A power element overcurrent protection circuit based on hardware triggering

Abstract

The utility model provides a power element overcurrent protection circuit based on hardware triggering, including: a current sampling circuit, a temperature change acquisition circuit, a comparator and a protection signal output terminal; the input terminal of the current sampling circuit is used to collect the current of the semiconductor power switch element, and convert the current into a voltage signal according to a preset ratio, and the voltage signal is output to the positive input terminal of the comparator through the output terminal of the current sampling circuit; the input terminal of the temperature change acquisition circuit is used to collect the temperature of the semiconductor power switch element, and convert the temperature into a temperature electrical signal that changes with the temperature, and the temperature electrical signal is output to the negative input terminal of the comparator through the output terminal of the temperature change acquisition circuit; the comparator compares the voltage signal and the temperature electrical signal to obtain a comparison result, and outputs it to the protection signal output terminal through the output terminal of the comparator to realize the overcurrent protection function. The utility model has good current and temperature monitoring effects, good overcurrent protection effects, and high reliability.

Description

Technical Field

[0001] The utility model relates to the technical field of protection circuits, and in particular to a power element overcurrent protection circuit based on hardware triggering. Background Art

[0002] In the field of electronic applications, in order to comply with safety regulations and strengthen the protection of electronic equipment, more and more electrical equipment needs to add overcurrent protection circuits. The switching speed and current of various power semiconductor devices widely used in the field of power electronics are getting larger and larger, but the overload resistance of power semiconductor devices is usually low. Therefore, how to design an overcurrent protection circuit with a faster response speed and make it have a complete overcurrent protection function is an issue that needs to be considered.

[0003] With the extensive use of power electronic switches, more and more devices use power switch tubes. The heat loss generated by the power switch tube during operation and the junction temperature of the power semiconductor device directly affect the size of the safe working area when the power element is turned on and switched.

[0004] The overcurrent protection circuit of power semiconductor devices generally adopts the hardware shutdown method. However, in the circuit that requires high-speed switching of power semiconductor devices, if the power semiconductor device has an overcurrent and triggers the hardware protection, due to the problem of software response speed, the control signal may not be interrupted. At this time, the power semiconductor device may cause the system to work in an unstable state, causing the power semiconductor device to age prematurely or even be damaged, resulting in poor system reliability. Utility Model Content

[0005] The utility model provides a power element overcurrent protection circuit based on hardware triggering, aiming to solve the problem of poor system reliability caused by overcurrent protection circuit loss in the prior art.

[0006] The utility model provides a power element overcurrent protection circuit based on hardware triggering, comprising: a current sampling circuit, a temperature change acquisition circuit, a comparator and a protection signal output end; the input end of the current sampling circuit is used to collect the current of the semiconductor power switch element, and convert the current into a voltage signal according to a preset ratio, and output the voltage signal to the positive input end of the comparator through the output end of the current sampling circuit; the input end of the temperature change acquisition circuit is used to collect the temperature of the semiconductor power switch element, and convert the temperature into a temperature electrical signal that changes with the temperature, and the temperature electrical signal is output to the negative input end of the comparator through the output end of the temperature change acquisition circuit; the comparator compares the voltage signal and the temperature electrical signal to obtain a comparison result, and outputs it to the protection signal output end through the output end of the comparator to realize the overcurrent protection function.

[0007] Preferably, the current sampling circuit includes a sampling resistor and an amplifier circuit, the first end of the sampling resistor serves as the input end of the current sampling resistor and is connected to the first end of the amplifier circuit, the second end of the sampling resistor is connected to the second end of the amplifier circuit, the third end of the amplifier circuit serves as the output end of the current sampling circuit, the fourth end of the amplifier circuit is connected to pin 5 of the comparator and is grounded, and pin 2 of the comparator is used to connect the power supply voltage; the current of the sampling resistor flows from the first end of the sampling resistor to the second end of the sampling resistor, and the amplifier circuit is used to amplify the voltage signal and output it to the comparator.

[0008] Preferably, the temperature change acquisition circuit includes a first resistor and a thermistor, the first end of the first resistor serves as the input end of the temperature change acquisition circuit for connecting to a power supply voltage, the second end of the first resistor is connected to the first end of the thermistor, the second end of the thermistor is grounded, and the second end of the first resistor also serves as the output end of the temperature change acquisition circuit.

[0009] Preferably, a reference voltage Vref between the second end of the first resistor and the first end of the thermistor=Vcc*R2 / (R1+R2);

[0010] Wherein, Vcc represents the supply voltage, R1 represents the resistance value of the first resistor, and R2 represents the resistance value of the thermistor.

