Input overvoltage protection circuit of switching power supply

Abstract

The utility model discloses an input overvoltage protection circuit of a switching power supply. The input overvoltage protection circuit comprises a power supply chip U1, a transformer T1, an MOS tube Q1 connected with the transformer T1, a triode Q2 of which one end is connected with a power supply VCC end and the other end is connected with a voltage stabilizing diode U2, and a resistor R3 which is connected in parallel with the voltage stabilizing diode U2 and is used for monitoring input voltage and setting an overvoltage threshold value. The power supply chip U1 comprises a feedback input pin FB connected with the triode Q2 and a driving output end DRV used for driving the MOS tube Q1. According to the utility model, through accurate voltage detection, rapid protection response and simplified design, the safety, reliability and cost effectiveness of a power supply system are effectively improved. The design is suitable for various switching power supply scenes, and particularly has remarkable advantages in the application of industries and household appliances in which the input voltage is possibly unstable.

Description

Technical Field

[0001] The utility model belongs to the technical field of electrical equipment, and in particular relates to an input overvoltage protection circuit of a switching power supply. Background Art

[0002] The primary purpose of adding an input overvoltage protection circuit to a switching power supply is to prevent damage to the device due to excessive input voltage. This circuit protects downstream electrical equipment from output voltage exceeding the designed threshold, caused by a failure in the switching power supply's internal voltage regulation loop or improper user operation. This circuit ensures that the output voltage remains within a safe range. Furthermore, the overvoltage protection circuit prevents damage to electronic components caused by high-voltage surges.

[0003] There are many types of overvoltage protection circuits available, the most common ones include:

[0004] 1. Protection circuit composed of transistors and relays: When the input voltage exceeds the set threshold, the voltage regulator breaks down, triggering the transistor to turn on and the relay to disconnect the input.

[0005] 2. Self-locking control circuit: In the power supply system, when the feedback loop fails, the output voltage is uncontrolled and the voltage rises beyond the specified range. At this time, the excessively high output voltage may cause damage to subsequent electrical equipment.

[0006] 3. Zener diode protection circuit: When the output voltage is reversed and enters the switching power supply, the output Zener diode will be turned on to prevent the voltage from entering and causing damage to the internal components of the power supply.

[0007] While these overvoltage protection circuits can effectively protect devices to a certain extent, they also have some shortcomings. For example, the voltage clamping time of the Zener diode is short, and prolonged clamping can easily damage it. Furthermore, if the input is incorrectly wired and additional voltage is applied to components such as filter capacitors and switching transistors, these components may be damaged at best, or even cause serious circuit failures if their voltage resistance is insufficient. Therefore, designing an effective overvoltage protection circuit requires considering the magnitude and duration of the overvoltage and setting an appropriate threshold voltage. Utility Model Content

[0008] In order to solve the above technical problems, the utility model provides an input overvoltage protection circuit for a switching power supply.

[0009] The technical solutions provided by this utility model are as follows:

[0010] An input overvoltage protection circuit for a switching power supply includes a power chip U1, a transformer T1, a MOS transistor Q1 connected to the transformer T1, a transistor Q2 having one end connected to a power supply VCC terminal and the other end connected to a voltage stabilizing diode U2, and a resistor R3 connected in parallel with the voltage stabilizing diode U2 and used to monitor the input voltage and set an overvoltage threshold. The power chip U1 includes a feedback input pin FB connected to the transistor Q2, and a drive output pin DRV for driving the MOS transistor Q1.

[0011] Furthermore, the power chip U1 further includes a multi-function pin RT, and the multi-function pin RT is grounded via a resistor R6 for over-temperature protection.

[0012] Furthermore, the power chip U1 further includes a current detection input terminal CS, which is connected to the MOS transistor Q1 and is grounded via a resistor R8.

[0013] Furthermore, the resistor R3 is connected in series to the voltage input terminal VIN through the resistor R2 and the resistor R1.

[0014] Furthermore, a capacitor C1 is connected in parallel to the series branch formed by the resistor R1, the resistor R2 and the resistor R3.

