Power supply circuit for illuminating lamp

Abstract

The utility model relates to the technical field of power supplies, aims to solve the technical problem that current is unstable when power is supplied to an LED lamp panel, and discloses a power supply circuit for an illuminating lamp, which comprises a constant current circuit used for inputting a wide voltage range and adjusting and outputting constant current through the constant current circuit. The brightness change caused by too light or too heavy load is avoided; the constant current circuit is provided with a switch tube, a gate drive circuit used for driving the switch tube, a current induction comparator U16 used for detecting output current, and an under-voltage locking comparator U15 used for detecting output voltage of the rectification filter circuit. The base voltage circuit is used for providing reference voltage for the under-voltage locking comparator U15, the voltage stabilizer U18 is used for supplying power to the base voltage circuit, a drain electrode of the switch tube is used as an output port V-for supplying power to an LED lamp panel, and the current induction comparator and the under-voltage locking comparator are respectively connected with the gate driving circuit. And stable and reliable constant-current driving is realized through cooperative work of all circuits.

Description

Technical Field

[0001] The utility model relates to the technical field of power supply, and in particular to a power supply circuit for lighting fixtures. Background Art

[0002] In modern lighting applications, LEDs have been widely used in various lighting applications due to their high efficiency, energy saving, long life, and fast response. However, LED lamps have high requirements for power supply and require a stable constant current power supply to ensure their normal operation. Directly converting AC power into DC power through rectification and filtering, and then using a simple current limiting circuit to power the LED, has some obvious disadvantages:

[0003] The current is unstable. When the load of the LED power supply changes, the output current is prone to fluctuate, resulting in unstable brightness of the LED lamp, which not only affects the use effect, but may also shorten the life of the LED.

[0004] The input voltage adaptability is poor, and the adaptability to input voltage fluctuations is poor. When the input voltage changes, it cannot provide a stable output current, which can easily cause abnormal operation of the LED lamp.

[0005] There is a lack of protection mechanism and complete over-current protection, under-voltage protection and other functions. The circuit is easily damaged when encountering abnormal situations, resulting in poor system reliability.

[0006] In view of the above problems, an improved power supply circuit is needed, which aims to solve the problems of unstable current, poor input voltage adaptability and inadequate protection through constant current control, wide voltage adaptation, and perfect protection mechanism, so as to improve the overall performance and reliability of the LED lighting system. Utility Model Content

[0007] The utility model aims to provide a power supply circuit for lighting fixtures to solve the technical problem of unstable current when supplying power to an LED light panel.

[0008] To achieve the above-mentioned purpose, the specific technical solution of a power supply circuit for a lighting fixture of the utility model is as follows:

[0009] A power supply circuit for lighting fixtures, including a transformer for converting commercial AC power into low-voltage AC power, a rectifier and filter circuit for rectifying the low-voltage AC power into low-voltage DC power is arranged at the rear stage of the transformer, the positive output end of the rectifier and filter circuit is used as an output port V+ for supplying power to an LED lamp panel through a current-sensing resistor, the first end of the current-sensing resistor is connected to the positive output end of the rectifier and filter circuit, the second end of the current-sensing resistor is connected to the output port V+, a constant current circuit is arranged for inputting a wide voltage range, and the output constant current is adjusted by the constant current circuit to avoid the negative voltage. The brightness changes due to the load being too light or too heavy; the constant current circuit is provided with a switching tube, a gate drive circuit for driving the switching tube, a current sensing comparator U16 for detecting the output current, an undervoltage lockout comparator U15 for detecting the output voltage of the rectifier and filter circuit, a base voltage circuit for providing a reference voltage to the undervoltage lockout comparator U15 and a voltage regulator U18 for supplying power to the base voltage circuit, the drain of the switching tube is used as the output port V- for supplying power to the LED light board, and the current sensing comparator and the undervoltage lockout comparator are respectively connected to the gate drive circuit.

