Overcurrent protection circuit and overcurrent protection method for DC power supply

Abstract

The present invention discloses an overcurrent protection circuit and an overcurrent protection method for a DC power supply, the circuit comprising: an upper power tube current limiting module, used for sampling the current flowing through the upper power tube, and generating a first feedback signal according to the sampling result; a lower power tube current limiting module, used for sampling the current flowing through the lower power tube, and generating a second feedback signal according to the sampling result, wherein, when the current flowing through the upper power tube meets the first preset condition, the upper power tube is turned off and the lower power tube is turned on; when the current flowing through the lower power tube meets the second preset condition, the upper power tube is allowed to be turned on and the lower power tube is allowed to be turned off. The overcurrent protection of the output current in the DC power supply is jointly performed by the upper power tube current limiting module and the lower power tube current limiting module, which helps to realize the controllable output current when the output is short-circuited or overloaded, so that even in a small switching cycle of the DC power supply, its output current will not increase infinitely, thereby expanding the scope of application.

Description

Technical Field

[0001] The present invention relates to the technical field of overcurrent protection, and in particular to an overcurrent protection circuit and an overcurrent protection method for a DC power supply. Background Art

[0002] As we all know, if the output voltage of a DC power supply is short-circuited or the output load is overloaded, the current flowing through the power tube will increase. If the current is too large, the power switch tube will be burned. Therefore, it is necessary to set an overcurrent protection circuit in the DC power supply for overcurrent protection. At present, there are many kinds of overcurrent protection circuits for DC power supplies. The principle is to convert the current signal into a voltage signal and then compare it to determine whether to perform the protection action. The protection method is mainly divided according to the different sampling points and protection actions. From the different sampling points, it can be divided into inductor current sampling, power tube current sampling, resistor current sampling, etc. From the different protection actions, it can be divided into overcurrent protection signal locking after overcurrent and overcurrent protection signal self-recovery after overcurrent. Among them, the protection signal locking requires the circuit to be restarted to eliminate the protection signal, while the protection signal self-recovery does not require the circuit to be restarted. When the current value drops below the protection point, the protection signal is automatically eliminated.

[0003] For the protection method of power tube current sampling, the common overcurrent protection circuits are as follows Figure 1 As shown, the overcurrent protection function of the DC power supply is mainly to sample the current of the main power tube (upper power tube), thereby controlling the current flowing through the main power switch tube to keep it within the limited value range. Figure 1 As shown in FIG. 1 , it is a working principle diagram of a step-down DC power supply. Among them, the upper power tube M1 and the lower power tube M2 are PMOS transistors and NMOS transistors respectively, and M1 is the main power tube. L is an inductor, and D1 is a parasitic body diode of the lower power tube M2. Co is an output capacitor. CLK is a clock signal.

[0004] refer to Figure 3 ,for Figure 1 The ideal timing waveform of each signal in the circuit shown in the figure, in an ideal state, when the clock signal CLK is at a high level, the upper power tube M1 is turned on. The function of the sampling circuit 2 is to sample the current flowing through the upper power tube M1 and send the signal generated by the sampling circuit 2 to the current limiting circuit 3. Figure 2 The pulse generating circuit 4 generates a high level signal shot with a pulse width of t1 within the time t1 after the upper power tube M1 is turned on. During the time t1, the signal generated by the sampling circuit 2 will be shielded, that is, the current signal of M1 will not be sampled within the time t1.

[0005] The current-limiting circuit 3 processes the signal sent by the sampling circuit 2. When the current flowing through the upper power transistor M1 (corresponding to the output current IL) exceeds the set value I_limit, the feedback signal Limit output by the current-limiting circuit 3 becomes high level and is sent to the drive control circuit 1. The drive control circuit 1 will make the first control signal PON become low level to turn off the upper power transistor M1, thereby preventing the output current IL from further increasing.

[0006] Reference Figure 4 , is the timing waveform diagram of the output current under a small switching period of the DC power supply. In practical applications, since there will be a large amount of noise when the power transistor is turned on, which affects the accuracy of sampling, the overcurrent protection function is generally shielded within a period of time t1 after the power transistor is turned on to avoid the phenomenon of accidentally turning off the power switch transistor due to the influence of noise even when the current is very small, that is, the minimum turn-on time of the upper power transistor M1 is t1. When the output voltage is short-circuited, the rising slope Kr of the output current IL = VIN / L, then the value of the output current IL rising within the time t1 is: VIN * t1 / L. And the falling slope Kf of the output current IL = VD / L, where VIN is the input voltage and VD is the conduction voltage of the diode D1. Assuming that the switching period of the DC power supply is T, then the time for the output current IL to fall is T - t1, so the value of the output current IL falling is: VD * (T - t1) / L. When T < VIN * t1 / D + t1, VIN * t1 / L > VD * (T - t1) / L, that is, the amount of increase in the output current IL within the time t1 is greater than the amount of decrease within the time T - t1. As Figure 4 shown, in this way, the overcurrent protection function of the DC power supply fails. The output current IL of the DC power supply will increase without limit, eventually causing the chip to be damaged.

