Current limiting protection circuit

Abstract

The application provides a current limiting protection circuit, which comprises a driving circuit, a power tube, a current copying unit and an overcurrent detection circuit, the driving circuit is used for providing a bootstrap voltage for the power tube in a linear region; the power tube is used for outputting a corresponding sampling voltage according to a change value of an input current, the bootstrap voltage is used for the power tube in the linear region; the current copying unit is used for current copying of a power supply voltage for current comparison of an output current of the power tube; the overcurrent detection circuit is used for determining an output voltage according to the sampling voltage and the power supply voltage, determining a conduction state of a target triode according to a current corresponding to the output voltage and a copying current output by the current copying unit, and limiting an actual current of the power tube to a target value in the conduction state of the target triode. The current limiting protection circuit provided by the application realizes monitoring and regulation of the current of the power tube, and improves the safety of the current limiting protection circuit during operation.

Description

Technical Field

[0001] This invention relates to the field of electronic circuit technology, and in particular to a current limiting protection circuit. Background Technology

[0002] In related technologies, existing current limiting protection circuits have limitations in terms of sensitivity, response speed and accuracy, especially in dealing with transient or high-frequency overcurrents. They lack monitoring and limiting of the current of the power transistor. If the current in the power transistor exceeds the limit, it will damage the circuit load or the power transistor. At best, it will not work properly, and at worst, it will cause circuit damage. Summary of the Invention

[0003] This invention provides a current limiting protection circuit to address the shortcomings of existing current limiting protection circuits, which lack monitoring and limiting of the current of the power transistor. If the current in the power transistor exceeds the limit, it will damage the circuit load or the power transistor, thus improving the safety of the current limiting protection circuit during operation.

[0004] This invention provides a current limiting protection circuit, comprising:

[0005] A driving circuit, the driving circuit being used to provide a bootstrap voltage, the bootstrap voltage being higher than the power supply voltage output by the power supply;

[0006] The power transistor is a cascaded structure of at least two transistors. The first port of the power transistor is connected to the driving circuit, and the second port of the power transistor is connected to the power supply. The power transistor is used to output a corresponding sampling voltage according to the change value of the input current, and the bootstrap voltage is used to keep the power transistor in the linear region.

[0007] A current replication unit is provided, the input terminal of which is connected to the power supply. The current replication unit is used to replicate the power supply voltage to the current so that the output current of the power transistor can be compared.

[0008] An overcurrent detection circuit is provided, comprising a cascaded structure of at least two transistors. The first port of the overcurrent detection circuit is connected to the third port of the power transistor, the second port of the overcurrent detection circuit is connected to the power supply, and the port of the overcurrent detection circuit is connected to the current replication unit. The overcurrent detection circuit is used to determine the output voltage based on the sampled voltage and the power supply voltage, and to determine the conduction state of the target transistor based on the multiple relationship between the current corresponding to the output voltage and the replicated current output by the current replication unit.

[0009] The target transistor belongs to the overcurrent detection circuit. One input terminal of the target transistor is connected to the output terminal of the driving circuit. The target transistor is used to limit the actual current of the power transistor to a target value when it is turned on. The target value is determined based on the current sampling ratio of the power transistor, the resistance value of the external resistor, and the current replication ratio of the current replication unit.

[0010] According to a current limiting protection circuit provided by the present invention, the current limiting protection circuit further includes:

[0011] The signal processing circuit has a first port connected to the first port of the target transistor and a second port connected to the power supply. The signal processing circuit is used to shape the waveform of the output voltage of the overcurrent detection circuit.

[0012] According to a current limiting protection circuit provided by the present invention, the signal processing circuit includes:

[0013] Two inverters connected in series, with the first input of each inverter connected to the power supply and the second input of each inverter connected to the first port of the target transistor.

[0014] According to a current limiting protection circuit provided by the present invention, the power transistor includes:

[0015] The first transistor has its first port connected to the power supply and its second port connected to the driving circuit.

[0016] The second transistor has its first port connected to the power supply via the external resistor, and its second port connected to the driving circuit via the second port of the first transistor.

[0017] The branch consisting of the second transistor and the external resistor is connected in parallel with the branch containing the first transistor.