[0010] Furthermore, a buffer is provided, wherein the buffer input terminal is connected to the positive output terminal of the rectifier and filter circuit, and the buffer output terminal is connected to the gate drive circuit. The buffer comprises an operational amplifier U19, an operational amplifier U20 and an operational amplifier U21. The output terminal of the operational amplifier U19 is connected to the non-inverting input terminal of the operational amplifier U20 and the non-inverting input terminal of the operational amplifier U21. The output terminal of the operational amplifier U21 is connected to the inverting input terminal of the operational amplifier U21. The output terminal of the operational amplifier U20 is connected to the inverting input terminal of the operational amplifier U20. The output terminal of the operational amplifier U20 is connected to the gate drive circuit via a resistor R78, and the output terminal of the operational amplifier U21 is connected to the gate drive circuit via a resistor R78. The inverting input terminal of the operational amplifier U19 is connected to the gate drive circuit via a resistor R80, and the non-inverting input terminal of the operational amplifier U19 is connected to the positive output terminal of the rectifier and filter circuit via a resistor R77.

[0011] Furthermore, a diode D15 and a diode D16 are connected between the output terminal of the operational amplifier U19 and the inverting input terminal of the operational amplifier U19, the anode of the diode D15 is connected to the cathode of the diode D16, and the cathode of the diode D15 is connected to the anode of the diode D16.

[0012] Furthermore, the positive output terminal of the detection rectifier and filter circuit provides a detection voltage to the under-voltage lockout comparator through a first series voltage divider circuit, the first series voltage divider circuit includes a resistor R74 and a resistor R75 connected in series, the upper end of the first series voltage divider circuit is connected to the positive output terminal of the rectifier and filter circuit, the lower end of the first series voltage divider circuit is grounded, and the common node of the resistor R74 and the resistor R75 is connected to the inverting input terminal of the under-voltage lockout comparator.

[0013] Furthermore, the reference voltage circuit includes a three-terminal voltage regulator U17, the cathode of the three-terminal voltage regulator U17 is connected to the output terminal of the voltage regulator through a resistor R83, the anode of the three-terminal voltage regulator U17 is grounded, the reference electrode of the three-terminal voltage regulator U17 is connected to a second series voltage divider circuit, the second series voltage divider circuit includes two series-connected resistors R81 and R82, the common node of the resistors R81 and R82 is connected to the reference electrode of the three-terminal voltage regulator U17, the upper end of the second series voltage divider circuit is connected to the cathode of the three-terminal voltage regulator U17, and the lower end of the second series voltage divider circuit is grounded.

[0014] Furthermore, the cathode of the three-terminal regulator U17 is connected to the non-inverting input terminal of the under-voltage lockout comparator, and a capacitor C3 is connected in parallel to both ends of the three-terminal regulator U17.

[0015] The power supply circuit for lighting fixtures provided by the utility model has the following advantages:

[0016] First, the constant current circuit ensures that a constant current is provided to the LED light board through the cooperation of the switch tube and the gate drive circuit, avoiding unstable brightness due to load changes, thereby improving the stability of lighting and extending the service life of the LED. Secondly, the power supply circuit can accept a wide range of input voltages and adjust the output through the constant current circuit to ensure that the LED light board can still obtain a stable current supply even when the input voltage fluctuates, increasing the adaptability and reliability of the system. The city AC is converted into low-voltage AC through a transformer, and then converted into low-voltage DC through a rectifier and filter circuit. The design of the rectifier and filter circuit ensures the smoothness and stability of the output voltage and reduces the impact of voltage ripple on the LED light board. In addition, the current sensing comparator U16 and the undervoltage lockout comparator U15 detect the output current and the output voltage of the rectifier and filter circuit respectively, and respond in time when the current is too large or the voltage is too low to prevent overcurrent or undervoltage from occurring, thereby effectively avoiding damage to the circuit and LED light board due to abnormal conditions and improving the reliability of the system. The constant current circuit ensures the constancy of the output current. The current-sensing resistor monitors the current in real time, and feedback control is performed through the current sensing comparator U16 to ensure timely adjustment or shutdown when the current exceeds the set value, thereby preventing component damage and safety hazards caused by overcurrent. The undervoltage lockout comparator U15 detects the output voltage of the rectifier and filter circuit. When the voltage is lower than the set threshold, the protection mechanism is triggered in time to prevent the low voltage from affecting the LED light board and other components, thereby ensuring the stable operation of the system. Through the comprehensive application of multiple protection mechanisms (such as overcurrent protection, undervoltage protection, etc.), the power supply circuit can respond and protect in time under various abnormal conditions, thereby improving the overall reliability and stability of the system, and is suitable for various lighting scenarios. In summary, the power supply circuit has multiple advantages such as constant current output, wide voltage adaptation, and protection functions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a functional structure diagram of the power supply circuit for lighting fixtures provided by the utility model;

