High-precision temperature detection circuit and charging socket

Abstract

The invention discloses a high-precision temperature detection circuit and a charging socket, and belongs to the technical field of temperature detection.The detection circuit comprises a voltage division circuit and a controller, and the voltage division circuit comprises a thermistor RT, a resistor R1 and a resistor R2 which are connected between a power source VCC and a grounding end in series; the power supply end of the controller is connected to a power supply VCC, the controller is provided with an ADC module, and the ADC module is used for collecting a voltage value of an input pin of the ADC module relative to the power supply VCC; two input pins of the ADC module are respectively connected to the common ends of the resistor R1, the thermistor RT and the resistor R2; the controller calculates the resistance value of the thermistor RT according to the voltage value acquired by the ADC module, and calculates the temperature value by combining the resistance-temperature meter of the thermistor RT; according to the temperature detection circuit provided by the invention, calibration is not needed, and relatively high temperature sampling precision can be obtained under the conditions of high temperature and low temperature.

Description

Technical Field

[0001] This invention relates to the field of temperature detection technology, and in particular to a high-precision temperature detection circuit and a charging socket. Background Technology

[0002] With the continuous development of the electric vehicle industry, its production scale and market penetration are constantly increasing. Correspondingly, the safety requirements for electric vehicles are also becoming increasingly stringent. In addition to fulfilling the basic functions of a socket, the charging socket for electric vehicles also has a temperature monitoring function. It can detect the temperature of the charging core components in real time and upload the temperature information to the vehicle's VCU (Vehicle Control Unit) via LIN or CAN communication. The VCU decides whether to derating or stop charging based on the core component temperature reported by the socket. Therefore, the accuracy of temperature detection is crucial; otherwise, it can easily lead to erroneous stopping or failure to stop when it should, resulting in dangerous situations.

[0003] To obtain high-precision temperature detection results, the principles of commonly used methods are as follows: Figure 1 As shown (R5 is a high-precision resistor, temp1 is an NTC resistor): A high-precision voltage reference chip (Ref IC) is used. Through circuit design, the voltage reference chip outputs a reasonable voltage V1 (assuming the output V1 is 4990mV and the MCU's ADC accuracy is 10 bits). Then, the resistance value Rtemp1 of temp1 is calculated as follows, and the temperature value is deduced from the NTC's resistance-temperature table:

[0004]

[0005]

[0006] In the above formula, Rt is the reference voltage of the ADC module, an analog quantity, typically 3.3V or 5V, but this value varies depending on the microcontroller; Dvalue is the value acquired by the ADC module, a digital quantity; R5 and V1 are fixed values, therefore, Rtemp1 can be calculated according to the above formula.

[0007] The above technical solution will have two sources of error:

[0008] Error source 1-V1: V1 is the voltage generated by the reference chip. Even the most accurate reference chip will have errors and temperature drift, especially at low or high temperatures. The error of the reference chip can reach hundreds of mV. Treating V1 as a fixed value to calculate Rtemp1 will produce a large error at high temperatures.

[0009] Error source 2- ADC reference voltage Generally, there are errors and temperature drift, and these will fluctuate with the MCU power supply voltage.

[0010] To obtain high-precision temperature results using the above methods, it is necessary to adjust V1, Calibration is required, which necessitates measuring V1 using a high-precision meter. The actual value is calculated to determine the deviation. The deviation value is then written into the MCU's FLASH through a calibration program. The formal program is then burned. In the formal program, the calibration value needs to be read out to correct the calculation result. The process is cumbersome, time-consuming, and labor-intensive, which greatly reduces production efficiency. Summary of the Invention

[0011] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-precision temperature detection circuit and charging socket, solving the technical problems of existing technical solutions having many errors and time-consuming and laborious error correction.

[0012] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0013] In a first aspect, the present invention provides a high-precision temperature detection circuit, comprising:

[0014] The voltage divider circuit includes a thermistor RT, a resistor R1, and a resistor R2 connected in series between the power supply VCC and the ground terminal.