[0015] Furthermore, a capacitor C2 is connected in series to the parallel branch of the voltage stabilizing diode U2 and the resistor R3.

[0016] Furthermore, the secondary side of the transformer T1 is provided with a filter and rectifier circuit consisting of a diode D2, a capacitor C3 and a resistor R9.

[0017] Preferably, the model of the power chip U1 is TM5105, and the model of the voltage regulator diode U2 is AZ431.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects:

[0019] 1. Timely response overvoltage protection mechanism:

[0020] When the input voltage exceeds a preset value (e.g., 400V), the circuit triggers a protection mechanism by detecting the voltage change across resistor R3. Transistor Q2 then conducts, causing the voltage at the feedback input pin (FB) of power supply chip U1 to rise rapidly. When the voltage at the FB pin exceeds the normal operating range, chip U1 stops driving the power MOSFET (i.e., no signal is output from the DRV pin), immediately shutting off the power supply. This rapid response mechanism effectively prevents high voltage damage to subsequent circuits and equipment.

[0021] 2. Automatic power-off protection device:

[0022] If the input voltage rises, the circuit automatically cuts off the switching power supply's output, preventing the excessive input voltage from being transmitted to subsequent load devices. This automated protection not only reduces the need for manual monitoring of equipment but also provides greater safety in emergency situations (such as voltage surges), preventing damage to electrical equipment due to high voltage, especially in unstable power grids.

[0023] 3. Wide applicability and stability:

[0024] Key components in this circuit, such as chip U1 and MOS transistor Q1, can effectively handle a wide range of voltage fluctuations, especially when the power input voltage exceeds 400V. Their designed voltage regulation characteristics enable the circuit to provide stable protection across a wide range of input voltages without causing circuit failure due to transient voltage increases.

[0025] 4. Simplify circuit design and reduce the number of components:

[0026] This overvoltage protection circuit features a streamlined design, using only a few components, including chip U1, transistor Q2, and MOS transistor Q1. This simple circuit layout effectively reduces circuit complexity and production costs. This design not only facilitates manufacturing and maintenance but also reduces points of failure, thereby improving system reliability.

[0027] 5. Efficient power management:

[0028] When overvoltage protection is triggered, the circuit quickly cuts off power output, preventing increased power consumption or device damage caused by high voltage. This efficient power management not only protects the power-consuming equipment but also optimizes power efficiency and extends the life of the power supply equipment.

[0029] In summary, this utility model effectively improves the safety, reliability, and cost-effectiveness of power supply systems through precise voltage detection, fast protection response, and simplified design. This design is applicable to various switching power supply scenarios, especially in industrial and household appliance applications where the input voltage may be unstable. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention.

[0031] Figure 1 This is a schematic diagram of a switching power supply input overvoltage protection circuit provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0032] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0033] like Figure 1 As shown, this embodiment provides an input overvoltage protection circuit for a switching power supply, including a power chip U1, a transformer T1, a MOS transistor Q1 connected to the transformer T1, and a transistor Q2 having one end connected to a power supply VCC terminal and the other end connected to a voltage regulator diode U2.

[0034] The main components of the circuit and their functions are as follows:

[0035] (1) Power chip U1: This chip model is TM5105, which controls the entire circuit. The functions of each pin of this chip are as follows:

[0036] Pin 1 (GND): Negative pole of power supply.

[0037] Pin 2 (FB): Feedback input pin, used to receive feedback signals to adjust the output. When the input voltage is too high, U1 detects the feedback voltage through this pin and stops the output of the power supply.

[0038] Pin 3 (RT): Multi-function pin, which can be connected to ground through a resistor to achieve over-temperature protection control (OTP).

[0039] Pin 4 (CS): Current detection input, monitors current changes.

[0040] Pin 5 (VDD): Positive power supply, provides operating voltage.

[0041] Pin 6 (DRV): Drive output terminal, used to drive Q1.

[0042] (2) Transformer T1: Connected to MOS transistor Q1, it is used for power conversion and isolation. The function of transformer T1 is to perform voltage conversion. The circuit adjusts the output voltage of the circuit by driving Q1.