[0018] Figure 2 This is a schematic diagram of a power supply circuit for a lighting fixture provided by the utility model. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the utility model more clear, the utility model is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model and are not used to limit the utility model.

[0020] See also Figure 1 and Figure 2 The utility model provides a power supply circuit for lighting fixtures, including a transformer T1 for reducing the voltage of commercial AC power to form low-voltage AC power. The rear stage of the transformer T1 is provided with a rectifier filter circuit for shaping the low-voltage DC power to form low-voltage DC power. The positive electrode of the rectifier filter circuit is used as an output port V+ for supplying power to an LED lamp panel through a current-sensing resistor R76. The first end of the current-sensing resistor R76 is connected to the positive output end of the rectifier filter circuit, and the second end of the current-sensing resistor R76 is connected to the output port V+. A constant current circuit is provided for inputting a wide voltage range, and the output constant current is adjusted by the constant current circuit to avoid changes in brightness due to too light or too heavy a load.

[0021] The constant current circuit includes a current sensing comparator U16, an undervoltage lockout comparator U15, a buffer circuit, a reference voltage circuit, a first series voltage divider circuit, a voltage regulator U18, a gate drive circuit and a switch tube Q9.

[0022] The voltage stabilizer U18 is used to provide a stable working voltage for each part of the constant current circuit, and the input end of the voltage stabilizer U18 is connected to the positive output end of the rectifier and filter circuit, which ensures the reliability and stability of the circuit, so that the voltage after rectification and filtering can be stably provided to each part of the circuit.

[0023] The first series voltage divider circuit is used to provide the voltage from the positive output terminal of the rectifier and filter circuit to the under-voltage lockout comparator U15 for detection, and includes a resistor R74 and a resistor R75 connected in series. The upper end of the first series voltage divider circuit is connected to the positive output terminal of the rectifier and filter circuit, the lower end of the first series voltage divider circuit is grounded, and the common node of the resistor R74 and the resistor R75 is connected to the inverting input terminal of the under-voltage lockout comparator U15.

[0024] A reference voltage circuit is provided for providing a reference voltage for the undervoltage lockout comparator U15, including a three-terminal voltage regulator U17, the cathode of the three-terminal voltage regulator U17 is connected to the output terminal of the voltage regulator U18 through a resistor R83, the anode of the three-terminal voltage regulator U17 is grounded, the reference electrode of the three-terminal voltage regulator U17 is connected to a second series voltage divider circuit, the second series voltage divider circuit includes two series-connected resistors R81 and R82, the common node of the resistors R81 and R82 is connected to the reference electrode of the three-terminal voltage regulator U17, the upper end of the second series voltage divider circuit is connected to the cathode of the three-terminal voltage regulator U17, and the lower end of the second series voltage divider circuit is grounded. The cathode of the three-terminal voltage regulator U17 is connected to the in-phase input terminal of the undervoltage lockout comparator U15, and a capacitor C3 is also connected in parallel to both ends of the three-terminal voltage regulator U17.