[0015] The controller has its power supply connected to the power supply VCC. The controller has an ADC module, which is used to acquire the voltage value of its input pin relative to the power supply VCC. The two input pins of the ADC module are respectively connected to the common terminal of the resistor R1 and the thermistor RT and the resistor R2. The controller calculates the resistance value of the thermistor RT based on the voltage value acquired by the ADC module, and calculates the temperature value by combining the resistance-temperature table of the thermistor RT.

[0016] Optionally, a filter capacitor C1 is connected between the common terminal of the resistor R1 and the thermistor RT and the power supply VCC, and a filter capacitor C2 is connected between the common terminal of the resistor R1 and the resistor R2 and the power supply VCC.

[0017] Optionally, the controller uses Melexis' MLX series microcontroller chip, with a power supply VCC voltage of 12V.

[0018] Optionally, the temperature detection circuit further includes a protection circuit, which includes a reference voltage chip, resistor R3, and resistor R4. Resistors R3 and R4 are connected in series between the power supply VCC and resistor R2. The reference terminal of the reference voltage chip is connected to the common terminal of resistors R3 and R4. The cathode of the reference voltage chip is connected to the power supply VCC, and the anode of the reference voltage chip is connected to the non-grounded end of resistor R2.

[0019] Optionally, the voltage between the anode and cathode of the reference voltage chip is:

[0020]

[0021] In the formula, The reference voltage and reference current of the reference voltage chip; Here are the resistance values ​​of resistors R3 and R4;

[0022] The voltage satisfy: The unit is V. This is the highest sampling voltage at the input pin of the ADC module.

[0023] Optionally, calculating the resistance value of the thermistor RT based on the voltage value acquired by the ADC module includes:

[0024] The voltage value at the common terminal of the resistor R1 and the thermistor RT for:

[0025]

[0026] The voltage value at the common terminal of resistor R1 and resistor R2 for:

[0027]

[0028] According to voltage value Calculate the resistance value of the thermistor RT:

[0029]

[0030]

[0031] In the formula, The digital values ​​acquired by the two input pins of the ADC module. This is the reference voltage for the ADC module. This represents the number of bits used in the ADC module's precision. Let R1 be the resistance value of the resistor and RT be the thermistor.

[0032] Optionally, the resistor R1 is a high-precision resistor.

[0033] Secondly, the present invention provides a charging socket for an electric vehicle, including the high-precision temperature detection circuit described above.

[0034] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0035] This invention provides a high-precision temperature detection circuit and a charging socket. The controller's ADC module collects the voltage across the common terminal of resistor R1, the thermistor RT, and resistor R2 relative to the power supply VCC, and constructs a calculation formula to address factors affecting detection accuracy. Without V1 involved, the resistance of the thermistor RT is calculated, and then the temperature value is calculated by combining the resistance-temperature table of the thermistor RT. Compared with existing technologies, this eliminates the need for... The calibration with V1 improved the detection accuracy;

[0036] Meanwhile, in order to meet the controller's requirements for the ADC module to acquire the voltage value of its input pin relative to the power supply VCC, a protection circuit is set up to limit the sampled value of the ADC module's input pin within a safe threshold, ensuring the safety of circuit operation.

[0037] Applying a temperature detection circuit to a charging socket allows for real-time monitoring of the temperature of the charging core components, enabling decisions to reduce charging rate or stop charging altogether, thereby improving the safety of electric vehicle charging. Attached Figure Description

[0038] Figure 1 This is a topology diagram of a temperature detection circuit in the prior art provided in the background section of this invention;

[0039] Figure 2 This is a topology diagram of the high-precision temperature detection circuit provided in an embodiment of the present invention. Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0041] Example 1:

[0042] like Figure 2As shown, this invention provides a high-precision temperature detection circuit, including a voltage divider circuit and a controller U1. The voltage divider circuit includes a thermistor RT, a resistor R1, and a resistor R2 connected in series between the power supply VCC and the ground terminal. The power supply terminal of the controller U1 is connected to the power supply VCC. The controller U1 has an ADC module, which is used to acquire the voltage value of its input pin relative to the power supply VCC. The two input pins of the ADC module are respectively connected to the common terminal of the resistor R1 and the thermistor RT and the resistor R2. The controller U1 calculates the resistance value of the thermistor RT based on the voltage value acquired by the ADC module, and calculates the temperature value by combining the resistance-temperature table of the thermistor RT.

