An intelligent low-side power switch circuit applied to a vehicle

Abstract

The application provides a kind of intelligent low-side power switch circuit applied to vehicle, and the intelligent low-side power switch circuit is provided with power interface, ground interface, switch interface and output interface, and the intelligent low-side power switch circuit comprises: control module, control module connects switch interface and power interface;Field effect transistor, field effect transistor is provided with gate, drain and source, gate is connected to power interface and switch interface by control module, drain connects output interface, and source connects ground interface;Wherein, control module controls the conduction and shutdown of field effect transistor according to the logic level signal of switch interface, to further control the communication state of output interface and ground interface, and realizes protection and detection function by control module.The application solves the technical problems that the existing large current low-side control scheme generally adopts the mode of special low-side driving chip + MOSFET, which is extremely complex, high in cost and difficult to be widely applied.

Description

Technical Field

[0001] This invention relates to the field of vehicle electronics and electrical technology, and more specifically, to an intelligent low-side power switching circuit for use in vehicles. Background Technology

[0002] With the rapid development of the automotive industry, the level of vehicle electrification and intelligence is constantly improving, which puts forward higher requirements for the reliability, intelligence and cost control of vehicle electrical systems. Due to cost and reliability reasons, the automotive industry generally adopts a single-wire power supply and negative ground electrical design: the battery and generator or DC / DC are directly connected in parallel, the positive terminal of the power supply is used to supply power to the whole vehicle, and the negative terminal of the battery is directly connected to the metal part of the vehicle body to ground, forming a complete power supply circuit.

[0003] Based on this power supply method in vehicles, high-side power switches are widely used in vehicle electrical systems, and corresponding chip solutions (such as HSD chips) are becoming increasingly mature. HSD chips can simultaneously replace traditional relays and fuses, acting as intelligent high-side power switches to power electrical equipment or directly control vehicle loads, meeting the needs of most automotive scenarios. However, in certain specific applications, low-side power switches remain irreplaceable, but currently there are very few low-side switch solutions or dedicated chips in the industry, especially high-current intelligent low-side power switches, which lack mature products.

[0004] Furthermore, the relevant technologies have at least one of the following problems: existing high-current low-side control schemes generally use a dedicated low-side driver chip + MOSFET approach, but the low-side driver chip usually does not have dedicated protection and detection functions, and various detection and protection functions need to be added to be used as an intelligent low-side power switch. This makes the scheme extremely complex, costly, and difficult to promote and apply on a large scale. Summary of the Invention

[0005] This invention addresses the technical problem that existing high-current low-side control schemes generally employ a dedicated low-side driver chip + MOSFET approach, which results in extremely complex schemes, high costs, and difficulties in large-scale application.

[0006] To address the aforementioned problems, this invention provides an intelligent low-side power switching circuit for vehicles. The intelligent low-side power switching circuit includes a power interface, a ground interface, a switching interface, and an output interface. The circuit comprises: a control module connected to the switching interface and the power interface; and a field-effect transistor (FET), which has a gate, a drain, and a source. The gate is connected to the power interface and the switching interface via the control module, the drain is connected to the output interface, and the source is connected to the ground interface. The control module controls the on / off state of the FET based on the logic level signal of the switching interface, thereby controlling the connection state of the output interface and the ground interface. Furthermore, the control module implements protection and detection functions.

[0007] Compared with existing technologies, the technical effects achieved by this solution are as follows: This application uses logic level signals to realize the on / off control of field-effect transistors, which is simple and intuitive. It can directly interface with the output signals of the vehicle controller without the need for additional signal conversion modules, resulting in lower costs. Through standardized power interfaces, ground interfaces, switch interfaces, and output interfaces, the connection difficulty with vehicle electrical equipment is reduced, making it suitable for various low-side control scenarios such as vehicle lights, motors, and air conditioning. This circuit can realize intelligent low-side power switching functions at low cost through the control module. The intelligent functions include overcurrent protection, overheat protection, short circuit protection, overvoltage protection, undervoltage protection, short circuit self-locking, and automatic recovery after fault clearance, which greatly improves the stability, reliability, and durability of the low-side power switch in the complex environment of the vehicle.

[0008] In one embodiment of the present invention, the control module includes: a first transistor having a first base, a first collector, and a first emitter, the first base being connected to a switch interface via a first resistor, and the first emitter being grounded; and a second transistor having a second base, a second collector, and a second emitter, the second base being connected to the first collector via an undervoltage protection unit, the second emitter being connected to a power interface, and the second collector being connected to the gate via a seventh resistor.

