Direct current input protection circuit

Abstract

The application relates to a direct current input protection circuit, comprising a first protection circuit, a second protection circuit, a third protection circuit, a fourth protection circuit, a fifth protection circuit and a sixth protection circuit, the first end of the first filter circuit is connected with the third end of the first protection circuit, and the second end of the first filter circuit is connected with the negative electrode end of the direct-current power supply; the first end of the second protection circuit is connected with the third end of the first filter circuit; the first end of the third protection circuit is connected with the second end of the second protection circuit, and the second end of the third protection circuit is connected with the negative electrode end of the direct-current power supply; and the first end of the second filter circuit is connected with the third end of the third protection circuit, and the second end of the second filter circuit is connected with the negative electrode end of the direct current power supply. Based on the circuit provided by the invention, the suppression of the abnormal surge voltage can be realized, and the limiting requirement of the impulse current can be met.

Description

Technical Field

[0001] The present application relates to the technical field of electronic circuits, and in particular to a direct current input protection circuit. Background Art

[0002] The design and application of the onboard 28V DC input circuit needs to take into account the operating requirements of the aircraft in extreme environments. For example, it usually needs to comply with the relevant requirements of standards such as DO160G to ensure its reliability and safety under flight conditions.

[0003] Standard DO160G specifies requirements for abnormal surge voltage, that is, the airborne 28V DC input circuit needs to meet the high voltage working condition of 80V / 100ms, and most of the existing airborne 28V DC input circuits are designed based on this requirement. However, standard DO160G also specifies requirements for limiting the impact current, but the existing airborne 28V DC input circuits often ignore the requirements for limiting the impact current, so that the impact current damages the device, and even causes safety accidents in serious cases. Utility Model Content

[0004] In view of the above problems in the prior art, the present application provides a DC input protection circuit, which can not only meet the requirements for abnormal surge voltage specified in standard DO160G, but also meet the requirements for limiting impact current specified in standard DO160G, thereby achieving protection of circuit components and ensuring flight safety and reliability.

[0005] To achieve the above-mentioned purpose, the first aspect of the present application provides a DC input protection circuit, including: a first protection circuit, wherein the first end of the first protection circuit is connected to the positive end of a DC power supply, and the second end of the first protection circuit is connected to the negative end of the DC power supply; a first filtering circuit, wherein the first end of the first filtering circuit is connected to the third end of the first protection circuit, and the second end of the first filtering circuit is connected to the negative end of the DC power supply; a second protection circuit, wherein the first end of the second protection circuit is connected to the third end of the first filtering circuit; a third protection circuit, wherein the first end of the third protection circuit is connected to the second end of the second protection circuit, and the second end of the third protection circuit is connected to the negative end of the DC power supply; and a second filtering circuit, wherein the first end of the second filtering circuit is connected to the third end of the third protection circuit, and the second end of the second filtering circuit is connected to the negative end of the DC power supply.

[0006] As described above, through the multi-level protection of the first protection circuit, the second protection circuit, and the third protection circuit, the protection of the DC input is achieved, and the safety of the circuit operation is guaranteed from many aspects.

[0007] As an implementation of the first aspect, the first protection circuit includes: an overcurrent protection branch, wherein the first end of the overcurrent protection branch serves as the first end of the first protection circuit and is used to be connected to the positive terminal of the DC power supply; an overvoltage protection branch, wherein the first end of the overvoltage protection branch serves as the second end of the first protection circuit and is used to be connected to the negative terminal of the DC power supply; the second end of the overvoltage protection branch is connected to the second end of the overcurrent protection branch, and the connection point serves as the third end of the first protection circuit and is used to be connected to the first end of the first filter circuit.

[0008] As described above, over-current protection and over-voltage protection of the input signal are achieved through the first protection circuit.

[0009] As an implementation of the first aspect, the first filtering circuit includes: a first capacitor branch, wherein the first end of the first capacitor branch serves as the first end of the first filtering circuit and is used to be connected to the third end of the first protection circuit; the second end of the first capacitor branch serves as the second end of the first filtering circuit and is used to be connected to the negative terminal of the DC power supply; a first inductor branch, wherein the first inductor branch is connected in parallel to both ends of the first capacitor branch; and a second capacitor branch, wherein the second capacitor branch is connected in parallel to the first inductor branch, and the first end of the second capacitor branch serves as the third end of the first filtering circuit and is used to be connected to the first end of the second protection circuit.