[0018] According to a current limiting protection circuit provided by the present invention, the overcurrent detection circuit includes:

[0019] The fourth transistor has its first port connected to the third port of the power transistor, and its second port connected to the output terminal of the current replication unit.

[0020] The fifth transistor has its first port connected to the power supply, the second port and the third port of the fourth transistor are respectively connected to the second port of the fifth transistor, and the third port of the fifth transistor is connected to the first port of the target transistor.

[0021] The second port of the target transistor is connected to the driving circuit through the first port of the power transistor, and the third port of the target transistor is connected to the input port of the signal processing circuit.

[0022] According to the current limiting protection circuit provided by the present invention, the fourth transistor and the fifth transistor may be at least one of a PNP type BJT transistor and a P type MOSFET.

[0023] According to a current limiting protection circuit provided by the present invention, the current replication unit includes:

[0024] Three third transistors connected in series, wherein the third transistors include at least one of conventional current mirrors and common-source cascode current mirrors.

[0025] According to a current limiting protection circuit provided by the present invention, the current limiting protection circuit further includes:

[0026] A reference circuit, wherein the input terminal of the reference circuit is connected to a power supply, and the output terminal of the reference circuit is connected to the input terminal of the current replication unit.

[0027] According to the current limiting protection circuit provided by the present invention, the plurality of transistors in the power transistor and the target transistor are at least one of N-type MOSFETs and NPN-type BJT transistors.

[0028] According to the current limiting protection circuit provided by the present invention, the external resistor includes any one of the following:

[0029] A fixed resistor or an adjustable resistor;

[0030] The resistance of at least two resistors connected in series or in parallel

[0031] The current limiting protection circuit provided by this invention provides a bootstrap voltage to the power transistor through a driving circuit to ensure that the power transistor operates in the linear region. A current replication unit replicates the power supply voltage for comparison with the power transistor's output current. An overcurrent detection circuit determines the output voltage based on the sampled voltage and the power supply voltage. The circuit determines the conduction state of the target transistor based on the multiple relationship between the current corresponding to the output voltage and the replicated current output by the current replication unit. When the target transistor is conducting, the actual current of the power transistor is limited to the target value, thus achieving monitoring and control of the power transistor current and improving the safety of the current limiting protection circuit during operation. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0033] Figure 1 This is one of the structural schematic diagrams of the current limiting protection circuit provided by the present invention;

[0034] Figure 2 This is the second schematic diagram of the current limiting protection circuit provided by the present invention;

[0035] Figure 3 This is one of the structural schematic diagrams of the current replication unit provided by the present invention;

[0036] Figure 4 This is the second schematic diagram of the current replication unit provided by the present invention;

[0037] Figure 5 This is the third schematic diagram of the current limiting protection circuit provided by the present invention;

[0038] Figure 6 This is the fourth schematic diagram of the current limiting protection circuit provided by the present invention;

[0039] Figure 7 This is the fifth schematic diagram of the current limiting protection circuit provided by the present invention;

[0040] Figure 8 This is the sixth schematic diagram of the current limiting protection circuit provided by the present invention;

[0041] Figure 9 This is the third schematic diagram of the current replication unit provided by the present invention;

[0042] Figure 10 This is the fourth schematic diagram of the current replication unit provided by the present invention.

[0043] Figure label:

[0044] 110: Driver circuit; 120: Power transistor; 130: Current replication unit;

[0045] 140: Overcurrent detection circuit; 141: Target transistor; 150: Signal processing circuit;

[0046] 160: Reference circuit. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0048] In the description of the embodiments of the present invention, it should be noted that the terms "upper," "lower," "front," "rear," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0049] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, a wired communication connection, or a wireless communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0050] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0051] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0052] The current limiting protection circuit proposed in this invention is applicable to any CMOS process, Bipolar process, and BCD process.

[0053] The following is combined Figures 1-10 The current limiting protection circuit of the present invention is described.

[0054] Figure 1 This is one of the structural schematic diagrams of the current limiting protection circuit provided by the present invention, such as... Figure 1 As shown, the current limiting protection circuit includes a drive circuit 110, a power transistor 120, a current replication unit 130, an overcurrent detection circuit 140, and a target transistor 150.

