Switching converter and corresponding control method and control circuit therefor

Abstract

Disclosed are a switching converter and a corresponding control method and control circuit thereof. An overcurrent reference threshold is selected according to an output voltage sampling signal, and an overcurrent protection trigger signal is generated when an output current sampling signal and the overcurrent reference threshold satisfy a predetermined condition, so that the switching converter enters a protection state. Thus, overcurrent protection can be provided for the switching converter under the premise of meeting the requirements of a limited power supply, and safety hazards are reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, and in particular to a switching converter and a corresponding control method and control circuit thereof. BACKGROUND

[0002] In order to reduce safety hazards, the switching converter needs to meet the specifications of the LPS (Limited Power Source) at different output voltages. Specifically, the LPS specifies the output voltage, output current and output power of the switching converter. In order to prevent damage to the circuit caused by excessive output current or excessive output power, an overcurrent protection circuit is usually provided in the switching converter, and when the output current exceeds a certain value, the switching converter is controlled to be turned off to reduce safety hazards.

[0003] The overcurrent protection method in the prior art has a large overcurrent protection point when the output voltage is low, which exceeds the LPS limit on the output current. That is, it cannot simultaneously meet the LPS requirements and overcurrent protection. SUMMARY

[0004] Therefore, the purpose of the embodiments of the present application is to provide a switching converter and a corresponding control method and control circuit thereof, which can provide overcurrent protection for the switching converter under the premise of meeting the requirements of the limited power source, thereby reducing safety hazards.

[0005] In a first aspect, the embodiments of the present application provide a control method applied to a switching converter, the method comprising:

[0006] selecting an overcurrent reference threshold according to an output voltage sampling signal representing the output voltage of the switching converter, the overcurrent reference threshold meeting the current requirement of the limited power source; and

[0007] in response to the output current sampling signal representing the output current of the switching converter and the overcurrent reference threshold meeting a predetermined condition, generating an overcurrent protection trigger signal to make the switching converter enter a protection state.

[0008] In some embodiments, in response to generating a valid overcurrent protection trigger signal, the power switch of the switching converter is controlled to be turned off to make the switching converter enter the protection state; and

[0009] in response to generating an invalid overcurrent protection trigger signal, the power switch of the switching converter is controlled to be turned on or off, so that the output voltage and / or the output current of the switching converter meet the predetermined requirements.

[0010] In some embodiments, the over-current reference threshold is configured to gradually decrease with the increase of the output voltage within a predetermined range of the output voltage.

[0011] In some embodiments, the output voltage sampling signal is obtained by sampling an output voltage of the switching converter, and the output current sampling signal is obtained by sampling an output current of the switching converter.

[0012] In some embodiments, when the switching converter is configured as an isolated switching converter, the output voltage sampling signal is determined by an auxiliary voltage sampling signal;

[0013] wherein the auxiliary voltage sampling signal is obtained by sampling a voltage across an auxiliary winding coupled to a primary winding of a transformer in the isolated switching converter.

[0014] In some embodiments, the output current sampling signal is obtained by:

[0015] obtaining a demagnetization time of the transformer;

[0016] obtaining a current peak sampling signal representing a peak value of the primary current of the switching converter; and

[0017] determining the output current sampling signal such that the output current sampling signal is in a positive proportional relationship with a product of the current peak sampling signal and the demagnetization time, and in an inverse proportional relationship with a switching period.

[0018] In some embodiments, the predetermined condition is that the output current sampling signal continuously exceeds the over-current reference threshold for a time length reaching a predetermined time length.

[0019] In some embodiments, the method further comprises:

[0020] maintaining an input signal of the filter circuit as the current peak sampling signal during a demagnetization of the transformer in a switching period;

[0021] controlling the input signal of the filter circuit to be zero when the demagnetization is detected to be completed; and

[0022] obtaining the output current sampling signal at an output end of the filter circuit.

[0023] In a second aspect, embodiments of the present application provide a control circuit applied to a switching converter, the control circuit comprising:

[0024] The over-current protection circuit comprises a reference threshold generating circuit configured to generate an over-current reference threshold according to an output voltage sampling signal representing an output voltage of the switching converter, and a trigger signal generating circuit configured to generate an over-current protection trigger signal in response to an output current sampling signal representing an output current of the switching converter and the over-current reference threshold satisfying a predetermined condition, the over-current reference threshold satisfying a current requirement of the limited power supply; and

[0025] A control signal generating circuit configured to control the switching converter to enter a protection state in response to receiving the over-current protection trigger signal.

[0026] In some embodiments, the control signal generating circuit is further configured to generate a switching control signal to control a power switch of the switching converter to turn on or turn off, so that the output voltage and / or the output current of the switching converter satisfy a predetermined requirement in response to an invalid over-current protection trigger signal, and to control the power switch of the switching converter to turn off so that the switching converter enters the protection state in response to receiving a valid over-current protection trigger signal.

[0027] In some embodiments, the over-current reference threshold is configured to gradually decrease with the increase of the output voltage within a predetermined range of the output voltage.

[0028] In some embodiments, the output voltage sampling signal is obtained by sampling the output voltage of the switching converter, and the output current sampling signal is obtained by sampling the output current of the switching converter.

[0029] In some embodiments, when the switching converter is configured as an isolated switching converter, the reference threshold generating circuit comprises:

[0030] An output voltage sampling circuit configured to obtain the output voltage sampling signal according to an auxiliary voltage sampling signal, wherein the auxiliary voltage sampling signal is obtained by sampling a voltage across an auxiliary winding coupled to a primary winding of a transformer in the isolated switching converter; and

[0031] A threshold determining circuit configured to determine the over-current reference threshold according to the output voltage sampling signal and the over-current protection curve.

[0032] In some embodiments, the over-current protection circuit further comprises:

[0033] The output current detection circuit is configured to acquire the demagnetization time of the transformer and a current peak sampling signal characterizing the peak value of the primary current, and to determine the output current sampling signal such that the output current signal is directly proportional to the product of the current peak sampling signal and the demagnetization time, and inversely proportional to the switching period.

[0034] In some embodiments, the output current detection circuit includes:

[0035] The demagnetization time sampling circuit is configured to acquire a demagnetization time sampling signal based on an auxiliary voltage sampling signal, the demagnetization time sampling signal being used to characterize that the transformer of the switching converter is in the demagnetization period;

[0036] A peak current sampling circuit is configured to acquire a peak current sampling signal based on the primary-side current sampling signal; and

[0037] A current determination circuit is configured to determine the output current sampling signal based on the demagnetization time sampling signal and the current peak sampling signal.

[0038] In some embodiments, the predetermined condition is that the duration for which the output current sampling signal is continuously greater than the overcurrent reference threshold reaches a predetermined duration.

[0039] In some embodiments, the trigger signal generation circuit includes:

[0040] A comparator circuit is configured to acquire a comparison result between the output current sampling signal and the overcurrent reference threshold; and

[0041] A timing circuit is configured to output the overcurrent protection trigger signal in response to the comparison result that the output current sampling signal is greater than the overcurrent reference threshold for a predetermined time.

[0042] In some embodiments, the current determination circuit includes:

[0043] The first input terminal is configured to receive the current peak sampling signal;

[0044] The first output terminal is configured to output the output current sampling signal;

[0045] First switch;

[0046] A filter circuit, connected in series with the first switch between the first input terminal and the first output terminal, includes at least one capacitor.

[0047] A second switch is connected in series with the first switch between the first input terminal and the ground terminal; and

[0048] logic circuitry configured to, in one operating cycle, control the first switch to be turned on and the second switch to be turned off during demagnetization of the transformer to keep an input signal of the filter circuit as the current peak sampling signal, and control an input signal of the filter circuit of the current determination circuit to be zero when it is detected that the demagnetization is completed, so that the filter circuit outputs the output current sampling signal.

[0049] In some embodiments, the logic circuitry is configured as an RS flip-flop, a set terminal of which receives the switch control signal, a reset terminal of which receives the demagnetization time sampling signal, and an output terminal of which generates the control signal to control the first and second switches respectively.