[0011] Preferably, the thermistor is an NTC temperature sampling resistor.

[0012] Preferably, the amplifying circuit is a power amplifier.

[0013] Compared with the prior art, the utility model has the beneficial effect that the input end of the current sampling circuit is used to collect the current of the semiconductor power switch element, and the current is converted into a voltage signal according to a preset ratio, and the voltage signal is output to the positive input end of the comparator through the output end of the current sampling circuit; the input end of the temperature change acquisition circuit is used to collect the temperature of the semiconductor power switch element, and the temperature is converted into a temperature electrical signal that changes with the temperature, and the temperature electrical signal is output to the negative input end of the comparator through the output end of the temperature change acquisition circuit; the comparator compares the voltage signal with the temperature electrical signal to obtain a comparison result, and outputs it to the protection signal output end through the output end of the comparator to realize the overcurrent protection function. The current and temperature values ​​are coupled together through hardware circuit design to establish a hardware circuit in which the current protection threshold decreases as the temperature increases, ensuring that the power element works at different temperatures, the safe working area is different, and the protection threshold is different. In this way, the characteristics of the hardware circuit being simple and reliable and the response speed being fast are retained, and the deficiency that the current design protection threshold of the general hardware circuit cannot change with the temperature of the power element is made up. It is used to ensure that the element works in a reasonable safe working area and improve the reliability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The utility model is described in detail below in conjunction with the accompanying drawings. The above and other aspects of the utility model will become clearer and easier to understand through the detailed description made in conjunction with the following drawings. In the accompanying drawings:

[0015] Figure 1 It is a module diagram of a power element overcurrent protection circuit based on hardware triggering provided by an embodiment of the utility model;

[0016] Figure 2 It is a circuit diagram of a power element overcurrent protection circuit based on hardware triggering provided by an embodiment of the utility model;

[0017] Figure 3 This is a relationship diagram between the typical shell temperature and the current that can be carried by the power switch tube provided by the embodiment of the utility model;

[0018] Figure 4 This is a typical curve diagram of the change of the resistance value of the NTC temperature sampling resistor with the temperature provided by the embodiment of the utility model;

[0019] Figure 5 It is a schematic diagram of thermistor according to an embodiment of the utility model changing with temperature;

[0020] Figure 6 It is a schematic diagram of a Hall current sensor provided in an embodiment of the utility model.

[0021] In the figure, 1. current sampling circuit, 2. temperature change acquisition circuit, 3. comparator, 4. protection signal output terminal, 5. amplifier circuit. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the utility model more clear, the utility model is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model and are not used to limit the utility model.

[0023] Combined with Figure 1-Figure 6 As shown, an embodiment of the utility model provides a power element overcurrent protection circuit based on hardware triggering, comprising: a current sampling circuit 1, a temperature change acquisition circuit 2, a comparator 3 and a protection signal output terminal; the input terminal of the current sampling circuit 1 is used to collect the current of the semiconductor power switch element, and convert the current into a voltage signal according to a preset ratio, and output the voltage signal to the positive input terminal of the comparator 3 through the output terminal of the current sampling circuit 1; the input terminal of the temperature change acquisition circuit 2 is used to collect the temperature of the semiconductor power switch element, and convert the temperature into a temperature electrical signal that changes with the temperature, and the temperature electrical signal is output to the negative input terminal of the comparator 3 through the output terminal of the temperature change acquisition circuit 2; the comparator 3 compares the voltage signal with the temperature electrical signal to obtain a comparison result, and outputs it to the protection signal output terminal through the output terminal of the comparator 3 to realize the overcurrent protection function.

[0024] Specifically, the current of the semiconductor power switch element is collected through the current sampling circuit 1, and the target current is converted into the voltage signal we need according to a certain ratio; a comparison signal that changes with temperature is output through the temperature change collection circuit 2, and the comparison signal is an analog signal voltage signal, and the signal source is the temperature of the semiconductor power switch element or an electrical signal that can reflect the temperature change of the protected power element. The current sampling signal and the comparison signal that changes with temperature are input into the comparator 3 for comparison. The comparison result is a switch quantity, which is output through the comparator 3. A transient response signal is provided to the system, which can be used to reflect whether the circuit has overcurrent protection. In this way, the current and temperature values ​​are coupled together through hardware circuit design, and a hardware circuit is established in which the current protection threshold decreases with the increase of temperature, so as to ensure that the power element works at different temperatures, the safe working area is different, and the protection threshold is different. In this way, the characteristics of the hardware circuit are simple and reliable, and the response speed is fast, and the deficiency that the current design protection threshold of the general hardware circuit cannot change with the temperature of the power element is made up. It is used to ensure that the element works in a reasonable safe working area and improve the reliability of the system.