[0055] The drive circuit 110 is used to provide a bootstrap voltage, which is higher than the power supply voltage output by the power supply.

[0056] In this embodiment, the driving circuit 110 can provide a gate voltage or base voltage higher than the power supply voltage to the gate or base of the transistor in the power transistor 120, i.e., a bootstrap voltage, to ensure that the power transistor 120 is in the linear region under normal operating conditions.

[0057] The power transistor 120 is a cascaded structure of at least two transistors. The first port of the power transistor 120 is connected to the drive circuit 110, and the second port of the power transistor 120 is connected to the power supply. The power transistor 120 is used to output a corresponding sampling voltage according to the change value of the input current, and the bootstrap voltage is used to keep the power transistor 120 in the linear region.

[0058] In this embodiment, the plurality of transistors in the power transistor 120 and the target transistor 141 are at least one of N-type MOSFETs and NPN-type BJT transistors.

[0059] For example, power transistor 120 may include two N-type MOSFETs, or power transistor 120 may include two NPN type BJT transistors, or power transistor 120 may include one N-type MOSFET and one NPN type BJT transistor.

[0060] The following explanation uses the N-type MOS transistor as an example of the power transistor 120. The N-type MOS transistor includes a source, a gate, and a drain.

[0061] In this embodiment, the first port of the power transistor 120 can be the gate of a MOS transistor, that is, the gate of one of the MOS transistors of the power transistor 120 is electrically connected to the output terminal of the driving circuit 110.

[0062] It should be noted that the gate is the control terminal of the MOSFET, responsible for controlling the flow of current. By applying voltage to the gate, the electric field between the gate and the source can be changed, thereby affecting the current path between the drain and the source. Changes in the gate control voltage will directly affect the conduction and cutoff states of the MOSFET, thus achieving control over the current flow.

[0063] In this embodiment, the second port of the power transistor 120 is the source of the MOSFET, which is connected to the power supply to provide input current to the power transistor 120.

[0064] Figure 2 This is the second schematic diagram of the current limiting protection circuit provided by the present invention. Figure 2 In the illustrated embodiment, power transistor 120 includes two MOSFETs: N1 and N2. The gate of N1 is connected to the drive circuit 110, the source of N1 is connected to the power supply VDD, the gate of N2 is connected to the gate of N1, the source of N2 is connected to the power supply VDD through resistor R1, and the drains of N1 and N2 are connected to the output port OUT of power transistor 120. When power transistor 120 operates and an overcurrent occurs, N2 samples the current on N1 using the following formula:

[0065]

[0066] Among them, I N1 For the current passing through N1, I N2 K represents the current passing through N2, and K is the current sampling ratio of power transistor 120.

[0067] In this embodiment, the current input to the power supply forms a voltage drop ΔV1 across R1. An increase in current will cause ΔV1 to increase, which means that the sampling voltage Vsense will decrease.

[0068]

[0069] Where R1 is the resistance value of resistor R1.

[0070] The input terminal of the current replication unit 130 is connected to the power supply. The current replication unit 130 is used to replicate the power supply voltage for current comparison with the output current of the power transistor 120.

[0071] In this embodiment, the current replication unit 130 is used to replicate the reference current corresponding to the power input current and output the corresponding replicated current.

[0072] In this embodiment, the current replication unit 130 includes three third transistors connected in series, the third transistors including at least one of conventional current mirrors and common-source cascode current mirrors.

[0073] Figure 3 This is one of the structural schematic diagrams of the current replication unit provided by the present invention. Figure 3 In the described embodiment, the conventional current mirror is composed of three MOS transistors N3, N4, and N5. The source A of N3 is used to input the reference current. The source of N3 is connected to the gate of N4. The source B of N4 and the source C of N5 are both connected to the overcurrent detection circuit 140. The drains of N3, N4, and N5 are grounded. K2 and K3 are the current replication ratios of the current replication unit 130.

