Heating control circuit and heating protection module for a nitrogen oxide sensor sensing chip

Abstract

The utility model discloses a kind of heating control circuit and heating protection module for nitrogen-oxygen sensor sensing chip, comprising: power supply voltage detection module, its input end is connected to power input end, output end exports feedback voltage signal;Pulse signal processing module, its input end is used to receive heating pulse width modulation signal, output end exports analog drive signal;Comparison control module, including first switch piece and second switch piece;Heating switch device;Wherein, the output end of power supply voltage detection module is connected to the control end of second switch piece;The output end of pulse signal processing module is connected to the control end of first switch piece.

Description

Technical Field

[0001] This utility model relates to the field of automotive electronics technology, and in particular to a heating protection circuit and heating protection module for a nitrogen oxide sensor chip. The circuit can quickly limit the heating current when the power supply voltage changes abruptly, thus preventing damage to the sensor chip. Background Technology

[0002] Automotive nitrogen oxide sensors use zirconia ceramic substrate chips as nitrogen oxide sensing chips. Zirconia ceramics need to be heated to a certain temperature and kept stable to achieve good detection performance. During vehicle startup and driving, power fluctuations (such as sudden load changes, inductive interference, etc.) may generate instantaneous high-voltage pulses, causing sudden changes in heating power and easily burning out the nitrogen oxide sensor's sensing chip. Existing technologies sometimes use digital control schemes (such as MCU + ADC sampling) for power limiting, but these suffer from slow response speed, high cost, and low reliability. Therefore, a purely hardware-implemented fast-response protection circuit is needed to automatically limit the heating current during power supply voltage changes, preventing damage to the sensing chip. Utility Model Content

[0003] The technical problem to be solved by this utility model is: how to overcome the shortcomings of existing digital solutions such as slow response, high cost and insufficient reliability, and provide a purely hardware circuit structure that can quickly respond to power supply voltage changes and limit heating power.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A heating control circuit for a nitrogen and oxygen sensor sensing chip includes: a power supply voltage detection module, whose input terminal is connected to a power supply input terminal and whose output terminal outputs a feedback voltage signal; a pulse signal processing module, whose input terminal receives a heating pulse width modulation signal and whose output terminal outputs an analog drive signal; a comparison control module, including a first switch and a second switch; and a heating switch device; wherein the output terminal of the power supply voltage detection module is connected to the control terminal of the second switch; and the output terminal of the pulse signal processing module is connected to the control terminal of the first switch.

[0005] In some embodiments, at least one of the following technical means is also included: The emitter of the first switching element is connected to the emitter of the second switching element, the collector of the first switching element is connected to the control terminal of the heating switching device, and the collector of the second switching element is connected to ground.

[0006] The power supply voltage detection module includes a Zener diode and a series voltage divider circuit. One end of the series voltage divider circuit is connected to the power input terminal, and the other end is grounded through the resistor. The feedback voltage signal is led out from the connection point between the series voltage dividers.

[0007] The pulse signal processing module includes a waveform transformation circuit, which includes at least one resistor and at least one capacitor.

[0008] The heating control circuit also includes: a diode for quickly releasing the charge stored in the capacitor during the high level when H_PWM is low, so as to avoid affecting the output voltage amplitude of the next pulse; a second resistor for limiting excessive current; and a third resistor connected in series with the resistor to adjust the output voltage amplitude for easy matching with the feedback signal voltage of the voltage detection module.

[0009] The heating switch device is a MOSFET.

[0010] This utility model also adopts the following technical solution: A heating protection module for a nitrogen and oxygen sensor sensing chip, integrating the heating control circuit described in any one of the above.

[0011] Compared with the prior art, the beneficial effects of this utility model are as follows: This invention achieves rapid limiting and protection of the heating power of a nitrogen and oxygen sensor chip through a purely hardware circuit structure. Specifically, the power supply voltage detection module generates a feedback voltage signal proportional to the power supply voltage in real time through a voltage divider circuit and a voltage reference device; the pulse signal processing module converts the input PWM signal into an analog drive signal through a resistor-capacitor network; and the comparison control module, through the coupling of a first and a second switching device, directly controls the on / off state of the heating switching device based on the comparison result between the analog drive signal and the feedback voltage signal. This circuit structure can rapidly limit the heating current when the power supply voltage changes abruptly (microsecond-level response), preventing damage to the sensor chip due to power surges.