[0043] For ease of description, let's denote the common terminal of resistor R1 and thermistor RT as terminal x, and the common terminal of resistor R1 and resistor R2 as terminal y. The input pin of the ADC module is connected to terminal x to acquire the voltage across power supply VCC from terminal x, and the input pin of the ADC module is connected to terminal y to acquire the voltage across power supply VCC from terminal y (from...). Figure 2 As can be seen above, the voltage across the reference voltage chip U2 is used simultaneously. To improve the accuracy of the sampling signal, a filter capacitor C1 is connected between the x-end and the power supply VCC, and a filter capacitor C2 is connected between the y-end and the power supply VCC.

[0044] Based on the temperature detection circuit described above, the resistance value of the thermistor RT is calculated according to the voltage value acquired by the ADC module, including:

[0045] The voltage value at the common terminal of resistor R1 and thermistor RT for:

[0046]

[0047] Voltage value at the common terminal of resistors R1 and R2 for:

[0048]

[0049] According to voltage value Calculate the resistance of the thermistor RT:

[0050]

[0051]

[0052] In the formula, The digital values ​​acquired by the two input pins of the ADC module. This is the reference voltage for the ADC module. This represents the number of bits used in the ADC module's precision. Let R1 be the resistance value of the resistor and RT be the thermistor.

[0053] As can be seen from the above formula, the calculation of the resistance value of the thermistor RT is related to... Input voltage ( Figure 1 This is independent of V1 in the existing technology, thus overcoming the limitations of V1 in the existing technology. The error introduced by V1 is eliminated, and the temperature drift caused by changes in external temperature is reduced, thus improving the accuracy of temperature detection.

[0054] Since the resistance value of the thermistor RT is related to the resistance R1, a high-precision resistor is used for R1 to improve the accuracy of temperature detection.

[0055] Specifically, in this embodiment, the controller U1 uses Melexis' MLX series microcontroller chip, with a power supply VCC voltage of 12V. MLX series microcontroller chips, such as MLX81113, MLX81123, and MLX81124, have a power supply voltage of 12V and can be directly powered by a small vehicle battery, making them convenient to use. Traditional microcontroller chips' ADC modules are used to detect the voltage between the endpoints and ground. However, the MLX series microcontroller chips are special; they detect the voltage relative to the power supply VCC. Since the highest sampling voltage of the input pins of the MLX series microcontroller chip's ADC module is typically 5V, while the power supply VCC voltage is 12V, without proper limitation, the input pins and the ADC module can easily be burned out.

[0056] Design a protection circuit, which includes a reference voltage chip U2, resistors R3 and R4. Resistors R3 and R4 are connected in series between the power supply VCC and resistor R2. The reference terminal of the reference voltage chip U2 is connected to the common terminal of resistors R3 and R4. The cathode of the reference voltage chip U2 is connected to the power supply VCC, and the anode of the reference voltage chip U2 is connected to the non-grounded end of resistor R2.

[0057] The voltage between the anode and cathode of the reference voltage chip U2 is:

[0058]

[0059] In the formula, The reference voltage and reference current for the reference voltage chip U2; Here are the resistance values ​​of resistors R3 and R4;

[0060] Voltage satisfy: The unit is V. This is the highest sampling voltage at the input pin of the ADC module.

[0061] Specifically, in this embodiment, a 2.5V reference voltage signal, such as TL431, is selected. , Resistors R3 and R4 are both 4.7kΩ. and 5.1k The resistance, calculated using the above formula, .

