An overcurrent protection method, an overcurrent protection circuit and a power supply using the same

Abstract

The present invention discloses an overcurrent protection method, an overcurrent protection circuit and a power supply using the same. A first signal representing an output voltage is obtained from a power supply, an overcurrent threshold signal is obtained according to the first signal, a second signal representing an output current is obtained from the power supply, an overcurrent protection signal is obtained according to the second signal and the overcurrent threshold signal. When the second signal is greater than the overcurrent threshold signal, it represents that the output current of the power supply is overcurrent, and the power supply performs overcurrent protection. The overcurrent threshold signal is equal to a first overcurrent threshold when the first signal is below a first reference value, and is less than the first overcurrent threshold when the first signal is greater than the first reference value.

Description

Technical Field

[0001] The present invention relates to electronic circuit technology, and in particular to an overcurrent protection method, an overcurrent protection circuit and a power supply using the same. Background Art

[0002] For current mobile phones, laptops, etc. that require adapters with wide output voltages, there are corresponding full-load powers under different output voltages. According to the OPP (over power protection) converter, there will often be a high over power protection point under low voltage output conditions. Especially for the current PD chargers, considering the requirements of safety certification, there will generally be LPS (limited power supply) restrictions, which require that the output current cannot exceed 8A under different output voltages, so corresponding over current protection is required.

[0003] Taking the flyback converter as an example, its OPP (over power protection) is generally limited by the maximum peak current of the primary side. For applications working at full load in the critical continuous mode of the inductor current, when the input voltage is 90VAC to 264VAC, due to the delay of the peak current comparator and the difference in operating frequency, the over power point varies greatly under different inputs, and it is often necessary to add an input voltage comparison circuit. Generally, the input voltage information is compensated into the current sampling, so that the output power difference under different inputs is not large.

[0004] Figure 1 It is the over-power protection and over-current protection curve diagram of the flyback converter in the prior art, where Vvs is the first signal representing the output voltage, Vio_e is the second signal representing the output current, the dotted OPP curve is the over-power protection curve designed according to the minimum input voltage, and the solid OCP curve is the over-current protection curve. The OCP curve is a straight line, and the over-current threshold is V ocpA , the OCP curve and the OPP curve intersect at point A, and the first signal Vvs value corresponding to point A is V A . When the first signal Vvs is less than V A When the OCP curve is lower than the OPP curve, the overcurrent protection (OCP) is effective. A The overcurrent thresholds are equal within the corresponding output voltage range, and accordingly the current protection points are equal and will not be affected by the input voltage. A When the input voltage increases, the OCP curve is higher than the OPP curve. At this time, the overcurrent protection (OCP) does not work, and the overpower protection (OPP) really works, that is, there is a problem of overcurrent protection failure. As the input voltage increases, the OPP curve will move up, so when the first signal Vvs is greater than V A Within the corresponding output voltage range, the current protection point will change with the input voltage. Summary of the invention

[0005] In view of this, the present invention proposes an overcurrent protection method, an overcurrent protection circuit and a power supply using the same, so as to solve the technical problem of overcurrent protection failure in the prior art.

[0006] According to a first aspect of the present invention, there is provided an overcurrent protection method for performing overcurrent protection on a power supply, the overcurrent protection method comprising:

[0007] Obtaining a first signal representing an output voltage from the power supply, and obtaining an overcurrent threshold signal according to the first signal;

[0008] Obtaining a second signal representing the output current from the power supply, obtaining an overcurrent protection signal according to the second signal and the overcurrent threshold signal, and when the second signal is greater than the overcurrent threshold signal, indicating that the output current of the power supply is overcurrent, the overcurrent protection signal is valid, and the power supply performs overcurrent protection;

[0009] The overcurrent threshold signal is equal to a first overcurrent threshold when the first signal is below a first reference value, and is less than the first overcurrent threshold when the first signal is greater than the first reference value.

[0010] Optionally, when the first signal is greater than the first reference value, the overcurrent threshold signal decreases as the first signal increases.

[0011] Optionally, when the first signal is greater than the first reference value, the overcurrent threshold signal decreases linearly as the first signal increases.

[0012] Optionally, when the first signal is greater than the first reference value, the overcurrent threshold signal linearly decreases in stages as the first signal increases.

[0013] Optionally, when the first signal is greater than the first reference value, in a partial voltage interval of the first signal, the overcurrent threshold signal decreases linearly as the first signal increases, and in the remaining partial voltage interval of the first signal, the overcurrent threshold signal remains unchanged.

[0014] Optionally, the first reference value is adjustable according to output voltage and output current requirements of the power supply.

[0015] Optionally, the slope of the overcurrent threshold signal that linearly decreases as the first signal increases is set to be adjustable.

[0016] Optionally, when the overcurrent protection signal is valid, the power supply performs overcurrent protection by restarting or shutting down.

