Low-current LED output driving circuit with low cost and diagnosis function

Abstract

The invention relates to a low-current LED output driving circuit with low cost and a diagnosis function, which comprises a second NPN triode, a first PNP triode, a first diode D1 and a first resistor R1, the positive electrode of the first diode D1 is connected with the positive electrode of a power supply, and the positive electrode and the negative electrode of the first diode D1 are connected with the emitting electrode of the first PNP triode; the first resistor R1 is connected in series between the collector electrode of the first PNP triode and the output port, the base electrode of the second NPN triode is connected with the MCU control port, the collector electrode of the second NPN triode is connected with the base electrode of the first PNP triode, the emitter electrode of the second NPN triode is grounded, and the other end of the first resistor R1 is connected with the LED output port. Compared with an intelligent power chip for driving the LED, the low-current LED output driving circuit with the low cost and the diagnosis function has the obvious cost advantage, has the function of preventing reverse connection of a power supply and the function of limiting current during short circuit, can meet the requirement of a vehicle gauge electrical load test, and is achieved at low cost.

Description

Technical Field

[0001] The present invention relates to the field of automotive electronic control technology, in particular to the field of vehicle-mounted low-power LED output drive, and specifically refers to a low-cost low-current LED output drive circuit with a diagnostic function. Background Art

[0002] Many lights in cars are LED lights. LEDs are small in size and have low drive current, so they are widely used in car environments. Car LEDs are mostly used for interior lighting, and most of these LEDs are driven and controlled by the body controller.

[0003] When designing the LED drive circuit of the body controller, low-power components are used to build the output circuit, and the fault conditions of short circuit and open circuit at the output port must also be considered. When a fault occurs, the circuit can withstand the fault conditions of short circuit to ground and short circuit to power supply, and diagnose the fault condition in time and report it. When the output port is short-circuited, the output needs to be turned off in time to avoid damage to the control circuit.

[0004] Today's automobile interiors are diverse, and the number of interior lamps is increasing, most of which are LED lamps. Therefore, the output ports of the body controller are increasing, and a low-cost LED output driver circuit with diagnostic function is needed. This circuit is mainly used for low-current LED drive control, high-side output, and can diagnose the fault status (short circuit, open circuit) of the output port, and quickly shut down the output when the output port is short-circuited. This circuit is lower in cost than the circuit designed using intelligent power driver chips. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a low-cost, low-current LED output drive circuit with diagnostic function that has simple structure, low circuit cost and a wide range of applications.

[0006] In order to achieve the above object, the low-cost low-current LED output drive circuit with diagnostic function of the present invention is as follows:

[0007] The low-cost, low-current LED output drive circuit with diagnostic function has the following main features: the system includes a second NPN transistor, a first PNP transistor, a first diode D1 and a first resistor R1; the anode of the first diode D1 is connected to the anode of the power supply, the cathode of the first diode D1 is connected to the emitter of the first PNP transistor, the first resistor R1 is connected in series between the collector and the output port of the first PNP transistor, the base of the second NPN transistor is connected to the MCU control port, the collector of the second NPN transistor is connected to the base of the first PNP transistor, the emitter of the second NPN transistor is grounded, the other end of the first resistor R1 is connected to the LED output port, and the redundant control module is connected to the collector of the second NPN transistor.

[0008] Preferably, the system also includes a sixth resistor R6 and a seventh resistor R7, the sixth resistor R6 and the seventh resistor R7 are connected, one end of the sixth resistor R6 is connected to the LED output port, one end of the seventh resistor R7 is grounded, and one end of the seventh resistor R7 is connected to the AD sampling port of the MCU as output port state feedback.

[0009] Preferably, the system also includes a first capacitor C1 and a second capacitor C2, one end of the first capacitor C1 is connected to the LED output port, and the other end is grounded, one end of the second capacitor C2 is connected to the AD sampling port of the MCU, and the other end is grounded, the first capacitor C1 is a port filter capacitor for port electrostatic protection, and the second capacitor C2 is an MCU port filter capacitor.