[0025] The output end of the undervoltage lockout comparator U15 is connected to the gate drive circuit.

[0026] The reference voltage circuit provides a stable reference voltage for the undervoltage lockout comparator U15 to ensure the accuracy of undervoltage detection. In this way, the undervoltage lockout comparator U15 can reliably determine the state of the input voltage.

[0027] The cathode of the three-terminal regulator U17 is connected to the output terminal of the regulator U18 through the resistor R83, and is connected in parallel through the capacitor C3 to filter out noise and transient interference, further improving the stability of the voltage reference. This design not only improves the overall stability of the circuit, but also enhances the reliability of the undervoltage detection and protection function.

[0028] The output end of the undervoltage lockout comparator U15 is connected to the gate drive circuit. When an undervoltage condition is detected, the gate drive circuit can be quickly turned off to protect subsequent power components and loads and avoid damage caused by undervoltage.

[0029] When an undervoltage condition is detected, the undervoltage lockout comparator U15 can shut down the circuit in time to avoid unnecessary current consumption and reduce the power consumption of the entire system.

[0030] It can be seen that the circuit provides a stable working voltage through the voltage regulator U18, and the undervoltage lockout comparator U15 performs undervoltage detection through a series voltage divider circuit, and provides a reliable reference voltage in combination with the reference voltage circuit, and has an excellent undervoltage protection function. It not only improves the stability and reliability of the circuit, but also effectively protects the circuit components and reduces power consumption, which has significant practical value.

[0031] The inverting input terminal of the current sensing comparator U16 is connected to the first end of the current sensing resistor R76, the non-inverting input terminal of the current sensing comparator U16 is connected to the second end of the current sensing resistor R76, and the output terminal of the current sensing comparator U16 is connected to the gate drive circuit.

[0032] The current passing through the load is detected by the voltage difference of the current-sensing resistor R76. This connection method can accurately sense the magnitude of the current and ensure the accuracy of current detection.

[0033] The current sensing comparator U16 can respond quickly to current changes. When it detects that the current exceeds the set threshold, it immediately outputs a signal to the gate drive circuit. This fast response capability can protect the circuit in time when the current is too large, avoiding component damage caused by excessive current.

[0034] Through the detection of the current sensing comparator U16, protective measures can be taken in time when the current is overloaded or short-circuited to prevent the circuit from burning due to overload. The output end of the current sensing comparator U16 is directly connected to the gate drive circuit. When the current exceeds the threshold, the drive circuit can be quickly shut down to protect the power device and the load.

[0035] By using the feedback of the current sensing comparator U16, the load current can be accurately controlled. For example, in an LED driving circuit, the brightness of the LED can be controlled by adjusting the threshold of the current sensing comparator U16, thereby achieving constant current driving.

[0036] The current sensing comparator U16 provides a real-time current monitoring function. By cooperating with the current sensing resistor R76, the current can be accurately monitored and controlled to avoid circuit instability caused by current fluctuations and improve the overall stability of the system.

[0037] By monitoring the current in real time, the current sensing comparator U16 can help optimize power consumption management. For example, when the current exceeds the set safety range, the current can be reduced or part of the circuit can be shut down in time, thereby reducing unnecessary power consumption and extending the service life of the device.

[0038] It can be seen that the current sensing comparator U16 can achieve accurate current detection and control through cooperation with the current sensing resistor R76, has the functions of fast response and enhanced circuit protection, improves the stability and reliability of the system, and optimizes power consumption management.

[0039] The buffer input end is connected to the positive output end of the rectifier filter circuit, and the buffer output end is connected to the gate drive circuit.

