Open-circuit protection circuit for constant-current power supply system

Abstract

The utility model relates to the field of circuit design, in particular to an open-circuit protection circuit for a constant-current power supply system. The output of a voltage comparator U10B is connected with the input end of a bidirectional common-anode diode D11, the output end of an AND gate circuit U9D is connected with the other input end of the bidirectional common-anode diode D11, the output end of the bidirectional common-anode diode D11 is connected with two input ends of an AND gate circuit U9B, and the AND gate circuit U9B is connected with a power ground through a resistor R43; one input end of the AND gate circuit U9D is connected with a WDG signal generated by a watchdog circuit of the single chip microcomputer, and the other input end of the AND gate circuit U9D is connected with a CPU PWM signal. According to the utility model, power supply can be automatically recovered after faults are eliminated, and stable operation and minimum maintenance cost of the system are ensured.

Description

Technical Field

[0001] The utility model relates to the field of circuit design, in particular to an open circuit protection circuit of a constant current power supply system. Background Art

[0002] As a key node in the global transportation network, the stability and reliability of the lighting system of the airport is directly related to flight safety, passenger guidance, energy efficiency management and other aspects. LED lamps are widely used in modern airport lighting systems due to their advantages such as high efficiency and energy saving, long life and high light quality. However, the realization of these advantages is highly dependent on a set of sophisticated drive and control systems.

[0003] The existing airport LED lamp drive circuit design generally uses a single-chip microcomputer (microcontroller) as the core control unit to achieve precise adjustment of LED brightness and fault protection. The single-chip microcomputer outputs a pulse width modulation (PWM) signal to adjust the front-end constant current conversion constant voltage circuit to ensure that a stable current is provided to the LED, which is the basis for maintaining the normal operation of the LED lamp and extending its service life. PWM technology is widely used in the field of LED driving due to its flexibility and efficiency.

[0004] However, the airport environment is complex and changeable. Electromagnetic interference (EMI), power supply fluctuations, extreme climate and other factors may pose a threat to the normal operation of the MCU. Once the MCU crashes or becomes abnormal due to external interference, internal software errors, hardware failures and other reasons, the PWM signal it outputs will be interrupted or distorted, resulting in failure to control the constant current circuit. At this time, the characteristics of the constant current circuit make the constant voltage part of its front end lose effective supervision, and the voltage may rise sharply, exceeding the tolerance range of the subsequent circuit components, causing overvoltage damage. In severe cases, it may cause the paralysis of the entire lighting system, and even cause safety accidents such as fires, posing a major threat to the safety of airport operations.

[0005] Due to the above risks, it is particularly important to develop a protection mechanism that can effectively detect and promptly respond to open-circuit faults in constant-current power supply systems, especially those caused by control circuit failures.

[0006] The Chinese invention patent "Filament open circuit protector for constant current dimming system of airport navigation lights" (application number: CN200810010530.9) discloses a filament open circuit protector for constant current dimming system of airport navigation lights, which is mainly composed of a micro power supply, a small relay, a semiconductor bidirectional switch, and a voltage detection circuit to form a four-terminal device, which is connected in series between the secondary socket of the isolation transformer and the halogen tungsten lamp plug of the constant current dimming system of the airport navigation lights. When the load circuit is normal, the protector does not affect the normal operation of the system. Once the load is open, the protector immediately short-circuits the secondary of the isolation transformer, so that the isolation transformer is in a no-load working state, thereby completely eradicating the possibility of damage caused by the open circuit of the secondary circuit of the isolation transformer caused by the filament of the constant current dimming system of the airport navigation lights, reducing the cost of operation and maintenance of the constant current dimming system of the navigation lights, reducing the labor intensity of the lighting station staff, improving work efficiency, and enhancing the operating reliability of the navigation lighting system and the safety of aircraft take-off and landing. However, the patent does not target the pulse width modulation PWM signal of the single-chip microcomputer, and cannot automatically resume work after the pulse width modulation PWM signal is restored. Summary of the invention

[0007] In view of the shortcomings of the prior art, the utility model provides an open circuit protection circuit for a constant current power supply system. The utility model can automatically identify the abnormality of the WDG signal through intelligent judgment processing of multiple AND gates, automatically stabilize the voltage when abnormal, and automatically restore the normal working state after the WDG signal returns to normal.

