A hud self-locking and ultra-low power standby current control circuit

Abstract

This invention provides a HUD self-locking and ultra-low power standby current control circuit, including an automotive battery, an MCU, an automotive-grade low-dropout linear regulator (LDO), an ignition signal detection circuit, a transistor Q2, and a CAN_INH signal terminal. The automotive battery outputs 12V voltage to the input terminal of the LDO, and the output terminal of the LDO is connected to the MCU to provide a 3.3V operating voltage. The input terminal of the ignition signal detection circuit is connected to the ignition signal IGN+, and the output terminal of the ignition signal detection circuit is connected to the enable terminal EN of the LDO. The CAN_INH signal terminal is also connected to the enable terminal EN of the LDO. The collector of the transistor Q2 is connected to the enable terminal EN of the LDO, and the base of the transistor Q2 is connected to the MCU-OFF / ON pin of the MCU through a base current-limiting resistor. This invention can solve the problem that existing power supply control circuits cannot meet the self-locking requirements.

Description

Technical Field

[0001] This utility model relates to the field of hardware design technology for vehicle HUD products, specifically to a HUD self-locking and ultra-low power standby current control circuit. Background Technology

[0002] As a human-machine interface device that enhances driving safety, the stable operation of a car head-up display (HUD) relies on the power supply provided by the car's battery and requires coordinated control with the car's electronic systems, such as the ignition signal and CAN bus. In existing technologies, HUD power supply control typically involves the ignition signal IGN+ triggering a low-dropout linear regulator (LDO) to start, thereby providing operating voltage to the core control unit (MCU). When the ignition signal is lost, such as when the vehicle is turned off, the LDO stops outputting due to the loss of its enable signal, the MCU is powered off, and the HUD enters a shutdown state.

[0003] However, in real-world automotive applications, even if the ignition signal is lost, the CAN bus may still need to operate for a short period to transmit critical data, such as fault diagnosis information and status parameters. In this case, the HUD, as a crucial data exchange terminal on the CAN bus, must continue operating to receive and process the relevant data. Existing HUD power supply control circuits lack an effective self-locking mechanism, failing to maintain the LDO's enabled state via CAN bus signals after the ignition signal is lost. This leads to the LDO stopping power, the MCU losing power, and the HUD failing to operate continuously. Consequently, CAN bus data transmission is interrupted, critical data is lost, and subsequent status analysis and maintenance decisions for the automotive electronic system are affected.

[0004] Based on the above problems, there is an urgent need for a technical solution that can ensure a continuous and stable power supply to the HUD when the ignition signal is lost and the CAN bus is working, so as to solve the problem that the existing power supply control circuit cannot meet the self-locking requirements. Utility Model Content

[0005] The purpose of this invention is to provide a HUD self-locking and ultra-low power standby current control circuit, including an automotive battery, an MCU, an automotive-grade low-dropout linear regulator (LDO), an ignition signal detection circuit, a transistor Q2, and a CAN_INH signal terminal. The automotive battery outputs 12V voltage to the input terminal of the LDO, and the output terminal of the LDO is connected to the MCU to provide a 3.3V operating voltage. The input terminal of the ignition signal detection circuit is connected to the ignition signal IGN+, and the output terminal of the ignition signal detection circuit is connected to the enable terminal EN of the LDO. The CAN_INH signal terminal is also connected to the enable terminal EN of the LDO. The collector of the transistor Q2 is connected to the enable terminal EN of the LDO, and the base of the transistor Q2 is connected to the MCU-OFF / ON pin of the MCU through a base-limiting current resistor. The emitter of the transistor Q2 is grounded. The ignition signal detection circuit performs voltage division and debouncing processing on the input ignition signal IGN+ and outputs a high level to the LDO. The enable pin EN of the LDO is activated, causing the LDO to output a 3.3V voltage to the MCU. When the ignition signal IGN+ is de-energized, the CAN_INH signal outputs a high level to the enable pin EN of the LDO, enabling the LDO to maintain a 3.3V output voltage to the MCU for self-locking. When the MCU needs to enter sleep mode, the MCU-OFF / ON pin of the MCU outputs a voltage that turns on the transistor Q2, which pulls the enable pin EN of the LDO low. The LDO stops outputting and enters a static operating state. The quiescent current of the LDO in the static operating state meets the ultra-low power consumption requirements. When the MCU needs to be woken up, the ignition signal IGN+ is processed by the ignition signal detection circuit and outputs a high level to the MCU. The MCU-OFF / ON pin of the MCU outputs a voltage that turns off the transistor Q2, and the enable pin EN of the LDO returns to a high level. The LDO restarts and outputs a 3.3V voltage to the MCU.

[0006] Preferably, the LDO model is SCT71403F33Q-TWDR.