[0010] Preferably, the system also includes a second resistor R2 and a third resistor R3, one end of the second resistor R2 is connected to the base of the first PNP transistor, and the other end is connected to the emitter of the first PNP transistor, one end of the third resistor R3 is connected to the base of the first PNP transistor, and the other end is connected to the collector of the second NPN transistor.

[0011] Preferably, the system also includes a fourth resistor R4 and a fifth resistor R5, one end of the fourth resistor R4 is connected to the MCU control port, and the other end is connected to the base of the second NPN transistor, and one end of the fifth resistor R5 is connected to the MCU control port, and the other end is connected to the emitter of the second NPN transistor.

[0012] Preferably, the system is adapted to the output AD sampling feedback of a 12V or 24V power supply system by setting different resistance values ​​of the sixth resistor R6 and the seventh resistor R7.

[0013] Preferably, the first resistor R1 is a 2512 package with a power of 1W, and the resistance value is selected according to the power supply voltage and the maximum current of the collector of the PNP transistor that is continuously conducted.

[0014] Preferably, when the output port of the first resistor R1 is short-circuited to the ground, it limits the current of the circuit and protects the circuit from damage.

[0015] Preferably, when the MCU control port of the system outputs a high level of 5V, the base of the second NPN transistor obtains a forward voltage, the second NPN transistor is in an on state, the first PNP transistor is in an on state, the power supply is connected to the controller output port, and the LED lamp is driven to light up.

[0016] Preferably, the redundant control module includes a UJA1135 chip and its peripheral circuits, the UJA1135 chip includes eight I / O pins, one of the I / O pin ports is a low-side output driver, and the I / O pin port is connected between a third resistor R3 and a collector of a second PNP transistor; if the control port output of the MCU fails, the I / O pin of the redundant control module is turned on, outputs a low-side driver, pulls down the level of the third resistor R3, and turns on the first PNP transistor.

[0017] The low-cost, low-current LED output drive circuit with diagnostic function implemented by the present invention has obvious cost advantages compared to the use of intelligent power chips to drive LEDs. The cost of two transistors, a diode and several resistors and capacitors is significantly lower than the price of mainstream intelligent power chips on the market. At the same time, this circuit is also equipped with a "redundant control module". When the MCU fails, the "redundant control module" can control the output and achieve a backup control function. In this circuit, a group of voltage-dividing resistors connected to the collector of the PNP transistor can monitor the status of the external port. When the external port is already short-circuited or open-circuited, the output is no longer turned on. At the same time, this circuit also has a function to prevent power reverse connection and a current limiting function during short circuit, which can meet the requirements of automotive electrical load tests. Both functions are achieved at a low cost. This circuit is simple and easy to operate, and the maximum current of the PNP transistor used for output can meet the LED drive requirements with a working current of less than 100mA. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The present invention is a schematic diagram of the circuit structure of a low-cost, low-current LED output drive circuit with a diagnostic function.

[0019] Figure 2 The circuit structure diagram of a specific embodiment of the present invention for realizing a low-cost, low-current LED output drive circuit with a diagnostic function. DETAILED DESCRIPTION

[0020] In order to more clearly describe the technical content of the present invention, further description is given below in conjunction with specific embodiments.

[0021] The low-cost, low-current LED output drive circuit with diagnostic function of the present invention includes a second NPN transistor, a first PNP transistor, a first diode D1 and a first resistor R1, wherein the anode of the first diode D1 is connected to the anode of the power supply, the cathode of the first diode D1 is connected to the emitter of the first PNP transistor, the first resistor R1 is connected in series between the collector and the output port of the first PNP transistor, the base of the second NPN transistor is connected to the MCU control port, the collector of the second NPN transistor is connected to the base of the first PNP transistor, the emitter of the second NPN transistor is grounded, the other end of the first resistor R1 is connected to the LED output port, and the redundant control module is connected to the collector of the second NPN transistor.

