An overcurrent protection circuit and switching power supply

Abstract

The application discloses an overcurrent protection circuit and a switching power supply. When the absolute value of a voltage signal V1 representing the output current of the switching power supply is greater than a first set value and less than or equal to a second set value, the overcurrent protection circuit outputs a constant current control signal V8 to control the switching power supply to output a constant current with a first current value when a set time reaches. When the absolute value of the voltage signal V1 is greater than the second set value, the constant current control signal V8 immediately controls the switching power supply to output a constant current with a second current value, and outputs the constant current control signal V8 to control the switching power supply to output a constant current with the first current value when the set time reaches. The switching power supply using the overcurrent protection circuit can meet the output capacity in transient over-power state, control the time when the switching power supply works beyond the rated current, prevent overheat damage, and ensure that the output current of the switching power supply is not greater than the rated current value of internal devices to prevent device overcurrent breakdown.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of switching power supply, in particular to a protection circuit for switching power supply when overcurrent. BACKGROUND

[0002] With the rapid development of power electronics technology, switching power supply is applied more and more widely, especially the demand for high power, high power density, low cost and high reliability switching power supply is increasing. When the load of switching power supply is a relay or a motor driving system, or the load works in a frequent start-stop state, the current value required during the load starting process (also known as transient current value or transient over-power current value) is often greater than the current value during normal operation (also known as rated steady-state current value or rated current value), even up to 2-3 times.

[0003] When selecting a switching power supply, if the power of the switching power supply is selected according to the load starting process, the size and cost of the switching power supply will be greatly increased. If the switching power supply is selected according to the steady-state power, it will bring the risk of damaging the switching power supply during the load starting process. Therefore, in order to meet the demand for transient large current output, most switching power supplies currently increase the overcurrent protection function in the control. SUMMARY

[0004] Therefore, the technical problem to be solved by the present application is to provide an overcurrent protection circuit and a switching power supply, so that the switching power supply using the overcurrent protection circuit of the present application can not only improve the output capability during transient over-power, but also can exceed the rated current output within a specified time to prevent the switching power supply from overheating and being damaged. At the same time, it is ensured that the output current of the switching power supply will not be greater than the limit current value allowed by the switching power supply, so as to prevent the switching power supply from being damaged by overcurrent.

[0005] As a first aspect of the present application, the technical scheme of the overcurrent protection circuit is as follows:

[0006] An overcurrent protection circuit applied to a switching power supply, wherein the switching power supply comprises a power conversion unit and a feedback control unit, and the overcurrent protection circuit comprises:

[0007] a current detection circuit for converting the output current of the switching power supply into a voltage signal V1 representing the size of the output current;

[0008] a reference source generation circuit for generating a first reference voltage V2;

[0009] a timing control circuit for superimposing and dividing the voltage signal V1 and the first reference voltage V2 to output a second reference voltage V3, and judging the size of the second reference voltage V3 and a ground voltage signal to output a voltage signal V4;

[0010] a timing circuit for timing and outputting a voltage signal V5 according to the voltage signal V4;

[0011] a constant current control circuit for superimposing and proportionally dividing the voltage signal V1 and the first reference voltage V2 according to the level state of the voltage signal V5, outputting a third reference voltage V6, and judging the size of the third reference voltage V6 and a ground voltage signal, and outputting a constant current control signal V8, which is input to the feedback control end of the feedback control unit;

[0012] when the absolute value of the voltage signal V1 is less than or equal to a first set value, the constant current control signal V8 does not control the switching power supply to operate;

[0013] when the absolute value of the voltage signal V1 is greater than the first set value and less than or equal to a second set value, the constant current control signal V8 controls the switching power supply to output a first current value when the timing time of the timing circuit reaches a timing time set value;

[0014] when the absolute value of the voltage signal V1 is greater than the second set value, the constant current control signal V8 immediately controls the switching power supply to output a second current value, and the constant current control signal V8 controls the switching power supply to output the first current value when the timing time of the timing circuit reaches the timing time set value;

[0015] the output current rating of the switching power supply ≤ the first current value ≤ the second current value ≤ the output current limit of the switching power supply.

[0016] Further, the value of the second reference voltage V3 corresponding to the high level of the voltage signal V4 is denoted as V3a, the value of the second reference voltage V3 corresponding to the low level of the voltage signal V4 is denoted as V3b, the value of the third reference voltage V6 corresponding to the high level of the voltage signal V5 is denoted as V6a, and the value of the third reference voltage V6 corresponding to the low level of the voltage signal V5 is denoted as V6b; V3b < V6b < V3a < V6a.

[0017] Further, when the absolute value of the voltage signal V1 is less than or equal to a first set value, the second reference voltage V3 is greater than or equal to a ground voltage signal, the voltage signal V4 is high, the voltage signal V5 is high, the third reference voltage V6 is greater than or equal to the ground voltage signal, a voltage signal V7 obtained by comparing the third reference voltage V6 and the ground voltage signal through an operational amplifier is high, and a constant current control signal V8 is high, which does not affect the working state of the switching power supply.

[0018] When the absolute value of the voltage signal V1 is greater than the first set value and less than or equal to a second set value, the second reference voltage V3 is less than the ground voltage signal 0V, the voltage signal V4 is low, the voltage value of the voltage signal V5 gradually decreases from high to a preset value, the time required for the decrease is the timing time set value, the third reference voltage V6 is greater than or equal to the ground voltage signal before the timing time set value is reached, the voltage signal V7 is high in this stage, the constant current control signal V8 is high, which does not affect the working state of the switching power supply, the third reference voltage V6 is less than the ground voltage signal after the timing time set value is reached, the voltage signal V7 is low in this stage, and the control signal V8 controls the switching power supply to output constant current with a first current value.