[0050] In a third aspect, embodiments of the present application provide a switching converter, which comprises:

[0051] a power stage circuit comprising at least a power switch; and

[0052] The control circuit according to the second aspect.

[0053] In a third aspect, embodiments of the present application provide an integrated circuit, which comprises the control circuit according to the second aspect.

[0054] The technical solution of the embodiments of the present application determines an overcurrent reference threshold value according to an output voltage sampling signal and a predetermined overcurrent protection curve, generates an overcurrent protection trigger signal when an output current sampling signal and the overcurrent reference threshold value meet a predetermined condition, and makes the switching converter enter a protection state. Thus, overcurrent protection can be provided for the switching converter under the premise of meeting the requirement of the limited power supply, and the safety hazard is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0055] The above and other objects, features and advantages of the present application will become more apparent from the following description of embodiments of the present application taken in conjunction with the accompanying drawings, in which:

[0056] Figure 1 is a circuit diagram of a switching converter of an embodiment of the present application;

[0057] Figure 2 is a circuit diagram of a switching converter of another embodiment of the present application;

[0058] Figure 3 is a schematic diagram of a control circuit of an embodiment of the present application;

[0059] Figure 4 is a signal waveform diagram of a switching converter of an embodiment of the present application;

[0060] Figure 5 is a circuit diagram of an overcurrent protection circuit of an embodiment of the present application;

[0061] Figure 6 is a circuit diagram of a current determination circuit of an embodiment of the present application;

[0062] Figure 7 is a schematic diagram of an over-current protection curve of an embodiment of the present application;

[0063] Figure 8 is a schematic diagram of an over-current protection curve of another embodiment of the present application;

[0064] Figure 9 is a schematic diagram of an over-current protection curve of yet another embodiment of the present application;

[0065] Figure 10 is a circuit diagram of a reference threshold generation circuit of an embodiment of the present application;

[0066] Figure 11 is a schematic diagram of an LPS curve of an embodiment of the present application;

[0067] Figure 12 is a flow chart of a control method of an embodiment of the present application. DETAILED DESCRIPTION

[0068] The present application is described herein based on embodiments, but the present application is not limited to these embodiments. In the following detailed description of the present application, some specific details are described in order to provide a thorough understanding of the present application. The present application can be fully understood without these details. In order to avoid obscuring the essence of the present application, well-known methods, procedures, processes, elements, and circuits are not described in detail.

[0069] In addition, those of ordinary skill in the art will understand that the drawings provided herein are for illustrative purposes and are not necessarily drawn to scale.

[0070] At the same time, it should be understood that in the following description, "circuit" refers to a conductive loop composed of at least one element or sub-circuit through electrical or electromagnetic connection. When an element or circuit is said to be "connected to" another element or said to be "connected between" two nodes, it can be directly coupled or connected to another element or there can be intermediate elements, and the connection between elements can be physical, logical, or a combination thereof. On the contrary, when an element is said to be "directly coupled to" or "directly connected to" another element, it means that there is no intermediate element between the two.

[0071] Unless the context clearly requires otherwise, throughout the description, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

[0072] In the description of the present application, it should be understood that the terms "first", "second" and the like are used only for descriptive purposes, and cannot be construed as indicating or implying relative importance. In addition, in the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specified.

[0073] Figure 1 is a circuit diagram of a switching converter of an embodiment of the present application. In Figure 1 the embodiment shown, the switching converter is taken as an example of an isolated switching converter, which specifically includes a primary side circuit and a secondary side circuit, the primary side circuit and the secondary side circuit are connected through a transformer T1, the transformer T1 outputs the electrical signal output by the primary side circuit after transformation to the secondary side circuit, wherein the transformer T1 includes a primary winding Lp of the primary side circuit and a secondary winding Ls of the secondary side circuit.

[0074] Further, the primary side circuit obtains a direct current signal Vin after rectification and filtering of the received external alternating current signal Vac, and outputs it to the secondary side circuit through the transformer T1 (the primary winding Lp and the secondary winding are coupled), the secondary side circuit obtains an output voltage Vout after rectification and filtering of the received electrical signal, and outputs it through an output port XP1.

[0075] Specifically, the primary side circuit includes a power stage circuit, an auxiliary voltage sampling circuit, a primary current sampling circuit, a control circuit U1 and other circuits. Among them, the power stage circuit includes input terminals A1 and A2, a primary rectification circuit, a primary winding Lp and a power switch M1.

[0076] The input terminals A1 and A2 are used to receive an external electrical signal Vac. Further, the external electrical signal is an alternating current signal. The embodiments of the present application do not limit the external electrical signal, which can be a 220V or 380V alternating current mains, or other alternating current signals. At the same time, the way the input terminals A1 and A2 receive the electrical signal is not limited, which can be directly connected to the external power source through a plug, or can receive the external electrical signal wirelessly.

[0077] The primary rectification circuit is connected with the input terminals A1 and A2, and is used to rectify the external electrical signal Vac. In Figure 1 the embodiment shown, the primary rectification circuit is a full-bridge rectification circuit, which includes diodes D1, D2, D3 and D4.

[0078] It should be understood that the rectification circuit of the embodiments of the present application is not limited to Figure 1 the way shown, and rectification circuits with other structures (such as half-bridge rectification) are also applicable. It should also be understood that the present application takes diode rectification as an example for description, but the rectification circuit can also adopt synchronous rectification, which realizes rectification of the external electrical signal through multiple controlled switches.

[0079] Further, the primary side circuit further comprises a capacitor C1 connected at the output of the primary rectifier circuit for filtering the electrical signal output by the rectifier circuit. The signal output by the rectifier circuit after filtering is Vin.

[0080] The power switch M1 and the primary winding Lp are connected in series between the output of the rectifier circuit and the ground. The power switch M1 is controlled to be turned on and turned off to control the output current and / or the output voltage of the primary winding Lp.

[0081] In the embodiment, the power switch M1 is a transistor, and the transistor Qa can be a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). It should be understood that a bipolar junction transistor (BJT) or an Insulated Gate Bipolar Transistor (IGBT) can also be applicable to the technical solution of the embodiment of the present application.

[0082] Further, the primary side circuit further comprises a capacitor C2, a resistor R1 and a diode D5, wherein the capacitor C2 and the resistor R1 form a parallel circuit, the parallel circuit is connected in series with the diode D5 to form a series circuit, and the series circuit is connected across the primary winding Lp, thereby forming an RCD snubber circuit to absorb leakage energy and avoid voltage spikes.

[0083] It should be understood that the embodiment of the present application is not limited to Figure 1 The power stage circuit shown can be replaced by a power converter having other structures, for example, a switching converter having a boost topology, a buck topology or a buck-boost topology, as long as the intensity of the output current and / or voltage can be adjusted by controlling the duty cycle or the switching frequency of the power switch of the switching converter.

[0084] Further, the auxiliary voltage sampling circuit is used to obtain an auxiliary voltage sampling signal, wherein the auxiliary voltage sampling signal is used to represent the voltage across the auxiliary winding La. At the same time, the voltage across the auxiliary winding can also be used to supply power to other circuits after the circuit is started.

[0085] The auxiliary voltage sampling circuit further comprises a resistor R2 and a resistor R3, wherein the resistor R2 and the resistor R3 are connected in series across the auxiliary winding to form a voltage dividing network to output the auxiliary voltage sampling signal Vsen at the connection point of the resistor R2 and the resistor R3.

[0086] The primary-side current sampling circuit is configured to obtain a primary-side current sampling signal Vcs, and includes a resistor R4 connected between the power switch M1 and a ground terminal to obtain the primary-side current sampling signal Vcs, and transmit the primary-side current sampling signal Vcs to the control circuit through a resistor R5. The primary-side current sampling signal Vcs is used to represent the primary-side current Ia, and the primary-side current is the current flowing through the primary winding Lp.