[0040] The buffer includes an op amp U19, an op amp U20 and an op amp U21. The output of the op amp U19 is connected to the in-phase input of the op amp U20 and the in-phase input of the op amp U21. The output of the op amp U21 is connected to the inverting input of the op amp U21. The output of the op amp U20 is connected to the inverting input of the op amp U20. The output of the op amp U20 is connected to the gate drive circuit through a resistor R78. The output of the op amp U21 is connected to the gate drive circuit through a resistor R78. The inverting input of the op amp U19 is connected to the gate drive circuit through a resistor R80. A diode D15 and a diode D16 are connected between the output of the op amp U19 and the inverting input of the op amp U19. The anode of the diode D15 is connected to the cathode of the diode D16. The cathode of the diode D15 is connected to the anode of the diode D16. The in-phase input of the op amp U19 is connected to the positive output of the rectifier filter circuit through a resistor R77.

[0041] The gate drive circuit is used to drive the gate, that is, the gate, of the switch tube Q9. The gate drive circuit is respectively connected to the output ends of the current sensing comparator U16, the undervoltage lockout comparator U15 and the buffer. The output end of the gate drive circuit is connected to the gate of the switch tube Q9. The source of the switch tube Q9 is grounded, and the drain of the switch tube Q9 serves as the output port V- for supplying power to the LED light board.

[0042] The output of op amp U19 is protected by diodes D15 and D16 to prevent reverse current and voltage overshoot, further stabilizing the output voltage.

[0043] The buffer circuit improves the driving capability through the cascade amplification of multiple operational amplifiers (U19, U20, U21). The outputs of operational amplifiers U20 and U21 are connected to the gate drive circuit through resistor R78, which can provide sufficient drive current for the switch tube Q9, ensuring that the switch tube Q9 can switch quickly and reliably, thereby improving the response speed and efficiency of the system.

[0044] The inverting input of the op amp U19 is connected to the gate drive circuit through resistor R80, and the output of the op amp U19 and its inverting input are protected by diodes D15 and D16. This design not only prevents the op amp input from overloading, but also protects the entire circuit from voltage spikes and reverse current, enhancing the reliability and life of the circuit.

[0045] The buffer circuit ensures the stability and reliability of the entire system through stable voltage output and enhanced driving capability. Especially when driving the switch tube Q9, it can effectively prevent the switch tube from being damaged due to unstable voltage or insufficient driving, thereby protecting the subsequent load (such as LED light board).

[0046] It can be seen that the buffer circuit achieves stable voltage output, enhanced driving capability and protection function through the coordinated work of op amps U19, U20 and U21. The gate drive circuit is connected to the current sensing comparator U16, the undervoltage lockout comparator U15 and the output of the buffer to ensure the reliability and stability of the system. The output of the gate drive circuit is connected to the gate of the switch tube Q9, and by controlling the on and off of the switch tube Q9, reliable power supply to the LED light board is achieved.

[0047] In summary, the utility model provides a power supply circuit for lighting fixtures, in which the reference circuit generates a stable reference voltage to provide a reference voltage reference for other comparators. The current sensing comparator is used to monitor the input current signal. The current sensing input signal is compared with the reference voltage, and when the current signal exceeds the preset threshold, an output signal is generated to control the gate drive circuit. The undervoltage lockout comparator monitors the input voltage. When it is lower than the set threshold, a signal is triggered to turn off the gate drive circuit to protect the circuit. The buffer receives the dimming control signal and transmits it to the gate drive circuit to adjust the duty cycle of the output signal to achieve the dimming function, and the brightness is fixed in this embodiment. The gate driver drives the external power switch tube Q9 according to the control signal from the current sensing comparator and the buffer, controls the current of the load (such as LED), and thus realizes constant current drive. Through the coordinated work of the above-mentioned circuit parts, a stable and reliable constant current drive is achieved, which is suitable for applications such as LED drive.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A power supply circuit for a lighting fixture, comprising a transformer (T1) for converting commercial AC power into low-voltage AC power, a rectifier filter circuit for rectifying the low-voltage AC power into low-voltage DC power is arranged at the rear stage of the transformer (T1), a positive output end of the rectifier filter circuit is used as an output port V+ for supplying power to an LED light board through a current sensing resistor (R76), a first end of the current sensing resistor (R76) is connected to the positive output end of the rectifier filter circuit, and a second end of the current sensing resistor (R76) is connected to the output port V+, characterized in that: A constant current circuit is provided, which includes a switch tube (Q9), a gate drive circuit for driving the switch tube, a current sensing comparator (U16) for detecting an output current, an undervoltage lockout comparator (U15) for detecting an output voltage of a rectifier filter circuit, a base voltage circuit for providing a reference voltage to the undervoltage lockout comparator (U15), and a voltage regulator (U18) for supplying power to the base voltage circuit. The drain of the switch tube is used as an output port V- for supplying power to an LED light board. The current sensing comparator (U16) and the undervoltage lockout comparator (U15) are respectively connected to the gate drive circuit.