[0019] When the absolute value of the voltage signal V1 is greater than the second set value, the second reference voltage V3 is less than the ground voltage signal, the voltage signal V4 is low, the voltage value of the voltage signal V5 gradually decreases from high to a preset value, the time required for the decrease is the timing time set value, the third reference voltage V6 is less than the ground voltage signal before the timing time set value is reached, the voltage signal V7 is low in this stage, the constant current control signal V8 immediately controls the switching power supply to output constant current with a second current value, the third reference voltage V6 is less than the ground voltage signal after the timing time set value is reached, the voltage signal V7 is low in this stage, and the control signal V8 controls the switching power supply to output constant current with the first current value.

[0020] As a specific embodiment of the current detection circuit, it comprises a resistor R1, one end of the resistor R1 is used for inputting the output current of the switching power supply, and the other end of the resistor R1 outputs the voltage signal V1.

[0021] As a specific embodiment of the reference source generating circuit, it comprises resistor R2 and 431 chip U2; one end of the resistor R2 is used for connecting the power supply voltage Vdd, the other end is connected with the cathode of the 431 chip U2 and the reference end of the 431 chip U2 to output the first reference voltage V2, and the anode of the 431 chip U2 is used for connecting the ground.

[0022] As a specific embodiment of the timing control circuit, it comprises resistor R3, resistor R4, resistor R5 and operational amplifier U1A; one end of the resistor R3 is connected with the negative input end of the operational amplifier U1A, and the other end is used for connecting the ground, one end of the resistor R4 is used for inputting the voltage signal V1, the other end is connected with one end of the resistor R5 and the same input end of the operational amplifier U1A to output the second reference voltage V3, the other end of the resistor R5 is used for inputting the first reference voltage V2, and the output end of the operational amplifier U1A outputs the voltage signal V4.

[0023] As a specific embodiment of the timing control circuit, it further comprises resistor R6, one end of the resistor R6 is connected with the same input end of the operational amplifier U1A, and the other end is connected with the output end of the operational amplifier U1A.

[0024] As a specific embodiment of the timing circuit, it comprises resistor R7, capacitor C1, capacitor C2 and diode D1; one end of the resistor R7 is connected with the anode of the diode D1 to input the voltage signal V4, the other end of the resistor R7 is connected with the cathode of the diode D1, one end of the capacitor C1 and one end of the capacitor C2 to output the voltage signal V5, the other end of the capacitor C1 is used for inputting the power supply voltage Vdd, and the other end of the capacitor C2 is used for connecting the ground.

[0025] As a specific embodiment of the constant current control circuit, it comprises resistance R8, resistance R9, resistance R10, resistance R11, resistance R12, resistance R13, capacitor C3, diode D2, MOS tube Q1 and operational amplifier U1B; one end of the resistance R8 is used for inputting the voltage signal V1, the other end of the resistance R8 is connected to one end of the resistance R10, one end of the resistance R11 and the same direction input end of the operational amplifier U1B at the same time, and outputs the third reference voltage V6, one end of the resistance R9 is used for inputting the first reference voltage V2, the other end of the resistance R9 is connected to the other end of the resistance R10 and the drain of the MOS tube Q1 at the same time, the other end of the resistance R11 is connected to the source of the MOS tube Q1, the gate of the MOS tube Q1 is used for inputting the voltage signal V5, one end of the resistance R12 is connected to the negative direction input end of the operational amplifier U1B and one end of the capacitor C3 at the same time, the other end of the resistance R12 is used for grounding, the other end of the capacitor C3 is connected to one end of the resistance R13, the other end of the resistance R13 is connected to the output end of the operational amplifier U1B and the cathode of the diode D2 at the same time, and the anode of the diode D2 outputs the constant current control signal V8.

[0026] An overcurrent protection circuit, characterized in that it comprises:

[0027] A current detection circuit comprising resistance R1; one end of the resistance R1 is used for inputting the output current of the switching power supply, and the other end of the resistance R1 outputs a voltage signal V1 representing the size of the output current;

[0028] A reference source generation circuit comprising resistance R2 and 431 chip U2; one end of the resistance R2 is used for inputting a power supply voltage Vdd, the other end of the resistance R2 is connected to the cathode of the 431 chip U2 and the reference end of the 431 chip U2 at the same time, and outputs a first reference voltage V2, and the anode of the 431 chip U2 is used for grounding;

[0029] A timing control circuit comprising resistance R3, resistance R4, resistance R5 and operational amplifier U1A; one end of the resistance R3 is connected to the negative direction input end of the operational amplifier U1A, and the other end of the resistance R3 is used for grounding, one end of the resistance R4 is used for inputting the voltage signal V1, the other end of the resistance R4 is connected to one end of the resistance R5 and the same direction input end of the operational amplifier U1A at the same time, and outputs a second reference voltage V3, the other end of the resistance R5 is used for inputting the first reference voltage V2, and the output end of the operational amplifier U1A outputs a voltage signal V4;

[0030] Timing circuit, including resistance R7, capacitor C1, capacitor C2 and diode D1;The one end of resistance R7 is connected with the anode of diode D1 together input voltage signal V4, the other end of resistance R7 is connected with the cathode of diode D1, one end of capacitor C1 and one end of capacitor C2 simultaneously and then output voltage signal V5, the other end of capacitor C1 is used to input supply voltage Vdd, the other end of capacitor C2 is used to ground;

[0031] Constant current control circuit, including resistance R8, resistance R9, resistance R10, resistance R11, resistance R12, resistance R13, capacitor C3, diode D2, MOS tube Q1 and operational amplifier U1B;The one end of resistance R8 is used to input voltage signal V1, the other end of resistance R8 is connected with one end of resistance R10, one end of resistance R11 and the same direction input end of operational amplifier U1B simultaneously and then output third reference voltage V6, the one end of resistance R9 is input first reference voltage V2, the other end of resistance R9 is connected with the other end of resistance R10 and the drain of MOS tube Q1, the other end of resistance R11 is connected with the source of MOS tube Q1, the gate of MOS tube Q1 is input voltage signal V5, one end of resistance R12 is connected with the negative direction input end of operational amplifier U1B and one end of capacitor C3 simultaneously, the other end of resistance R12 is used to ground, the other end of capacitor C3 is connected with one end of resistance R13, the other end of resistance R13 is connected with the output end of operational amplifier U1B and the cathode of diode D2 simultaneously, the anode of diode D2 outputs constant current control signal V8.