[0007] More preferably, the LDO has an input voltage range of 3V to 40V, a fixed output voltage of 3.3V, and a maximum output current of 300mA.

[0008] More preferably, the LDO integrates an overcurrent protection circuit, an overtemperature protection circuit, and an undervoltage lockout circuit. The overcurrent protection circuit supports short-circuit protection, and the undervoltage lockout circuit is used to cut off the output of the LDO when the input voltage of the LDO is lower than a preset threshold that ensures the stable operation of the LDO.

[0009] More preferably, the ignition signal detection circuit includes a voltage divider resistor R207, a voltage divider resistor R208, a de-jitter capacitor C39, and a Zener diode D2. The cathode of the Zener diode is connected to the ignition signal IGN+, and the anode, after receiving voltage, is connected to one end of R207. The other end of the voltage divider resistor R207 is connected to one end of the voltage divider resistor R208, one end of the de-jitter capacitor C39, and the base of the transistor Q4. The other end of the voltage divider resistor R208 is grounded, the other end of the de-jitter capacitor C39 is grounded, and the base of the transistor Q4 is connected to the enable terminal of the LDO. The voltage divider resistors R207 and R208 form a voltage divider circuit, and the de-jitter capacitor C39 is used to eliminate the jitter interference of the ignition signal IGN+.

[0010] More preferably, the transistor Q2 is a 3904, and the base current limiting resistor has a resistance of 1KΩ.

[0011] More preferably, when the ignition signal IGN+ is powered off and the CAN bus is in operation, the CAN_INH signal terminal outputs a 5V high level to the LDO's enable terminal EN.

[0012] More preferably, when the MCU needs to enter sleep mode, the voltage output by the MCU-OFF / ON pin of the MCU is 3.3V.

[0013] More preferably, the over-temperature protection circuit of the LDO is triggered at a preset temperature value, which does not exceed 150°C, to prevent the LDO from being damaged due to excessive temperature.

[0014] More preferably, a diode D4 is connected in series between the CAN_INH signal terminal and the LDO enable terminal EN. The type of D4 is S-L1SS355T1G. The diode D4 is used to prevent reverse current from flowing into the CAN_INH signal terminal.

[0015] Compared with the prior art, this utility model has the following advantages: By connecting the CAN_INH signal terminal to the LDO enable terminal, and combining the voltage divider debouncing processing of the ignition signal detection circuit with the on / off control of transistor Q2, a self-locking and ultra-low power collaborative mechanism is constructed. The technical effect is as follows: It effectively solves the core problem in the background technology where, when the ignition signal is powered off and the CAN bus is operating, the HUD lacks a self-locking mechanism, leading to LDO power failure and interruption of critical CAN bus data transmission. At this time, the CAN_INH signal terminal outputs a high level, ensuring the LDO continuously outputs 3.3V, guaranteeing stable MCU operation for processing CAN data. Simultaneously, the ignition signal detection circuit ensures the reliability of LDO startup, and the transistor controls the LDO to enter a static operating state to meet ultra-low power requirements, improving the collaborative reliability between the HUD and the automotive electronic system. Attached Figure Description

[0016] To more clearly illustrate the embodiments of this utility model or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0017] Figure 1 This is the circuit diagram for the power supply self-locking and ultra-low power standby current control of this utility model; Figure 2 This is the circuit diagram for the IGN ignition switch detection of this utility model. Detailed Implementation

[0018] 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.

[0019] The concepts involved in this application will first be described with reference to the accompanying drawings. It should be noted that the following descriptions of various concepts are only for the purpose of making the content of this application easier to understand and do not constitute a limitation on the scope of protection of this application; furthermore, the embodiments and features in the embodiments of this application can be combined with each other unless otherwise specified. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] In existing technologies, the power supply control circuit of HUD often has two key problems. First, when the car ignition signal IGN+ is powered off, if the CAN bus still needs to continue working, the HUD is prone to failure to achieve continuous self-locking operation due to power interruption, resulting in interruption of CAN bus related data transmission. Second, in standby mode, the static current of the power management circuit of HUD is large, which cannot meet the ultra-low power consumption requirements of automotive electronic systems. Long-term standby can easily cause the car battery to lose power.