[0012] Because this invention is constructed entirely using analog electronic components (such as resistors, capacitors, diodes, transistors, etc.), without the need for any digital processing units (such as MCUs), ADC sampling circuits, or software algorithms, it boasts advantages such as low cost, fast response speed, and high reliability. Furthermore, the circuit structure is simple, easy to implement and integrate, and exhibits strong anti-interference capabilities, making it suitable for the harsh environments of automotive electronics. Attached Figure Description

[0013] Figure 1 This is a schematic diagram showing the relationship between the power supply voltage and the upper limit of the effective duty cycle for heating; Figure 2 This is a schematic diagram of the module connections and waveform timing of the heating control circuit; Figure 3 This is a circuit schematic diagram of a specific embodiment; Figure 4It is a schematic diagram showing the relationship between the voltage waveforms at various points on the circuit and the limitation on the heating voltage; Figure 5 This is a schematic diagram showing the relationship between the power supply voltage and the feedback voltage. Detailed Implementation

[0014] The embodiments of this utility model are described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of this utility model.

[0015] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as "connected to" another component, it can be directly connected to or indirectly connected to that other component. Furthermore, a connection can be used for both fixing and circuit / signal connectivity.

[0016] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0017] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified.

[0018] The basic concept of this utility model is as follows: A heating control circuit for a nitrogen and oxygen sensor sensing chip, the heating control circuit mainly includes three functional modules: a power supply voltage detection module 201 (specifically a voltage detection module), a pulse signal processing module 202 (specifically a waveform transformation circuit), and a comparison control module 203 (specifically a comparison circuit).

[0019] Module Connections: The input of the power supply voltage detection module 201 is connected to the power supply VBAT, and its output (generating a feedback voltage signal) is connected to the control terminal of the second switch (e.g., Q9) in the comparison control module 203. The input of the pulse signal processing module 202 receives the heating pulse width modulation signal H_PWM from the MCU, and its output (generating an analog drive signal) is connected to the control terminal of the first switch (e.g., Q3) in the comparison control module 203. The output of the comparison control module 203 is used to control the gate of the heating switching device (e.g., Q10), ultimately switching the heating current flowing to the sensing chip on and off.

[0020] The module connection relationship and waveform timing of key signals of the heating control circuit of this utility model are as follows: Figure 2 As shown.

[0021] The output terminal of the pulse signal processing module 202 is connected to the control terminal of the first switch Q3, and is used to provide an analog drive signal to the first switch. The output terminal of the power supply voltage detection module 201 is connected to the control terminal of the second switch Q9, and is used to provide a feedback voltage signal to the comparison control module.

[0022] The first switch Q3 and the second switch Q9 are coupled to each other and are simultaneously turned on or off, depending on the difference between the analog drive signal voltage and the feedback signal voltage. When the voltage difference is greater than 1.2V, the switch is turned on, and when it is less than 1.2V, the switch is turned off.

[0023] The comparison control module transmits the signal to the control terminal of the heating switch Q10 through the third resistor R35, thereby controlling the on / off state of the heating switch.

[0024] When the power supply voltage VBAT increases, the feedback voltage signal output by the power supply voltage detection module 201 increases accordingly, shortening the conduction time of the second switch Q9 and the first switch Q3, thereby shortening the conduction time of the heating switch Q10 and limiting the heating power. Conversely, when the power supply voltage VBAT decreases, the feedback voltage signal decreases, the conduction limitation time of the second switch Q9 and the first switch Q3 increases, and the conduction limitation time of the heating switch Q10 also increases.

[0025] Through the connection relationship of the above hardware circuits, the function of automatically reducing the heating current as the power supply voltage increases is realized.

[0026] Figure 1This diagram illustrates the relationship between the power supply voltage VBAT and the upper limit of the effective duty cycle of the heating pulse in this invention. The horizontal axis represents the power supply voltage VBAT, and the vertical axis represents the upper limit of the effective duty cycle of the heating pulse. As shown, the two are inversely proportional. When the power supply voltage VBAT increases (e.g., from the normal 24V to 38V), due to the rapid response of the comparison control module 203, the upper limit of the effective duty cycle of the heating pulse will decrease accordingly (e.g., from approximately 30% to close to 0%). This automatic, inversely proportional adjustment relationship ensures that even if the power supply voltage changes abruptly, the heating power delivered to the sensing chip (P = VBAT² / R * Duty) can be effectively limited within a safe range, thereby avoiding the risk of burning out the chip due to a sudden increase in power.