[0007] Therefore, in the existing solutions, the switching period of the DC power supply cannot be too small, which limits the application range.

[0008] Therefore, it is necessary to provide an improved technical solution to overcome the above technical problems existing in the prior art. Summary of the Invention

[0009] To solve the above technical problems, the present invention provides an overcurrent protection circuit and an overcurrent protection method for a DC power supply, which jointly perform overcurrent protection on the output current in the DC power supply through an upper power transistor current-limiting module and a lower power transistor current-limiting module, helping to achieve controllability of the output current in case of output short-circuit or overload, so that even under a small switching period of the DC power supply, its output current will not increase without limit, expanding the application range.

[0010] In one aspect, according to an overcurrent protection circuit of a DC power supply provided by the present invention, the DC power supply comprises: an upper power tube and a lower power tube connected in series between an input voltage input terminal and a reference ground, the upper power tube is a PMOS transistor, and the lower power tube is an NMOS transistor;

[0011] an inductor and an output capacitor connected in series between the drain of the upper power tube and a reference ground; and

[0012] A driving control circuit, used for generating a first control signal and a second control signal for controlling the on and off of the upper power tube and the lower power tube respectively according to the clock signal;

[0013] The overcurrent protection circuit comprises:

[0014] An upper power tube current limiting module, connected to the upper power tube, for sampling the current flowing through the upper power tube, and generating a first feedback signal to the drive control circuit according to the sampling result;

[0015] A lower power tube current limiting module is connected to the lower power tube and is used to sample the current flowing through the lower power tube and generate a second feedback signal to the drive control circuit according to the sampling result.

[0016] Wherein, when the current flowing through the upper power tube meets the first preset condition, the drive control circuit controls the upper power tube to be turned off and controls the lower power tube to be turned on based on the first feedback signal;

[0017] When the current flowing through the lower power tube meets the second preset condition, the drive control circuit controls the upper power tube to be turned on and controls the lower power tube to be turned off based on the second feedback signal and the clock signal.

[0018] Optionally, when the current flowing through the upper power tube flows in from the source of the upper power tube and flows out from the drain of the upper power tube, the first preset condition is: the current flowing through the upper power tube is greater than a first threshold,

[0019] The second preset condition is: the current flowing through the lower power tube is less than a second threshold value,

[0020] The first threshold and the second threshold are both positive values, and the absolute value of the first threshold is greater than the absolute value of the second threshold.

[0021] Optionally, when the current flowing through the upper power tube flows in from the drain of the upper power tube and flows out from the source of the upper power tube, the first preset condition is: the current flowing through the upper power tube is less than a first threshold value,

[0022] The second preset condition is: the current flowing through the lower power tube is greater than a second threshold value,

[0023] The first threshold and the second threshold are both negative values, and the absolute value of the first threshold is greater than the absolute value of the second threshold.

[0024] Optionally, the upper power tube current limiting module includes:

[0025] a first sampling unit, connected to the upper power tube, and configured to sample the current flowing through the upper power tube;

[0026] The first current limiting unit is connected to the first sampling unit, and is used to process the sampling result of the first sampling unit based on the first threshold value, and generate the first feedback signal according to the processing result.

[0027] Optionally, the upper power tube current limiting module further includes:

[0028] The first pulse generating unit is used to receive the first control signal and generate a shielding signal with a first pulse width when the first control signal is valid, wherein the shielding signal is used to control the first sampling unit and / or the first current limiting unit to not work.

[0029] Optionally, the first pulse width is smaller than a valid duration of the first control signal in one signal cycle.

[0030] Optionally, the lower power tube current limiting module includes:

[0031] a second sampling unit, connected to the lower power tube, and used to sample the current flowing through the lower power tube;

[0032] The second current limiting unit is connected to the second sampling unit, and is used to process the sampling result of the second sampling unit based on the second threshold value, and generate the second feedback signal according to the processing result.

[0033] Optionally, the lower power tube current limiting module further includes:

[0034] The second pulse generating unit is used to receive the second control signal and generate a shielding signal with a second pulse width when the second control signal is valid, wherein the shielding signal is used to control the second sampling unit and / or the second current limiting unit to not work.