[0022] As a preferred embodiment of the present invention, the system also includes a sixth resistor R6 and a seventh resistor R7, the sixth resistor R6 and the seventh resistor R7 are connected, one end of the sixth resistor R6 is connected to the LED output port, one end of the seventh resistor R7 is grounded, and one end of the seventh resistor R7 is connected to the AD sampling port of the MCU as output port state feedback.

[0023] As a preferred embodiment of the present invention, the system also includes a first capacitor C1 and a second capacitor C2, one end of the first capacitor C1 is connected to the LED output port, and the other end is grounded, one end of the second capacitor C2 is connected to the AD sampling port of the MCU, and the other end is grounded, the first capacitor C1 is a port filter capacitor for port electrostatic protection, and the second capacitor C2 is an MCU port filter capacitor.

[0024] As a preferred embodiment of the present invention, the system also includes a second resistor R2 and a third resistor R3, one end of the second resistor R2 is connected to the base of the first PNP transistor, and the other end is connected to the emitter of the first PNP transistor, one end of the third resistor R3 is connected to the base of the first PNP transistor, and the other end is connected to the collector of the second NPN transistor.

[0025] As a preferred embodiment of the present invention, the system also includes a fourth resistor R4 and a fifth resistor R5, one end of the fourth resistor R4 is connected to the MCU control port, and the other end is connected to the base of the second NPN transistor, and one end of the fifth resistor R5 is connected to the MCU control port, and the other end is connected to the emitter of the second NPN transistor.

[0026] As a preferred embodiment of the present invention, the system is adapted to the output AD sampling feedback of a 12V or 24V power supply system by setting different resistance values ​​of the sixth resistor R6 and the seventh resistor R7.

[0027] As a preferred embodiment of the present invention, the first resistor R1 is a 2512 package with a power of 1W, and the resistance value is selected according to the power supply voltage and the maximum current of the collector of the PNP transistor that is continuously conducted.

[0028] As a preferred embodiment of the present invention, when the output port of the first resistor R1 is short-circuited to the ground, it limits the current of the circuit and protects the circuit from damage.

[0029] As a preferred embodiment of the present invention, when the MCU control port of the system outputs a high level of 5V, the base of the second NPN transistor obtains a forward voltage, the second NPN transistor is in an on state, the first PNP transistor is in an on state, the power supply is connected to the controller output port, and the LED lamp is driven to light up.

[0030] As a preferred embodiment of the present invention, the redundant control module includes a UJA1135 chip and its peripheral circuits, the UJA1135 chip includes eight I / O pins, one of the I / O pin ports is a low-side output driver, and the I / O pin port is connected between a third resistor R3 and a collector of a second PNP transistor; if the control port output of the MCU fails, the I / O pin of the redundant control module is turned on, outputs a low-side driver, pulls down the level of the third resistor R3, and turns on the first PNP transistor.

[0031] In a specific embodiment of the present invention, a low-cost low-current LED driver circuit with diagnostic function is provided, which can reduce the cost and quickly shut down the output when the output port is short-circuited, protect the controller from damage, and diagnose the fault state. At the same time, the cost of this hardware circuit is lower than that of the circuit designed using the intelligent power driver chip.

[0032] The low current LED output drive circuit uses an NPN transistor to control the conduction and cutoff of another PNP transistor. The base of the NPN transistor is connected to the MCU control port. When the NPN base is energized, the NPN transistor is saturated and turned on, so that the base of the PNP transistor generates current. The PNP transistor is saturated and turned on to control the drive LED output. The PNP transistor is selected according to the power (working current) of the output load, and the maximum collector continuous conduction current (Ic) is the PNP transistor selection parameter.