[0017] According to a second aspect of the present invention, there is provided an overcurrent protection circuit for overcurrent protection of a power supply, the overcurrent protection circuit comprising:

[0018] An output current sampling circuit, sampling from a power supply to output a second signal representing an output current of the power supply;

[0019] an overcurrent threshold generating circuit, receiving a first signal representing an output voltage of the power supply to output an overcurrent threshold signal, wherein the overcurrent threshold signal is equal to a first overcurrent threshold when the first signal is below a first reference value, and is less than the first overcurrent threshold when the first signal is greater than the first reference value;

[0020] A comparison circuit receives the second signal and the overcurrent threshold signal, and outputs an overcurrent protection signal according to a comparison result of the second signal and the overcurrent threshold signal. When the second signal is greater than the overcurrent threshold signal, it indicates that the output current of the power supply is overcurrent, the overcurrent protection signal is valid, and the power supply performs overcurrent protection.

[0021] Optionally, the overcurrent threshold generating circuit includes:

[0022] A first current generating circuit receives the first signal and generates a first current;

[0023] A calculation circuit receives the first current and a preset second current to obtain a third current, wherein the value of the preset second current can be set;

[0024] The over-current threshold generating circuit outputs the over-current threshold signal according to the third current.

[0025] Optionally, when the first signal is below a first reference value, the first current remains unchanged; when the first signal is greater than the first reference value, the first current increases as the first signal increases.

[0026] Optionally, the first current generating circuit includes:

[0027] A first voltage-controlled current source has a first input terminal receiving the first signal, a second input terminal receiving the first reference value, and an output terminal outputting a first controlled current, wherein the first controlled current serves as the first current.

[0028] Optionally, the first current generating circuit further includes:

[0029] The second current-controlled current source receives the first controlled current and outputs a second controlled current, where the second controlled current serves as the first current.

[0030] Optionally, the calculation circuit performs a difference operation on the preset second current and the first current to obtain the third current.

[0031] Optionally, when the second signal is a current signal, the over-current threshold generating circuit outputs the third current as the over-current threshold signal.

[0032] Optionally, when the second signal is a voltage signal, the first current generating circuit further includes an output circuit,

[0033] The output circuit converts the third current into a corresponding voltage signal, and outputs the voltage signal as the overcurrent threshold signal.

[0034] Optionally, the output current sampling circuit samples from a power supply to output the second signal, the power supply is a flyback power supply, and the output current sampling circuit includes:

[0035] A sampling resistor, the first end of which is connected to the primary main power tube, the second end of which is grounded, and the voltage at the first end is the sampling resistor voltage;

[0036] An auxiliary winding voltage splitting circuit outputs an auxiliary winding voltage splitting signal through the auxiliary winding voltage splitting;

[0037] a sampling and holding circuit, receiving the sampling resistor voltage and the auxiliary winding voltage-divided signal, obtaining a sampling peak voltage according to the sampling resistor voltage and the auxiliary winding voltage-divided signal, obtaining a secondary side conduction time according to the auxiliary winding voltage-divided signal, and outputting a sampling and holding signal according to the sampling peak voltage and the secondary side conduction time;

[0038] an averaging circuit, receiving the sample-and-hold signal, and performing an average operation to output the second signal;

[0039] The voltage value of the sample-and-hold signal during the secondary side conduction time is the sample peak voltage.

[0040] According to a third aspect of the present invention, there is provided a power supply, the power supply comprising the overcurrent protection circuit.

[0041] The overcurrent protection circuit generates an overcurrent protection signal, and when the overcurrent protection signal is valid, the power supply performs overcurrent protection.

[0042] Compared with the prior art, the present invention has the following advantages: the overcurrent protection method and overcurrent protection circuit proposed by the present invention have an overcurrent threshold value that varies with the output voltage, and different overcurrent protection points can be set at different output voltages as required to avoid overcurrent protection failure. The overcurrent protection method and overcurrent protection circuit are applicable to any power supply that needs to have different overcurrent protection points at different output voltages. When the overcurrent protection method and overcurrent protection circuit are applied to a flyback converter with overcurrent protection in a primary current estimation mode, the overcurrent threshold signal value can be set to not exceed the corresponding overpower threshold signal value at different output voltages, which can solve the problem that the current protection point will change with the increase of input voltage due to the failure of overcurrent protection, and achieve a constant current protection point under different input voltage conditions at any fixed output voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a curve diagram of over-power protection and over-current protection of a flyback converter in the prior art;

[0044] Figure 2 is a circuit block diagram of an overcurrent protection circuit according to an embodiment of the present invention;

[0045] Figure 3a Schematic diagram of the structure of an overcurrent protection circuit of a flyback converter according to a first embodiment of the present invention;

[0046] Figure 3b A schematic diagram of the structure of an over-current threshold generating circuit according to a first embodiment of the present invention;

[0047] Figure 3c The over-power protection and over-current protection curve diagram of the first embodiment of the present invention;

[0048] Figure 4a A schematic diagram of the structure of an overcurrent protection circuit according to a second embodiment of the present invention;

[0049] Figure 4b is an over-current protection curve diagram of the second embodiment of the present invention;

[0050] Figure 5a A schematic diagram of the structure of an overcurrent protection circuit according to a third embodiment of the present invention;

[0051] Figure 5b This is an over-current protection curve diagram of the third embodiment of the present invention. DETAILED DESCRIPTION

[0052] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitution, modification, equivalent method and scheme made within the spirit and scope of the present invention.

[0053] In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without these detailed descriptions.