[0009] Compared with existing technologies, the technical effects achieved by this solution are as follows: A two-stage driving structure of "first transistor + second transistor" is adopted, with the first and second transistors working together to control the conduction and turn-off of the field-effect transistor; the cooperation between the undervoltage protection unit and the second transistor provides hardware support for the subsequent implementation of undervoltage protection, preventing abnormal operation of the field-effect transistor due to excessively low power supply voltage; the seventh resistor acts as a current limiter, preventing damage to the gate of the field-effect transistor due to excessive current and extending the service life of the core device.

[0010] In one embodiment of the present invention, the control module further includes: a fourth transistor, the fourth transistor having a fourth base, a fourth collector and a fourth emitter, the fourth base being connected to the first collector through a charging unit, the fourth emitter being connected to the output interface, and the fourth collector being connected to the gate through a short-circuit protection unit.

[0011] Compared with existing technologies, the technical effects achieved by this solution are as follows: The emitter of the fourth transistor is connected to the output interface, which can sense the potential change of the output interface in real time. When the output is short-circuited, the fourth transistor quickly turns on, triggering the short-circuit protection unit to act, forming a complete short-circuit protection trigger link; the charging unit isolates the control signal of the first transistor from the trigger signal of the fourth transistor, avoiding interference of the protection function with the normal switching control logic, and ensuring stable operation of the circuit when there is no fault; through the linkage between the fourth transistor and the short-circuit protection unit, hardware support is provided for the short-circuit self-locking function, ensuring that the field-effect transistor remains in the off state when the short-circuit fault is not eliminated, preventing the fault from expanding.

[0012] In one embodiment of the present invention, the short-circuit protection unit includes: a fifth transistor and a first diode; the fifth transistor has a fifth base, a fifth collector and a fifth emitter, the fifth base is connected to the fourth collector in sequence through an eighth resistor and the first diode, the fifth collector is connected to the gate and the fifth emitter is grounded; wherein, the first diode has a first anode and a first cathode, the first anode is connected to the fourth collector and the first cathode is connected to the fifth base through the eighth resistor.

[0013] Compared with existing technologies, the technical effects achieved by this technical solution are as follows: the fifth transistor acts as the actuator for short-circuit protection, which is used to forcibly turn off the field-effect transistor when the output is short-circuited; the eighth resistor plays a current-limiting role, stabilizing the base current of the fifth transistor, ensuring that the fifth transistor can quickly turn on when short-circuit triggered and reliably turn off when there is no fault, thus avoiding false triggering of protection.

[0014] In one embodiment of the present invention, the short-circuit protection unit further includes a ninth resistor, one end of which is connected to the fifth base, and the other end of which is grounded.

[0015] Compared with existing technologies, the technical effects achieved by this solution are as follows: by using the voltage divider between the ninth and eighth resistors, the conduction threshold voltage of the fifth transistor can be precisely set, ensuring that it only conducts when a valid short-circuit trigger signal is input, thereby further improving the accuracy of the protection logic.

[0016] In one embodiment of the present invention, the charging unit has a first terminal and a second terminal. The first terminal is connected to a first collector, and the second terminal is grounded. The charging unit includes a fourth resistor and a first capacitor connected in series. An adjustment node is provided between the fourth resistor and the first capacitor, and the adjustment node is connected to a fourth base. The fourth resistor is located between the first terminal and the adjustment node, and the first capacitor is located between the adjustment node and the second terminal.

[0017] Compared with the existing technology, the technical effect achieved by adopting this technical solution is as follows: The fourth resistor and the first capacitor form a charging unit. When the output interface is pulled high due to leakage current or low impedance, the first capacitor charges to maintain the potential of the fourth base, avoids the fourth transistor from being mis-conducted, ensures that the field-effect transistor can start normally, and effectively distinguishes between normal high potential and short-circuit fault high potential.

[0018] In one embodiment of the present invention, the undervoltage protection unit includes a third resistor and a third diode connected in series. The third diode has a third anode and a third cathode. The third anode is connected to the first collector, and the third cathode is connected to the second base through the third resistor.