[0035] Optionally, the second pulse width is smaller than a valid duration of the second control signal in one signal cycle.

[0036] On the other hand, according to an overcurrent protection method of a DC power supply provided by the present invention, the DC power supply comprises: an upper power tube and a lower power tube connected in series between an input voltage input terminal and a reference ground, the upper power tube is a PMOS transistor, the lower power tube is an NMOS transistor,

[0037] The overcurrent protection method comprises:

[0038] Monitor the current flowing through the upper power tube, and when the current flowing through the upper power tube meets a first preset condition, control the upper power tube to be turned off and control the lower power tube to be turned on;

[0039] The current flowing through the lower power tube is monitored, and when the current flowing through the lower power tube meets a second preset condition, the upper power tube is controlled to be turned on and the lower power tube is controlled to be turned off.

[0040] Optionally, when the current flowing through the upper power tube flows in from the source of the upper power tube and flows out from the drain of the upper power tube, the first preset condition is: the current flowing through the upper power tube is greater than a first threshold,

[0041] The second preset condition is: the current flowing through the lower power tube is less than a second threshold value,

[0042] The first threshold and the second threshold are both positive values, and the absolute value of the first threshold is greater than the absolute value of the second threshold.

[0043] Optionally, when the current flowing through the upper power tube flows in from the drain of the upper power tube and flows out from the source of the upper power tube, the first preset condition is: the current flowing through the upper power tube is less than a first threshold value,

[0044] The second preset condition is: the current flowing through the lower power tube is greater than a second threshold value,

[0045] The first threshold and the second threshold are both negative values, and the absolute value of the first threshold is greater than the absolute value of the second threshold.

[0046] The beneficial effects of the present invention are as follows: the overcurrent protection circuit and overcurrent protection method of the DC power supply disclosed in the present invention not only samples and monitors the current flowing through the upper power tube through the upper power tube current limiting module connected to the upper power tube, so as to control the upper power tube to be turned off and the lower power tube to be turned on when the current meets the first preset condition, thereby realizing the control of the first terminal value (one of the maximum value and the minimum value) of the output current in the DC power supply, but also samples and monitors the current flowing through the lower power tube through the lower power tube current limiting module connected to the lower power tube, so as to allow the upper power tube to be turned on and the lower power tube to be turned off when the current meets the second preset condition, thereby realizing the control of the second terminal value (the other of the maximum value and the minimum value) of the output current in the DC power supply, so that the output current can be controlled when the output is short-circuited or overloaded, effectively avoiding the problem that the output current in the DC power supply will increase without limit under a small switching cycle of the DC power supply when there is only the upper power tube current limiting module in the existing overcurrent protection circuit, thereby expanding the scope of application.

[0047] On the other hand, for DC power supplies with different current directions, the corresponding overcurrent protection function can be achieved by simply changing the preset conditions required for judgment, avoiding the limitation of application scenarios and improving the applicability of the circuit.

[0048] It should be noted that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings.

[0050] Figure 1 A schematic diagram showing the circuit structure of an existing overcurrent protection circuit for a DC power supply is shown;

[0051] Figure 2 A timing waveform diagram showing some signals in a DC power supply circuit;

[0052] Figure 3 The ideal timing waveform diagram of each signal in the overcurrent protection circuit of the existing DC power supply is shown;

[0053] Figure 4 A timing waveform diagram showing the output current of an overcurrent protection circuit of a conventional DC power supply under a small switching cycle of the DC power supply;

[0054] Figure 5 A schematic diagram showing the circuit structure of an overcurrent protection circuit of a DC power supply provided according to an embodiment of the present disclosure is shown;

[0055] Figure 6 A timing waveform diagram of each signal in the overcurrent protection circuit of a DC power supply provided according to an embodiment of the present disclosure is shown;

[0056] Figure 7 A flow chart of an overcurrent protection method for a DC power supply provided according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0057] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0058] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0059] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

[0060] Figure 5 A schematic diagram of the circuit structure of an overcurrent protection circuit of a DC power supply provided according to an embodiment of the present disclosure is shown. Figure 6 The timing waveform diagram of each signal in the overcurrent protection circuit of the DC power supply provided according to the embodiment of the present disclosure is shown.