[0010] As an implementation method of the first aspect, the second protection circuit includes: a first diode, the positive terminal of the first diode serves as the first end of the second protection circuit, which is used to be connected to the third end of the first filter circuit, and the negative terminal of the first diode serves as the second end of the second protection circuit, which is used to be connected to the first end of the third protection circuit; a second diode, the positive terminal of the second diode is connected to the positive terminal of the first diode, and the negative terminal of the second diode is connected to the negative terminal of the first diode.

[0011] As described above, the protection function against reverse connection is realized by the second protection circuit.

[0012] As an implementation of the first aspect, the third protection circuit includes: a surge voltage suppression branch, the surge voltage suppression branch includes a control chip and a MOSFET, the gate of the MOSFET is connected to the GATE pin of the control chip through a first resistor; the drain of the MOSFET serves as the first end of the third protection circuit, and is used to be connected to the second end of the second protection circuit; the V SSThe pin is connected to the first end of the second resistor, and the second end of the second resistor serves as the second end of the third protection circuit, which is used to be connected to the negative end of the DC power supply; the source of the MOSFET serves as the third end of the third protection circuit, which is used to be connected to the first end of the second filter circuit; the impact current suppression branch includes a third resistor, the first end of the third resistor is connected to the gate of the MOSFET, and the second end of the third resistor is connected to the drain of the MOSFET.

[0013] From the above, the third protection circuit is used to suppress abnormal surge voltage and impact current, thereby protecting circuit components. In the circuit provided by the present application, the protection against impact current only requires adding a resistor to the circuit, and cooperating with the components in the surge voltage suppression branch to form a discharge loop, thereby avoiding damage to circuit components caused by impact current and ensuring safe operation of the circuit.

[0014] As an implementation of the first aspect, the V DD The TIMER pin of the control chip is connected to the first end of the third capacitor, and the second end of the third capacitor is connected to the V SS The GATE pin of the control chip is also connected to the first end of the fourth capacitor, and the second end of the fourth capacitor is connected to the negative terminal of the DC power supply; the OUTPUT pin of the control chip is connected to the source of the MOSFET, and the OUTPUT pin of the control chip is also connected to the first end of the fifth capacitor, and the second end of the fifth capacitor is connected to the V SS Pin connection; the control chip F B The pin is connected to the first end of the fifth resistor, the second end of the fifth resistor is connected to the source of the MOSFET, and the F B The pin is also connected to the first end of the sixth resistor, the second end of the sixth resistor is connected to the negative terminal of the DC power supply, and the F B The pin is also connected to the first end of the seventh resistor, the second end of the seventh resistor is connected to the first end of the sixth capacitor, and the second end of the sixth capacitor is connected to the negative terminal of the DC power supply; the BASE pin of the control chip is connected to the V SS Pin connections.

[0015] As a result, the abnormal surge voltage is suppressed.

[0016] As an implementation of the first aspect, the second filtering circuit includes: a third capacitor branch, the first end of the third capacitor branch serves as the first end of the second filtering circuit, and is used to be connected to the third end of the third protection circuit; the second end of the third capacitor branch serves as the second end of the second filtering circuit, and is used to be connected to the negative terminal of the DC power supply; a fourth capacitor branch, the fourth capacitor branch is connected in parallel to both ends of the third capacitor branch; and a fifth capacitor branch, the fifth capacitor branch is connected in parallel to both ends of the fourth capacitor branch.

[0017] As an implementation manner of the first aspect, the overcurrent protection branch includes a fuse, a first end of the fuse serves as the first end of the overcurrent protection branch, and a second end of the fuse serves as the second end of the overcurrent protection branch.

[0018] From the above, overcurrent protection is achieved by disconnecting the fuse when the input is overcurrent.

[0019] As an implementation of the first aspect, the overvoltage protection branch includes a transient voltage suppressor, the positive terminal of the transient voltage suppressor serves as the first end of the overvoltage protection branch, and the negative terminal of the transient voltage suppressor serves as the second end of the overvoltage protection branch.

[0020] From the above, when the input is over-voltage, the voltage is clamped by the transient voltage suppressor to achieve over-voltage protection.