[0074] Figure 4 This is the second schematic diagram of the current replication unit provided by the present invention. Figure 4 In the described embodiment, the conventional current mirror is composed of three BJT transistors, Q3, Q4, and Q5, and... Figure 3 Correspondingly, the source of the MOSFET is the emitter of the BJT transistor, the gate of the MOSFET is the base of the BJT transistor, and the drain of the MOSFET is the collector of the BJT transistor. The connection relationships between Q3, Q4, and Q5, and the connection between Q3, Q4, and Q5 and the overcurrent detection circuit 140 are referenced. Figure 3 The description of the embodiments shown will not be repeated here.

[0075] The overcurrent detection circuit 140 is a cascaded structure of at least two transistors. The first port of the overcurrent detection circuit 140 is connected to the third port of the power transistor 120, the second port of the overcurrent detection circuit 140 is connected to the power supply, and the port of the overcurrent detection circuit 140 is connected to the current replication unit 130. The overcurrent detection circuit 140 is used to determine the output voltage based on the sampling voltage and the power supply voltage, and to determine the conduction state of the target transistor 141 based on the multiple relationship between the current corresponding to the output voltage and the replication current output by the current replication unit 130.

[0076] In this embodiment, the overcurrent detection circuit 140 is a structure obtained by cascading multiple transistors. The transistors can be PNP type BJT transistors or P type MOS transistors.

[0077] exist Figure 2In the illustrated embodiment, the overcurrent detection circuit includes two PNP BJT transistors, namely Q1 and Q2. Each PNP BJT transistor includes an emitter, a base, and a collector. The emitter of Q1 is connected to the source of N2, the collector of Q1 is connected to port B of the current replication unit 130, the base of Q1 is electrically connected to the collector of Q1, and the base of Q1 is connected to the base of Q2. The emitter of Q2 is connected to the power supply VDD, and the collector of Q2 is connected to port C of the current replication unit 130.

[0078] In this embodiment, since the current of Q1 is limited to a fixed value by N4, the change in the magnitude of the sampling voltage Vsense output by N2 will affect the base voltage of Q1, causing the base voltage of Q1 to drop. Since the base voltages of Q1 and Q2 are the same, the base voltage of Q2 drops. The power supply voltage connected to the emitter of Q2 remains unchanged, therefore, the collector voltage of Q2 will increase, leading to an increase in the current of Q2. The changes in current flowing through Q1 and Q2 are described by the following formula:

[0079]

[0080]

[0081] Among them, I s0 This is the reverse-bias saturation current of the transistor, V. BE V is the voltage between the base and emitter of the transistor. T Thermoelectric voltage; I Q1 For the current flowing through Q1, I Q2 This represents the current flowing through Q2.

[0082] Among them, the target transistor 141 belongs to the overcurrent detection circuit 140. One input terminal of the target transistor 141 is connected to the output terminal of the drive circuit 110. The target transistor 141 is used to limit the actual current of the power transistor 120 to a target value when it is turned on. The target value is determined based on the current sampling ratio of the power transistor 120, the resistance value of the external resistor, and the current replication ratio of the current replication unit 130. The first electrode of the target transistor 141 is connected to the fourth port of the overcurrent detection circuit 140, and the second port of the target transistor 141 is connected to the drive circuit 110 through the first port of the power transistor 120.

[0083] In this embodiment, the target transistor 141 can be an N-type MOSFET or an NPN-type BJT transistor.

[0084] Taking the target transistor 141 as an N-type MOSFET as an example, Q2 and the current replication unit 130 can form a current comparator. The current replication ratio in the current replication unit 130 is 1:K2:K3. When the current of Q2 increases to When the current comparator outputs a multiple of I1 (reference current), the output voltage of Q2 at point VC will increase. As the voltage at point VC increases, the target transistor 141N6 turns on, pulling down the gate voltages of N1 and N2. However, it does not pull them down to 0, but keeps the gate voltages at a certain value, allowing the power transistor 120 to enter the saturation region from the linear region, thereby limiting the current of the power transistor 120 to a constant value.

[0085] The specific overcurrent value can be calculated using the following formula:

[0086]

[0087] The preceding I Q1 and I Q2 We can obtain,

[0088]

[0089] The overcurrent value is:

[0090]

[0091] In this embodiment, by reasonably setting the values ​​of K, K2, K3, and R1, the overcurrent value I can be controlled. max Set it to a desired value, that is, set it as the target value.

