An ACC detection circuit with on-board conducted immunity

Abstract

The utility model discloses a kind of ACC detection circuits of vehicle-mounted conduction anti-interference, belong to the field of automotive electronics.The circuit includes ACC signal input end, MCU signal output end, power supply end and ground end, high-frequency suppression unit is successively connected in ACC signal input end after;And the filter voltage division network consisting of first resistance, second resistance, first capacitor and stable capacitor;The output end of the filter voltage division network is electrically connected to the base of a triode, the emitter of the triode is grounded, and its collector is electrically connected to MCU signal output end;A third resistance is electrically connected between power supply end and the collector of the triode.The utility model can effectively filter out the conduction interference in vehicle-mounted power network by the above cascaded filter and isolation structure, and form reliable electrical isolation protection to the microcontroller of rear end, solve the problem that existing circuit is easily interfered and leads to misjudgment and damage, with the advantages of strong anti-interference ability, high reliability, simple structure and low cost.

Description

Technical Field

[0001] This utility model relates to the field of automotive electronics technology, and in particular to an ACC detection circuit for vehicle-mounted conducted interference immunity. Background Technology

[0002] With the development of automotive intelligence and networking, in-vehicle electronic products such as infotainment systems, dashcams, and smart cockpit controllers have become standard equipment in vehicles. These electronic products need to be turned on and off at the correct time, and the switching of their working states generally relies on the accurate detection of the ACC (Accessory Control) signal. The ACC signal, as a key "wake-up" signal, indicates that the vehicle has entered a power-on standby state and is the core basis for in-vehicle products to determine whether they should enter working mode.

[0003] However, the electrical environment inside a car is extremely complex and is not a pure DC power supply system. Engine ignition, window motors, wiper motors, relays, and various electronic control units generate a large amount of high-frequency noise, voltage spikes, and transient surges during operation. These interferences are conducted through the vehicle's wiring harness network. As the bridge connecting the vehicle's main electrical system and onboard electronics, the ACC signal line inevitably couples with these conducted interferences, making the originally clear switching signal extremely "dirty."

[0004] In existing technologies, some simple ACC detection circuits directly connect the ACC signal to the input pin of the microcontroller (MCU) using a resistor divider. This makes them particularly vulnerable to the complex electromagnetic interference described above. The lack of effective suppression and filtering of conducted interference allows noise and voltage spikes to easily reach the microcontroller. This can cause the microcontroller to misjudge the ACC status—for example, misinterpreting an interference pulse as a power-on signal, leading to abnormal device startup after the vehicle is turned off, continuously draining the battery; strong voltage surges can directly impact or even damage the microcontroller, a core component, posing a serious threat to the reliability and lifespan of the entire product.

[0005] Therefore, this utility model proposes an ACC detection circuit for vehicle-mounted conducted interference immunity to overcome the shortcomings of the prior art. Utility Model Content

[0006] To overcome the above deficiencies, this utility model provides an ACC detection circuit for vehicle-mounted conducted interference immunity. It aims to improve the existing technology where the vehicle-mounted ACC detection circuit lacks an effective filtering and isolation structure, resulting in weak anti-conducted interference capability and easy transmission of noise signals to the back end, which can lead to microcontroller misjudgment or even damage, affecting the reliability and safety of the product.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: an ACC detection circuit for vehicle-mounted conducted interference suppression, comprising: an ACC signal input terminal, an MCU signal output terminal, a power supply terminal, a ground terminal, a high-frequency suppression unit, a first resistor, a second resistor, a first capacitor, a stabilizing capacitor, a transistor, and a third resistor.

[0008] The various units of this circuit are electrically connected in a specific cascading manner. The high-frequency suppression unit is connected in series between the ACC signal input terminal and the subsequent circuit. One end of the first resistor is electrically connected to the high-frequency suppression unit, and the other end serves as a common node. One end of the second resistor and one end of the first capacitor are both electrically connected to the common node, and the other end of the second resistor and the other end of the first capacitor are both electrically connected to the ground terminal. The stabilizing capacitor is connected in parallel across the two ends of the second resistor.