[0054] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the accompanying drawings are all in a relatively simplified form and are not in exact proportions, and are only used for the purpose of conveniently and clearly assisting in explaining the embodiments of the present invention.

[0055] Embodiment 1

[0056] Figure 2 The circuit block diagram of the overcurrent protection circuit of the embodiment of the present invention is shown, and the overcurrent protection circuit includes: an output voltage sampling circuit 10, an output current sampling circuit 20, an overcurrent threshold generating circuit 30 and a comparison circuit 40. Among them, the output voltage sampling circuit 10 samples from the power supply to output a first signal representing the output voltage of the power supply; the output current sampling circuit 20 samples from the power supply to output a second signal representing the output current of the power supply; the overcurrent threshold generating circuit 30 receives the first signal to output an overcurrent threshold signal, wherein the overcurrent threshold signal is equal to the first overcurrent threshold when the first signal is below the first reference value, and is less than the first overcurrent threshold when the first signal is greater than the first reference value; the comparison circuit 40 receives the second signal and the overcurrent threshold signal, and outputs an overcurrent protection signal OCP_Fault according to the comparison result of the second signal and the overcurrent threshold signal. When the second signal is greater than the overcurrent threshold signal, it represents that the output current of the power supply is overcurrent, the overcurrent protection signal OCP_Fault is valid, and the power supply performs overcurrent protection, for example, the power supply performs overcurrent protection by restarting or shutting down, so as to achieve the purpose of protecting the power supply or the load of the power supply.

[0057] like Figure 3a , which is a schematic diagram of the structure of the overcurrent protection circuit of the flyback converter of the first embodiment of the present invention, the primary main power tube Qp is connected to the primary winding, and this embodiment uses the primary current to estimate the output current, and then performs overcurrent protection. The overcurrent protection circuit includes: an auxiliary winding voltage divider circuit 110, an output current sampling circuit 120, an overcurrent threshold generation circuit 130, and a comparison circuit 140.

[0058] The auxiliary winding voltage divider circuit 110 outputs an auxiliary winding voltage divider signal Vvs by voltage divider of the auxiliary winding, including the auxiliary windings N connected in series. AUX , the first voltage dividing resistor R up and the second voltage divider resistor R down , the first voltage dividing resistor R up and the second voltage divider resistor R downThe common end of the auxiliary winding is used as the output end to output the auxiliary winding voltage-scaling signal Vvs. When the primary main power tube Qp is turned on, the auxiliary winding voltage-scaling signal Vvs can represent the information of the input voltage; when the primary main power tube Qp is turned off, the secondary side is in a freewheeling state, the auxiliary winding voltage-scaling signal Vvs can represent the information of the output voltage, and the secondary side conduction time Tons can be obtained according to the auxiliary winding voltage-scaling signal Vvs. In this embodiment, the auxiliary winding voltage-scaling circuit 110 serves as an output voltage sampling circuit, and when the primary main power tube Qp is turned off, the auxiliary winding voltage-scaling signal Vvs serves as the first signal that can represent the output voltage information.

[0059] For example, the output current sampling circuit 120 includes a sampling resistor Rcs, an auxiliary winding voltage regulator circuit 110, a sampling and holding circuit 1201 and an averaging circuit 1202. The first end of the sampling resistor Rcs is connected to the primary main power tube to receive the primary current, the second end is grounded, and the voltage of the first end is the sampling resistor voltage Vcs. The sampling and holding circuit 1201 receives the sampling resistor voltage Vcs and the auxiliary winding voltage regulator signal Vvs, obtains a sampling peak voltage Vcs_peak according to the sampling resistor voltage Vcs and the auxiliary winding voltage regulator signal Vvs, obtains a secondary side conduction time Tons according to the auxiliary winding voltage regulator signal Vvs, and outputs a sampling and holding signal SH according to the sampling peak voltage Vcs_peak and the secondary side conduction time Tons, wherein the voltage value of the sampling and holding signal SH within the secondary side conduction time Tons is the sampling peak voltage Vcs_peak, and is 0 at other times. Since the peak current control comparator still has a delay, the current overshoot degree will be different under different input voltages, so the peak current information of each switching cycle still needs to increase the input voltage compensation amount, which is achieved by compensating the auxiliary winding voltage signal Vvs to the sampling resistor voltage Vcs of the current cycle when the primary main power tube Qp is turned on, and obtaining the final sampling peak voltage Vcs_peak. The averaging circuit 1202 receives the sample hold signal HS, and performs an average calculation to output the second signal Vio_e representing the output current.

[0060] Please refer to Figure 3b The over-current threshold generating circuit 130 includes a first current generating circuit 1301, a calculation circuit 1302 and an output circuit 1303. The first current generating circuit 1301 receives the first signal Vvs and generates a first current i 1 When the first signal Vvs is below the first reference value Vref1, the first current i 1 When the first signal Vvs is greater than the first reference value Vref1, the first current i 1 The voltage increases with the increase of the first signal Vvs.