[0019] Compared with existing technologies, the technical effects achieved by this technical solution are as follows: The third diode, as a Zener diode, has a fixed breakdown voltage characteristic. When the voltage on the third diode is higher than the breakdown voltage, the third diode breaks down and conducts, providing the conduction condition for the second transistor; when the voltage on the third diode is lower than the breakdown voltage, the third diode is cut off, cutting off the driving circuit of the second transistor and realizing accurate triggering of undervoltage protection; the third resistor, as a current-limiting resistor, limits the base current of the second transistor.

[0020] In one embodiment of the present invention, the control module further includes: a second resistor, one end of which is connected to the first base and the other end of which is grounded; a fifth resistor, one end of which is connected to the second base and the other end of which is connected to the power interface; and a sixth resistor, one end of which is connected to the fourth base and the other end of which is connected to the output interface.

[0021] Compared with existing technologies, the technical effects achieved by this technical solution are as follows: the second resistor acts as a pull-down resistor for the first transistor, ensuring that the first base is grounded when there is no switch control signal, thus reliably turning off the first transistor; the fifth resistor acts as a pull-up resistor for the second transistor, ensuring that the second base is connected to the power supply when the first transistor is turned off, thus reliably turning off the second transistor; the sixth resistor is connected to the base and emitter of the fourth transistor, providing a pull-up to the fourth base and preventing the fourth base from being left floating, which could lead to false turn-on.

[0022] In one embodiment of the present invention, the control module further includes an NTC resistor, one end of which is connected to the gate and the other end of which is grounded; wherein the NTC resistor and the field-effect transistor are arranged adjacent to each other.

[0023] Compared with existing technologies, the technical effects achieved by this solution are as follows: When the load current exceeds the rated value, the power consumption of the field-effect transistor increases, the temperature rises, and the resistance of the NTC resistor decreases significantly with the increase in temperature. Through the voltage division effect with the seventh resistor, the gate drive voltage of the field-effect transistor drops to the turn-off threshold, and the field-effect transistor automatically turns off, avoiding device damage caused by overcurrent. The NTC resistor is placed adjacent to the field-effect transistor, which can detect the temperature of the field-effect transistor in real time. Even without overcurrent, when the ambient temperature is too high or the field-effect transistor operates for a long time and the temperature exceeds the standard, the resistance of the NTC resistor decreases, which also triggers the field-effect transistor to turn off, thus achieving dual temperature protection.

[0024] In one embodiment of the present invention, the control module further includes a second diode, which has a second anode and a second cathode, the second anode being grounded and the second cathode being connected to a gate.

[0025] Compared with existing technologies, the technical effects achieved by adopting this technical solution are as follows: the second diode acts as a Zener diode, the second cathode is connected to the gate of the field-effect transistor, and the second anode is grounded, providing voltage regulation protection for the gate of Q3, preventing overvoltage damage to the gate of Q3, effectively resisting voltage fluctuations and instantaneous overvoltage impacts in the vehicle power system, extending the service life of the field-effect transistor, and reducing the failure rate of the circuit.

[0026] By adopting the technical solution of the present invention, the following technical effects can be achieved:

[0027] (1) This application realizes the on / off control of the field-effect transistor based on logic level signals. The control method is simple and intuitive. It can be directly connected to the output signal of the vehicle controller without the need for an additional signal conversion module, and the cost is low.

[0028] (2) The circuit can realize the intelligent low-side power switch function at low cost through the control module. The intelligent functions include overcurrent protection, overheat protection, short circuit protection, overvoltage protection, undervoltage protection, short circuit self-locking, and automatic recovery after fault clearance, which greatly improves the stability, reliability and durability of the low-side power switch in the complex environment of the vehicle.

[0029] (3) By standardizing the power interface, ground interface, switch interface and output interface, the difficulty of connecting with vehicle electrical equipment is reduced, and it is compatible with various low-side control scenarios such as vehicle lights, motors, and air conditioners. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings to be used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a circuit diagram of an intelligent low-side power switching circuit for vehicles, provided in Embodiment 1 of the present invention.

[0032] Explanation of reference numerals in the attached figures:

[0033] 11. Power interface; 12. Ground interface; 13. Switch interface; 14. Output interface. Detailed Implementation

[0034] To make the above-mentioned objectives, features, and advantages of the present invention more apparent and understandable, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1

[0036] See Figure 1 This is a circuit diagram of an intelligent low-side power switch circuit for vehicles provided in the first embodiment of the present invention. The intelligent low-side power switch circuit has a power interface 11, a ground interface 12, a switch interface 13, and an output interface 14. The intelligent low-side power switch circuit includes a control module and a field-effect transistor. The control module is connected to the switch interface 13 and the power interface 11. The field-effect transistor has a gate, a drain, and a source. The gate is connected to the power interface 11 and the switch interface 13 via the control module, the drain is connected to the output interface 14, and the source is connected to the ground interface 12. The control module controls the conduction and cutoff of the field-effect transistor according to the logic level signal of the switch interface 13, thereby controlling the connection state of the output interface 14 and the ground interface 12. The control module also realizes protection and detection functions.