[0021] Based on this, please refer to Figure 1 and Figure 2 This embodiment provides a HUD self-locking and ultra-low power standby current control circuit, including an automotive battery, an MCU, an automotive-grade low-dropout linear regulator (LDO), an ignition signal detection circuit, a transistor Q2, and a CAN_INH signal terminal. The automotive battery outputs a 12V voltage to the input terminal of the LDO, and the output terminal of the LDO is connected to the MCU to provide a 3.3V operating voltage. The input terminal of the ignition signal detection circuit is connected to the ignition signal IGN+, and the output terminal of the ignition signal detection circuit is connected to the enable terminal EN of the LDO. The CAN_INH signal terminal is also connected to the enable terminal EN of the LDO. The collector of the transistor Q2 is connected to the enable terminal EN of the LDO, and the base of the transistor Q2 is connected to the MCU-OFF / ON pin of the MCU through a base-limiting current resistor. The emitter of the transistor Q2 is grounded. The ignition signal detection circuit performs voltage division and debouncing processing on the input ignition signal IGN+ and outputs a high level to the LDO's enable terminal. When the ignition signal IGN+ is powered down, the CAN_INH signal outputs a high level to the LDO's enable pin EN, causing the LDO to maintain a 3.3V output to the MCU for self-locking. When the MCU needs to enter sleep mode, the MCU-OFF / ON pin of the MCU outputs a voltage that turns on transistor Q2, which pulls the LDO's enable pin EN low, causing the LDO to stop outputting and enter a static operating state. The quiescent current of the LDO in the static operating state meets the ultra-low power consumption requirements. When the MCU needs to be woken up, the ignition signal IGN+ is processed by the ignition signal detection circuit and outputs a high level to the MCU. The MCU-OFF / ON pin of the MCU outputs a voltage that turns off transistor Q2, causing the LDO's enable pin EN to return to a high level, and the LDO restarts and outputs a 3.3V output to the MCU.

[0022] This technical solution establishes a power supply link between the automotive battery and the LDO-MCU, and, in conjunction with the ignition signal detection circuit, transistor Q2, and the control logic formed by the CAN_INH signal terminal, achieves self-locking control and ultra-low power standby management for the HUD. The ignition signal detection circuit ensures the reliability of the LDO startup triggered by the ignition signal IGN+ through voltage division and debouncing, avoiding false startup or shutdown caused by signal jitter. The CAN_INH signal terminal provides a high-level enable signal when the ignition signal IGN+ is powered off, maintaining continuous output of the LDO and solving the self-locking requirement. Transistor Q2 is controlled by the MCU-OFF / ON pin of the MCU, and adjusts the EN level of the LDO enable terminal by switching between on / off states, realizing the switching between the working and static states of the LDO, thereby controlling the sleep and wake-up of the MCU.

[0023] The technical effects achieved by the above solution include: when the ignition signal IGN+ is powered off and the CAN bus is working, the high-level enable of the CAN_INH signal terminal enables continuous power supply to the LDO, ensuring stable operation of the MCU, meeting the self-locking function requirements of the HUD, and avoiding interruption of CAN bus data transmission; when the MCU controls the transistor Q2 to turn on and put the LDO into a static working state, the static current of the LDO meets the ultra-low power consumption requirements, effectively reducing the standby loss of the automotive battery and extending the battery life; the voltage division and debouncing processing of the ignition signal detection circuit improves the accuracy of the ignition signal triggering the LDO to start, reduces power supply abnormalities caused by signal interference, and ensures the stability of HUD operation; at the same time, the MCU realizes flexible control of the LDO state through the MCU-OFF / ON pin, ensuring smooth switching between sleep and wake-up modes of the HUD, taking into account both power consumption control and fast response requirements.

[0024] In the existing technology, the LDO selected for the power supply control circuit of HUD often has insufficient model compatibility, which leads to unstable operation in automotive-grade environments, such as wide temperature range and high transient voltage, or inability to match the HUD's requirements for output voltage accuracy and quiescent current, thus affecting the overall operational reliability of HUD.

[0025] Based on this, the model of the LDO is SCT71403F33Q-TWDR.

[0026] This technical solution provides a specific and feasible hardware option for the core power supply module in the above embodiments by specifying the specific model of the LDO. As an automotive-grade LDO, the SCT71403F33Q-TWDR has electrical characteristics such as a wide input voltage range, low quiescent current, and high transient voltage withstand capability, which are highly compatible with the self-locking control and ultra-low power consumption requirements of the HUD in the above embodiments. It can meet the stable power supply requirements in the automotive environment without the need for additional complex peripheral circuit design.

[0027] The technical effects achieved by the above solution include: clearly defining the LDO model makes the technical solution feasible, allowing those skilled in the art to directly select this model of LDO to build the circuit, avoiding power instability problems caused by improper LDO model selection; the automotive-grade characteristics of the SCT71403F33Q-TWDR ensure that the HUD can still operate stably under complex automotive conditions, such as low-temperature start-up and voltage fluctuations, improving the environmental adaptability of the HUD; the low quiescent current characteristics of this model of LDO directly match the ultra-low power standby requirements, achieving low power consumption in the static working state of the LDO without additional optimization, simplifying circuit design complexity, and reducing R&D costs and circuit size.

