Overcurrent protection circuit and device

Abstract

The utility model relates to an overcurrent protection circuit, which is used for protection control of a power switch tube and comprises a voltage feedback comparison circuit and a threshold comparison circuit. The voltage feedback comparison circuit synchronously obtains the voltage of the control end and the second end of the power switch tube, and outputs the difference voltage of the control end and the second end to the threshold comparison circuit; the difference voltage has correlation with the magnitude of the current of the power switch tube; and the threshold comparison circuit compares the difference voltage with a preset threshold voltage, and outputs a signal to control on or off of the power switch tube. According to the utility model, through directly monitoring the working parameters of the power switch device, rapid and accurate over-current protection is realized, and the over-current protection circuit is suitable for various power devices and has the advantages of simple structure, rapid response and easy integration.

Description

Technical Field

[0001] This utility model relates to the field of electronic circuits, specifically to an overcurrent protection circuit and device. Background Technology

[0002] Overcurrent protection is typically used when a chip load experiences a short circuit or is too small. When the load is short-circuited or too small, the circuit generates a very large current, exceeding the circuit's allowable current capacity. This large current is often undesirable, as the switching chip cannot withstand it. When an overcurrent anomaly occurs, the detection module sends a signal back to the control module, enabling it to react promptly, shutting down the drive circuit and subsequently the power device, thus preventing irreversible damage to the chip.

[0003] Currently, the most common overcurrent detection circuit uses resistance feedback. By connecting a sampling resistor in series in the main circuit, the voltage across the sampling resistor can be measured to obtain the corresponding current. A comparison circuit then makes a judgment, and the control circuit controls the preceding circuit. However, this method has a problem: in power circuits, due to the large current, the large current flowing through the sampling resistor will cause a certain degree of power loss. If the load is directly used as the feedback resistor, it will limit scenarios with large variations in load impedance. When the load impedance is unknown, the voltage corresponding to the changing impedance will not accurately reflect the current, making it difficult to perform appropriate overcurrent protection without accurate current judgment. On the other hand, because the main circuit current in power circuits is large, some solutions use proportional mirror circuits to improve power loss, but this adds many components and also presents the problem of balancing the accuracy of overcurrent protection with the cost of the solution due to the large range of load impedance variations. Some MOSFETs with integrated overcurrent protection circuits also have the above problems: either the large number of components in the protection circuit results in a large chip area, or there are limitations in power applications with varying load impedances, and the timeliness or accuracy of overcurrent protection is insufficient. Therefore, further in-depth research is necessary. Summary of the Invention

[0004] This invention provides an overcurrent protection circuit that provides more economical and effective protection and control for high-side electronically controlled switching devices in a wide range of power circuit applications.

[0005] To achieve the above objectives, the present invention adopts the following solution:

[0006] An overcurrent protection circuit for the protection control of a high-side power switch includes: a voltage feedback comparison circuit and a threshold comparison circuit; the voltage feedback comparison circuit synchronously acquires the voltages at the control terminal and the second terminal of the power switch, and outputs the voltage difference between the control terminal and the second terminal to the threshold comparison circuit; the voltage difference is correlated with the magnitude of the power switch current; the threshold comparison circuit compares the voltage difference with a preset threshold voltage and outputs a signal to control the power switch to turn on or off.

[0007] Compared to traditional sampling resistor current sensing, this method directly acquires the voltage of the power switch and a preset threshold voltage to establish correlated control of the power switch current, thereby reducing power loss caused by the sampling resistor. For the power switch, which is used as an electronically controlled switching device, its operating state switches between the cutoff and saturation regions. In scenarios where a MOSFET is used as the power switch, ,because It is the threshold voltage of the MOSFET. These are the process parameters for the MOSFET. Given the device dimensions of a MOSFET, and ignoring channel modulation and substrate effects, the MOSFET current can be determined simply by knowing the difference between the gate and source voltages. For IGBTs used as power switches, the current can be obtained by acquiring... Then the correlation of IGBT currents can be constructed under saturation conditions. Although the accuracy of IGBT current detection is lower than that of MOSFET, it is still a viable alternative, depending on the device parameters.