[0043] (3) MOS tube Q1: connected to transformer T1, acts as a switch, and is driven on and off by the DRV output of chip U1 to control the output of the power supply.

[0044] (4) Transistor Q2: One end is connected to the power supply VCC, and the other end is connected to the voltage-stabilizing diode U2. Q2 is primarily responsible for conducting in overvoltage conditions, thereby cutting off the power supply. When the input voltage exceeds the set value, Q2 conducts, causing the voltage on U1's FB pin to rise, triggering the power supply's overvoltage protection function.

[0045] (5) Resistor R3: Used to monitor the input voltage. When the input voltage is higher than 400V, the voltage across R3 is higher than the reference voltage of 2.5V, and Q2 turns on, thereby stopping the power output through the feedback mechanism.

[0046] (6) Zener diode U2: Model AZ431, used in conjunction with R3 to set the circuit's overvoltage threshold; together with transistor Q2, it forms a voltage detection and protection circuit. When the voltage exceeds the set threshold, the Zener diode conducts, driving transistor Q2, putting the power chip into protection mode.

[0047] When the input voltage is lower than 400V, the voltage across resistor R3 is lower than 2.5V, Zener diode U2 and transistor Q2 are non-conductive, and the voltage at the FB pin of power supply chip U1 reaches the normal feedback voltage. Power supply chip U1 operates normally and the power supply has output. When the input voltage is higher than 400V, the voltage across resistor R3 is higher than 2.5V, AZ431 and transistor Q2 conduct, and the power supply's VCC voltage (typically 15-20V) is applied to the FB pin of chip U1 (the FB pin's operating voltage range is -0.3V-7V). When power supply chip U1 detects that the FB pin voltage is higher than normal, the DRV pin outputs no drive signal, and the power supply has no output.

[0048] This embodiment provides an input overvoltage protection circuit for a switching power supply. This circuit can promptly cut off the power supply to a power supply chip when the input voltage increases, thereby stopping the switching power supply and cutting off the power supply to subsequent electrical devices. This better protects the electrical devices, thereby avoiding damage to the electrical devices caused by excessively high input voltage and improving the safety of the electrical devices.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the above embodiments describe the present invention in detail, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. An input overvoltage protection circuit for a switching power supply, characterized in that: The power supply chip U1 includes a power supply chip U1, a transformer T1, a MOS transistor Q1 connected to the transformer T1, a transistor Q2 having one end connected to the power supply VCC terminal and the other end connected to the voltage-stabilizing diode U2, and a resistor R3 connected in parallel with the voltage-stabilizing diode U2 and used to monitor the input voltage and set the overvoltage threshold. The power supply chip U1 includes a feedback input pin FB connected to the transistor Q2, and a drive output pin DRV for driving the MOS transistor Q1.

2. The input overvoltage protection circuit according to claim 1, wherein: The power chip U1 further includes a multi-function pin RT, and the multi-function pin RT is grounded via a resistor R6 for over-temperature protection.

3. The input overvoltage protection circuit according to claim 1, wherein: The power chip U1 further includes a current detection input terminal CS, which is connected to the MOS transistor Q1 and is grounded via a resistor R8.

4. The input overvoltage protection circuit according to claim 1, wherein: The resistor R3 is connected in series to the voltage input terminal VIN through the resistor R2 and the resistor R1.

5. The input overvoltage protection circuit according to claim 3, wherein: A capacitor C1 is connected in parallel to the series branch formed by the resistor R1, the resistor R2 and the resistor R3.

6. The input overvoltage protection circuit according to claim 1, wherein: A capacitor C2 is connected in series to the parallel branch of the voltage stabilizing diode U2 and the resistor R3.

7. The input overvoltage protection circuit according to claim 1, wherein: The secondary side of the transformer T1 is provided with a filter and rectifier circuit consisting of a diode D2, a capacitor C3 and a resistor R9.

8. The input overvoltage protection circuit according to claim 1, wherein: The model of the power chip U1 is TM5105, and the model of the voltage regulator diode U2 is AZ431.

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