[0032] Further, the timing control circuit further includes resistance R6, one end of resistance R6 is connected with the same direction input end of operational amplifier U1A, and the other end of resistance R6 is connected with the output end of operational amplifier U1A.

[0033] As a first aspect of the present application, the technical scheme of the switching power supply is as follows:

[0034] A switching power supply, characterized in that it comprises the over-current protection circuit according to any one of claims 1 to 11.

[0035] The working principle of the present application will be analyzed in detail in combination with specific embodiments, and the beneficial effects of the present application compared with the prior art are analyzed as follows:

[0036] For the switching power supply, the existing over-current protection mainly has two schemes:

[0037] The first solution is to adopt single-stage output power limitation, when the switching power supply load is a relay, a motor driving system or the load works in a frequent start-stop state, the output voltage of the switching power supply is reduced when the output current of the switching power supply exceeds the rated value, so that the total output power of the switching power supply is reduced, the demand of the switching power supply load for large current during starting is met, and the risk of damage of the switching power supply during starting is reduced. Although this solution can increase the transient current output capability of the switching power supply, the following disadvantages exist in this control solution:

[0038] (1) The output voltage reduction of the switching power supply will cause the load to fail to start normally;

[0039] (2) When the load current exceeds the rated current of the internal device of the switching power supply, the internal device of the switching power supply will be broken down by the current, and the switching power supply will be damaged.

[0040] The second solution is to adopt a hiccup protection mode, the output of the switching power supply is turned off when the output current of the switching power supply exceeds the limit current value, and the output is established again after a period of time, so that the switching power supply is prevented from being damaged due to continuous exceeding of the limit power. Although this solution can meet the demand of increasing the transient current output capability of the switching power supply to a certain extent, the following disadvantages exist in this control solution:

[0041] (1) The switching power supply has no protection function when the output current is greater than the rated value and less than the limit current value, and the switching power supply will be damaged due to overheating when working in this output current range for a long time;

[0042] (2) The limit current value of the internal device of the switching power supply is generally set to be within 1.5 times, which cannot meet the demand that the transient current during starting of the load will be 2-3 times of the normal working current of the switching power supply.

[0043] The overcurrent protection circuit of the present application effectively overcomes the disadvantages of the above two solutions, and the specific analysis is as follows:

[0044] (1) The overcurrent protection circuit provided by the present application can output the overcurrent control signal of the constant current control circuit to control the switching power supply to output constant current at the first current value when the output current of the switching power supply is between the rated current value and the limit current value, and the switching power supply can output constant current at the first current value after the set time value is reached through the set timing control circuit and timing circuit, so that the output capability of the switching power supply under the transient over-power state is met, and the switching power supply can exceed the rated current output within the specified time, so that the switching power supply is prevented from being damaged due to overheating;

[0045] (2) When the output current of the switching power supply reaches the limit current value, the overcurrent control signal output by the constant current control circuit can trigger the switching power supply to immediately output a second current value, and through the set timing control circuit and timing circuit, the switching power supply outputs a first current value after reaching the set value of the timing time, so as to ensure that the output current of the switching power supply will not be greater than the rated current value of the internal device of the switching power supply, thereby preventing the device from being overcurrent breakdown. BRIEF DESCRIPTION OF DRAWINGS

[0046] The application will be further described below in combination with the drawings and specific embodiments:

[0047] Figure 1 The figure is a principle diagram of the two-stage overcurrent protection of the application.

[0048] Figure 2 The figure is a principle diagram of a specific embodiment of the overcurrent protection circuit of the application.

[0049] Figure 3 The figure is a principle diagram of the switching power supply applied to the overcurrent protection circuit of the application. DETAILED DESCRIPTION

[0050] In order to make the technical scheme of the application clearer, the embodiments of the application will be described clearly and completely in combination with the drawings. Obviously, the described embodiments are part of the embodiments of the application, and other various forms of modification, replacement or change of the application made by those skilled in the art without creative labor still belong to the protection scope of the application.

[0051] Figure 1 The figure is a principle diagram of the overcurrent protection of the application, which is applied to a switching power supply. The switching power supply comprises a power conversion unit and a feedback control unit, and the overcurrent protection circuit comprises:

[0052] A current detection circuit is used to convert the output current of the switching power supply into a voltage signal V1 representing the size of the output current.

[0053] A reference source generation circuit is used to generate a first reference voltage V2.

[0054] A timing control circuit is used to superimpose and divide the voltage signal V1 and the first reference voltage V2 to output a second reference voltage V3, and judge the size of the second reference voltage V3 and a ground voltage signal to output a voltage signal V4.

[0055] A timing circuit is used to perform timing according to the voltage signal V4 and output a voltage signal V5.

[0056] The constant current control circuit is used for superimposing and voltage dividing the voltage signal V1 and the first reference voltage V2 according to the level state of the voltage signal V5, outputting a third reference voltage V6, and judging the size of the third reference voltage V6 and the ground voltage signal, and outputting a constant current control signal V8 which is input to the feedback control end of the feedback control unit.