[0008] The technical scheme of the utility model is: an open circuit protection circuit of a constant current power supply system, including an AND gate circuit U9A, an AND gate circuit U9B, and an AND gate circuit U9D, wherein the input end of the AND gate circuit U9A is connected to the WDG signal generated by the watchdog circuit of the single-chip microcomputer, and is characterized in that: the output end of the AND gate circuit U9A is connected to the base of the triode Q5 through a resistor R39, and the emitter of the triode Q5 is connected to the power ground; the collector of the triode Q5 is connected to the power supply voltage VC through a resistor R38 and a resistor R37; the connection point of the resistor R38 and the resistor R37 is electrically connected to the connection point of the resistor R40 and the resistor R41 through a wire, the resistor R41 is connected to the power ground, and the resistor R40 is connected to the positive input of the voltage comparator U10B, and the negative input of the voltage comparator U10B is connected to the voltage to be regulated V3 through the resistor R42; the output of the voltage comparator U10B is connected to the input end of the bidirectional common anode diode D11, the output end of the AND gate circuit U9D is connected to the other input end of the bidirectional common anode diode D11, the output end of the bidirectional common anode diode D11 is connected to the two input ends of the AND gate circuit U9B, and the AND gate circuit U9B is connected to the power ground through the resistor R43; one input end of the AND gate circuit U9D is connected to the WDG signal generated by the microcontroller watchdog circuit, and the other input end of the AND gate circuit U9D is connected to the CPU_PWM signal.

[0009] According to the open circuit protection circuit of a constant current power supply system as described above, it is characterized in that the AND gate circuit U9A, the AND gate circuit U9B, and the AND gate circuit U9D are three AND gates on the 74HCT08 chip.

[0010] According to the open circuit protection circuit of a constant current power supply system as described above, it is characterized in that the voltage comparator U10B is a LM393 voltage comparator.

[0011] According to the open circuit protection circuit of a constant current power supply system as described above, it is characterized in that: the negative electrode of the voltage comparator U10B input is connected to the power ground through a controllable precision voltage regulator U11, and the controllable precision voltage regulator U11 is a tl431 chip.

[0012] According to the open circuit protection circuit of a constant current power supply system as described above, it is characterized in that the bidirectional common anode diode D11 is a BAT54C diode.

[0013] According to the open circuit protection circuit of a constant current power supply system as described above, it is characterized in that the WDG signal generated by the microcontroller watchdog circuit is connected to the power ground through the resistor R43.

[0014] The beneficial effects of the utility model are: it has a rapid response capability to intervene immediately at the early stage of abnormal voltage rise to prevent energy accumulation and diffusion; it has an intelligent judgment function to automatically restore power supply after the fault is eliminated, ensuring the stable operation of the system and minimizing maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a block diagram of the working principle. DETAILED DESCRIPTION

[0016] The technical solution of the utility model is further described below in conjunction with the accompanying drawings.

[0017] like Figure 1As shown, a constant current power supply system open circuit protection circuit, the constant current power supply system adopts CPU_PWM signal control, CPU_PWM signal is the control signal of constant current to constant voltage generated by single chip microcomputer, WDG signal is generated by single chip microcomputer watchdog circuit, VC is the power supply voltage of constant voltage circuit, and the general power supply voltage VC is 40V. The circuit of the utility model finally outputs PWM signal through processing, that is, PWM signal is the control signal of constant current to constant voltage circuit after processing. The circuit of the utility model includes AND gate circuit U9A, AND gate circuit U9B, and AND gate circuit U9D, and AND gate circuit U9A, AND gate circuit U9B, and AND gate circuit U9D can be three AND gates on 74HCT08 chip. The input end of AND gate circuit U9A is connected to the WDG signal generated by the watchdog circuit of single chip microcomputer, and the output end of AND gate circuit U9A is connected to the base of triode Q5 through resistor R39, and the emitter of triode Q5 is connected to the power supply ground. The collector of triode Q5 is connected to the power supply voltage VC through resistor R38 and resistor R37. The connection point of resistors R38 and R37 is electrically connected to the connection point of resistors R40 and R41 through a wire, resistor R41 is connected to the power supply ground, resistor R40 is connected to the positive input of voltage comparator U10B, and the negative input of voltage comparator U10B is connected to the regulated voltage V3 through resistor R42. The negative input of voltage comparator U10B can also be connected to the power supply ground through a controllable precision voltage stabilizing source U11, and the controllable precision voltage stabilizing source U11 is a tl431 chip. The triode Q5 of the utility model can be a triode 8050; the voltage comparator U10B can be an LM393 voltage comparator.