[0033] D1 is a diode connected in series between the positive pole of the power supply and the emitter of the PNP transistor, which plays a role in preventing the power supply from being reversed. When the power supply is reversed, the unidirectional conduction characteristic of D1 makes it impossible for the negative pole of the power supply and the positive pole of the power supply to be conducted when the power supply is reversed, thus protecting the circuit from damage. The D1 diode is selected based on the maximum voltage value when reversed, and the maximum reverse breakdown voltage is the D1 diode selection parameter. R1 is a current limiting resistor, which is connected in series between the collector of the PNP transistor and the output port. When the output port is short-circuited to the ground, it limits the current of the circuit and protects the circuit from damage. The R1 resistor is a 2512 package with a power of 1W. The resistance value is selected based on the power supply voltage and the maximum current that the collector of the PNP transistor can continuously conduct.

[0034] R6 and R7 are used as voltage divider resistors, and one end of the ground resistor R7 is connected to the MCU AD sampling port as output port status feedback. The resistance values ​​of R6 and R7 are selected based on the reference power supply voltage value.

[0035] When the MCU fails, the "redundant control module" outputs a low level, pulls down the voltage at the lower end of the R3 resistor, turns on the Q1 PNP transistor, and controls the output to drive the LED to light up. This module serves as a backup control function to ensure that the output can continue to be controlled when the MCU fails.

[0036] The redundant control module consists of the UJA1135 chip (NXP Semiconductors UJA113xA series base chip) and its peripheral circuits. The UJA1135 chip is an SBC chip with an integrated buck-boost converter and CAN LIN transceiver, including 8 I / O pins that can be individually configured as high-side / low-side output drivers (low current).

[0037] In this circuit, one I / O port in the UJA1135 chip of the redundant control module is configured as a low-side output driver, and this port is connected between the R3 resistor and the collector of the Q2 NPN transistor. When the MCU control port output fails and cannot output a high level to the base of the Q2 NPN transistor (the Q2 NPN transistor cannot be turned on), the redundant control module replaces the Q2 NPN transistor, and the redundant control module I / O port connected therein is turned on, outputting a low-side driver, pulling down the R3 resistor level, and turning on the Q1 PNP transistor.

[0038] This LED driving circuit uses an NPN transistor to control the conduction and cutoff of another PNP transistor to control the power supply BATT to power the LED. The base of the NPN transistor is connected to the MCU control port. When the MCU control port outputs a 5V high level, the base of the NPN transistor obtains a forward voltage, and the NPN transistor is in the on state (working in the saturation area). At this time, the power supply BATT divides the voltage through the resistor, so that the base of the PNP transistor obtains a reverse voltage, and the PNP transistor is in the on state (working in the saturation area). After the PNP transistor is turned on, the power supply is connected to the controller output port, thereby driving the LED light to light up. At the same time, this circuit is also equipped with a "redundant control module". When the MCU fails, the "redundant control module" outputs a low level, pulls down the voltage at the lower end of the R3 resistor, and turns on the Q1 PNP transistor, thereby controlling the output and driving the LED to light up.

[0039] There is a set of voltage divider resistors at the collector of the PNP transistor, which is used to monitor the status of the external port. This set of voltage divider resistors consists of two resistors in series, one end of which is connected to the LED output port and the other end is connected to GND. Through resistor voltage division, the resistor voltage close to GND in the voltage divider resistor is transmitted to the AD sampling port of the MCU, and the state of the external port is judged by the voltage value sampled by the AD (when the PNP transistor is turned on, the voltage value of the AD port is 0V, indicating that the output port is short-circuited to the ground. When the PNP transistor is turned off, the voltage value of the AD port is 4-5V, indicating that the output port is short-circuited to the power supply). A diode is connected in series between the emitter of the PNP transistor and the power supply BATT. This diode is a reverse diode. When the power supply and the ground are reversely connected, it prevents the emission in the event of a short circuit and protects the circuit from being damaged. A resistor (2512 package) is connected in series between the collector of the PNP transistor and the output port to limit the current in the event of a short circuit to the ground, protecting the PNP transistor from being damaged when it is in the on state and short-circuited to the ground. The MCU performs fault diagnosis based on the AD sampling voltage value under different circumstances. When the PNP transistor is turned on, the AD port voltage value is 0V, indicating that the output port is short-circuited to the ground. When the PNP transistor is turned off, the AD port voltage value is 4-5V, indicating that the output port is short-circuited to the power supply. The AD port samples the fault voltage value and shuts down the output in time.