[0028] In the existing technology, if the LDO of the HUD power supply control circuit does not specify key parameters such as input voltage range, transient voltage withstand capability, output voltage and maximum output current, it is easy for the LDO to be mismatched with the power supply characteristics of the car battery. For example, if the battery voltage fluctuation exceeds the LDO input range, it will damage the LDO, or the LDO output capability cannot meet the power consumption requirements of the MCU and other HUD modules, resulting in abnormal HUD operation, such as insufficient output voltage causing the MCU to crash.

[0029] Based on this, the input voltage range of the LDO is 3V to 40V, the fixed output voltage of the LDO is 3.3V, and the maximum output current of the LDO is 300mA.

[0030] This technical solution clarifies the compatibility between the LDO and the automotive battery and its power supply capability to the MCU by defining the core electrical parameters of the LDO: the input voltage range of 3V to 40V covers the voltage fluctuation range of the automotive battery during normal operation, charging and discharging. The automotive battery voltage is usually around 12V, and transient low voltage may occur during startup or transient high voltage may occur during charging; the transient input voltage withstand capability of 45V can cope with transient voltage surges commonly found in automotive circuits, such as voltage spikes caused by load switching; the fixed output voltage of 3.3V matches the standard operating voltage of the MCU, ensuring stable operation of the MCU; the maximum output current of 300mA can meet the total current requirements of the MCU and other low-power modules of the HUD, avoiding power supply bottlenecks caused by insufficient output current.

[0031] The technical effects achieved by the above solution include: the LDO's input voltage range matches the characteristics of the automotive battery voltage, ensuring that the LDO can still operate normally when the automotive battery voltage fluctuates, avoiding damage to the LDO due to input voltage exceeding the range, and improving the circuit's resistance to voltage fluctuations; the 45V transient input voltage withstand capability effectively resists transient voltage surges in the automotive circuit, reducing LDO failures caused by voltage spikes and extending the circuit's lifespan; the fixed 3.3V output voltage provides a stable operating voltage for the MCU, avoiding MCU malfunctions due to voltage deviations, such as program crashes or data loss, ensuring the functional stability of the HUD; the maximum output current of 300mA provides sufficient margin for powering multiple modules of the HUD, ensuring that even when some HUD modules are operating under short-term high loads, the LDO can still output stably, avoiding HUD function interruptions due to insufficient power supply.

[0032] In the existing technology, if the LDO of the HUD power supply control circuit does not integrate overcurrent protection, overtemperature protection and undervoltage lockout protection functions, when the circuit has abnormal operating conditions, such as short circuit at the LDO output terminal causing overcurrent, high temperature environment causing LDO temperature to be too high, or low input voltage causing output instability, the LDO is easily damaged, which will lead to the overall failure of the HUD, and may even trigger a chain of failures in the car circuit, such as overcurrent causing overload of the car battery.

[0033] Based on this, the LDO integrates an overcurrent protection circuit, an overtemperature protection circuit, and an undervoltage lockout circuit. The overcurrent protection circuit supports short-circuit protection, and the undervoltage lockout circuit cuts off the LDO's output when the input voltage is lower than a preset threshold ensuring stable operation. This technical solution establishes an abnormal operating condition protection mechanism for the HUD power supply control circuit by integrating three core protection circuits within the LDO: the overcurrent protection circuit cuts off the output or limits the current in a timely manner when the LDO's output current exceeds the safe range or when there is a short circuit at the output terminal, preventing the LDO from burning out due to overcurrent; the overtemperature protection circuit triggers the protection mechanism when the LDO's operating temperature exceeds the safe range, preventing damage to the LDO due to high temperature; and the undervoltage lockout circuit cuts off the output when the LDO's input voltage is lower than a preset threshold (the minimum input voltage required for stable 3.3V output voltage), preventing the LDO from outputting low or unstable voltage when the input voltage is insufficient, which could lead to MCU malfunction.

[0034] The technical effects achieved by the above solution include: the overcurrent protection circuit effectively prevents LDO overcurrent damage caused by output short circuits, excessive loads, etc., while avoiding overload impact on the automotive battery, ensuring the overall safety of the automotive circuit; the overtemperature protection circuit enables the LDO to adapt to the high-temperature environment of the automotive, preventing LDO failure due to excessive temperature and improving the reliability of the HUD under high-temperature conditions; the undervoltage lockout circuit ensures that the LDO only operates when the input voltage meets the stable output conditions, preventing the LDO from outputting unstable voltage when the input voltage is too low, preventing the MCU from experiencing program errors or hardware damage due to insufficient voltage, further ensuring the working stability of the HUD; the three protection functions are integrated inside the LDO, eliminating the need for additional external protection circuit design, simplifying the circuit structure, reducing R&D costs and circuit size, while improving the protection response speed.

