Over / under-voltage input protection circuit, DC-DC circuit, DC power supply and electric equipment

Abstract

The invention relates to the technical field of DC-DC circuits, and discloses an overvoltage / undervoltage input protection circuit, a DC-DC circuit, a DC power supply and electric equipment. The overvoltage / undervoltage input protection circuit comprises an undervoltage protection unit and an overvoltage protection unit, a voltage stabilizing diode D2 is used for adjusting the minimum working voltage, and a voltage stabilizing diode D3 is used for adjusting the maximum working voltage. When the voltage of the input side of the DC-DC circuit does not reach a set low-voltage threshold value or when the input voltage exceeds a set high-voltage threshold value, the output of the DC-DC circuit is closed in time, the situations that devices are overused due to undervoltage and components are damaged by high voltage are avoided, and the circuit is simple in structure, high in feasibility and reliability and low in cost; moreover, the range of the working voltage can be correspondingly adjusted according to circuit requirements, and the operation is very convenient.

Description

Technical Field

[0001] The present invention relates to the technical field of DC-DC circuits, and in particular to an over / under voltage input protection circuit, a DC-DC circuit, a direct current power supply and electrical equipment. Background Art

[0002] A DC-DC circuit is a circuit used to convert a direct current voltage from one level to another, where DC stands for Direct Current. DC-DC circuits are widely used, such as power management systems, communication systems, etc. There are many ways to implement a DC-DC circuit, and the electronic components used are also diverse, and the corresponding functions are also different. However, a DC-DC circuit that has input undervoltage protection, overvoltage protection, and constant voltage output functions is rare. With the increasing demand of users for product safety, many electronic products need circuits that have input over / undervoltage protection and constant voltage output. However, the current field basically implements the above functions by adding an op amp IC (Integrated Circuit) or other functional IC to the circuit. However, this embedded IC implementation method is costly and not conducive to the subsequent inspection and maintenance of circuit faults.

[0003] In the actual production process, the circuit design must meet the producibility requirements. In order to make a profit, the cost must be considered. Therefore, there is an urgent need in this field to use simple components to design a DC-DC circuit with input undervoltage protection and overvoltage protection and constant output voltage.

[0004] The above information is presented as background information only to assist with understanding the present disclosure and no determination or admission is made as to whether any of the above may be used as prior art with respect to the present disclosure. Summary of the invention

[0005] The object of the present invention is to provide an over / under voltage input protection circuit, a DC-DC circuit, a DC power supply and an electrical device to solve or at least partially solve the technical problems existing in the prior art.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides an over / under voltage input protection circuit, comprising an under voltage protection unit and an over voltage protection unit;

[0008] The undervoltage protection unit includes a voltage stabilizing diode D2, a switch tube Q1 and a switch tube Q2; the cathode of the voltage stabilizing diode D2 is electrically connected to the positive terminal of the switch tube Q2 and the first end of the resistor R3, the anode of the voltage stabilizing diode D2 is electrically connected to the control end of the switch tube Q1 and the first end of the resistor R1, the positive terminal of Q1 is electrically connected to the control end of the switch tube Q2 and the second end of the resistor R3, and the second end of the resistor R1 is electrically connected to the negative terminal of the switch tube Q1;

[0009] The overvoltage protection unit includes a voltage stabilizing diode D3, a switch tube Q3 and a switch tube Q4; the positive terminal of the switch tube Q4 is electrically connected to the negative terminal of the switch tube Q2, the positive terminal of the switch tube Q3 and the first end of the resistor R4, the second end of the resistor R4 is electrically connected to the negative electrode of the voltage stabilizing diode D3 and the control end of the switch tube Q3, the negative terminal of the switch tube Q3 is electrically connected to the control end of the switch tube Q4 and the first end of the resistor R6, and the second end of the resistor R6 is electrically connected to the positive electrode of the voltage stabilizing diode D3; wherein the second end of the resistor R1 and the second end of the resistor R6 are both electrically connected to the reference ground;