[0092] In this embodiment, when overcurrent recovery is achieved for the power transistor 120, if the current on N1 decreases, the current on N2 decreases accordingly. This current forms a voltage drop ΔV2 across R1. ΔV2 decreases, thereby increasing the sampling voltage Vsense. Since the current of Q1 is limited to a fixed value by N4, the change in Vsense affects the change in the base voltage of Q1, causing the base voltage of Q1 to rise. Because the base voltages of Q1 and Q2 are the same, the base voltage of Q2 rises. The power supply voltage connected to the emitter of Q2 remains unchanged, therefore the VBE of transistor Q2 decreases, leading to a decrease in the current of transistor Q2. Transistor Q2 and the pull-down current replication unit 130 constitute a current comparator. The current replication ratio within the current replication unit 130 is 1:K2:K3. Therefore, when the current of Q2 decreases to... When the current comparator output is twice the size of I1, the voltage at point VC will decrease. As the voltage at point VC decreases, N6 turns off. At this time, the gate voltages of N1 and N2 return to normal, meaning that the drive circuit 110 provides a gate voltage higher than the power supply voltage, thereby realizing the recovery of the overcurrent state.

[0093] The current limiting protection circuit provided in this embodiment of the invention provides a bootstrap voltage to the power transistor 120 through the driving circuit 110 to ensure that the power transistor 120 is in the linear region when it is working. The current replication unit 130 replicates the power supply voltage for current comparison with the output current of the power transistor 120. The overcurrent detection circuit 140 determines the output voltage based on the sampled voltage and the power supply voltage. The conduction state of the target transistor 141 is determined based on the multiple relationship between the current corresponding to the output voltage and the replicated current output by the current replication unit 130. When the target transistor 141 is conducting, the actual current of the power transistor 120 is limited to the target value, thereby realizing the monitoring and control of the current of the power transistor 120 and improving the safety of the current limiting protection circuit during operation.

[0094] In some embodiments, the current limiting protection circuit further includes: a signal processing circuit 150, the first port of the signal processing circuit 150 being connected to the first port of the target transistor 141, the second port of the signal processing circuit 150 being connected to a power supply, and the signal processing circuit 150 being used to shape the waveform of the output voltage of the overcurrent detection circuit 140.

[0095] In this embodiment, the signal processing circuit 150 can convert the voltage output by the target transistor 141 into a high-level digital signal or a low-level digital signal, and can digitally display the analog signal.

[0096] In some embodiments, the signal processing circuit 150 includes two inverters connected in series, with the first input of each inverter connected to a power supply and the second input of each inverter connected to the first port of the target transistor 141.

[0097] exist Figure 2 In the embodiment shown, the target transistor 141 is an N-type MOSFET, the first port of the target transistor 141 (N6) is the gate, the two inverters of the signal processing circuit 150 are inv1 and inv2, and the signal processing circuit 150 can shape VC into high-level and low-level digital signals; if inv1 and inv2 are used simultaneously, the output overcurrent signal imax is a high-level indication of overcurrent; if only inv1 is used, it is a low-level indication of overcurrent.

[0098] In this embodiment, the inverter described above can be replaced with any circuit structure capable of shaping the waveform.

[0099] The current limiting protection circuit provided in this embodiment of the invention can shape the waveform of the output voltage of the overcurrent detection circuit 140 by setting a signal processing circuit 150 in the current limiting protection circuit to obtain a corresponding digital signal, which is convenient for display.

[0100] In some embodiments, the power transistor 120 includes: a first transistor, the first port of which is connected to a power supply, and the second port of which is connected to a drive circuit 110; and a second transistor, the first port of which is connected to a power supply via an external resistor, and the second port of which is connected to the drive circuit 110 via the second port of the first transistor; wherein the branch formed by the second transistor and the external resistor is connected in parallel with the branch containing the first transistor.

[0101] exist Figure 2 In the embodiment shown, the first transistor N1 and the second transistor N2 are both N-type MOS transistors. The gate of N1 is connected to the driving circuit 110, the source of N2 is connected to one end of the resistor R1, and the other end of R1 is connected to the power supply VDD. The gate of N2 is connected to the driving circuit 110 through the gate of N1.