[0035] In the existing technology, if the ignition signal detection circuit of the HUD power supply control circuit does not clearly define the component composition and function, it is easy for the ignition signal IGN+ to be not processed thoroughly. For example, failure to divide the voltage may cause high voltage to be directly input to the LDO enable terminal, damaging the LDO; failure to debounce may cause signal jitter to trigger the LDO to be enabled incorrectly; or the ignition signal status may not be effectively transmitted, resulting in abnormal LDO start / stop control and affecting the normal start-up and sleep of the HUD.

[0036] Based on this, the ignition signal detection circuit includes a voltage divider resistor R207, a voltage divider resistor R208, a de-jitter capacitor C39, and a Zener diode D2. The cathode of the Zener diode is connected to the ignition signal IGN+, and the anode, after receiving voltage, is connected to one end of R207. The other end of the voltage divider resistor R207 is connected to one end of the voltage divider resistor R208, one end of the de-jitter capacitor C39, and the base of the transistor Q4. The other end of the voltage divider resistor R208 is grounded, the other end of the de-jitter capacitor C39 is grounded, and the base of the transistor Q4 is connected to the enable terminal of the LDO. The voltage divider resistors R207 and R208 form a voltage divider circuit, and the de-jitter capacitor C39 is used to eliminate the jitter interference of the ignition signal IGN+.

[0037] This technical solution achieves precise processing of the ignition signal IGN+ by clearly defining the component composition and function of each component in the ignition signal detection circuit: voltage divider resistors R207 and R208 form a voltage divider circuit, which divides the high voltage of the automotive ignition signal IGN+ to a safe voltage range that the LDO enable terminal EN can withstand, avoiding direct high voltage input that could damage the LDO enable terminal; de-jitter capacitor C39 eliminates voltage jitter of the ignition signal IGN+ during switching through its charging and discharging characteristics, ensuring the stability of the signal input to the LDO enable terminal EN; diode D2 has unidirectional conductivity, which can prevent the current of the LDO enable terminal EN from flowing back into the ignition signal detection circuit, avoiding signal interference between circuits or component damage.

[0038] The technical effects achieved by the above solution include: the voltage divider effect of resistors R207 and R208 ensures that the voltage of the ignition signal IGN+ matches the input requirements of the LDO enable terminal EN, avoiding damage to the LDO enable terminal by high voltage and improving the safety of circuit components; the debouncing capacitor C39 eliminates jitter interference of the ignition signal, preventing the LDO from being falsely started or turned off due to signal jitter, ensuring the accuracy of LDO start / stop control, and thus ensuring the reliability of HUD start and sleep modes; the unidirectional conductivity of diode D2 blocks reverse current, avoiding signal crosstalk between the ignition signal detection circuit and the LDO enable terminal EN, maintaining the independent and stable operation of each part of the circuit, and reducing HUD function abnormalities caused by inter-circuit interference; the clear component composition and function make the ignition signal detection circuit feasible, and those skilled in the art can directly build the circuit according to the component parameters to achieve accurate processing of the ignition signal without additional debugging.

[0039] In the existing technology, if the transistor of the HUD power supply control circuit is not specified in terms of model and base current limiting resistor value, a mismatch between the transistor and the MCU output signal is likely to occur. For example, the MCU output voltage of 3.3V may not be able to turn on the transistor, or the base current may be too large, causing the transistor to be damaged. This will affect the level control of the LDO enable terminal EN, making it impossible for the MCU to effectively regulate the LDO state, resulting in the failure of the HUD sleep and wake-up functions.

[0040] Based on this, the transistor Q2 is model 3904, and the base current limiting resistor has a resistance value of 1KΩ. This technical solution ensures compatibility between the transistor Q2 and the MCU's control signals by specifying the transistor model and the base current limiting resistor value: the 3904 transistor is an NPN small-signal transistor with a low base forward voltage, which can be effectively driven by the 3.3V voltage output by the MCU, achieving on / off state switching; the 1KΩ base current limiting resistor limits the current output from the MCU to the base of transistor Q2 within a safe range. According to Ohm's law, current I = (input voltage V - forward voltage Vbe) / resistance R. When the MCU outputs 3.3V, the base current is approximately (3.3V - 0.7V) / 1KΩ = 2.6mA), preventing excessive base current from damaging transistor Q2 and ensuring sufficient base current to saturate and conduct transistor Q2, thereby reliably pulling down the LDO enable terminal EN.

[0041] The technical effects achieved by the above solution include: the selection of the 3904 transistor ensures that the 3.3V control signal output by the MCU can effectively drive the transistor to conduct, avoiding control failure caused by excessive transistor conduction voltage, and ensuring the reliability of the MCU's control over the LDO state; the setting of the 1KΩ base current limiting resistor not only prevents excessive base current from damaging the transistor, but also ensures that the transistor can saturate and conduct, so that the LDO enable terminal EN can be reliably pulled low, realizing the stable shutdown and static working state switching of the LDO, thereby ensuring the normal implementation of the HUD sleep function; the clear transistor model and resistor value make the circuit repeatable, and those skilled in the art can directly select the corresponding components to build the circuit without repeatedly debugging component parameters, reducing the R&D cycle and cost, while improving the consistency and stability of the circuit.