[0010] When the voltage at the cathode of the voltage stabilizing diode D2 is less than the predetermined low-voltage threshold, the voltage stabilizing diode D2 is not broken down, the switch tube Q1 is not turned on, and the voltage drop between the positive terminal and the control terminal of the switch tube Q2 does not reach the set turn-on voltage drop, and the switch tube Q2 is not turned on;

[0011] When the voltage at the cathode of the Zener diode D3 is greater than the predetermined high voltage threshold, the Zener diode D3 is broken down, the switch tube Q3 is turned on, and the voltage drop between the positive terminal and the control terminal of the switch tube Q4 does not reach the set turn-on voltage drop, and the switch tube Q4 is not turned on.

[0012] Optionally, the switch tube Q1 is an NPN transistor, the switch tube Q3 is a PNP transistor, and the switch tube Q2 and the switch tube Q4 are both PMOS switch tubes;

[0013] A resistor R2 is electrically connected between the control end of the switch tube Q1 and the anode of the voltage-stabilizing diode D2 ; a resistor R5 is electrically connected between the control end of the switch tube Q3 and the cathode of the voltage-stabilizing diode D3 .

[0014] In a second aspect, the present invention further provides a DC-DC circuit, comprising a constant voltage output circuit, wherein the voltage input side of the constant voltage output circuit is provided with an over / under voltage input protection circuit as described above.

[0015] Optionally, the constant voltage output circuit includes a voltage stabilizing diode D5, a switch tube Q5 and a switch tube Q6;

[0016] The negative terminal of the switch tube Q4 is electrically connected to the positive terminal of the switch tube Q5, the positive terminal of the switch tube Q6 and the first end of the resistor R8, the second end of the resistor R8 is electrically connected to the cathode of the voltage zener diode D5 and the control end of the switch tube Q6, and the anode of the voltage zener diode D5 is electrically connected to the reference ground;

[0017] The negative terminal of the switch tube Q5 is the constant voltage output terminal of the DC-DC circuit.

[0018] Optionally, the switch tube Q5 and the switch tube Q6 are both NPN transistors;

[0019] A resistor R7 is also electrically connected between the negative terminal of the switch tube Q4 and the positive terminal of the switch tube Q6.

[0020] Optionally, the negative terminal of the switch tube Q4 is also electrically connected to the anode of the diode D4, and the cathode of the diode D4 is electrically connected to the positive terminal of the switch tube Q5;

[0021] The cathode of the voltage stabilizing diode D2 is also electrically connected to the cathode of the diode D1 , and the anode of the diode D1 is electrically connected to the second end of the resistor R1 .

[0022] Optionally, the first end of the resistor R8 is also electrically connected to the positive electrode of the capacitor C1, and the negative electrode of the capacitor C1 is electrically connected to the positive electrode of the voltage stabilizing diode D5;

[0023] The negative terminal of the switch tube Q5 is also electrically connected to the positive electrode of the capacitor C2 and the positive electrode of the capacitor C3 respectively, and the negative electrode of the capacitor C2 and the negative electrode of the capacitor C3 are both electrically connected to the positive electrode of the voltage stabilizing diode D5.

[0024] In a third aspect, the present invention further provides a direct current power supply, including a DC-DC circuit, wherein the DC-DC circuit adopts a DC-DC circuit as described above.

[0025] Optionally, the DC power supply further includes a battery;

[0026] The positive terminal of the battery is electrically connected to the cathode of the voltage stabilizing diode D2, and the negative terminal of the battery is electrically connected to the reference ground.

[0027] In a fourth aspect, the present invention further provides an electrical device, comprising a DC power supply as described above.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The over / under voltage input protection circuit designed by the present invention is applied in a DC-DC circuit. When the voltage on the input side of the DC-DC circuit does not reach a set low voltage threshold or when the input voltage exceeds a set high voltage threshold, the output of the DC-DC circuit is promptly turned off to avoid excessive use of devices due to under voltage and damage to components due to high voltage. The circuit structure is simple, the feasibility and reliability are high, and the cost is low. Moreover, the range of the operating voltage can be adjusted accordingly according to the circuit requirements, wherein the voltage zener diode D2 is used to adjust the minimum operating voltage, and the voltage zener diode D3 is used to adjust the maximum operating voltage, which is very convenient.