[0021] As an implementation manner of the first aspect, the control chip includes: an LTC4366 chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The various technical features of the present application and the relationship between them are further explained below with reference to the accompanying drawings. The accompanying drawings are exemplary, and some technical features are not shown in actual proportion. In addition, some drawings may omit technical features that are commonly used in the technical field to which the present application belongs and are not essential for understanding and implementing the present application, or additional technical features that are not essential for understanding and implementing the present application may be shown. In other words, the combination of the various technical features shown in the accompanying drawings is not used to limit the present application. In addition, throughout the present application, the same figure numbers refer to the same content. The specific description of the drawings is as follows:

[0023] Figure 1 A structural diagram of a circuit for realizing abnormal surge voltage suppression provided by the related technology of this application;

[0024] Figure 2a This is an equivalent diagram of the first working mode of the circuit of the related technology of this application;

[0025] Figure 2bThis is an equivalent diagram of the second working mode of the circuit of the related technology of this application;

[0026] Figure 2c This is an equivalent diagram of the third working mode of the circuit of the related technology of this application;

[0027] Figure 3 This is a waveform diagram of the circuit related to the present application;

[0028] Figure 4 A circuit structure diagram of a DC input protection circuit provided in an embodiment of the present application;

[0029] Figure 5 This is a waveform diagram of the DC input protection circuit provided in an embodiment of the present application. DETAILED DESCRIPTION

[0030] The technical solution provided by the present application is further described below with reference to the accompanying drawings and examples. It should be understood that the system structure and business scenarios provided in the examples of the present application are mainly to illustrate the possible implementation methods of the technical solution of the present application and should not be interpreted as the only limitation on the technical solution of the present application. It is known to those of ordinary skill in the art that with the evolution of the system structure and the emergence of new business scenarios, the technical solution provided by the present application is also applicable to similar technical problems.

[0031] It should be understood that the embodiments of the present application provide a solution for DC input protection. Since the principles of solving the problems in these technical solutions are the same or similar, some repetitions may not be repeated in the introduction of the following specific embodiments, but it should be regarded as that these specific embodiments have been referenced to each other and can be combined with each other.

[0032] 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 application. In case of any inconsistency, the meaning described in this specification or the meaning derived from the contents recorded in this specification shall prevail. In addition, the terms used herein are only for the purpose of describing the embodiments of the present application and are not intended to limit the present application.

[0033] The DC input protection scheme provided in the embodiment of the present application is mainly used in the scenario of airborne 28V DC input, which requires the standard DO160G to meet the limitation of abnormal surge voltage (i.e., it needs to meet the 80V / 100ms high voltage impact) and the standard DO160G to meet the impact current limitation requirements (in the initial 3.0ms, the circuit needs to be able to withstand 9 times the maximum steady-state load current; from 3.0ms to 500ms, the circuit needs to be able to withstand 4 times the maximum steady-state load current; from 500ms to 2s, the circuit needs to be able to withstand 2 times the maximum steady-state load current; after 2s, the circuit needs to be able to return to its rated steady-state load current). Based on the DC input protection scheme provided in this application, the corresponding requirements can be met to achieve safety protection of circuits and flight.

[0034] like Figure 1 The figure shows a circuit for realizing abnormal surge voltage suppression provided by the related art. Figure 1 As shown, LTC4366-2 is the control chip, and the V DD The pin is connected through a resistor R IN Connected to the drain of the N-channel MOSFET (M1), the GATE pin of the LTC4366-2 is connected to the drain of the N-channel MOSFET (M1) through a resistor R G The OUT pin of LTC4366-2 is directly connected to the source of MOSFET (M1), the SD pin of LTC4366-2 is connected to the collector of transistor Q1 through a resistor R1, and the TIMER pin of LTC4366-2 is connected to the collector of transistor Q1 through a capacitor C T Connect to ground resistor R SS One end of the resistor R SS Connect to ground, and the Vss pin of the LTC4366-2 is connected to the ground resistor R SS One end of the resistor R SS Connect to ground, the BASE pin of the LTC4366-2 is connected to the ground resistor R SS One end of the resistor R SS Connected to ground. In addition, the BASE pin of LTC4366-2 is also connected to the source of MOSFET through a capacitor C1. B The FB pin of the LTC4366-2 is connected to the source of the MOSFET through a resistor RFB1, and the FB pin of the LTC4366-2 is also connected to ground through a resistor RFB2. Figure 1 As shown, the GATE pin of the LTC4366-2 is connected to the resistor R G There is also a capacitor C between G A connection point, capacitor C GThe other end of is connected to ground; the emitter of transistor Q1 is connected to ground, and the base of transistor Q1 is connected to external SD through a resistor R2. In this circuit, the output voltage during overvoltage transients is regulated by controlling the gate of MOSFET, thereby preventing the load from being damaged by transient high voltage.

