Overcurrent protection circuit and electric appliance

Abstract

The overcurrent protection circuit comprises a load and an NPN triode which are connected with the positive electrode end of a power supply, a field effect transistor connected with the other end of the load, and a sampling resistor connected with the source electrode of the field effect transistor. One end of the capacitor is connected with the other end of the load, and the other end of the capacitor is connected with the base electrode of the NPN triode; the positive electrode end of the diode is connected with the source electrode of the field effect transistor, and the negative electrode end of the diode is connected with the other end of the capacitor; wherein the collector electrode of the NPN triode is connected with the positive electrode end of the power supply, and the emitter electrode of the NPN triode and the other end of the sampling resistor are connected with the negative electrode end of the power supply; the drain electrode of the field effect transistor is connected with a load, and the grid electrode of the field effect transistor is connected with the collector electrode of the NPN triode. The utility model has the beneficial effects that the cost is low, and the structure is simple and reliable; the overcurrent response is fast; overcurrent protection is carried out in a hiccup mode, and intelligent recovery can be realized; the device can be conveniently applied to various electric appliances; the static power consumption is low.

Description

Technical Field

[0001] This utility model relates to the field of electrical technology, specifically to an overcurrent protection circuit and electrical appliance. Background Technology

[0002] Overcurrent protection circuits automatically disconnect the power supply from the load when the downstream load current is too high or a short circuit occurs, thereby preventing high current from damaging the power supply circuit. The circuit shown in the diagram is a discrete component overcurrent protection circuit. Currently, the main types of overcurrent protection circuits on the market are: 1. those using fuses; 2. those using IC control; and 3. those using field-effect transistors (MOSFETs).

[0003] The applicant argues that using fuses provides only one-time circuit breaking, requiring manual intervention to restore the circuit, which contradicts current green and energy-saving design principles. Furthermore, using IC control is too costly and hinders product adoption. Therefore, using MOSFET circuits for overcurrent protection should become the mainstream approach. However, current MOSFET overcurrent protection circuits are either overly complex, slow in response, and expensive, or overly simple and unreliable.

[0004] Therefore, there is an urgent need to develop an overcurrent protection circuit that can automatically restore conduction, has a simple structure, and is highly reliable. Utility Model Content

[0005] This utility model aims to solve at least one of the above-mentioned technical problems to a certain extent.

[0006] Therefore, the first objective of this utility model is to propose an overcurrent protection circuit that can automatically restore conduction, with a simple structure and high reliability.

[0007] The second objective of this utility model is to provide an electrical appliance.

[0008] To achieve the above objectives, an embodiment of this utility model discloses an overcurrent protection circuit, including a load RL1 connected to the positive terminal of a power supply and an NPN transistor Q2, a field-effect transistor Q1 connected to the other end of the load, and a sampling resistor R5 connected to the source of the field-effect transistor; it also includes a capacitor C1 with one end connected to the other end of the load, and the other end of the capacitor connected to the base of the NPN transistor; it also includes a diode D1, with the positive terminal of the diode connected to the source of the field-effect transistor and the negative terminal of the diode connected to the other end of the capacitor; wherein, the collector of the NPN transistor is connected to the positive terminal of the power supply, and the emitter of the NPN transistor is connected to the negative terminal of the power supply via the other end of the sampling resistor; the drain of the field-effect transistor is connected to the load, and the gate of the field-effect transistor is connected to the collector of the NPN transistor.

[0009] In addition, the overcurrent protection circuit according to the above-described technical solution of this utility model may also have the following additional technical features:

[0010] Optionally, it also includes a first voltage divider resistor disposed between the capacitor and the NPN transistor.

[0011] Optionally, a second voltage divider resistor is also included, disposed between the positive terminal of the power supply and the NPN transistor.

[0012] Optionally, the resistance value of the sampling resistor is between 0.1 and 1 ohm.