[0030] The present invention has other features and advantages, which will be apparent from or will be described in detail in the accompanying drawings and the following detailed description incorporated herein, which together serve to explain the specific principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 The present invention provides a circuit structure schematic diagram of a DC-DC circuit with over / under voltage input protection function.

[0033] Figure 2 yes Figure 1 Schematic diagram of the circuit structure of the undervoltage protection unit.

[0034] Figure 3 yes Figure 1 Schematic diagram of the circuit structure of the overvoltage protection unit.

[0035] Figure 4 yes Figure 1 The circuit structure schematic diagram of the constant voltage output circuit in . DETAILED DESCRIPTION

[0036] In order to explain in detail the possible application scenarios, technical principles, specific schemes that can be implemented, and the purposes and effects that can be achieved, the following is a detailed description of the specific embodiments listed in conjunction with the accompanying drawings. The embodiments described herein are only used to more clearly illustrate the technical solutions of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0037] Reference to "embodiment" herein means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The term "embodiment" appearing in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or association with other embodiments. In principle, in the present application, as long as there is no technical contradiction or conflict, the various technical features mentioned in the embodiments can be combined in any way to form a corresponding implementable technical solution.

[0038] Unless otherwise defined, the technical terms used in this document have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms in this document is only for describing specific embodiments and is not intended to limit this application.

[0039] In the description of this application, the term "and / or" is an expression used to describe the logical relationship between objects, indicating that three relationships may exist, for example, A and / or B, which means: A exists, B exists, and A and B exist at the same time. In addition, the character " / " in this article generally indicates that the objects before and after are in an "or" logical relationship.

[0040] In the present application, terms such as “first” and “second” are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship of quantity, priority or sequence between these entities or operations.

[0041] Without further limitations, in this application, the words "include", "comprises", "has" or other similar expressions used in the sentences are intended to cover non-exclusive inclusion. These expressions do not exclude the presence of additional elements in the process, method or product including the elements, so that the process, method or product including a series of elements may include not only those limited elements, but also other elements not explicitly listed, or also include elements inherent to such process, method or product.

[0042] Similar to the understanding in the Examination Guidelines, in this application, expressions such as "greater than", "less than", "exceed" and the like are understood to exclude the number itself; expressions such as "above", "below", "within" and the like are understood to include the number itself. In addition, in the description of the embodiments of this application, "multiple" means more than two (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups", "multiple times", etc., unless otherwise clearly and specifically limited.

[0043] In the description of the embodiments of the present application, space-related expressions used, such as "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "vertical", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicate the orientation or position relationship based on the orientation or position relationship shown in the specific embodiments or drawings, and are only for the convenience of describing the specific embodiments of the present application or facilitating the reader's understanding, and do not indicate or imply that the referred device or component must have a specific position, a specific orientation, or be constructed or operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0044] Unless otherwise expressly specified or limited, in the description of the embodiments of the present application, the terms such as "install", "connect", "connect", "fix", "set", etc. used should be understood in a broad sense. For example, the "connection" can be a fixed connection, a detachable connection, or an integrated setting; it can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. For technicians in the technical field to which the present application belongs, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0045] Embodiment 1:

[0046] See also Figure 1-Figure 3 , Figure 1 is a circuit structure schematic diagram of a DC-DC circuit with over / under voltage input protection function provided by an embodiment of the present invention, Figure 2 yes Figure 1 The circuit structure schematic diagram of the undervoltage protection unit in the Figure 3 yes Figure 1 Schematic diagram of the circuit structure of the overvoltage protection unit in the figure; for ease of description, in this embodiment, the upper end or left end in the figure is defined as the first end, and the lower end or right end is defined as the second end.