[0035] As above, the circuit structure of the surge voltage suppression circuit for 28V DC input provided by the related technology. The working mode of the circuit can be divided into the following Figure 2a to Figure 2c The first working mode is Figure 2a The startup mode shown in the figure is equivalent to a 7.5uA current in the circuit to charge the gate of the MOSFET during startup. When the gate voltage of the MOSFET rises to the threshold voltage, the output voltage of the OUT pin of the LTC4366-2 begins to rise. When the voltage difference between the OUT pin of the LTC4366-2 and the Vss pin exceeds 4.75V, the second working mode is entered. The second working mode is Figure 2b The circuit also includes a third operating mode, in which the GATE pin of the LTC4366-2 is charged to its final value at 20uA. Figure 2c As shown in the figure, the third operating mode is the regulation mode. After the circuit is powered on, the overvoltage regulation amplifier monitors the F B The voltage at the pin is used to regulate the overvoltage, thereby protecting the circuit load from being destroyed by transient high voltage.

[0036] In the study of related technologies, the circuit breaker is used as a switch to control the power on and off of the circuit. Figure 1 During the test, it was found that there would be excessive surge current, such as Figure 3 As shown, curve a represents the waveform of the impact current, curve b represents the waveform of the input voltage, and curve c represents the waveform of the output voltage. Figure 3 It can be seen that at the moment of power-on, a large inrush current will appear. As time goes by, the inrush current gradually decreases and tends to be flat. Therefore, when the power is frequently turned on and off, the inrush current will cause a large impact on the circuit load and affect the safety of the circuit.

[0037] Based on the research on the above-mentioned related technologies, in order to solve the impact of the impact current on the circuit during frequent power on and off, the present application provides a DC input protection circuit.

[0038] In the embodiment of the present application, the control chip in the DC input protection circuit can be selected as the LTC4366 chip. Before introducing the connection relationship of the DC input protection circuit, the function of each pin of the LTC4366 chip is first introduced.

[0039] 1) BASE pin: Base driver output for the PNP shunt regulator. This pin is connected to the anode of an internal 6.2V Zener diode (whose cathode is connected to the OUTPUT pin). SS resistor, connect the base of an external PNP to this pin (the collector of this PNP is grounded and the emitter is connected to V SS ). Connect this pin to V when not in use. SS .

[0040] 2) F B Pin: Overvoltage regulator amplifier feedback input pin. Connect this pin to an external resistive voltage divider between OUTPUT and ground. The overvoltage regulator amplifier controls the gate of the external N-channel MOSFET to B The pin voltage is regulated to 1.23V below OUTPUT. In the event of a fast overvoltage condition, the overvoltage amplifier will enable a 200mA pull-down current source on the GATE pin.

[0041] 3) GATE pin: used for gate drive of external N-channel MOSFET. During startup, an internal 7.5μA current source is drawn from V DD pin charges the gate of the external N-channel MOSFET. SS When it reaches 4.75V, the charge pump will complete the charging of GATE (12V higher than OUTPUT). In the event of a rapid overvoltage, a 200mA pull-down current source between GATE and OUTPUT is enabled, and then the overvoltage regulation amplifier regulates the GATE pin voltage.

[0042] 4) OUTPUT pin: Charge pump and overvoltage regulator amplifier supply voltage. Power input for floating circuits powered from the MOSFET source. When the OUTPUT voltage is above 4.75V (UVL02), the charge pump will turn on and draw power from this pin. When OUTPUT exceeds 2.55V (UVL01), it is used as a power supply and reference input for the overvoltage regulator amplifier. This pin is clamped at 5.7V and requires a 0.22μF or larger capacitor to bypass to V SS Pin.