[0061] In this disclosure, Figure 5 As shown, still taking the step-down DC power supply as an example, the DC power supply includes: an upper power tube M1, a lower power tube M2 (there is a parasitic body diode D1 between the drain and source ends of the lower power tube M2), an inductor L, an output capacitor Co, and a drive control circuit 1. Among them, the upper power tube M1 and the lower power tube M2 are connected in series between the input voltage VIN input terminal and the reference ground, and the upper power tube M1 is a PMOS transistor, and the lower power tube M2 is an NMOS transistor. The inductor L and the output capacitor Co are connected in series between the drain of the upper power tube M1 (i.e., the connection node of the upper power tube M1 and the lower power tube M2) and the reference ground. The drive control circuit 1 is connected to the gate of the upper power tube M1 and the gate of the lower power tube M2 respectively, and is used to generate a first control signal Pon and a second control signal Non for controlling the on and off of the upper power tube M1 and the lower power tube M2 respectively according to the clock signal CLK.

[0062] Since the channel types of the upper power tube M1 and the lower power tube M2 are opposite in the DC power supply, the drive control circuit 1 can optionally generate a first control signal Pon and a second control signal Non having the same level state and provide them to the gate of the upper power tube M1 and the gate of the lower power tube M2 respectively; or, the drive control circuit 1 can generate a first control signal Pon and a second control signal Non having opposite level states, and provide one of them directly to one of the gate of the upper power tube M1 and the gate of the lower power tube M2, and provide the other one of them to the other of the gate of the upper power tube M1 and the gate of the lower power tube M2 after passing through the inverter U1.

[0063] Further, the overcurrent protection circuit of the DC power supply includes: an upper power tube current limiting module 10 and a lower power tube current limiting module 20. The upper power tube current limiting module 10 is connected to the upper power tube M1, and is used to sample the current flowing through the upper power tube M1, and generate a first feedback signal Limit1 to the drive control circuit 1 according to the sampling result. The lower power tube current limiting module 20 is connected to the lower power tube M2, and is used to sample the current flowing through the lower power tube M2, and generate a second feedback signal Limit2 to the drive control circuit 1 according to the sampling result.

[0064] In the present disclosure, when the current flowing through the upper power tube M1 meets the first preset condition, the drive control circuit 1 controls the upper power tube M1 to be turned off and controls the lower power tube M2 to be turned on based on the first feedback signal Limit1; and when the current flowing through the lower power tube M2 meets the second preset condition, the drive control circuit 1 controls the upper power tube M1 to be turned on and controls the lower power tube M2 to be turned off based on the second feedback signal Limit2 and the clock signal CLK.

[0065] It can be understood that in the present disclosure, the current flowing through the upper power tube M1 and the current flowing through the lower power tube M2 are both the same as the inductor current.

[0066] In the first embodiment of the present disclosure, the current flowing through the upper power tube M1 is a forward current (i.e., the direction of the current is flowing from the source of the upper power tube M1 and flowing out from the drain of the upper power tube M1). Correspondingly, at this time, the first preset condition is: the current flowing through the upper power tube M1 is greater than the first threshold, and the second preset condition is: the current flowing through the lower power tube M2 is less than the second threshold. In this embodiment, the first threshold and the second threshold are both positive values, and the absolute value of the first threshold is greater than the absolute value of the second threshold.

[0067] Further, the upper power tube current limiting module 10 includes: a first sampling unit 11, a first current limiting unit 12 and a first pulse generating unit 13. Among them, the first sampling unit 11 is connected to the upper power tube M1, and is used to sample the current flowing through the upper power tube M1. The first current limiting unit 12 is connected to the first sampling unit 11, and is used to process the sampling result of the first sampling unit 11 based on the first threshold value, and generate a first feedback signal Limit1 according to the processing result. The first pulse generating unit 13 is used to receive the first control signal Pon, and when the first control signal Pon is valid (that is, when the first control signal Pon can control the upper power tube M1 to turn on), it generates a shielding signal shot1 with a first pulse width, and the shielding signal shot1 is used to control the first sampling unit 11 and / or the first current limiting unit 12 to not work. A first pulse generating unit 13 is provided in the upper power tube current limiting module 10, which can shield the overcurrent protection function of the upper power tube current limiting module 10 within a period of time after the upper power tube M1 is turned on, thereby avoiding the influence of large noise on sampling accuracy when the upper power tube M1 is turned on, and avoiding the upper power tube M1 being mistakenly turned off due to the influence of noise when the current is very small.