[0018] like Figure 1 As shown, the output of the voltage comparator U10B is connected to the input end of the bidirectional common anode diode D11, the output end of the AND gate circuit U9D is connected to the other input end of the bidirectional common anode diode D11, the output end of the bidirectional common anode diode D11 is connected to the two input ends of the AND gate circuit U9B, and the AND gate circuit U9B is connected to the power ground through the resistor R43; the output of the AND gate circuit U9B is the processed PWM signal of the constant current to constant voltage circuit. The bidirectional common anode diode D11 is a BAT54C diode.

[0019] like Figure 1 As shown, one input end of the AND gate circuit U9D is connected to the WDG signal generated by the watchdog circuit of the single-chip microcomputer, and the other input end of the AND gate circuit U9D is connected to the CPU_PWM signal. The CPU_PWM signal can be connected to the power ground through the resistor R43.

[0020] During the working process of the circuit of the utility model, the circuit CPU_PWM signal is the control signal of constant current to constant voltage generated by the single chip microcomputer, VC is the constant voltage circuit voltage, the PWM signal is the processed control signal of the constant current to constant voltage circuit, and the WDG signal is generated by the single chip microcomputer watchdog circuit. When the single-chip microcomputer is normal, the WDG signal is high, the transistor Q5 is turned on, and the voltage at pin 5 of the voltage comparator U10B is slightly lower than the 2.5V voltage at pin 6 when VC is 40V. At this time, pin 7 of the comparator U10B outputs a low level, which has no effect on the signal of the AND gate circuit U9D. If the single-chip microcomputer crashes, the WDG signal becomes low, the AND gate circuit U9D outputs a low level, the transistor Q5 is cut off, the voltage at pin 5 is greater than the voltage at pin 6, the voltage comparator U10B flips to a high level, and the AND gate circuit U9B also outputs a high level. The VC voltage is pulled down to a level lower than the voltage at pin 6, and pin 7 outputs a low level, completing a switch of the PWM signal. The voltage comparator U10B uses a high-speed comparator, and the flipping frequency of the comparator circuit is 15KHz, so that the VC voltage can be stabilized at around 15V, which can well protect the circuit from damage caused by the crash of the single-chip microcomputer.

Claims

1. A constant current power supply system open circuit protection circuit, comprising an AND gate circuit U9A, an AND gate circuit U9B, and an AND gate circuit U9D, wherein the input end of the AND gate circuit U9A is connected to the WDG signal generated by the watchdog circuit of the single-chip microcomputer, and is characterized in that: The output end of the AND gate circuit U9A is connected to the base of the transistor Q5 through the resistor R39, and the emitter of the transistor Q5 is connected to the power ground; the collector of the transistor Q5 is connected to the power supply voltage VC through the resistors R38 and R37; the connection point of the resistors R38 and R37 is electrically connected to the connection point of the resistors R40 and R41 through a wire, the resistor R41 is connected to the power ground, the resistor R40 is connected to the positive input of the voltage comparator U10B, and the negative input of the voltage comparator U10B is connected to the voltage to be stabilized through the resistor R42 voltage V3 is connected; the output of the voltage comparator U10B is connected to the input end of the bidirectional common-anode diode D11, the output end of the AND gate circuit U9D is connected to the other input end of the bidirectional common-anode diode D11, the output end of the bidirectional common-anode diode D11 is connected to the two input ends of the AND gate circuit U9B, and the AND gate circuit U9B is connected to the power ground through the resistor R43; one input end of the AND gate circuit U9D is connected to the WDG signal generated by the watchdog circuit of the microcontroller, and the other input end of the AND gate circuit U9D is connected to the CPU_PWM signal.

2. The open circuit protection circuit of a constant current power supply system according to claim 1, characterized in that: AND gate circuit U9A, AND gate circuit U9B, and AND gate circuit U9D are three AND gates on the 74HCT08 chip.

3. The open circuit protection circuit of a constant current power supply system according to claim 1, characterized in that: The voltage comparator U10B is a LM393 voltage comparator.

4. The open circuit protection circuit of a constant current power supply system according to claim 1, characterized in that: The negative input electrode of the voltage comparator U10B is connected to the power ground through a controllable precision voltage regulator U11, and the controllable precision voltage regulator U11 is a tl431 chip.

5. The open circuit protection circuit of a constant current power supply system according to claim 1, characterized in that: The bidirectional common anode diode D11 is a BAT54C diode.

6. The open circuit protection circuit of a constant current power supply system according to claim 1, characterized in that: The WDG signal generated by the microcontroller watchdog circuit is connected to the power ground through resistor R43.

Images