[0040] Figure 1 In the figure, Q1 is a PNP transistor, Q2 is an NPN transistor, Q2 and Q1 are saturated and turned on in turn to control the output. Q1 can be selected according to the working current of the output load.

[0041] Figure 1 In the circuit, R6 and R7 are a resistor divider AD sampling circuit, and the output AD sampling feedback of a 12V or 24V power supply system can be adapted by setting different resistance values ​​of R6 and R7.

[0042] R1 is a current limiting resistor in 2512 package, which is used for current limiting protection in case of short circuit. The resistance value can be set according to the maximum operating current of the EC pole of Q1 transistor and the power supply voltage, and current limiting protection can be performed when the output is short-circuited to ground.

[0043] D1 is an anti-reverse diode, which is used for reverse connection protection when the power supply is reversed. The D1 diode can be selected according to the power supply voltage value.

[0044] C1 is a port filter capacitor, which can also provide port electrostatic protection.

[0045] C2 is the MCU port filter capacitor and is placed close to the MCU AD sampling port.

[0046] The redundant control module is used to pull down the voltage at the lower end of the R3 resistor and control the Q1 PNP transistor to conduct when the MCU fails.

[0047] by Figure 2For example, the power supply voltage (BATT) is 24V. When driving the LED normally, the MCU control port outputs a 5V high level to the base of the NPN transistor Q2, and the NPN transistor Q2 is turned on. At this time, the power supply BATT makes the base of the PNP transistor Q1 obtain a reverse voltage through the voltage-dividing resistors R2 and R3, and the PNP transistor Q1 is turned on. After the PNP transistor Q1 is turned on, the controller power supply and the controller output port are turned on, and the external LED lights up. When the MCU fails, the "redundant control module" outputs a low level, pulls down the voltage at the lower end of the R3 resistor, and turns on the Q1 PNP transistor, thereby controlling the output and driving the LED to light up. In the above figure, the Q1 transistor is selected as MMBTA56Q, a car-grade PNP transistor, and the maximum collector continuous conduction current (Ic) is 500mA, which can meet the output drive of the LED load with a working current of 100mA. The diode D1 between the power supply BATT and the PNP transistor Q1 is an anti-reverse diode. In the figure above, D1 is selected as JSPI1100AH, with a maximum reverse breakdown voltage of 100V. It can withstand the reverse connection of the 24V power supply without breakdown. The maximum forward conduction current is 1A, which can fully cope with the load output current and the current impact during short circuit. R6 and R7 form a series voltage divider resistor. In the figure above, R6 = 100KΩ, R7 = 20KΩ, and the voltage at the grounding resistor R7 is input to the MCU AD sampling port to determine the status of the external port. When the external port is short-circuited to the ground, the LED AD voltage value is 0V, the MCU control end stops output, and quickly turns off the output, thereby protecting the circuit from damage. When the output is not turned on, the LED AD voltage value is greater than 4V, indicating that the output port has been short-circuited to the power supply, and the MCU no longer turns on the output. R1 is a 2512 package current limiting resistor, which is used to limit the current in the case of a short circuit to protect the PNP transistor Q1 from damage in the case of a short circuit. In the figure above, R1=1.5KΩ, the maximum power of the 2512 package resistor is 1W. When the output is turned on, the output port is short-circuited to ground, and R1 is used as a current limiter. In the case of a short circuit, its current is 16mA, and the power of R1 is 0.384W, which can fully withstand the transient current generated during a short circuit and perform current limiting protection.

[0048] The present invention is applied to the vehicle field and is powered by a vehicle-mounted 12V battery. These two usage scenarios are quite different. The use environment of electrical equipment in the civilian field is relatively ideal, while the vehicle-mounted use environment needs to cope with various harsh working conditions. Therefore, when designing the vehicle-mounted drive circuit, it is necessary to consider coping with various working conditions and passing the EMC test requirements.

