Voltage-limiting time-delay voltage-stabilizing circuit suitable for small current

Abstract

The utility model relates to the technical field of power supply circuits, in particular to a voltage-limiting delay voltage-stabilizing circuit suitable for small current, which comprises an under-voltage protection module, an overshoot protection module, a voltage-stabilizing module and a switching tube Q2, the under-voltage protection module comprises a voltage-stabilizing tube D1, an external power supply is connected with a control end of the switching tube Q2 through the voltage-stabilizing tube D1, and the switching tube Q2 is connected with the overshoot protection module through the overshoot protection module. One switch end of the switch tube Q2 is grounded, one end of the overshoot protection module is connected with the control end of the switch tube Q2, the other end of the overshoot protection module is grounded, one end of the voltage stabilization module is connected with an external power supply, and the other end of the voltage stabilization module is connected with the other switch end of the switch tube Q2. According to the voltage-limiting, time-delay and voltage-stabilizing circuit suitable for the small current, a Buck chip does not need to be used, the occupied space is small, the production cost can be reduced, and the production efficiency can be improved.

Description

Technical Field

[0001] The utility model relates to the technical field of power supply circuits, in particular to a voltage-limiting delay voltage-stabilizing circuit suitable for small current. Background Art

[0002] With the development of network technology and the Internet of Things, switches with Power over Ethernet (PoE) function are becoming more and more popular in the market. PoE technology can transmit power and data signals on standard Ethernet cables without additional power lines, greatly simplifying the deployment and maintenance of network devices. In the design of PoE switches, the DC-DC converter plays a crucial role, which is responsible for converting the input voltage into a stable output voltage for downstream devices to use.

[0003] At present, the DC-DC converters in most PoE switches adopt integrated Buck step-down chips. Such chips have the following characteristics:

[0004] High integration: integrating a controller, a switching transistor and other peripheral components, reducing the number of external components and simplifying the design.

[0005] Small footprint: the compact design enables it to meet the requirements of miniaturized devices.

[0006] High cost: integrated Buck step-down chips are usually relatively expensive, increasing the overall cost of the switch.

[0007] Electromagnetic compatibility problems: if the design is unreasonable, such chips may generate high electromagnetic interference (EMI), affecting the radiation and conduction performance of the system.

[0008] Especially in the face of small current applications, the cost-effectiveness of using such integrated Buck step-down chips is not high, because even at low current demands, the cost of such chips is still relatively high. In addition, unreasonable design may also lead to electromagnetic compatibility problems, further increasing the complexity and cost of the design.

[0009] Therefore, for small current application scenarios, it is particularly important to develop a DC-DC converter solution with lower cost, simpler design and good electromagnetic compatibility. Such a solution not only... Summary of the Invention

[0010] The utility model provides a voltage-limiting delay voltage-stabilizing circuit suitable for small current for the problems of the prior art, without using a Buck step-down chip, having a small footprint, being able to reduce production costs and improve production efficiency.

[0011] To solve the above technical problems, the present utility model adopts the following technical solutions: A voltage-limiting delay voltage-stabilizing circuit applicable to small currents, comprising an undervoltage protection module, an overshoot protection module, a voltage-stabilizing module, and a switching transistor Q2. The undervoltage protection module includes a voltage-stabilizing diode D1. External power supply is connected to the control terminal of the switching transistor Q2 through the voltage-stabilizing diode D1. One switching terminal of the switching transistor Q2 is grounded. One end of the overshoot protection module is connected to the control terminal of the switching transistor Q2, and the other end of the overshoot protection module is grounded. One end of the voltage-stabilizing module is connected to the external power supply, and the other end of the voltage-stabilizing module is connected to the other switching terminal of the switching transistor Q2.

[0012] Preferably, the undervoltage protection module further includes a voltage-stabilizing diode D3, a resistor R3, and a resistor R4. The external power supply is connected to the cathode of the voltage-stabilizing diode D1. The anode of the voltage-stabilizing diode D1 is connected to the control terminal of the switching transistor Q2 through the resistor R3. Both ends of the resistor R4 are respectively connected to the ground terminal and the control terminal of the switching transistor Q2. The cathode of the voltage-stabilizing diode D3 is connected to the control terminal of the switching transistor Q2, and the anode of the voltage-stabilizing diode D3 is grounded.

[0013] Preferably, the overshoot protection module includes a capacitor C1. One end of the capacitor C1 is connected to the control terminal of the switching transistor Q2, and the other end of the capacitor C1 is grounded.