[0047] The DC-DC circuit includes a constant voltage output circuit, and the voltage input side of the constant voltage output circuit is provided with an over / under voltage input protection circuit; the specific circuit structure is as follows:

[0048] An over / under voltage input protection circuit, including an under voltage protection unit and an over voltage protection unit;

[0049] like Figure 2As shown, the undervoltage protection unit includes a voltage stabilizing diode D2, a switch tube Q1 and a switch tube Q2; the cathode of the voltage stabilizing diode D2 is electrically connected to the positive terminal of the switch tube Q2 and the first end of the resistor R3, respectively; the anode of the voltage stabilizing diode D2 is electrically connected to the control end of the switch tube Q1 and the first end of the resistor R1, respectively; the positive terminal of Q1 is electrically connected to the control end of the switch tube Q2 and the second end of the resistor R3, respectively; the second end of the resistor R1 is electrically connected to the negative terminal of the switch tube Q1;

[0050] like Figure 3 As shown, the overvoltage protection unit includes a voltage stabilizing diode D3, a switch tube Q3 and a switch tube Q4; the positive terminal of the switch tube Q4 is electrically connected to the negative terminal of the switch tube Q2, the positive terminal of the switch tube Q3 and the first end of the resistor R4, the second end of the resistor R4 is electrically connected to the negative electrode of the voltage stabilizing diode D3 and the control end of the switch tube Q3, the negative terminal of the switch tube Q3 is electrically connected to the control end of the switch tube Q4 and the first end of the resistor R6, and the second end of the resistor R6 is electrically connected to the positive electrode of the voltage stabilizing diode D3; wherein the second end of the resistor R1 and the second end of the resistor R6 are both electrically connected to the reference ground;

[0051] When the voltage at the cathode of the voltage stabilizing diode D2 is less than the predetermined low-voltage threshold, the voltage stabilizing diode D2 is not broken down, the switch tube Q1 is not turned on, and the voltage drop between the positive terminal and the control terminal of the switch tube Q2 does not reach the set turn-on voltage drop, and the switch tube Q2 is not turned on;

[0052] When the voltage at the cathode of the Zener diode D3 is greater than the predetermined high voltage threshold, the Zener diode D3 is broken down, the switch tube Q3 is turned on, and the voltage drop between the positive terminal and the control terminal of the switch tube Q4 does not reach the set turn-on voltage drop, and the switch tube Q4 is not turned on.

[0053] The above-mentioned over / under voltage input protection circuit can timely shut down the output of the DC-DC circuit when the voltage on the input side of the DC-DC circuit does not reach the set low voltage threshold or when the input voltage exceeds the set high voltage threshold, so as to avoid excessive use of components caused by under voltage and damage to components caused by high voltage;

[0054] Furthermore, the above-mentioned over / under voltage input protection circuit uses only conventional circuit components such as resistors and switch tubes, and has low cost, simple structure, high feasibility and reliability.

[0055] As an optional implementation, the switch tube Q1 is an NPN transistor, the switch tube Q3 is a PNP transistor, and the switch tube Q2 and the switch tube Q4 are both PMOS switch tubes;

[0056] Since the transistor is a current-type control device, a resistor R2 is electrically connected between the control end of the switch tube Q1 and the anode of the voltage-stabilizing diode D2; a resistor R5 is electrically connected between the control end of the switch tube Q3 and the cathode of the voltage-stabilizing diode D3.

[0057] For the above-mentioned over / under voltage input protection circuit, the operating voltage range of the DC-DC circuit can be set by the Zener diode D2 and the Zener diode D3, wherein the Zener diode D2 is used to adjust the minimum operating voltage, and the Zener diode D3 is used to adjust the maximum operating voltage, which is very convenient.