[0049] The drive output circuit of the present invention adds a 10nF / 100V port filter capacitor (C1) at the output port, which is mainly used for anti-interference and port electrostatic absorption. An MCU AD detection port filter capacitor is also placed at the LED output AD detection port, which is mainly used to stabilize the AD sampling input signal, which can effectively improve the anti-interference ability of the entire drive output circuit and pass the corresponding EMC test.

[0050] The present invention connects a diode (D1) in series between the emitter of the PNP transistor and the power supply to prevent the power supply from being reversely connected, and can also achieve the effect of isolating different power supplies. A 2512 packaged current limiting resistor is connected in series between the collector of the PNP transistor and the output port to limit the conduction current of the PNP transistor in the event of a short circuit, thereby preventing the PNP transistor from being damaged. These two measures can prevent the drive circuit from being damaged due to reverse connection of the power supply and short circuit caused by operating errors during actual use. At the same time, these two circuit designs can also cope with corresponding electrical load test tests.

[0051] The present invention connects a "redundant control module" to the base of the PNP transistor to control the base voltage of the PNP transistor in the event of MCU failure. The "redundant control module" can output high and low levels to make the PNP transistor enter the "saturation" or "cut-off" working mode, thereby controlling the drive output and shutdown.

[0052] The specific implementation scheme of this embodiment can refer to the relevant description in the above embodiment, which will not be repeated here.

[0053] It can be understood that the same or similar parts of the above embodiments can be referenced to each other, and the contents not described in detail in some embodiments can refer to the same or similar contents in other embodiments.

[0054] It should be noted that, in the description of the present invention, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. In addition, in the description of the present invention, unless otherwise specified, the meaning of "plurality" refers to at least two.

[0055] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, segment or portion of code that includes one or more executable instructions for implementing the steps of a specific logical function or process, and the scope of the preferred embodiments of the present invention includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by those skilled in the art to which the embodiments of the present invention belong.

[0056] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution device. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0057] A person skilled in the art may understand that all or part of the steps in the method for implementing the above-mentioned embodiment may be completed by instructing related hardware through a program, and the corresponding program may be stored in a computer-readable storage medium, which, when executed, includes one of the steps of the method embodiment or a combination thereof.

[0058] In addition, each functional unit in each embodiment of the present invention may be integrated into a processing module, or each unit may exist physically separately, or two or more units may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of a software functional module. If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it may also be stored in a computer-readable storage medium.

[0059] The storage medium mentioned above can be a read-only memory, a magnetic disk or an optical disk, etc.

[0060] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0061] The low-cost, low-current LED output drive circuit with diagnostic function implemented by the present invention has obvious cost advantages compared to the use of intelligent power chips to drive LEDs. The cost of two transistors, a diode and several resistors and capacitors is significantly lower than the price of mainstream intelligent power chips on the market. At the same time, this circuit is also equipped with a "redundant control module". When the MCU fails, the "redundant control module" can control the output and achieve a backup control function. In this circuit, a group of voltage-dividing resistors connected to the collector of the PNP transistor can monitor the status of the external port. When the external port is already short-circuited or open-circuited, the output is no longer turned on. At the same time, this circuit also has a function to prevent power reverse connection and a current limiting function during short circuit, which can meet the requirements of automotive electrical load tests. Both functions are achieved at a low cost. This circuit is simple and easy to operate, and the maximum current of the PNP transistor used for output can meet the LED drive requirements with a working current of less than 100mA.

[0062] In this specification, the present invention has been described with reference to specific embodiments thereof. However, it is apparent that various modifications and variations may be made without departing from the spirit and scope of the present invention. Therefore, the specification and drawings should be regarded as illustrative rather than restrictive.