[0027] It should be noted that the 'H_COM' symbol appearing in each of the attached figures represents the output heating voltage.

[0028] Figure 4 This illustrates how the protection circuit works. After the pulse signal H_PWM passes through the processing module 202 (waveform conversion circuit), its output analog drive signal is a triangular wave Q3b. The voltage detection module outputs a feedback voltage Q9b, which, after passing through the comparison module, outputs an on / off signal to control the heating switch, resulting in an output heating voltage H_COM. It can be seen that changes in the feedback voltage Q9b affect the duty cycle of the final output voltage H_COM. An increase in Q9b forces the duty cycle of H_COM to decrease, and vice versa.

[0029] Figure 5 This diagram illustrates the relationship between the power supply voltage VBAT and the output feedback voltage signal Q9b in the power supply voltage detection module 201. The horizontal axis represents the power supply voltage VBAT, and the vertical axis represents the feedback voltage Q9b. When the VBAT voltage is higher than the breakdown voltage of the Zener diode Z2, the Q9b voltage increases linearly with VBAT (the slope is determined by the voltage division ratio of R66 and R67); when VBAT is lower than the breakdown voltage of Z2, the voltage division across the resistor is 0, and the output feedback voltage is 0. Z2 is introduced to facilitate the adjustment and calculation of the relationship between the feedback voltage and VBT.

[0030] This design enables the feedback voltage signal to sensitively reflect power supply changes within the normal voltage range, while quickly triggering the protection mechanism to shut off the heating switch Q10 under abnormal high voltage conditions.

[0031] Example 1: Combination Figure 3 This embodiment provides a heating protection circuit for a nitrogen and oxygen sensor sensing chip.

[0032] The power supply voltage detection module consists of a Zener diode Z2 and resistors R66 and R67 connected in series. The input of this module is connected to the power supply VBAT, and its output is a feedback voltage signal Q9b. The resistance ratio of R66 and R67 is calculated and determined based on the normal range of the power supply voltage, the breakdown voltage of the Zener diode Z2, and the required protection trigger threshold.

[0033] The pulse signal processing module consists of resistors R10, R36, and R42, capacitor C8, and diode D1. Its input terminal receives a heating pulse width modulation signal (H_PWM). A differentiating circuit composed of components such as R42 and C8 converts this PWM signal into an analog drive signal Q3b, whose waveform is ramp-shaped. Diode D1 is used to quickly discharge and restore capacitor C8 when the input PWM signal is low, ensuring that even when the PWM has a high duty cycle, it does not affect the analog output voltage amplitude of the next pulse.

[0034] In the comparison control module, the emitters of the first switch Q3 (NPN type) and the second switch Q9 (PNP type) are interconnected to form a common emitter node. The voltage of this node is jointly controlled by the analog drive signal Q3b and the feedback voltage signal Q9b.

[0035] When the feedback voltage signal Q9b is low, the common-emitter node voltage is clamped at approximately Q9b + Vbe_pnp (e.g., Q9b + 0.6V). At this time, if the analog drive signal Q3b is higher than this common-emitter voltage by approximately Vbe_npn (e.g., 0.6V higher), Q3 turns on, driving the heating switch device.

[0036] When the power supply voltage increases, causing the feedback voltage signal Q9b to rise, the common-emitter node voltage also rises. If the instantaneous value of the analog drive signal Q3b cannot reach the condition of the common-emitter voltage + Vbe_npn, Q3 will not conduct, thus cutting off the heating current. In this way, the increase in the feedback voltage signal Q9b will correspondingly increase the conduction threshold of Q3, thereby shortening the effective conduction time of the heating switch device and achieving power limiting protection while keeping the input PWM duty cycle unchanged.

[0037] The heating switch is a MOSFET Q10. Its control terminal (gate) is connected to the collector of the first switch Q3 through a resistor R35.

[0038] The circuit operates through the interaction of potentials at each node: the voltage of the analog drive signal Q3b drives Q3, the voltage of the feedback voltage signal Q9b drives Q9, which in turn controls the conduction and cutoff of Q10, ultimately limiting the heating power flowing to the sensing chip.