[0058] For example, the voltage zener diode D2 is a 13V voltage zener tube, the switch tube Q1 is an NPN transistor with a conduction condition of Vbe>0.7V, and the voltage zener diode D2 and the switch tube Q1 constitute a switch circuit for controlling the switch tube Q2;

[0059] like Figure 2 As shown, when the input voltage (i.e. Figure 2 V in+ ) is less than 13.7V, the Zener diode D2 is not broken down, the base voltage of the switch tube Q1 cannot reach the conduction condition, and the gate voltage of the switch tube Q2 is almost the same as the source voltage, so the switch tube Q2 is not turned on. At this time, the undervoltage protection is triggered, so the circuit has no output; when the input voltage is greater than 13.7V, the Zener diode D2 is broken down, and the voltage at the first end of the resistor R2 is V in+ Subtracting 13V, the conduction condition of the switch tube Q1 is met, so the switch tube Q1 is turned on. After the switch tube Q1 is turned on, the gate of the switch tube Q2 is immediately pulled low, so the switch tube Q2 is turned on.

[0060] like Figure 3 As shown, the voltage zener diode D3 is a 36V voltage zener tube, the switch tube Q3 is a PNP triode with a conduction condition of Vbe<-0.7V, and the voltage zener diode D3 and the switch tube Q3 constitute a switch circuit for controlling the switch tube Q4;

[0061] When the input voltage exceeds 36.7V, the Zener diode D3 is broken down, and the voltage at the left end of the resistor R5 is maintained at 36V, meeting the conduction condition of the switch tube Q3. Therefore, the switch tube Q3 is turned on, making the gate voltage and source voltage of the switch tube Q4 almost the same, and the switch tube Q4 is not turned on. At this time, the overvoltage protection is triggered, so the circuit has no output; however, when the input voltage does not exceed 36.7V, the Zener diode D3 is not broken down, and the base and emitter voltages of the switch tube Q3 are almost the same, the switch tube Q3 is not turned on, and the gate of the switch tube Q4 is pulled down by the pull-down resistor R6. At this time, the switch tube Q4 is turned on, and the DC-DC circuit outputs the DC voltage normally.

[0062] It is understandable that the switch tube Q1 may also be replaced by an NMOS switch tube, and the switch tube Q3 may also be replaced by a PMOS switch tube. The MOS switch principle is well known in the art and will not be described in detail here.

[0063] Further, such as Figure 4 As shown, the constant voltage output circuit includes a voltage stabilizing diode D5, a switch tube Q5 and a switch tube Q6;

[0064] The negative terminal of the switch tube Q4 is electrically connected to the positive terminal of the switch tube Q5, the positive terminal of the switch tube Q6 and the first end of the resistor R8, the second end of the resistor R8 is electrically connected to the cathode of the voltage zener diode D5 and the control end of the switch tube Q6, and the anode of the voltage zener diode D5 is electrically connected to the reference ground;

[0065] The negative terminal of the switch tube Q5 is the constant voltage output terminal of the DC-DC circuit.

[0066] Specifically, the switch tube Q5 and the switch tube Q6 are both NPN transistors;

[0067] A resistor R7 is also electrically connected between the negative terminal of the switch tube Q4 and the positive terminal of the switch tube Q6.

[0068] Specifically, the negative terminal of the switch tube Q4 is also electrically connected to the positive terminal of the diode D4, and the negative terminal of the diode D4 is electrically connected to the positive terminal of the switch tube Q5;

[0069] The cathode of the voltage stabilizing diode D2 is also electrically connected to the cathode of the diode D1 , and the anode of the diode D1 is electrically connected to the second end of the resistor R1 .

[0070] Specifically, the first end of the resistor R8 is also electrically connected to the positive electrode of the capacitor C1, and the negative electrode of the capacitor C1 is electrically connected to the positive electrode of the voltage stabilizing diode D5;

[0071] The negative terminal of the switch tube Q5 is also electrically connected to the positive electrode of the capacitor C2 and the positive electrode of the capacitor C3 respectively, and the negative electrode of the capacitor C2 and the negative electrode of the capacitor C3 are both electrically connected to the positive electrode of the voltage stabilizing diode D5.