[0008] By acquiring the voltage at the corresponding port of the power switch and comparing it with the threshold comparison circuit, the current control logic for the power switch is established. Different circuit types and application scenarios require different overcurrent protection thresholds. The parameter design of the threshold comparison circuit involves numerous options based on circuit structure and parameter requirements. Furthermore, by outputting a trigger control signal when the protection threshold is reached, the power switch is shut down after an overcurrent event, thus protecting both the power switch and the applied power circuit.

[0009] This invention also provides a device that integrates the aforementioned overcurrent protection circuit.

[0010] Compared to existing technologies, the above solution omits the sampling resistor, saving power. Compared to solutions using proportional current mirrors, it achieves better results with fewer components. Compared to solutions based on load impedance as sampling feedback, it can provide more accurate control and can be widely used in more power circuit applications, including motor control and temperature control.

[0011] The threshold comparison circuit includes a reference threshold adjustment circuit; the reference threshold adjustment circuit includes one of an adjustable resistor, an adjustable voltage regulator, and a DAC converter.

[0012] Other beneficial effects of this invention are explained in the specific embodiments. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of one type of overcurrent protection circuit in the prior art.

[0014] Figure 2 This is a circuit block diagram of Embodiment 1 of the present invention;

[0015] Figure 3 This is a circuit diagram of one embodiment of the present invention;

[0016] Figure 4 This utility model embodiment 1 includes a circuit diagram of an overcurrent detection module.

[0017] Figure 5 This is a schematic block diagram of one of the circuits in Embodiment 2 of this utility model;

[0018] Figure 6 This is a schematic diagram of another circuit in Embodiment 2 of this utility model. Detailed Implementation

[0019] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings. These exemplary embodiments can be implemented in various forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make the utility model more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. Throughout, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this utility model, and should not be construed as limiting this utility model.

[0020] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation", "connection", and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. For those skilled in the art, the specific meaning of the above terms in this utility model can be understood according to the specific circumstances.

[0021] Example 1

[0022] This embodiment uses an N-type MOSFET as the high-side power switch, and describes overcurrent protection and power switch control accordingly. Overcurrent is typically caused by a decrease in load impedance; during an overcurrent, the voltage across the load drops, affecting the voltage connected to the load. It will also decrease, leading to As the resistance of the MOSFET increases, its on-resistance decreases further, leading to a further increase in current and thus creating an avalanche effect. Therefore, when When increasing, a corresponding decrease is required. The on-resistance of the MOSFET is increased to limit the current. Overcurrent caused by overvoltage is not considered in this solution.

[0023] This embodiment provides an overcurrent protection circuit, such as Figure 2 As shown, it includes: a voltage feedback comparison circuit and a threshold comparison circuit; the voltage feedback comparison circuit synchronously acquires the gate voltage of the N-type MOSFET. With source voltage and output gate voltage With source voltage The voltage difference to threshold comparison circuit; because The correspondence between the voltage difference and the MOSFET current allows for overcurrent protection design using the aforementioned differential voltage information from the MOSFET. Based on the actual protection threshold requirements, circuit design, and parameter adaptation, the differential voltage portion can be designed accordingly in the voltage feedback comparison circuit. The differential voltage can be... , One of them. for and direct pressure difference, This is the proportionality coefficient. This is the DC bias voltage. Normally, it is directly output. It facilitates direct processing by subsequent circuits. When subsequent circuits require it in scheme selection and parameter design, the voltage can be scaled proportionally or the bias can be increased.