[0039] When the power supply voltage VBAT increases, the feedback voltage signal Q9b suddenly increases, shortening the conduction time of Q9 (when the Q3b drive voltage signal remains unchanged), causing Q10 to turn off prematurely, thus limiting the heating current. This circuit achieves a rapid response to voltage surges through the above-described purely hardware connection method.

[0040] Since this circuit is a purely analog voltage compensation control circuit, it features a fast response speed, which can compensate for the lag in MCU software protection. The protection circuit is of great significance for protecting against voltage surges and microsecond to millisecond-level high-voltage pulses. This invention uses a simple circuit to achieve the protection function, and is characterized by low cost, high reliability, and resistance to interference.

[0041] The implementation of this technical solution can achieve the following technical effects: 1. H_PWM is output by the MCU with a period of 10ms. The MCU power supply is 5V. The software limits the maximum duty cycle to 80%, which facilitates the acquisition of nitrogen and oxygen gas measurement signals during the low level period and can avoid the influence of heating pulse on the chip measurement value. 2. After passing through the waveform conversion circuit, H_PWM is transformed into an analog signal that approximates a triangular wave, with a peak value of approximately 4.1V and a maximum width of 8ms. 3. When the power supply VBAT is 24V, after voltage division by Z2, R66, and R67, the voltage of Q9b is 1.67V; 4. The PN junction voltage when Q3 and Q9 are turned on is 1.2V. When the voltage of Q3b is lower than 2.87V, Q3 will be forcibly turned off, and the maximum duty cycle (upper limit) of the heating pulse output is about 30% (3ms). When the VBAT voltage changes, the upper limit of the effective duty cycle also changes inversely to avoid damage caused by sudden power changes. 5. If the voltage suddenly changes to 38V, the voltage of Q9b is 2.94V, and the voltage of Q3b must be above 4.14V to conduct. Q3 will quickly turn off. When the voltage remains high, Q3 remains off. Even if the MCU outputs a high level or H_PWM signal by error, the heating switch will always be off. 6. After adopting this circuit scheme, experimental tests have shown that it can effectively suppress the overshoot of heating power caused by sudden changes in power supply voltage, and significantly reduce the risk of damage to the sensing chip due to such electrical stress impact.

[0042] Example 2: This embodiment provides a heating control circuit for a nitrogen and oxygen sensor sensing chip, wherein: The "power supply voltage detection module" is specifically a series voltage divider circuit composed of resistors R66 and R67 and a Zener diode Z2. In this module, the Zener diode Z2 uses a 5.6V regulated voltage to set the detection starting point. Resistors R66 and R67 form the voltage divider circuit, and their ratio is determined according to the following formula: Q9b = (VBAT - Vz) * (R67 / (R66 + R67)) (when VBAT > Vz). For example, to achieve Q9b ≈ 1.67V when VBAT = 24V and trigger deep protection when VBAT = 38V (Q9b ≈ 2.94V), R66 = 10kΩ and R67 = 1kΩ are calculated and selected.

[0043] The "pulse signal processing module" is specifically a waveform conversion circuit (differentiating circuit form) composed of resistors R10, R36, R42, capacitor C8, and diode D1. It is used to differentiate the H_PWM signal into a triangular waveform. In this module, C8 and R42 form an RC differentiating circuit, whose time constant τ must be greater than the high-level time of the H_PWM signal to ensure the formation of an effective triangular wave. For an H_PWM signal with a period of 10ms and a maximum duty cycle of 80% (i.e., a high-level time of 8ms), τ = R42 × C8 ≈ 10ms is selected, therefore C8 = 1μF and R42 = 10kΩ are chosen. Resistor R36 is used to divide the voltage with R42, thereby finely adjusting the peak amplitude of the output triangular wave Q3b to match the protection threshold voltage range of Q9b. R10 = 1kΩ limits the discharge current of C8 to less than 5mA, reducing circuit noise. The introduction of R36 and R10 also moderately increases τ, which is beneficial for the triangular wave time to be greater than 8ms without any negative impact.

[0044] The "first switching element" is transistor Q3, and the "second switching element" is transistor Q9; The “heating switch device” is MOSFET Q10.

[0045] The circuit connection relationship is as follows Figure 3 As shown: The H_PWM signal is output from the MCU and converted into an analog drive signal (triangular wave) by the waveform conversion circuit to drive the base of Q3; the power supply voltage VBAT is divided by Z2, R66, and R67 to generate a feedback voltage signal to drive the base of Q9; the emitters of Q3 and Q9 are connected, and the collector of Q3 controls the gate of Q10 through resistor R35, thereby controlling the on and off of the heating current.