[0062] To verify the detection performance of the high-precision temperature detection circuit provided in this embodiment of the invention, (1) five circuits were randomly selected. Figure 1 The PCB board of the scheme was tested at room temperature using an adjustable resistor and an NTC resistance-temperature meter to simulate different temperature values. The test results are shown in Table 1 below. (2) Five boards were randomly selected. Figure 2 The PCB board of the solution was tested at room temperature using an adjustable resistor and an NTC resistance-temperature meter to simulate different temperature values. The test results are shown in Table 2 below.

[0063] Table 1: Figure 1 Test results of the solution

[0064]

[0065] Table 2: Figure 2 Test results of the solution

[0066]

[0067] Comparing the test results in Tables 1 and 2, it can be found that: the test results provided by the embodiments of the present invention... Figure 2 The proposed method provides more accurate temperature measurements, especially at low temperatures. Figure 2 The error of the solution reaches 3~6℃. Figure 2 The error of the solution is within 1°C, which greatly improves the accuracy of temperature measurement.

[0068] Example 2:

[0069] This invention provides a charging socket for electric vehicles, including a high-precision temperature detection circuit as described above. The temperature detection circuit detects the temperature of the charging core in real time and uploads the temperature information to the vehicle-side VCU (Vehicle Control Unit) via LIN or CAN communication. The VCU decides to dredge the charging or stop charging based on the core temperature reported by the socket.

[0070] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-precision temperature detection circuit, characterized in that, include: The voltage divider circuit includes a thermistor RT, a resistor R1, and a resistor R2 connected in series between the power supply VCC and the ground terminal. The controller has its power supply connected to the power supply VCC. The controller has an ADC module, which is used to acquire the voltage value of its input pin relative to the power supply VCC. The two input pins of the ADC module are respectively connected to the common terminal of the resistor R1 and the thermistor RT and the resistor R2. The controller calculates the resistance value of the thermistor RT based on the voltage value acquired by the ADC module, and calculates the temperature value by combining the resistance-temperature table of the thermistor RT.

2. The high-precision temperature detection circuit according to claim 1, characterized in that, A filter capacitor C1 is connected between the common terminal of resistor R1 and the thermistor RT and the power supply VCC, and a filter capacitor C2 is connected between the common terminal of resistor R1 and resistor R2 and the power supply VCC.

3. The high-precision temperature detection circuit according to claim 1, characterized in that, The controller uses Melexis's MLX series microcontroller chip, and the power supply VCC voltage is 12V.

4. The high-precision temperature detection circuit according to claim 1, characterized in that, The temperature detection circuit also includes a protection circuit, which includes a reference voltage chip, resistor R3, and resistor R4. Resistors R3 and R4 are connected in series between the power supply VCC and resistor R2. The reference terminal of the reference voltage chip is connected to the common terminal of resistors R3 and R4. The cathode of the reference voltage chip is connected to the power supply VCC, and the anode of the reference voltage chip is connected to the non-grounded end of resistor R2.

5. The high-precision temperature detection circuit according to claim 4, characterized in that, The voltage between the anode and cathode of the reference voltage chip is: In the formula, The reference voltage and reference current of the reference voltage chip; Here are the resistance values ​​of resistors R3 and R4; The voltage satisfy: The unit is V. This is the highest sampling voltage at the input pin of the ADC module.

6. The high-precision temperature detection circuit according to claim 1, characterized in that, The calculation of the resistance value of the thermistor RT based on the voltage value acquired by the ADC module includes: The voltage value at the common terminal of the resistor R1 and the thermistor RT for: The voltage value at the common terminal of resistor R1 and resistor R2 for: According to voltage value Calculate the resistance value of the thermistor RT: In the formula, The digital values ​​acquired by the two input pins of the ADC module. This is the reference voltage for the ADC module. This represents the number of bits used to achieve the precision of the ADC module. Let R1 be the resistance value of the resistor and RT be the thermistor.

7. The high-precision temperature detection circuit according to claim 1, characterized in that, The resistor R1 is a high-precision resistor.

8. A charging socket for an electric vehicle, characterized in that, Includes the high-precision temperature detection circuit as described in any one of claims 1-7.

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