[0042] In the prior art, if the output voltage of the CAN_INH signal terminal of the HUD power supply control circuit is not clearly defined when the ignition signal IGN+ is de-energized and the CAN bus is working, the output voltage of the CAN_INH signal terminal is prone to being insufficient, which cannot effectively enable the LDO. As a result, the LDO stops outputting after the ignition signal is de-energized, the HUD loses power supply, and thus interrupts the transmission and processing of CAN bus related data, affecting the CAN bus communication function of the automotive electronic system.

[0043] Based on this, when the ignition signal IGN+ is de-energized and the CAN bus is active, the CAN_INH signal terminal outputs a 5V high level to the LDO's enable terminal EN. This technical solution ensures that the LDO enable terminal EN receives a sufficient high-level signal by clearly defining the output voltage of the CAN_INH signal terminal under specific operating conditions: the ignition signal IGN+ is de-energized and the CAN bus is active. The 5V high level matches the enable voltage threshold of the LDO enable terminal EN. Typically, the enable voltage threshold of automotive-grade LDOs is lower than 5V, which reliably triggers the LDO to maintain its enabled state and continuously outputs 3.3V to the MCU, avoiding LDO disabling due to insufficient output voltage at the CAN_INH signal terminal.

[0044] The technical effects achieved by the above solution include: the explicit 5V high-level output ensures that the LDO remains enabled when the ignition signal IGN+ is powered off and the CAN bus is working, maintaining a stable power supply to the MCU, ensuring the HUD's continuous reception and processing of CAN bus data, avoiding CAN bus communication interruption, and ensuring the normal functioning of the CAN bus in the automotive electronic system; the explicit output voltage value makes the control logic of the CAN_INH signal terminal feasible, and those skilled in the art can design the drive circuit of the CAN_INH signal terminal based on this voltage value to ensure that it stably outputs a 5V high level under specific operating conditions, improving the accuracy and reliability of the circuit design; this voltage setting is precisely matched with the LDO enabling requirements, avoiding damage to the LDO enabling terminal due to excessive voltage or enabling failure due to excessively low voltage, thus balancing circuit safety and functional reliability.

[0045] In the existing technology, if the MCU of the HUD power supply control circuit does not specify the output voltage of the MCU-OFF / ON pin when entering sleep mode, it is easy to have insufficient output voltage, which will prevent the transistor Q2 from conducting. As a result, the LDO enable pin EN cannot be pulled low, the LDO continues to output, the HUD cannot enter sleep mode, the standby power consumption remains high, and the car battery power is wasted; or the output voltage is too high, which will cause the base current of the transistor Q2 to be too large, damaging the transistor.

[0046] Based on this, when the MCU needs to enter sleep mode, the voltage output by the MCU-OFF / ON pin of the MCU is 3.3V. This technical solution ensures the reliable conduction of transistor Q2 by specifying the output voltage of the MCU-OFF / ON pin when the MCU is triggered in sleep mode: the 3.3V voltage matches the base conduction requirement of transistor Q2, and combined with the 1KΩ base current limiting resistor, a suitable base current can be generated. According to Ohm's law, the current I = (input voltage V - conduction voltage Vbe) / resistance R, which is approximately (3.3V - 0.7V) / 1KΩ = 2.6mA), causing transistor Q2 to saturate and conduct, thereby pulling the LDO enable pin EN low to a low level and triggering the LDO to enter a static working state.

[0047] The technical effects achieved by the above solution include: the 3.3V output voltage ensures reliable conduction of transistor Q2, effectively pulling the LDO enable pin EN low, stopping the LDO output and entering a static working state, allowing the HUD to smoothly enter sleep mode, achieving ultra-low power standby, and reducing the power loss of the car battery; this voltage value is consistent with the standard output voltage of the MCU, and the high level output of the I / O port of most automotive-grade MCUs is 3.3V, eliminating the need for additional voltage conversion circuit design, simplifying the circuit structure, and reducing R&D costs; the specific output voltage avoids transistor conduction failure or damage due to voltage deviation, ensuring the stability of the HUD sleep function and the safety of circuit components, and improving the overall circuit reliability.

[0048] In the existing technology, if the trigger temperature of the over-temperature protection circuit of the LDO in the power supply control circuit of HUD is not clearly defined, the trigger temperature is easily set too high, causing the LDO to work continuously at high temperature and be damaged; or the trigger temperature is set too low, causing the protection to be triggered falsely within the normal operating temperature range, resulting in the LDO frequently stopping output, HUD operation interruption, and affecting the user experience.