[0057] When the absolute value of the voltage signal V1 is less than or equal to the first set value, the constant current control signal V8 does not control the switching power supply to act.

[0058] When the absolute value of the voltage signal V1 is greater than the first set value and less than or equal to the second set value, the constant current control signal V8 controls the switching power supply to output a constant current with the first current value when the timing time of the timing circuit reaches the timing time set value.

[0059] When the absolute value of the voltage signal V1 is greater than the second set value, the constant current control signal V8 immediately controls the switching power supply to output a constant current with the second current value, and the constant current control signal V8 controls the switching power supply to output a constant current with the first current value when the timing time of the timing circuit reaches the timing time set value.

[0060] The output current rating of the switching power supply ≤ the first current value ≤ the second current value ≤ the output current limit of the switching power supply.

[0061] The power conversion unit is used for converting one kind of electric energy into another kind of electric energy, or realizing electrical isolation of input and output, and can be a forward topology, a flyback topology or other topologies.

[0062] The feedback control unit is used for controlling the switching power supply to output a constant voltage, and can be a feedback control circuit designed by discrete devices, a control circuit designed by a dedicated control chip, a single-chip microcomputer combined with a peripheral circuit, and other implementation schemes.

[0063] The feedback control end Reduce of the feedback control unit is used for receiving the constant current control signal, and the feedback control unit controls the switching power supply to output a constant current according to the constant current control signal.

[0064] Figure 2 The schematic diagram of a specific embodiment of the overcurrent protection circuit of the application is shown in FIG. 1. Figure 2 The composition and connection relationship of each unit circuit are as follows:

[0065] The current detection circuit 100 includes a resistor R1; one end of the resistor R1 is used for inputting the output current of the switching power supply, and the other end of the resistor R1 outputs a voltage signal V1 representing the size of the output current.

[0066] It should be noted that the actual current direction on the resistor R1 is from the load to the power conversion unit output negative terminal, so the voltage signal V1 representing the output current size at the current detection output terminal is negative.

[0067] The reference source generating circuit 200 includes the resistor R2 and the 431 chip U2; one end of the resistor R2 is used to input the power supply voltage Vdd, the other end is connected to the cathode of the 431 chip U2 and the reference terminal of the 431 chip U2 to output the first reference voltage V2, and the anode of the 431 chip U2 is used to ground.

[0068] The timing control circuit 300 includes the resistor R3, the resistor R4, the resistor R5 and the operational amplifier U1A; one end of the resistor R3 is connected to the negative input terminal of the operational amplifier U1A, and the other end is used to ground, one end of the resistor R4 is inputted with the voltage signal V1, and the other end is connected to one end of the resistor R5 and the same input terminal of the operational amplifier U1A to output the second reference voltage V3, the other end of the resistor R5 is inputted with the first reference voltage V2, and the output terminal of the operational amplifier U1A outputs the voltage signal V4.

[0069] The timing circuit 400 includes the resistor R7, the capacitor C1, the capacitor C2 and the diode D1; one end of the resistor R7 is connected to the anode of the diode D1 to input the voltage signal V4, the other end of the resistor R7 is connected to the cathode of the diode D1, one end of the capacitor C1 and one end of the capacitor C2 to output the voltage signal V5, the other end of the capacitor C1 is used to input the power supply voltage Vdd, and the other end of the capacitor C2 is used to ground.

[0070] The constant current control circuit 500 includes the resistor R8, the resistor R9, the resistor R10, the resistor R11, the resistor R12, the resistor R13, the capacitor C3, the diode D2, the MOS tube Q1 and the operational amplifier U1B; one end of the resistor R8 is used to input the voltage signal V1, the other end of the resistor R8 is connected to one end of the resistor R10, one end of the resistor R11 and the same input terminal of the operational amplifier U1B to output the third reference voltage V6, one end of the resistor R9 is inputted with the first reference voltage V2, the other end of the resistor R9 is connected to the other end of the resistor R10 and the drain of the MOS tube Q1, the other end of the resistor R11 is connected to the source of the MOS tube Q1, the gate of the MOS tube Q1 is inputted with the voltage signal V5, one end of the resistor R12 is connected to the negative input terminal of the operational amplifier U1B and one end of the capacitor C3, the other end of the resistor R12 is used to ground, one end of the capacitor C3 is connected to one end of the resistor R13, the other end of the resistor R13 is connected to the output terminal of the operational amplifier U1B and the cathode of the diode D2, and the anode of the diode D2 outputs the constant current control signal V8.

[0071] Figure 2 The working principles of the various unit circuits are as follows:

[0072] The resistance R1 in the current detection circuit 100 converts the load current into a voltage signal V1 representing the magnitude of the output current, Figure 2 The current direction is from the load ground to the power conversion unit output negative terminal, so the voltage signal V1 is negative voltage;

[0073] The resistance R2 in the reference source generation circuit supplies power to the 431 chip U2, and the reference terminal of the 431 chip U2 is connected to the cathode, constituting a voltage reference source and outputting a stable first reference voltage V2.

[0074] The timing control circuit 300 divides the voltage value obtained by superimposing the voltage signal V1 and the first reference voltage V2 through the resistances R4, R5, and R6, obtains a second reference voltage V3, and outputs a voltage signal V4 after comparing the second reference voltage V3 with the ground voltage. The resistance R3 provides impedance matching for the negative input terminal of the comparator U1A, so that the comparator U1A can work normally. The resistance R6 makes the value of the second reference voltage V3 when the voltage signal V4 is high Vdd greater than the voltage value when the voltage signal V4 is low 0V, so that the circuit has a hysteresis function and avoids voltage signal V4 oscillating between high Vdd and low 0V.