[0037] In one specific embodiment, Q3 is a field-effect transistor, specifically an NMOSFET. The power interface 11 of the intelligent low-side power switch circuit is connected to the power supply, the ground interface 12 is grounded, and the switch interface 13 serves as the circuit's switching control. When Q3 is on, the output interface 14 is at a low level. The output interface 14 is directly connected to the negative terminal of the electrical equipment requiring negative control, i.e., the equipment's ground. The circuit uses logic levels for switching control. The power interface 11 supplies power to the entire circuit. This application reduces the connection requirements with vehicle-mounted electrical equipment through standardized power interface 11, ground interface 12, switch interface 13, and output interface 14. This design addresses the complexity of low-side control scenarios, including vehicle lighting, motors, and air conditioning. Q3 acts as a low-side MOSFET switch, and its on / off state controls whether the output interface 14 is connected to ground. When the logic level signal of the switch interface 13 is high, Q3 is on, and the output interface 14 is connected to the ground interface 12. When the logic level signal of the switch interface 13 is low or there is no signal, Q3 is off, and the output interface 14 has high impedance. This application implements on / off control of the field-effect transistor based on logic level signals. The control method is simple and intuitive, and it can directly interface with the output signal of the vehicle controller without the need for an additional signal conversion module.

[0038] Meanwhile, this circuit, through its control module, can achieve intelligent low-side power switching functionality at low cost. Intelligent functions include overcurrent protection, overheat protection, short-circuit protection, overvoltage protection, undervoltage protection, short-circuit self-locking, and automatic recovery after fault clearance. This significantly improves the stability, reliability, and durability of the low-side power switch in complex vehicle environments. The circuit is built using purely hardware discrete components, with the power switching section implemented using MOSFETs. It eliminates complex dedicated chips and redundant peripheral circuits, completely replacing traditional relays and fuses to achieve intelligent switching and intelligent protection functions, reducing circuit complexity and production costs.

[0039] Preferably, the power input voltage of power interface 11 can support the 12V system of passenger vehicles or the 24V system of commercial vehicles. This depends on the specific hardware circuit component selection, especially the voltage rating of Q3. Generally speaking, for a 12V system, Q3 is selected with a voltage rating of 40V, and for a 24V system, Q3 is selected with a voltage rating of 80V or 100V.

[0040] The driving capability of the circuit depends on the selection of Q3. If a large current drive is required, a MOSFET with a larger current can be selected. For example, if a driving capability of 10A is required, a Q3 with an on-resistance of about 10mΩ can be selected; if the driving capability is 20A, a Q3 with an on-resistance of about 2mΩ can be selected; if the driving capability is 50A, a Q3 with an on-resistance of about 0.5mΩ can be selected, or two 1mΩ MOSFETs can be connected in parallel. If a larger driving current is required, simply increase the number of MOSFETs connected in parallel.

[0041] Furthermore, the control module includes: a first transistor and a second transistor. The first transistor has a first base, a first collector and a first emitter. The first base is connected to the switch interface 13 through a first resistor, and the first emitter is grounded. The second transistor has a second base, a second collector and a second emitter. The second base is connected to the first collector through an undervoltage protection unit, the second emitter is connected to the power interface 11, and the second collector is connected to the gate through a seventh resistor.

[0042] Specifically, Q1 is the first transistor, an NPN transistor; Q2 is the second transistor, a PNP transistor; R1 is the first resistor; and R7 is the seventh resistor. When a logic high level is input to switch interface 13, Q1 will turn on. After Q1 turns on, Q2 will also turn on, driving Q3 to turn on. Q1 and Q2 work together to control the on / off state of Q3. The undervoltage protection unit shuts off the gate pull-up power supply of Q3 when the power supply voltage is below the normal operating range. The gate voltage of Q3 is pulled to ground, and Q3 will automatically turn off, preventing abnormal operation of Q3 due to excessively low power supply voltage. R7 acts as a current-limiting resistor, limiting the current to prevent damage to the gate of Q3 due to excessive current and extending the lifespan of the core components.