[0068] The lower power tube current limiting module 20 includes: a second sampling unit 21, a second current limiting unit 22 and a second pulse generating unit 23. The second sampling unit 21 is connected to the lower power tube M2, and is used to sample the current flowing through the lower power tube M2. The second current limiting unit 22 is connected to the second sampling unit 21, and is used to process the sampling result of the second sampling unit 21 based on the second threshold value, and generate a second feedback signal Limit2 according to the processing result. The second pulse generating unit 23 is used to receive the second control signal Non, and when the second control signal Non is valid (that is, when the second control signal Non can control the lower power tube M2 to be turned on), a shielding signal shot2 with a second pulse width is generated, and the shielding signal shot2 is used to control the second sampling unit 21 and / or the second current limiting unit 22 to not work. A second pulse generating unit 23 is provided in the lower power tube current limiting module 20, so as to shield the overcurrent protection function of the lower power tube current limiting module 20 within a period of time after the lower power tube M2 is turned on, thereby avoiding the influence of large noise on the sampling accuracy when the lower power tube M2 is turned on, and avoiding the occurrence of the lower power tube M2 being mistakenly turned off due to the influence of noise when the current is very small.

[0069] It can be understood that the first pulse width is less than the effective duration of the first control signal Pon in one signal cycle, and the second pulse width is less than the effective duration of the second control signal Non in one signal cycle. The normal operation of the DC power supply is ensured. Optionally, the first pulse width and the second pulse width can be the same or different, and can be set according to the actual application scenario.

[0070] refer to Figure 6 , when the clock signal CLK is at a high level, the first control signal Pon output by the drive control circuit 1 is at a high level, which controls the upper power tube M1 to be turned on after passing through the inverter U1, and the output second control signal Non is at a low level, which controls the lower power tube M2 to be turned off. At this time, the first pulse generating unit 13 controls the first sampling unit 11 and / or the first current limiting unit 12 in the upper power tube current limiting module 10 not to work within the time corresponding to the first pulse width based on the shielding signal shot1 generated by the high-level first control signal Pon, and the upper power tube current limiting module 10 continues to output the first feedback signal Limit1 of a low level during this time, and the upper power tube M1 continues to be turned on. After the time corresponding to the first pulse width, if there is a situation such as an output short circuit or an output load overload in the DC power supply circuit, the first sampling unit 11 samples that the current flowing through the upper power tube M1 is greater than the first threshold value P-Limit, and then the first current limiting unit 12 outputs a high-level first feedback signal Limit1 to the drive control circuit 1. The trigger driving control circuit 1 changes the level states of the output first control signal Pon and the second control signal Non, thereby controlling the upper power tube M1 to be turned off and the lower power tube M2 to be turned on, so as to discharge through the lower power tube M2.

[0071] Then, the second pulse generating unit 23 controls the second sampling unit 21 and / or the second current limiting unit 22 in the lower power tube current limiting module 20 to not work within the time corresponding to the second pulse width based on the shielding signal shot2 generated by the high-level second control signal Non, and the lower power tube current limiting module 20 continues to output the second feedback signal Limit2 of a low level during this time, and the lower power tube M2 continues to be turned on for discharge. After the time corresponding to the second pulse width, if the second sampling unit 21 samples that the current flowing through the lower power tube M2 is greater than the second threshold value N-Limit, the second current limiting unit 22 will output a low-level second feedback signal Limit2 to the drive control circuit 1. At this time, even if the clock signal CLK is at a high level, it will force the drive control circuit 1 to output a low-level first control signal Pon, control the upper power tube M1 to be in a turned-off state, and make the lower power tube M2 continuously turned on to continuously discharge, until the second sampling unit 21 samples that the current flowing through the lower power tube M2 is less than the second threshold value N-Limit, triggering the second current limiting unit 22 to output a high-level second feedback signal Limit2 to the drive control circuit 1. At this time, the drive control circuit 1 can change the level state of the output first control signal Pon and the second control signal Non when the clock signal CLK is at a high level, thereby controlling the upper power tube M1 to be turned on and the lower power tube M2 to be turned off.

[0072] Based on the above description, it can be understood that in each switching cycle of each DC power supply, the starting point of the output current IL will not be higher than the second threshold N_Limit. Thus, as long as the value of the second threshold N_Limit is reasonably set, it can be made that N_limit + VIN * t1 / L < P_limit. In this way, the maximum value of the output current IL can be determined by the first threshold P_Limit (the output current IL is not greater than the first threshold P_Limit), realizing the controllability of the positive output current during output short circuit or overload. Furthermore, it effectively avoids the problem that in the existing overcurrent protection circuit with only the upper power transistor current limiting module, the output current in the DC power supply will increase without limit under the small switching cycle of the DC power supply, expanding the application range.

[0073] In the second embodiment of the present disclosure, the current flowing through the upper power transistor M1 is a negative current (i.e., the direction of this current is from the drain of the upper power transistor M1 flowing in and from the source of the upper power transistor M1 flowing out). Correspondingly, at this time, the first preset condition is: the current flowing through the upper power transistor M1 is less than the first threshold, and the second preset condition is: the current flowing through the lower power transistor M2 is greater than the second threshold.