[0075] The timing circuit 400 relies on the charging and discharging of the capacitors C1 and C2 to realize timing. The resistance R7 discharges the capacitors C1 and C2 by heat dissipation. When the capacitors C1 and C2 are discharged, the voltage value of the voltage signal V5 gradually decreases. When it decreases to the gate turn-on threshold of the MOS tube Q1, the MOS tube Q1 is turned off. The discharge time of the capacitors C1 and C2 is recorded as the timing time setting value. The calculation formula is as follows:

[0076]

[0077] In formula 1, R7 is the resistance value of the resistance R7, C1 is the capacitance value of the capacitor C1, C2 is the capacitance value of the capacitor C2, Vdd is the voltage value of the supply voltage Vdd input to the other end of the capacitor C1, and Vgs(th) is the gate turn-on threshold voltage value of the MOS tube Q1.

[0078] The diode D1 in the timing circuit 400 clamps the voltage signal V5 to a high level when the voltage signal V4 is high. This high level can be maintained by the fully charged capacitors C1 and C2.

[0079] The constant current control current is superimposed on the voltage value of the voltage signal V1 and the first reference voltage V2 through the resistors R8, R9, R10 and R11 to obtain the third reference voltage V6, and the third reference voltage V6 is compared with the ground voltage to output the voltage signal V7. The voltage signal V7 is output after passing through the unidirectional diode D2 to output the constant current control signal V8. The resistor R12 provides impedance matching for the negative input terminal of the comparator U1A, so that the comparator U1A can work normally. The capacitor C3 and the resistor R13 provide compensation for the comparator U1B, so that the response speed of the overcurrent protection circuit matches the response speed of the feedback control unit of the switching power supply, thereby avoiding causing a large current overshoot.

[0080] The voltage value of the second reference voltage V3 corresponding to the high level Vdd of the voltage signal V4 is denoted as V3a, the voltage value of the second reference voltage V3 corresponding to the low level 0V of the voltage signal V4 is denoted as V3b, the third reference voltage V6 corresponding to the conduction of the MOS tube Q1 is denoted as V6a, the third reference voltage V6 corresponding to the turn-off of the MOS tube Q1 is denoted as V6b, and the resistance value of each resistor is denoted as the code of the resistor. Then, the following equation is obtained:

[0081]

[0082] According to the equations 2 to 5 and the circuit shown in Figure 2 , by setting the first reference voltage V2, the resistance values of the resistors and the high level Vdd to set V3 and V6, the following conditions can be met:

[0083] (1) When the absolute value of the voltage signal V1 is less than or equal to the first set value, the constant current control signal V8 will not trigger the switching power supply to act;

[0084] (2) When the absolute value of the voltage signal V1 is greater than the first set value and less than or equal to the second set value, the constant current control signal V8 will trigger the switching power supply to enter the first constant current working state when the timing time of the timing circuit reaches the timing time set value;

[0085] (3) When the absolute value of the voltage signal V1 is greater than the second set value, the constant current control signal V8 will immediately trigger the switching power supply to enter the second constant current working state, and the constant current control signal V8 will trigger the switching power supply to enter the first constant current working state when the timing time of the timing circuit reaches the timing time set value.

[0086] According to the principle block diagram shown in Figure 3 , a switching power supply with the following parameters is designed as an example to analyze how the above control logic is designed and implemented:

[0087] Input voltage: 9-18VDC

[0088] Output voltage: 48VDC

[0089] Output current rating: 2.1A

[0090] Output current limit: 5A

[0091] Allowable overcurrent output time: 3S

[0092] The overload protection requirements of the switch power supply after adopting the overcurrent protection circuit of the application under different current loads are shown in Table 1:

[0093] Table 1

[0094]

[0095] As can be seen from the above table, the switch power supply after adopting the overcurrent protection circuit of the application can not only realize peak current limitation of the load, but also realize specified time output of overrated output load within the peak load range, constant current protection after exceeding the specified time, and self-recovery after fault removal. In combination with the design of the main power conversion unit, the short-time overload demand of the load is met and the safe and stable work of the product is ensured.

[0096] The parameters of the application corresponding to the above switch power supply are as follows:

[0097] The first current value: 2.5A;

[0098] The second current value: 4.5A;

[0099] The timing time setting value: 3.5S;

[0100] The first setting value: K*2.1A*R1, K is the proportion of the output current of the switch power supply when the output current is the output current rating 2.1A, flowing through the resistor R1;

[0101] The second setting value: K*5A*R1, K is the proportion of the output current of the switch power supply when the output current is the output current limit 5A, flowing through the resistor R1;

[0102] When the size of the resistor R1 is set, the first setting value and the second setting value are fixed values;

[0103] When the timing time setting value is determined, the resistance value of the resistor R1, the capacitance value of the capacitor C1 and the capacitor C2 can be determined according to formula 1;

[0104] The resistance values of other resistors need to meet the control logic in three states at the same time, which are as follows:

[0105] (1) When the absolute value of the voltage signal V1 is less than or equal to the first setting value

[0106] To realize the above control logic, the second reference voltage V3 is required to be greater than or equal to the ground voltage signal 0V, and the third reference voltage V6 is required to be greater than or equal to the ground voltage signal 0V;

[0107] When the second reference voltage V3 is greater than or equal to the ground voltage signal 0V, the voltage signal V4 is high, and the voltage value of the second reference voltage V3 needs to be calculated according to formula 2, which is V3a. Through formula 2, the configuration mode of the resistance values of the related resistors can be designed.