[0043] Furthermore, the control module also includes a fourth transistor, which has a fourth base, a fourth collector and a fourth emitter. The fourth base is connected to the first collector through a charging unit, the fourth emitter is connected to the output interface 14, and the fourth collector is connected to the gate through a short-circuit protection unit.

[0044] Specifically, Q4 is the fourth transistor, a PNP transistor. Q4 detects whether the output interface 14 is short-circuited to the power supply, triggering short-circuit protection. The fourth emitter is connected to the output interface 14, allowing real-time sensing of potential changes. When the switch interface 13 receives a high-level logic signal and the output is short-circuited, Q4 quickly turns on, triggering the short-circuit protection unit and forming a complete short-circuit protection trigger chain. The charging unit isolates the control signal of Q1 from the trigger signal of Q4, preventing the protection function from interfering with the normal switching control logic and ensuring stable operation of the circuit when there is no fault. The linkage between Q4 and the short-circuit protection unit provides hardware support for the short-circuit self-locking function, ensuring that Q3 remains off when the short-circuit fault is not eliminated, preventing the fault from escalating. The short-circuit protection unit can quickly respond to short-circuit faults at the output interface 14, triggering protection regardless of whether the fault occurs before or after Q3 turns on, adapting to the complex operating conditions of the vehicle's electrical system.

[0045] Furthermore, the short-circuit protection unit includes: a fifth transistor and a first diode; the fifth transistor has a fifth base, a fifth collector and a fifth emitter, the fifth base is connected to the fourth collector in sequence through an eighth resistor and the first diode, the fifth collector is connected to the gate and the fifth emitter is grounded; wherein, the first diode has a first anode and a first cathode, the first anode is connected to the fourth collector and the first cathode is connected to the fifth base through the eighth resistor.

[0046] Specifically, Q5 is the fifth transistor, an NPN transistor. As the short-circuit protection actuator, Q5, upon conduction, directly pulls the gate of Q3 low to ground, forcing Q3 to turn off, shortening the turn-off response time, and effectively preventing the impact of short-circuit current on the device. D1 is the first diode, employing a unidirectional conduction design, allowing only the short-circuit trigger signal output from Q4 to flow to Q5, preventing reverse current from flowing from Q5 to Q4, avoiding signal interference in the protection loop, and improving the stability of the protection logic. This application, through the "Q4+D1+Q5" link design, forms a closed-loop short-circuit protection mechanism, improving the reliability and anti-interference capability of short-circuit protection, and adapting to the complex electromagnetic environment of vehicle electrical systems. R8 is the eighth resistor, acting as a current-limiting resistor, limiting the base current of Q5, ensuring that Q5 quickly turns on during short-circuit triggering and reliably turns off when there is no fault, avoiding false triggering of the protection.

[0047] The short-circuit protection principle of Q3 is as follows: When the output of Q3 is normal, Q3 is turned on, and the output interface 14 is at a low level. Even if the fourth base of Q4 is pulled low by Q1, because the fourth emitter of Q4 is connected to the output interface 14, and Q3 is low when the output is normal, Q4 cannot be turned on, D1 cannot be turned on, and Q5 is in the cut-off state.

[0048] Furthermore, the short-circuit protection unit also includes a ninth resistor, one end of which is connected to the fifth base, and the other end of which is grounded.

[0049] Specifically, R9 is the ninth resistor; as a pull-down resistor, R9 pulls the fifth base low to ground when there is no short-circuit trigger signal, ensuring that Q5 is reliably turned off and avoiding false turn-on due to the fifth base being floating, thus ensuring the normal operation of Q3; at the same time, by using the voltage divider combination of R8 and R9 to drive Q5, the turn-on threshold voltage of Q5 can be precisely set, ensuring that it only turns on when a valid short-circuit trigger signal is input, further improving the accuracy of the protection logic.

[0050] Furthermore, the charging unit has a first terminal and a second terminal. The first terminal is connected to the first collector, and the second terminal is grounded. The charging unit includes a fourth resistor and a first capacitor connected in series. An adjustment node is provided between the fourth resistor and the first capacitor, and the adjustment node is connected to the fourth base. The fourth resistor is located between the first terminal and the adjustment node, and the first capacitor is located between the adjustment node and the second terminal.