[0074] In this embodiment, both the first threshold P - Limit and the second threshold N - Limit are negative values (relative to the above - mentioned first embodiment), and the absolute value of the first threshold is greater than the absolute value of the second threshold. Correspondingly, the current flowing through the upper power transistor M1 being less than the first threshold P - Limit means that the absolute value of the current flowing through the upper power transistor M1 is greater than the absolute value of the first threshold P - Limit; and the current flowing through the lower power transistor M2 being greater than the second threshold N - Limit means that the absolute value of the current flowing through the lower power transistor M2 is less than the absolute value of the second threshold N - Limit.

[0075] Based on a principle similar to that of the above - mentioned first embodiment, in this embodiment, as long as the value of the second threshold N_Limit is reasonably set, it can be made that the output current IL is not less than the first threshold P_Limit, realizing the controllability of the negative output current during output short circuit or overload.

[0076] In the present disclosure, only by changing the preset conditions required for judgment, overcurrent protection corresponding to different inductor current directions can be achieved, avoiding the limitation of the application scenario and improving the applicability of the circuit.

[0077] Figure 7 The flowchart of the overcurrent protection method for the DC power supply according to the embodiments of the present disclosure is shown.

[0078] As Figure 7 shown, in this embodiment, the overcurrent protection method for the DC power supply can be applied to such as Figure 5 and Figure 6The overcurrent protection circuit of the DC power supply shown in the method includes executing step S1 and step S2.

[0079] Specifically, refer to Figure 5 and Figure 6 In step S1, the current flowing through the upper power tube is monitored, and when the current flowing through the upper power tube meets the first preset condition, the upper power tube is controlled to be turned off and the lower power tube is controlled to be turned on.

[0080] In the first embodiment of the present disclosure, the current flowing through the upper power tube M1 is a forward current (i.e., the direction of the current is flowing from the source of the upper power tube M1 and flowing out from the drain of the upper power tube M1), and the first preset condition is that the current flowing through the upper power tube M1 is greater than the first threshold, and the second preset condition is that the current flowing through the lower power tube M2 is less than the second threshold. In this embodiment, the first threshold and the second threshold are both positive values, and the absolute value of the first threshold is greater than the absolute value of the second threshold.

[0081] Taking this embodiment as an example, when the clock signal CLK is at a high level, the first control signal Pon output by the drive control circuit 1 is at a high level, which controls the upper power tube M1 to be turned on after passing through the inverter U1, and the output second control signal Non is at a low level, which controls the lower power tube M2 to be turned off. At this time, the first pulse generating unit 13 controls the first sampling unit 11 and / or the first current limiting unit 12 in the upper power tube current limiting module 10 not to work within the time corresponding to the first pulse width based on the shielding signal shot1 generated by the high-level first control signal Pon, and the upper power tube current limiting module 10 continuously outputs the first feedback signal Limit1 of a low level during this time, and the upper power tube M1 continues to be turned on. After the time corresponding to the first pulse width, if there is a situation such as an output short circuit or an output load overload in the DC power supply circuit, the first sampling unit 11 samples that the current flowing through the upper power tube M1 is greater than the first threshold value P-Limit, and then the first current limiting unit 12 outputs a high-level first feedback signal Limit1 to the drive control circuit 1. The trigger driving control circuit 1 changes the level states of the output first control signal Pon and the second control signal Non, thereby controlling the upper power tube M1 to be turned off and controlling the lower power tube M2 to be turned on.

[0082] In step S2, the current flowing through the lower power tube is monitored, and when the current flowing through the lower power tube meets a second preset condition, the upper power tube is controlled to be turned on and the lower power tube is controlled to be turned off.

[0083] After the power transistor M2 is turned on under control, the second pulse generation unit 23 controls the second sampling unit 21 and / or the second current limiting unit 22 in the lower power transistor current limiting module 20 not to work within the time corresponding to the second pulse width based on the shielding signal shot2 generated by the second control signal Non at a high level. The lower power transistor current limiting module 20 continuously outputs the second feedback signal Limit2 at a low level during this time, and the lower power transistor M2 continuously conducts to discharge. After the time corresponding to the second pulse width, if the second sampling unit 21 samples that the current flowing through the lower power transistor M2 is greater than the second threshold N-Limit, the second current limiting unit 22 outputs the second feedback signal Limit2 at a low level to the drive control circuit 1. At this time, even if the clock signal CLK is at a high level, the drive control circuit 1 will be forced to trigger and output the first control signal Pon at a low level, controlling the upper power transistor M1 to be in an off state and keeping the lower power transistor M2 continuously conducting to continuously discharge until the second sampling unit 21 samples that the current flowing through the lower power transistor M2 is less than the second threshold N-Limit, triggering the second current limiting unit 22 to output the second feedback signal Limit2 at a high level to the drive control circuit 1. At this time, the drive control circuit 1 can change the level states of the output first control signal Pon and the second control signal Non when the clock signal CLK is at a high level, and then control the upper power transistor M1 to conduct and control the lower power transistor M2 to turn off.