Claims

1. A low-cost low-current LED output drive circuit with diagnostic function, characterized in that: The system includes a second NPN transistor, a first PNP transistor, a first diode D1, a first resistor R1 and a redundant control module, wherein the positive electrode of the first diode D1 is connected to the positive electrode of the power supply, the positive and negative electrodes of the first diode D1 are connected to the emitter of the first PNP transistor, the first resistor R1 is connected in series between the collector and the output port of the first PNP transistor, the base of the second NPN transistor is connected to the MCU control port, the collector of the second NPN transistor is connected to the base of the first PNP transistor, the emitter of the second NPN transistor is grounded, the other end of the first resistor R1 is connected to the LED output port, and the redundant control module is connected to the collector of the second NPN transistor.

2. The low-cost low-current LED output drive circuit with diagnostic function according to claim 1, characterized in that: The system also includes a sixth resistor R6 and a seventh resistor R7, the sixth resistor R6 and the seventh resistor R7 are connected, one end of the sixth resistor R6 is connected to the LED output port, one end of the seventh resistor R7 is grounded, and one end of the seventh resistor R7 is connected to the AD sampling port of the MCU as output port state feedback.

3. The low-cost low-current LED output drive circuit with diagnostic function according to claim 1, characterized in that: The system also includes a first capacitor C1 and a second capacitor C2, one end of the first capacitor C1 is connected to the LED output port, and the other end is grounded, one end of the second capacitor C2 is connected to the AD sampling port of the MCU, and the other end is grounded, the first capacitor C1 is a port filter capacitor for port electrostatic protection, and the second capacitor C2 is an MCU port filter capacitor.

4. The low-cost low-current LED output drive circuit with diagnostic function according to claim 1, characterized in that: The system also includes a second resistor R2 and a third resistor R3, one end of the second resistor R2 is connected to the base of the first PNP transistor, and the other end is connected to the emitter of the first PNP transistor, one end of the third resistor R3 is connected to the base of the first PNP transistor, and the other end is connected to the collector of the second NPN transistor.

5. The low-cost low-current LED output drive circuit with diagnostic function according to claim 1, characterized in that: The system also includes a fourth resistor R4 and a fifth resistor R5, one end of the fourth resistor R4 is connected to the MCU control port, and the other end is connected to the base of the second NPN transistor, and one end of the fifth resistor R5 is connected to the MCU control port, and the other end is connected to the emitter of the second NPN transistor.

6. The low-cost low-current LED output drive circuit with diagnostic function according to claim 2, characterized in that: The system is adapted to the output AD sampling feedback of a 12V or 24V power supply system by setting different resistance values ​​of the sixth resistor R6 and the seventh resistor R7.

7. The low-cost low-current LED output drive circuit with diagnostic function according to claim 1, characterized in that: The first resistor R1 is a 2512 package with a power of 1W, and the resistance value is selected according to the power supply voltage and the maximum current of the collector of the PNP transistor that is continuously conducted.

8. The low-cost low-current LED output drive circuit with diagnostic function according to claim 1, characterized in that: When the output port of the first resistor R1 is short-circuited to the ground, it limits the current of the circuit and protects the circuit from damage.

9. The low-cost low-current LED output drive circuit with diagnostic function according to claim 1, characterized in that: When the MCU control port of the system outputs a high level of 5V, the base of the second NPN transistor obtains a forward voltage, the second NPN transistor is in a conducting state, the first PNP transistor is in a conducting state, the power supply is connected to the controller output port, and the LED lamp is driven to light up.

10. The low-cost low-current LED output drive circuit with diagnostic function according to claim 1, characterized in that: The redundant control module includes a UJA1135 chip and its peripheral circuits. The UJA1135 chip includes eight I / O pins, one of which has a low-side output drive port, and the port of the I / O pin is connected between a third resistor R3 and a collector of a second PNP transistor. If the control port output of the MCU fails, the I / O pin of the redundant control module is turned on, outputs a low-side drive, pulls down the level of the third resistor R3, and turns on the first PNP transistor.

Images