[0051] Specifically, R4 is the fourth resistor, and C1 is the first capacitor. R4 limits the base current of Q4 and forms an RC circuit with C1 to adjust the short-circuit protection response time. When the output interface 14 is pulled high due to leakage current or low impedance, C1 charges to maintain the potential of the fourth base, preventing Q4 from being falsely turned on and ensuring that Q3 can start normally, effectively distinguishing between normal high potential and short-circuit fault high potential. When Q3 is short-circuited to the power supply, two cases need to be considered: before Q3 is turned on and after Q3 is turned on.

[0052] Before Q3 turns on, that is, before the entire circuit is turned on, if output interface 14 is short-circuited to the power supply, after a logic high level is input to switch interface 13, Q1 will turn on, followed by Q2 and then Q3. However, the conduction of Q3 will only last for a very short time. After C1 discharges, the fourth emitter is now at the power supply voltage, and the fourth base is pulled low by R4. Q4 will immediately turn on, turning on Q5 through D1, and Q5 will immediately turn off Q3. During this period, because the output of Q3 is short-circuited to the power supply, Q3 will withstand a huge short-circuit current. The length of this period depends on the time constant of R4 and C1. In practical applications, it can be set to about 10µs. A short-circuit current of 10µs is usually tolerable for Q3.

[0053] Capacitor C1 has two important functions: ①. Before Q1 is turned on, if output interface 14 is pulled high, whether due to a short circuit or leakage current from the load, C1 will be charged to the power supply voltage. If the switch is turned on at this time, Q1 will immediately turn on, followed by Q2 and Q3. Because the base of Q4 is maintained by C1, the voltage of C1 cannot change abruptly, and the base of Q4 will not be pulled low immediately. The voltage of C1 needs to be discharged to ground through R4. Before the voltage of C1 drops to the level required for Q4 to turn on, Q3 turns on first, and the emitter of Q4 is pulled low, so Q4 cannot turn on again. Unless output interface 14 is actually short-circuited to the power supply, Q3 cannot pull output interface 14 low. In this case, Q4 will immediately turn on, forcibly pulling Q3 low, thus achieving the short-circuit protection function. ②. Ensure that Q2 conducts before Q4 when there is a high output voltage, thus ensuring the normal opening of Q3: Because Q3 is a low-side switch, if the leakage current of the electrical equipment is large or the equipment impedance is low, the drain of Q3, i.e., output interface 14, will be pulled high before Q3 conducts, meaning the fourth emitter is high; at this time, if there is no C1, once the circuit switch input is high, Q1 will conduct, and Q2 and Q4 will conduct almost simultaneously; if Q4 conducts first, Q5 will pull the gate voltage of Q3 low, and even if Q2 conducts, Q3 will not be able to conduct; unless Q2 conducts before Q4, after Q2 conducts, Q3 will immediately conduct, pulling the output low, and the emitter of Q4 will also be pulled low, at which point Q4 will not be able to conduct.

[0054] After Q3 is turned on, that is, after the entire circuit is turned on, if the power supply of output interface 14 is short-circuited at this time, Q4 will be turned on immediately because the fourth base is pulled low by R4. Q5 will be turned on through D1, and Q5 will immediately turn off Q3. At this time, even if the switch control is still effective, Q3 will still be in the off state because Q5 forcibly pulls the gate of Q3 low.

[0055] In summary, whether the output is short-circuited before Q3 is turned on or after Q3 is turned on, the circuit will automatically protect itself and remain in the protected state. Once the circuit is protected, as long as the output short-circuit state persists, even if switch interface 13 is in an active state, Q5 will be in a stable forced low state, ensuring that Q3 is in a stable off state. The short-circuit protection will not fail after Q3 is turned off, preventing Q3 from operating in a switching oscillation state. This is the self-locking function of the protection.

[0056] The principle of the self-reset function after a fault is as follows: the output short circuit protection can only be released after the fault disappears. That is to say, if the switch interface 13 is in an active state and the output interface 14 is short-circuited to the power supply, Q3 will always be in the off state. Once the short circuit fault disappears, Q4 will automatically turn off, followed by Q5 turning off, Q3 will automatically turn on, and the low-side switch function will also automatically reset.

[0057] Preferably, by adjusting the resistance value of R4 and the capacitance value of C1, the time constant of the RC unit can be flexibly set, thereby adjusting the response time of the short circuit protection. This ensures rapid protection when a short circuit fault occurs, while avoiding the impact on normal operation due to excessively fast response, and is suitable for field-effect transistors with different characteristics.