[0025] In this embodiment, the current sampling circuit 1 includes a sampling resistor R3 and an amplifier circuit 5, the first end of the sampling resistor R3 serves as the input end of the current sampling resistor R3 and is connected to the first end of the amplifier circuit 5, the second end of the sampling resistor R3 is connected to the second end of the amplifier circuit 5, the third end of the amplifier circuit 5 serves as the output end of the current sampling circuit 1, the fourth end of the amplifier circuit 5 is connected to the 5th pin of the comparator 3 and is grounded, and the 2nd pin of the comparator 3 is used to connect the power supply voltage Vcc; the current of the sampling resistor R3 flows from the first end of the sampling resistor R3 to the second end of the sampling resistor R3, and the amplifier circuit 5 is used to amplify the voltage signal and output it to the comparator 3.

[0026] Among them, the positive input terminal of the comparator 3 is pin 3, the negative input terminal of the comparator 3 is pin 1, and the output terminal of the comparator is pin 4.

[0027] Optionally, the positive input terminal and the negative input terminal of the comparator 3 can be interchanged, resulting in a 0 / 1 change in the output type, which can also achieve the purpose;

[0028] Specifically, the current sampling circuit 1 samples by using a current sampling resistor R3 to convert the current signal into a voltage signal. A Hall current sensor (such as Figure 6 As shown), the current signal is converted into a voltage signal, which can also achieve the purpose of detecting current.

[0029] Among them, Figure 3 This is a typical relationship diagram between the shell temperature of the power switch tube and the current it can carry. From the figure, it can be seen that as the temperature increases, the current carrying capacity of the power switch tube decreases. In the temperature range that development and design pay more attention to, it can be approximately equivalent to a one-time function, taking this figure as an example.

[0030] Preferably, the temperature change acquisition circuit 2 includes a first resistor R1 and a thermistor R2, the first end of the first resistor R1 serves as the input end of the temperature change acquisition circuit 2 for connecting to the power supply voltage Vcc, the second end of the first resistor R1 is connected to the first end of the thermistor R2, the second end of the thermistor R2 is grounded, and the second end of the first resistor R1 also serves as the output end of the temperature change acquisition circuit 2.

[0031] Among them, Figure 4 This is a typical curve of the change of the resistance value of the NTC temperature sampling resistor with temperature, such as the temperature curve of A-10KΩ. In the range of development and design that is of particular concern, it can also be approximately equivalent to a linear function, taking this figure as an example.

[0032] From the data, we can see that both functions have a good linear relationship, and considering the design margin of protection in practical applications, they can be considered equivalent to a one-time function, which will not cause too much deviation in the design.

[0033] In this embodiment, the reference voltage Vref between the second end of the first resistor R1 and the first end of the thermistor R2 is Vcc*R2 / (R1+R2);

[0034] Wherein, Vcc represents the supply voltage Vcc, R1 represents the resistance value of the first resistor R1, and R2 represents the resistance value of the thermistor R2.

[0035] Specifically, the comparison signal that changes with temperature is generated by voltage division of the first resistor R1 and the thermistor R2. Signal size Vref = Vcc*R2 / (R1+R2). Wherein, A represents the voltage signal, and B represents the temperature electrical signal.

[0036] according to Figure 1 The conclusion:

[0037] When A=B, comparator 3 is triggered. Where:

[0038] A=I*K1; I is the actual current value, K1 is the proportionality coefficient

[0039] B = Vref = Vcc*R2 / (R1+R2);

[0040] Comparator 3 trigger condition: I*K1=Vcc*R2 / (R1+R2) K1, VCC, R1 are equivalent and regarded as constants. They do not change with temperature. At this time, I and R2 have a one-to-one correspondence and an inverse proportional relationship.

[0041] like Figure 4 The temperature curve in the figure is sampled to obtain the resistance value of R2 at different temperatures, assuming that VCC is equal to 5. The calculation results are as shown in the figure. Figure 5 shown.

