered and eliminated.
In order to facilitate the understanding of the inventive aspects, the principles of the present application are described below:
In the existing overcurrent protection circuit, a current detecting resistor is known Setting an overcurrent protection threshold voltage1V, when the voltage dividing module of the application is not present, and the current detecting resistorWhen the voltage drop is close to 1V, the current flows through the current detection resistorIs close to the current thresholdThus, the following formula is given:。
When the voltage dividing module of the present application exists, as shown in fig. 4, the voltage of the target connection node P is provided by two parts, the first part is a first voltage Vp1, the voltage generated by the transformer winding and the switching tube Q1 flowing through the current detecting resistor Rsense is generated by R2 and R1// R3, and the second part is a second voltage Vp2, and the second voltage is generated by the reference power VCC through R1 and R3// R2.
The first voltage Vp1 is: Wherein, the method comprises the steps of, wherein, For indicating the current through the sense resistor Rsense, the symbol "//" is used for indicating a parallel connection.
The second voltage Vp2 is:。
Thus, the voltage of the target connection node The expression of (2) is:
。
when the voltage of the target connection node P Approaching an over-current protection threshold voltageThe following formula is given:
。
as can be seen from the above, the first voltage Vp1 is smaller than the second voltage Vp2 And by configuring R1, R2 and R3, the current sensing resistance Rsense in the first voltage Vp1 can be made smaller than that in the existing overcurrent protection circuitThereby compared with the current detecting resistor in the prior artThe embodiment of the application can realize the same overcurrent protection effect while reducing the resistance value of the current detection resistor, namely, the resistance value of the current detection resistor can be set to be lower, the voltage drop at two ends of the current detection resistor can be reduced during overcurrent, and the power consumption of the current detection resistor is reduced, so that the overcurrent protection effect is realized and the design cost of a circuit is reduced.
As shown in fig. 5, fig. 5 is a schematic diagram of the voltage division module for realizing the reduction of the resistance value of the current detection resistor according to the embodiment of the present application, after the resistance value of the current detection resistor Rsense is set to a lower value, when the current reaches the current threshold valueIn the process, the voltage drop at two ends of the current detection resistor Rsense is greatly reduced, the power consumption is not required to be shared by a large-power resistor or multiple current detection resistor areas, the design cost of the circuit can be reduced, and the efficiency of the overcurrent protection circuit is improved.
At least one advantageous aspect of the overcurrent protection circuit provided by the embodiment of the application is that: the voltage division module outputs a voltage division signal according to the reference power VCC, the current signal of the flyback switching power supply is detected through the current detection resistor Rsense, the voltage division signal and the current signal are overlapped to form a target voltage signal, the controller is used for judging whether the overcurrent is caused or not according to the target voltage signal, if the overcurrent is caused, the flyback switching power supply is controlled by the controller to stop working, the current detection resistor can be designed to be a lower value, so that the voltage drop at two ends of the current detection resistor can be reduced when the overcurrent is caused, the power consumption of the current detection resistor is reduced, the overcurrent protection effect can be realized, and meanwhile, the power consumption is not required to be shared by a high-power resistor or multiple current detection resistor areas, and the design cost of a circuit can be reduced.
In order to solve the above defect 3, the present application adds a voltage follower module on the basis of fig. 3 to obtain fig. 6, and fig. 6 is a functional block diagram of an over-current protection circuit according to another embodiment of the present application, as shown in fig. 6, the over-current protection circuit 30 further includes: a voltage follower module 33.
The voltage follower module 33 is connected to the flyback switching power supply and the controller 31, respectively.
The voltage follower module 33 is configured to: and outputting a following voltage signal according to the input voltage of the flyback switching power supply.
The controller 31 is configured to: and receiving a target voltage signal, and controlling the flyback switching power supply to stop working when the target voltage signal is larger than a preset value, wherein the target voltage signal is a voltage division signal, a current signal and a signal which is overlapped with the voltage signal.
Through increasing voltage at overcurrent protection circuit and following the module, can also be in time protected when the voltage that the CS pin detected is greater than overcurrent protection threshold voltage under the higher circumstances of input voltage, promote circuit's overall security, reliability.