[0043] 5)TIMER pin: Timer input pin. When this pin is open, the overvoltage regulation time is 1μs, and then the fault is shut down. SS A capacitor is connected between the LTC4366-2 and LTC4366-2 to set a 278ms / μF overvoltage regulation time before the switch turns off.

[0044] 6) V DD Pin: STARTUP SUPPLY. Supply input for the 7.5μA startup current source that charges the gate of the external M-channel MOSFET. This pin is also used to power timers and logic that operate when the external MOSFET is off. This pin is clamped at V SS +12V. Do not bypass this pin with a capacitor.

[0045] 7) V SS Pin: Device return and substrate. The capacitors on the TIMER and OUTPUT pins should be connected back to this pin. Referring to the accompanying drawings, a DC input protection circuit provided by the present application is described in detail below.

[0046] like Figure 4 As shown, it is a circuit structure diagram of the DC input protection circuit provided in an embodiment of the present application. In this embodiment, the DC input protection circuit includes a first protection circuit 110, a first filter circuit 120, a second protection circuit 130, a third protection circuit 140, and a second filter circuit 150. In this embodiment, the DC power supply is a 28V DC power supply. Among them, the first end 110a of the first protection circuit 110 is connected to the positive terminal of the DC power supply, the second end 110b of the first protection circuit 110 is connected to the negative terminal (ground terminal) of the DC power supply, and the third end 110c of the first protection circuit 110 is connected to the first end 120a of the first filter circuit 120. The second end 120b of the first filter circuit 120 is connected to the ground terminal of the DC power supply, and the third end 120c of the first filter circuit 120 is connected to the first end 130a of the second protection circuit 130. The second end 130b of the second protection circuit 130 is connected to the first end 140a of the third protection circuit 140. The second end 140b of the third protection circuit 140 is connected to the negative end of the DC power supply, and the third end 140c of the third protection circuit 140 is connected to the first end 150a of the second filter circuit 150. The second end 150b of the second filter circuit 150 is connected to the negative end of the DC power supply.

[0047] Next, the various sub-circuits included in the DC input protection circuit are introduced in detail.

[0048] The first protection circuit 110 is used to implement overcurrent protection for input current and to implement overvoltage protection for input voltage (for example, the protection requirements for voltage spikes and indirect lightning strikes in standard DO160G). The first protection circuit 110 includes an overcurrent protection branch and an overvoltage protection branch. In this embodiment, the overcurrent protection branch includes a fuse F1. The first end of the fuse F1 is used as the first end of the overcurrent protection branch, and the first end of the overcurrent protection branch (the first end of the fuse F1) is used as the first end 110a of the first protection circuit 110 connected to the positive pole of the DC power supply, and the second end of the fuse F1 is used as the second end of the overcurrent protection branch for connecting to the overvoltage protection branch. In this embodiment, the overvoltage protection branch includes a transient voltage suppressor TVS1. The positive terminal of the transient voltage suppressor TVS1 is used as the first end of the overvoltage protection branch, and the first end of the overvoltage protection branch (the positive terminal of the transient voltage suppressor TVS1) is used as the second end 110b of the first protection circuit 110 for connecting to the negative end of the DC power supply, and the negative end of the transient voltage suppressor TVS1 is used as the second end of the overvoltage protection branch for connecting to the overcurrent protection branch. In addition, in this embodiment, the connection point between the second end of the overvoltage protection branch and the second end of the overcurrent protection branch is used as the third end 110c of the first protection circuit 110 for connecting to the first filter circuit 120.

[0049] The first filter circuit 120 is used to filter the output signal of the first protection circuit 110. The first filter circuit 120 includes a first capacitor branch, a first inductor branch, and a second capacitor branch. The first capacitor branch includes a first capacitor C1, the first inductor branch includes a first inductor L1, and the second capacitor branch includes a second capacitor C2. The first capacitor C1 is connected in parallel to both ends of the state voltage suppressor TVS1, the first inductor L1 is connected in parallel to both ends of the first capacitor C1, and the second capacitor C2 is connected in parallel to both ends of the first inductor L1, so that the input signal can be filtered through the first capacitor C1, the first inductor L1, and the second capacitor C2. In this embodiment, the first end of the first capacitor branch 121 is used as the first end 120a of the first filter circuit to connect to the third end 110c of the first protection circuit, the second end of the first capacitor branch is used as the second end 120b of the first filter circuit to connect to the negative electrode of the DC power supply, and the first end of the second capacitor branch is used as the third end 120c of the first filter circuit to connect to the first end 130a of the second protection circuit, thereby realizing the connection between the first filter circuit 120 and the front and rear stage circuits.