[0102] Figure 5 This is the third schematic diagram of the current limiting protection circuit provided by the present invention. Figure 5 In the embodiment shown, the first transistor P1 and the second transistor P2 are both P-type MOS transistors. The gate of P1 is connected to the driving circuit 110, the source of P2 is connected to one end of the resistor R1, and the other end of R1 is connected to the power supply VDD. The gate of P2 is connected to the driving circuit 110 through the gate of P1.

[0103] The current limiting protection circuit provided in this embodiment of the invention allows for adjustment of the type of transistor in the power transistor 120, thereby improving the flexibility of power transistor 120 configuration.

[0104] In some embodiments, the overcurrent detection circuit 140 includes: a fourth transistor, the first port of which is connected to the third port of the power transistor 120, and the second port of which is connected to the output terminal of the current replication unit 130; a fifth transistor, the first port of which is connected to the power supply, the second port of which and the third port of which are respectively connected to the second port of which, and the third port of which is connected to the first port of the target transistor 141; the second port of the target transistor 141 is connected to the drive circuit 110 through the first port of the power transistor 120, and the third port of the target transistor 141 is connected to the input port of the signal processing circuit 150.

[0105] In this embodiment, the fourth and fifth transistors can be at least one of a PNP BJT transistor and a P-type MOSFET.

[0106] For example, both the fourth and fifth transistors are PNP type BJT transistors, or both are P type MOSFETs.

[0107] In this embodiment, both the fourth and fifth transistors are implemented using P-type MOSFETs, for example... Figure 2 As shown in the corresponding embodiment, this embodiment will not be described again. The following is an example of how both the fourth and fifth transistors are PNP type BJT transistors.

[0108] Figure 6 This is the fourth schematic diagram of the current limiting protection circuit provided by the present invention. Figure 6 In the illustrated embodiment, the overcurrent detection circuit 140 includes two P-type MOSFETs, namely P1 and P2, wherein each P-type MOSFET includes a source, a gate, and a drain; the source of P1 is connected to the source of N2, the drain of P1 is connected to the B port of the current replication unit 130, the gate of P1 is electrically connected to the drain of P1, and the gate of P1 is connected to the gate of P2, the source of P2 is connected to the power supply VDD, and the drain of P2 is connected to the C port of the current replication unit 130.

[0109] In this embodiment, when an overcurrent occurs in power transistor 120, since the current of P1 is limited to a fixed value by N4, changes in the sampling voltage Vsense will affect the gate voltage of P1, causing a decrease in the gate voltage of P1. Because the gate voltages of P1 and P2 are at the same level, the gate voltage of P2 decreases. Since the source-to-source voltage of P2 remains constant, the voltage between the gate and source of P2 will increase, leading to an increase in the current of P2. The currents of P1 and P2 are calculated using the following formula:

[0110]

[0111]

[0112] Where, μ P C represents the carrier mobility. OX V is the gate oxide capacitance per unit area. GS1 This is the voltage between the gate and source of P1. V represents the width-to-length ratio of P1 and P2. TH I is the threshold voltage of the MOSFET; P1 For the current passing through P1, I P2 This represents the current flowing through P2.

[0113] exist Figure 6 In the illustrated embodiment, P2 and the current replication unit 130 constitute a current comparator, and the current replication ratio within the current replication unit 130 is 1:K2:K3; when the current of P2 increases to When the current comparator output is twice the size of I1, the voltage at point VC will increase. At the same time as the voltage at point VC increases, the target transistor 141 (N6) turns on, pulling down the gate voltages of N1 and N2. However, it will not pull them down to 0, but will keep the gate voltage at a constant value. The power transistor 120 enters the saturation region from the linear region, thereby limiting the current of the power transistor 120 to a constant value (this constant value is less than the overcurrent value), which is the target value.

[0114] In this embodiment, the overcurrent value of the power transistor 120 can be calculated using the following formula:

[0115]

[0116] The preceding I P1 and I P2 And from ΔV1, we can obtain:

[0117]

[0118] The calculated overcurrent value is:

[0119]

[0120] In this embodiment, by customizing the settings K, K2, K3, I1, R1 and R1 can set the overcurrent value to a desired value, i.e., the target value.