Fig. 7 is a schematic circuit diagram of an overcurrent protection circuit according to another embodiment of the present application.
In one embodiment, as shown in fig. 7, the voltage follower module 33 includes: a fourth resistor R4, a fifth resistor R5 and a voltage follower.
The first end of the fourth resistor R4 is connected with the flyback switching power supply, the second end of the fourth resistor R4 is connected with the input end of the voltage follower and the first end of the fifth resistor R5 respectively, the second end of the fifth resistor R5 is connected to the ground GND, the output end of the voltage follower is connected with the target connection node P, and the voltage of the target connection node P corresponds to the target voltage signal.
The controller 31 is configured to: and detecting the voltage of the target connection node P, outputting a control signal when the voltage of the target connection node P is larger than a preset value, and transmitting the control signal to the flyback switching power supply through the driving pin 312 to control the flyback switching power supply to stop working.
In one embodiment, as shown in fig. 7, the voltage follower includes: an operational amplifier U1, a sixth resistor R6 and a seventh resistor R7.
The non-inverting input terminal of the operational amplifier U1 is connected to the second terminal of the fourth resistor R4 and the first terminal of the fifth resistor R5, respectively.
The first end of the sixth resistor R6 is connected to the inverting input terminal of the operational amplifier U1, and the second end of the sixth resistor R6 is connected to the output terminal of the operational amplifier U1.
The first end of the seventh resistor R7 is connected to the output terminal of the operational amplifier U1, and the second end of the seventh resistor R7 is connected to the target connection node P.
In one embodiment, as shown in fig. 7, the power input terminal of the operational amplifier U1 is connected to the constant voltage power source VCC1, and the ground terminal of the operational amplifier U1 is connected to the ground GND. Note that the constant voltage power supply VCC1 may be the same as or different from the reference power supply VCC, and is not limited herein.
The input voltage is divided by the fourth resistor R4 and the fifth resistor R5, the divided voltage signals enter the operational amplifier U1, R6 and R7 to form a voltage follower, the following voltage signals are output to the target connection node P, the following voltage signals are overlapped with the divided voltage signals and the current signals at the target connection node P to form target voltage signals, and the voltage at the target connection node P is obtained, so that the controller judges whether overcurrent or not according to the voltage of the target connection node P.
In one embodiment, the present application provides a flyback switching power supply, comprising: the overcurrent protection circuit as described above.
In order to facilitate the understanding of the inventive aspects, the principles of the present application are described below:
as shown in fig. 7, R4 and R5 divide the input voltage of the flyback switching power supply, the divided voltage enters the operational amplifier U1, R6 and R7 to form a voltage follower, and a follower voltage signal is output to the target connection node P, and at this time, the voltage of the target connection node P is provided by three parts, which are respectively: the first voltage Vp1, the second voltage Vp2, and the third voltage Vp3.
The first voltage Vp1 is: Wherein, the method comprises the steps of, wherein, For indicating the current through the sense resistor Rsense.
The second voltage Vp2 is:。
the third voltage Vp3 is: Wherein, the method comprises the steps of, wherein, For indicating the input voltage of the flyback switching power supply.
Thus, the voltage of the target connection nodeThe expression of (2) is:
。
when the voltage of the target connection node P Approaching an over-current protection threshold voltageThe following formula is given:
=Vp1+Vp2+Vp3。
as can be seen from the above equation, since the third voltage Vp3 exists and the second voltage Vp2 remains unchanged, the current Isense flowing through the sensing resistor Rsense in the first voltage Vp1 will change with the change of the third voltage Vp 3. When the input voltage Vin becomes higher, the first voltage Vp1 decreases and the current Isense decreases, so that the current threshold value can be set Designed to be low, so that the current at the time of wave sealing (true wave sealing current) is reduced, thereby ensuring the current threshold value at the condition of high input voltage VinThe current in wave sealing is not higher, so that the safety of the circuit is ensured.