[0058] Furthermore, the undervoltage protection unit includes a third resistor and a third diode connected in series. The third diode has a third anode and a third cathode. The third anode is connected to the first collector, and the third cathode is connected to the second base through the third resistor.

[0059] Specifically, R3 is the third resistor, and D3 is the third diode. The conduction of Q2 depends on the breakdown of D3. After D3 breaks down, R3 is pulled low, and Q2 conducts. As the power supply voltage input to power interface 11 decreases, the voltage across D3 also decreases. When the voltage drops below the breakdown voltage of D3, D3 is cut off, Q2 stops conducting, and Q3 is turned off, thus achieving undervoltage protection for Q3. By cutting off the gate drive voltage of Q3, half-conductivity of Q3 under undervoltage conditions is avoided, preventing the device from burning out due to overheating and extending the lifespan of Q3. After the power supply voltage returns to the normal range, D3 automatically breaks down and conducts, and the circuit returns to normal operation without manual intervention, ensuring the continuous and stable operation of the vehicle-mounted electrical equipment.

[0060] Preferably, by selecting D3 with different breakdown voltages, it is possible to adapt to the power supply systems of 12V passenger cars and 24V commercial vehicles, thereby improving the versatility of the circuit.

[0061] Furthermore, the control module also includes: a second resistor, a fifth resistor, and a sixth resistor. One end of the second resistor is connected to the first base, and the other end of the second resistor is grounded. One end of the fifth resistor is connected to the second base, and the other end of the fifth resistor is connected to the power interface 11. One end of the sixth resistor is connected to the fourth base, and the other end of the sixth resistor is connected to the output interface 14.

[0062] Specifically, R2 is the second resistor, R5 is the fifth resistor, and R6 is the sixth resistor. R2 acts as a pull-down resistor for Q1, pulling the first base of Q1 low to ground when there is no switch control signal, preventing false turn-on due to the first base being floating, and ensuring that Q1 is reliably turned off when there is no control signal. R5 acts as a pull-up resistor for Q2, pulling the second base of Q2 high to the power supply voltage when Q1 is turned off, ensuring that Q2 is reliably turned off, cutting off the drive voltage of Q2, and preventing false turn-on of Q2. R6 acts as a pull-up resistor for Q4, keeping the fourth base of Q4 at the same potential as the output interface 14, ensuring that the fourth base and the fourth emitter are at the same potential when there is no short circuit fault, preventing false turn-on due to the fourth base being floating, and improving the stability of the short circuit protection logic.

[0063] Furthermore, the control module also includes an NTC resistor, one end of which is connected to the gate and the other end of which is grounded; wherein the NTC resistor and the field-effect transistor are arranged adjacent to each other.

[0064] Specifically, This is an NTC resistor, or negative temperature coefficient resistor. One end of the NTC resistor is connected to the gate, and the other end is grounded. The NTC resistor is used to monitor the temperature of the field-effect transistor in real time. Because the seventh resistor forms a voltage divider with the NTC resistor, the NTC resistor can be used for over-temperature control of the field-effect transistor gate drive. Over-temperature of the field-effect transistor is usually caused by overcurrent heating, or it may be caused by excessively high ambient temperature. Overcurrent protection means that when the load current exceeds the rated value, the temperature of the field-effect transistor will exceed the rated temperature. The NTC resistor will turn off the field-effect transistor to prevent it from being damaged by overload.

[0065] The gate drive voltage of the field-effect transistor is: , This is the gate drive voltage of the field-effect transistor. This refers to the voltage at power interface 11; the over-temperature protection principle of the field-effect transistor is: because Located near Q3, as the temperature of Q3 gradually increases, The resistance will continue to decrease. It will also decrease; when the temperature of Q3 reaches the set over-temperature threshold, The temperature will drop to the shutdown threshold of Q3, and Q3 will automatically shut down; only when the temperature of Q3 drops to a certain level will it shut down. After rising to a certain resistance value, Only when the voltage rises to its conduction threshold can Q3 be turned on normally, and the field-effect transistor will automatically resume operation without manual intervention, ensuring the continuous operation of the electrical equipment.