[0013] To achieve the above objectives, a second aspect of this utility model discloses an electrical appliance, including an overcurrent protection circuit as described in the first aspect embodiment.

[0014] The advantages of this utility model are: 1. Low cost and simple and reliable structure; 2. Fast overcurrent response and efficient protection; 3. Overcurrent protection in hiccup mode and intelligent recovery; 4. Flexible and adjustable overcurrent threshold, making it easy to apply to various electrical appliances; 5. Low static power consumption. Attached Figure Description

[0015] Figure 1 This is a circuit diagram of an overcurrent protection circuit provided in one embodiment of the present invention. Detailed Implementation

[0016] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or components / elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this utility model, and should not be construed as limiting this utility model.

[0017] The overcurrent protection circuit of this utility model embodiment is described below with reference to the accompanying drawings.

[0018] Figure 1 This is a circuit diagram of an overcurrent protection circuit provided in one embodiment of this utility model. (See diagram below.) Figure 1 As shown, the overcurrent protection circuit includes: a load RL1 connected to the positive terminal of the power supply and an NPN transistor Q2; a field-effect transistor Q1 connected to the other end of the load RL1; and a sampling resistor R5 connected to the source of the field-effect transistor Q1. It also includes a capacitor C1 with one end connected to the other end of the load RL1, and the other end of the capacitor C1 connected to the base of the NPN transistor Q2. Furthermore, it includes a diode D1, with the positive terminal of the diode connected to the source of the field-effect transistor Q1 and the negative terminal of the diode connected to the other end of the capacitor C1. The collector of the NPN transistor Q2 is connected to the positive terminal of the power supply, and the emitter of the NPN transistor Q2 is connected to the negative terminal of the power supply via the sampling resistor R5. The drain of the field-effect transistor Q1 is connected to the load RL1, and the gate of the field-effect transistor Q1 is connected to the collector of the NPN transistor Q2.

[0019] Specifically, when the load current is relatively small, the MOSFET is normally turned on. Because the current is small, the voltage drop across the sampling resistor is also small, less than the transistor's turn-on voltage. At this time, the NPN transistor is in the off state, and the gate of the MOSFET is at a high level (the MOSFET is normally turned on). We denote the voltage drop between the MOSFET's drain and source as Vds, and the voltage drop across the sampling resistor as Vr. Therefore, the voltage across the right end of capacitor C1 is Vr + Vds, and the voltage across the left end of C1 is Vr.

[0020] When the load current increases, the current flowing through the sampling resistor increases, and the voltage drop across the sampling resistor also increases. When the voltage drop across the sampling resistor is greater than or equal to the turn-on voltage between the transistor's BE, the transistor will saturate and conduct. At this time, the gate voltage of the MOSFET is close to 0V, and the MOSFET is turned off.

[0021] Since the voltage across a capacitor cannot change abruptly, when the MOSFET is turned off, the voltage on the right side of capacitor C1 is VCC, and the voltage on the left side of the capacitor becomes VCC - Vds. This Vds is the voltage difference between the drain and source when the MOSFET is turned on. At this time, capacitor C1 discharges through the resistor at the base of the transistor to maintain the current required for the transistor to saturate and conduct.

[0022] When the voltage at the left end of the capacitor discharges to a level lower than the turn-on voltage of the transistor, the transistor is turned off. At this time, the gate voltage of the MOSFET becomes high again, and the MOSFET turns on again.

[0023] When the MOSFET is fully turned on, the load current is still relatively large, and the voltage drop across the sampling resistor will exceed the transistor's turn-on voltage. This causes the capacitor to charge through the diode, resulting in very rapid charging. When the voltage across the sampling resistor exceeds the transistor's turn-on voltage, the transistor will saturate and turn on again, and then the MOSFET will turn off.

[0024] Because of the presence of the base resistor of the transistor, the charging time of the capacitor can be much shorter than the discharging time. Therefore, during overcurrent protection, the MOSFET is not always off, but constantly switching between off and on.