[0121] The current limiting protection circuit provided in this embodiment of the invention features an adjustable transistor type in the overcurrent detection circuit 140, which improves the flexibility of the overcurrent detection circuit settings.

[0122] In some embodiments, the current limiting protection circuit further includes: a reference circuit 160, the input terminal of which is connected to a power supply, and the output terminal of which is connected to the input terminal of the current replication unit 130.

[0123] exist Figure 1 In the embodiment shown, one end of the reference circuit 160 is connected to the power supply VDD, and the other end of the reference circuit 160 is connected to the current replication unit 130, which is used to convert the power supply voltage of the input current replication unit 130 into a stable and accurate voltage, thereby obtaining a stable reference current.

[0124] The current limiting protection circuit provided in this embodiment of the invention provides a stable reference current to the current replication unit 130 through the reference circuit 160, and provides stable data support for the subsequent overcurrent detection circuit 140 to detect the overcurrent status of the power transistor 120.

[0125] In some embodiments, the external resistor includes any of the following: a fixed resistor or an adjustable resistor; or a resistor consisting of at least two resistors connected in series or in parallel.

[0126] In this embodiment, the external resistor includes an on-chip resistor.

[0127] In this embodiment, one end of the external resistor is connected to the power supply, and the other end of the external resistor is connected to the power transistor 120. Specifically, the other end of the external resistor is connected to the source of an N-type power transistor 120 MOS in the power transistor 120, or the other end of the external resistor is connected to the emitter of a BJT transistor in the power transistor 120, which can provide a voltage drop for the power transistor 120, thereby adjusting the magnitude of the sampling voltage.

[0128] exist Figure 2 In the illustrated embodiment, the external resistor R1 can be implemented using a single resistor or multiple resistors connected in series or parallel.

[0129] The current limiting protection circuit provided in this embodiment of the invention provides a voltage drop to the power transistor 120 by setting an external resistor, thereby adjusting the magnitude of the sampling voltage. By setting a single resistor or connecting multiple resistors in series or parallel to the circuit, the resistance value of the external resistor can be flexibly set.

[0130] Figure 7 This is the fifth schematic diagram of the current limiting protection circuit provided by the present invention. Figure 7 In the embodiment shown, the power switch is switched to the low side, and the target transistor 141 is an N-type MOSFET (P1). The gate of P1 is connected to the collector of Q2, the source of P1 is connected to the drive circuit 110 through the gates of N1 and N2, and the drains of P1, N1, and N2 are grounded together.

[0131] Figure 8 This is the sixth schematic diagram of the current limiting protection circuit provided by the present invention. Figure 8 In the embodiment shown, the power switches (including P1 and P2) are switched to the low side, and the target transistor 141 uses a P-type MOS transistor (P3), wherein the gate of P3 is connected to the collector of Q2, the drain of P3 is connected to VDD, and the source of P3 is connected to the drive circuit 110.

[0132] Figure 9 This is the third schematic diagram of the current replication unit provided by the present invention. Figure 9 In the embodiment shown, the common-source common-gate current mirror is composed of three MOS transistors N3, N4 and N5. The sources of N3, N4 and N5 are connected to the power supply. The gates of N3, N4 and N5 are connected together. The drain of N3 is connected to the gate of N5.

[0133] Figure 10 This is the fourth schematic diagram of the current replication unit provided by the present invention. Figure 10 In the described embodiment, the common-source cascode current mirror is composed of three BJT transistors Q3, Q4, and Q5, and is connected to... Figure 9 Correspondingly, the source of the MOSFET is the emitter of the BJT transistor, the gate of the MOSFET is the base of the BJT transistor, and the drain of the MOSFET is the collector of the BJT transistor. The connection relationships between Q3, Q4, and Q5, and the connection between Q3, Q4, and Q5 and the overcurrent detection circuit 140 are referenced. Figure 3 The description of the embodiments shown will not be repeated here.