2. A power supply circuit for a lighting fixture according to claim 1, characterized in that: A buffer is also provided, wherein the buffer input terminal is connected to the positive output terminal of the rectifier and filter circuit, and the buffer output terminal is connected to the gate drive circuit. The buffer comprises an operational amplifier U19, an operational amplifier U20 and an operational amplifier U21. The output terminal of the operational amplifier U19 is connected to the non-inverting input terminal of the operational amplifier U20 and the non-inverting input terminal of the operational amplifier U21. The output terminal of the operational amplifier U21 is connected to the inverting input terminal of the operational amplifier U21. The output terminal of the operational amplifier U20 is connected to the inverting input terminal of the operational amplifier U20. The output terminal of the operational amplifier U20 is connected to the gate drive circuit via a resistor R78, and the output terminal of the operational amplifier U21 is connected to the gate drive circuit via a resistor R78. The inverting input terminal of the operational amplifier U19 is connected to the gate drive circuit via a resistor R80, and the non-inverting input terminal of the operational amplifier U19 is connected to the positive output terminal of the rectifier and filter circuit via a resistor R77.

3. A power supply circuit for a lighting fixture according to claim 2, characterized in that: A diode D15 and a diode D16 are connected between the output terminal of the operational amplifier U19 and the inverting input terminal of the operational amplifier U19. The anode of the diode D15 is connected to the cathode of the diode D16, and the cathode of the diode D15 is connected to the anode of the diode D16.

4. A power supply circuit for a lighting fixture according to claim 1, characterized in that: The positive output terminal of the detection rectification and filtering circuit provides a detection voltage to the under-voltage lockout comparator (U15) through a first series voltage divider circuit, the first series voltage divider circuit includes a resistor R74 and a resistor R75 connected in series, the upper end of the first series voltage divider circuit is connected to the positive output terminal of the rectification and filtering circuit, the lower end of the first series voltage divider circuit is grounded, and the common node of the resistor R74 and the resistor R75 is connected to the inverting input terminal of the under-voltage lockout comparator (U15).

5. A power supply circuit for a lighting fixture according to claim 4, characterized in that: The reference voltage circuit includes a three-terminal voltage regulator U17, the cathode of the three-terminal voltage regulator U17 is connected to the output terminal of the voltage regulator (U18) through a resistor R83, the anode of the three-terminal voltage regulator U17 is grounded, the reference electrode of the three-terminal voltage regulator U17 is connected to a second series voltage divider circuit, the second series voltage divider circuit includes two series-connected resistors R81 and R82, the common node of the resistors R81 and R82 is connected to the reference electrode of the three-terminal voltage regulator U17, the upper end of the second series voltage divider circuit is connected to the cathode of the three-terminal voltage regulator U17, and the lower end of the second series voltage divider circuit is grounded.

6. A power supply circuit for a lighting fixture according to claim 5, characterized in that: The cathode of the three-terminal voltage regulator U17 is connected to the non-inverting input terminal of the under-voltage lockout comparator (U15), and a capacitor C3 is connected in parallel between the two ends of the three-terminal voltage regulator U17.

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