[0072] For example,

[0073] Due to the action of the voltage stabilizing diode D5, the base voltage of the switch tube Q6 is clamped at a fixed value V d , the base current I of the switch tube Q6 o =(V in+ -V d ) / R8, the transistor is a current-type control device, so the transistor Q6 is turned on, and the emitter voltage V qe =V d-The conduction voltage drop of switch tube Q6, so switch tube Q6 is turned on. Similarly, switch tube Q5 is also turned on, and the output voltage is V d -The conduction voltage drop of switch tube Q6 -The conduction voltage drop of switch tube Q5. Since the voltage value of voltage regulator diode D5 is determined, the conduction voltage drop of switch tube Q6 and switch tube Q5 is also determined, so the output voltage is relatively constant (with a small range of variation). According to test verification, when the input voltage (V in+ ) is 18V, the output voltage (V OUT+ ) is 11.3749V, such as Figure 4 As shown; when the input voltage is 35V, the output voltage is 11.3766V.

[0074] It should be noted that the output is a constant voltage and the constant voltage value can be adaptively adjusted according to application requirements, that is, the parameters of the resistors, diodes, transistors and MOS tubes required in the circuit can be calculated according to the voltage and current requirements of the required circuit, and the corresponding components can be selected to achieve the functions of input undervoltage protection and overvoltage protection and output constant voltage, and the over / undervoltage input protection circuit is commonly used for any step-down circuit that requires an input overvoltage protection circuit.

[0075] In addition, in the above circuit structure, the role of the diode D1 is to prevent reverse connection, which utilizes the unidirectional conductivity of the diode. When the power supply is correctly connected, the high impedance characteristic of the diode prevents the current from passing, so that the power supply flows to the subsequent circuit; when the power supply is reversely connected, the diode allows the current to pass, and the power supply does not flow to the subsequent circuit, thereby protecting the circuit from damage by reverse current.

[0076] Embodiment 2:

[0077] Based on the same concept, this embodiment provides an electrical device, including a DC power supply, in which a DC-DC circuit is provided, and the DC-DC circuit adopts the DC-DC circuit as described in Embodiment 1. Since Embodiment 1 has made a relatively detailed description of the DC-DC circuit, it will not be repeated in this embodiment.

[0078] As an optional implementation, a battery is used as a power supply device in the DC power supply;

[0079] Specifically, Figure 1 As shown, the positive terminal of the battery is electrically connected to the cathode of the voltage-stabilizing diode D2, and the negative terminal of the battery is electrically connected to the anode of the diode D1; the negative terminal of the switch tube Q5 and the anode of the voltage-stabilizing diode D5 are electrically connected to the two ends of the load resistor RL respectively.

[0080] The function of the DC-DC circuit is to reduce the output voltage of the battery to the voltage required by the user and maintain a constant voltage output. When the battery is undervoltage / overvoltage, the DC-DC circuit can cut off the voltage output in time, effectively avoiding excessive use of devices caused by undervoltage and damage to components due to high voltage.

[0081] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An over / under voltage input protection circuit, characterized in that: Including undervoltage protection unit and overvoltage protection unit; The undervoltage protection unit includes a voltage stabilizing diode D2, a switch tube Q1 and a switch tube Q2; the cathode of the voltage stabilizing diode D2 is electrically connected to the positive terminal of the switch tube Q2 and the first end of the resistor R3, the anode of the voltage stabilizing diode D2 is electrically connected to the control end of the switch tube Q1 and the first end of the resistor R1, the positive terminal of Q1 is electrically connected to the control end of the switch tube Q2 and the second end of the resistor R3, and the second end of the resistor R1 is electrically connected to the negative terminal of the switch tube Q1; The overvoltage protection unit includes a voltage stabilizing diode D3, a switch tube Q3 and a switch tube Q4; the positive terminal of the switch tube Q4 is electrically connected to the negative terminal of the switch tube Q2, the positive terminal of the switch tube Q3 and the first end of the resistor R4, the second end of the resistor R4 is electrically connected to the negative electrode of the voltage stabilizing diode D3 and the control end of the switch tube Q3, the negative terminal of the switch tube Q3 is electrically connected to the control end of the switch tube Q4 and the first end of the resistor R6, and the second end of the resistor R6 is electrically connected to the positive electrode of the voltage stabilizing diode D3; wherein the second end of the resistor R1 and the second end of the resistor R6 are both electrically connected to the reference ground; When the voltage at the cathode of the voltage stabilizing diode D2 is less than the predetermined low-voltage threshold, the voltage stabilizing diode D2 is not broken down, the switch tube Q1 is not turned on, and the voltage drop between the positive terminal and the control terminal of the switch tube Q2 does not reach the set turn-on voltage drop, and the switch tube Q2 is not turned on; When the voltage at the cathode of the Zener diode D3 is greater than the predetermined high voltage threshold, the Zener diode D3 is broken down, the switch tube Q3 is turned on, and the voltage drop between the positive terminal and the control terminal of the switch tube Q4 does not reach the set turn-on voltage drop, and the switch tube Q4 is not turned on.