[0087] The control circuit U1 is configured to generate a switching control signal to control the duty ratio and the switching frequency of the power switch M1, so as to control the output current and / or the output voltage of the switching converter. Meanwhile, the control circuit is also configured to control the power switch M1 to be turned off when it is detected that the output current of the switching converter is overcurrent, so that the switching converter does not output the electrical signal.

[0088] In the embodiment, the secondary-side circuit includes a secondary winding Ls, a secondary rectifier circuit, a secondary filter circuit, a power transmission protocol control module U2 and other circuits.

[0089] The secondary winding Ls is configured to be coupled with the primary winding Lp, so as to receive the electrical signal transmitted by the primary winding.

[0090] The secondary rectifier circuit is configured to rectify the electrical signal output by the secondary winding Ls. In the embodiment, the secondary rectifier circuit is a diode D7, i.e., the rectification is performed in a half-wave rectification mode. It should be understood that the secondary rectifier circuit of the embodiment of the present application is not limited to the half-wave rectification mode shown in the figure, and other structures of rectifier circuits (such as bridge rectification or full-wave rectification) are also applicable. It should also be understood that the present application is described by taking the diode rectification mode as an example, but the rectifier circuit can also adopt a synchronous rectification mode to rectify the electrical signal through a controlled switch. Figure 1 Figure 1 The secondary filter circuit is configured to filter the electrical signal output by the secondary rectifier circuit.

[0091] The secondary filter circuit is configured to filter the electrical signal output by the secondary rectifier circuit. Figure 1 The filtering is implemented by a capacitor C5.

[0092] The secondary-side circuit further includes an optical coupler equipment (OCEP) including U3a and U3b, configured to feed back a compensation signal Vcomp from the secondary-side circuit to the primary-side circuit, so that the control circuit U1 controls the duty ratio and / or the switching frequency of the power switch M1 according to the compensation signal, so that the output current and the output voltage of the switching converter meet the selected voltage parameters and current parameters.

[0093] ​In some embodiments, the secondary side circuit further comprises a load switch SW1 connected between the output port XP1 and the secondary side rectifier circuit, and configured to be controlled to be turned on or turned off. When the load switch SW1 is turned on, the output voltage Vout is output through the output port XP1 to charge the connected charging device. When the load switch SW1 is turned off, the output port XP1 does not output an electrical signal.

[0094] The power delivery (PD) protocol control module U2 communicates with the connected charging device through the output port XP1, which is a USB Type-C interface in some embodiments, Figure 1 Only four pins CC1, CC2, D+ and D- of the output port XP1 are shown in the figure, and for the device connected to the output port XP1, data can be transmitted only after a successful PD protocol handshake, such as increasing the voltage and current level. Thus, when the output port XP1 of the switching converter is connected to a charging device, the charging device will query the registers inside the power delivery protocol control module U2 through XP1 to determine the output voltage and output current allowed by the switching converter, and then select the voltage and current parameters and inform the power delivery protocol control module U2.

[0095] The power delivery protocol control module U2 detects the output current Iout and the output voltage Vout in real time, and immediately turns off the load switch SW1 once the output power or the output current exceeds a limit value. For example, the output voltage range can be up to 3.3V-21V, the output power must not exceed 100W, and the output current must not exceed 8A, etc. In one implementation, the output current Iout is sampled by a resistor R8 connected between the output port XP1 and the ground terminal.

[0096] For ease of illustration, Figure 2 A schematic diagram of a switching converter according to another embodiment of the present application is shown. Figure 2 Only the pins of the control circuit U1 and the circuits connected to the pins are shown. In Figure 2 In the shown embodiment, the control circuit U1 comprises eight pins, which are as follows:

[0097] The pin VCC is used to receive a supply voltage. Specifically, the voltage across the auxiliary winding La is rectified and filtered by the diode D6 and the capacitor C3, and then output to the VCC pin of the control circuit U1 to supply power to the control circuit U1.

[0098] The pin NC is a null pin. In this embodiment, the NC pin has no use and only exists due to the packaging form.

[0099] The pin FB is used to receive an auxiliary voltage sampling signal Vsen, which is used to represent the voltage across the secondary winding.

[0100] Pin COMP is connected with optocoupler U3. The compensation signal Vcomp outputted by optocoupler U3 is filtered by capacitor C4 and then outputted to pin COMP of control circuit U1.

[0101] Pin HV is connected with the output end of the primary side rectification circuit, for receiving the output voltage of the primary side rectification circuit and taking the voltage as a starting voltage. Specifically, when the HV pin receives the starting voltage, the control circuit U1 starts, and after starting, the VCC pin supplies power to the control circuit U1.

[0102] Pin DRV is connected with power switch M1, for outputting a switch control signal to control the duty ratio and / or the switching frequency of power switch M1, so that the output current and the output voltage of the switch mode converter meet the selected voltage parameters and current parameters.

[0103] Pin CS is connected with the primary side current sampling circuit, for receiving the primary side current sampling signal Vcs.

[0104] Pin GND is grounded.

[0105] Further, Figure 3 is a schematic diagram of the control circuit of an embodiment of the present application. In Figure 3 In the embodiment shown, the control circuit U1 includes an overcurrent protection circuit 1 and a control signal generation circuit 2. The overcurrent protection circuit 1 is configured to obtain an overcurrent reference threshold value according to an output voltage sampling signal representing the output voltage of the switch mode converter, and generate an overcurrent protection trigger signal Sovp in response to the output current sampling signal representing the output current of the switch mode converter and the overcurrent reference threshold value satisfying a predetermined condition, wherein the overcurrent reference threshold value meets the current requirement of the limited power supply. The control signal generation circuit 2 controls the switch converter to enter a protection state in response to the valid overcurrent protection trigger signal Sovp. In this embodiment, the predetermined condition is set according to the application of the control circuit U1 to provide overcurrent protection and control the switch converter to enter the protection state when overcurrent occurs in the switch converter. When the switch mode converter does not have overcurrent, the overcurrent protection circuit 1 does not output the overcurrent protection trigger signal, or the outputted overcurrent protection trigger signal Sovp is an invalid signal, at this time, the control signal generation circuit 2 is only controlled by the compensation signal Vcomp and generates a control signal Gm to adjust the output voltage and / or the output current of the switch mode converter. When the overcurrent protection circuit 1 detects that the switch mode converter has overcurrent, the outputted overcurrent protection trigger signal Sovp is a valid signal, so that the control signal generation circuit 2 does not output the switch control signal Gm, or the outputted switch control signal Gm makes the power switch M1 turn off.

[0106] In the embodiment, the over-current protection circuit 1 is configured to select a corresponding over-current reference threshold according to the change of the output voltage by an algorithm or an analog / digital circuit. The over-current reference threshold is configured to gradually decrease with the increase of the output voltage within a predetermined range of the output voltage. In one implementation, the over-current protection circuit 1 sets an over-current protection curve according to the application environment, wherein the over-current protection curve is used to represent the corresponding relationship between the output voltage of the switching converter and the over-current reference threshold. The specific relationship can refer to Figure 6 ,7,8.

[0107] Further, the output voltage sampling signal is obtained by sampling the output voltage of the switching converter, and the output current sampling signal is obtained by sampling the output current of the switching converter. In the embodiment, the switching converter is configured as an isolated switching converter as shown in Figure 1 . The over-current protection circuit 1 is configured to generate the output voltage sampling signal according to the auxiliary voltage sampling signal Vsen, wherein the auxiliary voltage sampling signal is obtained by sampling the voltage across the auxiliary winding La coupled with the primary winding Lp of the transformer in the isolated switching converter. Further, the over-current protection circuit 1 is configured to obtain the output current sampling signal according to the auxiliary voltage sampling signal Vsen and the primary current sampling signal, wherein the primary current sampling signal is used to represent the current flowing through the primary winding.

[0108] In the embodiment, the control signal generation circuit 2 receives the compensation signal Vcomp, wherein the compensation signal is transmitted from the secondary side circuit to the control signal generation circuit 2 through an optocoupler.