[0042] Among them, Figure 5 As shown. R2_X, X is the sampling point, and the corresponding calculated V_ref_X value is shown in the figure. Then the current protection trigger value Vref is within the common working range of 30℃-110℃ power semiconductor. The comparison value gradually decreases. 110℃ is a voltage amplitude that is 60% lower than 30℃. Figure 3 The ratio of the case temperature to the allowable value of the collector current is close. If I*K = V_ref_3 or V_ref_4. The value of I is the system design protection current value. It can be seen that the protection value of comparator 3 decreases with the increase of temperature. The reduction ratio is Figure 3 On the left, the temperature of the component shell changes in accordance with the current limit, which can achieve effective protection.

[0043] In this embodiment, the thermistor R2 is an NTC temperature sampling resistor.

[0044] In this embodiment, the amplifying circuit 5 is a power amplifier.

[0045] Optionally, the power amplifier may be a transistor or a triode, etc.

[0046] The beneficial effects of the utility model are as follows:

[0047] From the perspective of hardware design, the utility model constructs a hardware-triggered protection circuit, which can simultaneously monitor the current of the power element and the temperature value of the power element itself or nearby during the working process of the power element.

[0048] This circuit mainly achieves the following control objectives:

[0049] Through hardware circuit design, the current and temperature values ​​are coupled together to establish a hardware circuit in which the current protection threshold decreases as the temperature increases, ensuring that the power components work at different temperatures, with different safe working areas and different protection thresholds. This not only retains the characteristics of the hardware circuit being simple, reliable, and fast in response, but also makes up for the deficiency that the current design protection threshold of the general hardware circuit cannot change with the temperature of the power components, thus improving system reliability.

[0050] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, article or device. In the absence of more restrictions, an element defined by the sentence "includes a ..." does not exclude the existence of other identical elements in the process, article or device including the element.

[0051] The embodiments of the present invention are described above in conjunction with the accompanying drawings. What is disclosed is only the preferred embodiments of the present invention. However, the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the enlightenment of the present invention, ordinary technicians in this field can also make many forms of equivalent changes without departing from the scope of protection of the purpose of the present invention and the claims, which are all within the protection of the present invention.

Claims

1. A power element overcurrent protection circuit based on hardware triggering, characterized in that: include: Current sampling circuit, temperature change acquisition circuit, comparator and protection signal output terminal; The input end of the current sampling circuit is used to collect the current of the semiconductor power switch element, and convert the current into a voltage signal according to a preset ratio, and output the voltage signal to the positive input end of the comparator through the output end of the current sampling circuit; The input end of the temperature change acquisition circuit is used to collect the temperature of the semiconductor power switch element and convert the temperature into a temperature electrical signal that changes with the temperature. The temperature electrical signal is output to the negative input end of the comparator through the output end of the temperature change acquisition circuit; the comparator compares the voltage signal with the temperature electrical signal to obtain a comparison result, and outputs it to the protection signal output end through the output end of the comparator to realize the overcurrent protection function.

2. The power element overcurrent protection circuit based on hardware triggering according to claim 1, characterized in that: The current sampling circuit includes a sampling resistor and an amplifier circuit, wherein the first end of the sampling resistor serves as the input end of the current sampling circuit and is connected to the first end of the amplifier circuit, the second end of the sampling resistor is connected to the second end of the amplifier circuit, the third end of the amplifier circuit serves as the output end of the current sampling circuit, the fourth end of the amplifier circuit is connected to the 5th pin of the comparator and is grounded, and the 2nd pin of the comparator is used to connect the power supply voltage; the current of the sampling resistor flows from the first end of the sampling resistor to the second end of the sampling resistor, and the amplifier circuit is used to amplify the voltage signal and output it to the comparator.

3. The power element overcurrent protection circuit based on hardware triggering according to claim 1, characterized in that: The temperature change acquisition circuit includes a first resistor and a thermistor. The first end of the first resistor serves as an input end of the temperature change acquisition circuit and is used to connect to a power supply voltage. The second end of the first resistor is connected to the first end of the thermistor, and the second end of the thermistor is grounded. The second end of the first resistor also serves as an output end of the temperature change acquisition circuit.

4. The power element overcurrent protection circuit based on hardware triggering as claimed in claim 3, characterized in that: A reference voltage Vref between the second end of the first resistor and the first end of the thermistor = Vcc*R2 / (R1+R2); Wherein, Vcc represents the supply voltage, R1 represents the resistance value of the first resistor, and R2 represents the resistance value of the thermistor.

5. The power element overcurrent protection circuit based on hardware triggering as claimed in claim 3, characterized in that: The thermistor is an NTC temperature sampling resistor.

6. The power element overcurrent protection circuit based on hardware triggering as claimed in claim 2, characterized in that: The amplifying circuit is a power amplifier.

Images