[0049] Based on this, the trigger temperature of the LDO's over-temperature protection circuit is a preset temperature value, which does not exceed 150°C, to prevent the LDO from being damaged due to excessive temperature. This technical solution balances the LDO's operating temperature range and safety protection requirements by limiting the trigger temperature of the LDO's over-temperature protection circuit to no more than 150°C: the 150°C upper limit covers common high-temperature operating conditions of automotive electronic systems, such as the temperature near the engine compartment, which usually does not exceed 120°C, ensuring that the LDO will not falsely trigger over-temperature protection within its normal operating temperature range; at the same time, when the LDO's temperature approaches or exceeds 150°C due to abnormal operating conditions, the over-temperature protection circuit is triggered in time to prevent the LDO from burning out due to high temperature.

[0050] The technical effects achieved by the above solution include: a trigger temperature setting not exceeding 150℃ ensures stable operation of the LDO under normal high-temperature automotive conditions, avoiding HUD operation interruption caused by false triggering of over-temperature protection, and improving the environmental adaptability and reliability of the HUD; when the LDO experiences abnormally high temperatures, the over-temperature protection circuit is activated in time to cut off the LDO output or limit its operating state, preventing LDO damage, extending LDO lifespan, and reducing HUD maintenance costs; a clear upper limit for the trigger temperature provides a basis for LDO selection and circuit heat dissipation design, allowing those skilled in the art to select an LDO with matching heat dissipation performance or design a suitable heat dissipation structure based on this temperature value, ensuring that the LDO operating temperature is controlled within a safe range, and further improving circuit stability.

[0051] In the prior art, if a current-limiting resistor is not set between the car battery and the LDO input terminal of the HUD power supply control circuit, the car battery is easily damaged by overcurrent when a short circuit or abnormally large current occurs at the LDO input terminal; if a diode is not set between the CAN_INH signal terminal and the LDO enable terminal EN, the current of the LDO enable terminal EN is likely to flow back into the CAN_INH signal terminal, interfering with the normal operation of the CAN bus, or even damaging the driving element of the CAN_INH signal terminal.

[0052] Based on this, a diode D4 is connected in series between the CAN_INH signal terminal and the LDO enable terminal EN. The type of D4 is S-L1SS355T1G. The diode D4 is used to prevent reverse current from flowing into the CAN_INH signal terminal.

[0053] This technical solution constructs two key circuit protections by setting a current-limiting resistor R104 between the car battery and the LDO input terminal, and a diode D4 between the CAN_INH signal terminal and the LDO enable terminal EN. The 10Ω current-limiting resistor R104 can limit the current magnitude according to Ohm's law when a short circuit or abnormally large current occurs at the LDO input terminal. Current I = Voltage V / Resistance R. For example, when the car battery outputs a voltage of 12V, the short-circuit current is approximately 12V / 10Ω = 1.2A, preventing the car battery from being damaged due to overcurrent. The S-L1SS355T1G diode D4 has unidirectional conductivity, allowing the current from the CAN_INH signal terminal to flow only to the LDO enable terminal EN, blocking the reverse current, and preventing the current from the LDO enable terminal EN from flowing into the CAN_INH signal terminal.

[0054] The technical effects achieved by the above solution include: the current-limiting resistor R104 effectively limits the abnormal current at the LDO input terminal, protecting the automotive battery from overcurrent impact, while preventing excessive current from damaging the LDO input terminal, thus improving the circuit's overcurrent protection capability; the unidirectional conductivity of diode D4 prevents reverse current interference with the CAN_INH signal terminal, ensuring the normal communication function of the CAN bus, avoiding damage to the CAN_INH signal terminal driving components due to reverse current, and improving the reliability of the CAN bus in the automotive electronic system; the clearly defined resistor values ​​and diode models make the circuit protection design feasible, allowing those skilled in the art to directly select corresponding components to build the protection circuit without additional debugging, reducing R&D difficulty and cost; the two protection designs target the risk points of the power supply link and signal control link respectively, comprehensively improving the safety and stability of the HUD power supply control circuit and reducing the probability of failure.

[0055] The embodiments and / or implementation methods described above are merely preferred embodiments and / or implementation methods for implementing the present utility model, and are not intended to limit the implementation methods of the present utility model in any way. Any person skilled in the art can make some modifications or alterations to other equivalent embodiments without departing from the scope of the technical means disclosed in the present utility model, but these should still be regarded as the same technology or embodiment as the present utility model.

[0056] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this application. The above descriptions are only preferred embodiments of this application. It should be noted that due to the limitations of textual expression, while there are objectively infinite specific structures, those skilled in the art can make several improvements, modifications, or changes without departing from the principles of this application, and can also combine the above technical features in an appropriate manner. These improvements, modifications, changes, or combinations, or the direct application of the inventive concept and technical solution to other situations without modification, should all be considered within the scope of protection of this application.