[0061] In one embodiment, the first current generating circuit 1301 includes a first voltage-controlled current source U01 and a second current-controlled current source U02. The first input terminal of the first voltage-controlled current source U01 receives the first signal Vvs, the second input terminal receives the first reference value Vref1, and the output terminal outputs a first controlled current i 11 When the first signal Vvs is below the first reference value Vref1, the first controlled current i 11 is 0; when the first signal Vvs is greater than the first reference value Vref1, the first controlled current i 11 =g˙(Vvs-Vref1), where g is the transconductance of the first voltage-controlled current source U01. The second current-controlled current source U02 receives the first controlled current i 11 , output the second controlled current β 1 ˙i 11 , where β 1 is the current ratio of the second current-controlled current source U02, the second controlled current β 1 ˙i 11 As the first current i 1 In other embodiments, the first current generating circuit 1301 may also only include a first voltage-controlled current source U01, and the first controlled current i output by the first voltage-controlled current source U01 is 11 As the first current i 1 .

[0062] In the embodiment, the calculation circuit 1302 receives the first current i 1 and the preset second current i 2 , to obtain the third current i 3 The calculation circuit 1302 calculates the preset second current i 2 and the first current i 1 Perform a difference operation to obtain the third current i 3 For example, the calculation circuit 1302 includes a third current source U03, and the third current source U03 generates the second current i 2 , wherein the second current i 2 The value of can be set according to the requirements. 2 The current paths intersect at a first node, and the first node outputs the third current i 3 , the third current i 3 The current value is equal to the second current i 2 and the first current i 1 The difference.

[0063] In one embodiment, the output circuit 1303 converts the third current i 3 The output circuit 1303 includes a fourth current-controlled current source U04 and a first resistor R01. The fourth current-controlled current source U04 receives the third current i 3 , output the fourth current i 4 , the fourth current i 4 =β 2 ˙i 3 , where β 2 The first end of the first resistor R01 is grounded, and the second end receives the fourth current i 4 , the first resistor voltage V at the second end of the first resistor R01 R In other embodiments, the output circuit 1303 may also only include a first resistor R01, and the first resistor R01 receives the third current i 3 , the first resistor voltage V on the first resistor R01 R The output is used as the over-current threshold signal Vocp.

[0064] In one embodiment, the comparison circuit 140 receives the second signal Vio_e and the overcurrent threshold signal Vocp, and outputs the overcurrent protection signal OCP_Fault according to the comparison result of the second signal Vio_e and the overcurrent threshold signal Vocp. When the second signal Vio_e is greater than the overcurrent threshold signal Vocp, it indicates that the output current of the power supply is overcurrent, the overcurrent protection signal OCP_Fault is valid, and the power supply performs overcurrent protection, for example, the power supply performs overcurrent protection by restarting or shutting down. For example, the comparison circuit 140 includes a first comparator U00, the first input terminal of the first comparator U00 receives the second signal Vio_e, the second input terminal receives the overcurrent threshold signal Vocp, and outputs the overcurrent protection signal OCP_Fault according to the comparison result.

[0065] In this embodiment, the second signal Vio_e output by the output current sampling circuit 120 can represent the output current information. Where N is the transformer primary-to-secondary turns ratio, Tons is the secondary conduction time, Tsw is the period of the flyback converter, Ipk is the primary current peak, Vcs_pk is the peak voltage on the sampling resistor, and Rcs is the sampling resistor for sampling the primary current. The output current overcurrent protection point is when the second signal The corresponding output current is obtained when , wherein Vocp is the over-current threshold signal generated by the over-current threshold generating circuit 130.

[0066] like Figure 3c As shown, it is an over-power protection and over-current protection curve diagram of the first embodiment of the present invention. Wherein Vvs is a first signal representing the output voltage, Vio_e is a second signal representing the output current, the dotted OPP curve is an over-power protection curve designed according to the minimum input voltage, and the solid OCP curve is an over-current protection curve diagram, and the OCP curve is generated by the over-current threshold generating circuit 130. The difference from the prior art is that: in the prior art, the reference Figure 1 , the OCP curve is a straight line, while the OCP curve of this embodiment is a broken line with a turning point B. To the left of the turning point B, that is, when the first signal Vvs is below the first reference value Vref1, the overcurrent threshold signal Vocp is equal to the first overcurrent threshold Vocp1; to the right of the turning point B, that is, when the first signal Vvs is greater than the first reference value Vref1, the overcurrent threshold signal Vocp decreases linearly with the increase of the first signal Vvs.

[0067] Among them, the first reference value Vref1, the first overcurrent threshold Vocp1 and the slope of the overcurrent threshold signal Vocp which decreases linearly with the increase of the first signal Vvs can be set accordingly according to the specifications and safety regulations of the power supply regarding output voltage, output current and power.