As shown in fig. 8, fig. 8 is a schematic diagram showing a real current reduction of the current sense circuit according to the embodiment of the present application, it should be noted that the value of the third voltage Vp3 is related to the value of the input voltage Vin, when the input voltage Vin is smaller, the value of the third voltage Vp3 is lower and can be ignored, and this corresponds to the circuit of fig. 4, so that the current Isense flowing through the current sense resistor Rsense reaches the current threshold valueAnd when the flyback switching power supply is controlled to stop working.
When the input voltage Vin is large, the value of the third voltage Vp3 is large, but due to the overcurrent protection threshold voltage: The second voltage Vp2 remains unchanged, the larger the third voltage Vp3 is, the smaller the first voltage Vp1 is, the lower the current Isense flowing through the current detection resistor Rsense is, the lower the current at the time of wave blocking is, and therefore, the current threshold can be set when the input voltage is large The current flowing through the current detection resistor Rsense is reduced to reach the value of a protection point, so that the current (real wave-sealing current) in wave sealing is reduced, overload protection power is stabilized in a preset range, the overload protection power is prevented from exceeding design power, and the safety and reliability of the circuit are guaranteed.
In the embodiment of the application, when the input voltage is increased, the voltage of the P point is continuously increased, and when the output is overloaded, the voltage of the P point is increased to reduce the real wave-sealing current, thereby avoiding the threshold voltage from being protected due to overcurrentToo low, resulting in too fast a rise in current after sealing, resulting in a current thresholdAnd the problem of bigger size.
In summary, the application designs the current detection resistor to be a lower value by introducing the voltage division module and the reference power supply VCC, when the current reaches the current threshold valueWhen the voltage drop at two ends of the current detection resistor is greatly reduced, the high-power resistor or multiple current detection resistor areas do not need to be adopted to share the power consumption, the design cost of the circuit can be reduced, the efficiency of the overcurrent protection circuit is improved, in addition, the input voltage is led into the detection pin, and meanwhile, the voltage following module is added, so that the influence of the increase of the input voltage on the output overload protection can be reduced, and when the input voltage is increased, the current threshold value can be setThe circuit is designed to be a lower value, so that timely protection is realized when the voltage detected by the CS pin is greater than the overcurrent protection threshold voltage, and the overall safety and reliability of the circuit are improved.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; the technical features of the above embodiments or in the different embodiments may also be combined within the idea of the invention, the steps may be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims (9)

1. An overcurrent protection circuit is applied to a flyback switching power supply, and the flyback switching power supply is provided with a current detection resistor Rsense, and is characterized in that the overcurrent protection circuit comprises: a controller and a voltage dividing module;
the voltage division module is respectively connected with a reference power supply VCC, the current detection resistor Rsense and the controller, and the controller is also connected with the flyback switching power supply;
the voltage dividing module is configured to: outputting a voltage division signal according to the reference power supply VCC;
the current sensing resistor Rsense is configured to: detecting a current signal of the flyback switching power supply;
the controller is configured to: receiving a target voltage signal, and controlling the flyback switching power supply to stop working when the target voltage signal is larger than a preset value, wherein the target voltage signal is a signal obtained by superposing the voltage dividing signal and the current signal;
the controller has: a detection pin and a driving pin; the voltage dividing module includes: a first resistor R1, a second resistor R2 and a third resistor R3;
The detection pin is respectively connected with the first end of the first resistor R1, the first end of the second resistor R2 and the first end of the third resistor R3, and forms a target connection node;
wherein the voltage of the target connection node corresponds to the target voltage signal;
the second end of the first resistor R1 is connected with the reference power supply VCC, the second end of the second resistor R2 is connected with the first end of the current detection resistor Rsense, the second end of the current detection resistor Rsense is connected to the ground, and the second end of the third resistor R3 is connected to the ground;
the driving pin is connected with the flyback switching power supply;
The controller is configured to: and detecting the voltage of the target connection node, and outputting a control signal when the voltage of the target connection node is larger than the preset value, and transmitting the control signal to the flyback switching power supply through the driving pin so as to control the flyback switching power supply to stop working.