[0050] The second protection circuit 130 is used to implement reverse connection protection for the circuit. The second protection circuit 130 includes a first diode D1 and a second diode D2 connected in parallel with the first diode D1. The positive terminal of the first diode D1 is connected to the third terminal 120c of the first filter circuit as the first terminal 130a of the second protection circuit, and the negative terminal of the first diode D1 is connected to the first terminal 140a of the third protection circuit as the second terminal 130b of the second protection circuit. In this embodiment, the positive terminal of the second diode D2 is connected to the positive terminal of the first diode D1, and the negative terminal of the second diode is connected to the negative terminal of the first diode D1. Through the above connection, the second protection circuit 130 is formed, thereby implementing reverse connection protection for the circuit.

[0051] The third protection circuit 140 is used to suppress surge voltage and impulse current. Therefore, the third protection circuit 140 includes a surge voltage suppression branch and an impulse current suppression branch.

[0052] Among them, the main components of the surge voltage suppression branch are the control chip U1 and the metal-oxide-semiconductor field-effect transistor (MOSFET) VT1. In this embodiment, the control chip may include an LTC4366 chip. Figure 4 As shown, the gate of transistor VT1 is connected to the GATE pin of control chip U1 through the first resistor R1, and the drain of transistor VT1 is connected to the second end 130b of the second protection circuit as the first end 140a of the third protection circuit. SS The pin is connected to the ground terminal of the DC power supply through the second resistor R2, wherein the end of the second resistor R2 close to the ground is used as the second end 140b of the third protection circuit. The source of the transistor VT1 is used as the third end 140c of the third protection circuit to be connected to the first end 150a of the second filter circuit. Specifically, in the surge voltage suppression branch, the V DD The TIMER pin of the control chip U1 is connected to the drain of the transistor VT1 through the fourth resistor R4; the TIMER pin of the control chip U1 is connected to the V SS The GATE pin of the control chip U1 is connected to the gate of the transistor VT1 through the first resistor R1 and is also connected to the negative terminal of the DC power supply through the fourth capacitor C4; the OUTPUT pin of the control chip U1 is connected to the source of the transistor VT1, and the OUTPUT pin of the control chip U1 is also connected to the V SS Pin; F of control chip U1 B The pin is connected to the source of transistor VT1 through the fifth resistor R5, and the FB The pin is also connected to the negative terminal of the DC power supply through the sixth resistor R6; the F B The pin is also connected to the negative terminal of the DC power supply through the seventh resistor R7 and the sixth capacitor C6 connected in sequence; the BASE pin of the control chip U1 is connected to the V SS Pin.

[0053] Among them, the main component of the impact current suppression branch is the third resistor R3 connected in parallel between the drain and gate of the transistor VT1. The third resistor R3 and the transistor VT1, the fifth resistor R5, the sixth resistor R6, the fourth capacitor C4, and the first resistor R1 in the surge voltage suppression branch form a discharge circuit, so that the impact current generated when the circuit is frequently powered on and off is released through the discharge circuit. The impact current suppression branch of the present application only adds a resistor between the drain and gate of the transistor, and is combined with the existing components in the surge voltage suppression branch, which can not only suppress the damage to the circuit components caused by the impact current of frequent power on and off, but also does not need to increase the complexity of the circuit, and also ensures the minimum cost.

[0054] The second filter circuit 150 is used to filter the output signal of the third protection circuit 140. The second filter circuit 150 includes a third capacitor branch, a fourth capacitor branch and a fifth capacitor branch. Among them, the third capacitor branch includes a seventh capacitor C7, the fourth capacitor branch includes an eighth capacitor C8, and the fifth capacitor branch includes a ninth capacitor C9. The first end of the seventh capacitor C7 is used as the first end 150a of the second filter circuit to be connected to the third end 140c of the third protection circuit, and the second end of the seventh capacitor C7 is used as the second end 150b of the second filter circuit to be connected to the negative pole of the DC power supply. The eighth capacitor C8 is connected in parallel to the two ends of the seventh capacitor C7, and the ninth capacitor C9 is connected in parallel to the two ends of the eighth capacitor C8. The output signal of the third protection circuit 140 is filtered by the seventh capacitor C7, the eighth capacitor C8, and the ninth capacitor C9, so as to obtain the filtered target signal.