[0109] Further, the compensation signal Vcomp of the embodiment is used to represent the difference between the output voltage Vout and the expected voltage, wherein the expected voltage is the charging voltage of the charging device obtained by the power transfer protocol control module U2. Specifically, as described above, the charging device will query the register in the power transfer protocol control module U2 through XP1 to determine the output voltage allowed by the switching converter, then select the voltage parameter and inform the power transfer protocol control module U2. Thus, the power transfer protocol control module U2 can obtain the expected voltage, and as shown in Figure 1 , the output end of the power transfer protocol control module U2 is connected to the output end of the secondary side circuit to obtain the output voltage Vout, so as to obtain the difference signal between the output voltage Vout and the expected voltage. The difference signal is output to the negative electrode of the light-emitting diode in the optocoupler U3a, and the positive electrode of the light-emitting diode in the optocoupler U3a is connected to the output end of the secondary side circuit through the resistor R7. The optocoupler generates the compensation signal Vcomp according to the difference signal, so that the control signal generation circuit 2 controls the conduction and turn-off of the power switch according to the compensation signal Vcomp to make the output voltage Vout of the switching converter correspond to the expected voltage.

[0110] It should be understood that, Figure 3 The illustrated embodiment is described as an example in which the control signal generation circuit 2 can simultaneously implement two functions, i.e., controlling the duty cycle and / or frequency of the power switch M1 when the switching converter is in a normal operating state, and controlling the switching converter to enter a protection state when the switching converter is in an overcurrent state. However, embodiments of the present application are not limited to the implementation described above, for example, the control circuit U1 can also have two control signal generation circuits, i.e., a first control signal generation circuit and a second control signal generation circuit. In the normal operating state of the switching converter, the first control signal generation circuit is in operation to control the duty cycle and / or frequency of the power switch M1, and the second control signal generation circuit is not in operation. In the overcurrent state of the switching converter, the second control signal generation circuit is in operation to control the switching converter to enter a protection state, and the first control signal generation circuit is not in operation.

[0111] Specifically, Figure 4 is a signal waveform diagram of the switching converter according to an embodiment of the present application. In Figure 4 In the illustrated embodiment, Figure 1 The switching control signal of the power switch M1 is a PWM (Pulse Width Modulation) signal in the illustrated embodiment of the isolation type switching converter. By controlling the duty cycle and / or frequency of the PWM signal, the output voltage and / or output current of the switching converter can be controlled. Thus, the output voltage and / or output current of the switching converter can be adjusted by the PWM signal to provide a suitable charging voltage and / or charging current for the connected charging device.

[0112] Further, according to the operating state of the power switch M1 and the transformer T1, one operating cycle can be divided into three stages. The operating cycle t2-t5 is described as an example:

[0113] In the first stage (t2-t3 period), the PWM signal is high, the power switch M1 is turned on, the current flowing through the primary winding Lp gradually rises, and the primary winding Lp is charged.

[0114] The auxiliary voltage sampling signal Vsen can be expressed as:

[0115]

[0116] where Na is the number of turns of the auxiliary winding La, Ns is the number of turns of the secondary winding Ls, and Vout is the output voltage of the switching converter.

[0117] Since Na, Np, R2, R3 are constants, the auxiliary voltage sampling signal Vsen is proportional to the output voltage Vout, thus, the auxiliary voltage sampling signal Vsen keeps constant during the time period t2-t3.

[0118] Meanwhile, the change trend of the primary current sampling signal Vcs is consistent with the change trend of the current flowing through the primary winding, both of which are gradually increasing.

[0119] The second stage (time period t3-t4) is the demagnetization time interval of the transformer T1, at this time, the PWM signal is switched to low level, the power switch M1 is turned off, the primary winding Lp transfers energy to the secondary winding Ls, the current flowing through the secondary winding Ls continues to decrease until the current decreases to zero.

[0120] At this time, the auxiliary voltage sampling signal Vsen can be expressed as:

[0121]

[0122] Wherein, Vout is the output voltage of the switching converter, Na is the number of turns of the auxiliary winding La, and Ns is the number of turns of the secondary winding Lp.

[0123] Since Ns, Na, R2 and R3 are constants, the auxiliary voltage sampling signal Vsen is proportional to the output voltage Vout.

[0124] Meanwhile, when the power switch M1 is turned off, the primary current sampling signal Vcs is zero.

[0125] Meanwhile, the secondary current Is of the secondary winding of the transformer T1 gradually decreases from the peak value to zero. Since the output current Iout of the switching converter is the average value of the secondary current Is, the peak value of the secondary current Is can be derived from the primary current sampling signal Vcs, thus, the demagnetization time Tdis (time t3 to time t4) of the transformer can be calculated to calculate the value of the output current Iout.

[0126] In the third stage (time period t4-t5), after the current of the secondary winding Ls decreases to zero, since the power switch M1 has not yet been turned on, the primary winding Lp, the power switch M1 and the parasitic capacitance of the circuit resonate, so that the auxiliary voltage sampling signal Vsen fluctuates around zero and the amplitude gradually decreases until the power switch M1 is turned on next time.

[0127] Thus, by the above method, the control signal generation circuit 2 can adjust the duty ratio and / or the switching frequency of the power switch M1 to make the output current and the output voltage of the switching converter meet the selected voltage parameters and current parameters.

[0128] In the embodiment, the over-current protection circuit 1 is configured to detect whether the switching converter is over-current, and output an over-current protection trigger signal Sovp as an effective signal to make the control signal generation circuit 2 not output the control signal Gm or output the switch control signal Gm to make the power switch M1 turn off if the switching converter is detected to be over-current.

[0129] Specifically, Figure 5 is a circuit diagram of the over-current protection circuit of the embodiment. In the embodiment, the over-current protection circuit is applied to Figure 1 a switching converter with isolation is taken as an example for illustration. In Figure 5 the embodiment shown, the over-current protection circuit 1 includes an output current detection circuit 11, a reference threshold generation circuit 12 and a trigger signal generation circuit 13. The output current detection circuit 11 is configured to determine an output current sample signal Viout_psr of the switching converter according to a primary side current sample signal Vcs and an auxiliary voltage sample signal Vsen. The reference threshold generation circuit 12 is configured to obtain an over-current reference threshold Viout_ocp according to an output voltage sample signal and a predetermined over-current protection curve, the over-current protection curve being configured to represent a corresponding relationship between the output voltage and the over-current reference threshold. The trigger signal generation circuit 13 is configured to generate an over-current protection trigger signal Sovp to make the switching converter enter a protection state in response to the output current sample signal Viout_psr and the over-current reference threshold Viout_ocp satisfying a predetermined condition.

[0130] In the embodiment, the output current detection circuit 11 includes a demagnetization time sampling circuit 111, a current peak sampling circuit 112 and a current determination circuit 113. The demagnetization time sampling circuit 111 is configured to obtain a demagnetization time sample signal Tdis_knee according to the auxiliary voltage sample signal Vsen, the demagnetization time sample signal Tdis_knee being configured to represent a demagnetization time of a transformer of the switching converter. The current peak sampling circuit 112 is configured to obtain a current peak sample signal Vcspk according to the primary side current sample signal Vcs. The current determination circuit 113 is configured to determine the output current sample signal Viout_psr according to the demagnetization time sample signal Tdis_knee and the current peak sample signal Vcspk.

[0131] The demagnetization time sampling circuit 111 is connected with the auxiliary voltage sampling circuit and receives the auxiliary voltage sample signal Vsen to obtain the demagnetization time sample signal Tdis_knee according to the auxiliary voltage sample signal Vsen. Specifically, in combination with Figure 4 , the time period of t3-t4 is the demagnetization time Tdis of the transformer of the switching converter.

[0132] The current peak sampling circuit 112 is connected with the primary current sampling circuit, receives the primary current sampling signal Vcs, and acquires the current peak sampling signal Vcspk according to the primary current sampling signal Vcs. Specifically, the current peak sampling circuit 112 determines the peak value of the primary current sampling signal Vcs, and maintains the peak value signal to output the current peak sampling signal Vcspk.