2. The overcurrent protection circuit of claim 1, wherein the voltage of the target connection node comprises: a first voltage Vp1 and a second voltage Vp2;
the first voltage Vp1 is: Wherein the said For indicating the current flowing through the sense resistor Rsense;
the second voltage Vp2 is: 。
3. the overcurrent protection circuit of claim 2, wherein the voltage of the target connection node The expression of (2) is:
。
4. the overcurrent protection circuit of claim 1, wherein the overcurrent protection circuit further comprises: a switching tube Q1;
the control end of the switching tube Q1 is connected with the driving pin;
the first end of the switching tube Q1 is connected with a transformer winding to receive the input voltage of the flyback switching power supply;
The second end of the switching tube Q1 is respectively connected with the first end of the current detection resistor Rsense and the second end of the second resistor R2;
The switching tube Q1 is configured to: when the control signal is received, the switching tube Q1 is cut off, so that the flyback switching power supply stops working.
5. The overcurrent protection circuit of claim 1, wherein the overcurrent protection circuit further comprises: a voltage follower module;
The voltage following module is respectively connected with the flyback switching power supply and the controller;
the voltage follower module is configured to: outputting a following voltage signal according to the input voltage of the flyback switching power supply;
The controller is configured to: and receiving a target voltage signal, and controlling the flyback switching power supply to stop working when the target voltage signal is larger than the preset value, wherein the target voltage signal is a signal obtained by superposing the voltage dividing signal, the current signal and the follow-up voltage signal.
6. The overcurrent protection circuit of claim 5, wherein the voltage follower module comprises: a fourth resistor R4, a fifth resistor R5 and a voltage follower;
the first end of the fourth resistor R4 is connected with the flyback switching power supply, the second end of the fourth resistor R4 is respectively connected with the input end of the voltage follower and the first end of the fifth resistor R5, and the second end of the fifth resistor R5 is connected to the ground;
The output end of the voltage follower is connected with the target connection node;
wherein the voltage of the target connection node corresponds to the target voltage signal;
The controller is configured to: and detecting the voltage of the target connection node, and outputting a control signal when the voltage of the target connection node is larger than the preset value, and transmitting the control signal to the flyback switching power supply through the driving pin so as to control the flyback switching power supply to stop working.
7. The overcurrent protection circuit of claim 6, wherein the voltage follower comprises: an operational amplifier U1, a sixth resistor R6, and a seventh resistor R7;
The non-inverting input end of the operational amplifier U1 is respectively connected with the second end of the fourth resistor R4 and the first end of the fifth resistor R5;
The first end of the sixth resistor R6 is connected with the inverting input end of the operational amplifier U1, and the second end of the sixth resistor R6 is connected with the output end of the operational amplifier U1;
the first end of the seventh resistor R7 is connected to the output end of the operational amplifier U1, and the second end of the seventh resistor R7 is connected to the target connection node.
8. The overcurrent protection circuit of claim 7, wherein the voltage of the target connection node comprises: a first voltage Vp1, a second voltage Vp2, and a third voltage Vp3;
the first voltage Vp1 is: Wherein the said For indicating the current flowing through the sense resistor Rsense;
the second voltage Vp2 is: ；
the third voltage Vp3 is: Wherein the said For indicating the input voltage of the flyback switching power supply.
9. A flyback switching power supply, comprising: the overcurrent protection circuit according to any one of claims 1 to 8.
CN202410571539.6A 2024-05-10 2024-05-10 Overcurrent protection circuit and flyback switching power supply Active CN118137428B (en)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101841250A (en) * 2010-04-27 2010-09-22 上海新进半导体制造有限公司 Switching power supply control circuit and primary winding-controlled flyback switching power supply
CN109075598A (en) * 2016-02-05 2018-12-21 广东欧珀移动通信有限公司 Adapter and charge control method

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101841250A (en) * 2010-04-27 2010-09-22 上海新进半导体制造有限公司 Switching power supply control circuit and primary winding-controlled flyback switching power supply
CN109075598A (en) * 2016-02-05 2018-12-21 广东欧珀移动通信有限公司 Adapter and charge control method

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