[0068] refer to Figure 3b and Figure 3c , the setting of the first reference value Vref1 can be specifically realized by setting the voltage of the second input terminal of the first voltage-controlled current source U01 in the first current generating circuit 1301. The first reference value Vref1 can be generated by a voltage source (not shown in the figure). The first reference value Vref1 can be set according to the maximum output voltage corresponding to the maximum current in the full output voltage range, and the first signal value corresponding to the maximum output voltage. The first overcurrent threshold Vocp1 = β 2 ·i 2 R, where i 2 is the second current generated by the third current source U03, β 2 is the current ratio of the fourth current-controlled current source U04, and R is the resistance value of the first resistor R01. The first overcurrent threshold Vocp1 can be set by setting the current value of the second current generated by the third current source U03, the current ratio of the fourth current-controlled current source U04, and the resistance value of the first resistor. The absolute value of the slope of the linear decrease of the overcurrent threshold signal Vocp as the first signal Vvs increases |k|=g·β 1 β 2 ·R, where g is the transconductance of the first voltage-controlled current source U01, β 1is the current ratio of the second current-controlled current source U02, β 2 is the current ratio of the fourth current-controlled current source U04, and R is the resistance of the first resistor R01. The setting of the slope of the overcurrent threshold signal Vocp linearly decreasing with the increase of the first signal Vvs can be specifically implemented by setting the transconductance of the first voltage-controlled current source U01, the current ratio of the second current-controlled current source U02, the current ratio of the fourth current-controlled current source U04, and the resistance of the first resistor.

[0069] In this embodiment, by appropriately setting the first reference value Vref1, the first overcurrent threshold Vocp1 and the slope of the overcurrent threshold signal Vocp that decreases linearly with the increase of the first signal Vvs according to the specifications and safety regulations of the power supply, it is possible to achieve a suitable overcurrent threshold signal value under different output voltage gears, and thus have a suitable output current overcurrent protection point. If the output current overcurrent protection point is too small, the output power may be too small and fail to meet the output power requirements. If the output current overcurrent protection point is too large, the overcurrent protection may fail in certain output voltage ranges, and the overpower protection may really work. In addition, in the embodiment, the way in which the overcurrent threshold signal Vocp decreases with the increase of the first signal Vvs can be linear or nonlinear. The present embodiment adopts a way in which the overcurrent threshold signal Vocp decreases linearly with the increase of the first signal Vvs, which has the advantages of simple circuit and easy control.

[0070] It can be understood that, in order to ensure that the overcurrent protection is effective under different output voltages, the embodiment has a constant overcurrent protection point that does not change with the input voltage, and in order to ensure sufficient output power at the same time, the turning point B of the OCP curve is set to the intersection of the OCP curve and the OPP curve. In other embodiments, the turning point B of the OCP curve can be above the OPP curve or below the OPP curve, and can be flexibly set according to the specific requirements of the power supply specifications and safety regulations on output voltage, output current and power.

[0071] Embodiment 2

[0072] The first embodiment of the present invention may represent a case where the second signal representing the output current information of the power supply is a voltage signal. The case where the second signal is a current signal is described below by taking the second embodiment as an example.

[0073] like Figure 4a, is a schematic diagram of the structure of the overcurrent protection circuit of the second embodiment of the present invention. The overcurrent protection circuit of this embodiment includes an output voltage sampling circuit 210, an output current sampling circuit 220, an overcurrent threshold generating circuit 230, and a comparison circuit 240. The output voltage sampling circuit 210 samples the power supply to obtain a first signal Vo_s that can characterize the output voltage information of the power supply. The output current sampling circuit 220 samples the power supply to obtain a second signal Io_s that can characterize the output current information of the power supply, wherein the second signal Io_s is a current signal. The overcurrent threshold generating circuit 230 receives the first signal Vo_s and generates an overcurrent threshold signal Iocp, wherein the overcurrent threshold signal Iocp is equal to the first overcurrent threshold Iocp1 when the first signal Vo_s is below the first reference value Vref1, and linearly decreases with the increase of the first signal Vo_s when the first signal Vo_s is greater than the first reference value Vref1. The first input terminal of the comparison circuit 240 receives the second signal Io_s, and the second input terminal receives the overcurrent threshold signal Iocp. The overcurrent protection signal OCP_Fault is output according to the comparison result. When the second signal Io_s is greater than the overcurrent threshold signal Iocp, it indicates that the output current of the power supply is overcurrent, the overcurrent protection signal OCP_Fault is valid, and the power supply performs overcurrent protection. For example, the power supply performs overcurrent protection by restarting or shutting down.

[0074] The overcurrent threshold generating circuit 230 of this embodiment includes a first current generating circuit 2301 and a calculation circuit 1302, which are basically the same as the overcurrent threshold generating circuit 130 of the first embodiment, except that the first input terminal of the first voltage-controlled current source U01 in the first current generating circuit 2301 of this embodiment receives the first signal Vo_s, and the overcurrent threshold generating circuit 230 of this embodiment has no output circuit, which will not be described here. The overcurrent threshold signal Iocp output by the overcurrent threshold generating circuit 230 of this embodiment is a current signal, which is a third current i output by the calculation circuit 1302. 3 As the over-current threshold signal Iocp.

[0075] Figure 4b This is an overcurrent protection curve diagram of the second embodiment of the present invention. The variation trend of the OCP curve corresponds to that of the first embodiment. Figure 3c The OCP curves in are basically the same, except that Figure 4bThe horizontal axis is the first signal Vo_s representing the output voltage information of the power supply, and the vertical axis is the second signal Io_s representing the output current of the power supply. The OCP curve is a broken line with an inflection point B. To the left of the inflection point B, that is, when the first signal Vo_s is below the first reference value Vref1, the overcurrent threshold signal Iocp is equal to the first overcurrent threshold Iocp1; to the right of point B, that is, when the first signal Vo_s is greater than the first reference value Vref1, the overcurrent threshold signal Iocp decreases linearly with the increase of the first signal Vo_s.