[0009] Furthermore, the base of the transistor is electrically connected to the aforementioned common node, its emitter is electrically connected to the ground terminal, its collector is electrically connected to the MCU signal output terminal, one end of the third resistor is electrically connected to the collector of the transistor, and the other end is electrically connected to the power supply terminal, together forming a multi-level processing and isolation protection structure from signal input to signal output.

[0010] Preferably, the high-frequency suppression unit is a ferrite bead.

[0011] Preferably, the transistor is an NPN transistor.

[0012] Preferably, the first resistor and the first capacitor together form an RC low-pass filter structure.

[0013] Preferably, the first resistor and the second resistor together form a voltage divider structure, and the voltage output terminal of the voltage divider structure is used to drive the base of the transistor.

[0014] Preferably, the collector-emitter path of the transistor is used to control the conduction, grounding, or shutdown of the MCU signal output terminal based on the voltage signal received at its base.

[0015] Preferably, the third resistor is a pull-up resistor, which is used to determine the level of the MCU signal output terminal as the level of the power supply terminal when the transistor is turned off.

[0016] Preferably, the ACC signal input terminal, the high-frequency suppression unit, the first resistor, the second resistor, the first capacitor, and the stabilizing capacitor together constitute a front-end isolation protection circuit; the transistor, the third resistor, and the MCU signal output terminal together constitute a back-end logic output circuit.

[0017] This utility model has the following beneficial effects:

[0018] 1. In this utility model, by setting a multi-stage filtering circuit in which a high-frequency suppression unit and an RC low-pass filter structure are connected in series, the problem that the ACC detection circuit in the prior art is easily affected by high-frequency noise and conducted interference from the vehicle due to the lack of effective filtering is solved, and the technical effect of effectively filtering out interference signals and ensuring that the back-end microcontroller receives pure and accurate signals is achieved.

[0019] 2. In this utility model, by using a transistor as an isolation switching unit, the front-end signal processing circuit and the back-end microcontroller signal output terminal are electrically isolated. This solves the problem in the prior art where voltage surges or strong interference at the front end may be conducted and damage the back-end microcontroller due to direct or indirect electrical connection between the front and back-end circuits. This achieves the effect of protecting the back-end core chip and significantly improving the reliability and safety of the entire product circuit. Attached Figure Description

[0020] Figure 1 This is a circuit diagram of an ACC detection circuit for vehicle-mounted conducted interference suppression proposed in this utility model. Detailed Implementation

[0021] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0022] Reference Figure 1 The present invention provides an embodiment of an ACC detection circuit for vehicle-mounted conducted interference suppression, which aims to solve the problem that the existing vehicle-mounted ACC detection circuit lacks a cascaded protection structure for effective filtering and electrical isolation of conducted interference signals, which leads to the back-end microcontroller being susceptible to interference and causing misjudgment or even damage.

[0023] The vehicle-mounted conducted interference suppression ACC detection circuit is built on a circuit board and has an ACC signal input terminal, an MCU signal output terminal, a power supply terminal, and a ground terminal for electrical connection with external automotive electrical systems. The circuit integrates a high-frequency suppression unit, a filter voltage divider network consisting of a first resistor R13, a second resistor R14, a first capacitor C168, and a stabilizing capacitor C12, a transistor Q1 for isolation switching, and a third resistor R10 for logic level determination. The high-frequency suppression unit is connected in series between the ACC signal input terminal and the filter voltage divider network to perform preliminary high-frequency filtering on the signal from the ACC signal input terminal. The filter voltage divider network further processes the signal from the high-frequency suppression unit and outputs the processed signal to the base of transistor Q1. Transistor Q1 controls the level state of the MCU signal output terminal according to the base signal, and the third resistor R10 provides a default high level for the MCU signal output terminal.