[0108] The voltage signal V4 is high, so the voltage signal V5 is high, the MOS tube Q1 is turned on, and the third reference voltage V6 needs to be calculated according to formula 4, which is V6a. Since the third reference voltage V6 is required to be greater than or equal to the ground voltage signal 0V, through formula 4, the configuration mode of the resistance values of the related resistors can be designed.

[0109] Since the third reference voltage V6 is greater than or equal to the ground voltage signal 0V, the voltage signal V7 at the output end of the comparator U1B is high, the diode D2 is reverse-biased and cut off, and the constant current control signal V8 is high, which does not affect the normal work of the power conversion unit and the feedback control unit in the switching power supply.

[0110] (2) When the absolute value of the voltage signal V1 is greater than the first set value and less than or equal to the second set value

[0111] To realize the above control logic, the second reference voltage V3 is required to be less than the ground voltage signal 0V, the third reference voltage V6 is required to be greater than or equal to the ground voltage signal 0V before the timing time set value is reached, and the third reference voltage V6 is required to be less than the ground voltage signal 0V after the timing time set value is reached.

[0112] When the second reference voltage V3 is less than the ground voltage signal 0V, the voltage signal V4 is low, and the voltage value of the second reference voltage V3 needs to be calculated according to formula 3, which is V3b. Through formula 3, the configuration mode of the resistance values of the related resistors can be designed.

[0113] Further, since the voltage signal V4 is low, the diode D1 is reverse-biased and cut off, the capacitors C1 and C2 start to discharge through the resistor R7, and the voltage value of the voltage signal V5 gradually decreases. When it decreases to the gate turn-on threshold of the MOS tube Q1 (i.e. the preset value), the MOS tube Q1 is turned off.

[0114] Before the timing time set value is reached, i.e. before the MOS tube Q1 is turned off, the voltage value of the third reference voltage V6 needs to be calculated according to formula 4, which is V6a. Since the third reference voltage V6 is required to be greater than the ground voltage signal 0V, through formula 4, the configuration mode of the resistance values of the related resistors can be designed.

[0115] Before the time setting value reaches, since the third reference voltage V6 is greater than or equal to the ground voltage signal 0V, the voltage signal V7 at the output end of the comparator U1B is high, the diode D2 is reverse cut-off, and the constant current control signal V8 is high, which does not affect the normal work of the power conversion unit and the feedback control unit in the switching power supply, thereby meeting the output capacity of the switching power supply in the transient over-power state;

[0116] After the time setting value reaches, i.e. after the MOS tube Q1 is turned off, the voltage value of the third reference voltage V6 needs to be calculated according to formula 5, which is V6b. Since the third reference voltage V6 is required to be less than the ground voltage signal 0V, the configuration mode of the values of the related resistances can be designed through formula 5.

[0117] After the time setting value reaches, since the third reference voltage V6 is less than the ground voltage signal 0V, the voltage signal V7 at the output end of the comparator U1B is low, the diode D2 is forward conducting, and the constant current control signal V8 will control the switching power supply to output constant current with the first current value. Since the output current rating of the switching power supply ≤ the first current value ≤ the second current value ≤ the output current limit of the switching power supply, the switching power supply can only exceed the rated current output within the specified time by setting the time, thereby avoiding overheating damage of the switching power supply.

[0118] (3) When the absolute value of the voltage signal V1 is greater than the second setting value

[0119] To realize the above control logic, the second reference voltage V3 is required to be less than the ground voltage signal 0V, and the third reference voltage V6 is required to be less than the ground voltage signal 0V.

[0120] The difference between this abnormal state and the second one is that the third reference voltage V6 is required to be less than the ground voltage signal 0V before and after the time setting value reaches. According to the setting requirement of the third reference voltage V6 in this state, the configuration mode of the values of the related resistances can be designed according to formula 4 and formula 5.

[0121] Before the time setting value reaches, the voltage signal V5 is high, the MOS tube Q1 is conducting, the third reference voltage V6 is less than the ground voltage signal 0V, the voltage signal V7 at the output end of the comparator U1B is low, the diode D2 is forward conducting, and the constant current control signal V8 will immediately control the switching power supply to output constant current with the second current value, which is the same as the second state.

[0122] After the time setting value reaches, MOS tube Q1 is turned off due to the low voltage signal V5, the third reference voltage V6 is less than the ground voltage signal 0V, the voltage signal V7 at the output end of the comparator U1B is low, the diode D2 is forward-biased, and the constant current control signal V8 controls the switching power supply to output a first current value, so that the output current of the switching power supply is less than the first current value, the second current value and the limit value of the output current of the switching power supply, thereby preventing the output current of the switching power supply from being greater than the rated current value of the internal device of the switching power supply and causing the device to be overcurrent broken.

[0123] The configuration mode of the resistance values of the related resistors in the above three states is different, and the configuration mode that can meet the three states at the same time is selected, so that the control logic of the application is realized.

[0124] As shown in Figure 3 The switching power supply principle block diagram applied to the overcurrent protection circuit of the application is shown, the overcurrent protection circuit of the application can be regarded as a two-terminal component as a whole, the input end of the current detection circuit is one end of the two-terminal component, and the output end of the constant current control circuit is the other end of the two-terminal component, and the application scenarios include the following two cases:

[0125] (1) The two-terminal component is designed in the switching power supply by the switching power supply manufacturer, and is placed in the line of the positive output end or the line of the negative output end of the switching power supply, Figure 3 The circuit shown embodies the negative output end of the switching power supply, and the advantage of this is that the negative output end is a low-voltage end, and no additional isolation component needs to be designed;

[0126] (2) The two-terminal component is designed in the circuit board of the user of the switching power supply.