[0076] Similarly, the first reference value Vref1, the first overcurrent threshold Iocp1 and the slope of the overcurrent threshold signal Iocp which decreases linearly with the increase of the first signal Vo_s can be set accordingly according to the specifications and safety regulations of the power supply regarding output voltage, output current and power.

[0077] refer to Figure 4a and Figure 4b The first reference value Vref1 can be set by setting the voltage at the second input terminal of the first voltage-controlled current source U01 in the first current generating circuit 2301. The first reference value Vref1 can be generated by a voltage source (not shown in the figure). The first overcurrent threshold Iocp1=i 2 Among them, i 2 is the second current generated by the third current source U03. The first overcurrent threshold Iocp1 can be set by setting the current value of the second current generated by the third current source U03. The absolute value of the slope of the linear decrease of the overcurrent threshold signal Iocp value with the increase of the first signal Vo_s |k|=g·β 1 , where g is the transconductance of the first voltage-controlled current source U01, β 1 The slope of the overcurrent threshold signal Vocp linearly decreasing with the increase of the first signal Vo_s can be specifically set by setting the transconductance of the first voltage-controlled current source U01 and the current ratio of the second voltage-controlled current source U02.

[0078] In this embodiment, by appropriately setting the first reference value Vref1, the first overcurrent threshold value Iocp1 and the slope of the overcurrent threshold signal Iocp linearly decreasing with the increase of the first signal Vo_s according to the specifications and safety regulations of the power supply, it is possible to achieve a suitable overcurrent threshold signal value under different output voltage gears, and then have a suitable output current overcurrent protection point, effectively solving the problem of overcurrent protection failure. In the embodiment, the way in which the overcurrent threshold signal Vocp decreases with the increase of the first signal Vo_s can be linear or nonlinear. This embodiment adopts the way in which the overcurrent threshold signal Vocp linearly decreases with the increase of the first signal Vvs, which has the advantages of simple circuit and easy control. And the overcurrent threshold signal Iocp generated by this example is a current signal, which can be well applied to the power supply whose output signal of the output current sampling circuit is a current signal.

[0079] Embodiment 3

[0080] The first and second embodiments of the present invention may represent a situation where the overcurrent threshold signal is always equal to the first overcurrent threshold when the first signal is below the first reference value, and linearly decreases as the first signal increases when the first signal is greater than the first reference value. The following takes the third embodiment as an example to introduce a situation where the overcurrent threshold signal is equal to the first overcurrent threshold when the first signal is below the first reference value, and changes in stages as the first signal increases when the first signal is greater than the first reference value.

[0081] like Figure 5a, is a schematic diagram of the structure of the overcurrent protection circuit of the third embodiment of the present invention, the overcurrent protection circuit includes an output voltage sampling circuit 310, an output current sampling circuit 320, an overcurrent threshold generating circuit 330, and a comparison circuit 340. Among them, the output voltage sampling circuit 310 samples from the power supply to obtain a first signal Vo_s that can characterize the output voltage information of the power supply. The output current sampling circuit 320 samples from the power supply to obtain a second signal Vio_s that can characterize the output current information of the power supply. The overcurrent threshold generating circuit 330 receives the first signal Vo_s and generates an overcurrent threshold signal Vocp, the overcurrent threshold signal Vocp is always equal to the first overcurrent threshold Vocp1 when the first signal Vo_s is below the first reference value Vref1, linearly decreases with the increase of the first signal Vo_s when the first signal Vo_s is greater than the first reference value Vref1 and less than the second reference value Vref2, and is always equal to the second overcurrent threshold Vocp2 when the first signal Vo_s is greater than the second reference value Vref2. The first input terminal of the comparison circuit 340 receives the second signal Vio_s, and the second input terminal of the comparison circuit receives the overcurrent threshold signal Vocp, and outputs the overcurrent protection signal OCP_Fault according to the comparison result. When the second signal is greater than the overcurrent threshold signal, it indicates that the output current of the power supply is overcurrent, and the overcurrent protection signal OCP_Fault is valid, and the power supply performs overcurrent protection, for example, the power supply performs overcurrent protection by restarting or shutting down. Exemplarily, the comparison circuit 340 includes a first comparator U00, the first input terminal of the first comparator U00 receives the second signal Vio_s, the second input terminal receives the overcurrent threshold signal Vocp,, and outputs the overcurrent protection signal OCP_Fault according to the comparison result.