Claims

1. A HUD self-lock and ultra-low power standby current control circuit, characterized in that, include: The system includes an automotive battery, an MCU, an automotive-grade low-dropout linear regulator (LDO), an ignition signal detection circuit, a transistor Q2, and a CAN_INH signal terminal. The automotive battery outputs 12V to the input of the LDO. The output of the LDO is connected to the MCU to provide a 3.3V operating voltage. The input of the ignition signal detection circuit is connected to the ignition signal IGN+. The output of the ignition signal detection circuit is connected to the enable terminal EN of the LDO. The CAN_INH signal terminal is also connected to the enable terminal EN of the LDO. The collector of transistor Q2 is connected to the enable terminal EN of the LDO. The base of transistor Q2 is connected to the MCU-OFF / ON pin of the MCU through a base-limiting current resistor. The emitter of transistor Q2 is grounded. The ignition signal detection circuit divides and debouncing the input ignition signal IGN+ and outputs a high level to the enable terminal EN of the LDO, enabling the LDO to start and output power. The ignition signal IGN+ is powered off, and the CAN_INH signal outputs a high level to the enable pin EN of the LDO, causing the LDO to maintain a 3.3V output to the MCU for self-locking. When the MCU needs to enter sleep mode, the MCU-OFF / ON pin of the MCU outputs a voltage that turns on the transistor Q2, which pulls the enable pin EN of the LDO low. The LDO stops outputting and enters a static operating state. The static current of the LDO in the static operating state meets the ultra-low power consumption requirements. When the MCU needs to be woken up, the ignition signal IGN+ is processed by the ignition signal detection circuit and outputs a high level to the MCU. The MCU-OFF / ON pin of the MCU outputs a voltage that turns off the transistor Q2, and the enable pin EN of the LDO returns to a high level. The LDO restarts and outputs a 3.3V voltage to the MCU.

2. The HUD self-lock and ultra-low standby current control circuit according to claim 1, characterized in that, The LDO model is SCT71403F33Q-TWDR.

3. The HUD self-lock and ultra-low standby current control circuit according to claim 2, characterized in that, The LDO has an input voltage range of 3V to 40V, a fixed output voltage of 3.3V, and a maximum output current of 300mA.

4. The HUD self-lock and ultra-low standby current control circuit according to claim 3, characterized in that, The LDO integrates an overcurrent protection circuit, an overtemperature protection circuit, and an undervoltage lockout circuit. The overcurrent protection circuit supports short-circuit protection, and the undervoltage lockout circuit is used to cut off the output of the LDO when the input voltage of the LDO is lower than a preset threshold that ensures the stable operation of the LDO.

5. The HUD self-lock and ultra-low standby current control circuit according to claim 4, characterized in that, The ignition signal detection circuit includes voltage divider resistors R207 and R208, a de-jitter capacitor C39, and a Zener diode D2. The cathode of the Zener diode is connected to the ignition signal IGN+, and the anode, after receiving voltage, is connected to one end of R207. The other end of the voltage divider resistor R207 is connected to one end of the voltage divider resistor R208, one end of the de-jitter capacitor C39, and the base of the transistor Q4. The other end of the voltage divider resistor R208 is grounded, and the other end of the de-jitter capacitor C39 is grounded. The base of the transistor Q4 is connected to the enable terminal of the LDO. The voltage divider resistors R207 and R208 form a voltage divider circuit, and the de-jitter capacitor C39 is used to eliminate the jitter interference of the ignition signal IGN+.

6. The HUD self-lock and ultra-low standby current control circuit according to claim 5, characterized in that, The transistor Q2 is a 3904, and the base current limiting resistor has a resistance of 1KΩ.

7. The HUD self-lock and ultra-low standby current control circuit according to claim 6, characterized in that, When the ignition signal IGN+ is de-energized and the CAN bus is in operation, the CAN_INH signal terminal outputs a 5V high level to the LDO's enable terminal EN.

8. The HUD self-lock and ultra-low standby current control circuit according to claim 7, characterized in that, When the MCU needs to enter sleep mode, the voltage output by the MCU-OFF / ON pin of the MCU is 3.3V.

9. The HUD self-lock and ultra-low standby current control circuit according to claim 8, characterized in that, The over-temperature protection circuit of the LDO is triggered at a preset temperature value, which does not exceed 150°C, to prevent the LDO from being damaged due to excessive temperature.

10. The HUD self-lock and ultra-low power standby current control circuit according to claim 9, characterized in that, A diode D4 is connected in series between the CAN_INH signal terminal and the LDO enable terminal EN. The type of D4 is S-L1SS355T1G. The diode D4 is used to prevent reverse current from flowing into the CAN_INH signal terminal.

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