[0133] As described above, the peak value of the secondary current Is can be derived according to the primary current sampling signal Vcs, and thus the demagnetization time Tdis of the transformer can be calculated to obtain the value of the output current Iout. Therefore, the current determination circuit 113 is connected with the output ends of the demagnetization time sampling circuit 111 and the current peak sampling circuit 112, receives the demagnetization time sampling signal Tdis_knee and the current peak sampling signal Vcspk, and determines the output current sampling signal Viout_psr according to the demagnetization time sampling signal Tdis_knee and the current peak sampling signal Vcspk.

[0134] Specifically, Figure 6 is a circuit diagram of the current determination circuit of the embodiment of the present application. As shown in Figure 6 , the current determination circuit 113 includes an input end B1, an output end B2, a switch SW2, a switch SW3, a filter circuit, and a logic circuit. The logic circuit is configured to control the switch SW2 and the switch SW3 to be turned on or turned off according to the control signal PWM of the power switch M1 and the demagnetization time sampling signal Tdis_kee representing the demagnetization time of the transformer, so that the output current sampling signal Viout_psr output by the output end B2 represents the output current equal to or close to the secondary output current in one working cycle.

[0135] Specifically, in one working cycle, the switch SW2 is controlled to be turned on during demagnetization, while the switch SW3 is turned off, so that the input end of the filter circuit, i.e. the voltage at point E, is the current peak sampling signal Vcspk; after the demagnetization of the transformer ends, the switch SW2 is controlled to be turned off, and the switch SW3 is controlled to be turned on, so that the input end of the filter circuit, i.e. the voltage at point E, is zero.

[0136] In the embodiment, the filter circuit is a two-stage RC filter. The first-stage RC filter includes a resistor R9 and a capacitor C6, which are connected in series between the input end of the filter circuit and the reference ground. The second-stage RC filter includes a resistor R10 and a capacitor C7, which are connected in series between the common point of the resistor R9 and the capacitor C6 and the reference ground. The non-ground end of the capacitor C7 is the output end B2.

[0137] In an optional implementation, the logic circuit is an RS flip-flop. Specifically, the set end S of the RS flip-flop receives the inverse signal PWMB of the control signal PWM, the reset end R receives the demagnetization time sampling signal Tdis_knee, and the two output ends are Q and Q', respectively. Figure 4 During the t3-t6 period, at the t3 moment, the signal PWMB is switched from low to high, the RS flip-flop is set, the output signal of the output end Q is high, and the output signal of the output end Q' is low. At this time, SW2 is turned on, SW3 is turned off, and the E point receives the current peak sampling signal Vcspk. At the t4 moment, the secondary side current Is drops to zero, indicating that the demagnetization of the transformer ends, and thus the demagnetization time sampling signal Tdis_knee is switched from low to high, the RS flip-flop is reset, the output signal of the output end Q is low, and the output signal of the output end Q' is high. At this time, SW2 is turned off, SW3 is turned on, and the E point receives zero voltage until the t6 moment, i.e., the end of a working period. Thus, the output current sampling signal Viout_psr can be obtained:

[0138]

[0139] where Tdis is the demagnetization time of the transformer (i.e. Figure 2 During the t3-t4 period, Tsw is the working period of the switching converter (i.e., the t0-t3 or t3-t6 period).

[0140] The calculation formula of the secondary side output current Iout is:

[0141]

[0142] Therefore, the relationship between the output current sampling signal Viout_psr and the output current Iout is:

[0143]

[0144] From the above formula, it can be seen that the output current sampling signal Viout_psr is proportional to the output current sampling Iout, and thus the signal Viout_psr can represent the secondary side output current Iout. As can be seen from the above formula, the output current sampling signal Viout_psr is proportional to the product of the current peak sampling signal Vcspk and the demagnetization time Tdis, and inversely proportional to the switching period Tsw.

[0145] In the embodiment, the reference threshold generation circuit 12 includes an output voltage sampling circuit 121 and a threshold determination circuit 122.

[0146] In the embodiment, the output voltage sampling circuit 121 is configured to obtain an output voltage sampling signal Vout_sample.

[0147] In an optional implementation, the output voltage sampling circuit 121 obtains the output voltage sampling signal Vout_sample by sampling the output voltage of the switching converter.

[0148] In another optional implementation, the output voltage sampling circuit 121 determines the output voltage sampling signal Vout_sample according to the auxiliary voltage sampling signal Vsen. The output voltage sampling signal Vout_sample is used to represent the output voltage Vout. The threshold determination circuit 122 is configured to determine the overcurrent reference threshold according to the output voltage sampling signal Vout_sample and the overcurrent protection curve.

[0149] Further, the output voltage sampling circuit 121 is configured to determine the output voltage sampling signal Vout_sample according to the auxiliary voltage sampling signal Vsen during demagnetization (i.e. within the time Tis). Wherein the relationship between the auxiliary voltage sampling signal Vsen and the output voltage Vout can be represented as:

[0150]

[0151] Wherein Vsen is the auxiliary voltage sampling signal, Vout is the output voltage of the secondary winding, Na is the number of turns of the auxiliary winding La, and Ns is the number of turns of the secondary winding Ls.

[0152] Thus, according to the above formula, the output voltage sampling circuit 121 can determine the output voltage sampling signal Vout_sample according to the auxiliary voltage sampling signal Vsen. Wherein the output voltage sampling signal Vout_sample can be equal to the output voltage Vout, or can be in a predetermined proportional relationship with the output voltage Vout.

[0153] Further, the threshold determination circuit 122 determines the overcurrent reference threshold according to the output voltage sampling signal Vout_sample and the overcurrent protection curve.

[0154] Specifically, Figure 7 is a schematic diagram of an overcurrent protection curve of an embodiment of the present application. In Figure 7 In the embodiment shown, the horizontal axis is the output voltage Vout, and the vertical axis is the signal overcurrent reference threshold Viout_ocp, wherein the overcurrent reference threshold Viout_ocp is used to represent the output current Iout.

[0155] Wherein:

[0156] When the output voltage Vout is less than the first threshold Vout1, i.e. Vout < Vout1, the overcurrent reference threshold Viout_ocp = Vref1.

[0157] When the output voltage Vout is not less than the first threshold Vout1 and less than the second threshold Vout2, i.e. Vout1≤ Vout < Vout2, the overcurrent reference threshold Viout_ocp varies with the change of Vout, where the overcurrent reference threshold is Viout_ocp = K*Vout, and K = -(Vref1-Vref2) / (Vout1-Vout2).

[0158] When the output voltage Vout is not less than the second threshold Vout2, Vout≥ Vout2, the overcurrent reference threshold Viout_ocp = Vref2.

[0159] Thus, the corresponding overcurrent reference threshold can be determined according to the output voltage sampling signal.

[0160] It should be understood that, Figure 7 The overcurrent protection curve shown is only an example of the embodiment of the present application, and the embodiment of the present application does not limit the curve of the overcurrent protection curve, and other types of curves are also applicable to the technical solution of the embodiment of the present application, for example, a segmented overcurrent protection curve and a curved overcurrent protection curve.

[0161] For example, Figure 8 is a schematic diagram of an overcurrent protection curve of another embodiment of the present application. In Figure 8 In the embodiment shown, the abscissa is the output voltage Vout, and the ordinate is the overcurrent reference threshold Viout_ocp, where the signal Viout_ocp is used to represent the output current Iout. Wherein:

[0162] When the output voltage Vout is less than the first threshold Vout1, i.e. Vout < Vout1, the overcurrent reference threshold Viout_ocp = Vref1.

[0163] When the output voltage Vout is not less than the first threshold Vout1 and less than the second threshold Vout2, i.e. Vout1≤ Vout < Vout2, the overcurrent reference threshold Viout_ocp varies with the change of Vout, where the overcurrent reference threshold is Viout_ocp = K1*Vout, and K1 = -(Vref1-Vref2) / (Vout1-Vout2).