[0024] The threshold comparison circuit compares the difference voltage with a preset threshold voltage and outputs a signal to control the power switch to turn on or off. In this scheme, the voltage feedback comparison circuit uses a differential amplifier circuit, such as... Figure 3 As shown, the differential amplifier circuit includes a first voltage divider resistor R1, a second voltage divider resistor R2, a third voltage divider resistor R3, a fourth voltage divider resistor R4, and an operational amplifier U1. The first voltage divider resistor R1 and the second voltage divider resistor R2 have the same resistance value, and the third voltage divider resistor R3 and the fourth voltage divider resistor R4 have the same resistance value. One end of the first voltage divider resistor R1 is connected to the gate of the MOSFET to obtain the corresponding voltage. The other end of the first voltage divider resistor R1 is connected to the inverting input terminal of operational amplifier U1; one end of the second voltage divider resistor R2 is connected to the source of the MOSFET to obtain the corresponding voltage. The other end is connected to the non-inverting input of operational amplifier U1.

[0025] Let the resistance of the first voltage divider resistor R1 and the second voltage divider resistor R2 be *a*, and the resistance of the first feedback resistor R3 and the second feedback resistor R4 be *b*. According to the voltage formula for a differential amplifier circuit, we have:

[0026] ,

[0027] That is, the voltage feedback comparator circuit outputs a differential voltage of 1 / 3. The proportional gain, depending on the resistor value, allows for more flexible parameter matching with subsequent circuits. Besides differential amplifier circuits built using operational amplifiers, MOSFETs and transistors can also be used. When a DC bias voltage needs to be added to the differential voltage, an economical solution is to use a bias resistor to change the operating point of a transistor-based differential amplifier circuit to achieve DC bias. Other methods include using an adder circuit or a series diode.

[0028] The threshold comparison circuit can employ a hysteresis comparator to improve anti-interference and overcurrent protection stability. As one embodiment, for a high-side N-type MOSFET, the gate voltage needs to be reduced to achieve... To reduce and suppress current, an inverting hysteresis comparator is needed to implement overcurrent protection control, such as... Figure 4 As shown, the upper threshold of the inverting hysteresis comparator With lower threshold They are respectively:

[0029] ;

[0030] .

[0031] in This is the saturation output voltage of operational amplifier U2. The low output voltage of operational amplifier U2 is related to the supply voltage of U2 and the chip type. Resistor R5 or R6 can be an adjustable resistor, thus constructing a reference threshold adjustment circuit. Changing the value of the adjustable resistor correspondingly changes the threshold of the hysteresis comparator.

[0032] As an alternative, the threshold comparator circuit can also use a general-purpose single-threshold comparator. Correspondingly, the reference voltage of the single-threshold comparator can be an adjustable regulator, such as a TL431 device or this circuit scheme, using different resistor ratios or adjustable resistors to adjust the reference voltage. As a digital implementation, the reference voltage of the single-threshold comparator circuit can also use a DAC, allowing the control unit to perform more precise control of the power switching transistors to adapt to the application requirements of power circuits under different operating modes, loads, temperatures, and scenarios.

[0033] In addition to single-limit comparators and hysteresis comparators, window comparators can also be used as threshold comparison circuits. Simply ensure that the window threshold voltage range covers the lowest voltage value corresponding to the overcurrent protection trigger.

[0034] Compared to existing technologies, this solution directly obtains the port voltage of the power switch, which is more economical than the sampling resistor solution, and provides better accuracy and timeliness of overcurrent protection control.

[0035] Example 2

[0036] The difference between this embodiment and Embodiment 1 is that the output of the threshold comparison circuit is not directly connected to the gate of the power switch, but is connected to the input of other control devices.

[0037] As an alternative implementation scheme, such as Figure 5 As shown, the overcurrent protection circuit includes a voltage feedback comparator circuit, a threshold comparator circuit, and a monostable multivibrator. When the monostable multivibrator receives the overcurrent protection trigger signal from the threshold comparator circuit, it outputs a control level for a certain duration. Through parameter design of the monostable multivibrator, the output level control ensures that the power switch operates within a safe current range for a certain period, providing reaction time to potential adverse factors that could lead to overcurrent. This prevents the power switch and the preceding and following circuits from continuously operating within the overcurrent boundary range, thus avoiding compromised device reliability.