[0024] Specifically, one end of the first resistor R13 is electrically connected to the high-frequency suppression unit, and the other end serves as a node, simultaneously connected to one end of the second resistor R14, one end of the first capacitor C168, and the base of the transistor Q1; the other end of the second resistor R14 is electrically connected to the ground terminal. The first resistor R13 and the second resistor R14 together form a voltage divider structure to reduce the voltage at the ACC signal input terminal; the other end of the first capacitor C168 is electrically connected to the ground terminal. The first capacitor C168 and the first resistor R13 together form an RC low-pass filter structure; the stabilizing capacitor C12 is connected in parallel across the two ends of the second resistor R14, and one end of it is electrically connected to the transistor Q1. The base node of transistor Q1 is connected to the ground terminal, and the other end is connected to the ground terminal to stabilize the base voltage of transistor Q1. The base of transistor Q1 receives the voltage signal from the filter voltage divider network, its emitter is directly connected to the ground terminal, and its collector is connected to the MCU signal output terminal and one end of the third resistor R10. Transistor Q1 controls the conduction or cutoff between its collector and emitter according to the presence or absence of the base voltage, thereby realizing the electrical isolation between the preceding and following circuits and the switching of the output signal. The other end of the third resistor R10 is connected to the power supply terminal as a pull-up resistor, which is used to clamp the level of the MCU signal output terminal to the level of the power supply terminal when transistor Q1 is cut off.

[0025] The raw signal from the ACC signal input first passes through a high-frequency suppression unit, which in this embodiment is preferably a ferrite bead. As the first barrier against conducted interference, it selectively attenuates high-frequency electromagnetic interference carried in the signal by utilizing its high impedance to high-frequency signals. The signal, after being initially purified by the high-frequency suppression unit, then enters an RC low-pass filter structure composed of a first resistor R13 and a first capacitor C168. This structure utilizes the low impedance of the capacitor to high-frequency signals to further bypass the residual, relatively low-frequency noise in the signal to the ground terminal, thereby achieving a second stage of filtering. At the same time, the first resistor R13 and the second resistor R14 electrically connected to its downstream stage together form a voltage divider structure. This voltage divider structure converts the 12 volts or higher voltage from the automotive electrical system into a low voltage signal suitable for driving the base of transistor Q1. The stabilizing capacitor C12 connected in parallel across the second resistor R14 stabilizes this low voltage signal to prevent voltage fluctuations from causing false triggering of transistor Q1.

[0026] The stable drive signal formed after the above filtering and voltage division is applied to the base of transistor Q1. The collector-emitter path of transistor Q1 is connected in series between the MCU signal output terminal and the ground terminal. Transistor Q1 acts as an electronically controlled switch and achieves electrical isolation between the front-end high-voltage circuit and the back-end low-voltage microcontroller circuit. When the base receives a valid high-level signal, transistor Q1 is saturated and conducts, pulling its collector directly to the grounded emitter, thus making the MCU signal output terminal present a low level. When the base signal is low, transistor Q1 is cut off, and its collector and emitter are disconnected. This ensures that any electrical disturbance in the front-end circuit is difficult to be transmitted to the back-end microcontroller, greatly enhancing the robustness and safety of the circuit.

[0027] As a preferred embodiment, in order to achieve efficient and reliable logic level switching, the transistor Q1 is specifically an NPN transistor, which conducts when its base receives a positive drive voltage through a filter voltage divider network, conforming to the low-level active control logic commonly found in automotive electronic circuits.

[0028] As another preferred embodiment, in order to provide a clear and stable high level to the MCU signal output during the off period of transistor Q1 and prevent the output from being in an uncertain floating state, the third resistor R10 is used as a pull-up resistor. Its resistance value can be selected according to the characteristics of the connected microcontroller GPIO pin to ensure that sufficient pull-up current is provided without generating excessive power consumption when transistor Q1 is turned on.

[0029] Furthermore, in order to clearly define the functions of the front-end circuit and the back-end circuit, the ACC signal input terminal, the high-frequency suppression unit, the first resistor R13, the second resistor R14, the first capacitor C168, and the stabilizing capacitor C12 together constitute a front-end isolation protection circuit. This front-end isolation protection circuit is responsible for filtering, reducing voltage, and stabilizing the input ACC signal. Meanwhile, the transistor Q1, the third resistor R10, and the MCU signal output terminal together constitute a back-end logic output circuit. This back-end logic output circuit is responsible for generating digital logic signals with clear high and low levels for the microcontroller to read based on the signals processed by the front-end circuit.