[0164] When the output voltage Vout is not less than the second threshold Vout2 and less than the third threshold Vout3, i.e. Vout2≤Vout<Vout3, the over-current reference threshold Viout_ocp=Vref2.

[0165] When the output voltage Vout is not less than the third threshold Vout3 and less than the fourth threshold Vout4, i.e. Vout3≤Vout<Vout4, the over-current reference threshold Viout_ocp varies with Vout, in the embodiment, the over-current reference threshold is Viout_ocp=K2*Vout, wherein K2=-(Vref2-Vref3) / (Vout3-Vout4).

[0166] When the output voltage Vout is not less than the fourth threshold Vout4, i.e. Vout≥Vout4, the over-current reference threshold Viout_ocp=Vref3.

[0167] For example, the over-current protection curve of the embodiment is shown in FIG. 2. In the embodiment, the horizontal axis is the output voltage Vout, and the vertical axis is the signal Viout_ocp, wherein the signal Viout_ocp is used to represent the output current Iout. In the embodiment, the over-current reference threshold Viout_ocp is a function of the output voltage Vout, and the relationship between the over-current reference threshold Viout_ocp and the output voltage Vout is shown in FIG. 2. Figure 9 Figure 9 When the output voltage Vout is less than the first threshold Vout1, i.e. Vout<Vout1, the over-current reference threshold Viout_ocp=Vref1.

[0168] When the output voltage Vout is greater than the second threshold Vout2, i.e. Vout>Vout2, the over-current reference threshold Viout_ocp=Vref2.

[0169] When the output voltage Vout is not less than the first threshold Vout1 and not greater than Vout2, i.e. Vout1≤Vout≤Vout2, the over-current reference threshold Viout_ocp varies with Vout, and the relationship curve is shown in FIG. 1.

[0170] When the output voltage Vout is not less than the first threshold Vout1 and not greater than Vout2, i.e. Vout1≤Vout≤Vout2, the over-current reference threshold Viout_ocp varies with Vout, and the relationship curve is shown in FIG. 1. Figure 9

[0171] In an optional implementation, the reference threshold generating circuit 12 can be implemented by a processor and a memory, wherein the memory is used to store one or more computer program instructions, the computer program instructions being the relationship curve between Vout and Viout_ocp, and the one or more computer program instructions are executed by the processor to realize obtaining the over-current reference threshold Viout_ocp corresponding to Vout.

[0172] ​​In another optional implementation, the reference threshold generating circuit 12 can also be implemented by a circuit. Figure 7 The overcurrent protection curve is described by taking the overcurrent protection curve shown in the figure as an example. Figure 10 FIG. 1 is a circuit diagram of a reference threshold generating circuit according to an embodiment of the present application. Figure 10 In the embodiment shown in the figure, I1, I1*k3, I1*k4 and I1*k5 are respectively currents output by a plurality of different current sources, the input signals of the reference threshold generating circuit are Vref and Vout, and the output signal is Viout_ocp, wherein Vref is a reference voltage, and Vout is an output voltage. According to the circuit shown in the figure, it can be known that: Figure 10

[0173] The calculation formula of the overcurrent reference threshold Viout_ocp is:

[0174] Viout_ocp=Rb*[I1*k3+I1*k4-I(M3)]

[0175] Wherein, I(M3) is a current flowing through the switch M3.

[0176] Further, the calculation formula of I(M3) is:

[0177] I(M3)=I(Rd)-I(Rc)

[0178] Wherein, I(Rd)=Vx / Rd, and I(Rc)=I1*k5.

[0179] According to the virtual short concept of the operational amplifier U5, the voltage at the non-inverting input terminal is the same as the voltage at the inverting input terminal, so Vout=Vx+I1*k5*Rc.

[0180] Therefore, it can be obtained that:

[0181]

[0182] That is:

[0183]

[0184] Wherein, I1=Vref / Ra.

[0185] In addition, in combination with Vref1 and Vref2 in the figure, Rb*I1*k3=Vref2, and Rb*(I1*k3+I1*k4)=Vref1. Figure 7

[0186] ​​Thus, when the output voltage Vout is relatively high, higher than the second threshold Vout2, I(M3)>(I1*k4), the current in D8 is 0, and Viout_ocp=Rb*I1*k3, even if the output voltage Vout is higher, the overcurrent reference threshold Viout_ocp is not affected, thus Viout_ocp=Rb*I1*k3=Vref2.

[0187] When the output voltage Vout is relatively low, lower than the first threshold Vout1, at this time I(M3) current is 0, Viout_ocp=Rb*(I1*k3+I1*k4)=Vref1, even if the output voltage Vout is lower, the overcurrent reference threshold Viout_ocp will remain unchanged.

[0188] When Vout1<Vout<Vout2, Viout_ocp is:

[0189]

[0190] Since Rb, I1, k3, I1, k4, k5, Rc, Rd are all constant values, the above formula can be simplified as:

[0191] Viout_ocp=K6-K7*Vout

[0192] Where K6, K7 are constants.

[0193] Thus, through the above circuit, the corresponding overcurrent reference threshold Viout_ocp can be output when the output voltage Vout is different. So that no matter how the input voltage or the output voltage changes, a relatively accurate overcurrent reference threshold can be provided.

[0194] Further, the overcurrent protection curve can be set according to LPS, or according to actual demand. Specifically, when the overcurrent protection curve is set according to LPS, assuming that the output power of the PD power supply is 65W, the LPS requirement is: the output voltage is 3V-21V, and the maximum output current is 8A. The corresponding curve is as shown in Figure 11 Figure 11 The relationship curves of the LPS limit current Iout_lps, the overcurrent reference threshold maximum value Iout_ocp_max, the overcurrent reference threshold standard value Iout_ocp_typical, the overcurrent reference threshold minimum value Iout_ocp_min, the output rated current Iout_rating and the output voltage Vout are shown respectively.

[0195] The uppermost curve is the curve of the LPS limit current Iout_lps, and the limit current Iout_lps is different at different output voltages Vout. ​

[0196] The lowermost curve is the output rated current Iout_rating, which is different at different output voltages Vout.

[0197] The middle three curves are overcurrent reference thresholds, considering the production deviation, the three curves are overcurrent reference threshold maximum Iout_ocp_max, overcurrent reference threshold typical Iout_ocp_typical and overcurrent reference threshold minimum Iout_ocp_min. The overcurrent protection curve of the embodiment of the present application can be the overcurrent reference threshold maximum Iout_ocp_max.

[0198] Further, referring back to Figure 5 The trigger signal generation circuit 13 is configured to output the overcurrent protection trigger signal in response to the output current sampling signal and the overcurrent reference threshold satisfying a predetermined condition. Further, the trigger signal generation circuit 13 includes a comparison circuit CMP. The comparison circuit is implemented by a comparator CMP, the non-inverting input terminal of the comparator CMP receives the output current sampling signal Viout_psr, the inverting input terminal receives the overcurrent reference threshold Viout_ocp, and outputs the comparison result of the secondary side output current Viout_psr and the overcurrent reference threshold Viout_ocp. The trigger signal generation circuit 13 triggers the overcurrent protection in response to the secondary side output current being greater than the overcurrent reference threshold. In addition, in order to avoid false triggering, the trigger signal generation circuit 13 further includes a timing circuit 131, which is configured to output the overcurrent protection trigger signal in response to the comparison result being that the output current sampling signal is greater than the overcurrent reference threshold for a predetermined time length.

[0199] Specifically, when the output current sampling signal Viout_psr is greater than the overcurrent reference threshold Viout_ocp, the comparison circuit CMP outputs a high level; when the output current sampling signal Viout_psr is less than the overcurrent reference threshold Viout_ocp, the comparison circuit CMP outputs a low level. The timing circuit 131 is configured to start timing when a high level is received, and output the overcurrent protection trigger signal Sovp when the timing satisfies a predetermined time length.