[0014] Preferably, the voltage-stabilizing module includes a switching transistor Q1, a voltage-stabilizing diode D2, a resistor R1, a resistor R2, and a capacitor C2. The external power supply is connected to the control terminal of the switching transistor Q1 through the resistor R1. Both ends of the resistor R2 are respectively connected to the external power supply and one switching terminal of the switching transistor Q1. The cathode of the voltage-stabilizing diode D2 is connected to the control terminal of the switching transistor Q1, and the anode of the voltage-stabilizing diode D2 is connected to the other switching terminal of the switching transistor Q2. The other switching terminal of the switching transistor Q1 is connected to the other switching terminal of the switching transistor Q2 through C2.

[0015] Advantages of the present utility model:

[0016] 1. It is not necessary to use a Buck step-down chip, which helps to reduce costs;

[0017] 2. The protection function of positive and negative reverse connection is realized through the switching transistor Q2 and the undervoltage protection module, which can well protect the backend chip;

[0018] 3. The overshoot voltage protection design, due to the delay design of the switching transistor Q2, can well prevent the problem of damage to the backend device caused by the overshoot of the input voltage during instant power-on. Description of the Drawings

[0019] Figure 1 It is the circuit schematic diagram of the present utility model. Detailed Embodiments

[0020] For the convenience of understanding by those skilled in the art, the present utility model will be further described below in conjunction with embodiments and the accompanying drawings. The content mentioned in the embodiments does not limit the present utility model. The present utility model will be described in detail below with reference to the accompanying drawings.

[0021] A voltage-limiting delay voltage-stabilizing circuit applicable to small currents provided in this embodiment is as Figure 1 shown, and includes an undervoltage protection module, an overshoot protection module, a voltage-stabilizing module, and a switching transistor Q2. The undervoltage protection module includes a zener diode D1. External power supply is connected to the control end of the switching transistor Q2 through the zener diode D1. One switching end of the switching transistor Q2 is grounded. One end of the overshoot protection module is connected to the control end of the switching transistor Q2, and the other end of the overshoot protection module is grounded. One end of the voltage-stabilizing module is connected to the external power supply, and the other end of the voltage-stabilizing module is connected to the other switching end of the switching transistor Q2.

[0022] Among them, the undervoltage protection module, overshoot protection module, and voltage-stabilizing module in this embodiment do not need to use a Buck step-down chip, and the design using discrete components makes the circuit principle simpler.

[0023] Specifically, as Figure 1 shown, the undervoltage protection module further includes a zener diode D3, a resistor R3, and a resistor R4. The external power supply is connected to the cathode of the zener diode D1. The anode of the zener diode D1 is connected to the control end of the switching transistor Q2 through the resistor R3. Both ends of the resistor R4 are respectively connected to the ground terminal and the control end of the switching transistor Q2. The cathode of the zener diode D3 is connected to the control end of the switching transistor Q2, and the anode of the zener diode D3 is grounded; the overshoot protection module includes a capacitor C1. One end of the capacitor C1 is connected to the control end of the switching transistor Q2, and the other end of the capacitor C1 is grounded; the voltage-stabilizing module includes a switching transistor Q1, a zener diode D2, a resistor R1, a resistor R2, and a capacitor C2. The external power supply is connected to the control end of the switching transistor Q1 through the resistor R1. Both ends of the resistor R2 are respectively connected to the external power supply and one switching end of the switching transistor Q1. The cathode of the zener diode D2 is connected to the control end of the switching transistor Q1, and the anode of the zener diode D2 is connected to the other switching end of the switching transistor Q2. The other switching end of the switching transistor Q1 is connected to the other switching end of the switching transistor Q2 through C2. The specific connection method is as Figure 1 shown.

[0024] The specific working principle of this embodiment is:

[0025] 1. The undervoltage protection module consists of a zener diode D1, a zener diode D3, resistors R3 and R4, a capacitor C1, and a switching transistor Q2. The switching transistor Q2 is a MOS transistor, and the resistors R3 and R4 are current-limiting resistors. When the input voltage V_IN comes in, if the input voltage at this time cannot break down the zener diode D1, the MOS at the back end of the zener diode D1 cannot be turned on. Since the MOS is connected in series between the two ends of the ground, a power supply loop cannot be formed, and power cannot be supplied at this time. The selection of the zener diode D1 can be based on the designed circuit. For example, if an input voltage greater than 30V is required, a 30V zener diode can be selected for D1;

[0026] 2. Overvoltage protection module. When the input voltage can break down the zener diode D1, after passing through the current-limiting resistor R3, the gate of the switching transistor Q2 has a voltage of 12V at this time. If the input voltage is lower than 12V, after the zener diode D1 is broken down, the gate of the switching transistor Q2 has a voltage, but this voltage cannot break down the zener diode D2 (12V zener diode), and the voltage at the gate of the switching transistor Q2 cannot reach the fully conductive state. Therefore, the input voltage must be greater than 12V. At this time, the capacitor C1 starts to charge, and the voltage at the gate of the switching transistor Q2 increases linearly, which is equivalent to delaying the opening speed of the switching transistor and extending the opening time of the switching transistor Q2, ensuring that at the moment of input, the voltage is too high and the subsequent devices are damaged. The switching transistor Q2 opens slowly, which can improve the voltage spike problem caused by sudden opening;