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A current-limiting protection circuit, characterized in that, include: A driving circuit, the driving circuit being used to provide a bootstrap voltage, the bootstrap voltage being higher than the power supply voltage output by the power supply; The power transistor is a cascaded structure of at least two transistors. The first port of the power transistor is connected to the driving circuit, and the second port of the power transistor is connected to the power supply. The power transistor is used to output a corresponding sampling voltage according to the change value of the input current, and the bootstrap voltage is used to keep the power transistor in the linear region. A current replication unit is provided, the input terminal of which is connected to the power supply. The current replication unit is used to replicate the power supply voltage to the current so that the output current of the power transistor can be compared. The current replication unit includes: The three third transistors connected in series form a current mirror, which includes at least one of a conventional current mirror and a common-source cascode current mirror; the current replication ratio between the three third transistors connected in series is 1:K2:K3. An overcurrent detection circuit is provided, comprising a cascaded structure of at least two transistors. The first port of the overcurrent detection circuit is connected to the third port of the power transistor, the second port of the overcurrent detection circuit is connected to the power supply, and the port of the overcurrent detection circuit is connected to the current replication unit. The overcurrent detection circuit is used to determine the output voltage based on the sampled voltage and the power supply voltage, and to determine the conduction state of the target transistor based on the multiple relationship between the current corresponding to the output voltage and the replicated current output by the current replication unit. The target transistor belongs to the overcurrent detection circuit. One input terminal of the target transistor is connected to the output terminal of the driving circuit. The target transistor is used to limit the actual current of the power transistor to a target value when it is turned on. The target value is determined based on the current sampling ratio of the power transistor, the resistance value of the external resistor, and the current replication ratio of the current replication unit. The target transistor is used to maintain the gate voltage of the power transistor at a certain value when it is in the on state, so that the power transistor can enter the saturation region from the linear region and limit the current of the power transistor to a constant value. The power transistor is used to restore the current from the overcurrent state when the target transistor is turned off and the gate voltage of the power transistor becomes a gate voltage provided by the driving circuit that is higher than the power supply voltage.

2. The current limiting protection circuit according to claim 1, characterized in that, The current limiting protection circuit also includes: The signal processing circuit has a first port connected to the first port of the target transistor and a second port connected to the power supply. The signal processing circuit is used to shape the waveform of the output voltage of the overcurrent detection circuit.

3. The current limiting protection circuit according to claim 2, characterized in that, The signal processing circuit includes: Two inverters connected in series, with the first input of each inverter connected to the power supply and the second input of each inverter connected to the first port of the target transistor.

4. The current limiting protection circuit according to claim 1, characterized in that, The power transistor includes: The first transistor has its first port connected to the power supply and its second port connected to the driving circuit. The second transistor has its first port connected to the power supply via the external resistor, and its second port connected to the driving circuit via the second port of the first transistor. The branch consisting of the second transistor and the external resistor is connected in parallel with the branch containing the first transistor.

5. The current limiting protection circuit according to claim 2, characterized in that, The overcurrent detection circuit includes: The fourth transistor has its first port connected to the third port of the power transistor, and its second port connected to the output terminal of the current replication unit. The fifth transistor has its first port connected to the power supply, the second port and the third port of the fourth transistor are respectively connected to the second port of the fifth transistor, and the third port of the fifth transistor is connected to the first port of the target transistor. The second port of the target transistor is connected to the driving circuit through the first port of the power transistor, and the third port of the target transistor is connected to the input port of the signal processing circuit.

6. The current limiting protection circuit according to claim 5, characterized in that, The fourth and fifth transistors are at least one of PNP BJT transistors and P-type MOSFETs.

7. The current limiting protection circuit according to claim 1, characterized in that, The current limiting protection circuit also includes: A reference circuit, wherein the input terminal of the reference circuit is connected to a power supply, and the output terminal of the reference circuit is connected to the input terminal of the current replication unit.

8. The current limiting protection circuit according to claim 1, characterized in that, The power transistors and the target transistor are at least one of N-type MOSFETs and NPN-type BJT transistors.

9. The current limiting protection circuit according to claim 1, characterized in that, The external resistor includes any one of the following: A fixed resistor or an adjustable resistor; The resistance of at least two resistors connected in series or in parallel.

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