[0127] After the overcurrent protection circuit of the application is added between the switching power supply and the load in the above two ways, when the absolute value of the voltage signal V1 is greater than the first set value and less than or equal to the second set value, the timing circuit 400 starts timing, and when the timing time setting value is reached, the overcurrent protection circuit of the application interferes with the feedback control unit to control the switching power supply to output a first current value, which can improve the output capability of the switching power supply in the transient over-power state, and also set the waiting time, so that the switching power supply exceeds the rated current output within a specified time, thereby avoiding overheating damage.

[0128] When the absolute value of the voltage signal V1 is greater than the third set value, the overcurrent protection circuit of the application immediately interferes with the feedback control unit to control the switching power supply to output a second current value, and the timing circuit 400 starts timing, and when the timing time setting value is reached, the switching power supply is controlled to output a first current value, so that the output current of the switching power supply is less than the rated current value of the internal device of the switching power supply, thereby preventing the device from being overcurrent broken.

[0129] The present application is not limited to the above-described specific embodiments, and according to the above-described content, other various forms of equivalent modifications, substitutions or changes can be made in accordance with ordinary technical knowledge and means in the art without departing from the above-described basic technical idea of the present application, and all fall within the scope of protection of the present application.

Claims

1. An overcurrent protection circuit applied to a switching power supply, the switching power supply comprising a power conversion unit and a feedback control unit, characterized in that, The over-current protection circuit comprises: a current detection circuit for converting an output current of the switching power supply into a voltage signal V1 representing the magnitude of the output current; a reference source generation circuit for generating a first reference voltage V2; a timing control circuit for superimposing and dividing the voltage signal V1 and the first reference voltage V2 to output a second reference voltage V3, and judging the magnitude of the second reference voltage V3 and a ground voltage signal to output a voltage signal V4; a timing circuit for timing and outputting a voltage signal V5 according to the voltage signal V4; a constant current control circuit for superimposing and dividing the voltage signal V1 and the first reference voltage V2 according to the level state of the voltage signal V5 to output a third reference voltage V6, and judging the magnitude of the third reference voltage V6 and a ground voltage signal to output a constant current control signal V8, which is input to a feedback control end of the feedback control unit; when the absolute value of the voltage signal V1 is less than or equal to a first set value, the constant current control signal V8 does not control the switching power supply to operate; when the absolute value of the voltage signal V1 is greater than the first set value and less than or equal to a second set value, the constant current control signal V8 controls the switching power supply to output a first current value when the timing time of the timing circuit reaches a timing time set value; when the absolute value of the voltage signal V1 is greater than the second set value, the constant current control signal V8 immediately controls the switching power supply to output a second current value, and the constant current control signal V8 controls the switching power supply to output the first current value when the timing time of the timing circuit reaches the timing time set value; the output current rating of the switching power supply ≤ the first current value ≤ the second current value ≤ the output current limit of the switching power supply.

2. The overcurrent protection circuit of claim 1, wherein: the value of the second reference voltage V3 corresponding to the high level of the voltage signal V4 is denoted as V3a, the value of the second reference voltage V3 corresponding to the low level of the voltage signal V4 is denoted as V3b, the value of the third reference voltage V6 corresponding to the high level of the voltage signal V5 is denoted as V6a, and the value of the third reference voltage V6 corresponding to the low level of the voltage signal V5 is denoted as V6b, wherein V3b < V6b < V3a < V6a.

3. The over-current protection circuit according to claim 1, wherein: ​ When the absolute value of the voltage signal V1 is less than or equal to the first set value, the second reference voltage V3 is greater than or equal to the ground voltage signal, the voltage signal V4 is high, the voltage signal V5 is high, the third reference voltage V6 is greater than or equal to the ground voltage signal, the voltage signal V7 obtained by comparing the third reference voltage V6 and the ground voltage signal through an operational amplifier is high, and the constant current control signal V8 is high, which does not affect the working state of the switching power supply. When the absolute value of the voltage signal V1 is greater than the first set value and less than or equal to the second set value, the second reference voltage V3 is less than the ground voltage signal 0V, the voltage signal V4 is low, the voltage value of the voltage signal V5 gradually decreases from high to a preset value, the time required for the decrease is the timing time set value, the third reference voltage V6 is greater than or equal to the ground voltage signal before the timing time set value is reached, the voltage signal V7 is high in this stage, the constant current control signal V8 is high, which does not affect the working state of the switching power supply, and the third reference voltage V6 is less than the ground voltage signal after the timing time set value is reached, the voltage signal V7 is low in this stage, and the control signal V8 controls the switching power supply to output constant current with the first current value. When the absolute value of the voltage signal V1 is greater than the second set value, the second reference voltage V3 is less than the ground voltage signal, the voltage signal V4 is low, the voltage value of the voltage signal V5 gradually decreases from high to a preset value, the time required for the decrease is the timing time set value, the third reference voltage V6 is less than the ground voltage signal before the timing time set value is reached, the voltage signal V7 is low in this stage, the constant current control signal V8 immediately controls the switching power supply to output constant current with the second current value, the third reference voltage V6 is less than the ground voltage signal after the timing time set value is reached, the voltage signal V7 is low in this stage, and the control signal V8 controls the switching power supply to output constant current with the first current value.

4. The overcurrent protection circuit of claim 1, wherein: The current detection circuit comprises a resistor R1, one end of the resistor R1 is used for inputting the output current of the switching power supply, and the other end of the resistor R1 outputs the voltage signal V1.

5. The overcurrent protection circuit of claim 1, wherein: The reference source generation circuit comprises a resistor R2 and a 431 chip U2, one end of the resistor R2 is used for connecting a power supply voltage Vdd, the other end of the resistor R2 is connected to the cathode of the 431 chip U2 and the reference end of the 431 chip U2, and the anode of the 431 chip U2 is used for grounding.