[0027] 3. Positive and negative reverse connection protection. Since the switching transistor Q2 is connected in series in the negative circuit, when the input voltage is satisfied and the switching transistor can be turned on, if the positive and negative poles of the input are reversed at this time, the zener diode D1 cannot be broken down, the gate voltage of the switching transistor Q2 is 0V, and it is in a non-conductive state. At this time, power cannot be supplied, and the circuit cannot work properly;

[0028] 4. Voltage regulation module. When the input voltage is normal and the front-end work is normal, the voltage will pass through the resistor R1 (protecting the zener diode D2 and limiting the current) and the resistor R2. The resistor R2 and the switching transistor Q1 are used for voltage division. The switching transistor Q1 is a switching transistor. Since the state of the switching transistor Q1 can be adjusted by adjusting the resistance value of the resistor R1 after the switching transistor Q1 is turned on, at this time, we adjust it to the saturation state. At this time, the conduction voltage drop between the base and the emitter is 0.7V. If our switch needs a 3.3V voltage at this time, only a 4V zener diode needs to be selected for the zener diode D2. Since voltage division is performed by the resistor R2 and the switching transistor Q1 at this time, the voltage drop of the resistor R2 and the power consumption of the switching transistor will be very large. Therefore, it is suitable for small-current circuits.

[0029] This embodiment does not require the use of a Buck step-down chip and is built with common discrete components, making the design cost lower than that of an integrated type. Moreover, it has protection functions against undervoltage, overcharge voltage, and positive and negative reverse connection, which can well protect the backend chip. The overcharge voltage protection design, due to the delay design of the MOS transistor, can well prevent the problem of damage to the backend device caused by overshoot of the input voltage during momentary power-on. Also, since no inductive components are used in the circuit, better results can be achieved in terms of radiation.

[0030] The above are only preferred embodiments of the present invention and do not impose any form of limitation on the present invention. Although the present invention is disclosed above in preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, when making some changes or modifications using the disclosed technical content to equivalent embodiments of equivalent changes, but as long as they do not depart from the content of the technical solution of the present invention, any simple modifications, equivalent changes, and modifications made to the above embodiments according to the technical means of the present invention all fall within the scope of the technical solution of the present invention.

Claims

1. A voltage-limiting and delay voltage-stabilizing circuit applicable to small current, characterized in that: It includes an undervoltage protection module, an overshoot protection module, a voltage stabilization module, and a switching transistor Q2. The undervoltage protection module includes a zener diode D1. The external power supply is connected to the control terminal of the switching transistor Q2 through the zener diode D1. One switching terminal of the switching transistor Q2 is grounded. One end of the overshoot protection module is connected to the control terminal of the switching transistor Q2, and the other end of the overshoot protection module is grounded. One end of the voltage stabilization module is connected to the external power supply, and the other end of the voltage stabilization module is connected to the other switching terminal of the switching transistor Q2.

2. The voltage-limiting delay voltage stabilizing circuit applicable to small current according to claim 1, wherein: The undervoltage protection module further includes a zener diode D3, a resistor R3, and a resistor R4. The external power supply is connected to the cathode of the zener diode D1. The anode of the zener diode D1 is connected to the control terminal of the switching transistor Q2 through the resistor R3. Both ends of the resistor R4 are respectively connected to the ground terminal and the control terminal of the switching transistor Q2. The cathode of the zener diode D3 is connected to the control terminal of the switching transistor Q2, and the anode of the zener diode D3 is grounded.

3. The voltage-limiting delay voltage stabilizing circuit applicable to small current according to claim 1, wherein: The overshoot protection module includes a capacitor C1. One end of the capacitor C1 is connected to the control terminal of the switching transistor Q2, and the other end of the capacitor C1 is grounded.

4. The voltage-limiting delay voltage stabilizing circuit applicable to small current according to claim 1, wherein: The voltage stabilization module includes a switching transistor Q1, a zener diode D2, a resistor R1, a resistor R2, and a capacitor C2. The external power supply is connected to the control terminal of the switching transistor Q1 through the resistor R1. Both ends of the resistor R2 are respectively connected to the external power supply and one switching terminal of the switching transistor Q1. The cathode of the zener diode D2 is connected to the control terminal of the switching transistor Q1, and the anode of the zener diode D2 is connected to the other switching terminal of the switching transistor Q2. The other switching terminal of the switching transistor Q1 is connected to the other switching terminal of the switching transistor Q2 through C2.

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