[0082] The overcurrent threshold generating circuit 330 of this embodiment includes a first current generating circuit 3301, a calculation circuit 1302 and an output circuit 1303. The calculation circuit 1302 and the output circuit 1303 of this embodiment are the same as those of the first embodiment, and are not described in detail here. The first current generating circuit 3301 of this embodiment is basically the same as the first current generating circuit 1301 of the first embodiment, except that the first current generating circuit 3301 of this embodiment receives a first signal Vo_s, and also includes a voltage stabilizing circuit 33011, which is not described in detail here. The first end of the voltage stabilizing circuit 33011 is grounded, and the second end receives the first signal Vo_s at a second node. When the first signal Vo_s is greater than the second reference value Vref2, the voltage stabilizing circuit 33011 clamps the voltage of the second node to the second reference value Vref2. The first input end of the first voltage-controlled current source U01 is connected to the second node to receive the voltage of the second node, the second input end receives the first reference value Vref1, and the output end outputs the first controlled current i 11 Wherein, the second reference value Vref2 is greater than the first reference value Vref1. When the first signal Vo_s is below the first reference value Vref1, the first controlled current i 11 is 0; when the first signal Vo_s is greater than the first reference value Vref1 and is less than the second reference value Vref2, the first controlled current i 11 =g˙(Vo_s-Vref1), where g is the transconductance of the first voltage-controlled current source U01; when the first signal Vo_s is greater than the second reference value Vref2, the first controlled current i 11 Keep constant, i 11 =g˙(Vref2-Vref1).

[0083] Figure 5b This is an overcurrent protection curve diagram of the third embodiment of the present invention, the horizontal axis is the first signal Vo_s representing the output voltage information of the power supply, and the vertical axis is the second signal Vio_s representing the output current of the power supply. The OCP curve is a broken line with two turning points B and C. To the left of the turning point B, that is, when the first signal Vo_s is below the first reference value Vref1, the overcurrent threshold signal Vocp is equal to the first overcurrent threshold Vocp1; to the right of the turning point B and to the left of the turning point C, that is, when the first signal Vo_s is greater than the first reference value Vref1 and is below the second reference value Vref2, the overcurrent threshold signal Vocp value decreases linearly with the increase of the first signal Vo_s; to the right of the turning point C, that is, when the first signal Vo_s is greater than the second reference value Vref2, the overcurrent threshold signal Vocp is equal to the second overcurrent threshold Vocp2.

[0084] Among them, the first reference value Vref1, the first over-current threshold Vocp1, the slope of the over-current threshold signal Vocp value linearly decreasing with the increase of the first signal Vo_s, the second reference value Vref2 and the second over-current threshold Vocp2 can all be set accordingly according to the specifications and safety regulations of the power supply regarding output voltage, output current and power.

[0085] refer to Figure 5a and Figure 5b , the specific setting method of the first reference value Vref1, the first overcurrent threshold value Vocp1, and the slope of the overcurrent threshold signal Vocp linearly decreasing with the increase of the first signal Vo_s is the same as that in the first embodiment, and will not be repeated here. The second reference value Vref2 can be specifically set by designing the voltage stabilizing circuit 33011. The second overcurrent threshold where β 2 is the current ratio of the fourth current-controlled current source U04, i 2 is the second current generated by the third current source U03, β 1 is the current ratio of the second current-controlled current source U04, g is the transconductance of the first voltage-controlled current source U01, Vref1 is the first reference value, which is the voltage input to the second input terminal of the first voltage-controlled current source U01, Vref2 is the second reference value, the magnitude of Vref2 is determined by the voltage stabilizing circuit 33011, and R is the resistance value of the first resistor R01. The second overcurrent threshold Vocp2 can be specifically set by setting the above parameters.

[0086] In this embodiment, by appropriately setting the first reference value Vref1, the first overcurrent threshold value Vocp1, the slope of the linear decrease of the overcurrent threshold signal Vocp as the first signal Vo_s increases, the second reference value Vref2 and the second overcurrent threshold value Vocp2 according to the specifications and safety regulations of the power supply, it is possible to achieve a suitable overcurrent threshold signal value under different output voltage gears, and then have a suitable output current overcurrent protection point, effectively solving the problem of overcurrent protection failure. In this embodiment, when the first signal Vo_s is greater than the first reference value Vref1, by setting the overcurrent threshold signal Vocp to change in stages as the first signal Vo_s increases, the output current overcurrent protection point changes in stages as the output voltage increases, which can meet some more demanding power supply specifications or application requirements, or achieve a more optimized output current overcurrent protection point.

[0087] It can be understood that no matter whether the second signal is a voltage signal or a current signal, it is easy for those skilled in the art to realize that the overcurrent threshold signal changes in stages as the first signal increases when the first signal is greater than the first reference value based on Embodiments 1 to 3, wherein the stages include any multiple stages of two or more. The staged changes include linear reduction in stages; or linear reduction in stages in some different sub-voltage intervals, and remaining unchanged in stages in the remaining different sub-voltage intervals; or linear reduction in stages in some different sub-voltage intervals, and linear increase in stages in the remaining different sub-voltage intervals; or linear reduction in stages in some different sub-voltage intervals, linear increase in stages in some different sub-voltage intervals, and remaining unchanged in stages in the remaining different sub-voltage intervals, etc.

[0088] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. An overcurrent protection method for overcurrent protection of a power supply, characterized in that: include: Obtaining a first signal representing an output voltage from the power supply, and obtaining an overcurrent threshold signal according to the first signal, wherein the overcurrent threshold signal is less than or equal to an overpower threshold signal; Obtaining a second signal representing the output current from the power supply, obtaining an overcurrent protection signal according to the second signal and the overcurrent threshold signal, and when the second signal is greater than the overcurrent threshold signal, indicating that the output current of the power supply is overcurrent, the overcurrent protection signal is valid, and the power supply performs overcurrent protection; The overcurrent threshold signal is equal to a first overcurrent threshold when the first signal is below a first reference value, and is less than the first overcurrent threshold when the first signal is greater than the first reference value.