[0025] It should be noted that the protection current threshold can be set by adjusting the value of R5 (e.g., 0.7V / 0.1Ω=7A), adapting to different load requirements. Therefore, the overcurrent protection circuit of this application is easy to apply to different electrical appliances, and its design and upgrade are very convenient.

[0026] The overcurrent protection circuit of this utility model has the following advantages: 1. No dedicated protection IC is required; only common components such as transistors, MOSFETs, resistors, and capacitors are used, significantly reducing costs. 2. Transistors and MOSFETs are directly driven, without complex logic delays, allowing for rapid circuit cutoff during overcurrent events (such as short circuits), preventing damage to the power supply or load. 3. When the MOSFET is on, the RDS(on) is extremely low (e.g., milliohm level), resulting in minimal power consumption under normal operating conditions, improving system efficiency. 4. After overcurrent trigger protection, capacitor C1 discharges through the base resistor, generating a delay. If the fault persists, the circuit periodically attempts to restart (conduction → detection → shutdown cycle), avoiding overheating caused by continuous short circuits and automatically recovering after the fault is cleared, without manual intervention. The charging and discharging time constant of C1 can suppress false triggering of short-term surge currents, improving anti-interference capability. 5. During normal operation, Q2 is off, with only the gate leakage current of the MOSFET and the small voltage drop of R5 (e.g., R5=0.1Ω, only 1mV) consuming energy, making it suitable for battery-powered devices.

[0027] According to one embodiment of the present invention, a first voltage divider resistor is further provided between the capacitor and the NPN transistor.

[0028] According to one embodiment of the present invention, a second voltage divider resistor is further provided between the positive terminal of the power supply and the NPN transistor.

[0029] Specifically, because NPN transistors are relatively sensitive, placing a voltage divider resistor at the positive terminal can protect the transistor. The capacitor side can also be considered the positive terminal.

[0030] According to one embodiment of the present invention, the resistance value of the sampling resistor is between 0.1 and 1 ohm.

[0031] Specifically, as mentioned above, when the load current is relatively small, the MOSFET is normally turned on. Because the current is small, the voltage drop across the sampling resistor is also small. In this case, the resistance value of the sampling resistor is designed to be relatively small, which can effectively reduce the static power consumption of the circuit.

[0032] Based on the above embodiments, embodiments of this application also propose an electrical appliance, including an overcurrent protection circuit according to the first aspect embodiment.

[0033] The above embodiments are preferred implementations of this application. In addition, this application can be implemented in other ways. Any obvious substitutions without departing from the concept of this application are within the protection scope of this application.

Claims

1. An overcurrent protection circuit, characterized in that, include: A load and an NPN transistor connected to the positive terminal of the power supply, a field-effect transistor connected to the other end of the load, and a sampling resistor connected to the source of the field-effect transistor; It also includes a capacitor with one end connected to the other end of the load, the other end of which is connected to the base of the NPN transistor; It also includes a diode, the positive terminal of which is connected to the source of the field-effect transistor, and the negative terminal of which is connected to the other end of the capacitor; The collector of the NPN transistor is connected to the positive terminal of the power supply, and the emitter of the NPN transistor is connected to the negative terminal of the power supply at the other end of the sampling resistor. The drain of the field-effect transistor is connected to the load, and the gate of the field-effect transistor is connected to the collector of the NPN transistor.

2. The overcurrent protection circuit according to claim 1, characterized in that: It also includes a first voltage divider resistor disposed between the capacitor and the NPN transistor.

3. The overcurrent protection circuit according to claim 1, characterized in that: It also includes a second voltage divider resistor disposed between the positive terminal of the power supply and the NPN transistor.

4. The overcurrent protection circuit according to claim 1, characterized in that: The resistance value of the sampling resistor is between 0.1 and 1 ohm.

5. An electrical appliance, characterized in that: Including an overcurrent protection circuit as described in any one of claims 1-4.

Images