[0055] Based on the DC input protection circuit provided in this embodiment, when the input is overcurrent, the fuse F1 in the first protection circuit will be disconnected, thereby realizing the first protection of the circuit. When the input is overvoltage (for example, a voltage spike or indirect lightning strike occurs), the transient voltage suppressor TVS1 in the overvoltage protection branch will clamp the input voltage, thereby realizing the second protection of the circuit. When the voltage is reversed, the first diode D1 in the second protection circuit will be cut off, thereby realizing the protection of the subsequent circuit. When an abnormal surge voltage occurs, the control chip U1 in the third protection branch will control the MOSFET to clamp the output voltage to the target value (for example, about 45V), thereby realizing the protection of the circuit under abnormal surge voltage conditions. When an inrush current occurs during frequent power on and off, the inrush current suppression branch in the third protection circuit will provide a discharge circuit to discharge the gate of the MOSFET so that the inrush current will not be too large during frequent power on and off. The test waveform can be seen in Figure 5 , Figure 5 The middle curve a represents the drain-source voltage of the MOSFET, and the curve b represents the input impact current. It can be seen that according to the circuit of the present application, no impact current exceeding the standard occurs during the power-on process, and the drain-source is in a cut-off state at the moment of power-on.

[0056] Next, the working principle of the impulse current discharge in the DC input protection circuit of the present application is introduced.

[0057] The third resistor R3, the transistor VT1, the fifth resistor R5, the sixth resistor R6, the fourth capacitor C4, and the first resistor R1 form a discharge loop.

[0058] The impedance of the discharge circuit is: R = R3 + R5 + R6 + R1;

[0059] The time constant of the capacitor discharge in the discharge circuit is: τ = RC4;

[0060] When the capacitor is discharged, uc = Uo × e^(-t / τ);

[0061] In the above formula, uc represents the voltage of capacitor C4 after time t, Uo represents the voltage of capacitor C4 before discharge, e is the base of natural logarithm, which is approximately equal to 2.71828, t represents the discharge time, and τ represents the time constant.

[0062] Generally, under the application condition of 28V airborne DC input, R1=10Ω, R5=13.3KΩ, R6=475KΩ, C4=10nF. After calculation by the above formula, when the resistance value of R3 is between 20MΩ and 40MΩ, it can generally meet the discharge time requirement. Preferably, the resistance value of R3 in this application is 27MΩ.

[0063] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention is described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, all of which belong to the protection scope of the present invention.

Claims

1. A DC input protection circuit, characterized in that: include: a first protection circuit, wherein a first end of the first protection circuit is connected to a positive terminal of a DC power supply, and a second end of the first protection circuit is connected to a negative terminal of the DC power supply; a first filter circuit, wherein a first end of the first filter circuit is connected to a third end of the first protection circuit, and a second end of the first filter circuit is connected to a negative end of the DC power supply; a second protection circuit, wherein a first end of the second protection circuit is connected to a third end of the first filter circuit; a third protection circuit, wherein a first end of the third protection circuit is connected to a second end of the second protection circuit, and a second end of the third protection circuit is connected to a negative terminal of the DC power supply; A second filtering circuit, wherein a first end of the second filtering circuit is connected to a third end of the third protection circuit, and a second end of the second filtering circuit is connected to a negative terminal of the DC power supply.

2. The circuit according to claim 1, characterized in that The first protection circuit comprises: an overcurrent protection branch, wherein a first end of the overcurrent protection branch serves as a first end of the first protection circuit and is used to be connected to a positive terminal of the DC power supply; an overvoltage protection branch, wherein a first end of the overvoltage protection branch serves as a second end of the first protection circuit and is used to be connected to a negative terminal of the DC power supply; The second end of the overvoltage protection branch is connected to the second end of the overcurrent protection branch, and the connection point is used as the third end of the first protection circuit, which is used to be connected to the first end of the first filtering circuit.