2. The over / under voltage input protection circuit according to claim 1, characterized in that: The switch tube Q1 is an NPN transistor, the switch tube Q3 is a PNP transistor, and the switch tubes Q2 and Q4 are both PMOS switch tubes; A resistor R2 is electrically connected between the control end of the switch tube Q1 and the anode of the voltage-stabilizing diode D2 ; a resistor R5 is electrically connected between the control end of the switch tube Q3 and the cathode of the voltage-stabilizing diode D3 .

3. A DC-DC circuit, comprising a constant voltage output circuit, characterized in that: The voltage input side of the constant voltage output circuit is provided with an over / under voltage input protection circuit as described in any one of claims 1-2.

4. A DC-DC circuit according to claim 3, characterized in that: The constant voltage output circuit includes a voltage stabilizing diode D5, a switch tube Q5 and a switch tube Q6; The negative terminal of the switch tube Q4 is electrically connected to the positive terminal of the switch tube Q5, the positive terminal of the switch tube Q6 and the first end of the resistor R8, the second end of the resistor R8 is electrically connected to the cathode of the voltage zener diode D5 and the control end of the switch tube Q6, and the anode of the voltage zener diode D5 is electrically connected to the reference ground; The negative terminal of the switch tube Q5 is the constant voltage output terminal of the DC-DC circuit.

5. A DC-DC circuit according to claim 4, characterized in that: Switching tube Q5 and switching tube Q6 are both NPN transistors; A resistor R7 is also electrically connected between the negative terminal of the switch tube Q4 and the positive terminal of the switch tube Q6.

6. A DC-DC circuit according to claim 4, characterized in that: The negative terminal of the switch tube Q4 is also electrically connected to the positive terminal of the diode D4, and the negative terminal of the diode D4 is electrically connected to the positive terminal of the switch tube Q5; The cathode of the voltage stabilizing diode D2 is also electrically connected to the cathode of the diode D1 , and the anode of the diode D1 is electrically connected to the second end of the resistor R1 .

7. A DC-DC circuit according to claim 4, characterized in that: The first end of the resistor R8 is also electrically connected to the positive electrode of the capacitor C1, and the negative electrode of the capacitor C1 is electrically connected to the positive electrode of the voltage stabilizing diode D5; The negative terminal of the switch tube Q5 is also electrically connected to the positive electrode of the capacitor C2 and the positive electrode of the capacitor C3 respectively, and the negative electrode of the capacitor C2 and the negative electrode of the capacitor C3 are both electrically connected to the positive electrode of the voltage stabilizing diode D5.

8. A direct current power supply, comprising a DC-DC circuit, characterized in that: The DC-DC circuit adopts a DC-DC circuit as described in any one of claims 3-7.

9. A DC power supply according to claim 8, characterized in that: Also includes batteries; The positive terminal of the battery is electrically connected to the cathode of the voltage stabilizing diode D2, and the negative terminal of the battery is electrically connected to the reference ground.

10. An electrical device, characterized in that: Comprising a DC power supply as described in any one of claims 8-9.

Images