6. The overcurrent protection circuit of claim 1, wherein: The timing control circuit comprises resistance R3, resistance R4, resistance R5 and operational amplifier U1A; one end of the resistance R3 is connected to the negative input end of the operational amplifier U1A, and the other end is used for grounding; one end of the resistance R4 is used for inputting the voltage signal V1, and the other end is used for outputting the second reference voltage V3 after being connected to one end of the resistance R5 and the same input end of the operational amplifier U1A; the other end of the resistance R5 is used for inputting the first reference voltage V2; and the output end of the operational amplifier U1A is used for outputting the voltage signal V4.

7. The overcurrent protection circuit of claim 6, wherein: The timing control circuit further comprises resistance R6, one end of the resistance R6 is connected to the same input end of the operational amplifier U1A, and the other end is connected to the output end of the operational amplifier U1A.

8. The overcurrent protection circuit of claim 1, wherein: The timing circuit comprises resistance R7, capacitor C1, capacitor C2 and diode D1; one end of the resistance R7 is connected to the anode of the diode D1 to input the voltage signal V4; the other end of the resistance R7 is used for outputting the voltage signal V5 after being connected to the cathode of the diode D1, one end of the capacitor C1 and one end of the capacitor C2; the other end of the capacitor C1 is used for inputting the supply voltage Vdd; and the other end of the capacitor C2 is used for grounding.

9. The overcurrent protection circuit of claim 1, wherein: The constant current control circuit comprises resistance R8, resistance R9, resistance R10, resistance R11, resistance R12, resistance R13, capacitor C3, diode D2, MOS tube Q1 and operational amplifier U1B; one end of the resistance R8 is used for inputting the voltage signal V1; the other end of the resistance R8 is used for outputting the third reference voltage V6 after being connected to one end of the resistance R10, one end of the resistance R11 and the same input end of the operational amplifier U1B; one end of the resistance R9 is used for inputting the first reference voltage V2; the other end of the resistance R9 is used for connecting to the other end of the resistance R10 and the drain of the MOS tube Q1; the other end of the resistance R11 is used for connecting to the source of the MOS tube Q1; the gate of the MOS tube Q1 is used for inputting the voltage signal V5; one end of the resistance R12 is used for connecting to the negative input end of the operational amplifier U1B and one end of the capacitor C3; the other end of the resistance R12 is used for grounding; one end of the capacitor C3 is used for connecting to one end of the resistance R13; the other end of the resistance R13 is used for connecting to the output end of the operational amplifier U1B and the cathode of the diode D2; and the anode of the diode D2 is used for outputting the constant current control signal V8.

10. An overcurrent protection circuit, characterized by It comprises: a current detection circuit comprising resistance R1; one end of the resistance R1 is used for inputting the output current of the switching power supply; and the other end of the resistance R1 is used for outputting the voltage signal V1 representing the size of the output current; a reference source generation circuit comprising resistance R2 and 431 chip U2; one end of the resistance R2 is used for grounding the supply voltage Vdd; the other end of the resistance R2 is used for outputting the first reference voltage V2 after being connected to the cathode of the 431 chip U2 and the reference end of the 431 chip U2; and the anode of the 431 chip U2 is used for grounding. Timing control circuit, comprising resistance R3, resistance R4, resistance R5 and operational amplifier U1A; one end of the resistance R3 is connected to the negative input end of the operational amplifier U1A, and the other end is used for grounding; one end of the resistance R4 inputs the voltage signal V1, and the other end simultaneously connects one end of the resistance R5 and the same input end of the operational amplifier U1A to output the second reference voltage V3; the other end of the resistance R5 inputs the first reference voltage V2; and the output end of the operational amplifier U1A outputs the voltage signal V4; Timing circuit, comprising resistance R7, capacitor C1, capacitor C2 and diode D1; one end of the resistance R7 is connected to the anode of the diode D1 to input the voltage signal V4; the other end of the resistance R7 simultaneously connects the cathode of the diode D1, one end of the capacitor C1 and one end of the capacitor C2 to output the voltage signal V5; the other end of the capacitor C1 is used for inputting the supply voltage Vdd; and the other end of the capacitor C2 is used for grounding; Constant current control circuit, comprising resistance R8, resistance R9, resistance R10, resistance R11, resistance R12, resistance R13, capacitor C3, diode D2, MOS tube Q1 and operational amplifier U1B; one end of the resistance R8 is used for inputting the voltage signal V1; the other end of the resistance R8 simultaneously connects one end of the resistance R10, one end of the resistance R11 and the same input end of the operational amplifier U1B to output the third reference voltage V6; one end of the resistance R9 inputs the first reference voltage V2; the other end of the resistance R9 simultaneously connects the other end of the resistance R10 and the drain of the MOS tube Q1; the other end of the resistance R11 connects the source of the MOS tube Q1; the gate of the MOS tube Q1 inputs the voltage signal V5; one end of the resistance R12 simultaneously connects the negative input end of the operational amplifier U1B and one end of the capacitor C3; the other end of the resistance R12 is used for grounding; the other end of the capacitor C3 connects one end of the resistance R13; the other end of the resistance R13 simultaneously connects the output end of the operational amplifier U1B and the cathode of the diode D2; and the anode of the diode D2 outputs the constant current control signal V8.

11. The overcurrent protection circuit of claim 10, wherein: The timing control circuit further comprises resistance R6, one end of the resistance R6 is connected to the same input end of the operational amplifier U1A, and the other end is connected to the output end of the operational amplifier U1A.

12. A switched mode power supply characterized by: The overcurrent protection circuit comprises the overcurrent protection circuit according to any one of claims 1 to 11.

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