3. The circuit according to claim 1, characterized in that The first filtering circuit comprises: a first capacitor branch, wherein a first end of the first capacitor branch serves as a first end of the first filter circuit and is used to be connected to a third end of the first protection circuit; and a second end of the first capacitor branch serves as a second end of the first filter circuit and is used to be connected to a negative terminal of the DC power supply; A first inductor branch, wherein the first inductor branch is connected in parallel to two ends of the first capacitive branch; A second capacitor branch, the second capacitor branch is connected in parallel to the first inductor branch, and a first end of the second capacitor branch serves as a third end of the first filter circuit, and is used to be connected to a first end of the second protection circuit.

4. The circuit according to claim 1, characterized in that The second protection circuit comprises: a first diode, wherein the positive terminal of the first diode serves as the first terminal of the second protection circuit and is used to be connected to the third terminal of the first filter circuit, and the negative terminal of the first diode serves as the second terminal of the second protection circuit and is used to be connected to the first terminal of the third protection circuit; A second diode, wherein an anode terminal of the second diode is connected to an anode terminal of the first diode, and a cathode terminal of the second diode is connected to a cathode terminal of the first diode.

5. The circuit according to claim 1, characterized in that The third protection circuit comprises: A surge voltage suppression branch, the surge voltage suppression branch includes a control chip and a MOSFET, the gate of the MOSFET is connected to the GATE pin of the control chip through a first resistor; the drain of the MOSFET serves as the first end of the third protection circuit and is used to be connected to the second end of the second protection circuit; the V SS The pin is connected to the first end of the second resistor, and the second end of the second resistor serves as the second end of the third protection circuit, and is used to be connected to the negative end of the DC power supply; the source of the MOSFET serves as the third end of the third protection circuit, and is used to be connected to the first end of the second filter circuit; The inrush current suppression branch comprises a third resistor, a first end of the third resistor is connected to the gate of the MOSFET, and a second end of the third resistor is connected to the drain of the MOSFET.

6. The circuit according to claim 5, characterized in that The control chip's V DD The TIMER pin of the control chip is connected to the first end of the third capacitor, and the second end of the third capacitor is connected to the V SS The GATE pin of the control chip is also connected to the first end of the fourth capacitor, and the second end of the fourth capacitor is connected to the negative terminal of the DC power supply; the OUTPUT pin of the control chip is connected to the source of the MOSFET, and the OUTPUT pin of the control chip is also connected to the first end of the fifth capacitor, and the second end of the fifth capacitor is connected to the V SS Pin connection; the control chip F B The pin is connected to the first end of the fifth resistor, the second end of the fifth resistor is connected to the source of the MOSFET, and the F B The pin is also connected to the first end of the sixth resistor, the second end of the sixth resistor is connected to the negative terminal of the DC power supply, and the F B The pin is also connected to the first end of the seventh resistor, the second end of the seventh resistor is connected to the first end of the sixth capacitor, and the second end of the sixth capacitor is connected to the negative terminal of the DC power supply; the BASE pin of the control chip is connected to the V SS Pin connections.

7. The circuit according to claim 1, characterized in that The second filtering circuit comprises: a third capacitor branch, wherein a first end of the third capacitor branch serves as a first end of the second filter circuit and is used to be connected to a third end of the third protection circuit; a second end of the third capacitor branch serves as a second end of the second filter circuit and is used to be connected to a negative terminal of the DC power supply; a fourth capacitor branch, the fourth capacitor branch being connected in parallel to two ends of the third capacitor branch; A fifth capacitor branch is connected in parallel to two ends of the fourth capacitor branch.

8. The circuit according to claim 2, characterized in that The overcurrent protection branch includes a fuse, a first end of the fuse serves as the first end of the overcurrent protection branch, and a second end of the fuse serves as the second end of the overcurrent protection branch.

9. The circuit according to claim 2, characterized in that The overvoltage protection branch includes a transient voltage suppressor, the positive terminal of the transient voltage suppressor serves as the first end of the overvoltage protection branch, and the negative terminal of the transient voltage suppressor serves as the second end of the overvoltage protection branch.

10. The circuit according to claim 6, characterized in that The control chip includes: LTC4366 chip.

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