2. The overcurrent protection method according to claim 1, characterized in that: When the first signal is greater than the first reference value, the overcurrent threshold signal decreases as the first signal increases.

3. The overcurrent protection method according to claim 1, characterized in that: When the first signal is greater than the first reference value, the overcurrent threshold signal decreases linearly as the first signal increases.

4. The overcurrent protection method according to claim 1, characterized in that: When the first signal is greater than the first reference value, the overcurrent threshold signal linearly decreases in stages as the first signal increases.

5. The overcurrent protection method according to claim 1, characterized in that: When the first signal is greater than the first reference value, in a partial voltage interval of the first signal, the overcurrent threshold signal decreases linearly as the first signal increases, and in the remaining partial voltage interval of the first signal, the overcurrent threshold signal remains unchanged.

6. The overcurrent protection method according to claim 1, characterized in that: The first reference value is adjustable according to output voltage and output current requirements of the power supply.

7. The overcurrent protection method according to any one of claims 3 to 5, characterized in that: The slope of the overcurrent threshold signal linearly decreasing as the first signal increases is set to be adjustable.

8. The overcurrent protection method according to claim 1, characterized in that: When the overcurrent protection signal is valid, the power supply performs overcurrent protection by restarting or shutting down.

9. An overcurrent protection circuit for overcurrent protection of a power supply, characterized in that: include: An output current sampling circuit, sampling from a power supply to output a second signal representing an output current of the power supply; an overcurrent threshold generating circuit, receiving a first signal representing the output voltage of the power supply to output an overcurrent threshold signal, wherein the overcurrent threshold signal is less than or equal to the overpower threshold signal, wherein the overcurrent threshold signal is equal to a first overcurrent threshold when the first signal is below a first reference value, and is less than the first overcurrent threshold when the first signal is greater than the first reference value; A comparison circuit receives the second signal and the overcurrent threshold signal, and outputs an overcurrent protection signal according to a comparison result of the second signal and the overcurrent threshold signal. When the second signal is greater than the overcurrent threshold signal, it indicates that the output current of the power supply is overcurrent, the overcurrent protection signal is valid, and the power supply performs overcurrent protection.

10. The overcurrent protection circuit according to claim 9, characterized in that: The overcurrent threshold generating circuit comprises: A first current generating circuit receives the first signal and generates a first current; A calculation circuit receives the first current and a preset second current to obtain a third current, wherein the value of the preset second current can be set; The over-current threshold generating circuit outputs the over-current threshold signal according to the third current.

11. The overcurrent protection circuit according to claim 10, characterized in that: When the first signal is below a first reference value, the first current remains unchanged; when the first signal is greater than the first reference value, the first current increases as the first signal increases.

12. The overcurrent protection circuit according to claim 10, characterized in that: The first current generating circuit comprises: A first voltage-controlled current source has a first input terminal receiving the first signal, a second input terminal receiving the first reference value, and an output terminal outputting a first controlled current, wherein the first controlled current serves as the first current.

13. The overcurrent protection circuit according to claim 12, characterized in that: The first current generating circuit further includes: The second current-controlled current source receives the first controlled current and outputs a second controlled current, where the second controlled current serves as the first current.

14. The overcurrent protection circuit according to claim 10, characterized in that: The calculation circuit performs a difference operation on the preset second current and the first current to obtain the third current.

15. The overcurrent protection circuit according to claim 10, characterized in that: When the second signal is a current signal, the over-current threshold generating circuit outputs the third current as the over-current threshold signal.

16. The overcurrent protection circuit according to claim 10, characterized in that: When the second signal is a voltage signal, the first current generating circuit further includes an output circuit, The output circuit converts the third current into a corresponding voltage signal, and outputs the voltage signal as the overcurrent threshold signal.

17. The overcurrent protection circuit according to claim 9, characterized in that: The output current sampling circuit samples from a power supply to output the second signal, the power supply is a flyback power supply, and the output current sampling circuit includes: A sampling resistor, the first end of which is connected to the primary main power tube, the second end of which is grounded, and the voltage at the first end is the sampling resistor voltage; An auxiliary winding voltage splitting circuit outputs an auxiliary winding voltage splitting signal through the auxiliary winding voltage splitting; a sampling and holding circuit, receiving the sampling resistor voltage and the auxiliary winding voltage-divided signal, obtaining a sampling peak voltage according to the sampling resistor voltage and the auxiliary winding voltage-divided signal, obtaining a secondary side conduction time according to the auxiliary winding voltage-divided signal, and outputting a sampling and holding signal according to the sampling peak voltage and the secondary side conduction time; an averaging circuit, receiving the sample-and-hold signal, and performing an average operation to output the second signal; The voltage value of the sample-and-hold signal during the secondary side conduction time is the sample peak voltage.

18. A power supply, characterized in that: The power supply comprises the overcurrent protection circuit according to any one of claims 9 to 17, The overcurrent protection circuit generates an overcurrent protection signal, and when the overcurrent protection signal is valid, the power supply performs overcurrent protection.

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