[0066] The overcurrent or overload protection principle of Q3 is basically similar to that of overtemperature protection: when Q3 is overloaded, i.e., overcurrent, Q3 will heat up rapidly, causing its temperature to rise quickly. Since it is located near Q3, The resistance value then decreases rapidly, making When the temperature of Q3 reaches the set over-temperature threshold, Q3 will automatically shut down and stop supplying power to prevent Q3 from being damaged due to overcurrent or overheating.

[0067] Furthermore, the control module also includes a second diode, which has a second anode and a second cathode, with the second anode grounded and the second cathode connected to the gate.

[0068] Specifically, D2 is the second diode, and Q3 has a Zener diode D2 at its gate to ground, with a preset fixed breakdown voltage. If the power supply voltage input to power interface 11 increases, the gate voltage of Q3 will also increase. When the gate voltage of Q3 exceeds the breakdown voltage... When Q2 breaks down and conducts, it clamps the gate voltage within a safe range. This ensures that the gate voltage of Q3 will not exceed the safe range, thus achieving overvoltage protection for Q3.

[0069] Preferred, It is usually set at around 10V.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention 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; and these 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 the present invention.

Claims

1. A smart low-side power switching circuit for use in vehicles, characterized in that, The intelligent low-side power switching circuit is provided with a power interface (11), a ground interface (12), a switch interface (13), and an output interface (14). The intelligent low-side power switching circuit includes: A control module, which is connected to the switch interface (13) and the power interface (11); A field-effect transistor, wherein the field-effect transistor has a gate, a drain and a source, the gate is connected to the power interface (11) and the switch interface (13) via the control module, the drain is connected to the output interface (14) and the source is connected to the ground interface (12); The control module controls the on and off of the field-effect transistor according to the logic level signal of the switch interface (13), thereby controlling the connection state of the output interface (14) and the ground interface (12); and the control module realizes protection and detection functions. The control module includes: The first transistor has a first base, a first collector and a first emitter. The first base is connected to the switch interface (13) through a first resistor, and the first emitter is grounded. The second transistor has a second base, a second collector, and a second emitter. The second base is connected to the first collector through an undervoltage protection unit, the second emitter is connected to the power interface (11), and the second collector is connected to the gate through a seventh resistor. The fourth transistor has a fourth base, a fourth collector and a fourth emitter. The fourth base is connected to the first collector of the first transistor through a charging unit. The fourth emitter is connected to the output interface (14). The fourth collector is connected to the gate through a short-circuit protection unit. The charging unit has a first terminal and a second terminal, the first terminal is connected to the first collector, and the second terminal is grounded. The charging unit includes: A fourth resistor and a first capacitor are connected in series, and an adjustment node is provided between the fourth resistor and the first capacitor, the adjustment node being connected to the fourth base. The fourth resistor is located between the first end and the adjustment node, and the first capacitor is located between the adjustment node and the second end.

2. The intelligent low-side power switching circuit according to claim 1, characterized in that, The short-circuit protection unit includes: a fifth transistor and a first diode; The fifth transistor has a fifth base, a fifth collector, and a fifth emitter. The fifth base is connected to the fourth collector in sequence through an eighth resistor and the first diode. The fifth collector is connected to the gate, and the fifth emitter is grounded. The first diode has a first anode and a first cathode. The first anode is connected to the fourth collector, and the first cathode is connected to the fifth base through the eighth resistor.

3. The intelligent low-side power switching circuit according to claim 2, characterized in that, The short-circuit protection unit further includes: The ninth resistor has one end connected to the fifth base and the other end grounded.

4. The intelligent low-side power switching circuit according to claim 1, characterized in that, The undervoltage protection unit includes: A third resistor and a third diode are connected in series. The third diode has a third anode and a third cathode. The third anode is connected to the first collector, and the third cathode is connected to the second base through the third resistor.

5. The intelligent low-side power switching circuit according to claim 1, characterized in that, The control module also includes: A second resistor, one end of which is connected to the first base, and the other end of which is grounded; The fifth resistor has one end connected to the second base and the other end connected to the power interface (11). A sixth resistor, one end of which is connected to the fourth base, and the other end of which is connected to the output interface (14).

6. The intelligent low-side power switching circuit according to claim 1, characterized in that, The control module also includes: An NTC resistor, one end of which is connected to the gate, and the other end of which is grounded; The NTC resistor and the field-effect transistor are arranged adjacent to each other.

7. The intelligent low-side power switching circuit according to claim 1, characterized in that, The control module also includes: The second diode has a second anode and a second cathode, the second anode being grounded and the second cathode being connected to the gate.

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