[0038] As an alternative implementation scheme, such as Figure 6 As shown, the overcurrent protection circuit includes a voltage feedback comparator circuit, a threshold comparator circuit, and a controller. Compared to a monostable multivibrator, the controller can more easily implement richer control logic in terms of control duration, control frequency, and voltage control combined with a DAC. The corresponding controller can be a microcontroller, and the output of the microcontroller can be directly connected to the gate of the MOSFET, while the gate and source of the MOSFET are connected to the input of the microcontroller.

[0039] Example 3

[0040] In this embodiment, any of the overcurrent protection circuits described in Embodiments 1 and 2 are integrated onto a single device using semiconductor manufacturing processes. Compared to... Figure 1 The existing technology shown uses fewer components and occupies less chip area. When the power switch and the overcurrent protection circuit are integrated into a single device, the thermal effect of the power switch can be used to achieve faster and more effective overcurrent protection. Taking the hysteresis comparator in Example 1 as an example, R5 is selected as a thermistor with a positive temperature coefficient, and / or R6 is selected as a thermistor with a negative temperature coefficient. By selecting a thermistor with a suitable temperature change point, such as 120 degrees Celsius, the overcurrent protection threshold can be lowered when the power switch operates in an overheated environment. This makes it easier for the acquired differential voltage to reach the upper limit threshold and thus receive timely protection.

[0041] Finally, it should be noted that in addition to MOSFETs, IGBTs can also be used as power switching transistors. The voltage feedback comparator unit can obtain the gate and emitter voltages accordingly. Other principles are similar and will not be elaborated further.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model and are not intended to limit it. Although this utility model has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this utility model without departing from the spirit and scope of the technical solutions of this utility model, and all such modifications or substitutions should be covered within the scope of the claims of this utility model.

Claims

1. An overcurrent protection circuit for protection control of a high-side power switch, characterized in that, The application relates to a power switch tube over-current protection circuit. The application relates to a power switch tube over-current protection circuit. The voltage feedback comparison circuit synchronously obtains the voltage of the control end and the second end of the power switch tube, and outputs the difference voltage of the control end and the second end to the threshold comparison circuit. The difference voltage is related to the size of the power switch tube current. The threshold comparison circuit compares the difference voltage with a preset threshold voltage, and outputs a signal to control the opening or closing of the high-side power switch tube.

2. An overcurrent protection circuit as claimed in claim 1, characterized in that: The voltage feedback comparison circuit comprises a differential amplification circuit.

3. An overcurrent protection circuit as claimed in claim 2, characterized in that: The differential amplification circuit comprises at least one of an operational amplifier, a MOS tube and a triode.

4. An overcurrent protection circuit as claimed in claim 1, characterized in that: The threshold comparison circuit comprises a reference threshold adjustment circuit, and the reference threshold adjustment circuit comprises at least one of an adjustable resistor, an adjustable voltage stabilizer and a DAC converter.

5. An overcurrent protection circuit as claimed in claim 1, characterized in that: The threshold comparison circuit comprises at least one of a single-limit comparator, a hysteresis comparator and a window comparator.

6. An overcurrent protection circuit as claimed in any one of claims 1-5, characterized in that: The application further comprises a controller, the input of the controller is connected with the output of the threshold comparison circuit, and the output of the controller is used for controlling the opening and closing of the power switch tube.

7. An overcurrent protection circuit as claimed in any one of claims 1 to 5, characterized in that: The application further comprises a monostable trigger, the input of the monostable trigger is connected with the output of the threshold comparison circuit, and the output of the monostable trigger is used for controlling the opening and closing of the power switch tube.

8. A device, characterized by: The application is integrated with the over-current protection circuit of any one of claims 1 to 7.

9. A device as claimed in claim 8, characterised in that: The application is further integrated with a power switch tube, and the output of the over-current protection circuit is connected with the control end of the power switch tube to control the opening and closing of the power switch tube.

10. A device as claimed in claim 9, characterised in that: The power switch tube is a MOS tube or an IGBT.

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