[0200] More specifically, the timing circuit 131 is configured to start timing when a high level is received, and end timing when a low level is received. In this way, the overcurrent protection trigger signal Sovp can be output when the time length during which the output current sampling signal Viout_psr is greater than the overcurrent reference threshold Viout_ocp exceeds the predetermined time length. In this way, false triggering caused by various noises such as ESD (Electro-Static discharge) of the circuit, pulse group, etc. on Iout can be avoided.

[0201] In the embodiment, the control signal generating circuit 2 is configured to control the switch mode converter to enter the protection state according to the over-current protection trigger signal Sovp.

[0202] Further, when the control signal generating circuit 2 does not receive the over-current protection trigger signal Sovp, the switch control signal is generated to control the power switch to be turned on or turned off, so that the output voltage and / or the output current of the switch mode converter meet the predetermined condition. When the over-current protection trigger signal Sovp is received, the power switch is controlled to be turned off, so that the switch mode converter enters the protection state.

[0203] It should be understood that, in the above embodiment, the output voltage sampling signal is calculated according to the auxiliary voltage sampling signal, but the embodiment of the present application is not limited thereto, and the output voltage of the switch mode converter can also be directly sampled. Meanwhile, the output current sampling signal is calculated according to the peak current sampling signal and the demagnetization time sampling signal, but the embodiment of the present application is not limited thereto, and the output current of the switch mode converter can also be directly sampled.

[0204] It should also be understood that, in the above embodiment, the switch mode converter is taken as an example of the isolated switch mode converter, but the embodiment of the present application is not limited thereto, and the control circuit of the embodiment of the present application can be applied to various switch mode converters.

[0205] The embodiment of the present application determines the over-current reference threshold value according to the output voltage sampling signal and the predetermined over-current protection curve, and generates the over-current protection trigger signal when the output current sampling signal and the over-current reference threshold value meet the predetermined condition, so that the switch mode converter enters the protection state. Thus, the over-current protection can be provided for the switch mode converter under the premise of meeting the requirements of the limited power supply, and the safety hazard is reduced.

[0206] Figure 12 is a flow chart of the control method of the embodiment of the present application. As shown in Figure 12 the control method of the embodiment of the present application includes the following steps:

[0207] Step S100, selecting an over-current reference threshold value according to an output voltage sampling signal representing the output voltage of the switch mode converter, the over-current reference threshold value meeting the current requirement of the limited power supply.

[0208] Step S200, generating an over-current protection trigger signal in response to the output current sampling signal representing the output current of the switch mode converter and the over-current reference threshold value meeting the predetermined condition, so that the switch mode converter enters the protection state.

[0209] In some embodiments, the over-current protection trigger signal is used to turn off a power switch of the switching converter so that the switching converter enters a protection state.

[0210] In some embodiments, the method further comprises:

[0211] In response to the over-current protection trigger signal not being generated, a switching control signal is generated to control the power switch of the switching converter to turn on or turn off so that an output voltage and / or an output current of the switching converter meets a predetermined requirement.

[0212] In some embodiments, the output voltage sampling signal is obtained by sampling an output voltage of the switching converter, and the output current sampling signal is obtained by sampling an output current of the switching converter.

[0213] In some embodiments, when the switching converter is configured as an isolated switching converter, the output voltage sampling signal is determined by an auxiliary voltage sampling signal;

[0214] wherein the auxiliary voltage sampling signal is obtained by sampling a voltage across an auxiliary winding coupled to a primary winding of a transformer in the isolated switching converter.

[0215] In some embodiments, the output current sampling signal is obtained by:

[0216] a demagnetization time sampling signal is obtained according to the auxiliary voltage sampling signal, the demagnetization time sampling signal being used to represent that the transformer is in a demagnetization period; and

[0217] the output current sampling signal is determined according to the demagnetization time sampling signal and a primary current peak value sampling signal.

[0218] In some embodiments, the predetermined condition is that the output current sampling signal is greater than the over-current reference threshold for a predetermined time length.

[0219] In some embodiments, the output current sampling signal being determined according to the demagnetization time sampling signal and the primary current peak value sampling signal comprises:

[0220] during the demagnetization period of the transformer in one working cycle, an input signal of a filter circuit of a current determination circuit is maintained as the primary current peak value sampling signal;

[0221] when it is detected that the demagnetization is completed, the input signal of the filter circuit of the current determination circuit is controlled to be zero; and

[0222] the output current sampling signal is generated by the filter circuit of the current determination circuit.

[0223] Embodiments of the present application select an over-current reference threshold according to an output voltage sampling signal, generate an over-current protection trigger signal when an output current sampling signal and the over-current reference threshold satisfy a predetermined condition, so as to make the switching converter enter a protection state. Thus, over-current protection can be provided for the switching converter under the premise of meeting the requirements of a limited power supply, and safety hazards are reduced.

[0224] Further, embodiments of the present application also provide an integrated circuit applied to a switching converter, the integrated circuit comprising:

[0225] an over-current protection circuit configured to select an over-current reference threshold according to an output voltage sampling signal representing an output voltage of the switching converter, generate an over-current protection trigger signal in response to an output current sampling signal representing an output current of the switching converter and the over-current reference threshold satisfying a predetermined condition, and the over-current reference threshold satisfying a current requirement of a limited power supply; and

[0226] a control signal generation circuit configured to control the switching converter to enter a protection state in response to receiving the over-current protection trigger signal.

[0227] In some embodiments, the control signal generation circuit is further configured to generate a switching control signal to control a power switch of the switching converter to turn on or turn off, so that the output voltage and / or the output current of the switching converter satisfy a predetermined requirement, in response to not receiving the over-current protection trigger signal.

[0228] In some embodiments, the over-current protection circuit comprises:

[0229] a reference threshold generation circuit configured to obtain an over-current reference threshold according to an output voltage sampling signal representing an output voltage of the switching converter; and

[0230] a trigger signal generation circuit configured to generate an over-current protection trigger signal in response to an output current sampling signal representing an output current of the switching converter and the over-current reference threshold satisfying a predetermined condition.

[0231] In some embodiments, the output voltage sampling signal is obtained by sampling the output voltage of the switching converter, and the output current sampling signal is obtained by sampling the output current of the switching converter.

[0232] In some embodiments, when the switching converter is configured as an isolated switching converter, the reference threshold generation circuit comprises:

[0233] The output voltage sampling circuit is configured to obtain an output voltage sampling signal according to an auxiliary voltage sampling signal, wherein the auxiliary voltage sampling signal is obtained by sampling a voltage across an auxiliary winding coupled to a primary winding of a transformer in the isolated switching converter; and

[0234] The threshold determination circuit is configured to determine the over-current reference threshold according to the output voltage sampling signal and the over-current protection curve.

[0235] In some embodiments, the over-current protection circuit further comprises:

[0236] The output current detection circuit is configured to obtain an output current sampling signal according to the auxiliary voltage sampling signal and a primary current sampling signal, the primary current sampling signal being used to represent a current flowing through the primary winding.

[0237] In some embodiments, the output current detection circuit comprises:

[0238] The demagnetization time sampling circuit is configured to obtain a demagnetization time sampling signal according to the auxiliary voltage sampling signal, the demagnetization time sampling signal being used to represent a period during which the transformer of the switching converter is in demagnetization;

[0239] The current peak sampling circuit is configured to obtain a current peak sampling signal according to the primary current sampling signal; and

[0240] The current determination circuit is configured to determine the output current sampling signal according to the demagnetization time sampling signal and the current peak sampling signal.

[0241] In some embodiments, the predetermined condition is that the output current sampling signal is greater than the over-current reference threshold for a predetermined time length.

[0242] In some embodiments, the trigger signal generation circuit comprises:

[0243] The comparison circuit is configured to obtain a comparison result of the output current sampling signal and the over-current reference threshold; and

[0244] The timing circuit is configured to output the over-current protection trigger signal in response to the comparison result being that the output current sampling signal is greater than the over-current reference threshold for a predetermined time length.