[0046] The specific defect addressed in this embodiment is: sudden changes in power supply voltage leading to sudden changes in heating power, resulting in damage to the sensing chip.

[0047] Detailed technical solution: Component names and connection relationships are listed above. Figure 3 .

[0048] Working principle: When VBAT increases, the base voltage of Q9 increases, requiring a higher base voltage of Q3 to turn on Q3 and Q9, thus limiting the conduction time of Q10; and vice versa.

[0049] Dimensions: R10=10kΩ, C8=1μF, R66=10kΩ, R67=2kΩ, Z2 voltage regulator value=5.6V, other resistor values ​​should be adjusted according to actual conditions.

[0050] The above component parameters are only an example of a specific implementation. The actual values ​​need to be recalculated and experimentally determined based on the system power supply voltage range, the characteristic parameters of the selected transistor / MOSFET, the H_PWM frequency, and the required protection threshold.

[0051] Implementation steps: 1. Provide the H_PWM signal (period 10ms) generated by the MCU; 2. The waveform conversion circuit converts H_PWM into a triangular wave; 3. The voltage divider circuit detects VBAT and generates a feedback voltage; 4. Q3 and Q9 compare the two signals to control the on / off state of Q10.

[0052] Example 3 This embodiment, based on embodiment 2, further defines the power supply voltage detection module as including a series voltage divider circuit and a Zener diode. Specifically, Z2 is a 5.6V Zener diode, R66 and R67 are voltage divider resistors, and their connection point leads out the feedback voltage signal.

[0053] Example 4 Based on Example 2, this embodiment further defines the pulse signal processing module as a waveform transformation circuit (differentiating circuit form). Specifically, R42 and C8 constitute the differentiating body, D1 is used for rapid discharge recovery of C8, R10 is used for current limiting, and R36 and R42 are connected in series to divide the voltage and adjust the output voltage amplitude resistor.

[0054] Example 5 This embodiment, based on embodiment 2, further specifies that the first switching device is an NPN transistor, the second switching device is a PNP transistor, and the heating switching device is a MOSFET. Specifically, Q3 is an MBT5551, Q9 is an 8550, and Q10 is an IRFR5410.

[0055] The above-described 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 the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A heating control circuit for a nitrogen and oxygen sensor sensing chip, characterized in that, include: The power supply voltage detection module has its input terminal connected to the power supply input terminal and its output terminal outputting a feedback voltage signal. The pulse signal processing module receives heating pulse width modulation signals at its input and outputs analog drive signals at its output. The comparison control module includes a first switching element and a second switching element; Heating switching devices; The output terminal of the power supply voltage detection module is connected to the control terminal of the second switching element; The output terminal of the pulse signal processing module is connected to the control terminal of the first switching device.

2. The heating control circuit according to claim 1, characterized in that, The emitter of the first switching element is connected to the emitter of the second switching element, the collector of the first switching element is connected to the control terminal of the heating switching device, and the collector of the second switching element is connected to ground.

3. The heating control circuit according to claim 1, characterized in that, The power supply voltage detection module includes a Zener diode and a series voltage divider circuit. One end of the series voltage divider circuit is connected to the power input terminal, and the other end is grounded through the resistor. The feedback voltage signal is led out from the connection point between the series voltage dividers.

4. The heating control circuit according to claim 1, characterized in that, The pulse signal processing module includes a waveform transformation circuit, which includes at least one resistor (R42) and at least one capacitor (C8).

5. The heating control circuit according to claim 4, characterized in that, Also includes: The diode (D1) is used to quickly release the charge stored in the capacitor when the H_PWM is low, so as to avoid affecting the output voltage amplitude of the next pulse; the second resistor (R10) is used to limit the current from being too large; the third resistor (R36), which is connected in series with the resistor (R42), is used to adjust the output voltage amplitude to facilitate matching with the feedback signal voltage of the voltage detection module.

6. The heating control circuit according to claim 1, characterized in that, The heating switch device is a MOSFET.

7. A heating protection module for a nitrogen and oxygen sensor sensing chip, characterized in that, It integrates the heating control circuit as described in any one of claims 1-4.

Images