[0084] As can be seen from the above, in each switching cycle of the DC power supply, the starting point of the output current IL will not be higher than the second threshold N_Limit. Thus, as long as the value of the second threshold N_Limit is reasonably set, N_limit + VIN * t1 / L < P_limit can be achieved. In this way, the maximum value of the output current IL can be determined by the first threshold P_Limit (the output current IL is not greater than the first threshold P_Limit), realizing the controllability of the forward output current in case of output short circuit or overload. Furthermore, it effectively avoids the problem that in the existing overcurrent protection circuit with only the upper power transistor current limiting module, the output current in the DC power supply will increase without limit in a small switching cycle of the DC power supply, expanding the application range.

[0085] In the second embodiment of the present disclosure, the current flowing through the upper power tube M1 is a negative current (that is, the direction of the current is flowing in from the drain of the upper power tube M1 and out from the source of the upper power tube M1). At this time, the first preset condition is: the current flowing through the upper power tube M1 is less than the first threshold, and the second preset condition is: the current flowing through the lower power tube M2 is greater than the second threshold. Among them, the first threshold P-Limit and the second threshold N-Limit are both negative values ​​(relative to the above-mentioned first embodiment), and the absolute value of the first threshold is greater than the absolute value of the second threshold. Correspondingly, the current flowing through the upper power tube M1 is less than the first threshold P-Limit, that is: the absolute value of the current flowing through the upper power tube M1 is greater than the absolute value of the first threshold P-Limit; and the current flowing through the lower power tube M2 is greater than the second threshold N-Limit, that is: the absolute value of the current flowing through the lower power tube M2 is less than the absolute value of the second threshold N-Limit.

[0086] Based on the principle similar to that of the first embodiment, in this embodiment, by reasonably setting the value of the second threshold value N_Limit, the output current IL can be made not less than the first threshold value P_Limit, so that the negative output current can be controlled when the output is short-circuited or overloaded. In this way, overcurrent protection corresponding to different inductor current directions can be achieved by simply changing the preset conditions required for judgment, avoiding the limitation of application scenarios and improving the applicability of the circuit.

[0087] In summary, the overcurrent protection circuit and overcurrent protection method of the DC power supply disclosed in the present invention not only samples and monitors the current flowing through the upper power tube through the upper power tube current limiting module connected to the upper power tube, so as to control the upper power tube to be turned off and the lower power tube to be turned on when the current meets the first preset condition, thereby realizing the control of the first terminal value (one of the maximum value and the minimum value) of the output current in the DC power supply, but also samples and monitors the current flowing through the lower power tube through the lower power tube current limiting module connected to the lower power tube, so as to allow the upper power tube to be turned on and the lower power tube to be turned off when the current meets the second preset condition, thereby realizing the control of the second terminal value (the other of the maximum value and the minimum value) of the output current in the DC power supply. In this way, the output current can be controlled when the output is short-circuited or overloaded, effectively avoiding the problem that the output current in the DC power supply will increase without limit under a small switching cycle of the DC power supply when there is only an upper power tube current limiting module in the existing overcurrent protection circuit, thereby expanding the scope of application.

[0088] On the other hand, for DC power supplies with different current directions, the corresponding overcurrent protection function can be achieved by simply changing the preset conditions required for judgment, avoiding the limitation of application scenarios and improving the applicability of the circuit.

[0089] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, an element defined by the sentence "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0090] Finally, it should be noted that: Obviously, the above embodiments are only examples for clearly explaining the present invention, and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the scope of protection of the present invention.