[0245] In some embodiments, the current determination circuit comprises:

[0246] The first input terminal is configured to receive the current peak sampling signal;

[0247] The first output terminal is configured to output the output current sampling signal;

[0248] a first switch;

[0249] a filter circuit connected in series with the first switch between the first input terminal and a first output terminal, and comprising at least one capacitor;

[0250] a second switch connected in series with the first switch between the first input terminal and a ground terminal; and

[0251] a logic circuit configured to, in a working period, control the first switch to be turned on and the second switch to be turned off during demagnetization of the transformer, so as to keep an input signal of the filter circuit as the primary-side current peak sampling signal, and control the input signal of the filter circuit of the current determination circuit to be zero when it is detected that the demagnetization is completed, so that the filter circuit outputs the output current sampling signal.

[0252] The embodiment of the present application determines an overcurrent reference threshold according to an output voltage sampling signal and a predetermined overcurrent protection curve, generates an overcurrent protection trigger signal when an output current sampling signal and the overcurrent reference threshold meet a predetermined condition, and makes the switching converter enter a protection state. Thus, overcurrent protection can be provided for the switching converter under the premise of meeting the requirement of the limited power supply, and the safety hazard is reduced.

[0253] The above merely describes the preferred embodiments of the present application and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A control method applied to a switching converter, characterized in that, The method comprises: selecting an over-current reference threshold according to an output voltage sampling signal representing an output voltage of the switching converter, the over-current reference threshold satisfying a current requirement of the limited power supply; and generating an over-current protection trigger signal to make the switching converter enter a protection state in response to an output current sampling signal representing an output current of the switching converter and the over-current reference threshold satisfying a predetermined condition; wherein the over-current reference threshold is configured to gradually decrease with the increase of the output voltage within a predetermined range of the output voltage.

2. The method of claim 1, wherein, controlling a power switch of the switching converter to be turned off in response to generating a valid over-current protection trigger signal to make the switching converter enter a protection state; and wherein the over-current reference threshold is configured to gradually decrease with the increase of the output voltage within a predetermined range of the output voltage. controlling a power switch of the switching converter to be turned off in response to generating a valid over-current protection trigger signal to make the switching converter enter a protection state; and 3. The method of claim 1, wherein, wherein the over-current reference threshold is configured to gradually decrease with the increase of the output voltage within a predetermined range of the output voltage.

4. The method of claim 1, wherein, The output voltage sampling signal is obtained by sampling an output voltage of the switching converter, and the output current sampling signal is obtained by sampling an output current of the switching converter. When the switching converter is configured as an isolated switching converter, the output voltage sampling signal is determined by an auxiliary voltage sampling signal; 5. The method of claim 4, wherein, wherein the auxiliary voltage sampling signal is obtained by sampling a voltage across an auxiliary winding coupled to a primary winding of a transformer in the isolated switching converter. The output current sampling signal is obtained by: obtaining a demagnetization time of the transformer; obtaining a current peak sampling signal representing a peak value of a primary current of the switching converter; and 6. The method of claim 1, wherein, determining the output current sampling signal such that the output current sampling signal is in a positive proportional relationship with a product of the current peak sampling signal and the demagnetization time and in an inverse proportional relationship with a switching period.

7. The method of claim 5, wherein, The predetermined condition is that a time length during which the output current sampling signal is continuously greater than the over-current reference threshold reaches a predetermined duration. The method further comprises: maintaining an input signal of a filter circuit as the current peak sampling signal during demagnetization of the transformer in one switching cycle; controlling the input signal of the filter circuit to be zero when it is detected that the demagnetization is completed; and generating the output current sampling signal at an output terminal of the filter circuit.

8. A control circuit applied to a switching converter, characterized in that, The control circuit comprises: an over-current protection circuit including a reference threshold generation circuit configured to generate an over-current reference threshold according to an output voltage sampling signal representing an output voltage of the switching converter, and a trigger signal generation circuit configured to generate an over-current protection trigger signal in response to an output current sampling signal representing an output current of the switching converter and the over-current reference threshold satisfying a predetermined condition, the over-current reference threshold satisfying a current requirement of the limited power supply; and a control signal generation circuit configured to control the switching converter to enter a protection state in response to receiving the over-current protection trigger signal; wherein the over-current reference threshold is configured to gradually decrease with the increase of the output voltage within a predetermined range of the output voltage.

9. The control circuit of claim 8, wherein, The control signal generation circuit is further configured to generate a switch control signal to control the power switch of the switching converter to turn on or turn off, so that the output voltage and / or output current of the switching converter meets the predetermined requirement, in response to an invalid over-current protection trigger signal; and control the power switch of the switching converter to turn off, so that the switching converter enters a protection state, in response to receiving a valid over-current protection trigger signal.

10. The control circuit of claim 8, wherein, The output voltage sampling signal is obtained by sampling the output voltage of the switching converter, and the output current sampling signal is obtained by sampling the output current of the switching converter.

11. The control circuit of claim 8, wherein, When the switching converter is configured as an isolated switching converter, the reference threshold generation circuit comprises: an output voltage sampling circuit configured to obtain an output voltage sampling signal according to an auxiliary voltage sampling signal, wherein the auxiliary voltage sampling signal is obtained by sampling the voltage across an auxiliary winding coupled to a primary winding of a transformer in the isolated switching converter; and a threshold determination circuit configured to determine the over-current reference threshold according to the output voltage sampling signal and an over-current protection curve.

12. The control circuit of claim 11, wherein, The over-current protection circuit further comprises: an output current detection circuit configured to obtain a demagnetization time of the transformer and a current peak sampling signal representing a peak value of the primary current, and determine the output current sampling signal, so that the output current sampling signal is in a positive proportional relationship with the product of the current peak sampling signal and the demagnetization time, and in an inverse proportional relationship with a switching period.

13. The control circuit of claim 12, wherein, The output current detection circuit comprises: a demagnetization time sampling circuit configured to obtain a demagnetization time sampling signal representing a demagnetization period of a transformer in the switching converter according to an auxiliary voltage sampling signal; a current peak sampling circuit configured to obtain the current peak sampling signal according to the sampling signal of the primary current; and a current determination circuit configured to determine the output current sampling signal according to the demagnetization time sampling signal and the current peak sampling signal.

14. The control circuit of claim 8, wherein, The predetermined condition is that the output current sampling signal continuously exceeds the over-current reference threshold for a time length reaching a predetermined time duration.

15. The control circuit of claim 8, wherein, The trigger signal generation circuit comprises: a comparison circuit configured to obtain a comparison result of the output current sampling signal and the over-current reference threshold; and a timing circuit configured to output the over-current protection trigger signal in response to the comparison result being that the output current sampling signal exceeds the over-current reference threshold for a predetermined time duration.

16. The control circuit of claim 13, wherein, The current determination circuit comprises: a first input end configured to receive the current peak sampling signal; a first output end configured to output the output current sampling signal; a first switch; a filter circuit connected in series with the first switch between the first input end and the first output end, and comprising at least one capacitor; a second switch connected in series with the first switch between the first input end and a ground end; and The logic circuit is configured to control the first switch to be on and the second switch to be off in a working cycle to keep the input signal of the filter circuit as the current peak sampling signal during demagnetization of the transformer, and control the input signal of the filter circuit of the current determination circuit to be zero when demagnetization is detected to be completed, so that the filter circuit outputs the output current sampling signal.

17. The control circuit of claim 16, wherein, The logic circuit is configured as an RS flip-flop, a set end of which receives a switch control signal, a reset end of which receives the demagnetization time sampling signal, and an output end of which generates a control signal to control the first switch and the second switch respectively.

18. A switching converter, characterized in that, The switching converter comprises: a power stage circuit comprising at least a power switch; and The control circuit according to any one of claims 8-17.

19. An integrated circuit, comprising: The integrated circuit comprises the control circuit according to any one of claims 8-17. The integrated circuit comprises the control circuit according to any one of claims 8-17.

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