[0030] Working principle: When the vehicle accessory power supply ACC is turned on, a high-voltage signal enters this circuit through the ACC signal input terminal. This signal first flows through the high-frequency suppression unit, where the high-frequency noise components contained therein are initially filtered out. Subsequently, the signal enters the filter voltage divider network. The RC low-pass filter structure in the network further filters out the residual noise in the signal. At the same time, the voltage divider structure reduces the high voltage to a stable low-voltage signal, which is sufficient to drive the base of transistor Q1 to saturate and conduct. The conduction of transistor Q1 forms a path between its collector and emitter, thereby directly pulling the MCU signal output terminal to the level of the ground terminal. The microcontroller thus detects a stable low-level signal and determines that ACC is in the on state.

[0031] When the vehicle accessory power supply ACC is turned off, the ACC signal input becomes low, and the voltage output from the filter voltage divider network to the base of transistor Q1 is zero. Transistor Q1 is thus cut off, and the path between its collector and emitter is broken. At this time, due to the turn-off effect of transistor Q1, the third resistor in the back-end logic output circuit, i.e., the pull-up resistor, pulls the level of the MCU signal output to the power supply level. The microcontroller therefore detects a stable high-level signal and determines that ACC is in the off state. Through the synergistic effects of high-frequency suppression, low-pass filtering, voltage division stabilization, and finally transistor isolation switching, this invention solves the problems of inaccurate detection due to interference and easy damage to the back-end circuit in the prior art.

[0032] Finally, it should be noted that the above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Although the present utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. An ACC detection circuit for vehicle-mounted conducted interference immunity, comprising an ACC signal input terminal, an MCU signal output terminal, a power supply terminal, and a ground terminal, characterized in that, Also includes: A high-frequency suppression unit is connected in series between the ACC signal input terminal and the subsequent circuit. The first resistor has one end electrically connected to the high-frequency suppression unit; The second resistor has one end electrically connected to the other end of the first resistor and the other end electrically connected to the ground terminal; The first capacitor has one end electrically connected to the connection point of the first resistor and the second resistor, and the other end electrically connected to the ground terminal; A stabilizing capacitor is connected in parallel across the second resistor; The transistor has its base electrically connected to the junction of the first resistor and the second resistor, its emitter electrically connected to the ground terminal, and its collector electrically connected to the MCU signal output terminal. The third resistor has one end electrically connected to the power supply terminal and the other end electrically connected to the collector of the transistor.

2. The ACC detection circuit for vehicle-mounted conducted interference immunity according to claim 1, characterized in that, The high-frequency suppression unit is a ferrite magnetic bead.

3. The ACC detection circuit for vehicle-mounted conducted interference immunity according to claim 1, characterized in that, The transistor is an NPN type transistor.

4. The ACC detection circuit for vehicle-mounted conducted interference immunity according to claim 1, characterized in that, The first resistor and the first capacitor form an RC low-pass filter structure.

5. The ACC detection circuit for vehicle-mounted conducted interference immunity according to claim 1, characterized in that, The first resistor and the second resistor form a voltage divider structure, and the voltage output terminal of the voltage divider structure is connected to the base of the transistor.

6. The ACC detection circuit for vehicle-mounted conducted interference immunity according to claim 1, characterized in that, The collector-emitter path of the transistor is used to control the conduction, grounding, or shutdown of the MCU signal output terminal based on the voltage signal received at its base.

7. The ACC detection circuit for vehicle-mounted conducted interference immunity according to claim 1, characterized in that, The third resistor is a pull-up resistor, used to determine the level of the MCU signal output terminal as the level of the power supply terminal when the transistor is turned off.

8. The ACC detection circuit for vehicle-mounted conducted interference immunity according to claim 1, characterized in that, The ACC signal input terminal, the high-frequency suppression unit, the first resistor, and the voltage divider structure connected to the base of the transistor together constitute a front-end isolation protection circuit, and the transistor, the third resistor, and the MCU signal output terminal together constitute a back-end logic output circuit.

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