Claims

1. An overcurrent protection circuit for a DC power supply, wherein: The DC power supply comprises: An upper power tube and a lower power tube connected in series between the input voltage input terminal and the reference ground, wherein the upper power tube is a PMOS transistor and the lower power tube is an NMOS transistor; an inductor and an output capacitor connected in series between the drain of the upper power tube and a reference ground; and A driving control circuit, used for generating a first control signal and a second control signal for controlling the on and off of the upper power tube and the lower power tube respectively according to the clock signal; The overcurrent protection circuit comprises: An upper power tube current limiting module, connected to the upper power tube, for sampling the current flowing through the upper power tube, and generating a first feedback signal to the drive control circuit according to the sampling result; A lower power tube current limiting module is connected to the lower power tube and is used to sample the current flowing through the lower power tube and generate a second feedback signal to the drive control circuit according to the sampling result. Wherein, when the current flowing through the upper power tube meets the first preset condition, the drive control circuit controls the upper power tube to turn off and controls the lower power tube to turn on based on the first feedback signal, so as to realize the control of one of the maximum value and the minimum value of the output current in the DC power supply; When the current flowing through the lower power tube meets the second preset condition, the drive control circuit controls the upper power tube to be turned on and controls the lower power tube to be turned off based on the second feedback signal and the clock signal, thereby controlling the other of the maximum value and the minimum value of the output current in the DC power supply.

2. The overcurrent protection circuit according to claim 1, wherein: When the current flowing through the upper power tube flows in from the source of the upper power tube and flows out from the drain of the upper power tube, the first preset condition is: the current flowing through the upper power tube is greater than a first threshold, The second preset condition is: the current flowing through the lower power tube is less than a second threshold value, The first threshold and the second threshold are both positive values, and the absolute value of the first threshold is greater than the absolute value of the second threshold.

3. The overcurrent protection circuit according to claim 1, wherein: When the current flowing through the upper power tube flows in from the drain of the upper power tube and flows out from the source of the upper power tube, the first preset condition is: the current flowing through the upper power tube is less than a first threshold value, The second preset condition is: the current flowing through the lower power tube is greater than a second threshold value, The first threshold and the second threshold are both negative values, and the absolute value of the first threshold is greater than the absolute value of the second threshold.

4. The overcurrent protection circuit according to claim 2 or 3, wherein: The upper power tube current limiting module comprises: a first sampling unit, connected to the upper power tube, and configured to sample the current flowing through the upper power tube; a first current limiting unit, connected to the first sampling unit, and configured to process a sampling result of the first sampling unit based on the first threshold value, and generate the first feedback signal according to the processing result; The first pulse generating unit is used to receive the first control signal and generate a shielding signal with a first pulse width when the first control signal is valid, wherein the shielding signal is used to control the first sampling unit and / or the first current limiting unit to not work.

5. The overcurrent protection circuit according to claim 4, wherein: The first pulse width is smaller than the effective duration of the first control signal in one signal cycle.

6. The overcurrent protection circuit according to claim 2 or 3, wherein: The lower power tube current limiting module comprises: a second sampling unit, connected to the lower power tube, and used to sample the current flowing through the lower power tube; a second current limiting unit, connected to the second sampling unit, and configured to process a sampling result of the second sampling unit based on the second threshold value, and generate the second feedback signal according to the processing result; The second pulse generating unit is used to receive the second control signal and generate a shielding signal with a second pulse width when the second control signal is valid, wherein the shielding signal is used to control the second sampling unit and / or the second current limiting unit to not work.

7. The overcurrent protection circuit according to claim 6, wherein: The second pulse width is smaller than the effective duration of the second control signal in one signal cycle.

8. A method for overcurrent protection of a DC power supply, wherein: The DC power supply comprises: an upper power tube and a lower power tube which are sequentially connected in series between an input voltage input terminal and a reference ground, wherein the upper power tube is a PMOS transistor and the lower power tube is an NMOS transistor. The overcurrent protection method comprises: Monitor the current flowing through the upper power tube, and when the current flowing through the upper power tube meets the first preset condition, control the upper power tube to turn off and control the lower power tube to turn on, so as to control one of the maximum value and the minimum value of the output current in the DC power supply; The current flowing through the lower power tube is monitored, and when the current flowing through the lower power tube meets the second preset condition, the upper power tube is controlled to be turned on and the lower power tube is controlled to be turned off, so as to control the other of the maximum value and the minimum value of the output current in the DC power supply.

9. The overcurrent protection method according to claim 8, wherein: When the current flowing through the upper power tube flows in from the source of the upper power tube and flows out from the drain of the upper power tube, the first preset condition is: the current flowing through the upper power tube is greater than a first threshold, The second preset condition is: the current flowing through the lower power tube is less than a second threshold value, The first threshold and the second threshold are both positive values, and the absolute value of the first threshold is greater than the absolute value of the second threshold.

10. The overcurrent protection method according to claim 8, wherein: When the current flowing through the upper power tube flows in from the drain of the upper power tube and flows out from the source of the upper power tube, the first preset condition is: the current flowing through the upper power tube is less than a first threshold value, The second preset condition is: the current flowing through the lower power tube is greater than a second threshold value, The first threshold and the second threshold are both negative values, and the absolute value of the first threshold is greater than the absolute value of the second threshold.

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